摘要
Abstract
The gneiss in the Dongping area was formed by medium-high grade regional metamorphism of Dakendaban group,which can be divided into granitic,plagioclase and calcareous gneisses.The major elements show the contents of SiO2 (57.47% ~75.32%),(Na2O +K2O) (2.62% ~7.40%),Al2O3 (11.08% ~16.29%)and A/CNK(0.84~1.78),indicating the Dongping gneiss is of intermediate-acid,high calc-alkaline and per-aluminous series.Analysis of REEs demonstrates the curves of LREEs enrichment and HREEs losses with right deviation.Most of samples have weak nega-tive europium anomalies.The trace elements suggest enriched Rb,Ba,and relatively depleted Nb,Ta,and Sr.According to petrologic and geochemical char-acteristics,the original rock type of plagioclase gneiss and calcareous gneiss is I-type granite with the feature of high potassium calc-alkaline,formed by the mixture of crust and mantle source materials.Differently,the original rock type of granitic gneiss belongs to the terrigenous S-type granite,formed by the condensation and crystallization of partially melting crust material.In combination with tectonic setting,this study suggests that the Dongping gneiss formed in an island-arc environment of an Early Paleozoic active continental margin.It reflects that the Dongping area experienced the plate convergence and collision of the northern Qaidam basin,northern Altyn fault and northern Qilian terrane after the Proto-Tethys closure.关键词
片麻岩/成因类型/构造背景/东坪地区/柴北缘Key words
gneiss/genetic types/tectonic setting/Dongping area/northern margin of Qaidam basin分类
天文与地球科学
