The structure of the Buller terrane west of the Anatoki thrust, upper Cobb Valley, Northwest Nelson, New Zealand.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The Buller terrane west of the Anatoki Thrust in the upper Cobb Valley area is composed of Ordovician marine sediments. Rocks in the field area are divided into two domains of different structural styles. In the west Domain 1 includes the Roaring Lion Formation which displays a series of mesoscopic gently plunging upright folds on the limb of a single megascopic fold. Folding is associated with low greenschist facies metamorphism. Domain 2 comprises rocks of the Aorangi Mine, Leslie, Douglas and Peel Formations; which contain three cleavage sets. The last cleavage is associated with a reclined fold in the east of Domain 2, which is correlated with folding at Gouland Downs to the north. Domain one was brought into contact with Domain two by thrusting and strike slip movement along the Fenella Fault Zone, a steeply dipping zone of bedding concordant faulting. Geochemistry shows the Roaring Lion Formation is very similar to the Greenland Group of Westland, the small differences shown by the Roaring Lion Formation are because it is slightly richer in quartz. Analysis of calcite fabrics from deformed Mount Patriarch Formation limestone which occurs as a fault sliver in the Anatoki Thrust Zone, indicates the last movement on the Anatoki "Thrust" was normal.