T. Guneshwar Singh^1*, Ibotombi Soibam², Kevilhoutuo Theunuo³, Tapan Pal⁴, C. Debojit Singh³, M. Pradipkanta Singh¹ and Khetrimayum Ajit²

¹Geological Survey of India, North Eastern Region, SUMN, Imphal-795001(MN), India

²Manipur University, Chancipur, Imphal-795003(MN), India

³Geological Survey of India, Western Region, Jaipur-302004(RJ), India

⁴Formerly with Geological Survey of India

(*Corresponding Author, E-mail: ttongbram@gmail.com)

Abstract

The reported garnet-clinopyroxene bearing metamorphic rocks occurs as metamorphic sole in the ophiolite belt of south-eastern Manipur. Textural evidence show preserved peak assemblages of grt+ cpx + amp +plg + rt ± qtz. The garnet porphyroblast has composition of (Ca _0.74-1, Mg _0.03-0.77, Mn _0.01-0.9, Fe ²⁺ _1.2-1.6) (Al _1.90-1.98, Cr _0-0.03, Fe ³⁺ _0.03-0.34) Si₃O₁₂ and shows a progressive phase metamorphism with higher Alm _42-52 Grs _25-32, Sps _{3.66- 6.91} and low Pyp _12-17 at the core and lower Alm _38-49 Grs_24-29, Sps _{0.25- 1.90} and high Pyp_18-29 towards the rim. The high X_Mg (0.74-0.84) value of Clinopyroxene and negligible amount of orthopyroxene suggest a high-grade metamorphism condition. The reported garnet-clinopyroxene bearing metamorphic rock has preserved progressive metamorphic assemblages at P-T condition of 7.5 ± .50 kbar and 700-800^oC. The estimated metamorphic pressures suggest a metamorphism at depths of around 25-28 km. The recorded high temperature and its mineral assemblages infer a metamorphism in a mafic granulite facies during Cenozoic continent-continent collision between Indian plate and Myanmar microplate. The intake prograde metamorphic textures with lack of prominent symplectite growth over garnet grains suggested a rapid exhumation. The exhumation history suggests a wedge exhumation along the foreland basin of the Neo-Tethyan sutures of Indo-Myanmar Ranges and is control by the presence of westerly dipping thrust that is normally out sequence to the regional thrust. Such wedge exhumation mechanism of granulite facies metamorphic sole has been reported in the central and eastern parts of Himalayas and in Kalaymyo, Myanmar, a southern extension Manipur-Nagaland ophiolite belt.

Keywords: Garnet-clinopyroxene, Metamorphic Sole, Subduction, Ophiolite, Symplectite, Out of Sequence Thrust