The protection of groundwater dependent ecosystems in Otago, New Zealand

Surface waters (streams, rivers, and wetlands) are the most important groundwater dependent ecosystems (GDEs) in Otago, New Zealand. Pumping wells in the vicinity can deplete water in the GDE. In Otago, most of the surface water resources are allocated and a method, which would assist in the implementation of water management policy, is needed to acknowledge the strong hydraulic link between surface and shallow groundwater. A simplified method has been developed which derives a numerical relationship between the bore pumping rate and the distance between the bore and surface water body beyond which depletion is considered insignificant. A range of GDE depletion scenarios are examined at various combinations of hydraulic parameters to find a minimum distance for a given pumping rate, at which 90% of the modelled surface water depletion scenarios become less than a threshold GDE depletion after a specified time. A buffer zone, based on the minimum distance is placed around GDEs, and groundwater abstraction rights within the buffer are subject to stricter rules. Applicants wishing to abstract from bores within the buffer zone will need to address the environmental impact of the proposed activity on the GDE.     

Petrology of Ocellar Lamprophyres from Western Otago, New Zealand

The southern part of a lamprophyre dyke swarm from West Otago,New Zealand comprises monchiquites and camptonites. Dykes arecompositionally similar to volatile-rich nephelinite or nephelinebasanite, and contain leucocratic ocelli and irregular veinsegregations of nepheline benmoreite composition. Ocelli arecommonly zoned with an upper globule or centrally disposed coreof analcime-carbonate and an alkali feldspar-kaersutite-richlining. Virtually identical zoning is developed in minerals common toboth lamprophyre host and ocellus. Kaersutite is progressivelyenriched in Fe, Mn, Al_vi, and Na + K, and depleted in Mg, andTi towards the rim. Titanaugite is concentrically zoned to aegirine-augite,and is sector zoned with prism sectors enriched in Ti and Al(and to a lesser extent in Fe and Na) compared to basal sectors.Brown micas are zoned from titanphlogopite cores to titanbiotiteand titaniferous lepidomelane rims. In monchiquites glass occurs as an intersertal phase and asan ocellus infilling. The glass is phonolitic and contrastssharply with the composition of the ultrabasic host, indicatingthat production of extreme differentiates without intermediatecompositions is possible by fractional crystallization. Identicalglass compositions in both lamprophyre groundmass and ocelluspreclude liquid immiscibility. Instead, it is suggested thatocelli are segregations of residual liquids drawn into gas vesiclesas a consequence of reduction of the vapour phase, volume duringcooling. The analcime-carbonate globule within the ocellus isinterpreted as the condensed vapour phase. At Haast River, in the northern part of the swarm the dyke associationof peridotite, camptonite, trachyte, tinguaite, and carbonatiteis readily explained in terms of this model. Fractional crystallizationof camptonite results in phonolitic late stage liquids which,if separated from the lamprophyre host crystallize as sodalitetinguaites, leaving a more ultrabasic residuum whose compositionis equivalent to damkjernitic peridotite. Vesiculation of thecamptonite results in separation of a volatile phase (fluidimmiscibility) which is carbonate and alkali-rich, the sourceof both carbonatites and the agent responsible for fenitization.     

苏北连云港地区蓝闪绿片岩相岩块的发现

在苏北连云港地区(红石咀、东西连岛及蟹脐沟)发现以岩块、岩片形式出现的蓝闪绿片岩相岩石，其由石榴石、蓝透闪石、冻蓝闪石、阳起石、钠长石、多硅白云母、榍石及文石等矿物组成。石榴石变斑晶作为低扩散的刚性矿物，经历了多期变质变形作用，变质反应证据保存在石榴石的成分环带及包体矿物组合中。蓝透闪石、冻蓝闪石及文石包体的存在表明，本区出露的绿片岩相岩系属早期经历低温高压变质作用、晚期又叠加绿片岩相变质作用的高压变质地体。这一发现为苏鲁高压地体的构造单元划分提供了重要依据。     

