Quantitative finite strain analysis of high-grade metamorphic rocks within the Mae Ping shear zone, western Thailand

Abstract

The NW trending Mae Ping shear zone exposes high-grade metamorphic rocks, the so called Lansang gneiss in the Tak region, western Thailand. The lithologies within the strike-slip zone mainly consist of orthogneisses and paragneisses. Using Fry's method for 2-dimensional strain analysis we find that the averaged finite strain ratio (R s ) of the XY-plane is R s = 1.35-1.69. Based on the kinematic vorticity analysis of the mylonitic gneisses in the shear zone, the kinematic vorticity number is W k = 0.8-1.0 with an average of W k = 0.95. The results imply that the homogeneously deforming rocks within the Mae Ping shear zone have a strong simple shear component with a minor pure shear contribution of about 15 %. The kinematic indictors from both outcrop and micro scopic scales indicate a sinistral strike-slip shear sense. We conclude that the Mae Ping shear zone accommodated crustal scale sinistral transpression.

Quantitative finite strain analysis of the quartz mylonites within the Three Pagodas shear zone, western Thailand

“…These results fit well with the extrusion model in the SE Asia region (Lacassin et al, 1993(Lacassin et al, , 1997. The Three Pagodas shear zone is characterized by flow geometry similar to that recorded in the parallel northward Mae Ping shear zone (Ponmanee et al, 2016) with a smaller kinematic vorticity numbers (W k ) (Fig. 10).…”

“…However, the area where these strike-slip systems mechanically interact is still poorly documented. Many authors reported that the Mae Ping strike-slip zone is splayed to the Klaeng fault zone in eastern Thailand, and the Three Pagodas strike-slip zone is extended to the Ranong shear zone in the southern Thailand (Lacassin et al, 1993(Lacassin et al, , 1997Leloup et al, 1995;Gilley et al, 2003;Geard, 2008;Nantasin et al, 2012;Ridd, 2012;Ponmanee et al, 2016). In other geological interpretations (e.g.…”

“…Lacassin et al, 1997;Palin et al, 2013). Especially in Thailand, syndeformational metamorphic rocks are exposed along the main ductile strike-slip shear zones (Lacassin et al, 1997;Kanjanapayont, 2015;Kanjanapayont et al, 2012a;Nantasin et al, 2012;Palin et al, 2013;Ponmanee et al, 2016) (Fig. 1).…”

Petrochemistry of Lan Sang metamorphic suites

“…Mountain ranges in this area extend stretchy towards the Mae Ping fault, which gradually changes the orientation along the fault directly to the NW-SE direction. They have been recognized as a sinistral strike-slip fault [7,8]. In Shan-Thai terrane, its basement is occupied by Precambrian high-grade metamorphic and Middle or Upper Paleozoic rocks characterized by various grades of metamorphism overprinting sedimentary sequences.…”

“…Rim region ages range [5]). Geologic map of Tak province (revised from [8,9]) reveals the location of the study area (in the red box).…”