Hydrogen and oxygen isotope variations in the high Himalaya peraluminous Manaslu leucogranite: evidence for heterogeneous sedimentary source

Journal Article · Mon Feb 01 00:00:00 EST 1988 · Geochim. Cosmochim. Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(88)90107-X· OSTI ID:5065191

France-Lanord, C; Sheppard, S M.F.; Le Fort, P

The Manaslu granite belongs to the High Himalaya leucogranitic belt which was produced by melting of the crust during postcollisional thrusting. deltaD and delta/sup 18/O values have been determined for whole rock and coexisting minerals from the approx. 8 km thick Manaslu massif and its 50 km long dyke sheet, its country rocks and the Formation 1 (F1) paragneisses which are the source of the granite. From the distribution of deltaD values in the granite and its country rocks, circulation of very low deuterium meteoric hydrothermal waters was extremely localized. Because these waters are depleted in deuterium by up to 50% relative to modern meteoric waters, the Manaslu area was either at an altitude substantially higher than that of today or a mountain chain once existed to the south. The F1 gneisses have delta/sup 18/O/sub quartz/ between 12 and 14.3 per thousand which confirms that the granite was generated from F1, but deltaD values are approx. = 20 per thousand higher than in the granite. Infiltration of low deltaD fluid (approx. =-90 per thousand) into the hot but dry F1 probably triggered partial melting; these fluids could have come from the dehydration of the Midlands sediments which are separated from the overlying F1 by the Main Central Thrust. The correlations among delta/sup 18/O, (/sup 87/Sr/sup 86/Sr)/sub 20 Ma/ and epsilon Nd values in both F1 and the granite indicate that the variations of these isotopic ratios in the Manaslu are inherited from those in F1 at the time of melting. In turn, these ratios in F1 are related to the proportion of quartz and phyllosilicates for the isotopic ratios of Nd and O, and to the quantity of radiogenic Sr generated within the sediment, which is a function of age and Rb content. Some other Himalayan leucogranites require either other crustal source rocks of the delta/sup 18/O and /sup 87/Sr/sup 86/Sr ratios to F1 vary along the Himalaya.

• Research Organization: CNRS Nancy, Vandoeuvre (France)
• OSTI ID: 5065191
• Journal Information: Geochim. Cosmochim. Acta; (United States), Vol. 52:2
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
GRANITES
ISOTOPE RATIO
PETROCHEMISTRY
PETROGENESIS
STRUCTURAL CHEMICAL ANALYSIS
NEPAL
GEOLOGIC DEPOSITS
GEOCHEMISTRY
GEOLOGIC HISTORY
HIMALAYAS
HYDROGEN ISOTOPES
MAGMATISM
ORIGIN
OXYGEN ISOTOPES
PARAGENESIS
VARIATIONS
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IGNEOUS ROCKS
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MOUNTAINS
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