The early metamorphic history of the Haast Schists and related rocks of New Zealand

Rare but widespread relics of sodic amphibole occur in metabasites and metacherts of the Haast Schists and related Caples Terrane rocks. Present main-stage metamorphic assemblages are frequently chemically equivalent to earlier sodic amphibole bearing assemblages, indicating that these rocks underwent an earlier, higher P/Tmetamorphism prior to formation of the present pumpellyite-actinolite and greenschist facies assemblages. The earlier assemblages were stable during and after early isoclinal folding, but were replaced by the present moderate P/T assemblages prior to the last major fabric-forming deformation. The change in conditions was due to thermal relaxation, probably accompanied by uplift and erosion, and peak metamorphic temperatures were about 350–370° C in the pumpellyite-actinolite zone of the Caples Terrane and near 390° C in the greenschist facies chlorite zone near Queenstown. According to Henley (1975) these greenschist facies rocks attained a pressure of at least 6.4±0.4 kb during their history, but a pressure of 4.6±0.6 kb has been estimated for a chlorite zone rock from Middlemarch, and so the 6.4 kb estimate probably refers to the maximum pressure attained during the earlier, higher P/T metamorphism. Similar changes in metamorphic facies series with time occur in some older and more complex metamorphic belts such as the Caledonides, and this study suggests that it may be possible to interpret particular elements in the metamorphic development of such belts in terms of specific circum-Pacific analogues.     

Regional hydrogeochemical patterns in ground water of Northwestern Ohio and their relation to Mississippi valley—type mineral occurrences

A cluster of minor Mississippi Valley-type deposits occurs in northwestern Ohio. The district, which forms a northeasterly trending belt that cuts across the Findlay Arch, extends from the Indiana border to the Lake Erie Islands. The minerals of the deposits — chiefly celestite, fluorite and sphalerite with lesser amounts of barite and galena — show variation in both geographic and stratigraphic distribution. Dolomites of Middle Silurian to Middle Devonian age, which are the host rocks, also form an important aquifer system. The deposits are of interest because they might be indicators of economic mineralization at depth.Through a reconnaissance study, one-hundred ground-water samples from shallow wells (less than 50 m deep) were collected across an area of approximately 19 000 km². Recharge takes place in the southern part of the area while ground-water flow is northward towards Lake Erie. The majority of the samples are high in sulfate with the source being evaporites within the carbonate sequence. The remainder of the water samples are rich in bicarbonate. Trend surface maps for the major constituents indicate that the ground-water chemistry for the region is established chiefly by the lithology and the flow system. Trend surface maps for F⁻, Sr and Ba reflect the geographic distribution of the minerals in the deposits. Correlations are weakened, however, due to the influence of geochemical barriers such as SO₄²⁻ on Ba and Sr, and Ca on F⁻. The map for Pb follows the trends of the major constituents instead of the mineralization.In a detailed study across northwestern Sandusky County, which lies near the center of the district, 46 samples were collected in an area of 78 km². Trend surface maps for Ca, Mg, SO₄²⁻ and total dissolved solids reflect the chemistry of the bedrock and display concentrations that increase along the local flow path. Maps for F⁻, Sr and Ba correlate with mineralization in the vicinity, the first of these displaying a local trend and the last two correlating with regional trends.     

Interdiffusion of H2O and CO2 in metamorphic fluids at ∼490 to 690°C and 1 GPa

Interdiffusion coefficients have been determined for H₂O-CO₂ mixtures by quantifying the flux of CO₂ between two fluid-filled chambers in a specially designed piston-cylinder cell. The two chambers, which are maintained at 1.0 GPa and at temperatures differing by ∼100°C, each contain the X_CO2-buffering assemblage calcite + quartz + wollastonite, in H₂O. The positive dependence of X_CO2 on temperature results in a down-temperature, steady-state flux of CO₂ through a capillary tube that connects the two chambers. This flux drives the wollastonite = calcite + quartz equilibrium to the right in the cooler chamber, producing a measurable amount of calcite that is directly related to CO₂-H₂O interdiffusion rates. Diffusivities calculated from seven experiments range from 1.0 × 10⁻⁸ to 6.1 × 10⁻⁸ m²/s for mean capillary temperatures between ∼490 and 690°C. The data set can be approximated by an Arrhenius-type relation:

