Made available in DSpace on 2014-06-11T19:32:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-10-14Bitstream added on 2014-06-13T19:42:56Z : No. of bitstreams: 1 silva_ch_dr_rcla.pdf: 785091 bytes, checksum: 6e1bc5d4c82f715e1777e80217b4a4b6 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O presente trabalho apresenta uma proposta de evolução geológica Neoproterozóica de um segmento da Faixa Brasília Meridional, na região de Tapira (SW de Minas Gerais). A partir de mapeamento geológico detalhado é da caracterização estrutural e metamórfica. As rochas desta região apresentam uma complexa evolução estrutural, onde a principal estrutura reconhecida é uma foliação em baixo ângulo (S4) orientada em média N43W/30SE, à qual associa-se uma lineação de estiramento e/ou mineral orientada N50W/10, atribuídas à fase D4. A foliação S4 normalmente é reconhecida como uma clivagem de crenulação, cuja superfície crenulada é uma foliação S2, sub-paralela ao acamamento sedimentar (S0). Em alguns locais S4 manifesta-se como uma xistosidade ou clivagem contínua. A foliação S4 também afeta dobras normais de escala quilométrica relacionadas à fase D3. Adicionalmente são reconhecidos dois conjuntos de dobras pós-fase principal com eixos de caimentos suaves e planos axiais íngremes, sendo os eixos de D5 de direção NW e os eixos de D6 de direção NNE. Relacionada à fase D5 associam-se três zonas de cisalhamento transcorrentes quilométricas, a partir das quais sub-divididiu-se a área em três domínios tectono-estratigráficos. No domínio oeste (DW) ocorrem duas escamas tectônicas separadas por falha de empurrão. A escama 1 apresenta rochas metapelíticas e pelítico-grafitosas com intercalações psamítica. A associação mineral muscovita + quartzo + granada l clorita l biotita l cloritóide l grafita l albita, permitem situar as rochas dessa escama na fácies xisto verde superior (zona da granada), com condições de T e P estimadas em 540°C e 7,5 kbar. Na escama 2 predominam rochas pelíticas com intercalações psamíticas, adicionalmente ocorrem intercalações de hornblenda-granada-mica xistos e rochas metamáficas e metaultramáficas... / This work was done to determine the Neoproterozoic evolution of a southern Brasilia Fold Belt segment, Tapira area (SW Minas Gerais state), using detailed geologic mapping and structural metamorphic characterization. A complex structural evolution is deduced for these rocks and the main structure recognized is a low angle S4 foliation (N43W/30SE), associated with N50W/10 stretching and/or mineral lineation of the D4 phase. The S4 foliation is a crenulation cleavage, where the pre-existing S2 foliation was folded parallel to sedimentary bedding (S0). In some areas, S4 is a schistosity or a continuous cleavage. The S4 foliation also affects kilometric normal folds of the D3 phase. Two post-S4 groups of folds are recognized with low angle axes and high angle axial planes: D5 and D6 with axes in NW and N-S direction, respectively. Three transcurrent shear zones are associated with the D5 phase, dividing the area into three tectonic stratigraphic domains: Western, Eastern and Southern. Two thrust sheets separated by a thrust fault characterize the Western Domain (WD). Metapelitic rocks and graphite-bearing pelites with metapsammitic lenses represent the thrust sheet 1. A muscovite + quartz + garnet l chlorite l biotite l chloritoid l graphite l albite association defines the rocks of thrust sheet 1 as upper greenschist facies (garnet zone), with T = 540 ºC and P = 7.5 kbar conditions. At the top, thrust sheet 2 is characterized by metapelitic rocks and metapsammitic lenses and hornblende-bearing garnet-muscovite schists intercalations, with metamafic and metaultramafic rocks. The muscovite + quartz + garnet l hornblende l chlorite l biotite l oligoclase and the hornblende + oligoclase + biotite associations suggest amphibolite facies with a range of T= 585 to 610 ºC and P= 8 to 10 kbar. The Eastern Domain (ED) comprises three...(Complete abstract click electronic access below)

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Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Restricted until October 2008. Bibliography: leaves 224-244. Also available online.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Supervisor: Paul Mann. Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Available also in an electronic version.

The origin of the Cantabrian orocline of the Variscan orogen in NW Iberia remains a topic of debate. We present a structural study of the Ponga Unit, a Cambrian to Carboniferous tectonostratigraphic package within the Variscan foreland fold and thrust belt that lies within the core region of the Cantabrian orocline. Our primary goal is to determine if the structure of the Ponga Unit is attributable to secondary orocline formation or if west-plunging regional folds in the area reflect lateral ramps in underlying Variscan thrust sheets. Our mapping and structural analysis within the Ponga Unit focuses on the Laviana, Rioseco and Campo de Caso thrust sheets, and associated bounding thrusts. More than 800 structural orientation measurements were collected across the study area during a four-week field campaign. These data, coupled with data compiled from regional geological maps, allow for analysis of the crustal structure. West-plunging folds of the Laviana, Rioseco and Campo de Caso thrust sheets form km-scale anticline-syncline pairs, producing a complex fold interference pattern that is characteristic of the Ponga Unit. Our analysis shows that: 1) the geometry of the west-plunging folds is inconsistent with a lateral-ramp related interpretation; 2) the map pattern resembles a mushroom fold interference pattern that is the result of two deformation phases including secondary, orocline-related N-S shortening immediately after the cessation of E-W Variscan shortening; and 3) paleomagnetic data, notably a ‘B’ remanence magnetism, in the Ponga Unit likely overlaps in time with the cessation of Variscan deformation and records post-Variscan deformation associated with the onset of oroclinal buckling. Our results indicate that early N-S trending folds, which resulted from Variscan orogenesis, were refolded by a N-S oriented compressive stress that is attributable to the secondary buckling of the Cantabrian orocline. / Graduate

