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Emeishan large igneous province (ELIP), one of the largest continental volcanic provinces worldwide (e. g., Karoo), is extensively distributed along the western margin of the Yangtze Block. Even though the consensus that the ELIP is of a plume-related origin has been reached for decades, the role of crustal contamination in the petrogenesis of these basalts is still debatable so far. This paper firstly reports the Ba isotopic compositions of the continental flood basalts from the Lijiang, Miyi and Emeishan regions to discuss the genesis of basalts from the ELIP. According to their TiO2 contents and Ti/Y ratios, these basalts are divided into two groups, the low-Ti basalts from Lijiang and the high-Ti basalts from Miyi and Emeishan. The Ba isotopic compositions show that the low-Ti basalts have the δ138/134Ba values from −0.33‰ to +0.23‰ with an average of −0.02‰ ± 0.40‰, and the high-Ti basalts from −0.38‰ to +0.38‰ with an average of 0.038‰ ± 0.36‰, all of which show a wider range of Ba isotopes relative to that of the primitive mantle (PM). This is unlikely to be explained by partial melting, fractional crystallization or even chemical weathering owing to little Ba isotopic fractionation during these processes. In contrast, variable extents of crustal contamination into the basaltic magmas more likely resulted in such isotopic diversity. The ratios of incompatible elements (e. g., Nb/U, La/Nb, and Nb/Y) further suggest that the low-Ti basalts experienced higher degrees of crustal contaminations than those high-Ti basalts, which is well consistent with their spatial distributions. In general, the basaltic magmas in the ELIP were probably contaminated by different degrees of crustal materials during their upwelling to the surface. [ABSTRACT FROM AUTHOR]

As a result of comprehensive study and laser 40Ar/39Ar dating of sanidines from the rocks of the Talakhtakh diatreme (TD) (Arctic Siberia), it has been found that the formation time of sanidine trachytes (lamproites) corresponds to the isochronous age value of 1497 ± 40 Ma or the weighted average age (as more accurate) of 1476 ± 17 Ma. The obtained age of the TD rocks is fully consistent with the formation time of the main rocks from the Kuonamka large igneous province (LIP). Thus, the Talakhtakh diatreme should be considered as an integral part of the Kuonamka LIP together with widely distributed basaltic sills, dikes, and covers on the Anabar Shield and within the Riphean sedimentary cover. [ABSTRACT FROM AUTHOR]

The association between Large Igneous Provinces (LIPs) and mass extinctions and anoxic events is attributed to the radical climatic changes in Earth. Even though the Early Cretaceous Paraná–Etendeka Igneous Province has a comparable erupted volume (>1 Mkm3) to other LIPs (e.g., Deccan, Emeishan and Siberian Traps), it remains controversial why this LIP did not contribute to a mass extinction and whether it is associated with the Weissert Event. This work presents new 40Ar/39Ar dating over a 425‐m vertical stratigraphic profile (out of 1,000 m) that spans three formations of the PE‐LIP in southern Brazil (low‐Ti Vale do Sol, high‐Ti Urubici, and high‐Ti Palmas). Our data demonstrate that this mafic lava pile was emplaced in c. 2.0 m.y., from c. 135.5 Ma to c. 133.5 Ma, and endorse the hypothesis that the basaltic and andesitic flows of the Vale do Sol Formation (peak of mafic magmatism) contributed to the Weissert Event. [ABSTRACT FROM AUTHOR]

A detailed contemplation is attempted to comprehend the likely connection of a large number of Early Cretaceous mafic, felsic, alkaline (kimberlite, lamproites, ultramafic lamprophyre, etc.), and carbonatite magmatic records of the eastern and north‐eastern region of the Indian Shield and adjoining regions. All these Early Cretaceous magmatic records occupied a large area, covering adjoining regions of south‐eastern Tibet, eastern and north‐eastern India, western Australia, Eastern Indian Ocean, southern Kerguelen Plateau, and north‐eastern Antarctica, are supposed to be part of the Greater Kerguelen Large Igneous Province (LIP) and likely to be related to the break‐up of East Gondwana. Available age results, chiefly ranging from ca. 145 to 100 Ma, support a genetic connection with the Kerguelen mantle plume. However, there are other lines of evidences, particularly radiogenic isotope data that preclude direct involvement of any mantle plume component; likely to be derived from decompression melting related to passive rifting. Two major magmatic phases, ca. 145–130 Ma and ca. 124–100 Ma, have been distinctly identified, which could be related to distinct rifting events. Break‐up of East Gondwana had happened at ca. 137 Ma with separation of Western Australia from Greater India. Later, ca. 124–122 Ma, separation of Antarctica from Eastern India occurred. The later magmatic phases (after ca. 120 Ma) are likely to have an indirect connection with the Greater Kerguelen LIP probably with the mantle plume providing extra heat for melting. [ABSTRACT FROM AUTHOR]

Stratigraphic, petrological and geophysical studies suggest that the Late Permian (~ 260 Ma) Emeishan Large Igneous Province in southern China may be formed by mantle plume activity. However, the plume impingement hypothesis remains controversial since interpretations based on volcano-stratigraphic analyses around plume induced domal uplift/inner zone suggest that the volcanism occurred under submarine environment rather than elevated sub-aerial (above sea level) conditions, usually associated with the dynamic topography effects of the ascending mantle plumes. Here, 2-D numerical and 3-D scaled laboratory (analogue) plume experiments are used to explore the coupled dynamics of plume-mantle-lithosphere interaction and their evolution of surface topography characteristics. Experimental results show that the initial (plume incubation) phase is characterized by rapid, transient domal uplift above the plume axis, subsequently, as plume head flattens, there is short wavelength topographic variation (ie. subsidence and uplift occurs synchronously) due to the shear stress imposed onto the base of the lithosphere and loss of gravitational potential energy. The surface depressions predicted by the plume models, next to the plume axial/inner/uplift zone, may explain the deposition of submarine volcanics at Lake Erhai, Dali in the western side and Xiluo and Daqiao in the eastern side, which may resolve the plume controversy for the formation of Emeishan Large Igneous Province. Notably, while experimental results from these two different techniques show some differences, (e.g much bigger plume head for the laboratory experiment), the overall characteristics of the predictions have robust similarities. For instance, the extension above the plume axis may explain the enigmatic cause of the Panxi rift system, in the middle of the inner zone where giant dyke swarms radiate from, and mafic magma underplatings in the lower crust has been described by seismological studies. [ABSTRACT FROM AUTHOR]

The timing of the emergence of subaerial landmasses is equivocally constrained as post-Archean and continues to be a much-debated issue. In this study, we document exceptionally 18O-depleted (δ18O < 4.7‰) Mesoarchean to early Neoarchean magmatism in India that shows a similarity with the coeval low-δ18O magmas reported from Australia, South America, and northern China. Such global-scale low-δ18O magmatism would require high-temperature meteoric water-rock interaction in the uppermost crust synchronous with magma generation, necessitating the emergence of a substantial volume of the continental crust. The timing of this low-δ18O magmatism coincides with the development of extensive, subaerial large igneous provinces, a downward shift in δ18O and Δ17O values in pelitic rocks, the rise of normalized 87Sr/86Sr in seawater, and an intermittent upsurge in the proportion of atmospheric oxygen. We propose that the emergence of substantial volumes of continental crust initiated at ca. 3.2 Ga and peaked at 2.8-2.6 Ga, facilitating the generation of globally distributed low-δ18O magmas, and this event can be linked to the first appearance of atmospheric oxygen. [ABSTRACT FROM AUTHOR]

The timing and mechanisms of the climatic and environmental perturbations induced by the emplacement of the Deccan Traps large igneous province (India) and their contribution to the Cretaceous-Paleogene (K-Pg) mass extinction are still debated. In many marine sediment archives, mercury (Hg) enrichments straddling the K-Pg boundary have been interpreted as the signature of Deccan Traps volcanism, but Hg may also have been derived from the Chicxulub (Mexico) impact. We investigated the Hg isotope composition, as well as the behavior of iridium (Ir) and other trace elements, in K-Pg sediments from the Bidart section in southwest France. Above the K-Pg boundary, Ir content gradually decreases to background values in the Danian carbonates, which is interpreted to indicate the erosion and redistribution of Ir-rich fallouts. No significant enrichment in Ir and W, or Zn and Cu, is observed just below the K-Pg boundary, excluding the hypothesis of downward remobilization of Hg from the boundary clay layer. Positive Δ199Hg and slightly negative values in the upper Maastrichtian and lower part of the early Danian are consistent with the signature of sediments supplied by atmospheric Hg2+ deposition and volcanic emissions. Up section, large shifts to strongly negative mass-dependent fractionation values (δ202Hg) result from the remobilization of Hg formerly sourced by the impactor or by a mixture of different sources including biomass burning, volcanic eruption, and asteroid impact, requiring further investigation. Our results provide additional support for the interpretation that the largest eruptions of the Deccan Traps began just before, and encompassed, the K-Pg boundary and therefore may have contributed to the K-Pg mass extinction. [ABSTRACT FROM AUTHOR]