Syn-metamorphic gold mineralisation,Invincible Vein,NW Otago Schist,New Zealand

The Invincible Vein fills a fault zone which strikes northeast and dips steeply southeast in the lower Rees Valley, NW Otago. The vein cuts north striking foliation in lower greenschist facies Otago Schist. Structures associated with the fault zone are both brittle and ductile, and the fault zone has had a complex history of post-mineralisation reactivation. Mineralised vein material filling parts of the fault zone consist of quartz, albite, muscovite, chlorite, calcite, pyrite, arsenopyrite and minor gold. These minerals have been strained and locally recrystallised during ductile deformation. Fluid inclusion homogenisation temperatures (140–175°C) and ice melting temperatures (0 to –1°C) indicate that the mineralising fluid was low salinity, low CO₂ water with a density between 0.88 and 0.93 g/cm₃. Arsenopyrite geothermometry implies a temperature of mineralisation of 370 ± 70°C. Mineralisation pressure lay between 2 and 5 kbar. Mineralisation pressure-temperature conditions and mineralogy are essentially the same as for metamorphism of the host schist. Vein calcite oxygen isotope ratios (+12 to +15 per mil) are similar to host schist values. Carbon isotope ratios of vein calcite (– 3 to –5 per mil) are distinctly different from ratios in host schist (–7 to –10 per mil). Elevated vein Cr contents, and isotopically depleted carbon data, are consistent with some degree of equilibration with metavolcanic rocks. It is inferred that metavolcanic rocks of the underlying Aspiring Terrane were a significant source for mineralising fluid and metals. Invincible mineralisation occurred in the latter stages of metamorphism, and is the earliest recognised gold-bearing vein system in the Otago Schist.     

Mineralogy and petrology of a piemontite-bearing schist, western Otago, New Zealand

Abstract. Pink piemontite-spessartine-bearing and grey-green spessartine-bearing manganiferous quartzose schists derived from siliceous pelagites, and green quartzofeldspathic schists, are described from the greenschist facies of the Haast Schist terrane, near Arrow Junction, western Otago. Electron microprobe data are reported for sphene, spessartine-rich garnet, manganoan epidote, piemontite, tourmaline, phengitic muscovite, chlorite, albite, haematite, rutile, manganoan calcite and chalcopyrite. Metamorphism occurred at about 6.4kbar, 400°C. X_co2 was above the quartz-rutile-calcite-sphene buffer (X_co2± 0.02) throughout the recorded metamorphic history of the piemontite schists. It dropped from above to below this critical buffering value in a spessartine-rich schist and it was close to or below the buffering value in the quartzofeldspathic schists. Production of piemontite required high f_O2, believed to be inherited from MnO_x in the parent pelagite. Substantial loss of O₂ (e.g. minimum of 0.19% by weight in one rock) during diagenesis and/or metamorphism is inferred. In the grey-green schists this inhibited piemontite formation. Slight loss of O₂ and Ca²⁺ accompanied minor late-stage replacement of piemontite by second generation spessartine. Observed zoning and mineral replacements indicate rise of temperature, drop in pressure, or invasion by solutions of lower f_O2 and X_CO2 equilibrated with surrounding schists. The detailed chemistry of the minerals studied correlates with available Mn and with bulk-rock (Fe³⁺ x 100)/(Fe²⁺+ Fe³⁺). The oxidation ratio ranges from 24 in average green quartzofeldspathic schist, through 78 in average grey-green manganiferous quartzose schist, to almost 100 in some piemontite-bearing schists. As Fe²⁺ gives way to Fe³⁺, Mg/Fe ratios tend to rise in chlorite, phengite, tourmaline, spessartine, and calcite, Mn increases and Ti decreases in haematite, Mn increases in spessartine and calcite, and Fe increases in rutile. Available divalent cations are depleted relative to Al; chlorite is more aluminous, and phengite more paragonitic than in typical Haast schists.     

The geochemistry of the Dunedin Volcano,East Otago,New Zealand: Rare earth elements

A variety of alkaline lavas from the Dunedin Volcano have been analyzed for the rare earth elements (REE) La-Yb. The compositions analyzed were: basalt-hawaiite-mugearite-benmoreite; basanite, nepheline hawaiite, nepheline trachyandesite and nepheline benmoreite; trachyte; phonolite. The series from basalt to mugearite shows continuous enrichment in the REE, consistent with a crystal fractionation model involving removal of olivine and clinopyroxene. From mugearite to benmoreite there is a depletion in the REE which is explained by the appearance of apatite as a liquidus phase. The chondrite normalized REE patterns for the phonolites are characterized by strong enrichment and fractionation coupled with a sharp depletion in Eu. Removal of plagioclase from benmoreite magma is suggested for the derivation of the phonolites. The series basanite-nepheline hawaiite, and basanite-nepheline hawaiite-nepheline benmoreite appear to be high pH₂O analogues of the series basalt-ben-moreite, with enrichment of the REE being achieved by removal of clinopyroxene, kaersutite and olivine. Compared with other lavas the trachyte has low REE abundances and is characterized by a striking positive Eu anomaly.     

