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Published April 2001 | public
Journal Article

Distribution and provenance of the middle Miocene Eagle Mountain Formation, and implications for regional kinematic analysis of the Basin and Range province

Abstract

Conglomeratic strata from middle Miocene sections in the central Resting Spring Range and nearby Eagle Mountain, California, contain a clast assemblage including marble, orthoquartzite, fusulinid grainstone, and coarse (∼1 m) monzogabbro, interstratified with tephras yielding laser-fusion ^(40)Ar/^(39)Ar ages of 11.6, 13.4, and 15.0 Ma. Petrographic and geochronologic evidence ties the clast assemblage to a source area in the southern Cottonwood Mountains, California, >100 km west-northwest of their present location. In the upper 100 m of the Resting Spring Range section, conglomerates are derived almost exclusively from the southern Cottonwoods source, and sandstone modes are as much as 50% angular plagioclase derived from the monzogabbro. The lack of dilution of this detritus by other sources and sedimentary features in both sections indicate (1) that deposition occurred on an alluvial fan with a north- northeast paleoslope and (2) that transport of the gravels by sedimentary processes was probably <20 km north-northeast, in a direction normal to the present azimuth to their source. Therefore, we interpret most or all of the net east-southeast transport as a result of extensional and strike-slip faulting between the Cottonwood Mountains and the Resting Spring Range since 11–12 Ma. Restoration of these deposits to a position 10–20 km north-northeast of the eastern margin of the monzogabbro source (east margin of the Hunter Mountain batholith) yields a net tectonic displacement of the Cottonwood Mountains relative to the Resting Spring Range of 104 km N67°W. This result confirms previous reconstructions based on the restoration of isopachs in the Cordilleran miogeocline, pre-Cenozoic structural features, and other proximal Tertiary deposits in the region.

Additional Information

© 2001 Geological Society of America. Manuscript Received by the Society March 30, 2000; Manuscript Accepted April 19, 2000. This research was supported by National Science Foundation (NSF) grants EAR-93–16797 and EAR-96–14780 (to Wernicke), EAR-95–26859 (to Saleeby), and an NSF Graduate Fellowship (to Niemi). Discussions and field excursions with S. Beard, R. Bohannon, J. Calzia, I. Cemen, H.D. Curry, K. Fowler, C.J. Fridrich, J. Friedmann, W. Hamilton, K.V. Hodges, M.R. McMackin, T.L. Pavlis, A.R. Prave, P. Ryder, J.K. Snow, L. Serpa, L.T. Silver, C.H. Stevens, D.J. Topping, B.W. Troxel, J.D.Walker, and L.A. Wright have contributed to the ideas presented here, but they are in no way liable for any errors in fact and interpretation. We thank Neil A. Niemi and J.A. Grover for field assistance and J.K. Snow, D.L. Lux, and L.A. Wright for providing copies of their manuscripts prior to publication. Constructive reviews by W. Taylor and an anonymous reader greatly improved the clarity and presentation of this manuscript. Stereonet and MacStrat by R.W. Allmendinger were used for the analysis and plotting of data.

Additional details

Created:
August 22, 2023
Modified:
October 26, 2023