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In this contribution, we document changes in detrital zircon ages in the upper Devonian (Famennian) to lower Carboniferous (Mississippian) Billefjorden Group on Bjørnøya, the southernmost island of Svalbard. This alluvial, coal‐bearing clastic succession is widely distributed across the archipelago and the Barents Shelf. The sediments were deposited in subsidence‐induced lowlands that formed just after regional post‐Caledonian collapse‐related extension, which created the classical 'Old Red Sandstone' basins during the Devonian, and prior to localised rift‐basin development in the middle Carboniferous (Serpukhovian–Moscovian). Moreover, the succession is little affected by Ellesmerian compressional deformation, which occurred in the latest Devonian. However, little is known of the provenance and regional sediment routing in this tectonically transitional period between the post‐Caledonian structuring events in the Devonian and the middle Carboniferous rifting. It has previously been invoked that a regional fault running parallel to the western Barents Shelf margin, the West Bjørnøya Fault, controlled sedimentation in the area. Here, we combine detrital zircon U–Pb ages and sedimentological data to investigate stratigraphic provenance variations and test whether tectonics controlled deposition of the Billefjorden Group on Bjørnøya. Sedimentological investigations demonstrate changes in fluvial style with intercalations between successions dominated by meandering channel fills and abundant overbank fines to sandstone‐dominated sheet‐like successions of braided stream origin. Palaeocurrent data show that two competing drainage directions accompany the changes in fluvial architecture. Northeasterly transport directions, recorded in the braided stream deposits, indicate possible fault‐transverse drainage. The detrital zircon content in these deposits indicates sourcing from Caledonian terranes in Northeast Greenland. Northwest‐oriented transport directions, measured in the meandering channel deposits, are inferred to represent axially positioned drainage systems. These may have been sourced from either Northeast Greenland, a more localised source, or Baltica. The latter would require long‐distance sourcing, which, given the tectonic setting of the region, seems unlikely. Although our sedimentological observations point to syn‐tectonic deposition, this is not clearly captured in the detrital zircon data, suggesting a common source for the Late Devonian–Mississippian fluvial systems of Bjørnøya. Thus, combined with previously published provenance data from Svalbard and Greenland, we demonstrate that the East Greenland Caledonides formed a long‐lived and significant source area which provided sediments to nearby basins from the Devonian to the Early Cretaceous. [ABSTRACT FROM AUTHOR]

Porphyry indicator zircons (PIZ) are often used as an exploratory guide to distinguish fertile granitoid-hosted porphyry copper deposits (PCD). Alumina-saturated granitoids with higher zirconium (> 200 ppm) contents are often the hosts of PCD. REE profiling of zircon is used here to evaluate the chemistry of zircon from a blend of I- and A-type granitoids that hosts the 'Kaziranga' porphyry copper mineralization in the Karbi Hills of the Shillong Plateau. Zircon Hf(t) (1.69–9.88; av.4.65) and whole rock 87Sr/86Sr (0.703) of the Kaziranga granitoids suggest magma derivation in an intraplate or primitive island arc tectonic setting, in which the active mechanism of magma derivation was partial melting of a metasomatically enriched lithospheric mantle that was probably fertilized by an intraplate mantle plume. The fertility indicators with PIZ are grouped with respect to the distribution pattern of normalized REEs, as they exhibit low LREE and enriched HREE, large + Ce, and small -Eu anomalies. The hypogene alteration zones have developed on a regular basis, the potassic alteration zone being close to the central zone around Kuthori in the north Karbi Hills. Although the hosts demonstrate expansion and development of the hypogene alteration zones, the zircons from the mineralized granitoids of Kuthori central zone and granitoids of the nearby Panbari–Dallamara shear zone have similar REE pattern. The target zone's zircon has higher values of ΣHREE, U, Th, Y, Nb, and Hf. The admissible range of fertile PCD is matched by the cross plots of critical element ratios, demonstrating high calculated Ti in zircon temperature (up to 828 °C). [ABSTRACT FROM AUTHOR]

The Gulf of Suez is a continental rift basin that has been developed during the Oligocene-Miocene as a northern extension of the Red Sea rift system. The Oligo-Miocene rift-activated flanks are represented by exposures of the Neoproterozoic basement rocks of the Arabian-Nubian Shield. An additional thermal overprint (i.e. mantle plume) and the preceding tectono-thermal events that also affected the rifting dynamics and the uplift of its flanks remain uncertain. We here present thermochronological data for 20 basement samples collected from the Gabal Somr ElQaa area at the northwestern flank of the Gulf of Suez. The resulted zircon fission-track ages could be divided temporospatially into two groups: the Cambrian and the Silurian-Devonian with average ages of 503 ± 14 Ma and 407 ± 11 Ma, respectively. While apatite fission-track data reveal three different age groups of the Devonian-Carboniferous, the Permian-Triassic, and the Late Cretaceous, with average ages of 349 ± 10 Ma, 246 ± 6 Ma, and 81 ± 5 Ma, respectively. The modelled t-T histories indicate four cooling pulses during the Neoproterozoic, the Devonian-Carboniferous, the Cretaceous, and the Oligocene-Miocene. Integrating our findings with the regional tectonism and depositional records indicates that these cooling pulses could be attributed to synchronous activities of the post-accretion erosional event, the Variscan tectonic event, the Mid-Atlantic Ridge spreading, and the Gulf of Suez rifting. The Gulf of Suez is a passive rift, formed by a single and rapid rifting pulse within the framework of the Red Sea rift system. An additional east-southward far-field thermal overprint from the Arabian marginal plume partially affected the Suez rifting process. This thermal print affected only the rift’s southern portion of its eastern flank, causing syn-rift cooling ages, highly elevated rift flanks, and an increased heat flow. The western rift flank and the northern segment of the eastern flank are characterized by pre-rift cooling ages, modest rift flanks, and reduction in heat flow. [ABSTRACT FROM AUTHOR]

U–Pb dating of zircon via laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) has become a primary method for determining the age of crystalline rocks and the provenance and maximum depositional age of (meta)sedimentary rocks. Although chemical abrasion has become a standard approach for mitigating Pb loss in zircon dated via high‐resolution thermal ionization mass spectrometry (CA‐TIMS), laser ablation dating is rarely accompanied by chemical abrasion. We evaluate the accuracy of U–Pb dates acquired via LA‐ICP‐MS relative to CA‐TIMS through analysis of a large database of paired analyses from the same zircon crystals. We show that laser ablation 206Pb/238U dates are systematically younger than their CA‐TIMS counterparts, with a greater shift in detrital zircon (−2.0%) versus igneous or metamorphic zircon (−0.9%). Although systematic biases related to “matrix effects” may be a contributing factor, our analysis suggests that unmitigated cryptic Pb loss is likely widespread in laser ablation U–Pb datasets. [ABSTRACT FROM AUTHOR]

Ultrahigh‐temperature (UHT; >900°C) metamorphism drives crustal differentiation and is widely recognized in the rock record, but its geodynamic causes are debated. Previous work on granulite‐facies metapelite xenoliths from San Luis Potosí, Mexico suggests the lower crust experienced a protracted UHT metamorphic event that coincided with the onset of regional extension. To determine the duration, conditions, and heat sources of UHT metamorphism recorded by these xenoliths, this study characterizes the major‐element, trace‐element, and U‐Pb isotopic systematics of quartz, rutile, feldspar, garnet, and zircon by in situ electron microprobe (EPMA) and laser‐ablation inductively coupled‐plasma mass spectrometry (LA‐ICP‐MS), and augments these data with detailed petrography, thermobarometry, phase equilibria modeling, and diffusion modeling. Thermobarometry and phase equilibria modeling suggest peak metamorphic conditions exceeded 0.7 GPa and 900°C. Zircon petrochronology confirms >15 Myr of UHT conditions since its onset at ∼30 Ma. A small population of zircon record elevated temperatures following transition from backarc compression to extension during the waning stages of orogenesis (60–37 Ma). Garnet preserves trace‐element zoning and mineral inclusions consistent with suprasolidus garnet growth and subsequent compositional modification by intracrystalline rare‐earth element diffusion during protracted heating, with diffusion chronometry timescales in agreement with zircon data, followed by fluid‐driven remobilization of trace elements along now‐healed fractures within ∼1 Myr of eruption. In sum, these data are most compatible with lithospheric mantle attenuation or removal as the dominant heat transport mechanism driving synextensional UHT metamorphism and crustal melting, which has bearing on models for crustal differentiation and formation of modern and ancient granulite terranes globally. Plain Language Summary: The production of melt in the deep crust has important implications for how continents are physically and chemically modified, which in turn controls the distribution of critical mineral resources and the expression of plate tectonics at Earth's surface. One setting where significant partial melting can occur is in a high‐temperature granulite terrane, such as the lower crust beneath the Basin and Range province of southwestern North America. The Basin and Range province is a region where the continent is actively experiencing tectonic extension and, in several places, has been interpreted to have lower crust that was (or is currently) heated to above 900°C. To understand the causality between continental extension in North America and these extreme metamorphic conditions, we study exotic rock fragments of the deep crust beneath San Luis Potosí, Mexico that were brought up by a geologically recent volcanic eruption. These rocks record chemical information that tracks the temperature of the geologically modern lower crust prior to eruption and the duration of extreme temperatures and melting in this crust over the last 60 million years. Using this chemical information, we further our understanding of how tectonic extension is actively driving deep crustal melting beneath southwestern North America. Key Points: Lower crustal metapelite xenoliths from San Luis Potosi, Mexico record ultrahigh (>900°C) temperature (UHT) metamorphismZircon petrochronology suggests protracted (>15 Myr) UHT conditions since the onset of regional extensionGarnet preserves complex trace‐element zoning despite extreme temperatures; garnet diffusion chronometry timescales agree with zircon data [ABSTRACT FROM AUTHOR]