     

Geography,planning and the law: a coastal perspective

This paper examines how legal structures interact with land‐use decisions in the coastal zone. The emphasis is on NSW where there has been a steady evolution of legislative and other measures to regulate how the coast is to be planned and managed. These measures arise from a long history of individual, corporate, local government and State agency actions directed more at private benefit than at protecting and conserving environmental values for the public good. Alienation of foreshores, restrictions on access, buildings located in hazardous areas, canals exposing soils rich in acids, and pollution of waterways are examples of degradation on this coast. Yet much remains to be protected. Expansion of coastal national parks over the past decade has helped. But new planning controls have been introduced to support the NSW Coastal Policy (1997 NSW Coastal Policy (1997) A sustainable future for the New South Wales coast NSW Government, Sydney  [Google Scholar]). In essence, there is evidence that the State government seeks to implement environmentally sustainable development principles to ensure that as the population continues to grow, decisions on future land uses will reflect the functioning of ecosystems and the dynamics of coastal and catchment geomorphology and hydrology. Pressures from individuals and corporations exercising traditional property rights need to be managed within a statutory framework that facilitates sustainability of coastal environmental values cherished by so many.     

Wetter or colder during the Last Glacial Maximum? Revisiting the pluvial lake question in southwestern North America

Well-preserved shorelines in Estancia basin and a relatively simple hydrologic setting have prompted several inquiries into the basin's hydrologic balance for the purpose of estimating regional precipitation during the late Pleistocene. Estimates have ranged from 86% to 150% of modern, the disparity largely the result of assumptions about past temperatures. In this study, we use an array of models for surface-water runoff, groundwater flow, and lake energy balance to examine previously proposed scenarios for late Pleistocene climate. Constraints imposed by geologic evidence of past lake levels indicate that precipitation for the Last Glacial Maximum (LGM) may have doubled relative to modern values during brief episodes of colder and wetter climate and that annual runoff was as much as 15% of annual precipitation during these episodes.     

Uptake and depuration of PAHs and chlorinated pesticides by semi-permeable membrane devices (SPMDs) and green-lipped mussels (Perna viridis)

Semi-batch seawater experiments were conducted to follow the uptake and release of selected PAHs (anthracene, fluorathene, pyrene and B[a]P) and organochlorine pesticides (α-HCH, aldrin, dieldrin, p,p′-DDT) in semi-permeable membrane devices (SPMDs) and green-lipped mussels (Perna viridis). Mathematical models were applied to describe the uptake and elimination curves of the contaminants for SPMDs, and kinetic parameters, such as uptake rate constants, and equilibrium triolein/water partitioning coefficients were calculated. SPMD data showed a good fit to estimate rate constant and partition coefficient equations, but only those contaminants which partitioned mainly in the dissolved phase (α-HCH and dieldrin) were well explained for mussels. Poor conformity of the other contaminants indicated mussels uptake by routes other than diffusion, such as ingestion of algae. An apparent equilibrium state was only noted for α-HCH in mussels. Aldrin was not detected in mussels in the first few days of exposure, indicating potential metabolism of this compound. B[a]P was not detected in the triolein of SPMDs, which suggests that the membrane may act as a reservoir. Loss of spiked B[a]P from the triolein was evident in a depuration experiment, which may indicate transfer to the membrane. Rate constants for mussels were higher than those for SPMDs, but the reverse was true for partition coefficients. Overall, mussels and SPMDs had similar uptake rates for all compounds in this study, excluding p,p′-DDT and dieldrin. Contaminant elimination took place more rapidly in mussels, implying that SPMDs are better candidates for detecting episodic discharge of organic contaminants.