Petrogenesis of the Greenhills Complex,Southland, New Zealand: magmatic differentiation and cumulate formation at the roots of a Permian island-arc volcano

A Permian (~265 Ma) intrusive complex which formed as a magmatic feeder reservoir to an immature island-arc volcano is fortuitously exposed in southern New Zealand. Known as the Greenhills Complex, this intrusion was emplaced at shallow crustal levels and consists of two layered bodies which were later intruded by a variety of dykes. Cumulates, which include dunite, olivine clinopyroxenite, olivine gabbro, and hornblende gabbro-norite, are related products of parent-magma fractionation. Both primary (magmatic) and secondary platinum-group minerals occur within dunite at one locality. Using the composition of cumulus minerals, mafic dykes and melt inclusions, we have determined that the parent magmas of the complex were hydrous, low-K island-arc tholeiites of ankaramitic affinities. Progressive magmatic differentiation of this parent magma generated fractionated melt of high-alumina basalt composition which is now preserved only as dykes which cut the Complex. Field evidence and cumulus mineral profiles reveal that the magma chambers experienced turbulent magmatic conditions during cumulate-rock formation. Recharge of the chambers by primitive magma is likely to have coincided with eruption of residual melt at the surface. Similar processes are inferred to account for volcanic-rock compositions in other parts of this arc terrane and in modern island-arc systems.     

The consumption of space: Land, capital and place in the New Zealand wine industry

Geographers have developed a keen interest in the social production of space - in the way meanings and values are ascribed to places as a result of changing social, cultural and political processes. There is a need to explore this approach further, seeing how social and economic values of places are inter-related and how these values are constructed in often deliberate and concerted ways. There is also a need to explore how such values are consumed: how the values in place are traded, appropriated and redistributed, both through the products of places and in land markets. This paper examines the New Zealand wine industry where certain wine regions have been identified and developed in ways which attempt to emphasise their distinctiveness in terms of wine quality and thus enhance the value of the wine produced. Different strategies have been employed in this process of place construction and this reflects the differential role of capital, striving on the one hand to increase the price and marketability of the products of distinctive places but, on the other, careful not to over-inflate land values and thus restrict further expansion. The paper suggests that the issue of consumption of space, involving a complex relationship amongst land, capital and place, is worthy of further exploration.     

Got green? addressing environmental justice in park provision

We present a pragmatic approach to assist planners in addressing racial inequities in park access. Utilizing the Los Angeles metropolitan region as an example, we used Thiessen polygons to delineate a service area for each park, and described potential park congestion or ‘pressure’ in each park service area. Results show that Latinos, African-Americans, and low-income groups in general were likely to live close to parks with higher potential park congestion. On the other hand, predominantly White, high-income areas were typically located close to parks with lower potential park congestion levels. The park service area analysis presented here facilitates the identification of areas with greater park need and provides a pragmatic way to redress existing disparities in park access. Built into a set of web-based decision support tools, the approach fosters greater community participation and empowers local stakeholders in the process of park provision.     

Calibration of the carbonate ‘clumped isotope’ paleothermometer for otoliths

Paleothermometry is an essential tool for understanding past changes in climate. The ‘carbonate clumped isotope thermometer’ is a temperature proxy related to ordering of ¹³C and ¹⁸O in the carbonate lattice (based on measurements of ¹³C¹⁸O¹⁶O in CO₂ produced by acid digestion of carbonate). This thermometer has been previously calibrated for inorganic calcite and aragonitic corals [Ghosh P., Adkins J., Affek H., Balta B., Guo W. F., Schauble E. A., Schrag D., and Eiler J. M. (2006) C-13-O-18 bonds in carbonate minerals: a new kind of paleothermometer. Geochim. Cosmochim. Acta70 (6), 1439-1456]. Here we determine the relationship between growth temperatures of aragonitic fish otoliths and abundances of ¹³C¹⁸O¹⁶O produced by acid digestion of those otoliths. Our calibration is based on analyses of otoliths from six species from four genera of modern fish sampled from a latitudinal transect of the Atlantic Ocean between 54° S and 65° N, plus one species from the tropical western Pacific. The temperatures at which fish otoliths precipitated were estimated by the mean temperature in the waters in which they lived, averaged over their estimated lifetimes. Estimated growth temperatures of our samples vary between 2 and 25 °C. Our results show that the abundance of ¹³C¹⁸O¹⁶O in CO₂ produced by acid digestion of fish otolith aragonite is a function of growth temperature, following the relationship: , where Δ₄₇ is the enrichment, in per mil, of ¹³C¹⁸O¹⁶O in CO₂ relative to the amount expected for a stochastic (random) distribution of isotopes among all CO₂ isotopologues, and T is the temperature in Kelvin. This relationship closely approaches that previously documented for inorganic calcite and aragonitic coral (Ghosh et al., 2006).     

