Joint 118th Annual Cordilleran/72nd Annual Rocky Mountain Section Meeting - 2022

Paper No. 16-6
Presentation Time: 10:05 AM


M LUTZ, Brandon, Earth & Environmental Science Dept, New Mexico Tech, 801 Leroy Pl, Socorro, NM 87801-4681

Ernie Anderson recognized the complex evolution of coupling within highly-extended continental lithosphere. His 1971 paper in particular was one of the first to describe thin “rafts” of continental crust “floating” on a weak, flowing middle crust. This landmark concept advanced views of rifted margins globally, but also paved the way for several generations of palinspastic reconstructions documenting the magnitude of extension in rifts.

Here, I present high-resolution palinspastic reconstructions of the central Basin and Range and discuss the 3D evolution of strain and coupling within the continental lithosphere. The reconstructions were made using GPlates and are based on a comprehensive database of offset features and slip rate studies spanning several decades. The reconstructions show that net extension rate and direction generally decreased (from ~25 mm/yr to ~11 mm/yr) and rotated clockwise (from WSW to NW) since middle Miocene time (ca. 16 Ma). Rift obliquity increased at ca. 12 Ma and ca. 8-7 Ma. These kinematic changes were likely coeval with similar ones in the northern Walker Lane and Gulf of California, suggesting a common mechanism. Clockwise rotations of the extension direction constrained herein suggest that progressive coupling of the Sierra Nevada block to the Pacific plate was the main driver of the kinematic changes.

Modeling dilational strain between crustal fault blocks reveals a narrow zone of syn-extensional ~N-S contraction, which coincides with the location of late Miocene metamorphic core complexes. The three-dimensional wedging pattern is reminiscent of previous models of tectonic escape in the Lake Mead belt (e.g., Anderson et al., 1994), but occurs between the Mojave Block and a strong keeled piece of lithosphere near the Nevada Test Site. Strengthening of the middle crust following metamorphic core complex exhumation led to vertical mechanical coupling and formation of a shear zone that penetrates the entire lithosphere.