Heat Flow in the State of Washington and Thermal

Heat Flow in the State of Washington and Thermal

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 95, NO. B12, PAGES 19,495-19,516,NOVEMBER 10, 1990
Heat Flow in the State of Washingtonand Thermal Conditions
in the CascadeRange
DAVID D. BLACKWELL,JOHNL. STEELE,AND SHARI KELLEY
Departmentof GeologicalSciences,SouthernMethodistUniversity,Dallas, Texas
MICHAEL
A. KOROSEC
WashingtonDepartmentof Natural Resources,Divisionof Geologyand Earth Resources,Olympia
Heat flow data for the state of Washingtonare presentedand discussed.The heat flow in the
Okanogan
Highland
averages
75mWm-2, andthegradient
averages
25øC
km-I . Theheatflowinthe
Columbia
Basinaverages
62mWm-2, andthemeangradient
is41øCkm-1. Bothof theseprovinces
areinterpreted
to havea mantleheatflowofabout55-60mWm-2, thesamevalueasin theBasinand
Range province to the south and the intermountainregion of Canada to the north. These areas
comprisethe highheat flow, back arc regionof the Cordillera.In the coastalprovincesand the western
part of the southernWashingtonCascadeRangethe heat flow is belownormaland averages40 mW
m-2 withanaverage
gradient
of26øCkm-1. Thislowheatflowisrelated
to theabsorption
of heatby
the subductingslab, part of the Juande Fuca plate, that is beneaththe PacificNorthwest. Thus the low
heat flow area represents the outer arc part of the subductionzone. Within the volcanic arc, the
Cascade Range, the heat flow pattern is complicated.The heat flow is best characterized in the
southern
Washington
Cascade
Range.Theheatflowthereaverages
75 mW m-2 andthe gradient
averages
45øCkm- •. Theheatflowpeaksatover80mWm-2 along
theaxialregion
thatcoincides
with
the Indian Heaven, Mount Adams, and Goat Rocks centersof Quaternary volcanism.As is the case
in northernOregonand southernBritishColumbia,the westernedgeof the regionof highheat flow has
a half width of 10km, implyinga heat sourceno deeperthan about10km. In the northernWashington
CascadeRangethe data are too sparseto determinethe averageheatflow. There are two saddlesin
the heat flow patternin Washington,alongthe ColumbiaRiver andin centralWashington.The origin
for the contrastingheat flow may be segmentation
of the heat sourceor somemore local effect. The
heat flow of the CascadeRangeis well characterizedin severallocations,and the patternis similarat
all localities.The most strikingfeatureis the 10km half width of the westernsideof the highheat flow
regionwhereit abutsthe low heatflowouterarcregion.The axialheatflowrangesfromabout80 to
greater
than100mWm-2. Themidcrustal
temperatures
areinterpreted
to range
fromabout400øC
to
800øC.The sourceof thesehightemperatures
is interpretedto be a long-livedmidcrustalzone of
magmaresidencethat is characteristic
of the CascadeRangeregardless
of crustaltype, rate of
volcanism,
or composition
of volcanism.
Forexample,in southern
Washington
theregionof highheat
flow spansthewidthof the Quaternary
zoneof volcanism
withMountSt. HelensandMountAdams
at the westandeastedges,respectively.On theotherhand,mostof the Oregonstratovo!canoes
are
near the center of anomalous region.
INTRODUCTION
of the conductiveportionof the heat transfer.The compli-
cated nature of heat transfer requires detailed heat flow
It has become clear in the last 10 years that the coastal
studiesand extensivedata coverage.The interestin geotherprovincesof the Pacific Northwest of the United States
mal energypotentialhas sparkedmuch study of volcanic
represent
a more typical subductionzone terrain than was
arcs. The Cascadiasubductionzone is unique in terms of the
initiallythought.The 1980 eruptionsof Mount St. Helens
emphasized
the active volcanism already demonstratedby amountandqualityof thermaldataavailable.One surprising
thefactthatmanyof the Cascadestratovolcanoes
havebeen result is that the altered volcanic rocks that comprise the
activein the last 200 years. Detailed seismicstudieshave bedrock of muchof the area are of generallylow permeabil-
heattransferby groundwater
motion
identifiedclear evidenceof a subductingslabunder Wash- ity sothat convective
does
not
predominate
and
a
generally
conductive
regional
ington[Weaverand Malone, 1987;WeaverandBaker, 1988;
of
Ludwinet al., 1990].In addition,evidencehasaccumulated picture can be detected.The thermal characteristics
indicating
thatlargesubduction
zoneearthquakes
mayoccur several areas in the Cascade volcanic arc in the United
in thePacificNorthwest,althoughperhapson a time scale States have been described [Blackwell et al., 1982; Mase et
more extended than those in areas with faster subduction a!., 1982;BlackwellandSteele,1983].Recentstudiesin the
rates[Atwater, 1987;Heaton and Hartzell, 1987].
OregonCascadeRangeare discussed
in a companion
paper
The thermal structureof volcanic arcs is of great interest, [Blackwellet al., this issue].The heat flow data in the
but regionalthermal characteristicsof volcanicarcs are CanadianCascadeRangehave alsobeenrecentlydescribed
difficultto obtain becauseof the nonconductiveheat transfer [Lewiset al., 1988].The first objectiveof this paperis to
processes
that operatein suchareasandthe complexnature present
anddiscuss
thermaldatain Washington;
thesecond
Copyright
1990by the AmericanGeophysical
Union.
Papernumber90JB01435.
0148-0227/90/90JB-01435505.
O0
is to discussin detail new heat flow data in the Washington
partof theCascade
Range;the thirdis to summarize
and
comparethe regionalthermalcharacteristics
of the whole
19,495
19,496
BLACKWELL
ET AL.: HEATFLOW,WASHINGTON
STATEANDCASCADE
RANGE
Cascade
Range.
Theimplications
ofthethermal
results
for ness,1983a,
b]. Theselogsarenotincorporated
intothis
magmatismin the crust will be discussedin detail.
Summawof tectonics. The tectonicsettingof the Washington CascadeRange is summarizedby severalpapersin
this volume [Leeman et al., this issue; Wells, this issue;
Weaver, 1989;Sherrod and Smith, this issue;Stanley et al.,
this issue], and more references may be found in those
papers. The details of the subductionof the Juan de Fuca
plate are becomingclearer, and the locationof the subducting slab has been mapped even in areas with no active
seismicityusing seismictomographyand electrical studies
[Rasmussenand Humphreys, 1988; Booker and Chave,
1989, Wannamaker et al., 1989].
The slab is seismicallyactive to a depth of up to 80 km
beneathnorthern California and in the Puget Sound region.
In Oregon,the slab doesnot appear to be seismicallyactive,
although because of the lack of detailed station coverage,
small-sizeslab earthquakesmay not be recorded. All studies
showthat the slabdips at moderateanglesfrom the trench to
the west edge of the Cascade Range. At that point the dip
rapidly increasesso that the slab is typically at depths of
100-150 km beneath
the volcanic
arc.
BACKGROUND OF THERMAL
MEASUREMENTS
The earliest geothermal measurement (directed by Van
Ostrand)have been tabulatedby Spicer [1964] and Guffanti
and Nathenson [ 1981]. Estimated heat flow values have been
calculated for two of these wells (20N/28W-8 and 11N/26E-
report.
DATA PRESENTATION
Geothermal
gradient,
heatflow,andancillary
informatio•n
fordrillholesin thestateofWashington,
excluding
pre-1974
published
data,aresummarized
inTable1.Onlyholes
where
gradients
orheatflowareconsidered
to beofC quality
(see
below)
orbetterareincluded
inTable1.Results
forthepoor
qualitydataaregivenbyBlackwell
et al. [1985,1989].
More
complete
information
onthesitesin Table1 aregiven
by
Blackwell et al. [1989].
Individualholesarelocatedby latitudeandlongitude
aM
by townshipand range.Thermalconductivityvaluesare
basedon measurements
of core or cuttingsamples,
or are
estimatedfrom lithology(valuesin parentheses).
Terrain
corrections
weremadefor all holeswherethe correction
was
estimatedto exceed5% of the measuredvalue.The terrain
correctionswere madeby the techniqueof Blackwellet el.
[1980] or Birch [1950]. Other aspectsof the heat flow/
geothermal gradient measurement and calculation techniques are discussedby Roy et al. [1968] and Sasset al.
[1971].A recent summaryof hardwaretechniquesfor heat
flow studiesis givenby Blackwelland Spafiord[1987].
Summarymapsof the heat flow and geothermal
gradient
datafromTable1areshownasFigures1and2, respectively.
Onlyonesymbolis shownfor eachsite, andwhereappro-
priate, the results from holes close together have been
20CC) based on thermal conductivityvalues that we mea- averaged.Both the geothermalgradientand heatflowmaps
sured on surface samplesfrom litho!ogicunits encountered have been contoured.The contouringwas doneby handand
in these holes.
in areasof sparsecontrolis basedon physiographic
setting.
In the efirly 1960s,R. F. Roy madeheat flow measure- This procedureis necessaryin the northern Washington
ments in northeasternWashington [Roy, 1963; Roy et al., CascadeRangeand coastalprovincesbecauseof thescarcity
1968] and measuredtemperaturesin DevelopmentAssoci- of data there. Another large data gap exists in southeastern
atesBasaltExplorer 1, a deep hydrocarbonexplorationwell Washington.There is only shallow groundwaterdevelopdrilled in the Columbia Basin (DABE-1, 21N/31E-10CB). ment along a broad northwest-southeast trending zone
Also in the 1960s Sass et al. [1971] made some heat flow throughthe east central Columbia Basin. With the exception
measurementsand investigationswere started by Blackwell of a few points near the center of this zone, an area 60-70km
[1969]. Preliminary results of additional statewide studies
were published by Blackwell [1974]. Revised heat flow
wide and 200 km long has no heat flow data available. It must
valuesfor these sitesare includedin this report.
an approximation of actual conditions and will not applyto
be emphasizedthat the gradientcontourmap particularily
is
In the 1970s, detailed heat flow studies of the Turtle Lake
any specificpoint. In addition, the gradientwill changewith
Quadrangle,northeasternWashington[Steele, 1975]and the depth as the thermal conductivity changes, perhapson a
Indian Heaven area in the southernWashingtonCascade very fine scale. In the following sections, geothermaldata
Range [Schusteret al., 1978] were published.In the mid- from eachmajor physiographic
divisionof the statewillbe
1970s,water chemistrystudiesindicatedthe possibilityof discussed.
anomalous heat flow values in the southern Columbia Basin
area [Swanbergand Morgan, 1979],andin 1978a reconnaissance temperature logging program was carded out there.
COASTAL PROVINCES
The mostrecentgeneraldiscussions
are a brief summaryof
CascadeRange heat flow [Blackwell and Steele, 1983] and
unpublishedfinal reports [Blackwell et al., 1985;Kososec,
1984].Final reports of data collectionare by Korosecet al.
[1983],Barnett [1986],andBarnett and Korosec[1989].This
Heat flow values from the Puget Lowland, the Coast
Ranges(WillapaHills), andthe westernpart of the southern
WashingtonCascadeRange(seeFigure 1) are generallylow.
Thereare no data in the OlympicMountainssubprovince.
