Thermal and Shock Metamorphism Effects on Siderophile Element Distribution and Hf-W Chronology in H Chondrites

Abstract

We performed in situ measurements of metal grains in 21 H chondrites (Type 3-6, shock stages 1-5) for 17 siderophile elements and measured 182Hf-182W isotopes for Tassédet 004 (H5-melt breccia) to better constrain the thermal evolution of the H chondrite parent body. The variations of siderophile element abundances observed in the metal of ordinary chondrites are consistent with condensation from a locally heterogeneous nebula that contains components reflecting a range of fO2 histories (i.e., reduced carbon co-existing with Fe-rich olivine), on a local grain-scale. Chondrites with impact-melt features have a disparity of siderophile variability between melted and unmelted metals. Chondritic material within Tassédet 004 cooled rapidly at a rate of at least 42°C/Ma before 182Hf-182W system closure ~8.2 Ma after CAI formation. A subsequent impact occurred ~20 Ma later, injecting the melt which cooled rapidly ~27.3 Ma after CAI formation.