The metamorphism in the Central Himalaya

Pêcher, Arnaud

doi:10.1111/j.1525-1314.1989.tb00573.x

Cited by 248 publications

(128 citation statements)

References 21 publications

(11 reference statements)

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“…Some workers (Caby et al, 1983;Pêcher, 1989Pêcher, , 1991Coleman, 1998) consider that the STD lies structurally below the Manaslu pluton, which has a top intrusive contact, whereas others (Searle & Godin, 2003) consider that the STD lies above the granite, as most often observed, and view the top contact of the granite as a tectonic one. For Guillot and collaborators (Guillot, 1993;Guillot et al, 1993Guillot et al, , 1995a, the normal shearing observed at the Manaslu top contact is local and related to the ballooning effect of the intrusion process.…”

Section: Top Contactmentioning

confidence: 99%

“…U-Pb dating of monazite suggests that the age of migmatization of the FIII orthogneisses is older than the FI migmatites, at around 36 Ma, or early Oligocene (Hodges et al, 1996;Coleman, 1998). Themobarometric studies have shown that peak metamorphic pressures at the base of the HHC (close to the MCT) are in the range 8-10 kbar, and decrease regularly upsection down to about 5 kbar at the top of the HHC (Pêcher, 1989;Coleman & Hodges, 1998;Guillot, 1999;Macfarlane, 1999). Peak temperature varies between 580 and 700 C within the HHC in this area (Pêcher, 1989;Coleman & Hodges, 1998;Guillot, 1999;Macfarlane, 1999).…”

Section: The Manaslu Leucogranite and Its Host Rocks Bottom And Top Hmentioning

confidence: 99%

“…Themobarometric studies have shown that peak metamorphic pressures at the base of the HHC (close to the MCT) are in the range 8-10 kbar, and decrease regularly upsection down to about 5 kbar at the top of the HHC (Pêcher, 1989;Coleman & Hodges, 1998;Guillot, 1999;Macfarlane, 1999). Peak temperature varies between 580 and 700 C within the HHC in this area (Pêcher, 1989;Coleman & Hodges, 1998;Guillot, 1999;Macfarlane, 1999). Temperatures up to 800 C have been estimated along other transects, such as in the Langtang section, some 75 km west of Manaslu , whereas other studies suggest a maximum temperature of 750 C even in rocks that are partially melted Harris et al, 2004).…”

Section: The Manaslu Leucogranite and Its Host Rocks Bottom And Top Hmentioning

confidence: 99%

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Thermal Constraints on the Emplacement Rate of a Large Intrusive Complex: The Manaslu Leucogranite, Nepal Himalaya

Annen¹,

Scaillet²,

Sparks³

2005

Journal of Petrology

102

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The emplacement of the Manaslu leucogranite body (Nepal, Himalaya) has been modelled as the accretion of successive sills. The leucogranite is characterized by isotopic heterogeneities suggesting limited magma convection, and by a thin (<100 m) upper thermal aureole. These characteristics were used to constrain the maximum magma emplacement rate. Models were tested with sills injected regularly over the whole duration of emplacement and with two emplacement sequences separated by a repose period. Additionally, the hypothesis of a tectonic top contact, with unroofing limiting heat transfer during magma emplacement, was evaluated. In this latter case, the upper limit for the emplacement rate was estimated at 3Á4 mm/year (or 1Á5 Myr for 5 km of granite). Geological and thermobarometric data, however, argue against a major role of fault activity in magma cooling during the leucogranite emplacement. The best model in agreement with available geochronological data suggests an emplacement rate of 1 mm/year for a relatively shallow level of emplacement (granite top at 10 km), uninterrupted by a long repose period. The thermal aureole temperature and thickness, and the isotopic heterogeneities within the leucogranite, can be explained by the accretion of 20-60 m thick sills intruded every 20 000-60 000 years over a period of 5 Myr. Under such conditions, the thermal effects of granite intrusion on the underlying rocks appear limited and cannot be invoked as a cause for the formation of migmatites.

