Petrology, mineralogy, porosity, and cosmic‐ray exposure history of Huaxi ordinary chondrite

Abstract

A meteorite fall was heard and collected on July 13, 2010 at about 18:00 (local time) in the Shibanjing village of the Huaxi district of Guiyang, Guizhou province, China. The total mass of the fall is estimated to be at least 1.6 kg; some fragments are missing. The meteorite consists mainly of olivine, low-Ca pyroxene, high-Ca pyroxene, plagioclase, kamacite, taenite, and troilite. Minor phases include chromite and apatite. Various textural types of chondrules exist in this meteorite: most chondrule textures can be easily defined. The grain sizes of secondary plagioclase in this meteorite range from 2 to 50 lm. The chemical composition of olivine and low-Ca pyroxene are uniform; Fa in olivine and Fs in low-Ca pyroxene are, respectively, 19.6 AE 0.2 and 17.0 AE 0.3 (mole%). Huaxi has been classified as an H5 ordinary chondrite, with a shock grade S2, and weathering W0. The weak shock features, rare fractures, and the high porosity (17.6%) indicates that Huaxi is a less compacted meteorite. The preatmospheric radius of Huaxi is~11 cm, corresponding tõ 21 kg. The meteorite experienced a relatively short cosmic-ray exposure of about 1.6 AE 0.1 Ma. The 4 He and 40 Ar retention ages are older than 4.6 Ga implying that Huaxi did not degas after thermal metamorphism on its parent body.

Radionuclide activities in recent chondrite falls determined by gamma‐ray spectrometry: Implications for terrestrial age estimates

“…1. We found no systematic influence on the density results from the variable numbers of scans needed to acquire the complete volumes when analyzing sample masses of 30-360 g. The measured densities of fragments from the Tamdakht and Huaxi meteorites are consistent with previous density measurements on smaller fragments, performed by El Abassi et al 2013and Li et al (2017), respectively, which suggest that the bulk density data presented here are accurate. (Consolmagno et al 2008) are outlined next to the legend.…”

“…The radionuclide data from Tamdakht are consistent with our measurements and shielding-dependent variations of 60 Co and 26 Al production rates. Huaxi and Kamargaon came from considerably smaller meteoroids according to calculations based on the noble gas contents in Huaxi giving a radius of~11 cm (Li et al 2017) and radionuclide activities in Kamargaon giving r ≤ 10 cm according to Ray et al (2017). While our data are consistent with the estimates for Huaxi, the considerably higher activity of 26 Al in Kamargaon measured by us contradicts the previous size estimate.…”

“…The Huaxi samples appear to have come from one single stone which made up the initial main mass. This stone shattered upon impact according to a recent detailed petrographic study which included noble gas measurements (Li et al 2017). The Xining samples have less well-documented find conditions as the initial find consisted of 10 individual stones, scattered across a~25 9 5 km area, which were first distributed to private collectors.…”

“…We measured two individual samples from each of the Huaxi and Xining meteorites, respectively. The inferred small pre-atmospheric size of the Huaxi meteorite (Li et al 2017) combined with the low total amount of recovered mass (1.6 kg) should not allow for any significant shielding-dependent variations of cosmogenic radionuclide activities between two different fragments. This is clearly reflected in our results on Huaxi as the activities of all detected isotopes in both studied samples agree within uncertainties.…”

“…Many cosmogenic radionuclides are produced in meteoroids due to irradiation by cosmic rays (e.g., Leya and Masarik 2009). Measurements of radionuclides can provide important information about the irradiation history of meteorites such as the pre-atmospheric shielding parameters and exposure times (e.g., Li et al 2017). The radionuclide record preserved in observed meteorite falls and meteorite finds can also be used to verify fall observations and provide accurate terrestrial age determinations.…”