Zircon is ubiquitous in granites, and is more resistant to isotopic disturbance by secondary geological processes such as metamorphism, alteration and weathering than most other minerals. These have resulted in its being possible to make increasingly precise analyses of ever smaller zircon samples (Williams, 1992).Also, the U-Pb system itself has the unique feature that, because it consists of two U isotopes that decay at different rates to two Pb isotopes, any isotopic disturbance that does occur can be detected by a simple test for internal consistency between the radiogenic Pb isotopic composition and the Pb/U ratios (Williams, 1992). Much slower to develop, however, has been an understanding of the properties of the zircon U-Pb system as such.The Khao Pret granite gives U-Pb zircon concordia age of 67.5 ± 1.3 Ma, which represents the timing of zircon crystallization from the granitic melt and accompanied sillimanite-grade contact metamorphism against surrounding metapelites and gneisses.Metamorphic rocks in the Doi Inthanon area also share the similar plutono-metamorphic history with the Khanom and the Hub-Kapong to Pran Buri areas.
Up to now several studies made on zircons, and not only the usefulness in age determination but also the petrological significance of isotopical characteristics of zircons have been shown great importance by these studies.
Its crust is continually being created, modified, and destroyed.
As a result, rocks that record its earliest history have not been found and probably no longer exist.
Focus on the lithic grains allowed more specific characterization of the provenance, distinguishing between arc, low-grade metamorphic, high-grade metamorphic, ophiolitic, and sedimentary sources (e.g., Dickinson and Suczek, 1979; Ingersoll and Suczek, 1979; Mack et al., 1981, 1983; Hiscott, 1984).
While sandstone petrography continues to provide unique information about provenance, more recently, detrital-zircon geochronology has evolved as the choice for provenance studies.