Inverted metamorphic sequence in the Sikkim Himalayas: crystallization history, <i>P–T</i> gradient and implications

Dasgupta, Somnath; Ganguly, Jibamitra; Neogi, Sudipta

doi:10.1111/j.1525-1314.2004.00522.x

Cited by 160 publications

(99 citation statements)

References 48 publications

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“…Available studies indicated that metamorphic rocks from the HHCS and the NHGD had experienced metamorphic reactions at pressure greater than 800 MPa, and temperature up to 800℃ [33][34][35] . Partial melting of amphibolite can occur at these conditions [36] .…”

Section: Mechanism For the Formation Of The Yardoi Leucogranitementioning

confidence: 99%

Early Oligocene anatexis in the Yardoi gneiss dome, southern Tibet and geological implications

et al. 2008

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The Yardoi gneiss dome is located to the easternmost of the North Himalayan Gneiss Dome (NHGD), southern Tibet. It consists of metapelite, garnet amphibolite, granite and leucogranite, and is a key subject to constrain the formation and tectonic evolution of NHGD. SHRIMP zircon U/Pb data on the leucogranite yield an age of 35.3±1.1 Ma, which is substantially older than that of the similar leucogranites to the west. Sr and Nd isotope systematics indicate that this leucogranite was derived from partial melting of the mixed garnet amphibolite and metapelite. Our data suggest that (1) during the early stage of Himalayan magmatism, amphibolite dehydration melting overwhelmed that of the metapelite; and (2) such a melting at middle-lower crust might be a major factor that initiated the movement along the Southern Tibetan Detachment System (STDS). leucogranite, metapelite, crustal anatexis, Himalayan Orogenic Belt, North Himalayan Gneiss DomeConvergence between the Indian and Eurasian plates resulted in intensive structural deformation, high-grade metamorphism and crustal anatexis in the Himalayan Orogenic Belt. In southern Tibet, the post-collisional tectonics is represented by the development of concurrent N-S compression and extension [1][2][3][4][5] , and intensive crustal anatexis [6][7][8][9][10] which formed two subparallel granitic belts separated by the Southern Tibetan Detachment System (STDS), e.g. the High Himalayan Granitic belt (HHG) to the south, and the North Himalayan Gneiss Dome (NHGD) to the north (Figure 1(a)). They have preserved the records on the nature of deformation, high-grade metamorphism, crustal anatexis and near-surface processes associated with the active continental collision between the Indian and Eurasian plates. Documenting the timing and nature of these processes is essential to addressing the way of interplay and degree of coupling between these processes. A large number of studies have been directed toward better understanding different aspects of the HHG and yielded abundant meaningful information with regard to how the crust behaved during the collision [1][2][3][4][5][6][7][8][9][10][11][12] . However, much less effort has been made on the NHGD.Gneiss and amphibolites within the NHGD commonly experienced amphibolite to granulite facies metamorphism at T > 800℃, and P > 800 MPa. Partial melting at these conditions is widespread and represented by the occurrence of migmatite and leucogranites [13][14][15][16] . Available data show that these high-grade metamorphic rocks and leucogranites have similar mineral and isotope compositions to those in the HHG, and experienced similar deformation. They were considered as the northern extension of High Himalaya Crystalline Sequence (HHCS) [16] . Both suites of rock from NHGD and HHG have been regarded as a mid-lower crustal channel [17,18] . Metamorphic rocks and granites in the NHGD are structurally lower than STDS. Knowledge of the relationship between NHGD and STDS is critical to test tectonic models for the evolution of southern Tibet

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Section: Mechanism For the Formation Of The Yardoi Leucogranitementioning

confidence: 99%

Early Oligocene anatexis in the Yardoi gneiss dome, southern Tibet and geological implications

et al. 2008

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“…One of the most well-known discontinuities is the Main Central Thrust (MCT) which separates the Higher Himalayan Sequence in the north from the underlying Lesser Himalayan Sequence in the south. The Higher Himalayan Crystalline Sequence (HHCS) consists of quartzofeldspathic gneisses of both igneous and sedimentary parentage that suffered high-grade amphibolite and granulite facies metamorphism (Neogi et al 1998;Catlos et al 2001;Dasgupta et al 2004). In the Darjeeling-Sikkim area, the base of the HHCS is represented by a strongly deformed granitic body called the Lingtse Gneiss (Acharyya 1978).…”

