GEODYNAMIC EVOLUTION AND TECTONIC HISTORY OF THE OPHIOLITES AND SERPENTINITE MÉLANGES IN THE GUATEMALA SUTURE ZONE

The Guatemala Suture Zone (GSZ) is the fault-bound region in central Guatemala that contains the present North American–Caribbean plate boundary. It is bounded by the Maya Block to the north and Chortís Block to the south and contains a variety obducted “ophiolites”, high-grade schist and gneisses, serpentinite mélanges, accreted metavolcanic bodies, low-grade schist and metasediments. This major composite geotectonic unit contains four major oceanic crust bodies and two serpentinite mélanges bearing high-pressure–low-temperature (HP–LT) rocks. The latter assemblages were previously defined as “ophiolites” and are thrust north and south of the active left-lateral transform, the Motagua fault system (MFS).

Classically, the GSZ has been interpreted as the result of a single progressive collision between an island arc related to the Chortís Block and the Maya Block passive margin. This model was based on the geochemical signatures of basaltic rocks from the “ophiolitic” sequences. Our research results challenge this geodynamic scenario because multiple metamorphic ages and PT paths recorded in the HP–LT rocks. Moreover, there are major contrasts in the geochemical signatures and geotectonic settings recorded by the “ophiolites” from both sides of the MFS.

Our new data suggest two major tectonic events occurred within the GSZ: first a Jurassic-Early Cretaceous oceanic accretion/collision and exhumation in the active margin, and second a Late Cretaceous island arc-passive margin collision-exhumation and subsequent obduction probably related to a back-arc closure. This two suture zone system was modified by a major Cenozoic left-lateral displacement along the then active margin which restructured the original tectonic arrangement into the present complex. Important distinctions in these interpretations are based on multiple lines of evidence, including the difference between ophiolite and serpentinite mélange, a sometimes overlooked or under-appreciated differentiation.