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

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STRUCTURAL GEOLOGY AND GEODYNAMIC MODELING OF LINKING FAULTS IN THE MARLBOROUGH FAULT ZONE, SOUTH ISLAND, NEW ZEALAND J.D. Eusden 1 ,P.O.Koons 2 ,J.R.Pettinga 3 &P.Upton 1&2 1 Dept. of Geology, Bates College, Lewiston, Maine, U.S. 2 Dept. of Geological Sciences, University of Maine, Orono, Maine, U.S. 3 Dept. of Geological Sciences, Canterbury University, Christchurch, New Zealand (deusden*bates.edu) We present the preliminary results of a combined field-based and 3-d geodynamic modeling study on cross faults that link the major faults in the Marlborough Fault Zone, South Island. Our goal is to understand the kinematic mechanisms for transfer of strain between the main dextral obliqueslip structures, which are, from northwest to southeast, the Wairau, Awatere, Clarence, Elliot and Hope Faults. There has been a gradual temporal southeastward migration in the loci of strike-slip displacement across these faults in the late Quaternary, with the Hope Fault currently carrying the highest slip rates. This is a response to the southeastward development of the Marlborough Fault System over time. We have combined lineament analyses on DEMs and air photographs with structural measurement in the field to unravel the structural geology, fault kinematics and tectonic geomorphology of the Marlborough Fault Zone. The 3-d modeling will allow for an integration of the surface and subsurface structures to depths of circa 30 km. This study will reveal the nature of strain partitioning in the Marlborough Fault Zone as well as plate-scale interactions between the strongly coupled overriding Australian and subducting Pacific plates. The active cross faults dissect the regions between the main Marlborough faults into large uplifted blocks. Kinematic mechanisms for the uplift include: 1) block rotation within a dextral-reverse duplex where opposite corners of the duplex will undergo either extension/collapse or collision/thrusting; or 2) up-dip partitioning along the main Marlborough faults which at the free surface are dominated by dextral strike-slip motion but in the hanging wall are a product of distributed reverse oblique slip displacement. DEM and air photograph analyses show the following: 1) north striking cross faults up to 40 km in length extend between the main Marlborough faults and have a sigmoidal S-shape indicating that they have been affected by dextral shear; 2) NNE striking fractures and faults are parallel to bedding form lines in the Torlesse; 3) these fractures are common and evenly distributed between the Wairau and Awatere faults, less abundant between the Awatere and Clarence faults and rare between the Clarence and Hope faults; 4) NE striking fractures and faults parallel to the main Marlborough Faults decrease in number from the Wairau to the Hope fault; 5) a roughly N striking pivot or hinge zone delineates a strike change from 080° (translational) to 065° (transpressional) for the main Marlborough faults; 6) this pivot zone is marked by at least two diamond-shaped faultbounded blocks up to 40 km in length; 7) one block is bounded by the Clarence-Eliot faults with another somewhat less well defined block between the Clarence and Awatere faults; 8) west of the pivot zone the cross faults are topographically entrenched and connect between the main Marlborough faults whereas east of the pivot they are shorter, discontinuous and have subdued geomorphic expression. POSTER A SEISMIC-GRAVITY STUDY OF THE SOUTHEASTERN BOUNDARY OF THE WANGANUI BASIN Erik Ewig , Tim Stern & Kiran Hudson School of Earth Sciences,Victoria University of Wellington, PO.Box 600 Wellington (erik.ewig*vuw.ac.nz) Located between the axial ranges of the North Island and the south Taranaki Basin, the Wanganui Basin is a region of broad crustal down-warp with predominantly reverse faulting. The Basin is of Pliocene-Pleistocene age, with sediments directly over Mesozoic basement. Sediments in the basin dip gently towards a central depocentre and are cut by NE-NNE-trending faults that are generally downthrown towards the centre of the basin. The depocenter of this basin has migrated southsouthwest with time, driven at least in part by the Quaternary uplift and doming of the central North Island. Offshore, the basin has been surveyed with a number of oil industry and CRI-funded multichannel seismic surveys. Onshore, the basin is known only from scattered geophysical surveys and a few exploration wells. Part of this study is directed to learn about the southeastern corner of the Wanganui Basin and the transition to the Tararua Ranges. We report three new active-source seismic lines and three reprocessed existing active source seismic lines. All these lines show clear evidence of faulting. The majority of the faults are high angle reverse faults. Because of the rapid deposition of sediments, and shifting sand dunes, these active to recently active faults could be classified as blind thrusts. However, there are also a 50 th Kaikoura05 -26- Kaikoura 2005
