Geochemical constraints on the bimodal origin of High Himalayan leucogranites

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doi: 10.1016/0024-4937(94)00052-4
Authors:Guillot, S.; Le Fort, P.
Author Affiliations:Primary:
CNRS, Laboratoire de géodynamique des chaînes alpines, Grenoble, France
Volume Title:Lithos (Oslo)
Source:Lithos (Oslo), 35(3-4), p.221-234. Publisher: Elsevier, Amsterdam, International. ISSN: 0024-4937
Publication Date:1995
Note:In English. 70 refs.; illus., incl. 1 table, geol. sketch map
Summary:Major and trace element and Rb-Sr isotope systematics of the Manaslu leucogranite, Central Nepal have been examined to constrain the role of mineral fractionation and fluids in peraluminous granite petrogenesis. Biotite and tourmaline are, for the most part, mutually exclusive, with a predominance of two-mica leucogranites over tourmaline leucogranites. The 87Sr/86Sr initial isotopic ratios (Sri) indicate that leucogranitic melts were derived from two different sources, the two-mica leucogranites having a metagreywacke origin (with Sri<0.752 and εNd<-15) and the tourmaline leucogranites a metapelitic one (Sri>0.752; εNd>-15). Such a bimodal nature of the source zone does not directly influence the magmatic evolution, except that probably the higher initial boron content in the metapelitic rocks may increase the Na2O/K2O ratio. In contrast, the amount of water present during melting principally controls in part anatectic processes and elemental behaviour. Water-saturated conditions probably occurred during melting of metagreywackeous rocks and favoured crystallization of two-mica leucogranites whereas water-absent conditions prevailed during melting of metapelitic layers and favoured biotite, plagioclase and monazite fractionation in the source zone and tourmaline crystallization in the leucogranite.
Subjects:Alkaline earth metals; Anatexis; Chemical composition; Fractional crystallization; Genesis; Geochemistry; Granites; Igneous rocks; Isotope ratios; Isotopes; Leucogranite; Magmas; Major elements; Metals; Mineral assemblages; Peraluminous composition; Petrography; Plutonic rocks; Sr-87/Sr-86; Stable isotopes; Strontium; Trace elements; Water; Asia; Himalayas; Indian Peninsula; Nepal; Central Nepal; Manaslu Leucogranite
Coordinates:N275500 N283500 E0850000 E0834500
Abstract Numbers:96M/4335
Record ID:1995043879
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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