نشریه پترولوژی
پیاپی 58 (تابستان 1403)

Mineral chemistry has a significant role in determining the stages of magma evolution. Amphiboles, Biotite, plagioclase, and chlorite are minerals whose chemical composition show the temperature and pressure conditions of magma. These minerals are often used for the petrogenesis of granitoid bodies and record the characteristics and geochemical features as well as tectonic conditions of the producing magma (Abdel-Rahman, 1994; Nachit et al., 2005). The granitoid bodies of west Yazd have wide outcrops with different compositions. These rocks are part of the volcano-plutonic belt of Central Iran (Aftabi and Atapour, 2000) with calc-alkaline nature, meta luminous, and mostly of I-type (Hassanzade et al., 2002). The Hamaneh monzogranite bodies, with light color and dark enclaves, are located in 45 km at E53°48ˊ to E53°58ˊ longitude and N31°50ˊ to N31°56ˊ latitude. This area is part of the Shirkuh Mountain in Yazd with a northeast-southwest trend. Hamaneh monzogranite belongs to the Oligocene magmatic activity. In the present research, the mineral chemistry of amphibole, biotite, plagioclase, and chlorite has been investigated to determine the origin and stages of formation and evolution of the magma.

Regional Geology:

The studied area geologically located in the middle part of the Urmia-Dokhtar magmatic zonewith a wide collection of Cenozoic magmatic rocks and is characterized by a length of about 2000 km, and a width of approximately 50 to 150 km, parallel to the metamorphosed zones of Sanandaj-Sirjan and Zagros, has a wide collection of Cenozoic magmatic rocks. This area has witnessed extensive magmatic activity in the Cenozoic, especially in the Eocene, which during the Oligocene-Miocene hosted numerous intrusive masses with different ages and compositions (Hassanzadeh et al., 2002). The oldest formation in the region is the green siltstone shale and sandstone of the Kahar Formation. The dolomitic rocks of the Soltanieh Formation are unconformably on the Kaher Formation with purple and cream-colored sand shale layers. The Permian sediments (Jamal Formation) composed of limestone and dolomite layers and the Mesozoic sediments started with a dark unit of volcanic laterite rocks with the Lower Triassic followed by dolomitic rocks belonging to the Otri Formation. The shale and sandstone of the Shemshak Formation are upper Triassic sediments. Cretaceous sediments are exposed in the form of destructive rocks. Upper Triassic (Sangestan Formation) has a variety of conglomerate and conglomerate sandstones with round to semi-round pieces of sandstone and Shirkuh granite. The Paleogene begins with the Kerman Formation conglomerate. Then, there are alluvial cones, alluvial plains, and alluviums of young rivers.

For the lithology and chemistry of minerals in Hamaneh monzogranite, 20 thin-section samples were selected for chemical analysis of amphibole, plagioclase, biotite, and chlorite minerals and sent to Oklahoma City University laboratory. Microprobe analyses were performed with the Cameca model SX100 device with an accelerating voltage of 15 KV and current intensity of 15 nA. The results of chemical data of amphibole, biotite, feldspar, and chlorite minerals are given in Tables 1 to 4.Petrography and Minerals Chemistry.It is often fine to medium grain texture, granophyric and perthitic texture. The main minerals are orthoclase, plagioclase, and quartz. Orthoclase with an abundance of 25 to 32% is amorphous to semi-amorphous, and plagioclase is a frequency of 24 to 44% that was often as shaped to semi-shaped with zoning. The quartzes are often amorphous and intergranular, and some have wave extinction and fractures with a frequency of 19 to 31. The minor minerals were amphibole, biotite, sphene, zircon, and opaque minerals. Amphibole is green with an abundance of 2.5 to 4.5%, shaped to semi-shaped with a simple twinning. Biotite crystals with an abundance of 2 to 4%. Mineral chemistry of amphiboles was shown as calcic magmatic amphiboles, ranging from magneiso-hornblende and actinolite. Which formed at 530-890℃ and up to 4.3 kbars. That was shown depth 3 to 5.40 km and fO2 (0.5). <Fe#, which corresponds to the calc-alkaline nature in a subduction environment (Anderson, 1996; Rieder et al., 1998). The Hamaneh amphiboles were formed in active continental margins related to subduction. Mineral chemistry of biotites point to a primary biotites that are magmatic and emplaced between annite and phlogopite in the Mg-biotite range. The Hamaneh biotites are I-type indicating the tectonic setting of the calc-alkaline granitoid magmatic series in the subduction zone. Biotites under study were formed at 650-730°C and a pressure of 10-11 to 10-14 kbar. Also, feldspar are (An21 to An32) (Or45 to Or59) orthoclase. The feldspars are of the oligoclase-andesine type, as well as in the feldspar thermometry diagram (Elkins and Grove, 1990; Deer et al., 1991) that was formed in 700 to 800ºC. Based on mineral chemistry, the chlorites are ripidolite and pycnochlorite in composition. Regarding the relatively high iron amount, they have formed at 330 and 360 ºC by alteration of biotite and amphiboles.

