Earth Sciences Commons^™

Petrology Of The Earliest Cascade Volcanic Units In Washington: The Northcraft, Tukwila, And Rattlesnake Mountain Formations And Implications For The Evolution Of The Cascade Arc, Louisa Cryan, Jeffrey H. Tepper

Summer Research

Cascade arc magmatism began ~45 million years ago, following the reconfiguration of the Farallon-North American subduction zone. This project seeks to classify the path of magmatism throughout the history of the Cascade arc, as well as categorize the earliest expressions of the Cascade arc. Three volcanic units, the Northcraft Formation (NF), Tukwila Formation (TF), and Rattlesnake Mountain Formation (RM) will serve as examples of the earliest Cascades-related lavas. Their categorization by field setting, geochemical characteristics, isotopic data, and age will create a better understanding of how Cascades magmatism began and developed over time.

Analysis has shown these units to contain …

Investigating Cascade Magmatism Through Dating And Chemical Analysis Of The Hatchet Mountain And Pe Ell Formations, Sw Wa, Robyn Organ, Jeffery Tepper, Wesely Von Dassow, Tabor Reedy

Summer Research

Modern Cascade arc magmatism began ~45 Ma, shortly after accretion of the Siletzia terrane culminated at ~50 Ma. The earliest expressions of this magmatism are several petrologically-diverse volcanic units in SW Washington including: (1) the Goble Volcanics (GV) / Hatchet Mountain Formation (HM), (2) the Pe Ell Formation (PE), and (3) scattered exposures of unnamed basalts (UB). These rocks, all dominantly subaerial lavas, occur west of the modern arc where they are interbedded with marine and deltaic sedimentary units, suggesting eruption in a forearc or volcanic front setting. Goals of this study are: (1) to characterize the elemental and Sr-Nd …

Petrology Of The Eocene Goble Volcanics, Southwest Washington: An Early Phase Of The Cascade Arc, Clara Phipps, Jeffrey H. Tepper

Summer Research

The Eocene Goble Volcanics (GV), comprised of >1000 km² of subaerial lavas and tuffs, are one of the most voluminous igneous formations in SW WA. Whole rock K-Ar ages of 45 to 32 Ma (Beck and Burr, 1979) suggest these rocks are an early expression of the Cascade arc, but their location is anomalous, lying between oceanic Crescent Fm basalts of the Siltezia terrane to the west and younger arc rocks to the east. The goals of this research are to determine the chemical and Sr-Nd isotopic traits of the GV and better establish the tectonic setting in which …

Comparison Of The Chemical And Isotopic Composition Of Groundwater And Surface Water In The South Sound Region, Andrew H. Oberhelman

Summer Research

This project seeks to characterize the chemical and isotopic compositions of groundwater and surface water in portions of Pierce and King Counties, with the goal of using these results to determine the water sources of local lakes. Specifically of interest are lakes studied by Puget Sound students over the past ~10 years where water analyses appear to define a mixing line, likely between surface runoff and the shallow groundwater (Figures 1, 2, and 3). Existing data pertain only to surface water from the lakes while data pertaining to groundwater is patchy or nonexistent and includes only a few of the …

Geochemistry And Origins Of Thermal Springs Waters Of The Olympic Peninsula And Cascade Range, Washington, Jon Kenneth K. Golla

Summer Research

The state of Washington contains 98 low temperature (surface temperatures between ~ 20 - 50 ^oC) geothermal springs, which are powered by the convective circulation of groundwater that is heated by the natural heat of the Earth. These systems operate in a cycle that begins when precipitation percolates downward into the subsurface and comes in contact with a heat source. Subsequently the heated water returns to the surface, in most cases, having interacted chemically with rocks in the reservoir and/or along its ascent path. Surveys done by the USGS between the 1970s – early 1990s show there is significant …

Geochemistry Of The Mt. Persis Volcanics And Evidence For Thickening Of Cascade Crust Over Time, Monica Hanson

Summer Research

The Cascade Range is a classic example of a continental magmatic arc, a belt of igneous activity resulting from subduction of the oceanic Juan de Fuca plate beneath the western margin of the North American plate. The Cascade arc, which started forming about 38 million years ago, is unique in that extensive uplift and erosion have exposed plutonic and volcanic rocks of similar age. This study will focus on the Mt. Persis area in the North Cascades, where a pluton of the Index batholith is surrounded by near-source volcanic rocks and suggests that the volcano may have originated from the …