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Magmatic activity of the Emeishan large igneous province (ELIP) of SW China is one of the most significant geological events of the late Paleozoic. The large volume flood basalts plus rare picrites were erupted in Late Permian. Previous studies indicate that the basalts are the derivatives of primary mantle-derived magma by fractional crystallization, but the depths at which this process took place remain unknown. To answer this question, we use phenocryst compositions and mineral-liquid thermobarometers to determine the P-T conditions of the magma reservoirs where crystallization occurred, then use these data to reconstruct the magma plumbing system of the igneous province. Thermobarometric calculations show that most picrite-hosted clinopyroxene phenocrysts crystallized at ∼25 km and 1200-1280°C, whereas most basalt-hosted clinopyroxene phenocrysts crystallized at depths <20 km and temperatures <1200°C. Some picrites containing primitive olivine with Fo up to Fo92 likely formed by eruption of the most primitive magma with composition similar to the primary magma from the deepest reservoir possibly at the Moho. Parental magmas yield mantle potential temperatures of 1740-1810°C, which are the highest such temperatures yet recorded for terrestrial magmas of any age. Less primitive picrites containing both olivine and clinopyroxene phenocrysts formed by eruption of moderately fractionated magma from a reservoir in the middle crust. Basalts and basaltic andesites formed by eruption of the most fractionated magmas from the reservoirs in the upper crust, coinciding with the depths of coeval sulfide ore-bearing and Fe-Ti-V oxide ore-bearing mafic-ultramafic intrusions. The reason that the Emeishan volcanic sequence is dominated by basalts is because most of the mantle-derived magma was trapped in the middle and upper crusts, undergoing variable degrees of crystal fractionation plus crustal contamination before eruption. Primitive picrites are rare because their eruption requires a trans-lithosphere conduit, which is difficult to create and maintain due to increasing lithospheric pressure with depth. The results from this study reveal that magma reservoirs at the crustal levels play a critical role in magma differentiation in a continental setting.

Southeastern Tibet, which has complex topography and strong tectonic activity, is an important area for studying the subsurface deformation of the Tibetan Plateau. Through the two-station method on 10-year teleseismic Rayleigh wave data from 132 permanent stations in the southeastern Tibetan Plateau, which incorporates ambient noise data, we obtain the interstation phase velocity dispersion data in the period range of 5–150 s. Then, we invert for the shear wave velocity of the crust and upper mantle through the direct 3-D inversion method. We find two low-velocity belts in the mid-lower crust. One belt is mainly in the SongPan-GangZi block and northwestern part of the Chuan-Dian diamond block, whereas the other belt is mainly in the Xiaojiang fault zone and its eastern part, the Yunnan-Guizhou Plateau. The low-velocity belt in the Xiaojiang fault zone is likely caused by plastic deformation or partial melting of felsic rocks due to crustal thickening. Moreover, the significant positive radial anisotropy ( V SH > V SV ) around the Xiaojiang fault zone further enhances the amplitude of low velocity anomaly in our V SV model. This crustal low-velocity zone also extends southward across the Red River fault and farther to northern Vietnam, which may be closely related to heat sources in the upper mantle. The two low-velocity belts are separated by a high-velocity zone near the Anninghe-Zemuhe fault system, which is exactly in the inner and intermediate zones of the Emeishan large igneous province (ELIP). We find an obvious high-velocity body situated in the crust of the inner zone of the ELIP, which may represent maficultramafic material that remained in the crust when the ELIP formed. In the upper mantle, there is a large-scale low-velocity anomaly in the Indochina and South China blocks south of the Red River fault. The low-velocity anomaly gradually extends northward along the Xiaojiang fault zone into the Yangtze Craton as depth increases. Through our velocity model, we think that southeastern Tibet is undergoing three different tectonic modes at the same time: (1) the upper crust is rigid, and as a result, the tectonic mode is mainly rigid block extrusion controlled by large strike-slip faults; (2) the viscoplastic materials in the middle-lower crust, separated by rigid materials related to the ELIP, migrate plastically southward under the control of the regional stress field and fault systems; and (3) the upper mantle south of the Red River fault is mainly controlled by large-scale asthenospheric upwelling and may be closely related to lithospheric delamination and the eastward subduction and retreat of the Indian plate beneath Burma.

