Evolution of gold-bearing veins in dykes of the Woods Point dyke swarm,Victoria     

A. H. Green  T. H. Donnelly  F. M. Jahnke  Reid R. Keays 《Mineralium Deposita》1982,17(2):175-192

The Woods Point dyke swarm comprises hundreds of narrow, subparallel igneous dykes and dozens of pipe-shaped dyke bulges within strongly deformed early Palaeozoic turbidites of the Melbourne trough. Porpylitic alteration accompanied dyke emplacement and was followed by microfracturing induced by high fluid pressures, involving CO₂ of magmatic origin, as the dykes solidified. Further stress caused through-going faults having ladder and other patterns. Isotopic studies suggest that metamorphically or geothermally-derived solutions filled the faults and other fractures with quartz and carbonate and altered immediately adjacent dyke rock. However earlier-formed vein and wall rock carbonates retained their magmatic isotopic composition. Fluid inclusions indicate vein deposition began at approximately 400°C with salinities up to 9 weight percent NaCl. Nine sulfide minerals and gold were deposited in the veins after ankerite, sericite and albite, while quartz deposition continued through all stages. Sulfur isotopic determinations indicate the vein sulfur could not have been derived from adjacent sedimentary rocks, nor exclusively from the dykes. Metamorphic waters of marine origin is a viable source for sulfur. Saline and CO₂-rich alkaline solutions reacted with the dyke wall rocks and probably evolved chemically prior to deposition of gold. Vug carbonates deposited by meteoric water that leached vein carbonates mark the end of vein formation.Present Adress: 631 Station Street, North Carlton 3054, Victoria, Australia  相似文献   

Crystallization of apatite in natural magmas under high pressure,hydrous conditions,with particular reference to ‘Orogenic’ rock series     

T. H. Green  E. B. Watson 《Contributions to Mineralogy and Petrology》1982,79(1):96-105

Two separate series of hydrous experiments involving (1) imposing apatite saturation on a series of igneous rock compositions from basanite to rhyolite, and (2) crystallizing similar natural rock compositions progressively until apatite appears, demonstrate a close dependence between apatite saturation and silica content of the magma, and determine P₂O₅ levels at a given silica value and temperature at which that composition may be expected to crystallize apatite. The effect of pressure on apatite solubility is not great, and is most significant for silicic compositions.P₂O₅ vs SiO₂ relationships of the low-K island arc suite, calcalkaline suite and high-K calc-alkaline suite, appear regular and characteristic for each suite, and when linked with the experimental work on apatite solubility, indicate the following: (1) the low-K and calc-alkaline series have low P₂O₅ contents (0.1–0.2 wt.%) and relatively flat P₂O₅-SiO₂ patterns; they do not show evidence of reaching apatite saturation until rhyodacite-rhyolite compositions are obtained for the low-K suite, and andesite-dacite compositions for the calc-alkaline suite; (2) the high-K calc-alkaline series has higher P₂O₅ contents (0.4–0.6 wt.%) in mafic compositions, and achieves apatite saturation over a wide compositional range for the series; (3) the calc-alkaline and high-K calc-alkaline series are probably lower temperature, and more hydrous than the low-K series; (4) anomalous P₂O₅-SiO₂ distributions may indicate non-equilibrium crystallization of apatite, magma-mixing and crystal accumulation processes active in generation of the orogenic volcanic series.  相似文献   

Automated statistical matching of multiple tephra records exemplified using five long maar sequences younger than 75 ka,Auckland, New Zealand     

Rebecca M. Green  Mark S. Bebbington  Shane J. Cronin  Geoff Jones 《Quaternary Research》2014

Detailed tephrochronologies are built to underpin probabilistic volcanic hazard forecasting, and to understand the dynamics and history of diverse geomorphic, climatic, soil-forming and environmental processes. Complicating factors include highly variable tephra distribution over time; difficulty in correlating tephras from site to site based on physical and chemical properties; and uncertain age determinations. Multiple sites permit construction of more accurate composite tephra records, but correctly merging individual site records by recognizing common events and site-specific gaps is complex. We present an automated procedure for matching tephra sequences between multiple deposition sites using stochastic local optimization techniques. If individual tephra age determinations are not significantly different between sites, they are matched and a more precise age is assigned. Known stratigraphy and mineralogical or geochemical compositions are used to constrain tephra matches. We apply this method to match tephra records from five long sediment cores (≤ 75 cal ka BP) in Auckland, New Zealand. Sediments at these sites preserve basaltic tephras from local eruptions of the Auckland Volcanic Field as well as distal rhyolitic and andesitic tephras from Okataina, Taupo, Egmont, Tongariro, and Tuhua (Mayor Island) volcanic centers. The new correlated record compiled is statistically more likely than previously published arrangements from this area.  相似文献   

On parameterizing thermodynamic descriptions of minerals for petrological calculations   总被引：2，自引：0，他引：2  

