Tectonic implication of quantitative micro-fabric analyses of quartz c-axis development within the Tutak gneiss dome, Zagros hinterland fold-and-thrust belt
Quartz c-axis fabrics, finite strain, and kinematic vorticity number analyses were used to investigate deformation characteristics of the Tutak gneiss dome located in the eastern edge of the basement-involved Zagros hinterland fold-and-thrust belt. The opening angle of the quartz c-axis fabric patterns was used to estimate deformation temperatures, which suggest greenschist-to-amphibolite-facies conditions (430 ± 50 °C to 660 ± 50 °C). The kinematic vorticity number varies from 0.6 to 0.95 (mean kinematic vorticity number of 0.81), which indicates that the metamorphic rocks of the Tutak gneiss dome experienced a sub-simple shear regime by contribution of both pure shear (39%) and simple shear (61%) deformation components. NW–SE-striking foliations have commonly SW and NE dips accompanied by mostly NW–SE-plunging and subordinate NE–SW-plunging-stretching lineations. These indicate more extension along the NW–SE trend to produce a prolate elliptical wedge shape in map view. Structural and vorticity analysis suggests that the Tutak gneiss dome has experienced earlier dome formation followed by thrust stacking rather than the two deformations occurring synchronously, and a protracted progressive deformation through a decreasing temperature regime.