Continental accretion and incremental deformation in the thermochronologic evolution of the Lesser Caucasus

Apatite fission-track analysis and thermochronologic statistical modeling of Precambrian-Oligocenc plutonic and metamorphic rocks from the Lesser Caucasus resolve two discrete cooling episodes.Cooling occurred during incremental crustal shortening due to obduction and continental accretion along the margins of the northern branch of the Neotethys.(1) The thermochronometric record of a Late Cretaceous(Turonian-Maastrichtian) cooling/exhumation event,coeval to widespread ophiolite obduction,is still present only in a relatively small area of the upper plate of the Amasia-Sevan-Akera(ASA) suture zone,i.e.the suture marking the final closure of the northern Neotethys during the Paleogene.Such area has not been affected by significant later exhumation.(2) Rapid cooling/exhumation occurred in the Early-Middle Miocene in both the lower and upper plates of the ASA suture zone,obscuring previous thermochronologic signatures over most of the study area.Miocene contractional reactivation of the ASA suture zone occurred contemporaneously with the main phase of shortening and exhumation along the Bitlis suture zone marking the closure of the southern branch of the Neotethys and the ensuing ArabiaEurasia collision.Miocene collisional stress from the Bitlis suture zone was transmitted northward across the Anatolian hinterland,which was left relatively undeformed,and focused along preexisting structural discontinuities such as the eastern Pontides and the ASA suture zone.