Structure and geochemistry of the adakitic Horoz granitoid, Bolkar

Transcription

International Geology Review
Vol. 52, Nos. 4 – 6, April– June 2010, 505–535
Structure and geochemistry of the adakitic Horoz granitoid, Bolkar
Mountains, south-central Turkey, and its tectonomagmatic evolution
Yusuf K. Kadioglua and Yildirim Dilekb*
a
Department of Geological Engineering, University of Ankara, Tandogan, Ankara, Turkey;
bDepartment of Geology, Miami University, Shideler Hall, Oxford, OH 45056, USA
Downloaded By: [Dilek, Yildirim] At: 17:15 15 February 2010
(Accepted 6 April 2009)
High-Al granitic and granodioritic rocks of the 55 Ma Horoz pluton in the Bolkar
Mountains of southern Turkey provide important new constraints on the early Cenozoic
evolution of the eastern Mediterranean region. The ENE– WSW-trending, sill-like
pluton is intrusive into late Palaeozoic – early Mesozoic metamorphic rocks of the
Central Tauride block, and is unconformably overlain by Plio-Pleistocene alluvial
deposits. The metaluminous to peraluminous granitoids have high-K calc-alkaline to
high-K shoshonitic compositions, and show enrichment in large ion lithophile and
depletion in high-field strength elements relative to ocean ridge granite. Their high
Al2O3 contents (15.9– 20.06 wt%) and low SiO2, MgO, and Mg numbers are consistent
with adakitic compositions. These geochemical features, coupled with low Sr/Y and
La/Yb ratios and trace-element patterns, suggest that the Horoz magmas were produced
in part by partial melting of a subduction-metasomatized mantle. The high-Al adakitic
and calc-alkaline compositions are consistent with partial melting of a hydrated
lithospheric mantle and an amphibolitic –eclogitic mafic lower crust that was triggered
by delamination-induced asthenospheric upwelling. We propose that, following
Palaeocene continental collision between the Tauride and Central Anatolian
Crystalline Complex, the inferred lithospheric delamination was a result of foundering
of the overthickened orogenic root. Asthenospheric upwelling beneath the young
orogenic belt thermally weakened the crust, and caused uplift and tectonic extension
leading to core complex formation (Nigde massif), development of an extensional
volcanic province (Cappadocia), and tectonic collapse of the Central Tauride block
(Bolkar Mountains). The shallow-level Horoz pluton was unroofed by ,23 Ma as a
combined result of crustal uplift and erosion throughout the Palaeogene.
Keywords: Turkey; Tauride block; adakitic magmatism; lithospheric delamination;
subduction-metasomatized mantle; granite and granodiorite plutons
Introduction
Granitoid magmatism was a significant component of crustal evolution and crustal growth
during the orogenic build-up in Anatolia (Turkey) throughout the latest Mesozoic and
Cenozoic (Bingöl et al. 1982; Harris et al. 1994; Erdogan et al. 1996; Erler and Göncüoglu
1996; Boztug et al. 1997, 2006; Altunkaynak and Yilmaz 1999; Gessner et al. 2001;
Ilbeyli et al. 2004; Köksal et al. 2004; Köprübasi and Aldanmaz 2004; Arslan and Aslan
2006; Dilek and Altunkaynak 2007, 2009; Glodny and Hetzel 2007; Özgenç and İlbeyli
*Corresponding author. Email: dileky@muohio.edu
ISSN 0020-6814 print/ISSN 1938-2839 online
q 2010 Taylor & Francis
DOI: 10.1080/09507110902954847
http://www.informaworld.com
506
Y.K. Kadioglu and Y. Dilek
2008; Oner et al. 2009, 2010). Granitoid plutons provide us with critical information and
insights about the tectonic evolution of these young orogenic belts, which have not yet
been deeply eroded. Active subduction tectonics, collisional, and post-collisional thermal
perturbation of a thickened continental crust and a lithospheric mantle, and asthenospheric
upwelling accompanied by lithospheric-scale continental extension, were the common
causes of granitoid magmatism in this region (Dilek and Altunkaynak 2009). However, it
is commonly difficult to differentiate between these geodynamic origins due to the lack of
systematic geochemical, isotopic, and geochronological studies of the granitoid plutons
and the well-constrained regional geology.
In this paper, we describe the geology and structure of an early Eocene granitoid
(Horoz pluton) in the central Tauride block in southern Turkey and present new
geochemical data from its granitic and granodioritic units. The Horoz pluton occurs
adjacent to the Inner Tauride Suture Zone between two continental blocks, the Tauride
platform and Central Anatolian Crystalline Complex (CACC). This tectonic position
makes the Horoz granitoid a critical geological entity to use in developing an internally
coherent and a regionally compatible geodynamic model for the latest Mesozoic –
Cenozoic evolution of the eastern Mediterranean region. We introduce our model as a
working hypothesis, which will be further tested with field-based petrological,
geochemical, geochronological, and isotopic studies in the future.
Regional geology
In this section, we describe the pertinent geological entities in southern Turkey that are
relevant to the tectonomagmatic evolution of the Horoz pluton.
Central Anatolian Crystalline Complex
The CACC consists mainly of Palaeozoic –Mesozoic metamorphic massifs and composite
plutons ranging in age from the Late Cretaceous to the Miocene (Figure 1; Güleç 1994;
Boztug 2000; Kadioglu et al. 2003, 2006; Ilbeyli et al. 2004). The three main massifs,
Kirsehir, Akdag, and Nigde, form the nucleus of the CACC and consist of interlayered
metacarbonate and metapelitic rocks. Despite apparent similarities in lithology, the
massifs can be distinguished by distinct metamorphic pressure –temperature – time paths,
particularly with respect to timing, rate, and primary mechanisms of unroofing (Whitney
and Dilek 1998).
Nigde massif
The Nigde massif in the southern part of the CACC (Figure 1) is exposed in a structural
dome (Gautier et al. 2002), which has been interpreted as a Cordilleran-type metamorphic
core complex (Whitney and Dilek 1997). A gently (, 308) S-dipping detachment fault
bounding the Nigde massif along its southern edge juxtaposes multiply deformed marble,
quartzite, and schist in the footwall from clastic sedimentary rocks of the Ulukisla Basin
(UB) in the hanging wall. The central part of the Nigde massif consists predominantly of
upper amphibolite-facies metasedimentary rocks and the Miocene peraluminous Uçkapili
granite.
The SW part of the CACC experienced relatively high-temperature metamorphism
associated with extensive Andean-type arc magmatism represented by the 80– 70 Ma
CACC plutons (see below). It then underwent Barrovian metamorphism at mid-crustal
pressures (, 5 – 6 kbar) and at high temperatures (. 7008C) possibly associated with
507
Figure 1. (a) Simplified tectonic map of Anatolia (Turkey) and (b) CACC, showing the plate
boundaries, suture zones, active faults, and major plutons. BF, Burdur Fault; BZSZ, Bitlis –Zagros
Suture Zone; DSF, Dead Sea Fault; EAF, East Anatolian Fault; EF, Ecemis Fault; IAESZ, Izmir –
Ankara – Erzincan Suture Zone; ITSZ, Inner-Tauride Suture Zone; LV, Lake Van; MS, Marmara
Sea; NAF, North Anatolian Fault; NEAF, Northeast Anatolian Fault.
