Kaghan Valley, Pakistan: metamorphic rocks, their chemistry and age

Wilke, Franziska;

2022 || GFZ Data Services

This data set is the source of my doctoral thesis and of three resulting publications. Through whole rock geochemistry of selected samples and microprobe and geochronological analyses of key minerals, formerly selected by extensive microscopical studies, standard geothermobarometry and modelling was applied. It has been shown that metamorphic rocks, in particular, the eclogites of the northern Kaghan Valley, Pakistan, were buried to depths of 140-100 km (36-30 kbar) at 790-640°C. Subsequently, cooling during decompression (exhumation) towards 40-35 km (17-10 kbar) and 630-580°C has been superseded by a phase of reheating to about 720-650°C at roughly the same depth before final exhumation has taken place. In the southern-most part of the Kaghan Valley, amphibolite facies assemblages with formation conditions similar to the deduced reheating phase indicate a juxtaposition of both areas after the eclogite facies stage and thus a stacking of Indian Plate units.

Radiometric dating of zircon, titanite and rutile by U-Pb and amphibole and micas by Ar-Ar reveal peak pressure conditions at 47-48 Ma. With a maximum exhumation rate of 14 cm/a these rocks reached the crust-mantle boundary at 40-35 km within 1 Ma. Subsequent exhumation (46-41 Ma, 40-35 km) decelerated to ca. 1 mm/a at the base of the continental crust but rose again to about 2 mm/a in the period of 41-31 Ma, equivalent to 35-20 km. Apatite fission track (AFT) and (U-Th)/He ages from eclogites, amphibolites, micaschists and gneisses yielded moderate Oligocene to Miocene cooling rates of about 10°C/Ma in the high altitude northern parts of the Kaghan Valley using the mineral-pair method. AFT ages are of 24.5±3.8 to 15.6±2.1 Ma whereas apatite (U-Th)/He analyses yielded ages between 21.0±0.6 and 5.3±0.2 Ma. The southern-most part of the Valley is dominated by younger late Miocene to Pliocene apatite fission track ages of 7.6±2.1 and 4.0±0.5 Ma that support earlier tectonically and petrologically findings of a juxtaposition and stack of Indian Plate units. As this nappe is tectonically lowermost, a later distinct exhumation and uplift driven by thrusting along the Main Boundary Thrust is inferred.

Out of this geochemical, petrological, isotope-geochemical and low temperature thermochronology investigations it was concluded that the exhumation was buoyancy driven and caused an initial rapid exhumation: exhumation as fast as recent normal plate movements (ca. 10 cm/a). As the exhuming units reached the crust-mantle boundary the process slowed down due to changes in buoyancy. Most likely, this exhumation pause has initiated the reheating event that is petrologically evident (e.g. glaucophane rimmed by hornblende, ilmenite overgrowth of rutile). Late stage processes involved widespread thrusting and folding with accompanied regional greenschist facies metamorphism, whereby contemporaneous thrusting on the Batal Thrust (seen sometimes equivalent to the MCT) and back sliding of the Kohistan Arc along the inverse reactivated Main Mantle Thrust caused final exposure of these rocks. Similar circumstances have been seen at Tso Morari, Ladakh, India, 200 km further east where comparable rock assemblages occur. In conclusion, as exhumation was already done well before the initiation of the monsoonal system, climate dependent effects (erosion) appear negligible in comparison to far-field tectonic effects. Thus, the channel flow model is not applicable for this part of the Himalayas.

