Oceanic lithosphere constitutes the upper boundary layer of the Earth’s convecting mantle. Its structure and evolution provide a vital window on the dynamics of the mantle and important clues to how the motions of Earth’s surface plates are coupled to convection in the mantle below. The three-dimensional shear-velocity structure of the upper mantle beneath the Atlantic Ocean is investigated to gain insight into processes that drive formation of oceanic lithosphere. Travel times are measured for approximately 10,000 fundamental-mode Rayleigh waves, in the period range 30-130 seconds, traversing the Atlantic basin. Paths with >30% of their length through continental upper mantle are excluded to maximize sensitivity to the oceanic upper mantle. The lateral distribution of Rayleigh wave phase velocity in the Atlantic upper mantle is explored with two approaches. One, phase velocity is allowed to vary only as a function of seafloor age. Two, a general two-dimensional parameterization is utilized in order to capture perturbations to age-dependent structure. Phase velocity shows a strong dependence on seafloor age, and removing age-dependent velocity from the 2-D maps highlights areas of anomalously low velocity, almost all of which are proximal to locations of hotspot volcanism. Depth-dependent variations in vertically-polarized shear velocity (Vsv) are determined with two sets of 3-D models: a layered model that requires constant VSV in each depth layer, and a splined model that allows VSV to vary continuously with depth. At shallow depths (~75 km) the seismic structure shows the expected dependence on seafloor age. At greater depths (~200 km) high-velocity lithosphere is found only beneath the oldest seafloor; velocity variations beneath younger seafloor may result from temperature or compositional variations within the asthenosphere. The age-dependent phase velocities are used to constrain temperature in the mantle and show that, in contrast to previous results for the Pacific, phase velocities for the Atlantic are not consistent with a half-space cooling model but are best explained by a plate-cooling model with thickness of 75 km and mantle temperature of 1400oC. Comparison with data such as basalt chemistry and seafloor elevation helps to separate thermal and compositional effects on shear velocity.

A região do Tupanci, localizada no noroeste do Escudo Sul-Rio-Grandense, apresenta um expressivo volume de depósitos vulcânicos de composição ácida, estratigraficamente correlacionados à Formação Acampamento Velho, da Bacia do Camaquã. Esta região apresenta a exposição mais setentrional deste episódio vulcânico, caracterizado por uma sequência vulcânica de rochas efusivas e piroclásticas, de composição dominantemente ácida, afinidade alcalina sódica e idades aproximadas a 550 Ma, cujos processos são vinculados aos magmatismo pós-colisional do ciclo orogênico Brasiliano/Pan-Africano no ESRG. As rochas vulcânicas ácidas ocorrem na forma de depósitos efusivos e, em menor volume, piroclásticos, distribuídas em dois Cerros: Tupanci e dos Picados. O Cerro Tupanci apresenta características de uma intrusão subvulcânica com morfologia alongada (N-S), representada por riolitos porfiríticos, com fenocristais de sanidina e quartzo envoltos por uma matriz quartzo-feldspática equigranular fina a afanítica, ocorrendo com intensa foliação de fluxo nas regiões de borda. No Cerro dos Picados ocorrem derrames riolíticos texturalmente semelhantes, porém com matriz afanítica de aspecto vítreo e presença de biotita, além de depósitos piroclásticos caracterizados por ignimbritos riolíticos. Os ignimbritos podem ser divididos em duas fácies, sendo: ignimbritos ricos em líticos, com alguns púmices desvitrificados e pouco estirados, além de pequenos e raros cristaloclastos; e ignimbritos reomórficos, onde ocorre abundância em púmices desvitrificados com uma destacável textura eutaxítica, maior frequência de cristaloclastos e raros litoclastos. O comportamento dos elementos maiores, traços e ETR de ambos os cerros permitem classificar o magmatismo como supersaturado em sílica, semelhante aos sistemas de alta sílica, afinidade alcalina, e tendência metaluminosa a levemente peralcalina, com características semelhantes aos granitos tipo “A”. As informações obtidas indicam uma vinculação genética destas rochas com o vulcanismo da Formação Acampamento Velho, confirmando, desta maneira, a correlação estratigráfica. / Volcanic and hypabyssal acid rocks occur in the area of Tupanci, located at the NW portion of the Sul-Rio-Grandense Shield. These rocks are stratigraphically correlated