THE THERMO-TECTONIC HISTORY OF SOUTHERN MEXICO, PRELIMINARY RESULTS FROM THE CHIAPAS MASSIF

Southern Mexico, comprising the Sierra Madre del Sur and the Chiapas Massif, records a tectonic history which has not been properly established between the Late Cretaceous and Miocene and which is currently matter of debate. Part of these discrepancies are due to the fact that the timing and style of the deformation and magmatism migration observed in Southern Mexico could not yet been linked with any definitive plate tectonic restoration.

The complex interaction between continental Mexico and other oceanic and continental crustal elements since the Late Cretaceous should be recorded in the thermal history of the rocks in question. In late 2011 we performed a systematic thermochronological aimed sampling along several traverses spanning the Sierra Madre Sur and the Chiapas Massif from Acapulco to the southern Mexican border with Guatemala in order to improve the constraints on the timing and magnitude of the tectonic events that affected and shaped the western margin of Southern Mexico. This thermochronological project includes different methods spanning temperatures below ~550°C (in order to constrain the upper 15-17 km of the crust), which will be complemented with currently on-going geochronological and tectonic studies.

We aim to see across- and along-strike variations in cooling and exhumation that could shed light on the time and mechanism of the deformation (e.g. the role of the passage of Chortis, the role of particular major faults) and the transfer of the deformation towards the foreland basins.

By the time of the conference we will present preliminary results from the Chiapas Massif including medium (apatite U-Pb, closure temperature of ~550-450°C) and low temperature thermochronology (apatite fission track, data between ~120-60°C) obtained from the Permian-Triassic metagranites and Tertiary intrusive rocks outlining the implications for the onset of the Chiapas Foreland Basin and subsequent fold and thrust history.