华南东部武夷山和西部龙门山晚新元古-早古生界沉积物源研究与对比

During the late Neoproterozoic to early Paleozoic time, the tectonic evolution of South China and its relation with the Rodinia breakup and the Gondwana assembly are important issues that have stimulated considerable research. Focusing on these issues, the applicant carried out some research work in 2018. The preliminary results show that during the late Neoproterozoic, the tectono-sedimentary processes on the eastern and western sides of South China were not synchronized, and their source regions were also different. This remarkable inconsistency indicates that the eastern and western segments of South China are controlled by distinct geodynamic mechanisms. Therefore, we selected the Longmenshan and Wuyishan areas on the eastern and western segments of South China, to carry out combined studies of sedimentological investigation, detrital zircon provenance analysis, zircon hafnium and oxygen isotope analysis. The obtained results will integrate published petrological, paleomagnetic and paleontological data, to clarify the sedimentary sequence, provenance character, and tectonic evolution of the eastern and western sides of South China. Results from this project have great implications on improving the understanding of early Paleozoic tectonic evolution of South China, as well as on reconstructing the paleogeography of South China with respect to the assembly of Gondwana.

晚新元古-早古生代，华南的沉积-构造演化过程及其与罗迪尼亚超大陆裂解-冈瓦纳大陆拼合事件的联系，是近年来地学界关注的热点问题。聚焦这个问题，申请者展开了预研究，初步研究结果表明：晚新元古以来，华南东、西两侧的沉积-构造过程不同步，沉积物源各异。这些差异性沉积-构造演化记录暗示，华南东、西两侧受控于不同大地构造背景。因此，本项目有针对性选择了华南东侧武夷山地区和西侧龙门山地区，围绕晚新元古-早古生代变质沉积岩系(碎屑岩和夹层火山岩)，拟开展沉积岩相学、碎屑锆石物源和Hf-O同位素的研究，在此基础上，拟结合区域基底组成、岩浆-变质热事件、古地磁及古生物组合标志等资料，展开华南东侧武夷山地区和西侧龙门山沉积序列、物源特征和沉积构造背景的反演和对比分析。项目的研究意义在于其可为全面理解整个华南大陆早古生代构造演化过程提供关键制约，并为进一步深入探讨华南在冈瓦纳大陆古地理位置演化提供地质资料参考。

华南大陆晚新元古-早古生代沉积-构造演化及其与罗迪尼亚超大陆裂解-冈瓦纳大陆拼合事件的联系，是近年来地学界关注的热点问题之一。聚焦这个问题，申请者选择龙门山和武夷山地区，围绕新元古-早古生代变质沉积岩系(碎屑岩和夹层火山岩)，展开了系统的野外观测分析和样品采集工作，在此基础上，进行了>1000颗碎屑锆石的U-Pb定年和Hf同位素测试分析，完成华南大陆东、西两侧物源对比分析。综合区域沉积物源对比和岩石学资料，获得如下认识：（1）晚新元古代以来，华南东、西两侧的沉积-构造过程不同步，沉积物源各异。这些差异性沉积-构造演化记录暗示，华南东、西两侧受控于不同大地构造背景，东、西两侧新元古代地层的沉积物源分别为攀西-汉南弧岩浆岩带和江南造山带岩浆岩。（2）在龙门山识别出寒武纪类磨拉石建造，其砾岩中含有大量的550-500 Ma碎屑锆石，它们的Hf值主体为正值，这些锆石可能源于自伊朗-土耳其地体边缘的580-500 Ma Cadomian弧岩浆岩带。（3）与华南西缘（包括龙门山）不同，华南东缘（包括武夷山）寒武纪沉积物中含有大量的中元古-早新元古代碎屑锆石，它们记录了源自于澳大利亚格林威尔期岩浆岩省的物源。（4）研究结果对约束华南在超大陆演化的古地理位置重建，以及追溯罗迪尼亚大陆裂解到冈瓦纳大陆拼合过程，提供了重要的地质依据。沉积物源的时空演变表明，华南新元古代-早古生代主体表现为持续向北的位移轨迹：新元古代可能与伊朗-土耳其地体和印度北部相连，至寒武纪可能已漂移至澳大利亚周边。这一块体运移轨迹，可能与原特提斯洋的斜向俯冲作用相关，其导致一系列的东亚块体逐渐增生至冈瓦纳大陆的北缘。