The composition and spatial distribution of Quaternary volcanism in the Trans-Mexican Volcanic Belt (TMVB) exhibit some remarkable correlations with the seismicity, age, and structure of ocean lithosphere being consumed at the Middle America Trench. In the west, the TMVB is related to aseismic subduction of the Rivera plate (2 cm/yr) and in the east to a moderately dipping (20-30°) rapidly subducting Cocos plate (6-9 cm/yr). These contrasting arc segments are bounded by the Colima Graben, a zone of high-angle faulting and contemporaneous alkaline/calc-alkaline volcanism, situated above a sinistral transform fault (4 cm/yr) developed in the downgoing slab at the Cocos/Rivera juncture. Geologic mapping and K-Ar dating of the lavas of Iztaccíhuatl, a major calc-alkaline volcano in the TMVB, have established two main phases of eruptive activity that began prior to 0.9 Ma. The substructure of Iztaccíhuatl (>0.6 Ma) is composed principally of two-pyroxene andesites and dacites (300 km³) erupted from Llano Grande and Ancestral Pies volcanoes. The second stage of cone construction (<0.6 Ma) involved horn- blende dacites and andesites (150 km³) extruded from NNW-SSE oriented vents to form the modern summit region. The earliest glacial deposits date prior to 0.27 Ma but moraine complexes on the flanks are Wisconsin to Neoglacial. The phenocryst mineralogy and chemistry of the Younger Andesites and Dacites indicate that magma mixing has played an important role in the evolution of Iztaccíhuatl magma chambers. Mixed lavas characterized by disequilibrium phenocryst assemblages involving magnesian olivine and in the crust and olivine-phyric basaltic magma ascending from depth. Mixing and homogenization are effected by liquid blending and dynamic fractional crystallization in turbulently convecting hybrid liquids. The whole-rock geochemistry of mixed lavas and hornblende dacites is used to derive the composition of each batch of basaltic magma periodically replenishing crustal magma chambers. Basaltic end-members exhibit significant variations in large-ion lithophile elements and Sr isotopic composition which are attributed to heterogeneities in mantle source regions. The primitive compositions of these magmas are compatible with an origin involving partial melting of fertile peridotite under hydrous high-pressure conditions. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

While the archaeology of the Northern Frontier of Mesoamerica is poorly understood, Pedro Armillas' hypothesis that climatically induced environmental change was the limiting factor for cultural change has become the ruling theory. In order to test this hypothesis original lacustrine pollen profiles were compared with a detailed inspection of the known archaeological record and the previously published paleoecological record. The archaeological evidence suggests that there was a dense human occupation in the northern reaches of Mesoamerica between about AD 600-900. The first indications of human settlements are related to the Chupicuaro culture that reached its apogee about 2000 years ago located along the Rio Lerma. A rustic variant of the Chupicuaro culture spread north and is associated with scattered hamlets. About AD 600 the sedentary population expanded considerably in conjunction with the development of regional centers and the Coyotlatelco red-on-buff ceramic tradition. This expansion can be seen all along the Northern Frontier of Mesoamerica from Alta Vista south to Tula. Between AD 900-1000 there was a dramatic change in settlement patterns and by about AD 1000 most of the northern reaches of Mesoamerica were once again under the control of semi-nomadic hunters and gatherers. A suite of four cores was collected in a transect that crosses the Northern Frontier of Mesoamerica. The goal of selecting sites that minimized human impact was not altogether successful since these cores identify the impact of agriculture. Within the limits of the dating and material available, the pollen profiles from these cores suggest an environmental change between AD 1000 and 1500. From the data available it is not clear if this change, or changes, was the result of changes in human settlement patterns or climatic change. As such Armillas' hypothesis remains unproven.

Thesis (Ph. D.)--University of Pennsylvania, 1923. / Folded map accompanied by leaf with descriptive letterpress. Bibliography: p. 186-205.

Thesis ( Ph.D.) -- University of Texas at Arlington, 2008.

Thesis (Ph. D.)--University of California, San Diego, 2001. / Vita. Includes bibliographical references (leaves 248-258).

No description available.

Thesis (Ph. D.)--University of Pennsylvania, 1923. / Folded map accompanied by leaf with descriptive letterpress. Bibliography: p. 186-205.

Thesis (M.A.)--Florida State University, 2004. / Advisor: Dr. Mary Pohl, Florida State University, College ofScience, Dept. of Anthropology. Title and description from dissertation home page (viewed Sept. 29, 2004). Includes bibliographical references.

Thesis (Ph. D.)--University of California, Riverside, 1987. / Includes bibliographical references (leaves 530-552).

Thesis (Ph. D.)--University of Wisconsin-Madison, 1985. / Typescript. Vita. Includes bibliographical references (leaves 101-108).