Turkish Journal of Earth Sciences
Turkish J Earth Sci
(2016) 25: 311-340
© TÜBİTAK
doi:10.3906/yer-1509-3
http://journals.tubitak.gov.tr/earth/
Research Article
Geochemistry, zircon U-Pb age, and tectonic constraints on the Bazman granitoid
complex, southeast Iran
1
1,
1
2
3
Mohammad Reza GHODSI , Mohammad BOOMERI *, Sasan BAGHERI , Daizo ISHIYAMA , Fernando CORFU
1
Department of Geology, University of Sistan and Baluchestan, Zahedan, Iran
2
Department of Earth Science and Technology, Faculty of Engineering and Resource Science, Akita University, Akita, Japan
3
Department of Geosciences, University of Oslo, Norway
Received: 06.09.2015
Accepted/Published Online: 15.03.2016
Final Version: 09.06.2016
Abstract: The Bazman granitoid complex (BGC), including a large zoned pluton, intrudes into the upper Paleozoic sedimentary cover
of the Lut block. It crops out on the southern slope of the Bazman volcano in Baluchestan Province of Iran. The intrusive rocks range
from gabbro to various metaluminous to weakly peraluminous granites, and they are classified as I-type magmatic series. They display
geochemical characteristics of typical volcanic arc magmatism at continental margins. Major- and trace-element variation diagrams
show that fractional crystallization was the major process and crustal contamination, a subordinate process during the evolution of
the BGC. The decrease in CaO, MgO, Al2O3, Fe2O3, TiO2, P2O5, and Sr, as well as the increase of K2O and Rb with increasing silica, are
possibly related to the fractionation of plagioclase, hornblende, apatite, and titanite, whereas the increasing K, Rb, Cs, Pb, and light rare
earth elements (LREEs) can be explained by crustal contamination. The BGC rocks are enriched by large ion lithophile elements (e.g.,
Rb, K, Cs) and the LREEs with respect to the high field strength elements (e.g., Zr, Hf, Nb, Ta, Y) and heavy rare earth elements. New IDTIMS U-Pb dating performed on zircon and titanite extracted from the granitic samples indicates that the BGC was emplaced during
the late Cretaceous period at 83–72 Ma by subduction of the Neo-Tethyan oceanic crust beneath the Eurasian continent. Subsequently,
the complex became part of the Lut block when it probably rotated counter-clockwise with respect to the Sanandaj-Sirjan zone and the
Urumieh-Dokhtar volcano-plutonic belt.
Key words: Zircon U-Pb age, Lut block, Neo-Tethyan subduction, Bazman, Iran
1. Introduction
The role of granite and granitic magma is crucial for the
understanding of the magmatic processes, continental
crust evolution, and tectonic setting of many terrains
(e.g., White and Chappell, 1983; Atherton, 1993; Brown,
2013). There are various complexities in the genesis of
granitoid magmas, but in general they fall into mantle and
crustal processes: 1) fractional crystallization of mantlederived mafic magma is a major process in producing
a wide diversity of granite compositions (e.g., Bowen,
1948; Huppert and Sparks, 1988; Pitcher, 1993); 2) hightemperature metamorphism leads to partial melting of the
continental crust and the formation of granites (Winkler,
1965; Chappell and White, 1974; Ashworth, 1985;
Mehnert, 1987). Most granitoids originate indirectly from
the mantle or consist of mixtures of continental crust and
mantle components (Wyllie, 1984; Atherton, 1990; Gray
and Kemp, 2009). There is also significant production of
granitoid rocks in nonconvergent plate tectonic settings,
*Correspondence: [email protected]
particularly some of the extensional tectonic regimes
(e.g., Leake, 1990; Eby, 1992; Atherton and Petford, 1993;
Vigneresse, 1995; Barbarin, 1999).
Over the past two decades there has been an increasing
interest in the petrogenesis and thermochronology
of granite in many parts of Iran. The oldest group of
granitoids cropping out in central Iran is attributed to
an early Cambrian magmatic belt associated with the
Proto-Tethyan subduction (Ramezani and Tucker, 2003;
Bagheri and Stampfli, 2008; Hassanzadeh et al., 2008).
The second group of granitoids is related to the PaleoTethyan subduction in central and northern Iran (Bagheri
and Stampfli, 2008; Mirnejad et al., 2013). A third group
of granitoids crops out in the Sanandaj-Sirjan Zone, a
Mesozoic magmatic belt (Berberian and King, 1981), that
lies to the NE and parallel to the Zagros fold-thrust belt
above the Neo-Tethyan subduction zone (Figure 1a) (e.g.,
Ahmadi Khalaji et al., 2007; Ghalamghash et al., 2009;
Shahbazi et al., 2010; Tahmasbi et al., 2010; Mahmoodi et
al., 2011; Esna-Ashari et al., 2012).
311
GHODSI et al. / Turkish J Earth Sci
60°00´
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Sistan Suture Zone
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outline
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1
Makran Accretionary Prisms
500Km
Oman Sea
65°00´
Figure 1. (a) Main tectonostratigraphic units of Iran, modified after Stöcklin (1977), Berberian and King (1981), Tirul et al.
(1983), and Bagheri and Stampfli (2008). (b) Main magmatic belts in the south and east of Iran. AJT: Anarak-Jandaq terrane;
Al: Alborz; BGC (Bazman granitoid complex); Bz: Bazman volcano; EIR: Eastern Iranian Ranges; Gb: Great Kavir Block;
Kd: Kopeh Dagh; Ks: Kuh-e-Sultan; Lu: Lut Block; Mp: Makran accretionary prisms; Pb: Poshteh-e-Badam terrane; SSZ:
Sannadaj-Sirjan Zone; Tb: Tabas Block; Tf: Taftan Volcano; UDB: Urumieh-Dokhtar volcano-plutonic belt, Yz: Yazd Block;
Za: Zagros fold and thrust belt. 1: Urumieh plutonic complex (Ghalghamash et al., 2009); 2: Astaneh pluton (Tahmasbi et al.,
2010); 3: Alvand plutonic complex (Shahbazi et al., 2010); 4: Borojerd granitoid (Ahmadi Khalaji et al., 2007); 5: Shir-Kuh
granite (Sheibi et al., 2011); 6: Sirjan granitoid; 7: Bajestan granitoid (Karimpour et al., 2011); 8: Shah Kuh granitoid (Esmaeily
et al., 2005); 9: BGC; 10: Band-e-Zyarat ophiolite; 11: Dehshir-Baft ophiolite.
The remaining enigmatic granitoids, which occur in
eastern Iran, are attributed to a variety of origins. Some
of those are interpreted as originated from syn-collision
magmatism along the Sistan suture zone (Figure 1a)
312
(Camp and Griffis, 1982; Sadeghian et al., 2005). The
granite formations exposed in the Lut block (Figure 1b),
in the eastern part of central Iran, are ascribed to the
subduction of the Sistan oceanic lithosphere under the
GHODSI et al. / Turkish J Earth Sci
Lut block (Esmaeily et al., 2005; Mahmoodi et al., 2010;
Arjmandzadeh et al., 2011; Zarrinkoub et al., 2012). There
is also ample evidence emphasizing eastward subduction
under the Afghan block (Camp and Griffis, 1982; Tirrul
et al., 1983; Fotoohi Rad et al., 2005; Saccani et al., 2010;
Angiboust et al., 2013).
The Bazman granitoid complex (BGC) is one of the
granitoid complexes that intruded the Lut block, north
of the present-day Makran range (Figure 1b), in the Late
Cretaceous (Berberian et al., 1982). It is composed of
different types of plutonic rocks with a wide range of silica
contents (Vahdati Daneshmand et al., 2004; Sahandi and
Padashi, 2005). Some primary contacts among the various
rock bodies are preserved; however, the metamorphosed
country rocks and blocks of roof pendant are dispersed
through the complex. These features, along with good
exposure, make the BGC suitable for studying the processes
involved in the evolution of granite. The BGC is situated
at the intersection of several volcano-plutonic belts in the
southeast corner of Iran, where several tectonostratigraphic
terranes (see Howell, 1989) with uncertain relationships
are present (Figure 1). This location is one of the few
direct sources of information that could shed light on the
magmatic evolution and tectonic history of terranes, and,
additionally, the recognition of terrane outlines.
There is little published geological information on
the geology, geochemistry, and petrogenesis of the BGC.
The most important source of fundamental knowledge
in this regard is the petrological and geochronological
study of Berberian (1981), who postulated that calcalkaline magmatism was generated by the Neo-Tethyan
oceanic lithosphere (Sea of Oman) that was subducted
beneath the Makran Range. The magmatic differentiation
was considered as the principal process involved in the
generation of the BGC (Berberian, 1981). More recent
efforts have focused on geological mapping to separate
the various granitic phases with different characteristics
(Vahdati Daneshmand et al., 2004; Sahandi and Padashi,
2005). However, there are inconsistencies in the grouping
of these granites between the eastern and western parts of
the BGC on the published geologic maps.
There are two main unanswered questions related to
the understanding of granite emplacement and genesis in
eastern Iran. First, the oldest accretionary prisms of the
Makran range are composed of Eocene-Oligocene flysch
(McCall, 1997, 2002), while the proposed late Cretaceous
formation of the BGC would have required the initiation
of subduction prior to the start of the Cretaceous period.
However, there is no preserved evidence, specifically in
the Makran area, that proves that subduction occurred
before the Cretaceous period. Accordingly, considering
the nature of the Makran volcanic arc, the second question
is self-evident: Why are the Eocene volcanic rocks and
the Oligocene-Miocene plutonic rocks, the obvious signs
of the Urumieh-Dokhtar volcano-plutonic belt in Iran,
almost nonexistent in the Makran volcanic arc?
The study of the BGC can help us to understand several
puzzling petrogenetic aspects in the region, because the
key tectonic setting of the BGC is within or near several
other magmatic belts in southeast Iran (Figure 1b). Finally,
the data emerging from research on the BGC could be
correlated with comparable plutonic rocks in adjacent
tectonic units, such as the Sanandaj-Sirjan Zone in Iran
(Berberian and Berberian 1981), or Lhasa and Karakorum
in the Himalayas (Searle et al., 2010). Accordingly, this
paper focuses on precise age determinations with ID-TIMS
U-Pb dating of the most common rock types in the BGC,
supported by petrography, whole-rock geochemistry, the
evolution of the magmatic rocks, and its relationship to
the overall tectonic setting and the changes therein. The
results are also critical to related discussions regarding the
southern outline of the Lut block and its tectonic behavior
since the late Mesozoic period.
2. Geological setting
The Iranian plateau is a part of the Alpine-Himalayan
orogenic system, which is one of the major structural
features of the planet Earth. The main tectonostratigraphic
units of Iran are shown in Figure 1a. All the units have been
attributed to the opening and closing of the Paleo-Tethyan
and Neo-Tethyan oceanic basins as a result of subduction
and collision events in the northern to southern parts of
Iran. The BGC is located at the southeastern extremity of
the Urumieh-Dokhtar volcano-plutonic belt, north of the
Makran accretionary prisms, west of the Sistan suture zone
(Flysch zone), and south of the Lut block where the Iranian
microcontinent experienced several subduction and
collision events with the Arabian plate beginning during
the Late Cretaceous period (Stöcklin, 1977; Berberian and
King, 1981) and continuing through to the Miocene arc
stage (Shahabpour, 2005; Agard et al., 2007) to Quaternary
volcanism (Farhoudi and Karig, 1977; Saadat and Stern,
2011) (Figure 1a).
