The Role of the Dynamics of the Subducting Plate in Generating Arc Magmatism

The thermal state of subducting plates is thought to be of great importance in the generation of the arc magmatism above them. The temperature of slabs affects dehydration, the primary driver of arc magmatism, but may also determine whether the slab itself undergoes partial melting. The focus of this study has therefore been slab temperature: how sensitive it is to the dynamic properties of the slab, and exactly what effect it has on arc magmatism today and back in Earth’s early history. Through the use of numerical models, we improve on existing proxies for slab temperature. Our models demonstrate that the temperature of different parts of the slab depend variably on slab age, trench normal convergence rate, slab dip and the decoupling depth of the subducting and over-riding plates. In addition to forward modelling, we worked backwards from real-world data. To this end we developed a tool to search for statistically significant correlations between the same slab parameters, as well as over-riding crustal thickness, and the trace element characteristics of arc lavas in global databases. We also investigate a recently proposed dynamic process which may have an effect on arc processes: the formation of plumes of slab derived material (relamination). We find that the relamination of mafic oceanic crust is more likely under Archean conditions, potentially explaining systematic differences between the chemistry of Archean rocks and more modern continental crust and arc rock. We also undertook a preliminary investigation on the feasibility and effect that episodically driven subduction could have on the thermal profile of subducting slabs. We demonstrate here that through forward numerical modelling and analysis of the chemistry of arc lavas, we can gain valuable insight into the thermal state and complex dynamics of the slab in the critical sub-arc region

Effects of basal drag on subduction dynamics from 2D numerical models

Subducting slabs are an important driver of plate motions, yet the relative importance of different forces in governing subduction motions and styles remains incompletely understood. Basal drag has been proposed to be a minor contributor to subduction forcing because of the lack of correlation between plate size and velocity in observed and reconstructed plate motions. Furthermore, in single subduction system models, low basal drag leads to subduction behaviour most consistent with the observation that trench migration velocities are generally low compared to convergence velocities. By contrast, analytical calculations and global mantle flow models indicate basal drag can be substantial. In this study, we revisit this problem by examining the drag at the base of the lithosphere, for a single subduction system, in 2D models with a free trench and composite non-linear rheology. We compare the behaviour of short and long plates for a range of asthenospheric and lithospheric rheologies. We reproduce results from previous modelling studies, including low ratios of trench over plate motions. However, we also find that any combination of asthenosphere and lithosphere viscosity that produces Earth-like subduction behaviour leads to a correlation of velocities with plate size, due to the role of basal drag. By examining Cenozoic plate motion reconstructions, we find that slab age and plate size are positively correlated: higher slab pull for older plates tends to be offset by higher basal drag below these larger plates. This, in part, explains the lack of plate velocity-size correlation in observations, despite the important role of basal drag in the subduction force balance.Lior Suchoy was supported by the Engineering and Physical Sciences Research Council (EPSRC) (grant no. EP/N509486/1). Ben Maunder and Saskia Goes were supported by the Natural Environment Research Council (NERC) (grant no. NE/K010743/1). Rhodri Davies was supported by the Australian Research Council (grant no. DP170100058)

Imaging slab-transported fluids and their deep dehydration from seismic velocity tomography in the Lesser Antilles subduction zone

Volatiles play a pivotal role in subduction zone evolution, yet their pathways remain poorly constrained. Studying the Lesser Antilles subduction zone can yield new constraints, where old oceanic lithosphere formed by slow-spreading subducts slowly. Here we use local earthquakes recorded by the temporary VoiLA (Volatile recycling in the Lesser Antilles) deployment of ocean-bottom seismometers in the fore- and back-arc to characterize the 3-D seismic structure of the north-central Lesser Antilles subduction zone. Along the slab top, mapped based on seismicity, we find low Vp extending to 130–150 km depth, deeper than expected for magmatic oceanic crust. The slab's most prominent, elevated Vp/Vs anomalies are beneath the fore- and back-arc offshore Guadeloupe and Dominica, where two subducted fracture zones lie with the obliquely subducting boundary between Proto-Caribbean and Equatorial Atlantic lithosphere. These structures, therefore, enhance hydration of the oceanic lithosphere as it forms and evolves and the subsequent dehydration of mantle serpentinite when subducted. Above the slab, we image the asthenosphere wedge as a high Vp/Vs and moderate Vp feature, indicating slab-dehydrated fluids rising through the overlying cold boundary layer that might induce melting further to the west. Our results provide new evidence for the impact of spatially-variable oceanic plate formation processes on slab dehydration and mantle wedge volatile transfer that ultimately impact volcanic processes at the surface, such as the relatively high magmatic output observed on the north-central islands in the Lesser Antilles

