New augite geothermometer for nakhlites
Introduction: nakhlites, together with shergottites and chassinites constitute the “SNC” group of Martian meteorites. MIL 03346 is a nakhlite, that was found at Miller Range, in Antarctica and is mainly composed of clinopyroxene (79%), with minor olivine (1%), and 20% vitrophyric intercumulus materi...
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ftunivmilanoair:oai:air.unimi.it:2434/478115 2024-04-21T07:48:00+00:00 New augite geothermometer for nakhlites A. M. Fioretti M. C. Domeneghetti M. Alvaro L. Marinangeli F. Camara A.M. Fioretti M.C. Domeneghetti M. Alvaro F. Camara L. Marinangeli 2014-09 http://hdl.handle.net/2434/478115 http://www.hou.usra.edu/meetings/metsoc2014/pdf/5013.pdf eng eng Wiley info:eu-repo/semantics/altIdentifier/wos/WOS:000341914200115 Annual meeting of the meteoritical-society volume:49 issue:supplement 1 firstpage:A118 lastpage:A118 numberofpages:1 journal:METEORITICS & PLANETARY SCIENCE http://hdl.handle.net/2434/478115 http://www.hou.usra.edu/meetings/metsoc2014/pdf/5013.pdf info:eu-repo/semantics/closedAccess nakhlite Martian meteorite geothermometer calibration MIL 03346 single crystal X-ray diffraction electron microporobe Settore GEO/06 - Mineralogia info:eu-repo/semantics/article 2014 ftunivmilanoair 2024-03-27T16:39:24Z Introduction: nakhlites, together with shergottites and chassinites constitute the “SNC” group of Martian meteorites. MIL 03346 is a nakhlite, that was found at Miller Range, in Antarctica and is mainly composed of clinopyroxene (79%), with minor olivine (1%), and 20% vitrophyric intercumulus material [1,2]. The clinopyroxene is augite with a homogeneous core (En36Fs24Wo40) and an iron enriched rim (En8Fs64Wo28). Since the first modern petrologic studies of Nakhla, the nakhlite group of meteorites has been interpreted as augite-rich cumulate igneous rocks, derived from basaltic magma, that erupted onto the surface of Mars [3,4]. The relative low closure temperature (Tc) of ca. 500 (±100)°C calculated for MIL 03346 by [5] with the available geothermometer [6] would correspond to a slow cooling rate that is in disagreement with the petrologic evidence for an origin from a fast cooled lava flow. Geothermometer calibration: ex-situ annealing experiments combined with high-resolution single-crystal X-ray diffraction (HR-SC-XRD) on crystals from MIL 03346 clearly showed that the degree of order remained unchanged at 600°C thus suggesting that the actual Tc is close to this temperature. We then undertook an ex situ annealing experiments combined with HR-SC-XRD at 600, 700, 800 and 900 °C until the equilibrium in the Fe2+-Mg exchange on two crystals from exactly the same fragment of MIL 03346 sample in order to obtain a new geothermometer for augites from Martian nakhlites: lnkD = -4421(±561)/T(K) + 1.46(±0.52) (R2=0.988) where kD = [(Fe2+M1)(MgM2) / (Fe2+M2)(MgM1)] Results: applying this new equation to MIL 03346 the closure temperature resulted to be 605(84)°C about 100°C higher than that calculated with previously available calibration (i.e. Brizi et al. 2000). However, this closure temperature of 605°C is still lower than expected based on petrologic evidences and suggests that MIL 03346 clinopyroxene bears record of a thermal event that postdates, or is superimposed on, the natural cooling path of the host lava ... Article in Journal/Newspaper Antarc* Antarctica The University of Milan: Archivio Istituzionale della Ricerca (AIR) |
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The University of Milan: Archivio Istituzionale della Ricerca (AIR) |
op_collection_id |
ftunivmilanoair |
language |
English |
topic |
nakhlite Martian meteorite geothermometer calibration MIL 03346 single crystal X-ray diffraction electron microporobe Settore GEO/06 - Mineralogia |
