Das Iranische Hochplateau: Ein kollisionales orogenes Plateau in statu nascendi
Zusammenfassung der Projektergebnisse
Located along convergent plate boundaries, orogenic plateaus are areally extensive, arid, lowrelief and elevated morpho-tectonic provinces that influence local- to far-field deformation processes. Orogenic plateaus strongly impact atmospheric circulation, rainfall patterns and thus erosion and the overall efficiency of surface processes. Over time scales of 106 to 107 years orogenic plateaus have a life cycle including: 1) a construction stage characterized by vertical and outward (orogenyperpendicular) growth; and 2) a destruction stage, during which the typical low-relief morphology is progressively lost. Although the largest orogenic plateaus on Earth (Tibet and Puna-Altiplano) have been the subject of research during the past three decades, several issues concerning their evolution are still a matter of debate. These include the role of mantle-driven and crustal shortening and thickening processes, as well as the potential contribution of surface processes (through multiple climate change) during both the building and destruction stages. To tackle these issues I have designed a multiproxy study in the poorly known Iranian Plateau (IP), which is considered a collisional orogenic plateau at its nascent stage. There, the combination of plateau size, the excellent outcrops, good infrastructure, and accessibility lend this region to an investigation of the early stages of plateau development, with the opportunity to obtain good temporal control. Moreover, the occurrence of recent river incision in the NW sectors of the plateau interior allows investigating the mechanisms that are currently leading to its demise. The major results obtained by my co-authors and I indicate that in the NW sectors of the IP crustal shortening and thickening processes had a major contribution to building the plateau. In particular, duplexing of the basement units in the plateau interior toward the plate suture generated a wide foreland basin to the NE between 16.5 and 10.7 Ma. The outward propagation of the deformation fronts from ~ 12 to 10 Ma led to basin compartmentalization and the development of a typical contractional basin-and-range morphology with several intermontane basins alternating with mountain ranges. My most extensive structural cross section covering almost two-thirds of the plateau width, suggests that ~ 65 km of post early Miocene plate convergence was accommodated during the buildup of the IP (almost 20% of the total plate convergence). The combination of both, long-term plate convergence and arid climate conditions resulting from the latitudinal position of the plateau with respect to the Hadley cell subsidence zone and orography, led to the reduction of erosive power and sediment evacuation from the orogen, fostering the evolution of internally drained sedimentary basins and the accumulation of thick sedimentary sequences. In turn, this protracted sediment storage resulted in the reduction of topographic relief, and in an increase of plateau-surface elevation. Overall, my new data document that by ~ 10 Ma, the IP had reached a width similar to the present-day. Basin-filling processes in the endorheic basins of the IP started after 10 Ma and lasted until ~ 4 Ma (or a bit later in the more internal sectors). The inception of plateau incision appears to coincide with the km-scale (1 ± 0.4 km) base-level fall of the Caspian Sea between ~ 6 and 3.2 Ma, suggesting possible causal relationships. My study along the Alborz mountains and the north-western margin of the IP shows that this ~ 3-Myr-long drop in base-level conditions triggered enhanced fluvial erosion, increasing sediment supply to the Caspian Basin. I suggest that efficient mass-redistribution processes associated with the base-level fall and basin subsidence triggered underthrusting of the South Caspian Basin beneath its southern and possibly northern (i.e., Alborz mountains and Aspheron Sill, respectively) margins. This inferred scenario suggests that the regional plate-tectonic reorganization at ~ 5 Ma as indicated by enhanced fault-related exhumation along the mountain belts of the Caspian Sea may have been partially driven by the base-level fall, and is thus intimately related to surface processes. Although knickpoints originated during the base-level fall propagated toward the plateau margin, there are apparently no causal relationships with the onset of plateau incision and excavation at ~ 4 Ma. My new stratigraphic and paleoclimatic data from the most external intermontane basin of the IP (Mianeh Basin) show that between ~5 and 4 Ma wetter climatic conditions affected this internally drained basin, causing aggradation and the development of an elevated lake. This ultimately promoted lake spillover and the formation of a ~1-km-deep, 100-km-long bedrock gorge that incises the plateau margin almost parallel to its structural trend, and which connected the plateau interior with the Caspian Sea depozone. This finding emphasizes the transitional nature of orogenic plateau landscapes on timescales of a few 106 years and underscores the role of surface processes in creating, preserving and destroying typical low-relief plateau morphologies.
