A Late Permian Tectonothermal Event In Grenville Crust Of The Southern Maya Terrane: U-Pb Zircon Ages From The Chiapas Massif, Southeastern Mexico

The Chiapas massif (CM) in southeastern Mexico is the crystalline basement of tire southern Maya terrane, which is a crustal block that comprises mainly the Yucatan Peninsula, the Mexican states of Chiapas, Veracruz, and parts of Oaxaca. The CM is composed of igneous rocks and medium-to high-grade metamorphic rocks. Zircon fractions from all samples are discordant, yielding Late Permian lower-intercept ages and > 1 Ga upper-intercept ages. The most precise results are from an orthogneiss that yielded intercept ages of 258.4 +/- 1.9 Ma arid 1046.6 +/- 5.6 Ma, and from two augen gneisses which yielded intercepts of 250.9 +/- 2.3 Ma arid 1017 +/- 27 Ma. We interpret the lower intercepts as either igneous crystallization or metamorphic ages and the upper intercepts as the age of inherited components. Results from all other samples are within error of these ages. These results demonstrate that the CM basement contains a Grenvillian component, arid that the most important tectonothermal event affecting the CM was of Late Permian age. The results favor a hypothetical model in which the Maya terrane is composed of separated blocks of different geologic histories.