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Abstract

Tightly curved mountain belts are prominent features of global topography. Typically, these ‘oroclines’ occur in areas of regional compression but enclose basins where extension has been contemporaneous with outward directed thrusting in the orogens. Examples of such basin–orogen pairs include the Alboran Sea–Gibraltar Arc, Tyrrhenian Sea–Aeolian Arc, Aegean Sea–Hellenic Arc and Pannonian Basin–Carpathian Arc, all in the western Tethys but matched in the eastern Tethys by the Banda Sea and Outer Banda Arc. The development of the basins has been variously explained by gravitational collapse of rapidly elevated mountain blocks and by extrusion prompted by asthenopheric flows, but it is not even universally agreed that similar processes have operated in all cases. Critics have cited gross differences in volcanic activity (absent from the Gibraltar Arc, modest in the Carpathians but intense in other examples) and in the presence or absence of recognizable Wadati–Benioff Zones. The superficial similarities between the Caribbean Sea–Antilles Arcs and typical oroclinal basin–orocline pairs have recently been invoked in support of an in situ Caribbean evolutionary model, even though the disputed origins of oroclines limit their reliability as analogues. The Caribbean's considerably greater area further emphasizes the need for caution, while the most obvious objection to identifying it as a member of the oroclinal group is its very long history. Oroclinal basins typically pass from initiation to effective stabilization in a few tens of millions of years, whereas the original Caribbean oceanic crust, which is now bounded to the east and west by active subduction zones, was probably formed in the Jurassic. Rather than invoking an overall common origin for the Caribbean and the Tethyan basins, it is more useful to look for shared causes of specific individual similarities. The impact of a rigid block might be as effective in imposing curvature on a mountain belt as rapid expansion in an adjacent area. However, it does seem that the case for the crust of the Caribbean being typical of oceanic large igneous provinces (LIPs) may have been overstated and, in the light of oroclinal analogues, that some features of the still poorly understood Beata Ridge and Lower Nicaragua Rise may be most easily explained by east–west extension promoted by the convergence between North and South America.

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