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

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eneath the detachment involved a component of simple shear parallel to the lineation with a top-tothe NE sense-of-shear. High-temperature quartz and feldspar deformation mechanisms, and minimal retrogression suggest that the lower plate tectonites preserve an early snapshot of extensional fabrics in the lower crust. These fabrics are preserved because they were exhumed by dominantly brittle processes, involving localised slip on a deeply penetrating detachment fault that transects the middle crust. Localisation of slip on the fault could be due to a weakening effect of high strain-rates on fault gouge material or deep embrittlement caused by prolonged maintenance of high pore-fluid pressures or high strain rates. ORAL LATE QUATERNARY LARGE-SCALE ROCK-MASS DEFECT CONTROLLED LANDSLIDES OF EASTERN NORTH ISLAND, NEW ZEALAND: TECTONIC AND CLIMATIC FORCING IN LANDSCAPE EVOLUTION Jarg Pettinga 1 ,JimMcKean 2 , Joshu Mountjoy 1 , Verne Pere 1 , Kerry Leith 1 & Ben Mackey 1 1 Geological Sciences, University of Canterbury, P.B. 4800, Christchurch, New Zealand 2 USDA Forest Service, Rocky Mountain Research Station, 316 E. Myrtle Street, Boise, ID 83702 USA (jarg.pettinga*canterbury.ac.nz) Rock mass defect controlled landslides are widespread in the Tertiary bedded marine soft rock terrain of eastern North Island. The location and frequency of these deep-seated bedrock landslides is somewhat predictable and the slides are a dominant process affecting both sediment fluxes and landscape evolution. Most slides appear to be base level controlled and occur after stream incision has exposed a critical stratigraphic horizon, defined by thin (typically
with 63.8%, and then [3] with 49.9%. The permeability of the Burrell Lapilli samples is generally up to 10 times higher at given porosities (e.g. 5.3x10 -11 m 2 at �=75.1%) compared to literature data for dacitic and rhyolitic pumice compositions. In cores drilled on three mutually perpendicular directions, there was no correlation between porosity and permeability. However, in four specimens with �>60%, the highest permeability occurred with the oriented core of intermediate porosity value. This result suggests that vesicle structure is anisotropic in respect to flow path. Long cores cut into two were analysed for reproducibility and homogeneity. The data clearly show that the four pumice types are internally homogenous with minor within-category differences in �of 0.1 – 4.0%. However, single larger pumice clasts are heterogeneous and their bulk vesicularity can vary up to 19.9% (n=6). The bulk rock compositions of all pumice types is nearly identical, implying the difference among pumice types is solely based on physical properties. Vesicle textures reveal that type [1] pumices have thinner bubble walls and less microlites as well as heterogeneous bubble size distributions compared to type [2]. Vesicles in [2] are often deformed, presumably causing higher porosities and permeabilities due to the creation of additional apertures between neighbouring vesicles. The development of different coloured pumice types is the result of slightly differing physical magma properties, such as temperature and viscosity, resulting in changes in vesicle texture and glass composition. This is directly controlled by syn-eruptive decompression and fragmentation processes rather than the pre-eruptive magma evolution. Type [1] pumice represents the initial heterogeneous magma foam just prior to eruption followed by type [2] which was able to crystallise microlites due to sudden decompression and/or slower ascent rate. During magma ascent these two magma foams mingle in the conduit imperfectly due to viscosity variations, as observed in [4]. Deformation in type [2] pumices is related to higher eruption temperature, and hence lower viscosity, than type [1] pumice. POSTER EXPLOSIVE VS. EFFUSIVE – THE JEKYLL AND HYDE NATURE OF TARANAKI ANDESITES T.Platz 1 ,S.JCronin 1 ,R.B.Stewart 1 , I. E. M. Smith 2 &S.F.Foley 3 1 Institute of Natural Resources, Massey University, Palmerston North, New Zealand 2 Department of Geological Sciences, University of Auckland, Auckland, New Zealand 3 Institut für Geowissenschaften, Universität Mainz, Mainz, Germany (t.platz*massey.ac.nz) The volcanic activity at Mt. Taranaki, New Zealand is principally characterised by three end member type eruptions: [1] lava flow eruptions (effusive), [2] lava dome forming eruptions (effusive/explosive), and [3] sub-Plinian eruptions (explosive). The geological record of volcanic events at Mt. Taranaki is predominantly marked by type [1] and [2]; in the past 800 years predominantly by [2]. The transition from effusive to explosive eruption style within one eruptive event and within long term eruptive periods is still poorly known. To understand the different eruptive behaviour, petrographical and geochemical studies have been undertaken to approach this problem. The Taranaki andesite rocks can broadly be subdivided into three categories: virtually hornblende (hbl) free rocks [1], hbl containing rocks with different degrees of hbl alteration [2], and unaltered hbl containing rocks [3]. The presence or absence of hbl in volcanic rocks is crucial in terms of water contents of the magma, which strongly influences the eruptive style. Petrographical data, e.g. degree of alteration of hbl and groundmass glass textures, as well as geochemical data based on e.g. melt inclusions in clinopyroxene and hornblende, give rise to the conclusion that there are two end member magma compositions. We propose the existence of a dry and a wet andesitic magma. The terms dry and wet are used to illustrate whether the magma contains hbl (wet) or not (dry). We conclude that both magmas are derived from the same initial parental melt at the base of the continental crust which then evolves differently during ascent within the crust. The two magma compositions erupt either as lava flow (dry) or pumice fall (wet), representing the effusive and explosive end members as observed on the earth’s surface. Lava dome forming eruptions producing predominantly block-and-ash flow deposits represent hybrid magmas caused by mixing/mingling of dry and wet magma. ORAL 50 th Kaikoura05 -69- Kaikoura 2005
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CHARACTERISATION OF NEW ZEALAND NEP
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myrtaceous. One 20 mm diameter flow
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ange of lower resolution or fragmen
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CRETACEOUS-EOCENE TRANSGRESSION MAR
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consists of a well-developed canyon
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model. The relative position of the
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converts to plate theory. Thus, the
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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
Page 59 and 60: These areas are also described in
Page 61 and 62: 3D IMAGING OF THE FORE- AND BACKTHR
Page 63 and 64: ascending methane fluids/gases of p
Page 65 and 66: THE GRIFFENS ROAD TEPHRAS: VALUABLE
Page 67: sideritic concretions that occur in
Page 71 and 72: U-Th-Ra disequilibria data. In part
Page 73 and 74: landslide tsunami in the past. Rece
Page 75 and 76: core complex mode, temperature driv
Page 77 and 78: truncating three plutonic suites of
Page 79 and 80: active, andesitic White Island volc
Page 81 and 82: and voluminous than at any on Earth
Page 83 and 84: oundaries and with immature source
Page 85 and 86: The new era of commercial viability
Page 87 and 88: TECTONICS OF THE GALATEA BASIN USIN
Page 89 and 90: performed by the electron backscatt
Page 91 and 92: 25km northeast of the volcano. Alth
Page 93 and 94: Most of the tectonic blocks in the
Page 95 and 96: TECTONIC AND NON-TECTONIC CAUSES OF
Page 97 and 98: The continental shelf of the Povert
Page 99 and 100: 5 Dept. of Mineral Sciences, Smiths
Page 101 and 102: Adams CJ...........................
Page 103 and 104: Naish T............................
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