Thin-and thick-skinned nappes of the southern slope of the Georgian Greater Caucasus: indicators of syn-collisional A-type subduction

Abstract

In the region of the Caucasus considered herein two large structural complexes have been identified: an autochthone, including the Gagra-Java zone (GJZ) of the Greater Caucasus fold-and-thrust belt, the Kura foreland basin (KFB), and an allochthone consisting of the Utsera-Pavleuri, Alisisgori-Chinchvelta, Sadzeguri- Shakhvetila, Zhinvali-Pkhoveli nappes and Ksani-Arkala parautochthone. The nappes are established on the basis of paleogeographic reconstructions, structural data, as well as drilling and geophysical data. The leading mechanism for the nappe formation is the advancement to the north and the underthrusting of the autochthone under the Greater Caucasus (A-type subduction). The nappes were formed mainly in the Late Alpine time (Late Eocene–Early Pliocene) and include only the sedimentary cover of the Earth’s crust (thin-skinned nappes). However the basal detachment (décollement) of the nappes, according to seismic data, penetrates deeply and cuts the pre-Jurassic crystalline basement, and even the entire Earth’s crust representing thick-skinned deformation. The total horizontal displacement of the flysch nappes of the southern slope of the Greater Caucasus in their eastern (Kakhetian) part is 90–100 km. While, considering the folding of the entire Greater Caucasus, the total transverse shortening of the Earth‘s crust within its limits is equal to 190–200 km.