Page by: Pier-Alexandre Pare
Kermadec, Tonga & Niuafo'Ou
This group of plates is found North of New Zealand, enclosed by the Australian plate and the Pacific plate. Before the formation of the plates, the region used to be a subduction zone where the Pacific plate was subducting under the Australian plate. This formed the, now below sea level, Lau-Havre island arc.
About 5-6 Ma ago, crustal extension began, (Smith and Price, 2006) then 4-5 Ma ago, back-arc sea-floor spreading began on the Lau-Havre Ridge. This was the birth of the Tonga-Kermadec Plate. The northern parts of the plate was growing faster than the southern parts and this lead to the separation of the Tonga and Kermadec plates. The Northern parts of the Tonga plate were still spreading faster than its southern part which lead to the formation of multiple spreading centers and the Niuafo'ou microplate. (Zellmer and Taylor, 2001)
About 5-6 Ma ago, crustal extension began, (Smith and Price, 2006) then 4-5 Ma ago, back-arc sea-floor spreading began on the Lau-Havre Ridge. This was the birth of the Tonga-Kermadec Plate. The northern parts of the plate was growing faster than the southern parts and this lead to the separation of the Tonga and Kermadec plates. The Northern parts of the Tonga plate were still spreading faster than its southern part which lead to the formation of multiple spreading centers and the Niuafo'ou microplate. (Zellmer and Taylor, 2001)
Plate location and overview.
TongaThe Tonga plate is located 2500km NNE of New Zealand. It’s is bounded to the Southwest by a spreading center with the Australian plate, to the northwest by a spreading centers with the Niuafo’ou micro-plate and by a transform zone to the South with the Kermadec plate. The Tonga trench marks the Eastern boundary, where the Pacific plate is being subducted. The Tonga trench is one of the fastest subduction zones, with a rate going up to 24cm/year.(Smith and Price, 2006)
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Niuafo'ouThe Niuafo’ou micro-plate is located west of the Tonga plate. It is bounded to the east by its spreading center with Tonga, but lack a defined border with Tonga in the southeast (Zellmer
and Taylor, 2001). The Pacific plate is subducting under it to the North. To the southwest, it is bounded by the Australian plate with which it shares a spreading center at the south of the boundary and a transform zone to the Northwest. Finally, it shares a spreading center with the Futuna plate to the west .
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KermadecThe Kermadec plate comprises of the northeastern part of New Zealand, and it extends north all the way to the southern part of the Tonga plate. It is bounded by the Kermadec Trench on the eastern side, where the Pacific subducts under the Kermadec plate. To the West it is bounded by a spreading center with the Australian plate. To the north, it has a transform zone with the Tonga plate.
In the south, the Kermadec plate reaches a point where its relative motion with the Australian plate is null, and south of that point, it has a convergent boundary with the Australian Plate. (Wallace & al., 2004) |
Regional Tectonic History.During the Pliocene the Pacific plate was subducting beneath the
Australian plate (Gill,
1976).
This produced the Lau-Colville Ridge, a now extinct volcanic arc that starts
from the North tip of Tonga, and ends at the northern tip of New Zealand. Around 6 Ma ago, the region started to
undergo crustal extension, which this led to the creation of the Tonga-Kermadec Ridge plate
through the separation of the
Tonga-Kermadec ridge from the Lau-Colville Ridge with the Lau Spreading Center in
the back arc, separating the Tonga and the Lau Ridges, and the Havre through
separating the Kermadec and the Colville Ridges (Smith and
Price, 2006).
The northern basin, (Lau Basin) is much wider than the southern one (Havre Basin), due to the rate of spreading variying from 96mm/year in the north to 39mm/year in the South (Martinez et al., 2006). This coincides with the rate of subduction of the Pacific plate to the west, which varies from 24cm/year in the North to 6cm/year in the South. This difference in movement rates led the Tonga Plate to separate from the Kermadec; they are separated by a transform zone. The rapid extension of the Lau basin led to many small spreading center; the Niuafo’ou micro-plate was formed by this in the northwestern part of the Tonga plate (Zellmer and Taylor, 2001). The Euler pole of the Kermadec plate relative to the Australian plate motion is found just a little south of where the plate boundary hits the land; this means that unlike the northern part of the plate, the southern tip of the Kermadec plate is colliding with the Australian plate. (Zellmer and Taylor, 2001),(Wallace et al., 2004). At the same latitude, you have the Pacific plate is subducting under the eastern side of the island,resulting in convergent boundaries on both sides. To the south west, the Australian plate subducting under New Zealand, which creates interesting features in the south of the island. 
