Veins in silicates of IIE iron Mont Dieu II: melt migration caused by impact?

Nadia Van Roosbroek, Vinciane Debaille, Lidia Pittarello, Lutz Hecht, Philippe Claeys

Research output: Contribution to journalMeeting abstract (Journal)

Abstract

Introduction: Mont Dieu II(MDII) can be classified as a IIE non-magmatic iron [1,2]. Several cm-sized silicate inclusions, containing large chondrules, can be linked to the H-chondrites based on the Fa and Fs molar contents (Fa15.7 ± 0.4 and Fs14.4 ± 0.5) and the oxygen isotopes (Δ 17O = 0.71 ± 0.02 ‰) [1,2].

Metal veins in silicate inclusions MDII: The silicate inclusions are crosscut by a network of two sorts of veins: a) a set of sub-parallel thick veins (100-200 µm wide) which consist of FeNi and Fe-P, and locally contain clasts of olivine, pyroxene, plagioclase and troilite, and (b) fine veinlets of 1-10 µm consisting of Fe-Ni-P or troilite locally containing small (< 5 µm) angular clasts of silicates and troilite, crossing the chondrules and the matrix and connected to the thick veins. At the margin of the thick veins, a porous, likely amorphous phase, rimmed by a Fe-P thin layer, occurs locally. In the thick veins, troilite is only present as small clasts, it is mainly concentrated in the silicate host, where it is more abundant than in average H-chondrites. The opposite is true for Fe metal, which is the groundmass of the vein but seems depleted in the host silicate portion with respect to average H-chondrites. Fa and Fs molar contents of olivine and lowCa pyroxene (Fa17.5 ± 0.4 and Fs14.8 ± 0.5) in the clasts are comparable to the Fa and Fs contents in the host silicate portion.

Hypothesis of formation for the veins in MDII: The in-situ formation of the veins is supported by the composition of the silicate clasts in the vein, similar to that of the silicate inclusions, and by the occurrence of a metal depleted silicate fraction surrounding the veins. Metal - sulfide was probably mobilized and separated from the silicate material. Metal was concentrated into already existing cracks or fractures, and has entrained silicates from the wall rock. The sulfide-rich melt probably migrated away from the metal into the silicate portion. This process is in agreement with a model of impact-generated melt migration proposed by [3], and that likely also took place on Portales Valley H6 chondrite, which contains metal-dominated veins in sulfideenriched silicates, similar to those observed in MDII [4]. The metal-sulfide mobilization was likely triggered by an impact event, that formed the MDII meteorite and took place early on in the formation of the solar system, indicated by the ~ 4.5 Ga 40Ar/39Ar ages of plagioclase and pyroxene inclusions in the silicate material of MDII.

Comparison with Techado IIE silicate: A chip of Techado IIE containing a mm-sized silicate inclusion was examined using SEM. A network of veins consisting of an Fe-Ni matrix and containing angular silicate clasts is present, showing similarities with the veins in MDII. A detailed comparison of these features will be carried out to investigate whether they could have formed in a similar way.
Original languageEnglish
Article number5178
Pages (from-to)A417-A417
Number of pages1
JournalMeteoritics & Planetary Science
Volume49
Issue numbers1
Publication statusPublished - Sep 2014
Event77th Annual Meeting of the Meteoritical Society - Casablanca, Morocco
Duration: 8 Sep 201413 Sep 2014

Keywords

  • Mont Dieu II
  • shock veins
  • impact event

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