DEFORMATION ASSOCIATED WITH THE NORTHERN MIGRATION OF THE MENDOCINO TRIPLE JUNCTION: THE MENDOCINO DEFORMATION ZONE

We reevaluate the generalized configuration of the Mendocino Triple Junction (MTJ) and present a block model which breaks out the tectonic domains which we interpret as comprising the transition zone between the Pacific, Gorda, and North America plate boundaries. In a global scale discussion, the trench-transform-transform description is certainly valid, but on a regional scale of ~200 km, there are identifiable domains which comprise NA that justify redefining the geometry of the boundary as it is manifested in North America. These domains within the portion of ‘North America’, along with the adjacent Pacific and Gorda plates, are collectively termed the Mendocino Deformation Zone (MDZ) as they represent more than just a simple 3 plate configuration, but a complex juxtaposition of 2 larger plates adjacent to several blocks, or micro-plates. We recognize that the Pacific plate is the only plate behaving rigidly in this region, and it is well documented that southern Gorda plate deformation is distinctively different from northern Gorda plate deformation. We use recent and published geologic, geomorphic, geodetic, seismic, and other available geophysical data to characterize the onland tectonic domains associated with Quaternary deformation occurring in the MDZ. The purpose of this study is to define a more detailed framework of the migrating triple junction to help provide for more accurate depictions of the geometry of the observed Quaternary boundaries. Moving forward, this study will aid other workers in applying realistic boundaries to quantify behavior of these blocks rather than the commonly used 3 plate geometry when evaluating the migrating triple junction region.