CHARACTERISATION OF NEW ZEALAND Recently QMAP Fiordland has investigated the NEPHRITE JADE USING ITS GEOLOGICAL southern-most part of the Cretaceous Western AGE AND STRONTIUM ISOTOPIC Fiordland Orthogneiss (WFO) suite and its COMPOSITION relationships to adjacent Paleozoic metasedimentary rocks. In central-west Fiordland, C. J. Adams1,H.J.Campbell1 & R. Beck2 10-20km to the north of the area mapped, previous 1GNS Science, PO Box 30368, Lower Hutt, New work indicates granulite facies (ca. 10-12kbar) Zealand. WFO is juxtaposed against Paleozoic amphibolite 2 27 Chelmsford Street, Invercargill, New Zealand. facies (ca. 7-9 kbar) metasedimentary rocks across (argon*gns.cri.nz) the Doubtful Sound Shear Zone (DSSZ). A more complex variety of gneisses and field relationships New Zealand pounamu (nephrite jade) occurs in characterise the southern-most part of the WFO several ‘fields’ in the South Island, mainly in suite. Breaksea Island, much of northern Resolution northern Southland and North Westland. The usual Island and the area between Breaksea Sound and occurrence is in metasomatic reaction zones the Coal River mouth are underlain by distinct forming tremolite of unusual texture, where coarse banded clinopyroxene-garnet and gabbro/dolerite/harzburgite undergoing plagioclase-garnet-clinopyroxene gneisses that are serpentinitization is adjacent to siliciclastic widely retrogressed to hornblendite and metasediments (and metavolcanics). plagioclase-hornblende gneiss. Igneous textures have been completely destroyed during For the probable Early Permian gabbro/dolerite metamorphism and deformation. These rocks are pounamu precursors, Rb-Sr age and Sr-isotope data collectively referred to as the Breaksea Gneisses. suggest a primitive origin, with initial 87Sr/86Sr Eastern Resolution Island, inner parts of Breaksea ratios, c. 0.7032. Sound, much of Wet Jacket Arm and the Acheron However, the Permian-Triassic metasediment Passage are underlain by a homogenous dioritic 87 86 precursors have more elevated initial Sr/ Sr orthogneiss in which igneous textures are widely ratios, whose values confirm their suggested terrane preserved despite granulite facies metamorphism origins: <0.7050 (Caples), 0.7050-0.7065 (Dun and development of garnetiferous anorthosite Mountain-Maitai), >0.7090 (Torlesse). Pounamu leucosomes. These rocks are referred to as from in situ occurrences in the Livingstone Malaspina Gneiss since they are contiguous with Mountains, northern Southland (Dun Mountain- WFO mapped in Doubtful Sound of the same name. Maitai terrane) and Arahura River, North Westland Dikes of Malaspina Gneiss cut layering in the 87 86 (Torlesse terrane), have initial Sr/ Sr ratios close Breaksea Gneiss indicating that the former is the to the metasediment values noted above. The younger unit. Significant deformation, gabbro and dolerite Sr contributions to pounamu metamorphism and recrystallisation appear to have formation thus clearly play a very minor role. separated emplacement of these two members of Sr isotopic ratios may thus provide a useful the WFO suite, but the magnitude of their age characteristic of the New Zealand nephrite jade difference is not known. ‘fields’. Since Torlesse and Caples terrane rocks Breaksea Gneisses are juxtaposed against Paleozoic occur within Alpine and Otago Schists of quite rocks across both broader ductile shears similar to different ages, it is possible that metamorphic age the DSSZ and younger brittle faults. variations may also play a finer-scale role in Reconnaissance thermobarometry of unretrogressed determining Sr-isotopic compositions. Breaksea Gneiss indicates peak metamorphic ORAL pressures of ca. 15-16kbar accompanied by growth of omphacitic clinopyroxene, probably before emplacement of the Malaspina Gneiss, making THE GRANULITE FACIES WESTERN these the highest grade rocks discovered to date in FIORDLAND ORTHOGNEISS IN Fiordland. Intrusive contacts between the younger SOUTHWEST FIORDLAND Malaspina Gneiss and adjacent rocks are still widely preserved indicating that the DSSZ does not A. Allibone1, I. Turnbull2,L.Milan3,S.Carroll3, enclose the entire circumference of the WFO in &N.Daczko3 southwest Fiordland. Trondhemitic leucosomes 1 School of Earth Sciences, James Cook University, with locally abundant peritectic garnet define a Townsville, Q4811, Australia narrow thermal aureole a few 100 metres wide 2Institute of Geological and Nuclear Sciences, along the intrusive margins of the Malaspina Gneiss Private Bag 1930, Dunedin in Paleozoic psammites and amphibolites, unnamed 3Department of Earth and Planetary Sciences, older gabbro, and the Cretaceous Supper Cove Macquarie University Orthogneiss. Rare xenoliths confirm the intrusive (rodinian*msn.com) relationship between Malaspina Gneiss