Orogen-scale Structural Architecture and Potential Seismic Sources Resulting from Cenozoic Closure of a Relict Mesozoic Ocean Basin in the Greater Caucasus
Abstract
Between the Black and Caspian Seas, virtually all Arabia-Eurasia convergence is currently localized within the Greater Caucasus. Thus, determining the late Cenozoic structural evolution of this range is essential for understanding its first-order structural architecture and associated potential seismic sources. New structural mapping, thermochonologic data, preliminary U-Th-Pb analyses of detrital zircons, and syntheses of the regional geology together indicate that the first-order architecture of the Greater Caucasus is broadly analogous to that of the Himalayas, with active faulting localized in a foreland-fold thrust belt above a gently north-dipping basal thrust that roots to the north into a crustal-scale ramp beneath the Greater Caucasus. Here we hypothesize that this geometry results from Cenozoic closure of a relict Mesozoic ocean basin, with closure starting in Late Eocene time and eventually leading to collision at about 5 Ma between the Lesser and Greater Caucasus. The Greater Caucasus is generally interpreted to result from tectonic inversion of a Jurassic-Cretaceous aged back-arc basin that originally opened north of similarly aged volcanic arcs in the Lesser Caucasus due to slab rollback of a north-dipping subduction zone along the northern margin of the Neotethys ocean [e.g., 1, 2, 3]. This back-arc basin appears to have remained open into the Miocene, forming a remnant ocean basin within the Arabia-Eurasia collision zone, broadly similar to the eastern Black Sea and South Caspian Basins to which it was connected. We hypothesize that Cenozoic closure of this basin produced a suture that is now hidden within the Greater Caucasus. Pilot results from U-Th-Pb analyses of detrital zircons from bedrock sandstone samples on opposite sides of the range support this idea. In detail, we find that turbidite and flysch deposits on the north side of the Greater Caucasus were derived from Paleozoic to early Mesozoic sources (northern domain) that are largely distinct from Mesozoic and younger sources for deposits on the south side of the range (southern domain). This contrast in provenance is consistent with the idea that an intervening ocean basin separated these sediments. Modern sand samples from two rivers draining the Greater Caucasus reflect simple mixing of materials derived from the northern and southern domains. Two modern rivers in the Lesser Caucasus have zircon populations that are broadly similar to those of the bedrock sandstone samples from the southernmost Greater Caucasus, suggesting that the Lesser Caucasus extends beneath the Rioni-Kura basin as a large composite terrane and is now exposed in thrust sheets on the southern margin of the Greater Caucasus. 1. Adamia, S., Lordkipandize, M.B., and Zakariadze, G.S., 1977, Tectonophysics, v. 40, p. 183-199. 2. Gamkrelidze, I.P., 1986, Tectonophysics, v. 127, p. 261-277. 3. Zonenshain, L.P., and Le Pichon, X., 1986, Tectonophysics, v. 123, p. 181-211.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.S43J..07C
- Keywords:
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- 7230 SEISMOLOGY / Seismicity and tectonics;
- 8102 TECTONOPHYSICS / Continental contractional orogenic belts and inversion tectonics;
- 8108 TECTONOPHYSICS / Continental tectonics: compressional