Other
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm...p41b02t&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #P41B-02
Other
1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 3600 Mineralogy And Petrology (Replaces, 5420 Impact Phenomena (Includes Cratering)
Scientific paper
The Gatun Structure, (Latitude N 09 deg 05' 58.1", Longitude W 79 deg 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 2.2km in diameter, which appears in aerial photographs and in radar imagery as an arcuate chain of islands with a raised central feature. Although deeply eroded, the structure possesses traits consistent with complex crater morphology: an elevated circular central uplift feature approximately 500-600 m in diameter and 50m high, and arcuate boundary ridges (a possible rim structure) ranging from 50-100 meters high. Within the central peak, highly altered and fractured siltstone of the Gatuncillo formation (Eocene) are uplifted and exposed through surrounding calcareous units of the Caimito formation (Oligocene), the major target rocks in the structure. 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. Analysis of mineral assemblages of units within the structure, and mineral compositions were measured via SEM-EDS and electron microprobe, using the JEOL SEM-Probe facility at the Center for the Study of Materials in Extreme Conditions (CeSMEC) at Florida International University. Bulk chemical and trace element analysis of whole rock samples were conducted via DC Plasma spectrometry at USF. Occurring concentrically within the structure, are limestones with anomalous spherical glass inclusions, both black and white hypocrystalline glasses (melt rocks?), lithic breccias, and melt-bearing breccias, some of which contain flow banding and evidence of selective melting. Three types of spherules (glass, fluid-drop and lithic), a pyroxene-quartz "necklace" disequilibrium structure and possibly shocked amphibole are all petrographic indicators of a possible impact event. In addition, the presence of maskelynite has been based on petrography, SEM-EDS and by RAMAN spectroscopy. RAMAN results indicated that many plagioclase grains in a blue-green clast bering breccia (suevite?) were highly disordered and amorphous. Considering the distance of the Gatun structure from the explosive volcanism of Panamanian arc (approximately 30 km away), and the presence of spherules, maskelynite and other disequilibrium shock features, an impact origin is our preferred interpretation for the Gatun structure.
Ryan Jeff G.
Stewart R. H.
Tornabene Livio L.
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