Deep seismic structure of the Tonga subduction zone: Implications for mantle hydration, tectonic erosion, and arc magmatism.

Contreras-Reyes, E.; Grevemeyer, I.; Watts, A.B.; Flueh, E.R.; Moeller, S.; Papenberg, C.; Peirce, C.

Abstract

[1] We present the first detailed 2D seismic tomographic image of the trench-outer rise, fore- and back-arc of the Tonga subduction zone. The study area is located approximately 100 km north of the collision between the Louisville hot spot track and the overriding Indo-Australian plate where ∼80 Ma old oceanic Pacific plate subducts at the Tonga Trench. In the outer rise region, the upper oceanic plate is pervasively fractured and most likely hydrated as demonstrated by extensional bending-related faults, anomalously large horst and graben structures, and a reduction of both crustal and mantle velocities. The 2D velocity model presented shows uppermost mantle velocities of ∼7.3 km/s, ∼10% lower than typical for mantle peridotite (∼30% mantle serpentinization). In the model, Tonga arc crust ranges between 7 and 20 km in thickness, and velocities are typical of arc-type igneous basement with uppermost and lowermost crustal velocities of ∼3.5 and ∼7.1 km/s, respectively. Beneath the inner trench slope, however, the presence of a low velocity zone (4.0–5.5 km/s) suggests that the outer fore-arc is probably fluid-saturated, metamorphosed and disaggregated by fracturing as a consequence of frontal and basal erosion. Tectonic erosion has, most likely, been accelerated by the subduction of the Louisville Ridge, causing crustal thinning and subsidence of the outer fore-arc. Extension in the outer fore-arc is evidenced by (1) trenchward-dipping normal faults and (2) the presence of a giant scarp (∼2 km offset and several hundred kilometers long) indicating gravitational collapse of the outermost fore-arc block. In addition, the contact between the subducting slab and the overriding arc crust is only 20 km wide, and the mantle wedge is characterized by low velocities of ∼7.5 km/s, suggesting upper mantle serpentinization or the presence of melts frozen in the mantle.

Citation

Contreras-Reyes, E., Grevemeyer, I., Watts, A., Flueh, E., Moeller, S., Papenberg, C., & Peirce, C. (2011). Deep seismic structure of the Tonga subduction zone: Implications for mantle hydration, tectonic erosion, and arc magmatism. Journal of Geophysical Research, 116(B10), Article B10103. https://doi.org/10.1029/2011jb008434

• Journal Article Type: Article
• Publication Date: 2011-10
• Deposit Date: Apr 11, 2011
• Journal: Journal of Geophysical Research. Solid Earth
• Print ISSN: 0148-0227
• Electronic ISSN: 2156-2202
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 116
• Issue: B10
• Article Number: B10103
• DOI: https://doi.org/10.1029/2011jb008434
• Keywords: Tonga, Arc magmatism, Hydration, Island arc, Mantle wedge, Tectonic erosion.
• Public URL: https://durham-repository.worktribe.com/output/1509835