to the Acampamento Velho Formation (about 550Ma), at the Camaquã Basin. This region has the northernmost exposure of this volcanic episode, which comprises a sequence of effusive/hypabyssal and pyroclastic rocks, with dominantly acid composition and sodicalkaline affinity, whose genetic processes are linked to the post-collisional stages of the Brasiliano/Pan-Africano orogenic cycle. In this region the acid volcanic rocks occur mainly as effusive deposits and secondarily as pyroclastic deposits, in two Cerros (Hills): Tupanci and Picados. The Cerro Tupanci defines an elongated morphology (N-S), interpreted as a subvolcanic intrusion, represented by porphyritic rhyolites with phenocrysts of alkali feldspar and quartz surrounded by a equigranular-fine-grained to aphanitic quartz-feldspar matrix, with a strong flow foliation on border regions. In the Cerro dos Picados, texturally similar rhyolitic rocks occur, but with aphanitic to glassy matrix and presence of biotite, and pyroclastic deposits, characterized by rhyolitic ignimbrites. The ignimbrites can be separated in two facies: lithic-rich ignimbrites, with a few devitrified and poorly elongated pumice and crystal fragments; and reomorphic, with abundance of devitrified pumices with a detachable eutaxitic texture, crystal fragments and rarely lithic fragments. The behavior of major elements, traces and REEs allows to classify the magmatism as silica oversaturated, similiar to the systems with high-silica, alkaline affinity and a metaluminous to slightly peralkalline trend with similiar characteristiscs to the “A” type granites. The petrographic and lithochemical data obtained indicate a genetic linkage with the Acampamento Velho Formation magmatism, confirming the stratigraphic correlation.

Master of Science / Geology / Matthew E. Brueseke / The Upper Wind River Basin (UWRB) is located in north-central Wyoming, to the south of the Yellowstone National Park boundary and east of Jackson Hole. Both Lava Mountain and Spring Mountain are Quaternary volcanoes in the UWRB. Lava Mountain is a shield volcano composed of 26 separate lavas capped by a scoria cone. Spring Mountain is located about ~36 km east of Lava Mountain, north of Dubois, WY, where eruptions of basalt cut through Paleocene and Eocene strata. The goal of this study aims to reconstruct the petrogenesis of magmas erupted at both volcanoes using geochemical, petrographic, and isotopic analyses. Important local events in geologic history played a large role in the development of the UWRB. This includes a long history of ancient and Cenozoic subduction, regional extension, and also the migration of the North American plate over the Yellowstone hotspot. The few previous studies on Lava Mountain claim the rocks are mafic in composition, however this was based solely on reconnaissance geological mapping. Geochemical evidence presented in this thesis show Lava Mountain rocks range from basaltic andesite to dacite. Basaltic andesite and dacite are interstratified at the base until approximately 2774 m; the rest of the volcano is andesite. All Lava Mountain samples are largely aphanitic and crystal-poor. Conversely, at Spring Mountain, localized normal faulting controls the location of eruptions of olivine-rich basalt. Petrographic analysis for both Lava Mountain and Spring Mountain display a range of evidence for open system processes, including sieved and/or resorbed pyroxenes, olivines and feldspars, as well as xenocrysts that suggest an influence from crustal assimilation. A petrogenetic model is introduced that discusses how Lava Mountain magma production occurred via fractional crystallization of basalt to dacite, then magma mixing of basaltic andesite and dacite, coupled with small amounts of crustal assimilation, to form the locally erupted andesites. All samples, including Spring Mountain basalts, have ⁸⁷Sr/⁸⁶Sr isotopes of 0.70608 and 0.70751, with ¹⁴³Nd/¹⁴⁴Nd isotopes of 0.51149 and 0.51157 and εNd values of -18 to -22. Pb isotopes plot to the left of the Geochron and directly on to slightly above the Stacey-Kramers curve. Strontium, neodymium, and lead isotope data suggest that Spring Mountain basalts are melts of ancient (e.g., 2.8 Ga Beartooth province) lithospheric mantle. The high ⁸⁷Sr/⁸⁶Sr values and exceptionally low εNd values separate the UWRB rocks from both Yellowstone and Snake River Plain volcanics, and suggest they originated from a different magma source. Finally, thermal evidence suggests melting genesis for UWRB rocks may not be Yellowstone plume related; rather it is more likely linked to Cenozoic extension.

