MIOCENE AND OLDER? DEFORMATION AND LANDSCAPE EVOLUTION, NE MOJAVE, CA

New mapping and stratigraphic, sedimentologic, and kinematic data from sparsely studied Cenozoic coarse-clastic rocks in the Old Dad Mtn area of the NE Mojave provide evidence for multiple Miocene and older? deformational events and paleodrainage reversals. Two regionally exposed volcanic units provide age control: 1) interbedded, partially welded ash flow tuff with sparse blue sanidine correlated with the 18.71 ± 0.13 Ma Peach Springs Tuff or the ≈15.8 Ma Wild Horse Mesa Tuff (Mt) and 2) overlying undeformed Plio-Quaternary basalt flows.

In the southern Old Dad Mtn area, ≈50m of SSW-flowing early Miocene and older? fluvial conglomerate (Tc1) nonconformably overlies crystalline basement and contains well rounded, polished, and chatter-marked boulders to 70 cm of quartzite, carbonate, plutonic rocks, and chloritized gneiss. A channel incised in upper Tc1 is filled with 5-15m of SW-flowing polymict conglomerate with rhyodacitic tuff and tuff breccia clasts (Tc2). Basement, Tc1, and Tc2 are overlain by Mt. All units are cut by high angle faults with 1-100m of stratigraphic throw that show reverse, normal, and strike-slip kinematic indicators. Mean SW dip decreases up section from 46° in Tc1 to 18° in Mt.

In a 10 x 30 km area between Old Dad Mtn and Kelso Mtn subparallel, high angle, NW-striking faults and NE-striking cross-faults deform ≈600m of moderately NW-dipping, mid-late Miocene polymict fanconglomerate, monomict breccia, megabreccia, and large-scale block glides (Mc1-3) with ≥10km of distributed dextral separation of marker beds and piercing points. Block glides and breccias are sourced from Old Dad Mtn or sources further west across what is now an alluviated valley. Structures in block glides indicate SE and NE transport. Paleoflow in fanglomerates was NE and in ≤100sqkm transtensional basins, NW and NE, parallel to basin bounding structures. Transpressive and transtensive deformation varied in space and time and sedimentation was syn-kinematic. Mc1-3 are overlain by ≈500m of shallowly NE-dipping, less deformed, late Miocene fanglomerate (Mc4) sourced in the Teutonia Batholith to the N. A model of early Miocene and older? extension and mid-late Miocene transtension and transpression is predictive of the location of mineralization, geophysical anomalies, and Quaternary deformation.