All theseareasare underlainby Cenozoicrocksthathave
paper presents heat flow values for all the data collected accretedto North America in the Cenozoic[Wells,1990;
between 1970 and 1988. These data consistof accurate, Stanleyet al., 1990;etc.]. Most of the rocksin theprovince
detailedtemperature-depthmeasurementsin selectedavail- are volcanic and volcanoclasticunits with abundantfeldableholessuchaswaterwellsandmineralexplorationholes spar,and thermalconductivity
valuestend to be below
("free holes")andin holesdrilledspecifically
for geothermal averagefor continentalmaterial.Hence for a givenheat
studies(in the CascadeRange). Additional temperature- flow, geothermalgradientsare higherthan in a baseme_at
depthlogshavebeencollectedby personnel
at Washington terrain. In northwesternWashingtonone heat flow measure
StateUniversity(WSU) over manyyears[Stoffeland Wid- ment(34N/1E-2CBB)
wasobtained
in quartzdiorite
thatis
BLACKWELLET AL.: HEAT FLOW, WASHINGTON
STATEAND CASCADERANGE
19,497
TABLE la. ThermalandLocationDatafor theHighHeatFlow Sitesin Southern
Washington
Cascade
Range
Township/
Range
Section
18N/9E
29'CB
14N/10E
8DCB
14N/10E
11AA
Depth
LatitudeN,
Longitude
W
47ø00.54',
46o42.89',
46ø43.40',
46ø40.39',
121o19.80 '
46039.10',
46ø39.00',
2AB
121o17.02 '
13N/llE
2DC
I3N/9E
121o23.49 '
46o38.32' ,
46ø37.22',
16BCA
12N/7E
16CC
11N/10E
35BC
!0N/6E
121o41.59 '
8DDA
122o04.47 '
!0N/6E
18BDB
!0N/!0E
122o06.40 '
15DBA
121o32.85 '
9N/5E
46ø31.37',
46o23.40' ,
46ø21.58',
46ø21.10' ,
46ø21.!0 ' ,
46O20.68',
46o20.25' ,
121o41.90 '
46o17.79' ,
46ø15.95',
8BB
121049.75 '
6N/10E
7ACD
6N/7E
23BAC
6N/9E
25ACC
4N/13E
24BC
4N/7E
21CDB
4N/7E
21CD
4N/9E
27CB
3N/SE
2.39
0.21
75-115
2.18
80-152
Flow,
Quality
øCkm-1
mWm-2
Rating
8
19.6
47
B
Miocene pyroxene
rhyolite
0.08
10
33.8
74
B
Eocene volcanics
2.50
0.13
6
39.3
95
B
CZ volcanics,
25-150
1.30
0.13
10
67.0
87
B
sediments
CR basalt
60-150
2.02
0.21
8
46.0
93
A
siltstone and
35-150
2.56
0.13
9
42.3
108
A
amphibolite(JR)
10-148
1.84
0.15
21
45.0
83
A
Eocene volcanics
10-152
1.59
0.10
19
43.5
69
A
volcanic sediments
35-129
1.75
0.08
10
41.6
73
A
50-115
2.10
0.13
7
49.0
103
B
CZ sandstone
120-270
3.68
0.17
6
18.5
68
C
dacite porphyry
205-210
3.85
0.13
6
18.0
69
C
dacite porphyry
1.55
0.08
5
44.6
69
B
2.05
0.10
4
55.7
114
B
volcanic sediments
and basalt
volcanic sediments
25-148.6
1.97
0.10
5
67.8
133
C
Oligocene volcanic
90-145
1.97
0.10
5
60.2
119
B
35-152
1.29
0.06
7
43.0
55
B
Oligocene volcanic
agglomerate
30-122
1.81
0.06
15
20.1
36
B
andesite lahars
30-152
1.46
0.07
7
59.4
87
B
CZ volcanic and
volcanic sediments
95-152
1.73
0.08
7
27.9
48
B
Oligocene volcanic
85-150
1.25
0.03
5
44.5
56
A
sediments
vesicular basalt
basalt and sediments
80-!09.7
200-305
46o13.48' ,
46ø11.69',
46o07.50' ,
25-141.6
1.34
0.07
5
47.2
63
C
121ø19.29'
46o06.25
',
25-75
1.34
0.07
5
43.0
58
C
46ø05.90
',
115-150
1.24
0.11
4
53.4
66
A
volcanoclastic
15-25
(1.17)
58.0
67
C
glacial sediment
55-150
1.30
0.07
5
18.3
24
B
basalt, sediments
100-150
1.23
0.06
6
49.8
61
A
basalt
100-150
1.42
0.03
8
52.7
75
A
volcanoclastic
70-110
1.39
0.13
6
37.1
51
C
CR basalt
45-330
1.77
0.08
5
79.4
141
B
Oligocene volcanic
50-150
1.22
0.13
9
75.4
92
A
sediments
volcanoclastic
mudflows
125-152
1.40
0.07
5
330.0
46
B
Oligocenevolcanic
25-305
2.80
0.08
5
23.2
65
A
quartz diorite
granodiorite
27
34
C
C
CR basalt
121ø42.00'
46ø02.90
',
121o45.00 '
46ø01.30
',
121o36.05 '
45ø59.90
',
121o53.60 '
45ø58.60
',
121o37.40 '
45o49.40
',
121ø07.72 '
45ø48.70
',
121o57.25 '
45o48.63
',
121ø57.19 '
45o48.23
',
121o40.02 '
45ø46.39
',
Averageof SevenHoles in SameSection
10CCB
3N/8E
21BDD
3N/7E
25DA
sediments
121o46.20 '
122ø12.18 '
3NI10E
Lithology Summary
mudstone (JR)
121o42.55 '
121o39.75 '
36C
115-140
Gradient,
121o35.53 '
9N/9E
34AD
8N/BE
7N/12E
9CCC
7N/9E
!7AA
7N/BE
N
121ø32.21 '
122o14.22 '
2BCD
SE
121o56.37 '
18BB
7N/8E
W m- • K- •
121o30.70 '
4AB
5DA
Conductivity,
Corrected
Heat
121o34.68 '
121o01.76 '
10N/10E
19ACC
10N/9E
21CAB
9N/9E
m
Corrected
121ø41.70 '
!4N/14E
25BCDC
13N/12E
13N/12E
Range,
Average
Thermal
45o45.36
',
99-263
121o32.68
'
199-263
45ø44.07
',
121o48.24
,
45042.88
'
121o52.90
,'
5-114
59-213
(1.59)
(1.59)
1.60
(1.26)
0.13
13
17.0
21.5
sediments
166.0
265
G
quartzdiorite
26.8
33
B
Volcanoclastic
rocks
19,498
BLACKWELL
ETAL.:HEATFLOW,WASHINGTON
STATEANDCASCADE
RANGE
TABLE
la.
(continued)
Average
Township/
Range
LatitudeN,
Depth
Range,
3N/llE
70-100
SectionLongitude
W
29CCA
3N/7E
36BDD
3N/11E
34DBB
2N/7E
16CCC
2N/7E
21BAC
2N/7E
20DCA
2N/5E
45ø42.76
',
m
Thermal
Conductivity,
Wm-1K-1
Corrected
SE N
Corrected
Gradient,
øCkm-l
Heat
Flow,
mWm-2
Averageof SevenHolesin SameSection(continued)
(1.59)
35.3
56
Quality
Rating Lithology
Summary
C
CR basalt
121ø27.61 '
45ø42.34
',
15-290
(1.46)
32.7
48
C
Oligocene
volcanics
25-100
(1.59)
36.6
58
C
CR basalt
80-155
(1.46)
82.4
120
G
volcanoelastic
rocks
50-195
(1.46)
129.6
190
G
volcanoclastic
rocks
100.6-179.9
1.40
49.3
69
B
volcanoelastic
rocks
30-50
(1.05)
54.2
57
C
basaltandsandy
121ø51.96'
45ø42.12
',
121ø24.66 '
45ø39.16
',
121ø57.61 '
45ø38.90
',
121057.24 '
45ø38.43
',
5
121058.52 '
45ø36.75
',
36DDA
2N/5E
122007.50
'
45ø36.72',
36DDB
122ø07.65'
50-90
30-55
(1.59)
(1.05)
45.5
55.9
55-105
105-129
72
59
C
B
(67)
B
35.8
(1.05)
63.7
clay
clay and basalt
B
CR, ColumbiaRiver; MI, Miocene; CZ, Cenozoic;JR, Jurassic;The sectionlocationis subdividedinto quarterswhere a designation
12
ABCD indicatesa well in the SE 1/4 of the SW 1/4 of the NW 1/4 of the NE 1/4 of section 12. SE is the standard error of the mean.Values
in parentheses
are estimated.N is the numberof thermalconductivity
samples.
The gradientshaveall beencorrectedfor topographic
effects
wherenecessary.
The statistical
errorsof theheatflowvaluesareusuallyverysmallsoan estimateof theerroris givenasa qualityrating
of A (_+5%),B (_+10%),C (_+25%)and G (geothermalsystemvalue, no error implied). More detailsfor each site (includingholename,
elevation,and uncorrectedgradient)as well as data for sitesof lessthan C qualityare givenby Blackwellet al. [1989].
part of the Middle to Upper Jurassic ophiolite complex
[Brandon et al., 1988] exposed on Fidalgo Island.
Throughout much of the Puget Lowland, there is a thick
mantle of glacial till and gravel. Gradients are abnormally
low within these depositsdue to the generally active groundwater flow in these very porous and permeable units. This
circulation causes lower temperatures at depth beneath
these areas than would be expected based on the average
gradientvaluesfound in the bedrock units. No data from this
geologicsetting are listed in Table 1.
Heat flow and geothermal gradient values for these provinces are shown in histogram form (from the data listed in
Table 1) in Figure 3. Geothermal gradientsrange from 10øto
exposuresof supracrustalrocks of Paleozoic and Mesozoic
age and of granitic basementrocks of Mesozoic and very
early Cenozoic age. A few areas of Cenozoic volcanicrock
exist, such as in the Republic graben and other similar
extensional features. These features generally developed
from 42 to 55 m.y. ago. The province has been quite stable
duringthe last 30-40 m.y. The topographicrelief is high,but
the area is not extremely rugged. Unlike areas of similar
geology and heat flow in central Idaho, there are no hot
springsin the OkanoganHighlands. In addition, no holesin
thisprovince
havea gradient
in excess
of 35øCkm-•.
Histograms of corrected gradients and heat flow are
shown in Figure 4. The average geothermalgradientis
38øCkm-•. Thehighergradients
areusuallyassociated
with 25.3-+0.9øCkm-• andthe averageheatflowis 74.6+ 2.4
mWm-2 (Table2). The measured
gradients
for theholes
of
ple, in drill hole 12N/IW-9CCC gradientsrange from 18øto acceptable
qualityrangefrom14øC
km-• for hole32N/40E33øCkm-• in association
with thermalconductivity
(lithol- 4ADD to 35øCkm-• in hole 39N/33E-13BCA.This rangein
lower thermal conductivity rocks (such as clays). For exam-
ogy) variations.
Theaverage
geothermal
gradientof 26.0ø+ 1.2øCkm-• in
this area is associatedwith the volcanic units that make up
the bulk of the exposed rocks. Heat flow values are below
gradientpredominantlyreflects variationsin thermalcon-
ductivityandnot variationsin heatflow. In general,gradientsof 30øCkm-• or higherare associated
withCenozoic
volcanicand sedimentary
rocks that have lowerthermal
normal,ranging
fromaslow as20 mWm-2 to ashighas55 conductivitiesthan the older rocks. Gradients between20ø
mWm-2. Theaverage
is 40.1ñ !.8 mWm-2, whichis well
and30øCkm-• areassociated
withgraniticrocksthatmake
belowthe typicalcontinental
averageof 60 mW m-2. The
up a largefractionof the bedrockof the Okanogan
Highonly thermal manifestationsare warm springsin the Olympic
Mountains. No heat flow or temperature gradient data have
been obtained in the vicinity of these warm springs.
lands.
Thereis a smallrangeof reliableheatflowvaluesinthe
Okanogan
Highlands.As discussed
by Blackwell[1974,
1978],heat flow valuesare typicalof thoseobserved
OKANoGAN HIGHLANDS
throughout
theCordilleran
ThermalAnomaly
Zone,which
the BasinandRangeprovinceandthe Northern
The Okanogan Highlands physiographicprovince occu- includes
in IdahoandMontana.No radioactivity
piesthe northeasternquarter of the stateand representsthat RockyMountains
arereported
as partof thisstudy,butthe
part of the larger Northern Rocky Mountains province determinations
presentin Washington.The geology is complex, reflecting
the tectonic history of the Cordillera. The area has extensive
correlation
ofradioactivity
andheatflowin thisprovince
is
described
by Blackwell
[1974].Lowervaluesof heatflow
BLACKWELL
ET AL.:HEATFLOW,WASHINGTON
STATEANDCASCADE
RANGE
19,499
TABLE lb. ThermalandLocationDatafor theHeat Flow Sitesin Washington
CoastalProvinces
Average
Thermal
Township/
Range
Section
LatitudeN,
Depth
Longitude
W
Range,
m
48ø27.48' ,
80-220
34N/1E
Conductivity,
Corrected
W m-l K -1
SE
N
2.96
0.04
25
47ø14.27',
20N/12W
Flow,
Quality
øCkm-1
mWm-2
12.6
37
A
quartz diorite
27.4
36
B
shale
22
26.5
38
A
gravel, sand, and
clay
blue clay
122ø38.04'
1CBB
Gradient,
Corrected
Heat
Rating
0.1
Lithology Summary
304.8-1066.8
(1.30)
60-155
1.48
110-128
1.99
1
20.6
41
B
120-135
1.06
1
29.4
47
C
50-565
(1.26)
29.0
36
A
shale, sandstone,
46ø32.35',
122ø49.46'
46o31.99',
110-365
260-578
100-380
(1.09)
(1.46)
(1.09)
0.04
0.04
0.04
27.3
21.5
32.8
30
31
36
A
A
A
shale, sandstone,
122ø48.66'
710-760
1.77
0.01
5
18.2
32
A
4603!.75',
90-348
(1.09)
0.04
59
34.8
38
A
shale, sandstone,
90-340
340-690
690-847
100-177
(1.09)
(1.46)
(1.76)
(1.72)
0.04
59
5
1
36
36
39
37
A
A
A
B
shale, sandstone,
0.01
32.7
24.8
22.2
21.5
120-246
(1.30)
1
32.1
42
B
sandstone and shale
122-192
192-215
30-73
(1.05)
(1.59)
1.34
9
40
41
49
B
B
B
clay and basalt
0.09
38.5
25.6
37.0
60-150
1.59
0.04
17
31.6
50
A
124o11.47 '
8
46o51.00' ,
16N/12W
24DAD
13N/4W
7ABA
13N/3W
35BAB
12N/1W
7AAB
12N/1W
8DAA
12N/1W
9CCC
12N/lW*
124ø06.00 '
17BAD
12N/!W
17ADA
122049.48 '
46o38.02',
123ø13.57 '
46034.49 ' ,
123ø01.51 '
46ø32.68',
!22ø50.81 '
46ø31.65' ,
122050.07'
5N/1E
45ø56.4!',
5CDC
and siltstone
59
59
and siltstone
shale, sandstone,
and siltstone
and siltstone
and siltstone
sandstone and shale
122042.87 '
5N/1E
45ø54.12' ,
23CBA
122o39.35 '
4N/2E
14BA
2N/3E
45ø50.22' ,
122o31.72
45ø38.33',
21DC
122o26.42 '
IN/3E
45ø35.92',
2DB
See Table
0.04
clay, basalt, and
gravel
basalt and claystone
122o23.88 '
la footnotes.
