High resolution X–ray computed tomography and scanning electron microscopy studies of multiphase solid inclusions in Oman podiform chromitite: implications for post–entrapment modification

抄録

We used high–resolution X–ray computed tomography (HRXCT) combined with scanning electron microscopy (SEM) to obtain 3D and 2D images of multiphase solid inclusions within chromite from the Samail ophiolite to investigate post–entrapment modification of the inclusions. Results indicate that the parental melt of the chromitite was supersaturated in chromian spinel. Chromite continued to crystallize on the inner wall of the host chromite after the melt was trapped. Rapid growth caused crystallization of high–Cr#[= Cr/(Cr + Al)] chromite lining around inclusions. The necking–down of originally large melt inclusions probably produced various assemblages of daughter minerals among the inclusions. We report two observations that are consistent with rapid growth of the host chromite: the 3D distribution of inclusions in host chromite and the host chromite showing skeletal morphology. High–temperature homogenization experiment was conducted to obtain the parental melt composition of the inclusions. We found that the homogenized glass does not represent the parental melt trapped in the host chromite because of the remaining of high–Cr# chromite lining and possible residual phases in the experiments.