Mafic-ultramafic subvolcanic intrusive complexes, at the 1–10-km scale, constitute favorable environments for the formation of orthomagmatic Ni-Cu-PGE sulfide deposits. Within 100–1000-km scale large igneous provinces (LIPs), the most favorable economic target areas may be difficult to identify using a traditional regional exploration approach. We report results of field and laboratory studies focused on an integrated geochemical-architectural model for the Ni-Cu-PGE sulfide potential of the High Arctic large igneous province (HALIP) of Canada, the largest and best-exposed portion of this circum-arctic LIP. Previous lithogeochemical studies of the Canadian HALIP (130–80 Ma) concluded that subalkaline mafic units located on Axel Heiberg Island were more prospective than younger, alkalic igneous rocks (alkaline basalts to basanites) exposed on northern Ellesmere Island. Mapping carried out for this study revealed the presence of abundant subalkaline igneous rocks on western Ellesmere Island. We interpret these units as an extension of the Schei Sills, a stratigraphically bound sequence of intrusions exposed along a ~ N-S belt on eastern Axel Heiberg Island. Samples from the Schei Sills and from the Middle Fiord Intrusive Complex (~ 20 km2, central Axel Heiberg Island) show Cu/Zr values above and below unity, consistent with complementary sulfide enrichment and removal, respectively, within these intrusive systems. The spatial association of the Schei Sills with the post-emplacement Eocene Stolz Thrust is noteworthy, as later thrusting associated with the Paleogene Eurekan Orogeny caused the uplift of deeper parts of the HALIP subvolcanic feeder system and associated wall-rock stratigraphy. Absolute Ir-group PGE contents are low throughout the HALIP; however, Pt-group PGE contents range widely among analyzed tholeiitic intrusive rocks. For example, relatively elevated Pt + Pd values of 10–30 ppb in samples from the Middle Fiord Intrusive Complex and the Schei Sills suggest heightened prospectivity in these two areas. In contrast, tholeiitic flood basalts in the Strand Fiord Formation and associated intrusions exposed in western Axel Heiberg Island (~ 95 Ma) exhibit Cu/Zr < 1 and low Pt + Pd contents (below 10 ppb). The ca. 120 Ma magmatic event associated with the Schei Sills and Middle Fiord Intrusive Complex appears to have generated magmas that are more prospective than those of the younger (ca. 95 Ma) magmatic pulse associated with the flood basalts of the Strand Fiord Formation. This work demonstrates that not all architectural elements of a LIP are equal in terms of metallogenic potential, and that nested zones of higher prospectivity can be identified through the integration of several geological constraints. [ABSTRACT FROM AUTHOR]

The Bushveld Large Igneous Province (BLIP) was emplaced in three stages (I, II, and III) over some 19 m.y. (c. 2061–2042 Ma). The Bushveld Complex is the main constituent of the BLIP and hosts the world's largest ferroan granite (Lebowa Granite Suite) and several granophyres (Rashoop Granophyre Suite) directly overlying the world's largest layered mafic intrusion (Rustenburg Layered Suite). New zircon U–Pb ages (measured by ID-TIMS) for the Lebowa Granite Suite and a textural variant termed Zwartbank Pseudogranophyre yield identical crystallization ages ranging from 2054.3 ± 0.7 to 2056.5 ± 0.9 Ma. Zircons from the uppermost Rustenburg Layered Suite (Upper Zone) yield an indistinguishable age of 2055.1 ± 2.1 Ma. These ages demonstrate that the Bushveld granitoids, together with the Rustenburg Layered Suite belong to BLIP Stage II. Additionally, most Lebowa Granite Suite samples contain zircons with primary growth zonation that yield ages up to 2064 Ma. We interpret these as antecrysts originating from BLIP Stage I. Isotope compositions of Hf in zircon (measured by LA-MC-ICPMS in situ and on solutions) are essentially uniform at εHf (2055 Ma) = − 7.2 to − 5.6, and indistinguishable from published data for the uppermost Rustenburg Layered Suite. We interpret the indistinguishable ages and similar isotopic compositions of the Lebowa Granite Suite and the Rustenburg Layered Suite as support for direct petrogenetic linkages. The Hf isotopic composition of the Rustenburg Layered Suite has been attributed to enriched mantle sources, but we show that crustal assimilation by mantle-derived magmas can also explain these compositions for both the Lebowa Granite Suite and Rustenburg Layered Suite. We propose that the Lebowa Granite Suite formed during Stage II, but zircon antecrysts indicate that some remobilization of granitic material formed during Stage I was also involved. [ABSTRACT FROM AUTHOR]

During the mid-Cretaceous, the Earth experienced several environmental perturbations, including an extremely warm climate and Oceanic Anoxic Events (OAEs). Submarine volcanic episodes associated with formation of large igneous provinces (LIPs) may have triggered these perturbations. The osmium isotopic ratio (187Os/188Os) is a suitable proxy for tracing hydrothermal activity associated with the LIPs formation, but 187Os/188Os data from the mid-Cretaceous are limited to short time intervals. Here we provide a continuous high-resolution marine 187Os/188Os record covering all mid-Cretaceous OAEs. Several OAEs (OAE1a, Wezel and Fallot events, and OAE2) correspond to unradiogenic 187Os/188Os shifts, suggesting that they were triggered by massive submarine volcanic episodes. However, minor OAEs (OAE1c and OAE1d), which do not show pronounced unradiogenic 187Os/188Os shifts, were likely caused by enhanced monsoonal activity. Because the subaerial LIPs volcanic episodes and Circum-Pacific volcanism correspond to the highest temperature and pCO2 during the mid-Cretaceous, they may have caused the hot mid-Cretaceous climate. "Mid-Cretaceous experienced a series of drastic environmental perturbations called Oceanic Anoxic Events. Here, the authors asses high-resolution Os isotopic records which indicate that most of these events were associated with massive submarine volcanic episodes, but some minor ones were not." [ABSTRACT FROM AUTHOR]

Fascinating circular hydrothermal bowls 0.5 m in diameter occur in paleodunes of the 1.2 million km2 Botucatu paleoerg in the Fronteira Oeste of Brazil, Rio Grande do Sul, and were exposed upon erosion of presumed 2,000 m of basalt and rhyodacite cover of the Paraná Volcanic Province (1 million km2) since the Cretaceous (135 Ma). The tops of the paleodunes display low-temperature (150-50°C) hydrothermal structures comparable to those in basalts and rhyodacites. The source beds of sand injectites display evidence of sequential fault-valve action. The bowls represent a new structure in continental paleodunes. They present circular rims sealed by quartz and a flat horizontal bottom with a central sealed vent. The inclined internal rims of the bowls exhibit a radial set of linear fractures filled with quartz, forming prominent, sharp, positive structures. Their origin is ascribed to the work of water vapor originated in the heated freshwater aquifer. The concave ceiling was lifted a few millimeters along circular fractures long enough for quartz to be deposited. Erosional exhumation of the buried Botucatu hyperdry sand sea has revealed the effects, including the new structures described here, of hydrothermalism associated with a major igneous province upon a giant paleoerg turned-aquifer. [ABSTRACT FROM AUTHOR]

Initiation of large igneous provinces (LIPs) and temporal and spatial variations in their chemical compositions provide unique opportunities to understand mantle dynamics. It has been recently revealed that water‐rich reservoirs in the mantle sources have played a significant role in the production of LIPs. However, the dominant causes for the chemical variations in primitive magmas of LIPs remain debated. In the Emeishan LIP (ELIP), there are several places where picrites accompany more abundant flood basalts. These picrites span a large range of Ti/Y, Sm/Yb, and TiO2/Al2O3. In this work, we have determined the water contents of picrites with Ti/Y > 500 from the ELIP, based on the water content of clinopyroxene phenocrysts and water partitioning coefficients. We have also calculated the water content of the mantle sources by applying batch and fractional partial melting models. We show that the chemical compositions of picrites in the ELIP closely correlate with the calculated water content in their mantle sources. Our model suggests that the variation in the chemical composition of the primary magmas of the ELIP both on a local and regional scale can be mainly explained by the complementary roles of relatively dry recycled pyroxenite and hydrated components in the mantle plume, without requiring catastrophic thinning of the lithospheric mantle. Our model thus implies that both the initiation and chemical variation of the ELIP are affected by water from the deep mantle. Plain Language Summary: Large igneous provinces (LIPs) represent a manifestation of the activity of a mantle plume. In most LIPs, the chemical compositions of basalts are heterogeneous and can usually be divided into high‐Ti and low‐Ti groups. This division has been used to infer differences in the mantle composition and/or partial melting conditions, which ultimately reflect the picture of the compositional and thermal structure of the deep mantle and their partial melting processes. In this study, we report that both the high‐Ti and low‐Ti type picrites of the Emeishan LIP were derived from hydrous mantle sources and such a compositional dichotomy is closely associated with the water content of the mantle sources. This case study provides a new perspective to connect the presence of volatiles in the deep mantle, the activity of deep‐seated mantle plumes, and widespread basaltic magmatism on the Earth's surface. Key Points: Both high‐Ti and low‐Ti picrites in the Emeishan large igneous province are hydrousThe major and trace element compositions of picrites are related to the water content in their mantle sourcesCompositional variations in a large igneous provinces are affected by volatiles in mantle plumes [ABSTRACT FROM AUTHOR]

