Los Angeles: The most differentiated basaltic martian meteorite

Los Angeles is a new martian meteorite that expands the compositional range of basaltic shergottites, Compared to Shergotty, Zagami, QUE94201, and EET 79001-B, Los Angeles is more differentiated, with higher concentrations of incompatible elements (e,g,, La) and a higher abundance of late-stage phase s such as phosphates and K-rich feldspathic glass. The pyroxene crystalliza tion trend starts at compositions more ferroan than in other martian basalt s, Trace elements indicate a greater similarity to Shergotty and Zagami tha n to QUE94201 or EET79001-B, but the Mg/Fe ratio is low even compared to po stulated parent melts of Shergotty and Zagami, Pyroxene in Los Angeles has 0.7-4-mum-thick exsolution lamellae, similar to 10 times thicker than those in Shergotty and Zagami. Opaque oxide compositions suggest a low equilibra tion temperature at an oxygen fugacity near the fayalite-magnetite-quartz b uffer. Los Angeles cooled more slowly than Shergotty and Zagami. Slow cooli ng, coupled with the ferroan hulk composition, produced abundant fine-grain ed intergrowths of fayalite, hedenbergite, and silica, by the breakdown of pyroxferroite. Shock effects in Los Angeles include maskelynitized plagiocl ase, pyroxene with mosaic extinction, and rare fault zones. One such fault ruptured a previously decomposed zone of pyroxferroite, Although highly dif ferentiated, the bulk composition of Los Angeles is not close to the low-Ca /Si composition of the globally wind-stirred soil of Mars.