and the adjacent units. Reconnaissance thermobarometry 50thKaikoura05 -1- Kaikoura 2005 indicates pressures of ca. 10-12kbar during aureole cathodoluminescence. The spar cements were development in Wet Jacket Arm. Amphibolite precipitated during shallowest burial (likely no facies assemblages remain outside the aureole more than about 200 m), involving mild pressure- indicating that equilibration to granulite facies dissolution of skeletons, and during subsequent assemblages only occurred within the immediate uplift when dissolution of aragonitic shells vicinity of the Malaspina Gneiss suggesting provided a later stage of equant and micro-equant reaction kinetics were an important control on the cement. Most of the limestones retain moderate extent to which granulite facies assemblages porosity in outcrop. developed in country rocks intruded by the WFO. The skeletal composition is consistent with ORAL deposition of all three limestones in a similar high energy, current swept seaway environment (Ruataniwha Strait) at inner shelf depths. LATE NEOGENE BARNACLE-RICH Deposition was associated with rapidly LIMESTONES, MATAPIRO-OMAHU, transgressing seas coupled with low terrigenous HAWKE’S BAY: THEIR LIFE FROM sediment supply, forming relatively thin DEPOSITION TO UPLIFT transgressive systems tract (TST) carbonate deposits. Highstand systems tract (HST) deposits 1,2 2 2 R.A. Baggs ,C.S.Nelson, P.J.J. Kamp ,K.J. are represented by the intervening, thicker, mid- 2 2 Bland & S.D. Hood shelf mudstones, which accumulated over longer 1 CRL Energy Ltd. P.O. Box 290, Greymouth durations than the limestones. Four major 2 Dept of Earth Sciences, University of Waikato, cyclothems (TST + HST) are identified for the Private Bag 3105, Hamilton mapped succession, the depositional settings being (rachelbaggs_nz*hotmail.com) primarily controlled by glacio-eustatic sea level fluctuations near the opening of the Ruataniwha A new GIS-based 1:40,000 scale geological map Strait into Hawke Bay in the Nukumaruan, during a has been produced for the Matapiro-Omahu region, period of slow basin subsidence followed between the Tutaekuri and Ngaruroro Rivers, west eventually by uplift and exhumation of the whole of Napier city in eastern North Island. The rocks succession. occupy the southern part of the regional Matapiro Syncline, are of late Pliocene-early Pleistocene age ORAL (Nukumaruan), are contained within the Petane Group, and comprise a cyclothemic succession of FISH, FRUSTULES, FRUITS, A FLOWER - formations of terrigenous mudstone and limestone, AND LOTS OF LEAVES: AN with some conglomerate. INVESTIGATION INTO THE BIOTA OF AN The three limestone units, in ascending order the EARLY MIOCENE MAAR LAKE Tangoio Limestone, Matapiro Limestone and Puketautahi Limestone, tend to stand proud in the J.M. Bannister1 &D.E.Lee2 landscape and provide good mappable horizons, 1Departments of Botany & Geology, University of while the intervening mudstones are poorly Otago, PO Box 56, Dunedin exposed. The Tangoio Limestone is restricted to the 2Department of Geology, University of Otago, PO eastern limb of the Matapiro Syncline and grades to Box 56, Dunedin fossiliferous greywacke gravels (Sherenden (jmb*clear.net.nz) Conglomerate Member) towards the west. The pebbly Matapiro Limestone is distributed Preliminary findings from a finely varved diatomite throughout the southern part of the syncline, while deposit formed during the Early Miocene in a maar the Puketautahi Limestone caps the hills on the lake near Middlemarch, Otago are presented. The western limb. varves are alternately dark and light and the light Sedimentological and petrographic analyses of the coloured layers are made up almost entirely of three limestones indicate that they are all barnacle- diatom frustules with some freshwater sponge dominated with an increasing proportion of bivalve spicules. The diatom flora is overwhelmingly material up through the units, and with small dominated by a single species, Encyonema jordanii amounts of bryozoans, echinoderms, benthic (Grunow) Mills. The sponge(s) probably encrusted foraminifera, and occasional serpulids and red plant material such as stems of water plants and algae. Skeletal grains are commonly microbored. dead leaves. Limited excavations in the upper few The rocks are mainly skeletal grainstones, less metres of the deposit have yielded several entire commonly skeletal packstones, and carbonate fish skeletons up to 15 cm long that belong to a new contents average 70-80%. Cements involve a species of galaxiid. The diatomite contains variety of calcite spar fabrics, including syntaxial numerous fruits and seeds in different states of rim, isopachous fringe, meniscus and equant types, preservation; these are mainly small and difficult to usually