Thesis (M.S.)--Oregon State University, 1965. / Typescript. Includes bibliographical references (leaves 103-105). Also available via the World Wide Web.

Recent regional bedrock mapping carried out on the Hall Peninsula, Baffin Island, Nunavut has revealed previously unknown rock units, structural relationships and metamorphic conditions achieved. Mafic and ultramafic rocks occur primarily intercalated with metasedimentary rocks in the east-central region of the Hall Peninsula. Focused mapping was carried out in the Quaqqanituaq Area (QA), now the type locality for metasedimentary-mafic/ultramafic occurrences on the Hall Peninsula. The QA records an east-west compression event, D1, which produced in the dominant regional S1 fabric and tight, nearly isoclinal F1 folds. The QA also records a north-south compression event, D3 (regional D2 event not observed in QA) resulting in an S3 crenulation cleavage and open F3 folds. U-Pb detrital zircon geochronology and U-Pb geochronology of a cross-cutting monzogranite dyke bracket sediment accumulation and mafic/ultramafic intrusion/extrusion between 2.13 and 1.87 Ga and place a maximum age on D1 at 1.87 Ga. Garnet – biotite – K-feldspar – ± sillimanite mineral assemblages observed in QA pelites indicate that upper amphibolite facies metamorphic conditions were reached. This observation is empirically confirmed by the implementation of winTWQ software which indicates that the peak pressure and temperature conditions reached in the QA were 4.8±2.1 kbars and 645±50°C. Whole-rock major and trace element geochemical data was obtained for 75 mafic and ultramafic samples from all regions of the Hall Peninsula including 20 from the QA. Mafic samples were classified on the basis of N-MORB normalized trace element geochemistry as being alkaline (La/Sm ~ 4.9; Gd/Yb ~ 2.7), calc-alkaline (La/Sm ~ 4.3; Gd/Yb ~ 2.4), tholeiitic (La/Sm ~ 2.1; Gd/Yb ~ 1.1), or transitional (La/Sm ~ 2.7; Gd/Yb ~ 1.6). A negative Nb anomaly, which is on average 5.4 times lower with respect to Th and Ce is observed in all mafic samples with the exception of alkaline mafic rocks. On the basis of their geochemical profiles and comparative study of adjacent terrains, the mafic rocks are concluded result from partial melting a subduction modified mantle source during plume-initiated rifting of the North Atlantic Craton.

We use scaled 3-D thermo-mechanical analogue models to investigate the formation of oroclines (originally linear orogens now curved in map view by buckling about vertical axes). The experimental setup consists of a tank of water (the asthenosphere) on top of which rest hydrocarbon plates (the lithosphere) with strain-softening behaviours and thermo-dependent elasto-plastic properties. An electric heating element below and 4 infrared lights above produce a constant vertical (geo)thermal gradient in the plates. A horizontal piston drives constant plate motion and gives rise to a compressional stress regime. Geometric, kinematic and dynamic variables are calibrated in accordance with a set of scaling laws and proper plate composition. Our results suggest that oroclinal buckling involves the entire lithosphere and cannot be confined to the crust only. A wide range of syn-oroclinal structures developed during buckling, including thin- to thick-skinned thrust belts, transform faults and extensional structures, as well as extensional basins and subduction zones in the lithosphere adjacent to the ribbons. During oroclinal buckling, a thrust belt forms upon complete closure of the interlimb region and is attributable to the trailing orocline limb overthrusting the leading orocline limb. An analogous syn-oroclinal thrust system characterizes the Central Iberian Orocline (CIO) of the Variscan orogen in Iberia where the north limb of the west-convex orocline exposes recumbent north-verging folds while the overriding south limb bears upright to gently north-verging folds. Our results imply that these structures developed during final closure of the CIO, and indicate that the north- and south- limbs of the CIO constitute the leading- and trailing-limbs, respectively, of an orocline that formed by overall northward translation. Modelling of magmatic arcs rotating about vertical axes yields late stage transform faults that bisect the buckling arcs. This outcome is analogous to the Panama Canal fault zone that severs the buckled Panamanian Isthmus. The hinge zones of modeled oroclines are the sites of subduction initiation, similar to subduction initiation of the Caribbean plate beneath the convex to the north, North Panamanian orocline, and of oceanic lithosphere from the Ionian Sea beneath the Calabrian orocline of Sicily. / Graduate / 0372 / gagnonl@uvic.ca

Thesis (M.A.)--University of Wisconsin--Madison, 1970. / Title from title screen (viewed Jan. 18, 2008). Includes bibliographical references. Online version of the print original.