滇西腾冲-保山和兰坪地块早古生代地层特征、碎屑锆石U-Pb年龄谱和Hf-O同位素示踪研究及其意义

The Tengchong-Baoshan and Lanping Terranes are situated at the conjunction of Euroasia and India plates and Tethys tectonic zone, in which very thick early Paleozoic detrital sediments were filled. It has been also confirmed that it is quite potential to explore polymetallic deposits and natural gas and oil in the terranes. Although some workers have studied the features of paleontology, sedimentary components, volcanic rocks in the basin, there are some key issues not to be resolved so far, such as the sedimentary provenance, geodynamic mechanism of basin development, the correlation between the old basins and surrounding terranes and orogenic belts. In this project, thus, we will carry out systematic studies on the early Paleozoic detrital materials in the Tengchong-Baoshan and Lanping Terranes, including field investigation, paleocurrence and whole-rock major-trace element geochemistry, particularly detrital zircon in-situ U-Pb dating, trace element pattern and Hf-O isotopic analysis by LA-MC-ICPMS and SIMS. It will reveal the real sedimentary provenance in the terranes and the closely coupling relationship between the old basin formation and the surrounding orogenies and then better understand the regional tectonic setting at that time.

滇西保山-腾冲和兰坪地块位于欧亚板块、印度板块和特提斯三大构造域的交汇部位，是我国重要的多金属成矿带。早古生代时期，该区堆积了巨厚的碎屑物质。对于这些沉积物的源区特征及来源机制以及与周缘造山带之间的耦合关系，目前还不是很清楚。虽然许多研究者针对滇西地区古生代的地层古生物、沉积组合、岩石(相)学特征进行了一些对比研究，而对古盆地沉积物物源示踪以及盆-山耦合关系方面的研究并未开始。本项目基于传统的沉积学并结合新的锆石U-Pb定年、微量元素及Hf-O同位素研究技术，对研究区早古生代地层沉积及其碎屑锆石进行系统研究，并配以典型样品的Nd同位素研究，建立各自地块碎屑锆石的年龄谱和Hf-O同位素特征值，反演其周缘造山带早古生代造山过程及其沉积响应，分析各自陆块不同时期沉积源区特征和性质、来源路径及可能的动力学机制，重塑晚早古生代古地理格局，解译周边板块真实的地质演化历史。

保山-腾冲和兰坪-思茅地块位于我国西南三江造山带的南部，向北延伸进入我国的青藏高原，向南延伸到东南亚地区。该区是多金属矿产富集地，沉积了不同厚度的早古生代的碎屑物质。对于这些沉积物的源区特征及来源机制以及与盆地周缘造山带之间的耦合关系，目前还不是很清楚。近年来，许多研究者对地层的古生物和沉积学，以及相关的火山岩、造山带构造等进行了研究和总结，而对沉积物物源示踪以及盆-山耦合关系方面的研究还很缺乏。本项目利用LA-(MC)-ICPMS和SIMS对不同陆块不同区域不同层位的碎屑锆石进行微区U-Pb定年、微量元素及Hf-O同位素组成的分析，并配以相应层位碎屑岩Nd同位素研究，获得以下重要认识：1）腾冲-察隅-密支那地块记录主要的泛非事件的年龄群；2）保山-Sibumasu地块以格林威尔晚期的岩浆时间的年龄为主，次为泛非事件峰值；3）兰坪-思茅地块记录以加里东期事件为主的年龄峰，次为格林威尔时间的年龄群，并且无泛非事件的记录。这些碎屑锆石的年龄坪谱特征的差别，反映了其沉积物源的差别，这也为重建各陆块在超级冈瓦纳大陆中的位置提供了重要的证据。