Physical Sciences and Mathematics Commons^™

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 …

Eruption Dynamics And Petrology Of The Most Recent Eruptions Of Nevado Del Ruiz Volcano, Colombia, South America, Richard Henry Young

LSU Historical Dissertations and Theses

Field measurements and petrographic analyses of pumices from the most recent tephra deposits of Nevado del Ruiz volcano provide a context in which to view the disastrous eruption of 13 November, 1985 (R0). The pumices are all crystal-rich, two-pyroxene andesites to dacites with whole rock SiO₂ contents of 62 - 66 wt.%, and magma water contents estimated to be between 1 - 4 wt.%. The 1985 tephra has greater petrologic diversity than earlier deposits which may be related to an input of a hotter, more basic magma into the Ruiz system, as suggested by xenocrystic olivine which is most …