508
orogenic crustal thickening during the latest Mesozoic – Palaeocene (Whitney and Dilek
1998). The Nigde core complex was exhumed to a depth of less than 2 km by tectonic
unroofing along low-angle detachment faults. Apatite fission track ages from the Nigde
rocks range from , 9 to 12 Ma and indicate slow to moderate cooling via exhumation at
rates of 30– 88C/m.y. (Fayon et al. 2001).
CACC plutons
The Late Cretaceous plutons intruded the W – SW part of the CACC after the emplacement
of the Cretaceous Tethyan ophiolites, which are rooted in the Izmir – Ankara – Erzincan
Suture Zone to the north (Figure 1). These plutons include designated Granite, Monzonite,
and Syenite Supersuites, which are distinguished by field occurrences and major
differences in their mineral and chemical compositions (Kadioglu et al. 2006). The Granite
Supersuite plutons commonly occur along the W –SW edge of the CACC (east of the Salt
Lake; Figure 1) and consist of calc-alkaline rocks ranging in composition from tonalite,
granodiorite, and biotite granite to amphibole biotite – granite and biotite – alkali feldspar
granite (Ataman 1972; Akıman et al. 1993; Kadioglu and Güleç 1996; Güleç and Kadioglu
1998; Boztug 2000). Plutons of the Monzonite Supersuite occur immediately east of the
Granite Supersuite plutons and are composed mainly of sub-alkaline quartz monzonite and
monzonite (Bayhan 1987; Kadioglu et al. 2006). The Syenite Supersuite represents the
youngest phase of plutonism in the Late Cretaceous (, 69 Ma) and generally occurs in the
inner part of the CACC (Düzgören-Aydin 2000; Ilbeyli 2004; Kadioglu et al. 2006;
Boztug et al. 2009). Rocks of this supersuite are composed of silica-saturated (quartz
syenite and syenite) and silica-undersaturated, nepheline- and pseudoleucite-bearing
alkaline rocks.
The CACC plutons show a progression from high-K calc-alkaline and high-K
shoshonitic compositions in the Granite Supersuite to typical shoshonitic compositions in
the Monzonite Supersuite rocks (Boztug et al. 1997; Kadioglu et al. 2006). Isotopic and
trace-element signatures of the Syenite Supersuite plutons suggest that their magmas were
more enriched in within-plate mantle components compared to the Granite and Monzonite
Supersuite plutons (Kadioglu et al. 2006). 40Ar/39Ar age data from these Granite,
Monzonite, and Syenite Supersuite plutons yield ages of 77.7 ^ 0.3, 70 ^ 1.0, and
69.8 ^ 0.3 Ma, respectively (Kadioglu et al. 2006), indicating a temporal shift towards
more alkaline magmatism inwards from the CACC margin.
Ophiolites, high-P rocks, and Inner-Tauride Suture Zone (ITSZ)
Discontinuous exposures of the Tethyan ophiolites and mélanges define a major suture, the
ITSZ, surrounding the CACC in the south (Figures 1(a) and 2). The Inner-Tauride
ophiolites (ITO) exposed along this suture zone (i.e. Alihoca, Aladag, Mersin) consist
mainly of tectonized harzburgites, mafic – ultramafic cumulates, and gabbros, and
commonly are not associated with sheeted dikes and extrusive rocks (Parlak et al. 1996,
2002; Dilek et al. 1999a). They are underlain by thin (, 200 m) thrust sheets of
metamorphic sole rocks, and both the ophiolitic units and the sole rocks are intruded by
mafic dike swarms composed of basaltic to andesitic rocks with island arc tholeiite (IAT)
affinities. 40Ar/39Ar hornblende ages of 92 –90 and 90 – 91 Ma from the metamorphic sole
and dike rocks, respectively, indicate Cenomanian –Turonian ages for the ITO (Dilek et al.
1999a; Parlak and Delaloye 1999; Çelik et al. 2006).
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Figure 2. Geological map of south – central Turkey, showing the distribution of major tectonic
units, faults, and the Horoz pluton in the Central Tauride block. BFF, Bolkar Frontal Fault.
The ITSZ is also marked by discontinuous exposures of blueschist-bearing mafic –
ultramafic and carbonate rocks along the northern edge of the Tauride block (Figure 1(a);
Okay 1986). The occurrence of sodic amphibole-containing metasedimentary and
metavolcanic rocks in the Bolkar Mountains region (Blumenthal 1956; Van der Kaaden
1966; Gianelli et al. 1972; Dilek and Whitney 1997) extends into the Tavsanli Zone in NW
Anatolia and into the Pinarbasi zone in the eastern Taurides in East-Central Anatolia
(Okay 1984; Önen and Hall 1993; Okay et al. 1998). These high-P/low-T rock
assemblages show anticlockwise PTt trajectories of their metamorphic evolution and
indicate increasing P/T ratio with cooling that was associated with continuous subduction
within the Inner-Tauride Ocean (Dilek and Whitney 1997, 2000).
A , 300-m-thick klippen of a dismembered ophiolite, the Kiziltepe ophiolite, rests
tectonically on the recrystallized carbonates of the Bolkar Mountains (Figure 3). The
Kiziltepe ophiolite includes meta-lavas and serpentinized peridotites, underlain by a
metamorphic sole of thin sliver of foliated amphibolite. Hornblende in this sole is crosscut
510
Figure 3. View to the south towards the Bolkar Mountains. The upper Palaeocene – Eocene clastic,
carbonate, and volcanic rocks of the Halkapinar Formation are in the foreground, and the upper
Palaeozoic – lower Mesozoic marble and schist units of the Central Tauride block in the Bolkar
Mountains are in the background. Nearly, ENE – WSW-running BFF in the valley south of the
Halkapinar Formation juxtaposes the Cretaceous Alihoca ophiolite and ophiolitic mélange against
the Tauride carbonates. The reddish-brown Kiziltepe ophiolite at the elevation of 2975 m rests
tectonically on the Tauride carbonates and is underlain by an amphibolite sole with blueschist-facies
overprint.
and rimmed by sodic amphibole minerals, indicating blueschist-facies overprint recording
a minimum pressure of 7– 8 kbar for a temperature range of , 300 – 5008C (Dilek and
Whitney 1997). These observations suggest that the Kiziltepe metamorphic sole was
dragged deeper into the subduction zone where the mineral assemblages were overprinted
by blueschist-facies minerals (crossite, Mg-riebeckite, albite, calcite, quartz) that resulted
from increasing P/T ratio. This anticlockwise PTt path of the Kiziltepe sole rocks shows
that the high-P metamorphic overprint was accompanied and succeeded by rapid uplift
along the northern edge of the Tauride block in the latest Cretaceous – early Tertiary (Dilek
and Whitney 1997).
Sedimentary basins
The Tuzgölü and Ulukisla sedimentary basins, which initially evolved as peripheral
foreland and/or forearc basins in the Late Cretaceous, delimit the CACC in the west and
the south (Figures 1(a) and 2). These basins developed in the latest Cretaceous when
compressional tectonics was dominant within the Neotethyan realm (Oktay 1982; Görür
et al. 1984, 1998). They were filled with Upper Cretaceous to Oligo-Miocene volcanic and
sedimentary materials and became part of a larger, shallow intra-continental basin
consisting mainly of lacustrine and fluvial deposits that covered much of Central Anatolia
throughout the Miocene and Quaternary (Oktay 1982; Demirtasli et al. 1984: Cater et al.
1991; Clark and Robertson 2002).
