地质学报2017，Vol.91Issue(7)：1454-1466,13.
扬子地块西北缘碑坝地区白玉～1.79 Ga A型花岗岩的发现及其对构造演化的制约
Discovery of the Baiyu ～1.79 Ga A-type Granite in the Beiba Area of the Northwestern Margin of Yangtze Block: Constraints on Tectonic Evolution of South China
摘要
Abstract
We firstly report geochronological and geochemical data obtained for the Baiyu granite from the Beiba area in the northwestern margin of the Yangtze Block.Zircon LA-ICP-MS U-Pb dating results show that the Baiyu granite crystallized at ～ 1790 Ma.The Baiyu granite is characterized by high Si,alkali and FeOT/(FeOT+MgO) ratio,low Mg,Ca,Mn and P,with A/CNK=0.92～0.96,suggesting its metaluminous characteristics.REEs data show that the granite is characterized by enrichment of Ga,Th,Zr and Y,depletion of Sr,P and Ti,high total REE concentration,high LREE/HREE ratio,and strongly negative Eu anomalies,and all these characteristics are consistent with that of A-type granite.The negative εHf(t) values ranging from-12.66 to-10.69 in zircons indicate that the Baiyu granite may derive from partial melting of ancient crust.The geochemical analysis and existing researches show that the Baiyu granite likely formed in the intracontinental rift basin.Combined with previous research results,we propose that in South China exits the records of subduction,collision and rifting related to the Columbia supercontinent.The arc-related granitoid rocks of the Houhe Group in the Beiba area have confirmed that the northwestern margin of the Yangtze Block was an active continental margin environment at about 2.10 Ga;the collision related to the amalgamation of Columbia supercontinent occurred in South China during 2.00～ 1.88 Ga;the continent-continent collision happened in the Kongling area of Yichang city at 2.00 ～ 1.94 Ga and should be earlier than in the southwestern area of Zhejiang Province (1.93～1.88 Ga);the Yangtze Block itself (the western and eastern parts of the Yangtze Block) and the Cathaysia Block (at least the western part) had amalgamated into a unified block in the Paleoproterozoic,associated with the assembling of the Columbia supercontinent.During 1.87～1.82 Ga,the A-type acidic rocks in South China were formed in the post-collisional setting,and were the product of oceanic lithosphere delamination following the collision.The South China entered the intracontinental breakup stage at about 1.79 Ga,which is consistent with that recording the time of Columbia supercontinent breakup in North China and other continents.关键词
古元古代/A型花岗岩/锆石U-Pb定年/Columbia超大陆/构造演化/扬子地块西北缘Key words
Paleoproterozoic/A-type granite/zircon U-Pb dating/Columbia supercontinent/tectonic evolution/northwestern margin of the Yangtze Block引用本文复制引用
邓奇,汪正江,王剑,崔晓庄,马龙,熊小辉..扬子地块西北缘碑坝地区白玉～1.79 Ga A型花岗岩的发现及其对构造演化的制约[J].地质学报,2017,91(7):1454-1466,13.基金项目
本文为国家自然科学基金项目(编号41402103,41372124,41502114,41672112)和中国地质调查局项目(编号DD20160193)联合资助的成果. （编号41402103,41372124,41502114,41672112）
