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Aqueous alteration vs. shock in Villalbeto de la Peña polymict chondritic breccia

AuthorsTrigo-Rodríguez, Josep María ; Moyano-Cambero, C. E. ; Martínez-Jiménez, M.; Fraxedas, J. ; Alonso-Azcárate, J.
Issue DateJul-2013
PublisherJohn Wiley & Sons
Meteoritical Society
CitationMeteoritics and Planetary Science 48(s1): 5181 (2013)
Abstract[Introduction]: Villalbeto de la Peña was the first meteorite fall recovered in Spain in 57 years, in the framework of the Spanish Fireball Network (SPMN) efforts to reconstruct its strewnfield. It was also the 9th meteorite with inferred heliocentric orbit thanks to the calibration of a video and pictures taken by casual eyewitnesses. Originally classified as a L6 ordinary chondrite, it has been reclassified as a polymict chondritic breccia. It has been recently identified evidence of aqueous alteration in its forming minerals. This new research on this meteorite emphasizes the interest of studying new chondrite falls, that quickly recovered have almost not experienced terrestrial alteration. In fact, these results have motivated us to make additional thin sections, particularly focusing in those specimens that were recovered just few days after its fall. We are building high-resolution mosaics of sections in order to get new evidence of these processes. Aqueous alteration has particularly played a role modifying the primordial bulk chemistry of chondrite materials, and homogenizing the isotopic content of their components.
[Experimental procedure]: Several thin sections of Villalbeto de la Peña have been created from fresh specimens recovered few days after the meteorite fall. So far we have analyzed one of them. Using a Scanning Electron Microscope (SEM) we are able to see microscopic details of a sample with a resolution of tens of nm. More detailed chemical information is obtained using Energy-Dispersive X-ray spectroscopy (EDX), ICP-MS, and Raman spectrometry to unequivocally identify shocked minerals.
[Results]: Villalbeto de la Peña is a chondritic breccia that has experienced a significant level of shock. In fact, in a previous Raman study of shock veins we found that merrillite Ca9MgNa(PO4)7 can be used to constrain shock-induced events because it may transform into a high-pressure polymorph with the structure of trigonal γ-Ca3(PO4)2 form. On the other hand, we are exploring in which way impacts and aqueous alteration promoted changes in the bulk mineralogy. Under the mild temperatures that materials were soaked in water into the parent body took place the oxidation of primordial ferrous iron (FeII), derived from olivine and pyroxene, to ferric iron (FeIII). Plagioclase feldspars are probably also transformed into albite. Evidence for water alteration occurred in ordinary chondrites is scarce. In this context, the results obtained so far are relevant.
DescriptionPresentado al 76th Annual Meeting of the Meteoritical Society celebrado del 29 de julio al 2 de agosto en Edmonton, Alberta, Canada.
Publisher version (URL)http://dx.doi.org/10.1111/maps.12165
Appears in Collections:(CIN2) Artículos
(ICE) Artículos
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