Ordovician to Silurian igneous rocks in southern Mexico and Central America: geochronologic and isotopic constraints on paleogeographic models

Exposures of Ordovician to Silurian magmatic rock in southern Mexico and Central America constitute dismembered parts of an early Paleozoic belt related to the interaction of terranes of northwestern Gondwana with southern Laurentia. Convergent and extensional tectonic scenarios have been proposed to explain the origin of the magmatic activity along this belt. New U-Pb geochronological data, as well as Hf and Nd isotopic analyses were performed on five representative granitoids from southern Mexico and Central America to evaluate the timing and environment of emplacement. Samples from the Acatlan Complex in southern Mexico, as well as from the Altos Cuchumatanes, Rabinal and Chuacds areas along the southern Maya block yield Ordovician (470.9 Ma) to Silurian (427.1 Ma) crystallization ages. These samples have epsilon Hf values ranging from -6.4 to + 1.0 and extraction ages (T-DM) between 1.15 and 1.53 Ga, which match with epsilon Nd whole rock values ranging from -2.4 to -5.3 and T-DM between 1.20 and 1.53 Ga. The Hf and Nd isotope compositions suggest incorporation of an evolved crustal reservoir, probably an Oaxaquia-type basement. Our data would better support a convergent tectonic scenario for the origin of the lower Paleozoic granitoids, possibly comprising an extension of the Famatinian arc of northwestern south America.