Section: Geological Backgroundmentioning

confidence: 99%

Integrated very low-frequency EM, electrical resistivity, and geological studies on the Lanta Khola landslide, North Sikkim, India

et al. 2009

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Landslides are very common in high-altitude Himalayan terrains. Major roads in the Himalayas are frequently blocked due to heavy landslides and remain closed for long periods of time. Permanent mitigatory solutions to these landslides are required to keep the highways open. Lanta Khola, located 71.2 km north of Gangtok (capital of the Indian state of Sikkim), is one of the oldest landslides on the North Sikkim Highway and is active since 1975. The rock types on either side of the landslide are different (augen gneiss in the east and metapelitic schist in the west), and it is believed that the Main Central Thrust passes through the slide zone. Since the slide is invariably activated in the aftermath of heavy rainfall, it is important to identify the subsurface structures that channel water below the landslide surface in order to understand the triggers of slide activity. This can only be accomplished by geophysical survey; however, an appropriate geophysical technique that can be applied in such terrains must be identified. Very low-frequency (VLF) electromagnetic survey was performed over the Lanta Khola landside in order to delineate subsurface structures. Although a very limited number of VLF transmitters are available worldwide, it was possible to pick up VLF signals from a number of VLF stations even in this highaltitude mountainous terrain. VLF measurements along five profiles perpendicular to the geological strike were recorded, and a high conducting zone was delineated from the VLF observations. This conducting zone correlates with the low resistive zone identified from gradient resistivity profiling. The anomalies confirm that there is a water-saturated zone (soggy zone) even in the subsurface of the slide parallel to the geological gneiss-schist contact within the Lanta Khola slide. This indicates that the conductive feature correlates with a weak water-saturated debris layer that lies along the slide and is parallel to the geological contact. Resistive structures on either side of the landslide zone can thus be correlated with the stable ground. It is necessary to drain out water from the soggy zone to minimize slide activity since this zone appears to penetrate into the body of the slide.

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“…Studies have variously bounded the Main Central Thrust zone with two named thrusts (Catlos et al 2004;Dubey et al 2005;Bhattacharyya & Mitra 2009, placed the Main Central Thrust at the top of the Main Central Thrust zone (Ghosh 1956;Acharyya 1975;Banerjee et al 1983) or placed the Main Central Thrust at the base of the Main Central Thrust zone (Searle & Szulc 2005). Furthermore, the distinctive Palaeoproterozoic Lingtse gneiss, strongly sheared along the Main Central Thrust zone throughout the Sikkim Himalaya, has been used in other studies as a defining lithology for determining the location of the Main Central Thrust (Neogi et al 1998;Chakraborty et al 2003;Dasgupta et al 2004).…”

Section: Geological Settingmentioning

confidence: 99%

Tectonic interleaving along the Main Central Thrust, Sikkim Himalaya

Mottram

Argles

Harris

et al. 2014

JGS

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Geochemical and geochronological analyses provide quantitative evidence about the origin, development and motion along ductile faults, where kinematic structures have been overprinted. The Main Central Thrust is a key structure in the Himalaya that accommodated substantial amounts of the India-Asia convergence. This structure juxtaposes two isotopically distinct rock packages across a zone of ductile deformation. Structural analysis, whole-rock Nd isotopes, and u-Pb zircon geochronology reveal that the hanging wall is characterized by detrital zircon peaks at c.

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Inverted metamorphic sequence in the Sikkim Himalayas: crystallization history, P–T gradient and implications

Cited by 160 publications

References 48 publications

Early Oligocene anatexis in the Yardoi gneiss dome, southern Tibet and geological implications

Early Oligocene anatexis in the Yardoi gneiss dome, southern Tibet and geological implications

Integrated very low-frequency EM, electrical resistivity, and geological studies on the Lanta Khola landslide, North Sikkim, India

Tectonic interleaving along the Main Central Thrust, Sikkim Himalaya

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