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Liu, Chaohui, Guochun Zhao, Fulai Liu, and Jia Cai. "A Palaeoarchean–Mesoarchean micro-continent entrained in the Jiao-Liao-Ji Belt at the southeastern North China Craton: evidence from the zircon record in the Bengbu area." Geological Magazine 156, no. 9 (2019): 1565–86. http://dx.doi.org/10.1017/s0016756818000869.
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AbstractThe Bengbu area in the southeastern North China Craton (NCC) consists predominantly of Archean–Palaeoproterozoic (gneissic) granitoids with minor supracrustal rocks (the Fengyang and Wuhe groups). This study presents new zircon laser ablation – inductively coupled plasma – mass spectrometry U–Pb and Lu–Hf isotopic data and trace-element contents for these granitoids, which improve understanding the Archean–Palaeoproterozoic crustal evolution of the NCC. Magmatic zircon U–Pb data reveal that zircons in the (gneissic) granitoids were generated by multi-stage events at 2.93, 2.73, 2.53–2.52 and 2.18–2.13 Ga. Metamorphic zircon U–Pb data obtained from these rocks show two distinct metamorphic ages of 2.49–2.52 and 1.84 Ga, suggesting that the Bengbu area experienced a regional metamorphic event at the end of the Neoarchean Era and encountered reworking by a tectonothermal event associated with the formation of the Palaeoproterozoic Jiao-Liao-Ji Belt. Trace-element compositions of magmatic zircons reveal the highest Ti concentrations (8.08±3.38 ppm) and growth temperatures (718±44 °C) for the zircons aged 2.13–2.17 Ga and an increase in zircon U/Yb ratios from 2.93 Ga (0.34±0.12) through 2.73 Ga (0.96±0.42) to 2.53 Ga (1.05±0.46), but an evident decrease at 2.17–2.13 Ga (0.61±0.40 ppm). Similar Palaeoarchean xenocrystic and detrital zircons with negativeɛHf(t) values, late Mesoarchean magmatic zircons with juvenile Hf isotopic features, early Neoarchean magmatic zircons with model ages of 2.9–3.0 Ga, and two regional metamorphic events at 2.52–2.48 and 1.88–1.80 Ga in the Bengbu and Jiaobei areas indicate a Palaeoarchean–Mesoarchean micro-continent entrained in the Jiao-Liao-Ji Belt at the southeastern NCC.
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Götze, J., U. Kempe, D. Habermann, L. Nasdala, R. D. Neuser, and D. K. Richter. "High-resolution cathodoluminescence combined with SHRIMP ion probe measurements of detrital zircons." Mineralogical Magazine 63, no. 2 (1999): 179–87. http://dx.doi.org/10.1180/002646199548411.
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AbstractCathodoluminescence (CL) microscopy and spectroscopy combined with SHRIMP ion probe measurements were carried out on detrital zircons from the Cretaceous Weferlingen quartz sand (Germany) to distinguish and characterize different zircon populations.Investigations by CL microscopy, SEM-CL and BSE imaging show that there are three main types of zircons (general grain sizes of 100–200 µm): (1) apparently weakly zoned, rounded grains with relict cores, (2) well rounded fragments of optically more or less homogeneous zircon grains showing CL zoning predominantly parallel to the z-axis, and (3) idiomorphic to slightly rounded zircon grains typically showing oscillatory euhedral CL zoning. A fourth type of low abundance is characterized by well-rounded grain fragments with an irregular internal structure showing bright yellow CL.High-resolution CL spectroscopic analyses reveal that blue CL is mainly caused by an intrinsic emission band centered near 430 nm. Dy3+ is the dominant activator element in all zircons, whereas Sm3+, Tb3+, Nd3+ have minor importance. Yellow CL (emission band between 500 and 700 nm) is probably caused by electron defects localized on the [SiO4] groups (e.g. related to oxygen vacancies) or activation by Yb2+ generated by radiation. Variations of the integral SEM-CL intensity are mainly controlled by the intensity of the broad bands and the Dy3+ peaks.SHRIMP analysis provides in situ high-resolution U-Pb dating of single zircon grains and confirms different ages for the evaluated different zircon types. The measurements show that the U-Pb ages of the zircons from Weferlingen scatter over a wide range (340 to 1750 Ma), backing up earlier conclusions that the quartz sand from Weferlingen is quite heterogeneous in terms of provenance.
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Watson, E. Bruce. "Dissolution, growth and survival of zircons during crustal fusion: kinetic principals, geological models and implications for isotopic inheritance." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 87, no. 1-2 (1996): 43–56. http://dx.doi.org/10.1017/s0263593300006465.
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ABSTRACT:Finite difference numerical simulations were used to characterise the rates of diffusion-controlled dissolution and growth of zircon in melts of granitic composition under geologically realistic conditions. The simulations incorporated known solubility and Zr diffusivity relationships for melts containing 3 wt% dissolved H2O and were carried out in both one and thre dimensions under conditions of constant temperature, linearly time-dependent temperature and for a variety of host system thermal histories. The rate of zircon dissolution at constant temperature depends systematically on time (t½−12;), temperature (exp T−1) and degree of undersaturation of the melt with respect to zircon (in ppm Zr). Linear dissolution and growth rates fall in the range 10−19 10−15 cm s−1 at temperatures of 650-850°C. Radial rates are strongly dependent on crystal size (varying in inverse proportion to the radius, r): for r>30 μm, dissolution and growth rates fall between 10−17 and 10−13 cm s−1. During crustal magmatism, the chances of survival for relict cores of protolith zircons depend on several factors, the most important of which are: the initial radius of the zircon; the intensity and duration of the magmatic event; and the volume of the local melt reservoir with which the zircon interacts. In general, only the largest protolith zircons (>120 μm radius) are likely to survive magmatic events exceeding 850°C. Conversely, only the smallest zircons (<50 μm radius) are likely to be completely consumed during low-temperature anatexis (i.e. not exceeding ≍700°C).The effects of stirring the zircon-melt system are unimportant to dissolution and growth behaviour; except under circumstances of extreme shearing (e.g. filter pressing?), zircon dissolution is controlled by diffusion of Zr in the melt.
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Breemen, O. van, and L. Corriveau. "UPb age constraints on arenaceous and volcanic rocks of the Wakeham Group, eastern Grenville Province." Canadian Journal of Earth Sciences 42, no. 10 (2005): 1677–97. http://dx.doi.org/10.1139/e05-079.
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Combined sensitive high-resolution ion microprobe (SHRIMP) and thermal ionization mass spectrometry (TIMS) UPb zircon data from a tightly constrained stratigraphic context of the Wakeham Group provide a precise depositional age for sedimentation within this extensive basin of the Grenville Province. Metavolcanic rocks at the eastern exposure of the Wakeham Group yield ages of 1511 ± 13, 1506 ± 11, 1502 ± 9, and 1491 ± 7 Ma. A crosscutting 1493 ± 10 Ma porphyry vein marks the end of volcanism. The older two volcanic rocks rest stratigraphically above metasediments, with a 1517 ± 20 Ma maximum age of sedimentation derived from the youngest detrital zircons of an arenite. Five 1.611.55 Ga inherited zircons in the volcanics, reinforced by coeval inheritance in nearby plutons, indicate a Labradorian basement source to the supracrustals. The predominant arenite detrital zircons dates are in the 1.951.75 Ga range, however, and feature both trace element and morphological evidence for metamorphism in the source terrane. Together with zircons as old as 2.95 Ga, the detrital age spectrum is consistent with a circum-Superior provenance. The ages obtained imply that Wakeham Group volcanism and sedimentation were, at least in part, coeval with the onset of 1.521.46 Ga Pinwarian plutonism along the southeastern margin of Laurentia. UPb zircon analyses record a late Grenvillian metamorphic event around 1019 Ma. UPb monazite analyses from one sample yield 10101000 Ma ages, and the end of Grenvillian metamorphism is marked by 990 Ma UPb titanite ages.
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Montero, P., F. Bea, F. González-Lodeiro, C. Talavera, and M. J. Whitehouse. "Zircon ages of the metavolcanic rocks and metagranites of the Ollo de Sapo Domain in central Spain: implications for the Neoproterozoic to Early Palaeozoic evolution of Iberia." Geological Magazine 144, no. 6 (2007): 963–76. http://dx.doi.org/10.1017/s0016756807003858.
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AbstractDating the pre-Middle Ordovician metavolcanic rocks and metagranites of the Ollo de Sapo Domain has, historically, been difficult because of the small compositional variation, the effects of the Variscan orogeny and, as revealed in this paper, the unusually high fraction of inherited zircon components. The first reliable zircon data (U–Pb ion microprobe and Pb–Pb stepwise evaporation) indicate that the Ollo de Sapo volcanism spanned 495±5 Ma to 483±3 Ma, and was followed by the intrusion of high-level granites from 483±3 Ma to 474±4 Ma. In both metavolcanic rocks and metagranites, no less than 70–80% of zircon grains are either totally Precambrian or contain a Precambrian core overgrown by a Cambro-Ordovician rim. About 80–90% of inherited zircons are Early Ediacaran (602–614 Ma) and derived from calc-alkaline intermediate to felsic igneous rocks generated at the end of the Pan-African arc–continent collision. In the Villadepera region, located to the west, both the metagranites and metavolcanic rocks also contain Meso-Archaean zircons (3.0–3.2 Ga) which ultimately originated from the West African Craton. In the Hiendelaencina region, located to the east, both the metagranites and metavolcanic rocks lack Meso-Archaean zircons, but they have two different inherited zircon populations, one Cryogenian (650–700 Ma) and the other Tonian (850–900 Ma), which suggest older-than-Ediacaran additional island-arc components. The different proportion of source components and the marked variation of the 87Sr/86Srinit. suggest, at least tentatively, that the across-arc polarity of the remnants of the Pan-African arc of Iberia trended east–west (with respect to the current coordinates) during Cambro-Ordovician times, and that the passive margin was situated to the west.
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Bussy, F., T. E. Krogh, W. P. Klemens, and W. M. Schwerdtner. "Tectonic and metamorphic events in the westernmost Grenville Province, central Ontario: new results from high-precision U–Pb zircon geochronology." Canadian Journal of Earth Sciences 32, no. 5 (1995): 660–71. http://dx.doi.org/10.1139/e95-055.