This study presents U-Pb age data obtained using an in situ LA-ICP-MS technique applied to wolframite samples from Polski Gradets (Bulgaria) and Barruecopardo (Spain). Analytical conditions were optimized using YGX2113 (wolframite) and GJ1 (zircon) natural standard reference materials (SRMs). Applying both SRMs, very similar U-Pb age results were obtained. Furthermore, the results were within the reported age error range of the host granites and granodiorites. The tungsten mineralization at Barruecopardo was dated at 315.2±5.3 Ma, while for Polski Gradets wolframite, an age of 79.0±6.8 Ma was obtained. The applied technique is assessed as applicable and suitable for further direct dating of tungsten deposits. [ABSTRACT FROM AUTHOR]

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The first U-Pb isotope-geochronological data were obtained on the age of early collisional granitoids of the Matut massif (Western Sangilen, SE Tuva). The rocks that have been studied are assigned to magnesian, calc-alkaline, high-potassium, and low-peraluminious varieties. LA-ICP-MS analysis on two zircon samples showed that the Matut granite massif formation age corresponds to 522 Ma (U/Pb, LA-ICP-MS, zircons, 520±3 Ma (sample KT-1070) and 524±3 Ma (sample KT-1324)). Thus, the Matut massif granitoids are among the most ancient in Western Sangilen and were formed at the early collisional stage of the structural evolution of the region. Based on the data obtained, an assessment was made of the duration of collisional orogeny on the northwestern margin of the Tuva-Mongolian massif. The initiation to collapse period of the orogen is at least 80 million years.

Simultaneous U–Pb and U–Th dating using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was performed on the ca. 0.1 Ma Toya tephra and the ca. 0.08 Ma SS14-28 U–Th zircon reference material. In U–Pb dating, both Th/U and Pa/U partitioning between magma and minerals were considered. In U–Th dating, both abundance sensitivity and molecular interferences on 230Th were reevaluated. As a result, the Toya tephra yielded an accurate weighted mean U–Pb age of 0.103 ± 0.029 Ma (2σ) using zircon and monazite. Conversely, the SS14-28 zircon yielded an inaccurate U–Pb age (0.25 ± 0.10 Ma), which was attributed to low 206Pb signal intensity. Both the Toya tephra zircon and the SS14-28 zircon yielded accurate U–Th model ages of 0.108 ± 0.014 Ma and 0.078 ± 0.007 Ma, respectively. The agreement of U–Pb and U–Th ages for Toya indicates that simultaneous U–Pb and U–Th dating is possible and viable. The inappropriate age of SS14-28 U–Pb age and appropriate U–Th model age also indicates it is preferable to apply both U–Pb and U–Th dating simultaneously for young (<0.4 Ma) zircons to check internal consistency. The proposed double dating approach may be especially useful for small grains when it otherwise would be impossible to obtain multiple ages from a single grain. By adopting simultaneous U–Pb and U–Th dating using LA-ICP-MS, zircon crystallization ages as old as 4.5 Ga to as young as 0.1 Ma (or even younger) can be obtained in a quick and cost-effective manner with a reasonable (~5% at 1σ) uncertainty. [ABSTRACT FROM AUTHOR]

We characterise zircon megacrysts from the Kawisigamuwa carbonatite as a new potential reference material for laser ablation‐inductively coupled plasma‐mass spectrometry U‐Pb and Hf isotope measurement. We studied ten 0.5–4 cm long, brown megacrysts that consist of oscillatory zoned (OZ) and nearly featureless cathodoluminescence‐bright recrystallised (RX) zircon domains. The zircons have low to moderate radiation damage (total α‐dose < 0.5 x 1018 events g‐1), tested by the measured FWHM of the ν3 (SiO4) Raman band < 5 cm‐1. An ID‐TIMS weighted mean 206Pb/238U age of 532.39 ± 0.66 Ma (2s uncertainty) was determined for OZ zircon domains of three grains. While hafnium content varies within and between crystals (6630–9960 μg g‐1) the in situ mean 176Hf/177Hf ratios of ten crystals overlap within uncertainty. We recommend a mean 176Hf/177Hf ratio of 0.282003 ± 0.000020 (2s) as preliminary working value for OZ domains. Two OZ megacrysts yield indistinguishable δ18OVSMOW of 12.1 ± 0.4‰ and 12.2 ± 0.4‰ (2s). Elevated Th/U (> 1.5), Zr/Hf (59–75) and low hafnium contents in OZ domains are similar to those of zircons from carbonatites of mantle origin, while high δ18O and low εHfi (‐15.8 to ‐17.1) indicate a crustal contribution. The zircons probably grew from crustal‐derived carbonate melts under high grade metamorphic conditions. [ABSTRACT FROM AUTHOR]

In the Chemnitz Basin (Saxony, central Germany), up to 1,500 m thick early Permian sediments with intercalated, predominantly acidic pyroclastics were deposited. Numerous fossil records allow a biostratigraphic correlation of the strata with other early Permian successions of the middle Variscides. Significant floral and faunal elements were found in the Planitz Formation of the Chemnitz Basin, which is bounded at the base by the Grüna Tuff and at the top by the Planitz Ignimbrite. Radioisotopic data are only available for the Planitz Ignimbrite, but they contradict biostratigraphic data. Based on LA-ICP-MS measurements, new U-Pb zircon ages are determined for the Planitz Ignimbrite and, for the first time, also U-Pb zircon ages for the Grüna Tuff. The challenge of deriving an extrusion age for both the Planitz Ignimbrite and Grüna Tuff from these data is discussed. [ABSTRACT FROM AUTHOR]

The emergence of the Tibetan Plateau is one of the most significant geological events in East Asia. The Central Qilian Shan connects North and South Qilian Shan in the northeastern part of the Tibetan Plateau. However, the exhumation history of the Central Qilian Block from the Mesozoic to Cenozoic remains unclear. Determining the cooling ages of detrital zircon and apatite in modern river sediments is an ideal method for tracing the evolutionary processes of orogenic belts. In this study, we present the first single-grain detrital apatite (153) and zircon fission-track (108) data for the Huangshui River sediments from the Central Qilian Shan. The decomposition of the dataset revealed major Mesozoic and Cenozoic age peaks at ca. 145–93, and 11 Ma. The Central Qilian Shan entered the intracontinental orogeny stage dating back to the Cretaceous (ca. 145–93 Ma) and Late Cenozoic (ca. 11 Ma) caused by the subduction of the Neo-Tethys and Indian–Asian collision. Therefore, we propose that the geomorphic framework of the northeastern margin of the Tibetan Plateau was initially established during the Mesozoic and further consolidated in the Late Miocene. [ABSTRACT FROM AUTHOR]

The in situ (U‐Th‐Sm)/He and U/Pb laser‐ablation double‐dating procedure is a valuable method that can provide a large dataset relatively efficiently in contrast with conventional bulk helium thermochronometry. In this study, we evaluate the potential age error associated with the double ablation procedure and report the in situ (U‐Th‐Sm)/He double‐ablation dating of 249 zircons from the Fish Canyon Tuff locality. With LA‐ICP‐MS pseudo‐depth profiling and 3D numerical modelling, we show that the concentric double‐ablation procedure in minerals with U‐Th‐Sm zoning can generate a significant (U‐Th‐Sm)/He age error (positive or negative), resulting in over‐scattering and/or an offset of the mean age. Pseudo‐depth profiling is insufficient to predict the individual age error, partly because of the superimposed ablations. To evaluate the consequence of this inherent bias, we confront a synthetic age distribution to the error expected for U‐Th‐Sm zoned zircons analysed with double‐ablation (U‐Th‐Sm)/He thermochronometry. As expected, a strong age bias causes the spreading of peak ages, downgrading the original signal. Yet, the throughput of the ablation‐based method can allow intra‐ and inter‐sample peak age identification and comparison, and the coupling of (U‐Th‐Sm)/He and U/Pb ages extends our ability to deconvolute a multimodal age spectrum. [ABSTRACT FROM AUTHOR]

By using the newly introduced GeoLas HD 193 nm ArF excimer laser ablation system and the Agilent 7900 quadrupole inductively coupled plasma mass spectrometer (ICP-MS) in the Key Laboratory of Paleomagnetism and Tectonic Reconstruction at the Institute of Geomechanics, we successfully established the in-situ zircon U-Pb dating method and trace element analytical method by LA-ICP-MS. U-Pb dating experiments were carried out on Plešovice, Temora1 and Qinghu zircons under the experimental conditions of 32 μm beam spot diameter, 5.0 J/cm2 energy density and 5 Hz denudation frequency using the standard zircon 91500 as the external standard. The ideal age results are consistent with their recommended values, and the measured U-Pb ages for Plešovice zircon remain stable in different periods. Meanwhile, a comparative study of the U-Pb dating results in different laboratories was carried out on an unknown sample 11-5, and the dating results are consistent with that obtained in the State Key Laboratory of Geological Processes and Mineral Resources at China University of Geosciences (Wuhan) within analytical error. Trace elements in zircon standard 91500 and glass standard NIST SRM 612 were analyzed by using NIST SRM 610 as an external standard and 29Si as an internal standard, and the measured values are consistent with the recommended values of trace element contents. In addition, the influence of different beam spot diameters on the zircon U-Pb age results was explored by using the Plešovice zircon as an example. The results show that a denudation diameter of 16~44 μm can obtain reliable zircon U-Pb ages similar to the recommended age, and under the same energy density and denudation frequency conditions, U-Pb ages obtained by using 32~44 μm beam spot diameters are more accurate than those obtained by 16~24 μm beam spot diameters.

