Petrogenesis of subvolcanic rocks from the Khunik prospecting area

Journal of Asian Earth Sciences 115 (2016) 170–182
Contents lists available at ScienceDirect
Journal of Asian Earth Sciences
journal homepage: www.elsevier.com/locate/jseaes
Petrogenesis of subvolcanic rocks from the Khunik prospecting area,
south of Birjand, Iran: Geochemical, Sr–Nd isotopic and U–Pb zircon
constraints
Somayeh Samiee a, Mohammad Hassan Karimpour a,⇑, Majid Ghaderi b,
Mohammad Reza Haidarian Shahri a, Urs Klöetzli c, José Francisco Santos d
a
Department of Geology, Ferdowsi University of Mashhad, Iran
Department of Economic Geology, Tarbiat Modares University, Tehran, Iran
c
Department of Lithospheric Science, Geochronology Laboratory, University of Wien, Austria
d
Department of Geosciences, Geobiotec Research Unit, University of Aveiro, Portugal
b
a r t i c l e
i n f o
Article history:
Received 15 March 2015
Received in revised form 6 September 2015
Accepted 16 September 2015
Available online 18 September 2015
Keywords:
Khunik
Magmatism
Geochemistry
Subduction
U–Pb dating
a b s t r a c t
The Khunik prospecting area is located 106 km south of Birjand in eastern Iran, and is considered as an
epithermal gold prospecting area. The mineralization is related to subvolcanic rocks. There are several
outcrops of subvolcanic intrusions in the area which intruded into Paleocene–Eocene volcanic rocks
(andesite, trachy-andesite and pyroclastic rocks). Petrographic studies indicate that subvolcanic rocks
consist mainly of diorite, monzonite, quartz-monzonite, monzodiorite and quartz-monzodiorite.
Mineralogically, these rocks contain plagioclase, K-feldspar, amphibole, pyroxene, biotite and quartz.
Geochemically, they have features typical of high-K calk-alkaline to shoshonitic and are metaluminous,
and also belong to magnetite granitoid series (I-type). Primitive mantle normalized trace element spider
diagrams display enrichment in LILE, such as Rb, Ba, and Cs, compared to HFSE. Chondrite-normalized
REE plots show moderately LREE enriched patterns (7.45 < LaN/YbN < 10.54), and no significant Eu anomalies. Tectonic discrimination diagrams also show affinities with modern convergent margin magmas, suggesting that magmas of Khunik area formed in volcanic arc setting related to subduction of the oceanic
crust under the Lut Block plate. The initial 87Sr/86Sr ratios (0.704196–0.704772) and eNdi values (+1.3 to
+3.3) are compatible with an origin of the parental melts in a supra-subduction mantle wedge. Zircon
U–Pb dating by LA-ICP-MS indicates the age of 38 ± 1 Ma (late Eocene) for subvolcanic units that are
related to mineralization. A biotite granodiorite porphyry is the testimony of the youngest magmatic
activity in the area, with an age of 31 ± 1 Ma (early Oligocene). The represented dates are interpreted
as magmatic crystallization ages of subvolcanic intrusions.
Ó 2015 Published by Elsevier Ltd.
1. Introduction
The Khunik prospecting area is in eastern Iran, and eastern side
of the Lut Block, in the southern portion of Khorasan Jonoubi
Province (Fig. 1). The Lut Block is an elongate rigid mass extended
about 900 km in a north–south direction from the Doruneh Fault in
the north to the Jaz-Mourian basin in the south and is about
200 km wide (Karimpour and Stern, 2009; Stocklin and Nabavi,
1973). The Lut Block is one of the several microcontinental blocks
interpreted to have drifted from the northern margin of
Gondwanaland during the Permian opening of the Neo-Tethys,
⇑ Corresponding author.
E-mail address: karimpure@um.ac.ir (M.H. Karimpour).
http://dx.doi.org/10.1016/j.jseaes.2015.09.023
1367-9120/Ó 2015 Published by Elsevier Ltd.
which was subsequently accreted to the Eurasian continent in
the Late Triassic during the closure of the Paleo-Tethys (Golonka,
2004). In spite of many studies on tectonic and magmatic evolution
of the Lut Block, the paleotectonic of the Lut Block has been highly
controversial. Some researchers (Jung et al., 1983; Samani and
Ashtari, 1992; Tarkian et al., 1983) have interpreted the Lut Block
within an extensional setting. The presence of ophiolitic complexes
in Eastern Iran between the Lut and the Afghan Blocks, led Saccani
et al. (2010) to eastward intra-oceanic subduction. Recently, asymmetric subduction models have been discussed for situations similar to that of the Lut Block (Arjmandzadeh, 2011; Arjmandzadeh
et al., 2011; Doglioni et al., 2009). The extended exposure of
Tertiary volcanic and subvolcanic rocks is the special characteristic
of the Lut Block. These rocks cover half of the Lut Block with a
thickness of 2000 m, and have been formed due to subduction
S. Samiee et al. / Journal of Asian Earth Sciences 115 (2016) 170–182
171
Fig. 1. Structural map of eastern and central portions of Iran. The red rectangle is the position of the study area (Sengör, 1990; Alavi, 1996; Bagheri and Stampfli, 2008). (For
interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
prior to the collision of the Arabian and Asia plates (Berberian et al.,
1999; Camp and Griffis, 1982; Tirrul et al., 1983).
Various types of mineralization are related to tertiary subduction under the Lut Block that led to extensive magmatic activity
in this area. Understanding this magmatic activity would be a useful exploration key for magmatic-related mineralization. The
Khunik prospecting area is located in a strategic part of the Lut
Block that include many instances of mineralization associated with
magmatism such as Qaleh Zari IOCG Deposit (Karimpour et al.,
2005; Richards et al., 2012), Maherabad porphyry-type Cu–Au
(Malekzadeh Shafaroudi et al., 2014; Richards et al., 2012),
Sheikhabad high-sulfidation and Hanich low sulfidation (Karimpour
et al., 2007), Cu porphyry type of Dehsalm (Arjmandzadeh,
2011), Kooh-Shah (Abdi et al., 2010), and Hired intrusive related
gold deposit (Karimpour et al., 2007). The potential for gold
mineralization at the Khunik was identified in stream silt and rock
samples analysis by the Geological Survey of Iran (2000). Pars
Kaneh Kish (2008) carried out diamond drilling (12 boreholes,
1808 meter), and sampling to identify mineralization process at
depth. The results from the core samples show mean value of
642.9 ppb Au. According to geology, alteration, geochemistry and
mineralization evidences, the Khunik area shows characteristics
similar to those of epithermal gold deposits. The aim of this paper
is not to discuss the process of mineralization but is to provide a
comprehensive understanding on the age, genesis and geodynamic
control of the magmatism related to mineralization in the
study area. In this contribution, at first, we present zircon
U–Pb ages by Laser Ablation Inductively Coupled Plasma Mass
172
S. Samiee et al. / Journal of Asian Earth Sciences 115 (2016) 170–182
Spectrometry (LA-ICP-MS) to precisely date the magmatism. We
also discuss the geochemical and Sr–Nd isotope data and results
of geochemical modelling to constrain the petrogenesis of the
subvolcanic rocks.
