Uranium—thorium dating , also called thorium dating , uranium-series disequilibrium dating or uranium-series dating , is a radiometric dating technique established in the s which has been used since the s to determine the age of calcium carbonate materials such as speleothem or coral. Instead, it calculates an age from the degree to which secular equilibrium has been restored between the radioactive isotope thorium and its radioactive parent uranium within a sample. Thorium is not soluble in natural water under conditions found at or near the surface of the earth, so materials grown in or from this water do not usually contain thorium. As time passes after such material has formed, uranium in the sample with a half-life of , years decays to thorium At secular equilibrium, the number of thorium decays per year within a sample is equal to the number of thorium produced, which also equals the number of uranium decays per year in the same sample. In , John Joly , a professor of geology from the University of Dublin , found higher radium contents in deep sediments than in those of the continental shelf, and suspected that detrital sediments scavenged radium out of seawater.
Helium dating - Wikipedia
Kinematic parameters derived from He diffusion is done through estimating He diffusion over a range of temperatures. The use of density functional theory helps in estimating energy barriers for He to overcome as it diffuses across various crystallographic directions. Discrepancies, however, between observed and predicted He diffusion rates is still a problem and likely stem from unresolved problems in crystal defects and radiation damage in natural grains as opposed to theoretical grains. For example, He diffusion in minerals such as zircon , rutile , and monazite have been shown to be strongly anisotropic. A relatively new dating method, tritium—helium dating has been developed for determining rates of oxygen utilization in the ocean. More information, however, can be concluded about a mineral's thermal history if an analysis of the He distribution in-situ is performed.
Combined single-grain (U-Th)/He and U/Pb dating of detrital zircons from the Navajo Sandstone, Utah
Metrics details. Topographic relief in arc-trench systems is thought to be formed by plate subduction; however, few quantitative investigations have so far been reported, with respect to the related mountain building process. Weighted mean AHe ages ranging from Using the AHe data, denudation rates were obtained for each sample. These data indicate a clear contrast in thermal and denudation histories between the tectonic units in this study area, similar to that previously reported from the southern part of NE Japan Arc.
Abstract This paper presents a significantly simplified method for in-situ U-Th-He dating removing the need to know any absolute concentrations or ablation pit volumes. We introduce an LA-ICP-MS-based method to correct for variable ablation depths between the standard and the unknown, using the strength of the ablated 29 Si signal. Finally, we propose a pseudo-depth profile method to assess the effects of compositional zoning on the accuracy of in-situ U-Th-He data. The effectiveness of the proposed method has been demonstrated on three samples of gem-quality Sri Lanka zircon, which yield ages that are in agreement with previously published conventional U-Th-He measurements.