The ‘giant’ Tambogrande volcanogenic massive sulphide (VMS) deposits within the Cretaceous Lancones basin of northwestern Perú are some of the largest Cu-Zn-Au-Ag-bearing massive sulphide deposits known. Limited research has been done on these deposits, hence the ore forming setting in which they developed and the key criteria that permitted such anomalous accumulation of base-metal sulphides are not understood. Based on field relationships in the host volcanic rocks and U-Pb geochronology, the deposits formed during the early stages of arc development in the latest Early Cretaceous and were related to an extensional and arc-rift phase (~105-100 Ma, phase 1). During this time, bimodal, primitive basalt-dominant volcanic rocks were erupted in a relatively deep marginal basin. Phase 1 rhyolite is tholeiitic, M-type, and considered to have formed from relatively high temperature, small batch magmas. The high heat flow and extensional setting extant during the initial stages of arc development were essential components for forming a VMS hydrothermal system. The subsequent phase 2 (~99-91 Ma) volcanic sequence comprises more evolved mafic rocks and similar, but more depleted, felsic rocks erupted in a relatively shallow marine setting. Phase 2 is interpreted to represent late-stage arc volcanism during a waning extensional regime and marked the transition to contractional tectonism. The Tambogrande deposits are particularly unusual amongst the ‘giant’ class of VMS deposits in that deposition largely occurred as seafloor mound-type and not by replacement of existing strata. Paleomorphology of the local depositional setting was defined by seafloor depressions controlled by syn-volcanic faults and rhyolitic volcanism. The depressions were the main controls on distribution and geometry of the deposits and, due to inherently confined hydrothermal venting, enhanced the efficiency of sulphide deposition. Geochemical and radiogenic isotope data indicate that the rhyolites in the VMS deposits were high temperature partial melts of the juvenile arc crust that had inherited the isotopic signatures of continental crust. Moreover, Pb isotope data suggest the metal budget was sourced almost wholly from mafic volcanic strata. Therefore, unlike the implications of many conventional models, the felsic volcanic rocks at Tambogrande are interpreted to have only played a passive role in VMS formation.

No description available.

Geological evidence suggests large-scale continental extension during the breakup of the eastern Gondwana margin was the predominant force controlling rifting of New Caledonia from the eastern Gondwana margin and formation of the Tasman Sea in the Late Cretaceous. Tectonic models suggest slab-rollback forces elongated and thinned the crustal lithosphere detaching crustal fragments from the Gondwana margin. Current tectonic models lack detailed timing and placement of this crustal detachment with respect to New Caledonia based on lack of evidence (rocks). An isotope and paleomagnetic study was carried out on a bi-modal assemblage of volcanic rock exposed on the southwest side of New Caledonia in the Nouméa Basin. U/Pb isotope ages of zircon grains found within siliceous volcanic rock in the Nouméa Basin provide temporal evidence that volcanism persisted both before and after the breakup of the eastern Gondwana Continent (100-90 Ma) in the Late Cretaceous. Four isotope ages >97 Ma and a series (11 samples) ranging from 91-76 Ma constrain the siliceous volcanism of the Nouméa Basin to the Late Cretaceous. A paleomagnetic inquiry utilizing statistics of both McFadden/Reid and Fisher carried out on 16 Nouméa Basin siliceous and mafic in situ formations place the oldest volcanic units found within the Nouméa Basin at 650 S latitude as New Caledonia began to separate from Gondwana (~100 Ma). The data suggests a well-developed arc signature in the region, which persisted for at least 15 Ma in the Late Cretaceous. Compared to current tectonic models of the southwest Pacific Region from the Late Cretaceous to Eocene, our data suggests New Caledonia was further south on the eastern Gondwana supercontinent prior to rifting in the Late Cretaceous than current models. / Geologic background -- Tectonic setting -- Methods -- Sampling -- Results -- Discussion. / Department of Geological Sciences

