政和-大浦断裂带以东早古生代闪长质侵入岩是陆内造山作用的产物吗？

The tectonic nature of the Caledonian Orogeny of South China is a hot issue to be solved urgently in the fundamental geological research. The most crucial question therein is whether there preserved Early Paleozoic ophiolite or arc igneous activity in South China. The Caledonian fold belt of South China is commonly bordered by the Zhenghe-Dapu Fault to the east. However, recently east of the fault, two-period Early Paleozoic dioritic intrusions were identified, in Datian County, Fujian Province, and the early one is characterized by adakitic geochemistry. This program will target these two Early Paleozoic intrusions, and adopt a suite of comprehensive methods, including petrology, minerology, bulk geochemistry and Sr-Nd isotopes, and zircon in situ U-Pb-Hf-O isotopes. Systematic studies will be carried out, such as the genetic type and tectonic setting of the dioritic intrusions, the type and genesis of mafic enclaves and the east boundary of the Caledonian fold belt, in order to estimate whether these two dioritic intrusions are Early Paleozoic arc magmatic rocks formed by NW-trending oceanic subduction beneath South China or not. By comparation with the Early Paleozoic granites and intermedium-mafic intrusions west of the fault, this program attempts to uncover the tectonic nature of the Caledonian Orogeny of South China, which may be intracontinental orogeny or continental collision orogeny, and ascertain its tectonic evolution history.

华南加里东期造山事件的构造属性是华南基础地质研究中一个亟待解决的热点问题，其中的关键性问题是华南大陆是否存在早古生代的蛇绿岩和弧岩浆活动。华南东部的加里东期褶皱基底通常以政和-大浦断裂带为东部边界，但我们最近在断裂带以东的福建大田县识别出两期早古生代的闪长质侵入岩体，且其中早期岩体呈现埃达克岩的地球化学特征。本项目将以它们为靶向岩体，采用岩相学、精细矿物学、地质年代学、同位素与地球化学等方法，开展包括岩体的成因类型、暗色包体的类型与成因、岩体形成的构造背景以及加里东褶皱造山带的东部边界等一系列研究，以期判定这两个闪长质侵入岩是否为大洋板块在早古生代时向华南大陆北西向俯冲形成的弧岩浆岩，并通过与断裂带以西的早古生代花岗岩和中基性侵入岩对比，试图揭示华南加里东期造山事件的构造属性是陆内造山抑或是陆陆碰撞造山，并查明华南加里东造山事件的构造演化过程。

加里东期造山运动的构造属性是华南大陆构造演化颇富争议的重大地质问题。迄今关于华南加里东期造山作用机制主要存在三种观点：（1）华南加里东期造山是由扬子、华夏地块间的古华南洋的闭合而导致的俯冲-碰撞造山事件；（2）华南加里东造山事件是华夏地块内部或华夏地块与扬子地块间相互作用的陆内造山；（3）华南加里东期造山是华南东部与未知地块(冈瓦纳)的俯冲和陆陆碰撞造山形成。本项目针对这一问题，选择了福建永安地区寒武纪至三叠纪的沉积岩以及福建大田-德化地区的早古生代岩体为研究对象。通过研究沉积岩中碎屑锆石的物源区以及岩浆岩的成因来确定华南板块东部在古生代的构造环境。.（1）永安地区寒武-奥陶纪的变沉积岩具有和印度北部、喜马拉雅地区同时代沉积岩相同的碎屑锆石年龄谱，表明华南地块东南部在晚新元古代至早古生代已经和东冈瓦纳北部相连，两者之间不存在洋壳俯冲。.（2）永安地区石炭纪-三叠纪的沉积岩含大量的晚古元古、新元古、早古生代和晚古生代的碎屑锆石年龄，表明碎屑源区主要为华南板块本身。此外晚古生代的构造作用在华南东部可能并不局限。.（3）福建大田-德化地区识别出三个早古生代中性岩体，际坑岩体（448-450 Ma）,杨梅岩体（451 Ma）,葛坑岩体（457-458 Ma）。他们具有富集和相同的锆石Hf，全岩Sr-Nd同位素，表明它们可能具有同一源区。.（4）际坑岩体,杨梅岩体和葛坑岩体具有高镁安山岩/闪长岩（MA-HMA）的地球化学特征，且具有高的Sr/Y、La/Y比值，高的SiO2含量，K/Na比值，类似于拆沉下地壳部分熔融形成的岩浆岩，可能是华南板块东部发生过地壳加厚的证据。