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Tectonic framework of the New Hebrides island arc

1972; Elsevier BV; Volume: 12; Issue: 3 Linguagem: Inglês

10.1016/0025-3227(72)90039-4

1872-6151

Daniel E. Karig, J. Mammerickx,

earthquake and tectonic studies

Although the New Hebrides island arc system has a number of anomalous characteristics, it conforms to the tectonic pattern observed in other western Pacific island arc systems. The two island chains represent the frontal and third arcs and are separated by a narrow extensional zone, or inter-arc basin, in which the troughs and ridges trend northerly rather than parallel to the arc system. Transverse lineations break the arc system into sections with different characteristics. The section including Santo, Malekula, Maewo and Pentecost is strongly uplifted, lacks a morphologic trench, and has a wider but inactive extensional zone. Despite the anomalous trench-frontal arc pair, the Benioff zone and volcanic chain pass through this section unchanged. South and east of 21 °S the arc system appears to be much younger with poorly developed features and no extensional zone. The 90–130 km trench-volcanic chain separation in the New Hebrides arc system is markedly smaller than in other, older arc systems. Lack of a mid-slope basement high and of the associated sediment apron suggest that oceanic crust and sediment are accreted to the forward edge of the frontal arc with time. The New Hebrides arc system apparently faced northeast before mid-Miocene time and was part of a continuous series of arcs from the Lau Ridge through the Solomon Islands. In the Late Tertiary, the New Hebrides arc reversed its polarity and began to move westward relative to Fiji, creating a trench-trench transform fault along the Matthew-Hunter Ridge, consuming a part of the South Fiji Basin, and opening the Fiji Plateau. In the Quaternary the Matthew-Hunter Ridge west of 175 °E became an arc system, and the inter-arc basin of the New Hebrides opened. The en-echelon pattern within the extensional zone is thought to reflect extension perpendicular to the arc system together with right lateral shear parallel to it.