新疆富蕴县北部金格岩体斜长花岗岩LA-ICP-MS锆石U-Pb年龄及其地质意义

LA-ICP-MS zircon U-Pb age of the Jinge plagiogranite in northern Fuyun of Xinjiang and its geological implications

对新疆富蕴县北部金格岩体斜长花岗岩进行LA-ICP-MS锆石U-Pb年龄测定,获得了402.7±2.9Ma(MSWD=0.17)的岩浆结晶年龄,表明岩体形成时代为早泥盆世。金格岩体岩性组合为英云闪长岩-奥长花岗岩-花岗闪长岩,具有TTG组合特征,暗示与洋俯冲作用有关。岩石地球化学具有高硅(SiO2=72.55%~77.41%),富钠(Na2O=4.94%~6.63%),贫钾(K2O=0.24%~0.95%)的特征,Al2O3含量为12.11%~15.30%,铝饱和指数在0.94~1.04之间,呈低钾拉斑玄武岩系列、准铝质-弱过铝质、I型花岗岩的特征。稀土元素显示轻稀土元素富集、重稀土元素相对亏损,中等-弱负Eu异常的右倾型,微量元素Rb、Th、U等大离子亲石元素富集,呈明显的"峰",Nb、Ta、Ti等高场强元素强烈亏损,呈明显"TNT"负异常,显示了与俯冲作用有关的岩浆岩特征。结合区域地质资料,金格岩体形成于与洋俯冲作用有关的活动大陆边缘的陆弧环境,金格-正格河地区在早泥盆世处于局部拉张环境。

LA-ICP-MS zircon U-Pb dating of the Jin’ge plagiogranite in northern Fuyun of Xinjiang shows that it was formed at402.7±2.9 Ma(MSWD=0.17). This age reveals that the rocks of the Jinge Plagiogranite were formed in the Early Devonian. The igneous petrotectonic assemblage of the Jin’ge rocks was probably related to oceanic subduction and belonged to TTG series of tonalite-trondhjemite-granodiorite. The granites show high-SiO2, rich Na2O and poor K2O characteristics, with SiO2 content ranging from 72.55% to 77.41%, Na2O from 4.94% to 6.63%, K2O from 0.24% to 0.95%. Al2O3 from 12.11% to 15.30% and A/CNK from 0.94 to 1.04, suggesting a suite of low-K calc-alkaline series rocks, being quasi-sialuminous-wearly per-aluminous I-type granites. The Jin’ge plagiogranite is characterized by enrichment of LREE, depletion of HREE, and strong light and heavy REE fractionation, with weak to moderate Eu negative anomalies. The trace element geochemical characteristics of the pluton show enrichment of Rb, Th, U(LILE) and La, Ce, Sm and depletion of Nb, Zr(HFSE) and Sr, P, Ti, exhibiting features of magmatic rocks related to subduction. In combination with previous studies, the authors hold that the Jin’ge pluton was formed in a continental arc under an active continental margin setting, which was related to the oceanic crust subduction, and this area was locally extensional in the Early Devonian period.