额尔古纳地块新元古代岩浆作用:锆石U-Pb年代学证据

本文拟在研究区确定新元古代岩浆作用期次,进而在一定程度上从岩浆活动的角度制约额尔古纳地块的构造属性,故在前人工作的基础上,对额尔古纳地块新元古代侵入岩进行了LA-ICP-MS锆石U-Pb定年。研究区内6个代表性侵入岩中的锆石大部分呈自形–半自形晶,显示出典型的岩浆生长环带或条痕状吸收的特点,暗示其为岩浆成因。结合前人研究结果及本文测年结果,可将额尔古纳地块上新元古代岩浆作用划分为七期:1~927 Ma的碱长花岗岩;2~890 Ma的二长花岗岩;3~851 Ma的正长花岗岩;4~830 Ma的正长花岗岩和二长花岗岩;5~790 Ma的双峰式火成岩(包括辉长岩、辉长闪长岩、碱长花岗岩、正长花岗岩和花岗闪长岩);6~762 Ma的花岗闪长岩;7~737 Ma的正长花岗岩和二长花岗岩。这些新元古代侵入岩的发现表明额尔古纳地块上存在前寒武纪地质体。结合全球岩浆构造热事件,可以判定额尔古纳地块新元古代岩浆作用应是对Rodinia超大陆演化的响应,并且这些岩浆事件可以同图瓦–蒙古地块和中蒙古地块上发育的同期岩浆事件相对比,这暗示额尔古纳地块与西伯利亚克拉通南缘的这些微陆块具有亲缘性。

Neoproterozoic Magmatisms in the Erguna Massif,NE China：Evidence from Zircon U-Pb Geochronology

This paper reports new zircon U-Pb dating results for the Neoproterozoic intrusive rocks in the Erguna Massif, combined with previously published zircon U-Pb ages, determines the Neoproterozoic magmatic events, and discusses the tectonic attribution of the Erguna Massif. Zircon grains from six representative intrusive rocks are euhedral-subhedral in shape, and display fine-scale oscillatory growth zoning or striped absorption in CL images, implying a magmatic origin. Zircon U-Pb dating results, together with previously published ages, demonstrate that the Neoproterozoic magmatisms in the Erguna Massif can be subdivided into seven stages: (1) ~927 Ma, a suite of alkali feldspar granites; (2) ~890 Ma, a suite of monzogranites; (3) ~851 Ma, a suite of syenogranites; (4) ~830 Ma, a suite of syenogranites and monzogranites; (5) ~790 Ma, a bimodal intrusive rocks (including gabbros, gabbro-diorites, alkali feldspar granites, syenogranites, monzogranites, and granodiorites); (6) ~762 Ma, a suite of granodiorites; and (7)~737 Ma, a suite of syenogranites and biotite monzogranites. The findings of these Neoproterozoic magmatisms indicate the existence of Precambrian terranes within the Erguna Massif. Combined with the global magmatic-tectonic-thermal events, the Neoproterozoic magmatic events in the Erguna Massif are correspondences of the evolution of the Rodinia Supercontinent. Additionally, ages of the Neoproterozoic magmatic events in the Erguna Massif are similar to those in the Tuva-Mongolian Massif and Central-Mongolian Massif, implying that the Erguna Massif has an affinity to these Massifs of the southern Siberian Craton.