Metamorphic evolution of high-pressure–low-temperature rocks from the northern section of the Guatemala Suture Zone: PTt paths and tectonic implications

Thursday, 18 December 2014
Kennet E Flores1, Sidney R Hemming2, George E Harlow1, Yue Cai2, Guillaume Bonnet1,3, Celine Martin1 and Hannes K Brueckner2, (1)American Museum of Natural History, New York, NY, United States, (2)Lamont -Doherty Earth Observatory, Palisades, NY, United States, (3)Ecole Normale Supérieure Paris, Paris, France
The Guatemala Suture Zone (GSZ) is located along the left-lateral strike slip boundary between the North American and Caribbean plates in central Guatemala. This highly tectonized geotectonic unit contains a variety of metamorphic complexes thrusted north and south of the plate boundary. The northern section of the GSZ consists of (a) a serpentinite-matrix mélange that contains high-pressure–low-temperature (HP–LT) rocks, (b) a continental high-grade felsic belt that includes relics of eclogite facies, (c) a low-grade disrupted volcano-sedimentary sequence, and (d) large ultramafic bodies associated with fragments of Cretaceous island arc sequences. Currently, this section of the GSZ is interpreted as the result of subduction-exhumation-collision and obduction in a back-arc basin.

However, our new petrochronological study challenges this simple interpretation because multiple metamorphic ages (Sm–Nd, U–Pb and Ar–Ar) and different PT paths are recorded in the HP–LT rocks. Eclogites within the mélange display a polymetamorphic history consisting of a metamorphic peak at 130–125 Ma and ~60 km depth, an early exhumation to the middle section of a subduction channel (~35 km) at 117–116 Ma, a subsequent metamorphic event at amphibolite facies and a final exhumation at ~85 Ma. In contrast, continental eclogites show a younger metamorphic peak of 77–75 Ma at ~80 km depth, and exhumation ages of ~76–66 Ma. Synchronous jadeitite and mica rocks within the mélange yielded crystallization and exhumation ages of ~ 95 Ma and ~77–53 Ma, respectively.

These PTt paths reveal a complex history that can be linked to multiple tectonic events during subduction. Ages and PT conditions of eclogites within the mélange suggest an early coupling and storage of eclogitic slices in the subduction channel. Their subsequent record at lower P and higher T may indicate the initiation of continental crust subduction which will have increased the subduction thermal gradient. Continuous subduction and fluid infiltration into the mantle wedge is indicated by the occurrence of jadeitites and mica rocks within the serpentinite mélange. Finally, the metamorphic peak of continental eclogites may mark the end of subduction and beginning of exhumation of the subduction channel and the subducted continental crust during a major collisional event.