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عنوان
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Petrogenesis and geodynamic implications of an Ediacaran (550 Ma) granite complex (metagranites), southwestern Saqqez, northwest Iran
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نوع پژوهش
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مقاله چاپشده در مجلات علمی
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کلیدواژهها
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,Ediacaran granite ,Subcontinental lithospheric mantle Gondwana ,Sanandaj-Sirjan zone Proto-Tethys
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چکیده
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The late Neoproterozoic (Ediacaran) igneous and metamorphic complex that constitutes the main part of the Precambrian basement in Iran is exposed in southwestern Saqqez in the northern Sanandaj-Sirjan zone (SaSZ), which is called the Ediacaran complex in this study. New zircon UüPb dating from five samples shows that the crystallization of the main granitic bodies happened 559 to 547 Ma in the late Neoproterozoic (Ediacaran). The Ediacaran complex in southwest Saqqez includes: (a) metarhyolite-sedimentary sequences; (b) metagranite; and (c) metadiorite-monzonitic bodies with some late stage dikes. Whole-rock compositions of the granites show high contents of SiO2 (62.9ü80.5 wt.%), K2O (0.1ü4.0 wt.%), and Al2O3 (9.7ü19.1 wt.%) with low contents of MgO (0.2ü2.4 wt.%), Fe2O3 (0.7ü6.9 wt.%), and TiO2 (0.1ü1.0 wt.%). Negative εNd(t) (−5.2 to −3.0) and high initial ratios of 87Sr/86Sr (0.7101 to 0.7328) indicate the main role of crustal components in the sources of the granitic bodies. The metadiorite-monzonitic rocks have high contents of Fe2O3 (6.4ü10.7wt.%), MgO (6.6ü8.1 wt.%), CaO (5.7ü9.7 wt.%), and TiO2 (0.4ü1.2 wt.%) with positive εNd(t) (+2.9 to +4.4) values. Whole rocks compositions and 87Sr/86Srü143Nd/144Nd isotope ratios show different sources for the metagranite and metadiorite-monzonite groups, which are consistent with continental crust and subcontinental lithospheric mantle released melts, respectively. The high contents of Th with low contents of the transitional elements such as Nb-Ta with calc-alkaline affinity of the both intermediate and acidic rocks infer the relation of these rocks to an active continental margin over the subduction zone in the late Neoproterozoic which is associated with Proto- Tethys subduction beneath northern Gondwana in that time.
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پژوهشگران
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یوشی هیرو آساها (نفر چهارم)، حاجی حسین عزیزی (نفر سوم)، محمد معانی جو (نفر دوم)، نرگس دانشور (نفر اول)
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