Preliminary Geology And Petrography Of Swat Kohistan

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cornruing conEuent with one mother, and have marked resembleace with Missisipian-Pensyl vanian corals (M.A. Khan, personal commuoication). The thin sections a-lso have columnals of crinoids and a few fragments of (1) fusulinids. The limestone, thus, appears to ba Carboniferous. The underlying thick qual?tzites and other metasedimentnry rocks may be of this age or even older (Siluro- Devonian). The group thus belongs to the many Middle to Late Paleeozoic rocks of the northwestern Pakistan (see Jan and Kempe, 1970). The Kohistan Basic Complex. The complex inclndes diorites, norites, amphibolites and the associated racks, previously called the Upper Swat Hornblendic Group by Martin et of* (1962). We propose the new name because it is mor meaningful than the old, arnbiguous one. Besides, such rocks are abundant in Kohistan of Dir and Hazara, and in southwestern part of Gilgit Agency. The rocks probably ex1 end as far to the east as Nangs Parbat, and to the west in Afghanistan (Jan, 1970). In the investigated area, the complex is dominated by norites and diorites, wit.h minor amphibolites, granites, and layers of pyroxenites and anorthosites. Davics (1964), who considered the rocks plutonic, has also reported granodiorites and syenites. Geologists of Peshawar University, who worked in various parts of Upper Swat, Indus Valley, and Timurgara (Dir), have proposed the following general subdivision of the complex : amphibolites, norites/diorites, perido tites, and granitic rocks. Jan and Kempe (in preparation) have recently shown that the granites and some peridoties are later in age and are not related genetically to the basic seriee. They have also suggested that the three major rock types (amphib olites, norites, arid diorites) repraan t o metamorphosed differentiated igneous series. A characteristic field feature of the norites is the flesh-pink plagioclase and dark, greenish-pink hypersthene. Where the feldspar is not pink, tila rocks look greyish to dark gabbroic. They turn light grey on weathering but, in the upper reaches of Mankial valley, they are dark brown due to arid weathering. Most of the rooks are medium-grained and gneissose. A few are fine-mained and some are characteristically coarse, such as those of the Miandam area. With rare exceptions, foliation is well-developed and, in a few, lens-shaped feldspar may impart the look of angen-gneisses. In rare oases, large crystals of pyroxene may be studded like buttons in planes often parallel to foliation. Some norites exhibit textural and/or GO mpositionol layering (Jan and Kempe, in preparation)
para.lle1 to foli~.tion. Moxt of the lnyers are about an inch thick and dimi~~ish laterally in short distances. Associated with these, a,ccording to Jam and Kempe, are thin layers and streaks of anorthosite and pyrexeaite. The latter may be ap to ten feet thick and often form zones that reach 60 feet thickness at tI:eir maximum and many hundred yards in length, although they are l?auch rare as compared to an~rt~hoeite lajers, The rocks are characterized by many seta of well-developed joints, general. jy spaced closely. In a few, they are widely spaced and the rocks Ere& into huge bloclrs with smooth surfaces. Over 1,050 poles of joint readings \'ere plotted on Schmidt's stereonct to determine the direction of fcrces. TIle rocks also have fractures, microfractures, and shear zones, that may brecciate the rock for many feet, with greenish colonr due to secondary chlorite, Rml hibole and epidote. In some, tho middle pnrt is crushed fine. $liakensides, at '3 laces abundant, are often coated by epidote andlor quartz mith, or wii hout, chlorite. In one case, 33 miles west of Madyan, shearing Has produced a flaser structure in a hornblende peg ma taite with davelopment, of ovoid feldspar an d smaller hornblende in a finely crushed groundmass of the two (Jan al;d Kempe, in preparation). The norites are essentially composed of labradorite, hypersihene, ancl alinopyroxene, the three making over 05% of the rocks in most cases. About tvo per cent of ore mjnersls (magnetite/ilmenite, rarely ppite), and even smaller proportion of hornblende, biotite, quartz, and apatite are their other constituents. The mafic minerals usually range from 35 to 40y0. The diorites, on the other $nag, lnoqmal1~7 have a higher quantity of biotite, hornblende, quartz (in oop e up to b20/,), and accessory sphano.. Most of the diorites arc prosene - bearing; their pla gioclnse is in the krldesine range. The anor thosit e and pyroxenite lagers (with mafia minerals less than 25 and more than 75%, respectively), besides plagioclase or pyroxene (s), may have any cf the above-mentioned winerals as accessory constituents. The plsgioclase, in some strained, is locally cloudy due to secondary clayey, sericitic or saussuritic alterations. In some, one set of twin lamellse is more altered than the alternate one. In rare cases, blabs of enother ('2) feldspar, ~vith lower'relief, are common in the plagioclase; these might be exsolvcd K-feId. spar. The pyroxenes show exsolution lamillae which ore usually traced by brown iron oxide. Some are changed to brown serpentine, talc, and/or ~lrulite. Such ph&omenon is more common along fractures and margins; in some, abundant secondary ore granules are associated. The hypersthene, whid is usually more abundant than the cliuopyroxeno, is always strongly pleochroie.
Page 1 and 2: Ecol. Bull. Univ. Peshawar, Val. 6,
Page 3 and 4: narrow gorges are formed rt some pl
Page 5 and 6: Dewangar Granite ? Middle Porphyrit
Page 7: They appear; to have been gradually
Page 11 and 12: Local, small intrusions of granites
Page 13 and 14: Fig. ll. Pegmatite near Brhrtn with
Page 15: preeence of chlorite, epidote, and
Page 18 and 19: some breccies to the southwest of K
Page 20 and 21: The rocks to the southwest of Dewan
Page 22 and 23: The roclrs are generally in the for
Page 24 and 25: The rocks are mediam-grained, hypid
Page 26: . development of a clinoampi~ibole
Page 29 and 30: ank do not extend on the eastern si
Page 31 and 32: Hovever, there are a few rooks in w
Page 33 and 34: most. The main metallic minerals no
Page 35: BIARTIN, N.R., SIDDIQUI, S.F.A. and

Preliminary Geology And Petrography Of Swat Kohistan

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