THE INFLUENCE OF TECTONIC INHERITANCE IN THE CENTRAL BASIN AND RANGE EXTENSIONAL PROVINCE WITH AN EMPHASIS ON THE WESTERN LAKE MEAD DOMAIN

Many workers have emphasized the role of the orientation of older tectonic belts in the faulting patterns that formed the central Basin and Range extensional province, a region dominated by transtensional faulting and west-facing tectonic wedges. The Neoproterozoic rifted margin of western North America, Paleozoic passive margin, Mesozoic Sevier thrust belt front, and northwest margin of the Cretaceous – Paleogene Laramide orogeny all have been proposed to have influenced the extensional development of the central Basin and Range. Here we emphasize the critical role of the Laramide orogeny on the central Basin and Range using the 500-km-wide model of the Laramide orogeny from Saleeby (2003). That model emphasizes the distinct NE-trending boundary formed in the latest Cretaceous between a shallowly subducting Farallon plate beneath the Mojave province and normal subduction of the northern Farallon plate (or Kula plate, Umhoefer and Blakey, 2006) beneath the southern Sierra Nevada. The Garlock fault formed during Miocene extension along this NE-trending margin of the Laramide orogeny. When the central Basin and Range is reconstructed back to 18 Ma, the initiation of extension, the left-lateral Garlock fault aligns with the left-lateral Lake Mead fault system in our study area. The Lake Mead fault system formed along the trend of many of the older tectonic belts including the Laramide orogeny of Saleeby. The transtensional faulting in the Lake Mead domain is expressed by NE-striking sinistral faults linked to north-striking normal faults producing a bulk east to west extension. West-facing tectonic wedges produced similar east-west extension when NW-striking dextral faults linked to the NE-striking sinistral faults. Our favored model for fault evolution in the western Lake Mead domain shows the prevalence of both of these styles of faulting. Normal faults formed from 17 – 14.5 Ma in the hanging wall of a major detachment fault and the early NE-striking, transtensional Lake Mead fault system in eastern Lake Mead. From 14.5 – 13.7 Ma, the dextral Las Vegas Valley shear zone propagated east and sinistral Lake Mead fault system propagated west to form a tectonic wedge in western Lake Mead that continued until ~8 Ma. The Las Vegas Valley shear zone was accompanied by a complex rotational deformation pattern at its eastern end.