A detailed investigation of cores from three Peru Margin sites drilled during Ocean Drilling Program (ODP) Leg 201 has been conducted to determine the occurrence of volcanic ash layers and ash accumulations within marine sediments along the Peru shelf. These sites were previously occupied during ODP Leg 112, which suffered from poor and/or disturbed recovery. Advancements in hydraulic piston coring realized since and employed during ODP Leg 201 resulted in better core recovery and less disturbance of sediment throughout the cored intervals. Since marine sediments potentially undergo less erosion and Leg 201 cores benefited from improved recovery, the tephrachronologic record from Leg 201 has yielded a more complete record of explosive activity for North- Central Andean volcanism than previous studies. The improved recovery of Leg 201 cores has enabled the detailed examination of cores from the above sites needed to test the hypothesis that volcanic ash layers and accumulations are more abundant in the study region than previously reported. Due to the low recovery of Leg 112 cores, Pouclet et al. (1993) document only six-ash layers, one ash pod, and eight ash-bearing layers (for a total of 14 cm of ash) from the three sites (Sites 684, 680, and 681) that were reoccupied during Leg 201 (Sites 1227, 1228, and 1229 respectively). This study reports a total of 332.0 cm of ash deposited into the study region which is approximately 24 times that previously reported. Explosive eruption cycles for the Andean region have been deduced from the documentation of Leg 201 ash layers. Our record of volcanic cycles indicates that explosive activity was less intense during the Miocene, in which one ash layer (1.3 cm) was deposited, compared to that of the Pliocene and Pleistocene which experienced most of the explosive volcanic activity in which 52 ash layers (total thickness equal to 208.6 cm) and 14 ash layers (total thickness equal to 122.1 cm) were deposited respectively (Fig. 14). These data are consistent with the previous study of Pouclet et al. (1990); however these data indicate that explosive activity during the Pliocene and Pleistocene was more intense than previously reported.

Thesis (M. Sc.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references (leaves 145-161). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

In order to investigate bubble formation and growth at 1 atmosphere, degassing experiments using a Stromboli basalt with dissolved H2O or H2O + CO2 were performed in a custom furnace on a beamline at the Advanced Photon Source. The glasses were synthesized at 1250°C and 1000 MPa, with ~3.0 wt%, ~5.0 wt%, or ~7.0 wt% H2O or with mixtures of H2O + CO2, ~3.0 wt% H2O and ~440 ppm CO2, ~5.0 wt% H2O and 880 ppm CO2, ~7.0 wt% H2O and ~1480 ppm CO2, then heated on the beamline while recording the bubble growth. The 3D bubble size distributions in the quenched samples were then studied with synchrotron X-ray microtomography. / The experimental results show that bubble nucleation and growth are volatile-concentration dependent. Bubbles can easily nucleate in melts initially containing high volatile concentrations. CO2 has no significant effect on bubble formation and growth because of low CO2 concentrations. Multiple nucleation events occur in most of these degassing samples, and they are more pronounced in more supersaturated melts. Bubble growth is initially controlled by viscosity near glass transition temperatures and by diffusion at higher temperatures where melt viscous relaxation occurs rapidly. Bubble foam forms when bubbles are highly connected due to coalescence, and bubbles begin pop, 10 to 20 seconds after the foam is developed. The degree of bubble coalescence increases with time, and bubble coalescence can significantly change the bubble size distribution. Bubble size distributions follow power-law relations at vesicularities of 1.0% to 65%, and bubble size distributions evolve from power-law relations to exponential relations at vesicularities of 65% to 83%. This evolution is associated with the change from far-from-equilibrium degassing to near-equilibrium degassing. / The experimental results imply that during basaltic eruptions both far-from-equilibrium degassing and near-equilibrium degassing can occur. The far-from-equilibrium degassing generally generates the power-law bubble size distributions whereas the near-equilibrium degassing produces exponential bubble size distributions Bubbles begin to pop when the vesicularities attain 65% to 83%. Bubble expansion in the foam possibly accounts for the mechanism of magma fragmentation. / Afin d'étudier la formation et la croissance de bulle; sous pression d'une atmosphère, desexpériences de dégazage sur un basalte de Stromboli, avec HiO ou H20 + CO2 dissouts,ont été exécutées dans un four pilote sous rayonnement synchrotron à l'APS (AdvancedPhoton Source). Les verres ont été synthétisés à une température de 1250°C et unepression de 1000 MPa, avec des teneurs en eau dissoute de ~ 3.0, ~ 5.0 ou ~ 7.0% (enpoids), et des mélanges H20 + C02 à teneurs de ~ 3.0% H20 (en poids) et 440 ppm CO2,~ 5% H20 et 880 ppm CO2, et de ~ 7.0% H20 et 1480 ppm CO2. La croissance des bullesest enregistrée pendant le chauffage du mélange en utilisant le rayonnement synchrotron.Les distributions tridimensionnelles de la taille des bulles dans les échantillons trempésont été étudiées par microtomographie à rayon X synchrotron.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 158-175).

Thesis (Ph. D.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 204-228).

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