GEOMETRY AND KINEMATICS OF MIOCENE TO PLEISTOCENE TRANSTENSION IN THE NORTHERN SLATE RANGE, CALIFORNIA

New field data from the northern Slate Range, California, illustrate the complicated style and geometry of extensional structures within transtensional tectonic regimes. The study area is located in the dextral, transtensional portion of the southwestern Basin and Range Province between Death Valley and the Sierra Nevada. At this location, strain is transferred in a right step from Searles Valley into Panamint Valley along the Manly Pass fault in the northern Slate Range. The Manly Pass fault is a moderate to low angle, curviplanar fault, with a strong gouge zone, that underlies the northern Slate Range. This fault cuts Miocene to Pliocene volcanic and sedimentary rocks and units as young as Pleistocene. The Miocene rocks were deposited on a relatively planar surface and now these rocks consistently dip eastward 30-50° in both the footwall and hanging wall. Using this surface as a datum, palinspastic restoration gives approximately 2000 m of horizontal extension and 800 m of vertical offset on the Manly Pass fault using an inferred azimuth of displacement to the northwest.

The Miocene and younger rocks in the hanging wall of the Manly Pass fault are cut by numerous normal faults. The dominant set of faults dip 40-20° to the NW and cut units as young as Pleistocene. These faults occur in a dense zone along the east side of the range. A set of relatively smaller displacement, steeply east- and west-dipping normal faults occurs structurally above the low-angle faults. There is also a set of NE-trending high-angle faults that have normal oblique sinistral offset. The low-angle faults terminate along these high-angle faults, but cannot be matched across the high-angle faults. The simplest model is that all the hanging wall normal faults are coeval and developed during a single episode of transtension; thus they are not representative separate episodes of deformation. These fault sets could accommodate ~400 m of horizontal and ~200 m of vertical slip across the northern Slate Range.

These results indicate that the Manly Pass fault and related hanging wall deformation have accommodated significant displacement and exhumation and give a first order method of reconstructing Tertiary deformation from the Panamint Range to the Argus Range. Deformation may have begun as early as Middle Miocene and is still active.