The Ojén nappe, an allochthonous unit that underlies the Ronda peridotites (Betic Cordilleras), is composed of Triassic marbles overlying a metapelitic sequence. In order to carry out an LA-ICP-MS U-Pb age determination and provenance analysis, detrital zircon grains from two quartzites interlayered within marbles and metapelites were extracted. The obtained results yield the youngest zircon population of 254 ± 3 Ma (Late Permian) with a mean Th/U ratio of 0.34 that supports both the Permian–Triassic age of the marble member and the felsic magma nature for zircon-bearing protoliths. The Permian zircons exhibit tight age peaks in three main populations of 292 ± 2 Ma, 278 ± 3 Ma, and 254 ± 3 Ma, in agreement with the main age populations reported from rhyolites and shallow crustal basaltic–andesite subalkaline rocks emplaced in transtensional Permian basins of the Variscan Orogen during the break-up of Pangea. Moreover, the analyzed detrital zircon grains yield age distributions with clear Tonian–Stenian (ca. 950–975 Ma), Ediacaran–Cryogenian (ca. 560–615 Ma), Ordovician (ca. 460–465 Ma), and Cisuralian peaks (ca. 280–290 Ma) and smoothed Mesoproterozoic peaks that point to a weak and residual Cadomian peri-Gondwanan terrane inheritance. The identified Middle Ordovician detrital zircon populations (460–465 Ma) strengthen the hypothesis that the Alborán domain would be located along the southern passive margin of the European Hunic superterrane. [ABSTRACT FROM AUTHOR]

In situ238U‐230Th dating was conducted using an ICP‐mass spectrometer coupled with a laser ablation sampling system (LA‐ICP‐MS). To minimise the contribution of mass spectrometric interferences on 230Th, a kinetic energy discrimination technique using a collision/reaction cell (CRC) system was employed. The major problem associated with the CRC‐ICP‐MS system is the lower transmission efficiencies of ions than sector field mass spectrometers. To improve the signal‐to‐background ratio for analytes, a combination of a multiple‐spot laser ablation (msLA) system together with a sensitivity‐enhanced dry plasma cone was employed. Analytical accuracy was evaluated through analyses of three zircon reference materials (GJ‐1, OD‐3 and Plešovice) and the resulting 230Th/238U ratios for GJ‐1 and Plešovice zircons agreed with the secular equilibrium value. The developed technique was applied to Quaternary volcanic zircon and monazite samples from Japan. The resulting ages are 113.5 +5.4‐5.2 ka for the Toya tephra, 105.1 +6.4‐6.1 ka for the Sambe Kisuki tephra, 55.2 +7.7‐7.2 ka for the Hikageyama lava and 16.2 +4.2‐4.1 ka for the Susaki pumice (95% confidence levels). The resulting ages are consistent with previous chronological constraints including zircon fission track ages. The data obtained here demonstrate clearly that the combination of the CRC‐ICP‐MS system and the msLA protocol can become a powerful analytical tool for in situ U‐Th disequilibrium dating. [ABSTRACT FROM AUTHOR]

Rondônia intrusive suites represent the youngest A-type magmatism that occurred in the SW of the Amazon craton, with mineralizations in Sn, Nb, Ta, W, and topaz. Petrological and isotopic studies (U-Pb and Lu-Hf by LA-ICP-MS) allowed the Massangana granite to be subdivided into São Domingos facies (medium to fine biotite-granite), Bom Jardim facies (fine granite), Massangana facies (pyterlites and coarse granites) and Taboca facies (fine granites). The crystallization ages obtained were between 995.7 ± 9.5 Ma to 1026 ± 16 Ma, and the εHf values vary significantly between positive and negative, showing predominantly crustal sources for forming these rocks. Petrographic studies on ore samples indicate the action of co-magmatic hydrothermal fluids enriched in CO2, H2O, and F. These ores are characterized by endogreisens, exogreisens, pegmatites, and quartz veins that are explored in the São Domingos facies area. The endogreisens and exogreisens are formed by topaz-granites and zinnwaldite-granites; the pegmatites are formed by topaz-zinnwaldite-cassiterite-granites; and the veins by cassiterite-sulfides and quartz. The geometries of the mineralized bodies indicate a dome-shaped contact with the host rocks in the magma chamber and can be attributed to residual accumulation. In this sense, the origin of these ores is related to the evolution of intrusive granitic bodies where the terminal phases of the fluid-enriched magma are lodged in the apical portions, and the origin of the mineralized bodies present a biotite-granite, albite-granite, and endogreisens evolution (potassium series), or biotite-granite, alkali-granite and endogreisens (sodic series) and these rocks present TDM ages that indicate a concerning relation to the non-mineralized rocks of Massangana granite. [ABSTRACT FROM AUTHOR]

Inter‐session excess variance of U/Pb and Pb/Pb ratios in LA‐ICP‐MS zircon dating is the largest contributor to systematic errors, which in turn limit the accuracy of age determinations. Quantifying long‐term excess variance of reference materials allows for the estimation of excess variance in samples, but such compilations are not available in the literature. Here, we present the results of over 100 measurement sessions over 6 years for seven common zircon reference materials and calculate a characteristic excess variance for each. For 206Pb/238U ages, these values (2s) are as follows: AusZ7‐1 = 1.7% (115 sessions), AusZ7‐5 = 0% (74), OD‐3 = 0.6% (19), Temora2 = 1.2% (86), Plešovice = 1.1% (100), 91500 = 1.0% (146) and Mud Tank = 3.0% (12). For 207Pb/206Pb ages, smaller excess variances are observed: Temora2 = 0.3%, Plešovice = 0.4%, Mud Tank = 1.7% and 91500 = 0.4%. These values are well‐constrained estimates of inter‐session excess variance for the ETH Zürich LA‐ICP‐MS laboratory using a sector‐field ICP‐MS, and may provide either a first‐order estimate for other laboratories or a value to compare against their own reference material compilations. [ABSTRACT FROM AUTHOR]

The Paleocene‐early Eocene continental magmatic arc (PECMA) in the Northern Andes is an example of arc magmatism following a major collisional event. This arc formed after the arc‐continent collision between the Caribbean Plate and the South American continental margin at ca. 72 Ma. We used detrital zircon LA‐ICP‐MS and CA‐ID‐TIMS geochronology and geochemistry to complement the limited plutonic record of the PECMA and better characterize the PECMA's magmatic evolution. Zircon geochronology and their respective trace element geochemistry were analyzed from Paleocene‐early Eocene strata of the Bogotá Formation in the foreland region. Our results show that after the collision of the Caribbean Plate, the magmas in the PECMA differentiated under a thick continental crust with limited subduction input at ca. 66 Ma. By 62–50 Ma, scattered patterns of Hf, U, U/Yb, and Yb/Gd ratios in detrital zircons suggest the existence of contrasting magmatic inputs attributed to different depths of crustal fractionation, varied temperatures of crystallization, and significant mantle and subduction inputs. These diverse magmatic patterns reflect the evolution of the continental crust. We proposed that oblique convergence and strike‐slip tectonics favored contrasting crustal architectures along the continental margin while local lithosphere dripping from a previously thickened crust promoted the formation of hot magmas under a thick continental crust. Key Points: Detrital zircon geochemistry was used to better refine the post‐collisional Paleocene to Eocene tectono‐magmatic evolution of the Northern AndesThe Paleocene‐early Eocene detrital zircons crystallized in contrasting magmatic conditions and under varying crustal thicknessesStrike‐slip tectonics, crustal dripping, and a previously thickened continental crust can explain the observed diverse magmatic trends [ABSTRACT FROM AUTHOR]

Copyright of Journal of Geomechanics is the property of Journal of Geomechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This contribution provides in-situ LA-ICP-MS U-Pb ages and trace element determinations of zircons from dacitic to rhyolitic lavas, ignimbrites and intrusions in the Southern Rocky Mountain Volcanic Field (SRMVF) in Colorado, USA. The data record a period of intense magmatic activity in the Oligocene-early Miocene (∼37–22 Ma) which gave rise to some of the largest explosive ignimbrites in the geological record (e.g. the Fish Canyon Tuff). Age data are drift corrected, but not corrected for radiation dosage or Th disequilibrium, in order to allow users to apply their own algorithms. Xenocrysts (much older crystals up to 2 Ga from the Proterozoic basement) are included in this record.