Volatile heavy metals are liberated from magmas during eruptive and passively degassing volcanic activity. Volcanic emanations have been estimated to contribute 20-40% of volatile elements such as Bi, Pb, As or Sb, and up to 40-50 % of Cd and Hg annually (Nriagu, 1989). Some workers, however, believe these ranges are too high (Hinkley, 1999) or too low (Zreda-Gostynska and Kyle, 1997) leading to considerable differences in global inventory budgets of these metals and the degree to which they load the atmosphere. The objective of this work is to investigate the behavior of volatile heavy metals such as Au, Tl, As, Pb etc. in subaerially erupted magmas and experimentally in silicate melts. Analysis of natural pumice samples confirm the futile, sporadic nature of Hg and associated heavy metals, suggesting these metals are fully degassed prior to deposition. Diffusion experiments were conducted in natural basalt, dacite and synthetic rhyolite (Ab-Or-Qz minimum eutectic) over a range of temperatures (1200 – 1430 °C) at 0.1 MPa. Starting compositions were doped with a heavy metal cocktail (Bi, Pb, Tl, Au, Re, Sb, Sn, Cd, Mo, As, Cu) and loaded into open top Pt capsules. One set of experiments examined the effect of melt composition (polymerization) on element diffusion, and the second investigated the effects of ligands on diffusion by adding known concentrations of Cl and S. During experiments of varying duration, concentration gradients arose in the volatile trace metals due to their varying volatility, as measured (normal to the melt/gas interface) by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in quenched glasses. Diffusion profiles followed an Arrhenius relationship from which diffusion coefficients (D) and activation energies (Ea) were obtained for Au, Tl, As, Cd, Re, Pb and Bi (in decreasing order of volatility). Results show Au and Tl are the most volatile in dacite and rhyolite yielding LogDDac Au = -10.7 ± 0.1 m2/s and LogDDac Tl = -10.9 ± 0.1 m2/s in dacite, and LogDRhy Au = -10.9 ± 0.1 m2/s and LogDRhy Tl = -11.3 ± 0.3 m2/s in rhyolite respectively. The D for Au could not be measured in basalt but Tl was the fastest diffusing species LogDBas Tl = -10.8 ± 0.2 m2/s. Ligands Cl and S were shown to increase the volatilities of all metals, with S having a more profound effect. Diffusivities were applied to a simple 1D bubble growth model (Smith 1955). Model results indicate diffusion coefficients play a major role in metal fractionation processes occurring at depths that ultimately dictate what metal ratios are measured at the surface of volcanoes.

The purpose of this study is to investigate the origin, source characteristics, evolution petrogenesis and emplacement mechanisms of Beypazari-Oymaaga&ccedil / granitoids. These granitoids are intruded into a metamorphic basement and nonconformably overlain by Neogene clastic rocks. Field work, petrographical and geochemical studies are carried out to determine the petrologic features and tectonic setting of the granitoid body. The Beypazari-Oymaaga&ccedil / pluton is a composite pluton with its host batholith, enclaves, aplite dykes and a pegmatite. The batholith is generally composed of quartz, K-feldspar, plagioclase and hornblende. Field observations and petrographic investigations indicate that the host batholith has granodiorite composition and shows distinct differences in the abundances of quartz, amphibole minerals (e.g., hornblende) and of enclaves. The samples taken from TavuktaSi Tepe contain relatively less amphibole and enclaves but more quartz. Compared with them, samples from the rest of the batholith have relatively abundant amphibole, K-feldspar megacrysts, and enclaves but less quartz. Enclaves derived from magma mixing/mingling processes are dioritic in composition. Geochemical data obtained from whole rock analyses show that the pluton is shallowly emplaced and has calc-alkaline, metaluminous to peraluminous chemistry. It is characterized by enrichments in LIL and LREE, especially in K, Rb and Th. Although, there is a distinct petrographic variation in the batholith, the geochemical characteristics are uniform throughout the pluton. The Oymaaga&ccedil / Granitoids which have I-type identity are typical representatives of magmatic arc environment. The present study suggests that the possible source of magma is the upper crust and can be compared with the coeval volcanism in Galatean Volcanic Arc.

