Slow Cooling Rate of Silicate in Mesosiderite Inferred from Exsolution Lamellae in Pyroxene

Lidia Pittarello, Seann McKibbin, Gang Ji, Dominique Schryvers, Vinciane Debaille, Philippe Claeys

Research output: Chapter in Book/Report/Conference proceedingMeeting abstract (Book)

Abstract

Mesosiderites are breccias consisting of a mixture of metal,
chemically similar to IIIAB iron meteorites, and silicates,
which resemble HED achondrites [1] [2]. From microscale
metallographic textures and geochemistry, the cooling of the
metal fraction from about 550°C appears to be uniquely slow
(cooling rate of 0.25-0.5°C/My [3]) despite some debate about
systematic error in these determinations [4]. On the other hand,
the silicate are believed to have cooled quite quickly (e.g., [5]).
The mesosiderite A 09545 [6] contains large grains of
pyroxene exhibiting two generations of exsolution lamellae,
which have been here investigated with electron microscopy
(SEM, TEM, and EPMA) and used for constraining the
thermal evolution of the silicate fraction in the sample.
The host pyroxene is clino-enstatite (Monoclinic, P21/c)
with composition Wo3En59Fs38 and contains thick (up to
25 µm) lamellae of augite (Monoclinic, C2/c, Wo42En41Fs17)
along cleavage. A second generation of exsolution lamellae
occurs within the augite lamellae, with thin (ca. 300 nm)
lamellae, apparently parallel to [001], and composition
Wo1En56Fs43. Geothermobarometry calculation [7] [8], lattice
parameters [9], lamellae orientation [10], and the inversion of
ortho- to clinopyroxene [11] have suggested a slow cooling
rate of the pyroxene from the crystallization of pigeonite (ca.
1150°C) to the inversion into clinoenstatite (ca. 570°C),
followed by the slow cooling recorded in the metal (e.g., [3]).
Original languageEnglish
Title of host publicationGoldschmidt 2015 Conference Abstracts
Number of pages1
Publication statusPublished - 2015
EventGoldschmidt 2015 - Prague, Czech Republic
Duration: 16 Aug 201521 Aug 2015

Conference

ConferenceGoldschmidt 2015
Country/TerritoryCzech Republic
CityPrague
Period16/08/1521/08/15

Keywords

  • mesosiderite
  • cooling rate

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