abstract: Planetary surface studies across a range of spatial scales are key to interpreting modern and ancient operative processes and to meeting strategic mission objectives for robotic planetary science exploration. At the meter-scale and below, planetary regolith conducts heat at a rate that depends on the physical properties of the regolith particles, such as particle size, sorting, composition, and shape. Radiometric temperature measurements thus provide the means to determine regolith properties and rock abundance from afar. However, heat conduction through a matrix of irregular particles is a complicated physical system that is strongly influenced by temperature and atmospheric gas pressure. A series of new regolith thermal conductivity experiments were conducted under realistic planetary surface pressure and temperature conditions. A new model is put forth to describe the radiative, solid, and gaseous conduction terms of regolith on Earth, Mars, and airless bodies. These results will be used to infer particle size distribution from temperature measurements of the primitive asteroid Bennu to aid in OSIRIS-REx sampling site selection. Moving up in scale, fluvial processes are extremely influential in shaping Earth's surface and likely played an influential role on ancient Mars. Amphitheater-headed canyons are found on both planets, but conditions necessary for their development have been debated for many years. A spatial analysis of canyon form distribution with respect to local stratigraphy at the Escalante River and on Tarantula Mesa, Utah, indicates that canyon distribution is most closely related to variations in local rock strata, rather than groundwater spring intensity or climate variations. This implies that amphitheater-headed canyons are not simple markers of groundwater seepage erosion or megaflooding. Finally, at the largest scale, volcanism has significantly altered the surface characteristics of Earth and Mars. A field campaign was conducted in Hawaii to investigate the December 1974 Kilauea lava flow, where it was found that lava coils formed in an analogous manner to those found in Athabasca Valles, Mars. The location and size of the coils may be used as indicators of local effusion rate, viscosity, and crustal thickness. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2018

Submitted by NUNO MANUEL MARTINHO VIEIRA null (nuno_ksudachix@hotmail.com) on 2017-07-08T09:52:07Z No. of bitstreams: 1 Dissertação Final - Nuno Vieira FINAL.pdf: 15615486 bytes, checksum: 943b208c4b937916de3dee0b7004da7a (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-07-13T19:13:50Z (GMT) No. of bitstreams: 1 vieira_nmm_me_rcla.pdf: 15615486 bytes, checksum: 943b208c4b937916de3dee0b7004da7a (MD5) / Made available in DSpace on 2017-07-13T19:13:50Z (GMT). No. of bitstreams: 1 vieira_nmm_me_rcla.pdf: 15615486 bytes, checksum: 943b208c4b937916de3dee0b7004da7a (MD5) Previous issue date: 2017-04-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / As rochas ácidas da Província Magmática do Paraná (PMP) cobrem cerca de 2,5% do volume total do vulcanismo intracontinental ocorrido durante o Cretáceo Inferior, o que levou à abertura do Atlântico Sul. As análises petrográficas e o estudo da química mineral dos principais constituintes minerais, plagioclásio, piroxênio (orto e clino) e Ti-magnetita, das rochas ácidas do tipo Palmas (ATP) e ácidas tipo Chapecó (ATC), permitiram obter dados inéditos e correlacionar, com maior rigor, os vários magmas-tipo que essas rochas geraram. Foi possível descriminar a mineralogia distinta do grupo Palmas, ao que diz respeito aos cristais de piroxênio, assim como as heterogeneidades geoquímicas deste mesmo grupo e de Chapecó. Ortopiroxênio é exclusivo das rochas ATP e especificamente do magma-tipo Caxias do Sul. Os clinopiroxênios, pigeonita e augita são comuns em todos os subtipos das ácidas, porém, esta última está ausente da associação mineralógicas das rochas do magma-tipo Santa Maria (ATP). Com o estudo detalhado da relação mineralógica entre os cristais permitiu inferir sobre a sequência de cristalização dos piroxênios e, por conseguinte das rochas tipo Palmas. As feições texturais, dados de química mineral e (raros) de geotermobarometria obtidos nas rochas ATP e ATC sugerem que os minerais presentes nestas rochas não estão em equilíbrio com o líquido que gerou a rocha hospedeira. As feições petrográficas encontradas nos cristais de piroxênio e plagioclásio, tais como, bordas corroídas, texturas corona e de embaiamento pela matriz, em “peneira” (sieve texture) entre outras, indicam o desiquilíbrio destes