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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 , 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 . 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.
- Mont Dieu II
- shock veins
- impact event
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OZR2725: ULB-VUB Joint Research Group: Brussels Institute for Geochemical Techniques in Earth Sciences - BIGE
Claeys, P. & Mattielli, N.
5/12/14 → 4/12/22
26/04/12 → 25/04/17