Abstract
The ranges in chemical composition of ancient achondrite meteorites are key to understanding the diversity and geochemical evolution of planetary building blocks. These achondrites record the first episodes of volcanism and crust formation, the majority of which are basaltic. Here we report data on recently discovered volcanic meteorite Northwest Africa (NWA) 11119, which represents the first, and oldest, silica-rich (andesitic to dacitic) porphyritic extrusive crustal rock with an Al–Mg age of 4564.8 ± 0.3 Ma. This unique rock contains mm-sized vesicles/cavities and phenocrysts that are surrounded by quench melt. Additionally, it possesses the highest modal abundance (30 vol%) of free silica (i.e., tridymite) compared to all known meteorites. NWA 11119 substantially widens the range of volcanic rock compositions produced within the first 2.5–3.5 million years of Solar System history, and provides direct evidence that chemically evolved crustal rocks were forming on planetesimals prior to the assembly of the terrestrial planets.
Highlights
The ranges in chemical composition of ancient achondrite meteorites are key to understanding the diversity and geochemical evolution of planetary building blocks
Petrologic examination of Northwest Africa (NWA) 11119 was conducted on the Institute of Meteoritics (IOM) deposit sample (Supplementary Fig. 1; 4.2 × 3.3 × 2.3 cm) as well as a polished slice (0.95 × 0.55 cm) of the deposit sample embedded in a 1-inch epoxy mount
NWA 11119 exhibits a porphyritic texture composed of millimeter-sized phenocrysts of pyroxene (
Summary
The ranges in chemical composition of ancient achondrite meteorites are key to understanding the diversity and geochemical evolution of planetary building blocks These achondrites record the first episodes of volcanism and crust formation, the majority of which are basaltic. Newly discovered achondrites have recently provided evidence that crusts on planetesimals early in the Solar System were comprised of more evolved rocks with higher silica contents than typical achondrites[1,2,3]. These evolved lavas, similar to Earth’s average continental crust, were long thought to be exclusive to large, planet-sized bodies. Spherical vesicles and irregularshaped cavities were observed throughout the stone
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