Temperatures of Aqueous Alteration on Cm Chondrite Parent Bodies Based on Carbonate ‘clumped-isotope’ Thermometry

Introduction: Aqueous alteration of primitive meteorites was among the earliest differentiation processes in the solar system [1], and a better understanding of it would help constrain and test models of the thermal and chemical evolution of planetesimals. One of the challenges is to establish the temperatures of alteration. Petrographic analysis of CM matrices [2] suggest their temperatures of aqueous alteration were below 125˚C, and broadly similar upper limits (<170˚C) are suggested by the presence of tochilinite [3]. However, much lower alteration temperatures, ranging from <20˚C to 50˚C, are suggested by oxygen isotope fractionations among matrix components [4,5,6,7]. But these oxygen isotope studies are only valid if matrix carbonate and phyllosilicate reach oxygen isotope exchange equilibrium. These phases differ from each other in Δ