Geochemical constraints on leucogranite magmatism in the Langtang Valley, Nepal Himalaya

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Authors:Inger, Simon; Harris, Nigel
Author Affiliations:Primary:
University of Leeds, Department of Earth Sciences, Leeds, United Kingdom
Other:
Open University, United Kingdom
Volume Title:Journal of Petrology
Source:Journal of Petrology, 34(2), p.345-368. Publisher: Clarendon Press, Oxford, United Kingdom. ISSN: 0022-3530
Publication Date:1993
Note:In English. 76 refs.; illus., incl. 4 tables, geol. sketch maps
Summary:A complex of crustally derived leucogranitic sills in sillimanite- grade psammitic rocks in the upper Langtang Valley of N Nepal forms part of the Miocene High Himalaya granite association. The leucogranites are peraluminous and alkali-rich and can be divided into a muscovite-biotite and a tourmaline-muscovite facies. Phase relations suggest that the latter crystallized from a water- undersaturated magma of minimum-melt composition at approx 3-4 kbar. Potential metasedimentary protoliths include a substantial anatectic migmatite complex and a lower-grade mica schist sequence. Isotopic constraints preclude the migmatites as a source of the granitic melts whereas trace-element modelling, together with the Nd and Sr isotopic signatures of potential protoliths, suggests that the tourmaline-bearing leucogranites were generated by fluid-absent partial melting of the muscovite schists (though REE and HFSE distribution cannot be reconciled with such a source). Tourmaline leucogranites with high Rb/Sr ratios represent low-fraction melts efficiently extracted from their protoliths under conditions of low aH2O, whereas the heterogeneous two- mica granites may have resulted from melting under somewhat higher aH2O conditions. [R.A.H.]
Subjects:Alkaline earth metals; Chemical composition; Granites; Igneous rocks; Isotope ratios; Isotopes; Leucogranite; Magmas; Metals; Nd-144/Nd-143; Neodymium; Partial melting; Plutonic rocks; Rare earths; Ring silicates; Silicates; Sr-87/Sr-86; Stable isotopes; Strontium; Tourmaline group; Trace elements; Asia; Himalayas; Indian Peninsula; Nepal; Langtang Valley
Abstract Numbers:93M/4471
Record ID:1995049583
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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