Th. Ph. D.--Faculté des sciences sociales et morales--Poona, [195-?].

No description available.

"Originally submitted in 1933 as a thesis for the master of arts degree of the Bombay University." / "Select bibliography": p. [204]-207.

New major, minor, and trace element data for the Chakhla- Delakari sill and three nearby lava flows in the proximal area of Tamia are presented. Based on abundances of trace elements, it is inferred that the sill was the feeder of the two uppermost lava flows which tapped magmas from a LREE-, Rb-enriched source. The oldest (lowermost) flow shows greater affinity with the western Deccan lavas. The association of the feeder sill with a large network of parallel trending sills and dikes, and the elongate Satpura Dome, is taken to infer that a major locus of eruption of the Deccan Trap lavas existed in the eastern part of the province. A model is presented for the evolution of the magma source of the sill and the two uppermost flows in a chamber beneath the Satpura Dome in the easternmost Deccan Traps. Results of equilibrium crystallization experiments at 6.35 kbars conducted on two compositions which represent probable near primary liquids are presented. One of these starting compositions has 9.5% MgO and the other 13% MgO. The sequence of crystallization in both starting liquids at 6.35 kbars is as follows: olivine; olivine + Ca- clinopyroxene; ol + Ca-clinopyroxene + Ca-poor clinopyroxene; olivine + Ca-clinopyroxene + Ca-poor clinopyroxene + plagioclase. Based on the present experimental data, it is inferred that typical Deccan magmas (MgO 5-9%) are produced by early fractionation of olivine, pyroxene (Ca-augite and pigeonite), and late fractionation of plagioclase. Deccan basalts with MgO 9-10% appear to have crystallized from melts lower in Ti02 than the starting materials of this study which fractionated olivine and plagioclase. Basalts with MgO2source which has fractionated olivine and plagioclase will produce of the bulk of Deccan basalts.

No description available.

The Deccan Trap basalts are the remnants of a massive series of lava flows that erupted at the K/T boundary and covered 1-2 million km2 of west-central India. This eruptive event is of global interest because of its possible link to the major mass extinction event, and there is much debate about the duration of this massive volcanic event. In contrast to isotopic or paleomagnetic dating methods, I explore an alternative approach to determine the lifecycle of the magma chambers that supplied the lavas, and extend the concept to obtain a tighter constraint on Deccan’s duration. My method relies on extracting time information from elemental and isotopic diffusion across zone boundary in an individual crystal. I determined elemental and Sr-isotopic variations across abnormally large (2-5 cm) plagioclase crystals from the Thalghat and Kashele “Giant Plagioclase Basalts” from the lowermost Jawhar and Igatpuri Formations respectively in the thickest Western Ghats section near Mumbai. I also obtained bulk rock major, trace and rare earth element chemistry of each lava flow from the two formations. Thalghat flows contain only 12% zoned crystals, with 87Sr/86Sr ratios of 0.7096 in the core and 0.7106 in the rim, separated by a sharp boundary. In contrast, all Kashele crystals have a wider range of 87Sr/86Sr values, with multiple zones. Geochemical modeling of the data suggests that the two types of crystals grew in distinct magmatic environments. Modeling intracrystalline diffusive equilibration between the core and rim of Thalghat crystals led me to obtain a crystal growth rate of 2.03x10-10 cm/s and a residence time of 780 years for the crystals in the magma chamber(s). Employing some assumptions based on field and geochronologic evidence, I extrapolated this residence time to the entire Western Ghats and obtained an estimate of 25,000 – 35,000 years for the duration of Western Ghats volcanism. This gave an eruptive rate of 30 – 40 km3/yr, which is much higher than any presently erupting volcano. This result will remain speculative until a similarly detailed analytical-modeling study is performed for the rest of the Western Ghats formations.

No description available.

