Rapid Pliocene exhumation of the central Greater Caucasus constrained by low‐temperature thermochronometry

Abstract

[1] Constraining the timing of onset and rates of deformation within the Greater Caucasus mountains is key to understanding their role in accommodating deformation across the Arabia-Eurasia orogen. We present new low-temperature thermochronometric constraints on the Cenozoic thermal evolution of the central Greater Caucasus that elucidate a three-phase cooling history. Between 50 and 30 Ma, cooling within the range was negligible. In Oligocene time, cooling rates throughout the range increased to ∼4°C/Myr. These rates remained constant until the early Pliocene time, when they increased again, reaching ∼25°C/Myr along the axial part of the range. Rates and timing of Oligocene exhumation are consistent with previous results from the western Greater Caucasus and are proposed to result from onset of subduction of the Greater Caucasus back-arc basin. Rapid exhumation of the Greater Caucasus, beginning in Pliocene time, contrasts with previously reported thermal histories for other portions of the range. Pliocene exhumation of the central Greater Caucasus appears to be tectonically driven and coincides with widespread evidence for a major reorganization of the Arabia-Eurasia plate boundary. We hypothesize that this exhumation, and regionally observed plate reorganization, results from the collision of the Lesser Caucasus with Eurasia, completing the subduction of oceanic lithosphere across this segment of the Arabia-Eurasia plate boundary.

Petroleum geology of the Black Sea: introduction

“…Lozar & Polino 1997;Adamia et al 2011) draw similar conclusions, and abundant evidence exists that Crimea experienced Eocene, then Oligocene, uplift (Panek et al 2009;Nikishin et al 2017). Conversely, Avdeev & Niemi (2011), Forte et al (2014 and Cowgill et al (2016) have suggested that the major phase of uplift occurred no earlier than c. 5 myr ago, whereas Rolland (2017) prefers a Miocene (c. 15 Ma) age for the onset of Caucasus uplift, based on geodynamic context and fission-track constraints on 'hard' Arabia-Eurasia collision (e.g. Okay et al 2010).…”

Decoupling of modern shortening rates, climate, and topography in the Caucasus

“…2a), mean k sn and S avg (Fig. 6c) with apatite (U-Th)/He and fission track cooling ages (Avdeev, 2011;Avdeev and Niemi, 2011;Král and Gurbanov, 1996;Vincent et al, 2011) suggest broadly similar patterns (Figs. 2 and 3).…”

“…1, Mosar et al, 2010) and are underlain by a north dipping subducted slab extending to at least 160 km depth (Mumladze et al, 2015). Thermochronometric data suggest more rapid uplift of ∼1 mm/y in the center of the range, with slower rates of exhumation as low as 0.1 mm/y along the tips (Avdeev, 2011;Avdeev and Niemi, 2011;Král and Gurbanov, 1996;Vincent et al, 2011). However, data is concentrated in the western GC so it is unclear if this pattern continues eastward (Fig.…”

“…1, Allen et al, 2004). The majority of active shortening structures within the GC are along the margins of the range and within the forelands but the interior of the GC is still experiencing active uplift (Avdeev and Niemi, 2011;Forte et al, 2014;Mosar et al, 2010).…”

The 2011 Mw 7.1 Van (Eastern Turkey) earthquake

“…The high geothermal gradients associated with the volcanism therefore imply that earthquakes are only likely to occur down to depths of less than 10-15 km, as observed in most other mountain ranges [Molnar and Lyon-Caen, 1989;Nissen et al, 2011]. One possibility for the deep extent of slip in the 2011 Van event lies within the portion of the Arabian Plate that was underthrust beneath the southern margin of the Turkish-Iranian Plateau before shortening jumped north to the Greater Caucasus at 5 Ma [Avdeev and Niemi, 2011]. Lake Van lies at the northern edge of the region of efficient Sn propagation mapped by Gök et al [2003], who suggest that the lithospheric mantle is hot or absent north of this boundary, and cooler south of it.…”