Progressive development of quartz fabrics in a shear zone from Monte Mucrone,Sesia-Lanzo Zone,Italian Alps

Quartz c-axis fabrics are described from a shear zone in a jadeite — garnet bearing meta-granite from Monte Mucrone, in the Sesia-Lanzo Zone of the western Italian Alps. Quartz blebs in the meta-granitoid are progressively deformed into cigar shaped lenses, and are recrystallized. Fabrics measured from individual blebs show considerable variation resulting from an initial orientation effect, and are not very enlightening. A synoptic diagram, however, has a pole-free area which can be correlated with the extension direction, and an asymmetry which is consistent with the known sense of shear operating in the zone.Although the technique of preparing synoptic diagrams is rather painstaking, its use is advocated for complex fabric situations, as it may allow partial removal of problems associated with non-random initial orientation distributions.     

Migration of hydrothermal systems in an evolving collisional orogen, New Zealand

The Pacific–Australian tectonic plate boundary through the South Island of New Zealand consists of the transpressional Southern Alps mountain belt and the transcurrent Marlborough Fault System, both of which have active tectonically driven hydrothermal systems, with topographically driven meteoric incursion and warm springs. The Southern Alps hydrothermal system is relatively diffuse, with little or no fault control, and is channelled through scattered extensional sites beneath the mountains, where gold mineralisation is occurring locally. The hydrothermal activity along the Marlborough Fault System is controlled by the principal faults in well-defined valleys separated by narrow high ridges. Lateral evolution of Marlborough fault strands southwestwards into the Southern Alps has caused diversion of diffuse Southern Alps hydrothermal activity into the structural superimposition zone, where fluid flow is increasingly being controlled by faults. This hydrothermal diversion was accompanied by major topographic reorientation and river drainage reversal in the late Quaternary. Vein swarms now exposed in the remnants of the Southern Alps north of the superimposition zone formed at shallow levels, with some evidence for fluid boiling, from a mixture of meteoric and deep-sourced fluid. These veins, some of which contain gold, are part of an abandoned <1 million-year-old hydrothermal zone beneath the fossil topographic divide of the Southern Alps that has now been dismembered by lateral incursion of the Marlborough fault strands. Observations on this active plate boundary provide some insights into processes that controlled orogenic gold mineralisation in ancient belts, particularly with respect to relationships between hydrothermal fluid flow, structure and topography.     

Towards a climate event stratigraphy for New Zealand over the past 30 000 years (NZ‐INTIMATE project)

It is widely recognised that the acquisition of high‐resolution palaeoclimate records from southern mid‐latitude sites is essential for establishing a coherent picture of inter‐hemispheric climate change and for better understanding of the role of Antarctic climate dynamics in the global climate system. New Zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the Southern Hemisphere westerly circulation zone, a critical transition zone between subtropical and Antarctic influences. New Zealand has mountainous axial ranges that amplify the climate signals and, consequently, the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions. Since 1995, INTIMATE has, through a series of international workshops, sought ways to improve procedures for establishing the precise ages of climate events, and to correlate them with high precision, for the last 30 000 calendar years. The NZ‐INTIMATE project commenced in late 2003, and has involved virtually the entire New Zealand palaeoclimate community. Its aim is to develop an event stratigraphy for the New Zealand region over the past 30 000 years, and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from Northern Hemisphere records (e.g. Last Glacial Maximum (LGM), Termination I, Younger Dryas). An initial outcome of NZ‐INTIMATE has been the identification of a series of well‐dated, high‐resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal. yr BP to the present day. High‐resolution records for the last glacial coldest period (LGCP) (including the LGM sensu stricto) and last glacial–interglacial transition (LGIT) from Auckland maars, Kaipo and Otamangakau wetlands on eastern and central North Island, marine core MD97‐2121 east of southern North Island, speleothems on northwest South Island, Okarito wetland on southwestern South Island, are presented. Discontinuous (fragmentary) records comprising compilations of glacial sequences, fluvial sequences, loess accumulation, and aeolian quartz accumulation in an andesitic terrain are described. Comparisons with ice‐core records from Antarctica (EPICA Dome C) and Greenland (GISP2) are discussed. A major advantage immediately evident from these records apart from the speleothem record, is that they are linked precisely by one or more tephra layers. Based on these New Zealand terrestrial and marine records, a reasonably coherent, regionally applicable, sequence of climatically linked stratigraphic events over the past 30 000 cal. yr is emerging. Three major climate events are recognised: (1) LGCP beginning at ca. 28 000 cal. yr BP, ending at Termination I, ca. 18 000 cal. yr BP, and including a warmer and more variable phase between ca. 27 000 and 21 000 cal. yr BP, (2) LGIT between ca. 18 000 and 11 600 cal. yr BP, including a Lateglacial warm period from ca. 14 800 to 13 500 cal. yr BP and a Lateglacial climate reversal between ca. 13 500 and 11 600 cal. yr BP, and (3) Holocene interglacial conditions, with two phases of greatest warmth between ca. 11 600 and 10 800 cal. yr BP and from ca. 6 800 to 6 500 cal. yr BP. Some key boundaries coincide with volcanic tephras. Copyright © 2007 John Wiley & Sons, Ltd.     