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The U–Pb isotopic ages of metamorphic zircons from deformed amphibolitized metadiabase dykes and associated unstrained anatectic pegmatites have been determined to constrain the times of postdyke ductile flow related recrystallization and deformation. Samples from the Central Gneiss Belt of the Grenville Province in the southern Georgian Bay region provide a means of linking areas formed during common episodes of ductile flow. Three zircon fractions from one attenuated dyke in the Moon River domain gave identical concordant ages of 1062, 1065, and 1064 ± 2 Ma, while those from another gave identical concordant ages of 1052, 1051, and 1050 ± 2 Ma for the time of metamorphism. Zircons from a folded dyke from the Go Home domain gave identical concordant ages of 1049, 1047, and 1046 ± 2 Ma, while a single overgrowth fragment from an unstrained anatectic pegmatite in the fold hinge gave a concordant age of 1047 ± 2 Ma, as if folding, metamorphic zircon growth and postfolding pegmatite are part of the same process. An anatectic pegmatite in a metadiabase boudin neck in the Ahmic domain gave two zircon fractions with identical concordant ages of 1079 and 1080 ± 2 Ma that match the concordant 1078 ± 2 Ma age of a single overgrowth type grain from the host migmatite. Zircons from the metadiabase have similar but less precise ages due to a low level of uranium and a low abundance. U–Pb results for the Love Lake granite situated at the Parry Sound–Ahmic domain boundary are equivocal but may imply folding of this structure after 1068 Ma, the age of contained titanite. Either the upper or lower end of the ca. 1050–1372 Ma zircon discordia may correspond to granite emplacement. Zircons from a dyke that postdates a granulite-grade migmatization in the Parry Sound domain record a metamorphism at 1114 ± 2 Ma but older inherited grains are present in other fractions. Ductile flow in the Go Home and Moon River domains occurred in the interval 1047–1064 Ma during which the latter was probably emplaced, whereas earlier (1080 Ma) ductile flow in the Ahmic domain may relate to the time of overthrusting of the Parry Sound domain. Parry Sound domain dyke metamorphic ages imply a lack of post 1114 Ma migmatization, and a predyke migmatization consistent with a more exotic derivation of this domain. A [Formula: see text] Ma age for a postmigmatite crosscutting pegmatite dyke sets an upper limit on the age of a late buckling event in the Ahmic domain.
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BERRA, FABRIZIO, MASSIMO TIEPOLO, VALERIA CAIRONI, and GIAN BARTOLOMEO SILETTO. "U–Pb zircon geochronology of volcanic deposits from the Permian basin of the Orobic Alps (Southern Alps, Lombardy): chronostratigraphic and geological implications." Geological Magazine 152, no. 3 (2014): 429–43. http://dx.doi.org/10.1017/s0016756814000405.
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AbstractU–Pb zircon ages from volcanic rocks of Early Permian age (Southern Alps, Lombardy), associated with fault-controlled transtensional continental basins, were determined with the laser ablation (LA)-ICP-MS technique. Four samples were collected at the base and at the top of the up to 1000 m thick volcaniclastic unit of the Cabianca Volcanite. This unit pre-dates the development of a sedimentary succession that still contains, at different stratigraphic levels, volcanic intercalations. Age results from a tuff in the basal part of the unit constrain the onset of the volcanic activity to 280 ± 2.5 Ma. Ignimbritic samples from the upper part of the unit show a large scatter in the age distribution. This is interpreted as the occurrence of antecrystic and autocrystic zircons. The youngest autocrystic zircons (c. 270 Ma) are thus interpreted as better constraining the eruption age, constraining the duration of the volcanic activity in the Orobic Basin to about 10 Ma. The new geochronological results compared with those of other Early Permian basins of the Southern Alps reveal important differences that may reflect (1) a real time-transgressive beginning and end of the volcanic activity or (2) the complex mixing of antecrystic and autocrystic zircon populations in the analysed samples.
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Zhang, Shao-Hua, Wei-Qiang Ji, Hao Zhang, et al. "Identification of Forearc Sediments in the Milin-Zedong Region and Their Constraints on Tectonomagmatic Evolution of the Gangdese Arc, Southern Tibet." Lithosphere 2020, no. 1 (2020): 1–20. http://dx.doi.org/10.2113/2020/8835259.
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Abstract The Xigaze forearc sediments revealed the part of the tectonomagmatic history of the Gangdese arc that the bedrocks did not record. However, the sediments’ development is restricted to the region around and west of Xigaze City. Whether the eastern segment of the arc had a corresponding forearc basin is yet to be resolved. In this study, a field-based stratigraphic study, detrital zircon U-Pb geochronology (15 samples), and Hf isotopic analyses (11 of the 15 samples) were carried out on four sections in the Milin-Zedong area, southeast Tibet. The analytical results revealed the existence of three distinct provenances. The lower sequence is characterized by fine-grained sandstone, interbedded mudstone, and some metamorphic rocks (e.g., gneiss and schist). The detrital zircon U-Pb age distribution of this sequence is analogous to those of the Carboniferous-Permian strata and metasediments of the Nyingtri group in the Lhasa terrane. The middle and upper sequences are predominantly composed of medium- to coarse-grained volcaniclastic/quartzose sandstones, which are generally interbedded with mudstone. The detrital zircon U-Pb ages and Hf isotope signatures indicate that the middle sequences are Jurassic to Early Cretaceous in age (~200–100 Ma) and show clear affinity with the Gangdese arc rocks, that is, positive εHft values. In contrast, the upper sequences are characterized by Mesozoic detrital zircons (150–100 Ma) and negative εHft values, indicative of derivation from the central Lhasa terrane. The overall compositions of the detrital zircon U-Pb ages and Hf isotopes of the middle to upper sequences resemble those of the Xigaze forearc sediments, implying that related forearc sediments may have been developed in the eastern part of the Gangdese arc. It is possible that the forearc equivalents were eroded or destroyed during the later orogenesis. Additionally, the detrital zircons from these forearc sediments indicate that this segment of the Gangdese arc experienced more active and continuous magmatism from the Early Jurassic to Early Cretaceous than its bedrock records indicate.
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BRÖCKER, MICHAEL, REINER KLEMD, ELLEN KOOIJMAN, JASPER BERNDT, and ALEXANDER LARIONOV. "Zircon geochronology and trace element characteristics of eclogites and granulites from the Orlica-Śnieżnik complex, Bohemian Massif." Geological Magazine 147, no. 3 (2009): 339–62. http://dx.doi.org/10.1017/s0016756809990665.
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AbstractU–Pb zircon geochronology and trace element analysis was applied to eclogites and (ultra)high-pressure granulites that occur as volumetrically subordinate rock bodies within orthogneisses of the Orlica-Śnieżnik complex, Bohemian Massif. Under favourable circumstances such data may help to unravel protolith ages and yet-undetermined aspects of the metamorphic evolution, for example, the time span over which eclogite-facies conditions were attained. By means of ion-probe and laser ablation techniques, a comprehensive database was compiled for samples collected from prominent eclogite and granulite occurrences. The 206Pb/238U dates for zircons of all samples show a large variability, and no single age can be calculated. The protolith ages remain unresolved due to the lack of coherent age groups at the upper end of the zircon age spectra. The spread in apparent ages is interpreted to be mainly caused by variable and possibly multi-stage Pb-loss. Further complexities are added by metamorphic zircon growth and re-equilibration processes, the unknown relevance of inherited components and possible mixing of different aged domains during analysis. A reliable interpretation of igneous crystallization ages is not yet possible. Previous studies and the new data document the importance of a Carboniferous metamorphic event at c. 340 Ma. The geological significance of this age group is controversial. Such ages have previously either been related to peak (U)HP conditions, the waning stages of eclogite-facies metamorphism or the amphibolite-facies overprint. This study provides new arguments for this discussion because, in both rock types, metamorphic zircon is characterized by very low total REE abundances, flat HREE patterns and the absence of an Eu anomaly. These features strongly suggest contemporaneous crystallization of zircon and garnet and strengthen interpretations proposing that the Carboniferous ages document late-stage eclogite-facies metamorphism, and not amphibolite-facies overprinting.
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Zhang, Xiaoran, Chia-Yu Tien, Sun-Lin Chung, et al. "A Late Miocene magmatic flare-up in West Sulawesi triggered by Banda slab rollback." GSA Bulletin 132, no. 11-12 (2020): 2517–28. http://dx.doi.org/10.1130/b35534.1.
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Abstract Cenozoic magmatism occurs throughout West Sulawesi, Indonesia, yet its detailed evolution remains enigmatic due mainly to the scarcity of precise dating. Here, we report new whole-rock geochemical and zircon U-Pb-Hf isotopic data of plutonic/volcanic rocks and river sediments from West Sulawesi to constrain the petrogenesis and magmatic tempo. The magmatic rocks are intermediate to felsic (SiO2 = 58.1–68.0 wt%), high-K calc-alkaline to shoshonitic (K2O = 2.2–6.0 wt%), metaluminous to weakly peraluminous, and I-type in composition. Trace element concentrations and ratios (e.g., Nb/U = 1.7–4.3 and Ti/Zr &lt; 28), along with negative zircon εHf(t) values (–17.0 to –0.4) and old crustal model ages (TDMC = 2.1–1.1 Ga), indicate a dominant magma source region from the underlying continental crystalline basement. U-Pb dating on zircons from ten magmatic rocks yielded weighted mean 206Pb/238U ages of 7.2–6.1 Ma, best representing the crystallization ages of host magmas, further consistent with the prominent age peaks (7.3–6.3 Ma) defined by detrital zircons from four sedimentary samples. Our new data, combined with available results, allow the identification of a noticeable climax of magmatism (flare-up) at ca. 7–6 Ma, forming a continuous magmatic belt throughout West Sulawesi. Given the absence of contemporaneous subduction and the coincidence of incipient opening of the South Banda Basin during ca. 7.15–6.5 Ma, the Late Miocene magmatic flare-up in West Sulawesi and coeval regional extension in eastern Indonesia are attributed to a resumed episode of Banda slab rollback.
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Hodych, Joseph P., and Richard A. Cox. "Ediacaran U–Pb zircon dates for the Lac Matapédia and Mt. St.-Anselme basalts of the Quebec Appalachians: support for a long-lived mantle plume during the rifting phase of Iapetus opening." Canadian Journal of Earth Sciences 44, no. 4 (2007): 565–81. http://dx.doi.org/10.1139/e06-112.
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It has been suggested that the rifting phase of Iapetus Ocean opening in Quebec involved a long-lived mantle plume centered near the Sutton Mountains whose dominant magmatism was first of continental flood basalt composition and later of ocean-island basalt (OIB) composition. We dated the Lac Matapédia and Mt. St.-Anselme basalts, which are thought to have originated from this plume and have dominant OIB-like composition. The U–Pb dating was done on individual zircon crystals using a laser ablation microprobe linked to an inductively coupled plasma – mass spectrometer. Zircons from two basalt flows at Lac Matapédia yielded ages of 565 ± 6 and 556 ± 5 Ma. Zircons from a basalt flow at Mt. St.-Anselme yielded an age of 550 ± 7 Ma. Although the basalts are allochthonous, these should be their ages of extrusion onto Laurentia, as shown by Grenvillian ages yielded by inherited zircons in both Lac Matapédia flows and by zircons in a granitic pebble from the Mt. St.-Anselme Formation. Our dating supports the hypothesis of a long-lived (~615 to ~550 Ma) Sutton Mountains mantle plume involved in Iapetus rifting. It does so by closing a possible gap of ~10 Ma between the end of flood basalt and the beginning of OIB magmatism, and by supporting ~540 (rather than ~570) Ma for the rift-to-drift transition in Quebec. Because plumes move slowly, this hypothesis implies that Laurentia moved slowly from ~615 to ~550 Ma. This is consistent with paleomagnetic evidence, although very rapid true polar wander at ~590 Ma may need to be invoked.
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Jourdan, Sébastien, Matthias Bernet, Elizabeth Hardwick, et al. "Geo-thermochronology of the Saint Antonin basin, south-eastern France." BSGF - Earth Sciences Bulletin 189, no. 3 (2018): 12. http://dx.doi.org/10.1051/bsgf/2018013.
