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Reconnaissance of Bulk Sediment Composition and Clay Mineral Assemblages: Inputs to the Hikurangi Subduction System

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Reconnaissance of Bulk Sediment Composition and Clay Mineral Assemblages: Inputs to the Hikurangi Subduction System Wallace, L.M., Saffer, D.M., Barnes, P.M., Pecher, I.A., Petronotis, K.E., LeVay, L.J., and the Expedition 372/375 Scientists Proceedings of the International Ocean Discovery Program Volume 372B/375 publications.iodp.org Contents https://doi.org/10.14379/iodp.proc.372B375.203.2020 1 Abstract 1 Introduction Data report: reconnaissance of bulk sediment 2 Methods composition and clay mineral assemblages: 5 Results 15 Conclusions 1 inputs to the Hikurangi subduction system 16 Acknowledgments 16 References Michael B. Underwood2 Keywords: International Ocean Discovery Program, IODP, JOIDES Resolution, Expedition 372, Expedition 375, Hikurangi Subduction Margin Coring, Logging, and Observatories, Hikurangi margin, clay mineral assemblage, bulk sediment Abstract derstand the behavior and spatial distribution of slow slip events (SSE) along the plate interface (Saffer et al., 2017). Drilling focused This report provides a reconnaissance-scale assessment of bulk on recovery of sediments, rocks, and pore fluids, acquisition of log- mineralogy and clay mineral assemblages in sediments and sedi- ging-while-drilling data, and installation of long-term borehole ob- mentary rocks that are entering the Hikurangi subduction zone, off- servatories. Interpretations of new compositional results from the shore North Island, New Zealand. Samples were obtained from transect area are challenging, however, because comparable infor- three sites drilled during Leg 181 of the Ocean Drilling Program mation is almost nonexistent from other sectors along the strike- (Sites 1123, 1124, and 1125) and 38 piston/gravity cores that are dis- length of the margin. The closest Ocean Drilling Program (ODP) tributed across the strike-length of the margin. Results from bulk- sites (1123, 1124, and 1125) are located far seaward of the Hikurangi powder X-ray diffraction show large variations in normalized abun- Trough (Figure F1). Shipboard X-ray diffraction (XRD) measure- dances of total clay minerals and calcite. The typical lithologies ments were not completed during that expedition, and only one range from clay-rich hemipelagic mud (i.e., mixtures of terrigenous published report contains postcruise compositional data (Winkler silt and clay with lesser amounts of biogenic carbonate) to calcare- and Dullo, 2002). Far to the southwest, XRD data from the Canter- ous mud, muddy calcareous ooze, and nearly pure nannofossil ooze. bury Basin and Canterbury slope (Land et al., 2010; Villaseñor et al., Basement highs (Chatham Rise and Hikurangi Plateau) are domi- 2015) are of limited value to Hikurangi studies because those sites nated by biocalcareous sediment, whereas most deposits in the capture a different system of detrital sources and dispersal routes off trench (Hikurangi Trough and Hikurangi Channel) and on the insu- the South Island of New Zealand (Figure F1). lar trench slope are hemipelagic. Clay mineral assemblages (<2 μm) The motivation for regional-scale reconnaissance of sediment change markedly as a function of geographic position. Sediment en- composition is to provide better context for forthcoming interpreta- tering the southwest side of the Hikurangi subduction system is en- tions of detrital provenance, sediment dispersal, and temporal evo- riched in detrital illite (>60 wt%) relative to chlorite, kaolinite, and lution of sedimentary systems. Quantitative compositional data are smectite. Normalized proportions of detrital smectite increase sig- also important for several ancillary reasons. The geologic hosts for nificantly toward the northeast to reach values of 40–55 wt% off- slow slip events near the Hikurangi IODP transect likely include shore Hawkes Bay and across the transect area for Expeditions 372 lithified and variably altered volcaniclastic sediments of Late Creta- and 375 of the International Ocean Discovery Program. ceous age, but incorporation of other rock types in the fault zone (e.g., siliciclastic mudstone, altered basalt, marl, and nannofossil Introduction chalk) is also possible (Davy et al., 2008; Barnes et al., 2010; see the Expedition 372B/375 summary chapter [Saffer et al., 2019]). If Expeditions 372 and 375 of the International Ocean Discovery chalk and marl are volumetrically significant at the depths where Program (IODP) drilled five sites on the overriding and subducting slow slip occurs, then the subducting carbonates might modulate plates of the Hikurangi convergent margin, offshore North Island, fault-slip behavior by crystal plasticity (Kennedy and White, 2001) New Zealand (Figure F1). The project’s overarching goal is to un- or diffusive mass transfer (Rutter, 1976). The purity of the 1 Underwood, M.B., 2020. Data report: reconnaissance of bulk sediment composition and clay mineral assemblages: inputs to the Hikurangi subduction system. In Wallace, L.M., Saffer, D.M., Barnes, P.M., Pecher, I.A., Petronotis, K.E., LeVay, L.J., and the Expedition 372/375 Scientists, Hikurangi Subduction Margin Coring, Logging, and Observatories. Proceedings of the International Ocean Discovery Program, 372B/375: College Station, TX (International Ocean Discovery Program). https://doi.org/10.14379/iodp.proc.372B375.203.2020 2 Department of Earth & Environmental Science, New Mexico Institute of Mining & Technology, Socorro NM 87801, USA. [email protected] MS 372B375-203: Received 26 August 2019 · Accepted 26 November 2019 · Published XX Month 2020 This work is distributed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. M.B. Underwood Data report: reconnaissance of bulk sediment composition and clay mineral assemblages Figure F1. Index map of the offshore eastern New Zealand region with major bodies of sediment accumulation and likely pathways of sediment dispersal. Ocean Drilling Program (ODP) sites were drilled during Leg 181. International Ocean Discovery Program (IODP) sites were drilled during Expeditions 372 and 375. CB = Canterbury Basin, CS = Cook Strait, RDA = Ruatoria debris avalanche. 35° o o o o o o S North Island Hikurangi 500 km Terrigenous supply fan-drift via turbidity currents N Deep Western RDA Hikurangi IODP Plateau Boundary Current l ODP Site 1124 40° Taupo volcanic zone CS Channel Hikurangi 1000100 0mm ODP Site Chatham Rise ODP Site 1123 South CB 1125 45° Island 40004000m m Bounty Channel ODP Site Sediment drift 1122 Bounty Fan Submarine fan Fan-drift 170° 175°E 180° 175°W 170° marl/chalk is a critical variable, however, as is the extent of replace- yses of standard mineral mixtures (Fisher and Underwood, 1995; ment of primary volcaniclastic constituents by expandable clay Underwood et al., 2003). Data from the standards were used to cal- minerals (smectite group). How much clay is present in these litho- culate a matrix of normalization factors with singular value decom- logies, and which clay minerals are dominant? How variable are the position (SVD), as well as a suite of regression equations that relate lithologies along the strike-length of the margin? This report pro- values of integrated peak area to mineral abundance (weight per- vides some preliminary compositional information to help answer cent). Because of differences in XRD hardware, tube fatigue, and those important questions. software, each individual instrument requires calibration and com- To build an archive of relevant compositional data, samples were putation of its own set of normalization factors and/or regression acquired for XRD analyses from ODP Sites 1123, 1124, and 1125 equations. It is also important to blend the “correct” mineral mix- (Figure F1) plus a representative distribution of piston/gravity cores tures using individual standards that match as close as possible to along the strike-length of the Hikurangi margin. Prominent bathy- the natural mineral assemblages of a particular study area. The metric features targeted by the sampling include (1) the Bounty “wrong” blend of clay minerals, for example, or the “wrong” crystal- Channel, which heads off the southeast coast of South Island and linity of calcite will exacerbate errors in their calculated values of directs gravity flows toward the southeast (Lawver and Davey, weight percent. Underwood et al. (in press) provided details re- 2005); (2) submarine canyons emanating from the Cook Strait sec- garding the standard mineral mixtures (both bulk powder and clay tor between South Island and North Island (Mountjoy et al., 2009); size), along with intralaboratory and interlaboratory tests of preci- (3) the Hikurangi Channel, which funnels gravity flows down the sion and comparisons of accuracy. The results reported herein were axis of Hikurangi Trough (toward the north-northeast) before used to inform choices for the Hikurangi-specific standards. bending sharply to the east (Lewis and Pantin, 2002); (4) the Ruato- ria debris avalanche, which remobilized accreted trench sediments Methods and slope deposits along the northernmost Hikurangi margin (Col- lot et al., 2001); and (5) two prominent basement highs on the sub- Samples ducting plate, Chatham Rise and the Hikurangi Plateau (Wood and A total of 61 specimens from Sites 1123, 1124, and 1125 were Davy, 1994; Davy et al., 2008). In addition, the array of sampling acquired from the Gulf Coast Repository in College Station, TX sites encompasses the region’s most influential ocean current, the (USA). The lithologies range from hemipelagic mud (defined here Pacific Deep Western Boundary Current (DWBC) (Shipboard Sci- as silty clay to clayey silt, or lithified equivalent, with subordinate entific Party, 1999a;
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