學術資源整合系統-相關推薦

 
作者何恭算
出版日期20160325
著作名稱華北漢諾壩和陽原火山岩區輝石岩包體之地化特性與成因研究:綜合全岩及礦物尺度來探討
計畫名稱華北漢諾壩和陽原火山岩區輝石岩包體之地化特性與成因研究:綜合全岩及礦物尺度來探討
其他資訊頁51
摘要Pyroxenite xenoliths of Hannuoba and Yangyuan volcanic fields are composed mainly by clinopyroxene, orthopyroxene and in minor amount olivine, feldspar, spinel, garnet, and opaque minerals. The 34 xenoliths analyzed may be divided into three groups, Al-augite pyroxenites, Cr-diopside pyroxenites, and garnet pyroxenites, based on the chemical classification of Whilshire and Shervais (1975). They show large variations in chemical and isotopic compositions (SiO2 = 44.27 to 54.49 wt.%, MgO = 12.60 to 32.02 wt.%, CaO = 2.33-23.19 wt.%, 87Sr/86Sr = 0.704447 to 0.713407, 143Nd/144Nd = 0.511076 to 0.512953) and less-radiogenic Pb isotopic ratios (206Pb/204Pb = 17.122-18.099, 207Pb/204Pb = 15.369-15.546, 208Pb/204Pb = 37.076-38.030). These pyroxenites have significantly negative Nb anomalies, suggesting possible contamination of crustal materials. Lithospheric extension was widespread in East China and adjacent areas during the Late Mesozoic and Cenozoic time. The formation of Al- and Cr-pyroxenites is probably caused by upwelling of asthenosphere and thinning of the North China craton lithosphere in times of extension. It is thus likely that the wide range in Sr-Nd isotopic compositions of Al- and Cr-pyroxenites resulted from mixing (interaction) between asthenosphere-derived melts and delaminated lower crust. The garnet pyroxenites have relatively high 87Sr/86Sr at given 143Nd/144Nd, values that are significant deviation from the isotopic array defined by the Al- and Cr-pyroxenites. In addition to, based on the spider diagrams of incompatible elements, these xenoliths show a positive Sr anomaly. These characters may have resulted from mantle contamination due to a paleo-subduction and lithospheric thinning events. Therefore, they were probably segregated from melts, which derived from partial melting of a mixture of altered MORB and delaminated lower crust.
系統號NO000004004

Aug 16 2018 10:46:44
nmns/nmnsweb_2nd_target(0)