Siberian Large Igneous Province Research Articles

GEOCHEMICAL CHARACTERISTICS OF MAFIC ROCKS IN THE STRUCTURE OF THE YENISEI-KHATANGA TROUGH AND THEIR BELONGING TO THE SIBERIAN TRAP PROVINCE

Consideration is being given to the geochemical composition of the rocks, representing the hidden part of the volcanic and intrusive material in the structure of the Yenisei-Khatanga Trough (YKT), in relation to its belonging to a large igneous province (LIP) of Siberia. The geochemical characteristics of mafic rocks, presenting in the sedimentary complexes of the YKT, correspond to three types of mafic rocks allocated to the Siberian LIP: Nadezhdinsky (low Ti), Morongovsky (low Ti), and, in limited quantities, Ivakinsky (rift-related high Ti). Based on the seismic data, there was constructed a deep structural-tectonic cross-sectional model, and there was considered the position of mafic intrusions in the sedimentary section in the western junction zone of the Siberian Platform and the Kara (Taimyr-Severozemelsky) orogen. The seismic data show an anomalous area in the lower crust and at the crust–mantle boundary immediately below the YKT depocenter, whose seismic section is characterized by a chaotic scattered wave field with no reflective boundaries.

Paleomagnetism of the Abinskaya Group of the Kuznetsk Depression (Southern Siberia) – Implications for the Evolution of the Siberian Large Igneous Province at the Permian–Triassic Boundary

Abstract —We report results of a systematic paleomagnetic study of the Abinskaya Group of the Kuznetsk depression, including a typical volcanic complex that reflects important features of the evolution of the Permian–Triassic Siberian large igneous province (LIP). Four zones of magnetic polarity have been established in the group’s deposits. We revise the correlation of the volcanic sheets of the Mal’tsevo Formation (Fm.) at the base of the group with the Ivakinsky Fm. of the Norilsk region, which is linked to the initiation of trap magmatism. The beginning of the eruption of the Saltymak complex volcanic rocks in the Kuznetsk area corresponds to the boundary between subchrons LT1n.1n and LT1n.1r (251.2 Ma) within the Kedrovka sub-formation of the Mal’tsevo Fm. This boundary was traced in the magnetostratigraphic sections of the Maimecha-Kotui, Koltogor-Urengoy, Western Taimyr, and Norilsk regions of the Siberian LIP and suggests a correlation of the Mal’tsevo Fm. volcanic rocks with the upper part of the undifferentiated interval of the Onkuchak – Tyvankit (?) fms., the base of the Korotchaev Fm., the Verkhnetam Fm. and the top of the Samoed Fm. The duration of this main pulse of volcanism in the Kuznetsk depression did not exceed 0.1 Myr. The volcanic sheets of the second, significantly weaker pulse of the Yamin Fm. are compared with the Maimecha Fm. of the Maimecha-Kotui area and the top of the Korotchaev Fm. of the Koltogor-Urengoy area. Thus, the accumulation of the entire Abinskaya Group, including the sedimentary complex of the Sosnovka Fm., lasted no more than 1.5 Myr. Except for the initial stage, this coincided with the eruption of most of the Maimecha-Kotui and Koltogor-Urengoy trap sections. The early magmatism of the Ivakinsky time and its analogs in other areas of the Siberian province during the Permian–Triassic boundary in the Kuznetsk depression probably corresponds to the break between the Taylugan Fm. and the Abinskaya Group. The mean paleomagnetic pole (PLat = 59.0°, PLon = 160.3°, A95 = 5.7°, N = 33) calculated for the entire studied section reflects the paleogeography of the Kuznetsk depression and can be considered a reference pole for the Permian–Triassic boundary.

Significant floral changes across the Permian-Triassic and Triassic-Jurassic transitions induced by widespread wildfires

