Geologic Mapping and Structural Studies of the Miocene Boundary Canyon Fault, Funeral Mountains, Death Valley, California
Understanding the deep crustal processes that drive active faulting and earthquakes in continental settings is viewed as a top scientific challenge in the earth sciences but is an inherently difficult problem to work on because of the minimum 5-10 km depth to the seismogenic base of the elastic crust. It's too deep to drill! Normal fault systems in the Basin and Range province are unusual in that they often provide an opportunity for detailed investigation of faults to great depths in the crust, even into the Elastico-Frictional to Viscous (EFV) (or brittle-ductile) transition zone.
Understanding the deep crustal processes that drive active faulting and earthquakes in continental settings is viewed as a top scientific challenge in the earth sciences but is an inherently difficult problem to work on because of the minimum 5-10 km depth to the seismogenic base of the elastic crust. It's too deep to drill! Normal fault systems in the Basin and Range province are unusual in that they often provide an opportunity for detailed investigation of faults to great depths in the crust, even into the Elastico-Frictional to Viscous (EFV) (or brittle-ductile) transition zone . These remarkable down-section views of faults owe their exposure to differential vertical uplift, doming and tilting related to flow of the deeper crust (Fig. 1).
The Miocene Boundary Canyon Fault in the Funeral Mountains, Death Valley, is a spectacular example of a large offset, tilted high angle, crustal penetrating normal fault. We are studying its map-scale structural evolution, determining its offset, characterizing the fault zone rocks developed along its exposed extent and specifying the nature/conditions of strain accommodation in footwall rocks with increasing depth in the crust.
Why study normal faults?
Rifting is one of the fundamental tectonic processes on Earth, leading to the formation of oceanic crust and ocean basins. Normal faults develop as a consequence of rifting in continental crust and provide important controls on sedimentary basin development and oil and gas migration/sequestration. Normal faults are usually associated with high heat flow and magmatism and serve as conduits for geothermal systems and ore-bearing hydrothermal fluids. In active tectonic settings, normal faults pose earthquake hazards. Rift-related normal faults are thus important fault systems to understand because of their broad relevance to resources and society.
Figure 1. Contrast in normal fault-zone evolution during rifting of a continental margin (West Iberian Margin as described by Ranero and Gussinye, 2010) (top) with faulting and core complex development in continental crust in the Basin and Range (cross-section A-A' modified after Gans and Miller 1983 and 1985 and Gans 1987) (bottom). Extensional faulting leading to continental break-up (top) does not expose the Elastico-Frictional to Viscous (EFV) transition and subsidence of thinned crust leads to increased water depth. In contrast, regions of high extension in the Basin and Range do not thin the whole crust and are compensated at depth by flow of crust and/or intrusion of magma (?) into more highly extended regions, causing uplift of the paleo EFV or seismogenic base of the upper crust. Cross-section A-A' also illustrates in a simple way how differential uplift related to crustal flow at depth can invert or uplift normal fault systems and their associated syn-extensional basins while bringing once ductile levels of the crust to the surface or near surface during extension. From Miller and Lee (2014)
