http://hdl.handle.net/1957/1718 Search the Channel search http://ir.library.oregonstate.edu/dspace/simple-search http://hdl.handle.net/1957/9028 Title: Spatial patterns of invasion by exotic plants in a forested landscape <br/> <br/>Abstract: Few landscapes are immune to invasion by exotic plant species. The forested landscape in the western Cascade Range of Oregon appears to have some barriers to invasion, but the extensive road network provides a corridor and habitat for a suite of exotic species to enter and become established. This study examined how biological factors and physical factors interact to produce the observed spatial pattern of invasion in the forested landscape, particularly along roads and streams. Results from a seed bank study indicated that dispersal barriers may be preventing movement of some exotics from the road into mature forest. Exotics that were found in the seed bank within mature forest have a high potential for dispersal, especially by wind. However, no exotic plants were found in the existing vegetation within the mature stands, suggesting that environmental barriers were preventing their establishment. Surveys at 1-km and 100-km scales showed that the most frequent species also had a high potential for dispersal. However, dispersal potential did not explain all of the observed spatial patterns. Confounding factors such as time since introduction, length of the "lag phase" after introduction, and various biological factors may have a strong influence on the spatial patterns of invasion. Exotic plant distribution at the 1-km scale varied among four habitat types that represent different levels of disturbance. The number and frequency of exotic species were much higher along high-use and low-use roads than along abandoned roads or streams. This pattern may reflect the more favorable light conditions along currently used roads, and the lower light levels along abandoned roads and streams may be barriers to invasion for many exotics. However, confounding factors such as competitive exclusion by natives and opportunities for dispersal may also be operating. Spatial patterns of exotics along the 100-km road network provide additional evidence that environmental barriers influence the pattern of invasion. Spatial analysis results provided evidence of patchiness and spatial gradients for some target species along some roads. The heterogeneous arrangement of patches on the landscape suggests that the process of invasion is generating multiple, discrete "foci" from which further invasion can occur. <br/> <br/>Description: Graduation date: 1998 http://hdl.handle.net/1957/9020 Title: The geochemistry and geochronology of the Eocene Absaroka volcanic province northern Wyoming and southwest Montana, USA <br/> <br/>Abstract: The Absaroka volcanic province is the largest of Eocene volcanic fields in the northern Cordillera of the western U.S., and consists of 25,000 km2 of lava flows, shallow intrusions, ash-flow tuffs and volcaniclastic deposits. It is aligned with northwest-trending Precambrian lineaments, and includes the remains of at least ten volcanic centers. This study presents 40Ar/39Ar geochronological data, and major, trace element and isotopic compositional data which are the result of detailed mapping and field sampling of four representative volcanic centers, peripheral lava flows, intrusions, and ash-flow tuffs. Age data show that volcanism occurred between 53 and 43 Ma in a general northwest to southeast age progression, and have allowed significant revisions in regional correlations across the volcanic province. Local dike orientations from one volcanic center suggest that volcanism occurred during extensional faulting. Geochemical and Nd, Sr and Pb isotopic data show that mafic lavas are enriched in incompatible elements derived from an ancient source. Mafic rocks (<53% SiO2, >5% MgO) are characteristically potassic, and are typical products of early eruptions at each of the Hyalite, Crandall, Ishawooa, and Rampart volcanic centers, and not spatially restricted to any one region. Although products of volcanism are broadly similar, volcanic centers exhibit distinct mineralogic, compositional and isotopic characteristics. Least squares calculations based on mineralogical data indicate that shoshonites can be produced from mafic samples by fractionation of olivine and augite t plagioclase. More silicic samples have petrographic features and compositions which indicate they are derived from a mixture of sources including continental crust. Changing chemical and isotopic compositions suggest that early eruptions contain a lithospheric mantle component, with an increasing melt contribution from crustal sources