Leucogranite intruding the South Tibetan Detachment in western Nepal: implications for exhumation models in the Himalayas

Carosi, Rodolfo; Montomoli, Chiara; Rubatto, Daniela; Visonà, Dario

doi:10.1111/ter.12062

Cited by 99 publications

(72 citation statements)

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“…Different mechanisms of exhumation have been proposed by Carosi et al (2010Carosi et al ( , 2013, Imayama et al (2012) and Montomoli et al (2013Montomoli et al ( , 2014 involving the downward and southward progressive migration of ductile shearing within the GHS, allowing the progressive exhumation of crustal slices of the GHS. In this framework the occurrence of folded isograds within the whole GHS, as postulated by the ductile extrusion and channel flow models, is not confirmed.…”

Section: Discussionmentioning

confidence: 99%

Eocene partial melting recorded in peritectic garnets from kyanite-gneiss, Greater Himalayan Sequence, central Nepal

Carosi

Montomoli

Langone

et al. 2014

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Anatectic melt inclusions (nanogranites and nanotonalites) have been found in garnet\ud of kyanite-gneiss at the bottom of the Greater Himalayan Sequence (GHS) along the Kali\ud Gandaki valley, central Nepal, c. 1 km structurally above the Main Central Thrust (MCT). In\ud situ U–Th–Pb dating of monazite included in garnets, in the same structural positions as melt\ud inclusions, allowed us to constrain partial melting starting at c. 41–36 Ma. Eocene partial\ud melting occurred during prograde metamorphism in the kyanite stability field (Eo-Himalayan\ud event). Sillimanite-bearing mylonitic foliation wraps around garnets showing a top-to-the-SW\ud sense of shear linked to the MCT ductile activity and to the exhumation of the GHS. These findings\ud highlight the occurrence of an older melting event in the GHS during prograde metamorphism in\ud the kyanite stability field before the more diffuse Miocene melting event.\ud The growth of prograde garnet and kyanite at 41–6 Ma in the MCT zone, affecting the bottom of\ud the GHS, suggests that inverted metamorphism in the MCT zone and folded isograds in the GHS\ud should be carefully proved with the aid of geochronology, because not all Barrovian minerals grew\ud during the same time span and they grew in different tectonic settings

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Section: Discussionmentioning

confidence: 99%

Eocene partial melting recorded in peritectic garnets from kyanite-gneiss, Greater Himalayan Sequence, central Nepal

Carosi

Montomoli

Langone

et al. 2014

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“…This indicates that they were derived from different sources. In addition, along the Himalayan belt, the majority of leucogranites formed at c. 35 -4 Ma and are characterized by low Na/K but high Rb/Sr ratios France -Lanord & Le Fort 1988;Ferrara et al 1991;Harris & Inger 1992;Harris et al 1993Harris et al , 1995Zeitler et al 1993;Harris & Massey 1994;Noble & Searle 1995;Harrison et al 1997;Searle et al 1997Searle et al , 2010Neogi et al 1998;Visonà & Lombardo 2002;Whittington & Treloar 2002;Cottle et al 2009;Kali et al 2010;Visonà et al 2012;Carosi et al 2013;Gao & Zeng 2014). As compared to those in the Miocene leucogranites, these older leucogranites show substantial differences in Na/K ratios as well as in Sr isotope compositions.…”

