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In modern plate tectonic regimes, continental crust is generated above subduction zones in magmatic island arcs. Models for continental growth-largely based on the modeling of geochemical processes that can transform mantle melts into the intermediate composition of bulk continental crust-have been hampered by a lack of definitive geochronology, which could clarify the temporal emplacement of igneous rocks at the base of island arc crust. The Kohistan Arc Complex (KAC) of Pakistan is a rare window into a nearly complete section of lower arc crust, revealing a sequence of igneous rocks representing discrete batches of magma underplated along the base of the arc crust. We present high-precision isotope dilution-thermal ionization mass spectrometry U-Pb geochronological data from zircon, and Lu-Hf and Sm-Nd isochron data from several mafic lower crustal cumulates within the KAC. These data establish a clear downward-younging age trend throughout this succession of cumulate complexes, demonstrating a total magmatic duration of ~20 m.y., corresponding to a rate of lower crust formation of up to 200-260 km³ km-1 Ma-1. These results provide the first direct evidence of a sequential process of underplating, revealing a fundamental mechanism responsible for building the root of island arc crust. [ABSTRACT FROM AUTHOR]

We present new high-precision geochemical and isotopic data showing that magmas related to the Central Atlantic Magmatic Province (CAMP) were emplaced at the base of the continental crust in the Ivrea Zone of northwest Italy. These results significantly extend the known footprint of one of the largest examples of a large igneous province (LIP) on the planet. The La Balma--Monte Capio (LBMC) intrusion ranges from dunitic at the base to plagioclasebearing pyroxenitic at the top. Zircons were extracted from two samples at different levels, and dated using the chemical abrasion--isotope dilution--thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb method. The two weighted-mean 206Pb/238U ages at 200.5 ± 0.3 Ma and 200.1 ± 0.5 Ma indicate a short-lived magmatic system that fractionated in place. The timing of emplacement is different from that of all other mafic-ultramafic intrusions in the Ivrea Zone and is consistent with magmatism associated with the CAMP. We suggest that exposure in the Ivrea Zone provides a unique glimpse into the presently unknown character of LIP magmas at the base of the continental crust, where the emplacement of this intrusion was facilitated by its location at a lithospheric suture. [ABSTRACT FROM AUTHOR]

The Butedale pluton, a ca. 100 km long compositionally zoned batholith, is part of the Coast Plutonic Complex that extends the length of the Canadian Pacific coast. Its age and thermal history are relevant to the Butedale pluton's role as a test case of the Baja-BC hypothesis, as paleomagnetic evidence suggests that it may have formed thousands of kilometres to the south and moved northward along what is now the Coast Shear Zone. High-resolution U-Pb (chemical abrasion - thermal ionization mass spectrometry (CA-TIMS), zircon) analysis of rocks across the width of the Butedale pluton indicates that it is actually made up of at least two distinct magmatic events that formed the West Butedale pluton (ca. 95 Ma) and the East Butedale pluton (ca. 85 Ma). The East Butedale pluton was reheated by the emplacement of a younger adjacent pluton, which may have caused partial Pb loss and resulting excess scatter of 206Pb/238U zircon ages within individual samples. The West Butedale pluton may be the same age as, and part of, the nearby Ecstall pluton, thereby doubling the length of the Ecstall pluton to ca. 200 km. Single-grain, high-precision U-Pb analysis of zircon reveals previously unknown complexity and detail of emplacement and thermal history in the Butedale plutons. Le pluton de Butedale, un batholite à composition zonée, d'une centaine de kilomètres de long, fait partie du Complexe Plutonique Côtier qui s'étend sur toute la longueur de la côte Pacifique du Canada. Son âge et son historique thermique sont pertinents au rôle du pluton de Butedale en tant que cas type de l'hypothèse Baja-BC, puisque, selon des évidences paléomagnétiques, il pourrait avoir été formé à des milliers de kilomètres au sud et avoir migré vers le nord le long de ce qui est maintenant la zone de cisaillement de la Côte. Des analyses U-Pb à haute résolution (CA-TIMS, zircon) de roches à travers toute la largeur du pluton de Butedale indiquent qu'il est en réalité composé d'au moins deux événements magmatiques distincts qui ont formé le pluton de Butedale Ouest (~95 Ma) et le pluton de Butedale Est (~85 Ma). Le pluton de Butedale Est a été réchauffé par la mise en place d'un pluton adjacent plus jeune, ce qui a possiblement causé une perte partielle du Pb et résulté en une dispersion excédentaire des âges 206Pb/238U sur zircons à l'intérieur d'échantillons individuels. Le pluton de Butedale Ouest pourrait avoir le même âge que le pluton Ecstall avoisinant et pourrait même en faire partie, doublant ainsi la longueur du pluton Ecstall à environ 200 km. Des analyses U-Pb de haute précision sur des grains uniques de zircon révèlent une complexité jusqu'alors inconnue et des détails sur la mise en place et l'historique des plutons de Butedale. [ABSTRACT FROM AUTHOR]

U–Pb baddeleyite ages and paleomagnetic poles obtained for dykes on Devon Island and Ellesmere Island in the Canadian Arctic and the Thule region of Greenland show that they are associated with the Franklin magmatic event. This study is the only one devoted to Franklin igneous rocks where a primary paleomagnetic remanence and U–Pb age have been obtained from the same rocks. Ages from this study range from 721 to 712 Ma, but paleomagnetic directional data show no clear age progression. The paleomagnetic poles from each of the two regional subsets are significantly different at the 95% confidence level from paleomagnetic results previously published for the Franklin event in the Canadian Shield. The difference in the pole locations can be accounted for, to first approximation, by a simple model of early Cenozoic block rotations among the North American plate, Greenland, and a hypothesized ancient microplate comprising Ellesmere, Devon, Cornwallis, and perhaps Somerset islands. A new grand-mean paleopole for the Franklin event, including restoration of Greenland and the proposed “Ellesmere microplate” to North America, is located at (8.4°N, 163.8°E, A95 = 2.8°, N = 78 sites) and is a key pole for Neoproterozoic supercontinent reconstructions. [ABSTRACT FROM AUTHOR]

