Global variations in H2O/Ce: 1. Slab surface temperatures beneath volcanic arcs

We have calculated slab fluid temperatures for 51 volcanoes in 10 subduction zones using the newly developed H2O/Ce thermometer. The slab fluid compositions were calculated from arc eruptives, using melt inclusion-based H2O contents, and were corrected for background mantle contributions. The temperatures, adjusted to h, the vertical depth to the slab beneath the volcanic arc, range from ~730 to 900°C and agree well (within 30°C on average for each arc) with sub-arc slab surface temperatures predicted by recent thermal models. The coherence between slab model and surface observation implies predominantly vertical transport of fluids within the mantle wedge. Slab surface temperatures are well reconciled with the thermal parameter (the product of slab age and vertical descent rate) and h. Arcs with shallow h (~80 to 100 km) yield a larger range in slab surface temperature (up to ~200°C between volcanoes) and more variable magma compositions than arcs with greater h (~120 to 180 km). This diversity is consistent with coupling of the subducting slab and mantle wedge, and subsequent rapid slab heating, at ~80 km. Slab surface temperatures at or warmer than the H2O-saturated solidus suggest that melting at the slab surface is common beneath volcanic arcs. Our results imply that hydrous melts or solute-rich supercritical fluids, and not H2O-rich aqueous fluids, are thus the agents of mass transport to the mantle wedge

Subduction factory: 4. Depth‐dependent flux of H 2 O from subducting slabs worldwide

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95328/1/jgrb16727.pd

Múltiples placas que se subducen debajo de Colombia, iluminadas por la sismicidad y la velocidad de la inversión conjunta de datos sísmicos y de gravedad.

Subduction beneath the northernmost Andes in Colombia is complex. Based on seismicity distributions, multiple segments of slab appear to be subducting, and arc volcanism ceases north of 5° N. Here, we illuminate the subduction system through hypocentral relocations and Vp and Vs models resulting from the joint inversion of local body wave arrivals, surface wave dispersion measurements, and gravity data. The simultaneous use of multiple data types takes advantage of the differing sensitivities of each data type, resulting in velocity models that have improved resolution at both shallower and deeper depths than would result from traditional travel time tomography alone. The relocated earthquake dataset and velocity model clearly indicate a tear in the Nazca slab at 5° N, corresponding to a 250-km shift in slab seismicity and the termination of arc volcanism. North of this tear, the slab is flat, and it comprises slabs of two sources: the Nazca and Caribbean plates. The Bucaramanga nest, a small region of among the most intense intermediate-depth seismicity globally, is associated with the boundary between these two plates and possibly with a zone of melting or elevated water content, based on reduced Vp and increased Vp/Vs. We also use relocated seismicity to identify two new faults in the South American plate, one related to plate convergence and one highlighted by induced seismicity

Seismic tomography and earthquake locations in the Nicaraguan and Costa Rican upper mantle

The Central American subduction zone exhibits large variations in geochemistry, downgoing plate roughness and dip, and volcano locations over a short distance along the arc. Results from joint inversions for Vp, Vp/Vs, and hypocenters from the Tomography Under Costa Rica and Nicaragua (TUCAN) experiment give insight into its geometry and structure. In both Costa Rica and Nicaragua, the intermediate-depth seismic zone is a single layer no more than 10 to 20 km thick. Tomographic images show that throughout Nicaragua and Costa Rica the slowest mantle P wave velocities appear below and behind the volcanic front, indicating likely zones of highest temperature extending 80 to 120 km depth. A sheet of high Vp/Vs, thought to be caused by melt, is imaged directly beneath the Nicaraguan volcanoes, whereas a weaker, broader anomaly is imaged beneath the Costa Rican volcanoes, potentially indicating a greater extent of melting beneath Nicaragua. Within the downgoing plate, anomalously low velocities occur at least 20–30 km below Wadati-Benioff zone seismicity, to depths of 140 km beneath Nicaragua and to 60 km depth beneath Costa Rica. They indicate 10–20% serpentinized upper mantle of the downgoing plate beneath Nicaragua, similar to that inferred from refraction seaward of the trench, but continuing to subarc depths. This unusually hydrated lithosphere may introduce more water into the Nicaraguan mantle, initiating increased amount of melting and fluid flux to the arc. <br/