NEW DEPARTURES IN LOW-TEMPERATURE THERMOCHRONOLOGY AND TECTONICS

Low-temperature thermochronometric dating techniques are powerful tools to constrain the cooling of rocks exhumed by tectonic processes and are widely used to elucidate time-temperature and exhumation histories of mountain belts, metamorphic terranes, sedimentary basins, et cetera. The approach is fundamentally based on the fact that rocks move relatively upwards and cool during tectonic faulting accompanied by erosion, leading to exhumation and cooling such that the timing, rate, and magnitude of tectonic activity can be estimated from thermochronometric data. Some commonly used thermochronometers include 40Ar/39Ar dating of K-feldspar, mica, and hornblende, fission track dating of apatite and zircon, and Th-U-Pb dating of titanite, rutile, and monazite. (U-Th)/He dating of apatite with a closure temperature of ~65-70°C (-dT/dt = 10°C/myr) is now a well-established and widely employed thermochronological technique. Besides apatite, (U-Th)/He dating has focused on zircon (closure temperature, Tc = ~180°C) and titanite (Tc = ~200°C). Additional minerals such as monazite (Tc = ~240°C), xenotime (Tc = ~120°C), rutile (Tc = ~220°C), and other silicate and oxide phases provide new tools for establishing time-temperature paths of rocks. This new tools offer the exciting possibility of constraining different portions of a rock's low-temperature thermal history, ranging from ~40ºC to ~250ºC. Expansion of thermochronometry to rocks that are often problematic to date using established radiometric techniques, such as (ultra-) high-pressure rocks, should have a significant impact on our understanding of the rates and thermal aspects in a wider range of tectonic environments. This continuing development of new thermochronometers offers exciting new tools for a more detailed understanding of tectonic exhumation. Increasingly more sophisticated, process-oriented numerical modeling of thermochronometric data has significantly improved our quantitative understanding, allowing us to more fully elucidate the complex interplay of structural, metamorphic and erosional processes. Development and refinement of new thermochronometers and systematic incorporation of these new analytical and numerical techniques will enable us to derive high-resolution reconstructions of tectonic cooling and exhumation in extensional and contractional tectonic settings.