*The thermal conductivity values for the wells in 12N/lW were estimated from Sass et al. [1971].
(65-70mW m-2) are associated
with lowervaluesof heat of knowledge of the aquifer system have been succinctly
described by Lindholm and Vaccaro [1988]. In the early
1980s,great interest was shown in the area for gas explora(withinthe80mW m-2 contourin Figure1), areassociatedtion, and several wildcat wells have been drilled with the
with graniteswith heat production values that range up to 4 deepest hole reaching 5340 m [e.g., Haug and Bilodeau,
/zWm-3 [Steele,!975].Similarheatflowandradioactivity 1985],but reliable temperaturedata for thesewells have not
correlationshave been reported for the southernCanadian been measured. In this case, knowledge of the subsurface
Cordilleraby Davis and Lewis [ 1984]andLewis et al. [1985]. temperaturesand geothermalgradientsis importantin evalThe mantleheat flow in this province is on the order of 60 uating the maturationlevel of organic material occurringin
generation.The highest heat flow values, particularly those
near the Spokane River in Townships 27N, 37, and 38E
mWm-2, andthe slopeon the Q-A plotis about10kin,
similarto other interior provincesin the Cordillera[Black-
the rocks beneath the basalt.
The thermal data for the Columbia
Basin
have been
collected by three different organizations: personnel from
the U.S. Geological Survey Water Resources Division
(USGS-WRD), Tacoma, Washington; personnel from the
COLUMBIA BASIN
Departmentof Hydrology at WashingtonState University
Introduction
(WSU), Pullman; and personnel from Southern Methodist
University (SMU)/Washington Department of Natural ReTheColumbiaBasinoccupiesthe southeastern
thirdof the
sources.Someaspectsof the copiousWSU data basehave
stateof Washington.Irrigation developmentof groundwater
been discussedbriefly by Stoffel and Widness[!983a, b] and
aquifersthat generallyoccur along flow contactsbetween
Widness[1983]. Many of the well logs have been presented
well, 1978].
basaltlayersandin interbedded
sedimentary
rockshasbeen
widespread.
Becauseof the largenumberof wellsandthe by Biggane[1981,1983]and Stoffeland Widness[1983b].
importance
of thegroundwater
resources,
extensive
hydrologicstudieshavebeencardedout in variouspartsof the Complexityof TemperatureLogs
Columbia
Basin.However,the regionalsettingof the deBlackwellet al. [1985]compiledan extensivedata baseof
tailedhydrologicstudiesand the interrelationships
of the
temperaturelogsin an attempt to evaluatethe background
whichthereis little information.The complexities
andstate thermal conditions of the Columbia Basin and look for local
manyaquifersand areas of developmentare subjectsfor
19,500
BLACKWELLET AL.' HEAT FLOW,WASHINGTON
STATEAND CASCADE
RANGE
TABLE
Township/
Range
Section
40N/27E
6BDC
40N/33E
2ACD
40N/33E
2DBB3
39N/33E
14ABB
39N/33E
13BCA
37N/26E
8DBC
37N/26E
24DCA
37N/32E
33AAC
36N/20E
19ADC
36N/20E
19DAB
34N/26E
23DA
33N/31E
14BDA
33N/31E
14ACB
33N/31E
14BDC
32N/40E
4ADD
31N/44E
34ADD
29N/37E
36DDD
28N/42E
5D
28N/37E
9DBD
28N/44E
31ADD
27N/37E
2BBB
27N/37E
3AAA
27N/38E
28BBB
26N/44E
12AAC
24N*44E
6BC
24N/44E
10AD
LatitudeN,
Longitude
W
48o59.74' ,
lc.
Thermal and Location Data for the Heat Flow Sites in Okanogan Highlands
Depth
Range,
m
Average
Thermal
Conductivity,
W m- 1K- 1
SE
N
Corrected
Gradient,
øCkm- 1
Corrected
Heat
Flow,
mWm-2
Quality
Rating
Lithology
Summary
60--180
3.16
0.08
19
22.3
70
A
75-205
3.17
0.13
22
22.7
72
A
Mesozoic
80-215
3.15
0.13
20
22.5
71
A
Mesozoic
29.6
68
C
granite
1
34.5
79
B
granite
26
21.5
75
A
biotitegranodiorit½
1
23.3
74
B
schistandgranite
17
31.1
76
A
Cenozoic an&site
greenstone schist
119ø29.19 '
48ø59.71',
118ø35.91 '
48ø59.67',
greenstone
118o35.95 '
48o53.11
',
greenstone
14-74
(2.30)
39-89
(2.30)
118o36.03'
48ø52.84',
118o35.32 '
48ø43.01',
165-435
3.50
24-123
(3.18)
150-260
2.41
0.13
119ø35.46 '
48ø41.15' ,
119o29.95 '
48ø39.99',
0.04
118ø46.38 '
48ø36.48',
0.2
140-275
2.88
0.08
15
26.7
77
A
Mesozoic
240-360
3.19
0.29
4
23.0
73
A
Mesozoic
104-184
(1.97)
!
27.0
53
B
metamorphics
granite
130-230
3.36
17
20.3
68
B
argilliteandquartz
120o23.07 '
48ø36.35',
metamorphics
120ø23.15 '
48ø25.77',
119o30.96 '
48ø21.75',
0.13
118o52.59 '
48ø21.75',
1.0
monzonite
205-270
3.11
0.08
9
22.4
69
A
quartz monzonite
120-200
3.36
0.13
18
19.5
66
A
porphyry
argi!liteand quartz
49-117
(4.39)
1
14.1
62
B
quartzite
95-155
(2.05)
1
27.7
57
B
granite
60-380
3.13
25
27.0
85
A
phyllite-argillite
19-144
(2.43)
27.5
66
B
6
25.1
76
B
sediment/clayto
granite
phyllite-argillite
1
24.9
68
B
6
26.7
87
B
118ø52.35'
48ø21.65',
118o52.78 '
48ø18.13' ,
monozonite
117o45.64 '
48ø08.77' ,
117o13.27 '
47o58.50' ,
.118ø04.00 '
47o56.90'
117o31.55 '
47o56.60' ,
!00-133
3.00
0.04
154-264
(2.76)
90-150
3.31
60-100
3.26
6
27.8
91
porphyritic quartz
100-145
2.54
2
33.0
84
Paleozoic marbhornfel
120-!59
(3.26)
1
27.2
89
granite
64-81
(2.38)
1
20.0
48
C
granite
25-147
(3.43)
1
30.1
!03
B
granite
118o09.20 '
47ø52.99',
117o16.98 '
47ø52.40',
0.04
118ø07.40 '
47o52.40' ,
monzonite
118ø07.40'
47ø49.00',
monzonite
118ø01.50 '
47ø46.10' ,
sediment/clayto
granite
porphyritic quartz
117ø10.80 '
47ø36.30',
117o17.99 '
47ø35.38',
117o13.22 '
See Table la footnotes.
thermal anomaliesthat might indicate higher than average variations in thermal conductivity that undoubtedlymust
potentialfor geothermalenergy in particularareas. In spite occur due to interbedded sediments and the different proof this extensive data base, however, there are still some portionsof vesicular versus nonvesicularbasalts.
uncertainities about the thermal conditions in the Columbia
Basin. Most of these uncertainties arise from the fact that all
the holesloggedwere drilled as water wells, and casingand
cementingis minimal. Furthermore, there are no holes that
have been continuouslycored and from which masonably
accurate in situ thermal conductivity estimatescan be obtained except on the Hanford reservation [Sasset al., 1971].
Hence we have little idea of possible vertical or lateral
The mostseriousproblem,however,is the natureof the
fluid flow associated
with the basaltaquifers.On a local
scale,permeability
acrossindividualbasaltflowsis quite
low, whereasalongcontacts
betweenflowspermeability
is
high.Thegeneralityof theseconditions
is indicated
by the
ubiquitous
upwardor downwardflow betweenaquifers
madepossible
by theopenholenatureof the wellcompletions.Consequently
temperature
logsfor waterwellsinthe
BLACKWELL
ET AL.: HEAT FLOW,WASHINGTON
STATEANDCASCADE
RANGE
TABLE ld.
Township/
Range
Section
26N/34E
10CAB
26N/33E
18ACA
24N/36E
16AAB
24N/31E
16BCC
47ø45.87' ,
47ø45.20',
118ø42.50'
47ø34.70',
8AB
117ø23.81'
22N/20E
26CBB
21N/31E
120o18.00 '
47ø22.11' ,
47ø20.00',
10CB
20N/22E
12ABC
19N/17E
23CBD
18N/26E
118o55.00 '
35C
16N/19E
12DB
16N/31E
15B
16N/21E
33CD
15N/17E
23ABC
15N/17E
119ø31.73'
36AAA
14N/16E
1CBD
120o38.49 '
13N/29E
13DB
12N/17E
11BBB
12N/20E
16CA
12N/22E
13CDC
12N/20E
36CD
11N/21E
47ø14.65',
47ø07.27',
47ø00.26',
46o53.37' ,
120o23.45
'
46•52.75',
46o49.63' ,
120o12.37 '
Flow,
mW m-2
!
55.4
88
B
CR basalt?
Quality
Rating
Lithology Summary
109-199
(1.59)
25-129
100-129
66-265
(1.59)
(1.59)
(! .59)
31.9
52.9
53.7
51
84
85
C
C
B
CR basalt
19-149
19-204
95-!25
(!.59)
(1.59)
(!.34)
52.8
58.3
41.6
84
93
56
B
B
B
CR basalt
28.4
62
A
rhyolite, arkose,
42.0
70
B
and sandstone
CR basalt
32.0
51
c
CR basalt
CR basalt
310-900
2.18
0.21
61-1250
1.67
0.21
18
CR basalt
49-264
(1.59)
10-170
(1.38)
29.4
41
B
70-100
(1.59)
49.8
79
C
CR basalt?
59-333
59-154
10-230
(1.55)
(1.55)
(1.59)
>27.3
29.4
59.1
>42
46
94
C
C
C
CR basalt
10-100
1.38
40-90
1.38
40-22
(1.59)
37.2
44.8
36.5
51
62
58
B
B
B
sandstoneand clay
75-595
(1.46)
31.6
46
B
clay, sand, gravel
20-110
(1.46)
35.9
53
C
andesite
54-89
(1.59)
22.9
36
C
CR basalt
20-55
(1.46)
39.0
57
C
sand and clay
50-160
(1.59)
32.8
52
B
CR basalt
10-2!0
(1.59)
48.3
77
C
CR basalt
80-120
(1.46)
64.2
94
C
grovel, clay, and
100-400
(1.59)
41.5
66
C
sand
CR basalt
60-200
(1.59)
33.3
53
B
10-350
(1.59)
32.3
51
C
85-450
(1.59)
32.9
52
B
130-210
(1.59)
41.0
65
C
150-330
(1.59)
28.8
44
B
sedimems and CR
basalt
sediments and CR
20-280
(1.59)
37.7
60
B
CR basalt
50-270
50-150
27-210
(1.59)
(1.59)
(1.59)
49.4
43.9
C
B
CR basalt
39.7
79
69
63
B
CR basalt
15-405
(1.59)
35.6
56
B
basalt with clay
10-192
(1.59)
32.0
51
B
CR basalt
10-90
(1.59)
27.2
43
C
CR basalt
5-120
(1.59)
34.3
54
C
CR basalt
110-605
(1.59)
41.1
66
B
CR basalt
1
CR basalt
46ø46.90',
120ø39.95 '
46ø45.13' ,
46ø43.77',
120o46.74 '
46ø43.72',
117o13.28 '
46ø40.40',
!20ø36.05 '
46ø37.50',
120o24.75 '
46ø36.77',
119ø07.28'
46ø33.06',
120ø40.11'
46ø31.56',
120o19.54 '
46ø31.25',
120ø00.71'
46ø28.64',
120o15.78 '
46ø27.53',
120ø12.15 '
22AC
120o10.53 '
46ø26.10' ,
46ø25.84',
46ø25.68',
23BB
119ø16.62 '
! !N/22E
46ø25.00' ,
120o07.13'
46ø24.57',
28CB
11N/46E
120ø04.51'
32BCA
11N/45E
32DAB
10N/41E
3DBD
!0N/28E
10ACC
117004.52 '
10N/28E
14ABB
Gradient,
øCkm-!
