GEOPHYSICAL ANALYSIS OF THE KLAMATH MOUNTAINS ACCRETIONARY SUPERTERRANE

The Klamath Mountains Superterrane of northwestern California and southwestern Oregon is a classic example of a mountain belt developed predominantly by accretionary processes. The region is made up of multiple tectonostratigraphic terranes, which are all tectonically, structurally and lithologically distinct from adjacent terranes. These terranes generally become younger to the west. The region has preserved an almost continuous record of accretion during the Mesozoic, and contains evidence of tectonism as far back as early Ordovician. The regional structure of the Klamath Mountains Superterrane can be characterized as amalgamated terrane slices that are individually bounded to the east and west by eastward dipping thrust faults, and it was subsequently faulted by high-angle thrusts by more local tectonic stresses. Further, the structures have been crosscut by multiple magmatic events, resulting in many plutons that range in age (early Paleozoic to early Cretaceous), size (stocks to batholiths) and composition as well (ultramafic to silicic). Both the intrusions and the successive imbrication of terranes led to a very complex and rich metamorphic history in the area, including near-blueschist facies and multiple ophiolite complexes found throughout the region. New gravity data collected during the summer of 2009 in the Condrey Mountain terrane provides new insight on the subsurface geometries of the enigmatic schist complex and possible origins of the metamorphism, and relationship to the younger Galice Formation. In our study, gravity and magnetic maps coupled with the sparse seismic data available provide an integrated analysis of the region. The estimated crustal thickness is approximately 25 km along the coast and thickens eastward to over 30 km.