Apatite u thhe dating dating and glastonbury
The concept of He-diffusion in apatite assumes that the diffusion path (a) is the grain size.Therefore, the geometry (A) of the mineral grain is very important (Meesters and Dunai, 2002a, b).During the last 10 years the understanding of the diffusion behavior of He in apatite has been increased (Lippolt et al., 1994; Wolf et al., 1996, 1998, Farley, 2000).The closure temperature of mineral grains that accumulate radiogenic He during the α-disintegration of 238U, 235U, 232Th and daughter products is dependent on: activation energy (E), a geometric factor for the crystal form (A), thermal diffusivity (D0), the length of the average diffusion pathway from the interior to the surface of the grain (a) and the cooling rate at closure temperature (d T/dt; Dodson, 1973).Thermochronologists exploit these phenomena to constrain a wide range of geologic problems, including the formation and evolution of mountain belts, deep-time landscape evolution , and the temporal and spatial evolution of fault systems.If you would like to read more about the (U-Th)/He technique, or about thermochronology in general, please link through to the world’s foremost thermochronology blog.
Finding a suitable standard is made difficult by the tendency of apatite to have low and variable U (and hence radiogenic Pb) concentration, variable common Pb, and to lose Pb by thermally induced diffusion at temperatures ca. Despite this, we have identified two seemingly reliable natural standards: apatite from the Mc Clure Mountain syenite, Colorado and our now preferred gem rough apatite from Madagascar.Check out this new entry describing how to pick and select apatites for (U-Th)/He Thermochronology!At CU we are equipped to measure (U-Th)/He ages on a variety of materials, and are always interested in pursuing new research directions developing new collaborative relationships.*Prices in US$ apply to orders placed in the Americas only.Prices in GBP apply to orders placed in Great Britain only.