Understanding the formation of the North Qilian Shan in the NE Tibetan Plateau provides insights into the growth mechanisms of the northern region of the plateau across time. Detrital zircon fission-track (ZFT) analyses of river sediments can provide a comprehensive understanding of the exhumation history during prolonged orogenesis. Here, we applied the detrital thermochronology approach to the Qilian Shan orogenic belt. This work presents the first single-grain detrital ZFT data from river-bed sediments of the upper Hei River catchment in North Qilian Shan. The single ZFT ages are widely distributed between about 1200 Ma and about 40 Ma. These data record the protracted history of the Qilian Shan region from the Neoproterozoic evolution of Rodinia and late Paleozoic amalgamation of Central Asia to the accretion of the Gondwanian blocks during the Meso-Cenozoic era. Strong post-magmatic cooling events occurred in North Qilian Shan at 1200~1000 Ma, corresponding to the assembly of the Rodinia supercontinent. The age population at 800 Ma documents the oceanic spreading in the late Neoproterozoic dismantling of Rodinia. ZFT ages ranging from about 750 Ma to 550 Ma (with age peaks at 723 Ma and 588 Ma) are consistent with the timing of the opening and spreading of the Qilian Ocean. The age peaks at 523 Ma and 450 Ma mark the progressive closure of that ocean ending with the collision of the Qilian block with the Alxa block—North China craton in the Devonian. The Qilian Ocean finally closed in Late Devonian (age peak at 375 Ma). In the late Paleozoic (275 Ma), the subduction of the Paleotethys Ocean led to extensive magmatic activity in the North Qilian Shan. During the Lower Cretaceous (145 Ma), the accretion of the Lhasa block to the south (and potentially the closure of the Mongol-Okhotsk Ocean to the northeast) triggered a renewed tectonic activity in the Qilian Shan. Finally, a poorly defined early Eocene exhumation event (50 Ma) suggests that the NE Tibetan Plateau started to deform nearly synchronously with the onset of the India-Asia collision. This study demonstrates the usefulness of combining modern-river detrital thermo-/geochronological ages and bedrock geochronological ages to understand large-scale orogenic evolution processes. [ABSTRACT FROM AUTHOR]

Changtian Basin is one of significant energy basins in Guangdong Province. To learn the geological structure, sedimentary material characteristics and tracer sandstone provenance in detail, microscopic identification, electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) are used to systematically study the typical sandstones of Nanxiong Group in Changtian Basin on the basis of field geological survey. The results show that the Upper Cretaceous Nanxiong Upper Subgroup is mainly composed of (carbonaceous) lithic quartz sandstone, followed by calcareous sandstone, (argillaceous) siltstone, fine sandstone, conglomerate and greywacke, generally developed with obvious secondary changes and metallization. The analysis of detrital zircons from Nanxiong Group reveals that most of the zircons in the samples have perfect oscillatory bands with Th/U values usually greater than 0.4, indicating the zircons are mainly of magmatic crystallization origin, with a few metamorphic zircons of complex origin. The U-Pb concordant ages can be roughly divided into five groups: 2506-1666 Ma, 1815-941 Ma, 510-434 Ma, 308-234 Ma, and 172-99 Ma, which correspond to the known tectonic events in northeast Guangdong, reflecting that the tectono-magmatic activities in the study area are mainly controlled by the magmatic activities in eastern China, with the characteristics of episodic development and evolution. Based on the systematic analysis of lithography, zircon U-Pb age and REE characteristics of clastic rocks from Nanxiong Group, and comparison with the possible provenance, it is concluded that the detrital materials were mainly derived from Mesozoic magmatic intrusions in the western margin of Changtian Basin. [ABSTRACT FROM AUTHOR]

BACKGROUND: With the development of high-precision negative thermal ionization mass spectrometry (N-TIMS) technology, Re-Os isotopic dating of carbonaceous mudstone is more and more widely used in the determination of sedimentary age. The controversy over the diagenetic and metallogenic ages of the Dabaoshan copper deposit in Guangdong Province has always been a key restricting the study of the genetic mechanism. OBJECTIVES: To constrain the diagenetic and metallogenic ages of the Dabaoshan copper deposit. METHODS: Re-Os isotope ratios were determined by high precision N-TIMS after dissolving carbonaceous mudstone powder by reverse aqua regia in the Carius tube. Zircon U-Pb age was determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). RESULTS: (1) The contents of Re and Os ranged from 0.976×10-9 to 2.997×10-9 and 0.067×10-9 to 0.115×10-9, respectively. The 187Re/188Os ratio varied from 78.236 to 154.799, and the 187Os/188Os ratio varied from 1.642 to 1.885. The Re-Os isotopic isochron age of black carbonaceous mudstone was 195±28 Ma (n=6, MSWD=17). (2) The 206Pb/238U age ranged from 2631 to 236 Ma, including two Mesozoic zircons, accounting for 2.50% of the total zircons, 19 Paleozoic zircons, accounting for 23.8% of the total zircons, 58 proterozoic zircons, accounting for 73% of the total zircons, 1 Archean zircon, accounting for 1% of the total zircons. The results of detrital zircon U-Pb age were broad and developed multiple peak periods, among which the youngest source magmatic zircon was formed in the Indosinian period. CONCLUSIONS: The diagenetic and metallogenic age of the Dabaoshan copper deposit in Guangdong Province was constrained to the early Yanshanian. The distribution characteristics of detrital zircon U-Pb age further indicate that the Lower Jurassic Jinji Formation was formed at the stable continental margin, and its detrital material comes mainly from the ancient continental basement. [ABSTRACT FROM AUTHOR]

Based on the LA-ICP-MS U-Pb zircon ages of four metamorphic samples, we discuss the geochronology and provenance of the Guadaiza nappe, an allochthonous unit that underlies the Ronda peridotites (Betic Cordilleras, Spain). The Guadaiza nappe is composed of Triassic marbles overlying a metapelitic sequence with schists and migmatites. Zircons from a quartzite interlayered with the marbles yield a maximum depositional age of ca. 289 Ma that supports the Triassic age. The idiomorphic morphology of these Paleozoic zircon crystals and the lack of late-Variscan metamorphism (ca. 300 Ma) supports a proximal source area, and suggests that the marbles were discordantly deposited over the metapelitic sequence, along the northern margin of the Alboran microplate. The zircon patterns from the metapelitic sequence mainly yield Paleoproterozoic (ca. 1.6–2.5 Ga), Tonian–Stenian (ca. 1000 Ma), Ediacaran–Cryogenian (ca. 600 Ma) and Paleozoic (ca. 500 Ma) age clusters. These results suggest provenance from areas within the triangle bound by the West African Craton, the Metasaharan Craton and the Hun Superterrane during the Paleotethys opening (Silurian–Devonian). A Silurian–Carboniferous deposition age for the schist protoliths is constrained by the youngest detrital zircon population (ca. 443 Ma) and the Variscan age of their migmatization by an additional peak of around 299 Ma in the migmatites. [ABSTRACT FROM AUTHOR]

U‐Th disequilibrium dating uses the ratio of the intermediate 230Th daughter isotope to the 238U parent isotope to date zircon crystallisation for volcanic and plutonic rocks in Pleistocene–Holocene deposits. It is frequently used to constrain the duration and rate of magma recharge in volcanic systems. While ≲ 350 ka zircon is not in secular equilibrium in the 230Th system, the current U‐Th disequilibrium methodology uses reference materials that are > 350 ka. No reference material ≲ 350 ka has been available to validate the accuracy of the approach and ensure methods are repeatable across laboratories. This study presents zircon SS14‐28 from Jeju Island (South Korea) as a suitable reference material for U‐Th disequilibrium dating. Zircon SS14‐28 was analysed using two analytical approaches (SIMS and LA‐ICP‐MS) and four instruments: CAMECA IMS 1280, ASI SHRIMP II, sector field high‐resolution LA‐ICP‐MS and multi‐collector LA‐ICP‐MS, in four laboratories. These methods each individually result in isochrons gradients within uncertainty (2s) of each other (CAMECA: 0.532 ± 0.051 (MSWD = 0.64); SF‐HR‐LA‐ICP‐MS: 0.536 ± 0.054 (MSWD = 1.3); MC‐LA‐ICP‐MS: 0.533 ± 0.041 (MSWD = 0.67); SHRIMP II: 0.68 ± 0.22 (MSWD = 0.3)). The age proposed in this study is 82 ± 6 ka calculated from a combined isochron gradient of 0.529 ± 0.025 (MSWD = 0.87, n = 132). [ABSTRACT FROM AUTHOR]

