TY - JOUR T1 - Along-strike structure of the Costa Rican convergent margin from seismic a refraction/reflection survey: Evidence for underplating beneath the inner forearc JF - Geochemistry, Geophysics, Geosystems Y1 - 2016 A1 - St. Clair, J. A1 - Holbrook, W. S. A1 - Van Avendonk, H. J. A. A1 - Lizarralde, D. KW - convergent margin KW - Costa Rica KW - subduction zone processes AB - The convergent margin offshore Costa Rica shows evidence of subsidence due to subduction erosion along the outer forearc and relatively high rates of uplift (∼3–6 mm/yr) along the coast. Recently erupted arc lavas exhibit a low 10Be signal, suggesting that although nearly the entire package of incoming sediments enters the subduction zone, very little of that material is carried directly with the downgoing Cocos plate to the magma generating depths of the mantle wedge. One mechanism that would explain both the low 10Be and the coastal uplift is the underplating of sediments, tectonically eroded material, and seamounts beneath the inner forearc. We present results of a 320 km long, trench-parallel seismic reflection and refraction study of the Costa Rican forearc. The primary observations are (1) margin perpendicular faulting of the basement, (2) thickening of the Cocos plate to the northwest, and (3) two weak bands of reflections in the multichannel seismic (MCS) reflection image with travel times similar to the top of the subducting Cocos plate. The modeled depths to these reflections are consistent with an ∼40 km long, 1–3 km thick region of underplated material ∼15 km beneath some of the highest observed coastal uplift rates in Costa Rica. VL - 17 UR - https://onlinelibrary.wiley.com/doi/abs/10.1002/2015GC006029 N1 - _eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015GC006029 ER - TY - JOUR T1 - New geophysical constraints on a failed subduction initiation: The structure and potential evolution of the Gagua Ridge and Huatung Basin JF - Geochemistry, Geophysics, Geosystems Y1 - 2015 A1 - Eakin, Daniel H. A1 - McIntosh, Kirk D. A1 - Van Avendonk, H. J. A. A1 - Lavier, Luc VL - 16 UR - http://doi.wiley.com/10.1002/2014GC005548 ER - TY - JOUR T1 - Crustal-scale seismic profiles across the Manila subduction zone: The transition from intraoceanic subduction to incipient collision JF - Journal of Geophysical Research: Solid Earth Y1 - 2014 A1 - Eakin, Daniel H. A1 - McIntosh, Kirk D. A1 - Van Avendonk, H. J. A. A1 - Lavier, Luc A1 - Lester, Ryan A1 - Liu, Char-Shine A1 - Lee, Chao-Shing KW - accretion KW - collision KW - rifted margin KW - subduction KW - Taiwan AB - AbstractWe use offshore multichannel seismic (MCS) reflection and wide-angle seismic data sets to model the velocity structure of the incipient arc-continent collision along two trench perpendicular transects in the Bashi Strait between Taiwan and Luzon. This area represents a transition from a tectonic regime dominated by subduction of oceanic crust of the South China Sea, west of the Philippines, to one dominated by subduction and eventual collision of rifted Chinese continental crust with the Luzon volcanic arc culminating in the Taiwan orogeny. The new seismic velocity models show evidence for extended to hyperextended continental crust, 10–15 km thick, subducting along the Manila trench at 20.5°N along transect T1, as well as evidence indicating that this thinned continental crust is being structurally underplated to the accretionary prism at 21.5°N along transect T2, but not along T1 to the south. Coincident MCS reflection imaging shows highly stretched and faulted crust west of the trench along both transects and what appears to be a midcrustal detachment along transect T2, a potential zone of weakness that may be exploited by accretionary processes during subduction. An additional seismic reflection transect south of T1 shows subduction of normal ocean crust at the Manila trench. VL - 119 UR - https://onlinelibrary.wiley.com/doi/abs/10.1002/2013JB010395 N1 - _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/2013JB010395 ER - TY - JOUR T1 - Deep crustal structure of an arc-continent collision: Constraints from seismic traveltimes in central Taiwan and the Philippine Sea JF - Journal of Geophysical Research: Solid Earth Y1 - 2014 A1 - Van Avendonk, H. J. A. A1 - Kuo-Chen, H. A1 - McIntosh, K. D. A1 - Lavier, L. L. A1 - Okaya, D. A. A1 - Wu, F. T. A1 - Wang, C. Y. A1 - Lee, C. S. A1 - Liu, C. S. KW - arc-continent collision KW - earthquakes KW - Philippine Sea Plate KW - seismic refraction KW - Taiwan KW - tomography AB - The collision of continental crust of the Eurasian Plate with the overriding Luzon Arc in central Taiwan has led to compression, uplift, and exhumation of rocks that were originally part of the Chinese rifted margin. Though the kinematics of the fold-thrust belt on the west side of the orogen has been described in detail, the style of deformation in the lower crust beneath Taiwan is still not well understood. In addition, the fate of the Luzon Arc and Forearc in the collision is also not clear. Compressional wave arrival times from active-source and earthquake seismic data from the Taiwan Integrated Geodynamic Research program constrain the seismic velocity structure of the lithosphere along transect T5, an east-west corridor in central Taiwan. The results of our analysis indicate that the continental crust of the Eurasian margin forms a broad crustal root beneath central Taiwan, possibly with a thickness of 55 km. Compressional seismic velocities beneath the Central Range of Taiwan are as low as 5.5 km/s at 25 km depth, whereas P wave seismic velocities in the middle crust on the eastern flank of the Taiwan mountain belt average 6.5–7.0 km/s. This suggests that the incoming sediments and upper crust of the Eurasian Plate are buried to midcrustal depth in the western flank of the orogen before they are exhumed in the Central Range. To the east, the Luzon Arc and Forearc are deformed beneath the Coastal Range of central Taiwan. Fragments of the rifted margin of the South China Sea that were accreted in the early stages of the collision form a new backstop that controls the exhumation of Eurasian strata to the west in this evolving mountain belt. VL - 119 UR - https://onlinelibrary.wiley.com/doi/abs/10.1002/2014JB011327 N1 - _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/2014JB011327 ER - TY - JOUR T1 - Structure and serpentinization of the subducting Cocos plate offshore Nicaragua and Costa Rica JF - Geochemistry, Geophysics, Geosystems Y1 - 2011 A1 - Van Avendonk, H. J. A. A1 - Holbrook, W. S. A1 - Lizarralde, D. A1 - Denyer, P. KW - Central America KW - Cocos Plate KW - Galápagos hot spot KW - plate bending and faulting KW - seismic velocities KW - subduction AB - The Cocos plate experiences extensional faulting as it bends into the Middle American Trench (MAT) west of Nicaragua, which may lead to hydration of the subducting mantle. To estimate the along strike variations of volatile input from the Cocos plate into the subduction zone, we gathered marine seismic refraction data with the R/V Marcus Langseth along a 396 km long trench parallel transect offshore of Nicaragua and Costa Rica. Our inversion of crustal and mantle seismic phases shows two notable features in the deep structure of the Cocos plate: (1) Normal oceanic crust of 6 km thickness from the East Pacific Rise (EPR) lies offshore Nicaragua, but offshore central Costa Rica we find oceanic crust from the northern flank of the Cocos Nazca (CN) spreading center with more complex seismic velocity structure and a thickness of 10 km. We attribute the unusual seismic structure offshore Costa Rica to the midplate volcanism in the vicinity of the Galápagos hot spot. (2) A decrease in Cocos plate mantle seismic velocities from ∼7.9 km/s offshore Nicoya Peninsula to ∼6.9 km/s offshore central Nicaragua correlates well with the northward increase in the degree of crustal faulting outboard of the MAT. The negative seismic velocity anomaly reaches a depth of ∼12 km beneath the Moho offshore Nicaragua, which suggests that larger amounts of water are stored deep in the subducting mantle lithosphere than previously thought. If most of the mantle low velocity zone can be interpreted as serpentinization, the amount of water stored in the Cocos plate offshore central Nicaragua may be about 2.5 times larger than offshore Nicoya Peninsula. Hydration of oceanic lithosphere at deep sea trenches may be the most important mechanism for the transfer of aqueous fluids to volcanic arcs and the deeper mantle. VL - 12 UR - https://onlinelibrary.wiley.com/doi/abs/10.1029/2011GC003592 N1 - _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2011GC003592 ER -