北羌塘地区北缘上三叠统若拉岗日岩群地层特征及沉积环境

Stratigraphic characteristics and sedimentary environments of the Upper Triassic Rola Kangri Group Complex on the northern margin of North Qiangtang continental block

关键词:  若拉岗日岩群  上三叠统  中基性火山岩  地层特征  沉积环境

Key words:  Rola Kangri Group Complex  Upper Triassic  intermediate to basic volcanic rock  stratigraphic characteristics  sedimentary environment

摘要:

北羌塘地区北缘上三叠统若拉岗日岩群分布于北羌塘陆块与拉竹龙-金沙江缝合带之间的若拉岗日冲断带,以砂泥质复理石、中基性-超基性火山岩及大理岩组合为特征,夹晚二叠世灰岩岩片及蛇绿岩残块。岩石低-中级变质,构造变形强烈,顶底均被断层切割断失,为总体无序、局部有序的构造-地层体。若拉岗日岩群中基性火山岩具有洋岛和岛弧型成因,它是金沙江洋盆在晚三叠世向南俯冲,而在其南缘形成的岛弧带沉积。在若拉岗日岩群采获大量上三叠统常见的孢粉、腕足、双壳类生物化石,其玄武岩年龄值为201±4Ma (Ar-Ar法),时代属诺利期。

Abstract:

The Upper Triassic Rola Kangri Group Complex on the northern margin of the North Qiangtang continental block occurs in the Rola Kangri thrust fault sandwiched between the North Qiangtang continental block and Lazhuglung-Jinshajiang suture zone,and consists of sandy and muddy flysch,intermediete,basic and ultrabasic volcanic rocks,and marble associations intercalated with the Late Permian limestone and ophiolite relicts.These rocks are slightly to moderately metamorphosed and highly deformed.The intermediate to basic volcanic rocks in the Rola Kangri Group Complex have an oceanic island and island-arc origin and generated during the southward subduction of the Jinshajiang oceanic basin during the Late Triassic.Abundant Late Triassic fossils including sporopollen,brachiopods and bivalves collected from the Rola Kangri Group Complex and Ar-Ar ages dated 201±4 Ma of basalt indicate that the Rola Kangri Group Complex should be traced back to the Norian(Late Triassic).