The north–south-trending Clarence Head dyke swarm, located on Devon and Ellesmere Islands in the Canadian High Arctic, has a trend orthogonal to that of the Neoproterozoic Franklin swarm that surrounds it. The Clarence Head dykes are dated by the U–Pb method on baddeleyite to between 716 ± 1 and 713 ± 1 Ma, ages apparently younger than, but within the published age range of, the Franklin dykes. Alpha recoil in baddeleyite is considered as a possible explanation for the difference in ages, but a comparison of the U–Pb ages of grains of equal size from both swarms suggests that recoil distances in baddeleyite are lower than those in zircon and that the Clarence Head dykes are indeed a distinctly younger event within the period of Franklin magmatism. The Clarence Head dykes represent a large swarm tangential to, and cogenetic with, a giant radiating dyke swarm ~800 km from the indicated source. The preferred mechanism for the emplacement of the Clarence Head dykes is the exploitation of concentric zones of extension around a depleting and collapsing plume source. While the paleomagnetism of most Clarence Head dykes agrees with that of the Franklin dykes, two dykes have anomalous remanence directions, interpreted to be a chemical remanent magnetization carried by pyrrhotite. The pyrrhotite was likely deposited from fluids mobilized southward from the Devonian Ellesmerian Orogeny to the north that used the interiors of the dykes as conduits and precipitated pyrrhotite en route. [ABSTRACT FROM AUTHOR]

U-Pb geochronology by isotope dilution– thermal ionization mass spectrometry (ID-TIMS) has the potential to be the most precise and accurate of the deep time chronometers, especially when applied to high-U minerals such as zircon. Continued analytical improvements have made this technique capable of regularly achieving better than 0.1% precision and accuracy of dates from commonly occurring high-U minerals across a wide range of geological ages and settings. To help maximize the long-term utility of published results, we present and discuss some recommendations for reporting ID-TIMS U-Pb geochronological data and associated metadata in accordance with accepted principles of data management. Further, given that the accuracy of reported ages typically depends on the interpretation applied to a set of individual dates, we discuss strategies for data interpretation. We anticipate that this paper will serve as an instructive guide for geologists who are publishing ID-TIMS U-Pb data, for laboratories generating the data, the wider geoscience community who use such data, and also editors of journals who wish to be informed about community standards. Combined, our recommendations should increase the utility, veracity, versatility, and “half-life” of ID-TIMS U-Pb geochronological data. [ABSTRACT FROM AUTHOR]

The lower crustal domain of the Ivrea‐Verbano Zone (NW Italy) hosts five ~300‐m‐wide pipe‐like ultramafic intrusions that are metasomatized and exhibit Ni‐Cu‐PGE sulphide mineralization. To better constrain the role of metasomatism in the ore genesis, we studied the best‐preserved pipe at Valmaggia which was emplaced 249 Myrs ago. Phlogopite 40Ar/39Ar analyses show that the pipe was infiltrated by metasomatic fluids derived from the subcontinental lithospheric mantle (SCLM) in two pulses at ~208 Ma and ~189 Ma which introduced sulphides into the pipe. Consequently, the pipe repeatedly acted as a preferred path for mass transfer from the SCLM into the lower crust over >60 Myrs (i.e., emplacement to second metasomatic pulse). Uplifted block margins, such as the Ivrea‐Verbano Zone, are potentially important exploration targets for magmatic sulphides. We argue that exploration strategies should focus on structures such as pipes that can focus metasomatic agents during ascent through the lithosphere. [ABSTRACT FROM AUTHOR]

The eruption of Emeishan lava in southwestern China and northern Vietnam is considered to be a contributing factor to the Capitanian mass extinction and subsequent global cooling event, but the duration of volcanism is uncertain. The difficulty in assessing the termination age is, in part, due to the lack of high-precision age data for late-stage volcanic rocks. The Tu Le rhyolite of northern Vietnam is the most voluminous silicic unit of the Emeishan large igneous province (ELIP) and is spatially associated with the Muong Hum and Phan Si Pan hypabyssal plutons. Chemical abrasion-isotope dilution-thermal ionization mass spectrometry U-Pb dating of zircons from the Tu Le rhyolite (257.1 ± 0.6 Ma to 257.9 ± 0.3 Ma) and Muong Hum (257.3 ± 0.2 Ma) and Phan Si Pan (256.3 ± 0.4 Ma) plutons yielded the youngest high-precision ages of the ELIP yet determined. The results demonstrate that Emeishan lavas erupted over a period of ~6 m.y,. with plutonism ending shortly thereafter. Thus, it is possible that Emeishan volcanism contributed to global cooling into the middle Wuchiapingian. It appears that these rocks represent a distinct period of ELIP magmatism, as they are young and were emplaced oblique to the main north-south-trending Panxi rift. [ABSTRACT FROM AUTHOR]

