扬子克拉通北缘新元古代A型花岗岩的发现及大地构造意义

发布时间：2018-06-27 17:43

本文选题：扬子克拉通北缘 + 大磊山地区　；参考：《地球科学》2017年06期

【摘要】：对大磊山片麻状花岗岩的研究可以为新元古代罗迪尼亚超大陆在扬子克拉通北缘裂解提供约束.在详细野外地质调查和岩相学工作基础上,对该片麻状花岗岩进行了系统的锆石U-Pb定年、全岩地球化学和锆石原位Lu-Hf同位素分析,研究发现,这些片麻状花岗岩富硅(SiO_2=73.18%~77.40%)、碱(Na_2O+K_2O=8.07%~8.70%)、贫铝(Al_2O3=12.11%~13.92%)和镁(MgO=0.10%~0.34%),富集LILE、Ga、Rb、Th,Zr和Hf元素具明显正异常,Nb、Sr、P、Ti等元素具明显负异常,表现出后造山A型花岗岩(A2型)的特征.这些花岗岩中,锆石均具典型的震荡环带,Th/U比值均大于0.5,为岩浆成因;两个样品的LA-ICP-MS(laser ablation inductively coupled plasma mass spectrometry)锆石的谐和分别是:801.3±3.0 Ma(MSWD=0.62,n=21)和796.1±6.3Ma(MSWD=1.70,n=15),其中一个样品继承锆石谐和年龄为845.0±12.0Ma(MSWD=1.30,n=6),表示他们是新元古代岩浆结晶产物.锆石εHf(t)值变化于-7.5~+8.0,正εHf(t)值对应的亏损地幔单阶段模式年龄(tDM1)为1 242~1 059Ma,负εHf(t)值对应的地壳两阶段模式年龄(tDM2)为1 636~1 981Ma,显示该地区存在的最古老物质是古元古代(老至1 981Ma).这些数据结果表明形成大磊山A型花岗岩的初始物质主要为元古代古老地壳物质,暗示该岩浆源自于壳幔混合作用,幔源端元可能源自于伸展拉张背景下地幔岩浆上涌.结合区域研究成果认为,该A型花岗岩的形成与罗迪尼亚超大陆聚合后-裂解中的陆缘弧后拉张环境所引起的深部古元古代地壳拉张垮塌有关.
[Abstract]:The study on the granitic granitoids in Dareishan can provide a constraint for the breakup of the Neoproterozoic Rodinia supercontinent in the northern margin of On the basis of detailed field geological survey and petrographic work, zircon U-Pb dating, whole-rock geochemistry and in-situ Lu-Hf isotopic analysis of zircon were carried out for the granitic granites. These granitic granites are rich in silicon (77.40%), alkaline (Na2OK2O8.07%), Al2O3 (Al2O3 12.1111 + 13.92%) and magnesium (MgO0.100.34%), and the enrichment of LILEGaRbSH-Zr and HF elements have obvious negative anomalies, showing the characteristics of post-orogenic A-type granite (A2 type). Among these granites, zircon has a typical Oscillation belt and the ratio of Th- / U is more than 0.5, which is magmatic origin. The two samples of LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) zircon are: 801.3 卤3.0 Ma and 796.1 卤6.3 Ma, respectively. One of them inherits 845.0 卤12.0Ma (MSWD1.30n6), indicating that they are the product of Neoproterozoic magma crystallization. The zircon 蔚 HF (t) varies from -7.5 to 8.0, the depleted mantle model age (tDM1) corresponding to the positive 蔚 HF (t) is 1 242U 1 059 Ma, and the negative 蔚 HF (t) corresponding to the crustal two stage model age (tDM2) is 1 6366 1 981Ma. it shows that the oldest material in this area is Paleoproterozoic (old to 1 981Ma). These data indicate that the primary material forming the Dareishan A-type granite is mainly the ancient Proterozoic crustal material, implying that the magma originated from the crust and mantle mixing, and the mantle source end element may originate from the mantle magma upwelling in the extensional and extensional background. Based on the regional research results, it is concluded that the formation of the A-type granite is related to the extensional collapse of the ancient Gu Yuan crust caused by the extensional environment of the continental margin back-arc in the post-pyrolysis of the Rodinia supercontinent.
【作者单位】：中国地质大学地球科学学院;湖北省地质调查院;中国地质调查局南京地质调查中心;东华理工大学地球科学学院;
【基金】：国家自然科学基金重点项目(No.41230206-1);国家自然科学青年基金项目(No.41402075) 中国地质调查局项目“大悟等4幅1∶5万区域地质矿产调查”(No.12120114048301)
【分类号】：P548;P588.121

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