Petrography of Pyroxene Granulites from Northern Swat and Kohistan
Abstract
The pyroxene granulites of Swat and Kohistan, formerly called norites, form a part of an extensive belt stretching between Nanga Parbat and central Dir. They are relatively uniform in composition and usually represented by leucocratic rocks essentially composed of plagioclase, orthopyroxene and clinopyroxene, with subordinate amounts of quartz, opaque mineral(s), apatite, amphibole, biotite and, locally, garnet; but some' of the rocks contain a higher proportion of amphibole and biotite. The proportion of quartz increases towards the intermediate members which may also have essential K-feldspar. The rocks are gneissose (foliated) and layered/banded, with some of the layers being pyroxenitic or anorthositic. Some of the bands are due to metamorphic segregation whilst others are relict igneous layers modified by metamorphism.
This paper presents a detailed account of the petrography of the rocks together with a discussion on the nature of the foliation, layering, and other aspects (xenoliths, hornblende-pegmatites, etc.), and details of the plagioclase in the granulite. Many of the features can be better explained by invoking metamorphism. It appears that the rocks crystalized plutonically from an andesitic basalt magma in an island arc or a continental margin, were metamorphosed (800oC, 7-5 kb) and finally intruded, as crystalline material capable of plastic flow, in the country rocks which were passing through amphibolite facies metamorphism.
References
Barth, T.F.W., 1950. Intrusive relations of bahiaite from southern Norway. Amer. Mineral. 35, 622-628.
Berglund, L. & Touret, J., 1976. Garnet biotite gneiss in 'System du Graphite' (Madagascar): Petrology and fluid inclusions. Lithos, 10, 139-148.
Binns, R. A., 1966. Granitic intrusions and regional metamorphic rocks of Permian age from the Wongwibinda District, N. S. W. Jour. R. Soc. N.S.W. 99, 5-35.
Bowes, D. R., Wright, A. E. & Park, R G., 1964. Layered intrusive rocks in the Lewisian of the North-West Highlands of Scotland. Q. Jour. Geol. Soc. Lond. 120, 153-192.
Brown, G. M., 1964, Layered intrusive rocks in the Lewisian of the North-West Highlands of Scotland. Discussion in Bowes et al. Q. Jour. Geol. Soc. Lond. 120, 153-192.
Buddington, A. F., 1939. Adirondack igneous rocks and their metamorphism. Geol. Soc. Amer. Mem. 7.
Buddington, A. F., 1969. Adirondack anorthosite aeries. In 'Origin of Anorthosteis and Related Rocks' (Y. W. Isachsen, ed.). No Y. State Mus. & Sci. Serv. Mem. 18, 2152-31.
Buddington, A. F., &. Lendsley, D.H., 1964. Iron-titanium oxide minerals and synthetic equivalentn. Jour. Petrol. 5, 310-357.
Cannon, R. T., 1966. Plagioclase zoning and twining in re1ation to the metamorphic history of some amphibolites and granulites. Arner. Jour. Sci. 264, 526-542.
Chaudhry, M. N. &Chaudhry, W.G., 1974. Geology of Khagram area, Dir District. Geol. Bull. Punjab Univ. 11, 21-43.
Chaudhry, M. N., Kausar, A. B. & Lodhi, S.A.K., 1974. Geology of Timurgara-Lal Qila area, Dir District, N.W.F.P. Geol. gull. Punjab Univ. 11, 53-73.
Chayes, F., 1952. On the Association of perthitic microcline with highly undulant and granular quartz in some calc-alkaline granites. Amer. Jour. Sci. 250, 281-296.
Crosby, P., 1969. Petrogenetic and statistical implications of modal studies in Adirondack anorthaires. In 'Origin of Anorthosites and Related Rocks' (Y. W. Isachsen, ed.). N. Y. State Mus. & Sci. Serv. Mem. 18, 289-303.
Crosby, P., 1972. Petrogenesis and significance of leuconorite inclusions in the main Adirondack anorthosite massif. Proc. 24th Int. Geol. Gong. 2, 312-319.
