The unusual low Mg rock clasts from Lohawat Howardite, India: Petrogenetic implications

摘要

We report here a few, unusual, low Mg rock clasts from Lohawat howardite, a megaregolith of matrix-dominated polymict breccia comprising clasts of ~16 diogenites, ~9 basaltic eucrites and ~3 cumulate eucrites. Low Mg rock clasts are largely characterised by silica-fayalitic olivine (Fa_(73-95))-ferroaugite (En_(3-29)Fs_(32-55)Wo_(34-41)) bearing symplectites along with ferroan pyroxenes, calcic feldspars (An 89.3), low Mg ilmenite (0.3 wt. MgO) and a quartz-ilmenite intergrowth phase. Two tiny melt inclusions include K-rich granite and Ca-rich granitic composition, respectively. These low Mg rock clasts appeared ballistically transported regolith fines of granite from some unidentified, distant areas where high-energy impact on eucrite crust could have generated limited parental melt (via impact-induced remelting) and ultimately produced the low Mg rocks and acidic melts, respectively.