A granite–gabbro complex from Madagascar: constraints on melting of the lower crust     

Andy?McMillan  Nigel?B.?W.?HarrisEmail author  Marian?Holness  Lewis?Ashwal  Simon?Kelley  Roger?Rambeloson 《Contributions to Mineralogy and Petrology》2003,145(5):585-599

The Ranomandry Complex is a Neoproterozoic, nested intrusion from central Madagascar composed of a gabbroic core within a coeval peraluminous granite ring intruding pelitic metasediments. Although xenocryst entrainment and magma mixing have both contributed to marginal phases of the granite, the primary melt is characterised by steep LREE/HREE ratios and negligible, or slightly positive, Eu anomalies. Both isotopic and trace element systematics preclude an origin from either partial melting of the metapelitic country rock or from fractional crystallisation of the gabbroic magma. However, trace-element modelling suggests an origin from the dehydration melting of a plagioclase-poor, garnet-bearing metagreywacke at temperatures of 850–900 °C and at lower crustal pressures (>10 kbar). Melting of an enriched subcontinental mantle generated gabbroic magmas that caused advective heating and anatexis at the base of thickened continental crust during their ascent. Transport of the resulting granite magma was facilitated by the pre-existing plumbing system that overcame thermal and mechanical problems associated with both diapirism and self-propagating dykes as mechanisms for long-distance transport of granite magmas. The nested geometry of the intrusions is an indication of a structurally homogeneous lower crust that contains no pre-existing shear zones or fault systems.  相似文献   

森林水文服务市场的开发与经济激励机制――思考和启示     

Danièle Perrot-Maitre 《湿地科学与管理》2002,(3)

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Monitoring vegetation dynamics in East Rennell Island World Heritage Site using multi-sensor and multi-temporal remote sensing data     

Mengmeng Wang  Natarajan Ishwaran  Tianhua Hong  Andy Bell  Zhaoming Zhang 《International Journal of Digital Earth》2020,13(3):393-409

ABSTRACT

East Rennell of Solomon Island is the first natural site under customary law to be inscribed on UNESCO’s World Heritage List. Potential threats due to logging, mining and agriculture led to the site being declared a World Heritage in Danger in 2013. For East Rennell World Heritage Site (ERWHS) to ‘shed’ its ‘Danger’ status the management must monitor forest cover both within and outside of ERWHS. We used satellite data from multiple sources to track forest cover changes for the entire East Rennell island since 1998. 95% of the island is still covered by undisturbed forests; annual average normalized difference vegetation index (NDVI) for the whole island was above 0.91 in 2015. However, vegetation cover in the island has been slowly decreasing, at a rate of –0.0011 NDVI per year between 2000 and 2015. This decrease less pronounced inside ERWHS compared to areas outside. While potential threats due to forest clearing outside ERWHS remain the forest cover change from 2000 to 2015 has been below 15%. We suggest ways in which the Government of Solomon Islands could use our data as well as unmanned air vehicles and field surveys to monitor forest cover change and ensure the future conservation of ERWHS.  相似文献   

Book Review: An introduction to environmental chemistry,by J.E. Andrews,P. Brimblecombe,T.D. Jickells,P.S. Liss and B.J. Reid. 2004. 296 pp. Blackwell Publishing,Oxford. Price: US $ 68.95: £24.99. ISBN 0-632-05905-2     

Andy Cundy 《Journal of Paleolimnology》2005,34(4):535-537

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Kinematic Modeling of Pyroclastic Flows Produced by Gravitational Dome Collapse at Soufriere Hills Volcano, Montserrat     

Donald M. Hooper  Glen S. Mattioli 《Natural Hazards》2001,23(1):65-86

Volcanic activity commenced 18 July 1995 at SoufriereHills volcano and has led to the creation of a newlava dome, which has repeatedly collapsed between 1996and 1999 resulting in highly mobile pyroclastic flows. The majority of associated pyroclastic flow phenomenaare consistent with initiation by gravitationalcollapse as blocks fall from oversteepened flanks ofthe new dome. If gravity controls the energy transferof such collapses, then areas likely to be affectedcan be predicted on the basis of topography. We focuson `dense' flows initiated by non-explosive,gravitational collapse (`Merapi-type' pyroclasticflows) and employ a graphical computer model (Flow3D)written to simulate this type of volcanic flow. Theprogram constructs a digital terrain model based upona 3D network of (x, y, z) triplets, which serves as thebasis for the numerical computations. A synthetic domewas added to the topographic model to improve theaccuracy of the simulations. After estimating thesmall number of key adjustable parameters, simulatedflow pathways, runout distances, and velocitiesclosely approximated observed Merapi-type pyroclasticflows on Montserrat. These simulations demonstrate thevalidity of a simple kinematic method to model densepyroclastic flow phenomena. While the simulationspresented here do not elucidate additional physics ofpyroclastic flow phenomena, this type of modeling canbe completed easily and without extensivea priori knowledge of volcano-specific parameters otherthan topography. Accordingly, it may serve as a rapidand inexpensive first-order approach for initialhazard assessment.  相似文献   