The Hamaneh monzogranite, with the main minerals of quartz, orthoclase, plagioclase, amphibole, biotite and secondary minerals of sphene, zircon, and apatite lies in the west of Yazd. The main textures are medium-fine-grained, granophyric, and myrmekite. This body is calc-alkaline and type I. Based on mineral chemistry data, the crystallization of minerals was according to the Bowen series. The calcic amphiboles of magnesio-hornblende to actinolite nature crystallized at 890-530 ℃.Simultaneously with this mineral, oligoclase-type plagioclase to andesine crystallized at 700-800 ℃ and magnesium biotites at 730-650 ℃. Finally, due to secondary alteration, chlorite was formed from the biotite and amphibole developed at a temperature of 330 to 360 ℃ All these minerals point to the mantle nature of the parent magma produced these mineral and have suffered crustal contamination during the ascent. This magma originated at a depth of 3 to 5.5 kilometers, pressure of 0.5 to 4.5 kbars, temperature of 530 to 890 ℃ and at oxidizing conditions. The parent magma of the rocks under study belongs to the subduction structural ground position related to the active continental margin.

The Cenozoic Urumieh-Dokhtar magmatic arc has characteristics similar to those of Andean-type magmatic arcs. Various types of magmatism occurred in this arc including calc-alkaline and K-rich calc-alkaline magmatism and less of them alkaline magmatism (Shahabpour, 1982). Kerman porphyry copper belt (KPCB) in the southern part of this arc includes two types of granitoids: (1) Jebal Barez-type (late Eocene–early Miocene) associated with minor Cu-mineralization, and (2) Kuh Panj-type (middle Miocene–Pliocene), which is associated with major porphyry copper deposits (Mirzababaei et al., 2016). Kuh-kapout porphyry deposit (Eocene) in the southern part of KPCB is affected by Jebal Barez type granitoids. This deposit has been studied to determine the genesis of magmatism, mineralization and tectonic setting, by the whole rock geochemistry of quartz diorite intrusions, this evaluation is based on trace and REEs geochemistry data.

Regional Geology:

This area is located in the southern part of the Urumieh–Dokhtar magmatic belt and in the Kerman porphyry copper belt. Arc-related magmatism events in this region include Paleocene to Oligocene magmatism and including andesite- dacite volcanic-sedimentary rocks with porphyry texture and quartz diorite intrusions with porphyry texture. In these rocks on the surface, there are intermediate argillic alteration events, and with increasing depth, quartz-sericite-pyrite zone and then potassic and alkali (potassium)-feldspar-sericite-chlorite-anhydrite zone are observed. Quartz diorite rocks include plagioclase and hornblende crystals (about 30 to 40 percent), biotite (10 to 15 percent), and potassium feldspar and quartz. Potassic alteration zone in depth is recognized by hydrothermal biotite, K-feldspar, magnetite and anhydrite. Mineralization in quartz diorite intrusions is more in the form of pyrite, chalcopyrite, and magnetite in association with the potassic alteration zone. Andesite-dacite volcanic-sedimentary rocks and quartz diorite rocks intruded by post-mineralized and barren micro diorite intrusion.

