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Cathodoluminescence color zonation in the Antarctic meteorite (enstatite chondrite) of Yamato 86004

Ohgo S., Mishima M., Endo M., Ninagawa K., Nishido H.

Geochronometria

2017

Vol. 44, no. 1

136--141

Enstatite in Yamato 86004 classified as EH melt rock shows cathodoluminescence (CL) zonation as arranged in a concentric pattern from within outward blue, light blue, red and non-CL areas (fusion crust). The zonation observed in the meteorite results from different distribution ratio of the enstatite with various CL colors. CL spectra of the enstatite have two broad emission bands at around 400 nm in the blue region and at around 670 nm in a red region. The emission components obtained by a spectral deconvolution can be assigned to three defect centers (2.73, 3.13–3.15 and 3.77 eV) in a blue region and to impurity centers of Cr3+ ion (1.71 eV) and Mn2+ ion (1.86–1.91 eV) in a red region. According to the CL related to structural defects in the enstatite, blue-CL enstatite might be originally formed from the melt by a quenching from the melt on the surface of parent body. The enstatite with light blue and red CL might be thermally altered from blue-CL enstatite with phase transitions during a flash heating when the meteorite passed through the atmosphere. Therefore, the color CL zonation reflects a thermal history recorded in the meteorite.

Primitive enstatite achondrites

Pilski A. S., Przylibski T. A., Łuszczek K.

Meteorites

2011

Vol. 0, No. 0

9-21

Conclusions drawn from the breadth of analytical data on primitive achondrites and enstatite chondrites paired with results of research performed by the authors have led the authors to propose the establishing of a new group of meteorites: primitive enstatite achondrites. The group is defined as the residual remaining after the partial melting of their protolith, which, in the case of primitive enstatite achondrites, is the parent body of enstatite chondrites. In this article are characterized textural features and characteristics of their mineral, chemical, and isotopic composition. The most important of these defining features are the presence of relic chondrules and/or triple junctions of crystal faces, as well as characteristic atomic and molar ratios of main elements: Si, Al, Fe, Mg, Mn and Ca, and particularly the molar ratios Fe/Mn and Fe/Mg. Another important characteristic is the isotopic composition of entrained noble gases, especially ratios of the heaviest of the isotopes and oxygen isotopes, whose values should be close to that typical for enstatite chondrites. It seems likely that the first meteorite to be classified as primitive enstatite achondrite will be the Zakłodzie enstatite achondrite.