118ø55.10 '
11N/21E
16CDB
11N/21E
11N/22E
N
120o40.88 '
120013.50 '
30BA
SE
120o00.78 '
7AAC
11N/28E
Conductivity,
W m-• K -1
Corrected
Heat
118o16.37 '
23N/43E
11DBC
Depth
Range,m
Corrected
118ø31.18 '
47ø34.55',
118o56.07'
47ø30.41',
14N/44E
1BCC
14N/18E
29DBB
13N/19E
Thermal and LocationData for the Heat Flow Sites in Columbia Basin
Average
Thermal
Latitude N,
Longitude W
!9,501
46ø23.49',
46ø23.28',
sediments and CR
basalt
CR basalt
basalt
117011.45 '
46ø22.37',
117ø39.50 '
46ø21.97
',
119o17.43 '
46ø21.73
',
119ø16.13 '
19,502
BLACKWELL
ET AL.: HEAT FLOW,WASHINGTON
STATEAND CASCADE
RANGE
TABLE
ld.
(continued)
Average
Township/
Range
LatitudeN,
Section Longitude
W
10N/24E
36BD
10N/39E
32BCA
9N/32E
13BA
9N/27E
23CA
8N/33E
21D
8N/25E
36AB
7N/46E
2AA
7N/36E
17CAD
7N/46E
13BA
7N/35E
25AAC
6N/33E
!DBD
6N/33E
!0AD
6N/19E
46018.70' ,
46ø18.33',
46ø!6.04',
46ø14.82
',
46ø09.31',
3N/21E
19BAB
mWm-2
34.0
54
C
CR basalt
31.6
50
C
CR basalt
Rating Lithology
Summary
125-200
(1.59)
49-229
(1.59)
135-210
(1.59)
34.8
55
B
160-350
(1.59)
43.1
69
B
basalt with
interbeds
CR basalt
50-200
(1.59)
37.7
60
B
CR basalt
5-240
(1.59)
35.0
46
C
160-275
(1.59)
36.1
57
C
CR basalt(?)
100-225
(1.59)
35.4
56
B
CR basalt
15--85
(1.59)
40.8
65
C
CR basalt
85-260
(1.59)
34.0
54
C
CR basalt
60-305
(1.05)
69.7
73
B
cementedgravel/
20-85
(1.05)
106.8
112
C
cementedgravel
59-139
(1.59)
1
41.2
65
C
CR basalt
74-224
224-394
40-137.5
(1.59)
(1.59)
(1.59)
78
44
50
D
C
B
CR basalt
1
49.2
27.2
31.2
55-145
(1.59)
24.7
39
B
Quaternary basalt
160-195
(1.59)
39.0
62
C
CR basalt
65-150
(1.59)
33.5
53
C
CR basalt
30-70
(1.59)
53.8
85
C
CR basalt
1
46ø08.38' ,
119o37.78 '
46ø07.99' ,
116o59.88 '
46ø05.39',
118o20.30 '
46ø05.25',
116ø59.0I '
46o03.66' ,
118o22.22 '
46ø01.46',
118o37.30 '
46ø01.01',
clay
118o40.65 '
45ø59.52',
121ø02.86 '
3N/13E
Quality
øCkm-1
118ø40.99 '
22BCB
2lAB
N
1 ! 9o24.17'
45ø55.00' ,
120o11.49'
45ø54.46',
13DA
SE
118ø45.21 '
5N/21E
16CAB
5N/14E
3N/13E
W m-i K -1
Heat
Flow,
117057.87 '
120o22.97 '
28DDD
Range,
m
Corrected
Corrected
Gradient,
119045.43 '
24BC
5N/15E
Depth
Thermal
Conductivity,
45ø53.04',
CR basalt
120ø55.60 '
45ø44.66',
121006.95 '
45ø44.23',
121o10.94 '
45ø44.12' ,
120o13.55 '
See Table la footnotes.
Columbia Basin are typically complex and are difficult to
interpret. Recharge to the aquifers is quite distant from the
pointsof developmentof the aquifers, and flow pathswithin
the aquifer system must be complex and time dependent.
When the holes are drilled, drilling stopswhen water flow
TABLE le.
Township/
Range
Section
38N/8E
20
Latitude N,
Longitude
W
48o45.85
',
of appropriate quantity is encountered. As a consequence,
water wells almost without exceptionbottom in orjust below
aquifers (sites of potential up-or-down flow in the hole).
Another limitation with many of the temperature logsmeasuredby WSU and USGS-WRD is that loggingstartsat the
Thermal and Location Data for the Heat Flow Sites in Northern WashingtonCascadeRange
Depth
Range,m
Average
Thermal
Conductivity,
Corrected
Gradient,
Corrected
Heat
øCkm-•
mWm-2
Flow,
Quality
5
(309)
720
G
Quaternary
0.17
7
26.1
70
B
biotite schist
phyllite, nearhot
W m-1 K -•
SE
N
10-140
2.33
0.10
40-150
2.68
Rating Lithology Summary
121o48.30 '
26N/13E
27BA
26N/13E
28CD
25N/9E
4ADA
22N/11E
4BDA
47ø43.20',
volcanics
121ø07.21 '
47ø42.66',
121o08.50
47ø40.97',
20-!00
2.06
0.17
7
48.4
100
B
60-100
2.06
0.17
7
55.6
115
B
spring
120-145
3.03
2
20.0
61
C
greenstone
110-145
2.97
7
!4.7
44
B
phy!lite
121ø38.92 '
47ø25.54',
121o24.80 '
See Table la footnotes.
0.21
BLACKWELL
ETAL.:HEATFLOW,WASHINGTON
STATE
ANDCASCADE
RANGE
19,503
TABLE!f. Thermal
andLocation
Data
fortheLowHeatFlow
Sites
inSouthern
Washington
Cascade
Range
Average
Thermal
Township/
Range
Latitude
N,
Depth
Section Longitude
W Range,
m
16N/4E
23DDD
15N/4E
14DDA
13N/SE
18ABD
12N/2E
46ø5!.0!',
122o15.36'
46ø46.78
',
122o15.32'
46ø36.96
',
122o13-63'
46ø32.86
',
5DCD
12N/2E
9DAD
12N/3E
17DCB
12N/3E
19CBD
10N/4E
! 22o34.73'
46ø32.07',
122ø33-!7'
46ø31.33' ,
122ø27.54
'
46ø30.44',
122o29.23'
46ø22.65',
2DBA
9N/2W
I^DB
8N/4E
122o15.95'
46ø17.72',
122ø52.!4'
46ø!0.37 ',
14DD
122ø16.10'
5N/2E
45ø53.16',
25DBC
122o30.08'
5N/3E
28CCC
4N/3E
20ADD
3N/3E
21DAB
3N/3E
21DBD
2N/3E
12CAD
25-86.5
Corrected
Conductivity,
Wm-1 K-1
SE N
(!.97)
Gradient,
Corrected
Heat
Flow,
Quality
øCkm-1
mWm-2
Rating
2
10.2
21
C
basalt
2
19.8
34
C
basalt
Lithology Summary
100-!22
1.72
10-55
(1.09)
26.9
29
C
Eocene(?)sedimentary
!25-155
(1.67)
25.4
38
B
Tertiary volcanics
60-205
(1.67)
23.0
38
B
basalt
90-138.5
(1.67)
20.5
34
B
Eocene(?) basalt
65-232.5
(1.67)
27.0
45
C
Eocene-Oligocene
4
36.9
72
B
1
14.2
23
C
24.2
45
B
0.17
volcanics
15-141
1.95
20-135
(1.59)
50-150
1.85
70-156
(1.59)
32.0
51
B
(2.01)
20.4
41
C
38.0
60
B
Eocene basalt
27.0
42
B
Eocene basalt
0.19
clay, sandstone,
and basalt
45ø52.96' ,
70-97.5
0.06
!7
basalt?
122o27.00'
45ø49.10' ,
135-220
(1.59)
30-103
(!.59)
30-188
(1.59)
1
27.0
42
B
Eocene basalt
25-127
(1.59)
1
23.1
37
B
Eocene basalt
1
122o27.33 '
45ø43.77',
122ø26.23 '
45ø43.60',
122o26.40 '
45ø40.03',
122ø22.58 '
See Table l a footnotes.
watertable. Thus, if the well has flow up to, or down from,
thewatertable, the first measuredtemperaturemay be much
different
from in situ rock temperature.Temperaturelogsof
manyof the wells consist of a vertical line (isothermal).
Given the propensity of fluid to flow within the wells
ing down the hole. It was opened by the USGS-WRD for
hydrologictests in 1972, at which time it was loggedby the
WSU group. The hole was then plugged back to a depth of
730 m and is maintainedas a water level monitor well by the
USGS-WRD. Well logsmeasuredin 1961, 1972, and 1981are
followingcompletion,it becomesvirtually impossibleto shown in Figure 5. In 1961, water entered the hole at the
decipherthe nature of the thermal and fluid flow conditions water table (about40 m), flowed down the hole to a depth of
existing
at a particularlocationfrom a singlewell. Basedon
localaquiferconditionswithin the wells, gradientsboth
higherand lower than the "true" value mightbe encountered.Thusonly the overall averagegradientscan be determinedwith the presentdata set.
Temperaturelogs clearly show differencesin aquifer
heads
andalsodemonstrate
that theseaquiferheaddifferencesmay changewith time. Thus it mightbe expectedthat
localverticalleaksalongdikes,in fractureszones,or at
erosional
gapsin flows could causelocal fluid circulation
anomalies.However, no convincing evidence has been
discovered
sofar for geothermal
anomalies
associated
with
fluidcirculationof this sort.
Someof thecomplexities
of temperature-depth
curvesfor
a singlewell are illustrated
by referenceto DABE-1(21N/
31E-10CB,
seeFigure5). Thiswellwasdrilledasa hydrocarbon
exploration
testin 1960.It wasfirstloggedby R. F.
Royin !96!. Subsequently,
theholehada checkered
history
700-800 m, and exited into the formation. Below 800 m, the
gradientis nearly constant,and the temperature-depthcurve
is linear except for the bottom part of the log. The bottom
isothermalsectionmay have been due to additional intrahole
water flow or due to the fact that the cable had hung up (and
this fact was not recognized).The hole was loggedto the end
of the cable at about 1250m. By 1972 the flow pattern had
changeddramatically,and water flow was both up and down
from an entry point at about 500 m. The rate of flow down
the hole wasquitelow and occurredbetweendepthsof about
500 and 800 m. Artesian (up) flow occurredbetween 500 and
300 m. The presenceof upflow is indicatedby temperatures
above the interpolatedtemperature-depthcurve from below
900 m and the surfacetemperature intercept (about 12øC).
The curvedtemperature-depthrelationshipbetween 200 and
300 m and the fact that the observed temperature is higher
than the interpolatedtemperature suggestupflow, with the
200-300 m portion of the hole being heated by the upward
flowingwarm water (from 500 m). The sharpnegative-slope
thatincluded
itsbeingplugged
withrailroad
cross
tiesfora
timebylocalranchers
because
theycouldhearfluidcascad- part of the curvebetween500 and 600 m is very difficultto
19,504
BLAC•W•:.iLL
ETAt..'HEATFLOW,WASHINGTON
STATE
ANDCASCADE
RANGE
117
$
NORTHERN
mm/
WASHINGTON
I
ß
OKANOOAN
CASCADE
RANGE
(
,2
HIGHLANDS
-*%
,lB
+
./
/
SPI
OLYMPIC
tlOUNTAINS
E •
SQP\
COLUMBIA BASIN
+ ß + /•n
ß
x
+
x/
%$45
+,
HILLS
+ $,.,...
'•)•"
•
BASIN
x
+./ ..__.