The samples were selected based on field observations and changes in mineralization-alteration rates from the weak alteration section of the quartz-sericite zone. For analyzing trace and rare earth elements, Samples were analyzed by the multi-acid method and used the Microwave Digest. Many of handpick and drill core samples were prepared to form thin sections for microscopic studies

Alteration and mineralization:

In this area, different types of hydrothermal alteration events including potassic, phyllic, propylitic, argillic and K-feldspar- chlorite- sericite, occurred that was influenced by fractures and faults. Quartz diorite intrusive rocks shows intense potassic and phyllic alteration zone, the main type of hydrothermal alteration zone is potassic and contains quartz ± chalcopyrite ± pyrite ± magnetite as mineralized veins and scattered event of pyrite, chalcopyrite, and magnetite. The phyllic alteration zone includes pyrite, which increases with depth. In the quartz-sericite-pyrite alteration zone, abundant chlorite and plagioclase are observed in the groundmass along with the occurrence of pyrite and anhydrite, and Cu mineralization in the form of scattered chalcopyrite.

Whole rock chemistry:

In this study, it seems that due to the presence of phases such as garnet and hornblende in the magma in the origin, a fractionation between HFSEs and LILEs has occurred (Green, 2006). Remaining of HFSEs and HREEs in the origin lead to low amounts of these elements in the resulting magma. The occurrence of negative anomalies in these elements, on the other hand, can be due to crustal contamination with mantle magmatism during their ascent to the surface. Anomaly in trace elements and ratios of REEs and trace elements, emphasizes that magmatism originated from the volcanic arc and subsequent events, according to the Th/Nb-Ba/Th diagrams and the La/Sm-Sm/Yb diagram, including the presence of lower crustal contamination and the significant role of fluid in the production of metasomatized magmatism. According to the studies on data normalized to the primary mantle, a depletion in Ba and Nb values and an enrichment in Rb and Cs have occurred.

Studying trace and rare earth elements in porphyry copper deposits is useful for determining the mineralization and fertility of magmatism, tectonomagmatism-setting, crustal contamination, and mantle metasomatism. Th-Co diagram (Hastie et al., 2007) and Th/Yb-Ta/Yb diagram (Hastie et al., 2007) indicate that most of the samples in this study area were plotted in the calc-alkaline magma region of the diagrams. Using the Sm/Yb versus La/Sm diagram (Aldanmaz et al., 2000) in the quartz diorite rocks shows a magmatism with higher Sm/Yb ratios than what is usually found for the spinel lherzolite. The plotting of the samples on diagrams indicates that the samples are located near the spinel + garnet lherzolite trend, indicating that the early magmatism originated from the spinel + garnet lherzolite mantle. High values of Ba/Th compared to low values of Th/Nb emphasize the contamination of subducting material or lower crust with magma; the (Dy/Yb)CN-Sr/Nd (Kelemen et al., 2003) diagram indicated that the process of fractional crystallization of plagioclase was effective in the evolution of magma; and finally, the study of samples in this deposit shows the relatively high water content in the magmatism, associated with the presence of garnet in the source and magma contaminated with the lower crust (Temel et al., 1998). In order to investigate the tectonic environment of the deposit, the diagrams of Pearce et al. (1984) were used. The samples are located in the active continental margin and associated with collision magmatism.

analysis of the trace and REEs of the quartz diorite rocks in the region, a magmatism related to the arc with the calc-alkaline series can be recognized. In terms of the evolution of magmatism, according to the interpretation of trace element data, from the origin to the surface, it can be considered a magmatism that originated from the partial melting of magma with the metasomatized spinel + garnet lherzolite composition in the source with the presence of garnet and amphibole phases. In terms of geochemical properties magmatism is more similar to Kuh-Panj type granitoid than the Jabal Barez type; and it is placed in the category of semi-economic to economic magmatism. Based on studies of trace elements from whole rock data, the tectonomagmatism of the rocks in the region is in the range of the active continental margin to collision setting.

The Khabr iron ore is located in about 55 km southwest of Baft and 15 km northeast of Khabr in the southeastern part of the Sanandaj-Sirjan zone. This zone hosts a large number of iron deposits of Iran such as Golegohar in Sirjan. The Khabr iron ore is a small and unknown deposit, mainly composed of supergene iron hydroxides outcrops. The Khabr iron ore is a hydrothermal mineralization that has occurred in marble during primary and secondary stages as oxide and sulfide (Dehghani Soltani, 2012). There is rare information about mineralogy, paragenesis and genesis of the study deposit This paper aims to study the mineralogy of hypogene and supergene ores and the chemistry of sulfide minerals.

