Thesis (Ph. D.)--University of Wisconsin--Madison, 2003. / Includes bibliographical references. Also available on the Internet.

<p dir="ltr">The Cascadia subduction zone features many along-strike variations in geophysical signatures that appear independent of properties in the subducting Juan de Fuca plate. Past studies have hypothesized that controls on these variations, namely subcretion, seem linked to overriding plate characteristics but may be influenced by characteristics of the downgoing slab as well. Nowhere is this more apparent than in southern Cascadia, which features the highest seismogenesis, broadest forearc topography, and lowest Bouguer gravity along the Cascadia margin. Additionally, the northward migration of deformation related to the San Andreas fault’s evolution and potential subslab buoyancies introduce further complexities making it difficult to parse contributions of tectonic processes to individual geophysical observations. To better understand contributions from Cascadia subduction and San Andreas evolution on tectonic processes, 60 Magseis Fairview nodal seismometers were deployed in southern Cascadia (Klamath Mountains) between April and May of 2020. We perform ambient noise tomography using Rayleigh and Love waves to constrain radial anisotropy and reveal seismic characteristics in the forearc. We find low VSV (<3.4 km/s) in the lower crust of the forearc consistent with previous studies. This is paired with high (>10%) positive radial anisotropy suggesting these materials are dominated by (sub)horizontal fabrics. We also observe relatively high VSV and VSH and negative radial anisotropy (~ -10%) in the upper crust of the forearc to ~10 km depth. These results suggest that the upper crust, which is dominated by the Klamath terrane, is characterized by (sub-vertical) deformational fabrics, likely related to brittle deformation superimposed on the accretionary history of the Klamath terrane, while the lower crust shows fabrics consistent with what would be expected due to basal accretion of oceanic crust (e.g, sedimentary rocks with or without basaltic slivers). The correlation of positive radial anisotropy with low shear-wave velocities (~3.4 km/s), low Bouguer gravity, high conductivity, and high rates of seismogenic activity (LFEs, tremor distribution, and episodic slow slip events) suggest that this basally accreted material may be infiltrated by fluids derived from the downgoing oceanic lithosphere.</p>

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No. of bitstreams: 1 1984_LuizJoseDelReySilva.pdf: 8874596 bytes, checksum: 3c70a62301cbb5b587fd6947661ded34 (MD5) / No Vale do Curaçá, situado na parte norte-nordeste do Estado da Bahia, distante cerca de 500 km da Capital, ocorrem cerca de três centenas de corpos máfico/ultramáficos potencialmente portadores de sulfetos de cobre, encerrando uma dezena de depósitos atualmente conhecidos, destacando-se dentre eles a mina Caraíba, a 29 maior jazida de cobre no País, com cerca de 185 milhões de toneladas de minério a 1% Cu, em média. Possivelmente entre 2,6 e 2,0 Ga instalou-se na crosta arqueana um sistema 'rift' norte-sul, com cerca de 300 a 400 km de comprimento norte-sul, tendo nele se implantado uma suíte de litologias supracrustais (sedimentos quartzo-feldspáticos, anfibolitos, rochas calcosilicatadas, quartzitos, formação ferrífera) a qual foi deformada e metamorfisada em três eventos principais, seguidos de pelo menos dois eventos tardios (cisalhamentos e falhas ou dobras abertas) de menor importância na montagem do arcabouço geológico. Os corpos máfico/ultramáficos, derivados de magma parental toleítico, foram intrudidos pré-tectonicamente como 'sills' diferenciados. A presença de mineralização é função do estágio inicial de diferenciação, sobretudo relacionada com os níveis basais de composição ortopiroxenítica. Os corpos onde predominam tipos gabróicos e gabro-noríticos são normalmente estéreis. O depósito Caraíba é o maior dos corpos hipersteníticos conhecidos e ocorre associado a uma suíte magnesiana (gabro-noritos, wherlitos, lherzolitos, serpentinitos) não mineralizada (potencialmente niquelífera) sendo que a primeira mostra-se mais jovem do ponto de vista estratigráfico, ainda que ambas sejam pré-tectônicas. O sistema 'rift' foi fechado com o advento de duas fases iniciais de deformações, as quais geraram movimentos de cavalgamento ('thrusting' e 'understhrusting') supostamente no sentido este para oeste (19 fase) e de sul para norte (2a fase) em cada uma das quais foram colocados corpos estratóides de ortognaisses de composição tonalítica e granodiorítica. A pilha original foi então espessada e submetida ametamorfismo anfibolítico alto (M1) e granulítico (M2) . Durante F1/M1 ocorreram intensos fenômenos de transposição e migmatização, gerando as dobras intrafoliais (D1) trapeadas ao longo do bandamento metamórfiS1. Durante F2 foram produzidas dobras D2 apertadas com planoaxial E-W a N60°W com mergulho 20°S e eixos horizontalizados. A consolidação crustal veio com uma terceira fase de deformação, de esforço compressivo E-W muito forte, que gerou dobras apertadas a