2. Geological setting
The Khunik prospecting area is located within the 1:250,000
(Eftekhar-Nezhad and Stocklin, 1992) and 1:100,000 Mokhtaran
geology map (Movahed Avval and Emami, 1978). Detailed field
work and geological mapping in 1:20000 were carried out by the
author. The major part of the study area is covered by Cenozoic
volcanic rocks that are intruded by subvolcanic rocks (Fig. 2).
According to the studies, the lithology of the Khunik area
can be divided into four groups: 1 – Paleocene conglomerate,
2 – pre-Eocene sequence of intermediate to felsic volcanic and
pyroclastic rocks including andesite, trachy-andesite, agglomerate
and tuff. 3 – Middle Eocene to early Oligocene intermediate
subvolcanic rocks that have intruded into the volcanic units
and are mainly diorite, monzodiorite, quartz-monzodiorite,
monzonite and granodiorite. These subvolcanic rocks (based on
type and abundance of phenocrysts, matrix and mafic minerals),
are divided into 13 compositional groups (Fig. 2) 4 – Quaternary
sediments including old and young alluvial deposits (Fig. 2).
The subvolcanic units in the study area have intruded into the
volcanic units as stocks and dykes (Fig. 3), and based on their
relation with mineralization, they are comprised of two groups:
1 – subvolcanic units that are related to mineralization, and outcrop at the center of the study area (Fig. 2). These are mostly
altered (argillic, propylitic, sericitic-silicified, gossan and
hydrothermal breccia), and some contain different amounts of
mineralization as disseminate, stockwork and hydrothermal
breccia; 2 – granodiorite porphyry unit that is younger than mineralization, and have no mineralization and less alteration.
3. Analytical techniques and methods
Thin sections (200 in total) from the studied subvolcanic rocks
were examined under the optical microscope. A total of 30 low
altered samples were analyzed for whole-rock major, trace, and
rare earth elements and 6 samples were selected for Rb–Sr and
Sr–Nd isotope compositions, two of which were dated using
LA-ICP-MS single zircon U–Pb age determination.
3.1. Whole-rock geochemical analysis
Samples were taken from the unaltered outcrops available at
each locality for geochemical analyses. Rock powders were prepared by removing altered surfaces and enclaves, crushing and
grinding by means of an agate ball mill. Twenty-four samples were
analyzed for major elements by wave length-dispersive X-ray
Fluorescence (XRF) spectrometry using fused discs and the Phillips
PW 1480 XRF at the Kansaran Binaloud Laboratory in Mashhad,
Iran. All of these samples were analyzed for trace elements using
Inductively Coupled Plasma Mass Spectrometry (ICP-MS), following a lithium metaborate/tetraborate fusion and nitric acid total
digestion, in the ACME Laboratories, Vancouver, Canada. This
method offers increased sensitivity for REEs and trace elements
occurring at low concentration levels (Cs, Ta, Th, U, Hf), with detection limits of around 0.01 ppm. Whole-rock analytical results for
major element oxides and trace elements are listed in Table 2.
Results of the analyses were evaluated using GCDKIT software
version 3 (Janousek, 2008).
3.2. Rb–Sr and Sm–Nd isotopic analysis
Strontium and Nd isotopic compositions were determined for
six whole-rock samples. The samples were analyzed in the Laboratório de Geologia Isotópica da Universidade de Aveiro, Portugal.
Fig. 2. Geological map of Khunik area. The sampling localities are also shown.
S. Samiee et al. / Journal of Asian Earth Sciences 115 (2016) 170–182
173
Fig. 3. Intrusions of subvolcanic rocks as dykes (a) and stocks (b) cutting the volcanic units.
The selected powdered samples were dissolved with HF/HNO3
solution in Teflon Parr acid digestion bombs at 200 °C temperature
for 3 days. After evaporation of the final solution, the samples were
also dissolved with HCl (6.2 N) also in acid digestion bombs, and
were dried again. The elements to analyze were purified using conventional ion chromatography technique in two stages; separation
of Sr and REE elements in ion exchange column with AG8 50 W
Bio-Rad cation exchange resin and purification of Nd from other
lanthanides in columns with Ln Resin (ElChrom Technologies)
cation exchange resin. All reagents used in the preparation of the
samples were sub-boiling distilled, and the water was produced
by a Milli-Q Element (Millipore) apparatus. Strontium was loaded
on a single Ta filament with H3PO4, whereas Nd was loaded on a
Ta outer side filament with HCl in a triple filament arrangement.
87
Sr/86Sr and 143Nd/144Nd isotopic ratios were determined using a
multi-collector Thermal Ionization Mass Spectrometer (TIMS) VG
Sector 54. Data were acquired in dynamic mode with peak measurements at 1–2 V for 88Sr and 0.5–1.0 V for 144Nd. Strontium
and Nd isotopic ratios were corrected for mass fractionation
relative to 88Sr/86Sr = 0.1194 and 146Nd/144Nd = 0.7219. During this
study, the SRM-987 standard gave an average value of
87
Sr/86Sr = 0.710259(19) (N = 12; conf. lim = 95%) and 143Nd/144Nd =
0.5120990(56) (N = 12; conf. lim = 95%, 2r) to JNdi-1 standard.
The Rb–Sr and Sm–Nd isotope compositions are listed in Table 3.
3.3. U–Pb zircon geochronology
Two samples of subvolcanic units, each of 15–20 kg were collected for U–Pb dating of zircon. Zircon crystals were separated
using standard techniques involving crashing, washing, heavy liquid and handpicking under the binocular microscope. Approximately 50 zircon grains (euhedral, clear, uncrack crystal with no
visible heritage cores and no inclusions) were hand-picked from
each sample under a binocular microscope, and then were cast in
epoxy, polished to expose the centers of the grains and then
cleaned in ultrasonic bath. Prior to analytical work, zircons mount
examined by cathodoluminescence (CL) imaging after carbon coating, using a Tescan Cl detector instrument at Geological Survey of
Vienna, Austria. CL image was used to study internal structure
and determine the origin of zircon grains.
Zircons were dated using the Laser Ablation (LA)-ICP-MS
method at the Laboratory of Geochronology, Center for Earth
Sciences, University of Vienna, Austria. Analytical procedures were
identical to the methodology outlined in Klötzli et al. (2009).