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Southern Lau Basin;
West-East cross-section. (ELSC : East Lau Spreading center) Image from (Smith and Price, 2006) 
Northern Lau Basin,
Notice multiple spreading centers. Image from(Smith and Price, 2006) 
Regional bathymetric map;
Notice the width of the Lau Basin in the NE compared to the Havre trough in the SW. Image from (Zellmer and Taylor, 2001). Motion of the GPS station on North Island, New Zealand, relative to the Australian plate. Error ellipses are at 68% confidence level. Image from (Wallace et al., 2004). |
Sources:
Smith, I. E. M. and Price, R. C.: The Tonga–Kermadec arc and Havre–Lau back-arc system: Their role in the development of tectonic and magmatic models for the western Pacific, J. Volcanol. Geotherm. Res., 156(3–4), 315–331, doi:10.1016/j.jvolgeores.2006.03.006, 2006.
Bird, P.: An updated digital model of plate boundaries: UPDATED MODEL OF PLATE BOUNDARIES, Geochem. Geophys. Geosystems, 4(3), 1027–1079, doi:10.1029/2001GC000252, 2003.
Gill, J. B.: Composition and age of Lau Basin and Ridge volcanic rocks: Implications for evolution of an interarc basin and remnant arc, Geol. Soc. Am. Bull., 87(10), 1384–1395, doi:10.1130/0016-7606(1976)87<1384:CAAOLB>2.0.CO;2, 1976.
Martinez, F., Taylor, B., Baker, E. T., Resing, J. A. and Walker, S. L.: Opposing trends in crustal thickness and spreading rate along the back-arc Eastern Lau Spreading Center: Implications for controls on ridge morphology, faulting, and hydrothermal activity, Earth Planet. Sci. Lett., 245(3–4), 655–672, doi:10.1016/j.epsl.2006.03.049, 2006.
Smith, I. E. M. and Price, R. C.: The Tonga–Kermadec arc and Havre–Lau back-arc system: Their role in the development of tectonic and magmatic models for the western Pacific, J. Volcanol. Geotherm. Res., 156(3–4), 315–331, doi:10.1016/j.jvolgeores.2006.03.006, 2006.
Wallace, L. M., Beavan, J., McCaffrey, R. and Darby, D.: Subduction zone coupling and tectonic block rotations in the North Island, New Zealand, J. Geophys. Res. Solid Earth, 109(B12), doi:10.1029/2004JB003241, 2004.
Zellmer, K. E. and Taylor, B.: A three-plate kinematic model for Lau Basin opening, Geochem. Geophys. Geosystems, 2(5), doi:10.1029/2000GC000106, 2001.
Smith, I. E. M. and Price, R. C.: The Tonga–Kermadec arc and Havre–Lau back-arc system: Their role in the development of tectonic and magmatic models for the western Pacific, J. Volcanol. Geotherm. Res., 156(3–4), 315–331, doi:10.1016/j.jvolgeores.2006.03.006, 2006.
Bird, P.: An updated digital model of plate boundaries: UPDATED MODEL OF PLATE BOUNDARIES, Geochem. Geophys. Geosystems, 4(3), 1027–1079, doi:10.1029/2001GC000252, 2003.
Gill, J. B.: Composition and age of Lau Basin and Ridge volcanic rocks: Implications for evolution of an interarc basin and remnant arc, Geol. Soc. Am. Bull., 87(10), 1384–1395, doi:10.1130/0016-7606(1976)87<1384:CAAOLB>2.0.CO;2, 1976.
Martinez, F., Taylor, B., Baker, E. T., Resing, J. A. and Walker, S. L.: Opposing trends in crustal thickness and spreading rate along the back-arc Eastern Lau Spreading Center: Implications for controls on ridge morphology, faulting, and hydrothermal activity, Earth Planet. Sci. Lett., 245(3–4), 655–672, doi:10.1016/j.epsl.2006.03.049, 2006.
Smith, I. E. M. and Price, R. C.: The Tonga–Kermadec arc and Havre–Lau back-arc system: Their role in the development of tectonic and magmatic models for the western Pacific, J. Volcanol. Geotherm. Res., 156(3–4), 315–331, doi:10.1016/j.jvolgeores.2006.03.006, 2006.
Wallace, L. M., Beavan, J., McCaffrey, R. and Darby, D.: Subduction zone coupling and tectonic block rotations in the North Island, New Zealand, J. Geophys. Res. Solid Earth, 109(B12), doi:10.1029/2004JB003241, 2004.
Zellmer, K. E. and Taylor, B.: A three-plate kinematic model for Lau Basin opening, Geochem. Geophys. Geosystems, 2(5), doi:10.1029/2000GC000106, 2001.
