1 10 2 https://theses.otagogeology.org.nz/files/original/d4d06c5c9345c095b6cb9ba405b1fb1c.pdf 0da3fa631abc646eb41ac3d74bd75217 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 MULTIPOLYGON (((-110.326873029723 35.1091344486426,-110.318230781959 35.1214432048754,-110.301394402982 35.112238115349,-110.290255505864 35.0951927799335,-110.303058835885 35.0945087871119,-110.326873029723 35.1091344486426))) Author last name Last name of the Author Re Project type Is it an MSc, PhD, BSc(Hons) or PGDipSci? PhD Advisers Who supervised/advised this student White, J.D.L. Ort, M. Abstract The Abstract for this thesis Many populated areas in the world (e.g., Flagstaff, AZ; Auckland, NZ; Mexico City, MEX) lie within active monogenetic volcanic fields that typically contain small volcanic cones and explosive maar craters formed over the course of a single eruptive cycle. Although much work has focused on the eruptive behaviour of monogenetic volcanoes, little geological information exists about their subsurface development and how the movement of magma through Earth’s shallow crust modulates the location and style of hazardous volcanic eruptions. Determination of the dynamics of magma intrusion and the transition from a coherent magma's ascent to its explosive fragmentation is crucial to our understanding of the controls on explosive versus effusive eruptive behaviour, thus to better evaluation of risks in a certain area. This study aims to determine the processes and relative timing of activity that took place below the ground surface of the deeply-eroded but well-preserved Jagged Rocks Complex, a cluster of monogenetic volcanoes within the Miocene Hopi Buttes Volcanic Field in northeastern Arizona, by combining detailed structural mapping, volcanological observation, paleomagnetic and geochemical analysis. The Jagged Rocks Complex, exposed at ~ 350 m below the pre-eruptive surface, comprises a well-preserved intrusive network, including dikes, sills and inclined sheets, associated with different type of fragmental bodies including buds, pyroclastic massifs and a diatreme, that represent different extents of shallow-depth fragmentation. These exposures at the Jagged Rocks Complex provide an excellent natural laboratory for examining the subsurface record of volcano initiation, and for constraining interpretations of processes controlling upward migration of magma from intrusion to eruption. This multidisciplinary approach allows an investigation at different levels from the source region to the surface, and aims to shed the light on the processes that regulate eruptions not only within monogenetic volcanic fields but also within small basaltic volcanoes in general. OURArchive handle The handle from the Otago University Research Archive (OURArchive) <a href="http://hdl.handle.net/10523/7358">http://hdl.handle.net/10523/7358</a> OURArchvive access level Open Access Department The department where the student is studying primarily. Geology Named locality Named locality describing the field area location. Arizona USA Thesis description Number of pages, maps, CDs, etc. 273 pages A4 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 2017Re Creator An entity primarily responsible for making the resource Re, Giuseppe (Peppe) Date A point or period of time associated with an event in the lifecycle of the resource 2017 Title A name given to the resource Evolution and dynamics of a monogenetic volcanic complex in the southern Hopi Buttes Volcanic Field (AZ, US): magma diversion and fragmentation processes at the Jagged Rocks Complex Subject The topic of the resource Volcanology Basaltic Conduit diatreme Dike Feeder Hopi Buttes Monogenetic volcano 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