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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.
The concordia ages of 2497 ± 13Ma, 787 ± 35Ma, 321 ± 10Ma, 217 ± 11Ma of zircons imply that the Tonghua area might geologically be located in the convergent region of the Yangtze Block (YB) and the North China Block (NCB) in the early Mesozoic and the zircons should be caught during magma intrusion.
The existence of the Early Cretaceous basic dyke swarm in the Tonghua area shows that an intensive extensional environment occurred in the Early Cretaceous.
b) from the northern Gascoyne Province (GSWA 169092).
This leucocratic granite (GSWA 169092) yielded two concordant ages 60 million years apart, none of which could be interpreted unequivocally as the crystallisation age.
Minor sericitisation, quartz recrystallisation and biotite replacement by chlorite is evidence of a weak metamorphic overprint.
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.The younger age component is within error of the igneous crystallisation age of c.1620 Ma for a batholith (Discretion Granite) about 250 km to the southeast (Fig. The Thirty-Three Supersuite comprises muscovite (–tourmaline) metamonzogranite, biotite-muscovite (–tourmaline) monzogranite and granodiorite and a belt of muscovite-tourmaline and rare-element bearing pegmatites (Sheppard et al. Crystallisation ages for Thirty-Three Supersuite granites have proven difficult to resolve via U–Pb zircon geochronology due to the presence of copious xenocrystic zircon.It is suggested that the magmatism and lithospheric extension in the Tonghua area should be related to the subduction of the Pacific plate.Although zircon is the most widely used geochronometer to determine the crystallisation ages of granites, it can be unreliable for low-temperature melts because they may not crystallise new zircon.The monazite geochronology has contributed to a more reliable tectonic history for a complex, long-lived orogen.Tags: Adult Dating, affair dating, sex dating