Shrimp dating zircon Kannada dating
For leucocratic granites U–Pb zircon dates, therefore, may reflect the ages of the source rocks rather than the igneous crystallisation age.In the Proterozoic Capricorn Orogen of Western Australia, leucocratic granites are associated with several pulses of intracontinental magmatism spanning ~800 million years.
The zircon crystals are equant to elongate and euhedral pale green to black, 30–250 μm long and 25–80 μm wide, with only a few grains showing subtle internal zoning (Nelson Representative photomicrograph images (cross polarised light) highlighting a weak post-magmatic overprint observed in the leucogranites samples a 139466: medium-grained equigranular biotite–muscovite granodiorite showing minor sericitisation and quartz recrystallization; b 169092: massive, medium-grained biotite–muscovite monzogranite, showing minor sericite, quartz recrystallisation and undulose extinction in the quartz; c 183287: medium- to coarse-grained, equigranular muscovite–tourmaline granodiorite with partly sericitised plagioclase and recrystallised quartz; d 187401: fine to medium-grained equigranular tourmaline–muscovite monzogranite showing recrystallised quartz and minor sericitisation This sample is from a leucocratic granite unit located in the northern Gascoyne Province where it intrudes 1840–18–1680 Ma metasedimentary rocks and is overlain by 1620–1450 Ma siliciclastic rocks (Sheppard et al.
Leucocratic granite samples analysed previously using U–Pb zircon geochronology were re-analysed in this study using U–Th–Pb monazite geochronology.
Presented below are the original zircon geochronology results for selected peraluminous, leucocratic samples from three generations of Proterozoic magmatism (Table a).
Early indications were that the granites belonged to the Paleoproterozoic Durlacher Supersuite (Culver ).
This appeared to be consistent with the fact that the leucocratic granites and pegmatites do not intrude Mesoproterozoic sedimentary rocks of the Bangemall Supergroup within the Ti Tree Shear Zone (Fig.
Search for shrimp dating zircon:
In this paper we use SHRIMP U–Th–Pb monazite geochronology to re-evaluate the emplacement ages of these granites in order to obtain reliable igneous crystallisation ages consistent with the existing geological framework.