Lavras do Sul: A New Equilibrated Ordinary L5 Chondrite from Rio Grande do Sul, Brazil

Abstract

The new Brazilian chondrite, Lavras do Sul was found in 1985 at Lavras do Sul, Rio Grande do Sul State. Brazil. (33°30'48"S; 53°54'65"W). It consists of one mass weighting about 1kg and being covered by a black fusion crust with grayish interior. Four polished thin sections were prepared from a slice weighing 67g on deposit at Museu Nacional/UFRJ. It consists mostly of chondrules and chondrule fragments dispersed in a recrystallized matrix. Most chondrules are poorly defined and range in size from 300µm to 2000 µm, although some of them show distinct outlines, particularly when viewed under cross-polarized transmitted and reflected light. The texture of chondrules varies from: non-porphyritic (e.g., barred-olivine, radial-pyroxene); to porphyritic ones (e.g., granular olivine as well as olivine-pyroxene). The meteorite contains mainly olivine (Fa24.9), low-Ca pyroxene (Fs22.6) and metal phases, with minor amount of plagioclase, chromite and magnetite. Mössbauer Spectroscopy studies indicate that the metal phase is kamacite, tetrataenite and antitaenite. Veins of secondary iddingsite crosscut the thin section and some ferromagnesian silicates. The chemical composition indicates that Lavras do Sul is a member of the low iron L chondrite group. The poorly delineated chondritic texture with little quantity of welldefined chondrules, the occurrence of few clinopyroxene and plagioclase (and maskelinite) with apparent diameters ranging from 5µm to 123µm in length, led us to classify Lavras do Sul in an equilibrated petrologic type 5. The shock features of some minerals, suggests a shock stage S3, and the presence of a small amount of secondary minerals such as iddingsite and goethite, a degree of weathering W1. The meteorite name was approved by the Nomenclature Committee

Applications of Mössbauer Spectroscopy in Meteoritical and Planetary Science, Part I: Undifferentiated Meteorites

“…In the studies of equilibrated L ordinary chondrites Villalbeto de la Peña L6 and Lavras do Sul L5 [88,89], the authors measured the Mössbauer spectra of both bulk material and extracted metal fraction after magnetic separation (see Figure 23). The bulk spectra of Villalbeto de la Peña L6 and Lavras do Sul L5 consist of four components with two magnetic sextets and two quadrupole doublets.…”

“…Parameters for the magnetic fraction were: δ = 0.04 mm/s, H eff = 314 kOe, A = 23.5% for taenite (1); δ = 0.02 mm/s, H eff = 337 kOe, A = 76.5% for kamacite (2). The authors of [89] found two sextets assigned to kamacite and tetrataenite in the spectrum of the metal separate from Lavras do Sul L5, as well as revealed an additional singlet peak related to the paramagnetic γ-Fe(Ni, Co) phase (a brief discussion about questionable term "antitaenite" see above in Section 6.1). An unusual result was obtained in the study of Ararki L5 ordinary chondrite in [90].…”

Self-assembled nanocrystals discovered in Chelyabinsk meteorite

“…Thus, following the standard classification 5 6 , this meteorite can be classified as a LL ordinary chondrite.…”