Zircon 206Pb/238U and 207Pb/206Pb ages were determined using a
193 nm solid state Nd–YAG laser (NewWaveUP193-SS) coupled
to a multi-collector ICP-MS (Nu Instruments HR). Ablation in a
He atmosphere was either spot- or raster-wise according to the
CL zonation pattern of the zircons. Spot analyses were 15–25 lm
in diameter, whereas line widths for rastering were 10–15 lm with
a rastering speed of 5 lm/s. Energy densities were 5–8 J/cm2 with a
repetition rate of 10 Hz. The He carrier gas was mixed with the Ar
carrier gas flow prior to the plasma torch. Ablation duration was
60–120 s with a 30 s gas and Hg blank count rate measurement
preceding ablation. Ablation Count Rates were corrected offline
accordingly. Remaining counts on mass 204 were interpreted as
representing 204Pb. Static mass spectrometer analysis was as follows: 238 Uina Faraday detector, 207Pb, 206Pb, and 204 (Pb + Hg)
were in ion counter detectors. 208Pb was not analyzed. An integration time of 1 s was used for all measurements. The ion counter–
Faraday and inter-ion counter gain factors were determined before
the analytical session using standard zircons 91500 (Wiedenbeck
et al., 1995) and Plesovice (Slama et al., 2006). Sensitivity for
206
Pb on standard zircon 91500 was c. 30,000 cps per ppm Pb.
For 238U, the corresponding value was c. 35,000. Mass and elemental bias and mass spectrometer drift of both U/Pb and Pb/Pb ratios
were corrected respectively using a multi-step approach: firstorder mass bias was corrected using a desolvated 233U–205Tl–203Tl
spike solution which is aspirated continuously in Ar and mixed to
the He carrier gas coming from the laser before entering the
plasma. This corrects the bias effects stemming from the mass
spectrometer. The strongly time-dependent elemental fractionation coming from the ablation process was then corrected in order
to use the ‘‘intercept method” by Sylvester and Ghaderi (1997).
The calculated 206Pb/238U and 207Pb/206Pb intercept values were
corrected for mass discrimination from analyses of standards
91500 and Plesovice was measured during the analytical session
using a standard bracketing method. The correction utilizes regression of standard measurements by aquadratic function. A common
Pb correction was applied to the final data using the apparent
207
Pb/206Pb age and the Stacey and Kramers (1975) Pb evolution
model. The final U/Pb ages were calculated at 2r standard deviation using the Isoplot program – version 3.7 (Ludwig, 2008).
3.4. Magnetic susceptibility measurements
Magnetic susceptibility of the subvolcanic rocks from the study
area was measured by GMS2 Sintrex device which was owned by
the Ferdowsi University of Mashhad. The accuracy of this device
is 1 105 SI.
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S. Samiee et al. / Journal of Asian Earth Sciences 115 (2016) 170–182
4. Petrography of subvolcanic rocks
About 13 subvolcanic units have been identified in the study
area. These rocks are mostly diorite, monzodiorite, quartzmonzonite, and monzonite; but based on the mafic phenocrysts,
they are divided into more detailed groups as they are shown in
the geological map (Fig. 2).
4.1. Monzonite-quartz monzonite porphyry
Quartz-monzodiorite has small outcrops in center and
south of the map (Fig. 2). It has porphyritic texture. The phenocrysts are mainly 20–25% plagioclase (andesine–labradorite)
(0.2–0.8 mm), 15–20% K-feldspar (0.2–0.4 mm), and 3–20% quartz
(0.1–0.3 mm), 10% green hornblende with euhedral to subhedral
shape. A few traces of magnetite and apatite are also present. It
is greenish gray in color, and has less to intermediate propylitic
(epidote + chlorite + calcite) alteration.
The Kh-366 was taken from px-diorite porphyry. The zircon
grains of this sample are white to colorless, small to long prismatic,
50–250 lm in size, and show good oscillatory zoning in Cl images
(Fig. 4a). Fourteen analyses on 12 zircon grains yielded a lower
intercept at 38 ± 1 Ma (Bartonian) (Decay-const error included:
MSWD = 4.9, Probability of fit = 0.0) (Fig. 5a). This age is known
as the maximum age of mineralization.
Sample Kh-317 was collected from biotite granodiorite porphyry. Zircons are generally clear to light pink, with excellent
prism and pyramid faces (Fig. 4b). They are between 200 and
400 lm long. Fifteen zircon grains were selected from this sample
for LA-ICP-MS U–Pb zircon dating, and provided 16 data points
(Table 1). These data points define a lower intercept age of
31 ± 1 Ma (Rupelian) (Decay-const error included: MSWD = 5.9
probability of fit = 0.0) (Fig. 5b). This age is known as the youngest
magmatism event in the study area that happened after
mineralization.
6. Chemical characteristics of the subvolcanic plutons
4.2. Diorite porphyry
6.1. Major and trace elements geochemistry
The diorite intrusion occurs in center, eastern and western parts
of the region (Fig. 2). These intrusive rocks are gray in color, display
porphyritic texture, and phenocrysts consist of plagioclase
(40–45%) (0.2 mm–1 cm), K-feldspar (5–7%) (0.1–0.5 mm), and
mafic minerals (hornblende biotite and pyroxene). Most plagioclases are altered to epidote, chlorite, and calcite; K-feldspar to sericite and clay minerals. Clinopyroxene is replaced by carbonate,
and hornblende by chlorite and calcite.
4.3. Monzodiorite-quartz-monzodiorite porphyry
This intrusive rock has porphyritic texture. Phenocrysts mainly
consist of plagioclase (25–30%) (0.3 mm–1 cm), K-feldspar
(10–15%) (0.2–0.4 mm), quartz (3–15%) (0.4–0.6 mm), and mafic
minerals (hornblende and pyroxene). The matrix is cryptocrystalline and has the same mineral content as phenocrysts. Plagioclase is andesine (An30-An40, averaging An35) and is slightly
altered to kaolinite, sericite, and epidote. Amphibole is extremely
altered to chlorite and calcite. Quartz phenocrysts have rounded
faces.
4.4. Granodiorite porphyry
This is the youngest subvolcanic unit in the study area and is
not related to mineralization. This unit outcrops at the northern
part of the map in the andesitic unit. It has porphyritic texture with
the phenocrysts consisted of plagioclase (10–15%) (0.1 mm–2 cm),
K-feldspar (2–3%) (0.1–0.4 mm), quartz (2–5%) (0.1–0.2 mm), and
biotite (7–10%) (0.2 mm–1 cm). The matrix is mostly quartz and
K-feldspar. Plagioclases show zoning and are altered to carbonate
from margins.
5. U–Pb zircon age determination results
LA-ICP-MS U–Pb analytical data are summarized in Table 1, Cl
images are indicated in Fig. 4(a) and (b), while graphically illustrated in the Tera-Wasseburg Concordia diagrams (Fig. 5a and b).
