Dextral transpressional shearing and strike-slip partitioning developments in the Central Myanmar Basin during the collision between the India Plate and West Myanmar Block

Abstract

Central Myanmar Basin (CMB) lies between the two major strike-slip faults: Sagaing Fault to the east and Kabaw Fault to the west. Central Volcanic Line of Myanmar emplaced en-echelon array of P-shears along the fault zone, which was active dextral as surrounding major faults at a low angle about 15° to the shear zone boundary. CMB was developed as strike-slip partitioned transpression model as proposed in this study. The transprsession tectonic is common with oblique convergence subduction as well as collision of India Plate to West Myanmar Block, especially effects on the CMB. Structural evidence are occurred as en-echelon folding and fracturing by satellite photos, field observation and 3D strain ellipsoid construction showing plane strain by pure shear upon ideal strike-slip with simple shear. In this study, two types of transpression distinguished as homogeneous and strike-slip partitioning which are developed within the frame of the strike-slip fault with progressive deformation. Under the condition of the strike-slip partitioned transpression, strain partitioning is distinctly occurred together with progressive deformation and reactivation of pre-existing structures such as cylindrical fold to double plunging fold, normal fault to oblique slip fault and positive flower structure. Deformation process related to the India Plate movement deduced the period of Late Miocene and Pliocene-Pleistocene based on the structural analysis in Rakhine Coastal region, western Myanmar. During the period between the Late Miocene to Pliocene-Pleistocene, pre-existing ophiolite zone in the Indo-Myanmar Ranges (IMR) was split up different zones by the Sagaing Fault displacement, accompanied to the West Myanmar Block movement with India Plate subduction. Accordance with the Sagaing Fault displacement and group of mud volcanoes shifting, the CMB moved northward about 450km with displacement rate 5–7cm per annum by the 45–50°convergent angle of India Plate collision to Eurasia Plate. Transpression deformation of northward compression was developed in the CMB, simultaneously on the other side transtension as pull-apart basin was formed by Andaman Sea opening at the south on the Sagaing Fault. During the Miocene time, collision of India Plate to Eurasia Plate was principal and caused the deformation at northern border the India, in which India Plate moved both in northwards and rotated anti-clockwise, whereas West Myanmar Block together with Sibumasu Block rotated clockwise becoming final closure of the northeasternmost Assam and Myanmar regions. During the Oligocene time, deposition of the shallow marine Barail formation in the Bengal Basin and shallow marine to continental shelf sequences in the CMB started as twin trough. This study provides the transpression deformation in the CMB and related regions during syn- and post-collision of India Plate to West Myanmar Block with position and kinematic structural interpretation.