There are seven volcanic and/or plutonic belts
intersecting each other in the southern and southeastern
parts of Iran near the study area (Figure 1b). They are
chronologically presented here.
2.1. Sanandaj-Sirjan plutonic belt
The magmatic part of the Sanandaj-Sirjan Zone comprises
mainly middle-late Jurassic, and infrequently Cretaceous,
plutonic rocks and other comparable extrusive rocks. It
is known as the Mesozoic magmatic belt of Iran and was
produced by the Neo-Tethyan oceanic crust subduction
(Berberian and King, 1981).
2.2. East plutonic belt of Lut
A few late-Jurassic plutonic bodies, such as the Shah
Kuh granite pluton (Esmaeily et al., 2005; Mahmoodi et
313
GHODSI et al. / Turkish J Earth Sci
al., 2010), and probable Cretaceous intrusions, such as
the Bajestan granite pluton (Karimpour et al., 2011), are
the main constituents of this belt (Figure 1a). There is no
consensus on the origin of this plutonic belt.
2.3. Chagai-Raskoh volcanic belt
This is the western volcanic belt of Pakistan with an
intraoceanic island-arc origin that developed between the
Cretaceous period and Eocene epoch in the Neo-Tethyan
Ocean and subsequently accreted to the northern active
margin of Eurasia (e.g., Siddiqui et al., 1986; Nicholson et
al., 2010).
2.4. Plutonic belt of the Sistan suture zone
Several late Eocene-Oligocene granitoid plutons were
emplaced along the north- to northwest-trending suture
zone situated between the Lut and Afghan blocks (Camp
and Griffis, 1982; Sadeghyan et al., 2005). Most of them
are characterized by the calc-alkaline syn-collision to
subduction-related magmatism that intruded during the
closing of the Sistan Ocean (Tirrul et al., 1983).
2.5. Urumieh-Dokhtar volcano-plutonic belt
The Urumieh-Dokhtar volcano-plutonic belt consists
mainly of Eocene calc-alkaline extrusive rocks and
Oligocene-Miocene granitoid intrusions (Berberian and
Berberian, 1981). It extends parallel to the Zagros foldthrust belt and is the product of the subduction of the NeoTethyan oceanic lithosphere under the Iranian continental
lithosphere (e.g., Berberian and King, 1981, Verdel et al.,
2011).
2.6. West volcano-plutonic belt of Lut
This belt includes Eocene calc-alkaline volcanic and
Oligocene-Miocene plutonic rocks. In spite of its
similarities to the Urumieh-Dokhtar volcano-plutonic
belt, the belt is oriented at a sharp angle with respect to the
Neo-Tethyan suture zone, and consequently identifying
its origin is problematic. Several researchers have ascribed
the belt to the subduction of the Sistan oceanic lithosphere
underneath the Lut block (Arjmandzadeh et al., 2011;
Karimpour et al., 2011).
2.7. Makran volcanic arc
This arc includes several recently active strato-volcanoes,
such as Bazman, Taftan, and Kuh-e-Soltan, which are
situated above the Makran subduction zone, parallel to
the Cenozoic Makran accretionary prisms, and north of
the Jazmurian Depression in a fore arc basin geodynamic
position (Farhoudi and Karig, 1977; Jacob and Quittmeyer,
1979; Saadat and Stern, 2011).
3. Geology of the BGC
The BGC consists of several plutonic bodies, including
a main elliptical pluton in the western part and several
small intrusions with complicated boundaries in the
eastern part. This complex covers an area of about 900 km2
314
(Figure 2). The BGC is strongly weathered and eroded,
and it displays a topography that is lower than that of the
surrounding sedimentary rocks. The general geology of the
study region is outlined in the 1/100,000-scale geological
maps of Bazman and Maksan (Vahdati Daneshmand et al.,
2004; Sahandi and Padashi, 2005), and it is presented in
a more detailed map in Figure 2. The BGC is surrounded
by Paleozoic sedimentary rocks that locally underwent
contact metamorphism. These sedimentary rocks include
the Carboniferous Sardar Formation (Cs), which consists
of shale, sandstone, and limestone, and the Permian Jamal
Formation (Pj) composed of siltstone, shale, sandstone,
and thick bedded limestone and dolomite (Figure 3a).
Blocks of crystallized carbonate and sandstone of
varying sizes, originating from the Cs and Pj formations,
can be observed with pronounced resorbed margins
dispersed in the main BGC granitic body. Close to the
contact, the sedimentary country rock associations
were metamorphosed to hornfels, quartzite, and marble
depending on the local lithological composition. The
hornfels in the aureole are intensively silicified and can be
divided into biotite, hornblende, and pyroxene hornfelses.
These rocks are unconformably overlain by Miocene to
Quaternary volcanic rocks, travertine, and recent alluvial
deposits. The Bazman volcanic rocks, including lava flows
and pyroclastic deposits, appear with extreme thicknesses
in the northern part as represented on the map (Figure 2).
The BGC is a polyphase granitoid complex that can be
divided into western and eastern parts. The western part
includes a zoned pluton with a diameter of 30 km, having
a gabbro to meladiorite rim characterized by an average
width of 1000 m (Figure 3b), changing inwardly to felsic
rocks with a composition shifting from monzodiorite to
granodiorite, to porphyritic granites in the core (Figures
3c and 3d) (Vahdati Daneshmand et al., 2004). The
widespread existence of various xenoliths, remnants of
roof pendant strata that reacted to the hornblende granite,
can be identified in the center of the pluton. In addition,
the metamorphosed outcrops of the country rocks
between the intrusions, especially in the eastern section,
are evidence that could potentially indicate the role of a
contamination process during the magmatic evolution of
the BGC.
The gabbro occurs mainly as a narrow ribbon-shaped
outcrop on the southern and western margins of the
complex (Figure 3e). These plutonic phases with different
lithology are cut by numerous granitic plugs and aplitic
dikes (Figure 3f). The aplitic dykes apparently follow an old
fracture system (N15°E) in the gabbro. The enclaves have
distinct boundaries with the host granite and granodiorite.
Enclaves are a common feature of the BGC and are mainly
gabbro and diorite in composition that occur as oval
bodies and irregularly shaped blobs, ranging from 1 to 50
cm in size (Figure 3g).
GHODSI et al. / Turkish J Earth Sci
59˚50'0"E
60˚0'0"E
60˚10'0"E
N
Dare Ahuo
B2
Bazman
27˚50'0"N
24
437
g7
447 11
10
Irans
Ja7 Ja8 111 320 Bz-2
330
hahr
316 318
Bz-7
27˚40'0"N
160
340
50
Spost
Maksan
Tanak
48
0
3
Fault
Road
13
Sample Location
Ja13
U/Pb Dating
12
6
9
12 km
85
Bz-3
Porphyritic granite
Contact Metamorphism
Alluvium
Basaltic lava flows
Pyroxene hornfels facies
Biotite, hornblende granite
Andesitic lavas, dacite, tuff, and
minor olivine basalt (Pliocene)
Hornblende hornfels facies
Biotite granite
Andesitic and dacitic lavas (Miocene)
Slightly metamorphosed
Granodiorite
Limestone of Jamal Formation (Permian)
Monzodiorite to quartz monzodiorite
Shale and sandstone of Sardar Formation
(Carboniferous)
Granite
Late Cretaceous
Quaternary
L E G E N D
Bazman Granitoid Complex
Village and Town
Gabbro - Diorite
Figure 2. Simplified geological map of the BGC (modified after Vahdati-Daneshman et al., 2004; Sahandi and Padashi, 2005).
The eastern part of the BGC has a general NE-SW
trend and consists of various types of granites, which
are wrapped by each other, demonstrating a complicated
pattern of emplacement. No regular pattern in their
distribution can be observed. It seems that the main
portion of eastern granites was covered by the younger
products of the Bazman volcano. Some parts of the eastern
granitoids obviously illustrate a different mineralogical
composition as they contain garnet and muscovite (Figure
3h).
The BGC is cut by two relatively young fault systems
(Figure 2); the first consists of en echelon, dextral strikeslip faults with a general N30°E trend distributed in the
eastern part of the complex, whereas another minor
system appears as sinistral strike-slip faulting with a
general N45°W trend in the western part of the complex.
These two fault systems are similar to those observed in
the Eastern Iranian Range, the so-called East Flysch Basin
(Freund, 1970; Stöcklin, 1974). The Iranian-Arabian plate
collision (e.g., Berberian, 1983; Mouthereau et al., 2012),
was certainly the main cause of this shear deformation.
Overprinting of this new deformation phase onto the
previous ones during the late Tertiary period crushed the
BGC and resulted in the flat topography, which differs
from the normal topographically irregular appearance of
granites.
4. Analytical methods
A total of about 300 samples from various intrusive phases,
including granite, granodiorite, monzodiorite, quartz-
315
GHODSI et al. / Turkish J Earth Sci
Bazman Volcano
Jamal Formation
Diorite
Sardar Formation
Granodiorite
Granite
a
Qz
Hbl
b
Bt
1 cm
c
Marble
0.8 cm
Enclave
d
Or
1 cm
Gabbro
ee
Grt
Aplite
Granite
f
g
Granite
h
Ms
0.8 cm
Figure 3. (a) Field photograph of the BGC’s rocks intruded into the sedimentary rocks, (b) diorite, (c)
granodiorite, (d) porphyritic granite with pink orthoclase megacrysts, (e) contact between gabbro and marble,
(f) aplitic vein/dikelet in porphyritic granite, (g) gabbroic enclave in granite, and (h) biotite-muscovite granite
contains garnet. Mineral abbreviations from Whitney and Evans (2010).
monzodiorite, diorite, and gabbro, as well as enclaves
of various compositions, were collected. Thin sections
of these samples were prepared and studied by optical
microscopy. Rock types were identified by modal analyses,
based on the counting of 3000 points for each sample.
Twenty-one samples were analyzed for major and some
minor elements by X-ray fluorescence (XRF). Trace and
rare earth elements were analyzed by inductively coupled
plasma-mass spectrometry (ICP-MS). The measurements
using XRF and ICP-MS were carried out with a Phillips
PW2404 XRF at the Faculty of Education and Human
Studies and a VG Elemental PQ-3 ICP-MS at the Faculty
of Engineering and Resource Sciences at Akita University,
Akita, Japan. Loss on ignition (LOI) was determined by
heating the samples at 900 °C for 2 h to determine relative
weight loss.
316
The U-Pb analyses were carried out by thermal
ionization mass spectrometry isotopic dilution (IDTIMS) at the University of Oslo (Norway). The rocks were
crushed and pulverized in a jaw crusher and hammer mill
and the heavy minerals concentrated with a succession of
Wilfley table flotation, free fall, and high gradient magnetic
separation and methylene iodide density separation.
