Temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the CM chondrites

Abstract

Aqueous alteration of primitive meteorites was among the earliest geological process during the evolution of our solar system. 'Clumped-isotope' thermometry of

Extended chronologies of aqueous alteration in the CM2 carbonaceous chondrites: Evidence from carbonates in Queen Alexandra Range 93005

“…The very strong similarity in mineral assemblages of polymineralic grains in QUE 93005 and the CR1 GRO 95577 imply that during carbonate mineralisation solution temperatures and/or solution chemistry, pH and Eh may have been comparable between the two meteorites. Suggested crystallisation temperatures for carbonates in the CM2s Cold Bokkeveld, Murray and Murchison from clumped isotope thermometry are 20-71 ºC (Guo and Eiler, 2007), which is lower 20 than temperatures suggested for CR aqueous alteration of <150 ºC (Zolensky et al, 1993) to 250-300 ºC (Weisberg and Huber 2007), although the very primitive nature of organic matter in the CRs would argue for temperatures lower than those previously published (see Alexander et al, 2010).…”

“…The chondrules could have expanded during hydration of their silicates and glass, and this is indeed the outcome if the major ions (Mg, Si and Fe) are immobile. For example, the replacement of forsterite and enstatite by chrysotile, as expressed in equation (2) (Guo and Eiler, 2007), is accompanied by a 44% increase in volume:…”

“…This rotation may have taken place before or during compaction, but another possibility is that abrasion accompanied fluidisation of the matrix by gas or vapour, and grain abrasion during fluidisation has been described from terrestrial pyroclastic deposits (Gravina et al, 2004). With regard to QUE 93005 the gas may have been CH 4 generated during serpentinisation (Guo and Eiler 2007), H 2 from oxidation of Fe (Wilson et al, 1999;Alexander et al, 2010) or the CO/CO 2 that contributed to carbonate crystallisation. Water vapour could also have been generated from deeper in the parent body by depressurisation following removal of overburden by impacts or by catastrophic overpressure (Wilson et al, 1999).…”

Evidence for the late formation of hydrous asteroids from young meteoritic carbonates

“…According to the oxygen isotopic compositions 23 and a simulation of chemistry during aqueous alteration 28 , the calcite in Murchison is likely to have precipitated at < 25 °C in the earliest stage of aqueous alteration (when less than a few percent of rock reacted with water). The clumped-isotope thermometry also suggests that the calcite in Murchison formed at a low temperature (20-33 °C) 29 . On the other hand, the dolomite in Sayama seems to have formed at a higher temperature ( > 120 °C), as inferred from the small isotopic fractionation of oxygen between the dolomite and the matrix 30 .…”

Accretion and Preservation of D-Rich Organic Particles in Carbonaceous Chondrites: Evidence for Important Transport in the Early Solar System Nebula

“…Indeed, organic matter exchanges its D with water and hydrous minerals in the timescale of hundreds of thousands years (Sessions et al 2004) in sedimentary basins, at temperature around 200 • C. In carbonaceous chondrites, organic matter and clay minerals are associated since the accretion of the parent body and then have evolved for 4.5 billion years. The temperature for most of the history of the parent bodies has remained low (below 0 • C), except for a few million years just after the formation of the parent body where it should have reached 20 • C-70 • C during hydrothermal activity on CI and CM parent bodies (Guo & Eiler 2007).…”