Myrmekite in ihe Ambela Granitic Complex, N. Pakistan: A Product of Deformation and Replacement in the Feldspar
Abstract
The Ambela Granitic Complex in N. Pakistan is locally intersected by strikeslip and thrust faults, which have resulted in the development of relatively sheared granites. A characteristic feature of the deformed granites is the occurrence of myrmekite in the K-feldspar porphyroclasts, which is otherwise absent in the complex. A detailed petrographic study shows that the myrmekites are localised along those margins of the porphyroclasts which are most strained and which are adjacent to the trails of secondary muscovite. A comparison with the established examples of strain-related myrmekites suggests that though the deformation may be important in the genesis of the Ambela myrmekite, there may be a greater role of metasomatic replacement accompanying deformation.
References
Becke, F., 1908. Ueber Myrmekite. Schweizerische Mineralogische und Petrographische Mitteilungen, 27, 377-390.
Berthe, D., Choukroune, P. & Jegouzo, P., 1979. Orthogneiss rnylonite, and non-coaxial deformation of granites: the example of South Armorican Shear Zone. J. Struc. Geol. 1, 31-42.
Bhattacharyya, C., 1971. Myrmekite from the charnokitic rocks, Eastern Ghats, India. Geol. Mag. 108, 433-438.
Drescher-Kaden, F.K., 1948. Die Feldspar-Quarz-Rcaklionsgefiege der Granite und Gneise und genctische. Bedeutung. Springer-Verlag, Berlin.
Eskola, P., 1914. On the petrology of the Orijarvi region in south-western Finland. Bulletin de La Commission Geologique de Finland, 40. pp. 285.
Futherer, K., 1894. Ueber ganit porphyr der Gneisscharle in der Zittlerlhalier Alpex Neues Jahrbusch furGeologie und Palaontologie. 9, 509-553.
Hibbard, M.J., 1987. Deformation of incompletely crystallized magma system; granitic gneisses and their tectonic implications. Geology, 95, 543-561.
Michel-Le'vy, A. 1875. De quelques Caracters micro-scopiques des riche anciennes acides, censide' re's dam leurs relations avec lage des eruptions Soc. Geol de France Bull. 3rd Series 3, 199-236.
LaTour, T.E. & Barnett, R. L., 1987. Mineralogical changes accompanying mylonitization in the Bitteroot dome of the Idaho batholith: implication for timing of deformation. Geol. Soc. Amer. Bull. 98, 356-363.
Phillips, E.R., 1974. Mymekite-one hundred years later. Lithos, 7, 181-194.
Phillips, E.R., 1980. On polygenetic myrmekite. Geol. Mag. 17, 29-36.
Phillips, E.R., & Can, G.R., 1973. Myrmekite associated with alkali-feldspar megacryst in felsic rocks from New South Wales Lithos, 6, 245-260.
Rafiq, M., 1987. Petrology and geochemistry of the Ambela granitic complex, N.W.F.P., Pakistan. Unpublished Ph.D Thesis, Univ. Peshawar.
Rafiq, M., & Jan, M.Q. 1987. Fibrolitic sillimanite in sheared rocks of the Ambela granitic complex, North-Western Pakistan. Geol. Bull. Univ. Peshawar 20, 181-188.
Rafiq, M., & Jan, M.Q., 1988. Petrography of the Ambela Granitic Complex, NW Pakistan. Geol. Bull. Univ. Peshawar, 21. (this volume)
Sarma, S.R & Raja, N., 1959. On myrmekite. Quart. J. Geol. Miner. Met. Soc. India, 31, 127.
Sederholm, J.J., 1899. Unerin archaische sediment-formation in Sudwestichen Finland etc. Comm. Geol Finlande Bull. 6.
Sederholm, J.J., 1916. On synantetic minerals and related phenomena (reaction rims, corona minerals, Kelyphite, myrmekite, etc.). Bulletin de la commission Geologique de finlandc, 48, 146 pp.
Schwantke, A., 1909. Die beimischung von Cain Kalifeldspat und die Mynnekitbildung. Centralb. Mineral. 311-316.
Shelly, D., 1964. On myrmekite. Amer. Mineral. 49, 41-52.
Simpson, C., 1983. Strain ad shape fabric variations associated with ductile shear zones, J. Struct. Geol., 5, 61-72.
Simpson, C., 1985. Deformation of granitic rocks across the brittle ductile transition. J. Struct. Geol. 7, 503-511.
Spencer, E., 1945. Myrmekite in graphic granite and in vein perthite. Min. Mag., 27, 79-98.
Tullis, J.A., 1983. Deformation of feldspars. In: Feldspar Mineralogy (P.H. Ribbe ed.), Min. Soc. of Amer. Short course notes, 2 ,297-323.
Vernon, R.H., William, V.A., D’Arcy, W.F., 1983. Grain-size reduction and foliatio development in a deformed in a granitoid batholith. Tectonophysics, 92, 123-145.
White, S.H., 1975. Tectonic deformation and recrystallization of plagioclase. Contrib. Mineral. Petrol. 50, 287-304.
Wintsch, R.P. & Knipe, R.J., 1983. Growth of a zoned plagioclase porphyroblast in a mylonite. Geology, 11, 360-363.
