摘要
南海新生代玄武岩中橄榄石斑晶颗粒相对较小(0.2～0.6mm),自形-半自形,有熔蚀现象,不具橄榄石捕虏晶所特有环状裂隙、变形结构。基质中橄榄石微晶粒径0.01～0.05mm,多数已完全伊丁石化。早期结晶出来的橄榄石并未受到重力分异的影响,而被寄主岩浆携带继续向地表运移,在此上升过程中与寄主岩浆发生了有限的相互作用,少数橄榄石颗粒保留有弱成分分带现象。利用呈弱成分分带现象的橄榄石斑晶的核、幔部的Fo组分与寄主岩浆的X_(Fe)值对南海底潜在地幔温度进行了估算,结果表明南海的潜在地幔温度平均值为1661℃,位于典型热点的地区夏威夷(1688℃)和冰岛(1637℃)之间,南海的潜在地幔温度与正常洋中脊地幔潜在温度之间的差值(186℃～208℃)也位于夏威夷(213℃～235℃)和冰岛地区(162℃～184℃)之间,表明南海地区下的地幔可能存在热量异常,支持了根据地球物理学和岩石地球化学的信息所提出的南海地区存在地幔柱的观点。
The Grain size of mostly olivine phenocrysts in Cenozoic basalts dredged from the South China Sea are relatively small （0.2-0.6mm ）, the shape of that is idiomorphic or hypidomorphic with slightly resorption. There don＇t take on the peculiar ringfracture and deformation structure which olivine xenocrysts have. In groundmass, the grain size of olivine microlites is just 0.01 - 0. 05mm, and most of them were totally transformed into iddingsite. Earlier olivine phenocryst crystallizing from the magma are not precipitate and remain in deeper mantle, but entrained and transported towards the surface by host magma. During the ascent of magma, there may be have a restricted interaction between earlier olivine phenocryst and host magma, and a extremely small amount of olivine phenocryst still held the phenomena of weak zoning belt in composition. Therefore, olivine phenocrysts in the studied area are not xenocryst. Using Putirka（2005） method, combined with Fo valule of core and mantle part of weak zoning olivine phenocryst and XFe value of host magma we have estimated mantle potential temperature （Tp） below the central basin of the South China Sea. The results indicate that the mean value of Tp for the South China Sea is 1661℃ and hotter than that of OIs（ ocean ridges） （1453℃ - 1475℃ ）, which lie in the middle part between Hawaii hotspot and Iceland hotspot. The contrast for Tp value between the South China Sea and normal OIs is 186℃ - 208℃, which also lie in he middle part between To values of Hawaii hotspot and Iceland hotspot whose To values are 213℃ -235℃ and 162℃ - 184℃, respectively. The results show that the mantle below the South China Sea may be exist thermally anomalous, support the idea that there may be exist mantle plume around the South China Sea which is put forward in the light of those evidence from geophysical and/or petrologic data.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2008年第1期176-184,共9页
Acta Petrologica Sinica
基金
科技基础性工作和社会公益研究专项项目(2003DIB3J114)
青岛市科技将才专项计划项目(05-2-JC-79)资助成果
关键词
橄榄石
碱性玄武岩
地幔潜在温度
地幔柱
南海
Olivine, Cenozoic basalt, Mantle potential temperature, Mantle plume, South China Sea