spellingShingle |
nakhlite Martian meteorite geothermometer calibration MIL 03346 single crystal X-ray diffraction electron microporobe Settore GEO/06 - Mineralogia A. M. Fioretti M. C. Domeneghetti M. Alvaro L. Marinangeli F. Camara New augite geothermometer for nakhlites |
topic_facet |
nakhlite Martian meteorite geothermometer calibration MIL 03346 single crystal X-ray diffraction electron microporobe Settore GEO/06 - Mineralogia |
description |
Introduction: nakhlites, together with shergottites and chassinites constitute the “SNC” group of Martian meteorites. MIL 03346 is a nakhlite, that was found at Miller Range, in Antarctica and is mainly composed of clinopyroxene (79%), with minor olivine (1%), and 20% vitrophyric intercumulus material [1,2]. The clinopyroxene is augite with a homogeneous core (En36Fs24Wo40) and an iron enriched rim (En8Fs64Wo28). Since the first modern petrologic studies of Nakhla, the nakhlite group of meteorites has been interpreted as augite-rich cumulate igneous rocks, derived from basaltic magma, that erupted onto the surface of Mars [3,4]. The relative low closure temperature (Tc) of ca. 500 (±100)°C calculated for MIL 03346 by [5] with the available geothermometer [6] would correspond to a slow cooling rate that is in disagreement with the petrologic evidence for an origin from a fast cooled lava flow. Geothermometer calibration: ex-situ annealing experiments combined with high-resolution single-crystal X-ray diffraction (HR-SC-XRD) on crystals from MIL 03346 clearly showed that the degree of order remained unchanged at 600°C thus suggesting that the actual Tc is close to this temperature. We then undertook an ex situ annealing experiments combined with HR-SC-XRD at 600, 700, 800 and 900 °C until the equilibrium in the Fe2+-Mg exchange on two crystals from exactly the same fragment of MIL 03346 sample in order to obtain a new geothermometer for augites from Martian nakhlites: lnkD = -4421(±561)/T(K) + 1.46(±0.52) (R2=0.988) where kD = [(Fe2+M1)(MgM2) / (Fe2+M2)(MgM1)] Results: applying this new equation to MIL 03346 the closure temperature resulted to be 605(84)°C about 100°C higher than that calculated with previously available calibration (i.e. Brizi et al. 2000). However, this closure temperature of 605°C is still lower than expected based on petrologic evidences and suggests that MIL 03346 clinopyroxene bears record of a thermal event that postdates, or is superimposed on, the natural cooling path of the host lava ... |
author2 |
A.M. Fioretti M.C. Domeneghetti M. Alvaro F. Camara L. Marinangeli |
format |
Article in Journal/Newspaper |
author |
A. M. Fioretti M. C. Domeneghetti M. Alvaro L. Marinangeli F. Camara |
author_facet |
A. M. Fioretti M. C. Domeneghetti M. Alvaro L. Marinangeli F. Camara |
author_sort |
A. M. Fioretti |
title |
New augite geothermometer for nakhlites |
title_short |
New augite geothermometer for nakhlites |
title_full |
New augite geothermometer for nakhlites |
title_fullStr |
New augite geothermometer for nakhlites |
title_full_unstemmed |
New augite geothermometer for nakhlites |
title_sort |
new augite geothermometer for nakhlites |
publisher |
Wiley |
publishDate |
2014 |
url |
http://hdl.handle.net/2434/478115 http://www.hou.usra.edu/meetings/metsoc2014/pdf/5013.pdf |
genre |
Antarc* Antarctica |
genre_facet |
Antarc* Antarctica |
op_relation |
info:eu-repo/semantics/altIdentifier/wos/WOS:000341914200115 Annual meeting of the meteoritical-society volume:49 issue:supplement 1 firstpage:A118 lastpage:A118 numberofpages:1 journal:METEORITICS & PLANETARY SCIENCE http://hdl.handle.net/2434/478115 http://www.hou.usra.edu/meetings/metsoc2014/pdf/5013.pdf |
op_rights |
info:eu-repo/semantics/closedAccess |
_version_ |
1796947837537222656 |