A Revised Shock History for the Youngest Unbrecciated Lunar Basalt - Northwest Africa 032

Abstract

Northwest Africa (NWA) 032 is the youngest radio metrically dated mare basalt, with concordant Rb-Sr and Sm-Ndages of 2.947 ± 0.016 Ga and 2.931 ± 0.092, respectively [1]. Measurement of the cosmogenic nuclides present in NWA 032 suggest an Earth-Moon transfer age of 0.5Ma, typical of lunar meteorites [2]. NWA 032 is an unbrecciate dolivine-pyroxene-phyric basalt, with olivine, pyroxene and plagioclase as major minerals (Fig.1). A previous description of shock effects in NWA 032 allowed for a shock pressure estimate of ~4060 GPa [2]; however, the shock state of plagioclase feldspar (shock-amorphized vs crystalline) was inconclusive, owing to the fine grain size of this mineral (≤1μm). The purpose of our study is to characterize the shock deformation and transformation effects in NWA 032 using field emission scanning electron microscopy (FESEM) and micro-Raman spectroscopy, focusing on the structural state of feldspar, shock deformation recorded in igneous olivine and pyroxene, as well as characterizing the crystallization products of shock melting. The latter have been demonstrated as useful criteria to evaluate shock conditions [3]. Our results more tightly constrain the shock history experienced by NWA 032.

Presented in absentia on April 27, 2020 at "Student Research Day" at MacEwan University in Edmonton, Alberta. (Conference cancelled)

Faculty Mentor: Erin L. Walton 

Department: Earth and Planetary Sciences