Following field study and sampling from the rock units, alteration zones, iron ore and sulfide veins, 45 thin sections and 12 polished sections were prepared and studied by transmission and reflective light microscopes at the University of Sistan and Baluchestan and X-ray diffractometry (XRD) at the Yamagata University. The sulfide minerals are analyzed by the Electron Probe Micro Analyze (EPMA) model of JEOL. JXA-8600 with an accelerator voltage of 15kv and current of 2×10-8 A in Yamagata University. 

Geology:

The oldest rocks in the Sanandaj-Sirjan zone are metamorphic rocks of the late Precambrian-Cambrian period (Ghorbani, 2008), In this zone, Paleozoic and Mesozoic rocks such as carbonate, quartzite, and volcanic rocks with layers of shale and sandstone are covered by Hamedan phyllites (Ghorbani, 2008). The Cretaceous rocks in this zone are mainly carbonated rocks and ophiolitic complex. The Tertiary outcrops in the Sanandaj-Sirjan zone are relatively small. Several intrusive bodies in the Sanandaj-Sirjan zone were formed in the Middle and Late Triassic, Late Jurassic, Late Cretaceous and Paleocene periods. They are mainly intermediate to acidic in composition (Ghorbani, 2008). Most pre-Mesozoic rocks in the Sanandaj-Sirjan zone were metamorphosed. The metamorphic complexes in the study area are Golegohar, Rutchun and Khabr (Figure 1B). The Khabr Iron mineralization is located in the Rutchun complex, which is on top of the Golegohar complex (lower Cambrian) and below the Khabr complex (Devonian) (Figure 1B). The host rock units in this area are an alternation of carbonate rocks, phyllite, greenschist, mica schist and quartz-schist ranging in age from Upper Cambrian to Ordovician. The dominant minerals in these rock units are calcite, quartz, biotite and muscovite including sericite, paragonite, chlorite and clay minerals.

 The iron mineralization occurs at the contact of carbonate rocks and phyllite and schists. The mineralization develops in a northeast-southwest orientation as hill-like and isolated outcrops including hypogene oxide and sulfide mineralization and supergene iron oxide mineralization. The hypogene iron mineralization is characterized by magnetite euhedral crystals, formed as replacements in carbonate rocks by hydrothermal solutions. The hypogene sulfide mineralization forms following the oxide mineralization as silica veins, cavities and open space filling. Sulfides are associated with quartz and composed of pyrite, arsenopyrite, chalcopyrite, bornite and covellite. The chemistry of arsenopyrite, pyrite and chalcopyrite contain low volumes of gold, silver, bismuth, Pb, Zn, Te and mercury. Some pyrite grains contain Au (maximum 700 ppm) (Table 2). The iron ore outcrops are mainly supergene-type formed as open space filling in fractures or around gangue grains boundary. The supergene iron mineralization is due to the weathering of hypogene minerals such as magnetite and sulfide minerals. The margin of the outcrops of the sulfide veins are partially altered to iron hydroxides in brown, red and yellow. The supergene ore minerals are mainly goethite, hematite and limonite. Calcite, dolomite, quartz and phyllosilicates are the predominant gangue minerals. There exist many secondary structures in iron ore like grape-like, colloidal, box-like, cavity-like, rhythmic, replacement and vein-like and open space filling all are indication of weathering and supergene processes. Some textures of the host rocks are similar to clastic rocks like the magnetite-rich sandstone. The magnetite texture reveals that, the Khabr hypogene iron mineralization is mainly formed as a replacement in carbonated rocks by hydrothermal solutions. High temperature acidic hydrothermal solutions containing chloride complexes, dissolve the carbonate rocks upon reaction with them (Robb, 2005). By dissolving carbonate rocks and increasing the pH, chloride complexes became unstable and magnetite replaced limestone. The Khabr sulfides mineralization in the quartz veins is more characteristic of hydrothermal solutions. The hydrothermal solutions containing metal-sulfide complexes had migrated along faults and permeable zones and then with a decrease in the temperature and pressure, the sulfides had been formed. The fluids responsible for the Khabr sulfide stage have the same salinity and temperature as of the those of epithermal deposits (Dehghani Soltani, 2012).The formation mechanism of supergene mineralization is well-known (Guibert and Park, 1986). The Khabr supergene iron ores are the result of magnetite and sulfide oxidation to goethite, hematite and limonite. The magnetites replaced in limestone and marble and magnetites in clastic sandstone have been weathered and altered by oxygen- and carbon dioxide-rich surface waters. The mineralization zone is severely faulted, crushed and permeable. As a result, the circulation of the oxygen-rich waters toward depths or decomposition of magnetite and sulfides had been possible.

