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Two linear NE–SW trending belts of platformal orthoquartzite-carbonate sequence, namely, the East Jahazpur Belt (EJB) and the West Jahazpur Belt (WJB), within a vast tract of slate–argillite–metagreywacke and subordinate metavolcanics of Hindoli Group (HG) together occur sandwiched between Vindhyan sediments to the east and Banded Gneissic Complex-II (BGC-II) to the west, at the eastern boundary of Aravalli Craton, Rajasthan, India. A NE–SW trending crustal-scale transpressive shear separates this low-grade supracrustal sequence from the gneisses of older Mangalwar Complex (BGC-II) to the west and the Great Boundary Fault (GBF) restricts it in the east against the Vindhyan rocks. A lensoid body of strongly deformed and mylonitised Jahazpur Granite (JG), is the basement for the supracrustal rocks and occupies the core of a SE verging D1-antiformal nappe defined by the EJB (Jahazpur Group-I) rocks. This large scale D1 thrust nappe structure in the EJB is manifested by stacking of early recumbent folds in the carbonate and quartzite units and a prominent zone of brecciation and ferruginisation all along the eastern margin of EJB. In the WJB (Jahazpur Group-II), D1 is represented by large scale isoclinal reclined fold geometry, likely to be influenced by the major transpressive shear and refolding at its western margin. D2 deformation phase, variably superposed over the D1 structures, together controls the NE–SW disposition of Hindoli and Jahazpur rocks. Based on the structural patterns and lithostratigraphic characters, we propose a revised stratigraphy of the Hindoli–Jahazpur rocks. Whole rock Rb–Sr dating of the strongly deformed and mylonitised Jahazpur Granite constrained the age of the tectono-metamorphic event that affected these rocks. Two suites of mylonitised Jahazpur Granite from two different localities yielded ages of 1423 ± 52 and 1393 ± 33 Ma, using Sector 54 TIMS. The tectonism that resulted in folding, thrust nappe, shearing and mylonitisation involving basement JG of Neoarchean age and the overlying Paleoproterozoic Jahazpur–Hindoli supracrustal sequences, therefore, represents a Mesoproterozoic (~1.4 Ga) orogeny that is correlatable with the breaking-up of Columbian Supercontinent along the eastern margin of the Aravalli craton. [ABSTRACT FROM AUTHOR]

Upper Precambrian basement of the Pechora Basin that is located between the Urals and Timan and is a part of the Pechora plate lies beneath 1-7 km of Ordovician-Cenozoic sediment cover. On the base of geophysical data and drilling the basement of the Pechora plate is subdivided into the Timan crustal block and the Bolshezemel crustal block which differ by composition and the character of magmatism. The boundary between the crustal blocks is a system of deep faults called the Pripechora and Ilych-Chikshino faults that strike in a northwestern direction, extending from the Urals to the Pechora Sea. Granitoids of Charkayu complex which were penetrated by several deep boreholes in Pripechora fault zone are interpreted as suprasubduction (island arc and collision) magmas associated with the Timan orogeny. First U-Pb dating (SIMS, using SHRIMP-II and SHRIMP-RG) of zircons from granitoids indicate that granitoid magmatism which accompanied the final stages of the Timanide orogeny occurred in the Late Vendian about 555-544 Ma. The age of zircons from granites of the 1-Charkayu borehole is 544 ± 6 Ma, from granites of 1-East Charkayu borehole is 545 ± 5 Ma, and from granodiorites of 1-South Charkayu borehole is 555 ± 2 Ma. [ABSTRACT FROM AUTHOR]

Granites, especially those that were decompressed as a result of processes of secondary transformations and tectonic movements, hold the greatest potential in the search for oil-bearing rocks in basements of sedimentary basins. Owing to the chemical dating of monazites from collision granites of the East Shebur area, the isochrone age of 274.5 ± 21 Ma was obtained. Zircons (SHRIMP-II) yield a concordant age of 277.5 ± 2 Ma (MSWD = 0.77). The Rb-Sr isochrone age of granites (247.4 ± 9.1 Ma) coincides with the emplacement time of the West Siberian rift system. This age records the process of intruding East Shebur granites into the upper crust level during riftogenesis and the extension of the study area. The younger age datings (231 Ma, 60 Ma (U-Pb); 220 Ma (K-Ar)) record the stages of tectonomagmatic activation, recorded in the basement of the Western Siberia oil-bearing areas. [ABSTRACT FROM AUTHOR]

This work presents the results of U-Pb isotope dating of zircons from granodiorites and plagiogranites of the Tallainskii gabbro-granodiorite-plagiogranite complex of the Karalon-Mamakan zone of the Baikal-Muya belt, ascribed to the Tallainskii pluton. The age datings obtained for granodiorite of the Eleninskii massif (605 ± 6 Ma) and plagiogranite of the Ust-Berezovo massif (609 ± 6 Ma) are in close agreement within the limits of error. Taking into account previously published data, the emplacement of the Tallainskii complex occurred within the age interval of 615-603 Ma in connection with postcollision extension. The 'island arc' geochemical characteristics of granodiorites and plagiogranites can be explained by magmatic differentiation and (or) participation in the formation of a melt source enriched in the suprasubduction component involved in petrogenesis during the preceding Neoproterozoic period. [ABSTRACT FROM AUTHOR]