minerais com o líquido que gerou a matriz. Os valores de coeficiente de distribuição (Kd) desses minerais também mostram o desiquilíbrio com a rocha total e sugerem um provável equilíbrio com líquidos de composição menos evoluída, tais como rochas básicas (i.e. basaltos) e/ou rochas intermediárias (i.e. andesitos). Com todos estes dados considera-se que grande maioria dos feno e microfenocristais, principalmente de piroxênio, e subordinadamente, plagioclásio, sejam antecristais, e assim teriam sido gerados no mesmo sistema magmático mas em líquidos com graus de diferenciação e/ou evolução diferentes. / The acid rocks of the Paraná Magmatic Province (PMP) cover about 2.5% of the total volume of intracontinental volcanism that occurred during the Lower Cretaceous, which led to the opening of the South Atlantic. Petrographic analyzes and the study of mineral chemistry of the main Palmas acid type (ATP) and Chapecó acid type rocks (ATC), made it possible to obtain unpublished data and correlate, with greater rigor, the various types of magmas these rocks generated. It was possible to discriminate the mineralogy distinct from the Palmas group, as regards the pyroxene crystals, as well as the geochemical heterogeneities of this group and Chapecó group. Orthopyroxene crystals are unique to ATP rocks and specifically to the Caxias do Sul magma-type. Clinopyroxenes crystals, pigeonite and augite, are very common in all acidic subtypes, but the latter is absent from the mineralogical association of the Santa Maria magma-type rocks (from ATP). With the detailed study of the mineralogical relationship between these crystals allowed us to infer about the crystallization sequence of the pyroxenes and, consequently, of the Palmas group. The textural features, mineral chemistry data and (rare) geothermobarometry data obtained in the ATP and ATC rocks suggest that the minerals present in these rocks are not in equilibrium with the liquid that generated the host rock. The petrographic features found in pyroxene and plagioclase crystals, such as corroded edges, corona and matrix impregnation, "sieve texture", among others, indicate the disequilibrium of these minerals with the liquid that generated the matrix. The distribution coefficient (Kd’s) values of these minerals also show unbalance with total rock and suggest a probable equilibrium with less evolved composition liquids, such as basic rocks (e.g., basalts) and / or intermediate rocks (e.g., andesites). With all these data it is considered that a great majority of the phenocrysts and microphenocrysts, mainly of pyroxene, and subordinately, plagioclase, are both anticrystals, and thus they would have been generated in the same magmatic system but in liquids with different degrees of differentiation and / or evolution.

A região do Tupanci, localizada no noroeste do Escudo Sul-Rio-Grandense, apresenta um expressivo volume de depósitos vulcânicos de composição ácida, estratigraficamente correlacionados à Formação Acampamento Velho, da Bacia do Camaquã. Esta região apresenta a exposição mais setentrional deste episódio vulcânico, caracterizado por uma sequência vulcânica de rochas efusivas e piroclásticas, de composição dominantemente ácida, afinidade alcalina sódica e idades aproximadas a 550 Ma, cujos processos são vinculados aos magmatismo pós-colisional do ciclo orogênico Brasiliano/Pan-Africano no ESRG. As rochas vulcânicas ácidas ocorrem na forma de depósitos efusivos e, em menor volume, piroclásticos, distribuídas em dois Cerros: Tupanci e dos Picados. O Cerro Tupanci apresenta características de uma intrusão subvulcânica com morfologia alongada (N-S), representada por riolitos porfiríticos, com fenocristais de sanidina e quartzo envoltos por uma matriz quartzo-feldspática equigranular fina a afanítica, ocorrendo com intensa foliação de fluxo nas regiões de borda. No Cerro dos Picados ocorrem derrames riolíticos texturalmente semelhantes, porém com matriz afanítica de aspecto vítreo e presença de biotita, além de depósitos piroclásticos caracterizados por ignimbritos riolíticos. Os ignimbritos podem ser divididos em duas fácies, sendo: ignimbritos ricos em líticos, com alguns púmices desvitrificados e pouco estirados, além de pequenos e raros cristaloclastos; e ignimbritos reomórficos, onde ocorre abundância em púmices desvitrificados com uma destacável textura eutaxítica, maior frequência de cristaloclastos e raros litoclastos. O comportamento dos elementos maiores, traços e ETR de ambos os cerros permitem classificar o magmatismo como supersaturado em sílica, semelhante aos sistemas de alta sílica, afinidade