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Evidence for middle Eocene and younger land emergence in central Panama; implications for isthmus closure

Camilo Montes, A. Cardona, R. McFadden, S. E. Moron, C. A. Silva, S. Restrepo-Moreno, D. A. Ramirez, N. Hoyos, J. Wilson, D. Farris, G. A. Bayona, C. A. Jaramillo, V. Valencia, J. Bryan and J. A. Flores
Evidence for middle Eocene and younger land emergence in central Panama; implications for isthmus closure
Geological Society of America Bulletin (January 2012) 124 (5-6): 780-799


The rise of the Isthmus of Panama, linked to a number of climatic, paleoceanographic, and biological events, has been studied mostly from indirect, often distal, geochemical and biotic evidence. We have upgraded existing geologic mapping in central Panama with more than 2000 field stations, over 40 petrographic analyses, and more than 30 new geochronological and thermochronological analyses. This data set suggests that the isthmus was an uninterrupted chain above sea level from late Eocene until at least late Miocene times. The basement complex of central Panama is a folded-faulted, approximately 3-km-thick arc sequence, intruded by granitoid bodies and onlapped by mildly deformed upper Eocene and Oligocene strata. Six U/Pb zircon ages in the granitoids-along with published geochronological data--reveal intense late Paleocene to middle Eocene magmatism (58-39 Ma), a temporary cessation of magmatic activity between 38 and 27 Ma, and renewed magmatism between 25 and 15 Ma in a position approximately 75 km south of the former magmatic axis. Thermochronological analyses in zircon (eight U-Th/He ages), and in apatite crystals (four U-Th/He ages and nine fission-track ages) obtained from a subset of 58-54 Ma granitoid bodies record a concordant Lutetian-age (47-42 Ma) cooling from approximately 200 degrees C to approximately 70 degrees C in approximately 5 m.y., and cooling below approximately 40 degrees C between 12 and 9 Ma. Cooling is linked to exhumation by an angular unconformity that separates the deformed basement complex below from mildly deformed, upper Eocene to Oligocene terrestrial to shallow-marine strata above. Exhumation and erosion of the basement complex are independently confirmed by lower Miocene strata that have a detrital zircon signature that closely follows the central Panama basement complex age distribution. These results greatly restrict the width and depth of the strait separating southern Central America from South America, and challenge the widely accepted notion that the Central American Seaway closed in late Pliocene time, when the ice age began.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 124
Serial Issue: 5-6
Title: Evidence for middle Eocene and younger land emergence in central Panama; implications for isthmus closure
Affiliation: Smithsonian Tropical Research Institute, Balboa, Panama
Pages: 780-799
Published: 20120113
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 105
Accession Number: 2012-037559
Categories: StratigraphyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendix; with GSA Data Repository Item 2012073; accessed on March 26, 2012
Illustration Description: illus. incl. sects., strat. cols., 4 tables, geol. sketch map
Source Medium: WWW
N08°45'00" - N09°49'60", W80°00'00" - W78°00'00"
Secondary Affiliation: Florida State University, USA, United StatesCorporacion Geologica Ares, COL, ColombiaUniversity of Arizona, USA, United StatesNorthwest Florida State College, USA, United StatesUniversidad de Salamanca, ESP, Spain
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201220
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