The Early Permian Tarim large igneous province (LIP) in northwestern China comprises voluminous basaltic lava flows, as well as ultramafic and silicic intrusions. The age and duration of the Tarim LIP remains unclear, and thus the rate of magma production and models of potential environmental effects are uncertain. Here we present high-precision chemical abrasion--isotope dilution--thermal ionization mass spectrometry zircon U-Pb ages for three newly discovered tuff layers interlayered with lava flows in the Kupukuziman and Kaipaizileike formations in the Keping area (Xinjiang, northwest China). The volcanism of the Kupukuziman Formation is constrained to a short duration from 289.77 ± 0.95 to 289.41 ± 0.52 Ma. An age for the overlying Kaipaizileike Formation is 284.27 ± 0.39 Ma, bracketing the duration of the entire eruptive phase of the Tarim flood basalts at ~5.5 m.y. The low eruption rate and relatively long duration of magmatism is consistent with a plume incubation model for the Tarim LIP. [ABSTRACT FROM AUTHOR]

The nature and source of magmatism associated with large igneous provinces (LIPs) remain disputed. Here we investigate the role of recycled materials that contributed to mantle heterogeneity in the Tarim Large Igneous Province (TLIP) in China through integrated Zn-Mg-Sr-Nd isotopes of a rare tephritic rock suite. The Sr--Nd isotopes [(87Sr/86Sr)i = 0.70368-0.70629; εNd(t) = -0.25-4.64] and δ26Mg values (-0.23‰ to -0.34‰) of the tephritic porphyries are consistent with a normal mantle origin. In contrast, the whole rock and pyroxene phenocrysts yield δ66Zn values of +0.28‰ to +0.46‰ and +0.30‰ to +0.39‰, which are slightly heavier than those of the terrestrial mantle (+0.16 ± 0.06‰) and mid-oceanic-ridge basalts (MORBs) (+0.27 ± 0.05‰). We exclude the possibility that the heavy Zn isotopes of the Wajilitag tephritic porphyries are caused by magmatic processes such as fractional crystallization and partial melting and correlate the isotopic features to the role of altered oceanic crust along with magnesite in the mantle source. The Wajilitag tephritic porphyry displays trace-element patterns similar to those of the melts from natural hornblendite, especially those of hornblendite + peridotite. Additionally, the geochemical characteristics such as enrichment in Nb and Ta, depletion in K, high TiO2, and constant Na2O/K2O ratios also suggest that the tephritic porphyries were derived from an amphibole-bearing source contributed by altered oceanic crust along with sedimentary carbonates. Our study provides insight into the contribution of subducted materials to the mantle heterogeneity beneath the TLIP and highlights the role of subduction in the deep carbon cycle and subducted slab-lithosphere-plume interaction in the generation of LIPs. [ABSTRACT FROM AUTHOR]

Paleosols that developed on large igneous province flood basalts provide a valuable opportunity to quantitatively reconstruct the terrestrial paleoclimate during a given period. This study uses a newly constructed basaltic soil–climate function to obtain terrestrial paleoclimatic data following the termination of the Emeishan basalt eruption in the late Lopingian (∼253 Ma). The constructed relationships are mean annual temperature of 32.81 e −0.4166 X ( R 2 = 0.55 , standard error [SE] = 4.6 ° C ) and mean annual precipitation of −875.5 ln (X) + 1792 ( R 2 = 0.69 , SE = 328 mm), where X = SiO 2 / ( Al 2 O 3 + Fe 2 O 3 ) (the Saf index). We collected samples from nine paleosol profiles developed on the last-phase Emeishan basalts and conducted field observations as well as micromorphological, mineral composition, and geochemical analyses. On the basis of these paleosols, we reconstructed the regional mean temperature and precipitation to be 18.9 ° C ± 4.6 ° C and 1546 ± 328 mm, respectively. The regional climate was cooler than those in modern equatorial regions of similar latitudes. The reduced CO2 concentration in the atmosphere resulting from rapid weathering of Emeishan basalts in a tropical climate could have played a dominant role in causing the regional cool terrestrial paleoclimate following the termination of the Emeishan basalt eruption. [ABSTRACT FROM AUTHOR]

The spatial distribution of the satellite lithospheric magnetic field is analyzed as a parameter associated with plume magmatism processes occurring in the territory of large igneous magmatic provinces. We showed that magnetic anomalies can be considered as images of mantle plumes of various geneses, along with tomographic images of seismic velocities. According to the methods developed by the authors, the parameters of the anomalous magnetic lithospheric field were extracted from the total geomagnetic field data with the CHAMP satellite. Maps of the modulus of total vector Ta and vertical component Za of anomalies of various scales and observation heights were constructed when its altitude was the lowest. The magnetic images of plumes are illustrated by the example of three plumes of different ages in order of decreasing age: Tarim (~280 Ma), Ethiopian (~60–30 Ma), and Iceland (~0–5 Ma). The relationship between magnetic-field anomalies and plume magmatism processes occurring in their territories is analyzed. We found that an ancient mantle plum is reflected in the lithospheric magnetic field as conformal positive anomaly of significant amplitudes. The lithospheric magnetic field of the comparatively "young" Ethiopian and still active Icelandic plumes is greatly reduced. We concluded that satellite observations of the lithospheric magnetic field, in combination with other geological and geophysical data of a regional scale, add valuable information to the overall picture of tectonic processes, allowing one to analyze their degree of magnetization and the temperature state of the lithosphere. [ABSTRACT FROM AUTHOR]

We investigated a 1‐km‐thick sequence of lava flows that erupted over the Afar plume axis in order to better understand the emplacement history of the ∼30 Ma Ethiopia‐Yemen Traps. Geochemical analyses reveal high‐titanium concentrations (TiO2 3.9 ± 0.5 wt%) in basalts close to picritic compositions. Indistinguishable 40Ar/39Ar ages throughout the section define a weighted‐mean of 31.18 ± 0.28 Ma (95% confidence). This date, together with solely normal polarity magnetization directions in 68 geomagnetically independent horizons, constrain the eruption to within chron C12n, with a maximum duration of a few hundreds of kyr for the entire 1‐km‐thick section. The rate of geomagnetic secular variation used as a chronometer refines the duration to only a few tens of kyr, leading to a local extrusion rate of 4–13 km3/yr for the Afar plume head, which greatly exceeds the average rate of 0.3–1.2 km3/yr for the entire Ethiopia‐Yemen Traps. Plain Language Summary: The Ethiopia‐Yemen Traps are the expression of an important geodynamic process where a mantle plume pierced the lithosphere, resulting in the massive outpouring of a few million km3 of basaltic lava over a geologically brief (1–3 Myr) interval. Here, we provide constraints on the extrusion rate of lava flows from the 1‐km‐thick Waja section, which originated from the Afar mantle plume head. Radioisotopic and magnetostratigraphic results indicate that the outpouring of the lava spanned only a few hundreds of kyr. Moreover, incessant eruption provides a continuous record of changes in the ancient magnetic field direction, called secular variation, which can also be used as a chronometer. A limited amount of secular variation at Waja refines the maximum duration to only a few tens of kyr. The corresponding extrusion rate of 4–13 km3/yr greatly exceeds the average rate of 0.3–1.2 km3/yr for the entire Ethiopia‐Yemen Traps. Consistent with geodynamic models predicting that plume head eruptions are the most intense, our results suggest that 20% of the trap basalts were emplaced within ∼0.02–0.2 Myr, whereas the remaining 80% were erupted over ca. 1.5 Myr. Key Points: 1‐km‐thick picritic basalts at the Waja section were emplaced at the onset of chron C12n (∼31 Ma) above the Afar mantle plume headThe Waja section was extruded in <260 kyr according to Ar‐Ar dating and at least 20 kyr using a secular variation geochronometerExtrusion rates above the Afar plume head were >10 km3/yr, compared to 0.3–1.2 km3/yr for the entire Ethiopia‐Yemen Traps [ABSTRACT FROM AUTHOR]

The volcanic rocks of the Colíder and Roosevelt formations are extensively exposed in the south-central portion of the Amazonian Craton where effusive and pyroclastic rocks have been mapped. Both units, topped by chemical sediments and oceanic facies as rhyolite and andesite lavas, rhyodacite, and porphyritic dacite, with frequent intercalations of pyroclastic and epiclastic deposits. Whole-rock geochemistry for 55 samples of rhyolitic to andesitic composition suggests the involvement of fertile mantle-derived components with E-MORB to OIB compositions. The analyzed rocks display calc-alkaline to shoshonitic affinity consistent with generation related to an active continental margin. The whole-rock Sm-Nd isotope data from selected felsic volcanic rocks of the Colíder and Roosevelt formations yield negative initial εNd values between –3 and –9, indicating the predominantly crustal nature of the parental magmas with early Archean to late Paleoproterozoic (ca. 2.5–2.0 Ga) depleted mantle model ages. [ABSTRACT FROM AUTHOR]