• New 1888 Ma mafic dyke swarm in southwest Yilgarn Craton, Western Australia has been discovered. • The new dyke suite suggests connection with India at ca. 1890 Ma and may be part of the Bastar-Cuddapah Large Igneous Province. • The dyke swarm is coeval with global mafic magmatism found on most other Precambrian cratons. The Archean Yilgarn Craton in Western Australia is intruded by numerous mafic dykes of varying orientations, which are poorly exposed but discernible in aeromagnetic maps. Previous studies have identified two craton-wide dyke swarms, the 2408 Ma Widgiemooltha and the 1210 Ma Marnda Moorn Large Igneous Provinces (LIP), as well as limited occurrences of the 1075 Ma Warakurna LIP in the northern part of the craton. We report here a newly identified NW-trending mafic dyke swarm in southwestern Yilgarn Craton dated at 1888 ± 9 Ma with ID-TIMS U-Pb method on baddeleyite from a single dyke and at 1858 ± 54 Ma, 1881 ± 37 and 1911 ± 42 Ma with in situ SHRIMP U-Pb on baddeleyite from three dykes. Preliminary interpretation of aeromagnetic data indicates that the dykes form a linear swarm several hundred kilometers long, truncated by the Darling Fault in the west. This newly named Boonadgin dyke swarm is synchronous with post-orogenic extension and deposition of granular iron formations in the Earaheedy basin in the Capricorn Orogen and its emplacement may be associated with far field stresses. Emplacement of the dykes may also be related to initial stages of rifting and formation of the intracratonic Barren Basin in the Albany-Fraser Orogen, where the regional extensional setting prevailed for the following 300 million years. Recent studies and new paleomagnetic evidence raise the possibility that the dykes could be part of the coeval 1890 Ma Bastar-Cuddapah LIP in India. Globally, the Boonadgin dyke swarm is synchronous with a major orogenic episode and records of intracratonic mafic magmatism on many other Precambrian cratons. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Shallow non-plume related magmatism during breakup of Rodinia. • Melting of trace element enriched and major element depleted sub-continental lithospheric mantle. • New age constraint on "Sturtian Snowball Earth". • Syn-glacial age constraint for the development of Cryogenian iron formation. Abstract Here we present a new U-Pb baddeleyite ID-TIMS age of 713.7 ± 0.9 Ma on the shoshonitic Tatonduk Suite near the Yukon-Alaska border in the Proterozoic Tatonduk inlier, which occur as mafic and intermediate dykes and a sequence of basaltic to andesitic volcanic flows immediately beneath iron formation-bearing Sturtian glacial deposits correlated with the early Cryogenian Rapitan Group. Considering the age overlap with what is inferred to represent the Franklin Large Igneous Province (LIP) of northern Canada, the Tatonduk Suite might logically be considered a far-flung component of the Franklin Large Igneous Province. However, the Tatonduk Suite was emplaced in an actively extending environment >1200 km from the plume head on Melville Island and does not obviously align with the Franklin dyke trend. Furthermore, major, trace and isotopic data on the Tatonduk Suite reveal a composition that is unique from the Franklin LIP and most likely reflects melting of potassic and trace element enriched sub-continental lithospheric mantle at pressures of less than 10 kb. These volcanics and dykes highlight the complexity in defining what constitutes a LIP. The Tatonduk Suite either represent a non-plume end-member composition of the Franklin LIP, or more likely, rift volcanics associated with extension along the actively extending margin of northwestern Laurentia. Although the plume and rifting may be geodynamically linked, this interpretation suggests that this new age for the Tatonduk Suite does not constrain the timing of Franklin magmatism. The Tatonduk Suite was emplaced during the Sturtian Snowball Earth event and contributes to the growing body of geochronological data that indicates the onset of glaciation at ca. 717 Ma. Furthermore, this age provides direct evidence for the syn-glacial origin of Sturtian iron formation in the Tatonduk inlier and further links iron formation to widespread mafic magmatism at this time. [ABSTRACT FROM AUTHOR]

The article presents a study on the Franklin Large Igneous Province, in Canada comprising a giant radiating dyke swarm and also a circumferential set of dykes. Observations in the article have implications for paleocontinental reconstructions that rely on dyke trends, ages and chemical affinities.It suggests that caution is required when making connections between sets of intrusions based on geo chemistry.

Mafic and ultramafic magmas that intrude into the lower crust can preserve evidence for metal and sulfur transfer from the lithospheric mantle into the lower continental crust. Here we focus on a series of ultramafic, alkaline pipes in the Ivrea Zone (NW Italy), which exposes deeply buried (6–11 kbar), migmatitic metasedimentary rocks intruded by voluminous basaltic magmas of the Mafic Complex, a major crustal underplating event precisely dated via U/Pb CA-IDTIMS on zircon at 286.8 ± 0.4 Ma. The ultramafic pipes postdate the Mafic Complex and from 100 to 300 m wide cumulate-rich conduits. They are hydrated and carbonated, have unusually high incompatible element concentrations and contain blebby and semi-massive Ni-Cu-PGE sulfide mineralisation. The sulfides occur as coarse intergranular nodules (>10 mm) and as small intragranular blebs (<1 mm) hosted in olivine, and have homogeneous, mantle-like δ 34 S (+1.35 ± 0.25‰). This homogeneity suggests that the pipes reached sulfide supersaturation without addition of crustal sulfur, and that the δ 34 S signature is representative of the continental lithospheric mantle. One of the pipes, the 249 Ma Valmaggia pipe, carries a very distinctive Sr-Nd-Hf-Pb isotopic composition in its core ( 87 Sr/ 86 Sr 0.70250, ε Nd-18 , ε Hf-18 , 206 Pb/ 204 Pb 16.0, 207 Pb/ 204 Pb 15.16, 208 Pb/ 204 Pb 35.87), very different from the margin of this pipe and from other pipes that have higher 87 Sr/ 86 Sr, ε Nd and 206 Pb/ 204 Pb. The unusual isotopic composition of the Valmaggia pipe requires a source with long-term (2500–1500 million years) U-, Th- and Rb-depletion and LREE enrichment. Such compositions are found in Late Archean/Early Proterozoic granulites and lower crustal xenoliths. We suggest that the unusual isotopic composition of the Valmaggia pipe reflects contamination of the mantle source of the pipe with a crustal component that is neither represented in the local Paleozoic crust nor in the isotopically anomalous hydrated mantle inferred as the source of the large-volume mafic underplate that formed the Mafic Complex. During post-collisional gravitational collapse of the Variscan Orogen, this source produced the alkaline, metal (Ni, Cu, PGE)- and volatile (H 2 O, CO 2 , S)-rich mafic–ultramafic magma that formed the deep-crustal intrusion at Valmaggia. U/Pb dating of other chemically and geologically comparable pipes in the area shows that this process was active over at least 40 Ma. The Ivrea pipes illustrate how the lower continental crust can be fertilised with mantle-derived metals and volatiles, which are available for later remobilisation into upper-crustal ore systems. World-class mineral deposits along the margins of lithospheric blocks may thus be the result of both favourable crustal architecture (focussing of magmas and fluids) and localised volatile and metal enrichment of the lower crust related to mantle-derived hydrous metasomatism. [ABSTRACT FROM AUTHOR]

