The active Banda arc–continent collision (Banda Orogen) provides many new constraints for resolving long-standing issues about the formative stages of collision. Some of these issues include evidence for trench retreat and subduction erosion, depth of continental subduction, emplacement and demise of forearc basement, relative amounts of uplift due to crustal and lithospheric processes, influence of inherited structure and lower plate heterogeneities, orogenic wedge taper adjustments, partitioning of strain, mélange development, plate motion versus structural geometry, erosional and extensional exhumation, continental contamination and accretion of volcanic arcs, slab tear, subduction polarity reversal and along strike tectonic variation.

Most of these issues link to the profound control of the lower plate crustal heterogeneities and inherited structure. The thermo-mechanical characteristics of subducting an old continental margin allow for underthrusting and uplift of extensive nappes of forearc basement, and subduction of continental crust to deep enough levels to contaminate the source regions of the Banda volcanic arc. Seismic tomography confirms subduction of continental lithosphere to at least 400 km with no evidence for slab tear. Trench retreat during this process resulted in subduction erosion and peri-collisional extension of the upper plate to the extent of opening young supra-subduction zone ocean basins between attenuated fragments of remnant continental arc crust.

Trench retreat is arrested by arrival of the Australian continental margin at the subduction zone near Wetar Island during the latest Miocene. The initiation of collision is recorded in ages of metamorphism of Australian continental margin lithologies in northern Timor and continental contamination of the volcanic rocks in Wetar. The age of arc contamination decreases westward along the Sunda Arc and eastward along the Banda Arc. Other aspects of the collision also decrease to the west and east from central Timor such as crustal shortening, forearc closure, topography, the age of various synorogenic sedimentary facies, and timing of island emergence as recorded by uplifted coral terraces.

One important exception to this trend is the emergence of Sumba Island and contamination and deformation of adjacent parts of the Sunda Arc. This irregularity is most likely caused by subduction of the Scott Plateau continental protrusion that arrived at the Sunda Trench a few million years before the neighboring NW Australian continental margin south of Savu and Rote.

One of the most profound influences of inherited structure is the ENE-WSW striking rift basins of the Australian continental margin and their mechanical stratigraphy. This structural heritage controls the way subducted material is incorporated into the orogenic wedge and the sub-parallelism between the convergence direction and structural grain.

The post-breakup Australian Passive Margin Sequence is incorporated into the orogenic wedge by frontal accretion and forms a classic imbricate thrust stack near the front of the Banda forearc (Banda Terrane). These mostly slope and rise deposits accrete as thin thrust slices that detach above a thick, over-pressured mudstone horizon near the breakup unconformity. The pre-breakup Gondwana Sequence below this unconformity continues into the subduction channel beneath the Banda forearc upper plate. The mud-rich upper part of the Gondwana Sequence is remobilized by high fluid pressures and strain rates to form the matrix of thick zones of mélange generated within the subduction channel. The mélange is a highly fluidized …