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Section: Top Contactmentioning

confidence: 99%

Section: The Manaslu Leucogranite and Its Host Rocks Bottom And Top Hmentioning

confidence: 99%

Section: The Manaslu Leucogranite and Its Host Rocks Bottom And Top Hmentioning

confidence: 99%

See 1 more Smart Citation

Thermal Constraints on the Emplacement Rate of a Large Intrusive Complex: The Manaslu Leucogranite, Nepal Himalaya

Annen¹,

Scaillet²,

Sparks³

2005

Journal of Petrology

102

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“…The grade of metamorphism increases structurally upward to upper-amphibolite facies, typically Sil ~z Crd at the structural level of maximum in situ melting (Brunel & Kienast 1986;Hubbard 1989;Mohan et al 1989;Swapp & Hollister 1991;Inger & Harris 1992;Macfarlane 1992;Hodges et al 1993;Meier & Hiltner 1993;Pognante & Benna 1993;Coleman 1996;Vannay & Hodges 1996). At least some of the apparent inversion is now known to be the result of polymetamorphism (Brunel & Kienast 1986;Hodges & Silverberg 1988;Swapp & Hollister 1991;Inger & Harris 1992), but there are several transects for which thermobarometric data indicate an inversion of metamorphic isograds developed during a single metamorphic event (Hubbard 1989;P~cher 1989). Four classes of models have been proposed to explain this phenomenon.…”

Section: Metamorphism and Anatexis In The Greater Himalayan Zonementioning

confidence: 99%

The thermodynamics of Himalayan orogenesis

Hodges

1998

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Geological and geochemical research in the internal zone of the Himalayan orogen reveal evidence for complex relationships between regional metamorphism, anatexis, thrust faulting and normal faulting in Miocene time. Such interactions share many characteristics with those that define the behaviour of non-equilibrium thermodynamic systems, like chemical oscillators. The internal ordering of such systems arises spontaneously and is maintained by continual exchange of energy with the outside world.Mountain ranges are open thermodynamic systems, equally capable of displaying selforganized behaviour. They accumulate energy through a variety of mechanisms, particularly crustal thickening, but their non-equilibrium structure is maintained through compensating mechanisms of energy dissipation. The simultaneous operation of normal faults and thrust faults in the Himalayan system, ejecting a wedge of middle crust southward from the orogen towards the Indian foreland, was a remarkably efficient method of mass (and therefore energy) dissipation in Miocene time. Research in many branches of science suggests that thermodynamic systems forced far from equilibrium by their boundary conditions may evolve towards establishing the most efficient possible mechanisms for counteracting those conditions. For the Himalaya, one possible explanation for development of a process set characterized by simultaneous normal faulting and thrust faulting, linked through metamorphism and anatexis, is that simple physical erosion alone was inadequate to lrmderate the extraordinary crustal thickness and topographic gradients that characterized the southern flank of the range in Miocene time. The orogenic system may have adapted to this condition through a new and more efficient mechanism of energy dissipation that required the coordination of a variety of thermal and deformational processes.One of the great success stories in the Earth sciences over the past quarter-century has been the integration of petrology, geochemistry, structural geology and geophysics to improve our understanding of the relationships between thermal and deformational processes in mountain belts. When faced with a question like 'What drives metamorphism?', physical chemistry tell us that the answer is largely 'Heat', but the metamorphic evolution of an orogen is dictated by complex interactions between heat and mass transfer processes that can only be fully appreciated from a multidisciplinary perspective. Though the more optimistic among us might argue that sophisticated numerical simulations, systematic structural studies, and a burgeoning petrologic and thermochronologic database have provided us with a good, basic understanding of how thermal, erosional and deformational processes are related in mountainous regions, a more difficult question is 'Why?'.

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“…In the Himalayas, studies on ultra-high pressure rocks denudated along the Main Central Thrust (MCT) revealed the great displacement along this intracontinental shear zone. Pêcher (1989) suggested the difference in thickness of hangingwall as a result of large erosion along the thrust, and Macfarlane (1993) discussed the various thermal structures within the hangingwall. However, lateral variations in footwall have been poorly investigated although inverted thermal gradient has been often discussed.…”

mentioning

confidence: 99%