Clinopyroxenes in the tawhiroko tholeiitic dolerite at Moeraki,north-eastern Otago,New Zealand

Clinopyroxenes from various lithologic units in a single tholeiitic dolerite intrusion 50 m thick were analysed with the electron microprobe. Microphenocrysts of augite in the chilled marginal rock have the least scattered CaMgFe ratios, around Ca₃₈Mg₅₀Fe₁₂, and lowest Ti/Al ratios, less than 1/4, of the augites examined; they crystallized prior to emplacement. The augites which crystallized in situ are more Fe-rich and have higher Ti/Al ratios, close to 1/2. Pigeonite started crystallizing later than augite and formed rims to augite crystals. Continuous zoning from augite to subcalcic augite as was previously reported by Benson (1944) for the same dolerite is not observed. Subcaloic ferroaugites, however, link augite and ferropigeonite in the outermost margins of pyroxenes in the later segregations. The small scale differentiation in situ gave rise to globules, veins, and pegmatoids, in which sector-zoning of augite is well developed. The {100} sectors are enriched in MgSiO₃, FeSiO₃, and MnSiO₃ components relative to the {010} and the {110} sectors, and are accordingly depleted in other components. The protosite theory of sector-zoning formation proposed by Nakamura (1973) is further developed and the environment which favours the development of sector-zoning is discussed. The formation of augite rims around quartz-rich xenoliths and the compositional characteristics of the augites concerned are due to local high silica activities. Comments are made concerning some lunar pyroxenes in the light of the present study.     

An occurrence of ardennite in quartz veins in piemontite schist,Western Otago,New Zealand

Summary Ardennite of complex composition: (Mn²⁺ _3.488Ca_0.509Ba_0.002)₌₄(Mg_0.916916 Fe³⁺ _0.165 Mn³⁺ _0.099Cu_0.033Ni_0.009Zn_0.006 Ti_0.008Al_4.764)₌₆(As⁵⁺ _0.823V⁵⁺ _0.022P_0.005B_0.069Al_0.042Si_5.039)₌₆O_21.81(OH)_6.17 occurs in crack-seal quartz veins in quartz-albite-piemontite-spessartine-phengitehematite-chlorite-rutile-tourmaline ± calcite schist of the Haast Schist Group near Arrow Junction, western Otago, New Zealand. The Mn²⁺/Mn³⁺-ratio is sensitive to calculations and to accuracy of analyses. Boron is detected in ardennite for the first time. Other properties include = 1.734(3), = 1.735(3), = 1.751(3), 2V_Z = 30(2)°;a = 8.721(1),b = 5.816(1),c = 18.545(3) Å,V = 940.7(2) ų. Associated mineral phases are spessartine, hematite, piemontite containing 0.7% SrO and 0.06% PbO, and phengite. Later-stage vein minerals comprise chlorite, albite, and manganoan calcite which were deposited under less highly oxidizing conditions. Digenite with minor intergrown covellite occurs in small amount with manganoan calcite and quartz in a cross-cutting late-stage veina chalcopyrite and native copper occur in other late-stage veins. Arsenic and other components of the ardennite and associated minerals are derived from highly oxidized ferromanganese oxide- and hydroxide-bearing siliceous pelagic sediments that formed the protolith for the piemontite schist. The veins formed at a relatively early stage after metamorphism peaked in the chlorite zone of the greenschist facies under conditions that have been estimated at about 4.5 kbar, 390 °C.

