Frontier Mountain meteorite specimens of the acapulcoite‐lodranite clan: Petrography, pairing, and parent‐rock lithology of an unusual intrusive rock

Abstract

Abstract-In this paper we reconstruct the heterogeneous lithology of an unusual intrusive rock from the acapulcoite-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 parent-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 coarse-grained igneous rock which intrudes a lodranite and entrains xenoliths. The igneous matrix is composed of enstatite (Fs 13.3 ± 0.4 Wo 3.1 ± 0.2 ), Cr-rich augite (Fs 6.1 ± 0.7 Wo 42.3 ± 0.9 ), and oligoclase (Ab 80.5 ± 3.3 Or 3.2 ± 0.6 ). The lodranitic xenoliths show a fine-grained (average grain size 488 ± 201 µm) granoblastic texture and consist of olivine Fa 9.5 ± 0.4 and Fe,Ni metal and minor amounts of enstatite Fs 12.7 ± 0.4 Wo 1.8 ± 0.1 , troilite, chromite, schreibersite, and Ca-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 specimen-to-meteorite ratio for the AL meteorites so far found at Frontier Mountain is thus 2.5.

The Northwest Africa 1500 meteorite: Not a ureilite, maybe a brachinite

“…Brachinites: Nehru et al (1983); Smith et al (1983); Warren and Kallemeyn (1989); Mittlefehldt et al (2003); Swindle et al (1998); Kring et al (1991); Wlotzka (1993b); Grossman (1998); Connolly et al (2006, 2008). Acapulcoites: McCoy et al (1996); Patzer et al (2004); Burroni and Folco (2008); Yugami et al (1998). Lodranites: Takeda et al (1994); Papike et al (1995).…”

“…2. Acapulcoites: Mittlefehldt et al (1996); Mittlefehldt et al (1998) and references therein; Burroni and Folco (2008). Lodranites: Takeda et al (1994), Nagahara and Ozawa (1986); Nagahara (1992); McCoy et al (1997); Mittlefehldt et al (1998) and references therein.…”

Magnetic classification of stony meteorites: 3. Achondrites

“…(obtained on several specimens of the same meteorite) and the median of specimen mass are also indicated. The same data for selected chondrite groups (after Rochette et al 2003 and2008) is indicated, as well as for examples of terrestrial extrusive rocks (basaltic and rhyolitic flow from the Ethiopian traps after Rochette et al 1999) and intrusive rocks (granites from Corsica and Sardinia after Gattacceca et al 2004). In the terrestrial case, N is the number of sites (flow or outcrop), each one consisting of 3 to 9 specimen of about 10 cm 3 each.…”

“…Typically, the s.d. for a given chondrite is less than 0.1 (on average 0.07 see Rochette et al 2003 and2008). Larger s.d.…”

“…Among the Antarctic FRO meteorites we separated two different falls according to Burroni and Folco (2008). For acapulcoite-lodranites only two falls exist: Acapulco at 5.07 and Lodran at 5.76.…”