Further selection was carried out by hand-picking under a
binocular microscope. All zircon fractions were subjected
to chemical abrasion, based on Mattinson (2005), but
by approximately following the procedure of Schoene et
al. (2006) with an annealing stage of 3 days at 900 °C, a
partial dissolution step with HF (+HNO3) at ca. 190 °C
overnight, and a hot plate step of 2 h in 6 N HCl after
removal of the solution and some rinsing. The dissolution
was carried out following Krogh (1973) as described by
GHODSI et al. / Turkish J Earth Sci
Corfu (2004), but using a mixed 202Pb–205Pb–235U spike.
Data were calculated using the decay constants of Jaffey
et al. (1971) and corrected for initial 230Th disequilibrium
(Schärer, 1984). The final ages are the weighted averages of
206
Pb/238U dates. Calculations and plotting were done with
the Isoplot program of Ludwig (2003).
5. Petrography
The modal compositions for the western and eastern
granitoids are given in Table 1. On the basis of the average
modal percentage of quartz, orthoclase, and plagioclase, the
BGC composition ranges from granite and granodiorite,
through quartz monzodiorite, monzodiorite, diorite, and
gabbro (Figure 4). Some of most striking petrographic
characteristics of these granitoids are summarized below.
5.1. The western granitoids
5.1.1. Porphyritic granite
Porphyritic granites cover the central part of the western
granitoids. The contact of porphyritic granite with the
surrounded rocks (granodiorite and diorite) is sharp. They
are white to pink in color and coarse-grained porphyritic
in texture with very large euhedral to subhedral pink
orthoclase megacrysts (Figure 3d). The orthoclase
megacrysts usually contain inclusions of zircon, apatite,
magnetite, biotite, and hornblende. The plagioclase grains
are subhedral, unzoned, and polysynthetically twinned,
and weakly altered to sericite and epidote. The quartz is
anhedral, with varying sizes, and displays undulatory
extinction. The groundmass consists mainly of medium-
grained quartz, plagioclase, and orthoclase as the main
minerals, with biotite and hornblende occurring rarely as
subhedral and anhedral phases. Myrmekitic intergrowths
are commonly seen between the quartz and plagioclase in
these rocks.
5.1.2. Granite
Granites are coarse- to medium-grained, granular
in texture, and gray in color. Major minerals include
K-feldspar, plagioclase, quartz, hornblende, and
minor minerals such as biotite, titanite, apatite, and
opaque minerals. The K-feldspars are large to small
subhedral to anhedral and show Carlsbad twinning. The
plagioclase occurs as subhedral large crystals, unzoned,
polysynthetically twinned, and weakly altered to sericite.
The quartz is anhedral, medium-grained, and with
undulatory extinction. The hornblende appears as euhedral
to subhedral crystals, which are the most common mafic
minerals in these rocks. The biotite typically occurs as
subhedral to anhedral, in irregular plates, and contains
inclusions of apatite and titanite.
5.1.3. Granodiorite
The granodioritic rocks display a variety of shapes in the
western granitoids. Some of them occur as a continuous
thin zone around the margin of the porphyritic granites
and some of them occur as a wide granodioritic zone near
the southern part of the porphyritic granite (Figures 2 and
3c). The granodiorite is mainly coarse-grained, pale gray in
color, and granular in texture (Figure 5a). The plagioclase
occurs as subhedral and anhedral small to large crystals,
Table 1. Modal mineralogical compositions of the BGC (Gb: gabbro, Mn: monzodiorite, Gd: granodiorite, G: granite,
PG: porphyritic granite, BG: biotite granite, BHG: biotite-hornblende granite, BMG: biotite-muscovite granite).
Western granitoid
Rock type
Gb
Sample no.
12
340
Eastern granitoid
Mn
Gd
G
PG
BG
BHG
BMG
111
13
330
Ja7
447
85
10
Plagioclase
65.7
47.1
66.6
41.5
33.9
29.8
37.3
41.4
24
Quartz
0.7
1.2
3.7
20.3
22
27.1
23.1
15.3
35
K-feldspar
7
4.7
17.6
26.2
34
39.6
32.2
22.7
36.7
Hornblende
0
31
9.8
9.2
8
0
0
10.3
0
Biotite
6.1
4.4
0
1.6
0.6
2.8
7.2
8.3
1.3
Clinopyroxene
13.5
6.6
0
0
0
0
0
0
0
Orthopyroxene
5.3
0
0
0
0
0
0
0
0
Muscovite
0
0
0
0
0
0
0
0
2
Garnet
0
0
0
0
0
0
0
0
1
Titanite
0
0
0.8
0.2
0.9
0.1
0
0.7
0
Opaque
1.7
5.1
1.5
1.1
0.5
0.7
0.2
1.8
0
Counted points
3000
3000
3000
3000
3000
3000
3000
3000
3000
317
GHODSI et al. / Turkish J Earth Sci
Q
e
iorit
nod
G ra
Granite
A
Qz-Monzodiorite
P
Monzodiorite Gabbro/Diorite
Figure 4. Modal compositions of representative samples of the
BGC in quartz-alkali-plagioclase (QAP) ternary diagram of
Streckeisen (1976).
variable in size, unzoned, polysynthetically twinned, and
partially altered to sericite and epidote. A few plagioclase
crystals are zoned. The K-feldspar is mainly anhedral in
crystal shape, medium-grained, with Carlsbad twinning,
and is partially altered to clay minerals. The quartz is
anhedral, medium to coarse-grained, and has undulatory
extinction (Figure 5a). The myrmekitic intergrowths
between the quartz and the plagioclase are common in the
granodiorite. The hornblende forms as isolated prismaticsubprismatic subhedral crystals and is the most mafic
mineral in the granodiorite. The hornblende is partially
altered to biotite, chlorite, and titanite. The primary biotite
appears as long flakes and irregular plates. Some mafic
minerals occur as mafic clots of amphibole, titanite, and
magnetite.
5.1.4. Monzodiorite to quartz monzodiorite
These rocks are also exposed near the margin and occur
locally as small bodies. They are generally coarse to
medium-grained and granular in texture and consist
of plagioclase, orthoclase, hornblende, and biotite as
the main minerals (Figure 5b). Pyroxenes are observed
in some samples. Apatite, titanite, zircon, monazite,
magnetite, and rutile are the main accessory minerals.
The secondary minerals are chlorite, sericite, epidote, and
clay minerals that were formed by alteration of the main
minerals. The plagioclase shows large variations in size
and is less altered. The orthoclase occurs as subhedral to
anhedral crystals and exhibits Carlsbad twinning. The
orthoclase contains inclusions of apatite, monazite, zircon,
and acicular rutile. Perthitic and myrmekitic intergrowths
318
are common in these rocks. Magnetite and ilmenite are the
main opaque minerals.
5.1.5. Dioritic rocks
The dioritic rocks occur as small bodies on the eastern
margin of the western granitoids. They are coarse-to
medium-grained, dark gray to gray in color, and granular
in texture (Figure 5c). The plagioclase grains are mainly
subhedral, unzoned, and polysynthetically twinned and
weakly altered to sericite. A few anhedral interstitial
quartz grains are present in some samples. Clinopyroxene
is not abundant in these rocks and seems to be replaced
by amphibole. Unaltered subprismatic and relicts of augite
are observed in one sample (No. 24, Figure 2). Hornblende
crystals are the dominant mafic mineral in the dioritic
rocks. They form subprismatic crystals, irregular plates, or
clusters. The hornblendes are partially replaced by biotite,
chlorite, and titanite. Primary biotites are present as
irregular large flakes with ragged outlines in some samples.
Titanite, apatite, magnetite, and ilmenite are the main
accessory minerals of these rocks. Orthoclase occupies the
interstices between plagioclase, contains small inclusion
of apatite, and often shows an anhedral shape. Rounded
enclaves of gabbro (1 to 20 cm in size) occur in the dioritic
rocks.
5.1.6. Gabbro
These groups of rocks are coarse- to medium-grained and
dark in color with various textures; some samples display
intergranular and myrmekitic textures, whereas others
have a granular texture (Figure 5d). Plagioclase crystals are
the dominant felsic mineral, ranging in size from very large
euhedral-subhedral laths to small anhedral crystals. The
anhedral interstitial crystals are pyroxene and amphibole.
Effects of deformation, such as strained boundaries,
are present in some plagioclase laths. Clinopyroxene is
not abundant in these rocks and seems to be replaced
by amphibole and biotite (Figure 5d). Hornblende is
the dominant ferromagnesian mineral in the Bazman
gabbro. They form subprismatic crystals, irregular plates,
or clusters. A few apatite prisms and abundant large to
small anhedral to subhedral grains of magnetite form
the accessory minerals. Clay, sericite, minor amounts of
actinolite, and some biotite are the secondary minerals.
The gabbros are the oldest part of the BGC as they occur as
enclaves within the other intrusive rocks (Figure 3g).
5.2. Eastern granitoids
5.2.1. Biotite granite
Biotite granites are the most abundant granitoids in the
eastern part of the BGC. They are granular in texture and
consist of plagioclase, K-feldspar, quartz, and biotite as the
main minerals and titanite, apatite, and opaque minerals
as accessory minerals (Figure 5e). Chlorite, epidote, and
clay minerals are the main secondary minerals. The quartz
GHODSI et al. / Turkish J Earth Sci
a
b
Ttn
Qz
Qz Hbl
Kfs
Hbl
Kfs
Plg
c
d
Plg
Plg
Plg
Hbl
Cpx
Plg
Bt
Plg
e
f
Zrn
Grt
Plg
Ap
Kfs
Qz
Plg
Ms
Figure 5. Photomicrographs of thin sections of representative BGC rocks (cross polarized transmitted
light): (a) granodiorite, (b) monzodiorite, (c) diorite (d) gabbro, (e) biotite granite, (f) biotite-muscovite
granite. Abbreviations: Bt = biotite; Cpx = clinopyroxene; Grt = garnet; Hbl = hornblende; Kfs = alkalifeldspar; Ms = muscovite; Plg = plagioclase; Qz = quartz; Ttn = titanite; Zrn = zircon. Mineral abbreviations
from Whitney and Evans (2010).
is typically anhedral, coarse-grained, and has undulatory
extinction. Plagioclase occurs as subhedral large crystals,
unzoned, and polysynthetically twinned. Biotite is the
only ferromagnesian phase in these rocks and occurs as
medium to small anhedral crystals. Some parts of this
granite were intruded by porphyritic granite.
5.2.2. Biotite-hornblende granite
Gray, coarse-to medium-grained, granular biotitehornblende granite (granodiorite) also covers a large area
in the eastern part of the BGC. Major minerals include
K-feldspar, plagioclase, quartz, hornblende, and biotite,
and the minor minerals are titanite, apatite, and opaque
minerals. K-feldspars are anhedral and occupy the
interstices between the other minerals. Plagioclase occurs
as large euhedral to subhedral crystals, unzoned, and
polysynthetically twinned. The quartz is anhedral, coarsegrained, and has undulatory extinction. Hornblende and
biotite occur as euhedral to subhedral crystals, frequently
associated with each other, but with the hornblende being
more abundant than the biotite. Some mafic minerals
occur as mafic clots of amphibole, titanite, and biotite.
Magnetite and ilmenite are the main opaque minerals.
