Calibration and applications of the dolomite clumped isotope thermometer to high temperatures

Abstract

Carbonate clumped isotope paleothermometry is based on the temperature-dependent formation of ^(13)C^(18)O^(16)O_2 ^(2-) ion groups within solid carbonate minerals. This thermometer has now been calibrated for various synthetic and natural biogenic and abiogenic minerals (calcite, aragonite and carbonateapatites [e.g., 1, 2]) at temperatures below ~ 50°C. Here we extend the use of the carbonate clumped isotope thermometer to shallow crustal environments by determining the Δ_(47) values of CO_2 extracted from natural and synthetic dolomites grown at know temperatures from 25 to 350ºC. The experimental temperature dependance is not linear in the Δ_(47) vs T^(-2) plot and resembles the predicted theoretical temperature dependence, both in shape and absolute value [3]. These data for synthetic dolomites overlap the previous calibrations for inorganic calcite and some forms of biogenic carbonates between 25 and 50˚C, and are consistent with a single trend that also intersects data for synthetic calcite equilibrated at 1200˚C. These observations suggest that a single temperature dependant relationship reasonably approximates the calibration for both phases. Data from a variety of slowly-cooled (i.e., over geological timescales) natural marbles and rapid (i.e., laboratory timescales) heating experiments provide insights into the kinetics of solid-state ^(13)C-^(18)O bond reordering in carbonates and its closure temperature. More generally, our new calibration and constraints on high-temperature kinetics have implications for the application of this technique to burial and metamorphic processes. These issues will be illustrated through estimates of the thermal history and oxygen isotopic compositions and abundances of pore fluids for several suites of late Neoproterozoic carbonates [e.g., 4].

Files

Additional details