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The clastic sedimentary formations of the Saint Antonin basin in the French Maritime Alps contain the record of the Early Oligocene erosional history of the Maures-Esterel massif, Sardinia and Corsica. Detrital apatite fission-track dating and zircon fission-track/U-Pb double dating of samples collected from the Saint Antonin basin confirm sediment provenance and allow obtaining first-order estimates of drainage basin maximum and long-term average exhumation rates. Whereas average exhumation rates were on the order of 0.1–0.2 km/Myr during the Early Oligocene, small parts of the Saint Antonin basin source areas may have experienced maximum exhumation rates on the order of 0.4–0.7 km/Myr. Although zircons and apatites with Early Oligocene fission-track cooling ages make up between 11–15% of the dated grains, a possible volcanic contribution is negligible, as only one single volcanic zircon grain was identified by fission-track/U-Pb double dating. Regional geodynamic processes with convergence in the Western Alps to the east and the end of the Pyreneo-Provençal compression phase by the early Oligocene controlled the differences in basin fill history and sediment provenance between the Saint Antonin basin and the largely contemporaneous Barrême basin in south-eastern France.
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AWDANKIEWICZ, MAREK, RYSZARD KRYZA, and NORBERT SZCZEPARA. "Timing of post-collisional volcanism in the eastern part of the Variscan Belt: constraints from SHRIMP zircon dating of Permian rhyolites in the North-Sudetic Basin (SW Poland)." Geological Magazine 151, no. 4 (2013): 611–28. http://dx.doi.org/10.1017/s0016756813000678.
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AbstractThe final stages of the Variscan orogeny in Central Europe were associated with voluminous granitic plutonism and widespread volcanism. Four samples representative of the main rhyolitic volcanic units from the Stephanian–Permian continental succession of the North-Sudetic Basin, in the eastern part of the Variscan Belt, were dated using the SIMS (SHRIMP) zircon method. Three samples show overlapping206Pb–238U mean ages of 294 ± 3, 293 ± 2 and 292 ± 2 Ma, and constrain the age of the rhyolitic volcanism in the North-Sudetic Basin at 294–292 Ma. This age corresponds to the Early Permian – Sakmarian Stage and is consistent with the stratigraphic position of the lava units. The fourth sample dated at 288 ± 4 Ma reflects a minor, younger stage of (sub)volcanic activity in the Artinskian. The silicic activity was shortly followed by mafic volcanism. The rhyolite samples contained very few inherited zircons, possibly owing to limited contribution of crustal sources to the silicic magma, or owing to processes involved in anatectic melting and magma differentiation (e.g. resorption of old zircon by Zr-undersaturated melts). The SHRIMP results and the stratigraphic evidence suggest that the bimodal volcanism terminated the early, short-lived (10–15 Ma) and vigorous stage of basin evolution. The Permian volcanism in the North-Sudetic Basin may be correlated with relatively late phases of the regional climax of Late Palaeozoic volcanism in Central Europe, constrained by 41 published SHRIMP zircon age determinations at 299–291 Ma. The Permian volcanism and coeval plutonism in the NE part of the Bohemian Massif can be linked to late Variscan, post-collisional extension.
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Waight, Tod E., Simon H. Serre, Sebastian H. Næsby, and Tonny B. Thomsen. "The ongoing search for the oldest rock on the Danish island of Bornholm: new U-Pb zircon ages for a quartzrich xenolith and country rock from the Svaneke Granite." Bulletin of the Geological Society of Denmark 65 (August 31, 2017): 75–86. http://dx.doi.org/10.37570/bgsd-2017-65-06.
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Previous geochronological studies on the Danish island of Bornholm have not identified any rocks older than c. 1.46 Ga. New LA-ICP-MS U-Pb zircon ages are presented for a xenolith within, and the country rock gneiss adjacent to, the Svaneke Granite on Bornholm. The xenolith is fine-grained and quartz-rich and was likely derived from either a quartz-rich sedimentary protolith or a hydrothermally altered felsic volcanic rock. The relatively fine-grained felsic nature of the country rock gneiss and the presence of large zoned feldspars that may represent phenocrysts suggest its protolith may have been a felsic volcanic or shallow intrusive rock. A skarn-like inclusion from a nearby locality likely represents an originally carbonate sediment and is consistent with supracrustal rocks being present at least locally. Zircon data from the xenolith define an upper intercept age of 1483 ± 12 Ma (2σ, MSWD = 2.5) with a poorly defined lower intercept age of 474 ± 250 Ma, and a weighted average 207Pb/206Pb age of 1477.9 ± 4.6 Ma; both these ages are older than the host Svaneke Granite (weighted average 207Pb/206Pb age of 1465.0 ± 4.8 Ma). Zircons from the gneiss define an upper intercept age of 1477.7 ± 6.8 Ma when anchored at 0 Ma, and a weighted average 207Pb/206Pb age of 1475.4 ± 6.6 Ma which overlaps statistically with the Svaneke Granite age. These ages are currently the oldest ages determined for in situ rocks on Bornholm. Evidence for substantially older basement lithologies (e.g. 1.8 Ga as observed in southern Sweden) remains absent. The zircons display clear oscillatory zoning, have Th/U typical of magmatic zircons and in some cases preserve inherited cores, all of which suggest that the ages are robust and do not represent resetting due to incorporation within or intrusion by the Svaneke Granite. Inherited zircons are not common; they have ages (c. 1.6–1.8 Ga) that are similar to those observed in other felsic basement lithologies on Bornholm. These new results suggest that prior to intrusion of the Svaneke Granite, the upper crust on Bornholm was dominated, at least locally, by lithologies similar in composition to the currently exposed felsic basement. The protoliths to the two samples investigated here must have been buried to mid-crustal depths over a relatively short time period (c. 10 Ma) prior to intrusion of the Svaneke Granite. This suggests a dynamic tectonic environment and is consistent with evidence for broadly simultaneous magmatism and deformation in basement rocks at 1.46 Ga in southern Scandinavia and burial and metamorphism of sediments in southern Skåne.
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Mortensen, J. K., J. R. Montgomery, and J. Fillipone. "U–Pb zircon, monazite, and sphene ages for granitic orthogneiss of the Barkerville terrane, east-central British Columbia." Canadian Journal of Earth Sciences 24, no. 6 (1987): 1261–66. http://dx.doi.org/10.1139/e87-120.
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Granitic orthogneiss forms an important component of the Barkerville terrane of southeastern British Columbia. Rb–Sr whole-rock ages for the orthogneisses are ambiguous and range from Late Proterozoic to mid-Paleozoic, with large associated errors. U–Pb dating of zircon, monazite, and sphene has been employed in an attempt to establish precise crystallization ages for two of the orthogneiss bodies. U–Pb systematics for zircons from both bodies show the combined effects of inheritance of zircon cores and postcrystallization Pb loss. This complexity precludes a precise estimate of the age of emplacement of the granitic protoliths of the gneiss. The data do, however, constrain possible emplacement ages for the bodies to between 335 and 375 Ma (Late Devonian – mid-Mississippian).A U–Pb age of 174 ± 4 Ma for metamorphic sphene from one of the orthogneiss bodies is interpreted as dating the end of the second phase of deformation in the area. Two nearly concordant U–Pb ages of 114 and 117 Ma for monazite from the second body remain problematical. These data suggest either that the monazite grew during a relatively young shearing and (or) metamorphic event that locally affected the Barkerville terrane or that the closure temperatue for the U–Pb system in monazite is lower than had previously been inferred, or both.
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Scott, J. M. J., T. D. Peterson, W. J. Davis, C. W. Jefferson, and B. L. Cousens. "Petrology and geochronology of Paleoproterozoic intrusive rocks, Kiggavik uranium camp, Nunavut." Canadian Journal of Earth Sciences 52, no. 7 (2015): 495–518. http://dx.doi.org/10.1139/cjes-2014-0153.
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We investigated the age and petrology of Paleoproterozoic granitic intrusions in the area of the Kiggavik uranium exploration camp, near the southeast margin of the Aberdeen subbasin of the Thelon Basin. A subset of these intrusions (e.g., the Lone Gull stock) is spatially associated with and mineralized by basement hosted, unconformity-related uranium deposits. Surface (outcrop) samples have field relations, textures, and compositions consistent with Hudson Suite granitoids and mixtures of monzogranite with minette. We obtained U–Pb (zircon) ages ranging from ca. 1818 to 1840 Ma, within the known range of the Hudson Suite and cogenetic minettes of the Baker Lake Group (1.80–1.84 Ga). Core samples of granitic rocks adjacent to mineralized zones are more complex and indicate an influence from the younger Nueltin Granite (Kivalliq Igneous Suite, ca. 1.77–1.73 Ga). One sample from the Lone Gull stock contains two zircon populations in texturally distinctive domains, one at 1806 ± 41 Ma and the other at 1748 ± 9.4 Ma. A porphyritic hypabyssal syenite below the Bong deposit yielded a U–Pb zircon age of 1837.8 ± 7.7 Ma and a U–Pb titanite age of 1758.5 ± 44 Ma. We recognize a Kivalliq-age overprint in the form of metasomatism and partial remelting or melt infiltration in the drill core samples, which is not evident at the surface and is consistent with the presence of a Nueltin Granite intrusive complex at depth. The geochemistry and primary igneous textures of the Bong syenite, including its euhedral zircons, resemble those of lava flows near the base of the Baker Lake Group, and we recognize a mixed magma (i.e., Martell Syenite) continuum between intrusive Hudson granitoids and minette with extrusive equivalents in the lower felsic minette member of the Christopher Island Formation.
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Wakita, Koji, Takanori Nakagawa, Masahiro Sakata, Natsuki Tanaka, and Nozomu Oyama. "Phanerozoic accretionary history of Japan and the western Pacific margin." Geological Magazine 158, no. 1 (2018): 13–29. http://dx.doi.org/10.1017/s0016756818000742.
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AbstractIt is generally accepted that oceanic plate subduction has occurred along the eastern margin of Asia since about 500 Ma ago. Therefore, the Japanese Islands have a >500 Ma history of oceanic plate subduction in their geological records. In this paper, the accretionary history of the Japanese Islands is divided into six main stages based on the mode and nature of tectonic events and the temporal gaps in the development of accretionary processes. In the first stage, oceanic plate subduction and accretion started along the margin of Gondwana. After detachment of the North and South China blocks in Devonian time, accretionary complexes developed along island arcs offshore of the South and North China blocks. After the formation of back arc basins such as the Japan Sea, accretionary processes occurred only along the limited convergent margin, e.g. Nankai Trough. Detrital zircons of sandstones revealed the accretionary history of Japan. An evaluation of a comprehensive dataset on detrital zircon populations shows that the observed temporal gaps in the development of the Japanese accretionary complexes were closely related to the intensity of igneous activity in their provenance regions. Age distributions of detrital zircons in the accretionary complexes of Japan change before and after the Middle Triassic period, when the collision of the South and North China blocks occurred.
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Emon, K. A., V. A. Jackson, and G. R. Dunning. "Geology and U-Pb geochronology of rocks of the Eokuk Uplift: a pre-2.8 Ga basement inlier in the northwestern Slave Province, Nunavut, Canada." Canadian Journal of Earth Sciences 36, no. 7 (1999): 1061–82. http://dx.doi.org/10.1139/e98-094.
