Volatiles and Fluids in Subduction Zones

Arc-parallel mantle flow

Geochemical and seismic anisotropy data were combined to address the question of flow in the mantle wedge. Mantle flow in subduction zones is poorly understood, particularly in the wedge region where arc magmas are generated. Many numerical and conceptual models are two-dimensional and only consider flow perpendicular to the trench driven by coupling of subducting slab motion to the mantle wedge. Isotope geochemistry of volcanic front lavas and seismic velocity anisotropy provide strong evidence that there is also a trench-parallel component of flow in the mantle wedge beneath Costa Rica and Nicaragua. The systematic variation in Nd-Pb-Hf isotope ratios from central Costa Rica to NW Nicaragua and the lead isotope geochemistry of Costa Rican volcanic rocks can be explained through addition of slab component with melt-like properties from the subducting seamount province of the Galapagos hotspot track to the mantle wedge beneath central Costa Rica. This mantle flows to NW Nicaragua at minimum rates of 63-190 mm/yr, similar to the magnitude of subducting Cocos Plate motion (~85 mm/yr). This study was carried out in close collaboration with collegues from the MARGINS group and from Central America; findings are published in Nature (Hoernle K, Abt DL, Fischer KM, Nichols H, Hauff F, Abers G, van den Bogaard P, Heydolph K, Alvarado G, Protti JM, Strauch W (2008) Arc-Parallel Flow in the Mantle Wedge Beneath Costa Rica and Nicaragua. Nature 451: 1094-1098, doi: 10.1038/nature06550).