Cette thèse s'appuie sur les travaux d'Alexander V. Sobolev sur le recyclage de matériel crustal dans le manteau terrestre en lien avec les processus de mise en place des provinces magmatiques et des iles océaniques. Il s'agit d'utiliser des outils pétrologiques et géochimiques couplés à des données de paléomagnétisme haute résolution, et à de la modélisation thermomécanique dans le but de contraindre les processus profonds à l'origine des Trapps du Deccan et leurs conséquences au niveau planétaire (extinction de masse). Dans un premier temps, cette thèse propose une réinterprétation des diverses contraintes temporelles sur la durée de l'éruption des Trapps du Deccan (datations radiochronologiques, paleomagnétisme, profiles d'altérations, et données paléo-environnementales) et suggère un scénario temporel pour la mise en place de cette province magmatique, le tout principalement basé sur des données paléomagnétiques de hautes résolution de Chenet et al (2008, 2009). Ce scénario implique que la phase principale de l'éruption des Trapps du Deccan s'est produite peu de temps avant la limite Crétacé-Paléogène et qu'elle correspond à la mise en place d'environ 1.106km3 de laves en 50ka. Ces chiffres sont équivalents à 150-200 fois le taux d'éruption actuel de l'ile volcanique d'Hawaii. Ce scénario temporel a ensuite été couplé à des données géochimiques élémentaires qui ont permis de mettre en évidence 1) une origine profonde pour la grande majorité des liquides primaires et 2) d'importantes variations de l'assimilation crustale au cours du temps, notamment juste avant la limite Crétacé-Paléogène. Ces phénomènes sont compatibles avec un unique épisode d'érosion lithosphérique de la plaque indienne par les processus magmatiques dans le manteau sous-jacent. Les données relatives aux Trapps du Deccan peuvent être comparées à celles des Trapps de Sibérie et révèlent notamment que l'importante érosion lithosphérique identifiée dans celles-ci n'ait pas eu lieu dans le cas des Trapps du Deccan malgré des caractéristiques mantelliques similaires. Cette différence peut être attribuée à la plus grande épaisseur de la plaque indienne, ainsi qu'à l'existence de zones de faiblesses, liées à l'héritage tectonique du bouclier indien. Ces zones de faiblesses auraient facilité le passage des magmas à travers la plaque de manière à ce qu'une faible proportion d'entre eux seulement ait été impliquée dans les processus de délamination lithospherique. Un ensemble de données géochimiques sur olivine ainsi que de modélisation des liquides magmatiques primaires et de leur source pour les Trapps du Deccan nous ont permis de montrer 1) l'importante contribution d'une source pyroxenitique à la composition des liquide magmatiques primaires (65%), 2) que la gamme de températures potentielles de ces mêmes sources avait due être de l'ordre de 1600°C et 3) que ces dernières contenaient environ 15% de matériel crustal recyclé. Des mesures et calculs similaires appliquées aux laves de la Réunion ont, par ailleurs, montrés des résultats très différents : 50% de liquides pyroxenitiques dans les liquides magmatiques primaires, une température potentielle mantellique de l'ordre de 1500°C et une teneur des sources magmatiques en matériel crustal recyclé de l'ordre de 7%. Ces résultats sont compatibles avec le modèle de panache matellique pour la mise en place des provinces magmatiques et des iles océaniques ainsi qu'avec l'hypothèse du refroidissement séculaire de ces mêmes panaches. Nous en concluons que l'éruption des Trapps du Deccan fut un événement d'une rapidité exceptionnelle et que son implication dans la crise biologique de la fin du Crétacé fut sans doute particulièrement importante. / This PhD aims to build on the previous work by Alexander V. Sobolev and colleagues on crustal recycling within the Earth mantle and LIPs/ocean island magmatism. The PhD focus will be to apply petrology and geochemistry coupled with high-resolution paleomagnetism, and thermo-mechanical modelling in order to constrain the deep processes behind the Deccan Traps (mantle melting and crustal recycling) as well as the consequences at the surface of the Earth (eruption rates and related degassing). Upon revisiting published time constraints on the Deccan eruptions (radiometric dating, paleomagnetism, inter-flow weathering profiles and paleoenvironmental data), we propose a new, paleomagnetism-based (Chenet et al., 2008, 2009), eruption scenario for the Main Deccan Province (Western Ghats). We suggest that the main phase of volcanic activity occurred just before and ended at the Cretaceous-Palaeogene boundary and was responsible for the emplacement of about 1.106km3 of lavas in ~50kyr. This is equivalent to 150 to 200 times present-day eruption rates in Hawaii. Coupling of the paleomagnetism-based timeframe with bulk-rock trace element concentrations revealed that Western Ghats lavas feature 1) a strong garnet signature (Heavy Rare Earth Element depletion), indicative of a deep origin and 2) significant temporal variations in the intensity of crustal assimilation undergone by the rising melts, especially just before the Cretaceous-Palaeogene boundary. We suggest that these excursions are part of a single and localized plume-induced lithospheric erosion event of the Indian lithosphere by the Deccan plume. A comparison of the Deccan Traps with the Siberian Traps exposes significant geodynamical differences. Most notably, the widespread and extensive lithospheric erosion observed in the Siberian Traps did not take place in the Deccan Traps, despite similar mantle characteristics. This difference is attributed to 1) a thicker Indian lithosphere and 2) to the existence of weaknesses in the form of pre-existing structural lineaments. These pre-existing structures facilitated the passage of deep mantle-derived magmas and thus precluded or limited their involvement in a freezing-delamination process. Olivine geochemistry and olivine-based primary melt and source modelling in Deccan Traps lavas showed 1) large contributions of pyroxenite-derived melts (65%) to the primary melts, 2) high potential temperatures of the mantle sources (~1590-1600°C) and 3) that the mantle sources of Deccan Traps magmas contained ~15% of recycled crustal material. These observations contrast with those obtained from Réunion Island lavas (50% of pyroxenite-derived melts, mantle potential temperatures of 1490-1500°C and 7% of recycled crustal material in the sources of Réunion Island magmas. Our results are compatible with the plume model for LIPs and ocean island magmatism as well as with a secular cooling of mantle plumes. We conclude, along with many authors, that the emplacement of the Deccan Traps was a remarkably swift and catastrophic event at the end of the Cretaceous and that it likely played a significant role in the end-Cretaceous mass extinction.