The Khabr Fe mineralization can be divided into hypogene and supergene stages. The hypogene stage can be divided into sub-stages of oxide and sulfide mineralization. The hypogene oxide stage is characterized by magnetite, formed as a replacement in limestone by hydrothermal solution or as clastic grains in sandstone. The remarkable features of the hypogene sulfide stage are the presence of arsenopyrite, pyrite and chalcopyrite in quartz veinlets precipitated from hydrothermal solutions like those of epithermal type. The supergene mineralization is characterized by iron oxides and hydroxides as hematite, goethite and limonite precipitated from surface waters.

The Cenozoic Urumieh–Dokhtar magmatic arc (UDMA) in Iran is a part of the Alpine-Himalayan orogenic belt hosts well-known porphyry Cu ± Mo ± Au ± Ag and epithermal Cu (± Au) deposits (McInnes et al., 2003; Hou et al., 2011; Richards et al., 2012, and references therein). The southeastern portion of UDMA in Kerman province contains many of these porphyry copper deposits, known as the Kerman porphyry copper belt (KPCB), where the Seridune porphyry copper deposit (SPCD) is located in its central part. This study deals with petrography and geochemistry of selected samples from the drilling boreholes to discern the geochemical characteristics, hypabyssal emplacement, and the overall tectonic setting environment of these magmatic rocks responsible for the formation of Seridune porphyry bodies.

Geology:

Seridune porphyry copper deposit, in the central part of KPCB in southeastern UDMA, is located in the northeast of the Sarcheshmeh porphyry copper mine. These intrusive bodies are intruded the Eocene volcanic rocks (i.e., andesite and dacite) and as a whole cut by N-S trending dacitic dykes. 

Based on fieldwork and petrographic studies, 14 samples of Seridune intrusive bodies with the lowest degree of alteration were selected for whole-rock geochemical analyses. Whole-rock major and trace-element compositions were analyzed using fusion Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and Inductively Coupled Plasma-Mass Spectrometry (ICP- MS) at the Zarazma company, Iran.

Petrography:

Petrographic studies revealed that in the Seridune area, the composition of the intrusive body responsible for mineralization is predominantly granodiorite porphyry to quartz monzonite porphyry. The other intrusive bodies in the Seridune deposit show a range of compositions varying from granodiorite to monzonite. Mineralogically, they consist mainly of quartz, orthoclase, and plagioclase with variable amounts of biotite, and amphibole phenocrysts setting in a fine-grained groundmass of the same mineral assemblage creating porphyritic texture. Accessory minerals are opaque, zircon, apatite, and titanite. Sericite, chlorite, secondary biotite and secondary alkali feldspar, calcite, anhydrite, clay minerals, and epidote also occur as secondary phases.

Geochemistry:

The results of whole rock analyses are presented in Table 1. In the A/CNK versus A/NK diagram (Shand, 1943), the hypabyssal intrusive Seridune porphyry intrusive body is meta-aluminous to slightly peraluminous, and other intrusive bodies in the Seridune deposit are also meta-aluminous nature. In the Seridune porphyry copper deposit, there is a negative correlation of P2O5 content with the increasing SiO2 content, similar to the I-type granite evolutionary trend (Chappell and White, 1992). On the chondrite-normalized REE patterns, there is a strong enrichment of LREE relative to HREE, whereas, on the primitive mantle-normalized multi-element diagrams, there are enrichments of large ion lithophile elements (LILE), Th and Sr, and depletions of high field strength elements (HFSE) including heavy rare earth elements (HREE).

