Exhumation Settings, Part I: Relatively Simple Cases

Abstract

Exhumation has been recognized as an important problem in tectonics and can be achieved by normal faulting, ductile thinning, and erosion. The exhumation of ultrahigh-pressure (UHP) rocks is the most challenging and least understood aspect of the exhumation problem. In this review, we focus on a variety of geologic settings with the goal of characterizing exhumation rates and maximum depths of exhumation in different settings. In Part I of this series of articles, we summarize exhumation in some relatively simple divergent (rifts and mid-ocean ridges) and convergent regions (subduction and collision zones). Our examples from rifts are from the East African rift, the Galicia margin, and the Cyclades in the Aegean. The Mid-Atlantic Ridge serves as an example of exhumation at a slow-spreading ridge. The examples from subduction settings are the Mariana ocean-ocean subduction zone, and the ocean-continent subduction zones of the Olympic, Franciscan, and Hikurangi complexes. For relatively simple collision belts, we describe the arc-continent collision of Taiwan and the continent-continent collision of the Southern Alps of New Zealand. For these relatively simple cases, we discuss near-end-member scenarios of exhumation settings. These examples may be divided into four classes: (1) rifting; (2) buoyancy-driven diapirism; (3) erosional exhumation associated with the development and maintenance of orogenic topography; and (4) underplating in convergent wedges. In general, it seems to be important that multiple processes cause exhumation. Asthenospheric upwelling associated with rifting appears to be significant for the initial ~100 km of exhumation of UHP peridotite.