./
$
SOUTHERN
+,
/+
i
WASHINGTON
SCAL•
UMATIL.LA BASIN
RANGE
/
KILOId[TtRS
COLUMBIA RIVER
/
Fig. 1. Heat flow map of Washington.Physiographic
provincesare outlinedwith dashedlines and identified.The
Pasco and Umatilla basins are subprovincesof the Columbia Basin. The volcanoesin the Cascade Range (large
asteriskswith a two-letter identification)are also shownfor reference.Locationsof StevensPass(SP), SnoqualmiePass
(SQP), SimcoeMountains(SM), andholeDABE-1
are identified.Data of acceptablequality(Table 1)are2 plottedonthis
2
figure. The map is contouredat 10 mW m- intervals. Heat flow symbolsare triangle,20-30 mW m-; circle, 30-40
mWm-2' cross,
40-50mWm-2- pluses50-60mWm-2. soliddiamond,
60-70mWm-:' solidsquare,
70-80mWm-:'
solidtriangle,80-90mW m-2' dot,90-100mWm-2' star,100-110
mWrf•-2' smallasterisk,
> 110mWm-2. The
location of the cross section in Figure 7 is indicated.
explainunlessup-or-downflow in an aquiferoutsidethe well
bore is included.The temperaturedata between 100and 200
m may represent the backgroundgradient unaffectedby
water flow. Following pluggingof the hole and its development as a water level monitor well, the flow pattern in the
hole changedagain. When the well was loggedduring 1981,
there was downflow through most of the hole, with water
entering at the water table and exiting at two locations,
between210 and 300 m and at a depth of approximately450
m. An aquifer at 300 m was either donating or extracting
on the western and eastern margins of the province.The
resultsof this studysuggestthat the high predictedSiO2heat
flow values in the Columbia Basin [Swanberg and Morgan,
1979] are related to the high gradients.
fluid.
aregenerally
50-60mWm-2 inareaswherethecrustismore
There are two interpretationsof the heat flow in the
Columbia Basin. The first is that the measured heat flow
values reflect the conductive heat flow from the crust below
the Miocenebasalt.Thishypothesisis supportedby thefact
that the heat flow variations are consistentwith probable
regionalvariationsof crustalradioactivity.Heatflowvalues
mafic[CatchingsandMooney, 1988]andalongthesouthern
Heat Flow and Geothermal
Gradients
andwesternmarginsof the provincewhere the crustappears
in composition
(westof the0.706lineofinitial
Basedupon analysisof the temperaturelogs [Blackwellet to betonolitic
Sr
isotope
ratios
[Kistler
and
Peterman,1978])andmost
of
al., 1985],the gradientrangethroughoutthe ColumbiaBasin
the exposedgranitoids
are very low in heat generation
is between 30ø and 55øCkm -] with a mean value of 40.6ø +
andBlackwell,1973].Similarheatflowvalues
are
!.8øCkm-]. The meanheatflow, excluding
datafromthe [Swanberg
found
in
western
Idaho
where
such
rocks
(of
Mesozoic
age)
westernedgeof the provinceis 62.2 +- 2.0 mW m-2.
[Blackwell
et al., 1990].Ontheother
Histograms of geothermal gradient are given in Figure 6. cropoutat thesurface
Basin,
There is a lack of detailedthermal conductivity information, hand,alongthe northcentralpartof the Columbia
rocksofhigherradioactivity
occur,heatflow
so it is not clear whether the variation in gradients is wheregranitic
associatedwith thermal conductivity variations within the valuesare 70-93mW m-2, typicalof thosefoundin basebasaltsor between basaltand sedimentaryrocks, or whether ment areas of the OkanoganHighlandsin northeastern
it reflectsgenuinechangesin heat flow in various locations Washington[Blackwell,1974;Steele, 1975].
Thesecond
majoreffectwhichmayinfluence
theheatflow
throughout the plateau. There is some evidence, as preofheatbygroundwater
flow.Thehighpermeabi!sentedin Figures 1 and 2, for higher than averagegradients istransfer
BLACKWELL
ETAL.:HEATFLOW,
WASHINGTON
STATE
ANDCASCADE
RANGE
125
123
121
19,505
119
117
q-
,,,
+
+
/
!
CASCADE
\
•
I
I
,,;
/
/"'
c.../
\ / •SqP
•
\
-" \
I
,
\
._.
%/
*.'
OLYIdPI½
\
IdOUHTAIN$
-
..T...\ \
WASHINGTON
\ ,n
//
\
/ q-
OKANO•AN
_. \
-
•HIGHLANDS
,,.
•
/
/•
m
DABr-1
"-'"/el--
COLUMBIA
BASIN
+//
+
WILLAPA
HILLS
[•
/
/.
SOUTHERN
+
WASHINGTON
CA, GAD[
I
&
i'•-. ßa]I
....,L...
•;•:s• ßP
•'
RANGE
• %.
BIA
RIVER
/ '"-"--__
.•LU[ ¾01
/
SCALE
UIdATILLA BASIN
/
KILOULr'rER•
Fig. 2. Geothermal
gradient
mapforWashington
(same
bascasFigm-c
1).Geothermal
gradients
fi'omholesor sites
of acceptable
quality(Tablci) m'cshown.Generalized
gradient
contours
arcshown.Gradientsymbols
a•c aim!c,
0%!0øC
kin-l, opcntriangle,
10•20øC
km-I;open
squa•c,
200-.30øC
kin-]' solid
tdanglc,
30ø-40øC
kin-l' solid
diamond,
$0ø-60øC
kin-i; clot,600--70øC
km-I .
ity of the basalt flow interbedsand the general lack of
coincidence
of piezometriclevelscertainlyindicatepotential
for groundwaterflow. Clearly, fluid flow must effect local
areas,but in spiteof the many holesdrilled in the basalt,no
anomalously
hot wells have been reported.Any flow that
'
St. Helens,and Mount Rainier. The two principallate
Cenozoicbasaltcentersare the QuaternaryIndian Heaven
area in the southcentralpart of the rangeand the Pliocene
Simcoevolcanicfieldin the southeastern
part of the range.
North of Mount Rainier, the bedrock geologyis predomiexistsmustbe relativelysubtle.There are severalhigh nantlypre-to mid-Cenozoic
crystallinerocks,includingboth
valuesof heat flow alongthe SnakeRiver in the Umati!la graniticintrusiverocks and metamorphicrocks. The only
subprovince;
these may indicate some flow toward the late Cenozoic volcanic rocks are the andesite-dacite volcatopographically
low areasalongthe fiver.
noes, Glacier Peak and Mount Baker.
Basedonthedataavailableat thistime,we conclude
that
The WashingtonCascadeRangeis the provinceof greatest
conductive
heat transferdominateson a provincewide geothermal activity in the state, with active or dormant
scale,althoughin local areasconvectionmightbe signifi- volcaniccenters,and severalhot springs.There are only a
cant.The surfaceheatflowpatternreflectsthe radioactivity few heat flow sites in the northern Washington Cascade
of the crustbelowthe basaltand the backarc regional Range,andonly three of them are far enoughwest to be near
setting.
Because
the heatflowfrombelowtheuppercrustal the areas of late Cenozoic volcanism. Two of the three are
radioactivity
layeris interpreted
to be similarfor theprov- associatedwith hot springareas [Korosec, 1983]. At Stevens
ince,eventhoughthesurface
heatflowvariesfromnortheast Pass(markedSP on Figure !; sites26N/13E in Table 1) one
to southwest,
the ColumbiaBasin is a singl• heat flow of the heat flow valuesis anomalouslyhigh and is obviously
province
in the sensedefinedby Roy et al. [1972].
affectedby the hot springcirculation, whereasthe other heat
flow valueis typicalof thoseseenin the southernWashington CascadeRange.The most northerly hole in Washington
is on the slopesof Mount Baker near Baker Hot Springs.It
Northern
Washington
Cascade
Range,
is also affectedby the hot spring circulation and does not
Snoqualmie
PassArea, ColumbiaRiver
give a typical background value for that area [Korosec,
WithinthestateofWashington
therearedifferences
inthe 1983].The sparseresultssuggestthat the regionalheat flow
geologic
natureof the CascadeRange.Southof approxi- may be similarto that foundin the British ColumbiaCascade
WASHINGTON CASCADE RANGE
mately47ø20
,, the basementof the Washington
Cascade Range(about80-90mWm-2 [Lewiset al., !988]).
Range
ispredominantly
composed
ofearlyto middle
Ceno-
Unlike the situationin Oregon, where the high heat flow
zoicvolcanic
rocks[Walshet al., 1987;Smith,1989].The zone has been identified for a north-south distance of at least
major
Quaternary
stratovolcanoes
areMountAdams,Mount 200 kin, the high heat flow zone along the Cascadeaxis in
19,506
BLACKWELL
ETAL.:HEATFLOW,WASHINGTON
STATE
ANDCASCADE
RANGE
COASTAL PROVINCES
COASTAL PROVINCES
N = 31
N=31
A
B
25
15
2O
F lO
F
R
Q
U
Q
R
E
E
U
E
N
C
Y
E
N
C
Y
s
lO
o
0
25
50
75
N=
lOO
150
HEAT FLOW (mW/m-m)
GRADIENT (DEG. C/KM)
S. CASCADE
50
o
100
RANGE
S. CASCADE
30
RANGE
N--30
C
D
15
25
2O
F 10 ...............................................................
R
E
Q
U
E
N
F
R
E 15
Q
U
E
N
C
Y
Y
0
25
50
GRADIENT
75
lO
lI,II[I
0
100
50
100
150
HEAT FLOW (mW/m*m)
(DEG. C/KM)
Fig. 3. Histogramsof geothermal
gradientand heat flow from Table 1. (a) and (b) For the coastalprovinces.
Provinces
includedarethePugetLowlands,OlympicMountains,
WillapaHills, andtheCascade
Rangewestof thehigh
heatflowzone.Barongradientplotshowsrangein gradientin hole12N/IW-9CCCassociated
with lithologicvariations.
(c) and (d) For the high heat flow region in the southernWashingtonCascades.
Washingtonseemsto be segmentedby areas of normal heat
flow around Snoqualmie Pass (SQP on Figure 1) and the
Columbia River. For many years the only heat flow values in
the Washington CascadeRange were near SnoqualmiePass
[Blackwell, 1969]. Heat flow values there are approximately
normal for continents, and there appeared to be no significant thermal anomaly in the Cascade Range. These data
stood uncontesteduntil drilling for heat flow measurements
beganin the late 1970s[Blackwellet al., 1982;Schuster
et
al., 1978].
Three new measurements
are low/normalandconfirmthe
valuesobtainedby Blackwell[1969].Oneholeis northwest
of theSnoqualmie
Passareaat a mineralexploration
loca-
tion,andtwoholes(22N/I1E-4BDA
and23N/IIE-33CAB)
weredrilledeastof thepassaspartof thisproject.
Finally,
theapparent
south
edge
oftheregion
ofnormal
heat.
flow
is
BLACKWELLET AL.: HEAT FLOW, WASHINGTONSTATE AND CASCADERANGE
19 )07
OKANOGAN HIGHLAND
OKANOGAN HIGHLAND
N = 26
N=26
A
B
15
'
25
20
F lO
F
R
R
E
Q
U
E
N
C
Y
E 15
Q
U
E
N
C
Y
s
lo
5
0
25
so
75
•00
0
GRADIENT (DEG. C/KM)
Fig. 4.
•00
•50
Histogramsof (a) geothermalgradientand (b) heat flow from Table I for the Okanogan Highlands.
poorlydefinedby a singlesite north of Mount Rainier.The
.reason
for the lower values observed in the Snoqualmie Pass
vicinityis not obvious. The values could be local anomalies
due to water circulation, although this explanation seems
unlikelysince the holes are scattered over a large area and
are in a variety of topographic settings. A discontinuous
regionalheat source at a depth is an alternative explanation
for these variations
so
HEAT FLOW (mW/m-m)
in heat
flow.
The
area
contains
a
structurallycomplex zone of transition between the southern
andnorthern Washington Cascade Range areas and is cut by
severalstrong lineaments, but there are no late Cenozoic
mW m ~, including those at the south edge of the Simcoe
volcanic field in Washington and north of the Mount Hood
area in Oregon [Blackwell et al., 1982, this issue]. The area
is most clearly defined on the gradient maps (Figures 2 and
9). Temperature-depth curves from holes along the Columbia River north and northeast of Mount Hood generally have
low gradients and are often curved, possibly indicating
regional downflow of water or recent climatic warming.
Temperature-depth curves from holes in the Quaternary
volcanics often are very complicated and in some cases
show
evidence
of transient
lateral
flow
of warm
water.
volcanics in the area.
