Collaborative Research: Lithospheric Structure and Evolution of the Rocky Mountains - beginning Phase 2 Geodynamic Processes

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0003577JohnsonThe western U.S. is one of the best places in the world to study continental evolution because there is a preserved unique record of the growth, stabilization, maturation, rifting, and incipient dismemberment of a continent. In particular, we can see how older lithospheric structures (in this case Archean and Proterozoic) influenced younger tectonic events, including development of the huge, presently active, orogenic plateau that dominates the western U.S. and the progressive dismemberment and dispersal of continental fragments along its active western margin. Continents are the long-term record keepers of plate interactions before 200 Ma. However, accumulated modification often obscures the previous record. The western U.S. is unique in that this part of the continent was assembled in the Proterozoic around an Archean "cratonic core", then was truncated in the Phanerozoic at a high angle so as to create a new continental margin oblique to the Precambrian structures. The result was the creation of a wide region - the western U.S. - where nature "caught" all stages of structural reactivation and continental modification.The main goal of the CD-ROM (Continental Dynamics of the Rocky Mountains) Project is to understand the processes of formation and modification of continental lithosphere. Phase 1 of the CD-ROM experiment was a three year project to improve our structural and petrologic knowledge of the lithosphere and to test the hypothesis that the lithospheric structure produced during assembly of southwestern North America has profoundly influenced physical and chemical modification of the continental lithosphere during all subsequent magmatic and tectonic events, including those related to the ongoing asthenospheric flow. The principal investigators studied two Proterozoic structures with a range of seismic and geologic methods: the Cheyenne Belt and the Jemez lineament. Reflection, refraction, and teleseismic investigations are providing crustal - and lithospheric - scale images of major structures. A more complete picture of the evolution of the lithosphere has been added by geologic studies of Precambrian shear zones and Phanerozoic structures, xenolith studies, and geomorphologic and exhumation studies of present landforms. Phase 1 brought together 18 investigators from 14 institutions, including collaboration with a German-funded refraction team. With these awards, one year of funding is provided to continue to process, interpret, and integrate the diverse data sets generated in Phase 1 and to begin developing geodynamic models. The Principal Investigators will also explore new methods of data integration towards the goal of developing a "master model" for lithospheric structure.***