We estimate the mantle source compositions for mantle plumes and, by implication, Earth's lower mantle by: (1) measuring trace (e.g, Sc, V, Cu) and minor (e.g., Ca, Mn, Ni) element concentrations of high-forsterite olivine grains from several plume localities, (2) estimating the parent liquid compositions from which they crystallized, (3) calculating mantle potential temperatures and degrees of partial melting, and (4) estimating trace element compositions of depleted and enriched mantle sources. Our sample set includes two continental flood basalt provinces (Emeishan and Deccan), a flood basalt that erupted in a continental rift setting (Baffin Island), our type example of a thermal mantle plume (Hawaii), and lavas from the Siqueiros Transform at the East Pacific Rise, which represent the mid-ocean ridge system. We also present olivine (Ol) compositions for peridotite xenoliths from Kilbourne Hole, New Mexico, U.S.A., which are commonly used as primary and secondary analytical standards. We find that trace elements in lava-hosted olivine grains are too far removed from their mantle source to provide anything but greatly hindered views of such. Olivine compositions reflect not only evolving liquid compositions (including partial melting conditions and later fractionation), but also evolving Ol+liq partition coefficients, which mostly increase with decreasing T during crystallization. Mantle compositions, delimited by maximum forsterite contents and estimates of parental magmas (and experimentally determined partition coefficients) indicate that our selected plumes reflect some combination of (1) a depleted mantle source that is quite similar to that obtained by other methods and (2) a variably enriched plume source that is more enriched than current estimates of pyrolite. The enriched plume mantle sources can be explained remarkably well as a mixture of subducted mid-ocean ridge basalt (MORB; Gale et al. 2013) and depleted MORB mantle (DM; Salters and Stracke 2004), with MORB:DMM ratios of 1:5 to 1:4. These ratios are most sensitive to estimates of melt fraction where plume parental magmas are last equilibrated with their mantle source, but are nonetheless consistent across a wide range of chemically very different elements, and estimates of MORB and DM obtained by very different means. Baffin Island is of particular interest. Like prior studies, we verify a high mantle potential temperature (Tp) of 1630 °C (compared to Tp = 1320-1420 °C for MORB from Cottrell and Kelley 2011 for Ol of Fo89.3-91.4). The Baffin source is also within error the same as DM with respect to trace elements, although still isotopically distinct; Baffin appears to be sourced in something that is akin to DMM that lies at the base of the mantle, where plumes acquire their excess heat. Thus while part of our analysis supports the concept of a \"slab graveyard\" at the bottom of the lower mantle (e.g., Wyession 1996), that cemetery is by no means ubiquitous at the CMB: subducted slabs are either unevenly interred, or efficiently excavated by later upwellings.

Superchrons represent critical phases in geomagnetic field evolution, offering insights into Earth's distinct internal states. However, the lack of research on how the longest Phanerozoic superchron (Permo‐Carboniferous Reverse Superchron, PCRS, ∼318–263 Ma) terminated limits our understanding of the geodynamic processes and the interaction mechanisms between the Earth's interior and surface environment. Here, we present reliable paleointensity results from lava flows of the Emeishan large igneous province (LIP), emplaced immediately following the permo‐carboniferous reverse superchron termination. Our results reveal that geomagnetic field intensity was exceptionally low during this period, averaging approximately one‐sixth of the modern field intensity. We find that major mass extinctions and environmental deterioration events coincide with extremely low geomagnetic field states and eruptions of LIPs. The observed temporal alignment among the geomagnetic field, biological evolution, and geodynamic processes may reflect associations between Earth's interior and surface processes. Plain Language Summary The geomagnetic field reflects Earth's internal states. This study indicates that the geomagnetic field was extremely weak after the end of the longest geomagnetic direction stabilization period in the Phanerozoic, which was also a period with large‐scale volcanic eruptions and severe environmental damage. We observe that major mass extinctions temporally coincide with intervals of extremely low geomagnetic field strength and the emplacement of large igneous provinces. These patterns suggest possible associations between Earth's surface environmental changes and its internal dynamics, though the nature of this relationship requires further investigation. Key Points The paleointensity was extremely low during the eruption of the Emeishan large igneous province The low absolute paleointensity results imply that high core‐mantle boundary heat flux leads to a low‐energy state in Earth's outer core The geomagnetic field and associated geodynamic processes may influence the environment

