A structural study of the Separation Point Batholith : emplacement mechanisms and the tectonic regime
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The Separation Point Batholith is a late Cretaceous granitic intrusion outcropping in the north-west Nelson region of New Zealand. The batholith is elongate, oriented north / south, and stitches the Paleozoic Takaka Terrane to the arc-derived Median Tectonic Zone. It has been found to be related geochemically to high-Al trondhjemite-tonalite-dacite suites, and hence to be related to the Western Fiordland Orthogneiss. This study investigates the structural features of the northern segment of the Separation Point Batholith where they are exposed along the coastline of the Abel Tasman National Park. Extensive measurements of the pervasive foliation and lineation indicate a consistent planar structure dipping moderately to steeply to the east, and a linear structure plunging gently to the north-east. Jointing systems are approximately consistent with this structure. The western margin is marked by a zone of intense strain, also producing structures dipping steeply to the east, and by the mixing of granitic and dioritic magmas. A model for the emplacement of the Separation Point Batholith has been developed based upon tectonic reconstructions for magma genesis and later post-compressional events. The batholith was emplaced in an active tectonic environment under a transpressional regime, along a major north-south striking oblique shear zone with dextral strike-slip and east-over-west thrusting. Dilational jogs along the shear zone provided the room for intrusion, and the batholith was finally emplaced into releasing bends of high-level fault systems.