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Revised model calculations for the thermal histories of ordinary chondrite parent bodies
Author(s) -
BENNETT Marvin E.,
McSWEEN Harry Y.
Publication year - 1996
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.1945-5100.1996.tb02113.x
Subject(s) - ordinary chondrite , chondrite , closure temperature , geology , parent body , mineralogy , thermal , geochemistry , meteorite , fission track dating , metamorphic rock , zircon , thermodynamics , physics , astrobiology
— Recent measurements of ordinary chondrite physical and thermal properties along with new geothermometry studies have provided the necessary parameters for updating a previously proposed model (Miyamoto et al ., 1981) for the thermal evolution and internal structure of ordinary chondrite parent bodies. Model calculations assumed a heat source term derived from the decay of 26 Al (justification is provided). Differences from the previous model include: varying the thermal diffusivity parameter with increasing temperature (and decreasing porosity), using variable physical and thermal parameters to provide end member models, and incorporating a shortened thermal history of 60 Ma (obtained from new Pb‐Pb chronology of phosphates) rather than 100 Ma. Times of isotopic closure in chondrite phosphates overlap the thermal model estimates, and postmetamorphic cooling rates from the model approximately coincide, in both trend and magnitude, with metallographic and fission track cooling rate data. Model calculations attempt to match peak metamorphic conditions in the central portions of these bodies and yield accretion ages between 1.4 to 3.1 Ma after calcium‐aluminum inclusion (CAI) formation. Model calculations also predict that both the H and the L chondrite parent asteroids consisted of ∼80% equilibrated and 20% unequilibrated chondritic material and that their original radii ranged from 80 to 95 km.