Precambrian crust within southern Chad and eastern Cameroon preserves rocks that were remobilized and emplaced during and after the Neoproterozoic (∼650 Ma to ∼610 Ma) collision between the Congo, São Francisco, West African cratons and the Saharan Metacraton. The Guéra Massif of south-central Chad and granites located near Lake Fitri are inferred to be of Neoproterozoic age but there are no radio-isotopic dates available to confirm their association with the Pan-African Orogeny (Central African Fold Belt). New zircon U/Pb geochronology of granitic rocks from the Guéra Massif, Lake Fitri region and the Doba Basin of the southern Chad yielded weighted-mean 206 Pb/ 238 U ages from 595 ± 8 Ma to 545 ± 6 Ma. The oldest inherited zircons indicate that the Guéra Massif is either built upon Meso- to Paleoproterozoic (1000 Ma–1900 Ma) continental crust or that pre-Neoproterozoic rocks were the source of the silicic Ediacaran rocks. The identification of ∼590 Ma volcanic-arc granites within the Guéra Massif suggest that subduction continued in the eastern regions of Chad after collision had occurred (≥610 Ma) in the west (Cameroon). The younger granites (≤570 Ma) are post-collisional in nature and are closely linked to deformation cycles recorded in eastern Cameroon after the main continental collision episode between the Congo Craton and the Saharan Metacraton. The post-collisional granites located in the Lake Fitri region likely represent a westward extension of the Guéra Massif as there are temporal and compositional similarities between the granitic rocks. The age and composition of the diorite from the Doba Basin of southern Chad is similar to post-collisional granites from the Central African Fold Belt of Cameroon and implies that the southern boundary of the Saharan Metacraton may be north of the Doba Basin. [ABSTRACT FROM AUTHOR]

The Beetaloo Sub‐basin, northern Australia, is considered the main depocentre of the 1,000‐km scale Mesoproterozoic Wilton package of the greater McArthur Basin – the host to one of the oldest hydrocarbon global resources. The ca. 1.40–1.31 Ga upper Roper Group and the latest Mesoproterozoic to early Neoproterozoic unnamed group of the Beetaloo Sub‐basin, together, record ca. 500 million years of depositional history within the North Australia Craton. Whole‐rock shale Sm–Nd and Pb isotope data from these sediments reveal sedimentary provenance and their evolution from ca. 1.35 to 0.85 Ga. Furthermore, these data, together with shale major/trace elements data from this study and pyrolysis data from previous publications, are used to develop a dynamic tectonic geography model that links the organic carbon production and burial to an enhanced weathering of nutrients from a large igneous province. The ca. 1.35–1.31 Ga Kyalla Formation of the upper Roper Group is composed of isotopically evolved sedimentary detritus that passes up, into more isotopically juvenile Pb values towards the top of the formation. The increase in juvenile compositions coincides with elevated total organic carbon (TOC) contents of these sediments. The coherently enriched juvenile compositions and TOC the upper portions of the Kyalla Formation are interpreted to reflect an increase in nutrient supply associated with the weathering of basaltic sources (e.g. phosphorous). Possible, relatively juvenile, basaltic sources include the Wankanki Supersuite in the western Musgraves and the Derim Derim–Galiwinku large igneous province (LIP). The transition into juvenile, basaltic sources directly before a supersequence‐bounding unconformity is here interpreted to reflect uplift and erosion of the Derim Derim–Galiwinku LIP, rather than an influx of southern Musgrave sources. A new baddeleyite crystallisation age of 1,312.9 ± 0.7 Ma provides both a tight constraint on the age of this LIP, along with its associated magmatic uplift, as well as providing a minimum age constraint for Roper Group deposition. The unconformably overlying lower and upper Jamison sandstones are at least 300 million years younger than the Kyalla Formation and were sourced from the Musgrave Province. An up‐section increase in isotopically juvenile compositions seen in these rocks is interpreted to document the progressive exhumation of the western Musgrave Province. The overlying Hayfield mudstone received detritus from both the Musgrave and Arunta regions, and its isotopic geochemistry reveals affinities with other early Neoproterozoic basins (e.g. Amadeus, Victoria and Officer basins), indicating the potential for inter‐basin correlations. [ABSTRACT FROM AUTHOR]

The initiation and peak magmatic periods of the Emeishan Large Igneous Province (LIP) are well constrained by both biostratigraphic and radioisotopic dating methods; however, the age of cessation of volcanism is poorly constrained and continues to be debated. Marine carbonates interbedded with volcanic ashes across the Guadalupian- Lopingian boundary (GLB) are widespread in south China, and these ashes provide an opportunity to study its timing, origin, and potential relationship with the Emeishan LIP. Here we present biostratigraphic constraints, mineralogical and geochemical characteristics, and high-resolution geochronology of ash layers from the Maoershan and Chaotian sections. Stratigraphic correlation, especially conodont biostratigraphy, confines these ashes to the early Wuchiapingian. Those altered ashes are geochemically akin to alkali tonsteins from the coal seams of the lower Xuanwei/Lungtan Formation in southwest China. The ashes postdating the GLB yield a coherent cluster of zircon U-Pb ages with weighted mean 206Pb/238U ages of 258.82 ± 0.61 Ma to 257.39 ± 0.68 Ma, in agreement with the ages of intrusive rocks (259.6 ± 0.5 Ma to 257.6 ± 0.5 Ma) in the central Emeishan LIP. Moreover, the Hf(t) values of zircons from the ashes vary from +2.5 to +10.6, a range consistent with that of the Emeishan LIP. The results collectively suggest that the early Wuchiapingian volcanic ashes are a product of extrusive alkaline magmatism and most likely mark the waning stage of the Emeishan volcanism, which may have continued until ca. 257.4 Ma in the early Wuchiapingian. [ABSTRACT FROM AUTHOR]