The end-Permian crisis was the most severe extinction event in the Phanerozoic. In Southwestern Gondwana, this crisis was related to the development of the Choiyoi Silicic Large Igneous Province. In the Southern Hemisphere, the Glossopteridales were dominant in the Permian, and they declined at the Permian–Triassic boundary and were replaced by the Dicroidium flora. Argentinean Permian and Triassic floras are known for more than a century, but recently, new stratigraphic schemes and more accurate geochronological information have put in question the previous evolution models. Here we proposed a new scenario for the vegetation evolution during the Permian–Triassic boundary and early Middle Triassic in Argentina. During the Wuchiapingian–early Changhsingian interval, the floras were dominated by Glossopteridales, Cordaitales, Asterothecaceae, and Voltziales, and the oldest record of Umkomasiales (=Corystospermales), Peltaspermales, and Cycadales occurs. The Glossopteris flora would have disappeared in the Changhsingian before the end-Permian crisis. The late Changhsingian vegetation was dominated by cycads typical of the Dicroidium flora surviving in a refuge zone. After the end-Permian crisis, the recuperation was carried out by corystosperms, cycads and sphenophytes in the Induan–Olenekian interval. The Anisian plant communities were well-stabilised and diverse, corresponding to radiation of the Dicroidium flora. [ABSTRACT FROM AUTHOR]

The early Permian basalts of the Tarim Basin of NW China are geographically widespread, covering over 200,000 km2 and are in places up to 1‐km thick and hence frequently referred to represent a Large Igneous Province (LIP). Available volume estimates are based on average lava thickness multiplied by area, using these values results in volumes exceeding 100,000 km3, and is commonly cited as being evidence of LIP status. Using a database of 58 boreholes, field sections, and seismic data we calculate a range of basalt isopach maps, and use these to estimate new, more refined overall eruption volumes. These volumes are significantly smaller than previously reported estimates. We demonstrate that the thickness distribution of erupted basalts is nonuniform and strongly skewed, indicating that volume estimates using an arithmetically averaged thickness of input data will result in overestimation of total volumes. We find that even with the addition of an estimated nonerupted volume component, representing cumulates and intrusions, that the total volume of the Tarim volcanics is significantly below the minimum threshold of a LIP. Using a simple Monte Carlo model we demonstrate that even while accounting for uncertainty and error in the input data, the probability of the total volume exceeding 100,000 km3 is very low. The new volume estimates imply a revision of the climate and environmental impact of the Tarim volcanism. We therefore suggest that the term Tarim Igneous Province should be used instead of Tarim Large Igneous Province. Plain Language Summary: The early Permian (287–267 million years ago) basaltic rocks of the Tarim Basin in Northwestern China are geographically widespread, and can be up to 1 km in thickness. This has led to the hypothesis that these rocks represent a period of significantly voluminous igneous activity across the area, in what is known as a Large Igneous Province (LIP). LIP are defined by a set of criteria including area, volume, and a short‐duration of emplacement. In this study, we have collated all available data to test whether the basalts within the Tarim Basin meet the minimum criteria to be classified as a LIP. In this study, we demonstrate that when integrating a large number of geographically widespread boreholes and outcrops, regional seismic data and published age data that the Tarim basalts represent a significant period of igneous activity, but do not meet the threshold of a LIP. This finding is important as the volume of igneous rock formed during periods of intense igneous activity is used in geological and climate models to infer past climatic effects and extinctions. We also demonstrate that relatively simple calculations of the volume of LIPs will typically overestimate their volume and thus environmental impact, and therefore suggest that all future studies of this nature should aim to integrate all available data and consider uncertainty and probability when estimating eruption volumes. Key Points: We estimate the erupted and total igneous volume of the upper Permian Tarim basaltsCalculated volumes are below the minimum definition of a Large Igneous Province (LIP) and we suggest the use of the term Tarim Igneous ProvinceWhen estimating LIP volumes, average thickness multiplied by area leads to overestimates of volume and should not be used [ABSTRACT FROM AUTHOR]

This study presents new whole rock major and trace element, Sr-Nd isotopic, petrographic, and geochronologic data for seven latest Permian (Changhsingian)-Late Triassic (Carnian) granitoid intrusions of the northwestern and northeastern Taimyr Peninsula in the Russian High Arctic. U-Pb zircon ages, obtained using secondary ion mass spectrometry (SIMS), sensitive high-resolution ion microprobe (SHRIMP), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), define the crystallization age of the Taimyr intrusions studied as ranging from ca. 253 Ma to 228 Ma, which suggests two magmatic pulses of latest Permian-Early Triassic and Middle-Late Triassic age. Ar-Ar dating of biotite and amphibole indicate rapid cooling of the intrusions studied, but Ar-Ar ages of several samples were reset by secondary heating and hydrothermal activity induced by the Middle-Late Triassic magmatic pulse. Petrographic data distinguish two groups of granites: syenite-monzonites and granites-granodiorites. Sr-Nd isotopic data, obtained from the same intrusions, show a variation of initial (87Sr/86Sr)i ratios between 0.70377 and 0.70607, and εNd(t) values range between -6.9 and 1.2. We propose that the geochemical and isotopic compositions of the Late Permian-Triassic Taimyr granites record the existence of a magma mush zone that was generated by the two pulses of Siberian Traps large igneous province (LIP) magmatism. [ABSTRACT FROM AUTHOR]

This article presents a detailed petrographic, mineralogical and geochemical study of clay, silt, sand and fine gravel generated in the Paraná–Etendeka large igneous province, once united and today exposed in contrasting climatic and orographic conditions on conjugate sides of the Atlantic Ocean. The comparison between low‐relief wetter Uruguay and steeper hyper‐dry Namibia allows to investigate the influence of weathering on basalt‐derived sediments spanning in grain size from <2 μm to >2000 μm. In Namibia, as in Uruguay, X‐ray diffraction analyses of mud samples from streams draining basaltic lavas show only smectitic clay minerals. Macroscopic and microscopic observations indicate that sand is composed in variable proportions of glassy to lathwork volcanic rock fragments, plagioclase and augitic clinopyroxene with minor pigeonite, and gravel dominantly consists of volcanic clasts with chalcedony or quartz geodes occurring locally. Geochemical data highlight the strong grain‐size dependence of weathering intensity. Whereas fine gravel closely reflects source‐rock composition in both Namibia and Uruguay, and mobile elements in sand are moderately depleted, αAlE indices increase notably in silt and reach maximum in clay, with mobility sequence Na >> Ca ≥ Mg > Sr > K. Differences in sand versus mud generation potential in the two regions are prominent. Namibian rivers draining the dry Etendeka Plateau carry purely volcaniclastic sand, whereas streams draining even exclusively the Paraná lava field carry sediments containing invariably significant and even overwhelming amounts of recycled quartz, testifying to the much greater sand‐generation potential of the very‐locally‐exposed underlying, interbedded or overlying quartz‐rich sandstones and loess deposits. Smectite is dominant throughout the Uruguay River catchment, even in the lower course where sand is pure quartzose and pyroxene negligible. A comparison with basaltic provinces worldwide indicates that, especially in low‐relief wet regions where weathering is intense, basalt generates gravel, very minor sand and abundant smectite. Kaolinite forms where chemical leaching is extreme. [ABSTRACT FROM AUTHOR]

Here we present reconstructions indicating the stationary position and paleogeography of the Iceland plume, as well as its direct connection to the Mesozoic–Cenozoic large igneous provinces of the northern Atlantic and the Arctic. The main evidence for the stationary position of the Iceland hotspot comes from paleomagnetic data for the trap formation of the Franz Josef Land archipelago. Our reconstructions show that the Barents Sea magmatic province included in these traps belongs to the trace of the Iceland plume and formed as part of the High Arctic Large Igneous Province during a single relatively brief event ca. 125 Ma. Older pulses of basaltic magmatism inferred previously for the Franz Josef Land archipelago for the Early and Middle Jurassic period do not have known analogs in adjacent territories of the present-day Arctic. [ABSTRACT FROM AUTHOR]

40Ar/39Ar geochronology is one of the most important techniques for constraining the timing of basaltic events due to the paucity of suitable minerals in basalts for other geochronological techniques such as U–Pb (e.g., zircon, baddeleyite). Among a variety of materials from basaltic rocks that have been used for 40Ar/39Ar dating, plagioclase is the most important due to its common presence in basalts as a primary crystallizing phase, and its transparency so that fresh grains can be selected during sample preparation. However, plagioclase 40Ar/39Ar geochronology has often been compromised by alteration (e.g., sericitization by hydrothermal events), which, in practice, is difficult to identify using a petrographic microscope when the amount of alteration is low (e.g., <1%). We used laboratory step-heating experiments and theoretical simulations to characterize the 40Ar/39Ar age and Ca/K spectra of altered plagioclase so that 40Ar/39Ar dating results on altered samples can be identified and better interpreted. The step-heating experiments and theoretical simulations yielded consistent results, and show that with the presence of even a tiny amount of sericite (~0.01% for K-poor samples and ~0.1% for K-rich samples), the plagioclase samples yielded alteration plateau ages that are 3%–4% younger than the crystallization age. The difference between the alteration age of sericitized plagioclase and its crystallization age is primarily controlled by the time lapse between the crystallization and sericitization events, but also by the Ca/K ratios of the plagioclase. For plagioclase samples that experienced the same alteration event, the higher the Ca/K ratio is, the more sensitive the 40Ar/39Ar age is to alteration. We propose that the alteration signatures of plagioclase can be effectively identified through inspecting the 40Ar/39Ar age spectra, the Ca/K spectra, and the degassing curves. We also investigated the effect of sericitization of plagioclase microliths in basaltic groundmass and modelled the 40Ar/39Ar age and Ca/K spectra of altered groundmass samples. We validate our approach by revisiting published 40Ar/39Ar dating results for large igneous provinces, and showed that these dates should have been interpreted as alteration ages (minimum eruption ages) rather than crystallization ages. Finally, we demonstrate that with high degrees of alteration (~50% for K-poor and >70% for K-rich plagioclase samples), the age of hydrothermal alteration can be successfully dated. [ABSTRACT FROM AUTHOR]

