U-Pb AGE CONTSRAINTS ON EARLY CRETACEOUS VOLCANISM AND STRATIGRAPHY IN CENTRAL HONDURAS

DROBE, John,§ Tombstone Explorations Co. Ltd., 409 Granville St., Vancouver, B.C. Canada V6C 1T2, and OLIVER, Douglas H., Dept. of Geological Sciences, Southern Methodist Univ., Dallas, TX, USA 75275, mailto:oliver@mail.smu.edu

Conglomerates containing volcanic clasts occur within a previously unrecognized stratigraphic succession in the Cordillera Central of west-central Honduras. The succession, informally called the San Antonio sequence, is exposed west of the town of Minas de Oro. The sequence consists of calcareous siliciclastic sediments that unconformably overlie maroon tuff and dacitic volcanics. The sediments fine upward from a basal conglomerate to calcareous sandstone and siltstone to discontinuous micritic limestone. Turbidites consisting of interbedded sandstone and siltstone cap the sequence. The San Antonio sequence has an aggregate thickness of approximately 750 m. The Minas de Oro area is structurally complex with NW-trending normal faults superimposed on pre-existing NE-trending sinistral shear zones and S-vergent folds. Emplacement of the ~65 Ma Minas de Oro granodiorite reactivated structures and resulted in widespread metasomatism in the calcareous host rocks. Sedimentation in central Honduras spanned the Late Jurassic to Late Cretaceous and is marked by a repetition of carbonate and silciclastic units with dacitic volcanics frequently reported from several different stratigraphic units. Consequently, the stratigraphic placement of the San Antonio sequence is not well constrained. U-Pb (zircon) dating of the dacite gave a concordant age of 124~2.0 Ma. This demonstrates that the dacitic volcanics are not genetically related to the Minas de Oro granodiorite and provides a maximum age for the San Antonio sequence. The Early Cretaceous age places the San Antonio sequence between the Albian-Aptian Yojoa Group and Upper Jurassic to Lower Cretaceous Honduras Group. The San Antonio sequence may be correlative with the thinly bedded marls of the Cantarranas Formation.

Reference:

Drobe, John (Tombstone Explorations Company, Vancouver, BC, Canada) and Oliver, Douglas H. U-Pb age constraints on Early Cretaceous volcanism and stratigraphy in Central Honduras [abstr.]: in 1998 abstracts with programs; the Geological Society of America 94th annual meeting; cordilleran section, Abstracts with Programs - Geological Society of America, 30(5), p. 12, March 1998.

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