Detailed geochronological, geochemical, and paleomagnetic studies of mafic dyke swarms, often associated with mantle plumes, can provide unique constraints on paleogeographic reconstructions. Mafic dykes with baddeleyite U–Pb ages of 1,233 ± 27 Ma (SIMS), 1,206.7 ± 1.7 Ma (TIMS), 1,214.0 ± 4.9 Ma (TIMS), and 1,236.3 ± 5.4 Ma (TIMS) have been identified in the eastern North China Craton. Geochemical data indicate subalkaline to alkaline basalt compositions with OIB‐like trace element signatures and an intraplate tectonic setting. In addition to these geochemical signatures, the radiating geometry of these dykes also suggests a 1.24–1.21 Ga large igneous province caused by a mantle plume event. A new ~1.24 Ga paleomagnetic pole at 2.0°N, 165.1°E, A95 = 11.0°, N = 9 and an ~1.21 Ga VGP at −23.0°N, 92.5°E, dp/dm = 4.7°/7.8° have been obtained from these dykes, with the 1.24 Ga pole supported by positive baked contact test. Our paleomagnetic analyses suggest that the North China Craton and the proto‐Australian continent could have been separated by 1.24–1.21 Ga from an established Nuna connection at ca. 1.32 Ga. By comparison with Laurentia paleopoles, we present the paleogeography of dispersing North China, proto‐Australian, and Laurentia cratons in the late Mesoproterozoic during the breakup of the supercontinent Nuna. Key Points: New 1.24–1.21 Ga Licheng large igneous province has been identified in the North China CratonA new key paleomagnetic pole of ~1.24 Ga has been obtained for the North China CratonPositions of North China, proto-Australian, and Laurentia cratons have been refined during Nuna breakup [ABSTRACT FROM AUTHOR]

Complex arrays of faults in extensional basins are potentially influenced by pre‐existing zones of weakness in the underlying basement, such as faults, shear zones, foliation, and terrane boundaries. Separating the influence of such basement heterogeneities from far‐field tectonics proves to be challenging, especially when the timing and character of deformation cannot be interpreted from seismic reflection data. Here we aim to determine the influence of basement heterogeneities on fault patterns in overlying cover rocks using interpretations of potential field geophysical data and outcrop‐scale observations. We mapped >1 km to meter scale fractures in the western onshore Gippsland Basin of southeast Australia and its underlying basement. Overprinting relationships between fractures and mafic intrusions are used to determine the sequence of faulting and reactivation, beginning with initial Early Cretaceous rifting. Our interpretations are constrained by a new Early Cretaceous U‐Pb zircon isotope dilution thermal ionization mass spectrometry age (116.04 ± 0.15 Ma) for an outcropping subvertical, NNW‐SSE striking dolerite dike hosted in Lower Cretaceous Strzelecki Group sandstone. NW‐SE to NNW‐SSE striking dikes may have signaled the onset of Early Cretaceous rifting along the East Gondwana margin at ca. 105–100 Ma. Our results show that rift faults can be oblique to their expected orientation when pre‐existing basement heterogeneities are present, and they are orthogonal to the extension direction where basement structures are less influential or absent. NE‐SW to ENE‐WSW trending Early Cretaceous rift‐related normal faults traced on unmanned aerial vehicle orthophotos and digital aerial images of outcrops are strongly oblique to the inferred Early Cretaceous N‐S to NNE‐SSW regional extension direction. However, previously mapped rift‐related faults in the offshore Gippsland Basin (to the east of the study area) trend E‐W to WNW‐ESE, consistent with the inferred regional extension direction. This discrepancy is attributed to the influence of NNE‐SSW trending basement faults underneath the onshore part of the basin, which caused local re‐orientation of the Early Cretaceous far‐field stress above the basement during rifting. Two possible mechanisms for inheritance are discussed—reactivation of pre‐existing basement faults or local re‐orientation of extension vectors. Multiple stages of extension with rotated extension vectors are not required to achieve non‐parallel fault sets observed at the rift basin scale. Our findings demonstrate the importance of (1) using integrated, multi‐scale datasets to map faults and (2) mapping basement geology when investigating the structural evolution of an overlying sedimentary basin. [ABSTRACT FROM AUTHOR]

Baddeleyite from a mafic dyke near Bhanupratappur of the central Bastar Craton (India) yielded a weighted-mean 207 Pb/ 206 Pb age of 1882.4 ± 1.5 Ma. The dykes are tholeiitic and have variable Mg# (41–60), TiO 2 (0.83–1.74 wt%) and low CaO (<10.9 wt%) indicating they are not representative of primary melts and differentiated prior to or during emplacement. Petrological modeling shows that the chemical variability of the dykes is primarily due to crystal fractionation and crustal contamination. The Sr and Nd isotopes ( 87 Sr/ 86 Sr i  = 0.7032–0.7068; ε Nd ( t ) = −1.1 to +1.7) are variable but broadly chondritic. Trace element modeling suggests the dykes were likely derived by partial melting of a mantle source from the spinel-garnet transition zone. The dykes from the central Bastar Craton have the same age and are chemically similar to NW trending dykes and sills from the southern Bastar Craton (1883.0 ± 1.4 Ma; 1883.5 ± 4.4 Ma; 1885.4 ± 3.1 Ma) and dykes from the Yilgarn Craton (1888 ± 9) of Western Australia. The similar age, complimentary orientations and geochemistry of the dykes from the Bastar and Yilgarn Cratons supports the notion that Southern India and Western Australia were once connected during the Paleoproterozoic and separated by ∼1.88 Ga. [ABSTRACT FROM AUTHOR]