The Neoproterozoic quartz potassic syenite of the Iwo area, Southwestern Nigeria has been investigated for its magmatic history and zircon saturation temperature. The zircon morphology showed irregular shapes with sectoral and oscillatory micro zoning. The majority of the zircon grains have embayment, which corresponds to magmatic resorption. The syenite crystallized from probably multiple recharge of less evolved magma. Both the magma injection and subsequent crystallization of the rock occurred over a length of time giving the rock some degree of protracted thermal history and slight fluctuation in chemistry, which are manifested as zonation in the analyzed zircon grains. The initial stage of zircon crystallization was marked by a lower cerium anomaly than the final stage, which indicates changes from lower oxidizing to higher oxidizing conditions. The protracted history does not affect the europium anomalies at any stage of crystallization. An average zircon saturation temperature of 865 °C estimated from titanium in zircon (TTiz °C) thermometer using titanium activity of 0.7 (aTiO2 ~ 0.7) is taken as reasonable crystallization temperature of the rock. This is fairly consistent with 877 °C deduced from the zircon solubility model. The titanium in zircon temperature of 910 °C at aTiO2 ~ 1 is rather too high to be a useful estimate. Both the temperatures 865 and 877 °C are however consistent with those of intermediate rocks. The size of the syenite and protracted crystallization history would have made the temperature to have impacted the metamorphic envelope around the syenite. [ABSTRACT FROM AUTHOR]

The Nemuro and Saroma Groups and Yusenkyo Formation occur in eastern Hokkaido and are considered to be forearc or intra‐arc basin sediments of the Paleo‐Kuril arc (PKA) deposited during the Late Cretaceous to middle Eocene. To further clarify the origin of the PKA, we examined the U–Pb ages of detrital zircons within these sandstones and acidic tuff beds; based on our results, we drew the following conclusions. (1) The PKA originated from an oceanic island arc on the oceanic Izanagi Plate around 85 Ma, to which the Nikoro Group greenstone complex was accreted between 81–80 Ma; the Lowest Unit of the Saroma Group covered the surface of the Nikoro accretional greenstone complex. (2) The PKA then first collided with NE Asia around the beginning of the deposition of the Hamanaka Formation (~70 Ma) and transitioned to a continental arc adjacent to NE Asia. This collision generated giant slump beds during deposition of the Akkeshi Formation. During deposition of the Kiritappu Formation, the entire Nemuro Peninsula was uplifted, supplying large volumes of clastic sediments. (3) Although we do not have data directly bearing on why the North American Plate was established in the edge of NE Asia, we speculate that it separated from the Eurasian continent around ~70 Ma when NE Asia first collided with the PKA. Subsequently, the PKA has behaved as part of the North American Plate. The Paleo‐Japan arc (or East Sikhote–Alin arc) and the PKA became joined via the Hidaka Belt. Around 40 Ma, during the deposition of coarse conglomerate beds of the Urahoro Group, the PKA was uplifted and bent clockwise due to a second collision with NE Asia. (4) The modern Kuril arc was established around 36 Ma (late Eocene–early Oligocene), and the Kuril backarc basin opened into the present tectonic setting in the late Oligocene–early Miocene. [ABSTRACT FROM AUTHOR]

Zircon is one of the most important minerals in geochronologic research. Isotopic ratios and trace elements in zircons are expected to reflect those of their parent magmas. Many geochemical researchers have proposed various discrimination diagrams for zircon to indicate tectonic setting and to identify source rock. Because most detrital zircons accumulated at river mouths are derived primarily from granitoids, the classification of zircon within granitoids is potentially meaningful. In our research, we focused on sediment involvement during granitoid formation and tried to identify trace‐element compositions in zircon that are sensitive to variation in sediment incorporation. To accomplish this, we examined trace‐element compositions of both the granitoids and the included zircons in the Kofu granitic complex and the Tanzawa tonalitic plutons in Japan. Among the high‐field‐strength elements (Th, U, Ta, Nb, Hf, and rare earth elements), only Nb and Ta concentrations in the granitoids increased as the rate of sediment contribution increased. However, the zircon did not show such trends in Nb and Ta content. Zircon Y and P contents exhibited a positive correlation, indicating that xenotime substitution occurs to some extent. Because P exists as pentavalent ions in igneous systems, its presence likely affects the concentrations of pentads in zircon. When we divided the Nb and Ta contents by the P content, it became clear that zircon Nb/P and Ta/P ratios increase depending on sediment involvement. While some exceptions exist, we found that zircon Yb/Gd ratios also respond to sediment involvement. Our data further demonstrated that zircons in granitoids with significant sediment incorporation are characterized by low Ce/P contents, which is partly attributable to monazite crystallization before zircon saturation. This study demonstrates that combining these element ratios is useful for indicating sediment incorporation. [ABSTRACT FROM AUTHOR]

Eclogites hosted in sillimanite‐bearing migmatites in the Montagne Noire dome (French Massif Central) have an oceanic protolith and recorded a prograde P–T path from ~19.5 kbar, 700°C to the pressure peak at ~21 kbar, 750°C (pseudosection modelling), suggesting metamorphism in a subduction setting. Subsequent exhumation to low‐P high‐T (LP–HT) conditions (~6 kbar, 730°C) is constrained by the equilibration conditions of the embedding migmatite. In samples of a fresh and a retrogressed eclogite, all zircon crystals but one display similar REE patterns (no Eu anomaly, flat HREE), usually ascribed to crystallization under eclogite‐facies conditions. Yet, the U–Pb apparent ages of zircon crystals from both eclogites spread from c. 360 Ma to a dominant data cluster at c. 315 Ma. The c. 315–310 Ma zircon U–Pb dates obtained from the embedding migmatite are interpreted as the age of crystallization of the partial melt during the LP–HT metamorphic stage. First‐order geological evidence, in particular the sedimentary record, excludes the existence of a subduction zone in the region at this period. Unless calling upon a major reappraisal of the tectonics of the European Variscan orogen, this suggests an ambiguous relation between REE patterns and U–Pb dates in the zircon population. Various scenarios that could account for the observations are discussed. Combining our data with the results of a previously published Sm–Nd dating of garnet, and regional considerations, we consider that 360 Ma is the best approximation of the minimum age of the eclogite‐facies event. We hypothesize that the eclogites formed farther north and were transferred to their present location by lower‐crustal flow. It is inferred that during the subsequent exhumation, eclogite‐facies zircon grains recrystallized and underwent partial to total resetting of their U–Pb system, whereas the REE system remained mostly unmodified. These results caution against the use of REE patterns as the only criterion to associate a specific zircon age with HP metamorphism in eclogites occurring in migmatitic domes. [ABSTRACT FROM AUTHOR]

A large number of intermediate basic volcanic rocks and porphyry Cu-Mo deposits as well as volcanic-hosted magnetite deposit have been recently discovered in the Xilekuduk area. However, no reports concerning petrogenesis and age or their relationship with mineralization have been published to date. The purpose of this study was to make up for the absence of previous studies on Devonian volcanic activities in the area and to confirm the relationship between two stages of volcanic activities and mineralization so as to provide important theoretical basis for mineral exploration. Based on research results of zircon U-Pb geochronology and element geochemistry of volcanic rocks in the area, the ages of dacite, andesite, and stomatal andesite are considered as 375.2 ± 2.9 Ma, 386.5 ± 3.0 Ma, and 317.9 ± 2.9 Ma, respectively, corresponding to the Middle Devonian and Late Carboniferous Period. The Devonian volcanic rocks belong to the high-K calc-alkaline series and island arc volcanic rocks, which are enriched in LREE, strongly enriched in large ion lithophile elements Th, Rb, Ba, and K and relatively depleted in high-field strength elements (HFSEs) Nb, Ta, and Ti. The Carboniferous volcanic rocks are enriched in LREE, as well as the large ion lithophile elements Th, Rb, Ba, and K are strongly enriched, while depleted in the HFSEs Nb, Ta, and Ti; moreover, the contents of TiO2 and V are 0.94–0.97% and 178–183×10–6, which are higher than those of island arc basalts. According to mineralogical typomorphic characteristics and geochemical analysis, magnetite mineralization is divided into two phases. The early stratiform magnetite ore MT1 has magmatic characteristics, forming a volcanic rock type magnetite deposit related to Devonian volcanic eruption and sedimentation (375–386 Ma). The magnetite MT2 in the magnetite-quartz vein is considered as hydrothermal genesis, which is a metal mineral in the early metallogenic stage of Carboniferous (317.1 ± 2.9 Ma) volcanic eruption and subvolcanism, and may be related to porphyry molybdenum mineralization. Therefore, the volcanism and Fe-Cu-Mo mineralization in this area is characterized by multistage superimposed mineralization.

Zircon U–Pb geochronology was carried out on plutonic rocks from Phnom Daek, Phnom Koy Rmeas, Svay Chras, Kon Mom, Koh Nheak, Andong Meas, Oyadav South, Svay Leu, and Phnom Soporkaley. The zircon U–Pb ages from the plutonic rocks determined in this study can be roughly divided into two groups. One is the Late Permian to Triassic ages of 278–202 Ma for the Phnom Daek, Phnom Koy Rmeas, Oyadav South, Svay Leu, and Phnom Soporkaley, and the other is the early Cretaceous ages of 118–98 Ma for the Svay Chras, Kon Mom, Koh Nheak, and Andong Meas samples. The plutonic rocks from Phnom Daek, Phnom Koy Rmeas, Svay Leu, Oyadav South, and Phnom Soporkaley were likely formed by magmatic activity in the Loei Fold Belt. These plutonic rocks were likely formed in an extensional setting and/or a region where the continental crust was thin. The plutonic rocks of Svay Chras, Kon Mom, Koh Nheak, and Andong Meas were likely formed by magmatic activity in the Dalat-Kratie Fold Belt, related to the NW-directed subduction of the Paleo-Pacific Ocean plate. These plutonic rocks are thought to correspond to the Dinhquan suite in southern Vietnam. The Kon Mom and Koh Nheak plutonic rocks fall within the alkaline series, which suggests that the magma genesis was deep and far from the western Paleo-Pacific Ocean plate. Magmatic activity in the Dalat-Kratie Fold Belt migrated oceanward as a whole during the Cretaceous.

