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 transfo= 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. Many of the various tectonic models proposed for the origin and tectonic evolution of ophiolites are supported by plate interactions in the Indonesian and New Guinea region (Dewey & Bird 1970; Silver & Smith 1983; Moores et al. 1984; Searle & Stevens 1984; Dilek & Moores 1990; Harris 1992; Dickinson et at. 1996). However, the geological associations of these interactions remain poorly resolved, allowing different parts of the region to be used as modern analogues for almost any tectonic scenario. Simple explanations based on plate kinematics alone fail to account for the increasing levels of complexity observed in the Indonesian and New Guinea region. New ideas and supporting evidence for mantle extrusion mechanisms (e.g. Flower et at. 2001) also rely heavily on descriptions of plate interactions in this region (Doglioni et at. 1999), and raise new questions about how these processes may relate to the spatial and temporal pattern of ophiolites. This paper provides a synthesis of the temporal and spatial patterns, and tectonic associations of marginal basins and ophiolites throughout the Indonesian and New Guinea region. It explores the relations between various plate boundary processes and ophiolite genesis and emplacement, such as the role of strain partitioning, trench rollback, subduction polarity asymmetry, asthenospheric flow and plate kinematics. Tectonic evolution of the Indonesian and New Guinea region and its contribution to the ophiolite debate The Indonesian and New Guinea region is an active collisional amalgamation of the complex Asian and Australian continental margins with crustal heterogeneities of the western Pacific (Hamilton. 1979; Hall & Blundell 1996; Hall 2002). Rapid changes in plate boundary location and function in this region are emblematic of incipient phases of continental collision manifest in ophiolite-bearing Cordilleran and Tethyan mountain systems. As in these regions, the Indonesian and New Guinea region has buffered the changing motion and boundaries of some of the Earth's largest plates. Convergence of the IndoAustralian plate from the SW has mostly been absorbed along the Sunda arc-trench system, whereas convergence of the Pacific plate from the east has progressed by sequential movement along an array of short-lived subduction zones and spreading centres. Similar plate boundary asymFrom: DILEK, Y. & ROBINSON P. T. (eds) 2003. Ophiolites in Earth History. Geological SocietY, London, Special Publications, 218, 481-505.0305-8719/03/$15 © The Geological Society of London 2003.