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Vorkommen von Ardennit in Quarzgängen aus Piemontit-Schiefern, West-Otago, Neuseeland

Zusammenfassung Ardennit mit der Zusammensetzung (Mn²⁺ _3.488Ca_0.509Ba_0.002)₌₄(Mg_0.916Fe³⁺ _0.165Mn³⁺ _0.099Cu_0.033Ni_0.009Zn_0.006 Ti_0.008Al_4.764)₌₆(As⁵⁺ _0.823V⁵⁺ _0.022P_0.005B_0.069Al_0.042Si_5.039)₌₆O_21.81(OH)_6.17 tritt in Crack-seal-Quarzgängen in Quarz-Albit-Piemontit-Spessartin-Phengit-Hämatit-Chlorit-Rutil-Turmalin ± Calcit-Schiefern der Haast Schiefer-Gruppe nahe der Arrow Junction, West-Otago, Neuseeland, auf. Die Proportionen von Mn²⁺/Mn³⁺ hängen von der Kalkulation und der Genauigkeit der Analyse ab. Bor wird zum ersten Mal im Ardennit bestimmt. Andere Eigenschaften sind: = 1.734(3), = 1.735(3), = 1.751(3), 2Vz = 30(2)°; a = 8.721(1), b = 5.816(1), c = 18.545(3) Å, V = 940.7(2) Å3. Assoziierte Mineralphasen sind Spessartin, Hämatit, Piemontit, der 0.7% SrO und 0.06% PbO enthält und Phengit. Spät gebildete Gangmineralien, wie Chlorit, Albit und Mn-Calcit, sind unter geringer oxidierenden Bedingungen entstanden. Digenit mit etwas Covellin tritt in kleinen Mengen zusammen mit Mn-Calcit und Quartz in einem querschlägigen Gang auf, Chalcopyrit und gediegenes Kupfer kommen in anderen späten Gängen vor. Arsen und andere Komponenten des Ardennites and der assoziierten Minerale können von hochoxidierten, Fe-Mn-Oxid- und Hydroxyd-führenden, Sireichen, pelagischen Sedimenten hergeleitet werden, die das Ausgangsgestein für den Piemontit darstellen. Die Gänge wurden in einem relativ frühen Stadium, nach dem Metamorphosehöhepunkt, innerhalb der Chloritzone der Grünschiefer-Fazies, unter ungefähr 4.5 kbar und 390°C, gebildet.

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With 4 Figures     

Evolution of the blueschist and greenschist facies rocks of Sifnos,Cyclades, Greece

The metamorphism on the island of Sifnos is characterized by the Eocene development of a coherent highpressure blueschist terrane and an early Miocene greenschist facies overprint. This study documents the metamorphic evolution of the blueschist assemblages, still preserved in the northern parts of the island, and their subsequent transformation into greenschists in the central and southern parts.The oxygen isotope geothermometry is based on calibrations for quartz, pyroxenes and magnetite (Matthews et al. 1983a) augmented by revised calibrations for the minerals muscovite ( _Qz–Mu=1.55×10⁶ T _–2), epidote ( _Qz–Ep= 1.56+1.92 _ps)10⁶ T _–2), and rutile ( _Qz–Ru=4.54×10⁶ T _–2).Oxygen isotope analyses of minerals from the Blueschist unit of northern Sifnos give consistent fractionations which are independent of rock type. An average temperature of 455° C was obtained, although the scatter in temperatures deduced from the various geothermometers suggests that equilibration occurs under slightly changing physicochemical conditions. Analyses of minerals and whole rocks shows that pervasive equilibration in the presence of a common metamorphic fluid has not occurred.The minerals and whole rocks of the greenschists of central Sifnos are systematically enriched in ¹⁸O relative to the blueschist assemblages. Chemical data indicate that the greenschist overprint was accompanied by a metasomatic enrichment of Ca²⁺ and CO₂. The petrologic, isotopic and chemical evidence favour a metamorphism governed by the infiltration of ¹⁸O-CO₂ enriched aqueous solutions. It is reasonable to assume that this is connected with the Miocene magmatic activity observed throughout the Cyclades. The marbles separating the Blueschist from the Greenschist unit probably acted as barriers to fluid infiltration into the blueschists and were responsible for their preservation.The pressure of the blueschist metamorphism is estimated at 14±2 kbar, corresponding to a depth of ca. 50 km. The structural style and stratigraphy of Sifnos are suggestive of the subduction of a continental margin sequence. It is clear that the considerable tectonic depression may be associated with continental collision and underthrusting.     