R. Powell  R.W. White  E.C.R. Green  T.J.B. Holland  J.F.A. Diener 《Journal of Metamorphic Geology》2014,32(3):245-260

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Thresholds of Adverse Effects of Macroalgal Abundance and Sediment Organic Matter on Benthic Habitat Quality in Estuarine Intertidal Flats     

Martha Sutula  Lauri Green  Giancarlo Cicchetti  Naomi Detenbeck  Peggy Fong 《Estuaries and Coasts》2014,37(6):1532-1548

Confidence in the use of macroalgae as an indicator of estuarine eutrophication is limited by the lack of quantitative data on the thresholds of its adverse effects on benthic habitat quality. In the present study, we utilized sediment profile imagery (SPI) to identify thresholds of adverse effects of macroalgal biomass, sediment organic carbon (% OC) and sediment nitrogen (% N) concentrations on the apparent Redox Potential Discontinuity (aRPD), the depth that marks the boundary between oxic near-surface sediment and the underlying suboxic or anoxic sediment. At 16 sites in eight California estuaries, SPI, macroalgal biomass, sediment percent fines, % OC, and % N were analyzed at 20 locations along an intertidal transect. Classification and Regression Tree (CART) analysis was used to identify step thresholds associated with a transition from "reference" or natural background levels of macroalgae, defined as that range in which no effect on aRPD was detected. Ranges of 3–15 g dw macroalgae m^?2, 0.4–0.7 % OC and 0.05–0.07 % N were identified as transition zones from reference conditions across these estuaries. Piecewise regression analysis was used to identify exhaustion thresholds, defined as a region along the stress–response curve where severe adverse effects occur; levels of 175 g dw macroalgae m^?2, 1.1 % OC and 0.1 % N were identified as thresholds associated with a shallowing of aRPD to near zero depths. As an indicator of ecosystem condition, shallow aRPD has been related to reduced volume and quality for benthic infauna and alteration in community structure. These effects have been linked to reduced availability of forage for fish, birds and other invertebrates, as well as to undesirable changes in biogeochemical cycling.  相似文献   

Small unmanned airborne systems to support oil and gas pipeline monitoring and mapping     

Cristina Gómez  David R. Green 《Arabian Journal of Geosciences》2017,10(9):202

Oil and gas transmission pipelines require monitoring for maintenance and safety, to prevent equipment failure and accidents. Unmanned aerial vehicles (UAVs) technology is emerging as an opportunity to supplement current monitoring systems. Small UAV technological solutions are flexible and adaptable and with a demonstrated capacity to obtain valuable data at small to medium spatial scales. Systematic surveys of extensive areas are better completed with fixed-wing platforms and automatic flight design, whilst multirotor platforms provide flexibility in shorter and localized inspection missions. The type of sensor carried by an aerial platform determines the sort of data acquired and the obtainable information; sensors also determine the need for specific mechanical designs and the provision of energy on-board required from the system. UAV systems prototyped to monitor pipelines are reviewed in this paper, and a number of monitoring scenarios are proposed and illustrated. Notwithstanding difficulties encountered in the generalization of use for civilian applications, small UAVs have demonstrated, through research and operational cases, the capacity to support the inspection and monitoring of oil and gas pipelines.  相似文献   

Analysis of growing season carbon and water fluxes of a subalpine wetland in the Canadian Rocky Mountains: Implications of shade on ecosystem water use efficiency     

Dylan M. Hrach  Richard M. Petrone  Adam Green  Myroslava Khomik 《水文研究》2022,36(1):e14425

Mountain regions are an important regulator in the global water cycle through their disproportionate water contribution. Often referred to as the “Water Towers of the World”, mountains contribute 40%–60% of the world's annual surface flow. Shade is a common feature in mountains, where complex terrain cycles land surfaces in and out of shadows over daily and seasonal scales, which can impact water use. This study investigated the turbulent water and carbon dioxide (CO₂) fluxes during the snow-free period in a subalpine wetland in the Canadian Rocky Mountains, from 7 June to 10 September 2018. Shading had a significant and substantial effect on water and CO₂ fluxes at our site. When considering data from the entire study period, each hourly increase of shade per day reduced evapotranspiration (ET) and gross primary production (GPP) by 0.42 mm and 0.77 g C m^?2, equivalent to 17% and 15% per day, respectively. However, the variability in shading changed throughout the study, it was stable to start and increased towards the end. Only during the peak growing season, the site experienced days with both stable and increasing shade. During this time, we found that shade, caused by the local complex terrain, reduced ET and potentially increased GPP, likely due to enhanced diffuse radiation. The overall result was greater water use efficiency during periods of increased shading in the peak growing season. These findings suggest that shaded subalpine wetlands can store large volumes of water for late season runoff and are productive through short growing seasons.  相似文献