Geochemical variability as an indicator for large volume eruptions in volcanic arcs

Caldera-forming eruptions have the potential to impact global climate and induce drastic socioeconomic change. However, the criteria to identify volcanoes capable of producing large magnitude eruptions in the future are not well constrained. Here we compile and analyse data, revealing that volcanoes which have produced catastrophic caldera-forming eruptions in the past, typically show larger ranges of long-term erupted bulk-rock geochemistry compared to those that have not. This observation suggests that geochemical variability is a measure of a magmatic systems size. Using a 2D thermal model that simulates the growth and evolution of crustal-scale magmatic systems by stochastic injection of dikes and sills, we show that such behaviour is consistent with differences in crustal magma fluxes. Higher injection rates accumulate greater melt volumes in more extensive crustal plumbing systems, leading to more variable distributions of temperatures and thus melt composition. We conclude that compositional variability should be included in the catalogue of criteria to identify volcanic systems with greater probabilities of producing future large eruptions. Importantly, this allows to identify stratovolcanoes with caldera-like geochemical signatures, which have not yet been recognized as systems with greater probabilities of producing large magnitude eruptions.

Far from boring: a new Grenvillian perspective on Mesoproterozoic tectonics

As determining when plate tectonics began on Earth is a highly debated subject, it is crucial to understand the “boring billion” (1.8 to 0.8 billion years ago), a period of tectonic quiescence inferred from proxies, such as the average chemical composition of the mineral zircon on Earth and the isotopic composition of seawater derived from marine rocks. Yet this period saw the construction of what may have been the biggest mountain belt that ever existed, the remnants of which are found in the Grenville Orogen of eastern North-America. This contribution first exposes a compilation of multidisciplinary geological datasets and new geochemical data from igneous suites emplaced during the Grenvillian Orogeny that are incompatible with the current tectonic paradigm. We then present a completely revised model for Grenvillian tectonics. In contrast with the actual Laurentian-centred paradigm, our model involves the construction of a newly revealed continent by amalgamation of volcanic arcs far away from Laurentia (the craton forming the core of actual North-America) and their collision 60 millions year later than the currently accepted timing. This new model resolves the longstanding contradiction between tectonic proxies and geological record and invalidates the view considering the Mesoproterozoic as a tectonically quiet Era.

Volcanic hazard exacerbated by future global warming–driven increase in heavy rainfall.

Heavy rainfall drives a range of eruptive and noneruptive volcanic hazards; over the Holocene, the incidence of many such hazards has increased due to rapid climate change. Here we show that extreme heavy rainfall is projected to increase with continued global warming throughout the 21st century in most subaerial volcanic regions, dramatically increasing the potential for rainfall-induced volcanic hazards. This result is based on a comparative analysis of nine general circulation models, and is prevalent across a wide range of spatial scales, from countries and volcanic arcs down to individual volcanic systems. Our results suggest that if global warming continues unchecked, the incidence of primary and secondary rainfall-related volcanic activity—such as dome explosions or flank collapse—will increase at more than 700 volcanoes around the globe. Improved coupling between scientific observations—in particular, of local and regional precipitation—and policy decisions, may go some way towards mitigating the increased risk throughout the next 80 years.

Tectonic regime of the area of the Sukhoi Log geological practice in the Middle Devonian and volcanic arcs in the basement of Western Siberia

The article briefly describes current understanding of the tectonic regime of study area. It is related to the field geological practice of students of Industrial University of Tyumen. Study area is located at the western edge of Sukhoi Log town, Sverdlovsk region. The relevance of the work is related to the educational process. Information about the geological structure of the Devonian and Carboniferous formations of study area is collected. Some of the most characteristic outcrops of Paleozoic are described. Actual information about the Ural mountain genesis is given. The list of studied objects includes the outcrop of Eifelian reefal limestones near to the Shata waterfall and the ruins of a volcano. According to other researchers, it is a part of Middle Devonian volcanic arc, which was formed over the subduction zone. Here the Ordovician-Silurian Paleouralian Ocean were subducted under the collage of different-age terrains and paleocontinents (Paleozoic basement of the modern West Siberian Plate). A possible section across the Middle Devonian subduction zone of study area is presented. Similar objects associated with the oil and gas are known in the Pre-Jurassic basement of Western Siberia. The limestones and volcanic massifs exposed near the Sukhoi Log are good natural equivalents of the objects of oil and gas exploration in Western Siberia.

