MARIANA Project Summary

We propose to carry out marine multi-channel seismic reflection, controlled-source wide-angle reflection/refraction, and passive recording of local and teleseismic earthquakes to provide a comprehensive velocity, attenuation, structural and stratigraphic image of the Mariana island-arc system, from the subducting Pacific Plate to the backarc, at 15° to 18°N. This will be the first completely integrated seismic study of any active arc.

Principal objectives are to determine:

• the velocity and attenuation structure of the mantle as a proxy for temperature/ partial melting of the mantle wedge below the backarc spreading center and the active arc and for hydration and metamorphism below the forearc;
• the large-scale pattern of flow in the mantle wedge, as reflected by seismic anisotropy, which controls the mantle magma supply to the arc and back-arc;
• the precise location and velocity structure of subducting oceanic crust, which will place constraints on the depth of various devolatization/metamorphism reactions and the basalt-eclogite transformation;
• the velocity and density structure of the crust as a proxy for the composition of an intra-oceanic arc, with implications for models of continental growth and crustal recycling to the mantle;
• the seismic stratigraphy and structure of the forearc, arc and remnant arc which, calibrated by existing drill hole data, record a 50 m.y. history of intra-oceanic sedimentation, magmatism and deformation involving subduction initiation, episodic arc volcanism - rifting - back-arc spreading, and serpentinite diapirism. othe possible identification of magma chambers below active volcanoes and of the conduits beneath forearc serpentinite seamounts;
• the possible existence of an intermediate depth double seismic zone and the relationship between slab seismicity and island arc volcanism;
• other updip and downdip limits of the seismogenic zone and implications for the largely aseismic subduction in the Mariana convergent margin.

Our study will provide the baseline seismic information required for the MARGINS Subduction Factory experiment in the Mariana system. We therefore plan to collect the data necessary to create images detailed enough to guide future geochemical measurements and proposed ODP drilling to understand the material fluxes input at the trench and output in the forearc, volcanic arc, and backarc.

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