Separated mass extinction occurred at the beginning and the ending of the Late Permian, called end‐Guadalupian and end‐Permian mass extinctions, respectively. Palaeoenvironmental changes in the middle of the Late Permian could give more insights into the environmental causes for the Permian extinctions. In this contribution, we analysed carbonate carbon isotope and carbonate‐associated‐sulphate sulphur isotope compositions to constrain the carbon and sulphur cycles across the Wuchiapingian‐Changhsingian boundary (WCB) at Yanglinqiao in Zigui in the Middle Yangtze Platform. Pyrite morphology and pyrite framboids size distribution were used to analyse redox conditions variations across the WCB. Our results show that an episodic euxinia event occurred across the WCB. This anoxic/euxinic event across the WCB was a global event, and was mainly caused by the upwelling during the cooling event. Both inorganic‐ and organic‐carbon isotopic compositions show covariance of a negative shift across the WCB at Yanglinqiao and other places in South China. This carbon‐isotopic negative excursion across the WCB was a regional carbon cycle perturbation and may be linked to the light‐carbon input from the upwelling water mass. Although the seawater δ34S across the WCB recorded a negative excursion in two locations in South China, it reflects the riverine input of 32S‐enriched sulphate and represent a regional signal. These environmental anomalies such as oceanic anoxia/euxinia, global carbon cycle perturbation, cooling, end of the Emeishan large igneous province movement across the WCB may have delayed the recovery from the end‐Guadalupian mass extinction. [ABSTRACT FROM AUTHOR]

In this study, we present a machine learning-based method to predict trace element concentrations from major and minor element concentration data using a legacy lithogeochemical database of magmatic rocks from the Karoo large igneous province (Gondwana Supercontinent). Wedemonstrate that a variety of trace elements, including most of the lanthanides, chalcophile, lithophile, and siderophile elements, can be predicted with excellent accuracy. This finding reveals that there are reliable, high-dimensional elemental associations that can be used to predict trace elements in a range of plutonic and volcanic rocks. Since the major and minor elements are used as predictors, prediction performance can be used as a direct proxy for geochemical anomalies. As such, our proposed method is suitable for prospective exploration by identifying anomalous trace element concentrations. Compared to multivariate compositional data analysis methods, the new method does not rely on assumptions of stoichiometric combinations of elements in the data to discover geochemical anomalies. Because we do not use multivariate compositional data analysis techniques (e.g. principal component analysis and combined use of major, minor and trace elements data), we also show that log-ratio transforms do not increase the performance of the proposed approach and are unnecessary for algorithms that are not spatially aware in the feature space. Therefore, we demonstrate that high-dimensional elemental associations can be modelled in an automated manner through a data-driven approach and without assumptions of stoichiometry within the data. The approach proposed in this study can be used as a replacement method to the multivariate compositional data analysis technique that is used for prospectivity mapping, or be used as a pre-processor to reduce the detection of false geochemical anomalies, particularly where the data is of variable quality. [ABSTRACT FROM AUTHOR]

The main phase of silicic volcanism from the Afro-Arabian large igneous province preserves some of the largest volcanic eruptions on Earth, with six units totaling >8,600 km3 dense rock equivalent (DRE). The large volumes of rapidly emplaced individual eruptions present a case study for examining the tempo of voluminous silicic magma generation and emplacement. Here were report high-precision 206Pb/238U zircon ages and show that the largest sequentially dated eruptions occurred within 48 ± 34 kyr (29.755 ± 0.023 Ma to 29.707 ± 0.025 Ma), yielding the highest known long-term volumetric extrusive rate of silicic volcanism on Earth. While these are the largest known sequential silicic supereruptions, they did not cause major global environmental change. We also provide a robust tie-point for calibration of the geomagnetic polarity timescale by integrating 40Ar/39Ar data with our 206Pb/238U ages to yield new constraints on the duration of the C11n.1r Subchron. Quantifying the tempo of large-volume silicic magma generation and eruption is a long-standing but elusive task. Here we show that the three largest sequentially dated eruptions, totaling >4,300 km3, occurred within 48 ± 34 kyr and yield the highest known long term volumetric extrusive rate of silicic volcanism on Earth. [ABSTRACT FROM AUTHOR]

The spatial relationships of the lower mantle D" layer elements with Phanerozoic Large Igneous Provinces (LIPs), as well as with the young hotspots and kimberlites in the African region, are discussed. Similar relationships are also shown for the Cape Karoo and Parana extended basins, which had developed as inherited structures along the marginal parts of the region since the Early Paleozoic. The specific locations are marked for all these superficial structures and plumes producing them. These locations indicate the connection between these structures origin and the domains where the Earth's core, Large Low-Velocity Provinces (LLSVPs), and slab graveyards contact with each other. The relationships between plume- and plate-tectonic processes in the Earth's evolution are considered. Constant interaction between the Pacific and Indo-Atlantic segments of the Earth is revealed in the course of these processes. The Pacific segment was characterized by ocean formation during the Phanerozoic time and subsequent subduction under the continental landmasses of Indo-Atlantic segment. The constant character of spreading in the Pacific Ocean was obviously determined by the presence of its direct connection with the Pacific LLSVP. Within the D" layer in the areas of contact between the Pacific subducting slabs and African LLSVP, plume generation occurred periodically, subsequently leading to supercontinental breakup. This determined the specific character of the Indo-Atlantic segment development: the alternation of convergence and continental breakup during the Phanerozoic. In general, despite the significant similarities between the antipodal African and Pacific LLSVPs, their role in formation of the superficial largest structural elements appears to be inequable. Perhaps this is what had become one of the main reasons that caused fundamental differences between these two segments and led to the formation of tectonic asymmetry of the Earth. [ABSTRACT FROM AUTHOR]

Non-marine tetrapods (amphibians, reptiles, birds and mammals) have apparently experienced at least 10 distinct episodes of intensified extinctions over the past 300 My. Eight of these ten non-marine extinction events are concurrent with known marine-extinction episodes, which previously yielded evidence for an underlying period of ~26.4 to 27.3 My. We performed circular spectral analysis and Fourier transform analysis of the ages of the ten recognised tetrapod-extinction events, and detected a statistically significant (99% confidence) underlying periodicity of ~27.5 My. We also find that the eight coeval non-marine/marine-extinction pulses all occurred at the times of eruptions of Large Igneous Provinces (LIPs) (continental flood-basalts and oceanic plateaus), with potentially severe environmental effects. Three of these co-extinction episodes are further correlated with the ages of the three largest (≥100-km diameter) impact craters of the last 260 My, which are also apparently capable of causing extinction events. These findings suggest that global cataclysmal events with an underlying periodicity of ~27.5 My were the cause of the coordinated periodic extinction episodes of non-marine tetrapods and marine organisms. [ABSTRACT FROM AUTHOR]

A new geodynamic model of the Cretaceous–Cenozoic evolution of the Arctic has been developed in recent years at the Shirshov Institute of Oceanology, Russian Academy of Sciences, with the participation of Geological Institute, Russian Academy of Sciences, and the Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences. In the framework of this model, the upper mantle convection associated with the Pacific subduction zone plays the main role; based on this model, we also propose a mechanism of crustal subduction, leading to the formation of oceanic depressions and sedimentary basins, as well as the emergence of large magmatic provinces in the Arctic. This mechanism is associated with the establishment of an upper mantle convection regime, which is more complex in comparison with the initial one; along with the existence of a long, horizontally elongated convective cell (which produces the effect of conveyor drag of the lithosphere), this regime is characterized by the appearance of inner isometric cells (which produce the effect of upper mantle plumes). These isometric cells lead to the formation of igneous provinces if, under conditions of stretching of the lithosphere, faults are formed to provide magma eruption to the surface. If the geomechanical conditions in the lithosphere impede the magma outflow, then, upon cooling, a lens of magma-derived volume, located at the base of the thinned lithosphere, should undergo a phase transition with the formation of heavy eclogite rocks, which causes the formation of deep basins and deep sedimentary basins in the Arctic. [ABSTRACT FROM AUTHOR]

