Martian meteorite Tissint records unique petrogenesis among the depleted shergottites

Abstract

Tissint, a new unaltered piece of Martian volcanic materials, is the most silicapoor and Mg-Fe-rich igneous rock among the "depleted" olivine-phyric shergottites. Fe-Mg zoning of olivine suggests equilibrium growth (<0.1°C h À1 ) in the range of Fo 80-56 and olivine overgrowth (Fo 55-18 ) through a process of rapid disequilibrium (~1.0-5.0°C h À1 ). The spatially extended (up to 600 lm) flat-top Fe-Mg profiles of olivine indicates that the early-stage cooling rate of Tissint was slower than the other shergottites. The chemically metastable outer rim of olivine (<Fo 55 ) consists of oscillatory phosphorus zoning at the impact-induced melt domains and grew rapidly compared to the early to intermediate-stage crystallization of the Tissint bulk. High-Ca pyroxene to low-Ca pyroxene and high-Ca pyroxene to plagioclase ratios of Tissint are more comparable to the enriched basaltic and enriched olivine-phyric shergottites. Dominance of augite over plagioclase induced augite to control the Ca-buffer in the residual melt suppressing the plagioclase crystallization, which also caused a profound effect on the Al-content in the late-crystallized pyroxenes. Mineral chemical stability, phase-assemblage saturation, and pressure-temperature path of evolution indicates that the parent magma entered the solidus and left the liquidus field at a depth of 40-80 km in the upper mantle. Petrogenesis of Tissint appears to be similar to LAR 06319, an enriched olivine-phyric shergottite, during the early to intermediate stage of crystallization. A severe shock-induced deformation resulted in remelting (10-15 vol%), recrystallization (most Fe-rich phases), and exhumation of Tissint in a time scale of 1-8 yr. Tissint possesses some distinct characteristics, e.g., impact-induced melting and deformation, forming phosphorus-rich recrystallization rims of olivine, and shock-induced melt domains without relative enrichment of LREEs compared to the bulk; and shared characteristics, e.g., modal composition and magmatic evolution with the enriched basaltic shergottites, evidently reflecting unique mantle source in comparison to the clan of the depleted members. Petrogenesis of Martian meteorite Tissint

Chemical layering in the upper mantle of Mars: Evidence from olivine‐hosted melt inclusions in Tissint

“…Details of the alphaMELTS calculation methods are mentioned in an earlier study by Basu Sarbadhikari et al. (), which further referred the possible sources of errors in the crystallization calculations of the Martian basalts and indicated the range of the errors for temperature (±50°C; Filiberto and Treiman ) and pressure (±0.1 GPa; Gross et al. ) in this model calculations than the experimentally derived ones.…”

“…; Basu Sarbadhikari ; Basu Sarbadhikari et al. ). Megacrystic olivines (Fo 80‐56 ) contain sparsely occurring melt inclusions.…”

“…; Basu Sarbadhikari ; Basu Sarbadhikari et al. ). Therefore, we were confident to use the Fe, Mg, Si, and Ca data of whole‐rock as the reference to calculate the amount of olivine addition to retrieve the parent magma of Tissint.…”

“…The pressure–temperature phase diagram of the whole‐rock of Tissint was shown by Basu Sarbadhikari et al. (). Here we observed modest differences of the P‐T phase diagram calculations between the parent magma (Fig.…”

“…15a of Basu Sarbadhikari et al. ) of Tissint. The significant differences are in (1) the extension of the stability field of Opx toward the lower pressure (up to ~3.5 kbar) for PM crystallization than that up to ~5 kbar for the WR; (2) appearance of augite at lower temperature (at ~1100 °C) from the PM than that (at ~1150 °C) from the WR; and (3) shrinking of the stability fields of plagioclase at low‐ P and garnet at high‐ P for ~100–150 °C lower temperature for the PM than that for the WR of Tissint.…”