5.2.3. Biotite-muscovite granite
These rocks are poorly exposed in the eastern part of the
map area and occur as small intrusions associated with
biotite granite. They are white in color, coarse-grained,
granular in texture, and contain garnet locally. The mineral
assemblages consist of quartz, orthoclase, microcline,
319
GHODSI et al. / Turkish J Earth Sci
plagioclase, biotite, muscovite, and garnet. Garnet is the
most important accessory mineral in this rock. The quartz
typically is anhedral, coarse-grained, and has undulatory
extinction. The microcline is subhedral to euhedral,
coarse- to medium-grained, and contains inclusions of
orthoclase, quartz, and plagioclase. The plagioclase grains
are mainly subhedral, unzoned, polysynthetically twinned,
and occupy the interstices between other minerals. The
biotite and muscovite occur as subhedral crystals but
the muscovite is more abundant than the biotite (Table
1). Garnet occurs as individual crystals, euhedral to
subhedral, and medium-grained (Figure 5f).
6. Geochemistry
The major- and trace-element data for representative
samples of the BGC’s rocks are listed in Table 2. The
Bazman intrusions vary from gabbro to granite in
composition (Figure 6).
6.1. Major elements
The rocks have a wide range of SiO2, from 47.15 to 81.57
wt. %. The more mafic samples are the gabbros, and the
more silicic samples are the aplite and pegmatite dikes. The
abundances of Fe2O3, MgO, CaO, TiO2, MnO, and P2O5
decrease with increasing SiO2, whereas K2O and Na2O
increase (Figure 7). Al2O3 has a bent trend, increasing to
60 wt. % SiO2 and then decreasing from this point onward.
Based on the alumina saturation index (ASI = A/CNK)
(molar Al2O3/(CaO+Na2O+K2O) of Shand (1947), the
rocks are metaluminous to weakly peraluminous (Figure
8a). In the A/NK versus A/CNK diagram, only one sample
overlaps the S-type granitoid field, and the other samples
plot on the I-type field (Figure 8a). The FeOt/(FeOt+MgO)
versus silica diagram (Frost et al., 2001) shows that the
BGC is mainly a magnesian I-type, similar to Cordilleran
batholiths (Figure 8b). The I-type geochemical character
of the Bazman granitoids is supported by the presence of
hornblende, magnetite, and titanite, and the absence of
high-grade regional metamorphism around the BGC.
In the diagrams of K2O+Na2O versus SiO2 (Middlemost,
1985) and AFM, all samples of the BGC plot within the
subalkaline and calc-alkaline fields (Figures 6 and 8c).
6.2. Trace elements
The abundances of large-ion lithophile elements (LILEs),
such as Rb and Sr, vary systematically with increasing SiO2
(Figure 9). Rb generally increases, whereas Sr decreases
with increasing SiO2. The high field-strength elements
(HFSEs), such as Y, Zr, and Ti, decrease with increasing
SiO2. The transition elements (Co, V, Zn) also display a
negative correlation with SiO2 (Figure 9).
Trace-element spider diagrams for the BGC,
normalized to MORB, are presented in Figure 10. All the
examined samples display considerable Ti, Hf, Y, and Yb
depletion and K, Rb, Ba, and Th enrichment. The trace-
320
element patterns of the granites show dissimilarities and
can be divided into three patterns; one sample exhibits
Sr depletion and a strong negative Ba anomaly. Although
most granite samples have negative Hf anomalies, there
is one sample that shows a positive Hf anomaly. The
trace-element spider diagrams of granodiorite, quartzmonzodiorite, monzodiorite, diorite, and gabbro are
quite similar. All the samples show strong negative Hf and
moderate negative Ti anomalies. Some samples of quartzmonzodiorite, monzodiorite, and diorite show strong
positive Th anomalies.
The rare earth element (REE) distribution patterns
for the BGC are normalized to chondrite abundances
(Boynton, 1984) in Figure 11. The chondrite-normalized
REE patterns show that all the rock types in the BGC are
enriched with light rare earth elements (LREEs) relative
to heavy rare earth elements (HREEs). These patterns also
show that the granite, diorite, and gabbro have a weak
negative Eu anomaly while the granodiorite and quartzmonzodiorite have a moderate negative Eu anomaly
and the monzodiorite has a weak negative Eu anomaly.
One granite sample that contains garnet shows a strong
negative Eu anomaly; the content of REEs in this sample is
lower than in the other samples. The REE patterns of the
granites exhibit a moderate to deep negative slope from
La to Ho and a moderate positive slope from Ho to Yb,
and they are flat from Yb to Lu. The patterns of REE for
granodiorite, quartz-monzodiorite, monzodiorite, and
diorite show a moderate to steep slope from La to Eu and a
moderate slope from Gd to Lu. The REE slope for gabbro
is low to flat.
6.3. U-Pb geochronology
Three samples were selected for U-Pb dating (Table 3;
Figures 12 and 13). Sample BZ-3 represents granodiorite,
BZ-2 is monzodiorite, and BZ-7 is porphyritic granite.
Zircon occurs in the granodiorite (BZ-3) as partly
broken prismatic to equant crystals. Cores were not
immediately evident, but analyses revealed the presence of
somewhat older components, especially in the two fractions
of residual grains that resisted the first dissolution (fractions
4 and 5, Table 3) and were dissolved separately (Nos. 1 and
2). The CL images of the grains in BZ-3 (Figure 13) display
regular and local sector zoning, but also multiple stages of
intermediate resorption, which confirm the U-Pb evidence
for intermediate growth stages. The results suggest that the
residues were enriched in an early growth component with
higher Th/U. They may represent antecrysts (e.g., Miller et
al., 2007; Schaltegger et al., 2009). The age of emplacement
of the granodiorite is best defined by the three zircon
analyses with the youngest 206Pb/238U ages, which average
83.07 ± 0.30 Ma (Figure 12). Titanite occurs as brown,
partly euhedral crystals rich in U (320–230 ppm) and gives
a slightly younger age of 81.32 ± 0.20 Ma.
GHODSI et al. / Turkish J Earth Sci
Table 2. Major (wt. %) and trace elements (ppm) in the BGC samples.
Sample no.
10
447
Ja7
160
11
48
Rock type
Granite
SiO2
81.57
71.28
71.52
70.06
71.59
76.50
TiO2
0.05
0.20
0.21
0.22
0.17
0.10
Al2O3
10.90
15.58
15.77
16.36
15.40
13.99
Fe2O3
0.87
2.24
2.38
2.55
1.99
1.15
MnO
0.19
0.07
0.07
0.08
0.08
0.02
MgO
0.00
0.58
0.47
0.54
0.41
0.23
CaO
0.38
2.36
2.84
3.13
1.92
2.01
Na2O
2.98
3.74
4.24
4.77
3.62
4.76
K2O
3.44
3.96
3.12
2.64
4.63
1.61
P2O5
0.05
0.06
0.07
0.10
0.06
0.06
LOI
0.42
0.37
0.30
0.43
0.48
0.32
Total
100.84
100.44
100.99
100.87
100.35
100.76
Li
64.71
47.07
50.53
59.22
46.64
10.42
Be
3.67
1.71
2.18
2.35
1.78
2.48
Sc
2.50
3.58
2.33
2.29
2.83
2.82
V
5.02
32.17
33.09
37.33
25.55
14.11
Cr
3.15
11.03
4.06
4.81
9.09
5.44
Co
0.72
3.39
2.77
2.97
2.65
2.10
Ni
1.19
4.65
1.77
1.99
3.51
2.21
Cu
6.19
12.62
7.33
8.19
6.57
13.77
Zn
20.35
36.52
29.37
36.67
42.54
9.28
Ga
16.08
31.19
40.35
32.18
95.59
31.99
Rb
181.70
118.60
148.10
109.10
129.50
74.30
Sr
34.43
399.50
431.20
445.40
341.80
267.20
Y
12.12
7.16
8.19
8.72
6.90
6.55
Zr
55.50
79.50
91.60
111.60
80.60
53.20
Nb
28.60
11.12
12.15
13.20
11.81
10.62
Ag
0.12
0.07
0.01
0.10
0.06
0.18
Cd
0.08
0.03
0.03
0.03
0.03
0.06
In
0.02
0.02
0.01
0.01
0.02
0.00
Sn
1.58
3.98
0.72
0.99
1.30
0.78
Sb
0.66
0.17
0.16
0.23
0.09
0.13
Cs
14.54
3.82
2.15
4.09
2.55
1.64
Ba
30.07
857.40
310.20
208.40
1084.00
165.70
La
7.39
12.68
10.59
24.12
18.23
15.09
Ce
14.90
22.04
21.20
38.86
31.85
21.15
Pr
1.80
2.62
2.69
4.12
3.67
2.94
Nd
6.46
9.60
10.22
14.43
12.71
10.52
Sm
1.73
1.83
2.00
2.27
2.41
1.81
Eu
0.11
0.83
0.68
0.66
0.83
0.64
321
GHODSI et al. / Turkish J Earth Sci
Table 2. (Continued).
Gd
1.57
1.71
1.76
2.09
2.09
1.61
Tb
0.28
0.23
0.23
0.26
0.27
0.21
Dy
1.85
1.30
1.36
1.46
1.40
1.17
Ho
0.40
0.25
0.27
0.30
0.25
0.22
Er
1.39
0.75
0.84
0.92
0.71
0.67
Tm
0.27
0.11
0.13
0.13
0.11
0.11
Yb
2.35
0.78
0.96
0.98
0.77
0.79
Lu
0.35
0.12
0.15
0.15
0.12
0.13
Hf
1.88
0.59
0.78
0.64
0.71
1.74
Ta
4.04
1.39
1.11
1.23
1.39
1.29
Pb
14.96
31.43
14.38
20.55
26.32
19.32
Bi
0.27
0.03
0.03
0.05
0.03
0.06
Th
6.47
5.55
7.20
17.08
7.42
7.95
U
1.97
1.01
2.19
3.19
1.36
2.34
Eu/Eu*
0.20
1.43
1.10
0.93
1.13
1.15
A/CNK
1.17
1.06
1.02
1.00
1.07
1.06
Table 2. (Continued).
Sample no.
Ja8
316
Rock type
Granodiorite
SiO2
69.07
63.88
TiO2
0.28
Al2O3
16.37
Fe2O3
MnO
MgO
85
13
320
B2
111
Qz monzodiorite
Monzodiorite
62.70
65.01
61.91
62.55
57.19
0.53
0.77
0.54
0.73
0.41
0.76
16.39
16.68
16.74
16.77
18.20
20.13
2.74
5.40
5.75
4.51
6.14
5.00
5.97
0.08
0.11
0.10
0.09
0.11
0.13
0.12
0.68
2.07
2.21
1.55
2.41
1.56
2.03
CaO
3.08
5.06
5.25
4.95
4.61
6.27
7.71
Na2O
4.14
3.81
4.03
3.73
3.96
5.13
5.61
K2O
3.75
3.06
2.31
3.24
3.28
1.11
1.04
P2O5
0.11
0.19
0.19
0.17
0.20
0.17
0.29
LOI
0.43
0.36
0.45
0.31
0.65
0.49
0.46
Total
100.73
100.86
100.44
100.85
100.77
101.02
101.31
Li
34.46
37.17
30.65
26.97
27.45
25.70
32.14
Be
2.01
2.37
1.95
1.89
1.68
1.85
2.54
Sc
2.97
9.75
8.32
6.24
10.35
7.23
9.49
V
43.19
111.40
140.70
83.25
109.50
82.77
95.87
Cr
5.71
22.55
32.50
6.74
12.28
13.45
8.79
Co
3.55
10.68
12.75
9.29
14.77
8.74
9.38
Ni
1.90
7.00
9.31
4.44
8.74
5.84
4.17
Cu
6.13
11.81
16.08
35.59
120.30
19.03
9.48
Zn
35.43
63.27
67.67
51.55
74.81
61.34
44.93
Ga
50.37
49.27
47.37
47.69
40.88
27.38
29.70
Rb
125.00
105.40
89.01
90.61
117.60
27.79
22.78
322
GHODSI et al. / Turkish J Earth Sci
Table 2. (Continued).