Osmium isotopes, whole rock and mineral geochemical data from peridotite xenoliths from two Miocene McMurdo Volcanic Group cinder cones in the Transantarctic Mountains (TAM) in Southern Victoria Land, Antarctica, reveal that the underlying mantle preserves evidence for major mid-Proterozoic lithosphere formation despite the crust being dominated by late Neoproterozoic-Ordovician (~0.65–0.47 Ga) rocks. The Hooper Crags xenolith suite is dominated by harzburgites with highly refractory olivine Mg# (up to 92.3) and depleted bulk rock major and platinum group element + Re abundances, with 187Os/188Os ratios indicating depletion in the mid-Proterozoic. Pipecleaner Glacier xenoliths, 18 km distant, are lherzolites with olivine Mg# (<91) and fertile major and platinum group element abundances, with Os isotope abundances defining an aluminochron that also indicates mid-Proterozoic depletion. Although exposed crust along this portion of Antarctica reveals only minor evidence for Proterozoic magmatism, the major episode of lithosphere formation indicated by the Os isotope data is supported by published bulk rock Sm-Nd isotope and zircon εHf mantle model ages of Neoproterozoic to Ordovician plutonic rocks. The heterogeneous circum-cratonic mid-Proterozoic mantle under Southern Victoria Land has therefore persisted on a Ga timescale, including through the formation and destruction of Rodinia and Gondwana supercontinents as well as extensive crustal melting and emplacement of the Ferrar large igneous province. This longevity may be due to the thick (>250 km) East Antarctic Craton lithosphere shielding the immediately adjacent circum-cratonic mantle from being affected by convective asthenosphere-driven erosion. This contrasts with mantle lithosphere accreted distally to the East Antarctic Craton (represented by the now-detached Zealandia continent), which did not attain extreme thickness and has therefore been more susceptible to tectonic reworking and lateral translation. [ABSTRACT FROM AUTHOR]

Many silicic plutonic rocks of the Late Permian Emeishan large igneous province (ELIP) are spatially and temporally related to oxide ore-bearing layered mafic–ultramafic intrusions. Their association suggests that there may be a petrogenetic link between the two rock types where the layered intrusion represents the cumulate portion of the magma system and the silicic rocks are the residual liquid portion. An alkali feldspar syenite collected in close spatial association with the Hongge-layered mafic–ultramafic intrusion yielded a weighted-mean zircon U–Pb age of 261.5 ± 2.4 Ma with a corresponding weighted-mean εHf(t) value of + 6.5 ± 0.5. The Hongge syenite is alkalic, metaluminous, and ferroan and somewhat similar to other A-type granitoids of the ELIP but, it is composed of ~ 90 vol% alkali feldspar. The rocks have initial 87Sr/86Sr ratios of 0.70570 and 0.70515 and εNd(t) values of − 0.3 and + 1.4. Rhyolite-MELTS and isotopic modeling indicate that the Hongge syenite is likely produced by crystal accumulation of a residual silicic liquid derived from a mafic parental magma that experienced localized crustal contamination during emplacement. Moreover, the age, location, and composition of the Hongge syenite suggests that it is the uppermost portion of the Hongge-layered intrusion and is representative of the residual silicic liquid of the mafic magmas that form the plagioclase-rich cumulate gabbros of the upper zone. [ABSTRACT FROM AUTHOR]

The evolutionary nature of the Neoarchean basement, concealed below 66 Ma Deccan Large Igneous Province, remains largely unknown. We present here detailed results of integrated geoscientific investigations, carried out on 43 basement cores that cover an entire 270 m thick column, penetrated by the KLR-1 deep scientific borehole, drilled in the epicentral zone of 1993 Killari earthquake (Maharashtra, India). They dominantly contain high velocity-high density, halogen-rich, retrogressed and metasomatized amphibolite to granulite facies mid-crustal rocks, with intercalations of TTG, which were subjected to temperatures between 540 and 860 °C and pressure 5–7 kb, equating to 15–21 km emplacement depth. The granitic-gneissic layer, typical of the upper crust, appears absent. Geochemically, these iron-rich rocks are characterized by wide variation in which SiO2, MgO and FeOT contents vary from 45.12 to 69.96 wt% (avg. 58.11 wt%), 0.18–11.95 wt% (avg. 4.22 wt%), and 0.34–22.92 wt% (avg. 9.01 wt%) respectively. Measured FeOT contents are even higher than the normal lower crust. The granulite rocks exhibit tholeiite affinity, while amphibolite (which dominate the lithology) and TTG rocks show calc-alkaline character. Further, chondrite and primitive mantle normalized plots, show consistent and complimentary REE patterns (except in HREE), with negative Eu anomalies and LILE enrichment, indicating source rock fractionation. Well-marked depletion in Nb–Ta, Zr–Hf, subordinate depletion in Sr and Ba, and their distinct calc-alkaline to tholeiite character, indicate their subduction zone/arc-related affinity. In addition, large-scale crust-mantle interaction and pervasive metasomatism, have led to considerable alteration to the basic fabric of the rock thereby making it weak and characterized by reduced velocities due to biotitization and substantial Fe-enrichment. Quite likely, earthquake nucleation in intraplate stable regions may have a close link with mantle metasomatism. [ABSTRACT FROM AUTHOR]

The 1.87-1.84 Ga Black Hills dike swarm of the Kalahari craton (South Africa) is coeval with several regional magmatic provinces used here to resolve the craton's position during Columbia assembly. We report a new 1850 ± 4 Ma (U-Pb isotope dilution-thermal ionization mass spectrometry [ID-TIMS] on baddeleyite) crystallization age for one dike and new paleomagnetic data for 34 dikes of which 8 have precise U-Pb ages. Results are constrained by positive baked-contact and reversal tests, which combined with existing data produce a 1.87-1.84 Ga mean pole from 63 individual dikes. By integrating paleomagnetic and geochronological data sets, we calculate poles for three magmatic episodes and produce a magnetostratigraphic record. At 1.88 Ga, the Kalahari craton is reconstructed next to the Superior craton so that their ca. 2.0 Ga poles align. As such, magmatism forms part of a radiating pattern with the coeval ca. 1.88 Ga Circum-Superior large igneous province. [ABSTRACT FROM AUTHOR]

The emplacement of the Karoo Large Igneous Province (LIP) occurred synchronously with the Toarcian crisis (ca. 183 Ma), which is characterized by major carbon cycle perturbations. A marked increase in the atmospheric concentration of CO2 (pCO2) attests to significant input of carbon, while negative carbon isotope excursions (CIEs) in marine and terrestrial records suggest the involvement of a 12C-enriched source. Here we explore the effects of pulsed carbon release from the Karoo LIP on atmospheric pCO2 and δ13C of marine sediments, using the GEOCLIM carbon cycle model. We show that a total of 20,500 Gt C replicates the Toarcian pCO2 and δ13C proxy data, and that thermogenic carbon (δ13C of −36 ‰) represents a plausible source for the observed negative CIEs. Importantly, an extremely isotopically depleted carbon source, such as methane clathrates, is not required in order to replicate the negative CIEs. Although exact values of individual degassing pulses represent estimates, we consider our emission scenario realistic as it incorporates the available geological knowledge of the Karoo LIP and a representative framework for Earth system processes during the Toarcian. The emplacement of the Karoo LIP occurred synchronously with the Toarcian crisis, which is characterized by negative carbon isotope excursions. Here the authors use carbon cycle modelling to show that thermogenic carbon released during LIP emplacement represents a plausible source for the negative excursions. [ABSTRACT FROM AUTHOR]

Mesoproterozoic period included several global tectonic events like break-up of Nuna and formation of Rodinia. However, although Siberia is a significant piece of both supercontinents, Mesoproterozoic time is marked by quiescence of magmatic and tectonic activity in it. We report here a mafic dyke (named Gornostakh dyke) in the southeastern Siberian Craton dated at 1419 ± 32 Ma by LA-ICPMS U–Pb geochronology of apatite. The dyke has tholeiitic compositions with high MgO and alkaline content, low-Ti, and arc-like trace element pattern. Due to the absence of subduction tectonics in the study area, geochemical data could be attributed to a significant contribution from metasomatically enriched subcontinental lithospheric mantle previously modified by subduction processes. That kind of composition is common for low-Ti dykes of intraplate flood basalt provinces similar to, for example, Permian–Triassic Siberian large igneous province (LIP). Paleogeographic reconstructions suggest that Siberia was connected to Laurentia and Baltica and their reconfiguration interrupts a prolonged tectonic quiescence in the Siberian Craton from ca. 1.88 Ga reflecting a transition from Nuna to Rodinia configuration. The mafic magmatism on 1419 Ma on the southeastern margin of the Siberian Craton together with coeval extensional tectonics observed in the structure of the Sette-Daban ridge proposes a hypothetical LIP which may be a direct consequence of the beginning of this transition. [ABSTRACT FROM AUTHOR]

The Late Triassic Carnian Pluvial Episode (CPE) saw a dramatic increase in global humidity and temperature that has been linked to the large-scale volcanism of the Wrangellia large igneous province. The climatic changes coincide with a major biological turnover on land that included the ascent of the dinosaurs and the origin of modern conifers. However, linking the disparate cause and effects of the CPE has yet to be achieved because of the lack of a detailed terrestrial record of these events. Here, we present a multidisciplinary record of volcanism and environmental change from an expanded Carnian lake succession of the Jiyuan Basin, North China. New U–Pb zircon dating, high-resolution chemostratigraphy, and palynological and sedimentological data reveal that terrestrial conditions in the region were in remarkable lockstep with the large-scale volcanism. Using the sedimentary mercury record as a proxy for eruptions reveals four discrete episodes during the CPE interval (ca. 234.0 to 232.4 Ma). Each eruptive phase correlated with large, negative C isotope excursions and major climatic changes to more humid conditions (marked by increased importance of hygrophytic plants), lake expansion, and eutrophication. Our results show that large igneous province eruptions can occur in multiple, discrete pulses, rather than showing a simple acme-and-decline history, and demonstrate their powerful ability to alter the global C cycle, cause climate change, and drive macroevolution, at least in the Triassic. [ABSTRACT FROM AUTHOR]

