Petrology
Marziyeh Abazari; Seyyed Saeid Mohammadi; Malihe Nakhaei
Abstract
Abbas Abad area is located in the northeast of Sarbisheh, in the northern part of Sistan suture zone and southern Khorasan province. In this area, Tertiary volcanic rocks with the composition of intermediate to acid, including basaltic andesite, andesite, and dacite are exposed. Constructive minerals ...
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Abbas Abad area is located in the northeast of Sarbisheh, in the northern part of Sistan suture zone and southern Khorasan province. In this area, Tertiary volcanic rocks with the composition of intermediate to acid, including basaltic andesite, andesite, and dacite are exposed. Constructive minerals of basaltic andesite include of plagioclase, pyroxene and olivine and in andesite consist of plagioclase, hornblende and pyroxene, and in dacite are plagioclase, quartz, biotite and hornblende. The studied rocks have medium to high-K calc-alkaline nature. Most samples show enrichment in LILEs (K, Rb, Sr, Cs) (except Ba) relative to HFSEs (Y, P, Ti, Ta, Nb), which indicates the relation of these rocks to subduction zone and active continental margin. The relatively low (La/Yb)N (7.67 to 13.48) and Dy/Yb (<2) in Abbas Abad lavas indicate that partial melting of mantle occurred in transitional zone of spinel-garnet lherzolite. Based on the concentration of trace elements such as Ce, Yb and Sm, magma originated from a depth of about 95 to 105 kilometers.
Petrology
Maryam Kouchi; Malihe Nakhaei
Abstract
In northeast of Sarbisheh city, southern Khorasan, outcrops of lava rocks are exist that from view of geological subdivisions, located in eastern part of Lut block. Lithologic composition of studied collections consist of andesite (pyroxene andesite, andesite, trachy andesite), dacite and rhyolite. The ...
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In northeast of Sarbisheh city, southern Khorasan, outcrops of lava rocks are exist that from view of geological subdivisions, located in eastern part of Lut block. Lithologic composition of studied collections consist of andesite (pyroxene andesite, andesite, trachy andesite), dacite and rhyolite. The main texture of these rocks are porphyry with microlitic-glass groundmass, glomeroporphyritic, poikilitic and vesicular. The mineral constituents of andesitic rocks are plagioclase, pyroxene and amphibole with small quantities of biotite and sanidine and in rhyolite and dacite include of quartz, sanidine, plagioclase, amphibole and biotite. Disequilibrium textures such as chemical zoning, sieve texture, rounded and gulf shape margins in phenocrysts of these rocks are observed. Geochemical study results show that these lavas belong to high to medium-K calc alkaline series. Enrichment in LREE and LILE, depletion in HREE and HFSE with negative anomaly of Ti, Nb and P in these rocks indicated active continental margin volcanic arc magmatism. Based on tectonic discrimination diagrams, also support the relation of Zoolesk area lavas with subduction zone and active continental margin. Low ratio of Dy/Yb(<2) in studied lavas, indicated spinel lherzolite mantle source for magma.
A. Baharvandi; S. S. Mohammadi; M. Nakhaei
Abstract
In the Boshgaz area in 50 kilometers northwest of Sarbisheh and eastern margin of Lut block, Tertiary volcanic rocks with basaltic andesite, andesite and dacite composition are cropped out. The main texture of these rocks are porphyry with microlithic-glass groundmass, glomeroporphyritic and vesicular. ...