Originally assigned keywords

Corresponding MSL vocabulary keywords

MSL enriched keywords

MSL enriched sub domains
  • microscopy and tomography
  • geochemistry
Source http://dx.doi.org/10.5880/gfz.3.1.2022.001
Source publisher GFZ Data Services
DOI 10.5880/gfz.3.1.2022.001
Authors
  • Wilke, Franziska
  • 0000-0002-3463-6176
  • GFZ German Research Centre for Geosciences, Potsdam, Germany;
Contributors
  • Microprobe Lab (GFZ German Research Centre for Geosciences, Germany)
  • HostingInstitution
  • GFZ German Research Centre for Geosciences, Potsdam, Germany;
  • Ar/Ar Geochronology Laboratory (University of Potsdam, Germany)
  • HostingInstitution
  • University of Potsdam, Potsdam, Germany;
  • X-ray Fluorescence Spectroscopy (XRF) (GFZ German Research Centre for Geosciences, Germany)
  • HostingInstitution
  • GFZ German Research Centre for Geosciences, Potsdam, Germany;
  • Fission Track Laboratory (University of Potsdam, Germany)
  • HostingInstitution
  • University of Potsdam, Potsdam, Germany;
  • FIERCE - Frankfurt Isotope & Element Research Center at Goethe Universität Frankfurt, Germany
  • HostingInstitution
  • Goethe Universität Frankfurt, Frankfurt, Frankfurt, Germany;
  • Geesthacht Neutron Facility (GeNF) (Helmholtz Centre hereon, Germany)
  • HostingInstitution
  • Helmholtz Centre hereon GmbH, Geesthacht, Germany;
  • ElMiE Elements and Minerals of the Earth Laboratory (GFZ German Research Centre for Geosciences, Germany)
  • HostingInstitution
  • GFZ German Research Centre for Geosciences, Potsdam, Germany;
  • Wilke, Franziska
  • ContactPerson
  • GFZ German Research Centre for Geosciences, Potsdam, Germany;
References
  • Wilke, F. D. H. (2010). Quantifying crystalline exhumation in the Himalaya [Universität Potsdam]. https://doi.org/10.25932/PUBLISHUP-4119
  • 10.25932/PUBLISHUP-4119
  • IsDocumentedBy
  • Lanphere, M. A., & Baadsgaard, H. (2001). Precise K–Ar, 40Ar/39Ar, Rb–Sr and U/Pb mineral ages from the 27.5 Ma Fish Canyon Tuff reference standard. Chemical Geology, 175(3–4), 653–671. https://doi.org/10.1016/s0009-2541(00)00291-6
  • 10.1016/S0009-2541(00)00291-6
  • Cites
  • Wilke, F. D. H., O’Brien, P. J., Gerdes, A., Timmerman, M. J., Sudo, M., & Khan, M. A. (2010). The multistage exhumation history of the Kaghan Valley UHP series, NW Himalaya, Pakistan from U-Pb and 40Ar/39Ar ages. European Journal of Mineralogy, 22(5), 703–719. https://doi.org/10.1127/0935-1221/2010/0022-2051
  • 10.1127/0935-1221/2010/0022-2051
  • Cites
  • Wilke, F. D. H., O’Brien, P. J., Altenberger, U., Konrad-Schmolke, M., & Khan, M. A. (2010). Multi-stage reaction history in different eclogite types from the Pakistan Himalaya and implications for exhumation processes. Lithos, 114(1–2), 70–85. https://doi.org/10.1016/j.lithos.2009.07.015
  • 10.1016/j.lithos.2009.07.015
  • Cites
  • Wilke, F. D. H., Sobel, E. R., O’Brien, P. J., & Stockli, D. F. (2012). Apatite fission track and (U–Th)/He ages from the Higher Himalayan Crystallines, Kaghan Valley, Pakistan: Implications for an Eocene Plateau and Oligocene to Pliocene exhumation. Journal of Asian Earth Sciences, 59, 14–23. https://doi.org/10.1016/j.jseaes.2012.06.014
  • 10.1016/j.jseaes.2012.06.014
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  • Cites
Contact
  • Wilke, Franziska
  • GFZ German Research Centre for Geosciences, Potsdam, Germany;
Citation Wilke, F. (2022). Kaghan Valley, Pakistan: metamorphic rocks, their chemistry and age [Data set]. GFZ Data Services. https://doi.org/10.5880/GFZ.3.1.2022.001
Geo location(s)
  • Kaghan Valley, Pakistan: study area
Spatial coordinates
  • eLong 74.0624
  • nLat 35.906
  • sLat 34.85
  • wLong 73.65