The ‘giant’ Tambogrande volcanogenic massive sulphide (VMS) deposits within the Cretaceous Lancones basin of northwestern Perú are some of the largest Cu-Zn-Au-Ag-bearing massive sulphide deposits known. Limited research has been done on these deposits, hence the ore forming setting in which they developed and the key criteria that permitted such anomalous accumulation of base-metal sulphides are not understood. Based on field relationships in the host volcanic rocks and U-Pb geochronology, the deposits formed during the early stages of arc development in the latest Early Cretaceous and were related to an extensional and arc-rift phase (~105-100 Ma, phase 1). During this time, bimodal, primitive basalt-dominant volcanic rocks were erupted in a relatively deep marginal basin. Phase 1 rhyolite is tholeiitic, M-type, and considered to have formed from relatively high temperature, small batch magmas. The high heat flow and extensional setting extant during the initial stages of arc development were essential components for forming a VMS hydrothermal system. The subsequent phase 2 (~99-91 Ma) volcanic sequence comprises more evolved mafic rocks and similar, but more depleted, felsic rocks erupted in a relatively shallow marine setting. Phase 2 is interpreted to represent late-stage arc volcanism during a waning extensional regime and marked the transition to contractional tectonism. The Tambogrande deposits are particularly unusual amongst the ‘giant’ class of VMS deposits in that deposition largely occurred as seafloor mound-type and not by replacement of existing strata. Paleomorphology of the local depositional setting was defined by seafloor depressions controlled by syn-volcanic faults and rhyolitic volcanism. The depressions were the main controls on distribution and geometry of the deposits and, due to inherently confined hydrothermal venting, enhanced the efficiency of sulphide deposition. Geochemical and radiogenic isotope data indicate that the rhyolites in the VMS deposits were high temperature partial melts of the juvenile arc crust that had inherited the isotopic signatures of continental crust. Moreover, Pb isotope data suggest the metal budget was sourced almost wholly from mafic volcanic strata. Therefore, unlike the implications of many conventional models, the felsic volcanic rocks at Tambogrande are interpreted to have only played a passive role in VMS formation.

Ruapehu is an active volcano located on the North Island of New Zealand, with the most recent major eruptions occurring in 1945, 1969, 1975, and 1995/96. Ruapehu is also home to the three major North Island ski areas, Whakapapa, Turoa, and Tukino. Because of the high frequency of eruptions, there is a significant volcanic hazard at the ski areas particularly from lahars which can form even after minor eruptions. Most recently, lahars have affected Whakapapa ski area in 1969, 1975, and 1995/96. The most significant risk at Turoa is from ballistic bombs due to the proximity of the top two T-Bars to the crater. Ash fall has also caused disruption at the ski areas, covering the snow and causing damage to structures. There is yet to be a death at the ski areas from a volcanic event; however the risk at the ski areas is too high to be completely ignored. The ski areas at Whakapapa and Turoa are currently operated by Ruapehu Alpine Lifts (RAL), who have been significantly improving their commitment to providing volcanic hazard training for their staff and preparing for handling a volcanic eruption. RAL is joined by the Institute of Geological Sciences (GNS) and the Department of Conservation (DoC) in trying to mitigate this risk through a range of initiatives, including an automated Eruption Detection System (EDS), linked to sirens and loudspeakers on Whakapapa ski areas, as well as by providing staff training and public education. The aim of this study was to provide RAL with recommendations to improve their staff training and warning system response. Staff induction week at both Turoa and Whakapapa ski areas was observed. Surveys were distributed and collected from staff at both ski areas, and interviews were conducted with staff at Whakapapa ski area. Data obtained from staff interviews and surveys provided the author with insight into staff's mental models regarding a volcanic event response. A simulation of the warning system was observed, as well as a blind test, to collect data on the effectiveness of training on staff response. Results indicated permanent and seasonal staff were knowledgeable of the volcanic hazards that may affect the ski areas, but had differing perspectives on the risk associated with those hazards. They were found to be confident in the initial response to a volcanic event (i.e. move to higher ground), but were unsure of what would happen after this initial response. RAL was also found to have greatly improved their volcanic hazard training in the past year, however further recommendations were suggested to increase training effectiveness. A training needs analysis was done for different departments at the ski areas by taking a new approach of anticipating demands staff may encounter during a volcanic event and complementing these demands with existing staff competencies. Additional recommendations were made to assist RAL in developing an effective plan to use when responding to volcanic events, as well as other changes that could be made to improve the likelihood of customer safety at the ski areas during an eruption.

