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)

Abstract

The NNW Iranian Plateau and west Alborz within the Arabia‐Eurasia collision zone are characterized by three main tectono‐stratigraphic zones, crosscut by the Qezel‐Owzan River (QOR) Basin. The interplay between present‐day deformation and climate, which control the landscape evolution of the region, is still poorly constrained. We addressed this gap by measuring millennial‐scale erosion rates from 10Be‐concentration in the QOR sands along with topographic/climatic metrics analyses. Results reveal low erosion rates in the Plateau and relatively high in the west Alborz. The regional consistency of topographic parameters with geomorphology suggests that they control sediment fluxes in the Plateau, while the surface uplift, active thrust‐faulting, and shallow crustal seismicity in the west Alborz are the main controlling factors. Climate has a secondary role on erosion rates. Furthermore, we calculated exhumation rates from published thermochronometric AFT/AHe ages to determine their relationship with 10Be short‐term data. Results imply that the exhumation rates increased slightly in the Plateau and west Alborz from ∼26 to ∼10 Ma, simultaneous with hard collision processes between the Arabia‐Eurasia. This trend accelerated from ∼10 to ∼2.8 Ma due to the isolation of the Caspian Sea and extreme base‐level fall. From ∼2.8 to ∼2 Ma, base‐level rise occurred under climate influence, and erosion rates decreased. Millennial‐scale data show the erosion rate decreased from ∼2 Ma to the Present‐day, which is attributed to the change in deformation style and fault kinematics from fold/thrusting to mainly strike‐slip faulting. The significantly lower erosion rates in the Plateau compared to west Alborz suggest a relatively stable plateau surface.

The Uplift of an Early Stage Collisional Plateau Unraveled by Fluvial Network Analysis and River Longitudinal Profile Inversion: The Case of the Eastern Anatolian Plateau

“…It is interesting that both paleolongitudinal profiles of the Kura and Arax rivers reconstructed from their segment upstream of the knickpoint at ∼1,500 m indicate a drop in elevation of ∼1,000 m suggesting the occurrence of a similar process (Figure 9). In both basins the mean erosion rate is ∼0.2 mm/yr (Kaveh Firouz, 2018): if we hypothesize a similar uplift rate, the incision of ∼1,000 m will occur in 5 Myr, a result similar to the one from the inversion of the Arax R. profile.…”

“…This configuration fits well with the modeling of the Arax R. profile: considering that the model is not reliable for response time >12 Ma, the inversion results indicate that before ∼10 Ma, the basin was affected by a low, almost constant uplift rate (∼0.1 mm/yr) that probably allowed the development of a low relief landscape, now standing at elevation higher than 2,500 m (Figure 10). It is noteworthy that most of the right tributaries of the Arax R. whose headwaters are along the divide with the Euphrates, Van and Urmia basins as well as the most upstream portion of the Arax R. itself have erosion rates equal or lower than 0.1 mm/yr (Kaveh Firouz, 2018). These low values fit well with a low‐relief landscape developed close to base level. Most of the rivers of the Kura, Arax, Ҫoruh basins have a segment characterized by a similar steepness, usually delimited downstream by a knickpoint at ∼1,500 m, and steeper than Trend 1, named Trend 2 (Figures 6 and 7).…”

“…The four trends suggest a difference in the landscape evolution of the EAP. To investigate this latter, we modeled the uplift history of the Arax R. alone since erosion rate data are available only for the Arax and Kura basins (Kaveh Firouz, 2018). Unfortunately, it is impossible to model the uplift history of the Kura R. because some of its tributaries drain the Greater Caucasus and the result would mix the history of this mountain chain with the EAP one.…”

“…By Equation 7, the K values are calculated for each erodibility domain starting from the best fit k sn and the average erosion rates (in our model we used the values obtained from 10 Be concentrations in alluvium sampled along the Arax R. main channel; see location in Figure 2b; Kaveh Firouz, 2018). So, the K values are not predetermined, but reflect primary and secondary (like weathering, joints) properties of the rocks that define the susceptibility to erosion.…”

“…The black lines are the study rivers named by a number, the white dashed line indicates the boundary of the Eastern Anatolia Plateau (EAP) that merges to the Iranian Plateau to the SE, the red star marks the location of a wind gap. The white dots along the Arax R. indicate the sampling locations for the estimation of the erosion rates, whereas the side numbers indicate the results in mm/yr (from Kaveh Firouz (2018)). (c) NNE‐SSW oriented swath profile across the EAP.…”