Temporal and spatial evolution of orogens: a guide for geological mapping

Orogens develop in convergent settings involving two or more continental and/or oceanic plates. They are tra-ditionally defined as zones of crustal deformation associ-ated with mountain building resulting from either accretion of a terrane and/or an arc, continent-continent collision or rift-inversion. However, this definition does not consider the genetic link between an oceanic domain and an intra-continental rift, even though extension associated with a scissor-shape opening can be demonstrated in many ocean -floored basins. Consequently, we propose a new concept of orogenic evolution based on the development of exten-sional margins subsequently subjected to crustal shorten-ing. Thus orogens that develop as a result of the closure of wide basins, are distinguished from mountain belts devel-oped above subduction zones or that result from conti-nental collision and inverted intra-continental rifts. Our review of several key orogens identifies similarities and differences in geodynamic processes through geological time including prior to the onset of plate tectonics ca. 2.5 Ga. We propose that mapping based on comparative tec-tonics is a good way to constrain such an evolution, and that this can start with a global-scale map of past-to-modern orogens aimed at re-exploring mountain building concepts spatially and temporarily. This is the primary objective of IGCP 667 project "World Map of Orogens".