西藏那曲县北聂荣微地块聂荣岩群中斜长角闪岩——Rodinia超大陆裂解的地质纪录

西藏那曲县北聂荣微地块聂荣岩群中斜长角闪岩原岩恢复为正斜长角闪岩,地球化学特征显示岩石属于拉斑系列基性火山岩,具有轻稀土元素富集、重稀土元素亏损的右倾型稀土元素配分模式。岩石富集大离子亲石元素Rb、Ba及高场强元素Nb、Ta,Sr、Th和U呈现明显的负异常,在构造环境判别图解中样品均投到板内玄武岩区,具有与裂谷火山岩相似的地球化学特征。通过高精度的LA-ICP-MS(激光剥蚀等离子体质谱仪)锆石微区原位U-Pb同位素测年,西藏那曲县北聂荣微地块聂荣岩群片麻状斜长角闪岩中获得863±10 Ma的谐和年龄,为原岩(基性火山岩)的形成时代,说明聂荣岩群形成于新元古代早期。该年龄相当于Rodinia超大陆裂解的地质记录。此外,还获得了2 539~1 006 Ma之间的捕获锆石年龄信息。

The amphibolite from Nyainrong Rock Group in northern Nagqu: geological records of break-up of the supercontinent Rodinia

The protolith of the studied amphibolite is ortho-plagioclase amphibolite,with the geochemical characteristics of tholeiite series basic volcanic rocks.The chondrite-normalized REE patterns are rightward inclined and the primitive mantle normalized trace element spidergrams are characterized by enriched Rb,Ba,Nb and Ta and depleted Sr,Th and U.In addition,the tectonic discrimination diagrams for Nyainrong Rock Group gneissic amphibolite show the attribution to intraplate basalt,which is compatible with the characteristics of rift-related volcanic rocks.High resolution LA-ICP-MS in situ dating yields the age of 863±10 Ma for gneissic amphibolite in Nyainrong Rock Group located in Nyainrong microblock,northern Nagqu County,Tibet,which indicates the protolith age of basic volcanic rocks and further restricts the formation age of Nyainrong rock group.This age is equal to the geological record of Rodinia supercontinent break event.Furthermore,the ages of 2 539～1 006 Ma for captured zircons are also yielded in Nyainrong Rock Group.