GLASSES IN METEORITES AND THE PRIMARY LIQUID CONDENSATION MODEL

VARELA, M.E; KURAT, G

Mitteilugen Der Osterreischischen Mineralogischen Gessellschaft

Österreichischen Mineralogischen Gesellschaft

Lugar: Innsbruck; Año: 2009 vol. 155 p. 279 - 320

1680-8959

of chondritic constituents and achondritic rocks. Conventional genetic models see them as residual liquids from which the associated minerals crystallized ? as demonstrated by terrestrial igneous rocks ? or as locally produced impact melts. These models are all closely related to ourexperiences with terrestrial geology and petrology and, consequently,make planetary processes, such as mixing and melting of solid precursors and planetary differentiation primarily responsible for the formation of the large variety of meteoritic rocks. However, different types of glasses(e.g., glass inclusions in minerals, mesostasis glasses, glass pockets, glass veins) in a variety of meteorites (chondrites and achondrites) have particular chemical features that cannot be reconciled with these models:1)Glasses do not show the chemical signature of crystallization of the minerals they are associated with ? a geochemical impossibility;2) All types of glasses in all types of meteorites reported here show very similar trace element abundance pattern with the refractory lithophile element abundances at ~ 10?20 x CI chondrite abundances.3) All refractory element abundance patterns in primitive glasses have unfractionated solar relative abundances (they are flat) and medium refractory and volatile elements are depleted relative to the refractory elements.4) Medium volatile and volatile elements, when present, display chaotic abundance patterns.The ubiquitous pattern for refractory elements signals vapor fractionation rather than geochemical (?igneous?) fractionation or stochastic mixing of precursor minerals (as in shock melts).It indicates that the same process must have been involved in the origin of all glasses in chondritic constituents as well as achondritic rocks and, consequently, in the formation of all meteorite types investigated. The chaotic abundances of volatile elements signal that chaotic processeswere involved during condensation.