Stratigraphy,composition and form of the Deccan Basalts,Western Ghats,India   总被引：9，自引：0，他引：9  

J. E. Beane  C. A. Turner  P. R. Hooper  K. V. Subbarao  J. N. Walsh 《Bulletin of Volcanology》1986,48(1):61-83

In the Western Ghats between latitudes 18° 20 N and 19° 15 N, 7000 km² of Deccan Basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts. Using over 70 measured vertical sections, major and trace element analyses of nearly 1200 samples, and rare-earth and⁸⁷Sr/⁸⁶Sr determinations for over 60 samples, we divide the basalt into three subgroups and ten formations. In this paper we describe the seven principal formations in the area and the most prominent individual flows.The Kalsubai Subgroup is formed by the lower five formations, the Jawhar, Igatpuri, Neral, Thakurvadi, and Bhimashankar formations, from botton to top. In these formations amygdaloidal compound flows predominate and have a typically high MgO content, including picrite basalt (> 10% MgO) and picrite (> 18% MgO) with phenocrysts of olivine and clinopyroxene. These flows are separated by others which contain giant plagioclase phenocrysts and have more evolved chamical compositions.The Lonavala Subgroup overlies the Kalsubai and is composed of two formations, the Khandala and the Bushe. Both are readily recognized in the field and by their chemical compositions.The Wai Subgroup includes the upper three formations, the Poladpur, the Ambenali, and the Mahabaleshwar. The whole subgroup is composed of simple flows with well-developed flow tops, small phenocrysts of plagioclase, pyroxene and olivine, and relatively evolved bulk compositions.Distribution and variation in thickness of the straitigraphic units within the Western Ghats provide a first comprehensive view of the development of the Deccan volcanic edifice. The persistent southerly dip and gentle southerly plunging anticlinal form of the flows, the lensoid shape of many of the formations, and nearly randomly oriented feeder-dike system are together interpreted as evidence of a central volcanic edifice formed as the Indian plate drifted northward over a mantle plume or hot spot.  相似文献   

Metamorphic fluid flow in the northeastern part of the 3.8-3.7 Ga Isua Greenstone Belt (SW Greenland): A re-evalution of fluid inclusion evidence for early Archean seafloor-hydrothermal systems     

Wouter Heijlen  Peter W.U. Appel  Andy Horsewell 《Geochimica et cosmochimica acta》2006,70(12):3075-3095

Fluid inclusions in quartz globules and quartz veins of a 3.8-3.7 Ga old, well-preserved pillow lava breccia in the northeastern Isua Greenstone Belt (IGB) were studied using microthermometry, Raman spectrometry and SEM Cathodoluminescence Imaging. Petrographic study of the different quartz segregations showed that they were affected by variable recrystallization which controlled their fluid inclusion content. The oldest unaltered fluid inclusions found are present in vein crystals that survived dynamic and static recrystallization. These crystals contain a cogenetic, immiscible assemblage of CO₂-rich (+H₂O, +graphite) and brine-rich (+CO₂, +halite, +carbonate) inclusions. The gas-rich inclusions have molar volumes between 44.8 and 47.5 cm³/mol, while the brine inclusions have a salinity of ∼33 eq. wt% NaCl. Modeling equilibrium immiscibility using volumetric and compositional properties of the endmember fluids indicates that fluid unmixing occurred at or near peak-metamorphic conditions of ∼460 °C and ∼4 kbar. Carbonate and graphite were precipitated cogenetically from the physically separated endmember fluids and were trapped in fluid inclusions.In most quartz crystals, however, recrystallization obliterated such early fluid inclusion assemblages and left graphite and carbonate as solid inclusions in recrystallized grains. Intragranular fluid inclusion trails in the recrystallized grains of breccia cementing and crosscutting quartz veins have CO₂-rich assemblages, with distinctly different molar volumes (either between 43.7 and 47.5 cm³/mol or between 53.5 and 74.1 cm³/mol), and immiscible, halite-saturated H₂O-CO₂-NaCl(-other salt) inclusions. Later intergranular trails have CH₄-H₂ (X_H2 up to ∼0.3) inclusions of variable density (ranging from 48.0 to >105.3 cm³/mol) and metastable H₂O-NaCl(-other salt?) brines (∼28 eq. wt% NaCl). Finally, the youngest fluid inclusion assemblages are found in non-luminescent secondary quartz and contain low-density CH₄ (molar volume > 105.33 cm³/mol) and low-salinity H₂O-NaCl (0.2-3.7 eq. wt% NaCl). These successive fluid inclusion assemblages record a retrograde P-T evolution close to a geothermal gradient of ∼30 °C/km, but also indicate fluid pressure variations and the introduction of highly reducing fluids at ∼200-300 °C and 0.5-2 kbar. The quartz globules in the pillow fragments only contain sporadic CH₄(+H₂) and brine inclusions, corresponding with the late generations present in the cementing and crosscutting veins. We argue that due to the large extent of static recrystallization in quartz globules in the pillow breccia fragments, only these relatively late fluid inclusions have been preserved, and that they do not represent remnants of an early, seafloor-hydrothermal system as was previously proposed.Modeling the oxidation state of the fluids indicates a rock buffered system at peak-metamorphic conditions, but suggests a change towards fluid-graphite disequilibrium and a logf_H2/f_H2O above the Quartz-Fayalite-Magnetite buffer during retrograde evolution. Most likely, this indicates a control on redox conditions and on fluid speciation by ultramafic rocks in the IGB.Finally, this study shows that microscopic solid graphite in recrystallized metamorphic rocks from Isua can be deposited inorganically from a fluid phase, adding to the complexity of processes that formed reduced carbon in the oldest, well-preserved supracrustal rocks on Earth.  相似文献   

