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ALPINE FAULT

This is an intracontinental transform fault cross-cutting the two islands of New Zealand and continues as the Karmadoc subduction zone in Pacific ocean. This photo taken from a book shows recent activity (displacement of alluvial fan ) along this fault. The estimated total displacement along this fault since early Palaeozoic is of the order of 450 km. The fault affects the Proterozoic granite greenstone association. Although not quite strictly true, most of the granite bodies occur to the east of the fault. The fault is a boundary between the Pacific and Indo Australian plates. Watch the BBC's online movie on bbc.co.uk as part of the series titled Horizon by the BBC. This one is titled The man who moved the mountains and also focuses on the movement of Indo-Australian plate with experiment by Tapponier et al.  As one encounters younger rocks along the fault, the amount of displacement gradually diminishes. The earliest movements appear to have begun during the mid-palaeozoic.

New Zealand's Alpine fault

         N Island - volcanic zone, oblique subduction (joins Tonga Kermadec arc to N).

         S Island - no volcanic arc, predominantly transpressional regime.

         reason for such quick changes? near pole of rotation.

         main fault strand - Alpine fault.

         transpressional (plate motion vector oblique to fault trace).

         E side uplift 17,000' in 4 +/- 2 Ma (Sheppard et. al. 1975).

         450 km of dextral offset: Dun mountain ultramafics provide displaced marker unit.

Displacement amounts:

         Molnar & others - 330 km in last 10 Ma on basis of geology.

         Wellman, 1973, - 300 km in past 10 Ma on basis of plate motions.

         recent movement rates .45 to 2.3 cm/year

There are en echelon folds developed and oblique motion on the main fault - can consider it a coupled or only partially decoupled system system.

Note northern faults forming - more pure transcurrent. Why? as thicken crust resistance increases, and more energy efficient to form new crust?