The UB includes a thick succession (ca. 2 km) of upper Palaeocene –lower Eocene
basaltic to andesitic submarine pillow lavas, lava flows, volcaniclastic rocks, and
intercalated limestones (Halkapinar Formation; Figure 3) that are underlain by the Late
Cretaceous Alihoca ophiolite (Dilek et al. 1999a; Figure 2). These Palaeogene rocks were
511
unconformably covered by Oligo-Miocene lacustrine to fluvial rocks. The UB formed
after the emplacement of the ITO and mélanges onto the Tauride platform during the
Late Cretaceous and underwent late Eocene emergence, deformation, and onset of OligoMiocene non-marine deposition (Blumenthal 1956; Demirtasli et al. 1984; Atabey et al.
1990; Görür et al. 1998; Clark and Robertson 2002). The geochemical features of the
Palaeogene basaltic to andesitic volcanic rocks within the UB indicate relative enrichment
of the large ion lithophile (LILE) and light rare-earth elements (LREE) in comparison to
mid-ocean ridge basalts (MORBs) and relatively much less enrichment of Nb. The Nb
concentrations in these rocks are more enriched, however, than the less incompatible highfield strength elements (HFSE) of Ti and Y. These geochemical features suggest a
subduction zone influence in the evolution of their magmas that involved low degrees of
partial melting in a within-plate setting (Clark and Robertson 2002).
Cappadocian Volcanic Province
The south-central part of the CACC includes the Cappadocian Volcanic Province
(Figure 1(a)), containing upper Miocene to Quaternary volcanic –volcaniclastic rocks and
polygenetic volcanic centres (Toprak et al. 1994; Dilek et al. 1999b). The Cappadocian
Volcanic Province represents a broadly NE – SW-oriented volcanic field that includes
upper Miocene to Quaternary volcanic – volcaniclastic rocks and polygenetic volcanic
centres marked by stratovolcanoes, cinder cones, volcanic ridges, and calderas (Innocenti
et al. 1975; Ercan et al. 1994; Toprak et al. 1994; Güçtekin and Köprübasi 2009). These
volcanic edifices commonly form linear clusters along and/or at the intersections of fault
systems.
Cappodocian volcanic rocks are made mainly of pyroclastic deposits and lava flows
that are calc-alkaline in character (Kürkçüoglu et al. 1998; Temel et al. 1998). Lava
compositions range from basalt to rhyolite (48.4 – 70.5 wt% SiO2) and pyroclastic
rocks – ignimbrites have andesitic to dacitic compositions. Alkaline basalts are also
common in the Cappadocian volcanic sequence (Güçtekin and Köprübasi 2009). Calcalkaline rocks show relatively high-Sr and -Nd isotopic ratios (0.703434 –0.705468;
0.512942 –0.512600), whereas these ratios for alkaline basalts are in the range of
0.703344 –0.703964 and 0.512920 – 0.512780 (Kürkçüoglu et al. 1998). The geochemical
features and isotopic signatures of all volcanic rock types of the Cappadocian Volcanic
Province indicate that their calc-alkaline magmas were the products of mixing of an ocean
island basalt-like (OIB) mantle melts with subduction-metasomatized asthenospheric
mantle melts (Güçtekin and Köprübasi 2009). These magmas were then further modified
by crustal contamination and assimilation – fractional crystallization (AFC) during their
ascent through the extending CACC.
Tauride block
The Tauride block south of the ITSZ is represented by the deformed and uplifted platform
carbonates that consist of variably metamorphosed, Palaeozoic to Upper Cretaceous
carbonates with siliciclastic and volcanic intercalations (Figures 2 and 3; Ricou et al.
1975, 1979; Özgül 1976, 1984; Demirtasli et al. 1984). The Tauride block has been
interpreted as a rifted fragment of Afro-Arabia (Robertson and Dixon 1984; Garfunkel
1998) and is tectonically overlain by discontinuous outcrops of the Cenomanian –
Turonian Neotethyan ophiolites along its entire length (Figure 2; Dilek and Moores 1990;
512
Dilek et al. 1999a; Parlak et al. 1996, 2002; Çelik et al. 2006; Çelik and Chiaradia 2008;
Elitok and Drüppel 2008).
Platform carbonates in the Bolkar Mountains are multiply folded and imbricated along
thrust faults, which caused substantial shortening and crustal thickening within the
platform. These contractional structures and crustal shortening developed first during
the obduction of the ITO from the north in the Late Cretaceous, and subsequently during
the collision of the Tauride block with the CACC in the latest Palaeocene – Eocene (Dilek
et al. 1999b). The Tauride block experienced gradual uplift in the footwall of a northdipping frontal normal fault system (Bolkar Frontal Fault, BFF; Figure 3) along its
northern edge starting in the Miocene, and developed as a southward-tilted, asymmetric
mega-fault block with a rugged, alpine topography (Dilek et al. 1999b).
Geology, petrography, and age of the Horoz granitoid
Plutonic rocks
The Horoz granitoid is a sill-like pluton intrusive into the platform carbonates of the
Central Tauride Belt in the Bolkar Mountains (Figures 2 and 4). The NE – SW-trending
Horoz granitoid has a sharp contact with the Tauride carbonates along which hornfels and
calc-silicate contact metamorphic rocks occur discontinuously (Figure 5). It is
unconformably covered by the alluvial sediments of the Horoz stream along its southern
edge. The granitoid rocks show brittle to cataclastic deformation along N508W-trending
faults (Figure 4).
The Horoz granitoid is composed mainly of granodiorite and granite, both of which
include mafic microgranular enclaves ranging in size from 1 cm up to 12 cm (Figure 6).
Granite is more abundant than granitoid and occurs in the central and southern parts of
the pluton. Medium- to coarse-grained granite has phaneritic to porphyro-phaneritic
textures and is mainly composed of quartz, feldspar, and biotite in the hand specimen
(Figure 6(a)). Quartz, orthoclase, oligoclase, biotite, and zircon constitute the main primary
Figure 4. Geological map of the Horoz pluton.
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Figure 5. (A) Field photo of the Horoz pluton, showing the contact relations between the granite
and granodiorite units, hornfels, and the host rocks of the Tauride carbonates (view to the north).
(B) Pervasively jointed Horoz granite is unconformably overlain by the Plio-Pleistocene
conglomerate of the Horoz stream (to the right). View to the NE.
mineral phases in a holocrystalline granular texture in the thin section (Figure 6(b)).
Epidote, chlorite, and sericite occur as secondary minerals in the granite. Granodiorite is
exposed in the northern part of the pluton against the marble and hornfels of the contact
metamorphic zone (Figure 4). It has a fine-grained phaneritic crystalline texture and is
mainly composed of quartz, feldspar, biotite, and amphibole in the hand specimen
(Figure 6(c)). It has a holocrystalline granular texture and consists of quartz, orthoclase,
oligoclase, biotite, amphibole, and opaque minerals in the thin section (Figure 6(d)).
Epidote, calcite, and chlorite occur in fractures as secondary minerals. A cataclastic mortar
structure is observed in the rock along the brittle, late-stage faults.
We determined the age of the Horoz pluton using U – Pb zircon dating of its granitic
end member. A relatively fresh, peraluminous granite sample yielded a 206Pb/238U zircon
age of 56.1 Ma (Y. Dilek, unpublished data), indicating an earliest Eocene (Ypresian)
crystallization age for the Horoz granitoid. Detailed documentation of the age and isotope
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Figure 6. Photographs and photomicrographs of the granite (a, b) and granodiorite (c, d) units of
the Horoz pluton.
data from the Horoz granitoid and other plutons in the Central Tauride block will be
reported elsewhere (Y. Dilek et al. in preparation).