Dearnley, R., 1963. The Lewisian complex of South Harris; with some observations on the metamorphosed basic intrusions of the Outer Hebrides, Scotland. Q. Jour. Geol. Soc. Lond. 119, 242-312.
Deer. W. A., Howie, R. A. & Zussman, J., 1966. An introduction to rock-forming minerals. Wiley, New York.
DE Waard, D., 1973. Classification and nomenclature of felsic and mafic rocks of high-grade metamorphic terrains. N. Jahrb. Min. Mh. 381-392.
Donnay, J. H. D., 1913. Plagioclase twinning. Geol. Soc. Amer. Bull. 54, 1645-1651.
Goraj, M., 1951. Petrological studies of plagioclase twins. Amer. Mineral. 36, 884-901.
Green, D. H. & Mysen, B.O., 1972. Genetic relationship between eclogite and hornblende + plagioclase pegmatite in western Norway. Lithos, 5, 147-161.
Hargraves, R.B., 1962. Petrology of the Allard Lake anorthosite suite, Quebee. In 'Petrologic studies' (A.E.J. Engel et al. eds.). Geo1. Soc. Amer. Buddington Vol. 163-159.
Hess, H.H., 1960. Stillwater igneous complex, Montana: a quantitative mineralogical study. Geol. Soc. Amer. Mem. 80.
Howie, R. A., 1955. The geochemistry of the charnockite series of Madras, India. Trans. R. Soc. Edinb. 62(3), 725-758.
Howie, R. A., 1965. The pyroxenes of metamorphic rocks, In 'Controls of Metamorphism' (W. S. Pitcher and G. W. Flinn, eds,). Oliver & Boyd, Edinburgh, 3 19-26.
Howie, R. A., 1967. Charnockites and their colour. Jour. Geol, Soc. India, 8, 1-7.
Hubbard, F. H., 1965. Antiperthite and mantled feldspar textures in charnockite (enderbite) from S. W. Nigeria. Amer. Mineral. 50, 2040-2051.
Jackson, E. D., 1967. Ultramafic cumulates in Stillwater, Greate Dyke, and Bushveld intrusions. In 'Ultramafic and Related Rocks' (P. J. Wyllie, ed.). Wiley, New York, 19-38.
Jackson, E. D., & Thayer, T. P., 1972. Some criteria for distinguishing stratiform, concentric and alpine peridotite-gabbro complexes. Proc, 24th In t, Geol. Cong. 2, 289-96.
Jan, M.Q., 1970. Petrography of the upper part of Kohistan and southwestern Gilgit Agency along the Indus and Kandia rivers. Geol. Bull. Univ. Peshawar, 5, 27-48.
Jan, M.Q., 1977 a. The mineralogy, geochemistry and petrology of Swat Kohistan, NW Pakistan. Unpub, Ph. D. thesis, Univ. London
Jan, M.Q., 1977b. The Kohistan basic complex. A summary based on recent petrological research. Geol. Bull. Univ. Peshawar, 9-10, 36-42.
Jan, M.Q., & KEMPE, D. R. C. 1973. The petrology of the basic and intermediate rocks of Upper Swat, Pakistan. Geol. Mag. 110, 285-300.
Jan, M.Q., & Mian, I., 1971. Preliminary geology and pertrography of Swat Kohistan. Geol. Bull. Uuiv. Peshawar. 6, 1-32.
Kakar, S: K., Mian, S. B. & Khan, J., 1971. The geology of the Jandul Valley, Western Dir. Geol. Bull. Univ. Peshawar, 6, 54-73.
Malik, I. A., 1975. Petrography of the Rabat area, Dir District, N.W.F.P. Pak. Jour. Sci. Res., 27, 115-123.
Mehnert, K.R., 1972. Granulites, Result of a discussion: 11. N. Jahrb. Min. Mh. 139-52.
Misch, P., 1949. Metasomatic granitization of batholithic dimension. Amer. Jour. Sci. 247, 209-245.
Misch, P., 1955. Zone plagioclase in metamorphic rocks. Amer. Mineral. 40, 327-328.
Parras, K., 1958. On the charnockites in the light of a highly metamorphic rook complex in southwestern Finland. Bull. Comm. Geol. Finlande, 181, 1-137.
