Tertiary stratigraphy and structure of the southern Lake Range northwest Nevada: Assessment of kinematic links between strike-slip and normal faults in the northern Walker Lane

The Walker Lane belt is a zone of dextral shear that accommodates ∼20% of the Pacific - North America plate motion. It marks a distinct boundary between the Sierra Nevada structural block to the west and the predominant north-northeast-trending topographic fabric within the Great Basin. The northern Walker Lane, in northwest Nevada and northeast California, is the northern termination of the Walker Lane belt; it consists of kinematically linked northwest-striking, left-stepping right-lateral faults, north-striking normal faults, and subordinate east-northeast-striking sinistral faults. The major dextral faults form a left-stepping en echelon pattern and terminate in arrays of obliquely oriented, northerly striking normal faults of the Great Basin. Regional relations suggest that basin development and approximately east-west extension began after 13 Ma and that dextral shear initiated ∼9-3 Ma in the northern Walker Lane. Complex kinematic links and strain partitioning characterize the intersection of strike-slip and normal fault systems in the northern Walker Lane, as well as many other transtensional terranes. Detailed analysis of strain budgets near these intersections can therefore elucidate the kinematic evolution of transtensional terranes.; The Pyramid Lake region contains an intriguing structural intersection at the eastern boundary of the northern Walker Lane in northwestern Nevada. Here, the northwest-striking right-lateral Pyramid Lake fault ends to the north in conjunction with the southward termination of a west-dipping normal fault system that includes major range-front faults bounding the Lake Range and Nightingale Mountains. Offset of a west-southwest-trending Oligocene paleovalley suggests ∼5-10 km of right-lateral displacement on the Pyramid Lake fault just south of its terminus beneath Pyramid Lake. To assess the potential kinematic links between the dextral Pyramid Lake fault and the west-dipping normal fault system, detailed geologic mapping, paleomagnetic investigations, 40 Ar/39Ar geochronology, and a gravity survey were conducted in the southern Lake Range and neighboring basins.; The Tertiary stratigraphy of the southern Lake Range includes a thin veneer of Oligocene ash-flow tuff and an ∼1 km thick section of middle Miocene (∼16 to 13.2 Ma) volcanic rocks that includes thick sequences of mafic lavas and minor intercalated dacite, ash-flow tuff, and conglomerate. The Tertiary rocks rest nonconformably on Mesozoic granitic and metamorphic basement. These strata are cut by a system of steeply west-dipping, northerly striking normal faults. The adjoining basins are complex, east-tilted half grabens, bounded by west-dipping range-front faults along the Lake Range and Nightingale Mountains, and cut by systems of intrabasinal west-dipping normal faults. Concordant dips of strata (∼20°) throughout the Miocene and Oligocene sections within the region indicate that major extension began after ∼13 Ma.; Cumulative normal displacement on west-dipping normal faults in the Pyramid Lake region includes: (1) ∼3.5 to 5.4 km in the Pyramid Lake basin and the Lake Range normal fault zone, (2) ∼1.8 km within the southern Lake Range, and (3) ∼5.4 km in the Winnemucca basin and the Nightingale Mountains fault zone. Thus, total normal offset across the Pyramid Lake region is ∼10.7 to 12.6 km. This amount is sufficient to have accommodated the transfer of ∼5-10 km of dextral slip from the Pyramid Lake fault zone, as well as some regional extension that predates the onset of strike-slip faulting ∼9 to 3 Ma.