Abstract: Eureka Fold and Thrust Belt: Antelope, Fish Creek an Pancake Ranges, East Central Nevada
S. F. Mcdonald
Upper crustal response to noncoaxial, ESE directed, brittle, simple shear of ?early Medial jurassic age in central Nevada was the Eureka old and Thrust Belt. Age determination is still imprecise but regional field relationships indicate a pre-Early Cretaceous, post-Early Triassic age for compression. The system places deformed, potential reservoir rocks above a tectonically thickened section of excellent source rocks in the general area between Pine and Railroad Valleys.
The duplex system mega-structure is three-fold. The structurally highest part is the Moody allochthon, composed of complexly folded Cambro-Ordovician Miogeoclinal rocks. It overlies she Greensprings allochthon, dominantly Devonian carbonates with some Mississippian carbonate a clastics and ?Penn-Permian conglomerate. An asymmetric ramp anticline in the Pancakes, suggests E-vergence. The structurally lowest allochthon is composed of lower Paleozoic Miogeoclinal rocks, Mississippian clastics and Penn-Permian carbonate and clastic rocks. Deformed Paleozoic conglomerates in this section have generally been widely mistaken in outcrop and subsurface for similar Teriary or Mesozoic clastic units leading to misapprehension of duplex system age. The lower allochthon is structurally distinct fr m the other, carbonate-quartzite dominated plates because of its thick, shale-dominated sections of the Antler clastic wedge. Nearly the entire Pancake and northern White Pine Ranges are assigned to this lowest allochthon. It is directly overlain by the Moody allochthon in the Antelopes Range.
The blind thrust flooring the duplex system may-have been reactivated in later compressional and extensional events to provide, alternately, paths or seals related to deep reservoir formation.
AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada