Два эпизода надсубдукционного интрузивного магматизма в пределах Печорской зоны фундамента Печорской синеклизы

On the petrogenesis of Paleoarchean continental crust: U-Pb-Hf isotope and major-trace element constraints from the Bastar Craton, India

U–Pb and Sm–Nd evidence for 1.76–1.77 Ga magmatism in the Moriru region, Mato Grosso, Brazil: implications for province boundaries in the SW Amazon Craton

Xiaopinggou, the northeast area of the Dabancheng, outcrop a set of pillow lava assemblage which has exposed this area completely. In this paper, we have taken this place as an example and explained the geological meaning of the U-Pb age of the single zircon grain which was based on magmatic crystallization and statistical theory. It provided an important clue for the geotectonic setting and geological age of the evolution of the Bogda structural belt. Rocks like Pillow basalt, dacite, and pyroclastic are found in the Xiaopinggou region of the Dabancheng pillow lava assemblage. The weighted average age of 21 single zircon grains in dacite using LA-ICP-MS U-Pb dating data was 326.0±2.8Ma. Only the primary zircon crystallization ages in the magma chamber were represented by these ages. The Pillow lava assemblage in Xiaopingou was not diagenetically older than the early stage of the Late Carboniferous (the end-stage of the Bashkirian), according to the four single-grain zircon ages of the most recent crystallization, which yields a concordant age of 315.4±1.3Ma. This age is consistent with the geological age determined by the fossils in the Liushugou formation.

U–Pb dating of serpentinization: hydrothermal zircon from a metasomatic rodingite shell (Sudetic ophiolite, SW Poland)

Late Permian–Early Triassic igneous activity in the Attic Cycladic Belt (Attica): New geochronological data and geodynamic implications

U–Pb analyses of zircon and titanite were carried out on eight rocks from the Belmont Lake Metavolcanic Complex, a volcano-sedimentary sequence in the Central Metasedimentary Belt of the Grenville Province of southeastern Ontario. The ages of concordant supracrustal rocks within the complex do not accord with stratigraphic position.The youngest volcanic age is [Formula: see text] from a rhyolite near the base of the sequence. The oldest age, [Formula: see text], is from a dacite in the middle. This is overlain by a rhyolite [Formula: see text] in age. A rhyolite at the top of the sequence appears to contain zircon inherited from a source about 1870 Ma old. The complex is therefore interpreted as comprising a lithotectonic sequence composed of structurally interleaved segments of contrasting age. Tectonic emplacement of these segments was most likely along previously unrecognized thrust faults.The supracrustal rocks were subjected to at least two major deformational events as well as a late metamorphism. The earliest event was probably associated with thrusting. The age of the youngest volcanic unit, [Formula: see text], is an upper age estimate for this event. A lower estimate is probably given by the age of the Cordova Gabbro, 1242 ± 3 Ma. The later event, including peak regional metamorphism, should be younger than [Formula: see text], the age of a sheared, recrystallized felsic sill intruded into the supracrustal rocks, and older than [Formula: see text], the age of the undeformed and unmetamorphosed Belmont Granite.Titanite fractions in the Belmont Granite and a volcanic andesite both give an age of 1071 ± 5 Ma. The age from titanite in the Belmont Granite may be due to thermal resetting during slow cooling. Titanite in the andesite is secondary and may have grown as a result of late metamorphic reactions.The youngest age measured, 1039 ± 5 Ma, is from a concordant analysis of a single zircon grain found within the oldest rhyolite. This may be an example of zircon growth from low-temperature, late-metamorphic fluids.

