CDROM: STRUCTURE OF THE JEMEZ LINEAMENT AND SANGRE DE CRISTO LARAMIDE THRUSTS IN NORTHERN NEW MEXICO

Among the seismic data sets acquired during the CDROM experiment in northern New Mexico are ~200 km of deep seismic reflection data. The goal of the combined seismic investigations is to image the structure of the crust and mantle of the Jemez Lineament and the surrounding Yavapai and Mazatzal terranes. The Jemez Lineament is an alignment of Cenozoic volcanic centers that appears to follow one of the SW-NE trending Proterozoic sutures formed during the rapid 1.8-1.6Ga accretion of island arc to the Archean passive margin during assembly of Laurentia. Previous mantle tomography to a depth of 100 km shows that the Jemez Lineament is underlain by low velocity (hot) mantle. This, and the mantle-derived Neogene basalts outcropping along the Lineament, suggests that hot mantle is penetrating the lithosphere along one of the Proterozoic-age lithospheric assembly boundaries. The North-South seismic profile that crosses the Jemez Lineament paralleling the Rocky Mountain front has a complex reflectivity structure. North of Las Vegas (NM) the line is dominated by a broad southward dipping, strongly reflecting ramp that appears to extend to at least 30km depth to the basal high velocity layer of the crust. We interpret this structure to be the 1.6 Ga paleo-subduction zone associated with island arc collision and accretion during continental assembly. Bright reflections overprinting the ramp are interpreted as the Neogene mafic magmatism associated with the Jemez Lineament. The East-West profile that enters the Sangre de Cristo Mountains clearly images mapped Laramide thrusts as they sole into a mid-crustal detachment layer at a depth 12 km. A deeper prominent reflector (28 km) that shallows beneath the Sangre de Cristo Mountain and extends beneath the Great Plains is a good candidate for a Laramide middle crustal master detachment.