Contrasting metamorphic and geochronologic evolution along the Himalayan belt

Abstract

Systematic different pressure-temperature-time paths are recorded along the internal zone of the Himalayan orogen. High-pressure rocks rapidly exhumed during the Eocene and Oligocene are restricted to the western part of the Himalayan belt. Farther to the east, both in the North Himalayan Crystalline massif sand in the High Himalayan Crystalline slab, there are upper amphibolite facies rocks, which were unroofed during the Miocene. In the High Himalayan Crystalline slab, a systematic decrease in mica 40 Ar/ 39 Ar cooling ages can be correlated with the degree of low-pressure anatexis to the east. The observed contrasts in both the metamorphic and geochronologic evolution along the Himalayan belt can be related to the counterclockwise rotation of the Indian plate during the India-Asia collision. Such rotation, together with a shallower dip of the intracontinental subduction plane to the east, would explain the delay in nappe stacking, a warmer thickened upper crust, and the observed decrease in ages from west to east.

Channel flow and the Himalayan–Tibetan orogen: a critical review

“…4a), this observation implies an eastward increase in exhumation rate over the time scales of landscape formation (c. 10 4 -10 5 years. (2) Across the Himalaya from Zanskar eastward to Bhutan (a distance of 1500 km) there is a regional decrease in 40 Ar/ 39 Ar mica cooling ages in the High Himalayan crystalline Series from 22-18 Ma to 13-11 Ma, as noted by Guillot et al (1999). Those workers interpreted this trend as evidence for oblique collision.…”

Temperature and age constraints on the metamorphism of the Tethyan Himalaya in Central Nepal: A multidisciplinary approach

“…Because no major discontinuity is known to exist between those two areas, we consider this temporal trend to be real. As already suggested by Guillot et al (1999), a working hypothesis for this migrating tectonothermal evolution could be the initial geometry of the Indian plate and the eastward propagating suturing associated with the counter-clockwise rotation of India. The Tertiary overprint in Dolpo is practically not datable by the illite K/Ar chronology.…”

“…In the central part of the mountain belt, three types of plutons occur: (1) the High Himalayan leucogranites, i.e., mainly Everest, Manaslu, Gangotri (Le Fort, 1981Le Fort et al, 1987;England et al, 1992;Guillot et al, 1999), (2) the circular bodies of the north Himalayan leucogranite belt (Debon et al, 1986;Zhang et al, 2004) including the Mustang granite (Le Fort and France Lanord, 1995) and (3) the unique huge elongated Mugu-Dolpo pluton (Le Fort and France Lanord, 1995). The TH sediments are locally intruded by Miocene leucogranites.…”

“…In the Tethyan Himalaya (TH) of central Nepal, most of the previous thermo-metamorphic studies have focused on (1) the granitic bodies and their contact aureole in order to understand their genetics and emplacement mechanisms (see for example Guillot et al, 1995Guillot et al, , 1999 and on (2) the relationships between the High Himalayan Crystalline (HHC) and the lower part of the TH (i.e., Godin et al, 1999a;Searle and Godin, 2003). Apart from the studies of Schneider and Masch (1993), Garzanti et al (1994) and Bollinger et al (2004), the pressure-temperature-time regime of the Himalayan orogeny (upper diagenesis to greenschist facies metamorphism) is still poorly constrained mainly due to the absence of indicative mineralogical assemblages.…”

Initial geometry of western Himalaya and ultrahigh-pressure metamorphic evolution

“…The higher Himalaya is divided into three units (Spencer et al, 1990;Kaneko et al, 2003): the lowest unit, which contains pelitic gneisses with minor amphibolite lenses, equivalent to the higher Himalayan crystalline rocks farther east (Guillot et al, 1999;Hodges, 2000), is bounded to the south by the MCT. The upper unit is composed of marbles and granitic gneisses, and is in contact with the Kohistan arc along the Main Karakorum Thrust (MKT).…”