Search results for "Isochron dating"
showing 6 items of 6 documents
Sapphire-bearing magmatic rocks trace the boundary between paleo-continents: A case study of Ilmenogorsky alkaline complex, Uralian collision zone of…
2021
Abstract Metamorphic gem corundum (mainly ruby) deposits are robust indicators of continent-continent collision processes. However, a systematic link of primary magmatic blue sapphire occurrences to orogenic belts is less understood. An example is the Ilmenogorsky alkaline complex, within the Ilmen Mountains region and part of the Uralian orogenic belt. The mobile belt is a product of the collision among Kazakhstania, Laurussia, and Siberia continents prior to the closure of the Paleo-Uralian ocean and formation of the Laurasia supercontinent (330–250 Ma). It is believed that the alkaline complex became inсluded into the separate Sysertsk-Ilmenogorsk microcontinent with unconstrained border…
Young ages from old garnet in the polyphase metamorphic terrane of the Limpopo Belt, South Africa
2020
Abstract The P–T–t path of high-grade metamorphic rocks is significant for understanding vertical motions and heating of the crust. In general, garnet is used to constrain P–T paths and metamorphic zircon is used to obtain t for different metamorphic stages. However, this approach may be complicated by polyphase tectonothermal events. The Central Zone of the Limpopo Belt in South Africa is a complex Precambrian metamorphic terrane that has experienced three distinct high-grade metamorphic events at 3.22 Ga (M1), 2.62 Ga (M2), and 2.02 Ga (M3), based on zircon dating. A previous investigation of a metapelite enclave in the Bulai pluton in the Central Zone showed that metamorphic zircon in th…
Evolution of Pan-African island arc assemblages in the southern Red Sea Hills, Sudan, and in southwestern Arabia as exemplified by geochemistry and g…
1991
Kr6ner, A., Linnebacher, P., Stern, R.J., Reischmann, T., Manton, W. and Hussein, I.M., 1991. Evolution of Pan-African island arc assemblages in the southern Red Sea Hills, Sudan, and in southwestern Arabia as exemplified by geochemistry and geochronology. In: R.J. Stern and W.R. van Schmus (Editors), Proterozoic Crustal Evolution in the Late Proterozoic. Precambrian Res., 53:99-117. We report Rb-Sr whole-rock and zircon ages for metavolcanic and plutonic associations in the southeastern part of the Red Sea Hills, Sudan, and show that these rocks constitute one of the earliest Pan-African arc assemblages within the Arabian-Nubian shield. The remarkable similarity in geochemistry and age bet…
230Th/U-dating of carbonate deposits from ancient aqueducts
2016
Abstract Carbonate deposits in aqueducts, known as calcareous sinter, can reach a considerable thickness and are commonly annually laminated. Environmental and palaeoclimate proxies measured in calcareous sinter samples, such as stable oxygen and carbon isotopes and trace elements, can provide important high-resolution information on hydrological conditions, temperature, and local precipitation in the catchment area of an aqueduct. In order to utilize the proxy data for palaeoclimate reconstruction, the sinter deposits must be dated by annual laminae counting and more precisely by 230 Th/U-dating. The major problem of 230 Th/U-dating of calcareous sinter in aqueducts is the relatively large…
U-Pb zircon and Sm-Nd dating of Moldanubian H P /H T granulites from South ohemia, Czech Republic
1994
Conventional multigrain U-Pb systematics of zircon and single-grain evaporation data of zircons in combination with Nd model ages are presented for pyroxene-free, felsic, garnetiferous granulites and orthopyroxene-bearing granulites of felsic, mafic and intermediate composition from the Blansky Les mountains granulite complex, S Bohemia. Zircons from mafic and intermediate granulites yield Concordia intercept ages between 346 ± 5 and 351 ± 6 Ma as well as a single-grain evaporation age of 346 ± 12 Ma. These ages define the time of Variscan high-grade metamorphism in S Bohemia and are supported by an internal Sm-Nd garnet-zircon-plagioclase-whole rock isochron age of 343 ± 21 Ma. Euhedral zi…
Sequential leaching of silicified Archaean carbonates: A Rb-Sr, Sm-Nd and Pb-Pb isotopic contribution to their tectonic-thermal history (Kaapvaal Cra…
2021
Abstract Sequential leaching was completed by successive interactions of ultra-pure H2O, HAc, HCl and HNO3 with silicified/carbonated Archaean whole rocks from Barberton Greenstone belt of South Africa. The purpose of this experiment was an identification of the minerals interacting with each reagent and, therefore, a detailed succession of isotopically dated tectonic-thermal episodes recorded in these minerals. The contents of the major, trace and rare-earth elemental, together with the Sr, Nd and Pb isotopic compositions of untreated, leachate and residue triplets allowed identification and analysis of various types of carbonates and sulfates mixed with insoluble silicates. The samples yi…