This comment addresses the incorrect treatment and presentation of data from laser ablation ICP-MS U–Pb age determinations of two samples of the Třebíč Pluton. This results in inaccurate ages and error assessment, invalidating the age interpretations of the authors. To corroborate our arguments, new high-precision chemical abrasion ID-TIMS data are presented that unequivocally define the emplacement age of the Třebíč pluton. [ABSTRACT FROM AUTHOR]

New re-evaluation of our U–Pb LA-ICP-MS data for strongly porphyritic melagranite 1322 from Petráveč (NE part of the Variscan ultrapotassic Třebíč Pluton, Moldanubian Zone of the Bohemian Massif) gives a weighted mean 207Pb/235U age of 335 ± 3 Ma (2σ). This, together with our previous U–Pb LA-ICP-MS zircon age of 335 ± 3 Ma and CA-ID-TIMS zircon age of 335.127 ± 0.11 Ma newly acquired by Schaltegger et al. from the central part of the Třebíč body pin-point its emplacement age to 335 Ma. Importantly, this datum constrains the oblique underthrusting of Brunia microcontinent, subvertical shortening and development of flat fabric in the Moldanubian Zone. Precise timing of the other Moldanubian durbachitic intrusions remains open to discussion. [ABSTRACT FROM AUTHOR]

In both nature and synthetic experiments, the common iron oxide haematite (α‐Fe2O3) can incorporate significant amounts of U into its crystal structure and retain radiogenic Pb over geological time. Haematite is a ubiquitous component of many ore deposit types and, therefore, represents a valuable hydrothermal mineral geochronometer, allowing direct constraints to be placed on the timing of ore formation and upgrading. However, to date, no suitable natural haematite reference material has been identified. Here, a synthetic haematite U‐Pb reference material (MR‐HFO) is characterised using LA‐ICP‐MS and ID‐TIMS. Centimetre‐scale 'chips' of synthesised α‐Fe2O3 were randomly microsampled via laser ablation‐extraction and analysed using ID‐TIMS. Reproducible U/Pb and Pb/Pb measurements were obtained across four separate chips (n = 13). Subsequently, an evaluation of the suitability MR‐HFO in constraining U‐Pb data via LA‐ICP‐MS is presented using a selection of natural samples ranging from Cenozoic to Proterozoic in age. The MR‐HFO normalised U‐Pb ratios are more concordant and ages more accurate versus the same LA‐ICP‐MS spot analyses normalised to zircon reference material, when compared with independently acquired ID‐TIMS data from the same natural haematite grains. Results establish MR‐HFO as a suitable reference material for LA‐ICP‐MS haematite U‐Pb geochronology. [ABSTRACT FROM AUTHOR]

A bstract: The geochemical character of detrital mineral grains carries information that can be used to track sediment generation and transport within the broader context of basin development and crustal evolution. Many provenance studies focus on single minerals, which, as a consequence of different source fertility, survivorship and sediment sample representativeness, generate bias and consequently potentially skew geological interpretations. While a range of approaches has been proposed to either quantify or mitigate some of these biases, a significant limitation associated with the most commonly employed provenance proxy – zircon – remains that the grains are remarkably robust and capable of surviving numerous cycles of erosion, deposition and uplift. Here, same‐sample integration of zircon and feldspar provenance information is used to propose a sediment recycling metric 'R'. This metric quantifies the degree of relative recycling of distinctive source components through comparison of provenance proxies with similar source region fertilities but different survivorship potential. This approach is applied to a case study of several thousand new zircon U‐Pb ages and K‐feldspar Pb‐isotope ratios from 25 Carboniferous to Palaeogene clastic samples from the poorly studied Wollaston Forland–Clavering Ø region in hydrocarbon prospective north‐east Greenland. Concordant detrital zircon populations are dominated by Palaeoproterozoic (ca 1.9 to 1.8 Ga) grains (>60%), with more minor Palaeozoic, Neo‐Mesoproterozoic and Archean subpopulations. Feldspar grain Pb‐isotope ratios almost entirely (>>60%) correspond to Caledonian granites (ca 0.4 Ga). Zircon and feldspar provenance proxies appear decoupled as a consequence of: (i) limited resolvable growth of zircon within Caledonian granites, and more importantly; (ii) significant upgrading of recycled zircon components via rift flanking sedimentary basins. Collectively, the integration of detrital mineral proxies with disparate survivorship potentials through sediment cycles (labile first cycle feldspar versus potentially polycyclic zircon) is essential to facilitate more nuanced definition of sediment source regions, routing pathways and basin evolution. [ABSTRACT FROM AUTHOR]

The Hidaka Metamorphic Belt is a well-known example of island-arc crustal section, in which metamorphic grade increases westwards from unmetamorphosed sediment up to granulite facies. It is divided into lower (granulite to amphibolite facies) and upper (amphibolite to greenschist facies) metamorphic sequences. The metamorphic age of the belt was considered to be 55 Ma, based on Rb-Sr whole-rock isochron ages for granulites and related S-type tonalities. However, zircons from the granulites in the lower sequence yield U-Pb ages of 21-19 Ma, and a preliminary report on zircons from pelitic gneiss in the upper sequence gives a U-Pb age of 40 Ma. In this paper we provide new zircon U-Pb ages from two pelitic gneisses in the upper sequence to assess the metamorphic age and also the maximum depositional age of the sedimentary protolith. The weighted mean 206Pb/238U ages from a biotite gneiss in the central area of the belt yield 39.6 ± 0.9 Ma for newly grown metamorphic rims and 53.1 ± 0.9 Ma for the youngest detrital cores. The ages of zircons from a cordierite-biotite gneiss in the southern area are 35.9 ± 0.7 Ma for metamorphic rims and 46.5 ± 2.8 Ma for the youngest detrital cores. These results indicate that metamorphism of the upper sequence took place at 40-36 Ma, and that the sedimentary protolith was deposited after 53- 47 Ma. These metamorphic ages are consistent with the reported ages of 37-36 Ma plutonic rocks in the upper sequence, but contrast with the 21-19 Ma ages of metamorphic and plutonic rocks in the lower sequence. Therefore, we conclude that the upper and lower metamorphic sequences developed independently but coupled with each other before 19 Ma as a result of dextral reverse tectonic movement. [ABSTRACT FROM AUTHOR]

Similar to the U‐Pb system, the 232Th‐208Pb decay scheme is also widely utilised in geochronology of Th‐rich accessory minerals. The matrix‐dependent systemic deviations observed between different accessory minerals and the paucity of well‐characterised reference materials for some minerals of interest (e.g., xenotime and allanite) are the major obstacles to yield accurate and precise Th‐Pb ages with laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS). In this study, we investigated the effects of the addition of nitrogen, oxygen and water vapour before the ablation cell on the accuracy of Th‐Pb dating of accessory minerals (i.e., zircon, monazite and xenotime) using NIST SRM 610 glass as the calibrating reference material. Our results demonstrate that the measured 208Pb/232Th ages in zircon, monazite and xenotime were approximately 9–24% lower than their isotope dilution thermal ionisation mass spectrometry (ID‐TIMS) ages in normal ablation (without addition of additional gases). The measured 208Pb/232Th ages of zircon (Plešovice, M257 and Qinghu), monazite (44069 and Trebilcock) and xenotime (BS‐1 and MG‐1) showed excellent agreement with their respective reference values with the addition of small amounts of water vapour before the ablation cell. This may be due to the dramatically reduced biases for the down‐hole fractionation of Pb/Th intensity ratios in NIST SRM 610 and accessory minerals in the presence of water vapour. The Th‐Pb ages of zircon, monazite and xenotime were successfully analysed using NIST SRM 610 glass as the calibrating reference material with both 193 nm ArF excimer laser ablation‐quadrupole‐inductively coupled plasma‐mass spectrometry (LA‐Q‐ICP‐MS) and 213 nm Nd:YAG laser ablation‐sector field‐inductively coupled plasma‐mass spectrometry (LA‐SF‐ICP‐MS) in combination with the developed water vapour‐assisted method. This method is an effective and notably simple approach for non‐matrix‐matched analysis of Th‐Pb ages in zircon, monazite and xenotime by LA‐ICP‐MS. [ABSTRACT FROM AUTHOR]

