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山东方城玄武岩(125Ma)中发现罕见的具有明显环带结构的橄榄石.橄榄石中心部分的组成(Mg#=87.2~90.7)类似于华北新生代玄武岩携带的橄榄岩捕虏体中橄榄石的组成,其边缘部分(Mg#=76.8~83.9)接近于玄武岩中斑晶橄榄石的组成(75.7~79.0).橄榄石的这种化学成分特征及其浑圆的晶体形态和较小的颗粒(300~800祄)皆说明这些橄榄石是地幔矿物捕虏晶,即地幔橄榄岩的解体矿物.其中心部分能够代表地幔橄榄岩的组成.橄榄石的环带结构是橄榄石捕虏晶与寄主玄武岩快速反应造成的.这种橄榄石与玄武质岩浆的相互反应可能在华北中生代岩石圈地幔中普遍存在,即为岩石圈地幔置换作用的重要方式.从而使古生代主量元素亏损的高镁橄榄岩转变为中生代晚期的主量元素饱满同位素富集的低镁橄榄岩,造成古老岩石圈地幔的消失.
The rare olivine with obvious zonal structure was found in the basalt of Fangcheng, Shandong Province (125Ma). The composition of the central part of olivine (Mg # = 87.2 ~ 90.7) is similar to that of olivine xenoliths carried by Cenozoic basalts in North China (Mg # = 76.8 ~ 83.9) is close to that of the basaltspectrophyllite (75.7 ~ 79.0) .The characteristics of this chemical composition of olivine and its rounded crystal morphology and its smaller size ( 300 ~ 800 祄) all indicate that these olivines are the mantle mineral xenocrysts, ie, the dissolved minerals of the mantle peridotite, and its central part can represent the composition of the mantle peridotite.The peridotitic structure of olivine is the host of olivine xenoliths and host Basalt rapid reaction caused by the reaction of olivine and basaltic magma may be ubiquitous in the Mesozoic lithospheric mantle in North China is the lithosphere mantle permutation of an important way so that the loss of the main element of the Palaeozoic high magnesium The rock became the isotopic enrichment of low-ductile ore with the major elements of the late Mesozoic, resulting in the disappearance of the ancient lithospheric mantle.