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Rocks of the Eokuk Uplift have been mapped in detail along the coast of Coronation Gulf and 10 key units have been dated by U-Pb analysis of zircon, monazite, and titanite. The combined data indicate that this inlier of the Slave Province has a >3.2 Ga crustal component, evidence of a granulite-grade orogenic event predating 2.8 Ga and a lack of evidence for any significant orogenic activity corresponding to the 2.7-2.6 Ga events common in the rest of the Slave Province. The oldest rocks in the study area are a succession of granitoid and supracrustal gneisses that have been metamorphosed to amphibolite to granulite facies. From field relationships, the oldest rock is a granodiorite to tonalite orthogneiss, with a zircon crystallization age of 3254+13-6 Ma. A granite gneiss, which may be a small felsic intrusion or an anatectic melt of the tonalite gneiss, yields a zircon age of 3216+14-13 Ma. A K-feldspar megacrystic monzogranite gneiss contains old, discordant, possibly inherited zircons with 207Pb/206Pb ages ranging from 3103 to 3039 Ma, together with coexisting 2879 ± 3 Ma zircon and monazite. These high-grade gneisses are intruded by two megacrystic granite plutons, dated at 2887 ± 2 and 2881+4-3 Ma. The absence of extensive recrystallization and complex structures in these plutons indicates that this igneous event postdated the high-grade metamorphism. An amphibolite-grade synplutonic metamorphic event is dated at ~2880 Ma by new monazite in the older gneiss units. A series of variably deformed mafic to felsic dykes and pegmatites intrude both the granites and gneisses and constrain the end of penetrative deformation in the area. Of these, a boudinaged diorite dyke, with a strong internal foliation parallel to the regional fabric, is dated at 2877 ± 3 Ma. A younger granodiorite dyke that crosscuts the regional fabric at a high angle and has only a weak internal foliation yields an age of 2864+3-9 Ma. An undeformed syenogranite pegmatite, which represents a suite that intrudes all other units in the study area, has a combined zircon-monazite age of 2852 ± 3 Ma. The varying degrees of deformation in these minor intrusive rocks constrains the end of deformation in the study area to ca. 2850 Ma. This contrasts with data from the rest of the Slave Province, where the main phases of deformation, metamorphism, and synmetamorphic plutonism have been dated at ca. 2.62-2.59 Ga. Metamorphic titanite ages from the diorite and granodiorite dykes indicate two lower amphibolite to greenschist facies metamorphic events: one at ca. 2705 Ma and one at ca. 2646 Ma. The youngest Archean magmatic event in the area is represented by granite intrusions at 2594+3-2 Ma, coeval with crystallization of titanite at greenschist-grade conditions in some of the older gneissic and intrusive rocks.
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Gong, Lin, Pete Hollings, Yu Zhang, et al. "Contribution of an Eastern Indochina-derived fragment to the formation of island arc systems in the Philippine Mobile Belt." GSA Bulletin 133, no. 9-10 (2021): 1979–95. http://dx.doi.org/10.1130/b35793.1.
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Abstract The Philippine Mobile Belt is a complex plate boundary with multiple terranes in Southeast Asia, yet its early tectonic evolution is still not fully understood due to a scarcity of solid evidence. Here we report new whole rock geochemical, Sr-Nd isotopic, and zircon U-Pb-Hf isotopic data for Cretaceous-Miocene arc magmatic rocks from the Cebu and Bohol Islands, Philippine Mobile Belt. Bulk geochemical data display arc affinities with enriched large ion lithophile elements (e.g., Sr and Ba) and depleted high field strength elements (e.g., Nb, Ta, and Ti). The high positive εNd(t) (+4.6 to +9.1) values and low initial 87Sr/86Sr ratios (0.7032–0.7048) suggest that these igneous rocks were generated by partial melting of mantle wedge in an arc setting. U-Pb dating of zircons revealed Cretaceous (ca. 120–90 Ma), middle Eocene to early Oligocene (ca. 43–30 Ma), and middle Miocene (ca. 14 Ma) crystallization ages for the arc magmatism with abundant Permian-Triassic zircon xenocrysts clustering at ca. 250 Ma. The Permian-Triassic grains show dominantly negative εHf(t) values ranging from −16.2 to −6.6, which are similar to those of coeval rocks in Eastern Indochina. Combined with previous paleomagnetic studies, we propose that an Eastern Indochina-derived continental fragment was involved during the formation of arcs in the Cebu and Bohol Islands, which highlights the potential contribution of ancient continental materials in the formation of intra-oceanic arcs. This scenario does not support the previously proposed model that the Cretaceous arc in the Philippine Mobile Belt formed in the northern margin of the proto-Philippine Sea Plate and Australian margin.
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Zhang, Rui-Gang, Wen-Yan He, and Xue Gao. "Geochronology, Oxidization State and Source of the Daocheng Batholith, Yidun Arc: Implications for Regional Metallogenesis." Minerals 9, no. 10 (2019): 608. http://dx.doi.org/10.3390/min9100608.
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The Daocheng batholith consists of granite, granodiorite and K-feldspar megacrystic granite, which is located in the north Yidun Arc. It is a barren batholith in contrast to plutons of the same age that contain major copper deposits, such as Pulang to the south. In the Daocheng, abundant mafic microgranular enclaves (MMEs) mainly developed within granodiorite and K-feldspar megacrystic granite, which are characterized by quenched apatite, quartz eyes and plagioclase phenocrysts. LA-ICP-MS zircon U–Pb dating of host granodiorite yielded ages ranging from 223 Ma to 210 Ma, with a weighted mean of 215.3 ± 1.8 Ma. Zircons from MMEs yielded ages ranging from 218 Ma to 209 Ma, with a weighted mean of 214.2 ± 1.4 Ma. Geochemical analyses show that granodiorite is high-K, calc-alkaline and I-type, with SiO2 contents ranging from 67.90% to 70.54%. These rocks are metaluminous to marginally peraluminous (A/CNK = 0.98–1.00) and moderately rich in alkalis with K2O ranging from 3.28% to 4.59% and Na2O ranging from 3.18% to 3.20%, with low MgO (1.08%–1.29%), Cr (12.7 ppm–16.8 ppm), Ni (5.19 ppm–6.16 ppm) and Mg# (35–49). The MMEs have relatively low SiO2 contents (56.34%–60.91%), higher Al2O3 contents (16.06%–17.98%), higher MgO and FeO abundances and are metaluminous (A/CNK = 0.82–0.83). The MMEs and host granodiorite are enriched in light rare-earth elements (LREEs) relative to heavy rare-earth elements (HREEs), with slightly negative Eu anomalies, and enriched in Th, U and large ion lithophile elements (LILEs; e.g., K, Rb and Pb), and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, P and Ti), showing affinities typical of arc magmas. The zircon εHf(t) values (−6.28 to −2.33) and ancient two-stage Hf model ages of 1.92 to 1.25 Ga, indicating that the magmas are generally melts that incorporated significant portions of Precambrian crust. The relatively low silica contents and high Mg# values of the MMEs, and the linear patterns of MgO, Al2O3 and Fe2O3 with SiO2 between the MMEs and host granodiorite, showing the formation of MMEs are genetically related to magma mixing. The Daocheng granodiorite is characterized by much lower zircon Ce4+/Ce3+ (average of 3.53) and low fO2 value (average of ∆FMQ = –10.84), whereas the ore-bearing quartz monzonite porphyries in the Pulang copper deposit are characterized by much higher zircon Ce4+/Ce3+ (average of 52.10) and high fO2 value (average of ∆FMQ = 2.8), indicating the ore-bearing porphyry intrusions had much higher fO2 of magma than the ore-barren intrusions considering that the high oxygen fugacity of the magma is conducive to mineralization.
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Fornelli, Annamaria, Salvatore Gallicchio, Francesca Micheletti, and Antonio Langone. "Preliminary U-Pb Detrital Zircon Ages from Tufiti di Tusa Formation (Lucanian Apennines, Southern Italy): Evidence of Rupelian Volcaniclastic Supply." Minerals 10, no. 9 (2020): 786. http://dx.doi.org/10.3390/min10090786.
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U-Pb spot ages have been determined on detrital zircons from two samples of volcaniclastic arenites belonging to the Tufiti di Tusa Formation (TTF) outcropping in the Lucanian Apennines (Southern Italy). Many petrographic and geochemical studies have been performed on these sandstones with the aim of defining their detritus source. A new and precise evaluation of the mineralogical composition of metamorphic lithic fragments, together with U-Pb detrital zircon ages, helps to clarify the deposition age of these syn-sedimentary volcaniclastic sandstones and constrains their source areas. Volcaniclastic arenites consist of andesitic fragments and single minerals of plagioclases, clinopyroxenes, and hornblendes, while the metamorphic lithics are mainly fragments of blue amphibole-bearing micaschists, serpentinites, ophicalcites, phyllites, and medium-grade micaschists. Phaneritic plutonic fragments consist of quartz, feldspar, and micas. Carbonate components include biomicritic and biosparitic fragments. Eighty age data collected from 56 zircons reveal a wide age spectrum, ranging from Neoarchean to Rupelian (from 2712 ± 25 to 30 ± 1 Millions of years (Ma)). The age data show that in volcaniclastic sandstones there is evidence of ancient crystalline basements involved in Cadomian and Variscan orogenesis (ages from 2712 ± 25 Ma to ≈260 Ma), whereas the measured ages of 157 Ma testify the events of Pangea fragmentation and the ages between 78 and 67 Ma are related to subduction metamorphism connected to the Alpine orogenesis. Fifty percent of the estimated detrital zircon ages show a mean concordant age of 33 ± 1 Ma, they have been measured on idiomorphic crystals with undisturbed magmatic oscillatory zoning. These data reveal the true sedimentation age of Tufiti di Tusa sandstones at least at the sampled levels, coeval with that recorded in other Rupelian volcaniclastic successions outcropping in the Northern Apennines and in the Western Alps (e.g., Val d’Aveto-Petrignacola Formation, Ranzano Formation and Taveyannaz Sandstone). These data represent preliminary suggestions of the sedimentation age of the Tufiti di Tusa Formation and Rupelian paleogeography in the Western Mediterranean area. During Priabonian-Rupelian times, the volcanic calc-alkaline detritus linked to a widespread syn-sedimentary igneous activity on the hinterland terranes of the foredeep basins in the Apennine-Maghrebian orogen extended from north to south in the Western-Central Mediterranean area.
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Wasteneys, Hardolph A., Richard J. Wardle, and Thomas E. Krogh. "Extrapolation of tectonic boundaries across the Labrador shelf: U–Pb geochronology of well samples." Canadian Journal of Earth Sciences 33, no. 9 (1996): 1308–24. http://dx.doi.org/10.1139/e96-099.