Errors on individual analyses are cited as 2r, and the weighted
mean 206Pb/238U ages are quoted at the 95% confidence level. Cl
images show zoning patterns (Fig. 4a and b) suggesting a magmatic origin. Th/U ratios (Table 1) of both samples are distinctly
higher than those of metamorphic zircons which have Th/U < 0.1,
and are in agreement with magmatic zircons (Burda and Klötzli,
2011; Zhou et al., 2012).
Representative analyses from 24 samples of subvolcanic units
in the Khunik area are given in Table 2. The samples exhibit a range
in SiO2 content from approximately 57% to 64% (Table 2). The TAS
diagram of Middlemost (1985) was chosen among recent schemes.
The samples plot in the field of diorite, monzonite, monzodiorite,
quartz-monzodiorite and granodiorite (Fig. 6a). The results of geochemical classification for the Khunik area have some differences
with modal classification based on petrographic studies, because
of less alteration of subvolcanic rocks. The wide range of alteration
is reflected by their Loss On Ignition (LOI: 0.92–5.16).
Using the K2O vs. SiO2 nomenclature of Peccerillo and Taylor
(1976), the granitoids are classified as high-K to shoshonitic suites
with the majority of the data plotting in the field of high-K field
(Fig. 6b). The aluminum saturation index is about 0.64–1.07. With
regard to the aluminum saturation index, most of the studied granitoids are metaluminous, with only one sample being plotted in
peraluminous field (Fig. 6c), due to the fact that it is typical of
I-type granitoids (Chappell and White, 2001). Moreover, the
plotted samples from the study area on Na2O vs. K2O (Fig. 6d) of
Chappell and White (2001) are consistent with the I-type character
of subvolcanic rocks. There is no significant gap between the
compositionally different rock types from the individual plutons,
suggesting that the rock series are cogenetic (Koprubasi and
Aldanmaz, 2004), and they may have similar petrogenesis and
magma source (Nabatian et al., 2014).
In order to determine the tectonic setting of samples from the
study area, the tectonic discrimination diagrams of Pearce et al.
(1984) are used (Fig. 7). In agreement with the metaluminous
and I-type characteristics of Khunik granitoids, these rocks plot
almost on the fields of the volcanic arc granites (VAG) (Fig. 7). In
the Rb/Zr vs Nb diagram from Brown et al. (1984), the samples plot
in the field of primitive island arc/continental margin arc (Fig. 8).
6.2. Rare earth elements
Considering the fact that REE are commonly immobile, and are
not affected by hydrothermal activity, they play an important role
in identifying the geochemical characteristic of the magma
(Rollinson, 1993).
According to chondrite normalized REE diagram (Nakamura,
1974), all the 38.4 Ma subvolcanic samples show similar patterns,
and are enriched in LREE (Fig. 9a). The LaN/YbN of subvolcanic rocks
(38.4 Ma) range between 7.45 and 10.54. These ratios are less than
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S. Samiee et al. / Journal of Asian Earth Sciences 115 (2016) 170–182
Table 1
U–Pb dating result of zircons from Kh-366 and Kh-317. n.d: not detected. ⁄indicate that the analyses were done with track.
Spot/tracks
Spot/track⁄
size (lm)
Final mass bias and common Pb corrected ratios
Final blank
corrected
intensities
238
Ua
232
Tha
Th/U
207
Pb/206Pb
Kh-366
Kh-366__a_01
Kh-366__b_01
Kh-366_a2_01
Kh-366_a3_01
Kh-366_a3_02
Kh-366_a5_01
Kh-366_b1_01
KH-366_b3_01
Kh-366_c2_01
Kh-366_c3_01
Kh-366_d_01
Kh-366_d_02
Kh-366_e_01
Kh-366_f_01
20⁄
25
20⁄
25
25⁄
25⁄
20⁄
25
25⁄
25⁄
25⁄
20
25⁄
25⁄
20.5
60.2
85.0
28.3
28.4
46.0
39.3
95.8
30.1
52.6
136.5
44.5
39.2
58.0
10.6
43.8
105.7
15.0
24.2
33.3
31.4
51.0
21.9
45.7
226.5
41.5
26.7
60.0
0.52
0.73
1.24
0.53
0.85
0.72
0.80
0.53
0.72
0.87
1.65
0.93
0.68
1.03
0.05
0.05
0.05
0.05
0.12
0.06
0.05
0.05
0.05
0.05
0.04
0.05
0.05
0.05
Kh-317
Kh-317_a1_01
Kh-317_a3_01
Kh-317_b2_01
Kh-317_b3_01
Kh-317_b4_01
Kh-317_b5_01
Kh-317_c2_01
Kh-317_c3_01
Kh-317_c4_01
Kh-317_d1_01
Kh-317_d3_02
Kh-317_d4_01
Kh-317_d5_01
Kh-317_e1_01
Kh-317_e1_02
Kh-317_e2_01
35⁄
35
35⁄
35⁄
35⁄
35⁄
35⁄
35⁄
35⁄
25
25
35⁄
35
25
25
35
539.7
419.8
433.1
649.8
518.9
425.0
303.6
425.0
450.7
212.2
274.0
516.9
532.6
273.5
313.6
467.1
132.7
259.0
136.2
186.7
335.3
199.1
116.5
251.8
232.6
57.3
134.5
159.7
205.2
125.8
159.1
168.8
0.24
0.62
0.31
0.29
0.65
0.47
0.38
0.59
0.52
0.27
0.49
0.31
0.38
0.46
0.51
0.37
0.0476
0.0742
0.0474
0.0474
0.0509
0.0495
0.0554
0.0502
0.0491
0.0478
0.0475
0.0483
0.0490
0.0470
0.0477
0.0470
2RSE (%)
207
1.76
3.79
2.64
18.96
20.08
22.52
107.27
1.99
3.72
1.25
15.26
2.93
1.02
1.55
0.56
15.42
0.43
0.28
2.52
0.45
8.84
0.54
0.96
2.58
3.27
1.03
1.04
0.95
0.85
0.72
Pb/235U
2RSE (%)
206
0.0405
0.0414
0.0432
0.0450
0.1229
0.0663
0.0415
0.0417
0.0455
0.0432
0.0418
0.0441
0.0414
0.0381
2.24
4.81
3.04
12.90
23.72
28.38
149.52
3.93
5.05
1.23
29.14
3.41
1.24
2.36
0.0311
0.0567
0.0316
0.0319
0.0337
0.0335
0.0424
0.0344
0.0331
0.0337
0.0332
0.0320
0.0336
0.0323
0.0326
0.0355
1.12
23.06
1.24
0.90
4.00
0.72
24.41
0.75
1.23
21.28
15.75
2.36
2.70
4.92
4.20
1.77
Pb/238U
2RSE (%)
Rho
208
Pb/232Th
0.0058
0.0060
0.0057
0.0062
0.0079
0.0060
0.0058
0.0060
0.0060
0.0061
0.0063
0.0059
0.0060
0.0058
1.01
7.41
1.38
21.54
7.58
4.35
35.14
5.75
3.10
0.92
40.53
1.04
0.38
0.62
0.23
0.77
0.23
0.83
0.16
0.08
0.12
0.73
0.31
0.38
0.70
0.15
0.15
0.13
0.0017
0.0018
0.0019
0.0020
0.0036
0.0023
0.0019
0.0019
0.0018
0.0018
0.0020
0.0018
0.0019
0.0017
1.73
17.80
1.99
19.96
26.67
12.38
44.23
18.58
4.56
1.56
2.77
1.97
0.70
1.24
0.0048
0.0050
0.0048
0.0049
0.0047
0.0049
0.0047
0.0049
0.0049
0.0051
0.0051
0.0047
0.0050
0.0050
0.0050
0.0054
0.75
2.64
0.87
0.88
1.67
0.42
2.48
0.58
1.31
21.85
13.61
2.50
3.35
4.51
4.23
1.58
0.33
0.06
0.35
0.49
0.21
0.29
0.05
0.38
0.53
0.51
0.43
0.53
0.62
0.46
0.50
0.45
0.0013
0.0020
0.0016
0.0014
0.0014
0.0016
0.0015
0.0014
0.0016
0.0015
0.0018
0.0017
0.0016
0.0016
0.0015
0.0016
n.d
12.41
2.21
3.16
n.d
1.58
21.54
4.33
3.05
11.05
9.77
2.83
1.31
1.87
1.60
1.41
2RSE (%)
Explanations.
