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The northeast- and northwest-trending faults may have been active conjugate structures, movingbroadly synchronously. Near Yam 0, the northwest-trending fault through Penny's Bay and thenortheast-trending Yam 0-Pui 0 Fault define a triangular block of rhyolite dykes from whichTsuen Wan Volcanic Group rocks are largely absent, whereas in adjacent blocks, they aredominant although they are intruded by many rhyolite dykes. It is inferred that the wedge betweenthe two faults has been faulted downwards.Eastnortheast-trending FaultsFew eastnortheast-trending faults were directly observed during field mapping, but asairport-related developments have proceeded along the northern coast of Lantau Island, cuttingsand ground investigations have encountered major fault zones of this orientation.Excavations on Yam Tsai, for the North Lantau Expressway, intersected aneastnortheast-trending zone, 100 m wide, that is intensely jointed, and includes zones ofbrecciated rock greater than 10m wide, and deeply weathered zones up to 20 m wide (Franks &Roberts, 1995). The contrasting styles of deformation indicate that the fault set had severalstages of development. These faults form part of the North Lantau Fault Zone identified byLangford (1994), which follows the northern coast of Lantau Island. On newly-reclaimed landnear Tung Chung, ground investigations revealed similarly complex structures related to thisfault zone. They include fault slivers of Carboniferous sedimentary rocks (including marble andskarn), brecciated zones and deep weathering. These faults show the oldest demonstrable activityalong the zone, since the Carboniferous strata were incorporated into the fault zone prior tomajor plutonic activity. Later activity brecciated granite, rhyolite dykes and Tsuen Wan VolcanicGroup rocks.West of Tung Chung, faults striking 070° occur near Sha Lo Wan, and north of Chek Lap Kok.Langford (1994) postulated a further, similarly-trending fault, the Tai 0 - Sui Lam Fault, and onthe southern side of Lantau Island, a strong photolineament trends 070° across the Chi Ma Wanpeninsula,Eastnortheast-trending faults were not active after the development of northwest-trendingstructures, as offsets at several northwest-trending faults cut the fault zone into segments, andnorthwest-trending quartz veins cross the fault zone without any displacement (e.g. at Yam Tsai).North-trending FaultsIn the granite headland west of Tung Chung a series of north-trending faults (striking between000° and 020°) have been mapped, mainly along coastal sections. The faults, which are notassociated with well-developed photolineaments, are 1 to 10 m wide, and intensively jointed, withzones of breccia and common quartz veins. The Chek Lap Kok Fault (Langford, 1994) is anorthnortheast-trending fault, which has a significant topographic expression (Plate 40) andoffsets dykes on Chek Lap Kok.North-trending faults have not been recognised in other parts of the district, although they arepresent in the Castle Peak area, in the western New Territories, along a continuation of the trendof the present fault set,The north-trending faults are offset by a few metres across eastnortheast-trending faults at HauHok Wan, and the north-trending fault set is therefore thought to have been active during the laststages of movement on the eastnortiiieast-tranding faults.99