Geology of the Fiordland Area - GNS Science

Data sourcesThis geological map includes data from numeroussources, including published geological maps and papers,unpublished data from university theses, unpublished GNSScience technical and map files, mining and oil companyreports, the New Zealand Fossil Record File (FRED), andGNS Science digital databases of geological resources andpetrological samples (GERM, PETLAB). Field mappingof poorly known areas, undertaken over six field seasonsbetween 2002 and 2008, ensured consistent data coverageover the map area. Landslides were mapped from air photosand field-checked in many cases. Offshore data wereobtained from published and unpublished surveys by NIWAand GNS Science. Data sources used for map compilationare shown in Fig. 2, and identified by an asterisk in thereference list.ReliabilityThis 1:250 000 map is a regional scale map, and should notbe used alone for land use planning, designing and planningof engineering projects, natural hazard assessments, or otherwork for which detailed site investigations are necessary.As much of Fiordland is covered in dense forest and/or isvery steep, the positions of contacts and faults shown withinforested areas are approximate in places. Some data fromsources older than the 1970s may be poorly located dueto the absence of reliable contemporary topographic maps.In many places, plutonic rocks have complex intrusiverelationships on scales from metres to hundreds of metres,and with further fieldwork, more detailed subdivision maybe feasible.REGIONAL SETTINGThe Fiordland geological map extends from the easternTasman Sea to the Hollyford valley in the north, the TeAnau and Waiau basins in the east, and western FoveauxStrait in the south. There are tourist facilities at Te AnauDowns, and Milford and Doubtful sounds. The towns of TeAnau and Manapouri support farming and tourist activities,and the Manapouri power scheme, but otherwise Fiordlandlacks permanent inhabitants. Road access is limited toSH94 from Te Anau to Milford; across the Borland Saddleand Wilmot Pass; and to Lake Hauroko. Elsewhere, visitorsmust fly, sail, or walk to reach the interior, the fiords andthe outer coast.Most of Fiordland is underlain by plutonic rocks, which wereintruded into metamorphosed Early Paleozoic sedimentaryrocks of New Zealand’s Western Province. Plutonism tookplace during Late Cambrian, Devonian, Carboniferous andTriassic-Early Cretaceous times, in response to repeatedphases of subduction along the margin of Gondwana. Allthe geographically contiguous plutonic rocks of Fiordlandare part of the regionally extensive Median Batholith(Mortimer et al. 1999b; Allibone et al. 2009a; Fig. 3).Several major intra-batholith shear zones were activeduring and immediately after plutonism. Late Paleozoic toMesozoic accreted terranes of the Eastern Province forma small portion of the map area in the northeast, and areseparated from the Median Batholith by Mesozoic shearzones that were reactivated in the Cenozoic (Mortimer etal. 1999a). Since separating from Gondwana in the middleto Late Cretaceous, Fiordland has been part of the nowlargely submerged microcontinent of Zealandia.When the Australian-Pacific plate boundary propagatedthrough Zealandia in the mid-Cenozoic, fault-boundedbasins developed along the southern and eastern marginsof Fiordland (Norris et al. 1978). These sedimentary basinscontinued to develop into the late Cenozoic, and expandedacross much of Fiordland. Latest Cenozoic erosion hassince removed most of these sedimentary cover rocks,which are now only preserved in basin remnants along thesouthern and eastern margins of Fiordland (see Fig. 46).Rapid changes in sedimentary facies within the basinsreflect changing motion on the developing plate boundary,particularly the beginning of subduction beneath Fiordlandin the Miocene, and the inception of strike-slip movementon the Alpine Fault (Walcott 1998; Lebrun et al. 2003;Sutherland et al. 2006a). Fiordland moved northwardduring the late Cenozoic, compressing the area aroundthe Hollyford valley and excising most of the PaleozoicEastern Province terranes and overlying Cenozoicsediments (Beggs & Ghisetti 2006). This deformation alsouplifted the Fiordland massif, particularly on its northernand eastern sides (House et al. 2005).Present-day plate boundary motion is distributed across awide zone of thrusting and strike-slip deformation abovea steeply east-dipping to vertical Wadati-Benioff Zone(Reyners et al. 1991, 2003; Eberhart-Phillips & Reyners2001). Plate motion changes from predominantly strikeslipin the north to more oblique convergence in the south(Sutherland 1995a; Barnes et al. 2002). Some 60–90% of thestrike-slip movement is accommodated on the Alpine Fault(Barnes et al. 2005; Sutherland et al. 2006a). The obliquelyconvergent component continues to uplift Fiordland (Houseet al. 2002), as shown by flights of uplifted marine terraceson the southern coast. The subductive component of platemovement has also given rise to the Solander volcanic fieldin Foveaux Strait (Reay & Parkinson 1997; Sutherland etal. 2006b).2