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The Dergaon (H5) chondrite: Fall, classification, petrological and chemical characteristics, cosmogenic effects, and noble gas records
Author(s) -
SHUKLA P. N.,
SHUKLA A. D.,
RAI V. K.,
MURTY S. V. S.,
BHANDARI N.,
GOSWAMI J. N.,
MAZUMDAR A. C.,
PHUKON P.,
DUORAH K.,
GREENWOOD R. E.,
FRANCHI I. A.
Publication year - 2005
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.1945-5100.2005.tb00967.x
Subject(s) - meteorite , chondrite , noble gas , cosmic ray , geology , parent body , allende meteorite , astrobiology , isotopes of argon , petrography , mineralogy , geochemistry , isotope , chemistry , astrophysics , physics , nuclear physics , organic chemistry
— A multiple fall of a stony meteorite occurred near the town of Dergaon in Assam, India, on March 2, 2001. Several fragments weighing <2 kg and a single large fragment weighing ∼10 kg were recovered from the strewn field, which extended over several tens of square kilometers. Chemical, petrographic, and oxygen isotopic studies indicate it to be, in most aspects, a typical H5 chondrite, except the unusually low K content of ∼340 ppm. A cosmic ray exposure of 9.7 Ma is inferred from the cosmogenic noble gas records. Activities of eleven cosmogenic radionuclides were measured. 26 Al and 22 Na activities as well as the 22 Na/ 26 Al activity ratio are close to the values expected on the basis of solar modulation of galactic cosmic rays. The low 60 Co activity (<1 dpm/kg) is indicative of a small preatmospheric size of the meteorite. Cosmic ray heavy nuclei track densities in olivine grains range from ∼106 cm −2 in samples from the largest fragment to approximately (4–9) × 105 cm −2 in one of the smaller fragments. The combined track, radionuclide, and noble gas data suggest a preatmospheric radius of ∼20 cm for the Dergaon meteorite.