Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 395-421). Available also in a digital version from Dissertation Abstracts.

The Matagalpa Formation, the oldest unit exposed (Oligocene? - Early Miocene?), consists of over 300 meters of hydrothermally altered mafic flows and some interbedded sedimentary rocks. Up to 1400 meters of siliceous volcanic and sedimentary rocks (Mid-Miocene-Pliocene?), correlative with the Padre Miguel Group in Guatemala, nonconformably overlie the Matagalpa Formation. The lower 1000 meters of this group consists mainly of rhyolitic to andesitic ignimbrites that were probably erupted from a vertically zoned magma. Faulting accompanied the extrusion of these ignimbrites. These are overlain by up to 400 meters of airfall tuffs, fluvial, lacustrine, and laharic deposits, and a series of structurally-controlled rhyolitic domes. The uppermost unit consists of several thin ignimbrites. Most of the faulting occurred after the deposition of the Padre Miguel Group, probably from Middle Pliocene to Early Pleistocene times. Normal faults trend N50-80°W, N10-25°E, N35°E, and N70°E. They are probably surficial features caused by left-lateral shear in the basement related to movement between the Caribbean and Americas plates. Minor northwest-trending folds formed contemporaneous with and perhaps prior to faulting. Olivine basalt was extruded from structurally-controlled vents after most of the faulting had ceased. Cut terraces and pediments formed adjacent to the ancestral Rio del Hombre, Subsequent downcutting may have been the result of regional uplift, stream capture along the Rio Choluteca, or both. / text

The Agalteca quadrangle is located in the Sierras of Northern Central America and straddles the N60W-trending Montaña de Comayagua structural belt near the southeastern limit of its known 130 km extent. The structural belt may extend into unmapped areas to the northwest toward Guatemala and to the southeast toward Nicaragua. The structural belt has a width of approximately 30 km in the vicinity of the Agalteca quadrangle. Mapping of the Agalteca quadrangle has clarified that the Montaña de Comayagua structural belt consists of a series of left-stepping, en echelon strike-slip faults produced by probable dextral strike-slip displacement of unknown magnitude in the Late Cretaceous to early Tertiary. Associated with these strike-slip faults are syntectonic high-angle reverse faults, thrust faults, folds and antithetic shears. The assemblage is a "flower structure" in cross section, and is believed to be the product of transpression, or wrenching with a component of compression. The axis of the N60W-trending Laramide wrench zone in the Agalteca quadrangle is structurally high and exposes a conformable sequence of highly deformed Mesozoic sedimentary rocks. A Paleozoic (?) metamorphic basement, the Cacaguapa Schist, is known to unconformably underlie the Mesozoic sequence in central Honduras, but is not exposed in the Agalteca quadrangle. The Mesozoic sedimentary rocks include the Upper Jurassic (?) to Lower Cretaceous Todos Santos Formation conglomerate which is conformably overlain by the Valanginian (?) to Albian limestone of the Atima Formation. The Atima Formation is conformably overlain by the Albian to Late Cretaceous redbeds of the Valle de Angeles Group, which includes an intercalated limestone member, the Cenomanian Esquías Formation. The Mesozoic sedimentary rocks are intruded by mafic to felsic stocks and dikes of Late Cretaceous to Tertiary age, and are unconformably overlain by Tertiary volcanic rocks. The volcanic rocks include andesite of the early Tertiary Matagalpa Formation and the Oligocene-Miocene ignimbrites, basalt flows and volcanogenic sediments of the Padre Miguel Group. Terrace deposits of late Tertiary to Quaternary age unconformably overlie the older rocks in the Agalteca quadrangle. The Laramide structures of central Honduras are overprinted by north-trending grabens of the Honduras Depression which began to form in the mid-Miocene and are still active. In a regional context, the western tip of the Caribbean Plate (the Chortis Block) is undergoing east-west extension. North-trending grabens, including the Honduras Depression, cut the Chortis block from the Pacific Volcanic Chain to the Motagua transform boundary. The Honduras Depression is the most complex of these graben systems. The southern part of the Honduras Depression consists of grabens and half-grabens which trend north from the Gulf of Fonseca and are interrupted by the N60W-trending structures of the Montaña de Comayagua structural belt near Tegucigalpa. The northern part of the Honduras Depression trends north to the Caribbean coast from its termination against the Montaña de Comayagua structural belt near Lake Yojóa. The northern and southern segments of the Honduras Depression were born with an apparent left-lateral offset along the Montaña de Comayagua structural belt. The Honduras Depression is a developing rift. A pre-existing zone of weakness along the Montaña de Comayagua structural belt inhibited the formation of a through-going rift and rejuvenated the Laramide structural belt as a dextral transform fault zone. Late Cenozoic magmatic uplifts are present within the rejuvenated structural belt, and economically important base metal concentrations such as the El Mochito and El Rosario deposits are localized at the intersections of the northern and southern segments of the Honduras Depression with the Montaña de Comayagua structural belt. Quaternary alkalic basalt is associated with the Honduras Depression and is also restricted to the intersections of the depression with the structural belt in the vicinity of Tegucigalpa and Lake Yojóa. / text

No description available.

Freiburg (Breisgau), Univ., Diss., 2003. / Computerdatei im Fernzugriff.

Freiburg (Breisgau), Univ., Diss., 2003. / Computerdatei im Fernzugriff.

0 / SPK / specialcollections@tulane.edu

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Costs and benefits associated with erosion reduction and adoption of soil conservation practices for a representative farm in a watershed in Honduras are examined in a linear programming framework. Special attention is paid to income-soil loss tradeoffs, income-risk tradeoffs, and on the effect of different farmers' planning horizons on net farm income. A representative farm model for the area was constructed to achieve the objectives of the study. Twelve farmers in the region were surveyed, crop budgets were prepared, and soil loss values were calculated to provide the information required to construct this representative farm. A linear programming model that maximizes net farm income is used to examine the effect of different soil loss levels on farm income. A MOTAD model that minimizes deviation in income (risk) is used to determine risk levels while income and/or soil loss levels restrictions are imposed. Results indicate that considerable reductions in the amount of soil loss can be achieved in the study area. Erosion is reduced from 328.24 ton./mn./year to 6.56 ton./mn./year1 when constraints are imposed on the model. The reduced erosion lowers income from L.5929.24/year for high erosion rates to L.2825.8l/year for low erosion rates. Low levels of soil erosion are achieved at the expense of higher levels of risk. High levels of income are associated with high levels of risk regardless of whether soil loss constraints exist or not. Small differences in income exist among the four planning horizons analyzed. The best soil conservation practices for this region turned out to be the cultivation of coffee on the highest slopes, the use of live barriers and terraces, and the use of conventional and minimum tillage. / Master of Science

acase@tulane.edu / 1 / Roy Jason Taylor