few normal faults visible especially in the coastal Levin area. The reverse faults agree well with the notion of crustal downwarp in a region of geodetically-determined, mild compression. Three possible explanations for the normal faults are a) a local second order effect due to dextral strike slip motion along the major faults, b) tensional forces have been or are still active in this area or c) flexural bending stresses superimposed on an overall compressive stress field. We have started to create models to test for the origin of the –150 mgal Bouguer/isostatic gravity anomaly that dominates Wanganui Basin. The anomaly can only partially be explained by the sediment fill and it is one of the most compelling geophysical observations in the Wanganui area, if not the whole North Island. Initial 3D models show that the gravity anomaly associated with the basin is generally consistent with a downwarp model of the entire crust. However, the downwarp of the Moho has to be significantly greater than the downwarp of the sediment-basement interface to fit the observed gravity anomaly. Hence we propose a model of lithospheric shortening where thickening increases with depth. POSTER WHAT SOURCE ROCK POTENTIAL DOES THE WAIPAWA FORMATION HAVE BEYOND THE EAST COAST BASIN? AN OUTCROP-BASED CASE STUDY FROM NORTHLAND B.D. Field, C.J. Hollis, E.M. Crouch & R. Sykes GNS Science, PO Box 30 368, Lower Hutt (b.field*gns.cri.nz) The Paleocene Waipawa (Black Shale) Formation is a known source of oil in the East Coast and north Taranaki basins. It is likely to be a significant source rock in adjacent basins in Northland and Canterbury and the Great South Basin. In order to determine the extent and character of the formation in northern Northland, we studied Waipawa-like dark-grey mudstones exposed in Price’s and Black’s quarries in the allochthonous sequence at Ohia, west of Taipa, and a shore platform exposure in the autochthonous sequence at Whatuwhiwhi, Karikari Peninsula. The Ohia and Whatuwhiwhi exposures are inferred to record distal and proximal deposition, respectively, off the northeastern margin of Northland within the so-called North Slope Basin. The quarry outcrops are highly deformed, making determination of stratigraphic orientation and thickness difficult. Dinoflagellate biostratigraphy shows that the sequence in Price’s Quarry is overturned and ranges in age from Late Cretaceous to late Paleocene. Although this age range encompasses that in which the Waipawa Formation was deposited, the distinctive geochemical signature of the formation is not evident in any of the quarry samples. Despite an oily smell and sulphurous efflorescence, all samples have low TOC and light bulk � 13 C values (less than 1% and - 26‰, respectively). Based on these features, the entire sequence is correlated with the siliceous mudstone facies of the Whangai Formation. In contrast, the typically high TOCs and heavy � 13 C values (> -24‰) of the Waipawa Formation are found in petroliferous mudstone exposed in Black’s Quarry, 1.5 km to the east. Dinoflagellates confirm a Paleocene age. Although a stratigraphic thickness of 40 m is suggested, it is difficult to confirm due to poor bedding and numerous faults. The formation here is immature (Tmax 421–427 °C) and TOC and HI values of 10–11% and 426–445 mg HC/g TOC, respectively, indicate good potential for both oil and gas generation. At Whatuwhiwhi, the wellbedded Haumurian–Teurian Waiari Formation includes a lower chert-dominated facies and an upper mudstone-dominated facies. The former has a Whangai-type geochemical signature whereas the latter has a Waipawa-type geochemical signature. However, a lack of palynomorphs and almost completely exhausted petroleum potentials (S2 < 0.15 mg HC/g rock) indicate that the Waipawa-like interval has been thermally altered by nearby Miocene intrusives to an extent that makes correlation with the Waipawa Formation uncertain. The heavy isotopic signature may be a result of this thermal alteration. The results of this study indicate that good quality Waipawa Formation source rock is likely to be present in the sedimentary succession offshore northeastern Northland. However, its thickness is uncertain and it is likely to grade laterally and vertically into comparatively organic-lean siliceous facies of the Whangai Formation. Seismic facies mapping and paleoenvironmental reconstructions are recommended to better define the extent and quality of this important source rock. POSTER DISTRIBUTION AND SEISMIC CHARACTERISATION OF GAS HYDRATES IN FIORDLAND, NEW ZEALAND Fohrmann, Miko 1 ; Gorman, Andrew R. 1 ; Pecher, Ingo A. 2 , Jarvis, Kevin D. G. 3 1 Department of Geology, University of Otago, P.O. Box 56, Dunedin, New Zealand 2 Institute of Geological & Nuclear Sciences (GNS), P.O. Box 30 368, Lower Hutt, New Zealand 3 Fugro-Jason Australia, 69 Outram Street, West Perth, WA 6005, Australia (fohmi830*student.otago.ac.nz) 50 th Kaikoura05 -27- 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 and 8: CRETACEOUS-EOCENE TRANSGRESSION MAR
Page 9 and 10: consists of a well-developed canyon
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: wider range. The youngest layer has
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 and 68: sideritic concretions that occur in
Page 69 and 70: with 63.8%, and then [3] with 49.9%
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
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truncating three plutonic suites of
Page 79 and 80:
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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