Title

Paleozoic Geology and Structure of the Northern Rowland Quadrangle, Northern Elko County, Nevada

Publication Date

5-1997

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Geology

Department

Geosciences

Major Advisor

D. L. Schwarz

Abstract

Throughout the early Paleozoic, sedimentation along the passive western margin of North America was characterized by deposition of shallow-water carbonate rocks on the continental shelf, which graded westward into siliceous basinal rocks. This passive margin was interrupted by two collisional tectonic episodes: the Late Devonian-Early Mississippian Antler orogeny, and the Late Permian-Early Triassic Sonoma orogeny. The Antler orogeny is characterized by the eastward thrust fault emplacement of the Roberts Mountains allochthon onto the miogeoclinal shelf edge. The Golconda allochthon was a similar thrust sheet of oceanic lithologies which was structurally emplaced on top of the Roberts Mountains allochthon. The structural fabric of both allochthons is characteristically asymmetric, east-directed folds and thrust faults.

As previously mapped, the Rowland quadrangle of northernmost Elko County, Nevada, contains the northernmost exposure of the Roberts Mountains allochthon in Nevada; north of this, Tertiary volcanic rocks cover the Paleozoic strata. The supposed Roberts Mountains allochthon here is composed of the Middle Ordovician Valmy Formation and possibly the Lower-Middle Ordovician Tennessee Mountain Formation, and is unconformably overlain by Mississippian-Permian rocks of the overlap assemblage. The basal Roberts Mountains thrust fault is not exposed in the study area. Emplacement of the Roberts Mountain allochthon elsewhere in Nevada is characterized by imbricate thrust faulting and contemporaneous folding. If the Ordovician strata in the Rowland quadrangle are indeed part of the Roberts Mountains allochthon, then they should exhibit a structural style similar to that of the allochthon elsewhere. In addition, the Ordovician strata should be more deformed than the post orogenic Antler overlap assemblage.

Paleozoic strata of the study area were mapped and structural data taken. Folds are present in all of the Paleozoic strata, and range from microscopic to macroscopic scale. No significant difference in structural style was observed between Ordovician strata and Mississippian-Permian strata, suggesting that folding postdates Permian strata. Also, all of the strata are offset by a post-Permian, pre-Miocene high-angle fault which divides the study area into two structural domains.

Thus, three possibilities exist regarding the Antler orogeny in the study area. First, the Roberts Mountains allochthon was emplaced along a thrust fault, not exposed in the area, with little internal deformation. Second, the Roberts Mountains allochthon has been eroded away, exposing rocks of the autochthonous or parautochthonous miogeocline in the study area. Finally, the Antler orogeny may not have been widespread enough to affect this region of northeastern Nevada, or may have exhibited a significantly different tectonic style than elsewhere in Nevada. This study indicates that all deformation recognized in the Rowland quadrangle is post-Antler in age, because Ordovician strata and Mississippian-Permian strata appear to be similarly deformed.

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