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Título

The Villalbeto de la Peña meteorite fall: Cathodoluminescence and Hyperspectral Raman Spectroscopy of Feldspars

AutorSánchez Muñoz, Luis CSIC ORCID; García-Guinea, Javier CSIC ORCID ; Tormo, Laura CSIC ; Crespo Feo, Elena CSIC; Ruiz Pérez, Javier CSIC ORCID; Martín-Herrero, A. I.; Cremades, Ana
Fecha de publicación2009
ResumenThe fall of the Villalbeto de la Peña meteorite on Janu-ary 4, 2004 (Spain) is one of the best documented in history for which atmospheric and orbital trajectory, strewn field area, and recovery circumstances have been described in detail. Moreover, the intrinsic com-plexity of composition, distribution and structural states of plagioclase crystals in L6 chondritic meteor-ites, such as the Villalbeto feldspars case, suggested us to perform this study by Electron Probe Microanalyses (EPMA), spatially-resolved spectra Cathodoluminescence (CL) and Hyperspectral-Raman contour-plot micro-analyses (Raman), exploring the Maskelynite-Plagioclase distribution of thr studied samples. We study polished sections of L6-chondrite specimens collected by ourselves in Villalbeto and stored later as international samples-type in our National Museum of Natural Science of Madrid. The Electron Probe Microanalyses (EPMA) were performed by a Jeol Superprobe JXA-8900M and by Environmental Scanning Electron Microscopy with X-ray Dispersive Spectrometry probe (ESEM-EDS) in a Inspect-S ESEM of the FEI company. The hyperspectral Raman contour plots were perfomed using a new ThermoFischer Raman Microscope with one micron spatial resolution and a laser source at 532 nm. The hot cathodoluminescence (CL) spectra of plaglioclase grains were obtained with an SEM-CL Hitachi S2500 electron microscope. The CL spectra were recorded with a Hamamatsu PMA-11 CCD cam-era. Cold CL images of Villalbeto feldspars distribution were taken in a optical CL 8200 MK4 system made by Cambridge Image Technology Ltd, with an electron beam exciting at 16 kV and a current of 0.5 mA. The results of the EPMA 45 spot analysis on feldspar phases are shown in ternary Na2O¿K2O¿CaO compositions of Villalbeto feldespathic samples. The K content of sodic plagioclase correlates with the temperature obtained from the structural state. This positive correlation suggests that sodic plagioclase has formed in the course of equilibration processes of alkali elements in prograde metamorphism, i.e. during heating processes. In addition, it is realistic, that our experimental results on metastable proportional K-Ca-Na compositions, sited in the triangle center, could be partially amorphous Maskelynite, together with other analysed more crystalline plagioclase species, e.g., Bytownite, Albite, Oligoclase. Spectral CL plot images demonstrate that the meteorite luminescence is mainly produced by feldspars, as follows: (i) red spots, Bytownite with Mn2+ point defects in structural Ca positions, (ii) blue masses, Oligoclase with [AlO4]º defects, (iii) Maskelenite sodic glasses with low UV-blue emission. The Maskelenite Raman spectrum includes common peaks with plagioclases phases. This datum point to a tectonic origin for this, in accordance with previoous data reported indicating that Villalbeto meteorite was not severely shok-metamorphosed
URIhttp://hdl.handle.net/10261/82672
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