50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...

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the top of the group, which was probably thin and eroded during the inversion phase prior to accumulation of younger units. The Taumatamaire Formation comprises mainly massive mudstone. Along the western margin (Herangi High) the mudstone is interspersed with several limestone members (Awakino Limestone; Black Creek Limestone); the carbonate sediments were sourced along the contemporary rocky shoreline of the Herangi High underlain by Murihiku basement, and dispersed across a very narrow east-facing shelf and down the slope into the basin. Paleocurrent measurements derived from flute casts and tool marks indicate that the flysch facies were sourced from the south, and the depositional system probably prograded to the north. Muddy sediment and carbonate were locally derived from basement exposed along the Herangi High, but this was probably a minor source. The sandstone beds are cemented with calcite, and glauconite comprises a surprisingly high proportion of their content (10%). Mica is an accessory mineral, suggesting that schistose or gneissic terrane (in South Island) contributed sediments to the basin. POSTER MANTLE OR CRUST? FIRST RESULTS FROM A DETAILED ACTIVE-SOURCE SEISMIC EXPERIMENT ACROSS THE TAUPO VOLCANIC ZONE Adrian Benson 1 , Tim Stern 1 &Stephen Bannister 2 1 School of Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington. 2 Institute of Geological and Nuclear Sciences, PO Box 30-368, Lower Hutt. (adrian.benson*vuw.ac.nz) Seismic studies of the central North Island have consistently shown the Taupo Volcanic Zone to be a region of attenuated continental crust underlain by mantle of anomalously low seismic velocity (~7.4 km.s -1 ). However, the nature of the crust-mantle boundary beneath the rift and, in particular, the position of the Moho remain contentious. Active source data acquired during the 2001 NIGhT experiment detected two prominent reflectors at depth: a ~ 15 km deep horizon (PmP1) and an unusually strong set of reflections from an interface at ~30 km (PmP2). These NIGhT data have given rise to divergent models of the lower-crust and upper-mantle. Harrison & White (2004) place the base of the crust at 30 km (= PmP2) and infer that the 15 km interval between PmP1 and PmP2 is under-plated and/or intruded lower crust. Stratford & Stern (2004) suggest that the Moho lies between 15 and 20 km depth and interpret the PmP2 reflections as being from the top of an intra-mantle fluid/melt body of unknown thickness but limited lateral extent. We present preliminary results from a recently completed active source seismic experiment (MORC) that seeks to address the issue of what constitutes Mantle OR Crust beneath the TVZ. Building upon the results of NIGhT, the MORC experiment was designed to provide a enhanced data set to examine the character of the 30 km deep PmP2 reflector. Nine dynamite shots of between 500 and 1300 kg were detonated into a 120 km long array across the northern end of Lake Taupo. The shot geometry and the deployment of 714 receivers (600 IRIS Texans, 96 geophones on multi-channel systems, and 18 3-component seismometers) with an average spacing of ~200 m provides a ten-fold increase in spatial resolution relative to the NIGhT data. Reflections from the 15 km deep PmP1 horizon are present in the MORC data, however the dominant features are arrivals from PmP2 at a depth of ~ 30 km. The occurrence and amplitude of the PmP2 reflections are strongly dependent on both the shot position and receiver offset. Initial ray-tracing of the PmP2 reflections suggests the interface is of limited lateral extent and located directly below the active (eastern) part of the main TVZ rift. For stations with both PmP1 and PmP2 arrivals it is possible to directly compare the relative amplitude of these two phases. At large offsets the amplitude of PmP2 reflections are at least 5 times those of PmP1 phases, which are modelled as being from a < 6.0 km.s -1 to 6.8 km.s -1 velocity boundary (Stratford & Stern, 2004). These results indicate the PmP2 reflections must be due to a large change in the velocity and/or physical properties of rocks at 30 km depth. Further work to characterise the crust-mantle structure beneath the TVZ will include ray-trace and tomographic modelling of the combined MORC and NIGhT datasets, the production of a stacked low-fold seismic section, and detailed analysis of the AVO properties of the PmP2 and other reflectors. ORAL SEAFLOOR STRUCTURAL GEOMORPHIC EVOLUTION IN RESPONSE TO SUBDUCTION PROCESSES, POVERTY BAY INDENTATION, NEW ZEALAND K. L. Bodger 1 ,J.R.Pettinga 1 andP.M.Barnes 2 1 Dept. of Geological Sciences, University of Canterbury, Christchurch 2 National Institute of Water and Atmospheric Research (NIWA), Greta Point, Wellington (k.bodger*geol.canterbury.ac.nz) The >4000 km 2 Poverty Bay Indentation, in the northern sector of the Hikurangi subduction margin, 50 th Kaikoura05 -8- Kaikoura 2005
