The Geology of the Inskip Canyon Area, East Range, Nevada

Publication Date

5-2002

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Geology

Department

Geosciences

Supervisory Committee Chair

C. J. Northrup

Abstract

The Inskip Formation is located in the East Range, northwest Nevada. The formation is situated in the immediate vicinity of the Roberts Mountain Allochthon (RMA) and within a few miles of the Golconda Allochthon (GA).

The Inskip Formation, as mapped previously by Whitebread (1994; 1:48,000 scale) is divided into the Lower and Upper Inskip Formation. New detailed 1:12,000 scale mapping allows for the distinction of lesser units in the Inskip Formation. These layers are meta-conglomerate, quartz-muscovite phyllite, minor shale, chert-argillite, and metamorphosed fossiliferous and compositionally layered limestone in the Lower Inskip Formation. The Upper Inskip Formation contains layers of altered mafic and ultramafic rocks, quartz-muscovite phyllite, quartz-muscovite-biotite-homblende schist, quartzite, and metamorphosed limestone. The Inskip Formation is at least 9000 ft (2,743 m) in structural thickness and paleontologic data from previous works and this study indicate the Inskip Formation spans from the Late Devonian to late Early Permian (Silberling and Roberts, 1962, Whitebread, 1994, and Ketner and others, 2000).

The Valmy Formation (RMA) overlies the Inskip Formation in the east and the contact, as mapped previously, was interpreted to be a depositional disconformity (Whitebread, 1994). Detailed 1:12,000 scale mapping in Inskip Canyon, East Range, NV, require reinterpretation of this contact as a significant W-directed thrust that places Valmy structurally on the Inskip Formation. Evidence for a thrust contact includes a significant increase in penetrative strain intensity adjacent to the contact, and systematic variation in the bedding orientation within the Inskip, producing a W-vergent drag fold in the vicinity of the Valmy Formation contact.

The Inskip/Valmy thrust contact is interpreted to be part of the W-directed Clear Creek Thrust System and the trace ofthe thrust contact may be a southern extension of the Willow Creek Thrust (WCT) contact. The trace for the WCT in the East Range is reinterpreted to follow the Inskip/Valmy thrust contact. Timing for the Inskip/Valmy thrusting event would then be post-Triassic based on Triassic rocks in the footwall of the WCT in the East Range (Whitebread, 1994).

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