Este estudo se propôs a avaliar a influência da cristalinidade e da deformação do quartzo na ocorrência da reação álcali-agregado. A influência da cristalinidade do quartzo foi analisada através da mesóstase, material intersticial que constitui as rochas vulcânicas, que é um material composto por grãos sub-microscópicos de quartzo e feldspatos. Para tanto foram selecionadas duas rochas vulcânicas, constituídas por quartzo em diferentes quantidades e com diferentes graus de cristalinidade: um basalto, com pouca quantidade de sílica, sem quartzo livre e cuja mesóstase apresenta grãos pobremente cristalizados; e um riolito, com grande quantidade de sílica e de quartzo livre, além de uma mesóstase com grãos melhor cristalizados. A caracterização da cristalinidade do quartzo mostrou que a mesóstase, que tem aparência de material amorfo em microscopia ótica, apresenta diferentes feições quando observada através de microscopia eletrônica de varredura: mesóstase com grãos criptocristalinos de quartzo e K-feldspatos (Mm); mesóstase com grãos de quartzo e feldspato microcristalinos (Mq); mesóstase constituída predominantemente por argilominerais (Ma). Relacionando-se essas características com a reatividade das rochas verificou-se que o quartzo presente nas mesóstases Mm e Mq reage rápida e intensamente, sobressaindo-se à dissolução da mesóstase Mm, enquanto os grãos da mesóstase Ma são preservados. Através da compração dessas constatações, obtidas com o basalto e o riolito, com as características do material intersticial de um basalto inócuo, em ensaios acelerados e em campo, verificou-se que seu material intersticial da rocha inócua possui pouca quantidade de sílica livre (quartzo). Isso evidencia que a reatividade das rochas vulcânicas está relacionada à quantidade de sílica livre presente (quartzo) e a velocidade de ocorrência da reação com a cristalinidade do quartzo constituinte da mesóstase (Mm). A influência da deformação do quartzo no desencadeamento da reação álcali-agregado foi avaliada através do estudo de rochas graníticas com diferentes graus de deformação: uma rocha pouco deformada (granito), uma rocha com deformação intermediária (proto-milonito) e uma rocha muito deformada (orto-milonito). Os graus de deformação do quartzo foram caracterizados, através de microscopia ótica, como: grau 0= ausência de deformação; grau 1= grãos pouco deformados, com extinção ondulante leve; grau 2= quartzo muito deformado, com forte extinção ondulante, chegando a formar bandas de deformação; grau 3= forte deformação, com formação de subgrãos; grau 4= grãos recristalizados. O estudo mostrou que a presença preponderante de quartzo com grau 2 nas rochas denota uma maior velocidade de desencadeamento da reação álcali-agregado. A partir dessa constatação efetuou-se a avaliação das características texturais dos grãos de quartzo de rochas reativas em campo, verificando-se que quanto maior a quantidade de grãos com grau 2 mais rápida a ocorrência da reação em campo. / This research aims to study the influence of crystallinity and deformation of quartz to the occurrence of alkali-aggregate reaction. The influence of the cristallinitiy of quartz was analyzed through the interstitial material (volcanic glass/mesostase) into volcanic rocks. This material is composing by sub-microscopic grains of quartz and feldspars, thus it was selected a basaltic rock, with poor crystallized interstitial material and low silica content; and a rhyolitic rock, with better crystallized interstitial material and high silica content. The characterization of the crystallinity of the quartz showed that interstitial mesostase has appearance of amorphous material on the optical microscopy, but, at scanning electron microscopy it was observe the following features: mesostase with microcrystalline grains of quartz and K-feldspar (Mm); mesostase with better crystallized grains of quartz and K-feldspar (Mq); mesostase with clay predominantly (Ma). Reactivity potential tests showed that quartz in Mm and Mq react quickly and intensely, especially Mm, while quartz in Ma was preserved. Comparing these evidences, obtained with basalt and rhyolite, with interstitial material into innocuous basalt, it was found that interstitial material in innocuous rock has smaller amount of free silica (quartz). It proof that reactivity of volcanic rocks is related to the amount of free silica present into the rocks and poor cristalinity of quartz into mesostase make alkali-aggregate reaction quickness (Mm). The influence of the deformation of quartz on alkali-aggregate reaction was analyzed through granitic rocks with different degrees of deformation: a rock with very little deformation (granite), a medium deformed rock (proto-mylonite), a very deformed rock (orto-mylonite). Deformation degree of quartz was characterized through optical microscopy as follows: order 0= absence of the deformation; order 1= slightly deformed grain (weak ondulatory extinction); order 2= very deformed quartz, with strong ondulatory extinction and forming deformation bands; order 3= very deformed quartz, with formation of sub-grains, order 4= recrystallized quartz. The study showed that rocks with most quartz „order 2‟ denotes the development of alkali-aggregate reaction faster than rocks with other „orders‟ deformation of the quartz. From this conclusion it was obseve the textural characteristics of quartz grains in reative rocks on the field, confirming that quartz with deformation bands cause alkali-aggregate reaction quickly.

