DATING TECTONIC EVENTS on THE CHORTíS BLOCK

The Chortís block, a continental terrane now part of the Caribbean plate, has poorly constrained basement age data. We dated metamorphic and plutonic rocks from the Chortís block with U-Pb (zircon), ⁴⁰Ar/³⁹Ar (amphibole, white mica and biotite), fission track (zircon and apatite) methods. The Cacaguapa Schist forms the oldest unit of the Chortís block underlying the well-dated Jurassic to Cretaceous strata. The outcrop area mostly contains fine-grained phyllite with less abundant schists and metaigneous rocks. Metaplutonic units in central Honduras yielded U-Pb ages with lower intercepts of about 400 Ma and upper intercepts of 1 Ga. A white mica from the Cacaguapa Schist in east-central Honduras has a ⁴⁰Ar/³⁹Ar age of 330 Ma, and a metagranite south of the Valle de Catacamas an U-Pb zircon lower intercept age of about 270 Ma.

North of the Chamelecón fault in the Sula graben, Mesozoic sedimentary rocks do not overlie the metamorphic rocks. An amphibolite has a concordant U-Pb age of 88 Ma and an amphibole ⁴⁰Ar/³⁹Ar age of 40 Ma. A nearby metagranite has a concordant U-Pb zircon age of 38 Ma.

Zircon fission track ages from central Honduras area have ages from 177 Ma to 92 Ma. One sample has an apatite fission track age of 51 Ma probably representing slow cooling and exhumation of the Chortís block. However, the augen schist (24 Ma) and the member rich in sodic feldspar (14 Ma) have much younger apatite fission track ages dating the exhumation of the footwall of a graben.

The igneous and metamorphic rocks of the Sula graben show rapid exhumation with nearly concordant zircon fission track and biotite ⁴⁰Ar/³⁹Ar ages. Zircon fission track ages range from 27 to 15 Ma. Apatite fission track ages for the Sula graben range from 14 Ma to 10 Ma. These ages indicate late Tertiary exhumation of the Sula graben footwall.

The central core of the Chortís block developed in the Paleozoic with a Grenville inheritance. This is consistent with the block being derived from Laurentia. The northern margin of the Chortís block experienced tectono-thermal activity in the late Cretaceous and Eocene. The central core of the Chortís block resided at 100-250°C and was stable in the Mesozoic. Both the northern margin and the central core experienced exhumation of fault blocks in the late Cenozoic.