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Early Tertiary arc volcanics from eastern Panama

By
René C. Maury
René C. Maury
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Marc J. Defant
Marc J. Defant
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Hervé Bellon
Hervé Bellon
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Jelle Zeilinga de Boer
Jelle Zeilinga de Boer
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Robert H. Stewart
Robert H. Stewart
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Joseph Cotten
Joseph Cotten
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Published:
January 01, 1995

Early Tertiary volcanic clasts were collected from the streambed of the Rio Morti near the village of Morti, eastern Panama, as part of a reconnaissance study. The samples range from basalts to rhyolites. K-Ar dates cluster around 58 Ma. The phenocryst mineralogy of the samples is typical of that found in arc-related volcanics: plagioclase (the dominant phase), clinopyroxene, titanomagnetite, and minor orthopyroxene. The clinopyroxenes are augites that plot in the field of orogenic lavas. The geochemistry of the rocks—high ratios of large-ion lithophile elements to high-field strength elements, negative Nb and Ta anomalies, positive Ba anomalies, and relatively low Th to U values—confirms that they are arc related (specifically the calc-alkaline series) and strongly suggests that the samples are not cogenetic.

Volcanic rocks with similar ages are exposed in several other localities throughout Panama and Costa Rica (e.g., the Azuero and Sona Peninsulas in Panama and the Nicoya Peninsula in Costa Rica as well as other areas in the Darien of eastern Panama). We suggest that there may have been a more or less continuous arc from South America to the Chortis block of Nicaragua during the Paleocene-Early Eocene. The presence of the arc would imply that the breakup of the Farallon plate and its subduction below the new Caribbean plate in present-day southern Central America probably started some time close to the Cretaceous-Tertiary boundary.

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GSA Special Papers

Geologic and Tectonic Development of the Caribbean Plate Boundary in Southern Central America

Paul Mann
Paul Mann
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Geological Society of America
Volume
295
ISBN print:
9780813722955
Publication date:
January 01, 1995

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