Poldervaart, A. & Hess, H.H., 1951. Pyroxenes in the crystallization of basaltic magmas. Jour. Geol. 59, 472-89.
Rao, A. B. & Rao. M. S., 1953. Some observations on the plagioclase twinning in charnockitic rocks. Proc. Nat. last. Sci. India, 19, 501-506.
Sahu, K.N., Mahanty, B. K. & Pati, U. C., 1973. A note on colour of charnockiteo of Tapang, Orissa. Sci. & Culture, India, 39, 347-349.
Saxena, S. K., 1976. Two-pyroxene geothermometer: a model with in approximate solution. Amer. Mineral. 61, 643-652.
Shams, F. A., 1975. The pertrology of the Thak Valley igneous complex, Gilgit Agency, northern Pakistan. Accad. Naz. Lincei, Ser. 8, 59, 453-61.
Shelley, D. 1964. On myrmekite. Amer. Mineral. 49, 41-52.
Sighinolfi, G. P. & Gorgoni, C., 1975. Genesis of massif-type anothosite-the role of high-grade metamorphism. Contrib. Mineral. Petrol. 51, 119-126.
SimpsoN, E. S W., 1970. The anorthosites-of southern Angola: a review of present data. In ‘African Magmatism and Tectonism’ (T. N. Clifford & I. G. Gass, eds.). Oliver & Boyd, Edinburgh, 89-96.
Sorensen, H., 1967. Metamorphic and metasomatic processes in the formation of ultramafic rocks. In 'Ultramafic and Related Rocks' (P. J. Wyllie, ed.). Wiley, New York, 204-12/
Spray, A., 1969. Metamorphic Textures. Pergamon Press, Oxford.
Thayer, T. P., 1960. Some critical differences between alpine-type and stratiform peridotite-gabbro complexes. 21st Int. Geol. Cong. 13, 247-59.
Thayer, T. P., 1963. Flow-layering in alpine peridatite-gabbro complexes. Mineral. Soc. Amer. Spec. Pap. I, Int. Mineral. Assoc. 3rd Gen. Mtg. 35-61.
Thayer, T. P., & Himmelberg, G. R., 1968. Rook succession in the alpine-type mafic complex at Canyon Mountain; Oregon. 23rd Int. Geol. Cong. 1, 175-86.
Tobi, A. C., 1959. Petrographical and geological investigations in the Merdaret-Lac Crop region (Belledome massif, France). Leid. Geol. Meded. 24, 181-282.
Tobi, A. C., 1961. The recognition of plagioclase twins in sections normal to the composition plane. Amer. Mineral. 46, 1470-88.
Tobi, A. C., 1962. Characteristic pattern of plagioclase twinning. Norsk, Geol, Tidsskr. 42, 264-71.
Touret, J., 1971. Le 'facies granulite en Norvege Meridionale. 11. Les inclusions fluids. Lithos, 4, 423-436.
Turner, F. J., 1951. Observation of twinning of plagioclase in metamorphic rocks. Amer. Mineral. 36, 581-9.
Vernon, R. H., 1965. Plagioclase twins in some mafic gneisses from Broken Hill, Australia. Mineral. Mag. 35, 488-507.
Wadsworth, W. J., 1973. Magmatic sediments. Mineral. Sci. Engng. 5, 25-35
Wager, L.R. & Brown, G.M., 1968. Layered Igneous Rocks. Freeman, San Francisco.
Winkler, H.G.F., 1974. Petrogenesis of metamorphic Rocks. Springer Verlag, New York.
Winkler, H.G.F., & Sen, S.K., 1973. Nomenclature of granulites and other high grade metamorphic rocks. N. Jahrb. Min. Mh. 393-402.
Wood, B.J. and Banno, S., 1973. Garnet-orthopyroxene and orthopyroxene clinopyroxene relationships in simple and complex systems. Contrib. Mineral. Petrol. 42, 109-124.'
Yoder, H.S., 1969. Experimental studies bearing on the origin of anorthosite. In 'Origin of Anorthosites and Related Rocks' (Y. W. Isachsen, ed.). N. Y. State Mus. & Soi. Serv. Mem. 18, 13-22.
