Magnetic Fabric and Paleomagnetic Analyses of the Zaghar and Tafresh Areas, Central Urumieh-Dokhtar Magmatic Arc, Iran

Abstract

Magnetic fabric, paleomagnetic, and petrophysical studies were conducted on rocks in the Tafresh area of the central Urumieh-Dokhtar magmatic arc in Iran. The samples included Late Triassic dark gray sandstone, a mafic dyke, diorites, and a felsic dyke in the Zaghar region. Hydrothermal alteration in the Spid intrusion was investigated to understand the effects of alteration on magnetic fabric patterns. The AMS measurements support the theory that the Nayband Formation was constructed under a crustal extension regime. Magnetic susceptibility anisotropy in a microdioritic dyke indicates compression from the NNE-SSW, likely due to tectonic activity. AMS results from diorites in Zaghar suggest intrusions were emplaced in extensional spaces between the Tafresh and Chaghar thrust faults. The Spid intrusion’s magnetite is the primary carrier of magnetic susceptibility, but hydrothermal alteration has partly converted it into hematite, resulting in lower susceptibility and higher porosity in altered diorites. This process leads to a bimodal distribution of magnetic lineation trends. The Spid and Zaghar massifs underwent a northward tilt of about 30 degrees around an east-west axis following the Early Miocene. Post-Eocene rotations in the area are typically within ±20 degrees. This study demonstrates how magnetic properties can provide new insights into the evolution of tectono-magmatic processes and structural controls within a magmatic arc.

Keywords

• magnetic fabric
• paleomagnetism
• porosity
• magnetic mineralogy
• Urumieh-Dokhtar magmatic arc
• Iran