Fault interactons on different time and length scales: the North-Tehran-Thrust (NTT) and the Mosha-Fasham-Fault (MFF), Alborz mountains, Nothern Iran
Final Report Abstract
In areas that are far away from plate boundaries, the location of faults capable of generating destructive earthquakes is often unknown, because earthquakes in continental interiors typically have spatially and temporally disparate patterns and recurrence intervals far beyond the resolution of instrumental recordings and even historical accounts. The possible interaction of such seismogenic faults and the long-term evolution of fault arrays in these regions constitutes an unsolved scientific problem, and a daunting scenario for politicians and public policy-makers, who aim to ensure the welfare and sustainability of society. As such, intraplate seismicity and tectonic processes are societally important, especially in the realm of natural hazard and risk assessments, which require robust information on the degree of tectonic activity of faults. It is here, at the intersection of understanding complex fault interaction and deciphering tectonic activity in the interior of the continents where our study set out to characterize the evolution of linked fault systems on different timescales. The study region is located in the vicinity of the megacity of Tehran, in the southern sector of the Alborz Mountains. However, due to the fact that the Tehran region is highly impacted by human activity, it is difficult to find pristine deformation features that record tectonic processes on decadal to centennial timescales, although earthquakes attest to ongoing tectonic activity. We therefore concentrated on older geological archives comprised of the principal faults and sedimentary strata spanning the Pleistocene epoch and beyond. The Alborz Mountains are an integral part of the most important continental collision zone on Earth, which includes the region between the eastern Himalaya and the western European Alps, a region of disparate, yet protracted tectonic activity. In this setting we wanted to reveal the possible interaction between the North Tehran Thrust (NTT) and Mosha Fasham Fault (MFF), both capable of producing large-magnitude earthquakes. In our quest to decipher fault interaction and to retrieve information on the timing of tectonic processes associated with the principal structures, we bridged different spatial and temporal scales of deformation using remotesensing, dating methods, and topographic data from digital elevation models and field observations. We found that: (1) deformation of the Earth’s crust in the Tehran plain is characterized by contraction, with the bulk of deformation having occurred prior to 126,000 years, as documented by cosmogenic nuclide techniques; (2) there is a mechanical linkage between the NTT and MFF during an earlier stage of mountain building and deformation, when the direction of contraction was oriented northwestsoutheast. This regime of deformation was superseded by northeast-oriented shortening, resulting in the reactivation of the NTT and MFF into a large, linked structure (duplex). The duplex transfers leftlateral motion from the MFF across a set of frontal and oblique ramps. We used a thermochronological technique (apatite (U-Th)/He dating) to determine when formerly undisturbed rocks were uplifted and transferred into a cooler temperature regime, associated with the accumulation and diffusive loss of Helium during the temperature-controlled decay of Uranium and Thorium impurities within apatite crystals. This enabled us to record two pulses of SW-directed deformation and uplift events at ~ 18-14 and 9.5-7.5 Ma. Both episodes significantly affected landscape evolution, implying that fault interaction dominates the growth of topography and relief distribution. This was further corroborated by boundary-element modelling of vertical displacement fields, generating landscape elements that resemble the topographic and relief conditions found today; (3) earlier stages of mountain building and faulting are also recorded in the sedimentary successions of basins adjacent to the Alborz mountain range. These sediments document a systematic correlation between grain size and sedimentaccumulation rates on 105 to 106yr time scales, related to an increase in rainfall and erosion. This was driven by the tectonic uplift of the Alborz Mountains, which generated high topography and thus an efficient barrier to the free flow of moisture-bearing winds. For the first time our data unequivocally document the linked impact of climatic and tectonic processes on the architecture of sedimentary basins; (4) last but not least, our data provide new temporal constraints on the continental collision between the Arabian and Eurasian plates. We demonstrate that contractional deformation in the Alborz Mountains started shortly after 36 Ma, associated with slow deformation rates. Tectonic rates, however, increased around 20-18 Ma, when unstretched continental lithosphere began to be subducted. This information is pivotal for regional assessments of the tectonic evolution of the Near East and a better understanding of the deformation and uplift processes between eastern Turkey and Iran.
Publications
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(2008): Tectonic control on sedimentary facies pattern and sediment accumulation rates in the Miocene foreland basin of the southern Alborz mountains, northern Iran. Tectonics, v. 27, TC6001
Ballato, P., Nowaczyk, N.R., Landgraf, A., Strecker, M.R., Friedrich, A., Tabatabaei, S.H.
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(2009), Fault-kinematic and geomorphic observations along the North Tehran Thrust and Mosha Fasham Fault, Alborz mountains, Iran: implications for fault-system evolution and interaction in a changing tectonic regime: Geophysical Journal International, v. 177, p. 676-690
Landgraf, A., Ballato, P., Strecker, M. R., Friedrich, A., Shahpasandzadeh, M., and Tabatabaei, S. H.
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(2010): Middle to late Miocene Middle Eastern climate from stable oxygen and carbon isotope data, southern Alborz mountains, N Iran. Earth and Planetary Science Letters, v.300, p. 125-138
Ballato, P., Mulch, A., Landgraf, A., Strecker, M.R., Dalconi, M.C., Friedrich, A., Tabatabaei, S.H.
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Tectonic and climatic forcing in orogenic processes: the foreland basin point of view, Alborz Mountains, N Iran. PhD thesis
Ballato, Paolo
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(2011): Arabia-Eurasia continental collision: insights from late Tertiary foreland-basin evolution in the Alborz mountains, northern Iran. Geological Society of America Bulletin, v. 123, p. 106-131
Ballato P., Uba C.E., Landgraf, A., Strecker M.R., Sudo, M., Stockli, D.F., Friedrich A., Tabatabaei, S.H.
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Fault interaction at different time- and length scales: The North Tehran Thrust and Mosha Fasham Fault (Alborz mountains, Iran). PhD thesis
Landgraf, Angela
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(2013), Differentiating simple and composite tectonic landscapes using numerical fault-slip modeling with an example from the south-central Alborz Mountains. Journal of Geophysical Research - ES, 118, 1–14
Landgraf, A., Zielke, O., Arrowsmith, J.R., Ballato, P., Strecker, M.R., Friedrich A., Tabatabaei, S.H.
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(2013): Accommodation of transpressional strain in the Arabia-Eurasia collision zone: new constraints from (U-Th)/He thermochronology, N Iran. Tectonics v.32, TC003159
Ballato, P., Stockli, D.F., Ghassemi, M.R., Landgraf, A., Strecker, M.R, Hassanzadeh, J., Friedrich, A., Tabatabei, S.H.
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(2014): Assessing tectonic and climatic causal mechanisms in forelandbasin stratal architecture: insights from the Alborz Mountains, northern Iran. Earth Surface Processes and Landforms, v. 39, p. 110-125
Ballato, P., Strecker M.R.
