1:25万松西幅、温泉幅地质调查成果与进展

1:250 000 Sumxi and Wenquan Sheets in Xizang and Xinjiang

关键词:  1:25万  地质调查  松西幅  温泉幅  成果与进展  西藏  新疆

Key words:  1:250 000  geological survey  Sumxi Sheet  Wenquan Sheet  development  Xizang  Xinjiang

摘要:

地层方面,共确定组级地层单位27个,段级地层单位9个、非正式地层单位2个,绝大多数地层化石丰富,时代依据可靠;在拉竹龙组采获大量早中泥盆世珊瑚、腕足化石,且拉竹龙组不整合覆盖于奥陶系和志留系之上;发现了几个重要的不整合界面;在三岔口西部发现丰富的早奥陶世化石,建立了三岔口组,是羌塘地区目前有化石控制的最低层位;在龙木错北新发现志留纪地层;在测区中西部起用了中侏罗统龙山组;发现了大量新近系松西组安山质火山岩沉积盆地;在舒木营地—龙木错—多梁山一带发现3个古近纪陆相地层蚂蟥山组;在拉竹龙组中发现规模较大的珊瑚礁体,可细分出礁基、礁格架、礁前塌积角砾及礁间相沉积;在喀喇昆仑地层区发现台地相的石炭—二叠纪地层;在上石炭统擦蒙组中发现冰川坠石沉积。岩石方面,在羌塘北部首次发现碱性花岗岩类;详细调查了古生代辉绿玢岩岩石地球化学特征;发现大量古近纪安山质火山岩。构造方面,识别出3期褶皱,发现间隔状分布的南北向构造带,对龙木错-双湖断裂带、阿尔金断裂带和南北向断裂的研究取得进展。

Abstract:

Twenty-seven formation-scale and nine member-scale stratigraphic units, of which two are informal stratigraphic units, are established in the 1:250 000 Sumxi and Wenquan Sheets in Xizang and Xinjiang. Various fossils abound in most of the strata, especially abundant Early and Middle Devonian corals and brachiopods in the Lazhuglung Formation. The Lazhuglung Formation overlies unconformably the Ordovician and Silurian strata. Several important unconformities in northern Qiangtang are found to be intermediate between the Middle Triassic Heweitan Formation and its underlying strata, Heweitan Formation and its overlying Upper Triassic Keleqinghe Formation, Lower Jurassic Bagongbulansha Formation and its underlying Keleqinghe Formation, and Lower-Middle Jurassic Longshan Formation and Bagongbulansha Formation. Abundant Early Ordovician fossils are identified in the western part of Sanchakou. The Sanchakou Formation is redefined as the lowest fossil-controlled horizons in the Qiangtang region. The Silurian strata are recognized in the area north of the Lungmuco area. The Middle Jurassic Longshan Formation is used in the western and central parts of these Sheets. There exists a number of Neogene andesitic volcanic sedimentary basins named the Sumxi Formation, and three Paleogene continental basins named the Paleogene Mahuangshan Formation in the Shumuyingdi-Lungmuco-Duoliangshan zone. There occur larger-scale coral reefs that may be subdivided into reef base, reef frame, reef-front collapse breccias and inter-reef deposits. The platform Carboniferous-Permian strata are found in the Karakorum stratigraphic province, and glacial dropstone in the Upper Carboniferous Cameng Formation. The alkaline granites are observed for the first time in northern Qiangtang. The geochemistry and tectonic settings of the Palaeozoic diabase-porphyrite are also treated in detail. The additional discovery includes abundant Paleogene andesitic volcanic rocks arranged along the major faults. Other advances include the discovery of the gap-aligned NS-trending structural zones, and the examination of Lungmuco-Shuanghu fault, Altun fault and other NS-trending faults.