جستجوی مقالات مرتبط با کلیدواژه "calc-alkaline" در نشریات گروه "زمین شناسی"

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.

Middle Miocene igneous rocks are located in the Northeast of Joveinan, the middle part of the Urumieh-Dokhtar Magmatic Belt. The igneous rocks have intruded into the Eocene volcano-sedimentary units. The rocks consist of diorite, quartzdiorite, and monzodiorite. They contain plagioclase, hornblende, biotite, pyroxene, orthoclase, quartz, and opaque minerals, and have granular to porphyroid textures. Field and petrographic evidence such as a lack of thermal metamorphism and graphic texture suggests that the rocks crystallized at a shallow depth. The rocks exhibit characteristics of I-type granitoids and a calc-alkaline nature with metaluminous affinities. The enrichment of large ion lithophile elements (LILEs) and the negative anomaly of Ta, Nb, and Ti elements in the primary mantle normalized diagram demonstrate subduction-related magmatism in the continental arc setting. The chondrite normalized pattern of the rocks (Lan/Ybn= 3.68-5.64) suggests a low degree of partial melting and the absence of garnet as a permanent phase in the source region. Based on the petrological data, the parental magma has been produced in the subduction setting of the collisional zone. The primary magma resulting from the partial melting of the subducted lithospheric mantle intruded into the continental crust. The magma underwent numerous changes and evolution during ascent and created the intrusive rocks of Northeast Joveinan.

The kalasur_Kharil granitoid complex with Oligocene age, is located in SW Kaleybar of NW Iran, Alborz-Azarbaijan zone. The rocks are intruded into the Cretaceous volcanic and sedimentary rocks. The composition of plutonic rocks are consist of gabbro-diorite, diorite, quartz monzodiorite and granite. The major minerals in gabbro-dioritic and dioritic rocks are plagioclase, clinopyroxene, amphibole, biotite and major minerals in quartz monzodioritic and granitic rocks are potassium feldspar, plagioclase, quartz, amphibole and biotite. On the basis of mineral chemistry, the composition of clinopyroxenes is in diopside range. Amphibole minerals are calcic in study area. The calcic amphiboles indicates that the rocks of the studied area belong to type I granitoids. The Khari- Kalasour amphiboles are magnesio hornblende. The biotite in Kharil- Kalasur granite with Fe/(Fe+Mg)>3 is magnesio-biotite. The feldspar composition is albite-andesine in granite, labradorite, andsine and orthoclase in dioritic and quartz monzodioritic rocks. Mineral chemistry of the biotite, amphiboles and pyroxenes indicate that this rocks are calc-alkaline and have been crystallized in a subduction zone setting.

The granitoides of west Ardakan are outcropped in the middle part of the Central Iran zone. Quartz, orthoclase and plagioclase are the main minerals and amphibole, biotite, sphene, zircon and apatite are secondary minerals. The dominant textures are medium to fine grain granular, granophyry and myrmikite[r1] . According to mineral chemistry data, calcic amphiboles of magnesiohornblende to actinolite nature have crystallized at temperatures of 530-890 ºC. Oligoclase to andesine plagioclased crystallized at 700-800 ºC. Magnesium biotites was crystallized at 650-730 ºC. On the basis of the oxidant conditions, magnetite are formed as opaque. The chemical analysis of all these minerals show the mantle nature of the magma. Magma seems to suffer produced these minerals, moderate to severe crustal contamination during its ascent. These granitoides are I type and calc-alkaline and were formed in the subduction setting related to the active continental margin.

The studied area is located in the northwest of Iran, south of Ardabil Province, in the Alborz-Azerbaijan zone. The important volcanic phases in the region, based on K-Ar dating, include three sequences: Eocene (trachyandesite), Oligocene (basalt, basaltic andesite) and Miocene phase (basaltic andesite, basaltic trachyandesite and rhyolite). The Eocene sequence shows the nature of shoshonite and the Oligocene and Miocene sequences show the nature of calc-alkaline to calc-alkaline perpotassium. All three sequences in multi-element diagrams normalized to the primary mantle show negative Nb-Ti-Ta anolalies, depletion in Y,Yb,Ti and enrichment in Rb,Ba,K,Th. Most likely, the slab break-off of the Neotethys subducting plate, as a result of the creation of an asthenospheric window in facilitating the partial melting process, has caused the partial melting of the metasomatized continental lithospheric mantle and the formation of the Eocene-Oligocene volcanic sequence. The source of heat for Miocene-Quaternary volcanoes is also related to the rise of the asthenosphere, which is caused by the delamination of the lithosphere. Using this study, we improve our understanding of the nature, origin and magmatic evolution of the igneous rocks of northwestern Iran, which are influenced by geodynamic environments.