Wildfires are a major source of perturbations to the Earth’s system and have important implications for understanding long-term interactions between the global environment, climate, and organisms. In this study, current evidence for global warming, wildfires, and floral changes across the Permian-Triassic (P-T) and Triassic-Jurassic (T-J) transitions were reviewed, and their relationships were discussed. Available evidence suggests that global plant community turnover and the decline in plant diversity across the P-T and T-J boundaries were primarily driven by widespread wildfires. The Siberian Large Igneous Province and Central Atlantic Magmatic Province released large amounts of isotopically light CO2 into the atmospheric system, contributing to global warming and increased lightning activity. This ultimately led to an increase in the frequency and destructiveness of wildfires, which have significantly contributed to the deterioration of terrestrial ecosystems, the turnover of plant communities, and the decline in plant diversity. Furthermore, frequent wildfires also constitute an important link between land and ocean/lake crises. Large amounts of organic matter particles and nutrients from the weathering of bedrock after wildfires are transported to marine/lake systems through runoff, contributing to the eutrophication of surface water and the disappearance of aerobic organisms, as well as hindering the recovery of aquatic ecosystems. These wildfire feedback mechanisms provide an important reference point for environmental and climatic changes in the context of current global warming. Therefore, the interplay between global warming, wildfires, and biological changes and their feedback mechanisms needs to be fully considered when assessing current and future risks to the Earth’s surface systems.

Behavior of critical metals in cumulates of alkaline ultramafic magmas in the Siberian large igneous province: Insights from melt inclusions in minerals

Ultramafic-alkaline-carbonatite complexes (UACC), which are formed from mantle-derived carbonated alkali-ultramafic melts in large igneous provinces (LIPs), are important resources of Fe, Ti, U, Th, Nb, rare earth elements (REEs), Cu, Ni and platinum group elements (PGEs). Concentration of these metals and ore formation is assumed to be largely controlled by magmatic differentiation and post-magmatic hydrothermal processes. Although basic patterns of the metals’ partitioning during formation of the UACCs are constrained by geochemical and mineralogical features of the rocks, including in experimental studies, our understanding of their pathway “from primitive melt to ore deposit” is far from complete. In order to further constrain the metals’ behavior during differentiation of a carbonated alkali-ultramafic melt, we studied multiphase inclusions in olivine, chromite, perovskite, pyroxene and magnetite in the ultramafic rocks from three UACCs (Guli, Bor-Uryakh and Odikhincha), located in the Siberian LIP. Examination of both unheated and experimentally heated and quenched inclusions reveals a variety of compositions from melanephelinitic through to highly differentiated nephelinitic to alkali-rich carbonatitic. In addition, sulfide minerals, which turn into immiscible sulfide liquids during heating experiments, are widely distributed in the inclusions’ assemblages. We consider these inclusions to be snapshots of intercumulus melts, which were entrained into olivine-rich cumulate mush, and use their compositions to delineate plutonic differentiation of a carbonated alkali-ultramafic melt. Highly differentiated silicate melts, entrapped in Fe-rich chromite (Guli dunites), were rich in U, Th and Nb and crystallized Os-Ir-Ru phases in proximity to the host chromite. Concentrations of U, Th, Nb and REEs in alkali-rich carbonatite liquids, which were present in the intercumulus of Odikhincha and Bor-Uryakh peridotites, approached levels similar to mineralized carbonatites and support the concentration of these metals in an immiscible alkali-carbonatite fraction, which was enriched in S, P and Cl. Minor sulfide liquids, which are closely associated with these carbonatite fractions, were strongly enriched in Cu and Ni, thus explaining the origin of the Phalaborwa-like sulfide ores in carbonatites as a result of magmatic differentiation. Finally, our study provides insights into the formation of peridotite-hosted types of mineralization (perovskite-magnetite ores, mineralized carbonatite veins and PGE-bearing chromitites) and shows that these ore-bearing assemblages can be formed due to the infiltration of the metal-bearing intercumulus melts through the ultramafic matrix.

GEOCHEMICAL AND Sr-Nd ISOTOPE SYSTEMATICS OF THE LATE PERMIAN–EARLY TRIASSIC TRAPS FROM THE KUZNETSK BASIN: MAGMA SOURCES AND CORRELATION WITH THE NORIL’SK REGION VOLCANICS