We report new petrological and geochronological data of garnet‐cordierite (Grt‐Crd) gneiss as well as two types of leucocratic rocks (garnet‐bearing and cordierite‐bearing leucosomes) crystallized during prograde and near‐peak metamorphisms of the Wanni Complex (WC) in Sri Lanka, and investigate the pressure–temperature–time evolution of granulite‐facies metamorphism for unravelling the timing and tectonics of the Neoproterozoic collisional processes related to Gondwana amalgamation. Grt‐Crd gneiss, garnet‐biotite (Grt‐Bt) gneiss, garnet‐bearing leucocratic rock (Grt‐L), and cordierite‐bearing leucocratic rock (Crd‐L) discussed in this study were collected from Walpita in the margin of the WC along the boundary with the Highland Complex (HC). Grt‐L occurs as thin layers parallel to the foliation of matrix Grt‐Bt and Grt‐Crd gneisses. The occurrences of porphyroblastic garnet in quartzo‐feldspathic matrix and crystallised melt inclusions within the garnet suggest that the Grt‐L could have formed by partial melting of host Grt‐Bt gneiss during prograde to peak metamorphism. Crd‐L is coarse‐grained and massive, lacks obvious foliation, and crosscuts the foliation of host Grt‐Bt gneiss. These observations suggest that the Crd‐L could have intruded after the crystallization of the Grt‐L. Application of phase equilibria modelling in the system NCKFMASHTO for the rocks yielded three discrete thermal events: 600–800°C/4.0–6.0 kbar (Stage 1 from Grt‐L), 700–840°C/5.5–7.0 kbar (Stage 2 from Grt‐Crd gneiss), and 840–880°C/4.5–5.5 kbar (Stage 3 from Crd‐L), suggesting a clockwise P–T evolution. LA‐ICP‐MS zircon U–Pb dating of the leucosomes yielded several metamorphic events: >577 Ma (partial melting of Grt‐L), ~562 Ma (crystallization of Grt‐L), 537 ± 14 Ma (peak metamorphism and crystallization of Crd‐L), and 507–503 Ma (post‐peak cooling event). The results of this study therefore confirmed prolonged (>70 Myr) high‐grade metamorphism of the WC, although the duration might be shorter than that of the HC (>100 Ma). The continuous heat supply necessary for such long‐lived high‐grade metamorphism is explained by a recent tectonic model of Sri Lanka. The model suggests double‐sided subduction and continent‐continent collision, which could have given rise to subsequent slab delamination and differential heating of lower to middle crust. Such complex subduction–collision processes possibly controlled the difference in the style of P–T path and the duration of high‐grade metamorphism between the HC and the WC. [ABSTRACT FROM AUTHOR]

In situ LA-ICP-MS U–Pb geochronology has been performed on apatite and zircon within thermally recrystallized clast-laden and clast-poor impact melt rocks from the Brent impact structure. A total of 377 laser analyses on 120 impact melt-grown (n = 9) and impact-recrystallized zircon grains (n = 111) were obtained, from which a concordia age of 452.8 ± 2.7 Ma (MSWD 0.57, n = 11), and a weighted average mean 206Pb/238U age of 453.2 ± 2.9 Ma (MSWD 0.60) (n = 11) are calculated. A total of 300 laser analyses from 100 relict apatite grains were obtained, with an unanchored regression through all data yielding a lower intercept age of 453.2 ± 6.0 Ma (MSWD 5.8, n = 300), that overlaps within error of zircon. 207Pb/206Pb ratios obtained from feldspar clasts within clast-laden impact melt retain the same initial Pb composition as the target rocks from which they are derived, while feldspars that crystallized from impact melt have 207Pb/206Pb ratios indicative of isotopic re-equilibration between basement lithologies of two different ages. A similar variability in 207Pb/206Pb is recorded by apatite. This provides evidence for the involvement of Neoproterozoic Lake Nipissing alkaline suite, as well as Mesoproterozoic Grenville gneisses in the production of impact melt at Brent. Recrystallized apatite grains exhibit enrichments in light rare earth elements (LREEs) along neoblast grain boundaries, indicative of trace element substitution and phase precipitation during impact-induced recrystallization. An age of 452.8 ± 2.7 Ma from zircon and 453.2 ± 6.0 Ma from apatite places the impact event in the Late Ordovician, at or near the Sandbian–Katian boundary, confirming Brent's involvement in the Middle to Late Ordovician crater cluster event—a period of enhanced impactor flux to Earth related to the L-Chondrite parent body disruption. [ABSTRACT FROM AUTHOR]

In situ U-Pb geochronology has been conducted using laser ablation inductively coupled mass spectrometry (LA-ICP-MS) on shocked and thermally metamorphosed apatite, titanite, and zircon grains from the Steen River impact structure, Canada. The dated relict mineral phases occur within impact melt-bearing breccias that underwent post-deposition sintering at 450 °C > T < 800 °C. Apatite yields a refined lower intercept age of 141 ± 4 Ma, which we interpret as the best estimate age for the Steen River impact event. Titanite was only partially reset; yielding a lower intercept age of 113 ± 41 Ma. Zircon yields a lower intercept impact age of 120 ± 14 Ma, which is considered a minimum best-estimate impact age. The most reset zircon analyses that control this lower intercept are complicated by combinations of common-Pb incorporation and recent Pb loss associated with granularized and radiation-damaged (metamict) domains. All three phases preserve Paleoproterozoic crystalline basement ages, with a single concordant 206Pb/238U age of 1914 ± 39 Ma from apatite, an upper intercept age of 1882 ± 11 Ma from zircon, and an upper intercept age of 1842 ± 9 Ma from titanite. For apatite, the degree of isotopic resetting is largely thermally controlled, with the extent of reset closely associated with textural setting (degree of grain armouring, melt proximity and sample temperature) and, to a lesser extent, by shock/thermally generated microstructures (i.e., planar fractures, micro-vesicles, and recrystallized domains). While titanite records an impact age that falls within error of apatite and zircon, the majority of grains experienced only partial isotopic resetting, which we attribute to incomplete Pb loss associated with rapid cooling and post-depositional sintering of the breccia matrix below the titanite closure temperature (∼800 °C). In zircon, ancient (impact) Pb loss was facilitated along defect-related, fast-diffusion pathways within pre-impact metamict domains, shock defects, and via recrystallization. These same domains were also subject to recent (post-impact) Pb loss and common Pb contamination, significantly compromising the reliability of zircon ages. The distribution of U-Pb ratios in apatite and titanite is unlike those obtained in crystalline targets, a feature we interpret to be characteristic of impact structures developed in mixed (sedimentary – crystalline) targets, such as Steen River. In this case, disaggregated melt systems create thermal regimes distinct from those derived from predominantly igneous/metamorphic targets. With an age of 141 ± 4 Ma, Steen River joins the Dellen (Sweden), Gosses Bluff (Australia), Mjølnir (Barents Sea), and Morokweng (South Africa) impact structures in being formed at, or close to, the Jurassic-Cretaceous boundary. [ABSTRACT FROM AUTHOR]

We present a new LA–ICP–MS system for zircon fission‐track (FT) and U–Pb double dating, whereby a femtosecond laser combined with galvanometric optics simultaneously ablates multiple spots to measure average surface U contents. The U contents of zircon measured by LA–ICP–MS and standardized with the NIST SRM610 glass are comparable to those measured by the induced FT method, and have smaller analytical errors. LA–ICP–MS FT dating of seven zircon samples including three IUGS age standards is as accurate as the external detector method, but can give a higher‐precision age depending on the counting statistics of the U content measurement. Double dating of the IUGS age standards gives FT and U–Pb ages that are in agreement. A chip of the Nancy 91500 zircon has a homogeneous U content of 84 ppm, suggesting the possibility of using this zircon as a matrix‐matched U‐standard for FT dating. When using the Nancy 91500 zircon as a U‐standard, a zeta calibration value of 42–43 year cm2 for LA–ICP–MS FT dating is obtained. While this value is strictly valid only for the particular session, it can serve as a reference for other studies. [ABSTRACT FROM AUTHOR]

The Rencha basin is one of the typical Mesozoic-Cenozoic volcanic fault basins in northeastern Guangdong. The borehole data indicate that the basement is mainly composed of Paleozoic metamorphic rocks and Wenxiang granite. At present, the basement granite has been lacking in precise years. Then, to discuss its formation age and improve the understanding of the geological evolution of the area, LA-ICP-MS zircon U-Pb isotopic dating of Wenxiang granite cores from two boreholes in the Chagan area of the basin is carried out. The two harmonic ages are 179+1 Ma and 186 Ma, respectively. The results show that the basement Wenxiang granite in Rencha Basin was formed in late Early Jurassic, and it is the product of Yanshan's first volcanic activity. This age not only deepens the understanding of the formation and evolution of Rencha Basin but also provides new chronological data for the lack of magmatic activity in the Early Jurassic in northeastern Guangdong, China. [ABSTRACT FROM AUTHOR]