In the northwestern part of the Sanandaj-Sirjan zone, mafic intrusive bodies are aligned with the trend of the Zagros orogenic belt. In this part of the Iranian lithosphere, magmatic activity occurred during three main periods: Cretaceous, Eocene, and Miocene-Quaternary. In the first of two stages, the magmatic activity was associated with subduction-related magmatism at the active continental margin, whereas the last phase was characterized by calc-alkaline magmatism related to post-collision regime. The intrusive mafic bodies of Qobadlo, Chupankareh, and Qaraqoshun at the southern margin of Lake Urmia in the northern part of the Sanandaj-Sirjan zone intruded within the complex of Cretaceous shale, shale-sandstone, and siltstone. U-Pb dating on zircon performed on these bodies indicates an age of 99 Ma. The SiO2 content of these bodies ranges from 46.17 to 53.35%, Al2O3 13.1 to 18.49 % Fe2O3 3.11 to 5.8%, and their TiO2 content ranges from 1.9 to 4.0%. Positive anomalies of large ion lithophile elements and LREE compared with negative anomalies of elements such as Nb, P, Zr, and Ta (HFSE), the La/Nb, Ba/Nb ratios, and the REE pattern show a good correlation with the magmatic rocks of subduction zones.

The study area is located in the SaSZ, NE of Songhor city, Kermanshah Province. Based on field observations and mineralogical data, the Azizabad-Hazarkhani I-type calc-alkaline granitoid consists of granites, monzonites and diorites with small volumes of gabbroic rocks. Co-variations in major and trace elemental abundances do not indicate a continuous compositional suite and therefore do not suggest a co-magmatic origin. According to geochemical evidence, the samples are enriched in incompatible elements such as Th, Rb, La, Ce and Nd and depleted in Nb, Ti and Eu, with metaluminous affinity. These characteristics reflect the role of continental crust and crust-derived melts. Tectonic setting discrimination diagrams suggest that this complex belongs to the volcanic arc and is related to an active continental margin setting. According to the geological history of this area, it can be attributed to the subduction of Neo-Tethyan oceanic crust below the Central Iran microplate. We suggest that the Parishan and Darvazeh mantle-derived basaltic magmas may have provided the heat required for the partial melting of various source rocks, including amphibolites, meta-basites, and meta-andesites, through diffusive heating.

The Kuh-e-Kalut-e-Ghandehari is located about 40 Km northwest of the Anarak (northeast of Isfahan). This area is a part of the Central Iran that is situated in west of the Yazd block; near to the Ashin ophiolite and drastic directional changes of the Great Kavir Fault. In the northwest of Anarak, the Ashin ophiolite is covered by the Cretaceous limestones, and crossed by the Eocene volcanic rocks. The Upper Eocene gabbro-diorite stock cross cuts the Eocene volcanic rocks. Andesites are the predominant unit of the Eocene volcanic rocks. They are grey to dark- grey in colour and have amphibolite xenolith. The main textures of these volcanic rocks are porphyritic, poikilitic, trachytic, sieved texture and glomeroporphyritic. The main phenocrystic minerals of andesites are plagioclase, amphibole and clinopyroxene situated in a matrix of the same minerals and sanidine, magnetite and apatite. Secondary minerals are formed as a result of the hydrothermal alteration and comprise zeolite, chlorite, epidot, sericite, kaolinite and calcite. Mineral chemistry indicates that plagioclases are andesine to labradorite (An= 30-52%), K-feldspars are sanidine (Or= 68-71%), amphiboles are calcic with pargasite composition (Mg#= 0.58-0.71), and clinopyroxenes are diopside (Mg#= 0.91-0.93) in composition. Whole rocks chemical analyses indicate that these andesite and trachy-andesite rocks have calc-alkaline property. The chondrite and primitive mantle-normalized REE and multi-element patterns show LREE and LILE enrichment and HFSE (Ti, Ta, Nb) depletion, which are characteristics of the subduction-related magmas. These data indicate that the primary magmas were genarated by medium degrees of partial melting of the lithospheric mantle spinel lherzolite. Subduction of the Central-East-Iranian Microcontinent (CEIM)-confining oceanic crusts (Naein and Ashin oceanic crusts) are possibly the reason of this volcanism. Geochemistry of these volcanic rocks are similar to the arc-related ones.

