Lewis Cliff 86010 meteorite, Lewis Cliff, Buckley Island quadrangle, Eastern Antarctica, Antarcticai

Regional Level Types
Lewis Cliff 86010 meteorite	Meteorite Fall Location
Lewis Cliff	Cliff
Buckley Island quadrangle	Quadrangle
Eastern Antarctica	Region
Antarctica	Continent

Angrite [achondritic meteorite]
Found 1986, 6.9 g (1.5x1.5x1.5 cm3)

In 1986 a small round stone was discovered with mineralogical properties closely matching those of the unique Angra dos Reis meteorite fall of 1869. Lewis Cliff 86010 (or, LEW 86010) consists primarily of Fassaitic Pyroxene, Olivine, and Anorthitic Plagioclase plus small amounts of Hercynite, Kirschsteinite, and other minor phases. Today both Angra dos Reis and LEW 86010 are classified as Angrites. The precise assemblage and actual proportions of the Ca-Al-Ti rich minerals which characterize known angrites vary, sometimes considerably. Lewis Cliff itself 86010 is perhaps 50% Fassaite with subequal amounts of Anorthite and Ca-rich Olivine plus other minor constituents listed below. Textural arguments [Equilibrated olivine; unequilibrated Fassaite; exsolution lamellae] suggest that while Lewis Cliff 86010 is an igneous rock, it may have cooled more rapidly than, for example, Angra dos Reis with its equilibrated Fassaite. It has been suggested that the current Lewis Cliff 86010 assemblage in a moderately deep sub-crustal environment which was not quite so deep as the formative magmatic environment of other angrites.

Angrites, like other meteoritic achondrite groups, are clear products of igneous differentiation. While the angrites oxygen isotope ratios overlap those of HED meteorites, crucial geochemical parameters — Alkali deficiencies, Fe/Mn ratios, REE ratios, etc., — suggest strongly that the Angrites (22 are now listed) are a coherent chemical group with no apparent ties to other meteorite groups. And they are ancient rocks. Several Angrites have crystallization ages of ~4.56 billion years. Recent numbers (2007) from Pb-Pb dating suggest that Lewis Cliff 86010 with a reported age of ~4.558 billion years may belong to a subgroup of somewhat younger angrites.

Other Regions, Features and Areas containing this locality

References