High-pressure metamorphism in the High Himalayan Crystallines of the Stak valley, northeastern Nanga Parbat-Haramosh syntaxis, Pakistan Himalaya

Abstract

The High Himalayan Crystallines (HHC) from the little-known NE termination of the Nanga Parbat-Haramosh syntaxis (Stak and upper Turmik valleys, Pakistan) consist of kyanite-bearing gneiss with minor garnet-granulite and garnet-amphibolite. The HHC underwent a Himalayan metamorphism with a peak at high pressure (8–13 kbar) and high temperature (650–700° C). During exhumation the HHC rocks followed a rapid exhumation path at high temperature with little or no medium to low pressure re-equilibration. These lines of evidence, combined with geochronological and petrological data from Eocene eclogites recently found in the Kaghan nappe, indicate that, after subduction and high to very high pressure metamorphism, part of the HHC from northern Pakistan underwent very rapid cooling and exhumation. By contrast, exhumation along paths of increasing temperature are recorded by the HHC from regions located east of Pakistan (e.g. Nepal). These differences along strike in the HHC suggest that, during the Eocene collision between India and Eurasia, subduction and exhumation occurred at higher rates in northwestern than in central-eastern Himalaya.

Late Miocene tectonic evolution of the Karakorum–Nanga Parbat contact zone (northern Pakistan)

“…2) and is marked by a ductile shear zone with right-lateral strike-slip movement, indicated by rotation at map scale of the synmetamorphic structures (Pognante et al, 1993). This shear zone is superimposed by pervasive crenulation folds that indicate a similar right-lateral movement (Arc formations to the south), accompanied by retrograde metamorphism .…”

“…The gneisses are metamorphosed to amphibolite facies and partly migmatized. Locally, metabasic dikes record high-pressure garnet-granulite metamorphism of probable early Himalayan age (Pognante et al, 1993). These gneisses have also undergone very recent Pliocene-Pleistocene metamorphism and anatexis associated with high denudation rates (Zeitler et al, 1993;Craw et al, 1994;Winslow et al, 1994;Chamberlain and Zeitler, 1996).…”

“…It is either considered to be dominated by precollisional deformation in large parts of the core of the massif (Butler et al, 1992;Treloar et al, 1991;Wheeler et al, 1995), or to be syncollisional (Chamberlain and Zeitler, 1996). According to Chamberlain and Zeitler (1996), postmetamorphic cooling (and retrogression of the granulitic assemblage into an amphibolitic one as described by Pognante et al, 1993) occurred at a relatively slow rate from 45 to 25 Ma, and at a much higher rate from 25 to 16 Ma. They interpreted the high rate of cooling to be a result of tectonic denudation, as Kohistan moved northward along normal faults.…”

“…Preliminary reports have been published (Pognante et al, 1993;Rolfo, 1994;Lemennicier, 1996;Lemennicier et al, 1996;Villa et al, 1996aVilla et al, , 1996bRolfo et al, 1997). In this chapter we present the results of tectonic analysis, and show that the pattern of the Nanga Parbat-Karakorum contact zone results from the same young (late Miocene) tectonics dominated by a strong flattening followed by domal structure.…”

“…Pêcher and P. Le Fort Figure 2. The trace of the main foliation was drawn from field data by P. Le Fort (1987Fort ( , 1992Fort ( , 1993Fort ( , 1994Fort ( , 1996, Y. Lemennicier (1993), A. Pêcher (1988), P. Pertusati (1993, and F. Rolfo (1993).…”