Tectonics and evolution of the central sector of the Himalaya

Abstract

Following the India-Asia collision, intracrustal movements along the Main Central Thrust (MCT) and Main Boundary Thrust (MBT) in a piggy-back-style, thrust duplexes developed that uplifted the Vaikrita (Central) crystallines of the basement to more than 8000 m elevation. Blocking of subduction on the suture and slowing down of movement on the MCT led to the formation of the Trans-Himadri (Malari) Thrust between the Vaikrita basement and the Tethyan cover sediments, and to gravity-induced backfolds and backthrusts in the latter. The Vaikrita crystallines underwent upper amphibolite to lower granulite facies metamorphism at 600-650 °C and more than 5 kbar (1 kbar = 101 *8 Pa) and migmatistation associated with 28-20 Ma old S-type granites that formed at 15-30 km depth during the culmination of metamorphism and thrust deformation. Delimited by the MCT and MBT, the Lesser Himalaya is made of Proterozoic sediments beneath the Almora nappe constituted of low- to medium-grade metamorphics and 1900+ 100 Ma old granitic gneisses and 560 + 20 Ma old granites. The Lesser Himilaya underwent considerable neotectonic rejuvenation during differential movements along the MBT. The frontal Siwalik molasse below the MBT was severely thrusted and folded in the late Holocene, and continued underthrusting of the Indian Shield beneath the Himalaya is manifest in the development and activation of the deep Himalayan Front Fault (HFF), which separates the Siwalik from the subRecent-Recent alluvial plain of the Ganga Basin.

Radon Variations in Soil and Groundwater of Bhilagana Valley, Garhwal Himalaya, India

“…The higher value of radon in water sample #W 9 (160.1 Bq/l) is possibly due to the continued movement along the different shear planes, exhibiting extreme shearing and mylonitization. 29) Radon concentration in groundwater was measured from the joint/fault related and colluvial related springs. The higher radon values (121 Bq/l to 160 Bq/l) were recorded in joint/ fault related springs.…”

Quaternary extensional and compressional tectonics revealed from Quaternary landforms along Kosi River valley, outer Kumaun Lesser Himalaya, Uttarakhand

“…In the present study area of the outer Kumaun Lesser Himalaya, the geomorphic expressions of neotectonics are observed along the SAT, Garampani Fault (GF) and E-W trending system of Fig. 1 Geological map of the study area (Valdiya 1980(Valdiya , 1988b faults, e.g. the Amel and Betalghat-Basgaon Faults (Fig.…”

“…It shows intercontinental faults and rejuvenated topography (Valdiya 1993(Valdiya , 2005. A number of NNW-SSE trending right lateral tear faults have been recognized (Middlemiss 1890a, b;Gansser 1964;Valdiya 1976Valdiya , 1988b in the Kumaun Himalaya. The Himalaya is cut across by an extensively active fault system that extends from the Karakoram Fault to the Bengal Plain producing landforms pertaining to active faults (Nakata et al 1984;Nakata and Kumahara 2002).…”

“…Mehta and Sanwal (2011) have shown evidence of active tectonics along the Kosi River valley based on normal faulted Quaternary deposits. Valdiya (1988b) described mini-horst and mini-graben formed due to vertical movement along parallel to subparallel deep faults. The present study has been carried out along the SAT, RT, GF and the normal faults with an aim to present landforms associated with extensional and compressional tectonics along the same river valley (Valdiya 1988b).…”

A Critical Analysis of North-South Continuity of Landmasses across Indus-Yarlu-Tsangpo Suture Zone: Its Bearing on the Himalayan Evolution

“…Several studies have shown that the structural grains of Peninsula India extend up to the Lesser Himalaya (Auden, 1935;Valdiya, 1976Valdiya, , 1988Raiverman, 2002). Indeed, the pre-existing crosslineaments within the ophiolites of the Indus-Tsangpo Suture Zone of southern Tibet showing same concept are carried into the higher and Tethyan Himalaya, and up to trans-Himalaya (Gansser, 1980) .The Suru lineament, a major north-south Trans-Asiatic lineament, extends from the Punjab plains in India to the arctic Ocean, running close to the 60 o E meridian, and has been divided into eight segments (see : Raiverman, 1992 (Raiverman, 1992, fig.4) shows their continuity with those in the Eurasian block, as revealed in the spatial distribution pattern of the orographic axes of Eurasia ( Figure 3).…”