20. HISTORY OF CIRCUM-CARIBBEAN EXPLOSIVE VOLCANISM: 40Ar/39Ar DATING OF TEPHRA LAYERS1

H. Sigurdsson,2 S. Kelley,3 R.M. Leckie,4 S. Carey,2 T. Bralower,5 and J. King2

ABSTRACT

Drilling in the Caribbean Sea during Ocean Drilling Program Leg 165 has recovered a large number of silicic tephra layers and led to the discovery of three major episodes of explosive volcanism that occurred during the last 55 m.y. on the margins of this evolving ocean basin. The earliest episode is marked by Paleocene to early Eocene explosive volcanism on the Cayman Rise, associated with activity of the Cayman arc, an island arc that was the westward extension of the Sierra Maestra volcanic arc in southern Cuba. Caribbean sediments also document a major mid- to late Eocene explosive volcanic episode that is attributed to ignimbrite-forming eruptions on the Chortis Block in Central America to the west. This event is contemporaneous with the first phase of activity of the Sierra Madre volcanic episode in Mexico, the largest ignimbrite province on Earth. In the Caribbean sediments, a Miocene episode of explosive volcanism is comparable to the Eocene event, and also attributed to sources in the Central American arc to the west. Radiometric 40Ar/39Ar dates have been obtained for biotites and sanidines from 27 tephra layers, providing absolute ages for the volcanic episodes and further constraining the geochronology of Caribbean sediments. Volcanic activity of the Cayman arc is attributed to the northward subduction of the leading edge of the oceanic plate that carried the Caribbean oceanic plateau. Although the factors generating the large episodes of Central American explosive volcanism are unclear, we propose that they are related to contemporary major readjustments of plate tectonic configuration in the Pacific.

1Leckie, R.M., Sigurdsson, H., Acton, G.D., and Draper, G. (Eds.), 2000. Proc. ODP, Sci. Results, 165 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/165_SR/165TOC.HTM>. [Cited YYYY-MM-DD]

2Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, U.S.A. haraldur@gsosun1.gso.uri.edu

3Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom.

4Department of Geosciences, University of Massachusetts, Amherst, MA 01003, U.S.A.

5Department of Geological Sciences, University of North Carolina, Chapel Hill, NC 27599, U.S.A.

Date of initial receipt: 10 February 1999
Date of acceptance: 27 August 1999
Ms 165SR-021

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