Estudo Comparativo entre os meteoritos Lavras do Sul e Putinga (Petrografia e Mineralogia

ANTONELLO L; ZUCOLOTTO E.; SCORZELLI R,; MUNAYCO P.; DOS SANTOS E.; VARELA, M.E; SOUZA AZEVEDO, I.

Belen

Congreso; 45 congreso brasilero de Geologia; 2010

This paper compares petrographic and mineralogical chondritic meteorites Lavras do Sul and Putinga. The Lavras do Sul was discovered near the city's name sake in 1985 and Putinga had seen its fall on August 16, 1937 with "strewfield", in the municipalities of Putinga, Ilópolis and Arvorezinha. As the Lavras do Sul did not have fall observed and presents similarities with the meteorite Putinga this study was necessary before the proposal of the record of Lavras do Sul to the Nomenclature Comittee of the Meteoritical Society. Studies were conducted by optical microscopy in transmitted and reflected light, electron microprobe (WDS) and Mössbauer spectroscopy. It was found that between the two meteorites exist clear mineralogical and textural similarities, yet they are two different meteorites. In transmitted plane and crossed polarized light both meteorites have chondrules with internal texture varied as: barred olivine (BO), radial pyroxene (RP), granular (GL) cryptocrystalline (C), porphyritic olivine pyroxene (OPP) and olivine (PO) and granular (GL) which are typical of chondrites of the chemical group L. In the Lavras, chondrules present size ranging from 0.5 to 2.0mm, medium (0.9 mm) in diameter; in the size Putinga goes up to 7 mm (average 0.8mm). The difference between the two chondrules meteorites is mainly because they are much defined and preserved in Lavras which is more in line with the type 5.The matrix is recrystallized in both, but are intensely recrystallized in Putinga, showing silicate developed crystals with little matrix between them. The major minerals are olivine and pyroxene, the accessories minerals are plagioclase (almost transformed into maskelynite and glass), and opaque minerals. They also show secondary iron hydroxides, as brown spots of iddingsite and goethite due to the terrestrial weathering.