Phase relations of biotite and stilpnomelane in the greenschist facies

Phase relations of biotite and stilpnomelane and associated silicate minerals have been studied in rocks of the greenschist facies, chiefly from Otago, New Zealand and western Vermont, but also from Scotland, Minnesota-Michigan iron range, and northwest Washington. That stilpnomelane in the greenschicht facies crystallizes initially with nearly all iron in the ferrous state is indicated by chemical analyses, high p-T experiments, and phase relationships. Alteration of stilpnomelane after metamorphism not only oxidizes iron but leaches potassium; corrections for both effects must be made in using analyses of brown stilpnomelane in studies of phase relations. Two discontinuous reactions which produce biotite at the biotite isograd have been identified:

1. muscovite+stilpnomelane+actinolite→ biotite+chlorite+epidote
2. chlorite+microcline→ biotite+muscovite. Biotite produced by the first of these reactions has a limited range of variation in Fe/Mg. As grade advances within the biotite zone more magnesian and ferruginous biotites become stable in consequence of the two continuous reactions:
3. muscovite+actinolite+chlorite→ biotite (Mg-rich)+epidote
4. muscovite+stilpnomelane→ biotite (Fe-rich)+chlorite.

Stilpnomelane is stable in muscovite-free rocks throughout the biotite zone, and even up to the grade at which hornblende becomes stable. Phengitic muscovite is stable throughout the biotite zone in New Zealand and thus apparently does not contribute to the formation of biotite until a higher grade is reached.     

The subsolidus segregation of layer-parallel quartz-feldspar veins in greenschist to upper amphibolite facies metasediments

Abstract Layer-parallel (i.e. parallel to foliation or bedding) vein formation in the graywackes and pelites of the Quetico Metasedimentary Belt occurred during synchronous prograde metamorphism and regional (D₂) compression. In a traverse across metasediments which change in metamorphic grade from greenschist to upper amphibolite (migmatite) facies, layer-parallel veins show the following trends: (1) an increase in thickness and internal complexity, the latter due to successive boudinage; (2) low-grade veins are parallel to planes of anisotropy due to the original sedimentary fabric of the host rocks, but at higher grades other sites are also used and (3) a systematic increase in plagioclase/quartz ratio in the veins towards higher grade, adjacent mafic selvedges first exhibit quartz depletion then, in the amphibolite facies, plagioclase depletion. Mineralogical zoning is often preserved in a single vein, older parts are more quartz-rich than younger. Mass balance calculations and whole-rock geochemistry based on veins, mafic selvedges and country rock are consistent with a closedsystem subsolidus segregation origin. The layerparallel veins are syntectonic, and migration of the mobile components required to form their mineralogy is a stress-induced mass transfer. The source of these components appears to be dominantly pressure solution of the same minerals in the host rocks, although metamorphic reactions may also have contributed. Veins nucleated first at those sites where initial sedimentary heterogeneites, such as fine-scale graded bedding, provided gradients of normal stress across grain boundaries, and hence of chemical potential, necessary to drive the subsolidus segregation process. The earliest veins are thus parallel to bedding. Later, nucleation of the veins could also occur along more randomly distributed sites within the metasediments, and these veins grew parallel to the schistosity rather than bedding, if the two were distinct. Once formed, the veins themselves, which are more competent than the surrounding rock, provide the stress heterogeneity required for their further growth. The increasing plagioclase/quartz ratio in the veins may be due to a temperature dependent increase in plagioclase component mobility relative to quartz. Alternatively, the increasing transfer distances for silica, resulting from prior quartz depletion in the inner parts of the mafic selvedge, may increase the relative mobility of plagioclase component.     

Oxidation and microprobe-induced potassium mobility in iron-bearing phyllosilicates from the Otago schists,New Zealand

Biotite, chlorite and stilpnomelane have undergone post-metamorphic oxidation in situ in the Otago schist, due to surficial weathering. The oxidation results in changes in the chemistry of these minerals. Oxidation of biotite and stilpnomelane is accompanied by loss of potassium, and stilpnomelane with its full metamorphic potassium content is probably rare. analytical work such as KAr dating which depends critically on K₂O contents of biotite and stilpnomelane should therefore proceed with due caution. Potassium in stilpnomelane is very mobile under the microprobe beam, and only approximate K₂O analyses may be obtained.     

