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The reconstruction of thermal history is key to study the geodynamic evolution of sedimentary basins through burial, metamorphism, magmatism, deformation and exhumation. Carbonate clumped isotope thermometry enables such reconstructions in carbonate minerals, and complements ‘conventional’ low-temperature thermochronometers (e.g. apatite and zircon fission-tracks or U-Th/He systems) by constraining the peak burial temperature and the cooling rate.
Most published uses of carbonate clumped isotope thermometry aim to measure depositional temperatures of Earth-surface sedimentary carbonates. However, it has also been shown that carbonate clumped-isotope measurements of minerals formed or re-equilibrated at elevated temperatures can constrain thermal histories of sub-surface rocks. Only very recently have we had the experimental constraints on solid-state isotopic reordering to translate clumped-isotope measurements of such materials into quantitative statements about burial and exhumation. These data have led to a new generation of conceptual models describing changes in clumped-isotope composition during heating and cooling; taken together, these experiments and models enable a new approach to the study of burial, metamorphism and exhumation over long timescales and large areas. This presentation will discuss applications of this approach to constrain the thermal history of carbonate rocks exhumed in back-arc (Naxos, Greece) and mid-continental (Colorado Plateau) basins.
The exhumation of Naxos metamorphic core-complex entailed a complex thermal history, mineral-mineral and water-rock reactions, and deformation. These processes were registered in the bulk and clumped isotope composition of marbles. Calcite and dolomite marbles from Naxos show large variation of carbonate clumped-isotope values, in association with deformation and secondary mineralization fabrics. Results suggest that dynamic recrystallization of calcite can reset the carbonate clumped-isotope signal, which consequentially records the minimum temperature of dynamic recrystallization in natural samples. Carbonate clumped isotope data from the center of Naxos core-complex are consistent with the thermal history as recorded by multiple ‘conventional’ thermochronometers, but require a faster cooling rate than previously suggested, consistent with a heat shock driven by magmatic and hydrothermal activities.
Carbonate clumped isotope thermometry is used to study the burial, uplift and exhumation histories of the Colorado Plateau (USA). There, carbonate rocks were not recrystallized to marbles, and therefore their clumped isotope signals are expected to be sensitive to the peak-burial temperature. Given such constrains on the thermal history, it is straightforward to infer the thermal gradients during peak burial, and calculate total-exhumation (i.e. the volume of rock removed) in-situ. Preliminary results from the southwestern rim and the interior of the Plateau are so far consistent with published constrains on peak burial temperatures.