Introduction to special issues, Part II: Nature of tectonic boundaries in lithosphere of the Rocky Mountains

Abstract

This is the second of two issues of Rocky Mountain Geology that addresses the structure and evolution of continental lithosphere in a transect through the Rocky Mountains from Wyoming to New Mexico. Contributions are mainly from participants in the CDROM (Continental Dynamics – Rocky Mountain) project, recently funded by the Continental Dynamics Program of the National Science Foundation (Karlstrom, 1998). The overall theme for papers in both issues involves the present geometry and long-term evolution of tectonic boundaries within the 1000 km-wide Paleoproterozoic crust of the southwestern United States (Fig. 1). In this region, as in many other orogens, a first-order geodynamic problem is to understand where ancient accretionary structures are located and how they become reactivated in subsequent tectonic events. We would like to know which components of present lithospheric structure were “inherited” from the time of lithosphere formation. The first issue ( RMG , v. 33, no. 2, 1998) contains papers that discuss the concept of inheritance, the present geophysical structure of the region, and the Archean-Proterozoic boundary (Cheyenne belt) in Wyoming. The Cheyenne belt is one of the most profound lithospheric structural boundaries exposed anywhere and is well documented at crustal and mantle levels (Fig. 1). Figure 1. Location of Precambrian province boundaries in the Southwest and present mantle structure (from Fig. 2). Black represents Cenozoic volcanism along the Jemez and St. George lineaments; line pattern designates the Rio Grande rift. Numbers show locations of study areas in this issue: (1) Park Range (Foster et al.; Barinek et al.); (2) Yavapai–Mazatzal boundary of southern Colorado (Shaw and Karlstrom); (3) Tusas Mountains (Williams et al.); (4) Rincon Range (Read et al.); (5) Manzano Mountains (Marcoline et al.); (6) southwestern New Mexico (Change et al.); line pattern is the Rio Grande rift (Keller and Baldridge). Reflection experiments across the Cheyenne belt and …