Stable isotope thermometry of the Nanga Parbat-Haramosh Massif and the Kohistan-Ladakh arc, northern Pakistan
Abstract
The Nanga Parbat-Haramosh Massif in northern Pakistan represents the northernmost exposure of the Indian plate that have been metamorphosed in the Late Tertiary subsequent to the Himalayan collision and over thrusting of the Asian plate onto the Indian plate. The massif a complex mixture of parag- and orthogneisses, of minor metabasics and calc-silicate rocks, and of post-metamorphic pegmatite dikes. The 18O geothermometry results indicate that these gneisses are metamorphosed under peak temperatures of 700+ o C.
The 18O isotopic compositions of the rocks and their constituent minerals in the massif and adjacent areas of the Kohistan and Ladakh arc along the Indus and Astore Rivers vary as following: whole rock δ18OSMOW =7-15.3%o; quartz =7.4-16.4%o; feldspar=7-16.1%o; garnet=5.3-13.7%o; biotite=3.9-12.6%o; muscovite=6.7-12.7%o; and hornblende amphibole=4.4-7.2%. The majority of the mineral δ-values follow the “normal” sequence. 18O thermometry results were calculated from 18O fractionations among quartz, garnet, feldspar, biotite, muscovite and amphibole. Fifteen of the sixteen fractionations of Qtz-Gar-pairs (αQG) vary from 2.8%o to 3.8%o giving a range of temperatures from 764oC to 599oC respectively. The 1.0%o variation in fractionation is greater than the expected error and thus indicates a real variation in the temperatures. Among the analyzed minerals, the feldspars, which are isotopically least stable, indicate isotopic resetting during a later event.
References
Bottinga, Y. & Javoy, M., 1975. Oxygen isotope partitioning among the minerals in igneous and metamorphic rocks. Rev. Geophy. Space Phy., 13, 401-418.
Butler, R. W. H. & Prior, D. J., 1988. Tectonic controls on the uplift of the Nanga Parbat Massif, Pakistan, Himalayas. Nature, 333, 247-250.
Butler, R. W. H., Prior, D. J. & Knipe, R. J., 1989. Neotectonics of the Nanga Parbat syntaxis, Pakistan, and crustal stacking in the NW Himalayas. Earth Planet. Sci. Letts., 94, 329-343.
Chamberlain, C. P., Zeitler, P., & Jan, M. Q., 1989. The dynamics of the suture between the Kohistan island arc and the Indian plate in the Himalaya of Pakistan. J. Meta. Geology, 7, 135-149.
Chamberlain, C. P., Zeitler, P., &Jan, M. Q., 1991. A petrologic record of the collision between the Kohistan island arc and Indian plate, northwestern Himalaya. Geol. Soc. Am. Spec. Paper, 232, 23-32.
Craig, H., 1957. Isotopic standards for carbon and oxygen and correction factors for mass-spectrometeric analysis of CO2. Geochim. Cosmochim. Acta, 12, 133-149.
Craig, H., 1961. Standards for reporting concentrations ofdeuterium and oxygen-18 in natural waters. Science, 133, 1833-.
Ferry, J. M. & Spear, F. S., 1978. Experimental calibration of the partitioning of Fe and Mg between biotite and garnet. Contrib. Min. Pet., 66, 113-117.
Friedman, I. & O'Neil, J. R., 1977. Data of Geochemistry. Sixth Edition (M. Fleischer, ed.). USGS Prof. Paper, 440-KK.
Garlick, G. D., 1969. The stable isotopes of oxygen, in Handbook of Geochemistry, Vol. 2/1, p. 81B/ 1-81B/ 27, Springer, New York.
Hoefs, J., 1980. Stable isotope geochemistry (2nd ed.). Heidelberg: Springer-Verlag, l- 142.
Khattak, M. U. K., 1990. Geothermometry and Geobarometry of the Nanga Parbat-Haramosh Massif and adjoining Ladakh arc terrane, northern Pakistan. Unpubl. M.S. thesis, Univ. WashIngton.
Khattak, M. U. K., 1994. Petrology and stable isotope geochemistry of the Nanga Parbat-Haramosh Massif, northern Pakistan. Unpubl. Ph.D. Dissertation, Univ. South Carolina, U.S.A.
Khattak, M. U. K. & Stakes, D. S., 1993. New data on the geothermobarometry of the Nanga Parbat Haramosh Massif and adjoining Ladakh arc terrane, northern Pakistan. Geol. Bull. Univ. Peshawar, 26, 1-16.
Lawrence, R. D. Ghauri, A. A. K., 1983. Evidence of active faulting in the Chilas district, northern Pakistan. Geol. Bull. Univ. Peshawar, 16, 185-6.
Madin, I., 1986. Structure and neotectonics of the northwestern part of the Nanga Parbat-Haramosh massif. Unpubl. M.S. thesis. Oregon State Univ., USA.
McKinney, C. R., McCrea, J. M., Epstein, S., Allen, H. A. and Urey, H. C., 1950. Improvements in mass spectrometers for the measurement of small differences in isotope abundance ratios. Rev. Sci. Instrum. 21, 724-730.
Newton, R. C. & Hazelton, H. T., 1981. Thermodynamics of the garnet-plagioclase-A12SiOs-quartz geothermometer. In: Thermodynamics of Minerals and Melts (R. C. Newton, A. Navrotsky, & B. J. Wood, eds.). Springer-Verlag, New York, 129-145.
Nier, A. O. C., 1947. A mass spectrometer for isotope and gas analysis. Rev. Sci. Instrum., 18, 398-411.
Peterson, M. G. & Windley, B. F., 1985. Rb/Srdating of the Kohistan arc-batholith in the Trans-Himalaya of north Pakistan, and tectonic implications. Earth & Planet. Sci. Lett., 74, 45-57.
Powell, C. M.C.A., 1979. A speculative tectonic history of Pakistan and surroundings: Some con. straints from the Indian Ocean. In: Geodynamics of Pakistan (A. Farah & K. A. DeJong, eds.). Geol. Survey of Pakistan, Quetta, 5-24.
Sharp, Z. D., 1992. In situ laser microprobe technique for stable isotope analysis. Chemical Geology (Isotope Geoscience) 101, 3-19.
Valley, J. W., 1986. Stable isotope geochemistry of metamorphic rocks. In: MSA Reviews in Mineralogy (J.W. Valley, H. P. eds.). 16, 445-489.
Verplanck, P. L., 1986. A field and geochemical study of the boundary between the Nanga Parbat Haramosh massif and the Ladakh arc terrane, northern Pakistan. Unpubl. M.S. thesis, Oregon State University, U.S.A.
Zeitler, P. K., Sutter, J. F., Williams, l. S., Zartman, R., & Tahirkheli, R. A. K., 1991. Geochronology and temperature history of the Nanga Parbat Haramosh massif, Pakistan. Geol. Soc. Am. Spec. Pap., 232, 1-22.
Zeitler, P. K, Tahirkheli, R. A. K, Naeser, C. W., & Johnson, N. M., 1982b. Unroofing history of a suture zone in the Himalayas of Pakistan by means of fission track annealing ages. Earth Planet. Sci. Lett. 57, 227-240.