Sr
Y
Zr
Nb
Ag
Cd
In
Sn
Sb
Cs
Ba
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ta
Pb
Bi
Th
U
Eu/Eu*
A/CNK
470.70
10.44
110.40
13.81
0.04
0.02
0.06
1.12
0.12
6.27
455.40
18.77
35.41
4.26
15.50
2.78
0.87
2.53
0.31
1.80
0.35
1.09
0.16
1.13
0.17
0.47
1.06
14.02
0.10
7.13
1.55
1.00
0.99
444.70
24.49
165.90
19.18
0.11
0.07
0.05
2.41
0.31
2.84
423.50
30.27
60.16
7.85
29.74
5.72
1.33
5.38
0.72
4.30
0.83
2.48
0.36
2.42
0.36
0.61
1.80
15.14
0.10
17.66
3.71
0.74
0.87
369.70
16.72
220.70
16.35
0.05
0.04
0.03
1.38
0.34
2.89
352.30
26.26
46.59
5.77
21.84
4.11
1.18
3.89
0.51
3.10
0.60
1.75
0.25
1.63
0.23
0.52
1.37
8.32
0.05
8.37
2.78
0.90
0.89
461.90
29.15
160.40
23.00
0.04
0.03
0.04
1.93
0.36
2.56
465.40
71.13
122.40
13.96
50.02
9.05
1.72
7.87
1.00
5.68
1.07
3.20
0.47
3.13
0.43
0.75
3.08
19.65
0.05
25.69
4.32
0.62
0.90
380.30
20.54
235.50
17.65
0.17
0.12
0.05
1.95
0.86
6.78
366.10
29.51
55.73
6.60
23.57
4.55
1.09
4.37
0.60
3.64
0.73
2.17
0.32
2.12
0.30
0.55
1.69
30.57
0.04
29.96
6.81
0.75
0.91
596.40
15.87
124.70
10.48
0.07
0.08
0.04
1.47
0.27
0.83
137.90
21.25
38.10
4.72
18.80
3.77
0.99
3.52
0.48
2.92
0.59
1.80
0.25
1.77
0.27
0.65
1.20
16.61
0.06
6.67
1.97
0.83
0.86
894.40
25.45
203.60
23.16
0.11
0.06
0.04
2.34
0.18
0.80
137.80
37.61
84.88
10.59
40.46
7.51
1.88
6.62
0.88
4.86
0.97
2.83
0.40
2.58
0.39
0.96
2.20
6.59
0.06
7.48
2.01
0.82
0.83
Table 2. (Continued).
Sample no.
50
24
437
G7
Ja13
12
340
318
Rock type
Diorite
Gabbro
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
54.34
0.64
18.28
7.59
0.19
4.80
5.85
3.76
53.72
1.07
17.28
8.65
0.14
4.78
7.76
3.24
56.19
0.84
18.00
8.30
0.19
3.25
6.84
3.76
55.41
0.60
20.36
6.78
0.14
2.57
7.51
4.86
57.84
0.63
18.39
7.02
0.12
3.38
7.06
4.14
54.98
0.91
17.01
9.69
0.17
4.46
7.77
3.40
47.15
1.22
16.61
11.65
0.17
6.59
12.99
2.84
52.66
0.86
16.28
9.40
0.32
5.97
9.03
3.82
323
GHODSI et al. / Turkish J Earth Sci
Table 2. (Continued).
K2O
P2O5
LOI
Total
Li
Be
Sc
V
Cr
Co
Ni
Cu
Zn
Ga
Rb
Sr
Y
Zr
Nb
Ag
Cd
In
Sn
Sb
Cs
Ba
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ta
Pb
Bi
Th
U
Eu/Eu*
A/CNK
324
2.46
0.10
2.39
100.41
138.20
4.38
25.25
715.20
61.36
31.41
23.35
115.70
134.80
50.71
447.40
1137.00
13.99
108.90
9.89
0.09
0.03
0.06
2.76
0.12
10.84
265.20
9.19
17.16
2.43
10.75
2.60
0.82
2.65
0.40
2.43
0.50
1.46
0.21
1.39
0.20
0.47
0.88
5.85
0.03
5.00
1.07
0.95
0.94
2.01
0.41
1.67
100.74
32.62
1.87
21.98
199.90
78.30
24.94
24.18
59.15
65.45
44.57
50.65
578.50
23.80
200.40
22.77
0.17
0.10
0.06
2.13
0.67
5.65
396.80
36.21
75.66
9.43
37.71
7.36
2.01
6.60
0.84
4.67
0.91
2.55
0.34
2.24
0.31
1.24
1.57
7.40
0.13
13.48
1.92
0.88
0.80
2.02
0.29
1.13
100.80
44.19
2.71
15.14
304.00
15.78
15.76
7.13
12.15
84.55
54.43
64.24
502.60
22.93
185.00
25.00
0.07
0.04
0.08
5.40
0.23
2.86
384.60
25.30
50.89
6.87
30.53
5.52
1.45
4.97
0.68
4.13
0.81
2.37
0.33
2.13
0.33
0.98
1.49
5.69
0.05
11.69
3.90
0.85
0.87
1.25
0.23
0.91
100.63
28.12
1.78
11.03
166.00
21.61
14.61
10.53
7.75
84.21
52.18
27.94
728.50
20.26
191.50
9.16
0.03
0.06
0.05
1.94
0.13
0.95
386.40
21.04
43.05
5.75
23.00
4.73
1.33
4.45
0.62
3.75
0.73
2.18
0.31
2.08
0.30
0.63
1.06
9.23
0.02
2.65
0.79
0.89
0.89
1.43
0.19
0.82
101.01
15.07
1.34
14.50
274.90
24.28
22.37
15.14
177.50
86.02
38.24
55.89
544.40
15.92
152.90
9.06
0.04
0.06
0.05
1.26
0.53
5.07
240.50
17.21
33.12
4.39
18.74
3.80
1.11
3.58
0.49
2.84
0.56
1.67
0.24
1.54
0.23
0.48
1.02
62.41
0.08
4.24
1.00
0.92
0.87
1.97
0.18
0.14
100.68
17.46
1.43
26.70
343.10
31.01
28.71
20.65
218.50
111.40
35.58
56.79
388.20
21.75
195.70
10.84
0.14
0.10
0.05
1.91
0.94
5.24
232.30
16.41
31.94
4.50
19.71
4.40
1.30
4.41
0.63
3.76
0.79
2.41
0.35
2.33
0.35
1.15
1.18
12.31
0.04
6.17
1.92
0.90
0.78
0.78
0.28
0.81
101.08
17.89
0.85
35.97
650.10
19.20
39.16
22.74
14.52
87.84
35.44
11.31
633.50
17.08
48.70
5.29
0.11
0.13
0.08
1.46
0.14
4.00
224.10
13.41
29.23
4.73
23.01
5.51
1.68
5.23
0.68
3.73
0.68
1.87
0.24
1.51
0.21
1.73
0.92
6.81
0.01
1.17
0.32
0.96
0.57
1.20
0.19
0.84
100.55
37.98
3.03
29.07
192.50
359.00
23.29
43.47
56.75
151.30
25.26
61.08
334.90
31.55
147.70
20.90
0.10
0.11
0.13
3.33
0.15
2.29
82.06
22.90
49.72
7.29
32.68
7.18
1.20
6.86
1.02
5.81
1.14
3.31
0.47
3.06
0.45
0.73
1.31
9.41
0.13
2.79
0.97
0.52
0.68
Na2O+K2O
15
GHODSI et al. / Turkish J Earth Sci
10
Syenite
Monzonite
Quartz
Monzonite
Granodiorite
Diorite
Gabbro
Monzo
gabbro
Gabbroic
diorite
0
5
Monzo
diorite
Granite
SiO2 (wt. %)
Figure 6. Plots of the alkalis (Na2O+K2O) vs. silica (diagram
from Middlemost, 1985) showing distribution of the various
phases of granitoids analyzed (see Table 2).
The quartz monzodiorite (BZ-2) yielded a population
of zircon composed mainly of irregular fragments with
few crystal faces. Rare grains with cores are also present.
In CL images regular growth zoning is dominant but
also with evidence for late stages of resorption and new
growth. As in the previous sample, the zircon data reveal
some dispersion, with the older component enriched in
one residue of dissolution, and with generally higher Th/U
in the older components. The age of the monzodiorite of
81.53 ± 0.10 Ma is based on the 3 youngest zircon analyses.
Two fractions of brown, U-rich titanite give again a
younger age of 81.00 ± 0.15 Ma.
The porphyritic granite (BZ-7) had relatively sparse
zircon, generally short-prismatic and relatively rich in U
with very well-developed regular growth zoning and in
some grains multiple growth with intervening resorption.
The data in this case also show some dispersion with an
older group of analyses at about 73.4 Ma and a younger
group at 72.50 Ma ± 0.10 Ma. The latter is interpreted as the
time of final crystallization of the granite and in this case
it is identical within error with the age of the coexisting
titanite at 72.67 ± 0.34 Ma.
7. Discussion
7.1. Petrogenetic considerations and origin of the parent
magmas
On the basis of the geochemical data, the granitoid
compositions plot the field of the volcanic arc (VAG) in the
tectonic setting discrimination diagrams of Pearce et al.
(1984) (Figure 14). Furthermore, quantitative comparison
of the trace elements in granite through granodiorite,
diorite, and gabbro exhibits considerable LILE enrichment
(Ba, K, Rb, and Th) and HFSE depletion (Hf, Ti) relative
to MORB; in addition, we identify the higher LREE
enrichment than HREE relative to chondrite (Figures 10
and 11). Magmas with these geochemical characteristics
are generally ascribed to subduction-related environments
(e.g., Rogers and Hawkesworth, 1989; Foley and Wheeler,
1990; Sajona et al., 1996). High Th/Yb ratios are also
correlated with continental arc magmas (Figure 15)
(Condie, 1989).
Geochemical evidence in this study shows that most
of the samples from the BGC are I-type and subductionrelated. This conclusion is supported by the initial 87Sr/86Sr
(0.70564) ratio reported by Berberian (1981) from the
western granitoids of Bazman. This value is similar to
those found in predominantly I-type intrusions and is
characteristic of active continental margins (Chappell and
White, 1974). I-type calc-alkaline metaluminous granitic
magmas in continental margins are considered to have
a mixed origin that involves both crustal- and mantlederived components (Wyllie, 1984; Atherton, 1990; Gray
and Kemp, 2009).