Young felsic and mafic dikes
Mafic to felsic dikes crosscut the Horoz granitoid parallel to the main direction of the
intrusive body (Figure 5). Dikes range in thickness from 10 cm to 10 m and may continue
locally for 100– 250 m along-strike. They have sharp contacts with their granitoid host
rocks and represent the youngest magmatic unit in the pluton. They commonly occur as
fresh and erosion-resistant rocks exposed at relatively higher topographic levels in the
field.
Felsic dikes were emplaced mainly along fracture and fault planes within the pluton
with a general orientation almost parallel to the trend of the whole intrusive body. They
comprise alkali feldspar granite and granite porphyry rocks. In the thin section, these dike
rocks are composed mainly of quartz, plagioclase, and orthoclase with biotite. The granite
porphyry dikes also include muscovite. Quartz occurs as euhedral to anhedral grains
ranging in size from 0.1 to 2 mm. Plagioclase is rather small in size (0.1 – 0.3 mm) and
mainly occurs in the granite porphyry. Orthoclase is mostly observed in the alkali feldspar
granite and in the granite porphyry rocks.
Doleritic (diabasic) mafic dikes intrude both the granite and granodiorite with sharp
contacts. In the thin section, these doleritic rocks have holocrystalline porphyritic and
hypocrystalline textures. They are composed mainly of plagioclase and pyroxene.
Fine-grained (up to 0.1 mm) plagioclase constitutes the bulk of the groundmass in the
dike rocks.
63.32
15.36
5.66
0.08
2.90
4.78
4.12
2.12
0.65
0.25
0.45
99.69
58.98
17.79
6.28
0.18
5.25
3.98
4.45
2.13
0.63
0.40
0.84
100.93
6.58
0.51
11.54
10.57
408.70
512.60
39.30
154.90
20.50
56.40
22.80
1.10
56.50
46.60
7.10
2.60
18.00
50.10
6.00
SiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2O
TiO2
P2O5
LOI
Total
Alk
Mg#
Fe þ Mg
CNK
Ba
Sr
Y
Zr
Co
Zn
Ga
Ge
Rb
Nb
Sn
Cs
La
Ce
Hf
510.00
677.00
18.20
200.00
31.40
76.30
18.70
1.00
63.40
16.70
1.10
4.60
30.10
49.90
3.90
6.24
0.39
8.56
11.02
GD11
GD09
553.60
556.20
17.30
222.70
29.30
57.90
18.00
0.40
70.30
16.10
1.80
2.60
26.90
49.90
5.10
7.14
0.47
8.48
9.73
63.43
16.63
5.01
0.09
3.48
2.59
4.01
3.13
0.68
0.23
1.14
100.41
GD17
675.10
326.20
31.30
284.60
41.60
33.50
19.40
0.70
188.20
20.90
1.80
9.90
47.20
87.40
6.80
8.49
0.39
8.62
9.58
63.72
15.90
5.74
0.05
2.88
1.09
2.97
5.52
0.93
0.20
0.91
99.91
GD22
422.00
354.00
15.40
187.00
23.21
18.00
14.50
1.00
121.00
19.00
2.12
3.30
26.00
55.40
3.40
7.36
0.16
3.48
9.84
65.43
20.06
3.01
0.01
0.47
2.48
3.91
3.45
0.18
0.04
0.65
99.68
GD50
411.00
376.00
12.45
196.00
26.54
11.00
16.32
1.34
125.00
16.70
2.20
3.20
31.00
46.67
3.50
7.80
0.19
3.41
9.74
65.65
19.78
2.89
0.06
0.52
1.94
4.38
3.43
0.26
0.02
0.65
99.59
GD52
420.00
340.70
11.60
195.30
21.20
19.60
17.00
1.60
92.80
20.70
2.40
3.70
24.60
42.40
2.60
8.22
0.17
2.65
11.22
66.10
17.75
2.29
0.02
0.36
2.99
4.26
3.97
0.37
0.18
0.72
99.00
GR02
448.30
540.40
15.80
165.60
39.20
26.90
16.80
1.40
75.80
18.00
2.10
6.80
34.00
55.70
4.10
7.73
0.42
4.54
11.02
67.32
15.93
2.91
0.04
1.64
3.29
4.81
2.91
0.33
0.17
0.40
99.75
GR04
530.80
412.90
11.80
153.00
48.10
22.80
15.60
1.60
120.40
18.10
1.10
4.80
28.70
42.70
2.50
8.79
0.31
2.60
10.74
71.02
13.98
1.91
0.03
0.69
1.95
4.25
4.54
0.21
0.12
0.48
99.18
GR05
464.50
379.00
13.20
155.50
11.30
22.40
15.50
1.00
106.10
20.80
0.90
5.00
31.90
50.80
4.00
8.32
0.37
3.76
10.64
68.12
15.19
2.55
0.04
1.21
2.33
3.74
4.58
0.28
0.18
1.03
99.25
GR06
745.30
598.90
14.50
159.10
30.60
27.90
17.30
1.40
83.70
20.50
0.90
2.60
39.60
62.80
4.00
8.10
0.41
4.12
10.79
68.37
15.80
2.65
0.06
1.46
2.69
4.36
3.74
0.28
0.15
0.37
99.94
GR07
Table 1. Major and trace-element compositions of selected rock samples from the Horoz granitoid, Bolkar Mountains, Turkey.
