南岭东段早侏罗世岩浆岩的时空分布与成因研究

The calc-alkaline series magmas are dominant rock type in active continental margin, whereas the intra-plate magmas producted in the active continental margin usually indicate a specific tectonic process which is different to subduction of a normal oceanic lithosphere. The petrogenesis and tectonic process of the intra-plate magmas originated in a active continental margin setting is therefore being one of the hot issues. The late Mesozoic magmas are widespread in the South China, among them the calc-alkaline rocks are dominant except early Jurassic magmas which are typical bimodal volcanic and intrusive rocks with intra-plate affinity. So far we are still not totally understand what specific tectonic process involved in origin of the intra-plate magmas. In this project, temporal and spatial distridution and rock association variety of the early Jurassic magmas in eastern Nanling Range will be established on basis of high precision geochronology and systematacially field geological investigate. Otherwise, the mantle feature, physical and chemical condition and crustal contribution for the magmatic origin will be studied on basis of systematacial geochemical and multiple isotopes (Sr-Nd-Pb-Os and zircon Hf-O) research. These studies will provide important data for understanding what specific tectonic process was involved in origin of the early Jurassic as well as extensive late Mesozoic magmas in the South China.

活动大陆边缘最主要的岩石类型是岛弧钙碱性岩浆岩,具板内特征的岩浆岩出现常常反映经历特殊的构造过程，因此是活动大陆边缘岩浆作用研究的热点之一。华南晚中生代岩浆岩广泛发育，绝大部分为钙碱性岩浆岩，反映活动大陆边缘的构造环境。例外的是早侏罗世（~190Ma）岩浆岩为具板内特征的双峰式火山-侵入岩，这套岩浆岩所代表的特殊构造背景目前并不完全清楚。本项目将以系统的野外地质调查为基础，查明南岭东段早侏罗世岩浆岩的时空分布和岩石组合的变化。通过系统的高精度年代学和岩石地球化学，特别是多体系同位素（Sr-Nd-Pb-Os和锆石Hf-O）研究，确定岩浆岩形成的地幔性质和物理化学条件以及地壳物质的贡献，为解决早侏罗世岩浆岩形成的特殊构造背景以及华南晚中生代广泛的岩浆作用提供关键制约资料。

活动大陆边缘最主要的岩石类型是岛弧钙碱性岩浆岩，具有板内特征的岩浆岩出现常常反映经历特殊的构造过程，因此是活动大陆边缘岩浆作用研究的热点之一。华南早侏罗世以双峰式岩浆岩为代表的岩浆岩无论在分布特征还是岩石地球化学系列上均与广泛的晚中生代岩浆岩有显著的差异，因此对该时代岩浆岩的时空分布和成因研究是揭示华南内陆早中生代地幔特征及其热状态，了解晚中生代华南大地构造背景的关键。本次研究通过野外地质调查和系统的高精度年代学和岩石地球化学研究认为：（1）华南早侏罗世岩浆岩在分布上从赣粤闽边界-湘东南地区，可以向东扩展到接近福建沿海的南靖地区；（2）形成时间上单个火山岩盆地岩浆岩形成时限在~5Ma，整个岩浆活动的时限在~15Ma，并具有从东向西逐渐年青的趋势；（3）定量制约的华南内陆早中生代岩石圈厚度为~60-70km，地幔具有亏损地幔特征，地幔潜能温度为~1400℃，具有类似北美盆岭省的壳幔结构；（4）系统的锆石O同位素分析，发现大量低18O锆石存在，表明岩浆形成和演化过程中存在高温水岩反应，将为深入研究低18O岩浆岩的成因提供重要的证据。本次研究表明，华南晚中生代时期为活动大陆边缘构造背景，类似于新生代北美西部盆岭省。定量估算的岩石圈厚度及地幔潜能温度等地幔参数，将为深入研究华南中生代构造-岩浆演化提供重要的指标。