Radiogenic Heat Production
The record of high temperature processes in the continents is often cryptic because high temperatures cause melting, deformation, and metamorphic phase changes that severely alter the composition and appearance of continental rocks. We are discovering that ultrahigh (>900 degrees Celsius) temperatures occurred in many continental settings, but the causes and effects of these metamorphic events remain uncertain. My work suggests that radioactive elements (primarily uranium, thorium, and potassium) can cause focused heating to ultrahigh temperatures.
My research has focused on a geologic terrane in southern Madagascar, where rocks that were once buried in a Himalaya-type continental collision are now exposed on the surface. I performed petrochronology (trace element and U-Pb isotope geochronology) to determine the timescales of heating, 4+ cation thermometry (Zr-in-rutile and Ti-in-quartz) thermometry to constrain peak temperatures, and numerical modeling to evaluate thermal evolution scenarios. My results indicated that high concentrations of uranium, potassium, and especially thorium caused preferential heating in certain rocks, leading to ultrahigh temperature conditions regionally. We are still evaluating the role of other factors.
For more information about ultrahigh temperature metamorphism in Madagascar, see my papers:
Holder, R.M., Hacker, B.R., Horton, F., Michel Rakotondrazafy, A.R., 2018, Ultrahigh-temperature osumilite gneisses in southern madagascar record combined heat advection and high rates of radiogenic heat produection in a long-lived high-T orogen: Journal of Metamorphic Geology, v. 36, p. 855–880.
Horton, F., Hacker, B., Kylander-Clark, A., Holder, R., Jöns, N., 2016, Focused radiogenic heating of middle crust caused ultrahigh temperatures in southern Madagascar: Tectonics, v. 35, p. 293–314.