Magnetotelluric Imaging of Lower Crustal Melt and Lithospheric Hydration in the Rocky Mountain Front Transition Zone, Colorado, USA. Issue 12 (4th December 2017)

• Record Type: Journal Article
• Authors: Feucht, D. W.; Sheehan, A. F.; Bedrosian, P. A.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 12(2017)
• Page Start: 9489
• Page End: 9510
• Publication Date: 2017-12-04
• Subjects: magnetotellurics -- mantle hydration -- partial melt -- lithosphere -- Rocky Mountains -- Great Plains; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2017JB014474
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: We present an electrical resistivity model of the crust and upper mantle from two‐dimensional (2‐D) anisotropic inversion of magnetotelluric data collected along a 450 km transect of the Rio Grande rift, southern Rocky Mountains, and High Plains in Colorado, USA. Our model provides a window into the modern‐day lithosphere beneath the Rocky Mountain Front to depths in excess of 150 km. Two key features of the 2‐D resistivity model are (1) a broad zone (~200 km wide) of enhanced electrical conductivity (<20 Ωm) in the midcrust to lower crust that is centered beneath the highest elevations of the southern Rocky Mountains and (2) hydrated lithospheric mantle beneath the Great Plains with water content in excess of 100 ppm. We interpret the high conductivity region of the lower crust as a zone of partially molten basalt and associated deep‐crustal fluids that is the result of recent (less than 10 Ma) tectonic activity in the region. The recent supply of volatiles and/or heat to the base of the crust in the late Cenozoic implies that modern‐day tectonic activity in the western United States extends to at least the western margin of the Great Plains. The transition from conductive to resistive upper mantle is caused by a gradient in lithospheric modification, likely including hydration of nominally anhydrous minerals, with maximum hydration occurring beneath the Rocky Mountain Front. This lithospheric "hydration front" has implications for the tectonic evolution of the continental interior and the mechanisms by which water infiltrates the lithosphere. Key Points: We image 2‐D anisotropic electric resistivity structure beneath the Rocky Mountains and Great Plains to depths of 150 km High electrical conductivity in the lower crust beneath the Rocky Mountains is attributed to partial melt and crustal fluids Eastward deepening mantle conductivity beneath the Great Plains is interpreted as a hydration front