The origin of carbonates in impact melt-bearing breccias from Site M0077 at the Chicxulub impact structure, Mexico

1Nicolas D. GARRONI,1Gordon R. OSINSKI
Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.13993]
1Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

Carbonates from the impact melt-bearing breccia in the 2016 IODP/ICDPExpedition 364 drill core at Site M0077 were systematically documented and characterizedpetrographically and geochemically. Calcite, the only carbonate mineral present, is abundantthroughout this deposit as five distinct varieties: (1) subangular carbonate clasts (Type A); (2)subround/irregular carbonate clasts with clay altered rims (Type B); (3) fine-crystalline matrixcalcite (Type C); (4) void-filling sparry calcite (Type D); and (5) microcrystalline carbonatewith flow textures (Type E). Quantitative geochemical analysis shows that calcite in allcarbonate varieties are low in elemental impurities (<2.0 cumulative wt% on average);however, relative concentrations of MgO and MnO vary, which provides distinction betweeneach variety: MgO is highest in calcite from Types A, B, and C carbonates (0.2–0.8 wt% onaverage); MnO is highest in calcite from Types B, C, and D carbonates (0.2–1.3 wt% onaverage); and calcite from Type E carbonate is most pure (<0.1 wt% on average MgO andMnO, cumulatively). Based on textural and geochemical variations between carbonate types,we interpret that some of the carbonate target rocks melted during impact and wereimmiscible within the silicate-dominated melt sheet prior to the resurgence of seawater. TypeB clasts were formed by molten fuel–coolant interaction, as the incoming seawater erodedthrough the melt sheet and encountered carbonate melt (Type E). Post-impact meteoric-dominated hydrothermal activity produced the Mn-elevated calcite from Type C and Dcarbonates, and altered the Type B clasts to be elevated in Mn and host a clay-rich rim.


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