The presence of basic rocks, such as gabbro and mafic
enclaves, and weak negative Eu anomalies, and the low
Y and Yb contents of the western granitoids show that
basaltic mantle-derived magma played an important role
in the formation of the western granitoids. High Th and
the presence of garnet-muscovite granite in the eastern
granitoids suggest a significant crustal contribution.
Experimental melts derived from the partial melting
of various crustal source rocks, such as felsic pelites,
metagreywackes, various gneisses, and amphibolites fall
into distinct fields based on major oxide ratios or molar
ratios (Patino Douce, 1999). The geochemical characters
of the BGC show that the melted crustal rocks are mainly
igneous protoliths of mafic to intermediate composition
(Figure 16). This is also characteristic of the mantlederived I-type granitoids (Patino Douce, 1999).
The higher LILE and lower Ti, Nb, and Ta contents
in the BGC, as shown in the spider diagrams, reflect a
metasomatized source composition. Magma was probably
derived from the melting of a peridotite source belonging
to the suprasubduction zone mantle wedge. Hydration
and metasomatism of this peridotite lowered the mantle
solidus temperature to the point at which melting begins
(Tatsumi et al., 1986; Peacock, 1993; Arculus, 1994). The
product of such melting is basaltic in composition. Certain
HFSEs, such as Ti, Nb, Hf, Y, and Yb, are not mobilized by
this metasomatic process, while LILEs such as K, Cs, and
Ba, are liberated during slab devolatilization.
In the study area, the mantle-derived basaltic magma
probably ascended from the melted mantle wedge and near
the base of the crust formed an underplating melt layer.
At this stage, some minerals, such as olivine, pyroxene,
and spinels, crystallized as the magma cooled. The
crystallization of these minerals released additional heat
325
GHODSI et al. / Turkish J Earth Sci
1.6
TiO
Granite
Granodiorite
Quartz monzodiorite
Monzodiorite
Gabbro
Diorite
2
1.2
2
12
2 3
0.4
4
0
0
4
2
0
6
PO
MnO
Na2O
2 5
0.4
0.3
MgO
6
8
0.8
0.4
Fe O
4
0.2
0.2
0.1
0
0
KO
2
4
2
CaO
12
Al O
20
2 3
15
8
10
2
4
0
45
55
65
SiO2
75
85
0
45
5
55
65
SiO2
75
85
0
45
55
65
SiO 2
75
85
Figure 7. Selected major oxides (wt. %) vs. SiO2 (w.t %) contents for the BGC rocks (Harker diagram).
that was added to the base of the crust. This heat caused
partial melting and assimilation of the lower crustal rocks,
especially evident in the eastern granitoids.
The crustal and mantle-derived magmas probably
mixed and, as a result, dioritic magma formed. This
derivative dioritic magma ascended into the crust (cooling
and depressurization) to produce diorite, granodiorite, and
granite through assimilation and fractional crystallization
(AFC) processes. The strong positive Ti anomaly and high
Pb content indicate that the new magma was continually
altered by crustal contamination.
Hornblende and biotite are the most abundant
ferromagnesian minerals in the western granitoid of
326
the BGC. Towards the center of the western granitoid,
pyroxene, hornblende, and plagioclase decrease in
abundance, whereas K-feldspar and quartz gradually
become the predominant minerals (Table 1). The zonation
in the western granitoids of the BGC is consistent with
fractional crystallization, as high temperature rocks
(gabbro and diorite) were formed first on the walls and
lower temperature rocks (granodiorite and granite) were
crystallized later toward the center.
The major- and trace-element variation trends
also indicate that fractional crystallization affected
the evolution of the BGC. The decrease in CaO, MgO,
Al2O3, Fe2O3, TiO2, P2O5, and Sr, as well as the increase
GHODSI et al. / Turkish J Earth Sci
0
Peralkaline
0.4
0.6
0.8
1
1.1 1.2
1.4
1
F
c
A-type granites
field
0.6
0.7
0.8
0.9
Ferroan
0.4 0.5
4
3
1
2
A/NK
I-S Line
FeOtotal/(FeOtotal+MgO)
Peraluminous
5
6
Metaluminous
1.1
b
7
a
1.6
Magnesian
45
A/CNK
55
65
SiO2 (wt. %)
75
Calc-alkaline Series
85
A
M
Figure 8. (a) A/NK vs. A/CNK for rocks from the BGC (Shand, 1947), (b) FeOt/(FeOt+MgO) vs. SiO2 diagram with ferroan and
magnesian (Frost et al., 2001). (c) AFM diagram for BGC samples (Irvine and Baragar, 1971) (see Figure 7 for symbols).
800
V
160
Co
30
600
Zn
120
20
400
200
10
0
0
2
80
40
0
Y
Eu
30
1.6
1.2
250
Zr
200
150
20
0.8
100
10
0.4
50
0
0
0
800
Ba
1000
Rb
600
800
Sr
800
600
400
400
200
0
1200
400
200
45
55
65
SiO 2
75
85
0
45
55
65
SiO 2
75
85
0
45
55
65
SiO 2
75
85
Figure 9. Selected trace elements (ppm) vs. SiO2 (wt. %) contents for the BGC rocks.
327
1000
1000
GHODSI et al. / Turkish J Earth Sci
10
0.1
1
Sample/MORB
100
10
1
0.01
0.01
0.1
Sample/MORB
Granodiorite
100
Granite
K Rb Ba Th Ta Nb Ce
Sr
P Zr Hf Sm Ti Y Yb
P Zr
a
Hf Sm Ti Y Yb
Monzodiorite
0.1
0.01
0.01
0.1
1
1
10
10
Sample/MORB
Sample/MORB
100
100
Quartz monzodiorite
K Rb Ba Th Ta Nb Ce
1000
1000
Sr
Sr
P Zr Hf Sm Ti Y Yb
P Zr
Hf Sm Ti Y Yb
0.1
1
10
Sample/MORB
100
Gabbro
0.01
0.01
0.1
1
10
Sample/MORB
100
Diorite
K Rb Ba Th Ta Nb Ce
1000
K Rb Ba Th Ta Nb Ce
1000
Sr
Sr
K Rb Ba Th Ta Nb Ce
P Zr Hf Sm Ti Y Yb
Sr
K Rb Ba Th Ta Nb Ce
P Zr
Hf Sm Ti Y Yb
Figure 10. MORB-normalized trace-element spider diagrams for the various phases of BGC rocks. Normalization value is from
Pearce (1983).
of K2O and Rb with increasing silica, are related to
the fractionation of plagioclase, hornblende, apatite,
and titanite. Plagioclase fractionation results in lower
abundances of Sr and moderate negative Eu anomalies in
the chondrite-normalized REE pattern of the granodiorite
328
and monzonite. The fractionation of hornblende causes
an increase in the LREE/HREE ratio of the residual melt,
which therefore develops a concave-upward REE pattern
(e.g., Romick et al., 1992). The increase in K2O and Rb with
increasing silica indicates that K-feldspar was not an early
GHODSI et al. / Turkish J Earth Sci
1000
100
100
10
1000
Granodiorite
Rock/Chondrites
Granite
Rock/Chondrites
Rock/Chondrites
1000
10
Quartz Monzodiorite
100
10
Biotite-muscovite granite
1
1
1000
Diorite
100
100
10
10
1
1
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
1000
Rock/Chondrites
Monzodiorite
Rock/Chondrites
Rock/Chondrites
1000
1
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Gabbro
100
10
1
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Figure 11. Chondrite-normalized rare earth element plot of the BGC rocks. Normalization value from Boynton (1984).
fractionation phase. The depletion of P results from the
removal of apatite during fractional crystallization. The
negative Ti anomalies in the spider diagram are consistent
with titanite fractionation. The fractionation of accessory
phases, such as zircon, allanite, and titanite, account for
the depletion of Zr and Y.
Fractional crystallization, assimilation, partial melting,
and associated contamination can also be distinguished
by plotting a compatible versus a compatible (Co-V and
Co-Sc), an incompatible versus an incompatible (Ce-La),
and a compatible versus an incompatible element (Sr-Rb)
(Martin, 1987; Pearce et al., 1999). The linear positive
correlation in Figures 17a–17c indicates that the BGC was
affected by AFC. Th/Yb versus SiO2 (Figure 17d) is helpful
in determining that AFC processes that occurred during
formation of the BGC.
7. 2. Geotectonic considerations
Taking the geotectonic setting of the BGC into
consideration, it is necessary to evaluate which one of the
main tectonostratigraphic units in southeast Iran is the
actual host of the BGC. A thick succession of detritalcarbonate sedimentary rocks found around the BGC was
metamorphosed in the various thermal metamorphic
facies. Until recently, only Triassic fossils had been extracted
from the upper part of the sedimentary country sequence,
while the older recrystallized beds, in consideration of
the lithostratigraphical studies, have been attributed to
the Sardar and Jamal Formations (Sahandi and Padashi,
2005). However, a few kilometers to the west of the BGC, a
nearly entire sequence of Paleozoic sedimentary rocks has
been recognized (Vahdati Daneshmand et al., 2004).
The above described succession is similar to that of
the Paleozoic/early Mesozoic platform-type deposits that
can be found in most Iranian tectonic units, such as Lut,
Tabas, Yazd, and Alborz (Figure 1a), belonging to a larger
terrane named the Cimmerian block (Şengör, 1984). The
continental platform deposits surrounding the BGC are
obviously different from the deposits identified in the
East Iranian Ranges and the Makran accretionary prisms.
These terrains are characterized by Tertiary deep-water
siliciclastics and turbidites. Therefore, we assert that a
continental terrane such as the Lut block, the nearest terrane
to the BGC, is the real host of this complex. Considering
the BGC’s origin, on the basis of the geochemistry
represented above, the presence of a subduction zone
under the Lut block during the Late Cretaceous epoch
would have been necessary. Consequently, the magmatic
belts of the west volcano-plutonic belt of Lut and the east
plutonic belt of Lut are the most significant candidates for
the main magmatic arc of this subduction zone.
