The Fraser fault in central Westland, New Zealand, and its associated Rocks

Abstract

In central Westland a major fault, extending for 30 miles from Waitaha

The Fraser Complex: High‐grade metamorphic, igneous and mylonitic rocks in central Westland, New Zealand

“…The lithologic variation and structural complexity indicate that Fraser Complex is a more appropriate name for this rock unit than the Fraser Formation of Young (1968). The high-grade gneisses include; sillimanite-bearing gneisses with an upper amphibolite facies metapelitic mineralogy, quartzofeldspathic migmatitic gneisses, and hornblende gneisses with an epidote-amphibolite mineralogy.…”

“…Formation status was considered appropriate by Young because "The lithological differences between the rock types, which often interfinger and are intercalated, are not discrete enough, in spite of Morgan's [1908] mapping, to allow the definition of two or more formations as would be required to establish a Fraser "Group" " (p. 295), and "The rocks differ mostly only in the degree of cataclasis each type has been subjected to,..." (p. 291). I, however, consider there are distinct and mappable lithologic variations, of diverse igneous and metamorphic origins, within the rock unit described by Young (1968), and that formation status is now inappropriate. Another important aspect of this rock unit is the discontinuous and complicated structure resulting from mylonitisation of the gneissic and igneous rocks (Rattenbury 1987b).…”

“…Young (1968) established the Fraser Formation for these distinctive rocks "... in order to bring into one grouping the cataclastically deformed rocks and…”

Gneissic rocks of the Bonar Range, central Westland, New Zealand

“…Geology between Urquhart Creek and the Fraser Fault is compiled from Young (1968) and Green (1982). Geology east of the Waitaha River is compiled from Warren (1967), Young (1968), and Green (1992). Rb-Sr geochronology locations of Aronson are derived from Nathan (1967).…”

Late Jurassic‐Early Cretaceous metamorphic age of Fraser Complex migmatite, Westland, New Zealand

“…These rocks were collectively described as the Fraser Formation by Young (1968), but renamed the Fraser Complex by Rattenbury (1991). The Fraser Complex is bounded to the west by the Cambro-Ordovician Greenland Group (Cooper 1989) and granitoids of probable midPaleozoic age (Tulloch 1983;Tulloch et al 1986), and to the east across the Alpine Fault by Alpine Schist.…”