The formation of large igneous provinces (LIPs) has been widely believed to be linked to mantle plume activity. However, how the plume modifies the overlying lithosphere, particularly its compositional structure, remains uncertain. Here, we characterize the deep thermochemical structure beneath the Emeishan LIP (ELIP), which is a well‐known Permian plume‐related LIP in China, by taking a multi‐observable probabilistic inversion. Our results find a clear correlation between the lithospheric composition with the ELIP's concentric zones. We infer that the fertile feature of the lithospheric mantle in the ELIP's inner zone was caused by the plume‐derived fertile magmas which infiltrated into and chemically refertilized the ambient depleted lithosphere. This plume‐modified lithospheric compositional structure is likely to be preserved after the plume event, while the present lithospheric thermal structure has been mainly influenced by the subsequent thermal‐tectonic activity. Our results improve our understanding of the physicochemical interactions between the lithosphere and ancient plume. Plain Language Summary Gaining insights into the nature of large igneous provinces (LIPs) helps understand mass extinction and climate change in the past, since the outpouring of large accumulations of igneous rocks associated with LIPs could alter ancient climates and environments. Here, we focus on a well‐known plume‐related LIP during the Permian in China, Emeishan LIP (ELIP), to construct its deep thermochemical structure based on a multi‐observable probabilistic inversion method. Our results suggest that the bulk fertile feature (not depleted by melt extraction) of the lithospheric mantle in the vicinity of the ELIP's inner zone was caused by the plume‐derived fertile magmas which infiltrated into the ambient depleted (deficient in minerals extracted by partial melting of the rock) lithospheric mantle and chemically refertilized it by melt‐rock interaction. However, the imaged thermal structure shows a large ongoing asthenospheric upwelling and small‐scale thermal convection, implying that the present‐day lithospheric thickness has been mainly influenced by the subsequent tectonic events. Our results improve the understanding of the physicochemical interactions between the lithosphere and ancient plume and contribute to the knowledge of the nature of LIPs. Key Points Image the thermochemical structure beneath the Emeishan Large Igneous Province via novel joint inversions Reveal plume refertilization of the lithosphere beneath the Emeishan Large Igneous Province's inner zone Image complex mantle circulation patterns beneath the Emeishan Large Igneous Province region

Mafic continental large igneous provinces (LIPs) erupted rapidly and may have overwhelmed Earth's atmospheric and biospheric systems. However, the exact balance and interplay between short‐term climate warming caused by CO2 emissions and long‐term cooling due to LIP weathering remains poorly understood. To investigate the influence of LIP emplacement on long‐term climate change, we quantified the mass fluxes during the late Permian associated with the Emeishan LIP and its weathering products in the western Yangtze Cratonic Basin of southwestern China. The minimum value of the average denudation rate of the Emeishan LIP during the late Permian (Wuchiapingian) was 170.8 t/km2/yr, indicating enhanced capacity for atmospheric CO2 consumption at that time. The estimated minimum dissolved element fluxes from the Emeishan LIP to the surface ocean were 2.29 × 106 t/yr Si, 11.7 × 103 t/yr P, and 68 × 103 t/yr Fe, which account for 1.3%–3.4% of the fluxes from modern global rivers. These high nutrient fluxes led to an atmospheric CO2 removal rate of 8.5–85 × 106 t/yr through enhanced biological productivity, as estimated by the Fe fertilization model and dissolved Fe flux. This rate is approximately one order of magnitude higher than those resulting from Emeishan LIP basalt weathering and accounts for 0.05%–0.5% of the modern global CO2 sink, which could have led to a reduction in atmospheric CO2. Our results highlight the key role of LIPs in modulating Earth's climate over long time periods and in driving long‐term cooling due to enhanced CO2 drawdown caused by enhanced nutrient input to the surface ocean.

The Xiaojiang fault system (XJFS), located to the southeast of the Tibetan Plateau, has a complicated tectonic history and is an ideal location to study the Tibetan Plateau in terms of its deep material transport mechanism and the effects of past tectonic events. In this study, broadband and long-period magnetotelluric data were collected above this fault system and inverted to build a 3-D resistivity model of the lithosphere. As shown in the model, at upper-middle crustal depths, three high-resistivity anomalies separate the strike-slip faults located in the study area, which may be the remnants of the Emeishan large igneous province that was destroyed and modified by Cenozoic crustal activity. The lower crust is characterized by significant low-resistivity anomalies that extend downward to the upper mantle. The low-resistivity anomalies in the upper crust may be caused by brines or/and conductive minerals (e.g., graphite and sulfides), and the possible reason for the low-resistivity anomalies that were imaged in the lower crust and upper mantle may be the presence of hydrogen in nominally anhydrous minerals and partial melts. According to the seismic activity distribution and resistivity structure, we propose dividing the seismic activity of the study area into three categories: tectonic earthquakes, earthquakes with no active faults on the surface, and other scattered earthquakes with no general features. Seismic activities are controlled by tectonic activities, fluid transportation, and the adjustment of the Earth’s stress field. It is believed that there is a mutually reinforcing relationship between seismic activity and deep fluids. Fluids could lower the frictional force in faults, promote movement, and thus induce earthquakes; on the other hand, seismic activities and the long-term strike-slip movements of faults could generate heat and increase the connectivity of fluids, which decreases the strength of the crust and facilitates the flow of fluids. Based on the resistivity model, it is demonstrated that the present tectonic activity in the XJFS is complicated and characterized by rigid block extrusion along strike-slip faults in the upper crust, ductile deformation with channel flow in the lower crust, and the upwelling of mantle materials. In combination with previous studies, our results indicate that the weak crustal materials from the Tibetan Plateau are blocked by (1) the lithosphere modified by the Emeishan plume and (2) the South China block when flowing through the Sichuan-Yunnan block. Therefore, these weak materials turn to the southwest direction along the XJFS, then pass through the Red River fault and enter the Indochina block.

