Oscillating modes of orogeny in the Southwest Pacific and the tectonic evolution of New Caledonia

Abstract

Abstract This paper presents a new interpretation of the tectonic evolution of New Caledonia, based on the extrapolation of detailed structural analysis at several different scales. The coherent high-pressure schist belt of northern New Caledonia contains clear evidence for cyclicity in the orogenic process. Two switches from large-scale crustal shortening to extensional tectonism can be recognized. We propose that orogenesis initially resulted in significant crustal thickening, obduction, and high-pressure (15–20 kbar) metamorphism. There is a close temporal link between ophiolite emplacement and high-pressure metamorphism. The high-pressure rocks were exhumed during the first period of extensional tectonism ( c. 40–36 Ma) as a large coherent terrane (>1500 km 2 ). During the second period of crustal shortening the New Caledonia orogen was folded into upright megafolds. Basin and Range style normal faulting then took place, bringing the folded extensional terrane and the high-pressure rocks to their present crustal level. Metamorphic grade changes in the high-pressure belt are structurally controlled by these late-stage normal faults. However, movement on these faults is responsible for only the very last stages of exhumation.