Dalfard granitoid complex is located in the southeast of Kerman Province between  57˚ 30 ˊ to 57° 45 longitudes and 28˚ 55ˊ to 29˚ 10 ˊ latitudes. This granitoide complex contains granite, granodiorite, quartz-diorite, diorite, in the margins, and is mainly composed of quartz-diorite. The main texture is granular and include quartz, plagioclase, amphibole, biotite and alkali-feldspar, with some mafic microgranular enclaves in them. The EMPA data showed that plagioclase are andesine and alkali-feldspar with orthoclase composition. Biotites with Fe/Fe+Mg > 3.3 rato fall in the magnesium-rich biotites area. Amphiboles are calcium type and they have magnesiohornblende in composition, which indicates that their host magmas are I-type. The low values of Na2O in amphiboles, their calc-alkaline nature, and the high oxygen fugacity indicate that they belong to the subduction environment and mantle derived magmas along with the crustal compounds contributed to the formation of their host magmas. Geo-thermo-barometry calculations estimate the average crystallization pressure of 1.4 kb and temperature of 681 °C for the studied hornblende.

Numerous intrusive rocks of various sizes, dominated by granodiorite-granite, intrude the Sanandaj-Sirjan Zone (SSZ) (Torkian et al., 2008; Mollaei Yeganeh, 2018). They are S-I-and A-types in composition and ideal for studying the linkage between tectonic settings and the magmatic evolution of igneous rocks. Diverse scenarios have been proposed to explain the origin of A- type granitoids: (i) extreme fractional crystallization of parental mafic magmas derived from the mantle (with/ without crustal contaminations, (ii) high temperature partial melting of crustal granitic rocks (iii) partial melting of granulites OR charnockite, (iv) a metasomatic origin (Eby, 1992). These Atype granites are generally thought to have formed in an extensional setting, but their source regions and tectonic attributes are still a topic of debate. The present paper describes the field relationships, petrography and whole-rock geochemistry of A-type granitoid; these data are then used for the interpretation of the magma sources, tectonic setting and magma-generation processes for A2-type granitoid in NE-Sonqor.

The volcanic complex of North Khour  located in southern Khorasan province, 90 km northwest of Birjand in the Eastern of  Iran. The rocks under study are basaltic andesite, andesite and trachyandesite, latite, dacite to rhyodacite with tuff and breccia as pyroclastic rocks. The volcanic rocks are predominantly calc-alkaline nature with some tholeiitic affinity and porphyry texture. Iron mineralization developed as magnetite, hematite and small amount of goethite with magmatic origin, on the base of field observations. Bornite as the only and the primary Cu ore occurred as a small body. The presence of minor amounts of bornite and pyrite as the sulfide phases as well as the absence of the other Cu primary sulfide ores in the area along with secondary Cu mineralization phases reflect a hydrothermal solution with high oxidation degree which has passed the latest magmatic differentiation and gave rise to form surface Cu ores as chalcocite in supergene zone. The thermobarometry of fluid inclusions studies from Ghar Kaftar and Hoze Sabz, yield temperature range of 178 -324 C for Cu mineralization. Therefore, it seems that Cu mineralization is related to epithermal to mesothermal conditions.

The magmatic complex of Azadegan, composed of basalt, andesitic basalt, andesite, gabbro and diorite, located 45 km northwest of Shahrekord and in the middle part of the Sanandaj-Sirjan zone.. The study rocks are dominated by plagioclase, olivine, pyroxene, hornblende as well as biotite and calcite as minor minerals. Geochemically, the rocks under study are calc-alkaline in nature and are characterized by Ce, Zr, Ba, and Sr depletion. Chondorite- normalized REE pattern illustrates LREE enrichment relative to HREE. Geochemical data of the studied samples indicate partial melting of the mantle source with the influence of fluids and sediments of the subducted crust during subduction. The ratio of Th/Yb (2-2.75) values are in consistent with those of the mature arc islands magma. Also, Ce /Y and Sr/Y ratios indicate the thickening of arc islands along with orogenic processes and maturation of arc islands in the study area. The for mentioned ratios also represent the thickness of crust up to 50 km., during orogenic processes at the end of subduction stages of the Neotethys.

