HR: 1340h
AN: T23D-1633    [Abstracts]
TI: Kinematic Evolution of the North-Tehran Fault (NTF), Alborz Mountains, Iran
AU: * Landgraf, A
EM: landgraf@uni-potsdam.de
AF: Inst. für Geowissenschaften, Universität Potsdam, Haus 27 K.-Liebknecht Strasse 24-25, Golm, 14476, Germany
AU: Ballato, P
EM: ballato@geo.uni-potsdam.de
AF: Inst. für Geowissenschaften, Universität Potsdam, Haus 27 K.-Liebknecht Strasse 24-25, Golm, 14476, Germany
AU: Strecker, M R
EM: strecker@geo.uni-potsdam.de
AF: Inst. für Geowissenschaften, Universität Potsdam, Haus 27 K.-Liebknecht Strasse 24-25, Golm, 14476, Germany
AU: Shahpasandzadeh, M
EM: mshahpasandzadeh@gmail.com
AF: International Institute of Earthquake Engineering and Seismology, No. 26, Arghavan str., North Dibajee, Farmanieh, Tehran, 19395-3913, Iran (Islamic Republic of)
AU: Friedrich, A
EM: friedrich@lmu.de
AF: Department für Geo- und Umweltwissenschaften, Universität München, Luisenstrasse 37, München, 80333, Germany
AU: Tabatabaei, S H
EM: htabatabaei@bhrc.ac.ir
AF: Building and Housing Research Center, Sheik Fazlollah Exp. Way, Tehran, 13145-1696, Iran (Islamic Republic of)
AB: The ENE-to NW-striking NTF is an active frontal thrust that delimits the Alborz Mountain range to the south with an up to 2000 m topographic break with respect to the adjacent Tehran plain. Eocene rocks of the Alborz range are thrusted over Neogene and Quaternary sediments of the alluvial Tehran embayment. The fault consists of right- stepping segments and merges to the east with the active Mosha-Fasham strike-slip fault (MFF). The complex tectonic history, involving changes in the direction of SHmax, has resulted in a composite tectonic landscape with inherited topographic and fault-kinematic fingerprints along the NTF. We therefore used a combination of fault-kinematic measurements and geomorphic observations to unravel the temporal tectonic evolution of this fault. Presently, the NTF is virtually inactive, although the tectonically overprinted landforms reflect tectonic activity on longer time scales during the Quaternary. Being located adjacent north of the Tehran megacity, there is thus considerable interest to decipher its youngest tectonic evolution and to better understand the relation with other fault systems. Our fault kinematic study has revealed an early dextral kinematic history for the NTF. Dextral strike-slip and oblique reverse faulting took place during NW-oriented shortening. The overall fault-geometry of the NTF suggests that it has evolved in relation to dextral transpression along the MFF. This early kinematic regime was superseded by NE-oriented shortening, associated with sinistral-oblique thrusting along the fault segments. Fault linkage between the semi-independent ENE-striking NTF-segments and NW-striking thrusts (Emamzadeh Davud Fault [EDF], Purkan Vardij Thrust [PVT], NTF-prolongation) point towards an evolution into a nascent transpressional duplex. In this scenario the NTF segments constitute lateral ramps and the NW-striking faults act as frontal ramps. Topographic residuals, as an expression of high-uplift zones, indicate that the central segment of the NTF, incorporating the EDF was most effective in accommodating oblique convergence during this time. However, subtle knickpoints in the longitudinal river profiles crossing the PVT may indicate a relatively recent transfer of deformation onto this block. The youngest manifestations of deformation along the NTF, however, are left-lateral and normal faulting. This youngest phase of activity is documented by numerous striated and rotated conglomeratic clasts, meter-scale fault gouge zones with shear-sense indicators of oblique normal faulting, and multiple colluvial wedges with drag phenomena. Rupture traces and filled extensional cracks reaching the surface also document the seismogenic nature of these features. Since recent left-lateral transtension is also known from neighboring faults, e.g., the eastern MFF, our observations suggest that this youngest phase of tectonic activity of the NTF is a regional phenomenon, rather than the result of locally-determined geometries.
DE: 8107 Continental neotectonics (8002)
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Fall Meeting