西大别造山带夏店岩体锆石U-Pb年代学、地球化学特征及其A型花岗岩的厘定

对西大别造山带夏店岩体进行了系统的锆石LA-ICP-MSU-Pb定年、岩石地球化学研究,发现该岩体化学成分具富硅、碱,贫钙、镁、铝等特点;岩石轻稀土元素富集,重稀土元素亏损,轻重稀土元素分馏明显,Eu亏损明显;Rb、K、Th等大离子亲石元素和Pb元素富集,Ta、Nb、Ti等高场强元素亏损和Sr、Ba元素亏损;岩石成因类型上属于A型花岗岩。LA-ICP-MS锆石U-Pb定年结果显示夏店岩体~(206)Pb/~(238)U加权平均年龄为130.0±1.8 Ma,代表岩体的结晶年龄,显示该岩体为早白垩世岩浆活动的产物。夏店岩体A型花岗岩形成于造山期后环境,预示着桐柏-大别造山带板内演化阶段的到来。

Zircon U-Pb dating and geochemical characteristics of the Xiadian magmatic rock body in Western Dabie orogenic belt and its redefinition as the A-type granite

In this paper, the authors systematically performed zircon LA-ICP-MS U-Pb dating and studied rock geochemistry for Xiadian magmatic rock body in Western Dabie orogenic belt. The study shows that the rock body has characteristics of richer silicon and higher alkali, and poor Ca, Mg and Al. The rock body is characterized by enrichment of LREE, depletion of HREE, obvious fractionation between LREE and HREE, and strong depletion of Eu. The rocks are enriched in LILE (Rb, K, Th, etc) and Pb elements, and are depleted in HFSE (Ta, Nb, Ti, etc) and Sr and Ba elements. The rock body belongs to A-type granite in rock type. LA-ICP-MS zircon U-Pb dating yielded a ²⁰⁶Pb/²³⁸U weighted average age of 130.0±1.8 Ma for Xiadian magmatic rock body, which represents the crystallization age of the rock body, suggesting the Early Cretaceous magmatism product. A-type granites of Xiadian magmatic rock were formed in a post-orogenic environment, which indicates that the Tongbai-Dabie orogenic belt entered the plate evolution stage.