The study provides whole-rock geochemical and Rb-Sr and Sm-Nd isotope examinations of Permian-Triassic volcanics (basalts, basaltic andesites) and sills (trachydolerites, monzodiorites) from the Kuznetsk Basin, which is part of the Siberian Large Igneous Province. It is shown that the volcanic section of the Kuznetsk Basin consists of the Lower (I and II units: TiO2 = 1.6–1.9 wt.%, Gd/Yb = 2.0–2.1) and Upper (III–VIII units: TiO2 = 1.4–1.8 wt.%, Gd/Yb = 1.7–1.9) Sequences. The Mayzass sill is geochemically correlated with the Unit II basaltic andesite of the Lower Sequence, and the Syrkashev sill is geochemically akin to the Upper Sequence. The Kuznetsk traps originated from the partial melting of a Sr-Nd isotopically heterogeneous subduction-modified lithospheric mantle. They are geochemically comparable to low-Ti basalts of the low–middle Nadezhdinsky suite from the Noril’sk region, but differ in Sr-Nd isotope composition. The Sr-Nd isotope signatures of the uncontaminated lavas and Syrkashev sill rocks (εNd(T) = (+4.6)–(+2.4), (87Sr/86Sr)T = 0.7047–0.7054) are inherited from the ancient lithospheric mantle and do not represent the contribution of the Siberian plume. The Mayzass sill rocks (εNd(T) = (+2.2)–(+2.1); (87Sr/86Sr)T = 0.7055–0.7063)are derived from a parental melt contaminated with crustal carbonates.

Remnant of the late Permian superplume that generated the Siberian Traps inferred from geomagnetic data

Mantle plumes have played a key role in tectonic events such as continental break-up and large magmatic events since at least the formation of Gondwana. However, as their signatures on Earth’s surface, many of large igneous provinces have disappeared into the mantle during Earth’s long-term evolution, meaning that plume remnants in the mantle are crucial in advancing mantle plume theory and accurately reconstructing Earth history. Here we present an electrical conductivity model for North Asia constructed from geomagnetic data. The model shows a large high-electrical-conductivity anomaly in the mantle transition zone beneath the Siberian Traps at the time of their eruption that we interpret to be a thermal anomaly with trace amounts of melt. This anomaly lies almost directly over an isolated low-seismic-wave-velocity anomaly known as the Perm anomaly. The spatial correlation of our anomaly with the Siberian Traps suggests that it represents a remnant of a superplume that was generated from the Perm anomaly. This plume was responsible for the late Permian Siberian large igneous province. The model strengthens the validity of the mantle plume hypothesis.

Geochronology and origin of the carbonatites of the Central Taimyr Region, Russia (Arctica): Constraints on the F-Ba-REE mineralization and the Siberian Large Igneous Province

Geochronology and origin of the carbonatites of the Central Taimyr Region, Russia (Arctica): Constraints on the F-Ba-REE mineralization and the Siberian Large Igneous Province

The coal-forming environment during mass extinction in the latest permian: Evidence from geochemistry of rare Earth elements

The C1 coal of Latest Permian during mass extinction in eastern Yunnan was studied to reveal the terrestrial paleoenvironment and influence of geological events on coal-formation during mass extinction. An analysis of Rare Earth Elements (REEs) was conducted on the C1 coal from the Yantang Mine of Xuanwei, eastern Yunnan Province, which was deposited during the latest Permian. A total of 24 samples from coals, partings, roofs and floors from the C1 coal were taken from the fresh face in the underground mine. The results of the REEs analysis indicated that the total REE content (∑REE) in the C1 coal varies from 23.99 μg/g to 267.94 μg/g, averaged 122.69 μg/g. The C1 coal is enriched in light REE (LREE) relative to heavy REE (HREE), signifying the fractionation between LREE and HREE. Most samples of the coal seam C1 are depleted in Eu in various degrees and slightly depleted in Ce, especially two partings in sub-seams B1 and B3 which show the significant negative Eu anomalies. The geochemical characteristics of REE reveal that the C1 coal was deposited in a weak oxidation environment; the sedimentary environment was turbulent during the middle-later stage of coal-forming process; the C1 coal was affected by the basalt clastic materials from the Khangdian Oldland and acidic synsedimentary volcanic ash in the coal-forming period. The geochemical characteristics of Tonsteins in C1 coal are similar to those of marine Permian-Triassic boundary (PTB) volcanic ash layers in South China, which are both derived from the felsic volcanism caused by the closure of the Paleo-Tethys at the southwestern margin of the South China. Furthermore, the C1 coal was also affected by the eruption of Siberian large igneous province (SLIP) in the early stage.

