Oceanic plateau of the Hawaiian mantle plume head subducted to the uppermost lower mantle

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.

Indian plate paleogeography, subduction and horizontal underthrusting below Tibet: paradoxes, controversies and opportunities

The India–Asia collision zone is the archetype to calibrate geological responses to continent–continent collision, but hosts a paradox: there is no orogen-wide geological record of oceanic subduction after initial collision around 60–55 Ma, yet thousands of kilometers of post-collisional subduction occurred before the arrival of unsubductable continental lithosphere that currently horizontally underlies Tibet. Kinematically restoring incipient horizontal underthrusting accurately predicts geologically estimated diachronous slab break-off, unlocking the Miocene of Himalaya–Tibet as a natural laboratory for unsubductable lithosphere convergence. Additionally, three endmember paleogeographic scenarios exist with different predictions for the nature of post-collisional subducted lithosphere but each is defended and challenged based on similar data types. This paper attempts at breaking through this impasse by identifying how the three paleogeographic scenarios each challenge paradigms in geodynamics, orogenesis, magmatism or paleogeographic reconstruction and identify opportunities for methodological advances in paleomagnetism, sediment provenance analysis, and seismology to conclusively constrain Greater Indian paleogeography.

On the relative temperatures of Earth's volcanic hotspots and mid-ocean ridges

Volcanic hotspots are thought to be fed by hot, active upwellings from the deep mantle, with excess temperatures (T_ex) ~100° to 300°C higher than those of mid-ocean ridges. However, T_ex estimates are limited in geographical coverage and often inconsistent for individual hotspots. We infer the temperature of oceanic hotspots and ridges simultaneously by converting seismic velocity to temperature. We show that while ~45% of plume-fed hotspots are hot (T_ex ≥ 155°C), ~15% are cold (T_ex ≤ 36°C) and ~40% are not hot enough to actively upwell (50°C ≤ T_ex ≤ 136°C). Hot hotspots have an extremely high helium-3/helium-4 ratio and buoyancy flux, but cold hotspots do not. The latter may originate at upper mantle depths. Alternatively, the deep plumes that feed them may be entrained and cooled by small-scale convection.

Linking the Wrangellia flood basalts to the Galápagos hotspot

The Triassic volcanic rocks of Wrangellia erupted at an equatorial to tropical latitude that was within 3000 km of western North America. The mafic and ultramafic volcanic rocks are compositionally and isotopically similar to those of oceanic plateaux that were generated from a Pacific mantle plume-type source. The thermal conditions, estimated from the primitive rocks, indicate that it was a high temperature regime (T_P > 1550 °C) consistent with elevated temperatures expected for a mantle plume. The only active hotspot currently located near the equator of the eastern Pacific Ocean that was active during the Mesozoic and produced ultramafic volcanic rocks is the Galápagos hotspot. The calculated mantle potential temperatures, trace elemental ratios, and Sr-Nd-Pb isotopes of the Wrangellia volcanic rocks are within the range of those from the Caribbean Plateau and Galápagos Islands, and collectively have similar internal variability as the Hawaii-Emperor island chain. The paleogeographic constraints, thermal estimates, and geochemistry suggests that it is possible that the Galápagos hotspot generated the volcanic rocks of Wrangellia and the Caribbean plateau or, more broadly, that the eastern Pacific (Panthalassa) Ocean was a unique region where anomalously high thermal conditions either periodically or continually existed from ~ 230 Ma to the present day.