Mesozoic tectonics, North Island, New Zealand

Age/isotopic characterisation of the Waipapa Group in Northland and Auckland, New Zealand, and implications for the status of the Waipapa Terrane

“…On the contrary, the (t)-(i) data lend support to Spörli's (1978) original designation of a single Waipapa Terrrane in North Island. The original definition of the Waipapa Terrane (Spörli 1978) was intrinsically uncertain, as no boundary faults have been observed. The problem is exacerbated by the lack of good basement outcrop in crucial parts of Northland, and presence of the overlying Northland Allochthon and other Cenozoic cover sequences.…”

“…In detail, the structure is complex; early melange formation, subsequent open folding, and imbrication are described (Brothers 1956;Spörli 1978;Bayrante & Spörli 1989;Spörli et al 1989). Along the east coast, there is a regional NNW-SSE strike (dip to the west).…”

“…Along the east coast, there is a regional NNW-SSE strike (dip to the west). Deformation and metamorphism are largely synchronous but there is also late metamorphic zeolite veining (Spörli 1978;Black 1989). Generally the rocks are within the textural zone (tz) I (Bishop 1972(Bishop , 1974, but locally tzIIA (Black 1989).…”

“…There is an east-west transition from zeolite to prehnitepumpellyite metamorphic facies. Tables 1 and 2) and major terrane boundaries (heavy dashed lines) as defined by Spörli (1978) and Isaac (1996). Waipapa Group sedimentary associations (in dotted envelopes with large open letters) from Black (1994) are: (A) Omahuta-Puketi; (B) Western Bay of Islands; (C) Eastern Bay of Islands; (D) Whangarei to Hunua Ranges; and, in addition, area (E) Manaia Hill Group of Coromandel (Skinner 1972) and Great Barrier Island (Moore & Kenny 1985).…”

“…Like the Waipapa Group, it comprises metagreywacke-dominated sequences, in an accretionary prism environment, which essentially form the extensive Torlesse (composite) Terrane in the southern North Island and South Island . Although boundary faults are only inferred, Spörli (1978) defined a Waipapa Terrane encompassing all basement rocks, to the north and west of the Kaimanawa Ranges (the probable northernmost extension of the Torlesse composite terrane), and east of the Junction Magnetic Anomaly (a subsurface geophysical feature inferred to indicate the Dun MountainMaitai Terrane (Hatherton & Sibson 1970)). The terrane thus extends from Northland, through North and South Auckland districts, the Coromandel Peninsula, and southwestwards to west of Lake Taupo (Beetham & Watters 1985), with a probable boundary at the northwest margin of the Kaimanawa Ranges (Fig.…”