New constraints on the timing of partial melting and deformation along the Nyalam section (central Himalaya): implications for extrusion models

Abstract

New structural, U-Th/Pb and Ar/Ar data along the Nyalam section constrain the timing of partial melting, crystallization and deformation in the Greater Himalayan Sequence. Prograde metamorphism was followed by the onset of partial melting at c. 30 Ma. In the central Greater Himalayan Sequence, in situ melts crystallized between 24 and 18 Ma. Subsequent cooling was very fast (c. 200 8C Ma 21 ) and coeval with the emplacement of undeformed dykes that lasted until c. 15 Ma. In the upper Greater Himalayan Sequence, fast cooling continued until c. 13 Ma. Combined with published P -T and thermochronological data from the Langtang and Dudh Kosi valleys, these data imply that: (a) the partial melt zone thinned over time; (b) the end of melting preceded the end of motion on the Main Central Thrust and the South Tibetan Detachment by 6 and 2 Ma, respectively; (c) the South Tibetan Detachment possibly initiated at c. 25 Ma, probably reactivating a pre-existing thrust; and (d) the present-day topography has been established for ,6 Ma and focused erosion on the present-day southern slopes of the Himalaya was not active at the time of the exhumation of the Greater Himalayan Sequence. These observations suggest that the Main Central Thrust/South Tibetan Detachment systems are not passive structures induced by focused erosion, as has been suggested previously by some lower crustal channel flow models.

Preservation of the Early Evolution of the Himalayan Middle Crust in Foreland Klippen: Insights from the Karnali Klippe, West Nepal

“…The 40 Ar/ 39 Ar recrystallization age of sample JD‐33 nevertheless implies that top‐to‐the‐NE shearing was ongoing at 16 ± 2 Ma in the upper part of the shear zone, while the base of the shear zone was inactive. Deformation therefore propagated up section in the STD high‐strain zone at progressively lower temperature, as observed in northwest India (Iaccarino, Montomoli, Carosi, Massonne, & Visonà, ), central Nepal (Cottle et al, ; Leloup et al, ), and eastern Nepal (Cottle et al, ). Whether the STD was continuously deformed between 30 Ma (Soucy La Roche et al, ) and 16 ± 2 Ma or was deformed episodically cannot be resolved with the current data set.…”

Two Tertiary metamorphic events recognized in high‐pressure metapelites of the Nevado‐Filábride Complex (Betic Cordillera, S Spain)

“…In order to reconstruct mountain-building processes resulting from continent-continent collision, one of the key tasks is to unravel the pressure (P)-temperature (T)-time (t) paths for metamorphic rocks in crystalline areas, that are usually exposed after significant denudation of the orogenic chain formed by this collision. Precise P-T-t trajectories that were, for example, recently derived for the Central Himalaya have significantly contributed to the understanding of the tectonic history of this mountain chain (Carosi et al, 2016;Iaccarino et al, 2015;Leloup et al, 2015;Shrestha, Larson, Guilmette, & Smit, 2017;Wang, Rubatto, & Zhang, 2015). The Betic Cordillera in southern Spain is, in fact, not only a much smaller orogenic chain but it also formed in the Tertiary, being the result of the collision of the African plate and the southwestern edge of the Eurasian plate (DeMets, Gordon, & Argus, 2010;Koulali et al, 2011;Pla-Pueyo, Viseras, Soria, Tent-Mancl us, & Arribas, 2011;Platt, Behr, Johanesen, & Williams, 2013).…”

Tectonometamorphic evolution of the tip of the Himalayan metamorphic core in the Jajarkot klippe, west Nepal

“…19 Ma. Upward strain propagation within the STD zone has been described in the adjacent Karnali klippe (Soucy La Roche, Godin, Cottle, et al., ) and elsewhere in the Himalaya (e.g., Burchfiel et al., ; Cottle, Waters, Riley, Beyssac, & Jessup, ; Cottle et al., ; Iaccarino, Montomoli, Carosi, Montemagni, et al., ; Leloup et al., ). The early activity of the STD at 27–26 Ma is interpreted to be syn‐burial in the Jajarkot klippe, based on syn‐kinematic garnet growth at increasing pressure.…”

“…In contrast, the white mica 40 Ar/ 39 Ar step-heating spectrum of sample JK-98 tentatively indicates that deformation at the top of the STD zone was still ongoing at c. 19 Ma. Upward strain propagation within the STD zone has been described in the adjacent Karnali klippe (Soucy La Roche, and elsewhere in the Himalaya (e.g., Burchfiel et al, 1992;Cottle, Waters, Riley, Beyssac, & Jessup, 2011;Cottle et al, 2009;Iaccarino, Montomoli, Carosi, Montemagni, et al, 2017;Leloup et al, 2015). The early activity of the STD at 27-26 Ma is interpreted to be syn-burial in the Jajarkot klippe, based on syn-kinematic garnet growth at increasing pressure.…”