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

Dwijesh Ray & Sambhunath Ghosh

Journal of Earth System Science, Volume 131, Article number: 125 (2022)
Published: 26 May 2022

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“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 (Fa73–95)–ferroaugite (En3–29Fs32–55Wo34–41) bearing symplectites along with ferroan pyroxenes, calcic feldspars (An 89.3), low Mg ilmenite (<0.3 wt.% MgO), troilite and SiO2 polymorph. A few low Mg clasts without symplectites contain ferro-pigeonite (En30Fs55.8Wo14), ternary calcic feldspar (An81.8Ab17.4Or0.8), 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.”