The Permian-Triassic Riftogen Rocks in the Norilsk Area (NW Siberian Province): Geochemistry and Their Possible Link with PGE-Cu-Ni Mineralization

The volcanic rocks in the Vologochan syncline, the Khikey River valley, and Mount Sunduk, within the Norilsk area in the NW Siberian large igneous province, have been studied. They belong to the Ivakinsky, Syverminsky, Gudchikhinsky, Khakanchansky, Nadezhdinsky, Tuklonsky, and Morongovsky Formations. These Formations consist of trachybasalts, picritic basalts and tholeiitic basalts with aphyric and porphyritic textures, and intersertal and poikiloofitic structures. For the first time, we demonstrate the variations in the structure and composition of these Formations along the strike, based on 151 analyses of the major and trace elements in the rocks. The thickness of all the Formations, excepting the Morongovsky, reduce dramatically from the Yenisey–Khatanga trough to the Tunguska syneclise, and they pinch out in the east of the Norilsk area and are attributed to riftogen (rift) basalts. The rock compositions also change in this direction, especially in the Gudchikhinsky and Nadezhdinsky Formations. The two subformations of the Gudchikhinsky formation, the lower and upper, disappear in the east, so the Gudchikhinsky consists only of high-Mg rocks, picritic basalts, and picrites. The composition of the Nadezhdinsky formation varies intensely in its (Gd/Yb)n and (Th/Nb) ratios from the Vologochan syncline to the Khikey River valley. These structural and compositional variabilities differ between the rift formations and the platform ones. Two gabbro–dolerite sills from these areas that are close to the Norilsk and Ergalakh intrusive complexes have been studied. The metal contents in volcanic and intrusive rocks are similar and do not differ from the barren rocks of the South Pyasinsky massif comprising the PGE-Cu-Ni deposits. Only the Gudchikhinsky Formation contains elevated Cu and Ni concentrations. These features and the coinciding spatial distribution of the ore-bearing intrusions and picrites of the Gudchikhinsky rocks in the Norilsk–Igarka paleorift suggest their genetic link. It is proposed that the initial sulfides could have been formed in the mantle, as the Gudchikhinsky picrites, transported to the lower crust, and then involved by the trap magmas in the origin of the ore-bodies in the Norilsk deposits.

Climate change controls on extreme organic matter enrichment in Late Permian marine–terrestrial transitional shales in Guizhou, south China

Black organic-rich shale is an important target for unconventional natural gas exploration. However, compared with marine shale, the mechanism of organic matter enrichment in shale deposited in the marine–continental transitional environment is controversial because of the strong heterogeneity. In this study, an integrated sedimentological and elemental geochemical investigation was conducted for the dark shales in the Lopingian coal-bearing strata of western Guizhou, South China. This study aims to clarify the detailed control mechanism of major geological events on the organic matter accumulation in the transitional facies. Sedimentological observations show that the Lopingian in the Liupanshui area is mainly composed of coal, tight sandstones, and dark mudstones, which were deposited in the tidal flat-lagoon and fluvial delta. Petrological and geochemical evidence suggests the provenance was mainly resulted from the Emeishan basalt weathering in the west of the study area. In addition, the geochemical proxies indicate that the Longtan shales are characterized by low primary productivity, oxic–suboxic bottom water, and a relatively low depositional rate. The paleoclimate index indicates that the climate was predominantly warm and humid with intense chemical weathering during the Lopingian period, and changed to an extremely hot climate in the Early Triassic. Combined with the previous research, this study proposes that the Large Igneous Province (LIP) played a critical role on the organic matter enrichment of the Lopingian across the western Yangtze Block. Firstly, the onset of Emeishan LIP created an essential tectonic background and paleogeographic pattern for massive terrigenous debris to gather here from the west. Secondly, the climate was significantly affected due to the continuous weathering of the Emeishan basalt plateau and the greenhouse gases emission from the Siberian LIP. During the Lopingian, the plants flourished under the tropical rainforest climate and supplied the terrigenous organic matter. Accompanying chemical weathering increased, massive reworked coal fragments were brought into the brackish tidal flat-lagoon environment. Particularly, global warming related to the Siberian LIP and regional transgression occurred in the late Lopingian, forming the black shales with the highest organic matter content (up to 26.39%) of member Ш of the Longtan Formation. However, both the production and supplementation of organic matter significantly decreased because of the end-Permian mass extinction, thus stopped the organic matter enrichment in the Early Triassic Feixianguan Formation.

