Structural, metamorphic and geochronological relations between the Zanskar Shear Zone and the Miyar Shear Zone (NW Indian Himalaya): Evidence for two distinct tectonic structures and implications for the evolution of the High Himalayan Crystalline of Zanskar

Robyr, Martin; Epard, Jean-Luc; Korh, Afifé El

doi:10.1016/j.jseaes.2013.09.007

Cited by 16 publications

(24 citation statements)

References 54 publications

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“…On the southern limb of this dome, the Miyar Valley represents an excellent natural cross‐section, revealing the structure and metamorphic zonation of the HHC of Zanskar. The geological setting of the Miyar Valley has been the subject of several studies, and the kinematic and metamorphic evolution of the HHC along this section is now well constrained (Pognante et al ., ; Steck et al ., ; Robyr et al ., , , ; Horton et al ., ).…”

Section: Geological Settingmentioning

confidence: 99%

“…). However, in Upper Lahul and SE Zanskar (NW Indian Himalaya), the HHC unit does not correspond to a SW‐directed thrust sheet as observed in most Himalayan sections, but forms a large‐scale dome structure referred to as the Gianbul dome (Dèzes et al ., ; Robyr et al ., , ; Horton et al ., ) (Fig. ).…”

Section: Geological Settingmentioning

confidence: 99%

“…This structure is a SW‐dipping ductile shear zone, some 3 km wide, that affects the contact between the Kade orthogneiss and the underlying amphibolite facies metasedimentary rocks of the Phe Formation. Kinematic analyses revealed that the MSZ initially acted as a NE‐directed synmetamorphic thrust (Pognante et al ., ; Steck et al ., ; Robyr et al ., ; see review in Robyr et al ., ). The formation of that thrust is associated with an early phase of crustal thickening related to NE‐directed movements.…”

Section: Geological Settingmentioning

confidence: 99%

“…The dominant penetrative schistosity and the NE–SW stretching and mineral lineations observed all along the section is a consequence of this NE‐directed phase of crustal thickening. This phase most likely took place during the Early to Middle Eocene and is linked to the prograde metamorphic field gradient preserved in the metasedimentary rocks of the Miyar Valley (Steck et al ., ; Robyr et al ., ). Moving up the valley, from the village of Udaipur to the south to the Gumba glacier to the north, a sequence across chlorite, biotite, garnet, staurolite, kyanite and sillimanite zones is crossed (Fig.…”

Section: Geological Settingmentioning

confidence: 99%

“…The High Himalayan Crystalline (HHC) of SE Zanskar (NW India) is selected for this study because it offers the unique advantage of having a single stratigraphic unit of pelitic and psammitic rocks that preserves a gradual increase in metamorphic conditions from the chlorite zone to the sillimanite–migmatite zone, all in response to one orogeny (e.g. Robyr et al ., and references therein). The chemical and textural evolution of monazite and allanite along this well‐studied section yields particularly reliable information on the conditions of formation of allanite and monazite during prograde metamorphism of pelites.…”

Section: Introductionmentioning

confidence: 99%

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Pressure and temperature conditions for crystallization of metamorphic allanite and monazite in metapelites: a case study from the Miyar Valley (high Himalayan Crystalline of Zanskar, NW India)

Goswami-Banerjee

Robyr

2015

Journal Metamorphic Geology

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The textural and chemical evolution of allanite and monazite along a well‐constrained prograde metamorphic suite in the High Himalayan Crystalline of Zanskar was investigated to determine the P–T conditions for the crystallization of these two REE accessory phases. The results of this study reveals that: (i) allanite is the stable REE accessory phase in the biotite and garnet zone and (ii) allanite disappears at the staurolite‐in isograd, simultaneously with the occurrence of the first metamorphic monazite. Both monazite and allanite occur as inclusions in staurolite, indicating that the breakdown of allanite and the formation of monazite proceeded during staurolite crystallization. Staurolite growth modelling indicates that staurolite crystallized between 580 and 610 °C, thus setting the lower temperature limit for the monazite‐forming reaction at ~600 °C. Preservation of allanite and monazite inclusions in garnet (core and rim) constrains the garnet molar composition when the first monazite was overgrown and subsequently encompassed by the garnet crystallization front. Garnet growth modelling and the intersection of isopleths reveal that the monazite closest to the garnet core was overgrown by the garnet advancing crystallization front at 590 °C, which establishes an upper temperature limit for monazite crystallization. Significantly, the substitution of allanite by monazite occurs in close spatial proximity, i.e. at similar P–T conditions, in all rock types investigated, from Al‐rich metapelites to more psammitic metasedimentary rocks. This indicates that major silicate phases, such as staurolite and garnet, do not play a significant role in the monazite‐forming reaction. Our data show that the occurrence of the first metamorphic monazite in these rocks was mainly determined by the P–T conditions, not by bulk chemical composition. In Barrovian terranes, dating prograde monazite in metapelites thus means constraining the time when these rocks reached the 600 °C isotherm.

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