Paleostress analysis in the Zagros orogeny, Shiraz area, Iran

The stress field reconstruction of deformed rocks is a key for understanding tectonic events. In order to study the brittle deformation of a zone between Zagros Folded Belt and Zagros Fold-and-Thrust Belt, we have chosen 4 methods (calcite twinning, fault-slip data, tension gash and stylolite) for determining paleostress in 10 stations in the Shiraz region of EZagros in Iran. Inversions have been performed using a computer program perform by Žalohar (2015) named T-Tecto studio X5. The paleostress reconstructions in the Shiraz area reveal N17°E, N26°E, N22°E and N18°E for σ1 by fault-slip data, calcite twining, (Eocene-Oligocene time) and N21°E, N27°E, N25°E and N21°E in Zagros Fold-and-Thrust Belt (Cretaceous time). Maximum stress directions determined within the Cenozoic and Mesozoic sedimentary rocks from stylolites and tension gashes which are remarkably consistent with the stress tensors deduced from inversion methods obtained from the fault planes and calcite analysis. Stylolites and fault-slip data gives close result as tension gashes and calcite twining. It may be caused by the rheology of calcite that exist in these two methods. Stylolites and fault slip data also may show the same history of deformation path. In general fault slip analysis give the minimum attitude (N2°E) and the calcite twining yield the maximum attitude (N34°E) for the maximum principal stress. Maximum standard deviation for attitude of σ1 are in station Bamu, Bardaj, Chah Anari and Sadra. These stations are near or inside the High Zagros fault zone so the deformation history in these stations are more complex than adjacen