Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Tertiary history of the Pacific Northwest is closely tied to that of the Columbia River Flood Basalt (CRB) events. The region is, geologically, one of the least well understood parts of the continental United States. Throughout the Neogene, the Columbia Basin and surrounding terrains appear to have been shaped not by horizontal tectonic forces, but by deep dynamic forcing, driving apparent “vertical tectonics.” This class of phenomena appears to be at odds with the traditional tenets of plate tectonics, and yet may prove to be ubiquitous geologic processes worldwide. Many of the processes described here are unique to volcanically-active regions, such as those affected by CRB eruptions and deposition. In the following chapters I will discuss several physical mechanisms by which lithosphere can deform in the absence of horizontal tectonic stress. These include analyses of the mechanisms associated with metamorphic densification, rheologic transformation owing to magmatic intrusions, and the dynamics of lithospheric delamination. All code and documentation to reproduce the results presented here can be found in the supplemental files included with this dissertation. Appendices A and B document the purpose, usage, and functionality of each supplementary file. This dissertation includes previously published and unpublished coauthored material.

Thesis (Ph. D.)--Oregon State University, 2005. / Printout. Includes bibliographical references (leaves 170-186). Also available via the World Wide Web.

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published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

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This study uses multiple isotopic (2H, 18O, 13C, 15NNO3, 18ONO3, 87Sr/86Sr) and age tracers (3H, 14C, CFCs), in conjunction with elemental chemistry, to address the following research question: How have present day anthropogenic activities (i.e. surface water irrigation and fertilizer application) and past climatic events (i.e. cataclysmic flooding from glacial Lake Missoula and other modes of discharge from Cordilleran Ice Sheet) impacted the hydrology and geochemistry of the Columbia River Basalt Aquifers (CRBAs) in central Washington? Large-scale irrigated agriculture over the past ~60 years has resulted in the transport of high NO3- irrigation waters moving downward in the oxic CRBAs at rates of several meters per decade with a lack of denitrification. Deeper pristine regional groundwater in the CRBAs is Late Pleistocene in age and likely remnant Cordilleran Ice Sheet-related recharge waters (i.e. glacial Lake Missoula floodwaters).

Part of the Slave Structural Province, the Hope Bay Greenstone Belt is a 82 km long north-striking sequence of supracrustal rocks dominated by mafic volcanic rocks with lesser felsic volcanic and sedimentary rocks. Mapping of two transects in the southern section and two transects in the northern section have contributed to a robust stratigraphic framework the belt. Three recently discovered Archean lode gold deposits in the Hope Bay Greenstone belt have associations with major structures and specific lithologies (Fe-Ti enriched basalts). The Flake Lake and the Clover Transects are in the southern part of the belt and the Wolverine and Doris-Discovery Transects are in the northern part of the belt. This work subdivides the volcanic rocks into distinct suites based upon field, petrologic, geochemical, and geochronologic criteria. Some of the suites are stratigraphically continuous and can be correlated tens of kilometres along strike thereby linking the two parts of the Hope Bay Greenstone Belt. U-Pb geochronology supports work by Hebel (1999) concluded that virtually all the supracrustal rocks in the Hope Bay Greenstone Belt were deposited over at least 53 m.y. (2716-2663 Ma), with the majority of the volcanism occurring after 2700 Ma. A number of basalt groups are identified and include the normal basalt, the LREE-enriched basalt, the Ti-enriched basalt and the Ti-enriched Al-depleted basalt groups. They have chemical signatures that vary in trace elements particularly HFSE and REE’s, and can be easily be distinguished by geochemical screening. The felsic volcanic suites are also divided into three main groups, tholeiitic rhyolite, calc-alkaline dacite and calc-alkaline rhyolite groups. Nd and Hf isotope signatures are consistent with trace element signatures in identifying mafic and felsic volcanic groups, with the tholeiitic rhyolite showing highly variable signature. The Hope Bay Greenstone Belt has been show to have a number of felsic and volcanic cycles. An early construction phase of the belt is made up of primarily mafic volcanics which is followed by felsic volcanism equalled mafic volcanism which lacks basalts enriched in Ti. The geodynamic environment that created the Hope Bay Greenstone Belt can be explained by plume influenced subduction zone.

Shatsky Rise is oceanic plateau in the northwest part of the Pacific Ocean, and the formation of Shatsky Rise is poorly known. To get a better understanding of the formation Integrated Ocean Drilling Program (IODP) Expedition 324 drilled five sites: Sites U1347 and U1348 on Tamu Massif, Site U1349 and U1350 on Ori Massif, and Site U1346. Paleomagnetic measurements of the basaltic flows recovered can give insight into the timing and paleolatitude of each site. Relating the change in principle component inclination over depth at each site to the paleosecular variation of the geomagnetic field can better constrain the timing of the eruptions. Measurements were carried out by different sources during IODP Expedition 324 and after. This study is an amalgamation of the results from Sites U1346, U1347, U1349, and U1350. Samples from each site were divided into half and demagnetized using alternating field (AF) demagnetization and thermal (TH) demagnetization. After the drilling overprint was removed most samples displayed univectorial decay in the orthogonal vector plot. AF demagnetized samples displayed a low median destructive field (MDF) behavior, <10 mT, and a moderate MDF behavior, >10-20 mT. Thermal demagnetized samples displayed three behaviors: a rapid decline in magnetic intensity after moderate temperature steps behavior, a linear decline in magnetic intensity behavior, and some samples displayed a small segment of self-reversal at 300°-350°. Using the Cox and Gordon (1984) method Sites U1346, U1347, and U1349 displayed very little variation in principal component inclinations over depth, implying a relatively rapid lava emplacement of 10^2-10^3 years. Site U1350 display more variation, implying a longer eruptive time frame of 10^4-10^5years. With the assumption of a normal polarity the paleolatitude estimates are -11.0° +22.2°/-21.4° for Site U1346, 11.3° 27.4°/-28.5° for Site U1347, -5.0° +20.8°/-20.6° for Site U1349 and 1.6° ±7.7 ° for Site U1350. The site paleolatitudes imply that Ori Massif (Sites U1350 and U1349) formed at the equator and Tamu Massif (Site U1347) and Shirshov Massif (Site U1346) formed slightly north and south of the equator respectively. All results are consistent with the interpretation that Shatsky Rise formed near the equator.