班公湖-怒江缝合带是否存在白垩纪古洋壳：来自康穷蛇绿岩的证据

The Bangong-Nujiang Suture Zone (BNSZ) is the relic of the Bangong-Nujiang Tethys Ocean (BNO). Currently, there is an ongoing debate on that whether the BNO was closed before ~140 Ma or during ~120-100 Ma. The reason for this controversy is mainly due to the uncertainty on that whether there is Early Cretaceous oceanic materials within the BNSZ? Our recent work discovered ~136Ma MORB-type diabase from the Kangqiong ophiolite in the western segment of the BNSZ, and such type of rocks within ophiolite has not been reported previously. Our results imply that there is potential Early Cretaceous oceanic crust within the BNSZ and the BNO was not closed in this period. Additionally, the formation age of this MORB-type rocks is synchronous with the duration of the ~140-130Ma magmatic gap in the southern Qiangtang Terrane, indicating a possible geodynamic connection between them. In view of this, this project plans to conduct detailed field geology, geochronological, geochemical and mineralogical researches on the Kangqiong ophiolite, intending to detect their petrogenesis. These results will be further used to probe the environment of ophiolite along with evidence from the regional magmatic-tectonic-sedimentary situation, which has the potential to improve the existing Mesozoic tectonic evolutional model for the BNSZ.

班公湖-怒江缝合带(班怒带)代表班公湖-怒江特提斯洋(班怒洋)消失后的遗迹。目前对班怒洋何时闭合仍存在~140Ma以前和~120-100Ma两个时间段的激烈争论，引发争议的主要原因是不清楚班怒带内早白垩世时期的古洋是否仍存在？我们最近对班怒带西段康穷蛇绿岩的预研究发现存在~136Ma、具有MORB型成分特征的辉绿岩，该时期的含有MORB型岩石单元的蛇绿岩在班怒带内尚未见前人报导。我们的结果指示出班怒带内很可能存在早白垩世古洋壳，暗示班怒洋此时可能还未闭合。此外，MORB型岩石的形成时代正好与羌塘南缘在~145-130Ma的岩浆活动间歇期同时，预示两者形成的构造过程存在内在联系。本项目拟对康穷蛇绿岩进行详细的野外地质、年代学、地球化学和矿物学研究，以揭示各个岩性单元的成因机制，并结合区域岩浆-沉积-构造等证据综合探讨蛇绿岩的形成环境和示踪班怒洋构造演化过程,以期修正班怒带中生代构造演化模式。

项目实施的三年期间，我们对青藏高原中部班公-怒江缝合带康穷蛇绿岩及周缘的岩浆作用进行了系统的野外考察、年代学、岩相学、矿物和全岩地球化学综合研究，圆满的完成了项目的既定任务和研究目标。取得主要成果包括：（1）确定班怒带西段康穷地区保存有时代为~138 Ma (SIMS和LA-ICP-MS锆石年龄)、形成于弧前环境的大洋岩石圈残片，证实班中提斯洋此时并未闭合，结合班怒带及南羌塘岩浆-构造-沉积组合特征，提出了大洋高原阻塞和引发中特提斯洋俯冲的构造演化模型；（2）将尼玛地区达者错火山岩喷发时代由1:25万地质图建议的侏罗纪修订为早白垩世晚期（~105-100 Ma），发现~105Ma和~100Ma喷发的火山岩在全岩Sr、Zr 、Sr/Y、La/Yb和锆石Ti、Yb/Gd等元素组成的差异指示了区域地壳由深-冷向浅-热熔融转变过程，与岩石圈伸展有关；（3）在北羌塘中始新世高Mg埃达克岩识别出单斜辉石成分反环带，为榴辉岩熔体-地幔橄榄岩反应的成岩模式提供了关键证据，在南羌塘识别出一套晚始新世喷发、含二辉石斑晶的粗面英安岩，据此提出羌塘地块地壳增厚和隆升机制和热状态演化。有关成果在Tectonics、Geology、GSA Bulletin、JGR-SE和Journal of Petrology等杂志发表基金署名论文9篇。