Geological and structural development of the Tibetan Plateau

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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.