Mesozoic structural and metamorphic history of the central Ruby Mountains metamorphic core complex, Nevada

Abstract

The central Ruby Mountains experienced relatively little deformation during Tertiary uplift of the Ruby Mountains-East Humboldt Range metamorphic core complex, and so Mesozoic fabrics are well preserved. Three penetrative deformational events and two amphibolite-facies metamorphic events have been identified, all of which are interpreted to have occurred during emplacement of a suite of two-mica granites dated at 153 ± 1 Ma (Late Jurassic). Phase equilibria indicate that there was an increase in both temperature and pressure between M 1 (410-580 °C, 2.6-3.75 kb) and M 2 (540-660 °C, 3.5-4.7 kb). Peak M 2 pressures suggest a Jurassic paleodepth of 13-18 km, 3-8 km more than the known thickness of the overlying stratigraphic column. The Late Jurassic therefore appears to have been a time of major crustal shortening and thickening in northeastern Nevada. In contrast, there are no Cretaceous penetrative fabrics in the central Ruby Mountains, suggesting that the Sevier orogeny was not a significant event in the area. This lack of Cretaceous deformation in the mid-crustal rocks of the Ruby Mountains argues against recent models that link shortening in the Sevier belt to emplacement of the Sierra Nevada batholith via a regional mid-crustal shear zone extending across the hinterland.