Granite-migmatite genetic link: the example of the Manaslu granite and Tibetan Slab migmatites in central Nepal

Barbey, Pierre; Brouand, Marc; Fort, Patrick Le; Pêcher, Arnaud

doi:10.1016/0024-4937(96)00005-9

Cited by 55 publications

(32 citation statements)

References 45 publications

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“…1). Migmatization is prominent in F1 and increases upsection (Barbey et al, 1996;Coleman, 1998). U-Pb geochronology on monazite and zircon gives migmatization ages of 18-22Á5 Ma for FI migmatites (Hodges et al, 1996;Coleman, 1998).…”

Section: The Manaslu Leucogranite and Its Host Rocks Bottom And Top Hmentioning

confidence: 99%

Thermal Constraints on the Emplacement Rate of a Large Intrusive Complex: The Manaslu Leucogranite, Nepal Himalaya

Annen¹,

Scaillet²,

Sparks³

2005

Journal of Petrology

102

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The emplacement of the Manaslu leucogranite body (Nepal, Himalaya) has been modelled as the accretion of successive sills. The leucogranite is characterized by isotopic heterogeneities suggesting limited magma convection, and by a thin (<100 m) upper thermal aureole. These characteristics were used to constrain the maximum magma emplacement rate. Models were tested with sills injected regularly over the whole duration of emplacement and with two emplacement sequences separated by a repose period. Additionally, the hypothesis of a tectonic top contact, with unroofing limiting heat transfer during magma emplacement, was evaluated. In this latter case, the upper limit for the emplacement rate was estimated at 3Á4 mm/year (or 1Á5 Myr for 5 km of granite). Geological and thermobarometric data, however, argue against a major role of fault activity in magma cooling during the leucogranite emplacement. The best model in agreement with available geochronological data suggests an emplacement rate of 1 mm/year for a relatively shallow level of emplacement (granite top at 10 km), uninterrupted by a long repose period. The thermal aureole temperature and thickness, and the isotopic heterogeneities within the leucogranite, can be explained by the accretion of 20-60 m thick sills intruded every 20 000-60 000 years over a period of 5 Myr. Under such conditions, the thermal effects of granite intrusion on the underlying rocks appear limited and cannot be invoked as a cause for the formation of migmatites.

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Section: The Manaslu Leucogranite and Its Host Rocks Bottom And Top Hmentioning

confidence: 99%

Thermal Constraints on the Emplacement Rate of a Large Intrusive Complex: The Manaslu Leucogranite, Nepal Himalaya

Annen¹,

Scaillet²,

Sparks³

2005

Journal of Petrology

102

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“…The differences in composition between the metagreywackes from the Quetico (Sawyer 1987;Barbey et al 1996Solar & Brown 2001). An alternative is to use the compositions of melts derived from melting experiments done on rocks of similar bulk compositions and at the same pressures and temperatures as the natural anatexis.…”

Section: Discussionmentioning

confidence: 99%

“…The initial melt composition is unlikely to be found in the field, because leucosomes usually have compositions which are not that of the initial melt (Sawyer 1987;Barbey et al 1996;Sawyer et al 1999;Solar & Brown 2001). For this purpose the same anatectic melt composition used for the chemical modelling of the meltdepleted granulites (Chapter III) will be used.…”

Section: Some Reference Compositionsmentioning

confidence: 99%

Formation and evolution of granite magmas from migmatites :

Guernina¹

2007

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Many magmas in the continental crust are believed to have formed by partial melting in the lower to middle crust, and the transfer of that melt to the upper crust. However, it is poorly known how the compositions of these magmas evolve. In general, the principal processes involved are redistribution and contamination of the melt fraction with some of the host-rock it passes through and once magma ascends out of the anatectic zone and traverses cooler crust and begins to crystallize. The nature of the protolithrnigmatite-granite transition and the process that creates a granitic magma during anatexis, as well as the processes that control the magma composition outside the source region are of a particular interest as they enable us to constrain the morphological, mineralogical and geochemical variations of anatectic melts produced during anatexis of greywacke metasedimentary rocks.The Ashuanipi subprovince and contiguous metasedimentary subprovinces in the Superior province contains reworked Archaean crust that displays a continuous section from mid-crustal anatectic rocks to shallow level granite plutons. In other words, the superior province represents a crustal section which is continuous from partially melted source to upper crustal magma sink and the Ashaunipi portion of it is an example of a source region for granulitic magma. There, the transition from palaesome to granite was an open system process through intermediate stages of metatexite and diatexite.Field, pétrographie and geochemical methods have been used to estimate how much granitic melt was formed and extracted from granulite facies terrane, and to determine what the grain and outcrop-scale melt-flow paths were during the melt segregation process. More than 85 % of the metasediments in the Ashuanipi subprovince are of metagreywacke composition that was metamorphosed at mid-crustal conditions (820-900 °C and 6-7 kbar). Decrease in modal biotite and quartz as orthopyroxene and plagioclase contents increase, together with preserved former melt microstructures indicate that anatexis was by the biotite dehydration reaction: biotite + quartz + plagioclase = melt + orthopyroxene + oxides. Using melt/orthopyroxene ratios for this reaction derived from experimental studies, the modal orthopyroxene contents present in the Ashuanipi rocks indicate that the metagreywacke rocks underwent an average of 31 vol% partial melting.The metagreywackes are enriched in MgO, CaO and FeO and depleted in SÍO2, K2O, Rb, Cs and U, have lower Rb/SR, higher Rb/Cs and Th/U ratios and positive Eu anomalies compared to their likely protolith. These compositions are modelled by the extraction of between 20 and 40 wt % granitic melt from typical Achaean low-grade metagreywackes.The distribution of relict melt at thin section and outcrop scales indicates that in layers without leucosomes melt extraction occurred by a pervasive grain boundary (porous) flow from the site of melting, across the layers and into bedding planes between adjacent layers. In other rocks, pervasive g...

