THE TRANSPRESSIVE LEFT-LATERAL SIERRA MADRE DE CHIAPAS AND ITS BURIED FRONT IN THE TABASCO PLAIN (SOUTH MEXICO)

The Sierra Madre de Chiapas evolved in the vicinity of the triple junction between the Cocos, North America and Caribbean plates. Major exhumation and topographic growth occurred during the middle-late Miocene. This is constrained by fault activity, major stratigraphic unconformities along the SMC and the Tabasco coastal plain (i.e. southern Gulf of Mexico), major salt-related motion, northward progradation of sediments and by the northward migration of the buried deformational front. During Neogene, strike slip deformation and related exhumation has migrated landwards from the western edge of the Chiapas massif to the Chiapas Sierra. Horizontal displacement along the main strike-slip faults on the Sierra may be comprised between 30 and 43 km during the last 6-5 Ma involving 0.5-0.8 cm/a of lateral accommodation. These values suggest that a significant amount of the motion transferred from the Caribbean and North American plates is currently accommodated along the Chiapas area.

Sediment provenance and low temperature thermochronology results show that Palaeocene-Eocene terrigenous units (outcropping at the northern section of the Sierra) were derived from Grenville (~1Ga) basement whereas internal section of the chain display Chiapas massif-derived (270-250 Ma) components. Batholith-related input increases with the onset of major tectonic deformation at 16-9 Ma. Apatite fission track and (U-Th)/He data combined with previously published results define three main exhumation periods: 1) A slow 40-25 Ma exhumation affecting the massif and relatively unexpressed along the Chiapas Sierra; 2) A fast 16-9 Ma exhumation period related to the onset of major strike slip deformation related to the Caribbean-North American plates limit and affecting both Chiapas massif and Chiapas Sierra; and 3) A 6-5 Ma period affecting the Sierra and coincident with the landward migration of the plate limit. Stratigraphic, cinematic and termochronologic evidence suggests that the left-lateral strike-slip faults bounding the Chiapas Sierra to the west accommodates most of the current displacement between the North American and Caribbean plates.