Fission track dating ppt
Fission-track dating of detrital zircon is a widely applied analytical tool used to understand the tectonic evolution of source terrains that have left a long and continuous erosional record in adjacent basin strata.Early studies focused on using the cooling ages in detrital zircon from stratigraphic sequences to document the timing and rate of erosion of rocks in adjacent orogenic belts (mountain ranges).
The ratio of spontaneous to induced tracks is proportional to the age.A number of recent studies have combined U/Pb and/or Helium dating (U Th/He) on single crystals to document the specific history of individual crystals.This double-dating approach is an extremely powerful provenance tool because a nearly complete crystal history can be obtained, and therefore researchers can pinpoint specific source areas with distinct geologic histories with relative certainty.One method is by neutron irradiation, where the sample is irradiated with thermal neutrons in a nuclear reactor, with an external detector, such as mica, affixed to the grain surface.The neutron irradiation induces fission of uranium-235 in the sample, and the resulting induced tracks are used to determine the uranium content of the sample because the U ratio is well known and assumed constant in nature.Fission track analysis of these minerals provides information about the thermal evolution of the source rocks and therefore can be used to understand provenance and the evolution of mountain belts that shed the sediment.
This technique of detrital analysis is most commonly applied to zircon because it is very common and robust in the sedimentary system, and in addition it has a relatively high annealing temperature so that in many sedimentary basins the crystals are not reset by later heating.
Another method of determining uranium concentration is through LA-ICPMS, a technique where the crystal is hit with a laser beam and ablated, and then the material is passed through a mass spectrometer.
Unlike many other dating techniques, fission-track dating is uniquely suited for determining low-temperature thermal events using common accessory minerals over a very wide geological range (typically 0.1 Ma to 2000 Ma).
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Calculation based on: Old Testament – Earth is 6,015 years old James Ussher (1581-1656) 1658 Earth formed on Sunday, 23 October, 4004 BC. Thermodynamics I – Download Now An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
The density of fossil tracks correlates with the cooling age of the sample and with uranium content, which needs to be determined independently.