The Earth's gravity field measurements and their applications for resource exploration and geodynamic studies form an important part of geophysical studies initiated at the CSIR-National Geophysical Research Institute (CSIR-NGRI) since its inception. Finite Element analysis for regional-residual separation, scaling attributes of the source distribution, together with the mathematical formulation to density distribution in sedimentary basins have transformed the interpretation of gravity data. Collection, collation, and standardization of terrestrial gravity data have led to the compilation of the Gravity Map Series of India. Analyses of these data with contemporary computational technologies help in deciphering better-resolved density models under different parts of the Indian plate. These studies have provided well-constrained models of active and ancient continental collision zones, magmatic underplating beneath large igneous provinces, an integrated lithospheric density structure of Dharwar and Singhbhum cratons, the evolution of passive continental margins of India, and estimation of the effective strength of the Indian lithosphere. The studies on temporal gravity changes from terrestrial and satellite observations are also carried out to infer the redistribution of mass in the earthquake-prone regions and water storage variabilities over India. Recently, moving-platform gravity gradiometry has been introduced by the Institute in India. The gravity studies have continued to be a vital component of an integrated geophysical approach adopted by CSIR-NGRI for shallow and deep earth explorations. [ABSTRACT FROM AUTHOR]

The location of the West African craton (WAC) has been poorly constrained in the Paleoproterozoic-Mesoproterozoic supercontinent Nuna (also known as Columbia). Previous Nuna reconstruction models suggested that the WAC was connected to Amazonia in a way similar to their relative position in Gondwana. By an integrated paleomagnetic and geochronological study of the Proterozoic mafic dikes in the Anti-Atlas Belt, Morocco, we provide two reliable paleomagnetic poles to test this connection. Incorporating our new poles with quality-filtered poles from the neighboring cratons of the WAC, we propose an inverted WAC-Amazonia connection, with the northern WAC attached to northeastern Amazonia, as well as a refined configuration of Nuna. Global large igneous province records also conform to our new reconstruction. The inverted WAC-Amazonia connection suggests a substantial change in their relative orientation from Nuna to Gondwana, providing an additional example of large-magnitude cumulative azimuthal rotations between adjacent continental blocks over supercontinental cycles. [ABSTRACT FROM AUTHOR]

The Midcontinent Rift System of North America is a ∼1.1 Ga large igneous province comprising mainly flood basalts and intrusive rocks. We present new data for the Pillar Lake Volcanics and Inspiration Sill from the northern edge of the Midcontinent Rift in the northwestern Nipigon Embayment. The Pillar Lake Volcanics comprise a ∼20–40 m thick, flat-lying sequence of mafic pillowed and massive flows, pillowed flow breccia, and hyaloclastite breccia. They are characterized by SiO2 of 52–54 wt%, TiO2 of 1.2–1.3 wt%, and K2O of 0.9–1.1 wt%. They are light rare earth element (LREE) enriched, with La/Smn of 3.0–4.4 with fractionated heavy rare earth elements (HREE) (Gd/Ybn = 1.4–1.7). The Inspiration diabase sill is ≤ 50 m thick and is in direct contact with the underlying Pillar Lake Volcanics. Baddeleyite and zircon data from the Inspiration Sill yield a combined U–Pb upper intercept age of 1105.6 ± 1.6 Ma. The Inspiration Sill is characterized by uniform SiO2 of 52–53 wt%, TiO2 of 1.1–1.2 wt%, and K2O of 0.9–1.2 wt%. Inspiration Sill samples are LREE enriched with La/Smn of 3.2–3.3 and fractionated HREE (Gd/Ybn = 1.6). The Pillar Lake Volcanics are at least 1120 Ma, and perhaps as old as 1130 Ma, and represent an early, thin, and restricted mafic volcanic sequence, largely preserved below the younger Inspiration Sill. The Pillar Lake Volcanics and Inspiration Sill display a marked geochemical similarity, suggesting that they may represent magmatism associated with the earliest stages of Midcontinent rifting. [ABSTRACT FROM AUTHOR]

The article overviews the existing data and ideas about the structure of the Atlantic–Arctic rift system, the youngest segment of which is the Western Arctic. The main properties of this system are the direction of its progradation towards the North Pole, the submeridional orientation of the rifts, their separation by latitudinal faults, and predominantly left-lateral shear displacement of individual segments. It is assumed that such a structure reflects the regularities in the distribution of lithospheric masses under the influence of the rotational factor. Their striving towards an equilibrium position relative to the axis of rotation is realized due to movements towards and along the equator. These processes ensure growth of the rift system; however, no driving forces for its further development after reaching the pole have been identified. An analog model of the sequential segregation of segments in a growing rift system is proposed. [ABSTRACT FROM AUTHOR]

The Cretaceous High Arctic Large Igneous Province (HALIP) in Canada, although dominated by tholeiites (135–90 Ma), contains two main groups of alkaline igneous rocks. The older alkaline rocks (∼96 Ma) scatter around major fault and basement structures. They are represented by the newly defined Fulmar Suite alkaline basalt dykes and sills, and include Hassel Formation volcanic rocks. The younger alkaline group is represented by the Wootton Intrusive Complex (92·2–92·7 Ma), and the Audhild Bay Suite (83–73 Ma), both emplaced near the northern coast of Ellesmere Island. Fulmar Suite rocks resemble EM-type ocean island basalts (OIB) and most show limited crustal contamination. The Fulmar Suite shows increases of P2O5 at near-constant Ba–K–Zr–Ti that are nearly orthogonal to predicted fractionation- or melting-related variations, which we interpret as the result of melting composite mantle sources containing a regionally widespread apatite-bearing enriched component (P1). Low-P2O5 Fulmar Suite variants overlap compositionally with enriched HALIP tholeiites, and fall on common garnet lherzolite trace element melting trajectories, suggesting variable degrees of melting of a geochemically similar source. High-P2O5 Hassel Formation basalts are unusual among Fulmar rocks, because they are strongly contaminated with depleted lower crust; and because they involve a high-P2O5–Ba–Eu mantle component (P2), similar to that seen in alkali basalt dykes from Greenland. The P2 component may have contained Ba–Eu-rich hawthorneite and/or carbonate minerals as well as apatite, and may typify parts of the Greenlandic sub-continental lithospheric mantle (SCLM). Mafic alkaline Audhild Bay Suite (ABS) rocks are volcanic and hypabyssal basanites, alkaline basalts and trachy-andesites, and resemble HIMU ocean island basalts in having high Nb, low Zr/Nb and low 87Sr/86Sri. These mafic alkaline rocks are associated with felsic alkaline lavas and syenitic intrusions, but crustally derived rhyodacites and rhyolites also exist. The Wootton Intrusive Complex (WIC) contains geochemically similar plutonic rocks (alkali gabbros, diorites and anatectic granites), and may represent a more deeply eroded, slightly older equivalent of the ABS. Low-P2O5 ABS and WIC alkaline mafic rocks have flat heavy rare earth element (HREE) profiles suggesting shallow mantle melting; whereas High-P2O5 variants have steep HREE profiles indicating deeper separation from garnet-bearing residues. Some High-P2O5 mafic ABS rocks seem to contain the P1 and P2 components identified in Fulmar–Hassel rocks, whereas other samples trend towards possible High-P2O5 + Zr (PZr) and High-P2O5 + K2O (PK) components. We argue that the strongly alkaline northern Ellesmere Island magmas sampled mineralogically heterogeneous veins or metasomes in Greenlandic-type SCLM, which contained trace phases such as apatite, carbonates, hawthorneite, zircon, mica or richterite. The geographically more widespread apatite-bearing component (P1) could have formed part of a heterogeneous plume or upwelling mantle current that also generated HALIP tholeiites when melted more extensively, but may also have resided in the SCLM as relics of older events. Rare HALIP alkaline rocks with high K–Rb–U–Th fall on mixing paths implying strong local contamination from either Sverdrup Basin sedimentary rocks or granitic upper crust. However, the scarcity of potassic alkaline HALIP facies, together with the other trace element and isotopic signatures, provides little support for a ubiquitous fossil sedimentary subduction-zone component in the HALIP mantle source. [ABSTRACT FROM AUTHOR]