High‐Precision,High‐Accuracy Oxygen Isotope Measurements of Zircon Reference Materials with the SHRIMP‐SI

Analytical protocols for SHRIMP‐SI oxygen isotope analysis (δ¹⁸O) of a suite of zircon reference materials (RMs) are presented. Data reduction involved a robust estimate of uncertainties associated with the individual spot as well as for groups where the spot data are combined. The repeatability of δ¹⁸O measurements is dependent on both the analytical conditions and the choice of the primary reference material. Under optimised conditions, repeatability was often better than 0.4‰ (2s) allowing sample uncertainties to be obtained to better than 0.2‰ (at 95% confidence limit). Single spot uncertainty combined the within‐spot precision with the scatter associated with repeated measurements of the primary zircon reference material during a measurement session. The uncertainty for individual spots measured under optimised conditions was between 0.3 and 0.4‰ (at 95% confidence). The analytical protocols described were used to assess a variety of zircon RMs that have been used for geochronology and for which laser fluorination oxygen isotope data are available (Temora 2, FC1, R33, QGNG and Ple?ovice), as well as zircons that have been used as RMs for trace element or other types of determination (Mud Tank, Monastery, 91500, AS57, AS3, KIM‐5, OG1, SL13, CZ3 and several other Sri Lankan zircons). Repeated analyses over nine sessions and seven different mounts show agreement within analytical uncertainty for Temora 2, FC1, R33, QGNG, Ple?ovice and 91500, when normalised to Mud Tank. For existing ion microprobe mounts with these materials, an appropriate δ¹⁸O can be determined. However, care should be taken when using zircons from the Duluth Complex (i.e., FC1, AS57 and AS3) as reference materials as our data indicated an excess scatter on δ¹⁸O values associated with low‐U zircon grains.     

Great Victoria Desert: Development and sand provenance

Sands of the Great Victoria Desert, south‐central Australia, can be divided into three main groups on the basis of their physical and chemical characteristics (colour, grainsize parameters, mineralogy of heavy‐mineral suites, quartz oxygen isotopic composition, zircon U–Pb ages). The groups occupy the western, central and eastern Great Victoria Desert respectively, boundaries between them corresponding approximately to changes in the underlying rocks associated with the Yilgarn Craton to Officer Basin to Arckaringa Basin. Several lines of evidence suggest derivation of the sands mainly from local bedrock with very little subsequent aeolian transport. Ultimate protosources for the sands, each in order of importance, are: western Great Victoria Desert—Yilgarn Craton, Albany‐Fraser Orogen, Musgrave Complex; central Great Victoria Desert—Musgrave Complex; eastern Great Victoria Desert—Gawler and Curnamona Blocks, Adelaide Geosyncline, Musgrave Complex. Sediment from the Adelaide Geosyncline includes in addition an ‘exotic’ component from Palaeozoic sedimentary rocks probably derived mainly from Antarctica. Sediment transport of several hundred kilometres from these protosources to the sedimentary basins was dominantly by fluvial, not aeolian, means. Post‐Tertiary aeolian transport or reworking has been minimal, serving only to shape sand eroded from underlying sedimentary rocks or residual products of local basement weathering into the current dunes.     

Deformation history of the Naraku Batholith,Mt Isa Inlier,Australia: Implications for pluton ages and geometries from structural study of the Dipvale Granodiorite and Levian Granite

Plutons of the Naraku Batholith were emplaced into Proterozoic metasediments of the northern portion of the Eastern Fold Belt of the Mt Isa Inlier during two intrusive episodes approximately 200 million years apart. Structural relationships and geochronological data suggest that the older plutons (ca 1750 Ma) are contemporaneous with granites of the Wonga Batholith to the west. The Dipvale Granodiorite and the Levian Granite represent these older intrusive phases of the Naraku Batholith, and both contain an intense tectonic foliation, S₁, which is interpreted to have formed during the north‐south shortening associated with D₁ of the Isan Orogeny. The geometry of S₁ form surfaces at the southern end of the Dipvale Granodiorite, and of the previously unrecognised sheeted contact, defines a macroscopic, steeply south‐southwest‐plunging antiform, which was produced by the regional D₂ of the Isan Orogeny. S₁ form surfaces in the Levian Granite define open F₂ folds with wavelengths of several hundred metres. The structural age of emplacement of the Dipvale Granodiorite and the Levian Granite is interpreted to be pre‐ or syn‐ the regional D₁. An intense foliation present in some of the younger (ca 1505 Ma) granites that comprise the bulk of the Naraku Batholith is interpreted to represent S₃ of the Isan Orogeny. Foliations commonly have similar styles and orientations in both the pre‐D₁ and younger plutons. This emphasises the simplicity with which regional fabrics can be, and probably have been, miscorrelated in the Eastern Fold Belt, and that the classification of granites in general on the basis of structural and geometric criteria alone is fraught with danger.     

