东昆仑造山带海德乌拉铝质A型流纹岩成因及其意义

东昆仑造山带古生代后碰撞岩浆岩的成因及后碰撞伸展环境的形成机制一直备受争议。本文选择东昆仑造山带古生代海德乌拉流纹岩开展锆石U-Pb-Hf同位素地质学及全岩地球化学研究,分析其成因并探讨后碰撞伸展环境的起始时间和形成机制。锆石LA-ICP-MS U-Pb同位素定年结果显示,海德乌拉流纹岩形成于426Ma,属于志留纪罗德洛世岩浆活动产物。样品显示高钾钙碱性-钾玄岩系列岩石特征;其A/CNK值为1.04-1.18,属于过铝质-强过铝质岩石。在原始地幔标准化微量元素图解上,样品显示Th、U和Pb等元素相对富集,Nb、Ta、Ti、Ba和Sr等元素相对亏损的特征;在球粒陨石标准化稀土元素图解上,海德乌拉样品显示轻稀土相对富集且具有明显Eu负异常(δEu=0.03-0.06)。海德乌拉流纹岩显示出高FeO^T/MgO和10⁴×Ga/Al比值以及高场强元素总量(Zr+Nb+Ce+Y),属于A型岩浆岩范畴。样品的锆石ε_Hf(t)为+0.60～+2.39,对应的二阶段模式年龄介于1285～1370Ma之间。元素和同位素地球化学特征显示海德乌...

Genesis and implications of peraluminous A-type rhyolite in the Haidewula area, East Kunlun Orogen

The initiation time and formation mechanism of the post-collisional extension in the East Kunlun Orogenic Belt (EKOB) have been controversial. A combined study of zircon U-Pb chronology, geochemistry, and Hf isotope composition has been carried out for the Silurian rhyolite in the Haidewula region of the EKOB, to further reveal their genesis and formation mechanism. Zircon LA-ICPMS U-Pb isotope dating reveals that the Haidewula rhyolite formed at 426Ma, representing Silurian Radero magmatic activity. The samples belong to the high -K calc-alkaline to shoshonite series, and display peraluminous to strong peraluminous affinity with A/CNK ratio ranging from 1. 04 to 1. 31. In the primitive -mantle normalization trace element diagrams, the samples show Th, U, and Pb enrichment, and Nb, Ta, Ti, Ba, and Sr depletion. They are also rich in LREE with strongly negative Eu anomalies (delta Eu = 0. 03 similar to 0. 06). The Haidewula rhyolite belongs to A-type magmatic rock with high FeOT/MgO and 10(4) x Ga/Al ratios, and high contents of high -field strength element ( Zr + Nb + Ce + Y). The samples have zircon epsilon(Hf) (t) values of 0. 60 similar to 2. 39 with corresponding Hf isotope two -stage model age ranging from 1285Ma to 1370Ma. Elemental and isotopic geochemical characteristics reveal that the Haidewula A type rhyolite was formed by high -temperature, middle -crust pressure melting of Ordovician felsic igneous rocks. Combined with the chronologic and geochemical characteristics of Paleozoic magmatic rocks and metamorphic rocks, it is suggested that the EKOB was in a typical post-collisional extension during the Silurian Roderlo epoch, which may have been influenced by the post-collisional lithospheric delamination of the northeastern margin of Gondwana.