An angular unconformity below Cambrian rocks is present in the northwest Himalaya in the Hazara district, Pakistan. Low-grade metamorphism and folding with axial planar cleavage present in Precambrian rocks below the unconformity, but not in those above it, confirm orogenic deformation at this time. This is the first clear evidence for such a deformation episode and it may be referred to locally as the Hazaran orogeny. Anatectic peraluminous granites of the Himalaya are of only slightly younger age and may be related to this orogenic episode.

The Lower Swat rock sequence, in northern Pakistan, is composed of greenschist and amphibolite facies Indian plate rocks that crop out in a dome directly south of the Main Mantle thrust zone and Kohistan arc terrane. The metamorphism is Eocene to Oligocene in age and records the collision of the Indian plate with the Kohistan arc. This paper presents mineral assemblage, mineral composition and garnet zoning data on the Lower Swat rock sequence in order to estimate the pressure-temperature conditions of metamorphism and to infer a possible pressure-temperature-time path. The stratigraphic sequence consists of Precambrian to Cambrian(?) Manglaur formation unconformably overlain by late Paleozoic to early Mesozoic Alpurai group. The Alpurai group is further subdivided into the Marghazar, Kashala, Saidu and Nikanai Ghar formations. The Manglaur formation, in the core of the dome, is at kyanite grade. Metamorphic grade decreases in the overlying Alpurai group where a garnet "isograd" is mapped in calcareous schist of the Kashala formation. Mineral composition geothermometers and geobarometers indicate final metamorphic equilibrium conditions of about 600ø-700øC and 9-11 kbar in the Manglaur and Marghazar formations. These conditions are associated with a phase of static recrystallization which postdates the main phases of deformation. Correlation of the structural-tectonic history with the pressure-temperature estimates, and with the garnet zoning analysis, suggests that in the Eocene the Lower Swat rock sequence was subducted to a depth of 35 to 45 km beneath the MMT suture melange. Subduction was followed immediately by exhumation. The initiation of exhumation is believed to have been triggered by a change from subduction to strike slip motion in the MMT, thereby allowing the relatively buoyant Lower Swat crust to rise. The entire metamorphic-deformational cycle lasted from 7 to 16 m.y., ending in the late Eocene about 38 Ma when the rocks cooled through the argon blocking temperature in hornblende (=550øC).

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Radon concentrations were measured in kucha, semikucha and pucka houses located on the sedimentary rocks of Early Pleistocene-Pliocene Soan Formation, Pleistocene Mirpur conglomerate and recent deposits. The radon concentration was measured using CN 85 nuclear tracks etch detectors in box type dosimeters installed in the bedrooms and kitchens of the houses. It was found to vary from 14 AE 7 Bqm À3 to 258 AE 28 Bqm À3 with an average of 105 AE 17 Bqm À3 . The average radon concentration in the kucha, semi-kucha and pucka houses was 78 AE 15 Bqm À3 , 108 AE 18 Bqm À3 and 108 AE 18 Bqm À3 respectively. The increase in radon concentration from kucha to pucka houses was attributed to the type of house, differing humidity related to the Mangla Dam, temperature, bed rock geology, structures (joints, fractures and faults), aggregates and uraniumbearing sand. This study shows that the average radon level is within the accepted safe health limit (200 Bqm