Physical Sciences and Mathematics Commons^™

New Early Miocene 40ar/39ar Ages For Nakwai, Northwest Kenya, Africa, And Paleontological Analysis Of Meroehyrax Kyongoi Dentition, Dawn Elena Reynoso

UNLV Theses, Dissertations, Professional Papers, and Capstones

Nakwai is a fossiliferous region in the Turkana Basin of northwestern Kenya. Until recently the only ages for the Nakwai formation were based on biostratigraphic correlation with Losodok; a late Oligocene site located to the north of Nakwai. The new 40Ar/39Ar ages in this study range from 23 Ma to 15 Ma and constrain the upper portions of the Nakwai section to the early Miocene. These ages make it the only securely dated fossil locality in the region that represents the earliest Miocene; all of the other early Miocene fossil localities date back to ~20 Ma or younger. The time …

Geology Of The Southern Reveille Range, Nye County, Nevada, Matthew Alan Mckelvey

UNLV Theses, Dissertations, Professional Papers, and Capstones

The Reveille Range in central Nevada provides a unique window into the mid-Miocene geology and volcanology of the central Great Basin during the "ignimbrite flare up." Although faulted along its margins, the interior of the range is relatively undeformed thus preserving volcanic centers. The Reveille Range contains three mid-Miocene caldera complexes. Previous studies have identified the Goblin Knobs caldera (25.6 Ma) in the central Reveille Range and the caldera of northern Reveille Range (25.3 Ma) to the north. These calderas are completely filled with intracaldera tuffs. This study has identified a younger third caldera located in the southern part of …

Geochemical Evolution Of A Mid-Miocene Synextensional Volcanic Complex: The Dolan Springs Volcanic Field, Northwestern Arizona, Scott Michael Mcdaniel

UNLV Theses, Dissertations, Professional Papers, and Capstones

The Dolan Springs volcanic field (DSV), of northwestern Arizona, is dominated by andesite and basaltic-andesite flows and breccias, with minor amounts of basalt, rhyolite, and ash-flow tuff. Geochemistry is used here as a tool to evaluate the roles and contributions of the lithospheric and asthenospheric mantles to magmatism related to Miocene extension in the Colorado River extension corridor (CREC). The majority of synextensional volcanic rocks in the DSV are geochemically similar to regional trends, but rare tholeiitic basalts erupted near the end of extension. The tholeiites have trace element signatures similar to ocean island basalt (OIB), but have isotopic values …

The Geology Of The Tuff Of Bridge Spring: Southern Nevada And Northwestern Arizona, Shirley Ann Morikawa

UNLV Theses, Dissertations, Professional Papers, and Capstones

The Tuff of Bridge Spring (TBS) is a regionally-widespread, andesite to rhyolite (59.50 to 74.91 wt. %) ash-flow tuff of mid-Miocene age (ca. 15.2 Ma) that is exposed in the northern Colorado River extensional corridor of southern Nevada and northwestern Arizona. Determination of the areal distribution, geochronology, lithology, geochemistry, and internal stratigraphy of the TBS is important for its establishment as a reliable stratigraphic reference horizon for tectonic reconstructions of the extensional corridor during the middle Miocene. Based on reoccurring patterns of major and trace element variation, the TBS is divided into constant Cr/variable SiO₂ and variable Cr/variable SiO …

The Sloan Sag: A Mid-Miocene Volcanotectonic Depression, North-Central Mccullough Mountains, Southern Nevada, Hayden L. Bridwell

UNLV Theses, Dissertations, Professional Papers, and Capstones

In the Hidden Valley area of the north-central McCullough Mountains, southern Nevada, mid-Miocene andesite and dacite domes, flows and pyroclastic units (the Sloan volcanics) partially fill a sag in the underlying Hidden Valley volcanics. The 13.5 km diameter sag formed during and/or after the eruption of the Sloan volcanics. Sagging was accommodated by a combination of movement on the McCullough Wash fault system, and subsidence into evacuated chambers.

Major, trace and rare-earth element geochemistry suggests that the rocks of the Sloan volcanics belong to four groups, each of which were produced by partial melting of chemically distinct sources. With the …