Valu Fa and Eastern Lau `s (two regions along Lau's back-arc spreading center) observed axial morphology suggest that Valu Fa is more magmatically robust than Eastern Lau despite Eastern Lau's spreading rate nearly doubling Valu Fa's. Early geochemical [Pearce et al., 1994] and geophysical [Martinez and Taylor, 2002] studies predict a gradational decrease in melting moving north from Valu Fa to Eastern Lau, but more recent geochemical and seismic observations ([Escrig, .et al 2009]; [Dunn and Martinez, 2011]; [Dunn et al., 2011]) show a sharper stepwise decrease in melting as the spreading center's ridge axis sweeps away from the Tofua Volcanic-Arc. As the ridge sweeps away from the volcanic-arc, the influence of the slab hydrated mantle in the melting structure of the ridge decreases. Furthermore, Eastern Lau produces a thinner crust than expected for a robust spreading center. 2-D numerical studies [Harmon and Blackmon, 2010] show a gradational decrease in melting from Valu Fa to Eastern Lau but with no corresponding thinning of Eastern Lau's crust. To understand the melting dynamics underneath Lau's back-arc spreading center and the Tofua Volcanic-Arc implementing the effects of 3-D mantle flow and slab hydration appears to be required. To explain the observed geochemical and seismic observations, three 3-D numerical were performed, using a community developed mantle convection solver (CitcomS). The first model shows that observed geometric and surface kinematic boundary conditions cause a steep gradational increase in relative melting area (anhydrous) moving northward with increasing spreading rate along the ridge axis from Valu Fa to Eastern Lau caused by a northwestern along axis mantle flow. A peak in the relative melting area appears particularly close to Eastern Lau where crust is thinnest. These predictions run in opposition to the observations. The second model shows including a viscosity reduction in the mantle wedge due to slab hydration causes a more subdued relative melting increase with spreading rate and "saddle" shaped decrease in relative melting area north of 20.9°S. This saddle shaped melting structure is caused by a reversal in along axis flow towards the southeast, which takes hot mantle from Eastern Lau and transports it underneath Valu Fa accounting for the anomalously thin crust observed at Eastern Lau. Finally, introducing a hydrated solidus increases the melt production under Valu Fau and causes a stepwise decrease in melt production at Eastern Lau due to its decreased proximity to the slab-hydrated region, consistent with the observed geochemical and seismic studies.

