those that form during chemical reactions without breaking down).
The sensitive high-resolution ion microprobe (also sensitive high mass-resolution ion microprobe or SHRIMP) is a large-diameter, double-focusing secondary ion mass spectrometer (SIMS) sector instrument produced by Australian Scientific Instruments in Canberra, Australia.
Like other SIMS instruments, the SHRIMP microprobe bombards a sample under vacuum with a beam of primary ions that sputters secondary ions that are focused, filtered, and measured according to their energy and mass.
Radioactive dating is a method of dating rocks and minerals using radioactive isotopes.
This method is useful for igneous and metamorphic rocks, which cannot be dated by the stratigraphic correlation method used for sedimentary rocks. Some do not change with time and form stable isotopes (i.e.
Core domains, which are large, homogeneous and with undisturbed igneous oscillatory zoning, yielded preferentially ages between 430 and 460 Ma.
We therefore consider that granitic protolith formation took place at that time.
The rate of decay (given the symbol λ) is the fraction of the 'parent' atoms that decay in unit time.
For geological purposes, this is taken as one year.
These results imply that the Variscan HT crystallisation history of the Moldanubian granulites took place over a period of a few million years and was not an extremely rapid subduction-exhumation process.
SHRIMP measurements in the protolithic cores yield a cluster of (sub)concordant ages between ∼390 and 460 Ma and a few outliers at higher ages mostly represented by cores in cores.
Ion microprobes make in situ isotopic and chemical 'surface' analysis of solid targets by bombarding the sample with an ion beam with a diameter of several microns typically employing Kohler focussing.