766.00
348.30
17.90
144.30
14.20
13.90
15.20
1.10
137.70
28.50
1.30
5.50
18.50
36.60
3.70
9.60
0.40
2.08
12.66
67.27
16.38
1.36
0.04
0.72
3.06
2.84
6.76
0.27
0.16
1.01
99.86
GR08
420.60
378.80
12.60
114.40
14.40
20.80
15.10
1.50
120.20
24.60
1.20
3.70
21.10
36.40
3.90
8.01
0.42
3.39
10.18
70.05
14.18
2.15
0.05
1.23
2.18
3.52
4.49
0.29
0.12
0.99
99.25
GR12
613.50
493.30
13.20
139.20
19.30
28.80
16.10
1.30
95.50
18.70
1.20
8.90
32.80
53.10
3.70
8.24
0.46
4.83
8.81
68.82
17.84
2.89
0.01
1.93
0.57
5.29
2.95
0.07
0.21
0.97
99.56
GR13
515
8.37
0.35
4.00
10.94
587.00
458.30
14.20
161.60
25.40
25.10
16.50
Alk
Mg#
Feþ Mg
CNK
Ba
Sr
Y
Zr
Co
Zn
Ga
457.00
199.40
14.60
212.10
14.70
40.10
16.60
6.99
0.25
4.22
8.25
66.93
18.90
3.33
0.03
0.89
1.26
2.91
4.08
0.35
0.19
0.92
99.79
GR18
GR14
68.13
15.04
2.81
0.06
1.19
2.57
4.50
3.86
0.27
0.19
0.78
99.41
4.40
0.60
7.60
0.60
9.80
3.60
GD11
7.30
1.20
1.40
0.60
6.30
4.80
SiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2O
TiO2
P2O5
LOI
Total
Ta
Te
Pb
Bi
Th
U
GD09
Table 1 – continued
566.40
485.60
13.10
208.00
36.50
25.30
18.00
7.90
0.33
3.51
10.70
68.65
16.04
2.52
0.04
0.99
2.80
4.78
3.12
0.30
0.18
0.80
100.22
GR21
4.80
1.20
7.00
0.50
10.50
2.10
GD17
685.70
493.40
16.60
205.60
34.10
27.20
16.80
8.52
0.31
4.31
10.86
67.12
15.68
3.20
0.04
1.11
2.34
4.04
4.48
0.31
0.18
0.87
99.36
GR25
5.80
1.20
5.30
0.60
13.30
2.90
GD22
412.00
342.00
14.50
176.00
22.00
21.00
14.34
6.16
0.16
3.55
8.63
67.92
18.36
3.10
0.02
0.45
2.47
3.90
2.26
0.26
0.02
1.75
100.51
GR49
6.45
1.40
2.40
0.76
13.20
2.30
GD50
410.00
365.00
15.65
193.00
24.20
12.00
13.33
7.80
0.18
3.47
10.28
66.12
18.68
2.96
0.04
0.51
2.48
4.30
3.49
0.25
0.16
0.79
99.78
GR51
6.30
1.22
2.60
0.64
11.00
2.50
GD52
401.00
361.00
16.43
185.00
23.10
13.00
15.32
8.08
0.20
3.48
9.96
66.32
18.60
2.92
0.02
0.57
1.88
4.48
3.59
0.22
0.13
0.86
99.59
GR53
6.50
1.20
2.20
0.50
13.20
1.70
GR02
398.00
361.00
17.76
188.00
27.00
11.20
14.32
7.99
0.18
3.35
10.10
66.69
18.70
2.85
0.04
0.50
2.11
4.47
3.52
0.23
0.04
0.91
100.04
GR54
7.20
1.30
5.00
0.70
12.60
2.20
GR04
354.00
376.00
17.00
190.00
25.00
13.30
12.54
8.20
0.18
3.30
10.27
65.98
18.61
2.81
0.02
0.49
2.07
4.53
3.68
0.19
0.04
0.65
99.07
GR55
5.90
0.90
3.10
0.80
21.40
2.80
GR05
365.00
389.00
18.70
189.00
23.60
14.00
13.22
7.92
0.26
3.58
10.05
66.54
19.03
2.80
0.01
0.78
2.13
4.20
3.71
0.18
0.17
0.26
99.82
GR56
3.00
1.20
5.00
0.50
25.90
2.90
GR06
387.00
341.00
1.68
195.00
26.00
12.00
13.32
7.93
0.27
3.59
10.38
66.76
18.86
2.79
0.05
0.80
2.45
4.22
3.71
0.25
0.02
0.77
100.68
GR57
4.50
1.00
5.30
0.70
15.50
2.90
GR07
412.00
332.00
21.00
191.00
26.30
14.40
11.20
8.04
0.24
3.39
10.12
66.54
18.48
2.72
0.01
0.67
2.08
4.31
3.73
0.26
0.04
0.85
99.68
GR58
4.60
1.20
4.70
0.50
17.30
4.40
GR08
421.00
365.00
20.10
193.00
24.30
16.30
15.30
8.10
0.30
3.59
10.06
66.12
18.87
2.69
0.04
0.90
1.96
4.35
3.75
0.27
0.01
0.80
99.75
GR59
2.50
1.20
6.60
0.40
17.00
3.20
GR12
427.00
377.00
22.00
192.00
24.11
12.03
14.25
7.85
0.28
3.61
9.85
66.55
18.72
2.76
0.02
0.85
2.01
4.22
3.62
0.25
0.02
0.65
99.68
GR60
4.20
1.80
5.60
0.50
13.20
2.60
GR13
516
7.92
0.27
3.55
Alk
Mg#
Feþ Mg
8.23
0.33
3.48
66.43
19.88
2.50
0.01
0.98
1.32
4.44
3.79
0.15
0.11
0.72
100.34
GR62
GR61
66.76
18.75
2.76
0.02
0.79
2.01
4.24
3.67
0.16
0.17
0.64
99.97
1.10
119.00
20.90
1.30
8.10
52.90
85.60
4.20
3.80
1.20
3.10
0.50
14.80
3.10
GR18
1.40
105.60
20.50
1.00
4.40
30.50
51.80
3.80
4.90
1.20
6.00
0.60
16.70
4.40
SiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2O
TiO2
P2O5
LOI
Total
Ge
Rb
Nb
Sn
Cs
La
Ce
Hf
Ta
Te
Pb
Bi
Th
U
GR14
8.25
0.30
3.96
65.14
19.81
2.95
0.03
1.01
1.29
4.39
3.86
0.12
0.12
0.73
99.45
GR63
0.70
79.10
15.80
0.90
6.70
40.30
62.60
3.60
4.70
1.20
3.80
0.40
13.90
2.20
GR21
8.41
0.33
3.55
66.41
19.33
2.55
0.05
1.01
1.15
4.47
3.94
0.14
0.13
0.75
99.91
GR64
0.90
119.50
20.50
3.00
4.00
42.60
69.80
4.00
4.80
0.90
6.50
0.60
14.60
2.90
GR25
8.12
0.35
3.76
66.54
19.16
2.63
0.01
1.13
1.13
4.47
3.65
0.15
0.09
0.74
99.70
GR65
1.20
98.30
21.00
2.30
3.20
28.00
53.00
2.40
6.50
1.32
2.45
0.56
12.30
3.20
GR49
8.31
0.25
3.47
66.32
18.75
2.74
0.04
0.73
1.26
4.55
3.75
0.19
0.07
0.76
99.17
GR66
1.30
123.00
16.30
2.54
3.00
32.00
53.50
2.50
6.40
1.20
2.40
0.65
12.00
2.40
GR51
8.65
0.28
3.58
66.33
19.51
2.73
0.01
0.85
1.24
4.72
3.93
0.12
0.09
0.30
99.82
GR67
1.32
112.00
20.10
2.54
2.40
33.00
49.54
3.70
6.70
1.70
2.70
0.65
14.30
3.70
GR53
8.44
0.33
3.58
67.23
18.16
2.57
0.02
1.01
1.01
4.59
3.85
0.14
0.14
0.76
99.47
GR68
1.20
127.00
17.00
2.12
3.40
36.10
51.32
3.32
6.80
0.98
2.30
0.65
14.00
3.65
GR54
8.55
0.30
3.35
68.32
18.33
2.51
0.02
0.84
0.94
4.60
3.94
0.13
0.09
0.42
100.15
GR69
1.31
121.00
16.65
2.54
3.80
26.40
53.43
3.60
7.50
0.94
2.22
0.76
14.10
3.65
GR55
8.32
0.27
3.38
67.23
18.53
2.61
0.02
0.76
1.28
4.43
3.90
0.15
0.02
0.30
99.24