We present a new methodology for laser-induced steady-state photoluminescence (PL) spectroscopy of Dy3+ that aims at a direct quantification of the amorphous fraction f a present in zircon (ZrSiO4), which undergoes a transition from a crystalline to a metamict state due to cumulative self-irradiation damage caused by the radioactive decay of substituted U and Th. Using state-of-the-art confocal spectrometers attached to optical microscopes, measurements may be performed non-destructively on the micrometre length-scale with the option to visualize radiation-damage patterns as revealed by hyperspectral PL maps. Zircon from the Ratnapura district (Sri Lanka, ~520 Ma), was used as reference material to substantiate the applicability of the proposed method. The accumulation of radiation damage in this material was investigated in detail and obtained f a values correlate with calculated ff-doses in accordance to the direct impact model reported variously in the literature. The impact of chemically-induced, heterogeneous broadening of Raman and Dy3+ emission spectral bands is discussed on two examples from Mt. Malosa district, Malawi. A mean weighted U-Pb isotope age of 111 ± 1 Ma (pegmatitic-type) and a discordia age of 112 ± 1.6 Ma (hydrothermal-type) as obtained by LA-ICP-MS confirm their close genetic and temporal relationship. Studied zircon examples demonstrate that the amount of radiation damage present may have a substantial effect on the precision of LA-ICP-MS ages, but cannot be considered an exclusive cause for bias of obtained isotope ages. [ABSTRACT FROM AUTHOR]

To reveal the petrological characteristics, metamorphic evolution history and tectonic setting of the pelitic granulites from Ailaoshan Orogen, West Yunnan, China, a comprehensive study in mineral chemistry, petrogeochemistry and geochronology studies is presented in this paper. Two metamorphic stages of the granulites can be established: (1) the peak metamorphism recorded by the mineral assemblage of garnet, kyanite, K-feldspar and rutile, and the initial retrograde metamorphism shown by the mineral assemblage of garnet, sillimanite, sapphirine, spinel, K-feldspar, plagioclase and biotite; (2) the superimposed metamorphism recorded by the mineral assemblage of biotite, muscovite, plagioclase, quartz and ilmenite. Zircon LA-ICP-MS U-Pb dating indicates that the protolith of the granulite was deposited after 337 Ma. The initial retrograde metamorphism occurred at P-T conditions of 8.6–12 kbar at 850–920 ºC estimated by mineral assemblages, the low pressure limit of kyanite stability and GBPQ geothermobarometer in Indosinian (about 235 Ma), and the late superimposed metamorphism occurred at the P-T condition of 3.5–3.9 kbar at 572–576 ºC estimated by GBPQ geothermobarometer since 33 Ma. The first stage was related to the amalgamation of the South China and Indochina blocks during the Triassic, and the second stage was possibly related with the large scale sinistral slip-shearing since the Oligocene. It is inferred that the upper continental crust was subducted/underthrusted to the lower continental crust (deeper than 30 km) and underwent granulite-facies metamorphism and then quickly exhumed to the middle-upper crust (10–12 km) and initial retrograde metamorphism occurred due to the collision of the Indochina and South China blocks during Indosinian, which was followed by superimposition of the second stage of metamorphism since the Oligocene. [ABSTRACT FROM AUTHOR]

LA‐ICP‐MS U–Pb detrital zircon studies typically analyse 50–200 grains per sample, with the consequent risk that minor but geologically important age components (e.g., the youngest detrital zircon population) are not detected, and higher abundance age components are misrepresented, rendering quantitative comparisons between samples impossible. This study undertook rapid U–Pb LA‐ICP‐MS analyses (8 s per 18–47 μm diameter spot including baseline and ablation) of zircon, apatite, rutile and titanite using an aerosol rapid introduction system (ARIS). As the ARIS resolves individual single pulses at fast sampling rates, spot analyses require a high repetition rate (> 50 Hz) so the signal does not return to baseline and mass sweep times (> 80 ms) that span several laser pulses (i.e., major undersampling of the signal). All rapid U–Pb spot analyses employed 250–300 pulses, repetition rates of 53–65 Hz (total ablation times of 4.1–5.7 s) and low fluence (1.75–2.5 J cm−2), resulting in pit depths of ca. 15 μm. Zircon, apatite, rutile and titanite reference material data yield an accuracy and precision (2s) of < 1% for pre‐Cenozoic reference materials and < 2% for younger reference materials. We present a detrital zircon data set from a Neoproterozoic tillite where > 1000 grains were analysed in < 3 h with a precision and accuracy comparable to conventional LA‐ICP‐MS analytical protocols, demonstrating the rapid acquisition of huge detrital data sets. Key Points: A rapid U‐Pb LA‐ICP‐MS protocol (8 s per spot including baseline and ablation) for U‐bearing accessory minerals. Zircon, apatite, rutile and titanite reference material data yielded accuracy and precision (2s) of < 1% for pre‐Cenozoic reference materials. Neoproterozoic tillite detrital zircon data set results (> 1000 grains analysed in < 3 h) gave precision and accuracy comparable to conventional LA‐ICP‐MS protocols. [ABSTRACT FROM AUTHOR]

We present multitechnique U‐Pb geochronology and Hf isotopic data from zircon separated from rapakivi biotite granite within the Eocene Golden Horn batholith in Washington, USA. A weighted mean of twenty‐five Th‐corrected 206Pb/238U zircon dates produced at two independent laboratories using chemical abrasion‐isotope dilution‐thermal ionisation mass spectrometry (CA‐ID‐TIMS) is 48.106 ± 0.023 Ma (2s analytical including tracer uncertainties, MSWD = 1.53) and is our recommended date for GHR1 zircon. Microbeam 206Pb/238U dates from laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS) laboratories are reproducible and in agreement with the CA‐ID‐TIMS date to within < 1.5%. Solution multi‐collector ICP‐MS (MC‐ICP‐MS) measurements of Hf isotopes from chemically purified aliquots of GHR1 yield a mean 176Hf/177Hf of 0.283050 ± 17 (2s, n = 10), corresponding to a εHf0 of +9.3. Hafnium isotopic measurements from two LA‐ICP‐MS laboratories are in agreement with the solution MC‐ICP‐MS value. The reproducibility of 206Pb/238U and 176Hf/177Hf ratios from GHR1 zircon across a variety of measurement techniques demonstrates their homogeneity in most grains. Additionally, the effectively limitless reserves of GHR1 material from an accessible exposure suggest that GHR1 can provide a useful reference material for U‐Pb geochronology of Cenozoic zircon and Hf isotopic measurements of zircon with radiogenic 176Hf/177Hf. Key Points: We suggest a new Eocene zircon reference material, GHR1.U‐Pb and Hf isotopic systematics in GHR1 zircon are homogeneous with a 206Pb/238U date of 48.106 +/‐ 0.023 Ma (2s) and a 176Hf/177Hf of 0.283050 +/‐ 17 (2s).GHR1 fulfills a need for abundant and easily available Cenozoic zircon reference materials. [ABSTRACT FROM AUTHOR]

Earlier research has shown that several common late antique glass types circulate in Cyprus between the fifth and the seventh century AD, specifically Levantine 1, HLIMT, HIMTa, HIMTb and Egypt 1, HIT, Roman and a plant ash glass. By investigating the glass material from Yeroskipou-Agioi Pente, Maroni-Petrera, and Kalavasos-Kopetra, we aimed to refine the chemical groups present within three late antique Cypriot sites and define the relations between trace elements obtained from LA-ICP-MS. Our data demonstrate compositional patterns that can be exploited to provenance late antique glass by investigating the REE-bearing mineral fractions, the amount of zircon and the carbonaceous fraction of the sand. In addition, Nb and Ti display a strong linear relation which depends on the glass type. Finally, the paper discusses the occurrence of glass recycling on the island and how this activity influenced the concentration levels of specific trace elements. Our study thus sets out an analytical framework to identify recycling events tailored on each compositional type. [ABSTRACT FROM AUTHOR]

Late Palaeogene syn-tectonic volcanic products have been found in the Northern Alpine foreland basin and in the South Alpine hemipelagic basin. The source of abundant volcanic fragments is still in debate. We analyzed the geochronology and geochemistry of detrital zircons, and evaluated their temporal and genetic relationships with potential volcanic sources. The study shows that the detrital zircon U-Pb age patterns have two major age groups: a dominance (ca. 90%) of pre-Alpine zircons was found, as commonly observed in other Alpine flysch formations. These zircons apparently derived from erosion of the early Alpine nappe stack in South Alpine and Austroalpine units. Furthermore, a few Neo-Alpine zircons (ca. 10%) have ages ranging from Late Eocene to Early Oligocene (~ 41-29 Ma). Both source materials were mixed during long riverine transport to the basin margins before being re-deposited by gravity flows. These Palaeogene ages match with the activity of Peri-Adriatic magmatism, including the Biella volcanic suite as well as the Northern Adamello and Bergell intrusions. The values of REE and 176Hf/177Hf(t) ratios of the Alpine detrital zircons are in line with the magmatic signatures. We observe an in time and space variable supply of syn-sedimentary zircons. From late Middle Eocene to Late Eocene, basin influx into the South Alpine and Glarus (A) basins from the Northern Adamello source is documented. At about 34 Ma, a complete reorganisation is recorded by (1) input of Bergell sources into the later Glarus (B) basin, and (2) the coeval volcaniclastic supply of the Haute-Savoie basin from the Biella magmatic system. The Adamello source vanished in the foreland basin. The marked modification of the basin sources at ~ 34 Ma is interpreted to be initiated by a northwestern shift of the early Alpine drainage divide into the position of the modern Insubric Line. [ABSTRACT FROM AUTHOR]