The Tekieh intrusive complex is located in S-Qorveh in northern parts of the Sanandaj-Sirjan Zone. In this collection, the granite inclusions located in the granite host compound have a diorite composition and the inclusions located in the monzonite host compound have a gabbroic composition. The enclaves are scattered in rounded and elliptical shapes in the host rocks. Generally, they have a sudden contact with the host rock and are composed of igneous minerals. Amphiboles are calcic-type, and their composition is magnesio-hornblende and actinolite. The plagioclases have a range of composition from oligoclase to andesine and oligoclase to bytownite for host rock and enclaves samples, respectively. Based on geothermobarometry studies on amphiboles and also amphibole-plagioclase pairs, the temperatures of 660-5540C and 742-5920C with pressure ranges of 0.3 to 3.62 and 0.21 to 1.8 Kbar were estimated for host rock and diorite enclaves samples, respectively. Oxygen fugacity was high in magma that is consistent with calc-alkaline nature and the formation of rocks in its subduction setting.

In southwest of the Jandaq City (northeast of Isfahan Province) and northwest of the Central-East Iranian Microcontinent (CEIM), the Eocene dykes with trachy-andesitic composition cross cut the quartz monzodioritic intrusion. The texture of these dykes is granular, intergranular and porphyritic. The studied dykes are composed of plagioclase (andesine and labradorite), clinopyroxene (diopside and augite), sanidine, mica (Biotite), and quartz as primary minerals, and amphibole (tremolite-actinolite), chlorite, magnetite and calcite as secondary ones. Mineral chemistry and distribution of elements indicate that these minerals are formed in low to medium pressure (2-5 kbar), 1150 to 1200 °C, and the high Oxygen fugacity conditions. The source rock of the magma is a mantle peridotite which previously metasomatized by fluids and melts derived from subducting oceanic slab.  Mineral chemistry of clinopyroxene and biotite reveal that these dykes have calc-alkaline nature and are formed in a subduction-related environment.

Zardkuh igneous complex is located in 35 km Southeast of Iranshahr and is geologically situated flysh zone and the Sistan-suture zone. Rock units in the area are Ophilitic rocks (upper Cretaceous), Eocene flysh and Oligomiocene intrusive and extrusive rocks (Zardkuh igneous complex). Patterns of minor and rare earth elements normalized to Primitive mantle and Chonderit show low enrichment to LREE such as La, Ce and Sm than to HREE such as Ho, Yb, Tb and Lu. The dip of digram is soft to HREE and in the extrusive rocks is low increased. . it is thought that the constituent magma of these rocks from the mantle wedge above the subduction plate, which is usually affected by the fluids released from the subducted plate and its elements (including Silica, potassium and sodium) can produce such magma. So these rocks are related to magmatism and subduction Neo-Tehyan oceanic between Lut and Sistan blocks.

The Meshkin-Rasht Abad area is a small part of the western Alborz-Azarbaijan magmatic belt (AAMB). Field investigations reveal that andesitic-basalt rocks are the dominant rock units of the area with high-K calc-alkaline to shoshonitic affinities. On the basis of geochemical features all rocks are enriched in light rare earth elements (LREE), large ion lithophile elements (LILE) and have positive anomalies of Pb, U and Cs and Ti, Sr and Nb negative anomalies. These volcanic rocks have the criteria of active continental margin arcs on tectonomagmatic discrimination diagrams. Geochemical data, including low amounts of Cr, Ni, V, and Zr/Nb ratio suggest the enriched mantle source (lithospheric mantle) for the rocks under study. Moreover, the diagrams of the ratio of highly incompatible elements indicate the effect of slab-derived fluids on the magma generation. The Ce/Pb low value as well as various geochemical diagrams demonstrate that the magma is possibly contaminated by continental derived-crustal materials.