Becauseno deep holeshave been drilled along the Columbia
Another anomalous zone of heat flow along the Cascade
Rangeis associated with the Columbia River. East of 122ø
(excludingholes drilled near the Bonneville and Trout Creek
hot springs,marked with a G quality in Table 1), most heat
River, or in the Simcoe volcanic field, the observed heat flow
pattern may need some revision when such data are obtained. Geothermal conditions need to be tested by drilling
flowvaluesalong the Columbia River are less than 60-70
TEMPERATURE, DEG C
0
25
TABLE
2. Summary
ofGradient
and
Heat
Flow
for
Various 0 , , . .; • ....
Areas
$1
ø ....
75
Heat Flow,
Gradient,øCkm-•
Average SE
Coastalprovinces
(all low values)
Southern
N
mW m-2
Average SE
N
•: 500-
26.0 1.2 31 40.1 1.831 •
44.5
3.0 30
75.4
4.4 30
•
BASALT EXPLORER 1
Washington
+ 21H/31[-lOGB
Cascade
Range
1 ooo
ß 211•J1[-lOGI
(highheat flow
region)
(Columbia
River)
Okanogan
36.9
25.3
4.8
0.9
9
26
53.6
74.5
4.9
2.4
9
26
40.6
32.8
1.8
2.3
55
7
62.2
51.0
2.0
1.7
55
5
Highlands
Columbia
Basin(all)
ColumbiaBasin
(westernmargin)
15oo
Fig. 5. Temperature-depth
curvesfor DevelopmentAssociates
BasaltExplorer1. Three logsmeasuredover a 20-yearperiodare
SE is the standarderror and N is the numberof data points illustrated.Logswereobtainedby R. F. Roy (1961),personnelfrom
State University(1972),and SMU {,1981).Every fifth
averaged.Quality A, B, and C data are averaged,but the averages Washington
donotchange
significantly
if onlyA andB qualitydataareused. pointon eachlog is plottedby a symbol.
19,508
BLACKWELL
ETAL.' HEATFLOW,WASHINGTON
STATEANDCASCADE
RANGE
COLUMBIA BASIN
COLUMBIA BASIN
N-- 55
N=55
A
B
15
25
2O
F lO ....
- .......
R
E
o
E
Y
E 15
;:[
o
i•.
N
C
F
R
E
N
.:
5 .-
..:.•..•.
.
..................
lO
C
Y
0
0
0
25
50
75
100
0
50
GRADIENT (DEC. C/KM)
Fig. 6.
100
150
HEAT FLOW (mW/m-m)
Histograms of (a) geothermal gradient and (b) heat flow from Table I for the Columbia Basin.
specificallyfor heat flow/geothermal gradient studiesand to
depths greater than 150 m to unequivocally determine the
heat flow along the Columbia River.
In the Oregon and southern Washington Cascade Range
45øCkm-• . Theseresultsareillustrated
in Figures
1,2,and
most of the rocks
width of the change (10 km) is similar to that in Oregon
are volcanic
or volcanoclastic
and have
similar thermal conductivities. In the northern Washington
Cascade Range and in the Okanogan Highlands, however,
there is quite a wide range of conductivity, from very high
values in quartzite and dolomite (e.g., hole 23N/11E-4DD in
Snoqualmie Pass) to low values in volcanic rock. Consequently, gradients in the northern Washington Cascade
Range, even without variations in heat flow and fluid flow
effects, can be expected to be much more variable than in the
southern Washington Cascade Range. The fractured granitic
and metamorphic rocks in the northern Washington Cascade
Range may be more brittle and more capable of holding open
fractures, and thus be more susceptibleto fluid circulation.
Indeed the geothermal field at Meager Mountain in British
Columbia [Fairbank et al., 1981], where temperatures in
excess of 200øC have been obtained
from holes drilled
7. The changefrom the coastalheat flow of 30-50 mW m-2
to high heat flow is well constrained along the profileand
occurs over a distance of less than 20 km. Thus the half
[Blackwell et al., 1982, this issue] and in British Columbia
[Lewis et al., 1988]. The change occurs within the southern
Washington Cascade Range physiographic province. The
eastern boundary of the high heat flow zone is not as well
located as the western boundary and is of lower relief than
thewesternboundary
(10-20mW m-2 insteadof 30-40mW
m-2) becauseit adjoinsthe highheatflowbackarcregion.
The heat flow and gradient data for the high heat flow
region of the southern Washington Cascade Range are
summarizedin histogramsin Figures 3c and 3d from the data
in Table 1. All data in the region includingthe datacollected
as recently as 1988 [Barnett and Korosec, 1989] are included. There is a wide range in heat flow and gradient,
in
fractured granitic rocks, indicates that there is potential for
deep fluid circulation in the geologicalenvironment existing
in the northern Washington Cascade Range.
•
Southern Washington Cascade Range
•_25
In 1981 a transect of holes was drilled just south of Mount
Rainier. The results of the heat flow measurementsalongthis
corridor, includingdata obtained from water wells to the east
and west of the drilled holes, are shown in the cross section
in Figure 7 (the location is shown as AA' on Figure 1). A
pattern similar to that observed in Oregon [Blackwell et al.,
1982, this issue] was obtained, although with a reduced
amplitude. Heat flow values west of approximately 122øW
arebelowthe continental
averageof 60 mW m-2, whereas
heat flow values between
122 ø and 120ø45'W are 70-108 mW
75
' ' ' ' ! ....
I ....
I ....
I ' ' ' w-
o
o
..•-ø•o'--ø-%-- -.o.
•o__.o
-
0-
II
,2•-w
I
1230W
II
121•W
o
t••100
7
o_.oQ_-.
_o o
•___•%___3t
'50-•__o__
/
bJ
-r
0
,
....
'o
5
a ,
,
'
'•'o
m'--ø
Mr. Roinier
,
,
'
O
50
DISTANCE,km
a ß ,
i
' ....
I00
Fig. 7. Heatflowcrosssection
forthesouthern
Cascade
Range.
Dataareplotted
asa function
of distance
alonganwesttoeast
line
m-2, andgradients
rangebetween34øand67øCkm-• . East south
of MountRainier
(seeFigure1 forlocation).
Therange
of
gradient
inhole12N/lW-9CCC
associated
withlithologic
variations
than60mWm-2, andgeothermal
gradients
rangefrom30øto is shownby the vertical line at 50 km on the profile.
of approximately 120ø45
', heat flow values decreaseto less
BLACKWELLET AL.: HEAT FLOW,WASHINGTON
STATEANDCASCADE
RANGE
TEMPERATURE
19,509
•C
This assumptionis approximately valid althoughthe values
•> may increasesomewhatwith depth. The implicationsof the
_ conductivityassumptionare discussedin more detail by
Blackwell et al. [1982] in their description of the temperatures in the Oregon CascadeRange. Becausethe downward
continuationprocessis inherently unstable, the calculated
temperaturestend to become variable (noisy) as the source
is approached.Becausewe do not know the actual source
"•.•----•..-•. •,OA$(:;ADE
ANOMALY configurationand the heat flow anomaly is partly interpreted, there is no "correct" answer, and the two temperature distributionsare merely indications of the actual tem-
(ARBITRARYi'
i
IOO
E
I-
•
•\\',•Lq•,.
.i .5
[
Ii
'Ii
i
i' I
•ES
peratures at the depths shown.
Two different models were calculated, one with the
sourcesat a depth of 15 km and one with the sourcesat a
depthof 12.5km. Calculatedtemperaturesat a depthof 5 km
for the source at 15 km are shown in Figure 9b. For the
reason described above the calculated temperatures are
300
more variable in Figure 9d with the sourcesat 12.5 km than
Fig.8. Temperature-depth
curvesfor theSouthern
Washington in Figure 9c with the sources at 15 km. The maximum
Cascade
Rangeand Coastalprovinces.A constanttemperaturewas calculatedtemperaturesare higher in the second case besubtracted
from each curve to give a 0øCsurfacetemperature.Data causethe 10km depth is closer to the plane of sources.Both
for manyof the holes in the low and high heat flow regionsare of the modelswere calculated assumingsteady state condiillustrated.The two holes west of Mount St. Helens are clearly
associatedwith the low heat flow area.
tions, a reasonableassumptionif thermal conditionshave
The major contrastin heat flow and geothermalgradient
betweenthe coastalprovincesand the WashingtonCascade
Rangeis clearlyillustratedby the temperature-depth
curves
fromthe two regimesin the southernWashingtonCascade
not changeddrastically for 2 to 5 m.y.
The resultsare consistentwith temperaturesof 400ø-500øC
at 10 km over a regionof about 100 by 100 km in the southern
Washington Cascade Range. The highest temperatures
(500ø-600+øC)are alignedin a NNE-SSW direction in the
center of the anomalousarea. The positions of Mount St.
Helens (westedge)and Mount Rainier (north edge;although
the data on which the positionof the northwarddecreasein
heat flow are based are weak) are peripheral to the high-
Rangeshownin Figure 8. Most of the holesthat are in the
temperaturezone, and the area of highesttemperatureis
"CascadeAnomaly" are shown, as are about half of the
wellsin the low heat flow region to the west.
alignedthroughthe Indian Heaven and Goat Rocks centers
of late Cenozoic volcanism. Mount Adams may lie along the
indicating
that the thermalfieldin thisregionis complicated.
Theaveragegradientand heat flow for the area are 44.5ø __+
3.0øC
km-1 and75.4 -+4.4 mW m-2 respectively.
The difference between the two sets of data is clear.
apex of the anomaly.This broad area, and especiallythe
Temperature-depth
curvesfrom two holesimmediatelywest Goat Rocks area, is a major center of Quaternary volcanism
of Mount St. Helens are superimposedon Figure 8 and [Swansonand Clayton, 1983;Smith, 1989].Thus the area of
clearlyindicatetheir association
with thelow heatflowsetof highestcrustal temperaturesappears to be axial to the
holes.These holes were drilled in 1979, and hole 9N/5E- volcanicarc, the backgroundtemperaturein the arc is high,
18BB(STH-2) was buriedby the debrisflow associatedwith and as to the south in Oregon, there is a sharp edge to the
thecollapse
of the northsideof the volcanoonMay 18, 1980. west side of the high heat flow region (passingthroughthe
A drillingproject on the east side of Mount St. Helens site of Mount St. Helens). The locations of Quaternary
volcaniccentersmay occur anywhere within this area, so
plannedfor 1980 was not carded out.
The thermal data in the southern WashingtonCascade each volcano is not only an isolated spot of short lived
activitybut is alsopart of a crustalscalethermal
Rangeare of sufficientdensityto warrant detailedinterpre- magmatic
tation. Because the thermal conductivity does not vary a anomalythat has developedas magmatismhas proceeded.
Stanleyet al. [1987,this issue]have describedextensive
greatdeal in the volcanic rocks (see Table 1), a gradient
measurements
of crustalresistivityin westcontour
map(Figure9a) waspreparedandusedfor interpre- magnetotelluric
tation.Alternativeinterpretationsof the detailsof the pat- ern Oregonand Washington.Two of the conductanceconternarepossiblegiventhe sparsityof the data,but the main tours from their studiesare plotted with the 5-km temperafeatures
of the sharpeasternboundaryandthe northeast/ turesin Figure9b. Thereis not a one-to-onematchbetween
contours
of highesttemperature
andconducsouthwest
trendingaxial high are well constrained.The theinterpreted
interpretation
includespart of the Simcoevolcanicfieldin tance, but there are no thermal data that constrainthe
theregionof highheatflowalthoughthereareno heatflow northwest comer of the thermal anomaly where the two
interpretations
diverge.High crustaltemperatures
do exist
measurements that confirm this inclusion. Also the western
boundary
is assumedto be orientednorth-south.The hand- over about 3/4 of the area of the conductance anomaly.
contoured
gradients
weredigitizedon a 15km by !5 km grid Stanleyet ah [thisissue]concludethat !ithology(i.e., a deep
package(an underthrustwedge))is primarily
andinputinto an inversionproceduredevelopedby Brott et sedimentary
responsible
for the conductance
anomaly.
a/. [1981][seealsoBlackwellet al., !982].
in contrast,the low resistivity(high conductance)zonein
The downwardcontinuationtechniqueis based on the
spaplacing
of a seriesof pointheatsources
at a specified
depth. the OregonCascadeRangethat is closelyassociated
Uniform
thermalconductivity
is assumed
inthecalculation.cially with the high heat flow is interpretedto be due to
19,510
i3•.•,xc•,:'•,
ELLET AL.: HEATFLOW,WASHINGTON
STATEANDCASCADE
RANGE
30
'
t.•O
•¸
•20
150
180
210,,,,.,
0
30
60
I"''
,-,o,
•
90
120
180
2!
. MR
-150150•....' "
9o
150
R
9o
60•"•
3o•
• •LUMBIA
RIVER
60 60
OBSERVED
3o
• GRADIENTS
00/
I
I ......
!
