The Metamorphic and Deformational History of a Continental Collision Zone and its Geodynamic Process——as Evidenced by Qinling Complex,Western Henan,China

The Qinling orogenic belt is a collision zone between the North China and Yangtze cratons. The Qinling Complex is a Precambrian metamorphic complex, developed in the inner zone of the orogenic belt , which records the metamorphic and deformational history and PTt path of the regional meta-morphism of the collision zone . The present paper studies the metamorphic and deformational history and the PTt path of various tectono-metamorphic cycles in order to describe the geodynamic processes prevailing in that part of the Qinling orogenic belt since Proterozoic.The tectonometamorphic history and evolution of the Qinling Complex is divided into two stages: the stage of formation and the stage of modification During the stage of formation dated as Proterozoic,three deformational sequences are recognized. The amphibolite facies regional metamorphism is earlier than or synchronous with the first or second phase of folding. Three metamorphic zones, i.e. And-Ms ,Sil- Ms, Sil Kfs are delimited. During the stage of modification , the emplacement of Caledonian granite , superimposed thermal aureole (garnet K feldspar zone )and the development of ductile shear zones are major events.Metamorphic reactions are reconstructed in terms of analysis of re-equilibrium textures. Geothermobarometric calculations are conducted to calibrate the PT conditions of metamorphism .The metamorphic PTt paths have been estabh'shed. The PTt path of the Proterozoic tectonometamorphic cycle shows a clockwise pattern and is characterized by prominent decompression. The PTt path of the Caledonian tectonometamorphic cycle is characterized first by PT rising ,then isothermal decompression (rapid uplift), and finally by isobaric cooling The PTt path of the two tectonometamorphic cycles evidence the geodynamic processes: two major stages of collision and uplift in the Proterozoic and Caledonian Hercynian periods, respectively, during the evolution of Qinling orogenic belt.

Zircon SHRIMP U-Pb Dating and Neoproterozoic Metamorphism of Kangding and Yuanmou Intrusive Complexes,Sichuan and Yunnan

To clarify the relationship of the metamorphic intrusions along the west margin of the Yangtze craton and their metamorphic history after crystallization, the petrochemical and trace element geochemical characters, zircon SHRIMP U-Pb dating, and the chemical compositions of coexisting hornblendes and plagioclases from Neoproterozoic metamorphic intrusions in Kangding （康定）, Sichuan （四川） Province, and Yuanmou （元谋）, Yunnan （云南） Province, were studied. Combined with the former published data, it is indicated that the Kangding granitic plutons and Yuanmou complex in the west margin of the Yangtze craton generally formed at the same period. Metamorphic event at ~700 Ma existed extensively, at least covering from Kangding area in Sichuan to the Eshan （峨山） area in Central Yunnan. Moreover, amphibolite facies may represent the peak regional metamorphic condition.