Section: An Eocene Magmatic System Formed In Contraction and Thickenimentioning

confidence: 95%

Eocene magmatism in the Tethyan Himalaya, southern Tibet

Zeng

Gao

Tang

et al. 2014

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Recent studies in the Yardoi gneiss dome of the Tethyan Himalaya, southern Tibet demonstrated that the Himalayan orogenic belt experienced a major episode of crustal melting in the Mid-Eocene (c. 44–40 Ma), represented by the genesis of a suite of high Sr/Y two-mica granites (TMGs) accompanied by leucogranites. Geochemical and U–Pb age data indicate that (1) both the leucogranite and the porphyritic leucogranite formed at c. 44–41 Ma are characterized by similar Sr–Nd–Hf isotope systematics to those in the less evolved TMGs; (2) these three suites of rocks might represent a Mid-Eocene igneous complex derived from partial melting of amphibolite under crustal thickened conditions; and (3) in contrast with the TMGs, leucogranites experienced hydrothermal-magma interactions as well as plagioclase fractional crystallization as revealed from pronounced negative Eu anomalies, much lower Sr concentrations, and elevated common Pb and U concentrations in the latest magmatic zircon overgrowth. Our data suggest that magmatic differentiation of more primitive magmas could have played a critical role in the generation of leucogranites. Documentation of partial melting of deep crustal rocks during the earliest phase of the tectonic evolution of the Himalayan orogen implies that the large-scale collisional orogenic belt could experience intensive partial melting under contraction and thickening conditions, which could profoundly affect the geophysical and geochemical properties as well as rheological properties and facilitate the initiation of movement or flow of deep crustal rocks.

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“…Such an argument, however, does not take into account all factors controlling the potential lateral movement of the midcrust, which include temperature, convergence rate, material viscosity, and the associated pressure gradient (Grujic, 2006). While other factors such as the lack of coeval movement on bounding structures (e.g., Carosi et al, 2013) may act as evidence against lateral midcrustal flow, the recognition that the exhumed midcrust may be significantly thinner than originally thought does not exclude the possibility of its ductile, large-scale lateral translation.…”

Section: High-grade Tectonometamorphic Discontinuitiesmentioning

confidence: 99%

Metamorphism and geochronology of the exhumed Himalayan midcrust, Likhu Khola region, east-central Nepal: Recognition of a tectonometamorphic discontinuity

2014

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The exhumed Himalayan midcrustal core exposed in the Likhu Khola region of east-central Nepal includes upper-greenschist-to upperamphibolite-grade metamorphic rocks that record pervasive, top-to-the-south sense deformation. Metamorphic temperature estimates are within error across the mapped area ranging from 772 ± 37 °C in the structurally lower, southern part of the study area to 853 ± 58 °C in the structurally higher, northern area. Estimated metamorphic pressures are relatively constant at lower structural levels, but they decrease from 11.8 ± 1.4 kbar to a minimum of 6.5 ± 1.3 kbar up structural section. The decrease in pressures coincides with an abrupt change in pressure estimates up structural section that is interpreted to mark a tectonometamorphic discontinuity that separates two domains with distinct structural, thermal, and metamorphic histories. In situ laser-ablation split-stream monazite U-Th/Pb and rare earth element (REE) petrochronology outlines dates ranging from ca. 27.8 Ma to 15.1 Ma in the hanging wall of the interpreted discontinuity; monazite REE data indicate the spread in ages is the result of a protracted metamorphic history and late-stage anatexis. Metamorphic and petrochronologic data from the Likhu Khola are consistent with a kinematic model in which material structurally above the discontinuity was metamorphosed in the deep hinterland of the orogen and was subsequently incorporated into the foreland of the orogen. The transition from hinterland-to foreland-style processes was marked by a shift to discrete deformation and the development of the discontinuity. Movement across the discontinuity is interpreted to have driven metamorphism and deformation of the rocks structurally below at or after 15 Ma. Discontinuities similar to that identified in this study are being identified and described across the orogen, indicating they are important, orogenwide features.

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Leucogranite intruding the South Tibetan Detachment in western Nepal: implications for exhumation models in the Himalayas

Cited by 99 publications

References 49 publications

Eocene partial melting recorded in peritectic garnets from kyanite-gneiss, Greater Himalayan Sequence, central Nepal

Eocene partial melting recorded in peritectic garnets from kyanite-gneiss, Greater Himalayan Sequence, central Nepal

Eocene magmatism in the Tethyan Himalaya, southern Tibet

Metamorphism and geochronology of the exhumed Himalayan midcrust, Likhu Khola region, east-central Nepal: Recognition of a tectonometamorphic discontinuity

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