PETROLOGY
Year:2017 | Volume:8 | Issue:31 |Papers Count:8

The garnet-amphibolites in Aliabad-Damagh area, occurs as layers and are enveloped by staurolite-schist. They composed predominantly of garnet, hornblende, feldspar (± muscovite and quartz) with titanite, epidote, ilmenite and graphite as accessory minerals. The euhedral garnet porphyroblasts mainly composed of almandine and grossular components, with normal compositional zoning. The hornblende crystals as prophyroblast or in the matrix, are magnesio- and ferro-hornblende (amphibole core) to tchermakitic-hornbelende (amphibole rim) in composition. Muscovites, if present, with minor phengite and paragonite components, are foliated forming minerals. Feldspars vary from pure K-feldspar to sanidine composition in the vicinity of hornblendes and oligoclase in matrix. Epidotes as pure clinozoisite to epidote, form small crystals inside hornblende or in the matrix. Using different thermobarometry methods, T and P estimated as 600-620 (± 25) oC and 5-6 (± 1) kbar, respectively. Calculated P-T-t path, considering core and rim composition of hornblendes, is in accordance with low-pressure (at the beginning of metamorphism) to medium-pressure type (at the end). Considering P-T-t path, metamorphism could occur during Neo-Tethys subduction and collision process in the Mesozoic time

The study area is located the south of Gazik (east of Birjand) and along the eastern margin of the Sistan suture zone. The south of Gazic volcanics crop out as a north- south trending unit. They are predominantly intermediate extrusives including andesite and basaltic- andesite. Based on field relationships and the age of adjacent sedimentary rocks, the volcanics are late- Cretaceous (Maastrichtian) in age. Petrographically, plagioclase is the predominant phase and clinopyroxene appears as the main ferromagnesian mineral. The chondrite- normalized rare earth element (REE) patterns are characterized by moderate light REE (LREE) enrichment relative to heavy REE (HREE) and the ratio of (La/Yb)N in the ranges of 2.71 to 8.68. Furthermore, the chemical characteristics of the volcanics including enrichment of large ion lithophile elements (LILE) like K, Rb and Ba and depletion of high field strength elements (HFSE) like Nb, Ta and Ti are similar to subduction zone magmatism. Based on trace element concentrations, it seems that the melts were derived from a mantle wedge intensely modified by subduction zone fluids. Considering minor and trace element contents, the studied rocks are more similar to island arc volcanics. Therefore, the Sistan Ocean has probably recorded an active subduction zone in the late Cretaceous, which is in conflict with the pre- late Cretaceous Lut and Afghan continental collision.

The Ghaleh Yaghmesh plutonic massif is located the westernmost part of Yazd province and in the central part of the Urumieh – Dokhtar magmatic arc (UDMA). This massif with quartzdiorite, tonalite and granodiorite composition is Oligocene in age and intruded the volcanic and pyroclastic rocks including rhyolite, rhyodacite, and andesitic, as well as rhyodacitic and rhyolitic tuff belonging to the Eocene. Tonalite and granodiorite contain mafic microgranular enclaves with quartzdiorite composition. According to mineral chemistry, the plagioclases are oligoclase to labradorite in composition. The amphiboles have high magnesian and are calcic nature (magnesio-hornblende). The biotites from the tonalites are enriched in magnesian. Compositionally, clinopyroxene display augite and augite-diopside in quartz-diorite and enclaves respectively. Thermometery of the clinopyroxene and hornblende- plagioclase show 1100-1125oC and 730-900oC respectively. The pressure of the studied rocks, on the base of chemical data of magnesio-hornblende, ranges from 1.5 to 1.75 kbar, which is equal to the depth of about 5.5-6.5 km. The overall field, petrography and mineral chemistry data support the I-type calc-alkaline nature of the studied granitoid, which formed during high oxygen fugacity and volcanic arc, and subduction is suggested for its formation environment.

The Lat-Blukan area situated on the western Alborz zone, 45 Km to the north of Qazvin. The area contains intrusive and extrusive bodies with intermediate to acidic composition belonging to Eocene or younger in age (Karaj Formation). This lithological sequence can be divided into three main facies: sedimentary-pyroclastic deposits resulted from explosive alternative eruptions in a shallow-depth sedimentary basin, andesitic lava flows from subaerial effusive fissure eruptions and subvolcanic bodies including dioritic bodies, dacitic domes and parallel dyke swarms. Dykes also are subdivided into andesitic feeder dykes and post-magmatic dioritic dyke. Several evidences including  the Ba/La > 15, Ba/Ta > 450, enrichment of LREEs relative to HREEs, enrichment of LILEs and depletion of HSFEs (Ti and Ta) as well as different tectonic setting diagrams, the magmatic rocks appertain to the continental active margin. Geochemically and especially based on geochemical modeling of magmatic processes, the parent magma of these series is considered to be generated from the mantle that after the ascent and staying in lower continental crust, it contaminated by crustal components and created a variety of magmas in the area. Thus, it may be proposed that the andesitic lava flows formed as a result of the FCA process, diorites originated from the lower continental crust fragments assimilated in the evolved magma from initial magma and dacites are the products of the partial melts of the amphibolitic continental crust.