The Seridune porphyry copper deposit exhibits LREE and LILE enrichment coupled with depletion in Nb and Ti elements, which is typical of subduction-related magmas. This characteristic results from lack of these elements in the source, and/or involvement of the crust in the magmatic processes. The Seridune porphyry intrusive body belongs to the calc-alkaline series and has metaluminous to slightly peraluminous features, whereas other intrusive bodies in the Seridune deposit belong to the calc-alkaline series with a meta-aluminous nature. These features are typical of I-type granites formed by partial melting of mantle wedge which triggered the melting of lower crustal rocks in subduction zones and active continental margins (Chappell and White, 1974; 2001). This type of granite in orogenic belts appears to be resulted from the interaction of main magma with the continental crust through the processes of assimilation-fractional crystallization (AFC) (Dilek et al., 2009). Furthermore, the high values of Th (3.5-5.2 ppm) in the Seridune intrusive bodies have been assigned to the effects of crust contamination (Kaygusuz et al., 2014). The high values of the Th/Nb ratio in the Seridune porphyry copper deposit may point to characteristics of arc-related magmas, enriched by the continental crustal melting. Considering the enrichment of the samples in incompatible elements (i.e. K, Th, Rb, La, Ce, and Nd) and the negative anomalies of Ti, P, Nb, and Eu, it can be argued that the Seridune intrusive bodies were formed by crystallization of melts derived from the melting of lower crustal metabasic rocks as a result of the injection of mantle-derived mafic magmas (Searle and Fryer, 1986; Harris et al., 1986; Chappell and White, 1992). Finally, it can be concluded that the Seridune deposit was originated in a volcanic arc setting. Based on geological background of the area, the formation of these rocks must be related to the subduction of the Neotethys oceanic crust beneath the Central Iranian Micro-continent. The parent magma likely resulted from the partial melting of the lower crust, while the upper crust played a significant role in contaminating the magma at shallower levels.

Makran geological province of SE Iran is an east-west trending mountain range related to the Cretaceous-to-recent subduction of the Indian oceanic lithosphere beneath the southeastern edge of the Eurasian plate (McCall, 1997; Saccani et al., 2022). Makran subduction zone from north to south is composed of remnants of Neo-Tethys oceanic crust, and the Late Cretaceous-Miocene sediments called Makran accretionary wedge (Figure 1). Volcanic fields of Shahsavaran, Bazman, West of Khash and Taftan are located north of Makran and have been considered as a subduction related volcanic arc (Dupuy and Dostal, 1978; Moinevaziri, 1985; Biabangard and Moradian, 2008; Saadat and Stern, 2011; Pang et al., 2014).More than 3 kilometers of mainly clastic sedimentary rocks have been subducted beneath the southeastern edge of the Eurasian plate (Kukowsky et al., 2001). Geochemical characteristics of the more primary basalts from the Makran arc indicate that sediments may have caused mantle source enrichment in the Makran subduction zone (Saadat and Stern, 2011). Quantitative approach to the contribution of subducting sediments to the enrichment of the source of basalts in such a voluminous accretionary prism is hard to attain. However, it is assumed here that subduction of sediments is at least one of the enrichment agents of mantle wedge beneath the Makran subduction zone.In this study, chemical composition of Late Cretaceous-Miocene claystones of turbidite suquences from the Fanouj-Bent area are compared with the chemical composition of sediments from other active subduction trenches. They are also deployed to construct binary melt-sediment mixing models in order to evaluate the postulated sediment contribution to the petrogenesis of the Makran basalts. Sedimentary rocks from the Fanouj–Bent area are the oldest among the Makran turbidites, and are thought to be representative of the most viably-recycled sediments in the mantle source of the Makran volcanic arc. Composition of near primary basalts from Makran volcanic arc (MVA) are then compared with the composition of various binary mixtures between a model basaltic melt and sediment-derived melts and fluids.

Regional Geology:

The Late Cretaceous-Eocene (Mohammadi et al, 2016) deep marine turbidite sediments in this area are exposed together with the ophiolitic rocks of the oceanic crust of the Neotethys remnants (Figures 2A and 2B) and limestone (McCall, 1997). The younger Oligocene and Miocene turbidites include thick sequences of sandstone-claystone that were deposited in deep marine, continental slope, and delta environment in the course of evolution of the Makran accretionary wedge (Figures 2C, 2D).Volcanic rocks of MVA are mainly of andesitic and dacitic composition. The Bazman and Taftan stratovolcanoes are composed mainly of dacitic and andesitic pyroclastic rocks and lava flows. Basalts of MVA are: 1) volcanic centers of Shahsavaran whichare shields volcanoes composed mainly of thin basaltic lavas (Figures 2E and 2F), 2) numerous monogenic satellite cinder cones scattered around the main Bazman volcano, and 3) cinder cones of west of Kash. Takhte Rostam is a basaltic center located on the southern flank of Taftan volcano.

