Characterization of finite strain ellipsoid of the Late Permian-Early Triassic metamorphic complexes in the Kon Tum terrain

Abstract

The parameters of finite strain ellipsoid determined from the regional metamorphic rocks record the relevant tectonic regime. The ductilely deformed Late Permian-Early Triassic metamorphic rocks, formed at depth, are widely exposed in the Kon Tum terrane and record a long tectonic history. In order to characterize the Late Permian-Early Triassic tectonic regime for the Kon Tum terrane, 20 oriented samples of gneiss and crystalline schist were selected from the Kham Duc, Ngoc Linh, and Kan Nack complexes for analyzing the finite strain ellipse by Rf/Phi method and determination of the finite strain ellipsoid from a combination of 3 thin sections oriented perpendicularly to the three principal strain axes. The analysis results indicate that the Late Permian-Early Triassic metamorphic rocks in the Kon Tum terrane are characterized by 3-dimensional finite strain ellipsoids with maximum stretching axis X elongated in a northwest-southeast direction and a maximum shortening axis Z nearly vertically. These strain geometries are consistent with a northwest-southeast striking extensional regime during the Late Permian-Early Triassic with vertical shortenning during exhumation of ductile rocks in the Kon Tum terrane.