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.

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Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

La presente investigación está orientada a presentar algunas hipótesis que nos lleven a demostrar el fenómeno de aculturación religiosa en el área andina. / Tesis

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The Bolivian Altiplano is part of the inner arc Polymetallic Belt of the Andes, and is a Cretaceous-Cenozoic intermontane basin located between the Andean arc of the Western Cordillera and the Paleozoic fold belt of the Eastern Cordillera. Reconnaissance geological mapping shows that epithermal mineralisation in the NE Altiplano is related to silicic magmatism located on NW-trending Altiplano growth faults and intersections with NE and E-W lineaments. Magmatism was episodic and occurred during the Miocene arc broadening episode, which correlates with increased plate convergence rates. Most magmatism is mid Miocene (19-10 Ma), and formed flow-dome-sill-stock complexes. The upper (9-7.5 Ma) and late (6.5-4 Ma) Miocene episodes, in contrast, generally formed ash-flow calderas and strato-volcanoes. The three episodes are mainly dacites and rhyolites of the high-K calc-alkaline suite, with some shoshonites, and can only be distinguished isotopically, with progressively stronger crustal contamination in the younger episodes. Sr-Nd-O isotopes and trace elements show that the magmas evolved by variable fractionation and assimilation from subduction-related, mantle-derived magmas which were isotopically enriched by bulk contamination with Precambrian gneisses. Mapping, petrography and XRD show that the epithermal deposits have large areas of pervasive phyllic alteration with a propylitic halo. Tourmaline alteration occurs in the cores of Sn-bearing deposits. Argillic and silicic alteration in some deposits are subsurface features of hot spring systems. Mineralisation (Au-Ag-Cu-Pb-Zn) is disseminated and in sheeted veins and veinlets which have a NE-trend, related to the regional tectonic stress. Dating and O-H isotopes show that the mineralisation is genetically related to the dacitic magmatism and formed from a dominantly magmatic fluid, with meteoric mixing in the upper levels. Differences between the Polymetallic Belt and the Copper Belt are mainly a function of erosion level. Polymetallic deposits of the Eastern Cordillera contain important Sn and form the main part of the Tin Belt. Minor Sn also occurs in Altiplano deposits hosted by Paleozoic marine sediments, but not in those in Tertiary red beds. Tin was probably derived from the Paleozoic sediments, and is not related to deep subduction.

Thesis (M.S.)--University of Delaware, 2007. / Principal faculty advisor: Cort J. Willmott, Dept. of Geography. Includes bibliographical references.