Tectonic Implications of Newly Documented Early(?) Through Late Paleozoic Age Strata, Black Rock Desert Region, Northwest Nevada

Abstract

Early Paleozoic to Pennsylvanian age strata are exposed in several of the Paleozoic arc sequences of the western United States cordillera where they form depositional basement for thick volcanic and volcaniclastic sequences of Permian age. New work in the Pine Forest range, BRD, however, indicates that this range contains a previously unrecognized, but extensive and structurally intact section of metamorphosed middle (and early ) Paleozoic through Late Permian age strata. This section has been dated paleontologically and radiometrically, and consists of the following (protolith descriptions in ascending stratigraphic order): (1) quartzo-feldspathic sedimentary and mafic volcanic rocks of probable early Paleozoic and/or Devonian age, and mafic volcanic rocks of probable Devonian age; (2) generally deep marine, chert/argillite/quartz-rich clastic rocks of post-late Devonian( ) to Late Mississippian age; (3) shallow marine carbonate of middle Carboniferous age; (4) volcanic and volcaniclastic rocks of Early Pennsylvanian age; (5) shallow marine limestone and volcaniclastic rocks of Early Permian( ) age. This stratigraphic succession documents a history that is very similar to that recorded in other Paleozoic arc sequences of the western United States cordillera, including a record of early Paleozoic to Devonian( ) quartzose sedimentation and volcanism, Mississippian deep marine siliciclastic sedimentation, some renewed volcanismmore » in Pennsylvanian time, and generally shallow marine to emergent conditions in Pennsylvanian to Early Permian time. A significant difference between the Paleozoic record in the BRD and that in other arc sequences further west, however, is the much greater thicknesses of volcanic rocks in the latter areas. This relation suggests that the BRD lay in a back-arc position relative to the main axis of Paleozoic arc volcanism.« less