Lu hf dating site
The peak metamorphic temperature of the sample is lower than the Lu–Hf and Sm–Nd closure temperatures in garnet.
This, combined with the core-to-rim decrease in Mn and HREE concentrations, the slightly U-shaped Sm zonation across garnet and the exclusive occurrence of omphacite inclusion in garnet rim, are consistent with the Lu–Hf system skewing to the age of the garnet core and the Sm–Nd system favoring the rim age.
Last month we discussed dating methods using rare-earth elements (REEs), a group of seventeen metallic elements—i.e., the lanthanides plus scandium (Sc) and yttrium (Y). This introduces a time-dependent concentration into a time-independent linear equation.
Since both the daughter and index isotopes vary in time, establishing an initial daughter concentration (via the isochron method) becomes problematic because the y-intercept of the linear plot cannot be assumed to be the primordial ratio of Geochronologists solve this problem by using “stony meteorites” to establish a primordial isotope ratio for This method assumes that the terrestrial Nd has evolved in a uniform reservoir whose Sm/Nd ratio is equal to that of a chrondritic meteorite that is further thought to be similar in composition to the current photosphere of the sun minus the volatile elements.
In one of the other two, coarser-grained samples' garnet chemistry is identical.
The third sample, however, shows complex zoning in large garnet crystals.
A six-point isochron of this sample yields 32.8 ± 0.5 Ma (MSWD = 1.06), interpreted as the age of Alpine eclogite-facies metamorphism.An eclogite from the Bailang, eastern Lhasa terrane, was investigated with a combined metamorphic conditions of ~ 2.6 GPa and 465–503 °C, which is much lower than those of Sumdo and Jilang eclogites in this area.Garnet–whole rock–omphacite Lu–Hf and Sm–Nd ages of 238.1 ± 3.6 Ma and 230.0 ± 4.7 Ma were obtained on the same sample, which are largely consistent with the corresponding U–Pb age of 227.4 ± 6.4 Ma for the metamorphic zircons within uncertainty.The difference of peak eclogite-facies metamorphic conditions and the distinct metamorphic ages for the Bailang eclogite (~ 2.6 GPa and ~ 480 °C; histories and underwent (U)HP metamorphism at different times.The initiation of the opening the Paleo-Tethys Ocean in the Lhasa terrane could trace back to the early Permian.
Using the various types of radioisotope decay as clocks does not produce consistent results, nor are those results verifiable by observational evidence.