江西武功山热穹隆变质—岩浆作用及演化

Metamorphism-magmatism and evolution of the Wugong Mt thermal dome,Jiangxi

处于扬子与华夏古板块加里东期拼贴带的武功山热穹隆,以造山期变形花岗岩为中心,南华—寒武系遭受绿片岩相—低角闪岩相变质并形成变质矿物分带,环绕岩体分布,与中生代以来伸展形成的脆性断裂系统构成外环,共同组合形成屹立于晚古生代地层分布区的穹隆状构造。在区域递增变质带基础上,造山早期,深部初始重熔岩浆与深埋的变质岩发生交代形成原地型英云闪长质"混染岩浆",岩浆上浸过程中,活动组分不断作用于围岩,致使围岩的成分、结构构造产生重新调整,形成岩体边缘混合岩。同时,由于硅铝质围岩组分加入,酸度增加,而渐变过渡为花岗闪长质岩浆。造山晚期,进一步演化为岩浆型正常花岗岩,并呈套叠状侵入于早期岩体之中。从早到晚构成同源岩浆演化系列,并发育明显构造应力变形。热穹隆区加里东期形成递进渐增变质—岩体边缘混合—变形花岗岩"三位一体"分布格局。中生代伸展—岩浆作用的复合叠加,进一步强化了热穹隆的构造背景,大致在早白垩世末基本定型。

The Wugong Mt thermal dome,which lies in the Caledonian collage of the Yangtze and Cathysian old plates, is cored by orogenic deformational granite. The Nanhua-Cambrian system was subjected to green schist-low hornblende metamorphism forming metamorphic mineral zoning around the intrusion, and then it, along with extensional fragile faulting system developed since Mesozoic, makes up an outer ring, forming a dome-like structure as what we see loftily in the late Paleozoic strata today. On the basis of regional gradually upgraded metamorphic belt, during early orogenic period,deep-seated initially re-melted magma replaced with deep metamorphic rocks to form in-situ tonalitic＂contaminat- ed magma＂, in the process of upward intrusion, active magmatic components kept acting on wall rock to readjust its composition, texture and structure, and formed migmatite at the fringe of the intrusion. At the same time, salic wall rock components entered the magma adding to its acidity making it evolving toward granodioritic magma. In the late orogen- ic period, it further developed into magmatic syengranite,which invaded early intrusion in telescopic form. From early to late orogenic period,a comagmatic series was formed with development of conspicuous tectonic stress deformation. In Caledonian period,a ＂three in one＂ pattern,formed in the thermal dome area,i.e.,progressive metamorphism,migmati- zation at the fringe of intrusion and deformational granite. By superimposition of Mesozoic extension-magmatism,tecton- ic setting of the thermal dome was further strengthened and took its form roughly at the end of early Cretaceous.