Back-arc basin
Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean.
[1] Back-arc basins were initially an unexpected phenomenon in plate tectonics, as convergent boundaries were expected to universally be zones of compression.
[3] The restricted width of back-arc basins is due to magmatic activity being reliant on water and induced mantle convection, limiting their formation to along subduction zones.
[6] Though the magnetic anomalies are more complex to decipher, the rocks sampled from back-arc basin spreading centers do not differ very much from those at mid-ocean ridges.
[1] As the subducting plate descends into the asthenosphere it sheds water, causing mantle melting, volcanism, and the formation of island arcs.
[1] The rising magma and heat along with the outwards tension in the crust in contact with the convection cell cause a region of melt to form, resulting in a rift.
As the subduction zone and its associated trench pull backward, the overriding plate is stretched, thinning the crust and forming a back-arc basin.
[9] The age of the subducting crust needed to establish back-arc spreading has been found to be 55 million years old or older.
[16] From cores collected during the Deep Sea Drilling Project (DSDP) nine sediment types were found in the back-arc basins of the western Pacific.
[16] Debris flows of thick to medium bedded massive conglomerates account for 1.2% of sediments collected by the DSDP.
[16] Accessory materials include limestone fragments, chert, shallow water fossils and sandstone clasts.
[16] Submarine fan systems of interbedded turbidite sandstone and mudstone made up 20% of the total thickness of sediment recovered by the DSDP.
[16] Pelagic clays containing iron-manganese micronodules, quartz, plagioclase, orthoclase, magnetite, volcanic glass, montmorillonite, illite, smectite, foraminiferal remains, diatoms, and sponge spicules made up the uppermost stratigraphic section at each site it was found.
[16] Biogenic pelagic carbonates is the most common sediment type recovered from the back-arc basins of the western Pacific.
[16] Pyroclastics consisting of volcanic ash, tuff and a host of other constituents including nanofossils, pyrite, quartz, plant debris, and glass made up 9.5% of the sediment recovered.
The hypothesis that some convergent plate margins were actively spreading was developed by Dan Karig in 1970, while a graduate student at the Scripps Institution of Oceanography.
