Single-crystal dating and the detrital record of orogenesis

Single-crystal dating of detrital mineral grains confers a remarkable ability to reconstruct cooling histories of orogens and to place limits on the timing, magnitude, and spatial variations of erosion. Numerous grains from a detrital sample are typically dated, and the statistical variability between populations of ages in different samples provides keys to variations in cooling histories and exhumation rates within the hinterland. Given that detrital samples comprise minerals drawn from an entire catchment, they offer an integrated perspective that is almost always unattainable with bedrock samples. Moreover, because detrital ages are preserved within stratigraphic successions, the evolution of populations of cooling ages through time and across an orogen can be reconstructed from the sedimentary record. When combined with a known hinterland ‘stratigraphy’ of bedrock cooling ages, studies of detrital ages in modern river systems demonstrate the fidelity of the detrital signal, and reveal both the power and limitations of detrital single-crystal dating in sedimentary basins. Low-temperature thermochronometers can be sensitive to variations in hinterland erosion of as little as 1–2 km. Although recognized previously from a theoretical viewpoint, the impact exerted on modern detrital ages by the interplay between erosion rates and lithology within tributary catchments has only recently been documented and provides a basis for refining orogenic histories using detrital ages. Documentation of the downstream evolution of detrital ages emphasizes that the distribution of ages that reaches the mouth of a river may bear little resemblance to age distributions in the headwaters. Similarly, because lithological concentrations of minerals used for singlecrystal dating can vary by many fold within the hinterland, rapidly eroding tributary catchments do not necessarily dominate populations of detrital ages. An ability to exploit detrital ages to place limits on kinematic rates within collisional orogens as a function of cooling rates provides a potent new analytical tool. If uncertainties regarding kinematic geometries, related particle pathways through orogens and steady-state assumptions can be reduced, detrital ages in both modern rivers and the recent stratigraphical record can serve to reconstruct rates of deformation and erosion and to test the viability of proposed models of orogenic evolution.