Early Triassic Monzonite–Granite Series in Eastern Kazakhstan as a Reflection of Siberian Large Igneous Province Activity

We provide the results of studying the internal structure and composition of the rocks of the Semeitau and Delbegetei massifs located in Eastern Kazakhstan. It was previously believed that these massifs have different ages and were formed in different geodynamic settings. The U-Pb zircon age from the monzonites and quartz monzonites was determined to be 249 ± 2 Ma, which showed the same Early Triassic age of the massifs. Both massifs are composed of rocks of the same monzonite–granite series of rocks with a significant proportion of high-silica rocks (leucocratic granites). Intermediate rocks are formed due to the differentiation of subalkaline mafic magmas, and the felsic rocks (rhyolites and granites) are the result of partial melting of crustal substrates. The massif formation model assumes the intrusion of mafic magmas into the crust, their differentiation and mixing with crustal melts, and then the intrusion of various rocks into the upper crustal levels. Analysis of the geological position, age and composition of the rocks allows us to conclude that the Semeitau and Delbegetei massifs were formed in an intraplate geodynamic setting. The activity of the mantle plume is the most probable reason for their formation. The Semeitau and Delbegetei massifs can be included in the southern part of the range of the Early Triassic Siberian Large Igneous Province.

The Permian-Triassic Transitional Zone: Jordan, Arabian Plate; Linked to Siberian Large Igneous Province and Neo-Tethys Breakup Degassing via Climate Forcing, Atmospheric Hazard and Metal Toxicity

The Permian-Triassic Transitional Zone: Jordan, Arabian Plate; Linked to Siberian Large Igneous Province and Neo-Tethys Breakup Degassing via Climate Forcing, Atmospheric Hazard and Metal Toxicity

Global implication of mesoproterozoic (~\u20091.4\xa0Ga) magmatism within the\xa0Sette-Daban Range (Southeast Siberia)

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.

The Influence of the Permian-Triassic Magmatism in the Tunguska Basin, Siberia on the Regional Floristic Biota of the Permian-Triassic Transition in the Region

The end-Permian extinction event (EPEE) considered to have been caused by the eruption of the Siberian Large Igneous Province (SLIP), the age of which is critical for extinction-SLIP model evaluation. The Tunguska Basin flora during this time, in accordance with the EPEE model, supposed to have been killed by the massive injection into the atmosphere of poisonous substances such as methane, sulfates, mercury and massive combastion of coals. In addition, supposed numerous fires presumably devastated the regional flora. However, the diversity of the Tunguska Basin flora drasticly increased at the beginning of Induan or slightly earlier and become diverse at the species level in the Olenekian and Anisian, when the main phase of basalt eruption and associated intrusive activity occurred. The overall magmatic activity during the latest Permian and Early Triassic did not kill the flora, but rather stimulate their diversity. The geomagnetic secular variations from the intrusions revealed the similarity of paleomagnetic directions of the Norilsk group layered intrusions with those of the upper Olenekian and lower Anisian Mokulaev and Kharaelakh volcanic formations and intrusions of the Talnakh group with the Olenekian Moronga-Mokulaev formations. The U-Pb dates and the geomagnetic secular variations data expose the obvious discrepancy between these two datasets. The paleomagnetic data suggest that the Norilsk-1 intrusion is younger than the Talnakn and Kharaelakh intrusions, but the U-Pb dates indicate the opposite. The data from layered intrusions in Norilsk and the other regions suggest their prolonged duration and multi-stadial formation. The U-Pb dates from the intrusions of the Norilsk region roughly constrain the onset of the SLIP and generally postdate the end-Permian extinction.

Low Geomagnetic Field Paleointensity on the Permian–Triassic Boundary from Study of the Kuznetsk Basin Traps (Southern Siberia)

Abstract ––Here we report the first data on the absolute intensity value of the geomagnetic field on the Permian–Triassic boundary from basalts of the Kuznetsk basin. The latter are considered as one of the manifestations of the initial stage of trap magmatism during the formation of the Siberian large igneous province. The good preservation of information on the ancient geomagnetic field in the Mal’tsevskaya Formation basalts is due to the presence of small single domain and pseudo-single domain grains of primary magmatic titanomagnetite in the groundmass. The paleointensity values obtained following the Thellier-Coe method correspond to the generally accepted criteria of reliability and indicate that the geomagnetic field intensity during the formation of the Kuznetsk basin traps on the Permian–Triassic boundary was almost an order of magnitude lower than the present-day one. Moreover, the mean values of the virtual dipole moment for the Kozhukhta and the Vlasov units in the lower and middle Mal’tsevskaya Formation ((1.9 ± 0.6) ⋅ 1022 A ⋅ m2 and (1.1 ± 0.7) ⋅ 1022 A ⋅ m2, respectively) are in good alignment with determinations of the paleointensity during the accumulation of the Ivakinsky Formation of the Norilsk Region in the Siberian province, which confirms the accuracy of traditional regional correlations.