This is an integrated study of the stratigraphy, deformation, magmatism, and metamorphism in the vicinity of the Ida and Palmenhorst Domes, an area in the southwestern Central Zone of the Damara Orogen, Namibia. The principal aim is to understand the timing of tectonic events through high-precision U-Pb dating of structurally constrained intrusions and anatectic rocks, and link these tectonic events across the Damara Orogen and Pan-African Orogeny. A secondary aim is to compare the Central Zone and Damara Orogen to other collisional orogens. The stratigraphy of the study area is similar to that noted elsewhere in the Central Zone, but the mapped distribution of lithologies differs slightly from previous work. Specifically, Damara Supergroup rocks have been found infolded with the Abbabis Complex, and the stratigraphic positions of certain units in have been locally reclassified. The mapped distribution of lithologies suggests a Type-2 fold interference pattern across the study area. This Type-2 fold interference is confirmed by structural analysis. A D2 deformation event formed strongly S- to SE-verging km-scale recumbent to shallow NW-dipping folds with smaller-scale parasitic folds. The long limbs of these folds are extended, and a number of shear zones are found on these extending limbs, as well as near the contact between the Abbabis Complex and the Damara Supergroup. NE-SW extension is associated with the late stages of D2, and forms a conjugate set of shear bands and a shallow NE-plunging mineral stretching lineation. This D2 event was overprinted by upright to steeply WNW-dipping km-scale D3 folds to form the domes in the study area. Mesoscale fold interference structures are rare, but D2 structures are shown to be consistently reoriented by D3 structures. D3 deformation does not have a strong vergence, and mesoscale D3 folds are rare. D2 and D3 were preceded by a D1 fabric forming event locally observed as rootless isoclinal intrafolial folds, and followed by brittle deformation. The Ida Dome is a fairly simple domal structure formed by the km-scale interference between a shallow NNW-dipping D2 anticline and an upright to steeply WNW-dipping D3 anticline. East of the Ida Dome, NE-trending D3 structures predominate, but are seen to overprint earlier D2 structures. The Palmenhorst Dome is a larger area where Damara Supergroup rocks have been infolded into the Abbabis Complex during D2 deformation. These isoclinal, N- to NW-dipping D2 folds have been refolded by upright D3 folds to form a Type-2 fold interference pattern. D2 structures along the southern margin of the Palmenhorst Dome dip steeply towards the south, in contrast to D2 structures elsewhere. This is interpreted to be the result of a lower-intensity km-scale D2 fold. The orogen-parallel extension and orogen-perpendicular recumbent folding that took place during D2 cannot be explained by previous structural models for the Central Zone and a new model is suggested where these structures form as the result of coeval irrotational NE-SW extension and S- to SE-verging simple shear during extensional collapse of the orogen. A number of intrusive rock types are found in the study area and have been dated using SHRIMP U-Pb. Amphibolite dykes have a chemical affinity to mafic rocks of the Goas Suite, and are suggested to be either pre-Damaran or early Damaran intrusives as they cut the gneisses of the Abbabis Complex, and are affected by D2. They have been dated at 2026.9 ± 2.3 Ma (zircon) or 557.2 ± 7.4 Ma (zircon) with metamorphic overgrowths in this sample giving 520 ± 6.9 Ma. Red, potassic granites emplaced near the contact with the Abbabis Complex and Damara Supergroup contain a D2 gneissic fabric and give ages of 536 ± 7.2 Ma (monazite), and zircons have lower intercept ages of 539 ± 17 Ma and upper intercept ages of 1013 ± 21 Ma. Grey granites are abundant in the study area, and form a continuum from dark grey granites (which are tonalitic to dioritic in composition and contain hornblende and abundant biotite) to light grey granites (which are leucogranitic and contain abundant K-feldspar and minor biotite). These grey granites show a fractionation trend from dark to light varieties, and cross-cutting relationships indicate that the lighter variety is younger than the darker variety. The grey granites show syn-D2 structural relationships and contain a fabric subparallel to the S2 fabric, and which is more pronounced in the darker varieties. They show similarities with granites described by earlier workers, and two samples have been dated at 519.1 ± 4.2 Ma and 520.4 ± 4.2 Ma (zircon). A variety of sheeted granites are found – quartz-feldspar-magnetite pegmatitic granites are associated with grey granites, occur axial-planar to F2 folds, and have metamict zircons which are dated at 530-525 Ma. Garnet (± cordierite) granites are leucocratic, have garnet poikiloblasts, are emplaced axial planar to F2 folds and are also folded and boudinaged by D2. They are associated with pelitic units in the Damara Supergroup and are dated at 520.3 ± 4.6 Ma (zircon) and 514.1 ± 3.1 Ma (monazite). Uraniferous leucogranites found are similar to those widely described in the Central Zone, but metamict zircons give imprecise ages of between 515 and 506 Ma. Pink pegmatitic leucogranites comprise pink perthitic feldspar and milky quartz, are emplaced into more brittle structures and gives an age of 434.4 ± 2 Ma (zircon). Almost all granites analysed appear to be crustal-melt granitoids, with the exception of the darker grey granites, which show a calc-alkaline affinity. No Salem-type granites are found in the study area. In addition, SHRIMP U-Pb analyses of zircons from three Abbabis Complex gneisses give ages of 2056 +11/-10 Ma, 2044 +32/-27 Ma and 2044 +17/-14 Ma, and titanites from an amphibolite sample give ages of 493.4 ± 6.4 Ma. Two anatectic leucosomes