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991.
M. R. Ramesh Kumar Syam Sankar Chris Reason 《Theoretical and Applied Climatology》2012,110(1-2):209-227
Inter-annual variability in the formation of the mini warm pool [sea-surface temperature (SST)>30°C] over the south eastern Arabian Sea (SEAS) and its role in the formation of the monsoon onset vortex (MOV) has been examined using two independent SST data sets. The role of SST, convection, integrated columnar water vapour and the low-level jet in the setting up of the monsoon onset over Kerala (MOK) is examined. It is found that the MOV which forms over the SEAS region upsets the delicate balance between convection, buildup of moisture and strengthening and deepening of the westerlies over the SEAS that is needed for the setting up of the MOK. Thus, the formation over the SEAS of an MOV is not necessarily conducive for MOK. Furthermore, it is shown that a mini warm pool over the southeastern Arabian Sea is not a sufficient condition for the formation of an MOV because such a warm pool is present over this region during most of the years, but an MOV does not necessarily form over there. 相似文献
992.
Sustainable Household Capability: which households are doing the work of environmental sustainability? 总被引:2,自引:2,他引:0
Gordon Waitt Peter Caputi Chris Gibson Carol Farbotko Lesley Head Nick Gill 《The Australian geographer》2012,43(1):51-74
This paper presents a framework for analysing which households are doing ‘their bit’ for sustainability in an era of climate change, using a two-stage cluster analysis of sustainable household capabilities. The framework segments households by their reported level of commitment to ‘pro-sustainability’ practices common to conventional government policies. Results are presented from a large-scale survey of Wollongong households, New South Wales, Australia. Results illustrate the importance of approaching household sustainability through everyday practices. Attention is drawn to the wide variation in participation in specific household sustainability practices. Investigation into sustainable household capability by household segments shows the limits of even the most committed households. Results show the importance of socio-cultural contexts in differentiating sustainable household capabilities—with women, suburban-detached households and lower income segments of the population ultimately doing most of the work of being sustainable. 相似文献
993.
A U-series study of lavas from Kamchatka and the Aleutians: constraints on source composition and melting processes 总被引:1,自引:0,他引:1
Simon Turner Frank McDermott Chris Hawkesworth Pavel Kepezhinskas 《Contributions to Mineralogy and Petrology》1998,133(3):217-234
New data are presented for lavas from the Kamchatka Peninsula and the Aleutian arc. Radiogenic isotopes are strikingly homogeneous
in the Kamchatka lavas and although incompatible trace element ratios exhibit much greater variability, much of this appears
to result from shallow level, crystal fractionation. The data reveal little systematic across-arc change in radiogenic isotopes
or trace element ratios. The Nd and Pb isotope data overlap those for Pacific MORB and limit the amount of sediment that could
be incorporated in the mantle source region to <1% which is insufficient to account for the observed La/Ta ratios (50–68)
in the high-MgO lavas. The lack of a positive correlation between La/Ta and depth to the slab suggests that melt–wall rock
interaction was not important in controlling this ratio. Instead it is inferred that La/Ta increased during partial melting
and that DLa/DTa = 0.11–0.06, possibly due to residual amphibole. Ba, U, Sr and Pb were added to the source by an aqueous fluid from the subducting
slab and its inferred isotopic composition indicates that this fluid was derived from the altered oceanic crust. The addition
of U resulted in a large range of (238U/232Th) from 0.79–2.48 similar to that observed in the Mariana and Lesser Antilles island arcs. However, (230Th/232Th) = 0.79–2.34, and the majority of samples lie close to the equiline indicating that the time since U/Th fractionation is
generally ≥150 thousand years. The large width of the volcanic zone is assumed to reflect protracted fluid release from the
subducting slab over the depth interval 170–380 km possibly coupled with extension across the Central Kamchatka Depression.
The data from the Aleutians contrast strongly with those from Kamchatka. Radiogenic isotope data indicate that the Aleutian
lavas contain a significant recycled sedimentary component, consistent with elevated 10Be/9Be ratios. The Aleutian lavas have (230Th/232Th) = 0.79–2.34 and exhibit a significant range of U/Th disequilibria [(238U/230Th) = 0.75–1.01]. However, 10Be/9Be is positively correlated with (238U/230Th) suggesting that the 10Be signal was carried by the aqueous fluid from the slab. The U/Th disequilibria for the Aleutian lavas lie close to a 30
thousand year reference line suggesting that this fluid was released from the slab ∼30 thousand years ago similar to recent
estimates from the Lesser Antilles, Marianas, and Tonga-Kermadec island arcs from which it is inferred that fluid addition
was the trigger for partial melting. Given that the rate of convergence in Kamchatka is similar to that in the Aleutians,
Marianas and Tonga-Kermadec the inferred greater time since␣fluid release in Kamchatka requires further investigation.
Received: 24 September 1997 / Accepted: 7 July 1998 相似文献
994.
