ROBERTS MOUNTAINS ALLOCHTHON AND THE WESTERN MARGIN OF THE CORDILLERAN MIOGEOCLINE IN THE NORTHERN RITTER RANGE PENDANT, EASTERN SIERRA-NEVADA, CALIFORNIA

The truncated southwestern edge of the Roberts Mountains allochthon is exposed in the Northern Ritter Range pendant in the eastern Sierra Ne vada, structurally overlying parautochthonous rocks of the Cordilleran miogeocline. The Northern Ritter Range pendant exposes units that hav e the same stratigraphic affinities and structural relationships as ro cks of the Antler orogenic belt in Nevada. Paleozoic metasedimentary r ocks exposed in the pendant consist of two major units: (1) a structur ally complex, disrupted chert and argillite unit interpreted to be cor relative with the Roberts Mountains allochthon; and (2) a stratigraphi cally coherent siliceous and calcareous unit, the Rush Creek sequence, that is interpreted to be part of a transitional outer shelf and slop e assemblage of the lower Paleozoic Cordilleran miogeocline. In the No rthern Ritter Range pendant, the Roberts Mountains allochthon structur ally overlies the Rush Creek sequence along a north-striking, steeply dipping fault zone that may be a preserved remnant of the Roberts Moun tains thrust, which in north-central Nevada emplaced the allochthon ov er outer shelf and slope strata of the Cordilleran miogeocline during the Late Devonian-Early Mississippian Antler orogeny. These stratigrap hic and structural belts are truncated on the southwest side of the pe ndant by the Gem Lake shear zone, a northwest-trending dextral strike- slip fault associated with the Cretaceous Sierra Nevada batholith. The Northern Ritter Range pendant thus defines both the southwestern limi t of the Antler orogenic belt and the western-most exposures of paraut ochthonous miogeoclinal rocks in the central Cordillera.