Geological setting of the Siang Dome located at the Eastern Himalayan Syntaxis

Abstract

DOI = 10.3126/hjs.v5i7.1228 Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.16-17

The youngest marine deposits preserved in southern Tibet and disappearance of the Tethyan Ocean

“…In the eastern Himalayan syntaxis, collision-related final marine sediments are also preserved in the Siang window, NE of the Assam Basin (Acharyya, 2007;Acharyya and Saha, 2008). The Eocene marine strata in this region are not a continuous sequence.…”

“…1a), and preserves the Eocene final marine deposits of 44 Ma (Bhatia and Bhargava, 2006). South of the eastern Himalayan syntaxis, the collision-related final marine sediments outcrop as the lower Eocene Rengging Formation and the upper lower Eocene to Middle Eocene Yinkiong Formation in the Siang window region of Assam-Arakan Basin (Tripathi et al, 1978(Tripathi et al, , 1981Tripathi and Mamgain, 1986;Tripathi et al, 1988;Acharyya, 2007;Acharyya and Saha, 2008). Even younger final marine deposits occur in the Bengal basin, where the Sylhet limestone and overlying Kopili Formation are of Middle to upper Eocene age (Samanta, 1965(Samanta, , 1968(Samanta, , 1969Singh and Pratap, 1983;Alam et al, 2003).…”

Mylonitic volcanics near Puging, Upper Siang district, Arunachal Pradesh: Evidence of oblique-slip thrusting

“…The Siang dome is referred as orogen transverse antiformal structure (Acharyya and Saha 2008). As thrust spacing in the western side is both narrower and steeper (see map: dip is ∼70 westerly) than the eastern side, the mode of overthrusting of both Siyom and Rikor thrust sheets above the volcanics have to be oblique slip, producing a simple shear with a moderate simultaneous pure shear component (Fossen et al 1994).…”

“…Tripathi et al (1988) assigned the Eocene age for the Abor volcanics on the basis of fossil records from the Dalbuing area of Yamne valley. Towards the south of the Siang valley, the volcanics are folded and towards the further south, these are exposed against the younger Siwaliks along a splay of Main Boundary Thrust (MBT) (Acharyya and Saha 2008). In the extreme south of Puging, Abor volcanics are intermixed with the green and purple shales of the Yinkiong Group, while in the north and south of Puging, the volcanics are intrusive into the Rikor Group of rocks.…”

“…The kinematic indicators from the shear zones helped us constrain the sense of shear in the two shear zones. Combining the structural morphology of the Siang dome (Acharyya and Saha 2008) and shear sense in the two shear zones, we are proposing a model considering the compressions related to India-Asia and Indo-Burma collisions. Finally, we are also proposing that, considering the compression directions both from the west and from the east, the two shear zones are the manifestations of oblique-slip thrusting of the thrust sheets above the Yinkiong Group of rocks, both in the north and south of Puging.…”