西藏仲巴地区曲嘎组的拆解

根据1∶5万仲巴地区区域地质调查，对雅鲁藏布江缝合带西段夹持于2套混杂岩之间的仲巴微地体原二叠系曲嘎组进行了拆解。研究认为：①原曲嘎组可以解体为3套地层，分别是下古生界的奥陶系—志留系紫曲浦群、上古生界泥盆系纳登尔组和石炭系—二叠系曲嘎群，新建曲嘎群与原曲嘎组没有直接对应或者级别关系；②紫曲浦群以变质碳酸盐岩为主，下部紫曲电站组为紫红色、灰色大理岩与结晶灰岩组合，属中—晚奥陶世，上部紫曲石组以紫红色大理岩为特征，暂归志留纪；③纳登尔组由一套灰色千枚状板岩和钙质片岩组成，上部结晶灰岩增多，时代为泥盆纪，可归属马攸木群；④曲嘎群可划分为3个组：岗珠淌组，以灰色、灰绿色板岩、粉砂岩为主，向上砂岩和灰岩增多，属于石炭纪—早二叠世（乌拉尔世）早期；仲巴组，以肉红色灰质晶粒白云岩及杂色生物屑云质灰岩为特点，分为2个岩性段，属于早—中二叠世（乌拉尔世—瓜德鲁普世早中期）；卡扎勒组以深灰色钙质板岩为主或夹结晶灰岩和砂岩或互层，属于中—晚二叠世（瓜德鲁普世—乐平世）；⑤仲巴地区曲嘎组的拆解在仲巴微地体西部和老仲巴以东的应用有待证实，其在岩性上与相邻地体同期地层有较大差别，但在生物群组成方面具有相似性。

The disaggregation of the Permian Quga Formation in Zhongba area,southwestern Tibet

On the basis of the recent 1∶50000 regional geological investigation in Zhongba area, southwestern Tibet, the so-called Permian Quga Formation was studied in eastern Zhongba microterrane, which is sandwiched between two branches of the western Yarlung Zangbo suture. Based on the results obtained, the authors hold that the former Quga Formation was disaggregated into three parts, i.e., the Ordovician-Silurian Ziqupu Group, the Devonian Nadeng'er Formation, and the Carboniferous-Permian Quga Group. The Ziqupu Group characterized by metamorphic carbonate rocks can be divided into two parts: the lower is named the Middle-Upper Ordovician Ziqudianzhan Formation which is composed of purplish red and gray marble and crystalline limestone, and the upper part is named the Silurian Ziqushi Formation which is composed of purplish red marble. The Nadeng'er Formation consists of gray phylitic slate and calcic schist with upward-increasing crystalline limestone, and is tentatively assigned to the Mayoumu Group. The Quga Group is subdivided into three parts. The lower part named the Gangzhutang Formation comprises gray, grayish green slate and siltstone with upward-increasing sandstone and limestone, and is dated as belonging to Carboniferous-early Early Permian. The middle part, Zhongba Formation, is characterized by pinkish red dolomites and variegated dolomitic bioclastic limestone, and belongs to the Early-Middle Permian, as evidenced by fossils of brachiopods, bryozoans and corals. The upper part named the Kazhale Formation is dominated by dark gray calcic slate intercalated and/or interbedded with limestone and sandstone, belonging to the Middle-Late Permian as shown by fossils. Some problems remain unsolved: whether the disaggregation of the Quga Formation could be applied to other areas out of Zhongba area or not; the lithologic character is remarkably different from that of other areas in spite of the similarity in biota.