Abstract Dissimilatory microbial sulfate reduction (MSR) The specific objectives of the study were to provide the first measurements of sulfur isotope fractionation associated with acidophilic sulfate reducing-microorganisms, and to examine whether pH influences sulfur fractionation during MSR. The fractionation associated with the strains investigated was comparable to that of neutrophilic strains with similar metabolisms (4-12‰), but varied with pH. Two fractionation regimes were identified: one regime is consistent with fractionation during exponential growth, while the other – not identified previously - is not linked to active sulfate reduction and may result from internal sulfate accumulation. This would represent the first measurement of sulfur fractionation during sulfate uptake, the first step of MSR. Geological processes at the Cretaceous-Paleogene (KPg) boundary The KPg boundary is associated with one of the largest biological extinctions in the history of our planet. Two major geologic events - the Chicxulub bolide impact with evaporite terrane and the eruption of the Deccan continental flood basalts - coincide with the KPg boundary and have been identified as possible triggers for the extinctions, but their relative timing remains unresolved. The objectives of this study were to identify the contribution of these processes to the sulfur burden in the sedimentary environment of two freshwater KPg sections, and to determine their relative timing. The results demonstrate that the peak of Deccan volcanism post-dates the Chicxulub impact and the associated abrupt KPg mass extinction, thus precluding a direct volcanic causal mechanism, but shedding light on the underlying causes for the delayed recovery of ecosystems in the early Paleogene.

Thesis (Ph. D.)--University of Oregon, 2007. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 301-344). Also available for download via the World Wide Web; free to University of Oregon users.