1 10 2 https://theses.otagogeology.org.nz/files/original/99ab62d8ee34015ad8b1d54afd669882.pdf b4b0a97198b1b23dd34f27acf0db853a Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Geology theses OU Geology thesis Thesis or dissertation completed by University of Otago Geology students Location WKT (WGS84) The location stored in WKT (WGS84) format POLYGON ((-110.538039144707525 35.604813712081047,-110.324127389853018 35.663024395560669,-110.070998479941906 35.668843111302046,-109.839260745516228 35.494095647681959,-109.871347508744364 35.31896388243829,-110.174389161454911 35.084858422440377,-110.359779348995446 35.102439939710258,-110.57725629976413 35.359862293443044,-110.538039144707525 35.604813712081047)) Author last name Last name of the Author Lefebvre Project type Is it an MSc, PhD, BSc(Hons) or PGDipSci? PhD Advisers Who supervised/advised this student White, J.D.L. Kjarsgaard, B. Abstract The Abstract for this thesis Maar-diatreme volcanoes are unique in that most "eruptive" activity takes place below the ground surface, thus forming large conduit structures filled with pyroclastic deposits that are large relative to their volcanic edifices. These small-volume volcanoes are traditionally divided into three main levels based on common divergences in geometry and internal architecture at different depths: feeder dike, diatreme structure (conduit structure) and tephra ring (surface deposits). Although maar-diatreme volcanoes worldwide show generally very similar characteristics despite many different magma compositions, there is no consensus on how these volcanoes excavate the country rock and develop during an eruption. This study aims to determine the processes and relative timing of activity taking place below the ground surface by combining detailed mapping of three exemplary exposures of diatremes at different structure levels, from dike-widening transition to well-formed diatreme, within the Hopi Buttes volcanic field. Observations from different volcanoes are readily related to one another because the field had homogeneous preeruption hydrology, wall-rock stratigraphy, and magma composition, with a narrow range of eruption ages. Castle Butte Trading Post (CBTP) comprises four closely spaced narrow spatter-dikes and wider maar-diatremes ~150 m below the pre-eruptive surface. The spatter-dikes consist of bedded, variably welded deposits plus wall-rock debris in multiple NEyounging sequences demarcated by truncation surfaces. They reveal a shallow plumbing cycle of pulsating, weak, hot spatter fragmentation, concurrent wall-rock failure and periodic slips that truncated down dropped bedded deposits from repeated magma withdrawal and diversions during progressive NE fissure extension and vent stepping. Both Standing Rocks West (SRW) and East (SRE) diatremes, exposed ~300 m below the pre-eruptive surface, are part of a single larger volcanic complex formed along a series of irregularly offset NW-SE trending dikes. SRW comprises dominantly multiple, structureless irregular columns of well-mixed, poorly sorted juvenile-rich lapilli tuff deposits that contain abundant recycled material; they truncate local marginal layered deposits and peripheral country rock breccia. SRW mostly records late-stage activity of multiple, small-volume, explosions and jets within loose pyroclastic debris, which resulted in gradual mixing, recycling and remobilization of cognate diatreme debris, incremental addition of juvenile material and a well-formed diatreme. In contrast, SRE comprises predominantly country rock lithic-rich breccia of coarse inhomogeneously mixed wall-rock blocks, cross-cut by domains of lapilli tuff deposits that are overlain by spatter deposits and cross-cut by irregularly distributed dikes. SRE shows a progressive transition from fissure to diatreme, but an overall evolution from explosive to weak eruption styles, thus reflecting an arrested diatreme. Instead of simply representing vertical differences of a diatreme structure, CBTP, SRE and SRW reveal much volcano-to-volcano variation, and even within-eruption variation in eruption processes and intensity. Variability in eruption intensity is inferred at all scales i.e. between different en echelon dike systems, between the structures formed along segments within these systems and between the vents for individual volcanoes at the surface. These Hopi Buttes volcanoes show that the roots of weakly and strongly explosive small volcanoes are shared with changes in explosive intensity over short distances and not necessarily systematic variations in behaviour through time. The evolution of the shallow plumbing during an eruption involves local feedback effects that critically affect eruption style over short times and distances. Neither magma composition nor country-rock hydrology can be considered as the primary control on inter-eruption variation or on changes through a single eruption in the Hopi Buttes volcanic field. OURArchive handle The handle from the Otago University Research Archive (OURArchive) <a href="http://hdl.handle.net/10523/4268">http://hdl.handle.net/10523/4268</a> OURArchvive access level Abstract Only Department The department where the student is studying primarily. Geology Named locality Named locality describing the field area location. Hopi Buttes volcanic field Navajo Nation Arizona USA. Thesis description Number of pages, maps, CDs, etc. x, 279 leaves plus papers. Maps in colour in text; 30cm. Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Identifier An unambiguous reference to the resource within a given context 2013Lefebvre Creator An entity primarily responsible for making the resource Lefebvre, Nathalie Date A point or period of time associated with an event in the lifecycle of the resource 2013 Title A name given to the resource Volcanology of maar-diatreme volcanic vent complexes, Hopi Buttes Volcanic Field, Navajo Nation, Arizona, USA Subject The topic of the resource Volcanology diatreme fissure Hopi Buttes maar monogenetic root zone shallow plumbing volcanism https://theses.otagogeology.org.nz/files/original/721ea0ad9f3b4cc12f12062ee57478a3.pdf 2fb85b3def21e818552944d540fd5c8a Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Geology theses OU Geology thesis Thesis or dissertation completed by University of Otago Geology students Location WKT (WGS84) The location stored in WKT (WGS84) format POLYGON ((170.845821911633834 -45.355973015372307,170.87170887119035 -45.350266282770164,170.883647607033794 -45.374304531726061,170.859848784774414 -45.37814781914598,170.845821911633834 -45.355973015372307)) Author last name Last name of the Author Andrews Project type Is it an MSc, PhD, BSc(Hons) or PGDipSci? PGDipSci Advisers Who supervised/advised this student White, J.D.L. Abstract The Abstract for this thesis Eocene explosive submarine volcanism on the East Otago shelf is reported and discussed. Surtseyan lapilli tuff deposits with maximum stratigraphic thicknesses of at least 175 m record the existence of a volcano that built into storm wave base and may have emerged. A diverse range of large clast types, including schist xenoliths and dike fragments, show that the lapilli tuff was produced through a variety of fragmentation processes including Fuel-Coolant Interaction. Additionally, irregular shaped clasts exhibiting possible fluidal deformation indicate that magma was ejected from the vent while still molten. Stratigraphy also indicates that the volcano experienced two periods of major activity with a relatively quiescent interval between. Though widespread slumping and possible sector collapse have rendered accurate reconstruction of the volcano nearly impossible, orientations of dikes and data from two measured stratigraphic sections indicate that a large island near the centre of the field area may have been the vent. Both basalt and clastic dikes are emplaced in lapilli tuff at Moeraki. The basalt dikes are commonly banded with alternating layers of high and low vesicularity; these textures indicate formation through repeated injection of magma. The innermost bands of the dikes are often discontinuous and pinch out in fold hinges, indicating syndeformational emplacement. Irregular intrusions of basalt also occur at Moeraki and may be large intrusive pillows. The clastic dikes at Moeraki exhibit three textures; porcelainite breccia, mudstone breccia and mudstone. Though mudstone dikes occur discretely on one beach, a progression of all three occurs in association with basalt dikes at another locality. The dikes there grade from basalt through porcelainite to mudstone and indicate formation of clastic dikes as a result of explosive brecciation of sedimentary rocks. The brecciation is generated by the phreatomagmatic interaction of hot basalt dikes with wet low permeability mudstones. Numerical modelling of this process is presented. Department The department where the student is studying primarily. Geology Named locality Named locality describing the field area location. Moeraki Peninsula Thesis description Number of pages, maps, CDs, etc. 141 leaves : ill. (some col.), maps ; 30 cm. + 1 CDrom. Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Identifier An unambiguous reference to the resource within a given context 2001Andrews Creator An entity primarily responsible for making the resource Andrews, Benjamin J. (Benjamin James) Date A point or period of time associated with an event in the lifecycle of the resource 2001 Title A name given to the resource Physical volcanology of Moeraki Peninsula Subject The topic of the resource Volcanology volcanism