The Zeber Kuh prospect area is located southwest of Bardaskan, South Khorasan province, in the northeastern Iran. Lithologically, the area includes Rizu and Soltanieh Formations metamorphosed carbonate rocks, which were intruded by syenogranitic and syenodioritic intrusions. Field observations and laboratory studies such as structural controls of orebody, metasomatic replacement and formation of low temperature H2O-bearing minerals, and the occurrence of magnetite and pyrite associated with chlorite, epidote, calcite, and quartz indicate that the iron mineralization is low temperature skarn-type. The source of Fe mineralization is probably a younger intrusive rock at depth. Hydrothermal ore fluid was ascended within fault zone and/or contact between the intrusive rock and the carbonate unit and generated orebody. Iron grade ranges from 54 to 65 wt.% and sulfur value is > 3 wt.%. Magnetite chemistry and Ti, V, Al, Mn, Ni, and Cr contents are similar to skarn deposit. Biotite syenodiorite host rock has hypidiomorphic granular texture and it consists of plagioclase, K-feldspar, biotite, and apatite minerals. Chemically, this intrusive rock is K-series alkaline type, which was generated in within plate zone. This magma is characterized by strong enrichment in LREE, LILE (Rb, Cs, Ba, and K), HFSE (Nb, Zr, and Ti), and P elements. The primary magma is produced by low degree partial melting of garnet lherzolite from asthenospheric to boundary of asthenospheric-lithospheric mantle.

The Shakh Sefid Granitoid pluton and related Skarn are located 80 Km in the southeastern of Kerman and 20 Km north of Rayen. This area   is geologically located in the southeastern of the Lut block in the Central Iran. The Shakh Sefid Granitoid with Eocene-Oligocene age cuts the Cretaceous sedimentary rocks and led to the formation of Skarn. The granitoids are granite and granodiorite in composition composing of quartz, plagioclase, orthoclase, as primary minerals, biotite as minor and chlorite and sericite as secondary minerals. The sedimentary rocks are shale, sandstone, siltstone and limestone. Metamorphic rocks are marble and Skarns. The Skarn is calcic type. Garnet (grossular-andradite), tremolite and magnetite are the main minerals that are often accompanied with hematite, goethite and limonite. Pyrite, chalcopyrite and copper carbonate (malachite and azurite) are the other minerals in Skarn. Geochemical studies show that the amount of major and minor elements of granitoid with increasing SiO2 content do not change due to the uniform mass, low dispersion of elements which result from heterogeneous textures and low alteration zone. Spider diagrams from minor elements normalized to Chondrite and primitive mantle show enrichment of all elements except for Ti, positive anomalies of Th, Pb and negative anomalies of Ti, P and Sr for the Sakh Sefid granitoids are probably due to crustal contamination. They are enriched in light rare earth elements (LREE) between 10 to 100 times and heavy elements (HREE) enrichment between 1 to 10 times compared to the reference (chondrite) and regular pattern with approximately the same slope, the parallel trends indicate that the granitoid rocks share  a common source rock . The Shakh Sefid granitoid is I-type, metaluminous to peraluminous belonging to an active continental margin. Mineral and Mineralization in Kuh Shakh Sefid skarn is remarkably similar to iron skarn deposits. Minerals such as garnet and magnetite were formed in an anhydrous prograde stage at T<470oC and ¦O2 10-21 to 10-24 oxygen Fugacity and minerals such as epidote, tremolite, calcite and quartz were formed in a retrograde stage at T<450oC and about  ¦2 10-21 oxygen Fugacity.

The Eocene dykes in the north and the west of Zahedan exposed into the flysch and Zahedan granitoid rocks in the Sistan suture zone. These rocks, including mafic dykes, ultramafic and felsic are mostly alkaline in nature and sometimes are contaminated. The dykes in discussion, display mostly porphyritic and glomeroporhyric textures. Plagioclase, hornblende and biotite are the main phases as well as the matrix of the rocks. The presence of rounded plagioclase and corrosion Gulf of quartz, normative changes and variation in minor and trace elements are indicative of contamination with continental crust. Enrichment of LREE relative to HREE and the lack of Eu anomaly are important characteristics of all of the studied rocks. High ratios (La/Sm)N, and (La/Yb)N and(Sm/Yb)N and the alkaline nature of most of the samples, indicate a melting process about 1 percent of a mantle with garnet lherzolite composition. Such conditions may be completion of subduction of Sistan oceanic lithosphere beneath the Afghan block ended. Slab sinking to a considerable down, fluid released from the edge caused some chemical and mineralogical changes of mantle wedge, and to facilitate partial melting of the rocks. The fluid migration to higher levels due to the lower parts of the upper crust and mantle wedge are batch melting. As the molten materials increased, they were transferred to higher levels in the Oligo-Miocene period and have been emplaced in the upper parts of the crust. It seems that after the Oligo-Miocene time and as subduction continued, fractures developed and the ascending magma emplaced into these fractures, which finally gave rise to the formation of the study dykes.

The basaltic prisms assemblages of Poshtsar are located in the south-eastern of Germi city and include of mafic volcanic rocks such as olivine basalt. They are outcropped with about 1000 meters thickness in the eastern part to 10 meters thicknes in the western part of Moghan. The main minerals of these rocks are olivine phenocrysts, clinopyroxene (augite) and plagioclase. The dominant textures of the rocks studied are microlitic and microlitic porphyritic. According to geochemical diagrams, the study rocks were originated from an alkaline magma. Spider diagrams show that the parent magma has been enriched in LREE/HREE ratio and LILE to primordial mantle which indicates enrichment of mantle source of the parent magma The magma of the studied rocks were generated from garnet lherzolite in depth of around 100 Km. It seems these basalts have been formed in Back-arc basin due to subduction of the eastern Black Sea (northern branch of Neo-Tethys) beneath the Armenian microcontinent.