The character and significance of basement rocks of the southern Molucca Sea region

Geodynamic patterns of ophiolites and marginal basins in the Indonesian and New Guinea regions

Analysis of spatial, temporal, geological and geochemical patterns of ophiolites in the Indonesian and New Guinea region indicates a strong correlation with marginal basin development and closure. The spatial distribution of ophiolites is mostly linked 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. Suprasubduction zone (SSZ) spreading of these basins is enhanced by episodic extrusion of asthenosphere escaping collisional suture zones. Various 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. Collisions with buoyant lithosphere transform parts of these ocean basins into ophiolites. The connection between ophiolites and marginal basins is strongest where parts of actively spreading SSZ basins are partially represented as ophiolites in collision zones.

Timing and tectonic controls in the evolving orogen of SE Asia and the western Pacific and some implications for ore generation

SE Asia lies at the convergence of the Eurasian, Pacific and Australian plates. The region is made up of many active arcs, extensional basins, and the remnants of similar tectonic environments developed throughout the Cenozoic. There are many important hydrothermal mineral deposits and prospects in SE Asia but their formation is often poorly understood due to the complicated tectonic history of this region and the knowledge of relationships between mineralization and tectonics. Plate reconstruction offers a framework to integrate geological and geochemical data that can be used to unravel the large-scale tectonic processes that affected mineralized provinces. We present examples of the information that can be derived from this approach and discuss the implications for understanding the origin of some hydrothermal mineral deposits in SE Asia.