Schmid, Florian , Cremanns, Maximilian, Augustin, Nico , Lange, Dietrich , Petersen, Florian and Kopp, Heidrun (2020) Microseismicity indicates a current transition from rifting to spreading at the southern Fonualei Rift and Spreading Center in the Lau Basin. [Talk] In: AG Seismologie 2020. , 21.9.2020 - 24.9.2020, Online .

Abstract

Young extension centers in the proximity of back-rolling subduction zones constitute an ideal natural laboratory to investigate the early evolutional stages of back-arc basins. We present a catalog of 711 microearthquakes recorded during a 32-days deployment of ocean bottom seismometers at the southern part of the Fonualei Rift and Spreading Center in the Lau Basin. The majority of epicenters are concentrated along the central region of the axial valley and about 450 events are associated with an earthquake swarm that is likely linked to magmatic diking in the crust. The earthquake swarm location coincides with several volcanic mounds on the seafloor, covered by fresh lava flows. The spatial distribution of microearthquakes and the maximum depth of brittle faulting is more similar to oceanic spreading centers than to continental rift zones. We interpret our results in conjunction with refraction seismic data and magnetic anomaly data from the same region. In combing all findings, we conclude that the southern Fonualei Rift and Spreading Center is currently in transition from a rifting dominated mode of extension to a seafloor spreading dominated mode of extension. This transition may be associated with fundamental changes in the underlying mechanisms of melt generation leading to a diminishing influence of hydrous flux melting and the growing influence of decompression melting at this back-arc extension zone.

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