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Late quaternary uplift history from emerged reef terraces on Santo and Malekula islands, central New Hebrides island arc

Jouannic Christian, Taylor F.W., Bloom A.L., Bernat Michel. 1980. .
Late quaternary uplift history from emerged reef terraces on Santo and Malekula islands, central New Hebrides island arc
ARTICLE, (1980 ) - PUBLISHEDVERSION - Français (fr-FR)

OPENACCESS - .
Audience : RESEARCHERS

Sujet
TECTONIQUE DE PLAQUES, TERRASSE MARINE, EMERGENCE, DATATION, QUATERNAIRE, HOLOCENE
Domaines
Géologie
Description

Currently uplifting reef terraces on Santo and Malekula islands, in the central New Hebrides arc, offer a detailed record of vertical tectonics related to the subduction of the Australian plate beneath the Pacific plate. Inferred uplift rates on Santo range vary widely from 1 to 7 mm/y, generally increasing from east to west. They define an elliptical zone of maximum uplift, which corresponds to the western mountain belt of Santo. This must be related to the location of western Santo very close to the axis of the New Hebrides trench, which is interrupted in front of Santo. The uplift of southern Santo may be influenced particularly by subduction of the d'Entrecasteaux fracture zone, a major bathymetric feature on the underthrusting Australian plate. The uplifted reef terraces which form the Eastern Plateau Limestones, overlying the eastern half of Santo, are tilted E to ENE in the northeastern and central parts of the island, E to ESE in southeastern Santo and Malo. This is consistent with the apparently elliptical shape of the zone of maximum uplift rate. Such high uplift rates are not observed on Malekula, which is not on the trench axis, although still abnormally close to the thrust zone. Northern and southern parts of the island behave differently because they are separated by a tilt discontinuity across central Malekula. In northern Malekula, inferred uplift rates range from 0.5 to 4.3 mm/y, with a zone of maximum uplift in the southwestern part of north Malekula and a general tilt to the NE in its main northeastern part. The southern Malekula inferred uplift rates range from a few tenths of a mm to about 1 mm/y, with a zone of maximum uplift near the tilt discontinuity of central Malekula and a general tilt to the SE. Such an uplift pattern on Malekula island is likely to be related to the presence of the southern margin of the d'Entrecasteaux fracture zone which is being underthrust beneath northern Malekula. The main surface of the Eastern Plateau Limestones in Santo and the main terrace of northern Malekula are believed to correspond to the 125 O00 years old paleosea level by comparing the terrace levels of both islands with the paleosea levels as estimated for the last 140 O00 years in the Huon peninsula area (New Guinea). This correspondence of terraces with paleosea levels is supported by uranium-series dates for a few of the lower terraces on Malekula and Santo. If the inferred ages of the higher terraces are correct, then the uplift rates of both Santo and Malekula may have increased significantly some time between about 40 O00 y.b.p. and the Holocene epoch. In any case, it is clear that much of Santo and north Malekula emerged quite recently.

Mots-clés
Langue
Français (fr-FR)
Auteurs
Jouannic Christian, Taylor F.W., Bloom A.L., Bernat Michel
Contributeurs
Sources
Technical Bulletin - SCOPE/SOPAC, 1980, p. 91-108.
Couverture
NOUVELLES HEBRIDES
Nom du journal