Germanium isotope measurements of high-temperature geothermal fluids using double-spike hydride generation MC-ICP-MS     

Christopher Siebert  Andy Ross 《Geochimica et cosmochimica acta》2006,70(15):3986-3995

We present a double-spike isotope dilution MC-ICP-MS technique for the determination of germanium (Ge) isotope fractionation. Using this technique we determined Ge isotope compositions of geothermal spring fluids, a Columbia River Basalt sample, and an in-house diatom standard. Our technique uses a ⁷³Ge/⁷⁰Ge double spike in combination with hydride generation for Ge extraction from the sample matrix. Fractionation is determined on the ⁷⁴Ge/⁷²Ge mass ratio. The double spike allows us to effectively correct analytical isotope fractionation. Our external standard reproducibility is 0.4‰ (2 SD) over the course of several months. The minimum quantity of Ge needed for isotope analysis is approximately 2 ng. Consistent with previous work on geothermal fluids, Ge in the geothermal spring samples presented here is enriched over Si as compared to low temperature weathering signatures. This observation is typically interpreted as Ge exclusion during silicate mineral precipitation (e.g., quartz). Our isotope results indicate that the analyzed high temperature fluids fractionate Ge isotopes with a range in δ⁷⁴Ge between −0.4‰ and −1.4‰ relative to a Columbia River basalt. We cautiously interpret the observed fractionation as preferential removal of heavy Ge isotopes out of solution during cooling of the hydrothermal fluid and subsequent precipitation of quartz.  相似文献   

Speleology and magnetobiostratigraphic chronology of the Buffalo Cave fossil site, Makapansgat, South Africa     

Andy I.R. Herries  Kaye E. Reed 《Quaternary Research》2006,66(2):233-245

Speleological, stratigraphic, paleomagnetic and faunal data is presented for the Buffalo Cave fossil site in the Limpopo Province of South Africa. Speleothems and clastic deposits were sampled for paleomagnetic and mineral magnetic analysis from the northern part of the site, where stratigraphic relationships could be more easily defined and a magnetostratigraphy could therefore be developed for the site. This is also where excavations recovered the fossil material described. A comparison of the east and South African first and last appearance data with the Buffalo Cave fauna was then used to constrain the magnetostratigraphy to produce a more secure age for the site. The magnetostratigraphy showed a change from normal to reversed polarity in the basal speleothems followed by a short normal polarity period in the base of the clastic deposits and a slow change to reversed directions for the remainder of the sequence. The biochronology suggested an optimal age range of between 1.0 Ma and 600,000 yr based on faunal correlation with eastern and southern Africa. A comparison of the magnetobiostratigraphy with the GPTS suggests that the sequence covers the time period from the Olduvai event between 1.95 and 1.78 Ma, through the Jaramillo event at 1.07 Ma to 990,000 yr, until the Bruhnes-Matuyama boundary at 780,000 yr. The faunal-bearing clastic deposits are thus dated between 1.07 Ma and 780,000 yr with the main faunal remains occurring in sediments dated to just after the end of the Jaramillo Event at 990,000 yr.  相似文献   

Do firms adopt lower standards in poorer areas? Corporate social responsibility and environmental justice in the EU and the US   总被引：1，自引：0，他引：1  

Andy Gouldson 《Area》2006,38(4):402-412

Within the context of broader debates on corporate social responsibility (CSR) and environmental justice (EJ), this paper examines three key questions: first, how the standards that corporations adopt at the global scale trickle down into local site-level practices; second, whether levels of corporate environmental performance vary from place to place; and third whether any variations in corporate environmental performance relate to the principles of EJ. To do this, the analysis draws upon recently disclosed data to evaluate variations in the environmental performance of oil refineries across the US and the EU. It finds significant variations in emissions of some key pollutants. These exist both across the range of refineries, with dirtier refineries emitting at least five times as much as cleaner refineries, and between the EU and the US, with refineries in the EU emitting more than twice as much as refineries in the US. At the local level, it finds that there are correlations between higher levels of emissions from refineries and lower levels of income, employment and population density. Although these findings provide support for some of the contentions of the EJ movement, they do not say anything about causality, and as a result we cannot say definitively that companies adopt lower standards in poorer areas.  相似文献