Evolution of the SE-Asian continent from U-Pb and Hf isotopes in single grains of zircon and baddeleyite from large rivers

Find a match with triple-dating: Antarctic sub-ice zircon detritus on the modern shore of Western Australia

The Chelopech deposit is one of the largest European gold deposits and is located 60 km east of Sofia, within the northern part of the Panagyurishte mineral district. It lies within the Banat–Srednegorie metallogenic belt, which extends from Romania through Serbia to Bulgaria. The magmatic rocks define a typical calc-alkaline suite. The magmatic rocks surrounding the Chelopech deposit have been affected by propylitic, quartz–sericite, and advanced argillic alteration, but the igneous textures have been preserved. Alteration processes have resulted in leaching of Na2O, CaO, P2O5, and Sr and enrichment in K2O and Rb. Trace element variation diagrams are typical of subduction-related volcanism, with negative anomalies in high field strength elements (HFSE) and light element, lithophile elements. HFSE and rare earth elements were relatively immobile during the hydrothermal alteration related to ore formation. Based on immobile element classification diagrams, the magmatic rocks are andesitic to dacitic in compositions. Single zircon grains, from three different magmatic rocks spanning the time of the Chelopech magmatism, were dated by high-precision U–Pb geochronology. Zircons of an altered andesitic body, which has been thrust over the deposit, yield a concordant 206Pb/238U age of 92.21 ± 0.21 Ma. This age is interpreted as the crystallization age and the maximum age for magmatism at Chelopech. Zircon analyses of a dacitic dome-like body, which crops out to the north of the Chelopech deposit, give a mean 206Pb/238U age of 91.95 ± 0.28 Ma. Zircons of the andesitic hypabyssal body hosting the high-sulfidation mineralization and overprinted by hydrothermal alteration give a concordant 206Pb/238U age of 91.45 ± 0.15 Ma. This age is interpreted as the intrusion age of the andesite and as the maximum age of the Chelopech epithermal high-sulfidation deposit. 176Hf/177Hf isotope ratios of zircons from the Chelopech magmatic rocks, together with published data on the Chelopech area and the about 92-Ma-old Elatsite porphyry–Cu deposit, suggest two different magma sources in the Chelopech–Elatsite magmatic area. Magmatic rocks associated with the Elatsite porphyry–Cu deposit and the dacitic dome-like body north of Chelopech are characterized by zircons with ɛHfT90 values of ∼5, which suggest an important input of mantle-derived magma. Some zircons display lower ɛHfT90 values, as low as −6, and correlate with increasing 206Pb/238U ages up to about 350 Ma, suggesting assimilation of basement rocks during magmatism. In contrast, zircon grains in andesitic rocks from Chelopech are characterized by homogeneous 176Hf/177Hf isotope ratios with ɛHfT90 values of ∼1 and suggest a homogeneous mixed crust–mantle magma source. We conclude that the Elatsite porphyry–Cu and the Chelopech high-sulfidation epithermal deposits were formed within a very short time span and could be partly contemporaneous. However, they are related to two distinct upper crustal magmatic reservoirs, and they cannot be considered as a genetically paired porphyry–Cu and high-sulfidation epithermal related to a single magmatic–hydrothermal system centered on the same intrusion.

Four Middle-to-Late Miocene barren plutonic complexes that occur between the giant porphyry copper deposits of the central Chilean Andes were selected for U-Pb LA-ICPMS geochronology and Hf-isotope systematics on single zircon grains. Major and trace elements and Sr-Nd-Hf isotope whole rock geochemical studies were undertaken to compare with slightly younger or coeval barren and fertile intrusive rocks between 32° and 34°S. The studied granitoids yield resolvable crystallization ages of 11.3±0.1 Ma (Cerro Mesón Alto massif), 10.3±0.2 Ma (La Gloria pluton), 14.9±0.2 Ma/14.9±0.1 Ma (Yerba Loca stock) and 11.2±0.1 Ma/14.7±0.1 Ma (San Francisco Batholith). Major and trace elements discard an adakitic signature as suggested for coeval porphyric intrusions at 32°S, slightly younger mineralized porphyries at Río Blanco-Los Bronces deposit and other Cenozoic adakites. Volcanic host rocks are less fractionated than the intrusive rock units. The same observation can be made for the unmineralized northern plutons compared to the southern ones. Initial Sr-Nd isotope data show insignificant variation (0.703761-0.704118 and 0.512758- 0.512882), plotting in the mantle array. Trace element enrichment can be explained by addition of subducted-slab fluids and/or terrigenous sediments to the mantle wedge prior to and/or slight crustal input during magma ascent. Zircon grains separated from these barren intrusives share a similar initial εHf-data variation for the younger age group (10-12 Ma; 7.04-9.54) and show a more scattered range for the older one (14-15 Ma; 8.50-15.34); both sets plot between the DM and CHUR evolution lines. There is evidence that magma evolution was slightly distinct through time from older to younger barren magmatism, compared to a few fertile porphyritic rocks from Río Blanco-Los Bronces porphyry copper deposit. It is suggested that chronological inconsistencies within these complexes might be related to differential shortening across the NE-SW-trending Yeso Valley transfer fault, assumed as coeval, which also explains the local lack of easterly magmatic arc front migration.

