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Noble gases in enstatite chondrites I: Exposure ages, pairing, and weathering effects
Author(s) -
PATZER Andrea,
SCHULTZ Ludolf
Publication year - 2001
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2001.tb01932.x
Subject(s) - chondrite , enstatite , cosmogenic nuclide , weathering , noble gas , geology , meteorite , achondrite , astrobiology , geochemistry , cosmic ray , mineralogy , chemistry , astrophysics , physics , organic chemistry
— Cosmic‐ray exposure ages calculated from cosmogenic noble gas nuclides are reported for 57 enstatite (E) chondrites, 43 of them were measured for the first time. With a total of 62 individual E chondrites (literature and this data, corrected for pairing) the observed spectrum of ages ranges between 0.07 and 66 Ma. Three clusters seem to develop at about 3.5, 8, and 25 Ma, respectively. Since the uncertainty of ages is estimated to be ∼20% (in contrast to 10 to 15% for ordinary chondrites) and the number of examined samples is still comparatively small, these peaks have to be confirmed by more measurements. Regarding the two subgroups, EH and EL chondrites, no systematic trend is apparent in the distribution of cosmic‐ray exposure ages. Several E chondrites yield significantly lower 38 Ar ages compared to those calculated from cosmogenic 3 He and 21 Ne. For these E chondrites, we suggest a reduction of cosmogenic 38 Ar as a result of weathering. In order to prove the possible influence of terrestrial alteration on the cosmogenic noble gas record of E‐chondritic material, we simulated terrestrial weathering in an experiment of 12 weeks duration. The treatment showed that a significant amount of cosmogenic 38 Ar is lost on Earth by the influence of water.