OPS melange: a new term for melanges of convergent margins of the world

摘要

Ocean plate stratigraphy (OPS) is essential to understanding accretionary wedges and complexes along convergent plate margins. Melanges within accretionary wedges and complexes are the products of fragmentation and mixing processes during and following OPS accretion. A new term, OPS melange', is proposed here for melanges composed mostly of blocks of OPS with an argillaceous matrix, and for a mixture of melanges of multiple origins with either broken or coherent formations. An OPS melange results from the fragmentation and disruption of OPS, without admixing of other components. Three major types of OPS melange can be distinguished on the basis of their components: turbidite type, chert-turbidite type, and limestone-basalt type. These three types potentially form similar melanges, but they are derived from different parts of the OPS, depending on the level of the decollement surface. The concept of OPS melange' can be applied to most of the melanges in accretionary prisms and complexes worldwide. In addition, this proposal recognizes a distinction between processes of fragmentation and mixing of OPS components, and mixing of ophiolite components, the latter of which results in serpentinite melanges, not OPS melanges. Melanges composed of OPS sequences occur worldwide. The recognition of OPS melanges is a key aspect of understanding tectonic processes at convergent margins, which result in melange formation in orogenic belts globally.