【摘要】 东天山黄山-镜儿泉地区位于康古尔弧后盆地闭合带东段,该盆地于石炭纪末因弧-陆碰撞而闭合。二叠纪时本区进入碰撞后伸展阶段,并形成了时代相近的、如下一组地质特征:1)20多个镁铁-超镁铁岩体(其中有一部分产有工业铜镍矿床);2)低压高温变质作用和混合岩化;3)形成深度较浅(8～12 km)的韧性剪切带;4)原地改造型片麻状花岗岩;5)块状过铝花岗岩;6)与过铝花岗岩有关的锂铍伟晶岩矿床。此外,黄山-镜儿泉位于一个被推测为巨大镁铁质岩体的区域布伽重力和航磁高值区的边部。该处在人工地震剖面上表现为一个波速为6.99 km/s的高速层,其厚约22 km。这些特征表明,该区在二叠纪时期是一个热穹窿,其面积约5000～8000 km~2,而该热穹窿乃由地壳内部的一个幔源岩浆内侵体所引起。正是这个内侵体在黄山-镜儿泉地区造成了地壳岩石的低压高温变质作用、混合岩化和部分熔融。在内侵体热量和流体的影响下,韧性剪切得以在壳内较浅层次发生。与内侵有关的变质-超变质作用所释放出的流体和熔体强烈改造韧性剪切和细粒化的地壳岩石,即形成了片麻状花岗岩。部分熔融所产生的过铝花岗岩形成了以锂、铍等稀有金属为特色的伟晶岩矿床。本区存在同时代的钙碱性-高钾钙碱性花岗岩,表明底侵与内侵曾在这里相伴发生。众多的镁铁-超镁铁岩是底侵和内侵岩浆在地壳浅部的显示。侵入岩的年龄数据似乎表明,本区直接来自幔源岩浆的镁铁-超镁铁岩就位最早,与底侵有关的钙碱性-高钾钙碱性花岗岩次之,而作为内侵产物的过铝花岗岩最晚。过铝花岗岩与镁铁-超镁铁岩之间的时差可能代表了从幔源岩浆结晶到由内侵产生的岩浆结晶之间的时差。康古尔断裂是一条超岩石圈断裂,在碰撞后伸展阶段为幔源岩浆提供了良好的上升通道,因此内侵很容易在此地此时发生。与底侵一样,内侵是壳幔相互作用和地壳垂向增生的重要方式,也是花岗岩浆生成的重要机制。区域重力和航磁异常、人工地震中部地壳高速层、时代相近的地表镁铁-超镁铁岩、低压高温变质岩、混合岩、浅层次韧性剪切带、原地改造成因片麻状花岗岩、异地过铝花岗岩和有关的稀有金属矿床,过铝花岗岩中的幔源岩石包体或幔源流体可以用作为内侵体的识辨标志。更多还原

【Abstract】 The Huangshan-Jing’erquan region of eastern Tianshan belongs to the eastern section of the Kangguer back-arc basin, which was closed as a result of arc-continent collision by the end of Carboniferous.In the Permian,this region was affected by post- collisional extension,which resulted in a group of roughly coeval geological features.This group includes:1)More than 20 mafic- ultramafic intrusions,some of which have been endowed with commercial Ni-Cu deposits;2)Low pressure and high temperature metamorphism and migmatisation;3)A ductile shear zone formed at relatively higher crustal level(8～12 kin);4)Autochthonous gneissose granites;5)massive peraluminous granites;and 6)Li and Be mineralisations in pegmatite veins affiliated to peraluminous granites.Besides,this region is situated at the margins of a regional positive gravitational(Bouguer)and an aeromagnetic anomalies, which are suggested to be induced by a huge mafic intrusion.A high-velocity zone 22 km in thickness is also detected by seismic sounding in the middle crust.These features,collectively,are indicative of a Permian thermal dome,which occupied an area of about 5000～8000 km~2 and was caused by an intraplated body of mantle magma in the crust.It is just the intraplated magma body that resulted in low pressure and high temperature metamorphism,migmatisation and partial melting of crustal rocks.Heat and fluids from the intraplated magma facilitated formation of the ductile shear zone at a higher crustal level.Gneissose granites were formed by reaction of grain-reduced crustal rocks in the ductile shear zone with up-moving fluids and melts released due to metamorphism and ultra- metamorphism driven by intraplating.Mineralisations characterised by rare metals,such as Li and Be in pegmatites,were genetically affiliated to peraluminous granites produced by partial melting of crustal rocks.Coexistence of calc-alkaline to high-potassium calc- alkaline granites with peraluminous granites indicates that underplating accompanied intraplating in this region.Numerous mafic- uhramafic intrusions are high-level representatives of the underplated and intraplated magmas at depth.Isotope ages appear to suggest that mafic-ultramafic intrusions representing original mantle magmas were emplaced the earliest in this region,then the calc-alkaline to high-potassium calc-alkaline granites genetically related to underplating,and the latest is the peraluminous granites genetically related to intraplating.A time delay of 20～30 Ma of the peraluminous granites behind the mafic-ultramafic intrusions represents the time span from crystallisation of the mantle magma to crystallisation of the intraplating-induced new magmas,Localisation of intraplating in this region was constrained by the super-crustal Kanggur fault,which,enhanced by post-collisional extension,provided the mantle magma with a favourable conduit for its ascent.Like underplating,intraplating is a substantial way of crust-mantle interaction and vertical growth of the crust,and is also an important mechanism for granite magma generation.Collectively,regional gravitational and aeromagnetic anomalies,mid-crustal high-velocity zone detected by seismic sounding,and roughly coeval mafic-ultramafic rocks,low pressure and high temperature metamorphic rocks,migmatites,high-level ductile shear zone,autochthonous gneissose granites, allochthonous peraluminous granites and related rare metal mineralisations,and mantle-sourced rocks and fluids involved in peraluminous rocks can be used as indication for an intraplated body below the surface.更多还原