Three phases of carbonate minerals and two degrees of alteration in the Nogoya CM2 carbonaceous chondrite

No abstract available

Multiple pulses of aqueous solutions in QUE 93005 (CM2): evidence from oxygen isotopes

No abstract available

Three phases of carbonate minerals and two degrees of alteration in the Nogoya CM2 carbonaceous chondrite

No abstract available

The oxygen isotope evolution of parent body aqueous solutions as recorded by multiple carbonate generations in the Lonewolf Nunataks 94101 CM2 carbonaceous chondrite

The CM2 carbonaceous chondrite LON 94101 contains aragonite and two generations of calcite that provide snapshots of the chemical and isotopic evolution of aqueous solutions during parent body alteration. Aragonite was the first carbonate to crystallize. It is rare, heterogeneously distributed within the meteorite matrix, and its mean oxygen isotope values are δ18O 39.9±0.6‰, Δ17O -0.3±1.0‰ (1σ). Calcite precipitated very soon afterwards, and following a fall in solution Mg/Ca ratios, to produce small equant grains with a mean oxygen isotope value of δ18O 37.5±0.7‰, Δ17O 1.4±1.1‰ (1σ). These grains were partially or completely replaced by serpentine and tochilinite prior to precipitation of the second generation of calcite, which occluded an open fracture to form a millimeter-sized vein, and replaced anhydrous silicates within chondrules and the matrix. The vein calcite has a mean composition of δ18O 18.4±0.3‰, Δ17O -0.5±0.5‰ (1σ). Petrographic and isotopic results therefore reveal two discrete episodes of mineralization that produced Ca-carbonates with contrasting δ18O, but whose Δ17O values are indistinguishable within error. The aragonite and equant calcite crystallized over a relatively brief period early in the aqueous alteration history of the parent body, and from static fluids that were evolving chemically in response to mineral dissolution and precipitation. The second calcite generation crystallized from solutions of a lower Δ17O, and a lower δ18O and/or higher temperature, which entered LON 9410 via a fracture network. As two generations of calcite whose petrographic characteristics and oxygen isotopic compositions are similar to those in LON 94101 occur in at least one other CM2, multiphase carbonate mineralization could be the typical outcome of the sequence of chemical reactions during parent body aqueous alteration. It is equally possible however that the second generation of calcite in formed in response to an event such as impact fracturing and concomitant fluid mobilisation that affected a large region of the common parent body of several CM2 meteorites. These findings show that integrated petrographic, chemical and isotopic studies can provide new insights into the mechanisms of parent body alteration including the spatial and temporal dynamics of the aqueous system

Microstructure of calcite in the CM2 carbonaceous chondrite LON 94101: implications for deformation history during and/or after aqueous alteration

The microstructure of calcite in the CM2 carbonaceous chondrite LON 94101 has been characterized using electron backscatter diffraction (EBSD) analysis, to reconstruct the parent body deformation history during and/or after aqueous alteration. The results suggest that at least two events of calcite crystallization have taken place during aqueous alteration, and at least three episodes of deformation are recorded by the calcite. The first event of calcite crystallization produced calcite grains scattered throughout the matrix, and the second event formed a calcite vein via localized fluid flow. The first episode of deformation is recorded in the crystallographic preferred orientations of the calcite grains and occurred via a directed stress probably induced by compaction in shallow crustal levels of the parent body. The second episode of deformation is recorded in an e-twin microstructure and it suggests a deformation induced via directed stress by impact processing, also in shallow crustal levels. The third episode of deformation generated subgrains in the calcite vein and in some calcite grains, and fragmented and disrupted the calcite vein. This could have been a result of a relatively forceful deformation event, perhaps when the meteorite was released from its parent body. This study shows that carbonate microstructures in carbonaceous chondrites is a powerful and versatile tool for reconstructing the history of deformation during and/or after aqueous alteration