The Beaufort Group of the Karoo Basin, South Africa provides an important chrono- and biostratigraphic record of vertebrate turnovers that have been attributed to the end-Permian mass extinction events at ca. 252 and 260 Ma. However, an unresolved controversy exists over the age of the Beaufort Group due to a large data set of published U-Pb SHRIMP (Sensitive High Resolution Ion Microprobe) zircon results that indicate a ca. 274-250 Ma age range for deposition of the underlying Ecca Group. This age range requires the application of a highly diachronous sedimentation model to the Karoo Basin stratigraphy and is not supported by published palaeontologic and palynologic data. This study tested the strength of these U-Pb isotopic data sets using a magnetostratigraphic approach. Here, we present a composite ∼1500 m section through a large part of the Ecca Group from the Tanqua depocentre, located in the southwestern segment of the Karoo Basin. After the removal of two normal polarity overprints, a likely primary magnetic signal was isolated at temperatures above 450 °C. This section is restricted to a reverse polarity, indicating that it formed during the Kiaman Reverse Superchron (ca. 318-265 Ma), a distinctive magnetostratigraphic marker for early-middle Permian rocks. The Ecca Group has a corresponding palaeomagnetic pole at 40.8°S, 77.4◦E (A95 = 5.5°). U-Pb SHRIMP ages on zircons are presented here for comparison with prior isotopic studies of the Ecca Group. A weighted mean U-Pb age of 269.5 ± 1.2 Ma was determined from a volcanic ash bed located in the uppermost Tierberg Formation sampled from the O + R1 research core. The age is interpreted here as a minimum constraint due to a proposed Pb-loss event that has likely influenced a number of published results. A comparison with the Geomagnetic Polarity Time Scale as well as published U-Pb TIMS ages from the overlying Beaufort Group supports a ca. 290-265 Ma age for deposition of the Ecca Group. [ABSTRACT FROM AUTHOR]

This study focuses on the low-temperature mineralogical response of xenotime, a phosphate mineral routinely used as a geochronometer, to fluid-assisted alteration. The studied xenotime grain (z6413) comes from a ∼ 1000 Ma pegmatite from the Grenville Province, Canada, and is commonly used as reference material for U Pb analyses. At the microscale, the grain has a mottled texture, sub-micrometer porosity, and small domains dark in backscattered electron (BSE) images that are characterised by curviplanar, sharp boundaries. The small dark BSE domains are associated with Th-U-rich inclusions and larger porosity (2–3 μm) and are interpreted to result from localised fluid-assisted coupled dissolution-reprecipitation. Sensitive high-resolution ion microprobe (SHRIMP) U Pb analyses of unaltered and fluid-affected domains yield concordant crystallisation dates, irrespective of the textural domains. The apparently unaltered xenotime domain was characterised at the nanoscale to determine if the grain was affected by fluids beyond the altered domains defined by BSE imaging. Transmission electron microscopy (TEM) imaging results indicate the presence of randomly distributed Ca + Pb nanoscale precipitates. Atom probe tomography (APT) reveals the presence of spherical clusters (4 to 18 nm in size) enriched in radiogenic Pb, Ca, and Si atoms, which, combined with TEM observations, are interpreted as nanoscale inclusions of apatite. In addition to the inclusions, a dislocation enriched in Ca and fluid mobile elements such as Cl, Li, Na, and Mn was imaged from APT data indicating percolating of fluids further than the reaction front. APT 206Pb/238U nanogeochronology indicates that the nanoscale inclusions of apatite formed at 863 ± 28 Ma, 100–150 Ma after crystallisation of the host xenotime, with its formation attributed to fluid metasomatism. This study shows that fluid-xenotime reaction caused Pb* to be redistributed at the nanoscale, recording the timing of metasomatism. However, at the scale of SHRIMP analytical spot (10 μm), xenotime is concordant, indicating that Pb was not mobile at the microscale and fluid-altered xenotime can preserve its crystallisation age. Although the studied grain shows a limited amount of altered domains in BSE imaging, nanoscale analyses reveal a more pervasive re-equilibration of the minerals through the percolation of fluids along dislocations. • Multiscale analysis of fluid alteration textures in xenotime. • No correlation exists between geochronology and textural domains. • Nanoscale analysis shows evidence of fluid activity beyond the altered domains with Pb*-enriched apatite inclusions. • Implications on the stability of xenotime in fluid active settings. [ABSTRACT FROM AUTHOR]

Sri Lanka comprises three roughly north-south trending amphibolite- to granulite-facies lithotectonic complexes, from west to east the Highland Complex, the Wanni Complex, and the Vijayan Complex. These terranes were correlated with other East Gondwana continental terranes with similar lithologies forming at similar ages. The Wanni Complex and the Vijayan Complex have been interpreted as volcanic arc terranes brought together by a double-sided subduction. The Highland Complex represents the metamorphosed accretionary prism within the suture when the Wanni and Vijayan Complexes were juxtaposing against each other. In contrast to the Wanni and Highland Complexes, the Vijayan Complex has yielded only a few geochronological data with satisfactory precision. Previous studies suggested that the Vijayan Complex comprises ∼1100–924 Ma granitic gneisses, which were metamorphosed during ∼590–456 Ma. More recently, ∼772–617 Ma mafic intrusions have been identified. This study divides the Vijayan granitic gneisses and the associated melt products geochemically into a low-Nb series and a more primitive high-Nb series. Our SIMS U-Pb zircon data suggested that both series have protolith magmatic ages of ∼1062–935 Ma, and metamorphic ages of ∼580–521 Ma, which is consistent with previous work. However, some of the Vijayan granitic gneisses and granitic anatectic melt products at the Highland-Vijayan tectonic mixed zone preserve an additional Tonian-Cryogenian (∼820–630 Ma) age signal. This age signal suggested that felsic magmatism also occurred when mafic granulites were emplaced along the Highland-Vijayan boundary, which is broadly coeval with to the bimodal magmatism occurring along the Highland-Wanni boundary. This study also suggests that charnockitisation in the Vijayan Complex occurred at 562 ± 6 Ma during the Neoproterozoic regional metamorphism. The Tonian-Cryogenian signal preserved in the Highland-Vijayan tectonic mixed zone can also be found in the alkaline intrusion hosted by the Namuno Terrane and the Lurio Belt in Mozambique. This indicates a relationship between the Vijayan granitic gneisses and the Lurio foreland metagranitic basement, while the Namuno Terrane and the Lurio Belt are correlated with the Highland-Vijayan tectonic mixed zone. The ages and the isotope signatures of these granitic bodies further suggest a genetic relationship of these granitic bodies with various magmatic intrusions in East Antarctica. [ABSTRACT FROM AUTHOR]

