摘要
通常将华南克拉通的形成理解为扬子陆块与华夏陆块于新元古代沿江南造山带的碰撞拼合,但对两陆块内部的组成和演化关系的了解却相对有限。通过对比神农架地区和扬子陆核区前寒武纪地层碎屑锆石的年龄结构及其原位Hf同位素组成特征,分析了扬子陆块西北部中元古代晚期-新元古代早期的构造演化规律,并对其与统一华南克拉通形成的关系进行了探讨。对前人数据进行统计和对比的结果表明,神农架群碎屑锆石年龄谱中记录了约1.6Ga的年龄峰值,且其原位Hf-O同位素分析指示该期岩浆事件存在幔源物质加入,而相应的岩浆事件(锆石)在扬子陆块陆核区(崆岭地区)前寒武纪地层或岩浆岩单元中缺乏记录。结合神农架群细粒沉积岩Nd同位素地层学特征,指示中元古代时期神农架地区位于活动大陆边缘的构造环境,且神农架群沉积地层的碎屑物质并非由扬子陆核区的崆岭基底岩系经风化-剥蚀作用提供,即非扬子陆核区的边缘盆地。这些证据说明,在新元古代以前,神农架地区与扬子陆核区之间属于两个独立的次一级微陆块。
The South China craton is generally regarded to have formed during the Early Neoproterozoic through collision and welding between the Yangtze and Cathaysia continental blocks along the Jiangnan o- rogenic belt. However, our understanding about internal components and evolutional relationship of the two blocks are relatively limited. The present paper reports a comparative study of detrital zircon geochronology and Hf isotope features of Precambrian sedimentary strata between the Shennongjia region and Kongling area ,the nucleus of the Yangtze block. Accordingly, tectonic evolution of the northwestern Yangtze block during the Late Meso- to Early Neoproterozoic and its correlation with the final forming of the South China craton are discussed. Based on documented data and our statistical treatment,it shows that the detrital zir- cons from the Shennongjia strata is featured by a strike population at about 1.6 Ga,and their Hf and O iso- topes indicate an evident mantle input, but coeval zircons have not been recognized in the nucleus Yangtze continental of the block（the Kongling area）. Coupled with Nd isotope stratigraphy of the Shennongjia fine- grained sedimentary rocks,it is suggested that, during the Late Mesoproterozoic, the Shennongjia region was located at an active continental margin tectonic setting,and provenance of the Shennongjia sedimentary deposits was not derived from the basement of the Yangtze continental nucleus through weathering and e- rosion. This indicates that the sedimentary basin of the Shennongjia strata did not belong to a marginal ba- sin of the Yangtze continental nucleus during the Mesoproterozoic. It is thus suggested that the Shennon- gjia region and the Yangtze continental nucleus were two independent subordinate microcontinents before their Early Neoproterozoic weldim,
出处
《地质科技情报》
CAS
CSCD
北大核心
2014年第2期1-8,共8页
Geological Science and Technology Information
基金
国家自然科学基金项目(40873017
41173048
41303026)
关键词
扬子陆核
神农架地区
锆石年代学
前新元古代
微陆块
Yangtze continental nucleus
Shennongjia area
zircon U-Pb geochronology
Pre-Neoproterozoic
rnicrocontinent
