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Circum-Pacific and Caribbean Orogens |
Geological Survey, Private Mail Bag, G.P.O., Suva, Fiji
The Fiji islands are one of the circum-Pacific island groups, linked to the New Zealand/Polynesian area by ocean banks, a mainly volcanic accumulation characterized by major faulting which has displaced plutonic rocks to mountainous elevations.
Immediately to the east of the Fiji Group is the Lau-Tonga trench and ridge system, described elsewhere in this volume.
Segment: the Wainimala-Tholo orogenic belt described here is 110 km long and at least 60 km wide, but both margins are unexposed; the northern is covered by younger rocks and the southern lies beneath sea level.
Zones: the orogenic belt is described in terms of a Southern and a Northern zone. The former exposes some 13 km thickness of mainly volcaniclastic rocks, strongly faulted, heavily intruded and partly strongly metamorphosed, which are exposed down to Eocene and possibly older. The Northern Zone, with more than 5 km of Miocene volcaniclastics, is less deeply exposed, less strongly deformed and characterized by only mild metamorphism.
History: the oldest rocks known are ?L. Eocene and deformations occurred during Oligocene, Miocene and possibly Pliocene times. These deformed rocks are unconformably overlain by unfolded Pleistocene, Pliocene (and ?U. Miocene) strata.
16 The belt continues along the strike to the west of the selected segment but to the east it is concealed by later rocks. 24 General trend: the belt is arcuate, concave towards the north-east, and along a 300 km long stretch measured parallel to its trend it curves through approximately 140° with a radius of curvature of 65 km.
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