| 南海新生代玄武岩中单斜辉石地球化学特征
及其地质意义 |
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| 引用本文： | 闫纪元,李旭平,鄢全树.南海新生代玄武岩中单斜辉石地球化学特征
及其地质意义[J].地质论评,2014,60(4):824-838. |
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| 作者姓名： | 闫纪元 李旭平 鄢全树 |
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| 作者单位： | 山东科技大学，山东省沉积成矿作用实验室，山东青岛，266590；;山东科技大学，山东省沉积成矿作用实验室，山东青岛，266590；;国家海洋局第一海洋研究所，海洋沉积与环境地质国家海洋局重点实验室，山东青岛，266061 |
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| 基金项目： | 本文为国家自然科学基金资助重点项目(编号41230960)和山东科技大学创新团队项目（编号YCA110205）的成果。 |
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| 摘 要： | 南海新生代玄武岩中发育有大量的单斜辉石斑晶,与橄榄石、角闪石等斑晶共存,多数被熔蚀,呈浑圆状,部分发育有很窄的反应边。研究表明单斜辉石具有巨晶的特征,是在高压下在与寄主岩同源的岩浆中形成,没有经历长时间的沉淀生长而直接向上运移被带到地表,因而具有巨晶的主量及微量元素的特征却不具有巨晶的形态。单斜辉石稀土元素含量不高,HREE及LREE亏损,而MREE富集;大离子亲石元素Rb、Ba、Sr均出现明显的亏损,高场强元素Nb、Zr出现亏损而Hf略富集。Nb、Ta与Zr、Hf分馏明显。Th较为富集,而Pb强烈亏损,U的变化范围较大。研究发现南海新生代玄武岩中的单斜辉石的来源较为简单,为地幔柱的直接产物,并没有受到洋中脊—地幔柱相互作用的影响,由于岩浆上升速度较快压力迅速下降,橄榄石大量晶出,引起了岩浆成分的变化,致使单斜辉石与寄主岩成分和结构上没有达到平衡。
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| 关 键 词： | 单斜辉石 微量元素 新生代玄武岩 南海 |
| 收稿时间： | 2013/12/24 0:00:00 |
| 修稿时间： | 2014/6/15 0:00:00 |
Geochemical Characteristics and Geological Implications of
Clinopyroxenes in Cenozoic Basalts from
the South China Sea |
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| Abstract: | There are phenocryst clinopyroxenes, phenocryst olivines and phenocryst amphiboles in Cenozoic basalts dredged from the South China Sea. Most of clinopyroxenes are resorbed into rounded shape and have narrow reaction rims. Phenocryst clinopyroxenes with characteristics of megacryst are crystallized from parent magma which have the same source with the host lavas. Without long time crystallization, clinopyroxenes are carried up to the surface so that they don't have shape of megacryst. Clinopyroxene has lower REE abundance, and its REE content shows a heavily depletion of HREE and LREE in comparison with MREE. The LILE (such as Rb, Ba, Sr) and HFSE (such as Nb, Zr) show heavily depletions in comparison with Hf which shows lightly enrichment. Nb/Ta and Zr/Hf show obvious fractionation features. Th shows lightly enriched but Pb heavily depleted. This study shows the source of clinopyroxene is relatively simple. As a result of mantle plumes, they are not affected by the interaction between mid ocean ridge and mantle plumes. Due to the fast rising of parent magma, the pressure drops rapidly and lots of olivines crystallize out from magma. All these factors result in the variation of magma composition and finally lead to the disequilibrium of both composition and texture between clinopyroxene and host lavas. |
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| Keywords: | clinopyroxene trace elements Cenozoic basalt South China Sea |
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