@article{BallatoLandgrafSchildgenetal.2015, author = {Ballato, Paolo and Landgraf, Angela and Schildgen, Taylor F. and Stockli, Daniel F. and Fox, Matthew and Ghassemi, Mohammad R. and Kirby, Eric and Strecker, Manfred}, title = {The growth of a mountain belt forced by base-level fall: Tectonics and surface processes during the evolution of the Alborz Mountains, N Iran}, series = {Earth \& planetary science letters}, volume = {425}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2015.05.051}, pages = {204 -- 218}, year = {2015}, abstract = {The idea that climatically modulated erosion may impact orogenic processes has challenged geoscientists for decades. Although modeling studies and physical calculations have provided a solid theoretical basis supporting this interaction, to date, field-based work has produced inconclusive results. The central-western Alborz Mountains in the northern sectors of the Arabia-Eurasia collision zone constitute a promising area to explore these potential feedbacks. This region is characterized by asymmetric precipitation superimposed on an orogen with a history of spatiotemporal changes in exhumation rates, deformation patterns, and prolonged, km-scale base-level changes. Our analysis suggests that despite the existence of a strong climatic gradient at least since 17.5 Ma, the early orogenic evolution (from similar to 36 to 9-6 Ma) was characterized by decoupled orographic precipitation and tectonics. In particular, faster exhumation and sedimentation along the more arid southern orogenic flank point to a north-directed accretionary flux and underthrusting of Central Iran. Conversely, from 6 to 3 Ma, erosion rates along the northern orogenic flank became higher than those in the south, where they dropped to minimum values. This change occurred during a similar to 3-Myr-long, km-scale base-level lowering event in the Caspian Sea. We speculate that mass redistribution processes along the northern flank of the Alborz and presumably across all mountain belts adjacent to the South Caspian Basin and more stable areas of the Eurasian plate increased the sediment load in the basin and ultimately led to the underthrusting of the Caspian Basin beneath the Alborz Mountains. This underthrusting in turn triggered a new phase of northward orogenic expansion, transformed the wetter northern flank into a new pro-wedge, and led to the establishment of apparent steady-state conditions along the northern orogenic flank (i.e., rock uplift equal to erosion rates). Conversely, the southern mountain front became the retro-wedge and experienced limited tectonic activity. These observations overall raise the possibility that mass-distribution processes during a pronounced erosion phase driven by base-level changes may have contributed to the inferred regional plate-tectonic reorganization of the northern Arabia-Eurasia collision during the last similar to 5 Ma. (C) 2015 Elsevier B.V. All rights reserved.}, language = {en} } @article{CifelliBallatoAlimohammadianetal.2015, author = {Cifelli, Francesca and Ballato, Paolo and Alimohammadian, Habib and Sabouri, Jafar and Mattei, Massimo}, title = {Tectonic magnetic lineation and oroclinal bending of the Alborz range: Implications on the Iran-Southern Caspian geodynamics}, series = {Tectonics}, volume = {34}, journal = {Tectonics}, number = {1}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0278-7407}, doi = {10.1002/2014TC003626}, pages = {116 -- 132}, year = {2015}, abstract = {In this study we use the anisotropy of magnetic susceptibility (AMS) and paleomagnetic data for deciphering the origin of magnetic lineation in weakly deformed sedimentary rocks and for evaluating oroclinal processes within the Arabia-Eurasia collision zone. In particular, we have analyzed the Miocene Upper Red Formation (URF) from the outer curved front of the southern Central Alborz Mountains of north Iran, to test for the first time with paleomagnetic data the origin (primary versus secondary) of this orogenic arc. AMS data document the existence of a magnetic lineation parallel to the orientation of the major tectonic structures, which vary along strike from WNW to ENE. These directions are highly oblique to the paleoflow directions and hence suggest that the magnetic lineation in the URF was produced by compressional deformation during layer-parallel shortening. In addition, our paleomagnetic data document clockwise and anticlockwise rotations along vertical axis for the western and eastern sectors of the Central Alborz Mountains, respectively. Combined, our results suggest that the orogen represents an orocline, which formed not earlier than circa 7.6Ma most likely through bending processes caused by the relative motion between the rigid crustal blocks of the collision zone. Moreover, our study provides new insights into the Iran-Southern Caspian Basin kinematic evolution suggesting that the present-day SW motion of the South Caspian Basin with respect to Central Iran postdates oroclinal bending and hence cannot be as old as late Miocene to early Pliocene but a rather recent configuration (i.e., 3 to <1Ma).}, language = {en} } @article{DonnerGhodsKrueeretal.2015, author = {Donner, Stefanie and Ghods, Abdolreza and Kr{\"u}er, Frank and R{\"o}ßler, Dirk and Landgraf, Angela and Ballato, Paolo}, title = {The Ahar-Varzeghan Earthquake Doublet (M-w 6.4 and 6.2) of 11 August 2012: Regional Seismic Moment Tensors}, series = {Bulletin of the Seismological Society of America}, volume = {105}, journal = {Bulletin of the Seismological Society of America}, number = {2A}, publisher = {Seismological Society of America}, address = {Albany}, issn = {0037-1106}, doi = {10.1785/0120140042}, pages = {791 -- 807}, year = {2015}, abstract = {On 11 August 2012 an earthquake doublet (M-w 6.4 and 6.2) occurred near the city of Ahar, northwest Iran. Both events were only 6 km and 11 minutes apart, producing a surface rupture of about 12 km in length. Historical and modern seismicity has so far been sparse in this area. Spatially, the region represents a transitional zone between different tectonic domains, including compression in Iran, westward extrusion of the Anatolian plate, and thrusting beneath the Caucasus. In this study, we inverted the surface waveforms of the two mainshocks and 11 aftershocks (M-w >= 4.3) to obtain regional seismic moment tensors. The earthquakes analyzed can be grouped into pure strike slip (including the first mainshock) and oblique reverse mechanisms (including the second mainshock). The sequence provides information about faulting mechanisms at the spatial scale of the entire rock volume affected by the earthquake doublet, including coinciding deformation on minor faults (sub) parallel to the main fault and Riedel shears. It occurred on a so far unknown fault structure, which we call the Ahar fault. Alongside the seismological data, we used geological maps, satellite images, and digital elevation data to analyze the geomorphology of the region. Our analysis suggests that the adjacent North Tabriz fault, which accomodates up to 7 mm/yr of right-lateral strike-slip faulting, does not compensate the entire lateral shear strain, and that part of it is compensated farther north. Combined, our results suggest a temporally and spatially complex style of deformation (reverse and strike slip) overprinting older reverse deformation.}, language = {en} }