Early Proterozoic granite of the Taplejung Window, far eastern Lesser Nepal Himalaya

Abstract

The Lesser Himalayan Sequence of the Taplejung Window in the far eastern Nepal Himalaya can be divided into Taplejung Formation, Mitlung Augen Gneiss and Linkhim Schist (from bottom to top respectively). The window is a large domal shaped anticline plunging to the east.
 Two-mica granite bodies (Amarpur Granite, Kabeli Khola Granite and Tamor River Granite) have intruded the metasediments of Taplejung Formation. The granite bodies are discordant to subconcordant in relation to the country rocks. Quartz, alkali feldspar, plagioclase, muscovite, biotite and tourmaline are the main constituent minerals of the granite. Generally, the core of granite bodies is undeformed, whereas the marginal part is gneissfied with S-C mylonitic texture showing the top to south sense of shear. This sense of shear is related to the movement along the Main Central Thrust (MCT). All the samples from the granitic bodies fall under the granite field in the normative quartz-alkali feldspar-plagioclase (QAP) triangular diagram. The mineral composition shows that the granite is peraluminous in nature. The Kabeli Khola Granite has yielded a 40Ar/ 39Ar muscovite age older than 1.6 Ga indicating its magmatic age. The granites of the study area can also be correlated with the 1.8 Ga Ulleri type augen gneiss of central Nepal.

Review of the Geology of the Arun-Tamor Region, Eastern Nepal: Present Understndings, Controversies and Research Gaps

“…Similarly, the Lesser Himalayan Sequence has undergone a syn-MCT and a post-MCT metamorphic event in which they suffered the inverted and the retrogressive metamorphism, respectively. Upreti et al (2003) focused their studies on the granitic intrusive bodies in between the metasedimentary sequence of the Taplejung Window. The window is an east-plunging domal anticline.…”

“…The lithological sequence is well developed in the case of western Nepal, which is devoid of the crystalline nappe covers (Sakai, 1983(Sakai, , 1985Dhital et al, 2002;Dhital, 2015;Ulak, 2016a). The Arun-Tamor region of eastern Nepal contains very narrow stretches, north of MBT as frontal part, and large tectonic windows, beneath the crystalline covers at the deep gorges of the Arun and Tamor rivers of the Lesser Himalaya (Bordet, 1961;Akiba et al, 1973;Upreti et al, 2000Upreti et al, , 2003Dhital, 2015;Ulak, 2016a). The Lesser Himalaya, east of Dharan, nearly comes in direct contact with the Siwalik and is slightly broadened west of Dharan (Dhital, 2015;Rai et al, 2016;Ulak, 2016a).…”

“…They are comprised of diamictite, quartzite, shale and sandstone. The Arun and Taplejung Tectonic Windows consist of metasedimentary sequences of thickness about 5000 m (Andrews, 1985) and 6000 m, respectively (Upreti et al, 2003;Sakai et al, 2013). These tectonic windows are domal anticlines, with the Arun Window having an N-S axial trend and the Taplejung Window plunging to the east (Bordet, 1961;Akiba et al, 1973;Upreti et al, 2000Upreti et al, , 2003.…”

“…The Arun and Taplejung Tectonic Windows consist of metasedimentary sequences of thickness about 5000 m (Andrews, 1985) and 6000 m, respectively (Upreti et al, 2003;Sakai et al, 2013). These tectonic windows are domal anticlines, with the Arun Window having an N-S axial trend and the Taplejung Window plunging to the east (Bordet, 1961;Akiba et al, 1973;Upreti et al, 2000Upreti et al, , 2003. The metasedimentary succession consists of limestone, slate, phyllite, schist, and gneiss (Bordet, 1961;Akiba et al, 1973;Andrews, 1985;Schelling, 1992;Dhital, 2015).…”

“…The metasedimentary succession consists of limestone, slate, phyllite, schist, and gneiss (Bordet, 1961;Akiba et al, 1973;Andrews, 1985;Schelling, 1992;Dhital, 2015). The metamorphic section of the Tribeni-Dharan-Dhankuta region exhibits prograde metamorphism (Akiba et al, 1973;Maruo et al, 1979;Sunuwar, 1993), whereas the Arun and Tamor Tectonic Window section exhibit inverted metamorphism (Bordet, 1961;Meier & Hiltner, 1993;Upreti et al, 2000Upreti et al, , 2003Ghimire, 2001). The metamorphism grade ranges from green schist to almandine-amphibolite facies (Andrews, 1985;Meier & Hiltner, 1993;Sakai et al, 2013).…”