High‐pressure minerals in shocked meteorites

Abstract

Heavily shocked meteorites contain various types of high-pressure polymorphs of major minerals (olivine, pyroxene, feldspar, and quartz) and accessory minerals (chromite and Ca phosphate). These high-pressure minerals are micron to submicron sized and occur within and in the vicinity of shock-induced melt veins and melt pockets in chondrites and lunar, howardite-eucrite-diogenite (HED), and Martian meteorites. Their occurrence suggests two types of formation mechanisms (1) solid-state high-pressure transformation of the host-rock minerals into monomineralic polycrystalline aggregates, and (2) crystallization of chondritic or monomineralic melts under high pressure. Based on experimentally determined phase relations, their formation pressures are limited to the pressure range up tõ 25 GPa. Textural, crystallographic, and chemical characteristics of high-pressure minerals provide clues about the impact events of meteorite parent bodies, including their size and mutual collision velocities and about the mineralogy of deep planetary interiors. The aim of this article is to review and summarize the findings on natural high-pressure minerals in shocked meteorites that have been reported over the past 50 years. 2017

Shock history of the fossil ungrouped achondrite Österplana 065: Raman spectroscopy and TEM of relict chrome‐spinel grains

“…Silicate minerals present in the matrix of strongly shocked meteorites show high plastic and brittle deformation and presence of twins, phase transformation to high‐pressure phases, and amorphization, all of which are not seen in chromite grains within the same meteorite (Leroux ; Gillet et al. ; Tomioka and Miyahara ). This is also corroborated by the work of Rout et al.…”

Shock-Induced Olivine-Ringwoodite Transformation in the Shock Vein of Chondrite GRV053584

“…Second, ringwoodite rims are polycrystalline aggregates. Polycrystalline ringwoodite is a feature of incoherent growth mechanism [2]. Ringwoodite rims around olivine cores are also reported in Antarctic chondrite GRV 022321 [53], Asuka 09584 [23], and Dhofar 1970 [51].…”

“…The parent body of meteorites undergoes one or more impact events in space, and the minerals in the meteorites are modified by shock-induced high pressures and high temperatures. Therefore, shock effects seen in these minerals are records of the shock conditions [2,3]. Understanding the processes involved in formation of these shock effects is fundamental for any interpretations of the impact events.…”

“…The chemical formula of olivine is A 2 SiO 4 , where A is a mixed portion of Fe 2+ , Mg 2+ , Ni 2+ , Mn 2+ and Ca 2+ . Because of the hypervelocity impact on the parent body of the meteorite, olivine in the meteorites always has been modified by shock waves and they usually display shock metamorphic features, such as undulatory extinction, mosaicism, planar fractures, planar deformation features, phase transformation, melting, and decomposition [2,[6][7][8][9]. Olivine provides an index for a meteorite shock classification scheme, i.e., shock levels of S1 (unshocked) to S6 (very strongly shocked) [3,10,11].…”

Absence of olivine orientation fabric in highly shocked Martian dunite

“…; Ruzicka et al. ; Tomioka and Miyahara ; Ruzicka and Hugo ), and computational simulations (e.g., Baer and Trott ) have addressed the effects of shock exposure. The most common macroscopic and microscopic manifestations of shock wave exposure in meteorites are deformational, transformational, or a combination of both (Sharp and DeCarli ).…”