High-resolution Lithospheric Structure of the Zagros Collision Zone and
Iranian Plateau
Abstract
From a joint analysis of fundamental mode Rayleigh wave group velocities
and P-wave receiver functions, we derive a new, high-resolution
3D shear-wave velocity (Vs) model for the crust
and uppermost mantle of the Iranian Plateau. The thickest crust
(>55km) is located beneath the deforming belts of the
Plateau (e.g., the Sanandaj-Sirjan Zone (SSZ) and Talesh-Alborz-Binalud
Mountains), whereas regions of lower topography/deformation (e.g.,
central Iran and the Lut Block), and the regions of very younger
deformation such as the Makran Accretionary Wedge and the Zagros Simply
Folded Belt (SFB) have a thinner (<45km) crust. Our model
reveals a low-Vs tongue-shaped feature,
indicating the underthrusting of the Arabian crust beneath central Iran.
In the central Zagros, underthrusting of the Arabian crust is steeper,
resulting in a narrower (~150km) deforming zone with
thicker (~60-65km) crust compared to the crust beneath
the broader (~250km) deforming zone and somewhat thinner
(~55-60km) crust below the Lorestan Arc. Regions of
low-Vs in the upper crust correspond to regions
of thick sediments (e.g., the South Caspian Basin, the SFB and foreland
basin of the Zagros, and the Makran Subduction Wedge). The subcrustal
Rayleigh wave azimuthal anisotropy of the Plateau shows a rather uniform
and smoothly-varying pattern. In the NW Zagros the crustal and
subcrustal pattern of anisotropy agrees with that previously estimated
from the shear-wave core phases, implying that the whole lithosphere
deforms coherently, but for other regions (e.g., the western Alborz and
Kopet Dag), the anisotropic pattern does not support a coherent
deformational fabric throughout the lithosphere.