摘要
系统的年代学、元素地球化学和Sr-Nd同位素地球化学研究表明,琼南晚白垩世基性岩墙群形成于81Ma,富K(K2O约为1.95%～3.63%,K2O/Na2O约为0.61～1.12)、大离子亲石元素、轻稀土元素和Pb,亏损高场强元素,具高的87Sr/86Sr初始值(0.7078～0.7084)和负的εNd(t)值(-3.2～-2.3),为典型的钾玄质系列岩石,类似于与俯冲环境相关的高K/Ti-低Ti钾质岩石。该岩墙群形成于“后碰撞弧”的板内拉张环境,源自与俯冲作用有关的富钾和大离子亲石元素的交代地幔,并经历了明显的以单斜辉石为主的结晶分异作用。此外,琼南基性岩墙群和粤北及福建沿海地区晚白垩世基性岩脉的对比表明,晚白垩世中国东南部岩石圈地幔组成存在区域性的差异,这种差异很可能与区域构造演化历史的不同有关。
Systematic geochronologic, geochemical and Sr Nd isotopic analyses are reported for the Late Cretaceous mafic dike swarms in southern Hainan Island. The dikes were emplaced at 81 Ma. They are characterized by enrichment in K (K2O≈1.95%～3.63%, K2O/Na2O≈0.61～1.12), LILE, LREE and Pb, depletion in HFSE, high initial 87Sr/86Sr ratios (0.707 8 to 0.708 4), and negative εNd(t) values (-3.2 to -2.3), belonging to shoshonitic series and resembling high K/Ti and Low Ti potassic magmas formed in subduction related settings. Theshoshonitic magmas were formed in post collision extension setting by partial melting of subduction related metasomatized mantle sources enriched in K2O and LILE, followed by crystal fractionations of clinopyroxene. The different geochemical and Sr Nd isotopic characters of the Late Cretaceous mafic dikes in northern Guangdong, Fujian coastal areas and southern Hainan Island indicate the heterogeneities of sub continental lithosphere mantle beneath southeastern China, which should be related to the different histories of regional tectonic evolution.
出处
《地球化学》
CAS
CSCD
北大核心
2003年第1期11-20,共10页
Geochimica
基金
中国科学院知识创新工程重要方向项目(KZCX2-102)
国家杰出青年科学基金(49725309)