Major and trace element analyses for 2 claystone samples and 6 basaltic samples were performed using X-ray Fluorescence (XRF) spectrometry, and ICP-MS, respectively, at Acme Lab™, Canada. The 6 other claystone samples were analyzed for major and trace elements using XRF and ICP-OES methods in Central Lab of Isfahan University. Three samples of BCR-1 geostandard and three samples of an in-house standard were analyzed simultaneously in both labs, as unknown, to calculate accuracy and precision of the analyses. Table 1 shows geochemical data for the claystone and basaltic samples.

In spidrgrams normalized to continental crust (Figure 7), the claystone samples are enriched in Cs, Rb, Th, U, Ta, Nb, K, Pb, Zr, and Hf and depleted in Ba, and Sr relative to the GLOSS II. These samples seem to be the most enriched sediments among all oceanic trenches of active subduction zones. The quantity of mobile elements in the claystones is comparable to those of the basaltic samples, but the Sr, Ba and Rb amounts are not consonant. Claystone samples are characterized by depletion in Sr (Ave: 171 ppm) and Ba (Ave: 213 ppm), and remarkable enrichment in Rb (Ave: 185 ppm). Compared to claystone samples, the contents of Sr, Ba and Rb in coastal Makran sample (CM) are more comparable to those of the basaltic samples. These similarities suggest that the coastal sediments may have accompanied the Late Cretaceous-Miocene clastic sediments in the mantle enrichment process.The geochemical evidence provided so far for island arc magmas are indicative of the presence and the influence of slab-fluids within and/or from the subducting slabs (Johnson and Plank, 1999; Nakamura and Iwamori, 2009; Schmidt and Poli, 2014;Turner and Langmuir, 2022). Below the solidus temperatures Rb, Sr, Ba, and Pb show more mobility, while at the solidus temperature Th and Be are notably partitioned into the melt rather than fluids (Johnson and Plank, 1999).To evaluate the rate of sediment contribution as a melt (Figure 8) or fluid (Figure 9) in magma generation, two models have been provided in this study. The three end member compositions for calculation of the none-modal batch melting models (Shaw, 1970) are: (1) a near-primary basaltic composition calculated from 15% partial melting of a spinel-lherzolie (MM), (2) average composition of 15% melting of claystone samples (Av.C), and (3) 15% melting of the coastal Makran sample of Jarrard and Lyle (1991). Finally, the binary mixing models between the basaltic MM and the other two end members are compared with the composition of Makran basalts.Th/Yb, Th/Ce, La/Sm, and Sr/Nd ratios are used to show the sediment contribution to the composition of the basaltic samples. Variations of Th/Ce versus Th/Yb ratios and Sm/Yb versus log Th/Yb ratios in basaltic samples show relative consistency with MM-Av.C binary mixing trend (Figure 8). Using these ratios, the sediment melt contribution rate is determined to be up to 10 %.To evaluate the effects of fluids rising from the sediments, in addition to MM, 3 other end members are deployed as: (1) the average composition of 15% fluid released from the claystone samples at 650oC (2) the average composition of 55% fluid released from the claystone samples at 700oC, and (3) 15% fluid released from the coastal Makran sample at 650oC. Binary mixing between MM and about 10% to more than 50% fluid derived from the coastal Makran sample at 650oC (Figure 9), is fairly comparable to the variations of Rb/Nd versus Ba/La and Rb/La versus Sr/Nd ratios. In addition, Elevated Sr/Nd, Ba/La and somehow Ce/Pb ratios are indicative of the contribution of slab derived fluids to the petrogenesis of the basalts. In all calculations, partition coefficients, D values, are taken from Johnson and Plank (1999).

