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Acicular hornblende schists and associated metabasic rocks from North-West Pakistan

Published online by Cambridge University Press:  05 July 2018

D. R. C. Kempe
D. R. C. Kempe*
Affiliation:
Department of Mineralogy, British Museum (Natural History), London SW7 5BD
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Synopses

A suite of unusual acicular hornblende schists is found at Warsak (34° 10′ N. 71°C 23′ E.), some 30 km WNW. of Peshawar, North-West Pakistan. The schists occur in association with sill-like masses of amphibolite facies meta-igneous rocks, possibly a metamorphosed gabbroic and doleritic, dioritic, and granitic calc-alkaline series, and intrusions of alkaline granite and microgranite. These rocks lie within Palaeozoic metasediments and all are folded synclinally. The area was first described by Ahmad et al. (1969).

The rocks of the acicular hornblende schist suite (fig. I) consist essentially of large, idioblastic hornblende crystals—comprising some 30–60 % of the rock—in a fine-grained granoblastic matrix of oligoclase feldspar with minor quartz, iron oxide, biotite, and rutile. The boat-shaped, blue-green hornblendes, twinned on {100}, reach 5 mm in length and are often grouped in sprays or clusters; they are sieved with quartz, ilmenite, and patchy calcite. The groundmass also contains patches and veins of calcite, associated with ragged patchy areas of reddish brown, amorphous iron oxide or hydroxide, perhaps introduced hydrothermally. The schists coarsen in grain size outwards through the sill-form, the hornblendes reaching 4 cm, become rich in chlorite and biotite, and grade into the apparently metagabbroic amphibolitic rocks.

The acicular hornblende schists have a generally basaltic composition, while the hornblendes are tschermakitic. An analysed amphibole has 16·5% Al2O3, is slightly zoned with alumina increasing from core to rim, and has the formula:

Three hypotheses of the origin of the rocks were considered; metamorphism of a suite of basic tufts is the most favoured. Origins involving metamorphism of a lamprophyre-appinite suite or of a gabbroic marginal facies are therefore rejected. Texturally the rocks strongly resemble metatuffs (fig. 2) that occur associated with metagreywackes in the Otago schists of New Zealand (Turner, 1933); like many similar Alpine schists they also contain tschermakitic hornblendes. The Warsak tufts could have formed originally, together with the meta-igneous rocks, possibly as lavas, in an inter-plate tectonic environment; the high A1 content of the hornblende, which is typical of many amphiboles from the surrounding alpine environment in North-West Pakistan, and other mineralogical evidence in the region support a highpressure environment for the metamorphism of the rocks to just within the amphibolite facies, at moderate temperatures of approximately 465 °C.

Type
Research Article
Information
Mineralogical Magazine , Volume 42 , Issue 323 , September 1978 , pp. 405 - 406
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1978

