Chronological constraints on the thermal evolution of ordinary chondrite parent bodies from the 53Mn-53Cr system

The 53Mn-53Cr isotope systematics in ordinary chondrites constrains the accretion and thermal history of their parent bodies. Mineralogical observations olivine-spinel geothermometry suggest that chromite formed during prograde metamorphism with amount increasing petrologic grades type 3 to 6 chondrites. Assuming a chondritic evolution respective bodies, 53Cr/52Cr model ages for range from 3.99-0.79+0.93 11.1-2.8+6.0 Ma after formation calcium-aluminium-rich inclusions (CAIs). Chromite silicate-metal-sulphide isochrons define an age 2.78-0.50+0.55 15.4-1.6+2.4 Ma. Both isochron correlate petrological grade samples, which is consistent onion-shell structure chondrite study shows unlike ages, are prone impact-related disturbances or partial re-equilibration cooling high temperatures, not easily affected by later events yield robust mineral growth ages. results homogenous distribution 53Mn initial canonical 53Mn/55Mn = 6.28 × 10?6. estimated closure temperatures Mn-Cr system chromites ~760 °C ~540–620 imply correspond peak metamorphic temperature reached oldest obtained samples along established Al-Mg chondrule constrain bodies >2.1 CAI formation, implying planetesimal immediately followed formation.