30
I
60
I ,
90
I
I
120
I
I
! 50
I
•
180
3o
•
0
TEMPERATUR
I
AT5 KM
I
I
I
I
DISTANCE, KM
0
210
, 30
,,,,,,,
60
90
I
120
150
180
210
30
210 d2100
ß
60
90
60
•
COLUMBIA
I
120
I
150
180
2!0
I
60
I ,
90
I
I
I
I,
I
. I
120 150 180
500
60
RIVER
30 TEMPERATURE
,o
30
I
;SH '.
'
,,,I
I
..
E
I
I , I
•o
F
O0
I
•STANCE, KM
I
.................
3o 30 TEMPERATURE
I
I
•
DISTANCE, KM
00
I ,
I
30
I
I
60
I
[
90
I
I
I
I
I
I
I
,0
120 150 180 21•
DISTANCE, KM
Fig. 9. Interpretivemapsof gradientand temperaturefor the southernWashingtonCascadeRange.Heat flow sites
are shown on Figures 9c and 9d reference. (a) Observed geothermal gradient maps. (b) Downward continued
temperaturesat 5 km for a sourceplane at 15 km. The shadedregion containsthe I000 and 5000 S conductancecontours
from Stanley et al. [this issue]. (c) Downward continued temperature at 10 km for a source plane at 15 km. (d)
Downward continuedtemperaturesat 10 km for a sourceplane at 12.5 km.
"metamorphically produced fluids and partial melt in a
regionwhereductilebehavioroccursat the top of the 6.4-6.5
km/svelocitylayer" [Stanleyet al., thisissue].The question
of the validity of the extrapolationof the heat flow datafrom
the shallow holes to temperaturesat midcrustallevels in
Oregonhasbeen discussedin detail by Blackwellet al. [this
issue].Becausemostof the argumentsapplyto thisareain a
similarfashion,the discussion
will not be repeatedhere. So
assumingthat the interpreted location of the heat flow
anomalyis correctandthat the temperaturescalculatedare
reasonable,at the depth of the sedimentarypackagethe
temperaturesare quite high, and metamorphismmight modify the electricalpropertiesof the sediment.The rather close
geographicrelationshipof high electricalconductivityand
high midcrustaltemperaturein northern OregonaM in
southern Washington suggeststhat temperature, or tem•r-
ature relatedeffects,rather than rock compositional
effects
may be dominantin causingboth of the low resistivityzones,
DISCUSSION
Summary of Washington Heat Flow Distribution
Theaverage
heatflowandgeothermal
gradient
values
four
the various provinces discussedin this report are summa-
rized in Table 2. The thermal patterns in Washingtonare
similarto thosediscussed
by Blackwell[1978],except
t•,•h•':
•
thereisnowa significant
heatflowdatabaseinandwest
of
BLACKWELL
ET AL,' HEAT FLOW,WASHINGTON
STATEANDCASCADE
RANGE
19,511
theCascadeRange.The thermalprovincesincludethe low thoughsubductionis no longerpresentalongmuch of this
heatflow coastalregionwest of the WashingtonCascade length, the long thermal decay time of the low heat flow
Range
heatflowanomaly,whereheatflowaverages
40 mW preserves evidence of subduction for tens of millions of
m-2, the southernWashingtonCascadeRange heat flow
years. Thus the continuity of the low heat flow areas
anomaly
whereheatflowaverages
75 mW m-2, andthe dramaticallyconfirmsthe validity of the hypothesisthat
Okanogan
Highlandswhereheatflow alsoaverages75 mW
subductionwas continuousalong the west coast of North
America in the early and middle Cenozoic [Blackwell, 1971a;
-2
Averageheat flow in the ColumbiaBasinis 62 mW m , Roy et al., 1972]. The intermediate focus earthquakesbesignificantly
lowerthan in the Okanogan
Highlands.This neath the Puget Soundregion are contemporarymanifestadifferencein heat flow may be associatedwith differencesin tions of this subductionactivity.
heatlossfrom the mantle or differencesin the heat producIt is unfortunate that there are not many data for the
tion from radioactivity within the crust. The crust beneath transitionbetweenthe OkanoganHighlands/ColumbiaBasin
thepartof the ColumbiaBasinwherethe heatflowis lowest and the WashingtonCascade Range. Based on the results
appears
to be unusuallymafic,basedon seismicrefraction from this study and data from Canada [Lewis et al., 1985,
data[Catchingsand Mooney, 1988], so the heat flow from 1988], heat flow values in the two provinces are similar.
themantlewithin this province may be essentiallythe same However, the details of heat loss in these two provinces
as the heat flow at the surface. The average heat flow is must be quite different. The heat flow in the Washington
•m
-2
ß
nearly
equaltotheintercept
value(60mWm-2) onthelinear CascadeRangeis relatedto a heat sourceat an apparent
heatflow-heat productionline (heat flow at an upper crustal
radioactivityof zero; see Blackq4,ell[1971b] and Roy et al.
depth of about 10 km. In contrast, the high heat flow in the
OkanoganHighlands (and the provinces to the north and
[1972]for discussionsof the heat flow-heat production south, the Cordilleran Thermal Anomaly Zone of Blackwell
relationship)for the OkanoganHighlands.
[1969]) is related to back arc processeswith thermal source
The pattern of heat flow in the southern Washington regionsin the upper mantle and lower crust that are associCascadeRange is relatively well defined, although many ated with past and present thermotectonicevents affecting
detailsremainto be determined,particularly alongthe north, the whole Cordilleran Mountain chain. The back arc thermal
east, and southeast boundaries of the thermal anomaly. anomaly involves a much larger area and owes its origin to
Much of the variation may be due to lateral changesin the the interplay of several mechanisms such as extension,
strengthor depth to the heat sourcethat causesthe high heat magmatism, and thinning lithosphere [Roy et al., 1972;
flow. However, some of the variation may be due to fluid Lachenbruch and Sass, 1978; Blackwell et al., !990],
flow conditions, or other local situations.
whereas in the volcanic arc shallow crustal intrusion domi-
The geothermalgradient pattern for Washington is somewhatdifferentthan the heat flow pattern; for example, there
is almosta factor of 2 difference in the average gradient in
the southernWashington Cascade Range and in the Okahogan Highlands even though the heat flow values are
nates.
Cascade Range Heat Flow
Extensive studies of geothermal gradient and heat flow
have been carded out in the Cascade Range in Oregon.
tivity of the volcanic rocks in the southern Washington Major results include the location of a sharp eastward
CascadeRangeis lower. So in spite of the similar heat flow, increase from lower than normal heat flow to much higher
temperaturesat 10 km beneath the southern Washington than normal heat flow within the Western Cascade Range
Cascade
Rangemay be up to twice as highas thosebeneath (the mid-Cenozoicvolcanic arc) and mappingof the western
the OkanoganHighlands. High gradientsare also observed boundary of the high heat flow zone for half the length of
in the Columbia Basin. These high gradientsare partially Oregon. Average heat flow values in the high heat flow zone
similar. This difference
arises because the thermal
conduc-
related to the fact that the basalts have a low thermal
are 101mW m-2 andaveragegradients
are 64øCkm-l
conductivity.The averagegradientsare slightly lower than [Blackwell et al., 1982, this issue]. As part of the Oregon
theaveragein the southernWashingtonCascadeRange.The studies, extensive drilling was carried out near the Mount
geothermalgradient beneath the Columbia Basin will de- Hood volcano (25-50 km south of the Columbia River).
creasewith depth when the rocks beneath the basalt are Steele et al. [1982] concludedthat the backgroundheat flow
encountered
becausethe sedimentary/metamorphic/igneousvalue in the High CascadeRange decreasesfrom 100 mW
rocksthat make up the basementwill have higherthermal m -2 to 70-80 mW m-2 betweenMount Jeffersonand Mount
conductivities
than the volcanicrocks. Hence at a depthof Hood.
The transitionfrom high to low heat flow along the west
10 km the temperaturesbeneaththe ColumbiaBasin are
probably
closerto thosein the OkanoganHighlandsthanto sideof the CascadeRangeover a distanceof approximately
20 km is uniquelysharpfor a regionalthermal boundary.The
thosein the southernWashingtonCascadeRange.
Theoriginfor the low heatflow westof theCascadeRange half width of 10 km indicatesa depth of the sourceof about
is associatedwith the subduction of the Juan de Fuca 10 km. Heat flow measurements in British Columbia indicate
oceanicplate beneaththe westernpart of North America a similarpatternof low heat flow alongthe coastand high
[Blackwell,
1971a,b, 1978;Blackwellet al., 1982].As the heat flow inland, where the Cascade Rangeheat flow values
from65to90mWm-2. Thetransition
fromlowt.ohigh
oceanicblocksinksbeneaththe continentalplate, the upper range
partof the oceanicplate absorbsheat from the continental heat flow occursalonga line of gravity gradients,anomalous
block,causing
the low heatflow. Thiszoneof abnormally upliftrates,andfaulting[Hyndrnan,1976;Lewiseta!., 1985,
low heat flow has been identifiedfrom British Columbiato 1988].
Contoursof heat flow for the entire lengthof the Cascade
BajaCalifornia
[Royet al., !972;Hyndman,!976;Lewiset
a!., 1988;Blackwell,1978;Blackwellet al., 1990].Even Rangeare shownin FigureI0, and heatflow sitesare shown
19,512
I•l.**CK•,'EL
ETAL' HE-'•T
FLOW,
WASHINGTON
STATE
ANDCASCADE
RANGE
125ø
50ø
120ø
Idki
D
50ø
BRITISH
-
ß
to illustratethe data densityin the variousareas.The most
seriousdata gapsare in northernWashington,in southern
Oregon, and in northern California. The contoursoutlinea
thermalsegmentation
of the CascadeRange.This segmentation has been discussedin brief by Blac'k•,'elland Steel
[ 1983],and other categoriesof segmentationof the Cascades
0
'
Rangehavebeendiscussed
by Guffantiand Weaver[1988].
100
Major troughs in the Cascade thermal anomal) are at the
Scale. km
ColumbiaRiver and in central Washington.The originof
thesetroughsis not clear;they maybe due to gapsin magma
•ldB
productionalongthe arc over the last 5 m.y. or so. However,
thereare hot springsin bothgaps[Mariner et al., thisissue].
Deeper drill holes in both areas are neededto resolvethe
true crustal heat flow in the area.
The near constant half width {10 km) of the west side of
the thermal high is an interpretation, but it is documented
in
three widely separatedareas: British Columbia, southern
Washington,and northern Oregon. This half width ma•
characterize the depth to a thermal anomaly causedb.• a
zone of shallow crustal magma residence since it doesnot
appear to consistentlycoincide with any major, crustal,
seismicvelocity boundary (and by inference any lithologic
boundary).A superimposedthermal peak of about10+ mW
m -2 coincideswith the axis of greatestvolcanicproduction
in the southern Washington Cascade Range, and a similar
45 ø
45 ø
thermalpeak has been documentedat Mount Hood [Steele
et al., 1982]. Other such thermal concentrationshave not
been resolvedprobablydue to data limitationsratherthan
the lack of such features.
Blackv•,ellet al. [1982] calculated the ratio of intrusiveto
extrusive volume in central Oregon by assuming that the
excessheat flow above the backgroundrepresentedthe heat
lostby the intrusiveprocess.The calculations
werebased
on
volumes of extrusives estimated by White and McBirn v
[ 1978].New calculations
of intrusiveratealongstrikeforthe
wholerangeare shownin Figure11.Theseresultsarebased
on new along-strikeestimatesof volcanicextrusionvolume
for the last 2 m.y. presentedby Sherrodand Smith[thi•
issue],alsoshownin Figure11.Theseestimates
appear
tobe
conservative.
Priest[thisissue]estimates
20-30km3 (2
m.y.)-• km-• for centralOregon(about85%of which
is
basalt)and M. A. Korosec(unpublished
data, 1989)estimatesan additional10km3 (2 m.y.)-• for partof southern
Washington.
The observed
heatflowalongthearcandthe
assumed
heatflow background
are alsoshown.In calculat-
ing
theratesof intrusion
it wasassumed
thatthe100mW
-2
40
124ø
40 ø
120 ø
m heatflow observedalongthe westernsideof theHigh
Cascade
Rangein Oregonrepresents
the average
heat
all acrossthe arc. If the axial heat flow is higherlandit
probably
is),thevolume
estimates
wouldbeproportionall.•
increased.
Fig. 10. Summaryheatflow mapof the CascadeRange.Data
pointsandmajorvolcaniccentersareshown.Datapointsareshown
for locationonly.Datafromthispaper,Blackwell
et al. [thisissue],
higherthanthoseestimated
by Blackwell
et al. [19821
mW m-2; large asterisksare major CascadeRangevolcanoes
(identified
by two letterabbreviations).