consists of a well-developed canyon system, small accretionary wedge, landslide scars and debris flow deposits. Outboard of the Hikurangi trench the subducting plate incorporates the Hikurangi Plateau, a section of anomalously thick Mesozoic age oceanic crust (10-15 km) studded with seamounts and guyots (flat-topped seamounts). Morphologically the Hikurangi margin changes markedly from south to north of the Poverty Bay Indentation. To the south, the margin is characterised by a thick trench-fill turbidite section and a wide, low-taper accretionary wedge with numerous thrust ridges and slope basins. To the north of the indentation the margin is narrow, relatively steep, and characterised by non-accretion and tectonic erosion associated with reduced sediment supply, seamount/guyot subduction, and gravitational failures. The transition between the characteristics of the two sectors is evident in the study area with the developed accretionary wedge and gentler slopes in the southern half contrasting with the steep slopes and numerous failures to the north of the canyon system. High quality bathymetric images of the Poverty Bay Indentation and adjacent regions of the Hikurangi subduction zone acquired by NIWA using a SIMRAD EM300 multibeam system provide excellent seafloor morphologic resolution covering the entire continental slope from 50 – 3500 m water depth. These images have been converted into a Digital Elevation Model (DEM) allowing seafloor. three-dimensional analyses of the i. Initial DEM interpretations suggest that: seamount impact significantly influences the structure/tectonic evolution, and submarine geomorphology of the inboard slope of the Hikurangi subduction zone, including the ii. generation of large-scale gravitational collapse features; large gully systems located at the shelf – slope boundary are source areas for mega-debris flows recognised in mid-slope basins; iii. there exists a complex interaction between the evolving thrust-driven submarine ridges, ponded slope basins and the structural geometry and evolution of the near-surface fault zones iv. (imbrication); and the submarine canyons may initiate complex patterns of fault zone segmentation and v. displacement transfer within the accretionary slope. The addition of high quality 3.5 kHz singlechannel and multi-channel seismic reflection data complements the morphological and structural surface interpretation. In particular, this allows investigation into the impact of thrust fault loading and seamount subduction on the margin at a mid to deep crustal level. Correlation between the surface expressions of these processes and the underlying tectonics will be the next stage in this project. POSTER TRACE ELEMENT GEOCHEMICAL EVIDENCE FOR A LACUSTRINE ENVIRONMENT OF DEPOSITION OF LATE ARCHAEAN FORTESCUE GROUP STROMATOLITIC CARBONATES, WESTERN AUSTRALIA R.Bolhar 1 & M.J. Van Kranendonk 2 1 Department of Geological Sciences, University of Canterbury, Christchurch, NZ 2 Geological Survey of Western Australia, 100 Plain St., East Perth, Western Australia, 6004 (robert.bolhar*canterbury.ac.nz) The late Archaean Fortescue Group (2.78-2.63 Ga) in the Pilbara Craton, Western Australia, records a transition in depositional environments from subaerial in the lower part of the group, to marine in the upper part of the group. Stromatolitic carbonates (i.e. microbialites that formed by precipitation of minerals due to metabolic activity or decay of microbial communities and/or associated organic matter) occur throughout the stratigraphic section at various levels, and their trace element geochemistry is used to make inferences about the ambient water from which these carbonates were precipitated. In particular, rare earth elements (REE) and Yttrium were analysed to address whether i. Fortescue carbonates display a marine ii. geochemical signature or show compositional similarity to modern-day