1:25万查多岗日幅、布若错幅地质调查成果与进展

1:250 000 Chagdo Kangri and Burogco Sheets in Xizang

关键词:  1:25万  地质调查  查多岗日幅  布若错幅  成果与进展  西藏

Key words:  1:250 000  geological survey  Chagdo Kangri Sheet  Burogco Sheet  development  Xizang

摘要:

侏罗系和上三叠统肖茶卡组中采获较丰富的双壳类、腕足类、珊瑚、菊石、海绵等化石;首次在展金组、曲地组中发现瓣鳃、腕足类、介形虫、放射虫等古生物化石;首次在新近系唢呐湖组中发现瓣鳃类和植物化石;首次在图北湖一带曲地组中发现科化石,初步鉴定为Misellina等,属于典型的暖水相动物,常见于华南地区,说明早二叠世测区已进入古特提斯构造发展阶段;首次在原划若拉岗日岩群中发现放射虫化石。首次在一级河流阶地分别获取¹⁴C年龄值15600±540a和13390±670a,暗示了羌塘高原在更新世以来发生了一次明显隆升过程。新发现多处侏罗系小型生物礁(点礁)。查明若拉岗日岩群的物质组成及变形变质特征,建立了弯岛弧湖蛇绿构造混杂岩带。查明测区中部一带出露新生代花岗斑岩,岩石化学特征反映为橄榄粗玄岩序列,属于同碰撞花岗岩,代表燕山晚期造山作用的产物。对大横山构造带内出露岩浆岩调查取得新的认识,蛇绿岩残片的存在,对认识大横山构造带的构造属性起到重要的作用,肯定了金沙江结合带西延至测区。基本查明测区变质岩的岩石类型其分布特征,查明蓝闪片岩带岩石类型、变形变质特征、空间分布,硬柱石与蓝闪石共生说明了红脊山蓝闪片岩可能属于碰撞造成的产物。查明戈木日岩组(?)中级变质岩系的分布及岩石类型、变形变质特征。查明红脊山构造带的空间分布的变形、变质特征。基本查明了测区内断裂构造形迹的基本特征,甜水河-弯岛湖北西断裂带的是一条控相的左行走滑断层。

Abstract:

There occur abundant bivalves, brachiopods, corals, ammonites and sponges fossils in the Jurassic strata and Upper Triassic Xiaocaka Formation; pelecypods, brachiopods, ostracods and radiolaria fossils in the Zhanjin and Qudi Formations; pelecypods and plant fossils in the Neogene Suonahu Formation, and fusulinids fossils in the Qudi Formation in the Tubeihu region, which is tentatively identified as Misellina belonging to the warm-water faunas and common in southern China. All these evidences show that the above-mentioned surveyed areas developed into the Palaeo-Tethys during the Early Permian. The radiolaria fossils are found for the first time in the formerly Rola Kangri Group Complex. The 14 C age determinations of the Pleistocene soils from the first-grade terraces along the Bailongbing River and Erchagou zones are dated 15 600±540 Ma and 13 390±670 Ma, respectively, implying that the uplifting of the Qiangtang Plateau once took place during the Pleistocene. The Jurassic organic reefs (patch reefs) are observed as well in places. The lithologic compositions, deformation and metamorphism are ascertained for the Rola Kangri Group Complex, and the Wandaohu ophiolitic tectonic mélange zone is delineated. The Cenozoic granite porphyries cropped out in the central zones of the Sheets are assigned to the shoshonite series and syncollisional granites representing the orogenic products created during the late Yanshanian. The presence of the ophiolite relicts in the Dahengshan tectonic zone indicates that the Jinshajiang suture zone extends westwards to the Dahengshan tectonic zone, and thus may provide important data for the approaches to the tectonic attributes of the Dahengshan tectonic zone. The examination of glaucophane-schist as a kind of high-pressure metamorphic rocks and its association with lawsonite shows that the Hongjishan glaucophane-schist may result from the collision. Other work also includes the investigation of rock types, deformation and metamorphism of the medium-grade metamorphic series from the Gomori Formation Complex (?) and Hongjishan tectonic zone, and of structural features of the faults in the surveyed areas. The Tianshuihe-Wandaohu fault is a facies-controlled sinistral strike-slip fault.