The volcanoes
are, from
northto south,MM, MeagerMountain;MG, MountGaribaldi;MB,
above
givesomewhat
lowervolumes
of extrusion
ox.
erthe
last2 m.y.thanBlacku'ell
et al. [1982]inferred
fromthe
McBirney
andWhite[1978]
data.Typical
ratiosrange
from
Lewis et al. [1988],and Mase eta!. [1982].Heat flow contoursin
Mount Baker; GP, Glacier Peak; MR, Mount Rainier; SH, Mount
St. Helens; MA, Mount Adams: MH, Mount Hood; MJ, Mount
Jefferson;TS, Three Sisters;NV, Newberry volcano;CL, Crater
Lake; MM, Mount McLoughlin;MS, MountShasta;ML, Medicine
Lake; LP, Lassen Peak.
The ratiosof intrusionto extrusionshownin Figure11are
because
the recentdetailedgeologicstudiesmentioned
approximately
5or10-1incentral
Oregon
toperhaps
50-100
to 1in BritishColumbia.
Thisdifference
mightberelated
to
thecrustal
differences,
orperhaps
theextrusive
volumes
in
BritishColumbia
areunderestimated
because
of thehigh
ratesofglacial
erosion
there.Furthermore,
theestimates
lot
BLACKWELL
ET AL.' HEAT FLOW,•,•ASHINGTON
$T•,TEANDCASCADE
RANGE
19.513
I00 -
•
50
O"
I00 -
'""
..........
•'^.c eACKGROUNO
............
=
•:•
•
•
•:.J ea
•o
•
i
W^SH,,GTO,
I
O,EGO. I
MA
20
0
l
....
I•
MS
L
'-
5•
DISTANCE ALONG ARC,
0
KILOMETEES
Fig. 11. Volumes of volcanic rocks for the last 2 m.y. [Sherrodand Smith, this issue],heat flow, and inferred intrusive
volumes along the CascadeRange.
BritishColumbia relate almost exclusively to silicic volcanic
500øCin British Columbia and 600ø-800øCin Oregon. In this
case {assuminga constant background) the rate of intrusion
There are two major conditions that would modify the holds the heat flow constant, but the temperature varies. The
calculatedamounts of intrusion. First, because the heat flow
higher thermal conductivity of the upper crust in British
data have no depth-to-source resolution except along the Columbia more efficently transmits the intrusive heat to the
a est sideof the anomaly, high lower crustal heat flow along surface. Consequently, crustal type may play a role in the
thecenterand east side of the Cascade Range could decrease thermal regime of a volcanic arc.
the amountof shallow intrusion required below that calcuThe temperatures are high enough along most of the
lated in Figure 11. It might be argued that the appropriate Cascade Range that metamorphism should be occurring at
b ckgroundto use in the calculation is a high heat flow the present time. Temperatures in the range of 300ø to
typical of the Cordilleran Thermal Anomaly Zone or of a 600+øC at 8-12 km are well within the range of low-pressure
regionsubjectto a flux of lower crustal marie intrusions.In metamorphism of rocks to greenschist to granulite facies.
thiscasethe heat flow backgroundcouldrangefrom 20 to 40 Thus the area may be a natural laboratory for study of a
mW m-2 higherat variouslatitudesalongthe Cascade crustal region undergoing metamorphic processes. Barton
rocks.
Range,and the rate of upper crustal intrusionwould be
and Hanson [1989] [also Hanson and Barton, 1989] have
decreased. In British Columbia the rate of intrusion would
recently discussed the thermal requirements for lowpressuremetamorphism.They inferred that temperaturesin
30-10km3km-I (2 m.y.)-1 fromthevalueof 110km3km-l volcanic arcs are not high enough to form low-pressure
[2m.y.)-l shownin Figure11.Alongthewestboundary
of metamorphism for much of the time. In the Cascade Range,
theCascade
thermalanomaly,the 10-kmhalfwidthrequires however, it appears that temperatures are sustainedat high
thehighesthorizontalthermalgradientsto be in the mid- enough levels to cause metamorphism for long periods of
crust,so the outer arc heat flow is the correct background. time (several millions of years).
The ratio of intrusion to extrusion is probably a characSecond,
the heatflowmaybe higheralongthe axisof the
Cascade
Range,in Oregonespecially,
thanassumed
for the teristic property of volcanic arcs, but the relationship has
purposes of the calculation. In this case the intrusion rate
been difficult to quantify. It has been assumedfor volcanic
v•ouldbe underestimated,and so the real rate might be terrains in general that lower ratios might be associatedwith
more marie volcanism whereas higher ratios might be assohigher
thanthevaluesshownin Figure11.
be proportionally
mostaffectedand mightdrop as low as
Thesimilarityof the heatflow in the BritishColumbiaand
ciated with more silicic volcanism. This model was the basis
Oregon
Cascade
Range(about90mWm"2compared
tojust for the use of volcanic type in evaluating the geothermal
overILK}mW m-2) is not reflectedin the crustaltempera- resourcepotential of the United States [Smith and Shaw,
tures.At a depthcorresponding
to the half width and thus 1975]. The data presentedhere representthe first heat loss
nearthe source(10 kin), the temperaturesmay be 400ø-- measurementsthat can be related to magmaticprocessesand
HEATFLOW,WASHINGTON
STATEANDCASCADE
RANGE
thatdocumentquan•.i't'i•ei.y
this hypoihesis.
Whilethereare
a number of uncertaintiesassociated with the values calcu-
bodies.
Thermalmodelsare consistent
withthisorigin
the metamorphism [Yoreo et al., !989].
latedin thispaper,the ratesancttheirgeographic
variation Thesurprising
consistency
of the halfwidthof theheat
represent
a newsetof parameters
to helpin understandingflowtransition
in Oregon,southern
Washington,
andsouth.
the igneousprocesses
in volcanicarcs.
ernBritishColumbiarequiresa consistency
in heatsource
depththat is not affected
by volumerateof extru•c}a,
averagecomposition
of volcanics,crustaltype, or stress
state.As pointedout by Blackwellet al. [thisissue],the
Curiepointdepthsin Oregonareconsistent
withthedown.
The conclusionby Blackwellet al. [ 1982]that the Cascade
wardcontinuationof surfaceheatflow to depthsof at least
CascadeRange •'Magma Chamber"
Rangeis underlainby a broad upper crustalheat source
5-10km, wheretemperatures
are300ø-500øC.
Thegravity
(depth of 8-12 km) that is a magmastagingregion is not datain the centralOregonCascadeRangeare alsoconsistera
widely accepted.The favored spot for a zone of regional with a midcrustalregionof low density,althoughbecause
of
crustal residence, melting, assimilation, and fractional crysthe
complex
regional
field
and
upper
crustal
density
contalization in volcanic arcs is at the crust/mantle interface.
traststhe depth to this regioncannotbe well constrained.
In
For example,Leemah et al. [this issue]describethe evolu- Washingtonand British Columbia[Lewis et al., 1988]there
tion of Mount St. Helens dacite by open-system crustal are gravity gradientscorrespondingto the heat flow transianatexisat the crust mantle boundary. In discussingmagma
tion, althoughthe amplitudeof the gravity anomalythatcan
evolution in volcanic arcs in general, Hildreth and Moorbath
[1988, p. 485] conclude that the
data lead us to envisage deep beneath each large magmatic
center a zone of melting, assimilation, storage, and homogenization (MASH), in the lowermost crust or mantle-crust transition, where basaltic magmasthat ascendfrom the mantle wedge
becomeneutrally buoyant, induce local melting, assimilateand
mix extensively, and either crystallize completely or fractionate
to the degreenecessaryto re-establishbuoyant ascent. Magmas
ascendingfrom such zones may range from evolved basalts to
dacites, but all will have acquired a base-level isotopic and
trace-element signaturecharacteristicof that particular MASH
zone.
The requirements of such a zone to satisfy the geochemical data do not obviate
the need for shallower
zones of
residence, interaction and sourcing, particularly for large
volumes of very silicic melts to be generated and erupted.
There is no question that such large-scale upper crustal
zones existed in some settings in the past. For example, a
large system of this sort existed in Idaho during the Eocene
[Criss and Taylor, 1983],when a zone about 50 km wide and
severalhundred kilometers long was the site of shallowlevel
granitic intrusions probably overlain by massive caldera
systems.
On the North Island of New Zealand the Taupo graben
represents the site of a massive, upper crustal, silicic,
magma chamber in a volcanic arc setting [Wilson et al.,
1984]. In fact, andesite stratovolcanos typical of volcanic
arcs are located immediately south of the area of silicic ash
flow volcanism. In the Japanesevolcanic arcs there is very
little basalt erupted and the volcanicsare dominatelyandesitc and dacite in composition.The spacingof volcanoesis
about 50 km in contrast to the 75-km spacingof the Cascade
Range. Perhaps the midcrustal residencezone is an even
more continuous zone of crust at melting or near melting
temperatures than is the case in the Cascade Range.
Finally, during the Devonian a situationthat resultedin a
thermal pattern that is in many ways similar to the one
proposedfor the CascadeRange existed in Maine. In central
Maine there is a large region of low-pressure/hightemperature metamorphismgrading into a large region of
contact metamorphismalong strike to the southwest [Holdaway eta!., 1988]. Gravity evidence suggeststhat the
low-pressureregional metamorphismis associatedwith regional development of granite sills at an inferred eraplacement depth of 8-12 km, whereasthe contactmetamorphism
is associatedwith isolated, deeper, more equant, granite
be isolatedis lessthanthat in the OregonCascade
Range
[Blackn4,ellet al., this issue].
These results and interpretations, taken together, leadto
the followingmodel. Under most of the CascadeRange
where volcanismhas occurredover the last 2-5 m.y., a zone
of magma interception, storage, and crystallization existsin
the depth range of 8-15 km. The horizontal extent of this
zone is significantlylarger than individual centers,beingat
least 60 km wide in places, but over time, volcanic ventsand
major centers of volcanism map out most of the extent of the
zone. The correspondence is discussedby Blackwell et al.
[this issue], who compared the maps of volcanic vents
discussedby Guffanti and Weaver [1988] to the heat flow
anomaly in central Oregon. The temperature in this zoneisa
function of the rate of intrusion, which may or may not
reflected in the extrusion rate, and crustal type. The absence
of primitive basalts at the surface probably meansthat they
stall and fractionate within the crust. The high rate of silltic
volcanismin certain segmentsof many arcs may resultfrom
the fact that none of the basalt makes it through the crustaM
so is able to transfer its heat completely to the crust. An
extreme example of this situation is Yellowstone, where
volumesof basalticmagmasimilarto thosefoundin Hawaii
are being emp!aced in the crust with the result that huge
volumes of silicic magma are produced.
In Oregonthat time-averaged
temperatureis in the600•C
range,and at leastisolatedpocketsof melt probablyexist.
The overall effect may be enoughto result in a density
contrastcomparedto the crust outsidethe CascadeRange.
The rate of activity is high enoughthat the size of the zone
is independent
of individualvolcaniccenters.In Washington
and probablyin northernCaliforniaand southern
British
Columbia,the rate of intrusionis muchlessthanin central
Oregon,andthe temperature
in the residence
zoneis
500øC.In this case the peak thermal anomaliesare mr}re
closelyrelatedto long-livedcentersof intrusion.Thelower
temperatures
makethe geophysical
signitures
of thisheat
sourceregionmoresubtlethan in centralOregon.In nocase
isa continuous
layerof magma
envisioned
to existovert,•e
whole region at one time.
Acknowledgments.
The work in northeastern
Washington
was
supported
by NSFgrant11351
to SMU.Studies
in theColumbia
Basin,Washington
CascadeRange,andwesternWashington
were
supported
by DOEcontract
IDl12307-1
to SMUandby•E
BLACKWELLET AL.: HEAT FLOW,WASHINGTON
STATEAND CASCADF.
RANGE
19.515
contract
DE-A07-79ET27014
andDOEgrantDE-GF07-88IDI2740 Rangeand its correlationwith regionalgravity, Curie point
depths,andgeology,J. Geophys.Res., this issue.
totheWashington
Division
ofGeology
andEarthResources.
J. Eric
Schuster
wasinvolved
inmuchoftheworkandassisted
inthefield Booker,J. R., andA.D. Crave, Intrcxtuctionto the specialsection
studies
andSMU/WGER
coordination.
Reviews
byL. J.P. Muffler on the EMSLAB-Juande Fucaexperiment,J. Geophys.Res.,94,
14,093-14,098, 1989.
ar• W.Hildreth
werehelpful
inimproving
themanuscript,
andW.
Hildreth
pointed
outthatthebackground
heatflowin theCascade Brandon,M. T., D. S. Cowen, and J. A. Vance, The late Cretaceous
San juan thrustsystem,San Juan islands,Washington,Spec.
Range
mightbehigherthantheouterarcvalues.
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