3 research outputs found
Determination of major elements in igneous rocks using microwave plasma atomic emission spectrometry (MP-AES)
An analytical method for sample preparation of igneous rocks and subsequent determination of Si, Na, K, Ca, Mg, Al, Fe, Mn, Ba, Sr, and Ti by means of microwave induced emission spectrometry (MP-AES) was developed and validated. The proposed sample preparation procedure avoids the use of perchloric acid and provided accurate results even for silicon determination using an acid digestion with hydrofluoric acid. The determination of major elements in rocks is required for the design of classification diagrams that provides relevant information for geochemical analysis
Timing of deformation in the SarandĂ del YĂ Shear Zone, Uruguay: implications for the amalgamation of western Gondwana during the Neoproterozoic Brasiliano-Pan-African Orogeny
U-Pb and Hf zircon (sensitive high-resolution ion microprobe -SHRIMP- and laser ablation-inductively coupled plasma-mass spectrometry -LA-ICP-MS-), Ar/Ar hornblende and muscovite, and Rb-Sr whole rock-muscovite isochron data from the mylonites of the SarandĂ del YĂ Shear Zone, Uruguay, were obtained in order to assess the tectonothermal evolution of this crustal-scale structure. Integration of these results with available kinematic, structural, and microstructural data of the shear zone as well as with geochronological data from the adjacent blocks allowed to constrain the onset of deformation along the shear zone at 630-625 Ma during the collision of the Nico PĂ©rez Terrane and the RĂo de la Plata Craton. The shear zone underwent dextral shearing up to 596 Ma under upper to middle amphibolite facies conditions, which was succeeded by sinistral shearing under lower amphibolite to upper greenschist facies conditions until at least 584 Ma. After emplacement of the Cerro Caperuza granite at 570 Ma, the shear zone underwent only cataclastic deformation between the late Ediacaran and the Cambrian. The SarandĂ del YĂ Shear Zone is thus related to the syncollisional to postcollisional evolution of the amalgamation of the RĂo de la Plata Craton and the Nico PĂ©rez Terrane. Furthermore, the obtained data reveal that strain partitioning and localization with time, magmatism emplacement, and fluid circulation are key processes affecting the isotopic systems in mylonitic belts, revealing the complexity in assessing the age of deformation of long-lived shear zone
Reassessing the polyphase neoproterozoic evolution of the Punta del Este terrane, Dom Feliciano Belt, Uruguay
Some recent models challenge the position and extension of the assumed oceanic basins formed through the break-up of Rodinia, and the tectonic processes involved in the Gondwana assembly, making the investigation of the Early Neoproterozoic record of great relevance. Within the South-American Atlantic margin, the Punta del Este Terrane (PET) of the Dom Feliciano Belt (DFB) comprises a unique Tonian to Ediacaran record, and has a strategic position to reconstruct spatio-temporal relationships with the southern African orogenic belts. Novel zircon UâPb and LuâHf data from the PET basement orthogneisses display Tonian magmatic ages (805â760 Ma) and Hf isotopic signatures indicative of mainly crustal/metasedimentary sources, (Nd TDM ages: 2.2â1.9 Ga, and ΔHf(t): â12 to â4). The basement paragneisses yielded late Paleoproterozoic to Neoproterozoic UâPb ages, but dominantly positive ΔHf(t) values. The presented results confrm the correlation of the PET with the Coastal Terrane of the Kaoko Belt, and discard the idea of the Nico PĂ©rez Terrane as a source. Detrital zircon UâPb
and LuâHf data from the Rocha Formation yielded a main peak at ca. 660 Ma, with the Neoproterozoic grains showing a ΔHf(t) between+1 and+14. The deposition age of the Rocha Formation is constrained by the youngest detrital zircon age peak (660 Ma), and the beginning of the deposition of the Sierra de Aguirre Formation (580 Ma). The data indicate common sources with the Marmora Terrane, and it is thus proposed that the Rocha Formation belongs to the Gariep Belt, and it was juxtaposed during the Ediacaran to the DFB