扬子陆块东南缘古生代基性－中性－酸性火成岩及相关岩石的年代学、地球化学研究

There are still poor constraints on the formation timing span,rock type,genesis and teconic setting of the Paleozoic igneous rocks in South China ,which are a key to reveal the tectonic attribute and tectonic evolution of the Caledonian Orogen in South China.Previous studies on Paleozoic igneous rocks are mainly focus on granites.Most of the Paleozoic granites in South China are traditionally considered as S-type granites formed in intracontinental setting.However,some Paleozoic high Ba-Sr granites and appinitic rocks which may be generated by partial melting of enriched mantle have been recently discovered in northern Jiangxi province,which may indicate an early Paleozoic ocean subduction occurred along the southeastern margin of the Yangtze block. On the basis of the new discovery and recognition obtained in our previous work, study of geochronology,geochemistry and genetic mineralogy will be performed on the various Paleozoic igneous rocks including mafic-intermediate-felsic rocks, emphases will be put on the rock types which have received few attention in the previous work and the petrogenesis of the Paleozoic granites will be discussed in a new thinking way quite different from the traditional thought . This project will try to make clear the formation timing span of the igneous rocks,the igneous rock types and rock association,their petrogenesis and genetic relationship,tectonic setting.In addition, to gain some information on petrogenesis and tectonic evolution,related rocks which may be related to the generation and metamorphism of the Paleozoic igneous rocks will also be studied.Combined with the data on the Paleozoic igneous rocks and metamorphic rocks in South China,analysis will be carried out on the relationship between spatio-temporal distribution of the Paleozoic igneous rocks in various genentic type,metamorphic rocks and the boundaries of blocks,deep faults,which will provide important constraints on the tectonic attribute and tectonic evolution of the Caledonian orogen in South China.

目前对华南古生代火成岩的形成时限、岩石类型、成因、成岩的构造环境仍缺乏重要的制约。过去有关华南古生代火成岩的研究主要集中于花岗岩，多数花岗岩被认为是陆内造山环境中形成的S型花岗岩，然而，我们在赣北发现了古生代高Ba-Sr花岗岩和富集地幔来源的富闪深成岩，可能暗示华南在早古生代沿扬子陆块东南缘发生过洋壳的俯冲。本项目拟全面研究扬子陆块东南缘基性－酸性的各类火成岩，着重研究过去未受重视的岩石类型，查明岩浆活动的时限、岩石类型和组合，不同类型火成岩的成因关系，探讨岩石成因和成岩的构造环境，用不同于传统认识的思路重新探讨扬子陆块东南缘古生代花岗岩的成因；研究可能与古生代火成岩的形成、变质变形有关的岩石，获取岩石成因和区域构造演化的信息；分析华南古生代变质岩、不同成因类型火成岩的时空分布规律及其与块体边界、深大断裂的关系，为揭示加里东运动的构造属性、构造演化以及华南古生代以来的构造演化提供重要依据。

目前对华南古生代火成岩的形成时限、岩石类型、成因和形成的构造环境等仍缺乏重要的制约，这对探讨华南加里东运动的构造性质意义重大。此外，关于武功山一带新发现的古生代中基性岩石的成因和构造意义、古生代不同类型岩石之间的成因关系尚未清楚。本项目重点对华夏陆块北缘的古生代火成岩及与之有关的变质岩进行了详细的野外地质调查、岩相学观察、锆石U-Pb定年、全岩主量和微量元素、Sr-Nd同位素、锆石Hf同位素、矿物化学等方面的研究，进而探讨了各类岩石的成因和形成的构造环境，主要取得如下新认识和重要结果：1）厘定了华南古生代火成岩的形成时限为ca.400 Ma ~ ca.470 Ma，武功山混合岩和其附近的花岗岩、富闪深成岩形成时间为ca.440 ~ 450 Ma。2）华南早古生代岩浆活动的时间可能最早可追溯到480～500 Ma。3）探讨了富闪深成岩的成因机制：在早古生代华南陆内造山的构造背景下，作为板块拼合带的江绍断裂发生活化，沿断裂带形成局部的伸展环境，从而引发古俯冲带内的岩石圈地幔及周围的地壳物质发生部分熔融而形成富水的基性岩浆和酸性岩浆，经过地壳混染、结晶分异、岩浆混合等岩浆过程，最终形成了富闪深成岩－花岗岩的岩石组合。因此，古生代富闪深成岩的发现并非指示华南早古生代华南洋的存在，而是进一步证实了华南加里东运动为陆内造山性质。4）我们的研究表明，富闪深成岩不仅可形成于与洋壳俯冲－造山有关的构造环境，也可在陆内造山环境中由古代岩石圈地幔部分熔融形成。我们的工作丰富了该类岩石的成因类型和形成的构造背景。5）华南古代岩石圈地幔的同位素组成与地壳物质相似，有关其对华南过铝质花岗岩的贡献缺乏认识。我们的工作表明，古代岩石圈地幔对部分华南过铝质花岗岩具有较明显的物质贡献。6）对赣北－赣南地区部分中生代花岗岩、基性岩及其有关的矿床也开展了初步研究，所获得的资料和数据为建立该区岩浆活动的年代学框架、探讨花岗岩成因和矿床的形成机制补充资料，为进一步的矿产勘查工作提供一些依据。