GEOSCAN, résultats de la recherche


TitreSubduction metamorphism in the Himalayan ultrahigh-pressure TsoMorari massif: An integrated geodynamic and petrological modelling approach
AuteurPalin, R M; Reuber, G; White, R W; Kaus, B J P; Weller, O M
SourceEarth and Planetary Science Letters vol. 467, 2017 p. 108-119,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20150475
Documentpublication en série
Mediapapier; en ligne; numérique
Lat/Long OENS 77.0000 79.0000 34.0000 33.0000
Sujetszones de subduction; évolution tectonique; métamorphisme; zones tectonostratigraphiques; établissement de modèles; métamorphisme progressif; études de la croûte; croûte continentale; éclogîtes; géologie structurale; tectonique; géologie régional
Illustrationsphase diagrams; geological sketch maps; geophysical profiles
ProgrammeCartographie du substratum rocheux de Baffin, GEM2 : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
The Tso Morari massif is one of only two regions where ultrahigh-pressure (UHP) metamorphism of subducted crust has been documented in the Himalayan Range. The tectonic evolution of the massif is enigmatic, as reported pressure estimates for peak metamorphism vary from 2.4 GPa to 4.8 GPa. This uncertainty is problematic for constructing large-scale numerical models of the early stages of India-Asia collision. To address this, we provide new constraints on the tectonothermal evolution of the massif via a combined geodynamic and petrological forward-modelling approach. A prograde-to-peak pressure-temperature-time (P-T-t) path has been derived from thermomechanical simulations tailored for Eocene subduction in the northwestern Himalaya. Phase equilibrium modelling performed along this P-Tpath has described the petrological evolution of felsic and mafic components of the massif crust, and shows that differences in their fluid contents would have controlled the degree of metamorphic phase transformation in each during subduction. Our model predicts that peak P-Tconditions of 2.6-2.8 GPa and 600-620degC, representative of 90-100 km depth (assuming lithostatic pressure), could have been reached just 3 Myr after the onset of subduction of continental crust. This P-Tpath and subduction duration correlate well with constraints reported for similar UHP eclogite in the Kaghan Valley, Pakistan Himalaya, suggesting that the northwest Himalaya contains dismembered remnants of what may have been a 400-km-long UHP terrane comparable in size to the Western Gneiss Region, Norway, and the Dabie-Sulu belt, China. A maximum overpressure of 0.5 GPa was calculated in our simulations for a homogeneouscrust, although small-scale mechanical heterogeneities may produce overpressures that are larger in magnitude. Nonetheless, the extremely high pressures for peak metamorphism reported by some workers (up to 4.8 GPa) are unreliable owing to conventional thermobarometry having been performed on minerals that were likely not in equilibrium. Furthermore, diagnostic high-Pmineral assemblages predicted to form in Tso Morari orthogneiss at peak metamorphism are absent from natural samples, which may reflect the widespread metastable preservation of lower-pressure assemblages in the felsic component of the crust during subduction. If common in such subducted continental terranes, this metastability calls into question the reliability of geodynamic simulations of orogenesis that are predicated on equilibrium metamorphism operating continuously throughout tectonic cycles.
Résumé(Résumé en langage clair et simple, non publié)
Le massif Tso-Morari se trouve en Inde dans la chaîne de montagnes de l¿Himalaya. Ce massif expose des roches qui furent enfouies plus de 80 km et ensuite exhumées à la surface lors de la formation de l¿Himalaya. Ces roches sont relativement rares à la surface de la Terre, et leur étude fournit des contraintes importantes sur les processus reliés la formation des chaînes de montagnes. Les estimations courantes de la profondeur que ces roches ont atteintes varient entre ~80 et 150 km. Dans notre étude, une nouvelle approche de modélisation de l¿historique de ces roches est appliquée. Nos modèles indiquent que la limite inférieure de l¿intervalle de profondeur (90-100 km) est la plus appropriée. Ces résultats ont des implications importantes pour la compréhension de l¿Himalaya, et, de façon plus générale, comment les roches sont transformées (métamorphosées) lors de la construction de chaînes de montagnes.