abertas, com planos axiais verticalizados, xistosidade plano-axial penetrativa regionalmente e eixo de atitude norte-sul com caimento médio de 16 a 20 para sul na região da mina Caraíba. Concomitantemente ocorreu um enxame de intrusões de corpos graníticos potássicos elongados N-S e paralelos com as estruturas regionais, inclusive a intrusão do sienito Itiúba, hoje uma serra com cerca de 00 km norte-sul 10 km este-oeste. Esta última fase principal se deu em condições de metamorfismo anfibolito alto/localmente granulito, e esteve associada a fortes transposições e migmatização. Como resultado, o corpo Caraíba é hoje um cogumelo (Fig. 2 de interferência de Ramsay, 1967) resultante da superposição de um sinforme D3 sobre as dobras D2 com eixo N60°W. Essa estrutura está posicionada no flanco oeste do grande antiforme D3 Caraíba, flanco esse que tem direção N20°W e mergulho acentuado (70°) para oeste/sudoeste. Os sulfetos de cobre foram concentrados nas charneiras das dobras D2 , ao longo de corpos cilíndricos paralelos ao eixo B2 e à lineação L2l , originalmente horizontalizados portanto, mas tendo continuidade limitada. O corpo mineralizado Caraíba apresenta em superfície, na sua parte central, uma seqüência de quatro charneiras de dobras D2, com eixos B2 verticalizados pela superposição do sinforme D3 apertado, o qual tem eixo B3 caindo em média 16 a 20 para sul, mas que tem caimento abrupto (80 ) para norte na parte central, como resultado da acomodação à atitude pós-D2 e pré-D3 do corpo mineralizado naquela parte da jazida. O minério está então controlado ao longo de charutos verticalizados descontínuos. Os teores de cobre se distribuem de forma muito heterogênea horizontal e verticalmente na jazida, como resultado da intensa história evolutiva, implicando em diluição inevitável nas atividades de lavra a céu aberto e subterrânea para os métodos de extração em andamento. A mina encontra-se em operação de lavra a céu aberto, com produção de quatro milhões de toneladas de minério/ano a 0,83% Cu em média e preparação para início de lavra subterrânea (previsão de 1.800.000 toneladas de minério/ano a 1% Cu em média) tendo a infraestrutura global atual vida útil prevista para mais 11 anos. É proposto modelo geotectônico global para a evolução do Vale do Curaçá, serra de Itiúba, Vale do Jacurici ('Cr-belt') rochas do Grupo Jacobina Inferior e quartzitos da serra de Jacobina, como hipótese de trabalho. _______________________________________________________________________________ ABSTRACT / The Caraíba deposit, located in the northern part of Bahia State, in the Curaçá river valley, is a chalcopirite/bornite-bearing mafic/ultramafic sill, derived from a tholeiitic magma, which was intruded into a volcanic-sedimentary sequence composed of quartzfeldspar gneisses, leptinites, banded iron formation, calcsilicate rocks and amphibolites. Probably between 2.6 and 2.0 Ga, that sequence was deposited and submited to at least three main tectonic-magmatic events. The first two deformational events were thrust-undesthrusting types, producing a crustal thickening by interleaving of the layers and injection of several G1 and G2 orthogneissic sheet-like intrusions, tonalitic/trondhjemitic and granodioritic in composition. Amphibolite and granulite facies metamorphism acomppanied the first and second phases, resulting in a mixed pile with a strong metamorphic S1 foliation with transposed N-S trending D1 intrafolial folds, followed by N60°W trending tight folds. After the horizontal tectonic regime a strong E-W compressive stress field resulted in a regional sequence of tight to open D3 folds with N-S 80 S axial planes and 16° to 20°S plunging regional axes. M3 metamorphism reached high-amphibolite to locally granulite facies and, together with a strong deformation, created a very strong and penetrative foliation, S3 , marked by oriented quartz-plagioclasebiotite- hornblende crystals. Many of syntectonic pottassic lens shaped granitic bodies, were intruded during F3, including the huge Itiúba syenite, all of them strongly foliated and with a characteristic pink-red colour. As a result, the Caraiba copper deposit is now alobate interference pattern (type 2 of Ramsay, 1967) between a D3 tight synform positioned on the 70°W dipping limb of the major N-S trending D3 Caraiba antiform, refolding the recumbent tight D2 folds. The sulphide mineralization is now concentrated along vertical and disrupted rods which marked originally a horizontal N60°W lineation (or B2 ) . Because of this poliphase tectonic-metamorphic history with associated strong migmatization, the copper content is very heterogeneously distributed inside the pyroxenitic/noritic host -rocks, adding difficulties to the mining works, mainly the underground operations. Two later events of shearing are also described and probably one fourth folding fase, but not important for the ore control. A very hypothetical regional tectonic rift-valley system is proposed for the crustal evolution of the Curaçá region, Itiúba s y e n i t e and the Cr-belt on its eastern side, and the Jacobina Group, all of them enclosed between two Archean blocks.

