Bishop, D.G.; Blattner, P.; Landis, C.A. 1990 Hollyford. Scale 1:75,000. Lower Hutt: New Zealand Geological Survey. Miscellaneous series map / New Zealand Geological Survey 16 1 fold. map + 1 booklet
Abstract: The Hollyford map area comprises three distinct topographic and geological regions. The most rugged topography is developed on crystaline rocks of the Darran Mountains in the west:- Darran Leucogabbro and associated hornblende diorite; Mackay Intrusives (diorite to granite); and dikes of microdiorite, diorite porphyry, quartz diorite, and pegmatite. Radiometric dates suggest rocks as young as Cretaceous are present. In the centre of the area the Hollyford valley is eroded into less resistant rocks in a graben between the Glade-Darran Fault and the Livingstone Fault. The graben is formed of volcanogenic rocks of the Alabaster Group (Permian) in the west, separated from the ultramafic sequence and overlying Permian sediments of the Humboldt and Maitai groups in the east by the Hollyford Fault system. The structure of the Darran rocks is dominated by primary igneous features. The Maitai Group is folded into a very tight regional syncline. The Caples rocks are deformed into early, large-scale recumbent folds overprinted by post-metamorphic open folding. The most striking structural aspect of the whole region is the faulting, which controls both the physiography and the distribution of rock units. The juxtaposition of several, perhaps completely unrelated, suites of rocks indicates that some of the faults may be fundamental sutures between different geological terranes. Significant earthquake risk exists in the region. Roads and communications are likely to be cut during large earthquakes; and earthquake-induced avalanches, rockfalls, and landslide-dammed waterways are likely to pose considerable hazards.