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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The Gatun Structure: A geological assessment of a newly recognized impact structure near Lake Gatun in the Republic de Panama

Tornabene, Livio Leonardo 01 November 2001 (has links)
The Gatun Structure (N 09º 05’ 58.1”, W 79º 47’ 21.8”, situated in the triple-canopy rainforest 10 km to the WSW of the Gamboa and about 2 km south of the Isle of Barbacoas, Republic de Panama), is a partially inundated, quasi-concentric surface feature ~3km in diameter, which appears in aerial photographs and in radar imagery as an arcuate chain of islands with a raised center. Although the structure has been heavily weathered and altered, it has retained morphology consistent with complex craters: an elevated circular central uplift 500-600 m in diameter and approximately 70 m high, and arcuate boundary ridges (a rim structure?) ranging from ~50-110 meters high. Within the central peak, highly altered and fractured siltstone of the Gatuncillo Formation (?) (Eocene) ± older rocks are uplifted and exposed through surrounding calcareous units of the Caimito Formation (Oligocene) and the Las Cascadas Formation (Miocene), the major target rocks in the region. Lithologies in the structure include highly fractured siliciclastic rocks (siltstone, sandstones and greywackes), limestones with anomalous spherical glass inclusions, both black and white hypocrystalline glasses (possible melt rocks), lithic fragmental breccias, and melt-bearing breccias (possible impact melt breccias and suevites) containing flow banding and evidence for selective melting of minerals. Three types of spherules (glass, fluid-drop and lithic), a pyroxenequartz “necklace” disequilibrium structure (coronas), plagioclase feldspars exhibiting mosaicism and partially amorphization and zeolitization, possible liquid immiscibility between melts of calcite and felpspathic glass, as well as decomposition of titano-magnetite, are all petrographic criteria that suggest a hypervelocity impact event. The structure is crosscut by numerous dikes of unshocked basalt and basaltic andesite related to volcanism along the Panamanian segment of the Central American arc to the south. However, the lithologies of the Gatun Structure are chemically inconsistent with the regional volcanic rocks and the unshocked volcanic rocks that crosscut the structure. An impact origin is our preferred interpretation for the Gatun structure due to the lack of an igneous relationship between the Gatun structure and the explosive volcanism of Panamanian arc, the presence of classical impactite lithologies within the site, the occurrence of spherules, maskelynite (as suggested by Raman Spectroscopy) and other disequilibrium shock features in the Gatun suite of rocks.
2

The Gatun structure [electronic resource] : a geological assessment of a newly recognized impact structure near Lake Gatun in the Republic of Panama / by Livio Leonardo Tornabene.

Tornabene, Livio Leonardo. January 2002 (has links)
Title from PDF of title page. / Document formatted into pages; contains 558 pages. / Original thesis submitted in HTML and can be accessed at http://www.lib.usf.edu/ETD-db/theses/available/etd-10122001-142859/unrestricted/frame.html / td.pdf / Thesis (M.S.)--University of South Florida, 2002. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: The Gatun Structure, (Latitude N 09° 05&softsign; 58.1", Longitude W 79° 47&softsign; 21.8", situated in the triple-canopy rainforest 10 km to the WSW of the Gamboa and about 2 km south of the Isle of Barbacoas, Republic de Panama), is a partially inundated, quasi-concentric surface feature 2.2 - 3km in diameter, which appears in aerial photographs and in radar imagery as an arcuate chain of islands with a raised center. Although the structure has been heavily weathered and altered, it has retained morphology consistent with complex craters: an elevated circular central uplift 500-600 m in diameter and 50m high, and arcuate boundary ridges (a rim structure?) ranging from 50-100 meters high. Within the central peak, highly altered and fractured siltstone of the Gatuncillo (?) formation (Eocene) (+-) older rocks are uplifted and exposed through surrounding calcareous units of the Caimito formation (Oligocene) and the Las Cascadas formation (Miocene), the major target rocks in the region. / ABSTRACT: Lithologies in the structure include highly fractured siliciclastic rocks (siltstone, sandstones and greywackes), limestones with anomalous spherical glass inclusions, both black and white hypocrystalline glasses (possible melt rocks), lithic fragmental breccias, and melt-bearing breccias (possible impact melt breccias and suevites), some of which contain flow banding and evidence for selective melting of minerals. Three types of spherules (glass, fluid-drop and lithic), a pyroxene-quartz "necklace" disequilibrium structure (coronas), plagioclase feldspars exhibiting mosaicism and partially amorphization, possible liquid immiscibility between melts of calcite and felpspathic glass, as well as decomposition of titanomagnite or ulvospinel, are all petrographic indicators of a hypervelocity impact event. / ABSTRACT: The structure is crosscut by numerous dikes of unshocked basalt and basaltic andesite related to volcanism along the Panamanian segment of the Central American arc to the south. However, the lithologies of the Gatun Structure are chemically inconsistent with the regional volcanic rocks and the unshocked volcanic rocks that crosscut the structure. The lack of an igneous relationship between the Gatun structure and the explosive volcanism of Panamanian arc the presence of classical shock lithologies within the site, and the occurrence of spherules, maskelynite and other disequilibrium shock features in the rocks, an impact origin is our preferred interpretation for the Gatun structure. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

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