Projektbezogene Publikationen (Auswahl)
- (2014) Deformation styles and exhumation patterns in the Northern Iranian Plateau: New results from integrated balanced cross sections and low-temperature thermochronology (AHe and ZHe), EGU General Assembly, Conference Abstracts, 16, 6939
Balling, P., Ballato, P., Dunkel, I., Zeilinger, G., Heidarzadeh, G., Ghassemi, M., Strecker, M.R.
- (2014) Tectono-stratigraphic evolution of the Northern Iranian Plateau (N Iran), EGU General Assembly, Conference Abstracts, 16, 12795
Ballato, P., Heidarzadeh, G Zeilinger, G., Ghassemi, M., Cifelli, F., Mattei, M., Hassanzadeh, J., Sud, M., Balling, P., Strecker, M.R.
- (2014) Variations in erosional efficiency modulate orogenic growth of the Alborz Mountains (N Iran), EGU General Assembly, Conference Abstracts, 16, 13261
Ballato, P., Landgraf, A. Stockli, D. Schildgen T.F., Ghassemi, M.R., Kirby, E. Strecker M.R.
- (2014) Variations in erosional efficiency modulate orogenic growth of the Alborz Mountains (N Iran), EGU General Assembly, Conference Abstracts, 16, 13261
Ballato, P., Landgraf, A. Stockli, D. Schildgen T.F., Ghassemi, M.R., Kirby, E. Strecker M.R.
- (2015) Mio-Pliocene morphotectonic evolution of the Iranian Plateau: from outward expansion to incision and excavation. EGU General Assembly, Conference Abstracts, 17, 12134
Ballato, P., Heidarzadeh, G Zeilinger, G., Ghassemi, M., Cifelli, F., Mattei, M., Hassanzadeh, J., Balling, P., Dunkl, I., Sudo, M., Mulch, A., Strecker, M.R.
- (2015) Mio-Pliocene orogenic plateau building in the Arabia-Eurasia collision zone, Iran: from outward expansion to incision and excavation, Sedimentary Basin meeting, Jena 2015
Ballato, P.
- (2015) The growth of a mountain belt forced by base-level fall: Tectonics and surface processes during the evolution of the Alborz Mountains, N Iran. AGU Fall Meeting, Abstracts, 75517
Ballato, P., Landgraf, A., Fox, M., Stockli, D. Schildgen T.F., Ghassemi, M.R., Kirby, E. Strecker, M.R.
- (2015) The growth of a mountain belt forced by base-level fall: Tectonics and surface processes during the evolution of the Alborz Mountains, N Iran. Earth and Planetary Science Letters, 425, 204-218
Ballato, P., Landgraf, A., Fox, M., Stockli, D. Schildgen T.F., Ghassemi, M.R., Kirby, E. Strecker, M.R.
(Siehe online unter https://doi.org/10.1016/j.epsl.2015.05.051) - (2015) The growth of a mountain belt forced by base-level fall: Tectonics and surface processes during the evolution of the Alborz Mountains, N Iran. GeoBerlin 2015, Annual Meeting of DGGV and DMG
Ballato, P., Landgraf, A., Fox, M., Stockli, D. Schildgen T.F., Ghassemi, M.R., Kirby, E. Strecker, M.R.
(Siehe online unter https://doi.org/10.1016/j.epsl.2015.05.051) - Tectono-sedimentary evolution of the northern Iranian Plateau: insights from middle-late Miocene foreland-basin deposits. Basin Research Vol 29 Issue 4, August 2017, Pages 417-446
Ballato, P., Cifelli, F., Heidarzadeh, G., Ghassemi, M., Wickert, A., Hassanzadeh, J., Dupot- Nivet, G., Balling, P., Sudo, M., Zeilinger, G., Schmitt, A. K., Mattei, M., Strecker, M.R.
(Siehe online unter https://doi.org/10.1111/bre.12180)
