Potassic Magmatism in Western Sichuan and Yunnan Provinces, SE Tibet, China: Petrological and Geochemical Constraints on Petrogenesis

摘要: Potassic volcanism in the western Sichuan and Yunnan Provinces, SE Tibet, forms part of an extensive magmatic province eastern Indo-Asian collision zone during Paleogene (40–24Ma). The dominant rock types are phlogopite-, clinopyroxeneand olivinephyric calc-alkaline (shoshonitic) lamprophyres. They relatively depleted Na2O, Fe2O3, Al2O3 compared with late Permian–early Triassic Emeishan continental flood basalts Yangtze craton, have very high variable abundances incompatible trace elements. Primitive mantle-normalized element patterns marked negative Nb, Ta Ti anomalies similar to those K-rich subduction-related magmas, although geodynamic setting is clearly post-collisional. Spatially, some abundances, together inferred depths melt segregation based on Mg-15 normalized compositions samples, display progressive zonation trends from SW NE increasing distance boundary craton. Systematic variations major Sr–Nd–Pb isotope appear petrogenetic significance. systematic increases margin interior craton can be explained by progressively decreasing extents partial melting, whereas steady changes ratios attributed amount subduction-derived fluid added lithospheric mantle source region lamprophyres considered a refractory phlogopite-bearing spinel peridotite, heterogeneously enriched fluids derived earlier phases Proterozoic Palaeozoic subduction beneath Calculations non-modal batch melting model show that degree ranges 0 6% 15% proportion 1% 7% (higher-Ba fluid) or 5% 25% (lowerBa Some pre-existing faults might been reactivated area neighbouring Ailao Shan–Red River (ASRR) strike-slip belt, accompanying collision-induced extrusion Indo-China block left-lateral along ASRR shear zone. This, turn, could triggered decompression previously lithosphere, resulting lamprophyric magmatism