Geological and structural development of the Tibetan Plateau

1.青藏高原拉萨-那曲地区花岗岩主要分为晚白垩世-古近纪磁铁矿系列和早白垩世-中新世钛铁矿系列。磁铁矿系列花岗质岩石由花岗闪长岩和花岗岩组成，具有低的^<87>Sr/^<86>Sr初始值，分布于拉萨-那欧地区南部。白垩纪钛铁矿系列的钛铁矿主要由浅色花岗岩组成，具有高的^<87>Sr/^<86>Sr初始值，分布于北方。中新世钛铁矿系列的花岗质岩石侵入到岩石的中部。磁铁矿系列花岗岩和钛铁矿系列花岗岩分别形成于弧-陆缘体系和碰撞带.拉萨-那曲地区在构造上分为北方和南方。北方以基底变质岩和侏罗系为主，逆冲断层发育。蛇绿岩推覆体覆盖于侏罗系之上。南部以褶皱构造为主。拉萨-那曲地区属于冈瓦纳系。中朝-扬子板块缝合带的高压榴辉岩以孤立的透镜体或块状产出于片麻状岩（Ⅰ型）、蛇纹化橄榄岩（Ⅱ型）和大理岩（Ⅲ型）中。Ⅰ型榴辉岩是由P &gt; 28 kbar的高压俯冲变质作用形成的。第二类榴辉岩分为幔源榴辉岩和幔源榴辉岩。III型榴辉岩类似于金伯利岩中报道的榴辉岩。榴辉岩相和退变质阶段的温度在缝合带内由西向东逐渐升高，表明东部榴辉岩的来源位置比西部深。

1. Granitic rocks in the Lhasa-Naqu terrane in the Tibetan Plateau are divided mainly into the magnetite series of Late Cretaceous-Palaeogene, and the ilmenite series of Early Cretaceous and Miocene. The granitic rocks of the magnetite series consist of granodiorite and granite with low ^<87>Sr/^<86>Sr initial value, and are distributed in souther part of the Lhasa-Naou terrane. Those of the Cretaceous ilmenite series are mainly composed of leucocratic granite with high ^<87>Sr/^<86>Sr initial value, and are distributed in northern part. The granitic rocks of the Miocene ilmenite series are intruded into the central part of the terrane. The granitic rocks of the magnetite and ilmenite series were formed at arc-continental margin system and collision zone, respectively.2. The Lhasa-Naqu terrane is structurally divided into northern and southern parts. The northern part, which consists mainly of basement metamorphic rocks and Jurassic system, is characterized by the prevalence of thrusts. Nappe of ophiolite sequence overlies the Jurassic system. The southern part is characterized by the prevalence of folded structures. The Lhasa-Naqu terrane belongs to Gondwana system.3. High-pressure eclogites in the suture zone between the Sino-Korean and Yangtze cratons occur as isolated lenses or blocks in gneissic rocks (type I), serpentinized peridotites (type II) and marbles (type III). Type I eclogites were formed by high-pressure prograde metamorphism of P > 28 kbar. Type II eclogites are divided into prograde eclogites and mantle derived eclogites. Type III eclogites are similar to grospydite reported from kimberlites. Temperatures of the eclogite facies and retrograde stages tend to increase from west to east within the suture zone, suggesting that eclogites in the eastern part were derived from deeper position than those in the western part.