Prehnite–pumpellyite to greenschist facies transition, Smartville Complex, near Auburn, California

The Smartville Complex is a late Jurassic, rifted volcanic arc in the northern Sierra Nevada, California. Near Auburn, California, it consists of a lower volcanic unit, dominated by basaltic flows, and an upper volcanic unit of andesitic volcaniclastic rocks, both of which have been intruded by dykes and irregular bodies of diabase. These rocks contain relict igneous minerals, and the metamorphic minerals albite, chlorite, quartz, pumpellyite, prehnite, epidote, amphibole, titanite, garnet, biotite, K-feldspar, white mica, calcite, and sulphide and oxide minerals.
Prehnite–pumpellyite (PrP), prehnite–actinolite (PrA), and greenschist (GS) zones have been identified. The pumpellyite-out isograd separates the PrP and PrA zones, and the prehnite-out isograd separates the PrA and GS zones. The minerals Ab + Qtz + Mt + Tn are common to most assemblages in all three zones. The MgO/(MgO + FeO) ratio of the effective bulk composition has an important and systematic effect on the observed mineral assemblages in the PrP zone. Prehnite-bearing assemblages contain the additional minerals, Pmp + Amp + Ep + Chl in MgO-rich rocks, and either Pmp + Ep + Chl or Amp + Ep + Chl in less magnesian rocks. Subcalcic to calcic amphibole is common in the PrP zone. The mineral assemblage Prh + Act + Ep + Chl, without Pmp, characterizes the PrA zone, and the mineral assemblage Act + Ep + Chl, without Prh or Pmp, characterizes the GS zone. The disappearance of pumpellyite and prehnite occurred by continuous reactions.
The sequence of mineral assemblages was produced by burial metamorphism at P–T conditions of 300° 50°C at approximately 2.5 ± 0.5 kbar. During metamorphism, the composition of the fluid phase was nearly 100% H₂O and the oxygen fugacity was between the hematite–magnetite and quartz–fayalite–magnetite buffers.     

Reactions leading to the formation and breakdown of stilpnomelane in the Otago Schist, New Zealand

Semi‐pelitic rocks ranging in grade from the prehnite–pumpellyite to the greenschist facies from south‐eastern Otago, New Zealand, have been investigated in order to evaluate the reactions leading to formation and breakdown of stilpnomelane. Detrital grains of mica and chlorite along with fine‐grained authigenic illite and chlorite occur in lower‐grade rocks with compactional fabric parallel to bedding. At higher grades, detrital grains have undergone dissolution, and metamorphic phyllosilicates have crystallized with preferred orientation (sub)parallel to bedding, leading to slaty cleavage. Stilpnomelane is found in metapelites of the pumpellyite–actinolite facies and the chlorite zone of the greenschist facies, but only rarely in the biotite zone of the greenschist facies. Illite or phengite is ubiquitous, whereas chlorite occurs only rarely with stilpnomelane upgrade of the pumpellyite‐out isograd. Chemical and textural relationships suggest that stilpnomelane formed from chlorite, phengite, quartz, K‐feldspar and iron oxides. Stilpnomelane was produced by grain‐boundary replacement of chlorite and by precipitation from solution, overprinting earlier textures. Some relict 14 Å chlorite layers are observed by TEM to be in the process of transforming to 12 Å stilpnomelane layers. The AEM analyses show that Fe is strongly partitioned over Mg into stilpnomelane relative to chlorite (K_D≈2.5) and into chlorite relative to phengite (K_D≈1.9). Modified A′FM diagrams, projected from the measured phengite composition rather than from ideal KAl₃Si₃O₁₀(OH)₂, are used to elucidate reactions among chlorite, stilpnomelane, phengite and biotite. In addition to pressure, temperature and bulk rock composition, the stilpnomelane‐in isograd is controlled by variations in K, Fe³⁺/Fe²⁺, O/OH and H₂O contents, and the locus of the isograd is expected to vary in rocks of different oxidation states and permeabilities. Biotite, quartz and less phengitic muscovite form from stilpnomelane, chlorite and phengite in the biotite zone. Projection of bulk rock compositions from phengite, NaAlO₂, SiO₂ and H₂O reveals that they lie close to the polyhedra defined by the A′FM minerals and albite. Other extended A′FM diagrams, such as one projected from phengite, NaAlO₂, CaAl₂O₄, SiO₂ and H₂O, may prove useful in the evaluation of other low‐grade assemblages.     

A New Fossil Termite(Isoptera,Stolotermitidae,Stolotermes)from the Early Miocene of Otago,New Zealand

<正>The forewing of a termite from Early Miocene lake sediments in Otago,southern New Zealand is figured and described.It exhibits the generic characters of the damp-wood termite Stolotermes Hagen,but differs from forewings of the known species in size and venation pattern and is described as Stolotermes kupe sp.nov.S.kupe represents the first confident record of fossil Stolotermitidae and extends the fossil record of the family back to the Early Miocene.It also is the first direct evidence of fossil Isoptera from New Zealand,though silicified termite faecal pellets,referable to Kalotermes brauni,have been previously described.S.kupe indicates that Stolotermitidae has been present in the Australasian region since at least the Early Miocene.     

