首页 | 本学科首页   官方微博 | 高级检索  
     检索      


The reaction of carbonates in contact with laser-generated,superheated silicate melts: Constraining impact metamorphism of carbonate-bearing target rocks
Authors:Christopher Hamann  Saskia Bläsing  Lutz Hecht  Sebastian Schäffer  Alex Deutsch  Jens Osterholz  Bernd Lexow
Institution:1. Museum für Naturkunde, Leibnitz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, 10115 Berlin, Germany;2. Museum für Naturkunde, Leibnitz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, 10115 Berlin, Germany

Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstraße 74–100, 12249 Berlin, Germany;3. Fraunhofer-Institut für Kurzzeitdynamik, Ernst-Mach-Institut, Eckerstraße 4, 79104 Freiburg, Germany;4. Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany

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 CO2 at the silicate melt–carbonate interface. We identify several processes, i.e., (1) decomposition of carbonates releases CO2 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 CO2 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.
Keywords:
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号