SIGNIFICANCE AND CHARACTERISTICS OF OPHIOLITE SUITE IN LAJI SHAN, SOUTHERN QILIAN MOUNTAINS, QINGHAI PROVINCE,CHINA

Laji Shan is located in the eastern part of Qinghai Province,sandwiched between Xining and Hualong Basins.It is about 250km long and 10～20km wide from Riyueshan in the west to Minheguanting in the east.Laji Shan belongs to the Caledonian orogenic belt.Its basement consists of the rocks of Palaeo\|Protero zoic Hualong Group (Pt 1 hl ) and Neo\|Proterozoic Huangzhong Group (Pt\-3 h ).There are ptygmatic folds,closely linear type folds,strongly structural d ifferentiation and schistosity developed,suggesting that the basement underwent deep seated ductile deformation.The main part of Laji Shan is composed of Early\|Palaeozoic marine facies volcanic rocks and clastic sedimentary rocks,and suffered greenschist facies metamorphism and brittle\|ductile deformation.Others are composed of Ea rly\|Palaeozoic basic and ultrabasic rocks,intermediate\|acidic intruded rocks a nd dike rocks.Devonian molasse formation in Laji Shan is in uncomfortable contac t with underlying strata.Jurassic and Cretaceous systems are intermont basin dep osits,corresponding to a cover.

青海拉鸡山早古生代“开”、“合”演化的地球化学证据及成矿

位于青藏高原北部的拉鸡山下古生界为典型的火山—复理石活动类型建造,并赋含有丰富的矿产。本文基于地质、地球化学的方法,对拉鸡山早古生代火山盆地的“开”、“合”历史及“开”、“合”与铜、金等多金属矿产形成作用的关系进行了探索。认识到拉鸡山早古生代经历了3个旋回的“开”、“合”;拉鸡山铜、金等多金属矿源层形成于“开”的阶段,而“合”的作用最终促使矿物质活化、迁移和富集。“开”、“合”与成矿关系的认识,无疑会增加在成矿规律方面的知识,也有益于指导找矿。

青海拉脊山造山带早古生代火山岩

作者对青海拉脊山造山带早古生代火山岩的时空分布进行了简介，对火山岩的系列、类型、名称、组合进行了确定，对火山岩产出的构造环境及演化过程进行了分析，对开合作用的距离、时间、速度进行了估算，对蛇绿岩套特点与古地幔事件进行了讨论，对火山岩岩浆的来源及演化进行了探索。

青海天重峡金矿地球化学特征及矿床成因

在详细分析拉脊山地区天重峡金矿床成矿背景、矿床地质特征的基础上,对赋矿玄武岩进行了研究。岩石地球化学特征表明为低钾钙碱性岩石,稀土元素Eu具弱负异常特征,微量元素中Ba、Sr、Th、Ta、Ti相对贫化,Rb、K、Ce、Hf则相对富集。硫化物δ34S变化范围为4.49‰~5.8‰,均值为5.14‰,显示深源硫的特征。综合研究认为,天重峡金矿床为与岩浆期后热液作用有关的构造蚀变岩型金矿床。

青海拉脊山晚寒武世六道沟组火山岩岩石地球化学特征分析

通过对青海拉脊山晚寒武世六道沟组火山岩的岩石地球化学特征分析,判定青海拉脊山晚寒武世六道沟组火山岩的主要存类型,并阐述了六道沟组火山岩属于初始扩张的小洋盆环境,具有多岛洋的构造格局。通过岩石地球化学图解判别,推测拉脊山结合带内的中晚寒武世可能具有蛇绿混杂岩的特征,并划分了主要地幔类型。