The eruption of the Panjal Traps is associated with rifting along the Tethyan margin of Gondwana. A CA-ID-TIMS zircon U-Pb age of basalt collected from the southern Pir Panjal Range (SPPR) yielded a weighted-mean 206Pb/238U age of 288.2 ± 0.3 Ma. The rocks from the SPPR can be divided into three compositionally distinct groups (basalt: SiO 2 < 52 wt%; Mg# = 56–36, basaltic andesite: SiO 2 = 52–60 wt%; Mg# = 32–48, and silicic: SiO 2 > 64.0 wt%; Mg# = 27–23) and are chemically correlated with rocks from the eastern Kashmir Valley rather than the northern Pir Panjal Range (NPPR). The Sr-Nd isotopes (87Sr/86Sr i = 0.70860–0.71104; ε Nd (t) = −6.1 to −4.4) of the mafic rocks are similar and indicate that their magmas were derived from a subduction modified subcontinental lithospheric mantle (SCLM) source. The silicic rocks were derived by partial melting of the continental crust (87Sr/86Sr i = 0.71022–0.71093; ε Nd (t) = −8.7 to −7.2) and their discovery in the SPPR indicates that silicic volcanism was far more extensive than previously thought. The 187Os/188Os i isotopic ratios of basalts from different regions of the Panjal Traps range from 0.1230 to 0.2832. Two samples from the NPPR have ratios of 0.1230 and 0.1256 that are slightly higher than primitive upper mantle at the time of eruption whereas the remaining samples show enriched values (0.1343–0.2832). The new data suggest that it is likely that the mantle source of the Panjal Traps transitioned from a SCLM source to a sublithospheric source over time as seafloor spreading developed. • Basalt from the southern Pir Panjal Range yielded an age of 288.2 ± 0.3 Ma. • Basalts from the southern Pir Panjal Range were derived from modified SCLM. • Silicic rocks from the southern Pir Panjal Range are derived from the crust. • Isotopes indicate the Panjal Traps transitioned from a SCLM to a sub-LM source. [ABSTRACT FROM AUTHOR]

The article talks about the geochronology of the Tayatea Dyke Swarm that intrude the Rocky Cape Group (RCG) of northwest Tasmania, Australia providing timing of rift-related magmatism and evaluating the hypothesis of a drifting Tasmania. It talks of a zicron study of the RCG, a shallow-marine siltstone and records sedimentation during rifting of a passive margin that has constrained its maximum depositional age and provenance.

Atmospheric CO 2 levels and global climate are regulated on geological timescales by the silicate weathering feedback. However, this thermostat has failed multiple times in Earth's history, most spectacularly during the Cryogenian (c. 720–635 Ma) Snowball Earth episodes. The unique middle Neoproterozoic paleogeography of a rifting, low-latitude, supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo. Under these primed conditions, the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation. Weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios ( δ 13 C ) of Neoproterozoic seawater due to their elevated P contents. In order to test these hypotheses, we have compiled new and previously published Neoproterozoic Nd isotope data from mudstones in northern Rodinia (North America, Australia, Svalbard, and South China) and Sr isotope data from carbonate rocks. The Nd isotope data are used to model the mafic detrital input into sedimentary basins in northern Rodinia. The results reveal a dominant contribution from continental flood basalt weathering during the ca. 130 m.y. preceding the onset of Cryogenian glaciation, followed by a precipitous decline afterwards. These data are mirrored by the Sr isotope record, which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early–middle Neoproterozoic ocean, including a pulse of unradiogenic Sr input into the oceans just prior to the onset of Cyrogenian glaciation. Hence, our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average δ 13 C of seawater in the Neoproterozoic and to the initiation of the first (Sturtian) Snowball Earth. [ABSTRACT FROM AUTHOR]

Mantle-derived melts and metasomatic fluids are considered to be important in the transport and distribution of trace elements in the subcontinental lithospheric mantle. However, the mechanisms that facilitate sulfur and metal transfer from the upper mantle into the lower continental crust are poorly constrained. This study addresses this knowledge gap by examining a series of sulfide- and hydrous mineral-rich alkaline mafic–ultramafic pipes that intruded the lower continental crust of the Ivrea–Verbano Zone in the Italian Western Alps. The pipes are relatively small (< 300 m diameter) and primarily composed of a matrix of subhedral to anhedral amphibole (pargasite), phlogopite and orthopyroxene that enclose sub-centimeter-sized grains of olivine. The 1 to 5 m wide rim portions of the pipes locally contain significant blebby and disseminated Fe–Ni–Cu–PGE sulfide mineralization. Stratigraphic relationships, mineral chemistry, geochemical modeling and phase equilibria suggest that the pipes represent open-ended conduits within a large magmatic plumbing system. The earliest formed pipe rocks were olivine-rich cumulates that reacted with hydrous melts to produce orthopyroxene, amphibole and phlogopite. Sulfides precipitated as immiscible liquid droplets that were retained within a matrix of silicate crystals and scavenged metals from the percolating hydrous melt. New high-precision chemical abrasion TIMS U–Pb dating of zircons from one of the pipes indicates that these pipes were emplaced at 249.1 ± 0.2 Ma, following partial melting of lithospheric mantle pods that were metasomatized during the Eo-Variscan oceanic to continental subduction (~ 420–310 Ma). The thermal energy required to generate partial melting of the metasomatized mantle was most likely derived from crustal extension, lithospheric decompression and subsequent asthenospheric rise during the orogenic collapse of the Variscan belt (< 300 Ma). Unlike previous models, outcomes from this study suggest a significant temporal gap between the occurrence of mantle metasomatism, subsequent partial melting and emplacement of the pipes. We argue that this multi-stage process is a very effective mechanism to fertilize the commonly dry and refractory lower continental crust in metals and volatiles. During the four-dimensional evolution of the thermo-tectonic architecture of any given terrain, metals and volatiles stored in the lower continental crust may become available as sources for subsequent ore-forming processes, thus enhancing the prospectivity of continental block margins for a wide range of mineral systems. [ABSTRACT FROM AUTHOR]

