| Summary: | Recovery: Allan Hills 12073 is a 500 mg meteorite fragment, partially covered by fresh fusion crust, recovered from the Near Western Allan Hills ice field, during the 2012-2013 campaign of the Italian Programma Nazionale di Ricerche in Antartide (PNRA). Sampling and Methods: ALH 12073 was split into three fragments. One fragment (~150 mg) was used to prepare a thin section for petrographic description and EMP analysis. A second fragment of about 150 mg, devoid of fusion crust, was split in two smaller chips. The larger one, of about 105 mg, was prepared for solution ICP-MS analysis. The smaller one was ground and homogenized for triple oxygen isotope measurements. The third fragment was embedded in resin, sectioned and polished for bulk Hand-Held XRF analysis. Three pyroxene crystals, of about 300 microns in size each, were selected for X-ray single-crystal diffraction and structure refinement. Two plagioclases of about 4 mg in mass were extracted for 39Ar-40Ar dating (the plagioclases are under irradiation at the writing of this abstract, May 2016). Petrography: In thin section, ALH 12073 shows unbrecciated, inequigranular, medium- to fine-grained subophitic texture. It maily consists of subhedral plagioclase (46 vol%) and low-Ca pyroxene (34 vol%), plus minor euhedral tridymite (7 vol%), high-Ca pyroxene (4 vol%), Fe,Ni metal (4 vol%), sulfide (3 vol%), phosphates (2 vol%) and traces of chromite. Mineral Chemistry: The low-Ca pyroxene is orthopyroxene (En63.1, Fs33.9, Wo3.1) with a relatively uniform composition, and average Fe/Mn ratio of 26. It hosts few, local, fine-exolved Ca-rich lamellae. The plagioclase is anorthite (An92.4, Ab7.5, Or0.2). The high-Ca pyroxene is augite (En 43.3, Fs 16.1, Wo 40.5). It is exolved and displays two systems of Ca-poor lamellae. The chromite is Mg-rich with an average Mg# of 10%. The Fe,Ni metals are divided in low Ni-phase (kamacite) and high Ni-phase (taenite). Thermospeedometric constraints: Opx-Cpx pairs provide an average equilibrium crystallization temperatures of T = ...
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