Tourism and resource development conflicts on the Kawarau and Shotover Rivers,Otago, New Zealand

The Kawarau and Shotover Rivers are in the heart of Southern New Zealand's premier tourist region, focused upon Queenstown in Central Otago. Over the last fifteen years they have become important as the venue for a variety of adventure activities, principally jet boating and white water rafting. These have grown rapidly to become a major part of the regional tourism product. During the same time period, proposals for hydro electric power development on the Kawarau threatened to eliminate white water rafting and severely modify jet boating; during the last five years a revival of the region's gold mining industry, which was founded in the 1860s, has threatened rafting on the Shotover River. This paper examines the ways in which these conflicts were assessed and managed, and points to a new threat, namely that of overcrowding.     

Structural boundaries and biotite and garnet 'isograds' in the Otago and Alpine Schists, New Zealand

The Otago and Alpine Schist belts of southern New Zealand have traditionally been treated as structurally continuous metamorphic belts with minor modification by brittle faulting. Mapping of biotite and garnet isograds has been hindered by rock types unfavourable for index mineral growth. Closer examination of well-exposed boundaries between metamorphic zones shows that they juxtapose rocks of different type and structural history. Apparent structural continuity across these zones is due to development of a locally pervasive boundary-parallel foliation on both sides of the boundary, in a broad boundary zone (up to 2  km wide). This feature has implications for mapping and metamorphic petrology in other metamorphic belts, where structural continuity has traditionally been assumed. True metamorphic isograds may be rare, and metamorphic zones may more commonly represent structural slices of complex, tectonically disrupted metamorphic piles.     

Earthflow occurrence during high intensity rainfall in Eastern Otago (New Zealand)

The characteristics and effects of an unusually heavy rainstorm causing landsliding, are discussed. The storm produced up to 8 inches of rain in 48 h during a month, which, over the last 20 years, has had a mean of 2.03 inches. These weather conditions triggered numerous landslides in an area which is believed to have become progressively unstable over the last one hundred years.

A theory for the progressive development of unstable land in the locality is outlined. It centres around the change of soil properties induced by a removal of the indigenous forest.

The study lists the relevant morphological and geological characteristics of a typical earthflow and gives an account of the observed processes of earthflow occurrence.     

Reaction softening by dissolution–precipitation creep in a retrograde greenschist facies ductile shear zone,New Hampshire,USA

We describe strain localization by a mixed process of reaction and microstructural softening in a lower greenschist facies ductile fault zone that transposes and replaces middle to upper amphibolite facies fabrics and mineral assemblages in the host schist of the Littleton Formation near Claremont, New Hampshire. Here, Na‐poor muscovite and chlorite progressively replace first staurolite, then garnet, and finally biotite porphyroblasts as the core of the fault zone is approached. Across the transect, higher grade fabric‐forming Na‐rich muscovite is also progressively replaced by fabric‐forming Na‐poor muscovite. The mineralogy of the new phyllonitic fault‐rock produced is dominated by Na‐poor muscovite and chlorite together with late albite porphyroblasts. The replacement of the amphibolite facies porphyroblasts by muscovite and chlorite is pseudomorphic in some samples and shows that the chemical metastability of the porphyroblasts is sufficient to drive replacement. In contrast, element mapping shows that fabric‐forming Na‐rich muscovite is selectively replaced at high‐strain microstructural sites, indicating that strain energy played an important role in activating the dissolution of the compositionally metastable muscovite. The replacement of strong, high‐grade porphyroblasts by weaker Na‐poor muscovite and chlorite constitutes reaction softening. The crystallization of parallel and contiguous mica in the retrograde foliation at the expense of the earlier and locally crenulated Na‐rich muscovite‐defined foliation destroys not only the metastable high‐grade mineralogy, but also its stronger geometry. This process constitutes both reaction and microstructural softening. The deformation mechanism here was thus one of dissolution–precipitation creep, activated at considerably lower stresses than might be predicted in quartzofeldspathic rocks at the same lower greenschist facies conditions.