Fluid flow and diagenesis in the incoming oceanic plate lithostatigraphy to the Sumatra subduction zone: a geochemical approach
Final Report Abstract
On 26 December 2004 an earthquake with a moment magnitude of Mw ~9.2 nucleated at a depth of ~30-40 km along the plate boundary interface of the Sumatra subduction zone, where the Indo- Australian plate is subducting beneath the Burma-Sunda plates at a rate of 4.5-5.9 cm/a. The event ruptured ~1300 km of the plate interface offshore northern Sumatra with coseismic slip propagating seaward to the trench beneath the submarine accretionary prism causing a devastating tsunami. The event is unusual because the outermost forearc décollement of an accretionary prism is supposed to be aseismic according to the prevailing model of subduction zone seismogenesis. In 2016 International Ocean Drilling Program (IODP) Expedition 362 sampled the sediment sequence incoming to the Sumatra subduction zone to investigate the properties of the incoming sedimentary section and its potential effect on seismogenesis, tsunamigenesis, and forearc development. Within this framework the present study investigated the geochemical composition and physical properties of the incoming lithostratigraphy to shed light on the processes that affect sediment mechanical behavior within the subduction zone. The results of whole-rock geochemistry, lithium and boron isotope composition and scanning electron microscopy with energy dispersive x-ray analysis show that alteration of detrital components lead to authigenic growth of clays within the upper 200 meters below seafloor (mbsf). The analysis further shows that carbonate diagenesis seems to play an important role for the lithification of sediments down to 1250 mbsf, which may explain the observed compressive strength in consolidation tests. In the underlying pelagic sediment (1250 to 1425 mbsf) shipboard analysis revealed >20 wt-% amorphous silica, which has been identified as biogenic silica and palagonite and which represents an important reservoir of mineral-bound water. Forward modeling of diagenetic release of the bound water shows that fluid production through biogenic silica peaks before the sediments enter the trench and smectite/palagonite dehydration peaks close to the deformation front. These fluids exceed those produced by compaction-driven dewatering and the spatial occurrence is consistent with a high amplitude negative polarity reflector observable seaward of the North Sumatra trench. The completion of mechanical compaction and mineral dehydration along the proto-décollement before subduction rather than in the subduction zone shifts the transition from stable to unstable sliding behavior closer to the trench. Microstructural imaging and geochemical analysis of oceanic basement samples further revealed a substantially altered oceanic crust with abundant authigenic growth of hydrous clay minerals (e.g., saponite). The dehydration of these clays could be an important fluid source that affects mechanical processes in the subduction zone. Further reaction kinetic modeling is required to constrain the spatio-temporal distribution of the dehydration reaction.
Publications
- (2017). Understanding Himalayan erosion and the significance of the Nicobar Fan. Earth and Planetary Science Letters, 475, 134-142
McNeill, L. C., Dugan, B., Backman, J., Pickering, K. T., Pouderoux, H. F., Henstock, T. J., Katerina E.Petronotis, K.E., Carter, A., Chemale Jr., F., Milliken, K.L., Kutterolf, S., Mukoyoshi, H., Chen, W., Kachovich, S., Mitchison, F., Bourlange, S., Colson, T.A., Frederik, M.C.G., Guèrin, G., Hamahashi, M., House, B.M., Hüpers, A., Jeppson, T., Kenigsberg, A.R., Kuranaga, M., Nair, N., Owari, S., Shan, Y., Song, I., Torres, M.E., Vannucchi, P., Vrolijk, P.J., Yangae, T., Zhao, X., Thoma, E.
(See online at https://doi.org/10.1016/j.epsl.2017.07.019) - 2017. Release of mineral-bound water prior to subduction tied to shallow seismogenic slip off Sumatra. Science, 356 (6340). 841-844
Hüpers, A., Torres, M.E., Owari, S., McNeill, L.C., Dugan, B., Henstock, T.J., Milliken, K.L., Petronotis, K.E., Backman, J., Bourlange, S., Chemale, F., Chen, W., Colson, T.A., Frederik, M.C.G., Guèrin, G., Hamahashi, M., House, B.M., Jeppson, T.N., Kachovich, S., Kenigsberg, Abby R., Kuranaga, M., Kutterolf, S., Mitchison, F.L., Mukoyoshi, H., Nair, N., Pickering, K.T., Pouderoux, H.F.A., Shan, Y., Song, I., Vannucchi, P., Vrolijk, P.J., Yang, T. and Zhao, X.
(See online at https://doi.org/10.1126/science.aal3429) - 2019. Boron and Lithium isotope geochemistry of pore waters in subduction inputs to the Sumatra subduction zone. Abstract. IODP-ICDP Colloquium, Cologne, GER., 18-20 March
Hüpers, A., Bublies, L., Kasemann, S.A., Meixner, A., Kopf, A.