Based on previously published Rb-Sr ages of 74–64
Ma, the Bazman batholith was considered to be the result
of the subduction of the Oman oceanic crust beneath
central Iran during the Late Cretaceous/Early Paleocene
(Berberian et al., 1982). Our new geochronological
finding shows that one granodiorite sample derived from
the mesocratic outer part of the complex yields an age of
about 83 Ma, while one porphyritic granite sample from
329
330
BZ-3
Z tips ca4 [3]
Z fr ca5 [6]
Z sp [1]
Z tips [10]
Z fr [9]
Z fr [1]
Z fr [1]
T [10]
T [12]
BZ-2
Z fr ca14 [5]
Z tip [1]
Z lp-tip [1]
Z lp[8]
Z fr [2]
Z eq [5]
T [7]
T [2]
BZ-7
Z tips [5]
Z sp [6]
Z sp [1]
Z tips [2]
Z sp [5]
Z tip [1]
T [6]
T [2]
16
10
1
28
21
6
193
125
140
45
14
149
242
118
63
60
5
2
15
32
38
1
1
188
203
(b)
746
930
906
454
815
786
98
76
556
311
185
232
874
192
456
492
43
257
51
163
147
413
1189
231
320
(b)
[ppm]
[µg]
(a)
U
Weight
Properties
0.37
0.49
0.66
0.44
0.36
0.36
2.94
4.01
0.66
0.74
0.94
0.65
0.42
0.57
0.55
0.72
0.70
1.01
0.61
0.67
0.58
0.69
0.54
3.55
2.86
(c)
Th/U
Concentrations
Pbc
------------1.04
1.00
------------1.42
1.37
--------------0.98
0.98
(d)
1.8
2.0
0.7
103.2
2.5
1.3
198.7
124.5
31.5
7.9
1.8
3.5
5.5
3.7
89.7
83.1
2.0
4.6
4.9
1.3
1.8
1.7
8.6
183.5
197.7
(d)
[ppm] [pg]
Pbi
U
4671
3421
894
106
4865
2558
86
73
2012
1443
1160
7973
12682
4912
272
300
105
109
147
3283
2556
214
131
207
280
(e)
0.07530
0.07538
0.07474
0.07483
0.07416
0.07407
0.07459
0.07440
0.08474
0.08437
0.08387
0.08363
0.08366
0.08372
0.08276
0.08388
0.08528
0.08769
0.08841
0.08572
0.08547
0.08508
0.08387
0.08233
0.08391
(f)
235
Pb
204
207
Pb/
206
Pb/
Atomic ratios
0.00023
0.00026
0.00075
0.00607
0.00022
0.00031
0.00384
0.00465
0.00027
0.00044
0.00061
0.00021
0.00023
0.00022
0.00119
0.00127
0.00844
0.00371
0.00259
0.00038
0.00034
0.00327
0.00266
0.00178
0.00118
(f)
[abs]
±2 σ
0.011466
0.011448
0.011449
0.011343
0.011313
0.011300
0.011362
0.011300
0.012893
0.012853
0.012789
0.012731
0.012727
0.012724
0.012639
0.012650
0.013184
0.013117
0.013097
0.012998
0.012974
0.012927
0.012923
0.012681
0.012701
(f, g)
U
238
Pb/
206
0.000024
0.000023
0.000038
0.000053
0.000025
0.000024
0.000069
0.000082
0.000031
0.000044
0.000026
0.000027
0.000031
0.000027
0.000033
0.000034
0.000083
0.000053
0.000043
0.000036
0.000026
0.000053
0.000061
0.000058
0.000038
(f)
[abs]
±2 σ
0.75
0.68
0.50
0.77
0.83
0.61
0.09
0.06
0.81
0.76
0.45
0.93
0.95
0.89
0.22
0.30
0.75
0.47
0.44
0.76
0.61
0.52
0.30
0.27
0.25
(f)
rho
0.04763
0.04776
0.04735
0.04785
0.04754
0.04754
0.04761
0.04775
0.04767
0.04761
0.04756
0.04764
0.04768
0.04772
0.04749
0.04809
0.04692
0.04849
0.04896
0.04783
0.04778
0.04773
0.04707
0.04709
0.04791
(f, g)
Pb
206
Pb/
207
0.00010
0.00012
0.00042
0.00372
0.00008
0.00016
0.00244
0.00299
0.00009
0.00016
0.00031
0.00005
0.00004
0.00006
0.00067
0.00070
0.00443
0.00197
0.00137
0.00014
0.00015
0.00174
0.00144
0.00098
0.00065
(f)
[abs]
±2 σ
U
73.50
73.38
73.38
72.71
72.52
72.44
72.83
72.44
82.58
82.33
81.92
81.55
81.53
81.51
80.97
81.04
84.43
84.01
83.88
83.25
83.10
82.80
82.77
81.23
81.36
(f, g)
[Ma]
238
Pb/
206
Ages
±2 σ
0.15
0.15
0.24
0.34
0.16
0.15
0.44
0.52
0.20
0.28
0.17
0.17
0.19
0.17
0.21
0.21
0.53
0.34
0.27
0.23
0.16
0.33
0.39
0.37
0.24
(f)
[abs]
73.72
73.79
73.18
73.27
72.64
72.55
73.04
72.87
82.59
82.24
81.77
81.55
81.58
81.63
80.73
81.79
83.10
85.35
86.02
83.51
83.27
82.91
81.78
80.33
81.81
(f)
[Ma]
U
Pb/
235
207
±2 σ
0.22
0.25
0.70
5.72
0.21
0.29
3.63
4.39
0.26
0.41
0.57
0.20
0.21
0.21
1.11
1.19
7.87
3.46
2.41
0.35
0.32
3.06
2.49
1.66
1.11
(f)
[abs]
a) Z = zircon (all zircon grains treated with chemical abrasion (Mattinson, 2005)); T = titanite (not abraded; fr = fragment; sp = short-prismatic; lp = long-prismatic; ca4, ca5, and
ca14 = leftovers after dissolution of Nr. 4, 5, and 14, respectively (see text).
b) Weight and concentrations are known to better than 10%, except for those near the ca. 1 µg limit of resolution of the balance.
c) Th/U model ratio inferred from 208/206 ratio and age of sample.
d) Pbi = initial common Pb; Pbc = total common Pb in sample (initial + blank).
e) Raw data, corrected for fractionation and spike.
f) Corrected for fractionation, spike, blank (206/204 = 18.3; 207/204 = 15.555), and initial common Pb (based on Stacey and Kramers, 1975); error calculated by propagating the
main sources of uncertainty. The U-Pb ratio of the spike used for this work is adapted to 206Pb/238U for the ET100 solution as obtained with the ET2535 spike at NIGL.
g) Corrected for 230Th disequilibrium according to Schärer (1984) and assuming Th/U magma = 4.
18
19
20
21
22
23
24
25
10
11
12
13
14
15
16
17
1
2
3
4
5
6
7
8
9
Nr.
Table 3. U-Pb data, Bazman granitoid complex.
GHODSI et al. / Turkish J Earth Sci
GHODSI et al. / Turkish J Earth Sci
BZ-3
BZ-2
0.0131
zircon - 3 youngest analyses
84
84
81.53 ± 0.10 Ma
MSWD = 0.054
83
83
0.0129
82
82
zircon - 4 youngest analyses
83.07 ± 0.30 Ma
MSWD = 2.5
0.0127
81
81
titanite - 2 analyses
81.32 ± 0.20 Ma
titanite - 2 analyses
MSWD = 0.35
81.00 ± 0.15 Ma
MSWD = 0.22
0.0125
0.082
0.086
0.082
0.086
73.8
0.090
BZ-7
z i r c o n - 3 youngest analyses
analyses
73.4
206Pb/238U
0.01145
72.50 ± 0.10 Ma
MSWD = 1.12
73.0
0.01135
72.6
207Pb/235U
72.2
0.01125
ti ta n i te- 2 analyses
analyses
72.67 ± 0.34 Ma
71.8
0.01115
0.070
MSWD = 1.3
0.074
0.078
0.082
Figure 12. Concordia diagrams displaying U-Pb data from the Bazman granitoid complex. Ellipses represent 2σ errors; full
lines indicate zircon and dashed lines titanite. The calculated ages are weighted averages of 206Pb/238U ages. The oldest analysis
of sample BZ-3 (No. 1 in Table 3) is not shown as it plots outside the chosen diagram.
the inner felsic area shows an age of 72 Ma. Accordingly,
one could expect that the gabbro-diorite samples from
the marginal part of the main zoned pluton would have
probable ages older than 83 Ma. The existence of frequent
mafic xenoliths in the granites confirms this inference. As
a consequence, the BGC must have started to crystallize
during its emplacement sometime before the Santonian
age. Therefore, a subduction zone must have been
established under the Lut block several million years
before the Late Cretaceous epoch.
331
GHODSI et al. / Turkish J Earth Sci
BZ- 2
BZ- 3
BZ- 7
Figure 13. CL-images of zircon. The figure displays typical internal textures of zircon in the four samples from the BGC. They
generally show well-developed euhedral growth zoning, and locally sector zoning, but in part also with good evidence of magmatic
resorption followed by new crystallization periods, consistent with the prolonged crystallization history shown by the U-Pb data.
The crystals in all pictures range in size from 300 to 100 μm in length.
Late Mesozoic subduction-related granitoids similar to
those in the BGC had not been found in Iran previously,
except for the Bajestan granitoid (Karimpour et al., 2011),
with an age of about 77 Ma, emplaced to the north of Lut
(Figure 1a). The Shah Kuh granitoid, dated at about 162
332
Ma (Esmaeily et al., 2005), also crops out in the central
part of the Lut block (Figure 1a). Conversely, most of the
Cretaceous magmatism observed in submarine deposits
is associated with the ophiolitic assemblage emplaced in
the accretionary prisms and tectonic mélanges occurring
1000
Rb
WPG
10
VAG
1
10
100
Y+Nb
1000
VAG
ORG
1
ORG
1
10
Rb
syn-COLG
100
WPG
syn-COLG
100
1000
GHODSI et al. / Turkish J Earth Sci
1
Ta+Yb
10
100
Figure 14. (a, b) Rb vs. (Y+Nb) and Rb vs. (Ta+Yb) diagram of Pearce et al. (1984); ORG,
ocean-ridge granites; syn-COLG, syncollisional granites (S-type); VAG, volcanic arc granites
(I-type); WPG, within-plate granites (A-type).
to the east and south of the Lut block (McCall, 1985).
Accordingly, if we accept that the BGC is situated in line
with the above corresponding granites in the Lut block,
then our complex will not belong to any of the plutonic
belts of the Sistan suture zone and the Chagei-Raskoh
volcanic belt that is located east of the Lut block.
The origin of the oceanic lithosphere under the Lut
is still a matter of debate. The Birjand ophiolite, recently
dated at 113–107 Ma as the remnants of the Sistan Ocean
(a minor Neo-Tethyan seaway) (Zarrinkoub et al., 2012), is
one of the candidate oceanic lithospheres that could have
subducted under of the Lut block (Arjmandzadeh et al.,
2011). Surprisingly, however, the age of the termination
of this subduction was reported as 86 Ma (Zarrinkoub et
al., 2012). This inference cannot explain the widespread
existence of the thick pile of Eocene volcanic and OligoMiocene plutonic rocks of the Lut. In spite of this reality,
if we accept such interpretations regarding the age of the
Sistan suture zone formation, we must search for another
subduction zone as the source of the BGC.
1000
Continental Margin Arc
La/Yb
100
10
Island Arc
Primitive Island Arc
1
0.1
1
10
100
1000
Th/Yb
Figure 15. Th/Yb vs. La/Yb diagram after Condie (1989) for the
various phases of BGC rocks (see Figure 7 for symbols).
The Urumieh-Dokhtar volcano-plutonic belt, the
most important magmatic arc in Iran, is characterized
by voluminous Eocene calc-alkaline volcano-plutonic
products (e.g., Berberian and Berberian, 1981). However, it
surprisingly lacks Eocene volcanic rocks at its southeastern
extremity in the south of the Lut block (Aghanabati, 1993).
Hence, how can we possibly extend this belt to the Bazman
area? Our doubts regarding this issue are also intensified
by other observations.
