小兴安岭西北部晚古生代火山-沉积建造与物源:对黑河-嫩江缝合带闭合时限的制约

It has been a controversial issue for the closure timing of the Paleo-Asian Ocean along the Heihe-Nenjiang belt. To solve the problem, previous research has mainly focused on the Late Paleozoic igneous rocks, lacking of coeval sediments and their provenance. Therefore, this project studies geochronology, element-isotope geochemistry, associations and provenance of the Late Paleozoic volcanic-sedimentary formations in the northwestern Lesser Xing'an Range, combined with previous research results of coeval igneous associations and tectonic evolution, to determine the geotectonic settings of the volcanic-sedimentary formations, together with time-variations of their provenance, and to better constrain the closure timing of the paleo-oceanic basin in the Heihe-Nenjiang suture zone. This program is of important significance for not only revealing the tectonic evolution of the Heihe-Nenjiang suture, but also rebuilding the structural framework of the eastern Central Asian Orogenic Belt during the Late Paleozoic.

古亚洲洋沿黑河-嫩江一线的闭合时限一直存在较大争议，针对此问题前人主要集中于晚古生代火成岩的研究，而对该时期沉积建造与物源的研究很少。鉴于此，本项研究选择邻近黑河-嫩江缝合带的小兴安岭西北部晚古生代地层作为研究对象，通过其中火山岩和沉积岩的年代学、元素-同位素地球化学的系统研究以及沉积建造组合与物源分析，结合研究区同期火成岩组合与区域构造研究成果，查明小兴安岭西北部晚古生代火山-沉积建造所揭示的构造环境，结合沉积物源随时间的演变，限定黑河-嫩江一线古洋盆闭合的时限。该项研究不仅对揭示黑河-嫩江缝合带晚古生代构造演化历史，而且对重建中亚造山带东段晚古生代构造格局均具有重要意义。

本项目选择小兴安岭西北部晚古生代地层作为研究对象，通过对代表性岩石的年代学、元素-同位素地球化学的研究以及沉积物源的分析，查明小兴安岭西北部晚古生代火山岩的时空格架及相应产出的大地构造环境，进而揭示黑河-嫩江缝合带晚古生代的构造演化历史。通过本项目的研究，主要取得了以下认识：（1）小兴安岭西北部晚古生代火山作用期次主要可分为三个阶段，即早石炭世（356~349 Ma）、晚石炭世早期（~319 Ma）和晚石炭世晚期-早二叠世早期（307~290 Ma）；（2）额尔古纳-兴安地块提供了研究区晚古生代沉积物的单方向物质供给；（3）小兴安岭西北部晚古生代应处于古亚洲洋持续向北俯冲增生的活动大陆边缘环境。该项研究对黑河-嫩江缝合带晚古生代构造演化历史取得了新的初步认识，这对重建我国东北地区晚古生代构造格局具有重要意义。