Igneous cooling history of olivine-phyric shergottite Yamato 980459 constrained by dynamic crystallization experiments.

First, E. and Hammer, J.

Meteoritics & Planetary Science. doi: 10.1111/maps.12659
Article first published online: 10 MAY 2016


“Dynamic crystallization experiments were performed on a liquid having the bulk composition of olivine-phyric shergottite Yamato 980459, to constrain the igneous thermal history of this meteorite. Key characteristics of the meteorite’s mineralogy and texture, including several morphologically distinct olivine and pyroxene crystal populations and a glassy mesostasis devoid of plagioclase, were replicated upon cooling from 1435 to 909 °C at 1 atmosphere under reducing conditions. Three sequential cooling ramps are required to produce synthetic samples with textures and compositions matching Yamato 980459. Olivine phenocrysts formed at <1 °C h−1, presumably at depth in the Martian crust. Pyroxene phenocrysts formed mainly at ~10 °C h−1, consistent with crystallization within a lava flow at depths of 25–45 cm. Increased cooling rate (~100 °C h−1) in a third stage suppressed the formation of plagioclase and produced groundmass crystals, consistent with crystallization at lava flow depths of 5–7 cm. Although Y 980459 is unique among Martian meteorites (i.e., preserving a primary glassy mesostasis), its emplacement did not require unique physical conditions. Rather, the second and third cooling stages may reflect cooling within the core of a pāhoehoe-like flow and subsequent breakout on the surface of Mars."