青藏东缘新生代两类高钾岩浆活动的对比研究

Based on geological mapping in the typical areas, basin analysis, trace-isotope geochemical tracing and high-quality thermochronological data, we simply describe the new main conclusions as below..(1) Geochronologic dating and compilation of existing age data suggest that Cenozoic activities in the eastern Indo-Asian collision zone of southeast China and Indochina occurred in two episodes, each with distinctive geochemical signatures, at 42-24 Ma and 16-0 Ma. The older rocks are localized along major strike-slip faults such as the Red River fault system and erupted synchronously with transpression. The younger rocks are widely distributed in rift basins and are coeval with east-west extension of Tibet and eastern Asia. Geochemical data suggest that the early igneous phase was generated by continental subduction while the late episode was caused by decompression melting of a metasomatically altered, depleted mantle. The magmatic gap between the two magmatic sequences represents an important geodynamic transition in the evolution of the eastern Indo-Asian collision zone, from process controlled mainly by crustal deformation to that largely dominated by mantle tectonics. .(2) The xenoliths entrained in the early-stage high-K magmatic rocks belong to the metamorphic rocks in the mid-lower crust (20-50 km depth), and the xenoliths entraned in the late-pulse high-K magmatic rocks are the mantle-derived peridotites (45-75 km depth) with no compositional relation to their host rocks..(3) The emplacement age of lamprophyric magma in the Laowangzhai gold deposit, Yunnan ranges from 30.8±0.4 to 34.3±0.2 Ma, and gold mineralization took place at 26.4±0.2 Ma. PGE geochemical tracing indicates that gold in the gold deposit did not come from the primitive lamprophyric magma. The tempo-spatial paragenesis between lamprophyres and mesothermal gold deposits along the Jinsha-Red River belt may be attributed to that they formed in the same tectonic setting..(4) The systematical studies of the early Tertiary basins and magmatic rocks within them suggest that the coarse clastic rocks were formed in early Tertiary basins during 38~28 Ma, when is nearly coeval with the formation of the early Tertiary basins in the Hengduan Shan and disintegration of large basins in the Lanping-Simao area in eastern Tibet. The sedimentologic characteristics of early Tertiary coarse-grained clastic rocks, basin tectonics and magmatic activity indicate that one rapid tectonic uplift may have occurred in the Tibetan Plateau from Late Eocene to Early Oligocene..(5) The isotopic dating suggests that the mantle-derived volcanic rocks in the Lixian-Dangchang, western Qinling were erupted in the period of 21.1±0.7~25.4±0.8 Ma. The volcanism may be induced by coupling among ceasing of the rotation of the Lixian Pre-indosinian block, and bending and acceleratory movement of the Minxian-Dangchang fault along the strike direction in the temporal boundary between early and late Tertiary, which can be rationally explained using our new established tectonic model..

通过青藏东缘新生代两类高钾岩浆活动的构造背景、岩石学、元素－同位素和铂族元素地化及成岩时限的对比研究，揭示它们的共性和特性，探讨壳幔相互作用的多样性和复杂性、及其与该地区新生代构造转换的关系。对它们开展系统的对比研究，可为解决壳幔相互作用机制、青藏隆升、走滑旋转时限、盆地形成演化和元素超常富集机理等提供重要的科学佐证。