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Near Saglek Fiord, a northerly trending boundary between the early Archean Saglek block and the middle Archean Hopedale block extends between drill sites which, respectively, sampled Uivak amphibolite gneiss with U–Pb zircon intercept ages of 3742 ± 12 and 2752 ± 42 Ma, and migmatitic Lister gneiss with concordant ages of [Formula: see text] for restite and [Formula: see text], for leucosome. Titanite ages of ca. 2508 Ma are common to both rocks. A nearby metapsammitic gneiss has detrital zircon and monazite ages of 2681 ± 5, 2700 ± 4, ca. 2730, and 2750 ± 2 Ma representing high-grade metamorphism related to the Hopedale–Saglek collision and metamorphic monazite of ca. 2560 Ma age representing metamorphism of the sediment during reactivation of the Saglek–Hopedale suture. Two hundred kilometres southeast, a gneissic granite records a protolith age of 3170 Ma and Late Proterozoic Pb loss. Near the Nain–Makkovik boundary, 1269 ± 4 Ma zircons indicate a significant extension of the Nain Platonic Suite. South of the Makkovik boundary, a foliated granite yielded an upper intercept age defining intrusion at 1895 ± 8 Ma and concordant 1872 ± 5 Ma titanite ages that date subsequent metamorphism. Discordant U–Pb ages from an alkali-feldspar granite also constrain crystallization to ca. 1890 Ma and together with the gneiss represent the previously defined Iggiuk event in the Kaipokok domain. Wells near the southerly end of the transect record 1801 ± 5, 1813 ± 3, and 1806 ± 8 Ma ages, respectively, that are typical of the synorogenic granitoid suite representing the Cape Harrison domain of southern Makkovik Province.
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Brotodewo, Adrienne, Caroline Tiddy, Diana Zivak, et al. "Recognising Mineral Deposits from Cover; A Case Study Using Zircon Chemistry in the Gawler Craton, South Australia." Minerals 11, no. 9 (2021): 916. http://dx.doi.org/10.3390/min11090916.
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Detrital zircon grains preserved within clasts and the matrix of a basal diamictite sequence directly overlying the Carrapateena IOCG deposit in the Gawler Craton, South Australia are shown here to preserve U–Pb ages and geochemical signatures that can be related to underlying mineralisation. The zircon geochemical signature is characterised by elevated heavy rare-earth element fractionation values (GdN/YbN ≥ 0.15) and high Eu ratios (Eu/Eu* ≥ 0.6). This geochemical signature has previously been recognised within zircon derived from within the Carrapateena orebody and can be used to distinguish zircon associated with IOCG mineralisation from background zircon preserved within stratigraphically equivalent regionally unaltered and altered samples. The results demonstrate that zircon chemistry is preserved through processes of weathering, erosion, transport, and incorporation into cover sequence materials and, therefore, may be dispersed within the cover sequence, effectively increasing the geochemical footprint of the IOCG mineralisation. The zircon geochemical criteria have potential to be applied to whole-rock geochemical data for the cover sequence diamictite in the Carrapateena area; however, this requires understanding of the presence of minerals that may influence the HREE fractionation (GdN/YbN) and/or Eu/Eu* results (e.g., xenotime, feldspar).
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Brown, E. H. "Obducted nappe sequence in the San Juan Islands – northwest Cascades thrust system, Washington and British Columbia." Canadian Journal of Earth Sciences 49, no. 7 (2012): 796–817. http://dx.doi.org/10.1139/e2012-026.
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The San Juan Islands – northwest Cascades thrust system in Washington and British Columbia is composed of previously accreted terranes now assembled as four broadly defined composite nappes stacked on a continental footwall of Wrangellia and the Coast Plutonic Complex. Emplacement ages of the nappe sequence are interpreted from zircon ages, field relations, and lithlogies, to young upward. The basal nappe was emplaced prior to early Turonian time (∼93 Ma), indicated by the occurrence of age-distinctive zircons from this nappe in the Sidney Island Formation of the Nanaimo Group. The emplacement age of the highest nappe in the thrust system postdates 87 Ma detrital zircons within the nappe. The nappes bear high-pressure – low-temperature (HP–LT) mineral assemblages indicative of deep burial in a thrust wedge; however, several features indicate that metamorphism occurred prior to nappe assembly: metamorphic discontinuities at nappe boundaries, absence of HP–LT assemblages in the footwall to the nappe pile, and absence of significant unroofing detritus in the Nanaimo Group. A synorogenic relationship of the thrust system to the Nanaimo Group is evident from mutually overlapping ages and by conglomerates of Nanaimo affinity that lie within the nappe pile. From the foregoing relations, and broader Cordilleran geology, the tectonic history of the nappe terranes is interpreted to involve initial accretion and subduction-zone metamorphism south of the present locality, uplift and exhumation, orogen-parallel northward transport of the nappes as part of a forearc sliver, and finally obduction at the present site over the truncated south end of Wrangellia and the Coast Plutonic Complex.
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SAALMANN, K., I. MÄNTTÄRI, P. PELTONEN, M. J. WHITEHOUSE, P. GRÖNHOLM, and M. TALIKKA. "Geochronology and structural relationships of mesothermal gold mineralization in the Palaeoproterozoic Jokisivu prospect, southern Finland." Geological Magazine 147, no. 4 (2010): 551–69. http://dx.doi.org/10.1017/s0016756809990628.
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AbstractThe palaeoproterozoic Svecofennian orogen in southern Finland contains a number of orogenic gold occurrences. The Jokisivu gold deposit, comprising auriferous quartz veins, is hosted by syn-tectonic quartz diorites to gabbros. Mineralization occurs in approximately WNW–ESE- and WSW–ENE-trending shear zones, which probably branch from regional-scale NW–SE-trending shears. Ore zone fabrics post-date regional-scale folding and the metamorphic peak, and can be correlated with late Svecofennian regional shear tectonics (D6; 1.83–1.78 Ga), indicating that mineralization formed during the late stages of orogenic evolution. SIMS and TIMS U–Pb dating of three samples place tight constraints on the age of gold mineralization. Zircons from both unaltered and altered quartz diorites have ages of 1884±4 Ma and 1881±3 Ma, respectively. These are interpreted as the crystallization age of the rock and as providing the maximum age for mineralization. Zircon rims from an altered quartz diorite from the ore zone give ages of c. 1802±15 Ma, which overlap with the 1801±18 Ma titanite (mean Pb–Pb) age from the ore zone. The ages are similar to the age of the pegmatite dyke that cuts the ore zone and whose zircon age of 1807±3 Ma is approximately the same as the 1791±2 Ma monazite age (TIMS) giving the minimum age of the gold mineralization. The mineralization and its structural framework can be correlated with coeval late Svecofennian shear tectonics related to WNW–ESE-oriented shortening in southern Finland. Extensive c. 1.8 Ga granite magmatism, shear zone development and associated gold mineralization are of regional importance also in the northern and western Fennoscandian Shield (Finnish Lapand and Sweden). A Cordilleran-type setting can explain the widespread distribution of magmatism and gold mineralization associated with shortening, as well as the required heat source triggering hydrothermal fluid flow along shear zones.
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Kim, Dong-Yeon, Sung-Ja Choi, and Keewook Yi. "SHRIMP U-Pb Zircon Ages of the Metapsammite in the Yeongam-Gangjin Area." Economic and Environmental Geology 48, no. 4 (2015): 287–99. http://dx.doi.org/10.9719/eeg.2015.48.4.287.
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Mikulski, Stanisław Z., Ian S. Williams, Holly J. Stein, and Jan Wierchowiec. "Zircon U-Pb Dating of Magmatism and Mineralizing Hydrothermal Activity in the Variscan Karkonosze Massif and Its Eastern Metamorphic Cover (SW Poland)." Minerals 10, no. 9 (2020): 787. http://dx.doi.org/10.3390/min10090787.
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SHRIMP (Sensitive high resolution ion microprobe) zircon U-Pb dating of the two main igneous rocks types in the Karkonosze Pluton, porphyritic and equigranular monzogranite, yield 206Pb/238U ages between 312.0 ± 2.9 and 306.9 ± 3.0 Ma. These coincide, within uncertainty, with the majority of previous dates from the pluton, which indicate development of the main magmatic processes between ca. 315 and 303 Ma. They also coincide with molybdenite and sulfide Re-Os ages from ore deposits developed during magmatic and pneumatolitic-hydrothermal (e.g., Szklarska Poręba Huta and Michałowice) or/and metasomatic and hydrothermal (e.g., Kowary, Czarnów and Miedzianka) processes forming Mo-W-Sn-Fe-Cu-As-REE-Y-Nb-Th-U mineralization. The 206Pb/238U zircon age of 300.7 ± 2.4 Ma from a rhyolite porphyry dyke (with disseminated base metal sulfide mineralization) in the Miedzianka Cu-(U) deposit coincides with the development of regional tectonic processes along the Intra-Sudetic Fault. Moreover, at the end-Carboniferous, transition from a collisional to within-plate tectonic setting in the central part of the European Variscides introduced volcanism in the Intra-Sudetic Basin. Together, these processes produced brecciation of older ore mineralization, as well as metal remobilization and deposition of younger medium- and low-temperature hydrothermal mineralization (mainly Cu-Fe-Zn-Pb-Ag-Au-Bi-Se, and Th-U), which became superimposed on earlier high-temperature Mo-W-Sn- Fe-As-Cu-REE mineralization. A few 206Pb/238U ages > 320 Ma remain to be reconciled, but might be due to the high U and Th contents of the zircon and the strong influence of overprinting pneumatolitic-hydrothermal processes.
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Ding, Xiang-Li, Lin Ding, Li-Yun Zhang, Chao Wang, and Ya-Hui Yue. "Identification and Origin of Jurassic (~182 Ma) Zircon Grains from Chromitite within the Peridotite of the Jijal Complex, Kohistan Arc in North Pakistan." Minerals 10, no. 12 (2020): 1085. http://dx.doi.org/10.3390/min10121085.
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The Jijal ultramafic–mafic complex in Pakistan probably preserves the most complete fragments of the petrological Moho. However, a few studies argue for multiple origins (including petrogenetic speculations and tectonic reconstructions) for different lithologies. One of the main reasons for this dispute is the lack of direct age information of the ultramafic rocks. Zircon grains, despite generally being exotic in ultramafic rocks, can provide significant insights into the petrogenetic process of the host ultramafic rocks. This study reports the first zircon U–Pb age and Lu–Hf and trace element data for zircon grains separated from chromitite lenses within the peridotite, which is commonly considered the lowermost part of the Jijal complex. These zircon grains yield concordant 206Pb/238U ages of ~182 ± 3 Ma, which is much older than the late Early Cretaceous age (<120 Ma) of the Jijal complex, and lying above it, the other complexes of the Kohistan paleo-arc. Furthermore, these Jurassic zircon grains present radiogenic εHf(t) values (+9.7 to +6.0) which are obviously lower than the values for the Cretaceous zircon grains of the Kohistan arc. From integrated analysis of the zircon trace element signatures (e.g., high Th, U, Th/U, and U/Yb ratios) and regional geology, we speculate that these zircon grains came from a ‘missing’ Early Jurassic arc akin to the Gangdese belt to the east, and entered the mantle by oceanic subduction processes. Although these Jurassic zircon grains cannot actually constrain the formation age of the chromitite as well as the peridotite, it reminds us that some cryptic pre-Cretaceous complexes and geodynamic processes were incorporated in building the oceanic crust of the Jijal intra-oceanic arc, or the mantle section (at least part of it) should probably belong to the Indus ophiolite mélange. Further research, particularly chronological studies on mantle (or ultramafic) rocks, as well as detailed geological mapping, should be carried out in the future for solving this issue.
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Levashova, Ekaterina V., Sergey G. Skublov, and Vladimir A. Popov. "Distribution of Trace Elements Controlled by Sector and Growth Zonings in Zircon from Feldspathic Pegmatites (Ilmen Mountains, the Southern Urals)." Geosciences 11, no. 1 (2020): 7. http://dx.doi.org/10.3390/geosciences11010007.