The Wuda Tuff Flora in the North China Craton (NCC) is a "vegetational Pompeii" and one of the most completely preserved marsh ecosystems of the late Paleozoic Northern Hemisphere. However, the precise age, geochemistry, and petrogenesis of the thick tuff containing this peat-forming flora have not been established. We conducted a comprehensive petrographic, mineralogical, whole-rock geochemical, and zircon U Pb and Hf O isotopic investigation of five samples from a vertical section through the tuff bed. Our results confirm that the material that buried the flora is a volcanic tuff bed that has undergone intensive post-deposition alteration. Whole-rock Al 2 O 3 /TiO 2 ratios (65.8–103.5) and negative Eu/Eu* values (0.27–0.38) further suggest a felsic volcanic origin. Secondary ion mass spectrometry zircon U Pb dating of the altered tuff bed yielded a weighted mean 206Pb/238U age of 295.9 ± 1.4 Ma (1σ, MSWD = 0.94, n = 39), constraining the age of the Wuda Tuff Flora to the earliest Permian. Depletions of Nb and Ta in both the whole-rock and zircon compositions indicate an arc-related setting for the volcanism. The positive εHf(t) values (0.0 to +5.0) and δ18O values (5.05‰–6.17‰) of zircon grains from the Wuda Tuff suggest a juvenile crust origin of the volcanic magma. Geochemical comparisons with contemporaneous igneous rocks suggest that the volcanic eruption that led to the formation of the Wuda Tuff and associated vegetational Pompeii was most probably caused by arc volcanism along the western margin of the NCC related to subduction of Paleo-Asian Ocean oceanic crust, implying that the Alxa Terrane had not yet amalgamated with the NCC during the early Permian. • The Wuda Tuff was felsic arc-originated with juvenile crust. • The age of Permian Tuff Flora at Wuda Coalfield is 295.9 ± 1.4 Ma. • A magmatic arc may exist to the west of North China Craton during early Permian. [ABSTRACT FROM AUTHOR]

The Savannah (formerly Sally Malay) Ni-Cu-Co Camp is composed of a group of mineralised intrusions (Savannah and Savannah North) and petrologically similar mafic-ultramafic intrusions without known mineralisation (Sub-chamber D, Dave Hill, and Wilson's Creek). The results of a wide range of analytical techniques (geochemical, geochronological and geophysical) are integrated to gain a better understanding of the geometry of the Savannah mineralised magmatic intrusions and the timing of events. Magnetic anisotropy results suggest that Savannah and Savannah North have both been affected by similar deformation events, implying near-synchronous intrusion. However, Savannah and Savannah North show evidence of fundamentally different styles of deformation (strong folding at Savannah, as opposed to gentle tilting at Savannah North). This discrepancy can be reconciled with a resolvable variation in age, with Savannah North being the younger by ca. 0.8–2.5 Ma, as well as difference in the geometry and associate rheological properties of the intrusions: the larger more equant Savannah North intrusion may have been more resistant to deformation than the thinner elongated Savannah body. Isotopic and geochemical data on the mafic-ultramafic intrusions of the Savannah Ni-Cu-Co Camp indicate that the entire intrusive suite, with the exception of the early mafic granulite dykes, was derived from a similar parent magma of basaltic composition with likely continental arc affinity. Results of sulfide tenor calculations combined with mineral chemistry and in-situ S isotope data provide insight into ore genetic processes: in both the Savannah and Savannah North intrusions tenors are low, with median values in semi-massive ores of 3.8% Ni and 0.9% Cu in 100% sulfide for Savannah and 2.7% Ni and 1.0% Cu for Savannah North. PGE tenors are similar and extremely low in both deposits, ranging from below 5 ppb to 200 ppb for Pt (median 6 ppb) and from 40 ppb to 480 ppb (median 110) for Pd, with Pd/Ir of 25–160 and Pd/Pt of 3–50 (10th and 90th percentiles). For both Savannah and Savannah North, S isotopic analyses indicate a limited amount of incorporation of crustal S, and the contaminant does not appear to have been the immediately adjacent Tickalara Metamorphics, implying either a deeper crustal contaminant, or a component of subduction-derived crustal S in the mantle source. Finally, olivine records a history of postcumulus re-equilibration with trapped silicate melt and cumulus sulfide liquid, giving rise to distinctive compositional trends. The Savannah Ni-Cu-Co Camp provides further evidence that arc and collisional environments are conducive to the formation of intrusion-hosted orthomagmatic Ni-Cu-Co deposits. The multidisciplinary approach that we describe here allowed us to unravel the petrological, structural, and mineralisation history of a cryptic but prospective region, and provided insights to help evaluate the prospectivity of neighbouring intrusions. This approach can be used in a wide range of settings to resolve critical factors such as S source, timing of intrusion and mineralisation, and structural controls. [ABSTRACT FROM AUTHOR]