Transition from a singly vergent to doubly vergent wedge in a young orogen: The Greater Caucasus

Abstract

The Greater Caucasus Mountains, due to their youth (~5 Ma), provide an opportunity for insight into the early stages of orogen development during continent-continent collision. However, their recent tectonic evolution and first-order architecture remain unclear. Here we investigate the evolution of the orogen by integrating new observations of the fluvial geomorphology and neotectonics of the range with prior work on seismicity, geodetic strain, bedrock geology, and foreland basin structure. We find that the range contains four zones along strike that differ in structural architecture, topography, and first-order tectonic history. In particular, two south directed, singly vergent zones at the western and eastern tips of the orogen are separated by both a central doubly vergent zone that is dominated by north directed deformation and an eastern doubly vergent zone in which south directed thrusting dominates. We hypothesize that the along-strike changes in vergence and locus of deformation reflects different stages in the development of a doubly vergent orogen, with the tips of the range preserving an early, singly vergent form and the center recording a more advanced orogen. The differences between the two doubly vergent zones seem to be driven by the initial stages of collision between the structurally thickened crust of the Greater and Lesser Caucasus orogens, which initiated at~5 Ma.

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

“…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).…”

“…Major structural systems of the region. Greater Caucasus structure is from Forte et al (2014) and Lesser Caucasus, Eastern Pontide, and Eastern Anatolia structures are from Dhont and Chorowicz (2006) and Koçyigit et al (2001). (For interpretation of the references to color in this figure, the reader is referred to the web version of this article.)…”

“…In the simplest scenarios, higher convergence rates lead to wider orogens and greater relief, and greater erosivity leads to narrower orogens and lower relief (e.g., Whipple and Meade, 2004). In the GC, topographic metrics like local relief, mean elevation, and range width are similar along-strike despite the order of magnitude eastward increase in convergence rates determined from GPS velocity data and a moderate gradient in mean annual precipitation (e.g., Forte et al, 2014). Thus, in stark contrast to observations, modern gradients predict a wide, high relief orogen in the east and a narrow, low relief orogen in the west.…”

“…For example, (1) small rainfall events often do not generate enough runoff to incise into bedrock (e.g., Molnar et al, 2006) and thus mean rainfall may be a poor proxy for the geomorphically effective climate; and (2) base-level in this region is intimately linked with the history of the Caspian Sea, which experienced a partially climate driven 1-1.5 km base-level drop between 5.5 and ∼3.0 Ma ) that possibly drove increased exhumation of portions of the Caucasus draining into the Caspian (e.g., Ballato et al, 2015). With respect to tectonics, there may be an additional source of uplift in the western GC due to (1) slab detachment (Mumladze et al, 2015) or delamination (Ershov et al, 2003); and/or (2) an along-strike change in the accretion rate or crustal structure within the GC (Forte et al, 2014). Climatic and tectonic mechanisms make distinct predictions in terms of the spatial distribution of metrics of topography, climate, and uplift and erosion rates throughout the Caucasus regions.…”

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).…”