The origin of volatiles in the Emeishan large igneous province, China: Constraints from chemical and C–He–Ar isotopic compositions of volatiles in picrites and basalts

The Emeishan large igneous province (LIP) consists of Permian flood basalts and coeval intrusive rocks with compositions varying from mafic–ultramafic rocks to syenites and granites. The volatiles in the Emeishan LIP are dominated by H2O with high H2, indicating that the plume‐derived magma was generated under a reduced condition. Picrite has minor contents of H2S without detectable SO2, and the basalt samples show no detectable H2S and SO2, indicating that the basaltic magma may have undergone sulphur‐saturation during magma evolution. The δ13C values of CO2 and CH4 in picrites and basalts are between the values of mantle and crustal organic carbon. This, together with the distribution patterns among CH4 homologue, indicates contribution of recycled sediments to the Emeishan mantle‐derived magma. The 3He/4He ratios of volatiles extracted from olivine and pyroxene phenocrysts of picrites vary from 0.01 to 0.66 Ra, and those from pyroxene separates of olivine websterite samples in the Zhubu intrusion vary from 0.92 to 1.05 Ra. The low 3He/4He ratios of the picrites from Emeishan LIP are lower than those from the Siberian LIP, but within the values of continental crust and oceanic crust. The positive correlation between 4He/40Arc and 4He contents in Emeishan picrite suggests that the isotopic ratios were dramatically affected by crustal contamination rather than degassing. The He and Ar isotopes indicate that Emeishan picrite experienced addition of subducted oceanic crustal materials, and the Zhubu magma was contaminated by continental crustal materials.

Linking the Siberian Flood Basalts and Giant Ni‐Cu‐PGE Sulfide Deposits at Norilsk

AbstractThe world‐class magmatic sulfide deposits in the Norilsk region exhibit a remarkable spatial and temporal association with the Siberian large igneous province (LIP). However, the details of the causal connection between the Siberian LIP and the ore deposits have remained contentious. Here we address the problem by modeling of assimilation, crystallization and flow behavior of magmas based on aggregated data from the Norilsk camp. Crustal assimilation at depth by mantle‐derived picritic magma can account for the compositional and isotopic variations of the early tholeiitic basalts and the sequestering of sulfide liquid in a mid‐crustal conduit system. When the rate and volume of asthenospheric magma production dramatically increased, the metal tenors of the mid‐crustal sulfide reservoir were first upgraded by consequent reaction with the fresh, undepleted magmas, then entrained and flushed to higher crustal levels. The resulting sulfide‐rich emulsions were too dense to reach the surface to form lavas but were instead emplaced in multiple pulses within blind sill‐like bodies at shallow depth. Sulfide ores transported from the mid‐crust were deposited at the bases of the upper‐crustal sills, where sedimentary host rocks were assimilated wholesale by the already sulfide‐charged replenishing magmas; this shallow assimilation was itself not instrumental in forming the ores. Although the evolution and dynamics of flood basalts are thus inextricably linked with coeval subvolcanic economic intrusions, the mineralization itself is argued not to occupy feeders with direct links to the overlying lavas, suggesting major implications for exploration in other LIPs.

Isotopic Fingerprints of Ice‐Rafted Debris Offer New Constraints on Middle to Late Quaternary Arctic Circulation and Glacial History

