Paleostress analysis on Paleozoic syn-depositional faults in the eastern Alborz, northern Iran

• The Alborz Margin experienced persistent N-S extension throughout the Paleozoic. • Paleozoic stress field remained unchanged across diverse geodynamic regimes. • Study results confirm and supplement previous central Alborz analyses. • New data completes the Alborz’s Paleozoic paleostress evolution, including rifting. The Alborz Mountains of northern Iran stand out as an exceptional site for studying the Ediacaran-Paleozoic evolution of the northern Gondwana margin. The Alborz forms the inverted continental shelf of the Central Iranian microcontinent that was part of the northern Gondwana margin until the Permian period. Here, we present a paleostress analysis of the Paleozoic tectonic evolution in the eastern Alborz, supported by published studies of stratigraphy, petrology and regional tectonics. This analysis confirms and supplements the findings of a previous study in the central Alborz. The two studies complement each other. Late Neogene internal deformation has had less of an effect on the central Alborz, whereas the stratigraphy is more comprehensive in the eastern Alborz. The overall aim of the paleostress analysis in the central and eastern Alborz is to elucidate the Paleozoic structural-tectonic framework and the transition of geodynamic regimes, from the Cambrian active margin of Gondwana to the Permian Paleotethys post-rift passive margin of the Central Iranian Microcontinent. The paleostress tensor analysis of fault-slip data confirms that the Alborz Margin was dominated by a main N-S-directed (present-day reference frame) extension during the Paleozoic. This extension was nearly perpendicular to the main basin-bounding normal faults and the margin. The Paleozoic stress field remained unchanged during successive geodynamic regimes, from proto-Tethys subduction to Neotethys rifting. Research on past plate rotations and internal deformation in the Alborz and Central Iranian microcontinent may benefit from the findings.