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The present study contains the detailed ion microprobe data on trace and rare earth elements distribution in the large zircon crystal about 10 × 6 mm in size with distinct growth and sector zonings from Ilmen Mountains feldspathic pegmatite. The zircon crystal morphology is a combination of a prism {110} and a dipyramid {111}. It is found out that the growth sector of the prism {110} generally contains higher concentrations of Th, U, REE, Y, and Nb and exhibits a more gently sloping HREE distribution pattern and a steeper LREE distribution pattern, in contrast to zircon from the growth sector of the dipyramid {111} development. Such a sector zoning pattern was formed at a late stage in crystal growth, when the prism {110} began to prevail over the dipyramid {111}. The zircon studied displays the growth zoning formed of alternating bands in back-scattered electron (BSE) image: wide dark and thin light bands. The last ones contain elevated Th, U, REE, Y, Nb, and Ti concentrations, Th/U ratio and Ce/Ce*. This growth zoning is most probably due to simultaneous crystallization of other minerals that concentrate trace elements, e.g., apatite and monazite, and the lack of equilibrium between zircon and fluid (melt).
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Kim, Myoung Jung, Jeong-Woong Park, Tae-Ho Lee, Yong-Sun Song, and Kye-Hun Park. "LA-MC-ICPMS U-Pb Ages of the Detrital Zircons from the Baengnyeong Group: Implications of the Dominance of the Mesoproterozoic Zircons." Economic and Environmental Geology 49, no. 6 (2016): 433–44. http://dx.doi.org/10.9719/eeg.2016.49.6.433.
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STEPHAN, TOBIAS, UWE KRONER, and ROLF L. ROMER. "The pre-orogenic detrital zircon record of the Peri-Gondwanan crust." Geological Magazine 156, no. 2 (2018): 281–307. http://dx.doi.org/10.1017/s0016756818000031.
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AbstractWe present a statistical approach to data mining and quantitatively evaluating detrital age spectra for sedimentary provenance analyses and palaeogeographic reconstructions. Multidimensional scaling coupled with density-based clustering allows the objective identification of provenance end-member populations and sedimentary mixing processes for a composite crust. We compiled 58 601 detrital zircon U–Pb ages from 770 Precambrian to Lower Palaeozoic shelf sedimentary rocks from 160 publications and applied statistical provenance analysis for the Peri-Gondwanan crust north of Africa and the adjacent areas. We have filtered the dataset to reduce the age spectra to the provenance signal, and compared the signal with age patterns of potential source regions. In terms of provenance, our results reveal three distinct areas, namely the Avalonian, West African and East African–Arabian zircon provinces. Except for the Rheic Ocean separating the Avalonian Zircon Province from Gondwana, the statistical analysis provides no evidence for the existence of additional oceanic lithosphere. This implies a vast and contiguous Peri-Gondwanan shelf south of the Rheic Ocean that is supplied by two contrasting super-fan systems, reflected in the zircon provinces of West Africa and East Africa–Arabia.
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Böhm, Christian O., Larry M. Heaman, and M. Timothy Corkery. "Archean crustal evolution of the northwestern Superior craton margin: U-Pb zircon results from the Split Lake Block." Canadian Journal of Earth Sciences 36, no. 12 (1999): 1973–87. http://dx.doi.org/10.1139/e99-088.
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The Split Lake Block forms a partly retrogressed, granulite-grade basement segment located at the northwestern margin of the Superior Province in Manitoba. Unlike other segments along the craton margin, the effects of Proterozoic tectonism are relatively minor in the Split Lake Block, making it amenable to establishing firm temporal constraints for the Archean magmatic and metamorphic history of the northwestern Superior Province margin. Consequently, samples from the main lithological units within the Split Lake Block were selected for precise single-grain U-Pb zircon geochronology. Heterogeneous zircon populations isolated from representative enderbite, tonalite, and granodiorite samples reveal a complex growth history with pre-2.8 Ga protolith ages (e.g., 2841 ± 2 Ma tonalite), possibly as old as 3.35 Ga as indicated in a granodiorite sample. The youngest Archean granitic magmatism identified in the eastern Split Lake Block is represented by the 2708 ± 3 Ma Gull Lake granite. A U-Pb zircon age of 2695+4-1 Ma obtained for leucosome in mafic granulite is interpreted to reflect the timing of granulite-grade metamorphism in the Split Lake Block, supported by polyphase zircon growth and (or) lead loss at ca. 2.7 Ga in the enderbite sample. A younger phase of metamorphic zircon growth at ca. 2.62 Ga is documented in the tonalite and granodiorite zircon populations. The 2.70-2.71 Ga crust formation, the occurrence of ca. 2695 Ma high-grade metamorphism, and broadly contemporaneous Paleoproterozoic mafic dykes in both the Split Lake Block and Pikwitonei Granulite Domain imply a common evolution of these high-grade terrains along the northwestern Superior craton margin since the late Archean.
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Stearns, Michael A., John M. Bartley, John R. Bowman, et al. "Simultaneous Magmatic and Hydrothermal Regimes in Alta–Little Cottonwood Stocks, Utah, USA, Recorded Using Multiphase U-Pb Petrochronology." Geosciences 10, no. 4 (2020): 129. http://dx.doi.org/10.3390/geosciences10040129.
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Magmatic and hydrothermal systems are intimately linked, significantly overlapping through time but persisting in different parts of a system. New preliminary U-Pb and trace element petrochronology from zircon and titanite demonstrate the protracted and episodic record of magmatic and hydrothermal processes in the Alta stock–Little Cottonwood stock plutonic and volcanic system. This system spans the upper ~11.5 km of the crust and includes a large composite pluton (e.g., Little Cottonwood stock), dike-like conduit (e.g., Alta stock), and surficial volcanic edifices (East Traverse and Park City volcanic units). A temperature–time path for the system was constructed using U-Pb and tetravalent cation thermometry to establish a record of >10 Myr of pluton emplacement, magma transport, volcanic eruption, and coeval hydrothermal circulation. Zircons from the Alta and Little Cottonwood stocks recorded a single population of apparent temperatures of ~625 ± 35 °C, while titanite apparent temperatures formed two distinct populations interpreted as magmatic (~725 ± 50 °C) and hydrothermal (~575 ± 50 °C). The spatial and temporal variations required episodic magma input, which overlapped in time with hydrothermal fluid flow in the structurally higher portions of the system. The hydrothermal system was itself episodic and migrated within the margin of the Alta stock and its aureole through time, and eventually focused at the contact of the Alta stock. First-order estimates of magma flux in this system suggest that the volcanic flux was 2–5× higher than the intrusive magma accumulation rate throughout its lifespan, consistent with intrusive volcanic systems around the world.
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Barr, S. M., M. A. Hamilton, S. D. Samson, A. M. Satkoski, and C. E. White. "Provenance variations in northern Appalachian Avalonia based on detrital zircon age patterns in Ediacaran and Cambrian sedimentary rocks, New Brunswick and Nova Scotia, Canada." Canadian Journal of Earth Sciences 49, no. 3 (2012): 533–46. http://dx.doi.org/10.1139/e11-070.
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Avalonia in the northern Appalachian orogen is generally assumed to have originated near the margin of Gondwana, although its position along that extensive margin and the timing of its separation remain disputed. U–Pb ages determined by laser ablation – inductively coupled plasma – mass spectrometry are reported here for detrital zircon from Avalonian clastic sedimentary units, three in southern New Brunswick, and one in southeastern Cape Breton Island, with depositional ages ranging from ca. 630 to ca. 505 Ma. Considered in combination with previously published detrital data sets from two other samples from southern New Brunswick deposited in a similar age range, the samples show a wide spectrum of ages from Ediacaran to Neoarchean (as old as 3.2 Ga). The dominant zircon populations in all six samples are Ediacaran–Cryogenian with ages between 770 and 540 Ma and can be matched with known magmatic events in Avalonia. Pre-Avalonian cycle detrital zircon dates in the samples are relatively sparse and do not reveal a consistent signature that might be used to place Avalonia in a unique paleogeographic position, although they are compatible with Amazonian provenance. An increase in ca. 2.2–1.9 Ga zircon dates in Early Cambrian through Early Ordovician samples suggests that sources for zircon of those ages became available in Avalonia by the end of the Ediacaran, possibly by motion of Avalonia to a different part of the Amazonian margin or to the West African craton.
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Yin, Jingwu, Chunhua Liu, Jung Hyun Park, et al. "The Geochemical and Zircon Trace Element Characteristics of A-type Granitoids in Boziguoer, Baicheng County, Xinjiang." Economic and Environmental Geology 46, no. 2 (2013): 179–98. http://dx.doi.org/10.9719/eeg.2013.46.2.179.
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ALMARSHAD, ABDULLAH. "Oxygen Diffusion in Zirconia "During Reaction of Zircaloy-4 with Steam from 1173 to 1773 K." Journal of King Abdulaziz University-Engineering Sciences 10, no. 2 (1998): 115–21. http://dx.doi.org/10.4197/eng.10-2.7.
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Hanna, Waleed, Sahib Al-Saffar, and Baidaa Hassan. "The Effect of 5 wt %Yettria-Stabilized Zirconia on Crystallized Glass-Ceramic System at Different Temperature." Journal of King Abdulaziz University-Engineering Sciences 22, no. 1 (2011): 3–16. http://dx.doi.org/10.4197/eng.22-1.1.
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Ryazantsev, A. V., N. B. Kuznetsov, K. E. Degtyarev, T. V. Romanyuk, T. Yu Tolmacheva, and E. A. Belousova. "Reconstruction of the Vendian–Cambrian active continental margin of the Southern Urals: results of studying of detrital zircon from the Ordovician terrigenous rocks." Геотектоника, no. 4 (August 13, 2019): 43–59. http://dx.doi.org/10.31857/s0016-853x2019343-59.
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Detrital zircons of Ordovician terrigenous sequences are studied in various Southern Uralian tectonic units.The age of detrital zircons of the West Uralian and Transuralian megazones, Taganai–Beloretsk Zone, and Kraka allochthons spans from the Late Archean to the end of the Vendian– beginning of the Cambrian; Early Precambrian and Early–Middle Riphean zircons are the most abundant. Vendian–Cambrian detrital zircons are strongly dominant in the Uraltau Zone, Sakmara allochthons, and East Uralian Megazone; the zircons of other ages are absent or extremely rare. The Vendian–Cambrian detrital zircons of all Southern Urals zones probably derive from volcanic and granitic rocks of the marginal continental belt, which are part of the Uraltau Zone, Sakmara allochthons, and East Uralian Megazone. The Lu–Hf isotopic characteristics of Vendian–Cambrian detrital zircons indicate that their parental rocks formed on a heterogeneous basement that includes blocks of juvenile and ancient continental crust. According to a model of the pre-Ordovician tectonic evolution of the Southern Urals, at the end of the Late Riphean, the passive margin of the East European Platform collided with a block on a heterogeneous basement. The formation of the block terminated with the Grenville Orogeny. After collision, a volcano-plutonic belt originated in the Vendian–Cambrian at the actively evolved margin of the East European Platform.
