Thermal history of history of nakhlites: comparison between MIL 03346 and its terrestrial analogue Theo's flow
| Autor: | Domeneghetti M.C. [1], Fioretti A.M. [2], Cámara F. [3], McCammon C. [4], Alvaro M. [5 |
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| Jazyk: | angličtina |
| Rok vydání: | 2013 |
| Předmět: | |
| Zdroj: | Geochimica et cosmochimica acta (Online) 121 (2013): 571–581. doi:10.1016/j.gca.2013.07.044 info:cnr-pdr/source/autori:Domeneghetti M.C. [1], Fioretti A.M. [2], Cámara F. [3], McCammon C. [4], Alvaro M. [5, 6]/titolo:Thermal history of history of nakhlites: comparison between MIL 03346 and its terrestrial analogue Theo's flow/doi:10.1016%2Fj.gca.2013.07.044/rivista:Geochimica et cosmochimica acta (Online)/anno:2013/pagina_da:571/pagina_a:581/intervallo_pagine:571–581/volume:121 |
| DOI: | 10.1016/j.gca.2013.07.044 |
| Popis: | High resolution single-crystal X-ray diffraction (HR-SCXRD) and Mo¨ssbauer spectroscopy of the intracrystalline cation distribution have been performed on augitic core-crystals from a Miller Range nakhlite (sample MIL 03346,13) with approximate composition of En36Fs24Wo40. The Mo¨ssbauer data on the single-crystal yielded a very low Fe3+ content [Fe3+/Fetotal - 0.033(23) a.p.f.u.] that, together with the Electron microprobe analysis (EMPA) and the X-ray structural data allowed us to obtain the accurate cation site distribution and the Fe2+-Mg degree of order. This leads to a closure temperature (Tc) of 500 with a standard deviation of ±100 C that would correspond to a slow cooling rate, which is in disagreement with petrologic evidence that indicates that this sample originates from a fast cooled (3-6 C/h) lava flow. In order to clarify this discrepancy we undertook (i) a SC-XRD study of an augite (En49Fs9 Wo42) from a pyroxenite (TS7) of Theo's flow, a 120-m-thick lava flow regarded as a terrestrial analogue of MIL 03346; (ii) an annealing experiment at 600 C on a crystal from exactly the same fragment of MIL 03346. SC-XRD data from TS7 augite yields a Tc = 600(20) C, consistent with the cooling rate expected at 85 m below the surface. This Tc is higher, although similar within error, to the Tc = 500(100) C obtained for MIL 03346; thus suggesting relatively slower cooling for MIL 03346 with respect to TS7. The annealing experiment on the MIL 03346 crystal clearly showed that the degree of order remained unchanged, further confirming that the actual Tc is close to 600 C. This result appears inconsistent with the shallow depth of origin ( |
| Databáze: | OpenAIRE |
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