The stable carbonates in hypercollision zones

Experimental studies on high-pressure dolomite breakdown to aragonite + magnesite carried out over the last 20 years have shown discrepancies. As part of the sediment pile, high-pressure marbles are often present in ultra-high-pressure (UHP) terranes that experienced burial to more than 100 km in continent hypercollisions. Since this discovery the potential of carbonate minerals as UHP indicators has been outlined. Therefore, it is fundamental to elucidate this reaction, which has a >2 GPa uncertainty along the fast subduction pressure – temperature path that corresponds to UHP terranes. Here, we propose to bracket the dolomite breakdown reaction using materials that have been previously used for the studies that showed discrepant results. By combining in-situ phase diagram study and structural (ordering) study of the various dolomites, we will elucidate this reaction and to propose a robust guide to interpret high-pressure marble occurrence in continent hypercollision zones.