2:15 PM - 2:30 PM

# [SCG62-24] Detailed application of the microboudin palaeopiezometer: estimation of principal deviatoric stresses imposed on a metachert from the Warrawoona greenstone belt in East Pilbara Terrane, Western Australia

Keywords:palaeostress analysis, microboudin palaeopiezometer, metachert, tourmaline, microboudinage structure

_{0}is obtained the group of mineral lineation ± 15° and perpendicular to the mineral lineation ± 15° as 10.2 MPa and 5.3 MPa, respectively. Also, the values of σ

_{0}varied corresponding to the orientation of the tourmaline grains; relatively large value of σ

_{0}obtained from tourmaline grains oriented around the mean orientation defined as the mineral lineation, whereas relatively small value of σ

_{0}obtained from tourmaline grains oriented around perpendicular to the mineral lineation. Given that σ

_{1}- σ

_{3}and σ

_{1}- σ

_{2}are as 10.2 MPa and 5.3 MPa, respectively, magnitude of principal deviatoric stresses (σ'

_{1}, σ'

_{2}and σ'

_{3}) are obtained as σ'

_{1}= 5.3 MPa, σ'

_{2}= -0.1 MPa and σ'

_{3}= -5.1 MPa. In this stress state, the stress ratio φ = (σ

_{2}- σ

_{3})/(σ

_{1}- σ

_{3}) is 0.48 that indicates typical triaxial compression. As the microboudinage is considered to have occurred immediately before the rock encountered the brittle-plastic transition during the plastic deformation, these values correspond to conditions at approximately 10–15 km depth and 300°C within an Archaean greenstone belt.