Tirhert and Aouinet Legraa: Rare unbrecciated eucrite falls

1Taha Shisseh,1Hasnaa Chennaoui Aoudjehane,2Carl B. Agee,3Omar Boudouma
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13899]
1GAIA Laboratory, Faculty of Sciences Ain Chock, Hassan II University of Casablanca, km 8 Route d’El Jadida, 20150 Casablanca, Morocco
2Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, 87131 USA
3UPMC – Paris 06, UMR, 7193 Paris, France
Published by arrangement with John Wiley & Sons

Tirhert and Aouinet Legraa are the only documented unbrecciated eucrite falls in Africa. Aouinet Legraa fell in Algeria on July 17, 2013. Tirhert’s fall occurred about a year later in Morocco, on July 9, 2014. Both meteorites are covered by a black and glossy fusion crust as is typical of eucrites. Tirhert has a poikilitic texture with remnant subophitic pockets, and consists of millimeter-sized grains of plagioclase (An87-91), pigeonite (Mg# 42) with augite exsolution lamellae, and interstitial opaque minerals. Aouinet Legraa has a subophitic texture, and it is dominated by plagioclase laths (An82-89) enclosed by pigeonite (Mg# 37), with exsolution lamellae of augite. Remnant Ca zoning in pyroxene is observed in both rocks, although it is more abundant in Aouinet Legraa than Tirhert. The presence of exsolved pyroxenes suggests that these meteorites have undergone thermal metamorphism. Equilibration temperatures estimated from pigeonite and augite pairs using the QUILF program are ∼931 °C in Tirhert and ∼758 °C in Aouinet Legraa. This indicates that these rocks had distinct thermal histories. Aouinet Legraa has trace element abundances similar to the typical main group eucrite Juvinas, confirming its origin as a main group eucrite. The trace element abundances of Tirhert fall between those of cumulate and main group eucrites. Its rare earth element pattern is flat with a positive Eu anomaly. This likely suggests that Tirhert is a partial cumulate of plagioclase from a main group magma, or a flotation cumulate formed by flotation of plagioclase in a subvolcanic chamber or by scavenging crystals during eruption.

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