Shining a light on ancient mountains with petrochronology and synchrotron

Abstract

Mountain ranges or orogens are surficial expressions of deeper lithospheric deformation, metamorphism and igneous activity triggered by tectonic forces. Hence, metamorphic and igneous rocks are the prime record of the evolution of ancient orogens. Equilibrium thermodynamics forms the basis of petrological studies and allows pressure-temperature (P-T) conditions to be quantified for the successive evolutionary stages of rocks that can be dated by geochronological methods. The reconstruction of P-T-t paths provides unique estimates of orogenic rates and contrasting orogenic rates may highlight distinct geodynamic processes, including early Earth tectonics, subduction and collisional processes. Geodynamic numerical modeling is a crucial tool to simulate these different tectonic scenarios and compare with P-T-t paths recorded in ancient orogens. This proposal has a two-fold goal, including (i) the development of new routines for 2D and 3D sub-¼m chemical imaging on rock samples using the fourth-generation synchrotron light source facility at the Brazilian Synchrotron Light Laboratory (LNLS); and (ii) to use metamorphic records of contrasting Brazilian ancient orogenic belts to evaluate secular changes in the geodynamic processes of the Earth through time. The newly developed routines will be coupled with traditional methods currently used in petrochronological studies. Neoarchean and Paleoproterozoic orogens in both Amazonia (Carajás Domain, 2.9-2.0 Ga) and São Francisco (Quadrilátero Ferrífero area, 2.7-2.1 Ga) cratons will investigated to constrain early Earth geodynamic processes (stagnant lid tectonics vs plate tectonics), while Neoproterozoic the Brasiliano orogens (Araguaia and Araçuaí/Ribeira orogens, 620-500 Ma) will be used as examples of transitional geodynamic processes from "Precambrian Plate Tectonics" to "Modern Plate Tectonics". These new dataset will provide empirical data to calibrate new thermo-mechanical numerical models, including the numerical simulations that will be ran in this project. (AU)