Australia: The Land Where Time Began

A biography of the Australian continent 

Subduction – A record of Spontaneous Initiation in the Izu-Bonin-Mariana Arc

According to Arculus et al. the subduction of tectonic plates is poorly understood. If it is push from a distant mid-ocean ridge or pull of a subducted plate it is expected there would be compression and uplift of the overlying plate. Contrasting with this, spontaneous initiation of subduction which is driven by the subsidence of dense lithosphere along faults that are adjacent to the buoyant lithosphere would result in extension and magmatism. Arculus et al. say it typical for younger deposits to obscure the record in the rocks of the initiation of subduction with the result that the evaluation of these possibilities has proven to be elusive. In this paper Arculus et al. present the results of their analysis of the igneous characteristic of igneous basement rocks and overlying sediments, which had been sampled from the Amami Sankaku Basin in the northwest Philippine Sea. The uppermost of the basement rocks, which cover a widespread area, have been supplied by dykes. They are similar in composition and age, being constrained by the sediments which overlie them, to the basalts in the Izu-Bonin-Mariana forearc which are 52-48 million years old. It is indicated by the geochemical characteristics of the basement lavas there was a component of subducted lithosphere involved in their genesis, and the mantle source rocks from which the lavas were derived were more melt-depleted than those which were tapped at mid-ocean ridges. Arculus et al. propose that the abasement lavas were formed during the inception of subduction of Izu-Bonin-Mariana in a mode that is consistent with the spontaneous initiation of subduction.

Sources & Further reading

Arculus, R. J., O. Ishizuka, K. A. Bogus, M. Gurnis, R. Hickey-Vargas, M. H. Aljahdali, A. N. Bandini-Maeder, A. P. Barth, P. A. Brandl, L. Drab, R. do Monte Guerra, M. Hamada, F. Jiang, K. Kanayama, S. Kender, Y. Kusano, H. Li, L. C. Loudin, M. Maffione, K. M. Marsaglia, A. McCarthy, S. Meffre, A. Morris, M. Neuhaus, I. P. Savov, C. Sena, F. J. Tepley Iii, C. van der Land, G. M. Yogodzinski and Z. Zhang (2015). "A record of spontaneous subduction initiation in the Izu-Bonin-Mariana arc." Nature Geosci 8(9): 728-733.