The link between mantle plumes and the formation of large igneous provinces (LIPs) is well established although the anatomy of these remains equivocal. Recent experimental studies and geophysical data suggest that the mantle plume head is more likely to be irregular and asymmetric, rather than an axisymmetric flattened disk. The Emeishan large igneous province (ELIP) provides a unique opportunity to test this hypothesis. According to robust petrographic, geochronologic, and geochemical evidence from the late Permian basalts in the Sichuan Basin, and in conjunction with a comprehensive compilation of geologic maps and published geochemical data from the ELIP, we identified several giant radial “fingering” structures. Based on the shallow mantle source from the center to margin in the ELIP and relief of the lithosphere‐asthenosphere boundary, we propose a new mantle plume model to explain the evolution of the Emeishan plume periphery, where narrow finger‐like protrusions and plumelets developed outwards from the main body of the plume to the edges of the flattened plume head. Dragged fingers might have been torn apart into some plumelets, which dispersed and were trapped beneath the thinnest lithosphere relief, and eventually erupted to form small‐scale flood basalt in the Outer Zone of the ELIP. Key Points The spatio‐temporal and geochemical characteristics of the Emeishan basalts in the Sichuan Basin are determined The Emeishan large igneous province developed fingering structures A new model, that is, “fingering, torn apart and plumelets,” may interpret the evolution of the mantle plume periphery and surface manifestation of the large igneous province

The factors and processes that control trace-element partitioning among co-crystallizing cumulus minerals in layered intrusions have long been controversial. Here we address this issue using new laser ablation ICP-MS trace element data for magnetite, ilmenite, and clinopyroxene from the Panzhihua layered intrusion in the Emeishan large igneous province, SW China. The cumulus minerals display strong Ni, Co, and Cr depletions, indicative of parental magmas low in concentration of these elements probably due to prior sulfide removal and the fractionation of chromite or Cr-magnetite in a staging magma chamber at depth. Both magnetite and clinopyroxene show cyclical variations in some transition elements (e.g., Cr, V, and Ni) along the stratigraphic section. The average concentrations of these transition elements in magnetite are positively correlated with those in clinopyroxene, likely resulting from co-crystallization of magnetite and clinopyroxene. The incompatible element (e.g., Zr, Hf, and Nb) concentrations of the cumulus minerals from the Lower Zone are highly variable compared to those of the Middle and Upper Zones. These large variations in trace element compositions are attributed to a \"trapped liquid shift\" in the Lower Zone. Ilmenite crystals from the Panzhihua intrusion may have undergone extensive modification of transition elements during subsolidus re-equilibration with magnetite, leading to the decoupled variations of transition elements in ilmenite across the Lower Zone stratigraphy. Our study indicates that systematic trace element variations of the main cumulus mineral assemblage, rather than a single mineral, need to be considered to better constrain the magmatic differentiation and elemental fractionation of layered intrusions.

A prominent large negative δ13Corg excursion and a coeval notable spike in mercury (Hg)/total organic carbon ratio are observed in the middle–upper Permian Gohan Formation in central Korea, located in the eastern Sino-Korean block (SKB), which may represent the Capitanian mass extinction event. The SKB was separated from the South China block by the eastern Palaeo-Tethys Ocean. This finding from the SKB supports the widespread Hg loading to the environment emitted from the Emeishan volcanic eruptions in SW China. This study demonstrates that the Hg cycle was globally perturbed in association with global carbon cycle perturbation that occurred during the Capitanian Extinction.