Physical Sciences and Mathematics Commons^™

Differential Incision And Uplift Of The Yakima River Terraces, Adrian M. Bender

WWU Graduate School Collection

The Yakima fold belt comprises fault-related folds deforming Miocene basalts and younger deposits of the Columbia Plateau in central Washington State. Geodesy implies ~2 mm/yr of modern, NNE-directed regional shortening; however the distribution of Quaternary deformation among individual structures remains unclear. South of Ellensburg, Washington, the Yakima River cuts a ~600-m deep canyon across several of the folds, preserving flights of strath terraces that record the progressive incision. Graded alluvial basins at the head and mouth of the canyon imply that terrace incision also records differential rock uplift. We integrate lidar analysis, field observations, and cosmogenic burial dating of eight …

High-Mg Andesites From The Northern Cascade Arc: Using Mineral Chemistry To Distinguish Between Hypotheses For Petrogenesis, May Sas

WWU Graduate School Collection

A fundamental question in the Earth Sciences is whether, in certain situations, subducting lithospheric plates can get hot enough to generate melt that consequently contributes to magmatic output in volcanic arcs. Because the subducting plate beneath the Cascade arc is relatively young, and therefore understood to be hotter than older subducting slabs, slab melt generation is considered possible. Recent work has shown that slab melt is involved in magma petrogenesis in the southern Cascade arc (Walowski et al., 2015). To better understand the role of slab melt in north Cascades magmas, this study focused on petrogenesis of high-Mg lavas from …

Paleomagnetic Determination Of Vertical-Axis Block Rotation And Magnetostratigraphy In The Mecca Hills And Coachella Valley, California, Cassidy W. (Cassidy Wade) Dimitroff

WWU Graduate School Collection

Our ongoing work on the paleomagnetism and magnetostratigraphy in the Coachella Valley has provided an improved understanding of the timing and spatial variations of sediment accumulation and deformation during evolution of plate-boundary fault zones. Here, we report updated results from the Palm Spring Formation of the Mecca Hills, and new paleomagnetic data from Pleistocene conglomeratic sandstone in Desert Hot Springs and the Plio-Pleistocene San Timoteo Formation from Live Oak Canyon.

From the Mecca Hills, new data were obtained-112 samples from 29 sites. The majority of the paleomagnetic results yielded well-defined components of magnetization, which allowed us to identify seven well …

Surface Slip During Large Owens Valley Earthquakes, Elizabeth K. Haddon

WWU Graduate School Collection

The 1872 Owens Valley earthquake ranks among the largest historical earthquakes in California. Relatively sparse field data and a complex rupture trace inhibited attempts to define the slip distribution and reconcile the total moment release. We present a new, comprehensive surface-slip record based on lidar and field investigation, documenting 183 measurements of laterally and vertically displaced landforms for 1872 and earlier Owens Valley fault earthquakes. Our lidar analysis uses a newly developed analytical tool to measure fault slip based on cross-correlation of sub-linear topographic features. This MATLAB-based GUI, OffsetXcor, produces a uniquely-shaped probability density function (PDF) of fault slip for …

High-Sr Volcanic Domes From The Lassen Volcanic Region, Southernmost Cascade Arc, Northern California: Implications For Andesite And Dacite Magma Generation, Christina M. Stout

WWU Graduate School Collection

The Onion Butte (OB) and Barkley Mountain (BM) groups are two lineaments of volcanic domes and lava flows located with the Lassen segment of the southernmost Cascades, northern California. The OB group (_~2.5 Ma) consists of 13 domes that are dominantly dacitic, but span the range from andesite to dacite. The BM group (_~1.5 Ma) comprises 21 domes that range from basaltic andesite to andesite, but are mostly andesitic.

The lavas of both groups are petrographically similar, but differ geochemically. The lavas are fine-grained, sparsely phyric containing needle-like hornblende phenocrysts, but lack the large plagioclase phenocrysts …