We examined two cases for times prior to anomaly 18, assuming a Late Cretaceous age of Australia-Antarctica separation. If the Pacific-Australia plate boundary has had its present trend since anomaly 18 time, reconstructions show 330+/-110 km of motion of the Pacific plate relative to the Lord Howe Rise since anomaly 5 time (9.8 m.y.), 420+/-110 km since anomaly 6 time (19.5 m.y.), 770+/-330 km since anomaly 13 time (35.6 m.y.), and 820+/-260 km since anomaly 18 time (43.0 m.y.). We combined these to yield a range of possible finite rotations describing the relative positions of the Pacific, Australia, Antarctica, and Lord Howe plates since the Late Cretaceous. We determined parameters that describe finite rotations and their uncertainity regions for relative plate motion at the spreading centers between the Pacific and Antarctic plates, between Australia and Antarctica, and between the Lord Howe Rise and Australia. As subduction is oblique, strike-slip movement has moved the forearc region east of the Axial Ranges from a position closer to the Coromandel Arc to its present situation. They cannot have come from the Quaternary Taupo Volcanic Zone, but were probably derived from the upper Miocene Coromandel Arc further to the NW. Early-upper Miocene rhyolitic tuff beds in trough-inner-slope flysch basins are the first sign of volcanic arc activity. A directional, morphological and geophysical break exists between the North Island and Kermadec subduction systems, probably caused by the Vening Meinesz Fracture Zone. Some sediment gravity flows reach the Hikurangi Trough via submarine canyons, bypassing the slope. Similar sedimentary facies have been cored in present-day offshore slope basins. Their sedimentary fills comprise sediment gravity flow deposits, hemipelagic muds, and arc-derived ash. Several are now exposed in the Coastal Ranges structural high. During the formation of the subduction complex, small basins were created by elongate narrow structural ridges parallel to the trough-inner-slope. Accreted oceanic sediments have not been recorded, but may be present in the lower part of the subduction complex, or, to a large degree, may have been subducted. The subduction complex consists of highly deformed autochthonous Cretaceous-Palaeogene strata, possibly deposited in a pre-subduction continental borderland. The forearc basin initially was shallow marine, but subsequently was filled with coarse debris shed from the rising arc massif, and is now above water. The forearc basin and subduction complex are riding passively on top of the Pacific plate to the east of the Benioff zone. Sensu stricto, The Hikurangi Trough, to the east of the subduction complex, is not a subduction trench. However, no subduction trench exists below the negative gravity anomaly. A negative gravity anomaly coincides with the surface extension of the Benioff zone. A west-dipping Benioff zone underlies the volcanic arc and arc massif. Several NE-trending zones can be distinguished: Taupo Volcanic Zone (volcanic arc), Axial Ranges (exposed part of arc massif), East Coast Depression (forearc basin), Coastal Ranges (structural high of subduction complex), continental shelf and slope (trough-inner-slope of subduction complex). Many geological and geophysical aspects of the North Island, both on land and offshore, are in agreement with models of subduction systems from elsewhere. Subduction of the Pacific plate underneath the North Island of New Zealand began near the beginning of the Neogene, when the Tonga-Kermadec Subduction System propagated southwards into the New Zealand continental crustal block, together with the southwards migration of the relative pole of rotation between the Pacific and Australian plates.
Such processes correlate spatially with zones of tectonic and physiographic disturbance. Evolution is interpreted here as proceeding largely by phases of population reorganisation, for example in the formation of Cretaceous hybrid swarms, and “recrystallisation” in which ancient ranges are “frozen”, even in weedy taxa. The altitude of many communities in New Zealand also appears to conform to biogeographic and tectonic trends, with higher altitude communities having been derived by the uplift of mid-Tertiary lowland-coastal communities. Other arcs may be the result of evolution along the Tertiary shores of inland bodies of water.
The major arcs of distribution correlate with zones of tectonic activity such as plate and terrane margins, fracture zones, and belts of granitic intrusion. The fracturing and creation of such parallel arcs by tectonic movement and erosion has brought about vast disjunctions in many plant and animal groups. Attention is drawn to the parallel arc patterns permeating much of New Zealand biogeographic structure.
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