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In the Boshgaz area in 50 kilometers northwest of Sarbisheh and eastern margin of Lut block, Tertiary volcanic rocks with basaltic andesite, andesite and dacite composition are cropped out. The main texture of these rocks are porphyry with microlithic-glass groundmass, glomeroporphyritic and vesicular. The main minerals in andesite lavas are plagioclase, pyroxene, amphibole and biotite and in dacites are plagioclase, quartz, amphibole and biotite. Geochemical investigations show that these rocks have medium to high-K calk alkaline nature. Enrichment of Sr, Zr, Cs, Th, K, depletion of Nb, Ti, P, Ba and enrichment of LREE relative to HREE in the studied rocks show that these rocks are related to a subduction zone and active continental margin setting. On the basis of trace elements diagrams, volcanic rocks of the Boshgaz area are formed in an immature arc or early stage of subdution. Mg# values in volcanic rocks of the Boshgaz area are ~48 indicating the role of mantle constituents in their formation. Low ratio of Sm/Yb(<2.5) in the studied lavas show absence of garnet in the source. Low ratio of Zr/Ba (average 0.34) and high ratio of La/Nb (2.22-3.19) for the studied lavas are characteristics of lithospheric mantle source. MREE/HREE diagrams show that lavas of the Boshgaz area originated from spinel-phlogopite lherzolite. Low ratio of Ba/Rb (<20) and high ratio of Rb/Sr (>0.1), support the existence of phlogopite in the source. The uniform pattern of REEs and medium values of La N /Lu N (8-14)inintermediate and acidic rocks of Boshgaz indicate genetic relationbetween them.
P Ketabi; S.S Mohammadi; M.H Zarrinkoub
Abstract
The volcanic–sub volcanic activities in the Shah Soleyman area located in southwest of Birjand, east of Iran have cropped out as two categories of Pyroclastic – lava and sub volcanic rocks. The pyroclastic rocks are tuff, agglomerate with breccias and volcanic rocks are andesite, trachy- ...
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The volcanic–sub volcanic activities in the Shah Soleyman area located in southwest of Birjand, east of Iran have cropped out as two categories of Pyroclastic – lava and sub volcanic rocks. The pyroclastic rocks are tuff, agglomerate with breccias and volcanic rocks are andesite, trachy- andesite and dacite. The porphyry and glomero- porphyric with micro granular to vitric groundmass are the main textures in these rocks. The porphyritic diorite is the unique sub volcanic unit in this area. Plagioclase, hornblende with oxidized rims, and biotite are the main phenocrysts. Sericitization, carbonatization and propylitic alterations are common in these rocks. Based on the geochemical study, these rocks have SiO2 in range of 56.8-61.9, high Al2O3 (16.5-18.1) and Sr (660-990), high Sr/Y (40.6-54.6), and low Y (16.1-19.7) that show adakites characteristic for the parent magmas. On the basis of geochemical characters, these rocks are high SiO2 adakites, which is considered to represent subducted basaltic slab melts that have reacted with peridotite during the ascent through mantle wedge. High ratio of LILE/HFSE, LREE/HREE and negative anomaly offor Nb and Ti show similarity with subduction- related magmatism. High Sr and negative anomalies of Ta, Nb, and Ti may be resulted from the lack of plagioclase and having iron and titanium oxides in the residual phase. The geochemical study showed that the source can be derived from subducted metamorphosed oceanic plate in east of Iran.
S. S. Mohammadi; M. Vossoughi Abedini; M. Pourmoafi; M. H. Emami; M. M. Khatib
Abstract
Bibi Maryam Granitoid body with 5 km2 exposure area is located in the east Iranian ophiolite mélange belt in Sistan suture zone. This intrusive body consists of tonalite- quartzdiorite and granodiorite. The main mafic minerals are hornblende and biotite in quartzdiorite-tonalite. Existence of ...
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Bibi Maryam Granitoid body with 5 km2 exposure area is located in the east Iranian ophiolite mélange belt in Sistan suture zone. This intrusive body consists of tonalite- quartzdiorite and granodiorite. The main mafic minerals are hornblende and biotite in quartzdiorite-tonalite. Existence of microdioritic enclave in tonalite and its absence in granodiorites is one of the main characteristics of the body. Perthitic and granophyric textures in granodiorites represent low water vapor pressure and relatively fast crystallization, respectively. Geochemical study of rock samples shows that the body is calc-alkaline and metaluminous to peraluminous. Trace element patterns in spider diagrams represent a trough for Nb and enrichment for K, Rb, Ba and Th that indicate contamination by crustal materials. Although Bibi Maryam intrusive body cuts the ultramafic rocks, it lacks petrographic and geochemical characteristics of oceanic plagiogranites. The geochemistry of the body is comparable with I-type granitoids and based on tectonic setting it can be classified as orogenic and VAG type.