Using techniques of microprobe analysis and Raman microspectroscopy, a study of the composition, structure, and age of high-uranium zircon from the Sharatash intrusion pegmatite was performed. The presence of a number of zones in crystals having different physicochemical characteristics has been revealed. The Id-e zones affected by a radiation dose of (30-130) × 10 α-dec/g were completely amorphized, and their chemical isochron age was estimated at 311.4 ± 7.1 Ma: this is interpreted as the time of zircon formation in the pegmatite. The age of uraninite coupled with zircon is 317.1 ± 2.3 Ma. These dating results clarify the formation time of the final phase (pegmatite) of the Shartash intrusion and determine the upper age limit of hydrothermal gold mineralization (Berezovsk deposit) associated with the granite massif. [ABSTRACT FROM AUTHOR]

The article discusses the geochronological study of the trachyrhyolites of the Ulkan Group. It states that the volcanic deposits overlie metamorphic rocks of the Early Proterozoic era. It mentions that Riphean deposit sequence is considered as Siberian hypostratotype. It adds that isochronous Rb-Sr method was used to identify the age of the crust located at the base of Lower Riphean Uyan Group. Furthermore, the chemical composition of volcanites correspond to igneous rocks while associated granites and acid volcanites correspond to granites which are A-type.

The article presents a study which discusses uranium (U)-lead (Pb) geochronological dating of Paleozoic era granitoide rock formation of the Kiviliyskii complex in the Bureya Terrane in Russia. It says that porphyroblastic granites and rare quartz diorites from the Kiviliyskii massif were used as samples, in which accessory zircon crystals were selected and were subjected to multiple removal of surface contamination with ethanol, acetone, and nitric acid (HNO3). It says that Krogh's modified procedure was used for the chemical decomposition of zircon and U and Pb separation and isotope analyses were performed with the use of the MAT 261 multicollector mass spectrometer from Finnigan Corp. Results show that the granitoides in the site have an early Paleozoic era age.

Data on the age of gneissic granites from the Precambrian Kharbei Complex (Polar Urals) have been obtained for the first time. Local U-Pb dating was carried out using a SHRIMP-II ion microprobe. Zircons were taken from three granitic bodies close in petrographic and petrochemical parameters. The formation of gneissic granites was implemented in two stages: during the Late Ediacarian (556 ± 2.2 Ma) and in the Late Cambrian (497 ± 3 and 487.1 ± 2.1 Ma). The rocks formed owing to rheomorphic flow of granitic material, caused by tectonic events related to Timanian (Baikalian) tectogenesis and epicontinental riftogenesis, which occurred prior to the appearance of the Paleouralian Ocean. [ABSTRACT FROM AUTHOR]

The article presents a study that investigates the age of granitoids and the ancient basement of the Western Siberian Platform. Data were gathered in an interfluve of the Elogui and Vakh rivers in the east of Western Siberian Plate and granitoids were in the alkaline granites field. Potassium-argon dating (K-Ar) of all rocks showed that Tyn'yarskii rhyolite'granite massif's age was probably Early Permian. Extraction and analysis of zircons from Samples Tyn-101/2590 meters (m) and Tyn-100/2204 m were performed. Results show that dipyramidal and molten resorbed zircon crystals in the samples had an age range of 270-280 mya (Ma). The study concludes that the basement may be ancient granite-metamorphic.

The Huashanguan rapakivi pluton in Zhongxiang, Hubei Province, China, is the first discovered Proterozoic rapakivi pluton in the Yangtze block. Based on field and petrographical observations, a typical rapakivi texture was found in the northern portion of the Huashanguan granitic pluton. Almost all the K-feldspar phenocrysts were round to oval in shape and most had plagioclase coatings known as rapakivi phenocrysts. Alkali feldspars and quartz had two or more generations. Petrochemically, the Huashanguan rapakivi granites were characterized as having high values of Si, K, Fe, Th, U, La, Ga, Ce, Sm and LREE, low values of Ca, Mg, Sr, Nb, Y and HREE, and a negative Eu anomaly. These geochemical characteristics of the Huashanguan granites were concordant with typical rapakivi granites, and had an affinity to A-type granites. LA-ICP-MS U-Pb zircon dating also was conducted. The dating yielded a207Pb/206Pb weighted mean age of 1851±18 Ma (MSWD =1.2), which represents the age of the pluton emplacement. The age of 803±170 Ma at the lower intercept in the concordia diagram corresponds to the age of a later deformation event which affected the pluton, and suggests that the Huashanguan pluton was influenced by Neoproterozoic thermo-tectonic events after its formation. The discovery of Paleoproterozoic Huashanguan rapakivi granites indicates continental rifting or a post-orogenic extensional event that took place in the Paleoproterozoic in the Yangtze block. These events may be related to the breakup of the Paleoproterozoic Columbia supercontinent. [ABSTRACT FROM AUTHOR]

The article presents a study on the age determination of the rare earth element (REE) distribution in Zircon from a granitoid sample from the Southern Prince Charles Mountains in Eastern Antarctica. It states that the presence of Ruker granite in the area indicates a series of felsic orthogneiss, metasedimentary and volcanic events. The researchers used a titanium geothermometer to estimate the crystallization temperature of zircon in the area. It concludes that the Sodruzhestva Series in the area was formed in the post-Archean time because signs of Archean - Paleoproterozoic tectonothermal processes are absent in the samples.