alcalina, e tendência metaluminosa a levemente peralcalina, com características semelhantes aos granitos tipo “A”. As informações obtidas indicam uma vinculação genética destas rochas com o vulcanismo da Formação Acampamento Velho, confirmando, desta maneira, a correlação estratigráfica. / Volcanic and hypabyssal acid rocks occur in the area of Tupanci, located at the NW portion of the Sul-Rio-Grandense Shield. These rocks are stratigraphically correlated to the Acampamento Velho Formation (about 550Ma), at the Camaquã Basin. This region has the northernmost exposure of this volcanic episode, which comprises a sequence of effusive/hypabyssal and pyroclastic rocks, with dominantly acid composition and sodicalkaline affinity, whose genetic processes are linked to the post-collisional stages of the Brasiliano/Pan-Africano orogenic cycle. In this region the acid volcanic rocks occur mainly as effusive deposits and secondarily as pyroclastic deposits, in two Cerros (Hills): Tupanci and Picados. The Cerro Tupanci defines an elongated morphology (N-S), interpreted as a subvolcanic intrusion, represented by porphyritic rhyolites with phenocrysts of alkali feldspar and quartz surrounded by a equigranular-fine-grained to aphanitic quartz-feldspar matrix, with a strong flow foliation on border regions. In the Cerro dos Picados, texturally similar rhyolitic rocks occur, but with aphanitic to glassy matrix and presence of biotite, and pyroclastic deposits, characterized by rhyolitic ignimbrites. The ignimbrites can be separated in two facies: lithic-rich ignimbrites, with a few devitrified and poorly elongated pumice and crystal fragments; and reomorphic, with abundance of devitrified pumices with a detachable eutaxitic texture, crystal fragments and rarely lithic fragments. The behavior of major elements, traces and REEs allows to classify the magmatism as silica oversaturated, similiar to the systems with high-silica, alkaline affinity and a metaluminous to slightly peralkalline trend with similiar characteristiscs to the “A” type granites. The petrographic and lithochemical data obtained indicate a genetic linkage with the Acampamento Velho Formation magmatism, confirming the stratigraphic correlation.

abstract: Early spacecraft missions to Mars, including the Marnier and Viking orbiters and landers revealed a morphologically and compositionally diverse landscape that reshaped widely held views of Mars. More recent spacecraft including Mars Global Surveyor, Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, and the Mars Exploration Rovers have further refined, enhanced, and diversified our understanding of Mars. In this dissertation, I take a multiple-path approach to planetary and Mars science including data analysis and instrument development. First, I present several tools necessary to effectively use new, complex datasets by highlighting unique and innovative data processing techniques that allow for the regional to global scale comparison of multiple datasets. Second, I present three studies that characterize several processes on early Mars, where I identify a regional, compositionally distinct, in situ, stratigraphically significant layer in Ganges and Eos Chasmata that formed early in martian history. This layer represents a unique period in martian history where primitive mantle materials were emplaced over large sections of the martian surface. While I originally characterized this layer as an effusive lava flow, based on the newly identified regional or global extent of this layer, I find the only likely scenario for its emplacement is the ejecta deposit of the Borealis Basin forming impact event. I also re-examine high thermal inertia, flat-floored craters identified in Viking data and conclude they are typically more mafic than the surrounding plains and were likely infilled by primitive volcanic materials during, or shortly after the Late Heavy Bombardment. Furthermore, the only plausible source for these magmas is directly related to the impact process, where mantle decompression melting occurs as result of the removal of overlying material by the impactor. Finally, I developed a new laboratory microscopic emission and reflectance spectrometer designed to help improve the interpretation of current remote sensing or in situ data from planetary bodies. I present the design, implementation, calibration, system performance, and preliminary results of this instrument. This instrument is a strong candidate for the next generation in situ rover instruments designed to definitively assess sample mineralogy and petrology while preserving geologic context. / Dissertation/Thesis / Ph.D. Geological Sciences 2012

