扬子陆块北缘古-中元古代构造格架:来自马鞍山岩群物源示踪的启示  

Paleoproterozoic to Mesoproterozoic Tectonic Framework on the Northern Yangtze Block: Inspirations from provenance of the Ma'anshan Group

作　　者：徐大良 邓新 彭练红 张维峰 刘浩 金鑫镖 彭旎 金巍 XU Da-Liang;DENG Xin;PENG Lian-Hong;ZHANG Wei-Feng;LIU Hao;JIN Xin-Biao;PENG Ni;JIN Wei(Wuhan Center,China Geological Survey(Geosciences Innovation Center of Central South China),Wuhan 430205,Hubei,China;School of Earth Sciences,Yunnan University,Kunming 650500,Yunnan,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质调查局武汉地质调查中心(中南地质科技创新中心),湖北武汉430205 [2]云南大学地球科学学院,云南昆明650500 [3]中国地质科学院地质研究所,北京100037

出　　处：《华南地质》2023年第2期235-258,共24页South China Geology

基　　金：中国地质调查局项目(DD20221634,DD20160030)。

摘　　要：识别并研究扬子陆块北缘古-中元古代的岩浆-变质-沉积事件,是全面理解该陆块古-中元古代构造演化的基础,也是重建其在Columbia超大陆向Rodinia超大陆转变阶段角色和位置的前提。本文对扬子陆块北缘桐柏地区马鞍山岩群的3件样品进行了碎屑锆石U-Pb定年和原位Lu-Hf同位素分析。结果显示,该岩群下部a岩组片岩中最年轻的单颗粒锆石谐和年龄为1725±30Ma,上部b岩组大理岩中最年轻的一批锆石谐和年龄为1626~1606 Ma,大致分别限定了其最早沉积时代,表明扬子陆块北缘桐柏地区可能存在中元古代早中期沉积地层。马鞍山岩群的碎屑锆石年龄谱范围是2643~1606 Ma,呈现出显著的1820 Ma单峰频谱特征,其潜在物源区可能主要来自于扬子陆块北缘外部的桐柏-大别-苏鲁地区(现已卷入中生代高压-超高压变质带)。现有资料指示,扬子陆块北缘在古-中元古代时期可划分为内部和外部两个大地构造单元,二者在古元古代呈现出截然不同的构造演化过程,各单元内中元古代早中期地层的物源区显著不同,可能分别靠近伸展环境的超大陆核部和汇聚环境的超大陆边部。The Northern Yangtze Block(NYB) consists of extensive Archean lithosphere and witnessed nascent stage(~2.0 Ga) of Columbia-assembly tectonics, but was less involved in subsequent supercontinent breakup. Identification and study the Mesoproterozoic magmatic-metamorphic-sedimentary events are the basis for seeking the Paleo-Mesoproterozoic tectonic evolution of the NYB, as well as the premise for reconstructing its role and location in the transition from Columbia to Rodinia supercontinent. In this paper, the detrital zircon U-Pb geochronology and in-situ Lu-Hf isotope analysis of three samples from the Ma'anshan Group in the Tongbai area of the NYB is studied. The results show that the youngest concordant zircon grain of the a Formation in the lower part of the Ma'anshan Group is 1725±30 Ma, and those of the b Formation in the upper part are concentrated among 1626 Ma and 1606 Ma, implicating the early to middle Mesoproterozoic sedimentary strata may exist in the Tongbai area of the NYB. Zircons grains of the Ma'anshan Group range from 2643 Ma to 1606 Ma, showing a significant 1820 Ma unimodal peak spectral, and their potential provenance should be mainly from the Tongbai-Dabie-Sulu area, exterior Northern Yangtze Block, which is now involved in the Mesozoic high to ultra-high pressure metamorphic belt. The available data indicate that the NYB can be divided into interior(INYB) and exterior(ENYB) tectonic units in Paleo-Mesoproterozoic with distinct rock configuration and tectonic evolution during the Paleoproterozoic. The INYB may be involved into an interior collision orogenic system in the Paleoproterozoic, while the ENYB likely experienced an exterior subduction process. The provenance of the early to middle Mesoproterozoic strata in the INYB and ENYB are significantly different, which may be close to the core in the extensional environment and the edge in the convergent environment of the Columbia supercontinent, respectively.

关 键 词：扬子陆块 古元古代 中元古代 碎屑锆石 Columbia超大陆 

分 类 号：P534.3[天文地球—古生物学与地层学] P544[天文地球—地质学]