Thermochronology is the study of the thermal evolution of a region of a planet. Thermochronologists use radiometric dating along with the closure temperatures that represent the temperature of the mineral being studied at the time given by the date recorded to understand the thermal history of a specific rock, mineral, or geologic unit. It is a subfield within geology, and is closely associated with geochronology.
A typical thermochronological study will involve the dates of a number of rock samples from different areas in a region, often from a vertical transect along a steep canyon, cliff face, or slope. These samples are then dated. With some knowledge of the subsurface thermal structure, these dates are translated into depths and times at which that particular sample was at the mineral's closure temperature. If the rock is today at the surface, this process gives the exhumation rate of the rock.
Common isotopic systems used for thermochronology include fission track dating in zircon, apatite, titanite, natural glasses, and other uranium-rich mineral grains. Others include potassium-argon and argon-argon dating in apatite, and (U-Th)/He dating zircon and apatite.
Radiometric dating is how geologist determine the age of a rock. In a closed system, the amount of radiogenic isotopes present in a sample is a direct function of time and the decay rate of the mineral. Therefore, to find the age of a sample, geologists find the ratio of daughter isotopes to remaining parent isotopes present in the mineral through different methods, such as mass spectrometry. From the known parent isotopes and the decay constant, we can then determine the age. Different ions can be analyzed for this and are called different dating.
For thermochronology, the ages associated with these isotopic ratios is directly linked with the sample's thermal history. At high temperatures, the rocks will behave as if they are in an open system, which relates to the increased rate of diffusion of the daughter isotopes out of the mineral.
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This timeline of natural history summarizes significant geological and biological events from the formation of the Earth to the arrival of modern humans. Times are listed in millions of years, or megaanni (Ma). The geologic record is the strata (layers) of rock in the planet's crust and the science of geology is much concerned with the age and origin of all rocks to determine the history and formation of Earth and to understand the forces that have acted upon it.
Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar). Potassium is a common element found in many materials, such as feldspars, micas, clay minerals, tephra, and evaporites. In these materials, the decay product is able to escape the liquid (molten) rock, but starts to accumulate when the rock solidifies (recrystallizes).
Chronological dating, or simply dating, is the process of attributing to an object or event a date in the past, allowing such object or event to be located in a previously established chronology. This usually requires what is commonly known as a "dating method". Several dating methods exist, depending on different criteria and techniques, and some very well known examples of disciplines using such techniques are, for example, history, archaeology, geology, paleontology, astronomy and even forensic science, since in the latter it is sometimes necessary to investigate the moment in the past during which the death of a cadaver occurred.
The recrystallization behaviour of Al-Mn alloys (AA3xxx series alloys) is affected by randomly distributed dispersoids present before annealing, by dispersoids precipitated at grain/subgrain boundaries before the onset of recrystallization, and by disperso ...
Recent advances in microscale (40)Ar/(39)Ar geochronology have revealed argon concentration gradients in naturally deformed muscovite that are incompatible with volume diffusion uniquely, and have been interpreted to result from intragranular defect-enhan ...
EAG2003
The responses of uranium-bearing accessory minerals to shock metamorphism have received growing interest, because under extreme pressure and temperature conditions, these phases can form unique microstructures and/or polymorphs and their radiometric ages c ...