Controls on back-arc crustal accretion: insights from the Lau, Manus and Mariana basins
Fernando Martinez, Brian Taylor, 2003. "Controls on back-arc crustal accretion: insights from the Lau, Manus and Mariana basins", Intra-Oceanic Subduction Systems: Tectonic and Magmatic Processes, R. D. Larter, P. T. Leat
Download citation file:
Together, the Lau, Manus and Mariana basins encompass a broad range of conditions of back-arc basin development. Marine surveys have determined the tectonic setting and reconnaissance-scale geophysical and geochemical properties of the extension axes in these basins. We review these data to examine crustal accretion characteristics in the back-arc setting. In each basin magmatism is enhanced in spreading centres near the arc volcanic front, but decreases becoming ‘deficient’ in axes further from the arc. In the Lau and Manus basins the axes extend far behind the arc and develop typical mid-ocean ridge (MOR)-like characteristics. We propose that these variations are controlled by the subducting slab, which shapes composition and flow within the mantle wedge: water released from the slab lowers the mantle solidus and increases in concentration toward the volcanic arc. Spreading centres near the arc advect the hydrated mantle material, enhancing melt production. Slab-induced flow carries melt-depleted mantle material back beneath the basin where it mixes with ambient mantle. Spreading centres further from the arc advect this mantle mixture and produce thinner than normal crust. Far from the arc, spreading centres advect essentially mid-ocean ridge basalt (MORB)-source mantle and their characteristics are MOR-like. Thus, in addition to spreading-rate effects on mantle melting that predominate at MORs, in back-arc basins the subducting slab introduces additional systematic effects.
Figures & Tables
Intra-Oceanic Subduction Systems: Tectonic and Magmatic Processes
Recycling of oceanic plate back into the Earth’s interior at subduction zones is one of the key processes in Earth evolution. Volcanic arcs, which form above subduction zones, are the most visible manifestations of plate tectonics, the convection mechanism by which the Earth loses excess heat They are probably also the main location where new continental crust is formed, the so-called ‘subduction factory’. About 40% modern subduction zones on Earth are intra-oceanic. These subduction systems are generally simpler than those at continental margins as they commonly have a shorter history of subduction and their magmas are not contaminated by ancient sialic crust. They are therefore the optimum locations for studies of mantle processes and magmatic addition to the crust in subduction zones.
This volume contains a collection of papers that exploit the relative simplicity of intra-oceanic subduction systems to provide insights into the tectonic, magmatic and hydrothermal processes associated with subduction.