Stress state and fluid pressure analyses using ultramafic dykes and calcite veins, SW Iran

Abstract

In this paper, orientations of ultramafic dykes and calcite veins of the Tange-Hana area (SW Iran) are used to determine the relative stress and fluid pressure (Pf) conditions by constructing a 3D Mohr circle. The pole distributions of ultramafic dykes have a wide range of orientation and mainly show the girdle pattern. The 3D Mohr circle construction for ultramafic dykes suggests a Pf > σ2 condition and shows high value of fluid pressure (Pf = 939.51) near to the maximum principal stress (σ1). Driving pressure ratio (R′) and stress ratio (O) were calculated as 0.78 and 0.7, for ultramafic dykes, respectively. Calcite vein polar distribution is so limited and mainly shows a cluster pattern. Limited distribution of calcite vein orientation indicates a Pf < σ2 condition. The 3D Mohr circle construction reveals small amount of fluid pressure (Pf = 288.55) near to the minimum principal stress (σ3). The amounts of driving pressure ratio (R′) and stress ration (O) were calculated to be equal to 0.07 and 0.27, for calcite veins, respectively. Our results show the occurrence of ultramafic dykes and that calcite veins are related to different stress phases. Also, according to our results, it revealed that ultramafic and calcite dykes and veins were generated in prolate and oblate stress ellipsoid conditions, respectively.