The Lohawat howardite: Mineralogy, chemistry and cosmogenic effects

Abstract

Abstract-The Lohawat meteorite is a texturally heterogeneous breccia having a variety of mineral and lithic fragments. Among mineral fragments, pyroxenes show a wide range of composition WOO,^^^^, 1 7 E n 0 , 3 7~. 7 8 F S 0 ,~~~) . 6 0 ) whereas plagioclase is anorthitic (An0.92Abo.070ro.007). Abundant rounded "chondrule-like" objects ranging in size up to -7 mm, some with concentric layering, have been observed. Petrographic features, trace element composition and rare earth element patterns show the presence of eucritic and diogenitic components confirming that it is a typical howardite. Cosmogenic tracks, rare gases (He, Ne, and Ar) and radionuclides (22Na and 26A1) were measured.Track density in olivine and plagioclase varies between 0.7 to 6 x 106/cm2. 38Ar exposure age is estimated to be -1 10 Ma, being the highest among howardites. The track production rates correspond to ablation of 9 to 15 cm, implying a radius for its preatmospheric size of -27 cm. 22Na /26AI = 1, as expected from the production models and solar modulation of galactic cosmic-ray fluxes before its fall, suggesting that the meteoroid did not undergo any fragmentation during the past -2 Ma in interplanetary space. The radiogenic age based on K-Ar method is 4.3 Ga while the U-Th-4He age is 3.3 Ga indicating partial loss of He.

The Vestan cataclysm: Impact‐melt clasts in howardites and the bombardment history of 4 Vesta

“…; Sisodia et al. ). The gray line shows the large number of impact‐affected samples around 4.48 Ga, a gap between then and around 4.0–4.1 Ga, and an increase in the number of affected samples between then and about 3.4 Ga.…”

Cosmic-Ray Exposure Ages of Meteorites

“…ALH 78019 is remarkable in having a CRE age of less than 100 ka; such low values are common only among Figure 10 Averaged 21 Ne and 38 Ar CRE ages for howardites from Welten et al (1997); Cartwright et al (2011aCartwright et al ( ,b, 2012. Data for Lohawat from Sisodia et al (2001).…”

Siderophile and other geochemical constraints on mixing relationships among HED-meteoritic breccias

“…The pristineigneous eucrite Nuevo Laredo (Warren and Jerde, 1987;cf. BVSP, 1981;Barrat et al, 2007) and the Lohawat howardite (Sisodia et al, 2001) are strangely Co-poor.…”