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板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、稀土元素中Ce异常值、(La/Ce)N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。
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 palaeogeographie 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 mieropalaeontologists, tectonic specialists and regional geologists, conducted field investigations and multiple resamplings of the localities where the reported fossils were collected. We also re-analyzed the published materials of the above-mentioned new findings. Our study shows that the putative radiolarian-bearing chert of the ophiolitie complex and the low-grade metamorphic strata do not yield any identifiable radiolarian fossils, although Mesoproterozoie and Neoproterozoie aeritarchs are discovered from them. Geochemical characteristics such as the element composition, Ce anomaly, Lan/Cen ratio and trace elements 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.
出处
《高校地质学报》
CAS
CSCD
北大核心
2006年第1期98-105,共8页
Geological Journal of China Universities
基金
国家自然科学基金项目(40172004)
中国科学院知识创新重点方向性项目(KZCX2SW129)资助。
关键词
放射虫
硅质岩
板溪群
江南古陆
赣东北
Radiolarians
chert
Banxi Group
Jiangnan Uplift
northeast Jiangxi Province