Widespread hydration of the back arc and the link to variable hydration of the incoming plate in the Lesser Antilles from Rayleigh wave imaging

Subduction zone dynamics are important for a better understanding of natural hazards, plate tectonics, and the evolution of the planet. Despite this, the factors dictating the location and style of volcanism are not well-known. Here we present Rayleigh Wave imaging of the Lesser Antilles subduction zone using the ocean bottom and land seismic data collected as a part of the VoiLA experiment. This region is an important global endmember that represents a slow (<19 mm/yr) convergence rate of old (80–120 Ma), Atlantic lithosphere formed at a slow spreading ridge. We image the fast slab, the fast-overriding plate and the slow mantle wedge across the entire arc. We find slow velocity anomalies (∼4.1 km/s) in the mantle wedge directly beneath the arc with local minima beneath Dominica/Martinique, Montserrat and the Grenadines. We observe that slow velocities in the wedge extend 200 km into the back arc west of Martinique. The slowest mantle wedge velocity anomaly is more muted than several global wedges, likely reflecting the lower temperatures and less partial melt predicted for the Antilles. Subducted fracture zones and plate boundaries are a potential source of hydration, since they are located near the anomalies, although not directly beneath them. To match our observations, geodynamic models with a broadly hydrated mantle wedge are required, which can be achieved via deep hydration of the slab, and fluid release further into the back arc. In addition, 3-D flow and melt migration or ponding are required to explain the shape and location of our anomalies

IFN-α-2a (Interferon) and ribavirin induced suicidal attempt in a patient of chronic HCV: A rare case report

Interferons (IFNs) are proteins produced by cells, fibroblasts and macrophages, in response to viral invasion, and mediates immune response. IFN-α and ribavirin are the approved treatment for HCV infection, but also carries a risk of neuropsychiatric adverse effects, viz. insomnia, irritability, mood changes, and depression

Author Correction: Variable water input controls evolution of the Lesser Antilles volcanic arc

In this Article, authors Michael J. Kendall and David Schlaphorst of the VoiLA consortium were incorrectly listed as being at the Department of Earth Sciences, Durham University, Durham, UK (affiliation 2), instead of at the School of Earth Sciences, University of Bristol, Bristol, UK (affiliation 1). This error has been corrected online

Variable water input controls evolution of the Lesser Antilles volcanic arc

Oceanic lithosphere carries volatiles, notably water, into the mantle through subduction at convergent plate boundaries. This subducted water exercises control on the production of magma, earthquakes, formation of continental crust and mineral resources. Identifying different potential fluid sources (sediments, crust and mantle lithosphere) and tracing fluids from their release to the surface has proved challenging1. Atlantic subduction zones are a valuable endmember when studying this deep water cycle because hydration in Atlantic lithosphere, produced by slow spreading, is expected to be highly non-uniform2. Here, as part of a multi-disciplinary project in the Lesser Antilles volcanic arc3, we studied boron trace element and isotopic fingerprints of melt inclusions. These reveal that serpentine—that is, hydrated mantle rather than crust or sediments—is a dominant supplier of subducted water to the central arc. This serpentine is most likely to reside in a set of major fracture zones subducted beneath the central arc over approximately the past ten million years. The current dehydration of these fracture zones coincides with the current locations of the highest rates of earthquakes and prominent low shear velocities, whereas the preceding history of dehydration is consistent with the locations of higher volcanic productivity and thicker arc crust. These combined geochemical and geophysical data indicate that the structure and hydration of the subducted plate are directly connected to the evolution of the arc and its associated seismic and volcanic hazards