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Circum-Pacific and Caribbean Orogens |
New Zealand Geological Survey, Box 30368, Lower Hutt, New Zealand
The New Zealand orogenic belt has developed since the late Pre-Cambrian as a result of compressive and strike-slip movements along the south-west margin of the Pacific ocean basin. Because of its unique situation on the mobile boundary of the Pacific, successive orogenies have been superimposed through Phanerozoic time giving a complexity of structure that has made this a testing ground for geologists and a graveyard for tectonic theories. Even now with modern plate tectonic theories carrying all before them difficulties remain in applying these theories rigorously to the New Zealand orogen.
The New Zealand orogen (Figs. 1 and 2) forms a strongly recurved arc, convex towards the Pacific in the north-east and towards the Tasman Sea in the south-west. These margins are presently active subduction zones characterized by lithospheric underflow, isostatic gravity anomalies, deep seismicity and active volcanism. The bulk of the orogen in between is a series of compressional mountain ranges in which large vertical movements are but a small fraction (10–20%) of greater dextral strike-slip displacements associated with the Alpine Fault and its branches. A total measurable offset of pre-Cretaceous rock belts of 480 km has been postulated on the Alpine Fault, of which probably two-thirds (330 km) is believed to have taken place in the Rangitata orogeny of late Jurassic-early Cretaceous age, and the remainder during the Kaikoura orogeny of Miocene-Recent age, which still continues.
The New Zealand structural zones formed in the Palaeozoic and Mesozoic as a result of island arc volcanism, metamorphism and plutonism along
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