53 Mn– 53 Cr radiometric dating of secondary carbonates in CR chondrites: Timescales for parent body aqueous alteration

摘要: Abstract We present 53Mn–53Cr ages of secondary carbonates in Renazzo-like (CR) chondrites, determined by ion mass spectrometry. The timing aqueous alteration CR chondrites has been unconstrained the literature. measured isotope systematics from three different CR-chondrite lithologies. Calcite interchondrule matrix Renazzo, calcite GRO 95577, and dolomite a dark inclusion Renazzo all show excesses 53Cr, interpreted as daughter product decay 53Mn. yields an initial ratio (53Mn/55Mn)0 = (3.6 ± 2.7) × 10−6, ranges (53Mn/55Mn)0 = (3.1 ± 1.4) × 10−6 (corrected to RSF standard) (3.7 ± 1.7) × 10−6 inferred RSF). When anchored D’Orbigny angrite, yield between 4563.6 4562.6 Ma, or ∼4.3–5.3 Myr after formation CV CAIs. heavily altered specimen 95577 shallower slope (53Mn/55Mn)0 = (7.9 ± 2.8) × 10−7, corresponding much younger age 4555.4 Ma, ∼12.6 Myr CAI formation. two are contemporaneous with Mn–Cr Tagish Lake, CI, CM but is uniquely young. These findings suggest that early on chondritic parent bodies was common occurrence, likely driven internal heating 26Al accretion. young carbonate either body sufficiently large sustain for ∼8 Myr, late-stage impact events supplied heat region where originated.