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Resolving The Timing Of Late Pleistocene Dome Emplacement At Mono Craters, California, From U–Th And Ar/Ar Dating, Mae Marcaida

Master's Theses

The Mono Craters chain in eastern California is one of the youngest sites of rhyolitic volcanism in North America and comprises at least 28 overlapping lava domes, flows, and tephra rings of mostly Holocene age. New U-series and ⁴⁰Ar/³⁹Ar geochronological data presented here extend the age of the Mono Craters into the Late Pleistocene. Ion microprobe ²³⁸U–²³⁰Th isochron dating of unpolished rims of allanite and zircon and ⁴⁰Ar/³⁹Ar laser fusion and step-heating dating of sanidine from the porphyritic biotite-bearing dome lavas of the Mono Craters yield Late Pleistocene ages, but the …

Structure, Construction, And Geochemistry Of The Highly Elongate, Cretaceous Seven-Fingered Jack Pluton In The Devil's Smokestack Area, North Cascades, Washington, Scott William Elkins

Master's Theses

This thesis provides an analysis of magmatic structures and geochemistry from a portion of the mid-crustal, ~92-90 Ma Seven-Fingered Jack pluton, North Cascades, Washington. The study area was divided into three separate domains. Rocks in the northern domain (~9 km2) are characterized by N-NNW- trending, moderately to steeply plunging magmatic folds that reflect regional shortening. The central (~3 km2) and southern (~3.5 km2) domains are structurally homogeneous and contain a dominant NW-striking magmatic foliation. Schlieren are locally developed, several meters long, thin (cm-scale), and strike NW and dip steeply to the NE. Field data indicate the pluton is constructed of …

Structure, Construction, And Geochemistry Of The Cretaceous Seven-Fingered-Jack Intrusive Complex In The Klone Peak Area, North Cascades, Washington, Kelly N. Dustin

Master's Theses

The highly elongate Seven-Fingered-Jack intrusive complex (SFJIC) of the North Cascades, Washington provides an excellent opportunity to study the construction, geochemistry, and structure of a well-exposed mid-crustal pluton. The interior ~92 Ma Main Body tonalite has markedly heterogeneous and mafic domains that may represent interactions between multiple batches of melt. The ~78 Ma marginal Kelly Mountain suite includes a mafic complex containing abundant hornblendite, diorites of variable heterogeneity, and tonalite. Field mapping and structural, petrographic, and geochemical analyses are interpreted to indicate that this intrusive complex was built incrementally by many batches of melt. The dominantly NW-striking and NE-dipping magmatic …

Structure, Construction, And Emplacement Of Jurassic And Cretaceous Plutons In The Keiths Dome-Echo Lake Area, Southwest Of Lake Tahoe, California, Pamela Jamie Clay

Master's Theses

Jurassic (Keiths Dome) and Cretaceous (Echo Lake, Glen Alpine) plutons and their host rocks were investigated, and structural and petrographic analyses were conducted, to elucidate the nature and timing of pluton construction and emplacement, deformation, and related tectonic regimes. Evenly distributed enclaves and a lack of internal contacts suggest pluton construction via thorough mixing of multiple increments of magma. Ductile flow of conglomerate host rocks, stoping of volcanic host rocks, and possibly other processes, facilitated emplacement. In Cretaceous plutons, margin-parallel magmatic foliations may record internal processes, whereas the Keiths Dome pluton contains foliations that are discordant to contacts and likely …

Structure And Emplacement Of Cretaceous Plutons In Northwest Yosemite National Park, California, Ashley Van Dyne

Master's Theses

The ~103-98 Ma Yosemite Valley Intrusive Suite, younger Granodiorite North of Tuolumne Peak, and ~97 Ma Yosemite Creek Granodiorite intrude plutonic and metasedimentary host rocks of the central Sierra Nevada batholith. Precambrian to Cambrian metasedimentary rocks separate the Yosemite Valley Intrusive Suite from the younger (94-85 Ma) Tuolumne Intrusive Suite and are interpreted to represent the original extent of the older suite. The Mt. Hoffman granodiorite and Taft Granite of the Yosemite Valley Intrusive Suite record evidence of the development of magma chambers, whereas the Tuolumne Peak and Yosemite Creek granodiorites were likely constructed via several small increments, and a …

Structure, Construction, And Emplacement Of The Yosemite Valley Intrusive Suite And The Yosemite Creek Granodiorite In The Central Sierra Nevada Batholith, Brendon L. Johnson

Master's Theses

The 103-98 Ma El Capitan and Taft granites and the ~97 Ma Yosemite Creek Granodiorite intrude plutonic and metasedimentary rocks in the central Sierra Nevada batholith. The El Capitan Granite and Yosemite Creek Granodiorite are divided in this study into several texturally and compositionally distinct units, whereas the Taft Granite is relatively homogeneous. Injection of a few large increments of magma or many increments intruded close in time probably formed small (2 km3) to large (≥20 km3 for Taft Granite) chambers in the Yosemite Valley Suite and parts of the Yosemite Creek Granodiorite. Units of the Yosemite Creek Granodiorite that …

Vertical Distributions Of Carbonite Lithologies, Bedding Features, And Macrofossils In The Broken Rib Member Of The Upper Devonian Dyer Formation Near Monument Lake, Garfield County, Colorado, Sharon Sadle

Master's Theses

The Broken Rib Member of the Upper Devonian Dyer Formation is a series of fossiliferous limestone beds deposited during the Famennian stage of the Late Devonian. The limestone units are well-exposed near Monument Lake in the White River National Forest of west-central Colorado, where they weather into a series of step-like, laterally continuous surfaces. A graphic log, recorded in the field, reveals that lithologies vary from carbonate mudstones to wackestones and reflect the fluctuating water depth associated with a transgressing and regressing sea. The fossil assemblages consist of well-preserved, identifiable brachiopods, bryozoans, pelmatozoans, and other minor taxa that occur in …

Collisional Reactivation Of Rift Margin Fracture Zones, Taiwan And The Taconic Allochthon, David C. Mirakian

Master's Theses

Chapter I. Transverse Topographic Development due to the Reactivation of a Partially-Subducted Fracture Zone: The Southwest Hsüehshan Range, Central Taiwan

Abstract — The southwest flank of the Hsüehshan Range is defined by a topographic break which cuts across regionally mapped structures in central Taiwan. The mountain front trends ~345°, slightly oblique to the Sanyi-Puli seismic zone which has been previously interpreted as a reactivated continental margin fracture zone. Structural data collected along the length of the topographic break reveal two populations of cross-cutting faults with distinct fault-zone materials and a series of southwest-plunging folds. Paleostress axes were reconstructed using the …

Metamorphism And Putative Bioalteration Of Basaltic Glass : Coast Range Ophiolite, Cynthia E. Schultz

Master's Theses

No abstract provided.

Intensity Of The 18 April 1906 Earthquake In And Near San Jose, California, Nancy C. Shostak

Master's Theses

Intensities of shaking for previously untapped, historical sources of damage data from the 1906 earthquake in and near San José, California, were developed with a refined and expanded version of the Modified Mercalli intensity (MMI) scale designed to bring out rich detail in the dense data. Sanborn fire insurance maps provide construction details and precise locations for 80 percent of the 607 intensity data points. Intensity values for 1906 range from MMI 6 to 9, with an average of 7.4. For damage data grouped by modern census blocks, the small variation in intensity within blocks indicates the 1906 intensity values …