Petrology and geochemistry of a silicate clast from the Mount Padbury mesosiderite: Implications for metal-silicate mixing events of mesosiderite

Abstract

Abstract-Petrological and bulk geochemical studies were performed on a large silicate clast from the Mount Padbury mesosiderite. The silicate clast is composed mainly of pyroxene and plagioclase with minor amounts of ilmenite, spinel, and other accessory minerals, and it shows subophitic texture. Pyroxenes in the clast are similar to those in type 5 eucrites and could have experienced prolonged thermal metamorphism after rapid crystallization from a near-surface melt. Ilmenite and spinel vary chemically, indicating growth under disequilibrium conditions. The clast seems to have experienced an episode of rapid reheating and cooling, possibly as a result of metal-silicate mixing. Abundances of siderophile elements are obviously higher than in eucrites, although the clast is also extremely depleted in highly siderophile elements. The fractionated pattern can be explained by injection of FeFeS melts generated by partial melting of metallic portions during metal-silicate mixing.The silicate clast had a complex petrogenesis that could have included: 1) rapid crystallization from magma in a lava flow or a shallow intrusion; 2) prolonged thermal metamorphism to equilibrate the mineral compositions of pyroxene and plagioclase after primary crystallization; 3) metal-silicate mixing probably caused by the impact of solid metal bodies on the surface of the mesosiderite parent body; and 4) partial melting of metal and sulfide portions (and silicate in some cases) caused by the collisional heating, which produced Fe-FeS melts with highly fractionated siderophile elements that were injected into silicate portions along cracks and fractures.

K‐Th‐Ti systematics and new three‐component mixing model of HED meteorites: Prospective study for interpretation of gamma‐ray and neutron spectra for the Dawn mission

“…K ⁄ Ti and K ⁄ Th 2r variations for the HED suite are shown as shaded areas. Data sources for the achondrite suites areRubin and Jerde (1987;,Mittlefehldt (2003),Mittlefehldt et al (2002),Yamaguchi et al (2002),Tamaki et al (2006), andDay et al (2009).…”

Petrology and mineralogy of mesosiderite Northwest Africa 12949: Implications for geological history on its parent body

“…(3) mixing of metal and silicates and rapid cooling (Delaney et al, 1981;Ganguly et al, 1994;Ruzicka et al, 1994;Tamaki et al, 2006); (4) deep burial and slow cooling (Bogard & Garrison, 1998;Haack et al, 1996;Hopfe & Goldstein, 2001;Yang et al, 1997); and (5) impact excavation and ejection at <4 Ga (Bogard, 2011;Bogard et al, 1990;Kring & Cohen, 2002). However, several key processes of mesosiderite formation have remained unclear, including the number of impact and reheating events, the time of metal and crustal silicate mixing, the degree and the peak temperatures of thermal metamorphism, and the emplacement depths in each thermal event (e.g., Caves, 2019;Pittarello et al, 2019;Sugiura et al, 2022).…”

“…Mesosiderites have experienced complicated thermal histories. The well‐accepted formation model of mesosiderites (e.g., Rubin, 1997; Rubin & Mittlefehldt, 1993; Scott et al., 2001) can be divided into the following stages: (1) accretion and initial crystallization of mesosiderite silicates at 4.56–4.47 Ga (Haba et al., 2019; Stewart et al., 1994; Wadhwa et al., 2003); (2) collisional disruption and intense brecciation (Haba et al., 2017; Jourdan et al., 2021); (3) mixing of metal and silicates and rapid cooling (Delaney et al., 1981; Ganguly et al., 1994; Ruzicka et al., 1994; Tamaki et al., 2006); (4) deep burial and slow cooling (Bogard & Garrison, 1998; Haack et al., 1996; Hopfe & Goldstein, 2001; Yang et al., 1997); and (5) impact excavation and ejection at <4 Ga (Bogard, 2011; Bogard et al., 1990; Kring & Cohen, 2002). However, several key processes of mesosiderite formation have remained unclear, including the number of impact and reheating events, the time of metal and crustal silicate mixing, the degree and the peak temperatures of thermal metamorphism, and the emplacement depths in each thermal event (e.g., Caves, 2019; Pittarello et al., 2019; Sugiura et al., 2022).…”