Este estudo se propôs a avaliar a influência da cristalinidade e da deformação do quartzo na ocorrência da reação álcali-agregado. A influência da cristalinidade do quartzo foi analisada através da mesóstase, material intersticial que constitui as rochas vulcânicas, que é um material composto por grãos sub-microscópicos de quartzo e feldspatos. Para tanto foram selecionadas duas rochas vulcânicas, constituídas por quartzo em diferentes quantidades e com diferentes graus de cristalinidade: um basalto, com pouca quantidade de sílica, sem quartzo livre e cuja mesóstase apresenta grãos pobremente cristalizados; e um riolito, com grande quantidade de sílica e de quartzo livre, além de uma mesóstase com grãos melhor cristalizados. A caracterização da cristalinidade do quartzo mostrou que a mesóstase, que tem aparência de material amorfo em microscopia ótica, apresenta diferentes feições quando observada através de microscopia eletrônica de varredura: mesóstase com grãos criptocristalinos de quartzo e K-feldspatos (Mm); mesóstase com grãos de quartzo e feldspato microcristalinos (Mq); mesóstase constituída predominantemente por argilominerais (Ma). Relacionando-se essas características com a reatividade das rochas verificou-se que o quartzo presente nas mesóstases Mm e Mq reage rápida e intensamente, sobressaindo-se à dissolução da mesóstase Mm, enquanto os grãos da mesóstase Ma são preservados. Através da compração dessas constatações, obtidas com o basalto e o riolito, com as características do material intersticial de um basalto inócuo, em ensaios acelerados e em campo, verificou-se que seu material intersticial da rocha inócua possui pouca quantidade de sílica livre (quartzo). Isso evidencia que a reatividade das rochas vulcânicas está relacionada à quantidade de sílica livre presente (quartzo) e a velocidade de ocorrência da reação com a cristalinidade do quartzo constituinte da mesóstase (Mm). A influência da deformação do quartzo no desencadeamento da reação álcali-agregado foi avaliada através do estudo de rochas graníticas com diferentes graus de deformação: uma rocha pouco deformada (granito), uma rocha com deformação intermediária (proto-milonito) e uma rocha muito deformada (orto-milonito). Os graus de deformação do quartzo foram caracterizados, através de microscopia ótica, como: grau 0= ausência de deformação; grau 1= grãos pouco deformados, com extinção ondulante leve; grau 2= quartzo muito deformado, com forte extinção ondulante, chegando a formar bandas de deformação; grau 3= forte deformação, com formação de subgrãos; grau 4= grãos recristalizados. O estudo mostrou que a presença preponderante de quartzo com grau 2 nas rochas denota uma maior velocidade de desencadeamento da reação álcali-agregado. A partir dessa constatação efetuou-se a avaliação das características texturais dos grãos de quartzo de rochas reativas em campo, verificando-se que quanto maior a quantidade de grãos com grau 2 mais rápida a ocorrência da reação em campo. / This research aims to study the influence of crystallinity and deformation of quartz to the occurrence of alkali-aggregate reaction. The influence of the cristallinitiy of quartz was analyzed through the interstitial material (volcanic glass/mesostase) into volcanic rocks. This material is composing by sub-microscopic grains of quartz and feldspars, thus it was selected a basaltic rock, with poor crystallized interstitial material and low silica content; and a rhyolitic rock, with better crystallized interstitial material and high silica content. The characterization of the crystallinity of the quartz showed that interstitial mesostase has appearance of amorphous material on the optical microscopy, but, at scanning electron microscopy it was observe the following features: mesostase with microcrystalline grains of quartz and K-feldspar (Mm); mesostase with better crystallized grains of quartz and K-feldspar (Mq); mesostase with clay predominantly (Ma). Reactivity potential tests showed that quartz in Mm and Mq react quickly and intensely, especially Mm, while quartz in Ma was preserved. Comparing these evidences, obtained with basalt and rhyolite, with interstitial material into innocuous basalt, it was found that interstitial material in innocuous rock has smaller amount of free silica (quartz). It proof that reactivity of volcanic rocks is related to the amount of free silica present into the rocks and poor cristalinity of quartz into mesostase make alkali-aggregate reaction quickness (Mm). The influence of the deformation of quartz on alkali-aggregate reaction was analyzed through granitic rocks with different degrees of deformation: a rock with very little deformation (granite), a medium deformed rock (proto-mylonite), a very deformed rock (orto-mylonite). Deformation degree of quartz was characterized through optical microscopy as follows: order 0= absence of the deformation; order 1= slightly deformed grain (weak ondulatory extinction); order 2= very deformed quartz, with strong ondulatory extinction and forming deformation bands; order 3= very deformed quartz, with formation of sub-grains, order 4= recrystallized quartz. The study showed that rocks with most quartz „order 2‟ denotes the development of alkali-aggregate reaction faster than rocks with other „orders‟ deformation of the quartz. From this conclusion it was obseve the textural characteristics of quartz grains in reative rocks on the field, confirming that quartz with deformation bands cause alkali-aggregate reaction quickly.

L'augmentation artificielle de la couche stratosphérique d'aérosol de sulfate a été proposée comme méthode pour réduire le réchauffement climatique causé par les émissions anthropiques de gaz à effet de serre. Dans cette thèse, nous présentons un modèle global atmosphère-aérosol nouvellement développé, évaluons sa performance par rapport aux observations et l'appliquons pour étudier l'efficacité et les impacts de cette forme possible d'ingénierie climatique. Nous trouvons que l'effet de refroidissement réalisable par unité de masse de soufre injectée peut diminuer de façon plus drastique qu'estimé précédemment pour des taux d'injection élevés et que des injections à plus haute altitude ou dans des régions plus grandes n'entraînent pas un refroidissement plus fort. L'efficacité de la méthode pourrait donc être plutôt limitée, tout au moins dans les cas d'injections tropicales de dioxyde de soufre que nous avons modélisées. Par ailleurs, il existe plusieurs effets secondaires potentiellement nocifs, tels que le chauffage stratosphérique dû à l'absorption de rayonnement par l'aérosol provoquant de fortes perturbations dans la dynamique atmosphérique, la composition chimique de la stratosphère et les nuages hauts. Enfin, nous trouvons que les effets radiatifs de l'injection d'aérosol stratosphérique et de l'éclaircissement des nuages marins, une autre technique de géo-ingénierie proposée, seraient largement additifs et complémentaires lors de leur application parallèle. Cela pourrait permettre de concevoir un port-folio d'approches pour atteindre des objectifs climatiques spécifiques et réduire les effets secondaires indésirables de l'ingénierie climatique. / The enhancement of the stratospheric sulphate aerosol layer has been proposed as a method to abate the global warming caused by anthropogenic greenhouse gas emissions. In this thesis we present a newly developed global atmosphere-aerosol model, evaluate its performance against observations, and apply it to study the effectiveness and impacts of this possible form of climate engineering. We find that the achievable cooling effect per injected sulphur mass unit may decrease more drastically for larger injections than previously estimated and that injections at higher altitude or over larger areas do not result in a stronger cooling. The effectiveness of the method may therefore be rather limited, at least when using tropical injections of sulphur dioxide as in our model experiments. In addition, there are several potentially harmful side effects, such as stratospheric heating due to absorption of radiation by the aerosol causing strong perturbations in atmospheric dynamics, composition, and high-level clouds. Furthermore, we find that the radiative effects of stratospheric aerosol injection and marine cloud brightening, another proposed geoengineering technique, would be largely additive and complementary when applying them together. This might allow the design of portfolio approaches to achieve specific climate goals and reduce unintended side effects of climate engineering.