Climatic control on the location of the Southern Andes volcanic arc

Volcanic arcs at convergent plate margins are primary surface expressions of plate tectonics. Although climate affects many of the manifestations of plate tectonics via erosion, the upwelling of magmas and location of volcanic arcs are considered insensitive to climate. In the Southern Andes, subduction of the Nazca oceanic plate below the South American continent generates the Southern Andes Volcanic zone. Orographic interactions with Pacific westerlies lead to high precipitation and erosion on the western slopes of the belt between 42-46°S. At these latitudes, the topographic water divide and the volcanic arc are respectively farther and closer to the subduction trench than at lower latitudes, despite a constant subduction dip angle along strike. Here, we use thermomechanical numerical modeling to investigate how magma upwelling is affected by topographic changes due to orography. We show that a leeward topographic shift may entail a windward asymmetry of crustal structures accommodating the magma upwelling, consistent with the observed trench-ward migration of the Southern Andes Volcanic Zone. A climatic control on the location of volcanic arcs via orography and erosion is thus revealed.

Modeling of convective heat-mass transfer in permeable parts of seismic focal zones of the Kamchatka region and associated volcanic arcs

<p>The paper presents a non-isothermal model of hydrodynamic heating of lithospheric rocks above magma chambers in application to the seismic focal zone of the Kamchatka region and associated volcanic arcs. The effect of convective heating of mantle and crustal rocks on dynamics of metasomatic changes and convective melting was studied. In the existing models of ore-forming systems, fluid mass transfer is determined mainly by the retrograde boiling of magmas in meso-abyssal intrusive chambers. Analysis of the manifestations of deposits of the porphyry formation of the Pacific Ocean active margins shows the decisive participation in their formation of mantle-crust ore-igneous systems. The model of convective heat-mass transfer in fluid mantle-crust systems coupled with magma chambers is designed with the consideration of effects of interphase interaction in rocks of permeable zones above igneous fluid sources. Numerical simulation of the dynamics of fluid systems under the volcanoes of the frontal zone of Kamchatka shows altered ultramafic rocks in metasomatic zoning and the presence of facial changes in the mineral composition of wehrlitized rocks. In the mantle wedge of the northwestern margin of the Pacific Ocean, over which epicontinental volcanic arcs developed in the post-Miocene stage, there is possible combination of the products of different-time and different-level igneous systems in the same permeable "earth's crust-lithospheric mantle" transition zones. Assuming that the "cratonization" of volcanic sections of the continental Earth's crust follows the "metasomatic granitization" pattern, the initial element of which is the wehrlitization of mantle wedge ultramafic rocks, the processes of metasomatic fertilization of mantle wedge rocks were investigated using a flow-through multiple-reservoir reactor. In the seismically active regions of the Pacific transition lithosphere, specific conditions for heating of areas of increased permeability above mantle fluid sources should be recorded. Metasomatic columns in such fluid systems can describe the formation of at least three levels of convective melting of metasomatized mantle wedge substrates, as well as the formation of a region of high-temperature fluid change of mafic intrusion rocks in the Earth's crust. The work was financially supported by the Russian Foundation for Basic Research, grants No. 19-05-00788.</p>

Melting of subducted sediments reconciles geophysical images of subduction zones

Sediments play a key role in subduction. They help control the chemistry of arc volcanoes and the location of seismic hazards. Here, we present a new model describing the fate of subducted sediments that explains magnetotelluric models of subduction zones, which commonly show an enigmatic conductive anomaly at the trenchward side of volcanic arcs. In many subduction zones, sediments will melt trenchward of the source region for arc melts. High-pressure experiments show that these sediment melts will react with the overlying mantle wedge to produce electrically conductive phlogopite pyroxenites. Modelling of the Cascadia and Kyushu subduction zones shows that the products of sediment melting closely reproduce the magnetotelluric observations. Melting of subducted sediments can also explain K-rich volcanic rocks that are produced when the phlogopite pyroxenites melt during slab roll-back events. This process may also help constrain models for subduction zone seismicity. Since melts and phlogopite both have low frictional strength, damaging thrust earthquakes are unlikely to occur in the vicinity of the melting sediments, while increased fluid pressures may promote the occurrence of small magnitude earthquakes and episodic tremor and slip.

Global chemical weathering dominated by continental arcs since the mid-Paleozoic

Earth’s plate tectonic activity regulates the carbon cycle, and hence, climate, via volcanic outgassing and silicate-rock weathering1,2,3. Mountain building, arc-continent collisions, and clustering of continents in the tropics have all been invoked as controlling the weathering flux4,5,6, with arcs also acting as a major contributor of carbon dioxide (CO2) to the atmosphere7. However, these processes have largely been considered in isolation when in reality they are all tightly coupled. To properly account for the interactions between these processes, and the inherent multi-million-year time lags at play in the Earth system, we need to characterise their complex interdependencies. Here we analyse these interdependencies over the past 400 million years, using a Bayesian network to identify primary relationships, time lags and drivers of the global chemical weathering signal. We find that the spatial extent of continental volcanic arcs — the fastest-eroding surface features on Earth — exerts the strongest control on global chemical weathering fluxes. We find that the rapid drawdown of CO2 tied to arc weathering stabilises surface temperatures over geological time, contrary to the widely held view that this stability8 is achieved mainly by a delicate balance between weathering of the seafloor and the continental interiors.