Mahiroud volcano-plutonic complex as an anticline (Lahnu-Mahiroud) forms a part of the Sistan suture zone (SiSuZ), and lies in the northern part of the Sistan suture zone (SiSuZ). According to Tirrul et al. (1983), the Mahiroud complex, which includes a series of metamorphosed intrusive and extrusive rocks, is related to the rifting of the ocean, and they also believe that the general nature of this complex is ophiolitic, but because layered gabbros and ultramafic rocks do not outcrop, this issue is not certain. Delavari et al. (2017) by studying the volcanic rocks of southern Gazik in the vicinity of the Mahiroud volcano-plutonic complex, believe these rocks belong to the magmatism of the island arc. Also, Keshtgar et al. (2019) studied the tonalitic stock of the Mahiroud volcano-plutonic complex and attributed these rocks to the environment above the subduction zones, especially the present-day island arc (IAT). The main purpose of the present study is to study and to determine the tectonomagmatism of the volcanic rocks of the Mahiroud volcano-plutonic complex. 

Regional Geology:

The oldest rocks of the studied area related to the ophiolitic and ultrabasic rocks of the Lower Cretaceous, and after that, the volcano-plutonic rocks of Mahiroud along with sandstone, limestone and shales of the Upper Cretaceous were exposed. The sequences of flysch sediments from Paleocene to Pliocene exist in this area, so that the Oligo-Miocene magmatism can also be seen in it. The largest outcrop of the Mahiroud complex is located in the southern part of this belt and consisting of two parts: (1) The western part, which mainly includes pillow lava, andesite, tuff, and conglomerate. (2) The eastern part, including a complex of sheeted dykes and diabase trending approximately north - south.

50 samples of the rocks under study with the least amount of weathering and alteration were collected from which, 20 thin sections were prepared for microscopic studies. Among these samples, 11 samples were selected for ICP-MS geochemical analysis for minor elements and AF-01-Lithium Fusion for major elements at the Zarazma Laboratory in Tehran. GCDkit, Excel and Corel Draw software were used to check the chemical results.

Petrography:

The rocks of the studied area include volcanic rocks ranging from andesite- basalt, basalt and diabase, crosscutting by a tonalitic stock of Upper Cretaceous (Keshtgar et al., 2019). The boundary between the sedimentary-volcanic units of this area is mainly fault type and is generally cut by two sets of strike-slip faults in the northwest and northeast directions. The texture of these volcanic rocks is amygdaloid and porphyry. Euhedral, subhedral or anhedral. plagioclase forms a high-volume percentage of these rocks, Also, anhedral and subhedral amphiboles with Carlsbad twins can be seen as micro and macro crystals. Small volume of subhedral. pyroxenes and anhedral alkali feldspars are present. Secondary minerals include sericite, chlorite, epidote, calcite and iron oxide (opaque mineral).

Whole Rocks Chemistry :

The whole rock analysis results of the investigated volcanics show that these rocks are classified as andesite-basalt, subalkali basalt and dacite-rhyodacite, placed mostly in the range of tholeiite series (low potassium) of the volcanic arc. This volcanic group is related to the Raskoh volcanic arc of Pakistan. The (Tb/Yb)N values less than 1.8 of these samples indicate the depth of magma melting in the range of 80 km and less than that from a spinel peridotite source. Therefore, the volcanic rocks of Mahiroud area composed of spinel lherzolite melting and the depth is less than the stability field of garnet in the island arc.

The Mahiroud rocks are related to orogenic and tholeiitic basalts of island arc. Compared to N-MORB, these rocks show enrichment in LILE and depletion of HFSE Enrichment in LILE is one of the characteristics of island arcs, which are formed due to the metasomatized of the subducted plate. Also, the Ce negative anomaly in these volcanic rocks is consistent with the characteristics of the island arc, which is the result of the formation of fluids caused by the melting and dewatering of the pelagic sediments of the subducting oceanic plate. The formation of these MORB-type in the subduction zones indicates the melting caused by the release of pressure and the rise of the mantle; It possibly related to the fracture of the thinned arc crust.

The volcanic rocks of Mahiroud volcanic-intrusive complex show a range of, andesite-basalt, subalkali basalt and dacite-rhyodacite. The texture of these volcanic rocks is amygdaloid and porphyry type and their constituent minerals are mainly plagioclase, amphibole, pyroxene, and quartz. The geochemical characteristics of the studied volcanics show that the parent magma is tholeiitic nature (low potassium) originated from the melting of spinel peridotite at a depth, lower than the stability field of garnet. In terms of tectonic setting, most of the samples ranging from volcanic arc basalts and are consistent with the samples of the Raskoh volcanic arc of Pakistan.