Caracterização de fases minerais de alta pressão no meteorito Paranaíba

Abstract

In this paper, we present results of a characterization by Raman spectroscopy of mineral phases in the Brazilian meteorite Paranaíba, classified as a chondrite oil type L6 and shock scale S6 characterized by the presence of dark parts severely altered by the action of shock. We identified, after a series measurements at various points in the sample, some accessory minerals, mineral phases olivine and orthopyroxene that are the majority in the Paranaíba meteorite, as well as the high-pressure polymorphs of olivine: ringwoodite and wadsleyita. Phase characterization minerals produced naturally by the effect of shock metamorphism (high pressures and high temperatures) in ordinary chondrite meteorites assists the study of the formation of minerals and phase transitions under high pressures present inside the Earth, for the formation of ferromagnesian mineral phases such as Ringwoodite - polymorph of olivine (Mg, Fe) 2SiO4 - is expected to occur in the so-called Transition Zone between the upper mantle and the lower mantle (about 400 to 660 km depth). This phase can also be found in the so-called shafts or pockets of meteorite shock, due to the effect of the action of shock waves in the parental body of the which meteorite originated. Olivine, α- (Mg, Fe)2SiO4, as the pressure increases, is transformed into wadsleyita (β phase)) and then into ringwoodite, γ-(Mg, Fe)2SiO4. Through the Raman mapping we visualize the surface distribution of the mineral phases olivine, orthopyroxene and ringwoodite.