PALEOMAGNETIC DATA FROM THE EASTERN MONO BASIN AND WESTERN-MARGIN OF THE MINA DEFLECTION: CLOCKWISE VERTICAL AXIS ROTATION ASSOCIATED WITH INTERCONTINENTAL DEFORMATION

Modern deformation between the North American and Pacific plates is distributed across a wide zone of the western margin of North America, from the San Andreas Fault eastward into the western Basin and Range province where at least 25% - 30% of the plate boundary strain is accommodated via intraplate deformation. We hypothesize that during the early to mid Miocene deformation associated with this transtensional system was initially located east of the Sierra Nevadan Mountain front in the Mono Basin prior to stepping east into the Mina Deflection in the late Miocene to early Pliocene. To test this hypothesis, paleomagnetic data were collected from the Miocene Jack Springs Tuff (JST) east of Huntoon Valley, and stratigraphically continuous sections of Pliocene basalt flows near Marietta, NV (MB), Pizona, CA (PB), and Queens Valley, CA/NV (QVB). The JST and basalts flows yield a stable magnetization that decays near linearly to the origin during alternating field demagnetization; although some yield a more complex behavior and required a combination of liquid N₂, alternating field, and thermal demagnetization to isolate the ChRM. Nineteen structurally corrected sites from the JST yield discordant results with respect to the reference location showing variable clockwise vertical axis rotation ranging from +20° ± 10° to +60° ± 11°. After structural correction, the results from the basalts yield discordant paleomagnetic data with respect to the Miocene expected field direction (D = 353.3°, I = 58.3°, A₉₅ = 3.1°). Twelve of thirteen sites from the MB yield a group mean direction D = 027°, I =57°, a₉₅ = 12.4° that is clockwise discordant with an inferred rotation (R) and flattening (F) of R = +33.9°+/-18.4° and F=1.3° +/- 10.6°. Seventeen of twenty-two sites from four sections in the PB yield interpretable results. Three sections are counter-clockwise discordant and one section plots on the expected field direction. Sixteen of twenty-three sites from five sections in the QVB yield interpretable results. Three sections are counter-clockwise discordant and two sections are clockwise discordant. These preliminary data support the hypothesis of strain being accommodated by vertical axis rotation east of the Sierra Nevadan Front and further constrain the timing of intraplate reorganization.