abstract: Lunar Reconnaissance Orbiter (LRO) and MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft missions provide new data for investigating the youngest impact craters on Mercury and the Moon, along with lunar volcanic end-members: ancient silicic and young basaltic volcanism. The LRO Wide Angle Camera (WAC) and Narrow Angle Camera (NAC) in-flight absolute radiometric calibration used ground-based Robotic Lunar Observatory and Hubble Space Telescope data as standards. In-flight radiometric calibration is a small aspect of the entire calibration process but an important improvement upon the pre-flight measurements. Calibrated reflectance data are essential for comparing images from LRO to missions like MESSENGER, thus enabling science through engineering. Relative regolith optical maturation rates on Mercury and the Moon are estimated by comparing young impact crater densities and impact ejecta reflectance, thus empirically testing previous models of faster rates for Mercury relative to the Moon. Regolith maturation due to micrometeorite impacts and solar wind sputtering modies UV-VIS-NIR surface spectra, therefore understanding maturation rates is critical for interpreting remote sensing data from airless bodies. Results determined the regolith optical maturation rate on Mercury is 2 to 4 times faster than on the Moon. The Gruithuisen Domes, three lunar silicic volcanoes, represent relatively rare lunar lithologies possibly similar to rock fragments found in the Apollo sample collection. Lunar nonmare silicic volcanism has implications for lunar magmatic evolution. I estimated a rhyolitic composition using morphologic comparisons of the Gruithuisen Domes, measured from NAC 2-meter-per-pixel digital topographic models (DTMs), with terrestrial silicic dome morphologies and laboratory models of viscoplastic dome growth. Small, morphologically sharp irregular mare patches (IMPs) provide evidence for recent lunar volcanism widely distributed across the nearside lunar maria, which has implications for long-lived nearside magmatism. I identified 75 IMPs (100-5000 meters in dimension) in NAC images and DTMs, and determined stratigraphic relationships between units common to all IMPs. Crater counts give model ages from 18-58 Ma, and morphologic comparisons with young lunar features provided an additional age constraint of <100 Ma. The IMPs formed as low-volume basaltic eruptions significantly later than previous evidence of lunar mare basalt volcanism's end (1-1.2 Ga). / Dissertation/Thesis / Ph.D. Geological Sciences 2013

abstract: Impact craters are ubiquitous throughout the Solar System, formed by one of the principal processes responsible for surface modification of terrestrial planets and solid bodies (i.e., asteroids, icy moons). The impact cratering process is well studied, particularly on the Moon and Mercury, where the results remain uncomplicated by atmospheric effects, plate tectonics, or interactions with water and ices. Crater measurements, used to determine relative and absolute ages for geologic units by relating the cumulative crater frequency per unit area to radiometrically-determined ages from returned samples, are sensitive to the solar incidence angle of images used for counts. Earlier work is quantitatively improved by investigating this important effect and showing that absolute model ages are most accurately determined using images with incidence angles between 65&deg; and 80&deg;, and equilibrium crater diameter estimates are most accurate at ~80&deg; incidence angle. A statistical method is developed using crater size-frequencies to distinguish lunar mare age units in the absence of spectral differences. Applied to the Moon, the resulting areal crater densities confidently identify expansive units with >300&ndash;500 my age differences, distinguish non-obvious secondaries, and determine that an area >1&times;104 km2 provides statistically robust crater measurements. This areal crater density method is also applied to the spectrally-homogeneous volcanic northern smooth plains (NSP) on Mercury. Although crater counts and observations of embayed craters indicate that the NSP experienced at least two resurfacing episodes, no observable age units are observed using areal crater density measurements, so smooth plains emplacement occurred over a relatively short timescale (<500 my). For the first time, the distribution of impact melt on Mercury and the Moon are compared at high resolution. Mercurian craters with diameters &ge;30 km have a greater areal extent of interior melt deposits than similarly sized lunar craters, a result consistent with melt-generation model predictions. The effects of shaking on compositional sorting within a granular regolith are experimentally tested, demonstrating the possibility of mechanical segregation of particles in the lunar regolith. These results provide at least one explanation toward understanding the inconsistencies between lunar remote sensing datasets and are important for future spacecraft sample return missions. / Dissertation/Thesis / Ph.D. Geological Sciences 2013

