New Mexico Geological Society Annual Spring Meeting — Abstracts

The goal of the Continental Dynamics of the Rocky Mountains Project (CD-ROM) experiment was to provide a new 4-D understanding of the structure and evolution of the lithosphere of the southern Rocky Mountain region. A wide variety of geological and geophysical data were collected and analyzed in an integrated fashion. In the mantle, the seismic data indicate the presence of relicts of several Proterozoic subduction zones. The northernmost one is associated with the Archean-Proterozoic boundary known as the Cheyenne belt. The present day heterogeneous mantle structure, although strongly influenced by ancient compositional variations, has undergone different degrees of partial melting due to Cenozoic heating and/or hydration caused by transient plumes or asthenospheric convection within the wide western U.S. active plate margin. The crust in the southern Rocky Mountains is relatively thick compared to the global average for the continents. The mafic lower crust and Moho of the Proterozoic provinces of the southwestern U.S. likely formed, and reformed, in several stages. Initial formation of juvenile continental crust took place by development and assembly of magmatic arcs between 1.8 and 1.6 Ga. Volcanic and plutonic rocks of this age record whole-crust differentiation and probably resulted in a mafic lower crustal residue that was enhanced between1.45 to 1.35 Ga as the crust underwent another period of differentiation leading to emplacement of A-type granites in the middle crust across southern Laurentia. This layer and ~10-km of Moho topography are interpreted to record progressive and ongoing differentiation of lithosphere, and a Moho that has changed position due to flux of basalt from the mantle to the crust. Epeirogenic uplift of the orogenic plateau in western North America, driven by mantle magmatism, continues to cause reactivation of the heterogeneous lithosphere in the Cenozoic, resulting in differential uplift of the Rocky Mountains.