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“…However, the strong similarity of the chemical composition of the Cenerigneisses, Ceneri augengneiss, and Gneiss Minuti conflicts with the well-known diversity in the geochemical patterns of partial melts and parent rocks. The REE patterns of such melts are complementary to those of the respective residual rocks, and show for the most part positive Eu anomalies (Sawyer, 1986;Barbey et al, 1996;Otamendi and Patino Douce, 2001). The REE patterns of the Cenerigneisses, Ceneri augengneiss, and Gneiss Minuti, instead, are almost identical (Fig.…”

Section: Sr Nd and Pb Isotope Characteristicsmentioning

confidence: 93%

Pre-metamorphic melt infiltration in metasediments: geochemical, isotopic (Sr, Nd, and Pb), and field evidence from Serie dei Laghi (Southern Alps, Italy)

et al. 2008

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SummaryGradual transitions from K-feldspar free gneisses to K-feldspar bearing augengneisses are sometimes observed in metamorphic terranes. They have been explained with metasomatic porphyroblastic growth connected with regional metamorphism, or with pre-metamorphic presence of magmatic megacrysts. A transition of this kind can be observed in the Serie dei Laghi (Southern Alps, Italy), where coarse-grained metaarenites (Cenerigneiss) grade into Ceneri augengneisses with large K-feldspar porphyroclasts, and banded amphibolites of the ''Strona Ceneri Border Zone'' grade into Hbl augengneisses rich in K-feldspar.The Ceneri augengneisses are chemically indistinguishable from the Cenerigneiss, but have higher 87 Sr =86 Sr (0.7256-0.7258 vs. 0.7215-0.7233), similar to those of the Ordovician granites that were intruded, before the regional metamorphism, into the protoliths of both Cenerigneiss and amphibolites. The Cenerigneiss contains two types of zircons: (1) highly luminescent, rounded grains or fragments, yielding U-Pb SHRIMP ages from 0.43 to 1.0 Ga; (2) euhedral grains with oscillatory zoning (magmatic), with U-Pb SHRIMP concordant ages of 466 AE 13 Ma. This age coincides with the Rb-Sr whole rock emplacement age of the Ordovician granitoids (466 AE 5 Ma).Correspondence: L. Pinarelli, CNR -Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via La Pira 4, 50121 Firenze, Italy e-mail: lapina@igg.cnr.itThe Hbl augengneisses form three groups with distinct geochemical patterns, whose distributions on inter-element diagrams trend towards the Ordovician metagranites and meta-aplites. In addition, the Hbl augengneisses have higher 87 Sr =86 Sr (0.7132-0.7147 vs. 0.7031-0.7046) and lower 143 Nd =144 Nd (0.51214-0.51219 vs. 0.51273-0.51297) than the amphibolites, suggesting the addition of an isotopically evolved component.The observed chemical and isotope patterns, as well as the vicinity of the augen gneisses to the Ordovician intrusions, lead us to conclude that the Ceneri augengneisses and Hbl augengneisses are the result of infiltration of residual hydrous magmas into the protolith of both the Cenerigneiss and the amphibolites at the time of Ordovician granite emplacement, long before the regional metamorphism in the Serie dei Laghi.

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Granite-migmatite genetic link: the example of the Manaslu granite and Tibetan Slab migmatites in central Nepal

Cited by 55 publications

References 45 publications

Thermal Constraints on the Emplacement Rate of a Large Intrusive Complex: The Manaslu Leucogranite, Nepal Himalaya

Thermal Constraints on the Emplacement Rate of a Large Intrusive Complex: The Manaslu Leucogranite, Nepal Himalaya

Formation and evolution of granite magmas from migmatites :

Pre-metamorphic melt infiltration in metasediments: geochemical, isotopic (Sr, Nd, and Pb), and field evidence from Serie dei Laghi (Southern Alps, Italy)

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