Computer Science
Scientific paper
Jul 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976esrv...12..197c&link_type=abstract
Earth Science Reviews, Volume 12, Issue 2-3, p. 197-233.
Computer Science
19
Scientific paper
The Melanesian Borderlands extend from New Guinea to Tonga and, as the name implies, occupy a border position between the India and Pacific plates. They include island chains with small land surface, deep trenches, basinal seas and real and apparent fracture systems. As morphotectonic elements, most show anomalous features in terms of today's models. The complex as a whole is treated as made up of seven subdivisions, most of which are Cainozoic tectonic unities. These are: Bismarck Sea and surrounds; Solomon Block; Coral Sea and eastern extension; New Hebrides and South Fiji Basins; New Hebrides Block; Fiji Plateau and Lau Basin; Fiji Platform, Lau and Tonga Ridges. The Bismarck Sea is not the model of a marginal sea. The surrounding land areas have arc-like features and bear the impress of one or more reversals in polarity but some features, especially geochemical ones, are difficult to relate to arc development: the Solomons, New Hebrides and Fiji-Lau-Tonga land areas echo, with varying emphases, this same condition. The Solomons appear to have been shaped, for at least the last half of their history, by sinistral shearing movement between the two major plates and by collision with the Ontong Java Plateau. The New Hebrides, following apparent polarity reversal, has followed a subduction zone retreating to the southwest and is now on the point of collision with the Loyalty Ridge. This movement was coincident with creation of the Fiji Plateau and accommodated along the Hunter Fracture Zone. The Fiji Platform is peculiar in that it shows evidence of bodily rotation. It developed as an arc until this rotation became a dominant factor at least five million years ago. The Lau-Tonga ridges were part of the Fiji are until about the same time. Since then the Lau Basin has arisen as an interarc basin so that the Lau Ridge is now a remnant arc. The Coral Sea is an enigmatic basin the genesis of which is unknown although it is linked to the break-up of the northerly part of an old continental-cum-arc system bordering the Australian continent — Owen Stanley Metamorphics, Louisiade Archipelago, Rennell Ridge and New Caledonia. On the Pacific side of this Inner Melanesian system, the New Hebrides and South Fiji Basins are the remnants of a former Palaeogene marginal sea; the creation of the Fiji Plateau over the last 5 10 m.y. has effectively halved it. The northern boundary of the Fiji Plateau includes the Cape Johnson Trough and Vitiaz Trench; the latter can be extrapolated east to the northwestern termination of the Tonga Trench. This boundary has been viewed as a relic subduction zone. Much more data are needed, especially from the basinal seas, before a really convincing reconstruction can be attempted of the events which led to the present disposal of elements within the Melanesian Borderlands.
Coleman Patrick J.
Packham Gordon H.
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