Initial Al/Al in carbonaceous-chondrite chondrules: too little Al to melt asteroids

We report ²⁶Mg excesses correlated with Al/Mg ratios in five chondrules from the primitive CO3.0 chondrite Yamato 81020 that yield a mean initial ²⁶Al/²⁷Al ratio of only (3.8 ± 0.7) × 10⁻⁶, about half that of ordinary chondrite (OC) chondrules. Even if asteroids formed immediately after chondrule formation, this ratio and the mean Al content of CO chondrites is only capable of raising the temperature of a well-insulated CO asteroid to 940 K, which is more than 560 K too low to produce differentiation. The same ratio combined with the higher Al content of CV chondrites results in a CV asteroid temperature of 1100 K. We calculate that the mean initial ²⁶Al/²⁷Al ratio of about 7.4 × 10⁻⁶ found in LL chondrules is only able to produce small amounts of melting, too little to produce differentiation. These results cast serious doubt on the viability of ²⁶Al as the heat source responsible for asteroid differentiation. Inclusion of ⁶⁰Fe raises temperatures about 160 K, but this increment is not enough to cause differentiation, even of an LL-chondrite asteroid.     

Leucoxene fish as a micro-kinematic indicator

Asymmetric aggregates of fine-grained leucoxene and quartz are reported from siliceous L-S tectonites deformed by progressive simple shear. The leucoxene fish, morphologically similar to mica fish, consistently yield shear senses in agreement with other kinematic criteria. We interpret the leucoxene as a pre- or early syntectonic alteration product of detrital heavy-minerals in a siliciclastic protolith. The leucoxene fish behave as passive markers, and they record kinematics by modification of pre-existing aggregates rather than syndeformational mineral growth. For siliceous metasedimentary rocks otherwise lacking in micro-kinematic indicators, leucoxene fish may provide an alternative to quartz c-axis analysis.     

Heightened sensitivity of a poorly buffered high arctic lake to late-Holocene climatic change

A diatom-based paleolimnological investigation was conducted on late Holocene sediments from a poorly buffered lake, informally named “Rock Basin Lake”, on Ellesmere Island, Arctic Canada. The fossil diatom record is unlike any other obtained thus far from high arctic regions, exhibiting dynamic assemblage shifts over the entire 3300 yr sedimentary record. Multiple proxies (i.e., diatoms, pH reconstructions, biogenic silica, C/N ratios, total organic carbon) appear to sensitively track rapid limnological changes, which are associated with distinct climate intervals as inferred from other regional proxy records. The highly responsive nature of the diatom assemblages in Rock Basin Lake, relative to those recorded from nearby alkaline sites, appears to be related to this lake's limited ability to buffer changes in pH. The dynamic species responses suggest that the diatoms in Rock Basin Lake are faithfully tracking climatic changes, and that low-alkalinity lakes may provide the most sensitive diatom-based paleolimnological records from high arctic regions.     

The Record of an Extreme Flood in the Sediments of Montane Lillooet Lake, British Columbia: Implications for Paleoenvironmental Assessment

Severe rainfall in mid October, 2003 produced the largest floods in almost a century of record on rivers in the Cordillera of southwestern British Columbia. Sediment deposited in Lillooet Lake as a result of this event is clearly distinguished by stratigraphy, colour, texture, magnetic properties, and organic content. Each of these physical properties is related to the lacustrine processes, especially turbid underflow, that distributed the sediment through the lake. The flood, which lasted less than a week, delivered 8–12 times the amount of sediment that accumulates in most entire years in the deepest, central parts of the lake. Recognition of events of this type in the stratigraphic record offers a means of assessing the changing nature of extreme hydroclimatic events, and their relation to more ubiquitous, lower-energy processes.     

Tracking recent recovery from eutrophication in a high arctic lake (Meretta Lake, Cornwallis Island, Nunavut, Canada) using fossil diatom assemblages

Meretta Lake (Resolute Bay, Cornwallis Island, Nunavut, Canada) is a high arctic lake that received raw sewage for almost 50 years from the Canadian Department of Transport Base. The lake was sampled from 1968–72 during the International Biological Programme, as part of the Char Lake Project. As the number of users at the Transport Base declined throughout the 1990s, so too did the lake's nutrient levels, and Meretta Lake is now classified as oligotrophic. A previous diatom-based paleolimnological study revealed marked species assemblage shifts coincident with sewage inputs beginning in the late 1940s; however, because the core was taken at a time when nutrient levels were still relatively high (i.e., 1993), the diatom record did not yet track any signs of recovery. In this present study, we examined fossil diatom assemblages from a sediment core taken in 2001. Our results indicate a shift to the pre-impact diatom assemblages in the most recent sediments, indicating that the paleolimnological record is tracking the decreased nutrient inputs to this high arctic lake, and confirms that no significant lags exist in these largely ice-covered lakes.