![]() ![]() Volcanic glass shards are typically the most abundant component of such sediments and commonly the only datable phase. However, application of the zircon FT technique to the dating of distal tephra was often hindered by low abundance of zircons, fine grain size, and presence of detrital grains. Westgate, in Encyclopedia of Quaternary Science (Second Edition), 2013 Fission-track datingįission-track (FT) dating of tephra beds using coexisting zircon and glass phases has played a significant role in advancing the stratigraphy and chronology of Plio-Pleistocene successions in New Zealand, United States of America, Canada, Japan, and East Africa. These materials have different uranium concentrations and track retention properties, which determine their datable age range for the FT method ( Fig. Next to apatite, FTD is most applied to the minerals zircon and titanite, and to natural glasses. This temperature evolution can be reconstructed by numerical modeling of the distribution of the fission track lengths in a sample. Because fission tracks are formed through geological time, those formed first, when a rock specimen was at greater depth and at higher temperatures, are more shortened than tracks formed later when the rock cooled on its way to the surface. FT in apatite have an initial etched length of ~ 16 μm, which shorten at elevated temperatures. FTD is used for determining the timing, rate, extent and regional pattern of these geological processes. Crustal rocks heat up and cool due to tectonic processes, surface erosion and burial, magmatic intrusion or meteorite impact. This means that the measured fission track age is related to the cooling of the dated rock specimen in the top 2–12 km of the Earth's upper crust. FTD is a low-temperature thermochronometer.
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