The calc-alkaline Bergell intrusion is classically mapped as a main tonalite and main granodiorite unit, whose ages have been determined at 32 and 30 Ma, respectively. These units are separated by a mostly thin band interpreted as magmatic “transition zone”. High precision U–Pb dating of zircons and whole rock geochemistry of transition zone rocks are combined with a compilation of available geochemical analyses and ages to characterize the emplacement and magmatic evolution of the Bergell intrusion. Detailed field work shows that the transition zone is heterogeneous, characterized by multiple intrusions of tonalites to granodiorites to quartz-monzonites containing mafic enclaves and leucocratic dykes. Commonly, magmatic flow structures such as compositional banding, schlieren and accumulation of K-feldspar megacrystals are observed. The compositions of the transition zone intrusives as well as of the geochemically fairly heterogeneous tonalite and granodiorite units span a continuous range from 49–76 wt% SiO2 for mafic enclaves to leucocratic dykes. Major and trace element trends are consistent with a predominant fractional crystallization. High precision U–Pb dating of single zircon grains separated from tonalites and granodiorites of the transition zone yields crystallization ages of 31.22 ± 0.04 and 31.13 ± 0.10 Ma, respectively. Hence, the transition zone represents an own phase of intrusion during which a range of magma types were coeval. The available ages and compositional data suggest magmatic activity over the entire range from 28 to 33 Ma across the Bergell intrusion, which should not be described by two main “tonalite” and “granodiorite” stages but by a model with several magmatic main phases during which most magma types developed multiply. Geobarometry of tonalite boulders in the Como molasse (yielding a zircon crystallization age of 32.06 ± 0.13 Ma) indicate average erosion rates for the Bergell intrusion of 1.9 mm/a between 32–25 Ma and of 0.5 mm/a since then.

Research Article| June 01, 2002 U-Pb zircon age of Cape Granite Suite ignimbrites: characteristics of the last phases of the Saldanian magmatism. R. Scheepers; R. Scheepers Department of Geology, University of Stellenbosch, Private BagX1, Matieland, 7602, South Africa, e-mail: rsc@land.sun.ac.za Search for other works by this author on: GSW Google Scholar M. Poujol M. Poujol Economic Geology Research Institute-Hugh Allsopp Laboratory, University of the Witwatersrand, Private Bag 3, WITS, Johannesburg, 2050, South Africa. Search for other works by this author on: GSW Google Scholar Author and Article Information R. Scheepers Department of Geology, University of Stellenbosch, Private BagX1, Matieland, 7602, South Africa, e-mail: rsc@land.sun.ac.za M. Poujol Economic Geology Research Institute-Hugh Allsopp Laboratory, University of the Witwatersrand, Private Bag 3, WITS, Johannesburg, 2050, South Africa. Publisher: Geological Society of South Africa First Online: 07 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2002 Geological Society of South Africa South African Journal of Geology (2002) 105 (2): 163–178. https://doi.org/10.2113/105.2.163 Article history First Online: 07 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R. Scheepers, M. Poujol; U-Pb zircon age of Cape Granite Suite ignimbrites: characteristics of the last phases of the Saldanian magmatism.. South African Journal of Geology 2002;; 105 (2): 163–178. doi: https://doi.org/10.2113/105.2.163 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract The end of the Saldanian magmatic event is marked by a short period of peraluminous silicic magmatism, evident as a series of ignimbrite flows, quartz porphyry and tuffisite intrusions. There is a close relationship between high-level granitic intrusions present as granite porphyries in the Langebaan area and the volcanic event. The subvolcanic-volcanic rocks under discussion ended the fourth and final phase of the Cape Granite Suite magmatism, thus starting and ending with a peraluminous phase. U-Pb ID-TIMS zircon age determinations on the second of three mappable ignimbrite flows yielded an age of 515.5 ± 3.1Ma. Two single zircon grains with 207Pb/ 206Pb ages of ~1875Ma and ~1575 Ma respectively are interpreted to represent xenocrysts extracted from older crust or from sedimentary contaminants. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