a
Final blank corrected intensities in mV; 2RSE 2-sigma relative standard error (in%); Rho the error-correlation between the 206Pb/238U and 207Pb/235U ratios.2RSE: 2 Sigma
relative standard error (in%); Rho: error-correlation between the 206/238 and 207/235 ratios.
those in the magmas (>20 e.g., Martin, 1987) whose source contain
garnet, therefore spinel/amphibolite may be present in residual.
Sub-parallel chondrite-normalized REE patterns for subvolcanics
related to mineralization show that the 38.4 Ma group are
cogenetic.
The REE pattern for biotite granodiorite porphyry (31 Ma) is
completely different from the older subvolcanic rocks, while highly
depleted in HREE (Fig. 9a). The LaN/YbN ratio for the youngest
(31 Ma) unit is 26.6 for granodiorite porphyry suggesting presence
of garnet in residual (Rollinson, 1993; Wilson, 1989). The Khunik
samples have no Eu anomalies (Eu/Eu⁄ = 0.85–0.95). The normal
content of the Eu could suggest a lack of or low content of
plagioclase or high oxygen fugacity in the source (Martin, 1999)
and/or minimal fractionation of this mineral in early crystallization
stages (Best, 2003). The presence of H2O in melts could decrease
the pressure and temperature conditions of formation of
plagioclase and increase the crystallization field of amphibole
(Gill, 1981; Green, 1982).
In the primitive mantle-normalized spider diagram (Sun and
McDonough, 1989) (Fig. 9b), all samples are enriched in highly
incompatible elements such as LREE and large ion lithophile elements (LILE) such as Sr, K, Rb, and Ba, however depleted in high
field strength elements (HFSE), with prominent negative anomalies
of Ta–Nb and Ti. This high LIL/HFS pattern is now recognized as a
distinctive feature of subduction zone magmas (Gill, 1981; Ma
et al., 2014; Pearce, 1983; Rollinson, 1993; Wilson, 1989; Winter,
2001).
The negative anomaly in Nb, Ta and Ti can be explained by
retention in Ti-rich residual mineral phases (i.e., rutile, titanite
and ilmenite) either in the fractionating magmatic assemblages
or in residual associations in the source area (Best, 2003; Martin,
1999; Rollinson, 1993). They can also be related to a mantle source
previously enriched in LILE over HFSE by metasomatic activity of
fluids derived from the subducted slab or sediments (Gust et al.,
1977; Woodhead et al., 1993).
Negative Nb anomalies are also characteristic of the continental
crust and, in many cases, they are probably related with processes
of assimilation, contamination or mixing with crustal materials
(Asran and Ezzat, 2012; Rollinson, 1993; Wilson, 1989; Zhang
et al., 2006; Ma et al., 2014).
7. Magnetic susceptibility measurement
Granitoids with magnetic susceptibility value of >50 105 (SI
units), are classified as belong to the magnetite series (Ishihara,
1977, 1981). Measurement of magnetic susceptibility for the rock
types provides high values (236 105 SI to 4800 105 SI),
which is indicative of the magnetite series of Ishihara (1981).
8. Sr and Nd isotopic composition
The 87Sr/86Sr and 143Nd/144Nd isotopic ratio, and TDM ages of
the Khunik granitoids are summarized in Table 3. Initial
176
S. Samiee et al. / Journal of Asian Earth Sciences 115 (2016) 170–182
Fig. 4. Cathodoluminescence images of characteristic zircon populations from (a) Kh-366, (b) Kh-317. The red line and circle show approximate location of laser ablation
trenches and are not to scale. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. Tera-Wasseburg Concordia plot of (a) Kh-366; (b) kh-317. Data point error ellipses are 2 r.
143
Nd/144Nd and 87Sr/86Sr ratios were calculated using the crystallization age (details in U–Pb zircon age results) of 38 Ma for Kh-366
and 31 Ma for Kh-317 and other samples were calculated to their
probable age (38 Ma) based on the fact that they are approximately
simultaneous with Kh-366. The depleted mantle Nd model ages
(TDM) of all analyzed samples vary in a limited range of
0.42–0.70 Ga. Since the samples have similar radiogenic and relatively homogeneous Sr–Nd isotopic values, (87Sr/86Sr)i goes from
0.704196 to 0.704772 and eNd(i) varies between +1.3 and +3.3. If
sample Kh-324 is excluded, the ranges become even narrower:
0.704650 6 (87Sr/86Sr)i 6 0.704772;
+1.3 6 eNd(i) 6 +2.7.
The
values for the 31 Ma old granodiorite lie perfectly within these last
ranges, with (87Sr/86Sr)i = 0.70470 and eNd(i) = +2.0.
According to Chappell and White (1974), values of (87Sr/86Sr)i
below 0.708 are characteristic of I-type granitoids. Therefore, the
obtained values provide further evidence in favor of the I-type
nature of the studied granitoids.