Most significantly, at the southeastern end of the
Zagros Mountains, where the promontory edge of the
Arabian plate indented the Sanandaj-Sirjan Zone during
the Neogene period, the Dehshir-Baft ophiolitic belt has
been dextrally displaced tens of kilometers through the
Band-e-Zyarat ophiolite (Hassanipak et al., 1996) into the
inner Makran ophiolitic zone (McCall, 1997) (see Figure
1a). It is, however, not possible to see such a displacement
in the Urumieh-Dokhtar volcano-plutonic belt, which
extends parallel to the Zagros/Makran belt. Consequently,
in our opinion, the proposed continuation of the UrumiehDokhtar volcano-plutonic belt to the Bazman area, in spite
of its continuity, is not correct. In view of the fact that late
Cenozoic volcanic rocks are the most widespread products
of the subduction of the Semail oceanic plate under the Lut
block, the volcanic rocks of Bazman, previously attributed
to the Urumieh-Dokhtar volcano-plutonic belt, must
instead be assigned to the Makran volcanic arc.
On the other hand, according to the fact that the
Eocene and older accretionary prisms in the Makran
ranges are not extensive to the south of the inner Makran
ophiolitic belt in respect to the Sistan suture zone, it is
difficult to imagine a subduction zone under Markran
before the Eocene-Oligocene time. To create Cretaceous
suprasubduction zone magmatism, it would have been
necessary to establish a subduction zone at least a few
million years before the Late Cretaceous period (Figure
18a). However, it might be conceivable that the conditions
333
a
0.8
4
Metagreywackes
3
0.6
Experimental
melts of
amphibolites
2
Metabasaltic to
metatonalites
1
0.4
0
Felsic pelites
15
10
Experimental melts of
Felsic pelites
Metagreywackes
0
5
Amphibolites
10
15
20
25
30
35
Al2O3+FeO+MgO+TiO2
0.4
0.6
0.8
1
1.2
10
d
0.2
Felsic pelites
8
CaO+MgO+FeO+TiO2
c
0
25
6
20
Metagreywackes
4
15
Amphibolites
2
10
0
5
Metagrewackes
(Na2O+K2O)/ (FeO+MgO+TiO2)
0.2
0
Peraluminous
Leucogranites
0
Al2O3/(FeO+MgO+TiO2)
Felsic pelites
5
Molar Al2O3/(MgO+FeOtot)
CaO/(FeO+MgO+TiO)2
6
1
b
7
GHODSI et al. / Turkish J Earth Sci
6
8
10
12
14
16
18
Na2O+K2O+FeO+MgO+TiO2
Figure 16. Samples plotted on the (a) CaO/(FeO + MgO + TiO2) vs. CaO + FeO + MgO + TiO2, (b) Al2O3/(MgO + FeOtot) vs. CaO/
(MgO + FeOtot), (c) Al2O3/(FeO + MgO + TiO2) vs. Al2O3 + FeO + MgO + TiO2, and (d) (Na2O + K2O)/(FeO + MgO + TiO2) vs.
Na2O + K2O + FeO + MgO + TiO2 (Patino Douce, 1999). See Figure 7 for sample symbols.
of subduction, paleo-stress field, and/or position of the
main involved plates have been changed since the Eocene
epoch.
By way of comparison, there are undeniable similarities
between the large Mesozoic plutons and associated
metamorphic rocks of the Sanandaj-Sirjan zone and the
comparable plutons from the East plutonic belt of Lut. On
the other hand, taking this analogy further to the UrumiehDokhtar volcano-plutonic belt and the west volcanic belt
of Lut, it directs us to find a significant correspondence
between the two magmatic belts. In this connection,
other researchers have already discussed the comparable
stratigraphy and tectonic history of the Sanandaj-Sirjan
Zone and the Lut block (Davoudzadeh and Schmidt,
1983; Davoudzadeh and Weber-Diefenbach, 1987).
Consequently, it is difficult to resist the conclusion that the
east plutonic belt of Lut itself could be an interrupted part
334
of the Sanandaj-Sirjan Zone, which has rotated counterclockwise more than 90°.
The evidence, such as a lack of Eocene volcanic rocks
at the southeastern extremity of the Urumieh-Dokhtar
volcano-plutonic belt, the absence of accretionary prisms
older than Eocene-Oligocene in the south of the Lut block,
and a wide interruption between the Sanandaj-Sirjan Zone
and the Lut block, documents the anticlockwise rotation
of the Lut block around a vertical axis, rotation that was
confirmed by the old paleomagnetic studies (Conrad et al.,
1981; Davoudzadeh et al., 1981).
This rotation may have been caused by westward
extrusion of the Afghan block (Tapponier et al., 1981),
when the Indian plate indented Eurasia during the Eocene
epoch (Bagheri, 2008) (Figure 18b). This rotation was
probably accompanied by southward displacement of the
Lut block, the outward slab rollback of the Semail oceanic
GHODSI et al. / Turkish J Earth Sci
a
1000
100
b
FC AFC
100
Co
Ce
10
10
1
1
La
10
1
100
10
1000
100
V
c
100
1
20
d
Co
Th/Yb
15
10
10
5
1
1
10
100
Sc
0
45
55
65
75
85
SiO2
Figure 17. (a) Logarithmic concentration for an incompatible element vs. incompatible (in ppm), (b) and
(c) compatible elements vs. compatible (in ppm), (d) Th/Yb vs. SiO2 (wt. %) diagrams illustrating that AFC
processes have an important role during evolution of the BGC. See Figure 7 for sample symbols.
plate under the Makran ranges (Stampfli and Borel, 2002),
collapse of the arc-trench basin, and temporary cessation of
Eocene volcanism. It is also worth mentioning that Eocene
volcanism continued along both the Urumieh-Dokhtar
volcano-plutonic belt and the west volcano-plutonic belt
of Lut. The continuation of convergence and establishment
of a new stage of subduction since the Neogene brought a
new period of magmatism through the Makran volcanic
arc, when the rotation process was completed.
Perhaps, according to the age, geochemistry, and
tectonic setting of the Gangdese Batholith (e.g., Schärer et
al., 1984; Searle et al., 2010), a pluton that was emplaced
in the Lhasa terrane to the south of Tibet and north of the
Indus-Xangbo suture zone of the Himalayas, it is the best
choice for comparison with the BGC. This resemblance
may be explained by the fact that the Neo-Tethyan
subduction zone has been developed all along southern
Eurasia from western Iran to eastern Tibet.
8. Conclusions
The BGC has a broad compositional range from gabbro
to granite. The rocks are metaluminous to slightly
peraluminous, calc-alkaline series, I-type granite, and
display geochemical characteristics typical of volcanic arc
granites related to a continental margin setting. The BGC
rocks are enriched in LILEs (Rb, K, Cs) and LREEs, with
respect to HFSEs (Zr, Hf, Nb, Ta, Y) and HREEs. Majorand trace-element variation trends provide evidence that
fractional crystallization and assimilation occurred during
the evolution of the BGC. The new ID-TIMS U-Pb dating
indicates that the granite, granodiorite, and monzodiorite
were formed during the late Cretaceous period, the dated
335
GHODSI et al. / Turkish J Earth Sci
a
45°
50°
Gc
East Black Sea
60°
65°
70°
South Caspian Basin
Tc
Po
Al
Ta
Ss
25°
Paleo-Tethys suture zone
Kd
Gk
Yz
Tb
BGC
Bb
Fr
Lu
Hm
Spon Tang
Semail Ocean
Kh
Gondwanian domain
and associated island-arc
Ophiolite obduction
50°
Gc
South
Caspian Basin
Tc
Al
Ta
Ss
25°
Db
Aj
Pb
Sa
Tb Lu
Yz
Mk
?
45°
50°
θ=30
To
Bj Ssz
° 55°
0°
25°
Bb
Fr
Hm
Ka
Kh
20°
ψ= 5
1°
K
Fa arako
ult ru
m
6
θ=
latform
fghan P
North A
Fa
ult
s
gro
Ch
am
an
Za
Arabia
Tagh
Altyanult
F
75° 30°
Sz
eh F.
Dorun
CEIM
at
7° Her
ψ = 1 Fault
15°
Kd
Gk
Internal shear zone
20°
External shear
zone
?
70°
70°
an
EBS
30°
55°
60°
65°
Scythian-Turanian domain
50°
an
Oc
e
45°
65°
60°
55°
Fault
Magmatic activity
Strike-slip shear zone
Sis
t
b
15°
Indian Plate
Subduction zone
Arabian Plate
45°
25°
Pa
Ka
Eurasian domain
Kr
Hk
20°
Thinned continental
and/or oceanic crust
Intra-arc basin
20°
Ky
in
as
-Tajik B
n
Turkesta
Sz
Aj
Cimmerian Block
Neo-Tethys
15°
75°30°
Chaman
30°
55°
Scythian-Turanian domain
15°
India
Indian plate
65°
60°
70°
Figure 18. Schematic geodynamic reconstruction at (a) Late Cretaceous-Early Paleocene and (b) Eocene (Bagheri, 2007). Small pattern at bottom: plane-strain slip-line fields
for a wedge-shape indenter and indented rigid plastic media (modified after Tapponier and Molnar, 1976). Deformational fields are indicative of the geometry of strike-slip
faulting induced by collision in an idealized and oversimplified condition. Aj: Anarak-Jandaq terrane, Al: Alborz, Bb: Band-e-Bayan, BGC: the Bazman Granitoid Complex,
Bj: Birjand, CEIM: the Central-East Iranian Microcontinent, Db: Dehshir-Baft, EBS: East Black Sea, Fr: Farah Rud, Gc: Great Caucasus, Gk: Great Kavir Block, Hm: Helmand,
Hk: Hendu Kush, Ka: Kandahar, Kd: Kopeh Dagh, Kh: Kohistan, Kr: Kermanshah, Ky: Khoy, Lu: Lut, Mk: Makran, Pa: Pamir, Pb: Posht-e-Badam, Po: Pontide, Sa: Saghand,
Ss: the Sanandaj-Sirjan Zone, Sz: Sabzevar, Ssz: Sistan suture zone, Ta: Taurus, Tb: Tabas, Tc: Transcaucasus, To: Torbat, Yz: Yazd.
336
GHODSI et al. / Turkish J Earth Sci
phases spanning a period between 83 and 72 Ma. Therefore,
the diorite and gabbro, which are the oldest phases of the
BGC, have an age greater than 83 Ma.
A combination of geological, geochemical, and
geochronological data for the BGC, situated in the
southern part of the Lut block, suggests that this complex
probably belongs to the East plutonic belt of Lut (the
Sanandaj-Sirjan Zone) and is related to the subduction
of the Neo-Tethyan oceanic crust beneath the Lut block
during the late Cretaceous period.
Acknowledgments
The first author thanks the members of the Department of
Earth Science and Technology, Faculty of Engineering and
Resource Science for their hospitality and support during
his 5-month stay at Akita University. Kazuo Nakashima
at Yamagata University is thanked. The manuscript was
considerably improved by David R Lentz. Financial
support from the Ministry of Sciences, Research, and
Technology of Iran is acknowledged. We acknowledge the
editor and reviewers for their constructive criticism and
comments.
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