Clumped-Isotope Geothermometry And Carbonate U-Pb Geochronology Of The Alta Stock Metamorphic Aureole, Utah, Usa: Insights On The Kinetics Of Metamorphism In Carbonates

To assess thermal and kinetic influences on atomic mobility and mineral (neo)crystallization, clumped-isotope abundances of calcite and dolomite were measured alongside dolomite cation ordering and U-Pb dates, across metamorphic grade within the c. 35-30 Ma Alta stock contact metamorphic aureole, Utah, USA. Average Delta(47) values of dolomite inside the metamorphic aureole reflect the blocking temperature of dolomite (300 degrees C-350 degrees C) during cooling from peak temperatures. Dolomite Delta(47) values outside the metamorphic aureole record a temperature of similar to 160 degrees C. At the talc isograd, dolomite Delta(47) values abruptly change, corresponding to a decrease of similar to 180 degrees C over <50 m in the down-temperature direction. This observed step in dolomite Delta(47) values does not correlate with cation ordering in dolomite or U-Pb dates, neither of which correlate well with metamorphic grade. The short distance over which dolomite Delta(47) values change indicates strong temperature sensitivity in the kinetics of dolomite clumped-isotope reordering, and is consistent with a wide range of clumped-isotope reequilibration modeling results. We hypothesize that clumped-isotope reordering in dolomite precedes more extensive recrystallization or metamorphic reaction, such as the formation of talc. Dolomite U-Pb analyses from inside and outside the metamorphic aureole populate a single discordia similar to 60 Myr younger than depositional age (Mississippian), recording resetting in response to some older postdepositional, but premetamorphic process.