CHRONOTEC · Conditions and duration of High tempeRature metamOrphism in large hot orogeNs assessed through petrochronolOgy : insights from Grenville TECtonics

Conditions and duration of High tempeRature metamOrphism in large hot orogeNs assessed through petrochronolOgy : insights from Grenville TECtonics

Orogenic belts are among the most striking evidence of Earth Tectonics. During convergence processes, the crust can be buried, thickened and heated up, leading to creation and recycling of continental material. This is particularly well exemplified in Large Hot Orogens (LHOs), the roots of which can attain and maintain temperatures higher than 800°C over several tens of million years (m.y.), causing partial melting, crustal flow and potential development of orogenic plateaux. Exhumed core zones of ancient orogens give direct access to formerly deep and hot levels of crust that are still buried in modern analogues, offering unparalleled opportunities to both assess the condition and duration of high-T processes and investigate the tectonic evolution of orogenic roots. The Mesoproterozoic Grenville Province is a type example of an ancient LHO, active for over 100 m.y (~1090 – 980 Ma). Geodynamic modelling has addressed key tectonic features of this orogen, but metamorphic data, crucial for tectonic interpretations, are patchy and incomplete. In the last decades, the development of thermodynamic modeling and instrumental advances in elemental and isotopic analysis have open new avenues to unravel the Pressure-Temperature-time (P-T-t) paths of rocks, to assess the rates and duration of large-scale orogenic processes. In high-grade metamorphic rocks, the time dimension of P-T-t paths is mostly documented by zircon U-Pb dating coupled to its trace element record, that can be linked to the garnet growth, based on partitioning of trace elements. However, decoupling between trace element content and ages in zircon are documented, especially during high-grade metamorphism, resulting in misinterpretations and hampering P-T correlation and large-scale tectonic interpretation. This can be resolved by documenting the chronological record of U–Pb in zircon and Lu–Hf, Sm–Nd in garnet from the same sample, but such multifaceted studies are rare, calling to investigate both garnet and zircon chronometers in a variety of tectonic settings to bring better constraints from natural samples. The objectives of CHRONOTEC are dual: (i) to bring new insights on the fate of the continental crust in Large Hot Orogens, by assessing the timing, duration, and conditions of High-Temperature (high-T) metamorphism during continental collision, and (ii) to assess the age, chemical and isotopic record and links between chronometers zircon and garnet in high-T mafic rocks across a Pressure (P) gradient.

Data: CORDIS, © European Union