GR70
1.40
128.00
17.30
2.20
3.50
30.00
52.43
3.50
7.50
1.34
2.80
0.60
12.30
3.65
GR56
8.36
0.21
3.81
66.45
18.80
3.13
0.02
0.67
1.26
4.38
3.98
0.12
0.14
0.91
99.88
GR71
1.43
122.00
18.30
2.34
3.30
26.60
48.50
0.39
7.50
1.30
2.60
0.87
11.33
3.65
GR57
8.29
0.23
3.29
67.67
18.71
2.67
0.06
0.62
1.04
4.22
4.07
0.25
0.18
0.66
100.14
GR72
1.33
98.00
15.70
2.43
3.00
28.30
48.45
3.40
6.80
1.10
2.12
0.87
12.34
3.65
GR58
8.42
0.20
3.14
66.47
19.64
2.62
0.07
0.52
1.09
4.21
4.21
0.24
0.11
0.64
99.82
GR73
1.31
110.00
18.30
2.43
3.10
29.30
53.43
3.65
6.30
1.70
2.51
0.81
11.34
4.23
GR59
8.90
0.20
3.50
66.24
19.50
2.91
0.02
0.59
0.81
4.54
4.36
0.13
0.17
0.78
100.06
GR74
1.23
112.00
13.23
2.54
3.20
27.30
51.22
3.76
6.98
1.63
2.41
0.54
12.34
3.90
GR60
517
SiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2O
CNK
Ba
Sr
Y
Zr
Co
Zn
Ga
Ge
Rb
Nb
Sn
Cs
La
Ce
Hf
Ta
Te
Pb
Bi
Th
U
54.76
18.42
9.80
0.17
8.21
0.95
2.67
2.88
DB15
GR75
66.58
19.48
2.51
0.12
0.63
1.10
4.41
4.27
9.55
415.00
353.00
23.65
192.00
24.54
11.00
13.21
1.34
121.00
17.00
3.03
3.40
26.32
50.35
3.35
7.40
1.31
2.22
0.87
13.21
4.21
GR62
9.92
418.00
387.00
26.30
194.00
23.20
12.60
13.54
1.43
123.00
13.90
2.50
3.87
27.30
52.11
3.54
7.50
1.73
2.31
0.48
12.34
3.87
GR61
43.54
11.00
9.68
0.17
19.09
15.50
0.06
0.07
DB19
9.54
425.00
322.00
23.25
193.00
25.11
16.00
12.76
1.12
125.00
17.30
3.39
2.75
29.54
51.40
3.61
7.94
1.83
2.12
0.81
11.32
3.00
GR63
41.98
2.57
18.15
0.85
6.91
28.54
0.08
0.18
DB23
9.55
430.00
365.00
22.60
199.00
23.11
18.00
17.98
1.54
126.00
12.98
3.20
2.65
32.00
49.65
3.76
7.40
1.33
2.40
0.84
12.32
4.32
GR64
94.65
2.18
1.42
0.01
0.83
0.02
0.06
0.22
HF48
9.24
434.00
354.00
21.30
192.00
23.00
21.00
14.65
1.32
124.00
16.32
2.40
3.98
31.00
51.60
4.02
7.54
1.37
2.13
0.78
13.20
4.50
GR65
9.57
398.00
321.00
21.00
193.00
26.00
14.00
16.54
1.23
122.00
18.00
2.54
2.87
30.00
50.00
3.20
7.45
1.73
2.11
0.67
12.40
4.20
GR66
9.89
389.00
352.00
18.30
191.00
27.00
16.00
12.00
1.21
126.00
16.30
2.54
3.78
32.10
46.70
3.76
6.84
1.22
2.60
0.19
12.30
4.21
GR67
9.45
405.00
341.00
16.00
192.00
23.00
13.00
18.30
1.22
123.00
15.32
2.54
2.63
32.30
43.20
3.53
6.64
1.20
2.17
0.59
13.32
3.78
GR68
9.49
407.00
334.00
19.00
187.00
27.00
13.30
16.00
1.54
126.00
16.32
2.47
2.54
31.30
48.50
3.65
6.92
1.23
2.32
0.51
14.20
3.87
GR69
9.61
418.00
354.00
22.01
189.00
22.00
12.20
17.00
1.30
128.00
17.32
2.54
3.28
32.30
44.40
3.69
6.72
1.13
2.43
0.63
13.22
4.20
GR70
9.62
419.00
340.00
16.30
187.00
27.00
12.65
14.98
1.20
122.00
18.32
2.44
3.17
28.30
43.00
3.25
5.87
1.30
2.20
0.70
12.33
4.10
GR71
9.33
417.00
351.00
15.43
184.00
25.00
12.65
15.20
1.50
127.00
15.32
2.44
3.19
27.10
45.00
3.26
5.98
0.93
2.24
0.76
13.43
4.23
GR72
9.51
422.00
342.00
16.43
187.00
22.76
13.21
14.76
1.60
128.00
15.87
2.65
3.20
26.90
46.70
3.22
5.87
1.38
2.47
0.84
13.43
4.24
GR73
9.71
422.00
321.00
14.87
185.00
24.70
12.54
13.76
1.20
129.00
16.30
2.55
3.03
28.87
52.00
3.24
6.05
1.98
1.76
0.64
14.21
4.56
GR74
518
432.00
353.00
17.10
201.00
27.00
14.21
13.25
1.20
130.00
17.65
3.07
2.87
30.08
51.00
3.16
6.54
1.73
1.50
0.74
14.30
4.08
8.68
0.24
3.14
9.79
742.00
101.90
27.40
307.80
35.30
73.10
18.60
1.00
71.20
20.90
1.80
2.60
37.10
77.60
5.90
4.30
1.20
6.10
0.70
10.50
2.30
5.54
0.51
18.01
6.50
1.20
0.52
0.89
100.46
0.25
0.18
0.64
100.17
6.80
113.70
8.30
6.20
91.30
60.30
9.60
1.30
1.20
0.90
0.90
2.60
4.90
5.80
4.10
11.00
1.00
2.60
0.60
1.50
1.50
0.14
0.71
28.77
15.63
0.31
0.01
0.68
100.11
DB19
16.80
17.50
7.60
50.30
26.00
89.40
11.50
6.90
2.40
6.10
18.20
3.20
6.00
7.00
3.20
7.10
1.20
1.50
0.90
1.50
5.80
0.26
0.33
25.06
28.80
0.11
0.05
0.83
100.25
DB23
GD, Granodiorite; GR, Granite; DB, Diabase; HF, Hornfels.
Ba
Sr
Y
Zr
Co
Zn
Ga
Ge
Rb
Nb
Sn
Cs
La
Ce
Hf
Ta
Te
Pb
Bi
Th
U
Alk
Mg#
FeþMg
CNK
TiO2
P2O5
LOI
Total
DB15
GR75
93.80
3.70
3.60
37.80
40.50
22.40
3.00
1.60
17.20
2.30
0.70
6.90
11.40
20.80
1.30
4.90
1.20
3.80
1.20
1.00
1.50
0.29
0.43
2.25
0.31
0.12
0.04
0.77
100.21
HF48
519
520
Figure 7. Alkali vs. silica diagram of Irvine and Baragar (1971), with the Horoz samples plotting
mainly in the sub-alkaline field.
Geochemistry of the Horoz pluton
Major and trace-element analyses of a total of 42 representative samples were performed
using XRF and ICP in Petrology Research Laboratory housed in the Department of
Geological Engineering at the University of Ankara (Turkey). The results of these
analyses are given in Table 1. Analytical methods are described in Oner et al. (2009, this
issue).
As the SiO2 contents of the analysed rocks decrease systematically from the
granodiorite (65.7 –59.0 wt%) to the granite series (71.0 – 65.1 wt%), the Na2O þ K2O
Figure 8. AFM diagram of Irvine and Baragar (1971). Granite – granodiorite samples from the
Horoz pluton define a nearly linear trend in the calc-alkaline field.
