Two-mica and tourmaline leucogranites from the Everest-Makalu region (Nepal-Tibet). Himalayan leucogranite genesis by isobaric heating?. (Articolo in rivista)

Type
Label
  • Two-mica and tourmaline leucogranites from the Everest-Makalu region (Nepal-Tibet). Himalayan leucogranite genesis by isobaric heating?. (Articolo in rivista) (literal)
Anno
  • 2002-01-01T00:00:00+01:00 (literal)
Alternative label
  • Visonà D., Lombardo B. (2002)
    Two-mica and tourmaline leucogranites from the Everest-Makalu region (Nepal-Tibet). Himalayan leucogranite genesis by isobaric heating?.
    in Lithos (Oslo. Print)
    (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
  • Visonà D., Lombardo B. (literal)
Pagina inizio
  • 125 (literal)
Pagina fine
  • 150 (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#altreInformazioni
  • This paper reports new geological, petrological and geochemical data on leucogranites from the Everest–Makalu region (Nepal and southern Tibet), which set further constraints on the genesis of the Miocene Himalayan magmatism. A new petrological model is proposed which better fits the observational data than current models for the generation of the Himalayan leucogranites. (literal)
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  • 62 (literal)
Rivista
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  • Impact Factor, 2,198 (literal)
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  • Field, petrographic and geochemical studies show that the Miocene plutons of the Himalayas are composed of two mica±tourmaline leucogranite (2mg) and tourmaline leucogranite (Tg). Isotope geochemistry (Sr, Nd, Pb) is indicative of a sedimentary source that may correspond to the Ky/Sill metasediments of the lower High Himalayan Crystallines (HHC) which have suitable chemical and mineralogical compositions for producing leucogranites and which, during the Himalayan metamorphism, were subjected to metamorphic conditions compatible with the formation of leucogranite melts. Experiments with metasedimentary rocks of the HHC have shown that the Tg and 2mg may indeed have formed by muscovite and biotite dehydration melting (vapour-present or vapour-absent). The prograde character of the anatectic event in the Everest–Makalu area, first proven in the present paper, indicates that, the generation of the leucogranites cannot have taken place in a regime of adiabatic decompression. Specifically, nearly isobaric heating following nearly adiabatic decompression caused low-pressure dehydration melting of Muscovite in fertile metapelites of the top of both the HHC and Lesser Himalayan Crystallines (LHC), generating Tg melts which were emplaced at the same structural level of the partial melting zone. Dehydration melting of Bi in the biotite gneisses of both the HHC and LHC produced 2mg melts which were transported upward by dyking and eventually coalesced in the plutons of the upper HHC. (literal)
Note
  • ISI Web of Science (WOS) (literal)
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  • VISONA' D. a), LOMBARDO B. b) a) Dipartimento di Mineralogia e Petrologia, Università di Padova, Corso Garibaldi 37, I-35100 Padova, Italy and CNR—IGG Sez. Padovab) CNR—IGG Sez. Torino, c/o Dipartimento di Scienze Mineralogiche e Petrologiche, Univ. Torino, via Valperga Caluso 35 (literal)
Titolo
  • Two-mica and tourmaline leucogranites from the Everest-Makalu region (Nepal-Tibet). Himalayan leucogranite genesis by isobaric heating?. (literal)
Abstract
  • In the Higher Himalaya of the region from Cho Oyu to the Arun valley northeast of Makalu, the Miocene leucogranites are not hosted only in the upper High Himalayan Crystallines (HHC); a network of dykes also cuts the lower HHC and the Lesser Himalayan Crystallines (LHC). The plutons and dykes are mainly composed of two-mica (muscovite + biotite ± tourmaline ±cordierite±andalusite±sillimanite) leucogranite, with tourmalined2.6% and biotite>1.5% modal, and tourmaline (muscovite+tourmaline ± biotite ± sillimanite ± garnet ±kyanite ± andalusite ±spinel ±corundum) leucogranite, with tourmaline>2.2% and biotite<1.5% modal. Both leucogranite types were produced by partial melting in the andalusite–sillimanite facies series, under LP/HT conditions constrained by the occurrence of peritectic andalusite and cordierite. The geochemical features of the leucogranites suggest that tourmaline leucogranite was produced by muscovite dehydration melting in muscovite-rich metapelites at P~350 MPa and Te640°C, whereas two-mica leucogranite was produced by biotite dehydration melting in biotite-rich metapelites at P~300 MPa and Te660–710 °C. Melting in fertile muscovite-rich metapelites of the top of both the HHC and LHC produced magmas which were emplaced at the same structural level in which they had been generated. Melting in the biotite-rich gneiss of both the HHC and LHC produced hotter magmas which were transported upwards by dyking and eventually coalesced in the plutons of the upper HHC. A similar process also produced a network of two-mica granite at the top of the LHC in the Ama Drime–Nyönno Ri Range northeast of Makalu. The prograde character of leucogranite melt-producing reactions in the Everest–Makalu area suggests that, here, the generation of Miocene leucogranites took place in a regime of nearly isobaric heating following nearly adiabatic decompression. (literal)
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