Frontier Mountain meteorite specimens of the acapulcoiteâ€lodranite clan: Petrography, pairing, and parentâ€rock lithology of an unusual intrusive rock
Abstract— In this paper we reconstruct the heterogeneous lithology of an unusual intrusive rock from the acapulcoiteâ€lodranite (AL) parent asteroid on the basis of the petrographic analysis of 5 small (<8.3 g) meteorite specimens from the Frontier Mountain ice field (Antarctica). Although thes...
| Published in: | Meteoritics & Planetary Science |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2010
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| Subjects: | |
| Online Access: | https://www.openaccessrepository.it/record/205656 https://doi.org/10.1111/j.1945-5100.2008.tb00681.x |
| Summary: | Abstract— In this paper we reconstruct the heterogeneous lithology of an unusual intrusive rock from the acapulcoiteâ€lodranite (AL) parent asteroid on the basis of the petrographic analysis of 5 small (<8.3 g) meteorite specimens from the Frontier Mountain ice field (Antarctica). Although these individual specimens may not be representative of the parentâ€rock lithology due to their relatively large grain size, by putting together evidence from various thin sections and literature data we conclude that Frontier Mountain (FRO) 90011, FRO 93001, FRO 99030, and FRO 03001 are paired fragments of a medium†to coarseâ€grained igneous rock which intrudes a lodranite and entrains xenoliths. The igneous matrix is composed of enstatite (Fs13.3 ± 0.4 Wo3.1 ± 0.2), Crâ€rich augite (Fs6.1 ± 0.7 Wo42.3 ± 0.9), and oligoclase (Ab80.5 ± 3.3 Or3.2 ± 0.6). The lodranitic xenoliths show a fineâ€grained (average grain size 488 ± 201 μm) granoblastic texture and consist of olivine Fa9.5 ± 0.4 and Fe,Ni metal and minor amounts of enstatite Fs12.7 ± 0.4 Wo1.8 ± 0.1, troilite, chromite, schreibersite, and Caâ€phosphates. Crystals of the igneous matrix and lodranitic xenoliths are devoid of shock features down to the scanning electron microscope scale. From a petrogenetic point of view, the lack of shock evidence in the lodranitic xenoliths of all the studied samples favors the magmatic rather than the impact melting origin of this rock.FRO 95029 is an acapulcoite and represents a separate fall from the AL parent asteroid, i.e., it is not a different clast entrained by the FRO 90011, FRO 93001, FRO 99030, and FRO 03001 melt, as in genomict breccias common in the meteoritic record. The specimenâ€toâ€meteorite ratio for the AL meteorites so far found at Frontier Mountain is thus 2.5. |
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