AbstractFor the first time, ice‐rafted debris provenance related to the Quaternary glacial discharge and circulation was constrained using radiogenic Sr, Nd, and Pb isotopes from a sedimentary record (Core BN05) from the central Arctic Ocean. The record is composed of glacial/interglacial intervals estimated to span ~0.5 Ma (Marine Isotope Stages [MIS] 1–14). Nd versus Sr isotope data show two end member groups, further elaborated using Pb isotopes. Glacial data mostly point at North American sources with unradiogenic εNd and high 87Sr/86Sr values, including detrital carbonate (dolomite) layers originating from Paleozoic rocks eroded by the Laurentide Ice Sheet. The opposite end member group including estimated MIS6 and MIS4 samples indicates the Siberian Large Igneous Province eroded by the Eurasian Ice Sheet as the major source, possibly with additional inputs from the East Siberian Ice Sheet. The limited evidence for Siberian Ice Sheet provenance may result from the predominant distribution of this glaciation on the continental shelf providing weak, fine‐grained sediments. Glacial‐time western Arctic circulation inferred from isotopic data is mostly similar to the modern Beaufort Gyre but was more streamlined toward the Fram Strait during some glacial events. Interglacial/major interstadial, presumably sea ice transported sediments, shows a mixture of North American and Siberian sources, consistent with historically observed variations in the Transpolar Drift versus Beaufort Gyre circulation. Isotope pattern in major interglacials (e.g., MIS5e, MIS11, and MIS 13) resembles the recent trend of increased sediment ice transport from the East Siberian/Chukchi Sea, possibly in relation to the ongoing Arctic warming.

Dynamics of the Largest Carbon Isotope Excursion During the Early Triassic Biotic Recovery

The dynamics of the carbon cycle across different timescales is crucial for understanding past and present global climate changes. Following the Permian–Triassic boundary mass extinction (PTBME), the carbon cycle changed profoundly during the following 5.4 Myr, with magnitudes of changes comparable to those of the Precambrian. In pace with the successive cycles of the carbon budget, the recovery of the marine nekton underwent several evolutionary diversification and extinction cycles accompanied by eustatic sea-level changes and profound ecological reorganization of land plants, all indicative of climatic changes. Additional eruptive bursts of the Siberian Large Igneous Province (SLIP) are traditionally called upon as a plausible trigger for these climatic oscillations but firm evidence for coeval SLIP volcanism is still lacking. Based on new precise and accurate U-Pb zircon ages, we establish a high-resolution temporal calibration of the biggest positive carbon isotope excursion (CIE) spanning about 600 kyr in the late Smithian. The age of the Smithian-Spathian boundary (SSB) is established between 249.29 ± 0.06 and 249.11 ± 0.09 Ma. Our oldest U-Pb zircon ages indicate no overlap in time between the middle Smithian onset of the thermal maximum and the youngest available U-Pb zircon ages from SLIP volcanism. The constructed time line also indicates a duration of the global unconformity at the SSB that is compatible with glacio-eustatism. Potential cooling mechanisms such as a volcanic winter, the biological pump and the cessation of volcanism are discussed in the light of this new time line. In the low latitudes, the onset of the positive CIE remarkably predates the temperature drop by some 100 to 125 kyr. However, as long as the magnitude of such offset – if any – is unknown for the high latitudes, relations between the CIE and the cooling will remain an open question associated with largest Triassic extinction of the nekton.

Nature and origin of the volcanic ash beds near the Permian–Triassic boundary in South China: new data and their geological implications

AbstractPermian–Triassic boundary (PTB) volcanic ash beds are widely distributed in South China and were proposed to have a connection with the PTB mass extinction and the assemblage of Pangea. However, their source and tectonic affinity have been highly debated. We present zircon U–Pb ages, trace-element and Hf isotopic data on three new-found PTB volcanic ash beds in the western Hubei area, South China. Laser ablation inductively coupled plasma mass spectrometry U–Pb dating of zircons yields ages of 252.2 ± 3.6 Ma, 251.6 ± 4.9 Ma and 250.4 ± 2.4 Ma for these three volcanic ash beds. Zircons of age c. 240–270 Ma zircons have negative εHf(t) values (–18.17 to –3.91) and Mesoproterozoic–Palaeoproterozoic two-stage Hf model ages (THf2) (1.33–2.23 Ga). Integrated with other PTB ash beds in South China, zircon trace-element signatures and Hf isotopes indicate that they were likely sourced from intermediate to felsic volcanic centres along the Simao–Indochina convergent continental margin. The Qinling convergent continental margin might be another possible source but needs further investigation. Our data support the model that strong convergent margin volcanism took place around South China during late Permian – Early Triassic time, especially in the Simao–Indochina active continental margin and possibly the Qinling active continental margin. These volcanisms overlap temporally with the PTB biocrisis triggered by the Siberian Large Igneous Province. In addition, our data argue that the South China Craton and the Simao–Indochina block had not been amalgamated with the main body of Pangea by late Permian – Early Triassic time.