Relative contributions of crust and mantle to generation of Oligo-Miocene medium-K calc-alkaline I-type granitoids in a subduction setting-a case study from the Nabar Pluton, central Iran

被引:10
作者
Abbasi, S. [1 ]
Manesh, S. M. Tabatabaei [1 ]
Karimi, S. [1 ,2 ]
Parfenova, O. V. [3 ]
机构
[1] Univ Isfahan, Dept Geol, Esfahan 8174673441, Iran
[2] Islamic Azad Univ, Khorasgan Branch, Young Researchers Club, Esfahan, Iran
[3] Moscow MV Lomonosov State Univ, Dept Petrol, Moscow 119991, Russia
关键词
ISOTOPIC COMPOSITIONS; GENESIS; EASTERN; SR; GEOCHEMISTRY; CONSTRAINTS; BIOTITES; FRACTIONATION; PETROGENESIS; AMPHIBOLES;
D O I
10.1134/S0869591114030023
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
The Nabar pluton with the age of Oligo-Miocene located northwest of Isfahan, the Urumieh-Dokhtar magmatic belt, is composed of gabbro, gabbro diorite, diorite, quartz diorite, tonalite, and quartz monzonite. These rocks contain plagioclase, quartz, alkali-feldspar, magnesiohornblende, actinolite, tremolite-hornblende, actinolite-hornblende, anthophyllite, biotite, and Na-poor pyroxene. Application of the Al-in-hornblende barometry indicates pressures of 2-2.15 kbar, whereas the clinopyroxene barometry shows a pressure of 5 kbar. The temperature (i.e., 750-800A degrees C) is estimated using the amphibole-clinopyroxene thermometry in a dioritic sample. Magmatic water content was greater than 10% at the time of formation of dioritic rocks in the Nabar pluton. Based on chemistry of mafic minerals and geochemical data, the Nabar plutonic complex comprises medium-K, calc-alkaline, and I-type granitoid. The rocks are characterized by enrichment of lithophile elements (LILEs) and depletion of high-field-strength elements (HFSEs). The Nabar rocks have weak concave-upward rare earth element (REE) patterns, suggesting that amphibole played a significant role in their generation during magma segregation. Low (Al2O3/(FeO + MgO + TiO2) and (Na2O + K2O)/(FeO + MgO + TiO2) ratios, and the patterns of trace and rare earth elements suggest that these rocks formed along a destructive plate margin and were derived from a lower crustal source. The magma probably formed by partial melting of lower crustal protoliths (amphibolites). Lower crust contamination with magma derived from partial melting of the upper mantle has an important role in the formation of this intrusive body, and a fractional crystallization of melts in higher crustal levels generated this spectrum of rock types. Mantle-derived gabbroic magmas emplaced into the lower crust are the most likely heat sources for partial melting.
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页码:310 / 328
页数:19
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