<p dir="ltr">This dissertation uses a multidisciplinary basin analysis approach to document the sedimentary, structural, and volcanic response to Cenozoic oceanic plateau collision and translation along the northwestern Cordillera. During this time, two fragments of oceanic plateau accreted in the Pacific Northwest (Siletzia terrane) and in southeastern Alaska (Yakutat terrane). My research aims to test if the Siletzia and Yakutat terranes have an early shared history as the same spreading ridge-centered plateau in the Pacific Northwest and constrain timing of breakup and translation of the Yakutat terrane to southeastern Alaska. Chapter 2 focuses on development of a new U-Pb zircon geochronology technique to aid in a more accurate and precise understanding of sediment routing systems. The goal of developing this technique is to utilize it in pinpointing the source regions along the northwestern Cordillera supplying sediment to the basin on the Yakutat terrane as it made its northward journey to southeastern Alaska. Chapter 3 focuses on creating a regional chronostratigraphy for deep-marine Cenozoic sedimentary and volcanic rocks of the peripheral rock sequence on the northern Olympic Peninsula in Washington. These sedimentary rocks directly overlie the Siletzia plateau and record basin evolution before, during, and following its collision to the continental margin. Chapter 4 uses detailed lithofacies mapping and U-Pb geochronology of metasedimentary and volcanic rocks in the Olympic subduction complex to document the structural response to seamount subduction in the Eocene. Seamount subduction began shortly after collision of the Siletzia oceanic plateau to the Pacific Northwest and played a critical role in development of the early forearc region and Ancestral Cascades arc. Chapter 5 compares the lowermost sedimentary and geochronologic basin record on both Siletzia and Yakutat terranes to test if they have an early shared history in the Pacific Northwest.</p>

<p dir="ltr">The Intermontane terranes represent one of the largest composite accreted terranes that built the northern Cordillera. To better understand the interactions between the continental margin of Laurentia and the Intermontane terranes, this study analyzes twelve detrital zircon samples (n=3232) from a Neoproterozoic (?) to Cretaceous metasedimentary stratigraphic section exposed in central Alaska. Distinct detrital zircon populations have been identified and are interpreted to represent four stages in the geologic development of this part of western North America. Stage 1 extends from the Neoproterozoic (?) to the Early Paleozoic, and is characterized by Proterozoic and Archean detrital zircon populations that correlate with Laurentian sources of sediment. We interpret Stage 1 to represent deposition along the northwestern continental margin of Laurentia. Stage 2 extends from the Silurian (?) to the Devonian and is characterized by a dominant Devonian and Silurian detrital zircon population. We interpret Stage 2 to have been deposited in a backarc basin coeval with active volcanism as the Yukon-Tanana terrane was rifted away from the Laurentian continental margin as the Slide Mountain Ocean opened. Stage 3 extends from the Mississippian to the Jurassic and records a shift back to sediment sources with abundant Proterozoic and Archean zircon. We interpret this stage to represent deposition of Laurentian detritus along the eastern margin of the Slide Mountain Ocean basin. Stage 4 is represented by the Lower Cretaceous strata of the Manley basin that contain one major Late Triassic to Early Jurassic detrital zircon population. We interpret this population to be sourced from the syn-collisional and post-collisional Late Triassic to Early Jurassic plutons and related sedimentary basins of the Intermontane terranes that were exhumed and eroded during the closure of the Slide Mountain Ocean and the subsequent collision with the Laurentian continental margin. We interpret the Manley basin as a syn- to post-collisional extensional basin associated with regional detachment faults that formed because of crustal thickening in the collisional zone. From a regional perspective, an extensive clastic wedge prograded northward away from the zone of crustal thickening and can be identified in a series of Mesozoic sedimentary basins that are discontinuously exposed over 1500 km in southern Alaska. Results of our study better delineate the tectonic processes that set the framework for the construction of the Late Mesozoic and Cenozoic Cordilleran orogen.</p>