521
Figure 9. SiO2 vs. K2O diagram of Rickwood (1989). Granite –granodiorite samples from the
Horoz pluton plot mainly in the high-K calc-alkaline field with few samples falling into the medium-K
calc-alkaline and shoshonitic fields.
contents increase (Table 1). On the total alkali vs. silica (TAS) diagram, the granodiorite
and granite samples plot in the sub-alkaline field (Figure 7). They are calc-alkaline
in nature and display a linear trend, suggesting a transitional change in composition
(Figure 8). The analysed granodiorite and granite samples plot in the fields of high-K calcalkaline and high-K shoshonitic series on the SiO2 vs. K2O diagram (Figure 9). In general,
most of the granitic and granodioritic samples have high-Al2O3 contents (15.90 – 20.06
wt%), and these high-Al rocks have lower SiO2, MgO, and Mg numbers (Table 1) and
lower concentrations of compatible elements such as Cr, Ni, and Sc.
Figure 10.
SiO2 versus Fe2O3 þ MgO diagram.
522
The analysed samples display a linear trend on the SiO2 vs. Fe2O3 þ MgO diagram
(Figure 10), showing increases in their Fe2O3 þ MgO, as SiO2 decreases in the granitic to
granodioritic rocks. Conversely, decreasing Al2O3 contents from the granodiorite to
granite correlate with decreases in the total amount of CNK (CaO þ Na2O þ K2O;
Figure 11).
The Fe2O3, TiO2, MgO, CaO, and Al2O3 contents decrease with increasing SiO2 in
the Harker diagrams, whereas the K2O and Na2O appear to increase with increasing
SiO2 values, although somewhat scattered (Figure 12(A)). This phenomenon suggests
that the Horoz pluton magmas may have involved crystal fractionation processes
coupled with assimilation of the host platform carbonates. There is a negative
correlation of Zr, Y, and Ta but a positive correlation of Th with increasing SiO2
contents (Figure 12(B)).
Figure 13 shows the distribution of inter-elemental patterns in granitoid rocks on an
ocean ridge granite (ORG)-normalized (hypothetical ORG) diagram. In general, all
samples of the granite and granodiorite series show enrichment in LILE and depletion in
HFSE relative to ORG (Figure 13), similar to the patterns of rocks formed in subduction
and/or collision tectonic environments (Cox 1987; Wilson 1989).
On the tectonic discrimination diagrams of Pearce et al. (1984), all analysed samples
of the granite and granodiorite plot within the volcanic arc granite þ collision
granite þ ocean ridge granite (VAG þ COLG þ ORG) fields based on the correlation
of Y and Nb with silica (Figure 14). The Y vs. Nd diagram is used to differentiate
VAG þ Syn-COLG, within-plate granite (WPG), and ORG affinities of the rocks, and the
Y þ Nb vs. Rb diagram is used to differentiate between VAG and ORG, WPG, and SynCOLG affinities. Most samples plot mainly in the VAG field, close to the intersection of
the Syn-COLG, WPG, and VAG fields, suggesting that their magmas may have been
derived from a subduction-metasomatized mantle source.
Figure 11. Shand’s index diagram for the Horoz granitoid (Shand 1927). A/CNK, molar
Al2O3/(CaO þ Na2O þ K2O); A/NK, molar Al2O3/(Na2O þ K2O). Granite – granodiorite
samples from the Horoz pluton plot both in the metaluminous and peraluminous fields, showing a
transition from I-type to S-type granites.
523
Petrogenetic and tectonic evolution of the Horoz pluton
Petrogenesis
Geochemical features of the granite and granodiorite series of the Horoz pluton suggest
that the magmas of these rocks were derived from a mantle source that was enriched from
dehydration melting of metamorphosed basaltic (amphibolite and eclogite) and
sedimentary rocks, and that these magmas experienced fractional crystallization and
assimilation during their ascent through the continental crust. We used Y vs. Sr/Y, SiO2 vs.
524
Figure 12. Harker diagrams of the Horoz granitoid illustrating the variations of (a) major oxides
and (b) trace elements with SiO2.
MgO, and SiO2 vs. Mg# [MgO þ (0.79Fe2O3)] patterns to better understand the nature of
the magmas of the Horoz pluton (Figure 15(A –C)). Both granitic and granodioritic
samples of the Horoz pluton generally plot in the Adakite, the Archean Tonalite –
Trondhjemite – Diorite (TTD), and the Archean Tonalite-Trondhjemite-Granodiorite
525
Figure 13. ORG-normalized multi-element patterns for the granodiorite and granite samples from
the Horoz pluton. ORG normalization values are from Pearce et al. (1984).
(TTG) fields (Condie 2005; Thorkelson and Breitsprecher 2005). There is also a strong
geochemical resemblance between the Horoz granitoid rocks and the late Mesozoic
adakitic andesites from the Sulu collisional belt in eastern China (Figure 15). The adakitic
andesites in the Sulu orogenic belt were erupted after the continental collision between the
north China and Yangtze blocks in the Triassic, and their magmas were produced by
partial melting of a LILE- and LREE-enriched eclogitic lower continental crust (Guo et al.
2006). These authors suggested that delamination of the thickened lower crust led to
asthenospheric upwelling, which in turn induced melting of both the delaminated crust and
the eclogitic lower crust in the upper plate. We envision a similar tectonomagmatic
scenario for the adakitic Horoz granitoids. However, lower Sr/Y and La/Yb ratios (Figures 15
and 16) and lower MgO contents and Mg numbers of the Horoz granitoid rocks in
comparison to the typical adakites of southern Tibet (Gao et al. 2007) and elsewhere (Kay
1978; Kay and Kay 1993; Kay et al. 1993; Yogodzinski et al. 1995) indicate that the Horoz
magmas were strongly influenced by melt components derived from a subductionmetasomatized mantle. This feature is reflected on the arc affinity of the Horoz granitoid
rocks and their geochemical resemblance to the Archean TTG and TTD (Figures 15 and
16; Rapp et al. 1991).
Tectonic model
We interpret the tectonomagmatic evolution of the early Eocene Horoz granitoid
within the regional geological framework of the ITSZ and the bounding Tauride and
CACC blocks. Our earlier studies of both the CACC and the Tauride ophiolites (TO)
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Figure 14. Trace-element tectonic discrimination diagrams for the granodiorite and granite
samples from the Horoz pluton (fields from Pearce et al. 1984). VAG, volcanic arc granites; WPG,
within plate granites; ORG, ocean ridge granites; Syn-COLG, syn-collision granites.
provide important constraints on the nature and timing of the tectonic, magmatic, and
metamorphic events that controlled the crustal evolution of the Tauride and CACC
continental blocks and the ITSZ. The occurrence along the entire ITSZ of the
Cenomanian – Turonian suprasubduction zone ophiolites and the spatially and
temporally associated metamorphic sole and blueschist rocks and the existence of
the latest Cretaceous granitic – monzonitic – syenitic plutons along the W – SW edge of
the CACC collectively indicate that the Tauride and CACC continental blocks were
separated by a Tethyan basin, the Inner Tauride Ocean (Sengör et al. 1984; Dilek and
Moores 1990; Dilek et al. 1999a) during much of the Mesozoic. During the Late
Cretaceous, partial melting of the subduction-metasomatized mantle beneath the CACC
produced the granitic suites of the Andean-type magmatism (Figure 17(a)); partial
subduction of the northern edge of the Tauride continental block at the subduction
zone dipping north beneath the CACC facilitated the formation of the high-P
blueschist metamorphic assemblages (e.g. Kiziltepe).
