Growth of accretionary wedges and pulsed ophiolitic mélange formation by successive subduction of trench-parallel volcanic elevations

Abstract

Fault-bounded coherent belts alternating with belts of mélanges are common in accretionary wedges and are usually interpreted as a result of imbrication along subduction zone megathrusts. Using the Neoproterozoic/early Cambrian Blovice accretionary complex (BAC), Bohemian Massif, as a case example, we present a new model for the origin of alternating belts through the repetition of several cycles of (1) offscraping and deformation of trench-fill sediments to form the coherent units, interrupted by (2) arrival and subduction of linear, trench-parallel volcanic elevations. The latter process leads to an increase in the wedge taper, triggering mass-wasting and formation of olistostromes. At the same time, ophiolitic mélanges form by disruption of an upper part of the volcanic ridge and incorporation of the disrupted ocean-floor succession into the olistostromes. Specifically, the BAC represents a complete section across an accretionary wedge and records three such major pulses of ophiolitic mélange formation through subduction of an outboard back-arc basin. © 2014 John Wiley & Sons Ltd.