华南地区加里东期花岗岩:成岩和成矿作用的地质与地球化学特征

Caledonian Granites in South China:The Geological and Geochemical Characteristics on Their Petrogenesis and Mineralization

自20世纪50年代江西龙回和陡水岩体被发现,至今华南地区已经有160多个花岗质岩体被确认形成于加里东期(主要包含奥陶纪、志留纪和泥盆纪),其中只有14个岩体与金属矿(以钨矿为主,含少量钼、铜、锡和金矿)有成因关系,11个岩体与稀土矿有成因关系。前人对加里东期花岗岩特征的归纳主要集中在岩石学、地球化学和构造动力学等方面,而极少对该期成矿作用进行系统总结。通过搜集和整理已公开发表的280篇学术论文和学位论文中的800个成岩和成矿年龄,1248个样品的全岩主量、微量元素数据,428个样品的全岩Sr-Nd同位素数据和2352个测试点的锆石Lu-Hf同位素数据,从以下4个方面对加里东期花岗岩的含矿性特征进行了梳理:①岩浆活动与金属成矿的年龄峰值均集中在440~420 Ma;②成金属矿的花岗岩主要分布于大瑶山和桂北—桂东北地区,虽然都是以钨矿为主的岩石,但是这两个地区花岗岩的源区物质和分异程度均具有差异性;③成稀土矿的花岗岩主要分布于武夷和南岭地区,前者大多数发生了变质作用,而后者以块状构造为主;④与奥陶纪和泥盆纪花岗岩相比,志留纪花岗岩的分布面积最广,岩性最宽泛,物质来源也最为复杂。

Nowadays,more than 160 granitic plutons have been confirmed to form in Caledonian(including Ordovician,Silurian,and Devonian),since Longhui and Shangyou plutons in Jiangxi were firstly found in the 1950s.Among them,only 14 plutons are genetically related to the polymetallic mineralizations(major W with minor Mo,Cu,Sn,and Au),and 11 plutons are related to the REE mineralizations.Previous studies on Caledonian granites were mainly concentrated on the characteristics of petrology,geochemistry,and tectonic dynamics,but hardly on the mineralization.Based on 800 mineralization and crystallization ages,the data of whole-rock elements of 1248 samples,the whole-rock Sr-Nd isotopes of 428 samples,and the zircon Lu-Hf isotopes of 2352 analytical spots,which were collected from 280 papers and theses,four main conclusions about metallogenic characteristics of Caledonian granites were summarized as follows:①440-420 Ma is the peak of magmatic activity and metal mineralization;②Metallogenic granites are mainly focused in Dayaoshan and north-northeast areas of Guangxi,and their source materials and differentiation degrees are all different with each other;③REE-forming granites are primarily concentrated in Wuyi and Nanling areas,and most of the former experienced the metamorphism,but the latter did not;④Compared with Ordovician and Devonian granites,Silurian granites have the largest distribution area,the broadest lithologies,and the complicated source materials.