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奥拉(Oura)岩浆杂岩由层状镁铁质和超镁铁质深成岩石序列组成,其中的铬尖晶石为次要的堆积相,呈浸染状分布于富橄榄石的超镁铁质堆积岩中。随着岩浆结晶作用的进行,尖晶石中的Al_2O_3含量明显增加。Al_(尖晶石)/Al(岩浆)分配系数也随铬尖晶石的结晶而增加。根据从体系Fo—An—Di—Qz(含Mg Cr_2O_4尖晶石)获得的实验结果,分配系数的增加可以解释为,由于岩浆中橄榄石的分离,使斜长石组分富集。晚期分离的铬尖晶石Cr/(Cr+Al)比值推测为母岩浆化学条件的指示剂:在标准矿物Pl-Cpx—Opx图解上,随着岩浆中斜长石组分的增加,该比值降低。奥拉岩浆杂岩中出现高铝铬尖晶石,表明岩浆富斜长石和单斜辉石组分,贫斜方辉石组分。它明显与深海拉斑玄武岩浆类似,而不同于富斜方辉石组分的大岩墙和布什维尔德(Bushveld)岩浆。
Oura magmatic complexes consist of a sequence of layered mafic and ultramafic plutonic rocks, with the chromite spinel being the secondary sedimentary facies with disseminated ultramafic Accumulation in the rock. With the crystallization of magma, the content of Al 2 O 3 in spinel obviously increases. The Al_ (spinel) / Al (magma) partition coefficient also increases with the crystallization of the chromium spinel. Based on the experimental results obtained from the system Fo-An-Di-Qz (containing Mg-Cr 2 O 4 spinel), the increase of the distribution coefficient can be explained by the enrichment of plagioclase components due to the separation of olivine in the magma. The Cr / (Cr + Al) ratio of the lately isolated chromium spinel is presumed to be an indicator of the chemical conditions of the parent magma: on the Pl-Cpx-Opx plot of the standard mineral, with the increase of plagioclase components in the magma reduce. High aluminum-chromium spinel appears in the Ola magmatic complex, indicating that the magmatism is rich in plagioclase and clinopyroxenite and poorly orthopyroxene components. It is distinctly similar to deep-sea tholei basaltic magma but unlike the large rock walls rich in orthopyroxene and Bushveld magmas.