Building a Young Mountain Range: Insight Into the Growth of the Greater Caucasus Mountains From Detrital Zircon (U‐Th)/He Thermochronology and ¹⁰Be Erosion Rates

Abstract

The Greater Caucasus (GC) Mountains within the central Arabia‐Eurasia collision zone are an archetypal example of a young collisional orogen. However, the mechanisms driving rock uplift and forming the topography of the range are controversial, with recent provocative suggestions that uplift of the western GC is strongly influenced by an isostatic response to slab detachment, whereas the eastern half has grown through shortening and crustal thickening. Testing this hypothesis is challenging because records of exhumation rates mostly come from the western GC, where slab detachment may have occurred. To address this data gap, we report 623 new, paired zircon U‐Pb and (U‐Th)/He ages from seven different modern river sediments, spanning a ∼400 km long gap in bedrock thermochronometer data. We synthesize these with prior bedrock thermochronometer data, recent catchment averaged 10Be cosmogenic exhumation rates, topographic analyses, structural observations, and plate reconstructions to evaluate the mechanisms growing the GC topography. We find no evidence of major differences in rates, timing of onset of cooling, or total amounts of exhumation across the possible slab edge, inconsistent with previous suggestions of heterogeneous drivers for exhumation along‐strike. Comparison of exhumation across timescales highlight a potential acceleration, but one that appears to suggest a consistent northward shift of the locus of more rapid exhumation. Integration of these new datasets with simple models of orogenic growth suggest that the gross topography of the GC is explainable with traditional models of accretion, thickening, and uplift and does not require any additional slab‐related mechanisms.

Tectonics, Base‐Level Fluctuations, and Climate Impact on the Eocene to Present‐Day Erosional Pattern of the Arabia‐Eurasia Collision Zone (NNW Iranian Plateau and West Alborz Mountains)

“…These types of correlations are broadly similar to other studies of plateaus in convergence zones like the Kunlun‐Shan in central‐northern Tibetan Plateau (Li et al., 2014). Similarly, mountain ranges within collision zones such as the Greater Caucasus (Forte et al., 2016; Forte, Gutterman, et al., 2022; Forte, Leonard, et al., 2022) and Zagros Mountain (Collignon et al., 2019) also experience very weak coupling between climate and erosion rates. Across the northern zone, the impact of Alborz orographic barrier on precipitation amount reduces from east (Alamut) to west (Tarom, Figures 1 and 2b), corresponding to decrease elevation, relief and erosion rates (Table S4 in Supporting Information S2).…”

“…The west Alborz exhumation rate peaked in the Pliocene (Figure 7a). During this period, the Alborz, Caucasus, Pontides, and Taurus mountain ranges underwent major deformation (e.g., Allen et al., 2004; Avdeev & Niemi, 2011; Chu et al., 2021; Forte et al., 2014; Forte, Gutterman, et al., 2022; Madanipour et al., 2013). This phase of deformation was attributed to the thrust fault reactivations (e.g., Caspian and Alamutrud Faults in west Alborz, Figure 1; Alavi, 1996; Axen et al., 2001; Mattei et al., 2017) caused by sealing off the free face at the eastern side of the Arabia–Eurasia collision zone in the Pliocene (Allen et al., 2011; Treloar & Izatt, 1993).…”

Diverse Deformation Mechanisms and Lithologic Controls in an Active Orogenic Wedge: Structural Geology and Thermochronometry of the Eastern Greater Caucasus

“…Thus, the Late Miocene-Pliocene evolution of the eastern Greater Caucasus at the longitude of our study apparently cannot be attributed to entrance of lower-plate continental crust into the subduction zone. These results, together with the recent recognition that exhumation rates appear to be equivalent in both pre-and post-collisional portions of the orogen (Forte et al, 2022), underscore the need for further study of how continental collision affects the structural evolution of orogens.…”

“…The WNW-striking Greater Caucasus orogen is located within the Arabia-Eurasia collision zone and accommodates convergence between Eurasia to the north and the Lesser Caucasus continental block to the south (Figure 2a; Adamia et al, 2011;Cowgill et al, 2016;Forte et al, 2022;Mosar et al, 2010Mosar et al, , 2022Philip et al, 1989;Tibaldi et al, 2020;Vincent et al, 2016Vincent et al, , 2007Zonenshain & Pichon, 1986). The Caucasus region has a complex tectonic history, with multiple episodes of subduction, terrane accretion, and rifting during Phanerozoic time (Adamia et al, 2011;Şengör, 1984;Stampfli, 2013;Vasey et al, 2020).…”

Episodic evolution of a protracted convergent margin revealed by detrital zircon geochronology in the Greater Caucasus

“…Building on prior work studying the Caucasus Basin and related rocks (e.g. Forte et al, 2022; Mosar et al, 2022; Trexler et al, 2022; Vasey et al, 2020), we primarily organize our results into samples collected along major river corridors in the western Svaneti (SV) and the eastern Kazbegi (KZ) regions of Republic of Georgia, separated by ~200 km along‐strike (Figures 2b and 3). We also include a sample from Jurassic strata of the Northern Caucasus in Russia (RU) in a region of primarily magmatic and metamorphic rocks known as the Bechasyn Zone (Figure 2b; e.g.…”