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120 to 0 Ma tectonic evolution of the southwest Pacific and analogous geological evolution of the 600 to 220 Ma Tasman Fold Belt System

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Crawford, AJ and Meffre, S and Symonds, PA (2003) 120 to 0 Ma tectonic evolution of the southwest Pacific and analogous geological evolution of the 600 to 220 Ma Tasman Fold Belt System. In: Evolution and Dynamics of the Australian Plate. Geological Society of Australia Special Publication, Australia, pp. 377-397.

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Abstract

We review the tectonic evolution of the SW Pacific east of Australia from ca 120 Ma until the present. A
key factor that developed early in this interval and played a major role in the subsequent geodynamic
history of this region was the calving off from eastern Australia of several elongate microcontinental ribbons,
including the Lord Howe Rise and Norfolk-New Caledonia Ridge. These microcontinental ribbons
were isolated from Australia and from each other during a protracted extension episode from ca 120 to
52 Ma, with oceanic crust accretion occurring from 85 to 52 Ma and producing the Tasman Sea and
the South Loyalty Basin. Generation of these microcontinental ribbons and intervening basins was
assisted by emplacement of a major mantle plume at 100 Ma beneath the southern part of the Lord
Howe Rise, which in turn contributed to rapid and efficient eastward trench rollback. A major change
in Pacific plate motion at ca 55 Ma initiated east-directed subduction along the recently extinct spreading
centre in the South Loyalty Basin, generating boninitic lithosphere along probably more than 1000
km of plate boundary in this region, and growth of the Loyalty-Entrecasteaux arc. Continued subduction
of South Loyalty Basin crust led to the arrival at about 38 Ma of the 70-60 million years old western
volcanic passive margin of the Norfolk Ridge at the trench, and west-directed emplacement of the
New Caledonia ophiolite. Lowermost allochthons of this ophiolite are Maastrichtian and Paleocene rift
tholeiites derived from the underthrusting passive margin. Higher allochthonous sheets include a poorly
exposed boninitic lava slice, which itself was overridden by the massive ultramafic sheets that cover
large parts of New Caledonia and are derived from the colliding forearc of the Loyalty-Entrecasteaux
arc. Post-collisional extensional tectonism exhumed the underthrust passive margin, parts of which have
blueschist and eclogite facies metamorphic assemblages. Following locking of this subduction zone at
38-34 Ma, subduction jumped eastward, to form a new west-dipping subduction zone above which
formed the Vitiaz arc, that contained elements which today are located in the Tongan, Fijian, Vanuatu
and Solomons arcs. Several episodes of arc splitting fragmented the Vitiaz arc and produced first the
South Fiji Basin (31-25 Ma) and later (10 Ma to present) the North Fiji Basin. Collision of the Ontong Java
Plateau, a large igneous province, with the Solomons section of the Vitiaz arc resulted in a reversal of
subduction polarity, and growth of the Vanuatu arc on clockwise-rotating, older Vitiaz arc and South Fiji
Basin crust. Continued rollback of the trench fronting the Tongan arc since 6 Ma has split this arc and
produced the Lau Basin-Havre Trough.
This southwest Pacific style of crustal growth above a rolling-back slab is applied to the 600-220 Ma
tectonic development of the Tasman Fold Belt System in southeastern Australia, and explains key
aspects of the geological evolution of eastern Australia. In particular, collision between a plume-triggered
600 Ma volcanic passive margin and a 510-515 Ma boninitic forearc of an intra-oceanic arc had
the same relative orientation and geological effects as that which produced New Caledonia. A new
subduction system formed probably at least several hundred kilometres east of the collision zone and
produced the Macquarie arc, in which the oldest lavas were erupted ca 480 Ma. Continued slab rollback
induced regional extension and the growth of narrow linear troughs in the Macquarie arc, which
persisted until terminal deformation of this fold belt in the late-Middle to Late Devonian. A similar pattern
of tectonic development generated the New England Fold Belt between the Late Devonian and Late
Triassic. Parts of the New England Fold Belt have been broken from Australia and moved oceanward to
locations in New Zealand, and on the Lord Howe Rise and Norfolk-New Caledonia Rise, during the post-
120 Ma breakup. Given that the Tasman Fold Belt System grew between 600 and 220 Ma by crustal
accretion like the southwest Pacific since 120 Ma, facing the open Pacific Ocean, we question whether
the eastern (Australia-Antarctica) part of the Neoproterozoic Rodinian supercontinent was joined to
Laurentia.

Item Type: Book Section
Keywords: Australia, Lachlan Fold Belt, southwest Pacific, subduction, Tasman Fold Belt, tectonics
Journal or Publication Title: Geological Society of Australia Special Publication
Publisher: Geological Society of Australia Special Publication
Page Range: pp. 377-397
Date Deposited: 14 Feb 2007
Last Modified: 18 Nov 2014 03:13
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