COLLISIONAL MELANGE PROCESSES WITH SPECIAL REFERENCE TO INDONESIA AND CLOSURE OF THE TETHYS

Detailed field studies of melange in active collisions provide a unique setting for linking processes of active melange genesis with melange deposits. Places like Indonesia, where evolving oblique collisions provide a way to correlate melange deposits through various stages of suture zone development, lend considerable insight into how classic melanges form, such as those developed during the closure of the Tethys.

For example, one important distinction between actively forming melanges and interpretations of those formed in the past is the notable lack of indisputable olistostrome deposits. Many melanges interpreted as olistostromes should be re-evaluated for the unique features this rare type of melange manifests, such as interbedded syn-melange sedimentary units, little evidence of high strain in the matrix, and mostly angular and homogeneous block compositions. In the absence of these features other modes of stratal disruption are needed to explain the high strain and considerable mixing of blocks and matrix associated with most melanges. Processes responsible for most collisional 'block-in-clay' melanges in active tectonic settings connect with settings of decollement propagation and fluid assisted return flow mechanisms.