The reaction of carbonates in contact with laser‐generated, superheated silicate melts: Constraining impact metamorphism of carbonate‐bearing target rocks

Citations Over TimeTop 13% of 2018 papers

Abstract

Abstract We simulated entrainment of carbonates (calcite, dolomite) in silicate impact melts by 1‐bar laser melting of silicate–carbonate composite targets, using sandstone, basalt, calcite marble, limestone, dolomite marble, and iron meteorite as starting materials. We demonstrate that carbonate assimilation by silicate melts of variable composition is extremely fast (seconds to minutes), resulting in contamination of silicate melts with carbonate‐derived CaO and MgO and release of CO 2 at the silicate melt–carbonate interface. We identify several processes, i.e., (1) decomposition of carbonates releases CO 2 and produces residual oxides (CaO, MgO); (2) incorporation of residual oxides from proximally dissociating carbonates into silicate melts; (3) rapid back‐reactions between residual CaO and CO 2 produce idiomorphic calcite crystallites and porous carbonate quench products; (4) high‐temperature reactions between Ca‐contaminated silicate melts and carbonates yield typical skarn minerals and residual oxide melts; (5) mixing and mingling between Ca‐ or Ca,Mg‐contaminated and Ca‐ or Ca,Mg‐normal silicate melts; (6) precipitation of Ca‐ or Ca,Mg‐rich silicates from contaminated silicate melts upon quenching. Our experiments reproduce many textural and compositional features of typical impact melts originating from silicate–carbonate targets. They reinforce hypotheses that thermal decomposition of carbonates, rapid back‐reactions between decomposition products, and incorporation of residual oxides into silicate impact melts are prevailing processes during impact melting of mixed silicate–carbonate targets. However, by comparing our results with previous studies and thermodynamic considerations on the phase diagrams of calcite and quartz, we envisage that carbonate impact melts are readily produced during adiabatic decompression from high shock pressure, but subsequently decompose due to heat influx from coexisting silicate impact melts or hot breccia components. Under certain circumstances, postshock conditions may favor production and conservation of carbonate impact melts. We conclude that the response of mixed carbonate–silicate targets to impact might involve melting and decomposition of carbonates, the dominant response being governed by a complex variety of factors.

Related Papers

• → Application of calcite, Mg‐calcite, and dolomite as Raman pressure sensors for high‐pressure, high‐temperature studies(2020)15 cited
• → Atomistic simulation of the differences between calcite and dolomite surfaces(1998)85 cited
• → QUANTITATIVE DETERMINATION OF CALCITE AND DOLOMITE IN PURE CARBONATES AND LIMESTONES(1966)17 cited
• → AN INVESTIGATION OF THE INTERCEPT METHOD FOR DETERMINING THE PROPORTION OF DOLOMITE AND CALCITE IN MIXTURES OF THE TWO: II. Experimental rates of solution of dolomite and calcite in samples consisting of a number of crystals(1960)16 cited