The volcanic (~45-10 Ma) and plutonic rocks (~37-12 Ma) comprising the Western Cascades extend from northernmost California to southern British Columbia and are ancestral to modern arc magmatism. The ancestral arc hosts a series of small plutons that are locally associated with porphyry (Cu-Mo) and epithermal (Au) ore deposits. Three...
Comprehension of eruptive histories is critical in understanding the evolution of magmatic systems at arc volcanoes and may supply evidence to the petrogenesis of intermediate and evolved magmas. Within the 300 ka eruptive history of Mount St. Helens, Washington, the Kalama Eruptive Period, 1479- ~1750 CE was bracketed by interludes...
Magmatic-hydrothermal ore deposits are giant geochemical anomalies in the earth’s crust most often generated by normal magmatic terrestrial processes. They are often associated with oxidized and hydrous intermediate to highly evolved magmas that have concentrated metals and have the necessary components to efficiently extract and transport them as ascending magmatic-hydrothermal...
Supervolcanic eruptions are among the most catastrophic phenomena on Earth,
erupting 100s-1000s of cubic kilometers of magma, and producing devastating local effects and global climate perturbations. The largest supervolcanic eruption of the last 28 Ma was the 74 ka Youngest Toba Tuff (YTT) eruption from Sumatra, Indonesia, which erupted 2,800...
Several different petrological techniques have been applied to lava flows between
200 to 475,000 years old from Mount Hood, Oregon. Mount Hood is unusual, in comparison to nearby Mount St. Helens and Mount Jefferson, in that it has produced relatively homogeneous lava compositions over 475,000 years. Erupted lavas are mostly...
.
________________________________________________________________________
Cristina M. Darr, Author
ACKNOWLEDGMENTS
I would like to thank Adam Kent, Anita
This thesis develops a geology training manual for the Interpretation staff of Craters of the Moon National Monument and Preserve (CRMO) in southern Idaho. The manual will help the staff convey geologic principles to park visitors who are experiencing a landscape formed by volcanic processes. Basic geology and the most...
The eruptive history of the Quaternary Cascades arc has been relatively well characterized. However, much less is known about the frequency and sizes of explosive eruptions produced by earlier stages of the arc. The Late Neogene Deschutes Formation of Central Oregon preserves a remarkable record of heightened pyroclastic activity during...
This study is an effort to characterize the magma sources, plumbing system, and eruptive behavior of Mount Hood, a low-explosivity recharge-dominated volcano in the Oregon Cascades. The three manuscripts in this dissertation make use of melt inclusion data, phenocryst compositions, and whole rock petrology and geochemistry to build a schematic...
Oxidized hydrous intermediate composition magmas are responsible for porphyry copper (Cu ±Mo ±Au) deposits and epithermal Au ore deposits formed globally in the shallow crust (Sillitoe, 2010; Seedorff et al., 2005). Recently, zircon geochemistry has been used to characterize both productive and barren intrusions associated with porphyry Cu-Au ore deposits....
The sheeted complex of the ~92 Ma Tenpeak pluton, in the Northern Washington Cascades crystalline core, forms a <1.5-km wide zone with a moderate, NE-dip at the SW margin of the pluton. Sheeted magmatic complexes, such as the one in the Tenpeak pluton, are common in plutons and represent examples...
Three broadly interrelated problems of critical significance to the proper interpretation of melt inclusion (MI) data are addressed in this thesis. The first issue, the petrogenesis of anorthitic plagioclase phenocrysts in MORB lavas, has relevance due to the presence of numerous MI in many high-An feldspars. This problem was addressed...
Motivated by observations of locally enhanced sea level variability near steep
topographic slopes in regions of strong time-mean flows, effects of zonal ridge topography
on zonal oceanic jet flow are investigated. Unstable wave properties and the
dynamics of eddy-mean flow interaction are evaluated as a function of topographic
geometry using...
Constraining the development, evolution, and timescales of large silicic magma systems is important to understanding the development of granite batholiths, the relationships between volcanoes and their plutonic underpinnings, and the development of the continental crust.
The ignimbrite flare up that produced the Altiplano-Puna Volcanic Complex of the Central Andes is...
Distributed deformation in the backarc of Cascadia is complex. Off the west coast lies the Cascadia convergent margin. East of the plate boundary, clockwise rotation of the Oregon Coast Range block with respect to stable North America influences backarc deformation, causing extensional faults in southeast Oregon, contraction folding in southeast...
At least 105% nearly east-west extension of late Cenozoic age has been accommodated by down-to-the-east normal and oblique-slip faults in the central Wassuk Range. One northwest striking, right-lateral strike-slip fault probably contributes an additional component of WNW-ESE slip. Movement on the normal and oblique-slip faults in this area tilt the...
Magmatic sulfides from Yerington, Nevada, and Yanacocha, Peru, were analyzed by laser ablation-inductively coupled mass spectrometry (LA-ICPMS) and electron microprobe to determine copper, gold, and silver concentrations and ratios in order to examine the relationship to the metal content of related magmatic-hydrothermal ores. The magmatic sulfides occur in plutonic rocks...
The schist of Skookum Gulch (SSG) is an informal name applied to a fault-bounded melange composed mainly of schistose metamorphic rocks and less abundant sedimentary and igneous rocks located in the eastern Klamath Mountains of northern California. The SSG features outcrops of lawsonite+sodic amphibole blueschist and epidote+sodic amphibole rocks transitional...
The Inmaculada Mine is located in the Miocene belt of epithermal deposits that extends from southern Peru to northern Chile and Bolivia. This belt is known for its silver-rich epithermal veins that have been worked since colonial times. The Inmaculada Mine belongs to a mining district that includes, from north...