Reworking of the juvenile crust in the Late Mesozoic in North Qinling, Central China
Reworking of the juvenile crust in the Late Mesozoic in North Qinling, Central China
复制标题
北秦岭晚中生代新生地壳的改造
DOI：
10.1007/s12583-021-1521-0
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发表时间：
2022
影响因子：
3.3
通讯作者：
CHEN Fukun
中科院分区：
文献类型：
--
作者：
XUE Ying-Yu;LIU Hai-Yang;WANG Zhi-Yi;SUN Wei-Dong;CHEN Fukun
秦岭造山带是三叠纪南北陆块碰撞的产物。中生代花岗岩类广泛分布于该造山带内，其范围从三叠纪到白垩纪，为认识造山带的地壳演化和地球动力学演化提供了极好的线索。三叠系主要分布在南秦岭，白垩系主要分布在北秦岭。太白杂岩体位于两带的交汇处。本文介绍了太白杂岩体中出露的晚中生代花岗岩和微粒包体的锆石U-Pb定年、元素和Sr-Nd同位素地球化学数据。花岗岩和MME产生一致的U-Pb锆石年龄为124 - 118 Ma，表明它们是晚中生代岩浆活动的产物。花岗岩的成分为高钾、钙碱性、弱过铝质，以富集大离子亲石元素（如，Rb、Ba）、高场强元素的耗尽（例如，Nb、Ta、Zr、Ti）和7.64至63.6的可变Sr/Y比。MgO、Cr和Ni含量低，表明岩浆主要为壳源岩浆。花岗岩和MME的Sr-Nd同位素组成均相对亏损（初始87 Sr/86 Sr为0.7044 ~ 0.7067，初始εNd值为-3.4 ~-2.6），表明岩浆起源于较年轻的地壳岩石。这些Sr-Nd同位素特征明显不同于秦岭造山带其他地区晚中生代花岗岩类的Sr-Nd同位素特征，后者形成于更古老的富集源区，而来自地幔或新生地壳的贡献可以忽略不计。我们提出了一个在晚中生代的年轻地壳改造事件，是由构造伸展和随后发生在中国东部的软流圈上涌触发的。
The Qinling Orogen resulted from the collision between the North and South China blocks in the Triassic. Mesozoic granitoids, ranging from the Triassic to the Cretaceous, are widely distributed in this orogen, and they provide excellent clues for understanding the crustal evolution and geodynamic evolution of the orogenic belt. The Triassic belt is mostly located in the South Qinling, whereas the Cretaceous belt is located mostly in the North Qinling. The Taibai complex pluton is located at the conjunction of the two belts. Here we present a data set comprising zircon U-Pb dating and elemental and Sr-Nd isotopic geochemistry for Late Mesozoic granite and microgranular enclaves (MME) exposed in the Taibai complex pluton. The granite and MME yield concordant U-Pb zircon ages of 124 to 118 Ma, indicating that they were products of roughly simultaneous magmatism in the Late Mesozoic. The granite rocks are high-K, calc-alkaline, and weakly peraluminous in compositions, and they are characterized by enrichment in large ion lithophile elements (e.g., Rb, Ba), depletion in high field strength elements (e.g., Nb, Ta, Zr, Ti), and variable Sr/Y ratios of 7.64 to 63.6. Low MgO, Cr, and Ni contents imply that the magma(s) were essentially crust-derived. Both the granite and the MME show relative depletion in Sr-Nd isotopic composition (initial 87Sr/86Sr of 0.704 4 to 0.706 7, initial εNd values of -3.4 to -2.6), suggesting that the magma(s) originated from juvenile crustal rocks. These Sr-Nd isotopic characteristics are significantly different from those of other Late Mesozoic granitoids exposed elsewhere in the Qinling orogenic belt, which formed from much older and enriched sources and with negligible contributions from mantle or juvenile crust. We propose a reworking event of the juvenile crust during the Late Mesozoic that was triggered by the tectonic extension and subsequent asthenospheric upwelling that occurred in eastern China.