赣西北地区印支期花岗岩的岩石成因及其动力学意义

In recent years, intracontinental orogeny and magmatic activity have developed to be one of the intensively studied geologic scientific issues，and Indosinian South China fold belt shows the features of typical intracontinental orogenic belts. Due to the Indosinian granites were associated with the Indosinian orogenic magmatism, we could study these granites to decipher the geodynamic significance of Indosinian tectonic reactivation and magmatism in South China.Indosinian magmatism are widespread in South China, but most of them occur as batholiths distributed in the interior of South China.In the past, the studies for the Indosinian granites from inland South China mainly focused on the Indosinian granites in Central Hunan Province and Southern Jiangxi Province, whereas there is less research for the Indosinian granites in Northwestern Jiangxi Province between Central Hunan Province and Southern Jiangxi Province. Despite only a little Indosinian magma activities were distributed in the Northwestern Jiangxi Province, it is suggested that the Indosinian granites croped out at here include the two main types of rocks in the Indosinian South China (i.e. S-type granites bearing strong peraluminous minerals and I-type granites bearing amphibole). Therefore,carrying out detailed comparative studies on the two types of Indosinian granites in Northwestern Jiangxi Province,especially the source characteristics and their heterogeneity,the differences of petrology between the two types of granites and the emplacement physical-chemical conditions would be pay attention, which has broad significance for understanding the tectono-magmatic evolution in South China.

近年来，陆内造山作用及其相应的岩浆活动成为国内外地质科学研究的热点之一，华南印支期褶皱造山带具有典型的陆内造山带特征。而华南印支期花岗岩是与华南印支造山作用相伴生的岩浆活动产物，通过研究这些花岗岩，可以揭示华南印支期构造-岩浆作用的地球动力学背景。华南印支期岩浆活动分布广泛，但是主要分布于华南板块陆内地区，过去对华南陆内印支期花岗岩的研究主要集中在湘中和赣南地区的印支期花岗岩，而对介于湘中和赣南的赣西北地区印支期花岗岩研究相对比较薄弱。尽管赣西北地区岩浆活动出露较少，但却出露有华南印支期主要的两种岩石类型（即含强过铝质矿物的S型花岗岩和含角闪石的I型花岗岩）。因此，对赣西北地区两类印支期花岗岩开展系统的对比研究，关注其岩浆源区特点和差异、岩石学差别和成岩的物理-化学条件，对我们认识和理解华南印支期构造-岩浆演化具有十分重要的意义。

华南印支期花岗岩一个显著的特点是大量的花岗岩发育在远离大陆边缘的华南板块内部，并和陆内造山带相伴生，因此，这些花岗岩属于典型的陆内造山岩浆活动产物。本项目以赣西北地区金滩岩体和湘中地区白马山杂岩体为研究对象，系统开展年代学、岩相学、矿物学，锆石原位Hf同位素以及全岩地球化学和Sr-Nd同位素分析。结果显示，金滩岩体岩石中可见白云母、石榴石等过铝质矿物，主要有黑云母花岗岩和二云母花岗岩两种岩性，所有样品在TAS图解上均落入花岗岩范围，其中黑云母花岗岩形成于~221Ma，富硅（SiO2=69.66%～74.25%），强过铝质特征（ACNK=1.10～1.15），Isr＝0.711272～0.714144，εNd（t）=-9.89～-9.15，而二云母花岗岩形成于~223Ma，富硅（SiO2=71.38%～75.45%），强过铝质特征（ACNK=1.13～1.24），Isr＝0.704253～0.711540，εNd（t）=-9.99～-8.94。白马山岩体中可见角闪石、榍石等准铝矿物，主要包含黑云母花岗岩和二云母花岗岩两种岩性，样品在TAS图解上主要落入花岗闪长岩和花岗岩范围，其中黑云母花岗岩形成于216～217Ma，高硅（SiO2=66.42%～72.26%），弱过铝质到强过铝质特征（ACNK=0.97～1.32），Isr＝0.714109~0.725114，εNd（t）=-11.3～-7.8，εHf（t）=-7.35～-5.48；二云母花岗岩形成于~202Ma，富硅（SiO2=69.66%～74.25%），强过铝质特征（ACNK=1.15～1.26）， Isr＝0.729842~0.731499，εNd（t）=-12.9～-11.5，εHf（t）=-7.08。综合岩石学、矿相学和地球化学特征，可判定金滩岩体岩石为S型花岗岩，可能是接近纯地壳沉积物部分熔融产物，而白马山岩体岩石为I型花岗岩，属于壳幔岩浆混合产物。华南印支期I型花岗岩具有比S型花岗岩更高的岩浆温度和氧逸度。华南陆内印支期花岗岩可能形成于俯冲有关的陆内造山环境。