from D2 shear zones and shear bands give zircon ages of 511 ± 18 Ma and 508.4 ± 8.7 Ma in spite of high-U zircons. Lu-Hf data on zircons from an Abbabis Complex gneiss gives model ages of ca. 3 Ga, whilst similar data for a grey granite gives a model age of ca. 2 Ga. Zircons from the Abbabis Complex gneiss have variable O-isotopic values, whilst the grey granite gives O-isotopic values of ca. 7‰. These geochonological and isotopic data show that the Abbabis Complex is part of the Congo Craton, and that some amphibolites are pre-Damaran, whilst others may be related to the Goas Intrusive Suite, and represent a phase of early Damaran magmatism. In contrast to the chronology previously presented for the Central Zone, M1 in the study area appears to have occurred at 535-540 Ma, with M2 coeval with D2 deformation at 510-520 Ma. Elsewhere in the Central Zone, NW-verging D2 deformation is dated at 540-560 Ma, and the Central Zone appears to have a diachronous tectonometamorphic evolution along strike. It is suggested here that this represents the preservation of two separate tectonic events in the Central Zone at different crustal levels, one at 540-560 Ma and the other at 520-510 Ma. D3 deformation is suggested to have taken place at 508 Ma, immediately after D2 extension. The Central Zone began to cool following D2, and the 495 Ma titanite age reflects this cooling. Isotopic evidence from this and other studies shows that Damaran granitoids (with 1.5-2.2 Ga model ages) cannot be derived from the Abbabis Complex (with 3 Ga model ages) but must come from an alternative source, suggested here to be Kalahari Craton material subducted below the Congo Craton. Textural studies of a number of pelitic samples indicate syn-D2 low-pressure, high-temperature metamorphism. Differences in observed assemblages between various sample types are due to compositional differences, and samples appear to have reached similar conditions across the study area. Mineral compositional profiles show no prograde zoning, indicating mineral re-equilibration. Orthopyroxene is locally observed, suggesting lower-granulite conditions. This is confirmed by pseudosection modelling of a number of samples, which gives peak conditions of 750-850 °C and 4.5-5 kbar. This modelling shows lower-granulite facies conditions with higher temperatures than previous estimates based on mineral compositional geothermometers, which are affected by re-equilibration. These conditions are sufficiently high for fluid-absent biotite breakdown to form the voluminous anatectic leucosomes and granitoids in the southwestern Central Zone. Pseudosection modelling and phase relationships indicates a low-pressure (ca. 4 kbar) clockwise heating path, with slight decompression at the thermal peak. All metamorphism noted is 520-510 Ma M2 metamorphism, and no petrographic evidence exists for earlier 540-535 M1 metamorphism. This cryptic M1 is suggested to be related to the emplacement of the Goas Intrusive Suite and Salem-type granites early in the orogenic history, whilst M2 may be related to thermal relaxation following crustal thickening early in the orogenic history, but requires an additional heat source. The difference in ages for deformation and metamorphism between the study area and elsewhere in the lower grade portions of the Central Zone is suggested to be related to the preservation of different portions of the orogenic history in different areas. The results of this study together with previous work details a multi-stage evolution for the Central Zone involving subduction, continent-continent collision, crustal thickening, slab breakoff, magmatism, granulite-facies metamorphism and exhumation of the mid-crust. This multistage evolution explains the multiple ages for deformation and metamorphism in the Central Zone. NW-folding and thrusting documented in the Karibib area at 560-540 Ma is related to an early phase of crustal thickening owing to continent-continent collision following a brief period of subduction. Slab breakoff led to asthenospheric upwelling and heating of the lower crust, and produced the Goas Intrusive Suite and Salem-type granites, as well as providing heat for 540-535 Ma M1 metamorphism and the melting of the crust to produce anatectic red granites. SE-verging deformation, extension and granulite facies metamorphism recorded in this study is related to orogenic collapse following crustal thickening, and the heat source for low-P, high-T metamorphism may be highly radiogenic crust that was thickened , which is suggested to be either burial of crust enriched in heat-producing elements, or asthenospheric upwelling owing to delamination of the Congo Craton lithospheric mantle or asthenospheric upwelling owing to the position of the southwestern Central Zone on a major orocline. The events recorded for the Central Zone have been correlated across the entire Damara Orogen, and the timing of events can be correlated along strike into the Zambezi Belt. Events in the Kaoko Belt appear to predate those in the Damara Belt, which appears to also show a similar collisional timing to the Gariep Belt. It is therefore proposed that the Gariep and Damara Belts formed part of a younger orogenic episode to that which formed the Kaoko and Dom Feliciano orogenic belts. The Damara Belt shows similarities to both Alpine-style and Himalayan-style orogens. An evaluation is provided of a channel flow model for the Central Zone, but there are currently insufficient data for the Damara Belt to confirm or repudiate this model. Nonetheless, this study has identified a more complex tectonic history for the Central Zone than previously, with chronological and lithogeochemical evidence for two episodes of deformation and metamorphism that have been linked to the collisional history of the entire Damara Belt and have been correlated with events in other Pan-African belts.

