QUATERNARY TECTONICS OF MONO LAKE BASIN, EASTERN CALIFORNIA

Mono basin is located within a regional topographic high, the Mono Arch, along the west edge of the Great Basin and within the Walker Lane belt, a zone of transtensional intraplate deformation kinematically linked to Pacific-North American plate motion. The basin lies in the NW corner of a small, shallow tilted crustal wedge that lies near the crest of the arch, and within a broader half graben or axial graben. The NW corner of the asymmetric basin is bound by active faults and including segments of the Sierra Nevada frontal fault zone (SNFF). A fairly large river flowed through the late Miocene or early Pliocene paleo-Cascade landscape prior to segmentation by the currently active transtensive basins. The basin is one of several small nested structural depressions within a broader ‘super graben’ and hosts the youngest non-arc, intracontinental igneous activity in the Great Basin. Mono basin is also part of a broad gently north-northwest-tilted zone that’s antithetic to an east-tilted rollover on the hanging wall of the well integrated, west-dipping White Mountain fault zone. The depression that is now Mono basin may have initiated during Pliocene time, much later than initiation of the Owens Valley graben. Previous geophysical studies indicate the regional topographic high that underlies Mono basin is likely supported by mantle upwelling, as opposed to, for example, supported by relatively thickened crust. The evolution of Mono Basin, which occurs at the northern terminus of the south sloping Owens Valley ‘super graben’ structure, is strongly linked to the structural evolution and consequent transtensive opening of Owens and basins due east. Its evolution is also linked to a large-scale transtensional releasing bend in the Walker Lane that steps active transform displacement from a broad region to the south. Relative displacement of Mono basins north and south margins has affected the size and location of spillway limited lakes during Plio-Pleistocene time. The basin’s north and east margin are rimmed by an inactive Late Miocene intermediate-siliceous volcanic arc complex with flanking Pliocene to late Quaternary, largely bimodal volcanoes associated with transtensive deformation. Active volcanism occurs near the west margin of the basin associated with the strands of the SNFF.