Tyrone O. Rooney Pastora Franceschi Chris M. Hall 《Contributions to Mineralogy and Petrology》2011,161(3):373-388
Amphibole, while uncommon as a phenocryst in arc lavas, is increasingly recognized as a key constituent in the petrogenesis
of arc magmas. Fractional crystallization of water-saturated arc magmas in the lower crust can yield substantial volumes of
amphibole cumulates that, depending on the pressure of crystallization, may also contain garnet. Fractionation of this higher
pressure assemblage has been invoked as a possible mechanism in the production of magmas that contain an adakitic signature.
This study examines newly dated Late-Oligocene (25.37 ± 0.13 Ma) hypabyssal amphibole-rich andesites from Cerro Patacon in
the Panama Canal region. These andesites contain nodules of amphibole cumulates that are ~4–6 cm in diameter and are almost
entirely composed of 5–10-mm amphibole crystals (dominantly ferri-tschermakite). Geochemical variations, optical and chemical
zoning of the Cerro Patacon amphiboles are consistent with their evolution in a crystal mush environment that had at least
one recharge event prior to entrainment in the host andesite. Amphiboles hosted within the cumulate nodules differ from those
hosted in the Cerro Patacon andesite and contain consistently higher values of Ti. We suggest these nodules represent the
early stages of fractionation from a water-saturated magma. Cerro Patacon andesites have REE concentrations that plot at the
most depleted end of Central American Arc magmas and exhibit a distinctive depletion in the middle REE. These geochemical
and petrographic observations strongly support significant amphibole fractionation during formation of the Cerro Patacon andesite,
consistent with the petrographic evidence. Fractionation of water-saturated magmas is a mechanism by which adakitic compositions
may be produced, and the Cerro Patacon andesites do exhibit adakite-like geochemical characteristics (e.g., elevated Sr/Y;
28–34). However, the relatively elevated concentrations of Y and HREE indicate garnet was not stable in the fractionating
assemblage during this early stage of arc development. 相似文献
995.
Nicolle E. Dupuis James A. Braid J. Brendan Murphy Cecilio Quesada Chris McFarlane 《International Journal of Earth Sciences》2014,103(5):1403-1414
The formation and emplacement of syn-collisional mafic dykes that intrude suture zones and their association with orogenic processes are enigmatic. Southern Iberia records the Late Paleozoic amalgamation of Pangea and exposes today a fragment of Laurussia (South Portuguese Zone), which is spatially juxtaposed with autochthonous Gondwana. Fault-bounded oceanic metasedimentary rocks, mélanges and ophiolite complexes characterize the suture zone and are in turn crosscut by intrusive granitoid rocks and mafic dykes. The generation and emplacement of these mafic dykes and their relationship to the suture zone are undetermined. Field evidence shows the dykes were emplaced at high angles to pre-existing orogenic fabrics in the mélange, granitoid and metasedimentary rocks. Geochemical analyses (major, trace, rare earth elements) indicate the dykes exhibit a mid-ocean ridge basalt signature. U/Pb zircon geochronology reveals the crystallization age of the dykes is ca. 316 Ma and Sm–Nd isotopic analysis suggests a deep mantle source. Taken together, these data support existing temporal constraints on events leading up to the amalgamation of Pangea, and suggest progressive lower crustal delamination during the waning stages of continent–continent collision. 相似文献
996.
OluKayode J. Samuel Chris Cornford Martin Jones Olabisi A. Adekeye Samuel O. Akande 《Organic Geochemistry》2009,40(4):461-483
Biomarker and n-alkane compound specific stable carbon isotope analyses (CSIA) were carried out on 58 crude oil samples from shallow water and deepwater fields of the Niger Delta in order to predict the depositional environment and organic matter characteristics of their potential source rocks. Using a source organofacies prediction approach from oil geochemistry, the presence in the western deepwater oils relatively abundant C27 steranes, C30 24-n-propyl cholestane, low oleanane index, relatively low pr/ph ratios, gammacerane, and positive to nearly flat C12–C30 n-alkane compound specific stable carbon isotope profiles, suggests that the source facies that expelled these oils contain significant marine derived organic matter deposited under sub-oxic and stratified water column conditions. This contrasts with the terrigenous organic matter dominated source rocks accepted for shallow water Niger Delta oils. Oils in the shallow water accumulations can be separated into terrigenous and mixed marine-terrigenous families. The terrigenous family indicates expulsion from source rock(s) containing overwhelmingly higher plant source organic matter (average oleanane index = 0.48, high C29 steranes) as well as having negative sloping n-alkane isotope profiles. Oxic source depositional conditions (pr/ph > 2.5) and non-stratified conditions (absence to low gammacerane content) are inferred for the terrigenous family. The mixed marine-terrigenous family has biomarker properties that are a combination of the deepwater and terrigenous shallow water oils. Bitumen extracts of the sub-delta Late Cretaceous Araromi Formation shale in the Dahomey Basin are comparable both molecularly and isotopically to the studied western deepwater oil set, but with an over all poor geochemical correlation. This poor geochemical match between Araromi shale and the western deepwater oils does not downgrade the potential of sub-delta Cretaceous source rock contribution to the regional oil charge in the deepwater Niger Delta. 相似文献
997.