A região do Tupanci, localizada no noroeste do Escudo Sul-Rio-Grandense, apresenta um expressivo volume de depósitos vulcânicos de composição ácida, estratigraficamente correlacionados à Formação Acampamento Velho, da Bacia do Camaquã. Esta região apresenta a exposição mais setentrional deste episódio vulcânico, caracterizado por uma sequência vulcânica de rochas efusivas e piroclásticas, de composição dominantemente ácida, afinidade alcalina sódica e idades aproximadas a 550 Ma, cujos processos são vinculados aos magmatismo pós-colisional do ciclo orogênico Brasiliano/Pan-Africano no ESRG. As rochas vulcânicas ácidas ocorrem na forma de depósitos efusivos e, em menor volume, piroclásticos, distribuídas em dois Cerros: Tupanci e dos Picados. O Cerro Tupanci apresenta características de uma intrusão subvulcânica com morfologia alongada (N-S), representada por riolitos porfiríticos, com fenocristais de sanidina e quartzo envoltos por uma matriz quartzo-feldspática equigranular fina a afanítica, ocorrendo com intensa foliação de fluxo nas regiões de borda. No Cerro dos Picados ocorrem derrames riolíticos texturalmente semelhantes, porém com matriz afanítica de aspecto vítreo e presença de biotita, além de depósitos piroclásticos caracterizados por ignimbritos riolíticos. Os ignimbritos podem ser divididos em duas fácies, sendo: ignimbritos ricos em líticos, com alguns púmices desvitrificados e pouco estirados, além de pequenos e raros cristaloclastos; e ignimbritos reomórficos, onde ocorre abundância em púmices desvitrificados com uma destacável textura eutaxítica, maior frequência de cristaloclastos e raros litoclastos. O comportamento dos elementos maiores, traços e ETR de ambos os cerros permitem classificar o magmatismo como supersaturado em sílica, semelhante aos sistemas de alta sílica, afinidade alcalina, e tendência metaluminosa a levemente peralcalina, com características semelhantes aos granitos tipo “A”. As informações obtidas indicam uma vinculação genética destas rochas com o vulcanismo da Formação Acampamento Velho, confirmando, desta maneira, a correlação estratigráfica. / Volcanic and hypabyssal acid rocks occur in the area of Tupanci, located at the NW portion of the Sul-Rio-Grandense Shield. These rocks are stratigraphically correlated to the Acampamento Velho Formation (about 550Ma), at the Camaquã Basin. This region has the northernmost exposure of this volcanic episode, which comprises a sequence of effusive/hypabyssal and pyroclastic rocks, with dominantly acid composition and sodicalkaline affinity, whose genetic processes are linked to the post-collisional stages of the Brasiliano/Pan-Africano orogenic cycle. In this region the acid volcanic rocks occur mainly as effusive deposits and secondarily as pyroclastic deposits, in two Cerros (Hills): Tupanci and Picados. The Cerro Tupanci defines an elongated morphology (N-S), interpreted as a subvolcanic intrusion, represented by porphyritic rhyolites with phenocrysts of alkali feldspar and quartz surrounded by a equigranular-fine-grained to aphanitic quartz-feldspar matrix, with a strong flow foliation on border regions. In the Cerro dos Picados, texturally similar rhyolitic rocks occur, but with aphanitic to glassy matrix and presence of biotite, and pyroclastic deposits, characterized by rhyolitic ignimbrites. The ignimbrites can be separated in two facies: lithic-rich ignimbrites, with a few devitrified and poorly elongated pumice and crystal fragments; and reomorphic, with abundance of devitrified pumices with a detachable eutaxitic texture, crystal fragments and rarely lithic fragments. The behavior of major elements, traces and REEs allows to classify the magmatism as silica oversaturated, similiar to the systems with high-silica, alkaline affinity and a metaluminous to slightly peralkalline trend with similiar characteristiscs to the “A” type granites. The petrographic and lithochemical data obtained indicate a genetic linkage with the Acampamento Velho Formation magmatism, confirming the stratigraphic correlation.