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The nature and origin of orbicular rocks from near Deshai, Swat Kohistan, Pakistan

Published online by Cambridge University Press:  05 July 2018

R. F. Symes ,
J. C. Bevan  and
M. Qasim Jan
R. F. Symes
Affiliation:
Department of Mineralogy, British Museum (Natural History), Cromwell Road, London SW7 5BD
J. C. Bevan
Affiliation:
Department of Mineralogy, British Museum (Natural History), Cromwell Road, London SW7 5BD
M. Qasim Jan
Affiliation:
Institute of Geology and Mineralogy, University of Peshawar, Pakistan
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Abstract

Orbicular dioritic-noritic rocks from an area of mixed metemorphic and igneous rocks in Swat Kohistan, northern Pakistan, have been examined petrographically and chemically in order to determine the nature and origin of the orbicular texture. Using textural and compositional sequences it has been possible to relate the apparently different orbs to one another, and obtain a sequence of orb formation. The majority of the orbs comprise a series of distinct layers (shells) surrounding a central zone (core). Plagioclase, clinopyroxene, orthopyroxene and hornblende form the bulk of the shells. The cores have been extensively recrystallized. The development of a ‘comb-layered’ texture in some orbs and in associated layered rocks is comparable to that commonly described from other occurrences. A dual igneous/metasomatic crystallization history is invoked to explain the features of the orbs in this locality, the oscillatory zoning of the orbicular structure being caused by the alteration of primary minerals, such as pyroxene to amphibole, due to fluctuations in the pH2O of the magma.

Keywords

orbicular rocksdioritenoriteSwat KohistanPakistan
Type
Petrology and Geochemistry
Information
Mineralogical Magazine , Volume 51 , Issue 363 , December 1987 , pp. 635 - 647
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1987

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References

Barriére, M. (1972) Le gabbro orbiculaire des Albaresses. Bull. Soc. Fr. Mineral. Cristallogr. 95, 495-506.Google Scholar
Bryhni, I., and Dons, J.A. (1975) An orbicular lamprophyre from Vestby, Norway. Lithos. 8, 113-22.Google Scholar
Din, V.K., and Jones, G.C. (1978) The determination of total carbon and combined water in silicates using a C,H,N elemental analyser. Chem. Geol. 23, 347-52.Google Scholar
Donaldson, C.H. (1977) Laboratory duplication of comblayering in the Rhum pluton. Mineral. Mag. 41, 323-36.Google Scholar
Elliston, J.N. (1984) Orbicules: An Indication of the Crystallisation of Hydrosilicates. Earth Sci. Rev. 20, 265-344.Google Scholar
French, W.J., and Adams, S.J. (1972) A rapid method for the extraction and determination of Iron (II) in silicate rocks, and minerals. Analyst. 97, 828-31.Google Scholar
Gardner, P.M., and Robins, B. (1973) The olivineplagioclase reaction: geological evidence from the Seiland petrographic province, northern Norway. Contrib. Mineral. Petrol. 44, 149-56.Google Scholar
Jan, M.Q., and Asif, M. (1983) Geochemistry of tonalites and (quartz) diorites of the Kohistan-Ladakh (Transhimalayan’) granitic belt in Swat, NW Pakistan. In Granites of Himalayas, Karakorum and Hindu Rush (F. A. Shams, ed.). Lahore.Google Scholar
Jan, M.Q., and Asif, M. and Mian, I. (1971) Preliminary geology and petrography of Swat Kohistan. Geol. Bull. Univ. Peshawar. 6, 1-32.Google Scholar
Paruez, M.K., and Khaltak, M.U.K. (1984) Coronites from the Chilas and Jijal-Patan complexes of Kohistan. Ibid. 17, 75-85.Google Scholar
Leveson, D.J. (1963) Orbicular rocks of the Lonesome Mountain area, Beartooth Mountains, Montana and Wyoming. Bull. Geol. Soc. Am. 74, 1015-40.Google Scholar
Leveson, D.J. (1966) Orbicular rocks: A review. Ibid. 77, 409-26.Google Scholar
Leveson, D.J. (1973) Origin of comb layering and orbicular structure, Sierra Nevada Batholith, California. Ibid. 84, 4005-6.Google Scholar
Lofgren, G.E., and Donaldson, C.H. (1975) Curved branching crystals and differentiation in comb-layered rocks. Contrib. Mineral. Petrol. 49, 309-19.Google Scholar
Maggetti, M., Van Diver, B.B., Galetti, G., and Sommerauer, J. (1978) P/T conditions of orbicular gabbro from Reichenbach, West Germany. Neues Jahrb. Mineral. Abh. 134, 52-75.Google Scholar
Moore, J.G., and Lockwood, J.P. (1973a) Origin of comb layering and orbicular structure. Bull. Geol. Soc. Am. 84, 1-20.Google Scholar
Moore, J.G., and Lockwood, J.P. (1973b) Origin of comb-layering and orbicular structure, Sierra Nevada Batholith, California. Ibid. 84, 4007-10.Google Scholar
Mutanen, T. (1974) Petrography and protoclastic structures of the orbiculite boulders from Saakslahti, Toivakka, Finland, and the magmatic genesis of orbiculites. Bull. Geol. Soc. Finland. 46, 53-74.Google Scholar
Petterson, M.G., and Windley, B.F. (1985). Rb/Sr dating of the Kohistan arc-batholith in the Trans-Himalaya of northern Pakistan, and tectonic implications. Earth Planet. Sci. Letters. 74, 45-57.Google Scholar
Taubeneck, W.H., and Poldervaart, A. (1960) Geology of the Elkhorn Mountains, Northeastern Oregon. Pt. 2. Willow Lake intrusion. Bull. Geol. Soc. Am. 71, 1295-322.Google Scholar
Van Diver, B.B. (1968) Origin of the Jove Peak orbiculite in Wenatchee Ridge area, northern Cascades, Washington. Am. J. Sci. 266, 110-23.Google Scholar
Van Diver, B.B.and Maggetti, M. (1975) Orbicular gabbro from Reichenbach in the Bergstrasser Odenwald, Germany. Neues Jahrb. Mineral. Abh. 125, 1-26.Google Scholar