The exhumation of the western Greater Caucasus: a thermochronometric study

Abstract

-This study provides 39 new thermochronometric analyses from the western part of the Greater Caucasus, a region in which existing data are extremely limited and of questionable quality. The new results are consistent with field studies that identify Triassic to Middle Jurassic (Cimmerian) and Oligo-Miocene (Alpine) orogenic erosional events. An inverse relationship between the fission track and depositional ages of Oligo-Miocene sedimentary samples also implies some degree of Eocene erosion of the Greater Caucasus and intermediate sediment storage. Cooling ages and field relationships within the core of the range, west of Mt Elbrus, require ∼ 5 km of Permo-Triassic exhumation and restrict the overall amount of Cenozoic exhumation to ∼ 2.5 km. Current exhumation rates are typically low, and do not support a Plio-Pleistocene increase in climate-driven denudation. High (∼ 1 km Ma −1 ) rates of exhumation are restricted to the southern flank of the range in northwest Georgia. Despite a general lack of significant seismicity within the study region, this exhumation peak is close to the largest instrumentally recorded earthquake in the Caucasus (Ms = 7.0). This may suggest that exhumation is associated with the decoupling of the sedimentary succession from its crystalline basement in the southern part of the range and the inversion of the largely Jurassic fill of the Greater Caucasus basin. Rates of exhumation are compatible with this being driven by active shortening. Further sampling and analysis are required to provide a higher-resolution, low-temperature thermochronology of Alpine exhumation, to isolate the drivers for Palaeogene Dziruli Massif cooling and uplift, and to constrain better the extent of the current, localized phase of rapid exhumation.

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

“…At 30 Ma an increase in cooling rate to ∼3°C-4°C/Myr is observed in this sample. This is consistent with post-30 Ma cooling rates observed in several other samples (this study and that by Vincent et al [2010]). Rapid cooling at ∼20°C/Myr begins at ∼5 Ma, and is observed in samples from all three trans- .…”

“…[32] Our complete Cenozoic history of the amount, rates, and timing of exhumation of the central Greater Caucasus differ significantly from studies of the western Greater Caucasus [Vincent et al, 2010]. Both studies identify an exhumational event beginning in late Eocene or Oligocene time, and yield similar rates of exhumation, as derived from thermochronometric data, throughout the Oligocene and Miocene.…”

“…One, using apatite fission track methods [Kral and Gurbanov, 1996], yielded a variety of cooling ages from the central portion of the Greater Caucasus, ranging from Paleogene to Pliocene, from which the most robust conclusion that can be drawn is that at least some portions of the Greater Caucasus have undergone significant post-Miocene exhumation. Another study, concentrated on the western end of the Greater Caucasus [Vincent et al, 2010], reveals slow post-Eocene exhumation of modest magnitude (less than 5 km).…”

Subduction, ophiolite genesis and collision history of Tethys adjacent to the Eurasian continental margin: new evidence from the Eastern Pontides, Turkey

“…Comparable Eocene gravity flows and volcanics are reported for hundreds of kilometres laterally (e.g. from N of the Tokat Massif (Yılmaz et al, 1997) to the Lesser Caucasus (Nikishin, Korotaev, Ershov, & Brunet, 2003;Sosson et al, 2010;Vincent et al, 2011 for regional setting)). A possible driving force for the required crustal extension was southwards rollback of the oceanic plate after collision, possibly related to crustal delamination.…”

Geometry and Cenozoic evolution of the Crimean fold-thrust belt from cross-section balancing and kinematic forward modeling

“…Deformation along the Western Greater Caucasus accommodated Cenozoic dextrally transpressive deformation between the Eastern Black-Sea basin and the Scythian plate. There, post-Eocene exhumation decreases from southeast to northwest from ~7 km to <5 km [Vincent et al, 2010;Avdeev, Niemi, 2011]. The Odessa and Western Crimean sinistral strike-slip faults indicate a northwestward propagation of the East BlackSea basin and northwest-southeast shortening across the southern rim of the Crimean peninsula.…”