Mass-independent and mass-dependent Cr isotopic composition of the Rumuruti (R) chondrites: Implications for their origin and planet formation

Chromium (Cr) isotopes play an important role in cosmochemistry and planetary science because they are powerful tools for dating (53Mn–53Cr short-lived chronometry), tracing (54Cr nucleosynthetic anomalies) the origins of materials, studying processes involved volatile element fractionation differentiation (Cr stable isotopic fractionation). To use Cr these purposes, it is essential to precisely know compositions various chondritic reservoirs. However, isotope composition Rumuruti (R) chondrites remains unknown. Here, we report high-precision mass-independent (average 2SE uncertainty ?0.02 ?0.06 ?53Cr ?54Cr, respectively; ? indicates 10,000 deviation) mass-dependent (uncertainty average 0.03‰ ?53Cr; ? 1000 data 12 bulk R petrologic types 3–6 (including chondrite breccias), one chondrite-like clast (MS-CH) Almahata Sitta polymict ureilite. All show homogeneous ?54Cr values, ?0.06 ± 0.08 (2SD), similar only those Earth–Moon system enstatite chondrites. This first dataset provides significant addition ?54Cr–?17O diagram, positions them as a potential endmember precursors. The possess higher 55Mn/52Cr 0.68 0.04 relative most carbonaceous values 0.23 0.05 (2SD) groups. likely results from lower chondrule abundance compared that ordinary with ?53Cr = ?0.12 (2SD). Combined previous other groups chondrites, all 0.04‰ (2SD, N 42) independent type redox conditions. lack between suggests value also representative initial differentiated planets Solar System. Finally, MS–CH has (?53Cr 0.18 0.04, ?0.16 0.07, ?0.11 0.05‰) consistent (within error) being clast.