The field work associated with this grant was conducted in Spring 2010 using the SIO ship R/V Melville (MV1007 cruise May-June 2010).  All geophysical and multibeam data and metadata have been deposited in the UNOLS MGDS database (http://rvdata.us/catalog/MV1007  and http://www.marine-geo.org/tools/search/entry.php?id=MV1007). Over the past 2 years all the geophysical data that formed the core of the WHOI contribution to this research effort have been processed and reported on, primarily in 2 journal articles.  One was published in 2012 and the other has been accepted for publication in a AGU Monograph to be published in late 2012 or early 2013. These data have been used to resolve the regional fabric of the seafloor in the northern Galapagos and deduce crustal and upper mantle structure. S. Adam Soule and Eric Mittelstaedt, a post-doc at WHOI funded through this grant, have been primarily responsible for processing and analysis of the geological and geophysical data sets including multibeam, sidescan sonar, sea-surface magnetics and BGM-3 continuous gravity.  The maps and data summary figures have been published in Mittlestaedt et al. (2012) and (in press).The multidisciplinary approach we have undertaken with our collaborators, K. Harpp and D. Geist (at Colgate U. and U. Idaho) have enabled us to assess geodynamic models and significantly advance our understanding of plume-ridge interactions.

Multibeam and sidescan data have been processed and integrated within a GIS environment to permit cross-correlation of seamount and prominent structural seafloor features throughout the surveyed area.  Figures 1& 2 show the primary results of that integrated mapping effort as published in Mittelstaedt et al. (2012). Figure 3 shows the compiled data resulting from analysis of the multibeam and sidescan sonar to derive structural and volcanic lineament statistics for the surveyed area.

Raw gravity measurements collected during the MV1007 cruise were reduced to a free air anomaly (FAA) by applying a 360 s Butterworth filter, removing instrument drift (< 0.1 mGal) and the 1984 reference ellipsoid, correcting for ship motion (Eötvos correction), and, finally, decimating the data to one measurement every 60 s. The final compilation is gridded at a 2 km resolution using the Generic Mapping Tools’ greenspline function with a minimum curvature spline at a tension of 0.2 [Wessel and Smith, 1991] (Figure 4). Additional details regarding gravity data are presented in Mittelstaedt et al., in press).

Bathymetry and side scan sonar data reveal significant variations in faulting and volcanism across the study area. Fault populations were placed into three categories: (1) ridge-parallel; (2) transform-parallel; and (3) transform oblique. Categories (1) and (2) are consistent with a standard model of mid-ocean ridge spreading. However, the third set of faults, located in a ~60 km wide swath around the Galápagos Transform Fault, strikes 30° oblique to the trace of the transform and is not commonly observed at other transform faults. This orientation is likely associated with trans-tension across the GTF that is itself oblique to the ridge spreading direction.  Volcanism in the study area is distinctly different between the Nazca and Cocos Plates and may indicate a sharp change in melting regime across the GSC. On the Cocos Plate to the north of the GSC, the observed number (219) and volume (70 km³) of seamounts are small. In contrast, on the Nazca Plate to the south of the GSC, there are more than 500 identified seamounts with a total estimated volume of 1178 km3. Seamount volcanism on the Nazca Plate is concentrated within 3 volcanic lineaments, the largest of which is the WDL....

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