华南显生宙时期岩石圈地幔的性质与形成时代  

Nature and formation age of the Phanerozoic sub-continental lithospheric mantle in South China

作　　者：刘传周[1] 

机构地区：[1]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029

出　　处：《岩石矿物学杂志》2013年第5期637-651,共15页Acta Petrologica et Mineralogica

基　　金：中国科学院知识创新工程重要方向项目(KZCX2-EW-109);国家自然科学基金面上项目(41222037;4127304)

摘　　要：火山岩携带的橄榄岩捕虏体是研究深部岩石圈地幔成分特征与热结构状态的最直接样品。湖北大洪山早奥陶世钾镁煌斑岩携带的石榴二辉橄榄岩具有富集的地球化学特征，指示当时的岩石圈厚度可达110krn。华南内陆地区宁远和道县早侏罗世玄武岩所携带的地幔包体具有饱满的成分特征，代表遭受了较低程度部分熔融的地幔残留。宁远地幔包体的全岩Re—Os同位素特征显示该地区中生代大陆岩石圈地幔为从软流圈新增生而形成的新生地幔。这表明内陆地区古生代存在的富集地幔被完全拆沉，并被新生地幔所取代；中生代内陆地区的岩石圈拆沉作用可能与该地区自225Ma以来大规模的岩石圈伸展作用有关。华南新生代地幔包体主要分布在沿海地区。通过地幔包体矿物成分估算获得的温度与压力资料揭示新生代沿海地区岩石圈厚度约为80--90km，并具有热的地温梯度。无论是全岩还是硫化物的Re-Os同位素特征都表明沿海地区在新生代仍残留有古元古代岩石圈地幔，表明新生代沿海地区的拉张作用仅导致了岩石圈地幔的部分拆沉和减薄。Mantle xenoliths entrained in volcanic rocks are direct samples that could provide important informa- tion on both compositions and thermal state of the sub-continental lithospheric mantle （SCLM）. Garnet lherzo- lites trapped by lamproites that were emplaced during the Early Ordovician at Dahongshan of Hubei Province dis- play abundant characteristics of both trace elements and imtopes. Their p-t estimates indicate that the SCLM has a thickness of --110 kin. Mantle xenoliths trapped by the Early Jurassic basalts in the hinterland of South China （Ningyuan and Daoxian） have fertile compositions, representing the mantle residues that were subjected to low degrees of partial melting. The whole-rock Re-Os isotopes of Ninyuan mantle xenoliths support the exis- tence of juvenile mantle in these areas during the Mesozoic, which resulted from the accretion of the astheno- sphere. Therefore, the enriched mantle that had probably existed beneath Ningyuan during the Paleozoic was completely delaminated and replaced by juvenile mantle. The mantle delamination was geodynamically related to the large-scale lithospheric extension, which occurred since --225 Ma. The Cenozoic basalts widely distributed along the coastal areas of South China contain abundant mantle xenoliths, p-t estimates based on mineral compo- sition reveal that the lithospheric mantle has a thickness of 80- 90 km, with a hot geothermal gradient. Both whole-rock and sulfide Re-Os isotopes support the existence of ancient mantle ages beneath the coastal areas of South China during the Cenozoic. Therefore, the sion in this area only triggered partial removal of the ancient lithospheric mantle. residues of Paleoproterozoic Cenozoic lithospheric extension in this area only triggered partial removal of the ancient lithospheric mantle.

关 键 词：华南 大陆岩石圈地幔 地幔包体 RE-OS同位素 

分 类 号：P542.5[天文地球—构造地质学] P597[天文地球—地质学]