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References

Ahmad, (M.), Ali, (K. S. S.), Khan, (B.), Shah, (M. A.), and Ullah, (I.), 1969. The geology of the Warsak area, Peshawar, West Pakistan. Geol. Bull. Univ. Peshawar, 4, 44–78.Google Scholar
Bunch, (T. E.) and Okrusch, (M.), 1973. Al-rich pargasite. Am. Mineral. 58, 721-G.Google Scholar
Coulson, (A. L.), 1936. A soda-granite suite in the North-West Frontier Province. Proc. Natn. Inst. Sci. I, 2, 103-11.Google Scholar
Coulson, (A. L.), 1937. Marble of the North West Frontier Province. Rec. Geol. Suzo. Indqkz, 71, 328-44.Google Scholar
Griesbach, (C. L.), 1892. The geology of the Safed Koh. Ibid. 25, 59-109.Google Scholar
Hayden, (H.), 1898. On the geology of Tirah and the Bazar Valley. Ibid. 28, 96–117.Google Scholar
Hutton, (C. D.), 1940. Metamorphism in the Lake Wakatipu region, western Otago, New Zealand. Geol, M. Dept. Sci. Ind. Res. New Zealand, 5, 1–90.Google Scholar
Jan, (M. Qasim), 1977. The mineralogy, geochemistry and petrology of Swat Kohistan, NW Pakistan. Unpublished Ph.D, thesis, Univ. London.Google Scholar
Jan, (M. Qasim), Kempe, (D. R. C.), 1970. Recent researches in the geology of northwest West Pakistan. Geol. Bull. Uniu. Peshawar, 5, 62–89.Google Scholar
Jan, (M. Qasim), Kempe, (D. R. C.), 1973. The petrology of the basic and intermediate rocks of upper Swat, Pakistan. Geol. Mag. 110, 285–300.CrossRefGoogle Scholar
Jan, (M. Qasim), Kempe, (D. R. C.), Tahirkheli, (R. A. K.), 1969. The geology of the corundum-bearing and related rocks around Timurgara, Dir. Geol. Bull. Univ. Peshawar,, 4, 83-9.Google Scholar
Jan, (M. Qasim), Kempe, (D. R. C.), Tahirkheli, (R. A. K.), 1971. Corundum, altering to margarite, in amphiPolites from Dir, West Pakistan. Mineral. Mag. 38, 106-9.CrossRefGoogle Scholar
Kemp, (A.) and Leake, (B. E.), 1975. Two hydrous-rich aluminous hornbiendes. Ibid. 40, 308-11.Google Scholar
Kempe, (D. R. C.), 1973. Tilloids from N.W. Pakistan. Geol. Mag. 110, 373-4.CrossRefGoogle Scholar
Kempe, (D. R. C.), 1973b. The petrology of the Warsak alkaline granites, Pakistan, and their relationship to other alkaline rocks of the region. Ibid. 110, 385-404.CrossRefGoogle Scholar
Kempe, (D. R. C.), Jan, (M. Qasim), 1970. An alkaline igneous province in the North-West Frontier Province, West Pakistan. Ibid. 107, 395-8.CrossRefGoogle Scholar
Koller, (F.), 1976. Zur Detrologie der Hornblendegarbenschiefer der Dstalpen, Tschermaks Min. Pert. Mitt, 23, 275-315.Google Scholar
Leake, (B. E.), 1965a. The relationship between composition of calciferous amphibole and grade of metamorphism. In Controls of Metamorphism (ed. Pitcher, W. S. & Flinn, G. W.), pp. 299–318. Oliver and Boyd, Edinburgh and London.Google Scholar
Leake, (B. E.), 1965b. The relationship between tetrahedral aluminum and the maximum possible ocbahedrai aluminum in natural calciferous and subcalciferous amphiboles. Am. Mineral. 50, 843-51Google Scholar
Leake, (B. E.), 1971. On aluminous and edenitic hornblendes. Mineral Mag. 38, 389–407.CrossRefGoogle Scholar
Martin, (N. R.), Siddiqui, (S. P. A.), and King, (B. H.), 1962. A geological reconnaissance of the region between the Lower Swat and Indus Rivers of Pakistan. Geol. Bull. Univ. Punjab, 2, 1-14.Google Scholar
Mason, (B.), 1961. Metamorphism in the Southern Alps of New Zealand. Bull, Am. Nat. Hist. 123, 211-48.Google Scholar
Métais, (D.) and Chayes, (F.), 1963. Varieties of lamprophyre. Carnegie Inst. Wash. Yearb. 6, 158-7.Google Scholar
Misch, (P.), 1949. Metasomatic granitization of batholithic dimensions. Part I. Am. J. Sci. 247, 209-45.Google Scholar
Perchuk, (L. L.), 1966. Tmperature dependence of the coefficient of distribution of calcium between coexisting amphibole and plagioclase. Dokl. Acad. Sci. USSR, Earth. Sci. Sect. 169, 203-5.Google Scholar
Reed, (J. J.), 1958. Regional metamorphism in south-east Nelson. Bull. New Zealand Geol. Surv., n.s. 60, 64 pp.Google Scholar
Shams, (F. A.), 1972. Glaucophane-Dearing rocks from near Topsin, Swat. First record from Pakistan. Pakin J. Sci. Res. 24, 343-5.Google Scholar
Stauffer, (K. W.), 1968. Silurian-Devonian reef complex near Nowshera, West Pakistan. Bull. Geol. Soc. Amer. 79, 1331-50.CrossRefGoogle Scholar
Tahirkheli, (R. A. K.), 1970. The geology of the Attock-Cherat Range, West Pakistan. Geol. Bull. Univ. Peshawar, 5, 1-26.Google Scholar
Turner, (F. J.), 1933. The metamorphic and intrusive rocks of Southern Westland. Trans. New Zealand Inst. 63, 178-236.Google Scholar
Turner, (F. J.), 1938. Progressive regional metamorphism in southern New Zealand. Geol. Mag. 75, 160–174.CrossRefGoogle Scholar
Turner, (F. J.), 1968. Metorphio Petrology. McGraw Hill, New York, 403 pp.Google Scholar