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Boerboom, Terrence J., and Robert E. Zartman. "Geology, geochemistry, and geochronology of the central Giants Range batholith, northeastern Minnesota." Canadian Journal of Earth Sciences 30, no. 12 (1993): 2510–22. http://dx.doi.org/10.1139/e93-217.
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The Giants Range batholith is a large composite granitoid body that intrudes deformed supracrustal rocks in the western part of the Wawa Subprovince of the Archean Superior Province. Peak fabric development in the supracrustal rocks coincides with D2 deformation, the product of regional transpression across the southern Superior Province. U–Pb zircon ages on two phases of the Giants Range batholith bracket D2 deformation to an interval between 2685 and 2669 Ma. Two well-exposed components of the central part of the Giants Range batholith are the pre- to syn-D2 Britt granodiorite, which contains a linear D2 metamorphic fabric, and the syn- to post-D2 Shannon Lake granite, which cuts deformation fabrics in the Britt granodiorite and the supracrustal rocks. Geochemical discrimination plots imply emplacement of the Britt granodiorite in an arc environment and the Shannon Lake granite in a collision setting. Zircons yield U–Pb ages of 2681 ± 4 and 2685 ± 4 Ma for the Britt granodiorite and 2674 ± 5 and 2674 ± 27 Ma for the Shannon Lake granite. Timing of D2 deformation near the Giants Range batholith corresponds well with similar rocks exposed along strike 170 km to the east near Shebandowan Lake, Ontario, where the end of D2 deformation has been bracketed between 2692 and 2681 Ma. The slightly younger ages for D2 deformation in Minnesota reflect later volcanic-arc development and associated plutonism than at Shebandowan Lake, possibly due to oblique convergence along a westward-migrating tectonic front.
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Trop, Jeffrey M., Jeff Benowitz, Ronald B. Cole, and Paul O’Sullivan. "Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary." Geosphere 15, no. 4 (2019): 1066–101. http://dx.doi.org/10.1130/ges02014.1.
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AbstractThe Alaska Range suture zone exposes Cretaceous to Quaternary marine and nonmarine sedimentary and volcanic rocks sandwiched between oceanic rocks of the accreted Wrangellia composite terrane to the south and older continental terranes to the north. New U-Pb zircon ages, 40Ar/39Ar, ZHe, and AFT cooling ages, geochemical compositions, and geological field observations from these rocks provide improved constraints on the timing of Cretaceous to Miocene magmatism, sedimentation, and deformation within the collisional suture zone. Our results bear on the unclear displacement history of the seismically active Denali fault, which bisects the suture zone. Newly identified tuffs north of the Denali fault in sedimentary strata of the Cantwell Formation yield ca. 72 to ca. 68 Ma U-Pb zircon ages. Lavas sampled south of the Denali fault yield ca. 69 Ma 40Ar/39Ar ages and geochemical compositions typical of arc assemblages, ranging from basalt-andesite-trachyte, relatively high-K, and high concentrations of incompatible elements attributed to slab contribution (e.g., high Cs, Ba, and Th). The Late Cretaceous lavas and bentonites, together with regionally extensive coeval calc-alkaline plutons, record arc magmatism during contractional deformation and metamorphism within the suture zone. Latest Cretaceous volcanic and sedimentary strata are locally overlain by Eocene Teklanika Formation volcanic rocks with geochemical compositions transitional between arc and intraplate affinity. New detrital-zircon data from the modern Teklanika River indicate peak Teklanika volcanism at ca. 57 Ma, which is also reflected in zircon Pb loss in Cantwell Formation bentonites. Teklanika Formation volcanism may reflect hypothesized slab break-off and a Paleocene–Eocene period of a transform margin configuration. Mafic dike swarms were emplaced along the Denali fault from ca. 38 to ca. 25 Ma based on new 40Ar/39Ar ages. Diking along the Denali fault may have been localized by strike-slip extension following a change in direction of the subducting oceanic plate beneath southern Alaska from N-NE to NW at ca. 46–40 Ma. Diking represents the last recorded episode of significant magmatism in the central and eastern Alaska Range, including along the Denali fault. Two tectonic models may explain emplacement of more primitive and less extensive Eocene–Oligocene magmas: delamination of the Late Cretaceous–Paleocene arc root and/or thickened suture zone lithosphere, or a slab window created during possible Paleocene slab break-off. Fluvial strata exposed just south of the Denali fault in the central Alaska Range record synorogenic sedimentation coeval with diking and inferred strike-slip displacement. Deposition occurred ca. 29 Ma based on palynomorphs and the youngest detrital zircons. U-Pb detrital-zircon geochronology and clast compositional data indicate the fluvial strata were derived from sedimentary and igneous bedrock presently exposed within the Alaska Range, including Cretaceous sources presently exposed on the opposite (north) side of the fault. The provenance data may indicate ∼150 km or more of dextral offset of the ca. 29 Ma strata from inferred sediment sources, but different amounts of slip are feasible.Together, the dike swarms and fluvial strata are interpreted to record Oligocene strike-slip movement along the Denali fault system, coeval with strike-slip basin development along other segments of the fault. Diking and sedimentation occurred just prior to the onset of rapid and persistent exhumation ca. 25 Ma across the Alaska Range. This phase of reactivation of the suture zone is interpreted to reflect the translation along and convergence of southern Alaska across the Denali fault driven by highly coupled flat-slab subduction of the Yakutat microplate, which continues to accrete to the southern margin of Alaska. Furthermore, a change in Pacific plate direction and velocity at ca. 25 Ma created a more convergent regime along the apex of the Denali fault curve, likely contributing to the shutting off of near-fault extension-facilitated arc magmatism along this section of the fault system and increased exhumation rates.
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REISCHMANN, T., D. K. KOSTOPOULOS, S. LOOS, B. ANDERS, A. AVGERINAS, and S. A. SKLAVOUNOS. "Late palaeozoic magmatism in the basement rocks Southwest of Mt. Olympos, Central Pelagonian zone, Greece: Remnants of a permo-carboniferous magmatic arc." Bulletin of the Geological Society of Greece 34, no. 3 (2001): 985. http://dx.doi.org/10.12681/bgsg.17134.
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We dated basement rocks from several localities southwest of Mt. Olympos, as well as from a locality near the top of the mountain using the single zircon Pb/Pb evaporation technique. For the samples southwest of the mountain, the ages obtained range from ca. 280 to 290 Ma, with only a few zircon grains being around 300 Ma. By contrast, the sample from near the top of the mountain appears to be slightly younger, with ca. 270 Ma. These ages imply that the granitoids crystallized during Late Carboniferous - Early Permian times, and are therefore younger than the basement gneisses of other regions of the Pelagonian zone, which yielded zircon ages of around 300 Ma (e.g. Yarwood & Aftalion 1976, Mountrakis 1983, De Bono 1998, Engel & Reischmann 2001). However, the ages obtained in the present study are identical, within error, to the muscovite Ar-Ar cooling ages from Mt. Ossa (Lips 1998). Our geochronological data show that the magmatic evolution for this part of the basement of the Pelagonian Zone lasted at least 30 Ma.
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Crowley, J. L., S. A. Bowring, S. Z. Shen, Y. Wang, C. Cao, and Y. G. Jin. "U–Pb zircon geochronology of the end-Permian mass extinction." Geochimica et Cosmochimica Acta 70, no. 18 (2006): A119. http://dx.doi.org/10.1016/j.gca.2006.06.152.
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Gehrels, George, Victor Valencia, and Alex Pullen. "Detrital Zircon Geochronology by Laser-Ablation Multicollector ICPMS at the Arizona LaserChron Center." Paleontological Society Papers 12 (October 2006): 67–76. http://dx.doi.org/10.1017/s1089332600001352.
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Detrital zircon geochronology is rapidly evolving into a very powerful tool for determining the provenance and maximum depositional age of clastic strata. This rapid evolution is being driven by the increased availability of ion probes and laser ablation ICP mass spectrometers, which are able to generate age determinations rapidly, at moderate to low cost, and of sufficient accuracy for most applications. Improvements in current methods will probably come from enhanced precision/accuracy of age determinations, better tools for extracting critical information from age spectra, abilities to determine other types of information (e.g., REE patterns, O and Hf isotope signatures, and/or cooling ages) from the dated grains, and construction of a database that provides access to detrital zircon age determinations from around the world.
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Pereira, Manuel Francisco, and Cristina Gama. "Revisiting the Intermediate Sediment Repository Concept Applied to the Provenance of Zircon." Minerals 11, no. 3 (2021): 233. http://dx.doi.org/10.3390/min11030233.
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This paper revisits the intermediate sediment repository (ISR) concept applied to provenance, using a comparison of the detrital zircon population of Holocene beach sand from the southwest Portuguese coast with populations from their potential source rocks. The U–Pb age of detrital zircon grains in siliciclastic rocks allows for the interpretation of provenance by matching them with the crystallization ages of igneous source (protosource) rocks in which this mineral originally crystallized or which was subsequently recycled from it, acting as ISRs. The comparative analysis of the Precambrian, Paleozoic, and Cretaceous ages using recent statistical tools (e.g., kernel density estimator (KDE), cumulative age distribution (CAD), and multidimensional scaling (MDS)) suggests that the zircon age groups of Carboniferous, Triassic, and Pliocene-Pleistocene ISRs are reproduced faithfully in Holocene sand. Furthermore, the recycling of a protosource (Cretaceous syenite) in a sedimentary system dominated by ISRs is evaluated. It is argued that the ISR concept, which is not always taken into account, is required for a better understanding of the inherent complexity of local provenance and to differentiate sediment recycling from first- cycle erosion of an igneous rock.
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Meng, Yuanku, Zhongbo Wang, Baoping Gan, and Jinqing Liu. "Petrogenesis and Tectonic Implications of the Early Cretaceous Granitic Pluton in the Sulu Orogenic Belt: The Caochang Granitic Pluton as an Example." Minerals 10, no. 5 (2020): 432. http://dx.doi.org/10.3390/min10050432.
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The Sulu orogenic belt is the source of information on important magmatic events associated with the collision of the Yangtze craton and North China craton (NCC) and the destruction of the NCC during the Mesozoic in eastern China. In this study, we have, for the first time, identified a monzonitic granitic pluton. We hereby present petrological, geochemical, and zircon U-Pb-Hf-O isotopic data, shedding new light on the petrogenesis and tectonic implications for the granitic pluton in the Sulu belt. LA-ICP-MS and SHRIMP II analyses of zircon grains suggest that the monzonitic granitic pluton was crystallized in the Early Cretaceous (ca. 120 Ma). Geochemically, the granitic pluton shows sub-alkaline, high-K calc-alkaline, and metaluminous signatures, and is genetically of I-type granite, excluding the possibility of S-type granite, as evidenced by mantle-like zircon oxygen isotopic features. In addition, the pluton is enriched in light REE and large-ion lithophile elements (LILE) (e.g., La, Cs, Ba, K, and Pb), but depleted in high-field-strength elements (HFSE) (e.g., Nb, Ta, P, and Ti), suggesting an arc-related affinity. Zircon Hf isotopes (εHf(t) = −27.51~−32.35; TDM2 = 2979~3175 Ma) and mantle-like δ18O values (5.12–6.24‰) together indicate that the identified granitic pluton is derived from the partial melting (reworking) of the ancient mafic lower crustal material, with no supra-crustal material participation. Moreover, high Magnesium number (Mg# = 42–49) values and mafic micro-granular enclaves suggest that mantle-derived magma participated in the evolution of the granitic pluton in this study. Integrating the findings of this study and previous work, we propose that the Caochang granitic pluton is derived from the partial melting of the deep Yangtze basaltic lower crust during the Early Cretaceous, and that the large-scale thinning of the lithospheric mantle was the main factor that led to Early Cretaceous magmatic flare-up in the Sulu orogenic belt.