The volcanic rocks of Bayram Abad area, located 12 km northwest of Neyshabour, are dominated by the Paleogene units composing of dacite and andesite rocks. The essential minerals of the rocks under study are plagioclase and amphibole with predominant textures including porphyry, sieve, trachytic and glomeroporphyritic. Composionally, they are acidic to intermediate and calc-alkaline affinity. The absence of negative Eu anomaly, low HREE values (i.e. Yb=0.92-1.11 ppm, Y=8.7-11.4 ppm), high Sr values (293-1029 ppm), high Sr/Y (29.08-90.26), high SiO2 content (59.96-65.89 wt%) and low K2O/Na2O (0.27-1.13) are remarkable geochemical criteria of the rocks studied. Moreover, Both Chondrite-normalized rare earth element (REE) patterns enriched in LREE with respect to HREE and normalized to primitive mantle spider diagram indicate that these rocks are adakitic in nature belonging to group of silica-rich adakites (HSA) The negative anomalies in HFSE (i.e. Nb, P, Ti) and high La/Yb (over 12) point to the characteristics of magmas associated with the continental active margin. It is possible that the parent magma generated by the melting of the eclogite or amohibolite garnet rocks resulting from the metamorphism of the Sabzevar Neotethys subducted oceanic slab underneath the southern edge of the eastern Alborz zone during the Miocene.

In Zoolesk area, about 11km northeast of Sarbisheh city in South Khorasan Province, volcanic rocks including andesite, dacite and rhyolite have cropped out where andesitic lavas have the maximum distribution and have been studied in this research.The main textures of andesites are porphyry with microlitic-glassy groundmass, glomeroporphyry and vesicular. Minerals forming andesites include plagioclase, pyroxene, amphibole, biotite and rarely sanidine. Plagioclase phenocrysts have oscillatory zoning and sieve texture and so corrosion, rounding and resorption rims can be seen in the margin of some crystals. Based on microprobe analyses, the composition of plagioclases changes from Ab67,An33to Ab54, An46 and are andesine type. Clinopyroxene phenocrysts have augite with minor diopside composition (En39-41 Fs13-17 Wo43-47) and orthopyroxenes are enstatite (En41-74Fs13-43Wo2-3). The Mg# values in clinopyroxene and orthopyroxene are variable between 69-75 and 56-76 respectively. Thermometry studies showed that the crystallization temperature of clinopyroxenes is 1150 to 1200°C and for orthopyroxene is 1050 to 1100°C. The calculated pressure for genesis of clinopyroxene and orthopyroxene in the studied samples was less than 2 kbar.

In the southeast of Nir, south of Yazd Povince, several acidic volcanoes  rocks are exposed and form the youngest volcanic rocks in this region with dacite-rhyodacite composition. These rocks are composed of plagioclase, hornblende, biotite and quartz phenocrysts with trachytic and hyallomicrolithic porphyry texture. Based on geochemical data, the magmatic affinity of these rocks is calc-alkaline with enrichment of LILE and depletion of HFSE. These characteristics with steep decrease pattern of rare earth elements and negative anomaly of HFSE, such as Nb, Ti and P, indicate the formation of magma in active continental margin. Higher levels of SiO2, Sr, Sr/Y, and La/Yb with low levels of MgO, Yb, and Y, indicate high silica adakite affinity. It seems that the formation of parental magma of these rocks is consequence of the melting of garnet amphibolite or eclogite rocks of subducted metamorphosed Neotethys oceanic lithosphere in the Central Iran- Arabian plate collision zone during the Neogene time.

The study area in the south of Deh Tah, Lut Block comprise Oligocene volcanic rocks which are composed of andesite, trachyandesite, dacite and rhyolite. These lavas have porphyric to porphyritic textures with abundant amphibole phenocrysts. Most of the Oligocene lavas display calck alkaline to high-K calck alkaline magmatic affinities. In the binary diagrams, the andesitic to trachyandesitic samples cluster far away from the trachydacitic, dacitic and rhyolitic samples suggesting that they were not afftected only by magmatic differentiation. The REE patterns and spider diagrams show enrichement in light ion litophile element (LILE) and hight field strength element (HFSE) depletion. The normalized patterns of the andesite to trachyandsite have a reliable overlap with oceanic island basalt (OIB). The patterns of the acidic lavas are correlated with the patterns of continental crust. These geochemical evidence indicate that the andesitic to trachyandesitic lavas are generated from partial melting of lithospheric mantle which previously metasomatized by subduction components (melt-fluids). Partial melting of the continental crust has an important role in generation of the acidic lavas. Based on geological setting and geochemical data, it seems that the Oligocene volcanic rocks formed in a post-collision zone, due to thinning of the continental lithosphere in Lut Block. This process is probably related to lithospheric delamination which occurs in a post-collisional zone in Lut Block, as a part of the Alpine-Hymalaya orogenic belt.