The geology and geochemistry of the Hohonu Batholith and adjacent rocks, North Westland, New Zealand.

• Main Author: Waight, Tod Earle
• Format: Other/Unknown Material
• Language: English
• Published: University of Canterbury. Geology 1995
• Subjects: Greenland; Mount Graham; New Zealand; Pacific; Separation Point
• Online Access: http://hdl.handle.net/10092/5615; https://doi.org/10.26021/7125

The Hohonu Batholith lies within the Buller terrane, immediately adjacent to the Alpine Fault and inland from Hokitika and Greymouth on the West Coast of the South Island of New Zealand. Detailed mapping has identified ten distinct granitoids intruded into Greenland Group metasediments. Four geochemical suites are recognized within the Hohonu Batholith. Palaeozoic magmatism in the batholith is represented by the Summit Granite, which yields a Palaeozoic (381.2 Ma) age and displays affinites with granitoids of the Karamea Suite of Tulloch (1988a). The informal name Summit Granite suite is used to describe this pluton. The Summit Granite has acted as country rock and is intruded by two Cretaceous plutons. The poorly constrained Mount Graham Granite may also belong within the Summit Granite suite. The Hohonu Batholith is dominated by the mid-Cretaceous (114-109 Ma) I-type Hohonu Super-suite, which is considered to encompass the previously defined Rahu Suite of Tulloch (1988a). The Hohonu Super-suite is characterized by relatively restricted radiogenic isotopic compositions with Sr(110) = 0.7062 to 0.7085 and εNd(110) = -4.4 to -6.1, and represents melting of a complex source combining depleted mantle-derived material, similar in composition to the source of the Early Cretaceous Separation Point Suite, and a complex, heterogeneous and largely unconstrained lower continental crustal component. A model is proposed whereby the Hohonu Super-suite was generated following the collapse and thinning of Western Province crust previously over thickened by the generation of the Median Tectonic Zone volcanic arc and its subsequent collision with the Western Province. Collapse of the over thickened crust is believed to be a consequence of the cessation of subduction along the Pacific Margin of the New Zealand portion of Gondwana and the subsequent removal of compressional forces maintaining crustal thickening. Rapid isothermal uplift of the thickened crustal root resulted in partial melting of the lower crust. Ambient ...