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Hollis, Julie A., Dirk Frei, Jeroen A. M. Van Gool, Adam A. Garde, and Mac Persson. "Using zircon geochronology to resolve the Archaean geology of southern West Greenland." Geological Survey of Denmark and Greenland (GEUS) Bulletin 10 (November 29, 2006): 49–52. http://dx.doi.org/10.34194/geusb.v10.4908.
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Until recently, in situ U-Pb zircon geochronology could be carried out only using ion microprobes, requiring lengthy analysis times of c. 20 minutes. However, new developments in laser ablation inductively coupled plasma mass spectrometer technologies have resulted in zircon geochronology techniques that are much faster, simpler, cheaper, and more precise than before (e.g. Frei et al. 2006, this volume). Analyses approaching the precision obtained via ion microprobe can now be undertaken in 2–4 minutes using instruments such as the 213 nm laser ablation (LA) system coupled with Element2 sector-field inductively coupled plasma mass spectrometer (SF-ICP-MS) housed at the Geological Survey of Denmark and Greenland (GEUS). The up to tenfold decrease in analytical time means that zircon geochronology can now be used in a much wider range of studies. The Godthåbsfjord region, southern West Greenland, contains some of the oldest rocks exposed on the Earth’s surface reflecting a very complex Archaean geological evolution (Figs 1, 2). Over recent years GEUS has undertaken a range of mapping projects at various scales within the Godthåbsfjord region (see also below). These include the mapping of the 1:100 000 scale Kapisillit geological map sheet (Fig. 1), and regional and local investigations of the environments of formation and geological evolution of supracrustal belts, hosting potentially economic mineral occurrences. Zircon geochronology is an important tool for investigating a range of geological problems in this region. By breaking down the complex geology into a series of simple problems that can be addressed using this tool, the geological evolution can be unlocked in a stepwise manner. Three examples are presented below: (1) the mapping of regional structures; (2) characterising and correlating supracrustal belts; and (3) dating metamorphism and mineralisation. Although focus is on the application of zircon geochronology to these problems, it is important to note that the resulting data must always be viewed within a wider context incorporating geological mapping and structural, geochemical and petrographic investigations.
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Yang, Fan, Jinggui Sun, Yan Wang, et al. "Geology, Geochronology and Geochemistry of Weilasituo Sn-Polymetallic Deposit in Inner Mongolia, China." Minerals 9, no. 2 (2019): 104. http://dx.doi.org/10.3390/min9020104.
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The recently discovered Weilasituo Sn-polymetallic deposit in the Great Xing’an Range is an ultralarge porphyry-type deposit. The mineralization is closely associated with an Early Cretaceous quartz porphyry. Analysis of quartz porphyry samples, including zircon U-Pb dating and Hf isotopies, geochemical and molybdenite Re-Os isotopic testing, reveals a zircon U-Pb age of 138.6 ± 1.1 Ma and a molybdenite Re-Os isotopic age of 135 ± 7 Ma, suggesting the concurrence of the petrogenetic and metallogenic processes. The quartz porphyry has high concentrations of SiO2 (71.57 wt %–78.60 wt %), Al2O3 (12.69 wt %–16.32 wt %), and K2O + Na2O (8.85 wt %–10.44 wt %) and A/CNK ratios from 0.94–1.21, is mainly peraluminous, high-K calc-alkaline I-type granite and is relatively rich in LILEs (large ion lithophile elements, e.g., Th, Rb, U and K) and HFSEs (high field strength elements, e.g., Hf and Zr) and relatively poor in Sr, Ba, P, Ti and Nb. The zircon εHf(t) values range from 1.90 to 6.90, indicating that the magma source materials were mainly derived from the juvenile lower crust and experienced mixing with mantle materials. Given the regional structural evolution history, we conclude that the ore-forming magma originated from lower crust that had thickened and delaminated is the result of the subduction of the Paleo–Pacific Ocean. Following delamination, the lower crustal material entered the underlying mantle, where it was partially melted and reacted with mantle during ascent. The deposit formed at a time of transition from post-orogenic compression to extension following the subduction of the Paleo–Pacific Ocean.
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LIATI, ANTHI, NIKOS SKARPELIS, and GEORGIA PE-PIPER. "Late Miocene magmatic activity in the Attic-Cycladic Belt of the Aegean (Lavrion, SE Attica, Greece): implications for the geodynamic evolution and timing of ore deposition." Geological Magazine 146, no. 5 (2009): 732–42. http://dx.doi.org/10.1017/s0016756809006438.
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AbstractNumerous post-metamorphic Miocene granitoids occur in the area of Lavrion, SE Attica, at the western end of the Attic-Cycladic Belt of the Aegean. U–Pb ion microprobe-dating (SHRIMP) of zircon from a granitoid sill in the hanging-wall of a regional detachment fault reveals two distinct ages: (1) 11.93 ± 0.41 Ma, obtained from inherited zircon cores with metamorphic characteristics (homogeneous cathodoluminescence, low Th/U ratios) and granulite-type (round/resorbed) morphology. This age is interpreted as the time of a likely granulite-facies metamorphism of the precursor rock. (2) 8.34 ± 0.20 Ma, obtained by oscillatory zoned zircon domains with cathodoluminescence and Th/U characteristics typical for magmatic origin. This age is interpreted as the crystallization time of the granitoid sills. Although a granulite-facies metamorphic event has not been recognized so far for rocks of the Attic-Cycladic Belt, it seems to be the most plausible hypothesis to explain both the zircon systematics and age results. This hypothesis is consistent with an extensional regime predominating in the Aegean from Late Miocene times onwards. A possible granulite-facies metamorphism can be related to magmatic underplating at the initial stages of extension, setting an upper age of c. 12 Ma for the operation of the detachment fault. The 8.34 ± 0.20 Ma zircon crystallization age is, statistically, marginally different to a previous K–Ar feldspar date of hornblende-bearing dykes (9.4 ± 0.3 Ma) and identical to a 8.27 ± 0.11 Ma K–Ar biotite date of the main granitoid stock in the area, thus being generally consistent with prior age constraints from the region. Operation of the detachment fault in the Lavrion area is therefore bracketed between c. 11.9 Ma and at least 8.3 Ma. This time range is in line with the time of operation of detachment faults suggested previously for the Cycladic islands. Carbonate-hosted replacement-type massive sulphide Pb–Zn–Ag ores are spatially associated with the detachment fault and related extensional structures in the Basal Unit. Therefore, these Pb–Zn–Ag ores probably also formed within the above time span of c. 11.9 to at least 8.3 Ma. U–Pb ion microprobe (SHRIMP) dating of zircon from an orthogneiss within the metaclastic subunit of the Basal Unit in Lavrion yielded a protolith age of 240 ±4 Ma, consistent with ages of Triassic volcanism elsewhere in Greece.
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LUO, QUN, CHEN ZHANG, SHU JIANG, et al. "Partial melting of oceanic sediments in subduction zones and its contribution to the petrogenesis of peraluminous granites in the Chinese Altai." Geological Magazine 156, no. 4 (2018): 585–604. http://dx.doi.org/10.1017/s0016756817001029.
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AbstractLate Carboniferous magmatism in the Chinese Altai provides an important view of geodynamic processes active during crustal growth in the Central Asian Orogenic Belt (CAOB). In this study, five representative peraluminous granite plutons from the Chinese Altai were selected for systematic geochronological, geochemical and Sr–Nd–Hf isotopic analyses (Table 1). These granites were emplaced between 449 and 327 Ma in an active subduction zone, and have moderate to high SiO2 (66.54–76.13 wt%), moderate Na2O+K2O (6.27–7.66 wt%), and high Al2O3 contents (12.43–16.18 wt%). All granite samples in this study showed significant decoupling of the Nd and Hf isotope systems. Results show negative εNd(t) values (−3.3 to −0.9), and predominantly positive εHf(t) values (+0.24 to +8.01, n=57) except for a few negative εHf(t) values (−7.44 to −0.03, n=9), high Mg# values (28.69–53.33), high Nd/Hf ratios (4.26–43.57), and enrichment of large-ion lithophile elements (LILEs; e.g. Pb, Th, and U), suggesting that the granites were derived from the partial melting of oceanic sediments and the associated mantle wedge, with fractionation of plagioclase, K-feldspar and biotite. In situ zircon Hf isotopic analyses yield negative εHf(t) values from −30.6 to −13.7 for the zircon xenocrysts. The U–Pb ages and Hf isotopic ratios of these zircon xenocrysts were probably inherited from oceanic sediments. Zircon saturation temperatures suggest that these peraluminous granites were emplaced at 537–765°C. We propose that: (1) the Nd isotopic system more faithfully reflects the source of peraluminous magmas in the Chinese Altai than the Hf isotopic system, and (2) the oceanic sediment recycling was an important process during continental growth in the CAOB.
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Sereda, Elena, Boris Belyatsky, and Nadezhda Krivolutskaya. "Geochemistry and Geochronology of Southern Norilsk Intrusions, SW Siberian Traps." Minerals 10, no. 2 (2020): 165. http://dx.doi.org/10.3390/min10020165.
Full textAbstract:
The Norilsk ore region is characterized by the occurrence of numerous intrusions comprising the PGE–Cu–Ni deposits. The Turumakit area, within the Southern Norilsk Trough, also contains many mineralized mafic intrusions of probably similar economic potential to the known Norilsk deposits. We study igneous rocks from three boreholes within the Turumakit area, sampling gabbro-dolerites and trachydolerites related to the Norilsk and Ergalakh complexes, as well as an outcrop of the Daldykan gabbro-dolerite intrusion. Our petrographical, mineralogical and geochemical data, as well as the U–Pb dating of extracted baddeleyites and zircons, primarily discriminate between the sub-alkaline rocks of the main Turumakit area and the Ergalakh trachydolerites located in the Norilsk and Talnakh ore junctions. Coarser grained Turumakit trachydolerites (with pegmatite segregations) contrast finer grained Ergalakh trachydolerites by having: (1) higher TiO2 (up to 5.5 wt %) compared with 2.2 wt %–3.3 wt % in the typical Ergalakh rocks; (2) low U, lower La/Yb and La/Sm ratios (5–7), in contrast to 8–10 ppm, 2.5–2.6 and 3.0–3.3, respectively, for the Ergalakh trachydolerites; and (3) their age was determined by U–Pb methods on baddeleyite and zircon (244.8 ± 2.7 Ma), and it appears likely that the mafic rocks traditionally attributed to the Ergalakh complex within the Turumakit area are younger than the Norilsk intrusions (250 ± 1.4 Ma). These data strongly indicate an emplacement of Turumakit intrusions during the end of a ~5 Myr magmatic evolution of the Norilsk district. It is therefore proposed that the sub-alkaline rocks of the Turumakit area belong to a separate intrusive complex within the Norilsk district.