Across the Late Devonian biotic crisis, sclerobionts declined in diversity and abundance and the proportions of brachiopod shell textures changed radically. Most of the major sclerobiont clades were common to Givetian through Mississippian ecosystems. Microconchids, most abundant sclerobiont in most Devonian assemblages, were replaced by bryozoans in the Mississippian. Diversity and abundance of Mississippian sclerobionts were lower than Frasnian–Famennian assemblages. 相似文献
998.
Chris?HarrisEmail authorView authors OrcID profile Tanya?Dreyer Petrus?le?Roux 《Contributions to Mineralogy and Petrology》2018,173(1):8
Peralkaline syenite and granite dykes cut the Straumsvola nepheline syenite pluton in Western Dronning Maud Land, Antarctica. The average peralkalinity index (PI?=?molecular Al/[Na?+?K]) of the dykes is 1.20 (n?=?29) and manifests itself in the presence of the Zr silicates eudialyte, dalyite and vlasovite, and the Na–Ti silicate, narsarsukite. The dykes appear to have intruded during slow cooling of the nepheline syenite pluton, and the petrogenetic relationship of the dykes and the pluton cannot be related to closed-system processes at low pressure, given the thermal divide that exists between silica-undersaturated and oversaturated magmas. Major and trace element variations in the dykes are consistent with a combination of fractional crystallization of parental peralkaline magma of quartz trachyte composition, and internal mineral segregation prior to final solidification. The distribution of accessory minerals is consistent with late-stage crystallization of isolated melt pockets. The dykes give an Rb–Sr isochron age of 171?±?4.4 Ma, with variable initial 87Sr/86Sr ratio (0.7075?±?0.0032), and have an average ε Nd of ? 12.0. Quartz phenocrysts have δ18O values of 8.4–9.2‰, which are generally in O-isotope equilibrium with bulk rock. Differences in the δ18O values of quartz and aegirine (average Δquartz?aegirine = 3.5‰) suggest aegirine formation temperatures around 500 °C, lower than expected for a felsic magma, but consistent with poikilitic aegirine that indicates subsolidus growth. The negative ε Nd (< ? 10) and magma δ18O values averaging 8.6‰ (assuming Δquartz?magma = 0.6‰) are inconsistent with a magma produced by closed-system fractional crystallization of a mantle-derived magma. By contrast, the nepheline syenite magma had mantle-like δ18O values and much less negative ε Nd (average ??3.1, n?=?3). The country rock has similar δ18O values to the granite dykes (average 8.0‰, n?=?108); this means that models for the petrogenesis of the granites by assimilation are unfeasible, unless an unexposed high-δ18O contaminant is invoked. Instead, it is proposed that the peralkaline syenite and granite dykes formed by partial melting of alkali-metasomatised gneiss that surrounds the nepheline syenite, followed by fractional crystallization. 相似文献
999.
3-D geochemical subsurface models, as constructed by spatial interpolation of drill-core assays, are valuable assets across multiple stages of the mineral industry's workflow.However, the accuracy of such models is limited by the spatial sparsity of the underlying drill-core, which samples only a small fraction of the subsurface.This limitation can be alleviated by integrating collocated 3-D models into the interpolation process, such as the 3-D rock property models produced by modern geophysical inversion procedures, provided that they are sufficiently resolved and correlated with the interpolation target.While standard machine learning algorithms are capable of predicting the target property given these data, incorporating spatial autocorrelation and anisotropy in these models is often not possible.We propose a Gaussian process regression model for 3-D geochemical interpolation, where custom kernels are introduced to integrate collocated 3-D rock property models while addressing the trade-off between the spatial proximity of drill-cores and the similarities in their collocated rock properties, as well as the relative degree to which each supporting 3-D model contributes to interpolation.The proposed model was evaluated for 3-D modelling of Mg content in the Kevitsa Ni-Cu-PGE deposit based on drill-core analyses and four 3-D geophysical inversion models.Incorporating the inversion models improved the regression model's likelihood(relative to a purely spatial Gaussian process regression model) when evaluated at held-out test holes, but only for moderate spatial scales(100 m). 相似文献
1000.
Chris E. Ostrander Margaret A. McManus Eric H. DeCarlo Fred T. Mackenzie 《Estuaries and Coasts》2008,31(1):192-203
While the physical forcing mechanisms that govern the outflows of major rivers throughout the world are well documented in the literature, comparably less research has been done to examine the mechanisms that govern the contributions of small rivers and streams to coastal ocean systems. These rivers and streams provide a direct means for the transport of anthropogenic and terrigenous materials from watersheds to coastal oceans. This study describes the temporal and spatial variability of freshwater plumes from Kaneohe Stream, Hawaii, USA, after storm events in the Kaneohe Bay watershed. Freshwater plumes were examined using a combination of fixed moorings, synoptic shipboard surveys, and lagrangian surface drifters. Data sets were collected over the course of 19 months from August 2005 to March 2007 with particular attention paid to storms during the boreal winters. Stream discharge and duration were found to exert a primary control on plume persistence in the southern Kaneohe Bay system. Time series data show a strong coherence between wind forcing and surface currents, which, in combination with data derived from shipboard and aerial surveys, indicate that the spatial variability of freshwater plumes is primarily determined by atmospheric forcing. 相似文献