Polyphase Deformation in Phanerozoic Rocks of the Central Himalayan Gneiss, Northwest India

Powell, Christine; Conaghan, Patrick J.

doi:10.1086/627830

Cited by 51 publications

(18 citation statements)

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“…Miyar Thrust); (3) the involvement in the metamorphism of stratigraphically dated sequences of Mesozoic age like the Jurassic metasediments of Tandi (Powell & Conaghan, 1973).…”

Section: B Zircon and Monazite U-th-pb Isotope Resultsmentioning

confidence: 99%

The crystalline units of the High Himalayas in the Lahul–Zanskar region (northwest India): metamorphic–tectonic history and geochronology of the collided and imbricated Indian plate

et al. 1990

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-In the High Himalayan belt of northwest India, crustal thickening linked to Palaeogene collision between India and Eurasia has led to the formation of two main crystalline tectonic units separated by the syn-metamorphic Miyar Thrust: the High Himalayan Crystallines sensu stricto (HHC) at the bottom, and the Kade Unit at the top. These units are structurally interposed between the underlying Lesser Himalaya and the very low-grade sediments of the Tibetan nappes. They consist of paragneisses, orthogneisses, minor metabasics and, chiefly in the HHC, leucogranites. The HHC registers: a polyphase metamorphism with two main stages designated as Ml and M2; a metamorphic zonation with high-temperature recrystallization and migmatization at middle" structural levels and medium-temperature assemblages at upper and lower levels. In contrast, the Kade Unit underwent a low-temperature metamorphism. Rb-Sr and U-Th-Pb isotope data point to derivation of the orthogneisses from early Palaeozoic granitoids, while the leucogranites formed by anatexis of the HHC rocks and were probably emplaced during Miocene time.Most of the complicated metamorphic setting is related to polyphase tectonic stacking of the HHC with the 'cooler' Kade Unit and Lesser Himalaya during the Himalayan history. However, a few inconsistencies exist for a purely Himalayan age of some Ml assemblages of the HHC. As regards the crustal-derived leucogranites, the formation of a first generation mixed with quartzo-feldspathic leucosomes was possibly linked to melt-lubricated shear zones which favoured rapid crustal displacements; at upper levels they intruded during stage M2 and the latest movements along the syn-metamorphic Miyar Thrust, but before juxtaposition of the Tibetan nappes along the latemetamorphic Zanskar Fault.

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“…Miyar Thrust); (3) the involvement in the metamorphism of stratigraphically dated sequences of Mesozoic age like the Jurassic metasediments of Tandi (Powell & Conaghan, 1973).…”

Section: B Zircon and Monazite U-th-pb Isotope Resultsmentioning

confidence: 99%

The crystalline units of the High Himalayas in the Lahul–Zanskar region (northwest India): metamorphic–tectonic history and geochronology of the collided and imbricated Indian plate

et al. 1990

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“…Nevertheless, the main fabric is certainly Himalayan in age as: (i) all the Rb/Sr, K/Ar or A?/Ar*O isotopic ages on minerals range from 50 to 3 Ma (e.g. Saxena, 1981 for review; Maluski & Matte, 1984;Deniel et al, 1987) and (ii) further west, in Garhwal and Kashmir, this foliation is the axial cleavage of large synmetamorphic recumbent folds in which Mesozoic terranes are involved (Powell & Conaghan, 1973;Honneger, Dietrich, Frank, Gansser, ThiieN & Trommsdorff, 1982).…”

Section: 'mentioning

confidence: 99%

The metamorphism in the Central Himalaya

Pêcher

1989

Journal Metamorphic Geology

248

118

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Au along the Himalayan chain an axis of crystalline rocks has been preserved, made of the Higher Himalaya crystalline and the crystalline nappes of the Lesser Himalaya. The salient points of the metamorphism, as deduced from data collected in central Himalaya (central Nepal and Kumaun), are:1. The Higher Himalaya crystalline, also called the Tibetan Slab, displays a polymetamorphic history with a first stage of Barrovian type overprinted by a lower pressure and/or higher temperature type metamorphism. The metamorphism is due to quick and quasi-adiabatic uplift of the Tibetan Slab by transport along an MCT ramp, accompanied by thermal refraction effects in the contact zone between the gneisses and their sedimentary cover. The resulting metamorphic pattern is an upparenf (diachronic) inverse zonation, with the sillimanite zone above the kyanite zone.2. Conversely, the famous inverted zonation of the Lesser Himalaya is basically a primary pattern, aquired during a one-stage prograde metamorphism. Its origin must be related to the thrusting along the MCT, with heat supplied from the overlying hot Tibetan Slab, as shown by synmetamorphic microstructures and the close geometrical relationships between the metamorphic isograds and the thrust.3. Thermal equilibrium is reached between units above and below the MCT. Far behind the thrust tip there is good agreement between the maximum temperature attained in the hanging wall and the temperature of the Tibetan Slab during the second metamorphic stage; but closer to the.MCT front, the thermal accordance between both sides of the thrust is due to a retrogressive metamorphic episode in the basal part of the Tibetan Slab.

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“…Most of the workers opined that the Himalaya witnessed only one orogeny during the Tertiary, ruling out any earlier strong deformation involving folding and thrusting (Powell and Conaghan, 1973;Powell et al, 1979;Gansser, 1981;Windley, 1983). This is despite several unconformities observed in the Himalaya, most notable being an angular unconformity between the Cambrian and the Ordovician (Hayden, 1904).…”

Section: Introductionmentioning

confidence: 99%