In addition, the obtained Sr and Nd isotope ratios and their
limited variations suggest that the parental magmas of the subvolcanics share a subduction related magma source (Zhang et al., 2006).
177
S. Samiee et al. / Journal of Asian Earth Sciences 115 (2016) 170–182
Table 2
Whole rock major and trace-element data for the subvolcanic rocks from Khunik prospecting area, Eu⁄: expected concentration by interpolating between the normalized value of
p
Sm and Gd. N: normalized to a chondritic meteorites. Eu/Eu⁄ = Eu/ Sm Gd. Abbreviations: Di: diorite, Mz: monzonite, Mzd: monzodiorite, LOI: Lost On Ignition.
Sample
No
KH-178
KH-144
KH-69
KH-113
KH-353-2
H-382
KH-379
KH-324
KH-189
KH-72
KH-338
KH-105
Longitude
Latitude
59°100 1500
32°230 3400
59°100 3700
32°220 5400
59°100 3700
32°230 3900
59°90 800
32°230 1200
59°100 3300
32°220 3000
59°100 4°
32°220 1500
59°100 3400
32°220 5700
59°110 5000
32°220 3200
59°100 2600
32°230 1000
Px mzd
porphyry
Hbl-Mzd
porphyry
Px-Di
porphyry
59°90 3500
32°220
2000
Px-Di
porphyry
59°950 200
32°230 300
lithology
59°100 3700
32°230
1700
Hbl-Mz
porphyry
Hbl-Px
Mzd
porphyry
Px-Di
porphyry
Px-hbl
Dio
porphyry
Mzd
porphyry
Mzd
porphyry
Px-Mzd
porphyry
Mzd
porphyry
Wt%
SiO2
TiO2
Al2O3
FeOt
MnO
MgO
CaO
Na2O
K2O
P2O5
LOI
Total
ASI
60.32
0.66
16.08
5.67
0.16
1.67
5.24
3.51
4.68
0.46
0.92
99.14
0.78
58.77
0.73
14.96
6.15
0.15
4.19
4.13
3.95
3.15
0.39
2.84
99.16
0.85
57.16
0.67
15.33
6.36
0.2
3.32
5.8
4.38
2.93
0.38
3.85
99.16
0.73
57.84
0.71
14.8
6.69
0.2
3.825
6.47
3.76
2.7
0.44
1.85
99.09
0.7
58.91
0.6
15.09
5.91
0.19
3.33
6.67
3.32
2.52
0.34
2.53
99.13
0.74
60.47
0.73
15.59
5.93
0.16
2.21
5.4
3.69
3.78
0.38
1.03
99.10
0.78
60.43
0.75
14.18
5.7
0.13
2.93
6.23
2.97
2.22
0.41
3.48
99.12
0.76
59.02
0.82
14.51
6.56
0.15
4.15
5.38
3.78
2.47
0.38
2.03
99.05
0.77
59.05
0.63
16.24
5.25
0.15
1.69
5.61
3.35
4.06
0.34
3.15
99.16
0.8
59.8
0.59
14.79
5.66
0.17
3.48
4.8
4.59
3.27
0.36
1.99
99.19
0.74
57.95
0.66
14.83
5.5
0.15
2.08
6.79
4.32
3.33
0.36
3.56
99.19
0.64
59.91
0.57
14.92
6.25
0.18
4.88
3.81
4.32
1.67
0.28
2.66
99.21
0.94
ppm
Ba
Rb
Sr
Zr
Nb
Ga
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Y
608
114.1
905.8
140.2
5.1
16.6
31.8
60.9
7.29
28.2
6.08
1.54
5.01
0.73
4.15
0.78
2.26
0.33
2.33
0.35
21.6
579
84.1
704.8
110.2
5.1
18.6
26.1
53.1
6.07
24.1
5.03
1.47
4.72
0.68
3.63
0.71
2.18
0.34
1.87
0.34
20.3
616
73.8
859.3
110
3.9
3
30.3
63.2
7.07
27.8
5.62
1.58
5.13
0.78
3.81
0.82
2.15
0.38
2.19
0.39
22.8
559
73.5
905.6
106.3
4.6
18.8
28.2
57.9
6.65
26.5
5.34
1.54
5.23
0.75
4.1
0.81
2.28
0.33
2.15
0.34
21.8
629
55.5
851.3
98.2
3.9
17.3
25.6
47.8
5.75
24.1
4.73
1.37
4.64
0.63
3.48
0.73
2.04
0.3
2.16
0.34
20.4
560
93.1
1019
109.2
3.9
17.5
25.9
51.8
6.05
23.7
4.84
1.37
4.59
0.62
3.26
0.67
2.07
0.28
1.74
0.31
18.4
584
41.2
1227
105.2
4.1
16.3
26.6
48.8
6.03
21.2
4.86
1.40
4.19
0.61
3.65
0.7
1.95
0.26
1.90
0.29
18
516
50.3
935.9
79.5
3.3
17.8
20.4
41
4.94
19.3
4.41
1.29
4.41
0.57
3.52
0.65
1.84
0.29
1.57
0.29
16.8
754
82.1
1123
112.7
4.3
15.9
29
56.8
6.70
27.3
5.52
1.61
4.98
0.69
3.97
0.78
2
0.31
2.23
0.32
19.4
650
80.1
773.2
106.1
4.3
17.2
27.5
56
6.32
24.4
5.47
1.44
4.66
0.68
3.62
0.78
1.99
0.33
1.83
0.37
19.6
634
84.3
823.1
106.9
4.2
17.5
29.2
57.8
6.57
26.5
5.28
1.51
5.21
0.73
3.6
0.84
2.12
0.33
2.21
0.3
18.1
450
46.2
736.3
87.9
3.3
18.8
22.4
43.7
4.89
22.2
4.09
1.2
4.247
0.61
3.44
0.74
2.16
0.32
1.7
0.32
20.1
0.85
9.20
KH-311
0.92
9.41
KH-366
0.90
9.33
KH-196
0.89
8.84
KH-306
0.89
7.99
KH-8
0.89
10.04
KH-10
0.95
9.44
KH-147
0.89
8.76
KH-322
0.94
8.77
KH-303
0.87
10.13
KH-49
0.88
8.91
KH-317
0.88
8.88
KH-198
59°90 100
32°220 2900
Px-hblMz
59°100 2800
32°230 800
Px-Di
porphyry
59°90 2700
32°220 3800
Hbl-pxMzd
porphyry
60.57
0.65
14.92
6.1
0.18
2.65
6.1
3.12
2.98
0.44
1.62
99.08
0.76
59°90 700
32°230 1600
Px-Hbl-qtz
Mzd
porphyry
63.27
0.67
14.27
5.75
0.1
1.22
3.36
3.55
5.02
0.36
1.88
99.14
0.82
59°100 3100
32°230 0000
HblqtzMzd
porphyry
61.79
0.48
14.9
5.05
0.17
2.64
4.17
4.27
3.3
0.28
2.64
99.3
0.81
59°100 3500
32°230 800
Hbl-Mzd
porphyry
59°100 2900
32°220 2200
Hbl-Mzd
porphyry
59°90 3000
32°240 3000
Mzd
porphyry
59°80 5100
32°230 2700
Hbl-px Di
porphyry
59°100 1800
32°220 5800
Px-Di
porphyry
59°940 700
32°240 5700
Bio-Gd
porphyry
60.72
0.6
14.83
6.01
0.22
2.85
5.03
3.73
3.56
0.39
1.45
99.13
0.77
56.87
0.56
14.54
6.06
0.17
4.03
6.5
3.77
3.2
0.43
3.25
99.12
0.67
58.44
0.78
14.83
7.07
0.28
5
3.1
2.81
3.31
0.41
3.14
99.03
1.07
58.56
0.63
16.2
5.19
0.15
3.51
4.14
4.52
3.58
0.39
2.69
99.19
0.86
59°80 5600
32°220 5100
hbl-px
Mzd
porphyry
58.88
0.64
15.94
5.58
0.19
3.07
4.34
4.75
3.65
0.42
1.98
99.12
0.73
692
67
994.5
107.3
897
100.3
853.7
100.1
720
91.5
753.9
116.4
Ratios
Eu/Eu⁄
(La/Yb)N
Sample
No.