lacustrine waters and their deposits and to identify temporal trends in the geochemistry that may be consistent with a transition from deposition in a subaerial/lacustrine to marine environment. Detailed inspection reveals that Fortescue microbialites lack trace element characteristics that are diagnostic of carbonates deposited in a marine environment. In particular, the Fortescue Group samples lack distinct La (expressed as La/[3Pr- 2Nd] in shale-normalised diagrams) and Gd [Gd/(2Tb-Dy]shale anomalies and supra-chondritic Y/Ho ratios, which are well-developed in seawater carbonates formed throughout Earth history, from at least 3.4 Ga. The late Archaean microbialites also lack depletion of the light REE relative to the middle and heavy REE when shale-normalised, in contrast to seawater and marine carbonates, which are typically HREE enriched. Importantly, no temporal trends in the geochemistry that is 50 th Kaikoura05 -9- Kaikoura 2005
Page 1 and 2: CHARACTERISATION OF NEW ZEALAND NEP
Page 3 and 4: myrtaceous. One 20 mm diameter flow
Page 5 and 6: ange of lower resolution or fragmen
Page 7: CRETACEOUS-EOCENE TRANSGRESSION MAR
Page 11 and 12: model. The relative position of the
Page 13 and 14: converts to plate theory. Thus, the
Page 15 and 16: and on the following morning the mi
Page 17 and 18: the LGM grass peak. This period of
Page 19 and 20: offshore west coast to offshore eas
Page 21 and 22: 4 Institut de Recherche pour le Dé
Page 23 and 24: VEGETATION AND CLIMATE CHANGE AT TH
Page 25 and 26: wider range. The youngest layer has
Page 27 and 28: few normal faults visible especiall
Page 29 and 30: TRACKING CRUSTAL DIFFERENTIATION AN
Page 31 and 32: EMPIRICAL SCALING RELATIONS FOR SEI
Page 33 and 34: hydrovolcanic eruptions then took p
Page 35 and 36: and that the MTL marks a Late Carbo
Page 37 and 38: faunal changes within these cores w
Page 39 and 40: material at subsurface depths of se
Page 41 and 42: survived through in low numbers in
Page 43 and 44: in the TVZ and southern Havre Troug
Page 45 and 46: Tephra beds are commonly used to ai
Page 47 and 48: The MCC is bounded by deep-seated t
Page 49 and 50: distal alluvial plains where large
Page 51 and 52: Many of the molluscs in the highly
Page 53 and 54: incremental slip history and paleoe
Page 55 and 56: This paper explores what we know of
Page 57 and 58: volcanism and a linear vent oriente
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These areas are also described in
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3D IMAGING OF THE FORE- AND BACKTHR
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ascending methane fluids/gases of p
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THE GRIFFENS ROAD TEPHRAS: VALUABLE
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sideritic concretions that occur in
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with 63.8%, and then [3] with 49.9%
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U-Th-Ra disequilibria data. In part
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landslide tsunami in the past. Rece
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core complex mode, temperature driv
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truncating three plutonic suites of
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active, andesitic White Island volc
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and voluminous than at any on Earth
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oundaries and with immature source
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The new era of commercial viability
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TECTONICS OF THE GALATEA BASIN USIN
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performed by the electron backscatt
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25km northeast of the volcano. Alth
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Most of the tectonic blocks in the
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TECTONIC AND NON-TECTONIC CAUSES OF
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The continental shelf of the Povert
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5 Dept. of Mineral Sciences, Smiths
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Adams CJ...........................
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Naish T............................
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