Following the demise of the Inner-Tauride oceanic lithosphere at the NE-dipping
subduction zone and the emplacement of the incipient arc –forearc ophiolites (Dilek and
Flower 2003) onto the northern edge of the Tauride block, subduction was arrested by
the underplating of the buoyant Tauride continental crust. The leading edge of the
subducted Tethyan slab broke off from the rest of the Tauride continental lithosphere,
resulting in the development of an asthenospheric window (Figure 17(b)). The
juxtaposition of this asthenospheric heat source against the overlying continental
527
Figure 15. (a) Y vs. Sr/Y diagram, showing the distribution of the Adakite and classical arc series
fields (after Defant and Drummond 1990; Defant et al. 2002). Horoz granite and granodiorite
samples plot both in the Adakite and arc fields. Adakitic rocks from the Sulu orogenic belt (from Guo
et al. 2006) and south Tibet (from Gao et al. 2007) are also shown for comparison. (b) MgO vs. SiO2
diagram, showing the fields that represent Adakites, experimental basaltic melts, Archean TTD, and
arc xenolith glass inclusion. (c) Mg# vs. SiO2 diagram, showing the distribution of the Adakite,
TTG , 3.0 and TTG . 3.0 fields. Mg# ¼ [MgO þ (0.79Fe2O3)]. After Defant and Kepezhinskas
(2001).
528
Figure 16. La/(Yb)N vs. (Yb)N diagram, showing the distribution of the Adakite and typical arc
series (modified after Jahn et al. 1981; Martin 1986). Horoz granite and granodiorite samples
straddle the boundary between the Adakite and arc fields.
lithosphere caused melting of the metasomatized mantle layers, producing the high-K
shoshonitic magmas of the monzonitic plutons and then the more-enriched alkaline
magmas of the syenitic plutons (Figure 17(b)). This process is similar to slab breakoffrelated collisional magmatism described from other orogenic belts (Davies and von
Blackenburg 1995 and references therein) and in the early Cenozoic of Western
Anatolia (Dilek and Altunkaynak 2007).
Continued convergence between the Tauride and CACC blocks resulted in a
continental collision in the Palaeocene that led to deformation, crustal thickening, and
metamorphism in the hinterland, and to southward transport of the already-emplaced TO
and mélanges and flysch formation together with fold and thrust belt development in the
foreland (Figure 17(c)). Significant crustal thickening and development of a dense mafic
lower crust (eclogitic?) beneath the young orogenic belt resulted in foundering of the
orogenic root and eventually in partial delamination of the thickened lithosphere
(Figure 17(d)). Asthenospheric upwelling around and above the delaminated root provided
excess heat and enhanced geothermal gradient that triggered partial melting of the
hydrated lithospheric mantle and lower crustal rocks. This melting event produced the
high-Al adakitic magmas of the Horoz granitoid. The inferred asthenospheric upwelling
was also responsible for crustal uplift in the overlying Tauride and CACC blocks and for
thermal weakening of the orogenic crust, leading to tectonic extension in and across the
CACC (Figure 17(d)).
The Horoz pluton and the northern part of the Tauride block underwent a rapid
uplift in the footwall of the BFF during the Oligo-Miocene (Figure 17(e)). Apatite
fission track ages of 23.6 ^ 1.2 Ma from the Horoz granitoid support this interpretation
(Dilek et al. 1997). A south-dipping detachment fault along the southern edge of the
CACC accommodated top-to-the-south extension and crustal exhumation of the Nigde
core complex around 12– 9 Ma (Figure 17(e); Whitney and Dilek 1997). Apatite fission
track ages from the Nigde massif are consistent with this timing and indicate
529
530
exhumation-induced slow to moderate cooling of its mid-crustal rocks (Fayon et al.
2001). The sinistral Ecemis Fault Zone facilitated the vertical displacement and
unroofing of high-grade metamorphic rocks in the eastern part of the Nigde massif
during the late Tertiary (Dilek and Whitney 1998). The UB transitioned from a
remnant, restricted basin in the Palaeogene to a terrestrial depocentre in the Neogene
that had a supradetachment basin character along its northern part overlying the Nigde
metamorphic core complex.
The Cappadocian Volcanic Province developed within a fault-controlled, broad
topographic depression during the middle to late Miocene (Figure 17(e)). The early and
intermediate stages of volcanism in Cappadocia (13.5 – 2.7 Ma) are mainly characterized
by the eruption of widespread ignimbrite and felsic lavas accompanied by high-K dacitic
and andesitic flows; intrusion of domes and plugs dominated the magmatic output during
these stages, which was contemporaneous with the extensional deformation and crustal
exhumation in and across Central Anatolia (Dilek et al. 1999b). The bimodal nature of
volcanism with increasing amounts of alkaline basaltic (OIB-like) lava eruption during
this phase suggests the involvement of the asthenospheric mantle in melt generation
(decompressional melting; Güçtekin and Köprübasi 2009) in response to further
lithospheric extension and thinning (Figure 17(e)).
Conclusions
The early Eocene (55 – 54 Ma) Horoz granitoid is intrusive into late Palaeozoic –early
Mesozoic marble and schist units of the Central Tauride block in the Bolkar Mountains.
It is an ENE –WSW-trending, sill-like pluton exposed in the footwall of the north-dipping
BFF immediately south of the ITSZ. The Horoz pluton consists mainly of granitic and
granodioritic rocks that have high-K calc-alkaline to high-K shoshonitic bulk-rock
compositions. These rocks show enrichments in LILE and depletions in HFSE relative to
ORG, and their trace-element patterns suggest a subduction zone influence. Their high-Al
contents and lower SiO2, MgO, and Mg numbers, combined with the above geochemical
features, are reminiscent of adakitic rocks formed in convergent margin and collisional
tectonic settings.
The adakitic Horoz granitoid is a post-collisional pluton that was emplaced at
shallow crustal depths following the CACC– Tauride continental collision in the
Palaeocene. Asthenospheric upwelling, facilitated by the delamination of the
overthickened orogenic root, triggered partial melting of the mafic lower crust and
the hydrated lithospheric mantle, producing high-Al adakitic magmas of the Horoz
pluton. This asthenospheric upwelling was also instrumental in thermal weakening and
uplift of the orogenic crust, and in the onset of regional tectonic extension and core
complex formation. The Horoz pluton was unroofed by the early Miocene as a result of
both crustal uplift and erosion.
R
Figure 17. Sequential tectonic diagram, depicting the evolution of the ITSZ and the Tauride –
CACC collisional orogenic belt. AFC, assimilation fractional crystallization; AHO, Alihoca
ophiolite; CACC, Central Anatolian Crystalline Complex; EF, Ecemis Fault; HG, Horoz granitoid;
ITO, Inner-Tauride ophiolite; ITSZ, Inner-Tauride Suture Zone; KTB, Kiziltepe blueschist; MO,
Mersin ophiolite; SMM, subduction-metasomatized mantle; SSZ, suprasubduction zone; TO,
Tauride ophiolite; UB, Ulukisla Basin; ÜG, Üçkapili granite. See text for discussion.
531
Acknowledgements
This study was supported in part by grants to Y.K. Kadioglu from the Scientific and Technical
Research Council of Turkey (TUBITAK) and Devlet Planlama Teskilati (DPT 2003-K-120-190-4-1),
and to Y. Dilek from the National Science Foundation (NSF EAR-9317100); we acknowledge these
funds gratefully. We thank our colleagues, S. Altunkaynak, H. Furnes, C. Genç, N. Güleç, and N. Ilbeyli,
for insightful discussions on the Mesozoic–Cenozoic magmatism in Turkey. Constructive comments by
C. Eddy helped us improve the paper.
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Structure and geochemistry of the adakitic Horoz granitoid, Bolkar

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