OPHIOLITE FACTORY OF THE INDONESIAN AND NEW GUINEA REGION: HOW IT WORKS AND HOW IT MAY HAVE OPERATED IN THE CORDILLERA AND TETHYS

Analysis of spatial, temporal, geological and geochemical patterns of ophiolites in the Indonesian and New Guinea region indicate a strong correlation with marginal basin development and closure. Ophiolites are spatially linked mostly with marginal basin producing zones of oblique convergence and collision. Strain partitioning in these zones creates a series of ephemeral plate boundaries between several independently moving lithospheric blocks. Repeated disruption of the diffuse boundaries between the blocks by changes in plate motion and collision-induced mantle extrusion creates space that is rapidly filled by new ocean basins in the upper plate of subduction zones. The episodic nature of supra-subduction zone spreading may be linked to extrusion of asthenosphere escaping collisional suture zones. Various ocean closure events and global plate motion changes are reflected in the temporal distribution of marginal basin and ophiolite ages.

Most ophiolite slabs in the Indonesian and New Guinea region represent fragments of oceanic lithosphere with a subduction zone component, as indicated by the common refractory petrochemistry of the mantle sequence and occurrence of boninite. Age and compositional heterogeneity may indicate that some ophiolite bodies are composite terranes. However, this is commonly disproved by more detailed investigation. Many of the ultramafic bodies found without the overlying crustal sections typical of ophiolites, are mostly parts of sub-continental mantle exhumed by extension then inverted by collision. Most of these bodies are not ophiolites.

Collisions with buoyant lithosphere transform parts of marginal basins into ophiolites. This connection between ophiolites and marginal basins is strongest where parts of actively spreading supra-subduction zone ocean basins are found as ophiolites in encroaching collision zones.

The diversity of tectonic processes found in the Indonesian and New Guinea region provide a plethora of modern analogs for the genesis and emplacement of ophiolites along the western edge of North and South America, and throughout the Tethys during much of the Mesozoic. These processes include various combinations of strain partitioning, trench rollback, subduction polarity reversal and asthenospheric flow.