No description available.

Thesis (PhDGeoinformatics)--University of South Australia, 2001.

Thesis (M.S.)--University of Nevada, Reno, 2007. / "May, 2007." Includes bibliographical references (leaves 25-31). Online version available on the World Wide Web.

Thesis (Dr.-Ing.)--Universität Stuttgart zur Erlangung der Würde, 2003. / "September 2004"--P. [2] of cover. Includes bibliographical references (p. 89-101). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Permission letter tipped in. Includes bibliographical references (leaves 158-173).

Thesis (M.S.)--Brigham Young University. Dept. of Geology, 2005. / Includes bibliographical references (p. 15-19).

Thesis (Ph.D.)--Brown University, 2005. / Vita. Thesis advisor: Donald W. Forsyth. Includes bibliographical references (leaves 61-69, 98-103, 176-182, 224-229). Also available online.

Made available in DSpace on 2014-06-11T19:23:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2002Bitstream added on 2014-06-13T19:50:22Z : No. of bitstreams: 1 perez_jas_me_prud.pdf: 977367 bytes, checksum: 6b9550e8932dce0b607ca29641e6f1ba (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Atualmente, com a evolução das tecnologias desenvolvidas para fins de posicionamento, especialmente nos casos que envolvem Geodésia Espacial, várias outras aplicações dessas tecnologias surgem a partir de pesquisas desenvolvidas por vários cientistas. Neste contexto, o GPS (Global Positioning System) destacase de forma impressionante, não só pela variada gama de aplicações em que pode ser utilizado, mas também pela precisão e acurácia dos resultados que podem ser obtidos pelo mesmo. Desta forma, o GPS como “ferramenta” para a Geodinâmica torna-se vital em aplicações que requerem alta precisão, tais como: monitoramento e análise de movimento e deformação das placas litosféricas, previsão de terremotos em regiões sismicamente ativas, entre outras. Um método bastante eficiente nestes casos é o Posicionamento por Ponto Preciso (PPP), adequado para a utilização de produtos GPS disponibilizados pelo IGS (International GPS Service) ou pelo JPL (Jet Propulsion Laboratory). Além disso, existem softwares adequados para esse tipo de posicionamento, bem como para a utilização dos produtos fornecidos pelo IGS e JPL. Este trabalho envolve, basicamente, a utilização do Posicionamento por Ponto Preciso para o processamento de dados de estações geodésicas, no intuito de se obter um campo de velocidades dessas estações, em nível intercontinental. Para tanto, torna-se necessário um prévio embasamento sobre os principais fenômenos geodinâmicos relacionados ao movimento de placas litosféricas, bem como uma fundamentação teórica sobre as observáveis envolvidas no GPS e as possíveis fontes de erro nele atuantes... / Nowadays, with the evolution of the technologies related to positioning, specially those involved with Spatial Geodesy, several applications of these technologies arose from the researches carried out by several scientists. In this context, the GPS (Global Positioning System) has been widely emphasized, not only because of the amount of applications in which it can be used, but also because of the precision and accuracy of the results that can be obtained. Thus, GPS as “tool” for Geodynamics becomes essential in applications where high precision is required, such as monitoring and analysis of movements and deformations of the tectonic plates, prevision of earthquakes at seismically active regions, and others. A method very efficient in these cases is the Precise Point Positioning (PPP), which is suitable for using the GPS products available by IGS (International GPS Service) or JPL (Jet Propulsion Laboratory). Moreover, there are appropriated softwares for applying this method of positioning, as well as for using products provided by IGS and JPL. The present work involves, basically, the use of PPP to processing a set of geodetic stations data, in order to obtain the velocity’s field of these stations involved in an intercontinental scope. In order to reach this aim, it was necessary a previous basis about the main geodynamic phenomena related to the tectonic plate’s movement, as well as the theoretical basis concerning the GPS observables and the possible sources of errors acting on them. In order to analyze the accuracy of the results, comparisons between the final geodetic solution and the results provided by others geodetic sources and geophysical models of plate movements have to be carried out. This procedure has been made in the present work, and preliminary results were obtained for the velocity’s field of the RBMC... (Complete abstract click electronic address below)