Cretaceous High Arctic large igneous province (HALIP) sub-alkaline magmatic rocks in Canada are mostly evolved (MgO 2–7 wt%), sparsely plagioclase + clinopyroxene ± olivine-phyric tholeiitic basalts. There were two main HALIP continental flood basalt (CFB) eruption episodes: 135–120 Ma (Isachsen Fm.) and 105–90 Ma (Strand Fiord Fm.), both associated with cogenetic doleritic sills and dykes. Building on a large modern database, 16 HALIP tholeiite types are defined and grouped into genetic series using Ce vs Sm/YbNMORB distributions. Comparison with model melting curves implies that higher-Sm/Yb HALIP basalt types record low-degree melting of garnet-bearing mantle sources. More voluminous intermediate- and low-Sm/Yb HALIP basalt types separated from the mantle at shallower levels after further extensive melting in the spinel-peridotite field. Within a given Sm/Yb range, increases in incompatible elements such as Ce are coupled with progressive clockwise rotation of normalized incompatible trace element profiles. Trace element modeling implies this cannot be due to closed-system fractional crystallization but requires progressive and ubiquitous incorporation of a component resembling continental crust. The fractionation models imply that low-Sm/Yb HALIP basalts (∼7 wt% MgO) initially crystallized olivine gabbro assemblages, with lower-MgO basalts successively crystallizing gabbro and ilmenite-gabbro assemblages. In contrast, higher-Sm/Yb basalts fractionated more clinopyroxene and ilmenite, but extensive plagioclase fractionation is still required to explain developing negative Sr–Eu anomalies. Back-fractionation models require about 40 % addition of olivine to bring the most primitive HALIP basalts (∼7 % MgO) into equilibrium with Fo89 mantle. Inverse fractionation–assimilation modeling shrinks the CFB signature, making decontaminated model parental melts more similar to enriched mid-ocean ridge basalt. The progressive increase of the contamination signature within each HALIP tholeiitic differentiation series is not consistent with models involving derivation of HALIP basalts from a mantle source previously enriched by subduction. Strong interaction of basalt with Sverdrup Basin sedimentary rocks may cause localized over-enrichment in K–Rb–Th–U, but cannot explain strong Ba enrichment in the absence of concomitant K–Rb–Th–U enrichment. The localized Ba enrichment could reflect either a Ba-rich lithospheric mantle component that is strongly manifested in the coeval HALIP alkaline suites, or syn- to post-emplacement fluid-mediated transfer from Ba-rich host rocks. [ABSTRACT FROM AUTHOR]

The classical Backus–Gilbert method seeks localized Earth-structure averages at the shortest length scales possible, given a data set, data errors, and a threshold for acceptable model errors. The resolving length at a point is the width of the local averaging kernel, and the optimal averaging kernel is the narrowest one such that the model error is below a specified level. This approach is well suited for seismic tomography, which maps 3-D Earth structure using large sets of seismic measurements. The continual measurement-error decreases and data-redundancy increases have reduced the impact of random errors on tomographic models. Systematic errors, however, are resistant to data redundancy and their effect on the model is difficult to predict. Here, we develop a method for finding the optimal resolving length at every point, implementing it for surface-wave tomography. As in the Backus–Gilbert method, every solution at a point results from an entire-system inversion, and the model error is reduced by increasing the model-parameter averaging. The key advantage of our method stems from its direct, empirical evaluation of the posterior model error at a point. We first measure inter-station phase velocities at simultaneously recording station pairs and compute phase-velocity maps at densely, logarithmically spaced periods. Numerous versions of the maps with varying smoothness are then computed, ranging from very rough to very smooth. Phase-velocity curves extracted from the maps at every point can be inverted for shear-velocity (V S) profiles. As we show, errors in these phase-velocity curves increase nearly monotonically with the map roughness. We evaluate the error by isolating the roughness of the phase-velocity curve that cannot be explained by any Earth structure and determine the optimal resolving length at a point such that the error of the local phase-velocity curve is below a threshold. A 3-D V S model is then computed by the inversion of the composite phase-velocity maps with an optimal resolution at every point. The estimated optimal resolution shows smooth lateral variations, confirming the robustness of the procedure. Importantly, the optimal resolving length does not scale with the density of the data coverage: some of the best-sampled locations display relatively low lateral resolution, probably due to systematic errors in the data. We apply the method to image the lithosphere and underlying mantle beneath Ireland and Britain. Our very large data set was created using new data from Ireland Array, the Irish National Seismic Network, the UK Seismograph Network and other deployments. A total of 11 238 inter-station dispersion curves, spanning a very broad total period range (4–500 s), yield unprecedented data coverage of the area and provide fine regional resolution from the crust to the deep asthenosphere. The lateral resolution of the 3-D model is computed explicitly and varies from 39 km in central Ireland to over 800 km at the edges of the area, where the data coverage declines. Our tomography reveals pronounced, previously unknown variations in the lithospheric thickness beneath Ireland and Britain, with implications for their Caledonian assembly and for the mechanisms of the British Tertiary Igneous Province magmatism. [ABSTRACT FROM AUTHOR]

• Magnesium isotopic compositions are reported of magnetite in layered mafic intrusions for the first time. • Large Mg isotopic variation in magnetite is primarily governed by subsolidus processes. • Magnesium isotopic compositions of magnetite are related to mineral proportions in the cumulates. • Primitive Mg isotopic signature of coexisting Fe–Ti oxides indicates early crystallization in origin. To constrain the mechanisms governing the extremely large variations of Mg and Fe isotopes in magmatic Fe–Ti oxides in layered mafic intrusions, we investigate Mg isotopic compositions of magnetite, coupled with its chemical data and whole-rock major element and Sr-Nd isotope compositions from the Baima layered mafic intrusion in the Emeishan large igneous province, SW China. The Baima intrusion is mainly composed of magnetite-wehrlite and magnetite-troctolite (i.e., oxide-rich rocks) in the Lower Zone, and troctolite and gabbro (i.e., oxide-barren rocks) in the Middle and Upper Zones. Magnetite separates display large Mg isotopic variation, with δ26Mg ranging from −0.17 ± 0.06 to +0.58 ± 0.04‰ in the oxide-rich rocks and from −0.18 ± 0.06 to +0.98 ± 0.04‰ in the oxide-barren ones. The lack of correlation of δ26Mg with trace elements in magnetite and whole-rock Sr-Nd isotopic compositions indicates that the large Mg isotopic variation in magnetite was not produced by fractional crystallization, magma mixing, crustal contamination, and/or trapped liquid shift. Instead, equilibrium isotope fractionation induced by Mg–Fe re-equilibration between magnetite and ilmenite at different subsolidus temperatures controlled the Mg isotopic variation in the oxide-rich rocks; and kinetic isotope fractionation driven by Mg–Fe inter-diffusion between magnetite and olivine and/or clinopyroxene dominated the oxide-barren rocks. Both processes were primarily controlled by the assemblage and modal abundance of coexisting minerals to which magnetite adjoins. Overall, fractional crystallization and subsequent subsolidus diffusion played crucial roles in the genesis of the Fe–Ti oxides in the Baima intrusion. Our results also reveal widespread isotope disequilibrium between coexisting minerals in mafic magma chambers and suggest that Mg isotope geochemistry has a great potential to characterize the formation of Fe–Ti oxides in layered mafic intrusions. [ABSTRACT FROM AUTHOR]

The chemical compositions of Phanerozoic basalts of all known geodynamic settings (mid-ocean ridges, oceanic plateaus, oceanic islands, island arcs, fore-arc and back-arc basins, continental rifts, large igneous provinces) are compared with Archean basalts, including basalts of greenstone belts and high-grade gneiss complexes. Linear discriminant analysis has shown that the Archean basalts differ significantly from Phanerozoic basalts in terms of the content of the least mobile major and trace elements. In this regard, the geochemical systematics of Phanerozoic basalts in most cases cannot be used to reconstruct the geodynamic settings of Archean basalts. The results obtained are illustrated by the example of the Mesoarchean basalts of the Olondo fragment of the Tokko–Khani greenstone belt. [ABSTRACT FROM AUTHOR]

The paper reports first comprehensive geological, petrographic, mineralogical, and geochemical data on one of the world's oldest Tiksheozero ultramafic‒alkaline‒carbonatite complex (~1.99 Ga), which belongs to the Mid-Paleoproterozoic igneous province of the Baltic Shield. The complex was formed in three intrusive phases. The first phase is composed of the low-alkali mafic‒ultramafic rocks: dunites, wehrlites, clinopyroxenites, and gabbro. The rocks of the second phase are alkaline ultramafic rocks represented mainly by jacupirangites (alkaline clinopyroxenites) and foidolites (melteigites, ijoliltes, and urtites), with subordinate olivinites, alkaline gabbro, and nepheline syenites. The third intrusive phase is made up of carbonatites. Geochemical and mineralogical data indicate that all three phases were derived from different primary melts. It is shown that the nepheline syenites were obtained by fractionation of foidolites. A model of formation of such complexes through decompressional melting of mantle plume head enriched in carbonate fluid is proposed. [ABSTRACT FROM AUTHOR]

Large igneous provinces (LIPs) are commonly associated with mass extinctions. However, the precise relations between LIPs and their impacts on biodiversity is enigmatic, given that they can be asynchronous. It has been proposed that the environmental impacts are primarily related to sill emplacement. Therefore, the structure of LIPs' magma storage system is critical because it dictates the occurrence and timing of mass extinction. We use surface-wave tomography to image the lithosphere under the Permian Emeishan large igneous province (ELIP) in southwestern China. We find a northeast-trending zone of high shear-wave velocity (Vs) and negative radial anisotropy (Vsv > Vsh; v and h are vertically and horizontally polarized S waves, respectively) in the crust and lithosphere. We rule out the possibilities of rifting or orogenesis to explain these seismic characteristics and interpret the seismic anomaly as a mafic-ultramafic, dike-dominated magma storage system of the ELIP. We further propose that the anomaly represents a hidden hotspot track that was emplaced before the ELIP eruption. A zone of higher velocity but less-negative radial anisotropy, on the hotspot track but to the northeast of the eruption center in the Panxi region, reflects an elevated proportion of sills emplaced at the incipient stage of the ELIP. Liberation of poisonous gases by the early sill intrusions explains why the mid-Capitanian global biota crisis preceded the peak ELIP eruption by 2-3 m.y. [ABSTRACT FROM AUTHOR]