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赣东北蛇绿混杂岩带和变质岩系中"放射虫硅质岩"的再研究

王玉净1,杨群1,尹磊明1,舒良树2,楼法生3,王博2   

  1. 1. 中国科学院南京地质古生物研究所,南京 210008; 2. 南京大学地球科学系,南京210093; 3. 江西省地质调查研究院,南昌330201
  • 收稿日期:2006-03-20 修回日期:2006-03-20 出版日期:2006-03-20 发布日期:2006-03-20

The Putative¨Radiolarian Cherts¨from Ophiolitic and MetamorphicComplexes in Northeast Jiangxi:A Re-examination

WANG Yujing1, YANG Qun1, YIN Lei-ming1, SHU Liang-shu2, LOU Fa-sheng3, WANG Bo2   

  1. 1. Nanjing Institute of Geology & Palaeontology, CAS, Nanjing 210008, China ; 2. Department of Earth Sciences, Nanjing University, Nanjing 210093, Chian ; 3. Geological Survey of Jiangxi Province, Nanchang 330201, China
  • Received:2006-03-20 Revised:2006-03-20 Online:2006-03-20 Published:2006-03-20

摘要: 赣东北蛇绿混杂岩和变质岩中的硅质岩时代问题已成为研究华南区域构造和古地理的焦点之一,长期以来被地质学界认为属于江南古陆元古代“板溪群”的范畴。近年来,关于该构造岩系中存在晚古生代放射虫动物群的报道,导致一些学者怀疑该地区传统的构造古地理格局需要重新解释。对此,许多地学工作者提出异议。为了验证上述放射虫动物群的报道的准确性,从古生物学、构造地质学和区域地质调查等多领域进行了野外调查和样品的多次重复系统采集;同时,对已发表的资料进行了再分析。研究显示,赣东北蛇绿混杂岩和变质岩中的硅质岩和扳岩的岩石薄片和微体古生物分析样品中未产出放射虫化石,但是在部分硅质岩和板岩样品中却发现了中-新元古代的疑源类化石。有关硅质岩的主量元素、稀上元素中Ce异常值、(La/Ce)x比值和微量元素等地球化学特征显示其沉积作用与陆源物质有关,沉积环境接近大陆边缘、远离深海远洋环境。

Abstract: The age assignment of the putative radiolarian cherts from the ophiolitic/metamorphic complexes in northeast Jiangxi is widely regarded as one of the crucial issues in the tectonic interpretation of South China. Traditionally,these ophiolitic/lightly metamorphic complexes have been regarded as part of the Proterozoic"Banxi (=Penhsi)Group"of the Jiangnan Uplift.However,recent reports of late Palaeozoic radiolarians from the rock complexes have caused some researchers to question the traditional interpretation of the tectonic and palaeogeographic framework in the region,though other workers are suspicious about these findings. In order to test the reality of the putative radiolarians,we,an interdisciplinary study group including micropalaeontologists,tectonic specialists and regional geologists,conducted field investigations and multiple resamplings of the localities where the reported lossils were collected.We also reanalyzed the published materials of the above mentioned new findings.Our study shows that the putative radiolarian-bearing chert of the ophiolitic complex and the low-grade metamorphic strata do not yield any identifiable radiolarian fossils,although Mesoproterozoic and Neoproterozoic aeritarehs are diseovered from them.Geochemical characteristics such as the element composition, Ce anomaly,La/Ce ratio and trace e1ements indicate that the chert sedimentation is closely related with a terrestrial provenance. a setting far away from the deep oceanic settings.Because our investigation has not verified the Palaeozoic radiolarian findings,five probable causes for the radiolarian reports are discussed.