Paper No. 35
Presentation Time: 8:00 AM-4:45 PM
The Timpahute Lineament: Transfer Zone Between the Northern and Central Basin and Range
Transverse faults within the Great Basin tend to concentrate along E-W-trending lineaments or zones of aligned features whose role in regional extension is unclear. Here, we examine the kinematic and structural role of the Timpahute lineament, a broadly defined, 25 km wide zone that extends from the Groom Range, eastward to the eastern edge of the Caliente caldera complex, and possibly into Utah. New geologic map data (1:24,000 scale), geometric analyses, and kinematic analyses of the Crescent Spring fault zone (CSFZ), a transverse fault zone that defines the western part of the lineament, reveal four distinct Cenozoic extensional episodes: prevolcanic (pre-27 Ma), synvolcanic (~27-18 Ma), postvolcanic Miocene(?), and postvolcanic Miocene(?) - Pliocene or Quaternary extension. The timing, orientations, and kinematics of the CSFZ, combined, indicate that the stress field within the Great Basin reoriented at least twice during the Cenozoic, from E-W extension to N-S extension and back to E-W extension. Importantly, transverse faults along this part of the lineament are normal faults that accommodated a distinct N-S extensional event. N-S directed extension during the Miocene is problematic because (1) most of the recognized extension in the region is oriented ~E-W and (2) extensional models for central Basin and Range propose N-S shortening during large magnitude E-W extension. Such inconsistencies may be reconciled by a new regional tectonic model whereby N-S extension along the lineament is accompanied by southward gravitationally-driven flow of the middle to lower crust. Flow was induced by marked contrasts in gravitational potential energy across the lineament, generated by differences in extensional strain and magmatism between the northern and central Basin and Range. Thus, we suggest that the Timpahute lineament persisted through time as a major transfer zone that accommodated changes in the magnitude, timing, location and direction of extension between the northern and central Basin and Range.