青藏高原聂荣微陆块早古生代片麻状花岗岩地球化学、锆石U-Pb年龄和Lu-Hf同位素特征及构造背景

报道了西藏中部聂荣微陆块片麻状花岗岩的全岩地球化学、LA-ICP-MS锆石U-Pb年龄和Hf同位素研究资料。获得花岗岩中锆石206Pb/238U年龄为516±3 Ma（n=20，MSWD=1.60）。花岗岩属于高钾钙碱性岩石系列，具有类似I型花岗岩的地球化学特征，其稀土元素配分模式为轻稀土元素富集的右倾曲线，伴随负Eu异常，而微量元素蛛网图表现出Ba、Nb、Ta、Sr、P、Ti亏损和Rb、Th、Pb相对富集的分布特征。花岗岩具有富集的锆石Hf同位素组成（εHf（t）= -3.0~-0.1）、古老的锆石Hf模式年龄（tDMC= 1472~1659 Ma）和较高的Mg#值（32~47），可能形成于地幔岩浆对元古宙沉积物质的改造。综合上述测试结果及区域地质背景，推测聂荣微陆块寒武纪片麻状花岗岩应当是冈瓦纳大陆北缘安第斯型岩浆弧的一部分。

Geochemistry,zircon U-Pb age,Lu-Hf isotopes and tectonic setting of the Early Paleozoic gneissic granites from the Nyainrong microcontinent,Tibet Plateau

The geochemistry of the Cambrian gneissic granite from the Nyainrong microcontinent, central Tibet, and its zircon LA-ICP-MS U-Pb ages and Hf isotope data are reported.The granite was formed at 516±3 Ma(n=20, MSWD=1.60), and belongs to high-K calc-alkaline I-type.It is characterized by negative Eu anomaly and right-dip chondrite-normalized rare-earth element patterns, enrichment of Rb, Th, and Pb, and depletion of Ba, Nb, Ta, Sr, P, and Ti.It exhibits negative zircon εHf(t) values of -3.0~-0.1 and relatively high Mg# values of 32~47, and yields old zircon Hf model age of 1472~1659 Ma, suggesting a magma source of Proterozoic sedimentary materials modified by mantle-derived magma.Based on the above study results and regional geological setting, it is suggested that the Cambrian gneissic granite from the Nyainrong microcontinent could be attributed to one part of the Andean-type magmatic arc along the northern margin of the Gondwana supercontinent.