The deep-rooted serpentinite mud volcanism of the Mariana Forearc
Final Report Abstract
The overarching goal of the funded study was to understand temporal and spatial variability of serpentine mud volcanoes (SMVs) in the Mariana forearc, in order to link these features to the fluid and solid cycle of the Mariana convergent margin. Understanding how these features evolve is paramount for the interpretation of all the subduction-related processes they expose on the seafloor through their eruptive activity. SMVs are common on the Mariana forearc but basically absent elsewhere. Since their challenging location, just few ODP expeditions adventured to the area, but it was only during IODP 366 in late 2016 that Fantangisña, a conical-shaped SMV, was completely drilled up to the sedimentary basement and on the summit in 4 different holes. The drilling reached the forearc sediments underneath the SMVs only at Site U1498 where, according to data from this project, the biostratigraphic age of Fantangisña appears to be well constrained. The age estimation through biostratigraphy and argon thermochronology suggested, with a whole life span of 10.77 Myr, that not only this is the oldest MV ever dated, but also that its formation might be linked with the onset of the Mariana arc curvature in Late Miocene. Through extensive rheological studies of the serpentine mud, the viscosity of the latter was measured for different scenarios (i.e. changing water content, solid fraction, etc). These experiments not only confirm the hypothesized highly viscous characteristic of the mud breccia, but also identify different muds’ mineralogical compositions (i.e. serpentine-rich vs serpentine-poor sediments) and water contents as being responsible for the main rheological variations. The viscosity values, produced for the first time for natural samples of serpentine muds, were implemented along with data from onboard measurements in various analytical models, which allowed the determination of the active time of Fantangisña, just a fraction (2.41%) over the total age. These results confirm the extreme episodicity of the SMV and improve the understanding of such structures. In the end, a source depth for the mud was individuated at about 8.4 km depth, close to the limit between forearc crust and mantle individuated by other studies. There, the mantle gets hydrated from deeper fluids and becomes less dense. Consequently, the more buoyant serpentine mud would pile up against the (denser) forearc crust until meeting a fracture, which would allow the mud to rise. At the same time this sets a different origin of the fluids, which are supposed to be originated at plate interface. In conclusion, if seamount recycling is indeed happening through the SMVs of the Mariana forearc, as postulated by us, these project’s results would favor an idea of “shallow decapitation” of subducted seamounts between crust and mantle, in agreement with the model of Watts et al. (2010) for the Mariana forearc.
Publications
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(2018). Mariana Convergent Margin and South Chamorro Seamount. Proceedings of the International Ocean Discovery Program, 366: College Station, TX (International Ocean Discovery Program)
Fryer, P., Wheat, C.G., Williams, T., and the Expedition 366 Scientists
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(2019). Rheology and Biostratigraphy of the Mariana Serpentine Muds Unravel Mud Volcano Evolution. Journal of Geophysical Research: Solid Earth, 124, 10752–10776
Menapace, W., Tangunan, D., Maas, M., Williams, T., & Kopf, A.
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(2020). Mariana serpentinite mud volcanism exhumes subducted seamount materials: implications for the origin of life. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Science, 378(2165):20180425
Fryer, P., Wheat, C. G., Williams, T., Kelley, C., Johnson, K., Ryan, J., Kurz, W., Shervais, J., Albers, E., Bekins, B., Debret, B., Deng, J., Dong, Y., Eickenbusch, P., Frery, E., Ichiyama, Y., Johnston, R., Kevorkian, R., Magalhaes, V., Mantovanelli, S., Menapace, W., Menzies, C., Michibayashi, K., Moyer, C., Mullane, K., Park, J., Price, R., Sissmann, O., Suzuki. S., Takai, K., Walter, B., Zhang, R., Amon, D., Glickson, D., and Pomponi, S.
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(2020). Report and preliminary results of R/V METEOR cruise M149: Shipboard and Post-Cruise Analyses. Recurrence of tsunamigenic hazards from MeBo drilling records and hazard mitigation using MeBo observatories, Las Palmas (Canary Islands) – Cadiz (Spain), 24.07.2018 – 24.08.2018
Hüpers, A., Menapace, W., Magalhaes, V., Freudenthal, T., and Cruise Participants
