北大别的多期深熔作用及山根垮塌的新证据

大别山是由华南板块在245～210 Ma向华北板块之下俯冲并发生陆陆碰撞形成的。随着南、北板块的汇聚继续，地壳持续加厚。然而，加厚的下地壳岩石（特别是镁铁质下地壳岩石）在重力作用下密度增大、稳定性降低，在145～130 Ma 时发生深熔作用；130 Ma 左右加厚下地壳拆沉，引发软流圈上涌，产生了130～110 Ma的大规模镁铁质和花岗质岩浆作用以及北大别发生强烈的混合岩化作用。其中，北大别混合岩中不同类型浅色体（至少可以分为4种）和碰撞后变质闪长岩的甄别及其岩石地球化学和同位素年代学方面系统研究为大别山印支期深俯冲陆壳的折返以及燕山期镁铁质下地壳岩石拆沉和山根垮塌所引发的多期深熔作用提供了新的关键证据。山根垮塌诱发的地幔对流导致～145 Ma时岩石圈开始减薄，进而导致加厚镁铁质下地壳温度和地壳中下部地热增温率升高，并使其发生部分熔融；加厚下地壳的部分熔融导致造山带下地壳持续弱化，加剧其重力不平衡，从而引发深部俯冲的镁铁质下地壳岩石的大规模拆沉和山根垮塌。

New constraints on multiple anatexis in the North Dabie complex zone and mountain-root collapse in the Dabie Orogen,central China

The Dabie orogenic belt was formed by the northward subduction of the South China block beneath the North China block in the Triassic and henceforth its crust was progressively thickened along with convergence between the two blocks. The thickened lower-crustal rocks （especially mafic lower-crustal rocks） become unstable since minerals and rocks transformed into new assemblages with higher density due to the increasing gravity. As a result, anatexis of the lower-crustal rocks initiated at 145～130 Ma, whereas delamination and foundering of the thickened lower crust occurred at ca.130 Ma, which caused the asthenosphere upwelling resulted in large-scale mafic and granitic magmatism together with extensive migmatization in the North Dabie complex zone （NDZ） during 130～110 Ma. At present, various leucosomes （at least 4 types） within the migmatites and post-collisional meta-diorites have been identified in the NDZ. Furthermore, an integrated investigation of petrogeochemistry and isotopic geochronology on leucosomes and meta-diorites in this study sheds new light on exhumation of the Triassic deep subducted continental slab and multiple anatexis related to the initial stage of exhumation and post-collisional delamination of mafic lower-crustal rocks and subsequent mountain-root collapse in Yanshannian. Lithosphere thinning and mafic lower crust heating caused by the mountain-root collapse and mantle convection resulted in the geothermal gradient anomaly of middle-lower crust and partial melting of rocks. Also, partial melting of the thickened lower crust has weakened the lower crust in the Dabie Orogen and increased its gravity instability, thus triggering delamination and foundering of the mafic lower crust at depths and mountain-root collapse in the Early Cretaceous.