Longitude
Latitude
Lithology
SiO2
TiO2
Al2O3
FeOt
MnO
MgO
CaO
Na2O
K2O
P2O5
LOI
Total
ASI
Ppm
Ba
Rb
Sr
Zr
56.31
0.7
15.68
6.4
0.19
3.11
4.73
4.89
3.02
0.36
3.92
99.09
0.78
656
67.3
891.1
101.8
56.5
0.81
13.71
7.25
0.3
4.29
6.61
2.92
3.65
0.52
2.48
98.92
0.66
626
81
1019
118.8
687
81.5
920
100.9
612
79.5
886.1
100
1287
57.4
792.6
99.4
722
87.3
1065
108.6
56.67
0.79
13.59
6.35
0.19
4.67
5.23
3.99
3.34
0.44
3.74
99.13
0.7
567
83.6
985.5
114.2
64.17
0.41
14.54
2.59
0.18
1.02
5.9
2.5
2.36
0.16
4.97
98.69
0.83
5379
52.4
688.6
104.8
791
96
1567
111.8
(continued on next page)
178
S. Samiee et al. / Journal of Asian Earth Sciences 115 (2016) 170–182
Table 2 (continued)
Sample
No
Nb
Ga
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Y
Ratios
Eu/Eu⁄
(La/Yb)N
KH-178
KH-144
KH-69
KH-113
KH-353-2
4.1
9.15
27.7
52.4
6.34
28.4
5.01
1.45
4.90
0.65
3.7
0.83
2.18
0.33
2.19
0.34
20.1
5
18
31.1
61.5
7.45
30.8
6.13
1.72
5.33
0.72
3.84
0.80
2.10
0.32
2.24
0.32
20.6
4.8
17.3
24.4
50.5
6.21
28.6
5.56
1.47
4.56
0.63
3.46
0.74
2.01
0.32
1.97
0.33
19
3.5
12
24.5
47.8
5.88
23.2
4.47
1.27
4.01
0.53
3.34
0.66
1.73
0.27
1.69
0.27
16.1
4.7
16.9
26.4
52.7
5.58
22.3
4.38
1.25
4.13
0.62
3.42
0.74
2.1
0.3
2.12
0.35
18.6
0.89
8.53
0.92
9.36
0.89
8.35
0.92
9.77
0.9
8.40
H-382
KH-379
KH-324
KH-189
KH-72
KH-338
KH-105
3.4
16.7
25.1
45.9
5.58
22.2
4.57
1.31
4.26
0.58
3.19
0.78
2.05
0.36
2.27
0.36
18.9
4.1
17.3
23.6
44.8
5.37
21
4.5
1.31
4.14
0.56
3.05
0.67
1.69
0.25
1.51
0.27
16.5
4.4
17.8
27.9
51.9
6.16
24.4
5.24
1.41
4.66
0.66
3.68
0.75
2.39
0.35
2.12
0.36
20.3
5.1
17.1
25.7
51.6
6.15
25.3
4.93
1.42
4.28
0.63
3.21
0.73
1.9
0.31
2.08
0.35
18.2
4.1
3.2
30.1
63.5
7.26
29.9
5.8
1.57
4.99
0.7
3.40
0.78
2.16
0.3
1.73
0.33
19.6
7.7
14
28.8
47.5
4.38
16.2
2.39
0.64
2
0.20
1.39
0.23
0.90
0.12
0.73
0.11
7.5
4.5
18.5
25.7
57.4
6.47
27.8
5.44
1.49
4.89
0.68
3.61
0.81
1.89
0.3
1.73
0.33
19
0.91
7.45
0.93
10.54
0.87
8.87
0.95
8.33
0.89
9.95
0.9
26.6
0.88
10.02
Fig. 6. (a) Classification of subvolcanic rocks from Khunik area in Na2O + K2O vs SiO2 TAS diagram of Middlemost (1985). (b) Subvolcanic rocks from Khunik area are mainly
high-K calc-alkaline to shoshonitic based on K2O vs Na2O diagram (Peccerillo and Taylor, 1976). (c) Diagram for determination of aluminum saturation index of Khunik
samples (Shand, 1969). All samples except one are metaluminous. (d) Discrimination diagram for I and S-type granitoids by %Na2O vs %K2O (Chappell and White, 2001).
Boundary between I and S-types is Na2O = 3%.
The recorded small variation in isotopic ratios can be related
either to variable crustal assimilation (but always in small degrees)
or to heterogeneity in the magma source (Nabatian et al., 2014).
In the eNd(i) versus (87Sr/86Sr)i diagram (Fig. 10), with the
exception of Kh-324, all samples plot slightly to the right of the
so-called ‘‘mantle array”.
S. Samiee et al. / Journal of Asian Earth Sciences 115 (2016) 170–182
179
Fig. 7. Plot of subvolcanic rocks on tectono-magmatic diagram (Pearce et al., 1984). VAG = volcanic arc granite, syn-COLG = syn-collision granite, WPG = within plate granite,
ORG = orogenic granite.
However, hydrothermal alteration of the samples may also
cause some displacement of their isotope composition toward
higher 87Sr/86Sr ratios (Arjmandzadeh et al., 2011; Menzies et al.,
1993).
9. Genesis of the subvolcanic rocks
Fig. 8. Rb/Zr vs Nb diagram (Brown et al., 1984).
