Thermochronological comparison between evolution of hinterland near
field and far field of Zagros convergence margin
Abstract
To assess the tectonic response of near-field and far-field deformation
in the upper plate of a subduction/collision system, we present here a
thermochronological study on the subduction related-arc Sanandaj-Sirjan
Zone(SSZ) and North Central East Iranian Microcontinent (CEIM),
respectively as near-field and far-field of the upper plate of
Neo-Tethys subduction margin. Samples have been collected from late
Middle Jurassic Kolah-Ghazi granitoid (KGg) (ca. 165-170 Ma) in central
SSZ, from Upper Cretaceous Kasf granite (ca. 85-100 Ma) and
Paleocene-Eocene Kashmar-Azghand Intrusive Complex (KAIC) (ca. 60-41 Ma)
from North Doruneh fault which represents the northern mechanical
boundary of CIEM. Time-temperature (T-t) inverse modeling on the ZFT,
AFT and AHe data has been performed through HeFTY V1.9 program to
constrain the thermal/tectonics history of the SSZ and CEIM. Based on
the geological field evidence, some independent T-t constraints such as
crystallization ages, stratigraphic unconformities, present-day
temperature, have been adopted. The T-t inverse modeling of KGg shows:
(i) an early episode of cooling in early Lower Cretaceous, during which
the intrusive body has been exhumed to the surface (ii) a burial phase
during which the KGg as a whole entered the PAZ in consequence of
deposition of the Cretaceous successions, and (iii) a last stage
corresponding to final exhumation-related cooling started since the Late
Cretaceous-Paleocene boundary. The thermal modeling results of Kasf
granite shows (i) an early episode of cooling at Upper
Cretaceous-Paleocene during which the intrusive bodies and the hosting
units have been exhumed to the surface, (ii) second stage corresponding
to a burial phase when the Kasf granite as a whole entered the PAZ in
consequence of the deposition of the Paleocene-Eocene succession, and
(iii) a last stage corresponding to the final exhumation-related
cooling, starting since the middle-late Eocene. The thermal modeling
results of KAIC shows (i) an episode of enhanced cooling of KAIC at
Eocene-Oligocene boundary, (ii) Second stage is characterized by burial
phase to temperatures above the PAZ during the Oligocene, (iii) third
stage corresponds to exhumation-related cooling during the early
Miocene, and (iv) fourth stage corresponds to a renewed episode of
enhanced cooling starting at the Miocene-Pliocene transition, during
which the KAIC was finally exposed to the surface. These results document
that both hinterland near-field and far-field regions respond
contemporaneously to the Neotethyan subduction-related exhumation at the
Upper Cretaceous-Paleocene boundary. T-t modeling output for Kasf and
KAIC also shows Middle-Late Eocene exhumation-related cooling related to
the Middle-Late Eocene Zagros collision- related exhumation. T-t
modeling output for KAIC also shows Early Miocene and Late
Miocene-Pliocene exhumation-related cooling related to the Early Miocene
and Late Miocene-Pliocene Zagros collision-related exhumatio