U-Pb ages obtained from detrital zircon from terrigenous sediments are used to determine the sources. Present fluvial sand-bars of the Ogooué river yield age spectra of detrital zircons in agreement with Archean and Early Proterozoic sources found in the drainage. The large proportion of Late Proterozoic zircons cannot be derived from primary erosion of the watershed basement rocks, since there is no formation of that age in the area. This later group of zircons is in good agreement with reworking of the aeolian Paleogene Batéké Sands, by regressive erosion in the upper reaches of the Ogooué river, as they contain a majority of Late Proterozoic age zircons. The sources of Late Proterozoic zircons in the Batéké Sand are very distant, and transported and reworked – at least in part – by aeolian processes. Our results, together with the widely distributed Paleogene sediments over continental Africa, suggests that Paleogene was a time of subdued erosion of the cratonic areas and extensive reworking, transport and deposition within continental Africa. In contrast, our results from the Ogooué river indicate active present incision of the cratonic area, erosion of the previous continental sediments, and export of the river bed-load to the continental margin. This temporal evolution of erosion-transport-deposition is correlated with the drastic climate change that occurred during the Cenozoic, leading to a more efficient mechanical erosion, and it correlates with the increase of terrigenous flux to the margin, observed during the Neogene.

The origin and evolution of low-δ18O magma recorded by multi-growth zircons in granite

Zircon from Tomtor syenites and kamaphorites was dated following the U-Pb method (SHRIMP-II), and the distribution of trace and rare-earth elements (REE) was studied at the same zircon point using an ion microprobe. The main zircon population from syenites was dated at 402 ± 7 Ma, while the age range of single zircon grains was 700–660 Mа. Different-aged zircon groups from syenites exhibited the characteristics of magmatic zircon, but their concentrations of REE and other trace elements differed markedly. The REE distribution in 700–660-Mа zircon is consistent with that of the typical zircon from syenites (Belousova et al., 2002), while the heavy rare-earth elements (HREE), P, Ti, and Y concentrations of ca. 400-Ma zircon differ from those of older zircon.This is the first isotope-geochemical study of zircon from kamaphorites, and the U-Pb age of ca. 400 Mа is within the error limits with of the main zircon population from syenites. The considerable enrichment of REE, Cа, Ti, Sr, Y, Nb, and Ba in zircon from kamaphorites may be partly due to the presence of burbankite microinclusions. The trace-element distribution pattern of zircon from kamaphorites is very similar to the geochemical characteristics of zircon from Tiksheozero carbonatites (Tichomirowa et al., 2013).The new age dates for Tomtor syenites and kamaphorites, consistent with 700–660 Mа and ca. 400 Mа events, support the zircon (Vladykin et al., 2014) and pyrochlore (Antonov et al., 2017) age dates determined following the U-Pb method and those of biotite obtained following the 40Ar-39Ar method (Vladykin et al., 2014).