武当地区的元古宙

DISCUSSION ON THE PROTEROZOIC EONOTHEM OF WUDANG AREA

武当地区的元古宙,其研究内容,主要指陡山沱组以下的变质火山岩系。耀岭河群自上而下划分为吴家梁组、石门沟组及高庙组,底部紫色碎屑岩对应于莲沱组相应沉积物,主体是一套海相火山岩,组成细碧—角斑岩建造,底部具陆相特征,时限推定为700—850Ma之间,对应于新元古代的覆冰纪。原武当山群的杨坪组、档鱼河组及楼台组重新解体。杨坪组改称杨坪群,时限推定在850～1000Ma之间,对应于新元古代的加宽纪;档鱼河组及楼台组新称武当山群,时限推定在1100～2000Ma之间,属古—中元古代,为一套陆相火山喷发岩。晋宁运动在该区有较强的表现,澄江运动次之。杨坪群之底为一古韧性剪切滑脱面,印支得到加强,耀岭河群顶底韧性剪切滑脱带主要属印支期产物。

The Proterozoic Eonothem strata of Wudang area for discussion of the present paper is mainly confined to Yaolinghe group and Wudangshan group under the Doushantuo formation of upper Sinian series. Yaolinghe group is devided into Wujialiang formation, Shimengou formation and Gaomiao formation from top to bottom; It mainly consists of tholeiite and alka-lic spilite-keratophyre of submarine eruption; And there are unstable violet clastic rock on the bottom of Yaolinghe group, which corresponds to Liantuo formation of lower Sinian se-ries in Yangtze paraplatform, has characteristic of continental facies, belongs to the sedi-ments of continental interior rift after Jinning epoch. All of these showed that the sedimenta-ry environments of Yaolinghe group have gradually evolved from early continental shore slop to later a small oceanic basin. Orientation of distribution of the sediments controled by paleo-structure of Northwest direction which was formed in Jinning movement. There is a inter-rupt on the top of Yaolinghe group, and its bottom overlapped on fifferent strata of Wudang-shan group; A ductile shear decollement plane was formed on the top and bottom of Yaol-inghe group in Indo-Chinese epoch; According to these, the present paper infer that the time range of Yaolinghe group is 700～850 Ma., i. e. Yaolinghe group corresponds to Cryo-genian period of Eeoproterozoic. Wudangshan group consists of a suite of basic--acid volcanic rock, pyroclastic rock and pyroclastic sedimentary rock. The volcanic rock has the characteristic of dual-peak type paragenetic association of magmatic eruption; It belongs to the results of the rift of continen-tal margin. The Yangping formation, Dangyuhe formation and Lutai formation of former Wudangshan group are classified again in this paper. The former Yangping formation is new-ly called Yangping group, that is equal to Qingbaikou system of North China and corre- sponds to Tonian period. The former Dangyuhe formation and Lutai formation incorporate into newly Wudangshan group, of which time range is inferred from 1100 to 2000 Ma. and its geological time belongs to Paleoproterozoic-Mesoproterozoic. There is a important structu-ral level along the contact between Yangping group and Wudangshan group, within widely developed’A’type folds,’scabbard’shape folds and S-C fabrics. This is a paleo-ductile shear decollement plane, which was formed in Jinning epoch and was developed in later Indo-Chinese epoch.