International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Paleozoic xenoliths in Eocene plutons: The evidence for the destruction of pre-Jurassic crystalline basement beneath Adjara–Trialeti belt, Lesser Caucasus

Published:

Pages: 299 - 314

DOI: https://doi.org/10.31577/GeolCarp.72.4.2

Authors: AVTANDIL OKROSTSVARIDZE, YU-HAN CHANG, SUN-LIN CHUNG, FABIEN RABAYROL, GIORGI BOICHENKO, SALOME GOGOLADZE

Abstract: In Georgia the Paleogene Adjara–Trialeti riftogenic belt (length 350 km, width 50–2 km) is dominantly composed of trachytic and trachytic–andesitic pyroclastic deposits, though plutonic rocks also play an important role in the structure. In this article, we report new data on the (LA-ICP-MS) U–Pb zircon geochronology and petrochemistry of the plutons, their xenoliths and restite from this belt. The results indicate that the magmatism in the basin began in the Early Eocene (~50 Ma) associated with the formation of pyroclastic rocks. The mafic intrusions (~46–44 Ma) led to the assimilation and contamination of sialic crust and formation of monzo-syenite melts emplaced at ~43–42 Ma. The Eocene monzo-syenite plutons contain xenoliths of Paleozoic granites (312±7 to 474±5 Ma) and tholeiitic basalts that contain inherited zircon grains ranging in age from Neo-Proterozoic (747±33 Ma, 632±29 Ma) to Cambrian (515±9 Ma). Paleozoic granite xenoliths show complete mineralogical and age similarity to the Adjara–Trialeti belt adjacent pre-Jurassic massif granites. Inherited zircon grains most likely are captured by magmas during ascent that cuts through the Gondwana-derived old continental crust. Obtained results and regional geological analysis demonstrate that the riftogenic basin of the Adjara–Trialeti belt developed on the pre-Jurassic crystalline basement, from Late Cretaceous to Eocene into a back-arc extensional regime to post-collision geodynamic setting.

Keywords: Adjara–Trialeti belt, plutons, xenolith, zircon U–Pb geochronology

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