with time. The last eruptions include rhyolite from the southern Absaroka volcanic province and basanite with an asthenospheric isotopic composition sampled from a peripheral lava flow in the northern Absaroka volcanic province. <br/> <br/>Description: Graduation date: 2000; Presentation date: 1999-03-30 http://hdl.handle.net/1957/9018 Title: Fold growth due to kink-band migration in repeated earthquakes, Sierra de Villicum, San Juan, Argentina <br/> <br/>Abstract: Growth strata geometries and deformed geomorphic surfaces reflect the shorttimescale growth of Sierra de Villicum (San Juan Province, Argentina). Accumulated deformation in repeated earthquakes is recorded by the structural geometry of deformed geomorphic surfaces. Through geologic mapping and topographic surveying, six strath terraces were identified on the eastern flank of Sierra de Villicum. A comparison between the modem channel and long terrace profiles indicates that recent deformation is restricted to the eastern half of the study area. In this region, the terrace surfaces are folded - 15° from their original orientation with the fold axes of younger terraces located progressively to the east. This folding has created stepped topography that is interpreted to reflect eastward migration of an active axial surface through repeated earthquakes. Ages for the terrace surfaces were obtained through physical correlation with similar surfaces to the south of the study area. These surfaces are dated at 18700, 6800, and 1500 yr BP using cosmogenic radionuclide exposure age dating (Siame et al., 2002) Deformation rates were calculated by measuring the displacement between the preserved growth axial surface and the active axial surface for each terrace level. On the basis of the inferred terrace ages, the measured axial surface positions yields average vertical displacement rates of 1.25±0.3 mm/yr and average horizontal displacement rates of 4.6±1.0 mm/yr. The close correlation between historically documented deformation and measured fold displacements suggests the discovery of new evidence for fold growth during a devastating Ms. 7.4 earthquake in 1944. <br/> <br/>Description: Graduation date: 2004 http://hdl.handle.net/1957/9017 Title: Feeder dikes to the Columbia River flood basalts : underpinnings of a large igneous province <br/> <br/>Abstract: Feeder dikes to the Columbia River Basalt Group (CRBG) large igneous province provide a rare opportunity to examine magma transport through the shallow crust during flood basalt eruptions. Over 70% of the CRBG erupted from the Chief Joseph dike swarm, which is exposed across southeastern Washington, eastern Oregon, and western Idaho. The four manuscripts of this dissertation examine physical, thermal, and compositional characteristics of dikes from the southern Chief Joseph swarm. The majority of CRBG dikes are chilled against their wallrock, however, rare dikes have induced partial melting in their wallrock. Melt zones in tonalite wallrock adjacent to the Maxwell Lake dike are up to 4 in thick and contain up to 47 volume percent quenched silicic melt produced from dehydration-melting reactions involvir biotite, hornblende, quartz, orthoclase, and plagioclase. Melt zones record the thermal history of basalt flow and cooling in the Maxwell Lake dike, a feeder to Wapshilla Ridge flows (Grande Ronde Basalt). Results of one- and two-dimensional numerical modeling suggest that basalt flowed in the Maxwell Lake dike for 3-4 years, yielding maximum eruption rates of 3.4-4.6 km3/day for typical Wapshilla Ridge flows. The Maxwell Lake dike likely represents an upper crustal exposure of a long-lived point source in the CRBG. Chief Joseph dikes are concentrated into sub-swarms of 7-12 dikes per km2. Based on transects through four sub-swarms, dikes become more aligned, more frequent, thinner, and more closely spaced from northwest to southeast across the southern Chief Joseph swarm. Fewer than 2% of dikes, and less than 0.5% of cumulative dike length, had caused extensive melting in their wallrock. In the Cornucopia sub-swarm, numerical modeling of cross-cutting and compound dikes suggests that magmatic activity occurred intermittently over 2-4 years. Compositional data collected from -250 southern Chief Joseph dikes indicate that most are Grande Ronde Basalt, although isolated Imnaha and Dodge (Eckler Mountain Member, Wanapum Basalt) dikes also occur. Imnaha dikes are compositionally primitive, whereas Grande Ronde and Dodge dikes are more evolved. Subtle compositional differences between sub-swarms of Grande Ronde dikes suggest that each sub-swarm represents a discrete episode of Grande Ronde volcanism. <br/> <br/>Description: Graduation date: 2005