The Proterozoic evolution of northern Siberian Craton margin: a comparison of U–Pb–Hf signatures from sedimentary units of the Taimyr orogenic belt and the Siberian platform

Identifying the cratonic affinity of Neoproterozoic crust that surrounds the northern margin of the Siberian Craton (SC) is critical for determining its tectonic evolution and placing the Craton in Neoproterozoic supercontinental reconstructions. Integration of new U–Pb–Hf detrital zircon data with regional geological constraints indicates that distinct Neoproterozoic arc-related magmatic belts can be identified within the Taimyr orogen. Sedimentary rocks derived from 970 to 800 Ma arc-related suites reveal abundant Archean and Paleoproterozoic detritus, characteristic of the SC. The 720–600 Ma arc-related zircon population from the younger Cambrian sedimentary rocks is also complemented by an exotic juvenile Mesoproterozoic zircon population and erosional products of older arc-related suites. Nonetheless, numerous evidences imply that both arcs broadly reworked Siberian basement components. We suggest that the early Neoproterozoic (ca. 970–800 Ma) arc system of the Taimyr orogen evolved on the active margin of the SC and probably extended along the periphery of Rodinia into Valhalla orogen of NE Laurentia. We also suggest the late Neoproterozoic (750–550 Ma) arc system could have been part of the Timanian orogen, which linked Siberia and Baltica at the Precambrian/Phanerozoic transition.     

Road construction using lateritic soil

The suitability of a lateritic soil developed on olivine basalt in western southeast Queensland, Australia, as paving material has been investigated. The particle size distribution and plasticity characteristics of the soil do not comply with the standard specification for paving materials. However, the soil has a high shear strength, resulting in a low Western Australian Confined Compression Test class number. The high shear strength of the soil at its in situ moisture content is due to its high angle of shearing resistance and its suction under in situ moisture conditions. Volumetric shrinkage of the soil does not constitute a problem as its shrinkage is low. The in situ strength of a pavement constructed with the lateritic soil, determined using a Clegg impact hammer, and the field dry density, have increased with time and the passage of traffic since construction. The pavement performance was good. A criteria suitable for the selection of a lateritic soil as paving material under the climatic conditions prevailing in western southeast Queensland has been suggested.     

Stream Restoration Performance and Its Contribution to the Chesapeake Bay TMDL: Challenges Posed by Climate Change in Urban Areas

In large part driven by total maximum daily load (TMDL) mandates, the restoration community in the Chesapeake Bay region has been implementing novel best management practices (BMPs) and stream restoration designs in urban areas, such as regenerative stream/stormwater conveyance (RSC) structures and stream-wetland complexes (SWCs). However, the nutrient and sediment reduction efficiencies of these novel designs are virtually unknown, and the possibility of increasing riverine flow in the Chesapeake Bay watershed associated with climate change this century necessitates an evaluation of their performance to develop and utilize those that optimize reductions in nutrient and sediment fluxes. We compare pre- and post-construction loads (total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS)) from RSCs (i.e., upland BMPs) and a SWC (i.e., stream restoration) constructed at the outflow of a highly developed watershed in the Coastal Plain physiographic province of Maryland. The largest of the two RSCs performed best in relation to expected nutrient and sediment reductions because of superior water retention capability. By the length of river reach restored, the SWC attained from 79 to 88% of its N reduction TMDL goal, but only 19 to 23 and 2.7 to 3.1% for TP and TSS, respectively; by watershed area, % attainments of TMDL goals were much lower. Results indicate that SWCs have the potential to curtail N loading from developed catchments, but additional water quality benefits may be limited. Climate change projections indicate that there will be an increased frequency of larger-volume storms that will result in an increase in stormflow runoff from urban areas, and increased pollutant loads will likely curtail potential gains made by efforts to achieve TMDL goals. Given the large-scale implementation of BMPs currently underway to accommodate the Chesapeake Bay TMDL, the restoration community needs to adopt a concerted strategy of building climate resilience into many types of urban BMPs to help attain and maintain loads at TMDL levels in anticipation of a progressively wetter climate throughout this century.     

Arsenic in mine waters: an international study

 Hydrochemical data are presented for arsenic (As) in the mine waters of 34 gold and base-metal mining localities in seven countries of south-east Asia, Africa and Latin America, encompassing contrasting climatic settings and at least eight discrete styles of primary mineralization. Peak dissolved As concentrations at these sites range from 0.005–72 mg/l, with the United States Environmental Protection Agency (US-EPA) potable water threshold of 50 μg/l exceeded in 25 cases. Arsenate (As⁵⁺) constitutes the dominant species at over 80% of sites. Very high dissolved As concentrations (>1 mg/l) show no systematic between-site relationship with mine water pH/Eh regime. Important determinants of mine water As fluxes include iron hydrochemistry, the presence of cyanic ore processing effluents, site geology, the paragenetic sequence that follows sulphide oxidation, climate and mine management. Human toxicological impacts of As contamination have been recognized at only one case-study site, with a further four considered to warrant more detailed risk assessment. Received: 2 November 1999 · Accepted: 21 March 2000