The position of the studied samples to the right of the mantle
array might have been related to an origin of the most primitive
magmas by melting in a supra-subduction mantle wedge.
The Sr–Nd isotopic data (Table 3) of the studied rocks are clearly
different from the lower and upper continental crust source,
instead they resemble mantle-derived volcanic arc rocks. Previously, Arjmandzadeh et al. (2011) and Arjmandzadeh and Santos
(2014) obtained very similar isotope data in Oligocene associations
of K-rich granitoid rocks from Chah-Shaljami and Dehsalm (also in
the Lut Block), which were interpreted as representing suites
derived from parental magmas generated in supra-subduction
mantle wedge.
Since there isn’t any correlation between eNd and SiO2 content
in subvolcanic rocks of the study area, it is clear that crustal assimilation hasn’t occurred, and partial melting or fractional crystallization are known as the main process in their genesis (Li et al., 2008).
On the diagram of (La/Yb)N vs. YbN (Li et al., 2008) and Sr/Y vs. Y
(Defant and Drummond, 1990) (Figs. 11a and b), all samples are
Fig. 9. (a) Chondrite normalized (Nakamura, 1974) (REE) patterns for Khunik samples, and (b) primitive mantle normalized some REE and trace element spider diagram (Sun
and McDonough, 1989).
180
S. Samiee et al. / Journal of Asian Earth Sciences 115 (2016) 170–182
Table 3
Rb–Sr and Sm–Nd isotopic data for seven whole-rock samples from Khunik area. Errors are in 2r. Initial 143Nd/144Nd and 87Sr/86Sr ratios were calculated using the crystallizations
age of 38 Ma (except for Kh-317, which has an age of 31 Ma).
Sample
Sr
ppm
Rb
ppm
87
Error(2s)
(87Sr/86Sr)
m
Error(2s)
(87Sr/86Sr)i
Nd
ppm
Sm
ppm
147
Error
(2s)
(
Nd/144Nd)
m
Error(2s)
eNdi
TDM
(Ga)
Kh-366
KH-144
Kh-196
Kh-324
Kh-72
Kh-317
1019.4
704.8
994.5
935.9
773.2
688.6
81
84.1
67
50.3
80.1
52.4
0.230
0.345
0.195
0.155
0.300
0.220
0.007
0.010
0.006
0.004
0.008
0.006
0.704774
0.704943
0.704877
0.704280
0.704884
0.704789
0.000017
0.000017
0.000020
0.000024
0.000018
0.000017
0.704650
0.704757
0.704772
0.704196
0.704722
0.704692
30.8
24.1
28.6
19.3
24.4
16.2
6.13
5.03
5.56
4.41
4.47
2.39
0.120
0.126
0.118
0.138
0.136
0.089
0.006
0.007
0.006
0.007
0.007
0.005
0.512711
0.512729
0.512728
0.512793
0.512690
0.512718
0.000018
0.000023
0.000016
0.000016
0.000016
0.000014
1.8
2.1
2.1
3.3
1.3
2
0.56
0.57
0.52
0.53
0.70
0.42
Rb/86Sr
Sm/144Nd
Explanations: m: measured ratios, i: initial ratios.
low Y and Yb contents and high Sr/Y ratio (91.8), except for being
in affinity to adakite magmas, suggests melting of garnet at the
source. Adakite is characterized by high Sr/Y and (La/ Yb)N ratios
and low Y and YbN values (Defant and Drummond, 1990; Defant
et al., 2002; Martin et al., 2005). Given that amphibole can substantially fractionate middle LREE/HREE ratio (Rollinson, 1993), it may
confirm the involvement of amphibole rather than other geochemical parameters. All lines of evidence show that subvolcanic units
have been formed from a depleted mantle magma that has underwent partial melting of a subducted slab with an amphibole in a
residual (Fig. 11a).
10. Conclusions
Fig. 10. eNd(i) vs. (87Sr/86Sr)i diagram for Khunik subvolcanic rocks. Reference data
sources: upper continental crust (Taylor and McLennan, 1985); lower continental
crust (Rollinson, 1993; Rudnick, 1995) with those of MORB (Rollinson, 1993; Sun
and McDonough, 1989), DM (McCulloch and Bennett, 1994), OIB (Vervoort et al.,
1999), IAB (Arjmandzadeh and Santos, 2014), and mantle array (Wilson, 1989; Gill,
1981; McCulloch et al., 1994). Initial 143Nd/144Nd and 87Sr/86Sr ratios were
calculated using the crystallizations age of 38 Ma (except for Kh-317, which has
an age of 31 Ma).
plotted in the field of classic island arc except for the biotite granodiorite porphyry. The high Y and Yb concentrations in these magmas (rather than primitive mantle concentrations) preclude garnet
as a major residual phase. Biotite granodiorite porphyry which has
A combination of geochemical evidence, Rb–Sr isotopic composition and U–Pb dating on the Khunik area led us to the following
conclusions:
The subvolcanic rocks of the Khunik area have diorite,
monzodiorite, quartz-monzodiorite, monzonite and granodiorite
compositions.
The age of the subvolcanic rocks related to mineralization based
on U–Pb zircon dating is 38 ± 1 Ma that is interpreted as the age of
crystallization of the magma source, and maximum age of mineralization as well. The age of granodiorite that is the youngest unit
in the study area is 31 ± 1 Ma. This unit has no relation to the
mineralization.
Based on mineralogy, high values of magnetic susceptibility,
aluminum saturation index, and low initial 87Sr/86Sr ratios
(<0.704772), the subvolcanic rocks are classified as belong to the
magnetite-series of oxidized, I-type granitoids. These magmas
originated from a depleted mantle above a subduction zone. The
dehydration of the subducted plate or of the subducted sediments
produced fluid that ascended through the mantle wedge leading to
partial melting of overlaying mantle.
Fig. 11. (a) La/Yb N vs. Yb N (Li et al., 2008), (b) Sr/Yb vs. Y (Defant and Drummond, 1990) plots.
S. Samiee et al. / Journal of Asian Earth Sciences 115 (2016) 170–182
There is a close relationship between subvolcanic intrusions
and mineralization in the Khunik area. Therefore studying this
relationship can be a useful way for exploration of these types of
mineralization in eastern Iran, especially in the Lut Block.
Acknowledgments
We would acknowledge Franz Biedermann and Alembert
Alexandre Ganwa for technical help and helpful discussions. The
please acknowledge the University of Vienna for providing the
funding for the research group as such. Part of the funding also
came from the Austrian Science Foundation Grant FWF M-1371N19 to U. Klötzli and A. Ganwa. Sr and Nd isotope analyses were
financially supported by Laboratório de Geologia Isotópica da
Universidade de Aveiro (Portugal) through project Geobiotec
(PEst-OE/CTE/UI4035/2014).
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