The article offers information on the results of the dating of alkaline granitoids of the Ulug-Tanzek Massif deposit in Tuva, Russia through uranium-lead (U-Pb) method for zircon and Argon-Argon (Ar-Ar) method. A sample from polylithionite-bearing ribeckite granite was studied for Ar-Ar geochronological investigations, in which, results revealed that approximately 85% of Ar that has clearly formed reflected three-step plateau with an age of 296 plus-minus two million years (Ma). In U-Pb dating, a sample of muscovite quartz-albite-microline granite with a netlike texture was used, in which, the determined age of 301 plus-minus three Ma, is similar within the error limits of the age estimation for the first sample using Ar-Ar method.

This paper presents geochemical analyses of a lamprophyre intruding the Caledonian Doushui granite body in Shangyou County, southern Jiangxi Province. U-Pb dating and Hf-isotope analyses are especially carried out for zircons from it. Petrological and geochemical features show that the lamprophyre belongs to a high-K, weakly alkaline pyroxene-biotite lamprophyre. It is characterized by high Mg# (0.74), Ni (253 μg/g) and Cr (893 μg/g) contents, and also enriched in incompatible elements, such as REE, Rb, Sr, Ba and K. It is suggested that its primitive melt probably derived from enriched mantle metasomatized by non-crust-derived agent. Morphology and LAM-ICPMS dating results of zircons in the lamprophyre indicate that they are xenocrysts captured from deep crustal rocks. Most xenocrystic zircons formed at -.1.86 Ga, and a few in different Phanerozoic periods. The Paleoproterozoic zircons are of magmatic origin and have similar 176Hf/177Hf and 176Lu/177Hf ratios, indicating that they probably are from the same igneous basement rock. The ages and Hf-isotope compositions of zircons from this basement rock are similar to those of Paleoproterozoic Danzhu granite in the southern Zhejiang Province, but extremely distinguished from the Nanhing basement, suggesting that the study area probably is a westward extension part of Paleoproterozoic Wuyishan terrane in the eastern Cathaysia Block. These Paleoproterozoic zircons have low Hf-isotope compositions, characteristic of crustal source. Hf model ages of these zircons and the presence of older inherited cores within them, coupled with available other data reported by previous studies, suggest that the source of Paleoproterozoic magma is Neoarchaean crust, implying the existence of older basement in the Wuyishan terrane. U-Pb ages and Hf isotopes of five Phanerozoic zircons indicate that Paleoproterozoic basement underwent multi-reworking occurring in Caledonian, Indosinian and early Yanshanian, respectively. The Caledonian magmatism also involves reworking of juvenile crust. [ABSTRACT FROM AUTHOR]

Monazite dating is an important technique in geochronological studies. However, monazite U-Pb dating by SHRIMP is much less popular than zircon in geochronological applications. This paper compares the results of SHRIMP U-Pb dating of monazites and zircons separated from two granite samples, indicating that monazite SHRIMP U-Pb dating at the Beijing SHRIMP Centre is feasible and provides identical results within error. [ABSTRACT FROM AUTHOR]

Various shaped mafic microgranular enclaves (MMEs) together with several mafic massifs are developed within the Yuegelu granitoid pluton in the eastern part of the Eastern Kunlun. On the basis of detailed field geological surveying and of the results of the petrological and geochemical studies it is suggested that there must be some genetic relationship among the granodiorite host, the MMEs and the hornblende (Hb)-gabbro massifs. Magmatic zircon grains are extracted from samples of granodiorite host rock, Hb-gabbro and the MMEs for U-Pb dating. The U-Pb ages are determined by using SHRIMP II technique, which yields the ages of 242±6 Ma, 239±6 Ma and 241±5 Ma, respectively. The overall correspondence in the U-Pb dating results of them excludes the possibility that the MMEs in the granitoids are solid refractory relics from the source region or that they are xenoliths from the wall rocks. It can also rule out the possibility of a later emplacement of basic magma after the solidification of the granitoids. This dating result indicates that they are the products of magma mixing in early-mid Triassic epoch. Among them the granitoid host is chemically akin to the acidic end member during the magma mixing process, the Hb-gabbro is akin to the basic ones while the MMEs are the incompletely mixed basic magma clots trapped in the acidic magma. Combined with the results from other researches on this pluton it is reasonable to consider that in the mid-Triassic the Eastern Kunlun granitoid belt had undergone a process of magma mixing between the mantle-derived basic magma and the crustal acidic magma which indicates that the injection of mantle materials and energy into the crust and the reactions between them played an important role in the formation of the granitoid rocks. [ABSTRACT FROM AUTHOR]