摘要
对粤北白垩纪基性岩脉进行了系统的年代学、元素和Ｓｒ－Ｎｄ同位素地球化学研究。基性岩脉主要形成于～１４０Ｍａ、～１０５Ｍａ、～９０Ｍａ三个阶段，其化学成分以拉斑质玄武岩为主，高的εＮｄ（Ｔ）值（＋５）表明其母岩浆来源于一大离子亲石元素和轻稀土元素长期较亏损的地幔源。基性岩脉的地球化学特征总体上与板内玄武岩相似，但一些年龄为～１４０Ｍａ的基性岩脉的岛弧特征也很明显，反映了它们可能是在拉张环境下由先前被俯冲带流体交代的地幔源重熔形成的，该地幔源在微量元素组成上具有ＥＭＩ特征。综合本文的研究及已有的花岗岩、火山岩年代学和地球化学研究以及盆地演化的资料，我们认为华南白垩纪构造应力场以拉张为主，四次重要的拉张活动时代为～１４０Ｍａ、～１２４Ｍａ、～１０５Ｍａ、～９０Ｍａ。
Systematic radiometric, geochemical and Sr-Nd isotopic analyses are reported here for the Cretaceous mafic dikes from northern Guangdong, SE China in order to provide a better understanding of the origin of magma and its tectonic significance. The mafic dikes were emplaced in three principal episodes: at～140Ma, ～105Ma and ～90Ma. With the chemical characteristics of tholeiitic basalts, they were derived from a moderate time-integrated LREE depleted mantle source with ε Nd ( T) values of 5. The trace element chemistry of the dikes shows general similarities to within-plate basalts. However, some of the 140 Ma dike samples exhibit arc signitures with Th-enrichment and Zr-and Hf-depletion. Thus, these mafic dikes are interpreted as having been magmatism produced during a lithospheric extension from a mantle source influenced by earlier subduction processes. This mantle source shows an EMII signature in incompatible trace element ratios. The combined geochemical and geochronological constraints on the origin of the mafic dikes, together with results from previous studies of late Mesozoic granites, volcanic rocks and extensional (or rifted) basins indicated that SE China was dominated by an extensional tectonic regime during the Cretaceous, with four major episodes of extensional activities taking place at ～ 140Ma ,～124 Ma,～105 Ma and～90 Ma.
出处
《地球化学》
CAS
CSCD
北大核心
1997年第2期14-31,共18页
Geochimica
基金
国家自然科学基金
关键词
基性岩脉
同位素年代学
元素地球化学
mafic dikes, isotopic geochronology, elemental geochemistry, northern Guangdong Province
