The mantle origins of Karoo picrites     

R.J. Sweeney  T.J. Falloon  D.H. Green  Y. Tatsumi   《Earth and Planetary Science Letters》1991,107(2)

Karoo picrites are divided into a volumetrically dominant high Ti-Zr (HTZ) group and a less abundant low Ti-Zr (LTZ) group. Distinguished in this way, it is then possible to use the comparison of major element compositions with those of experimentally determined partial melts of mantle peridotites to constrain the depth of segregation for each magma type. This approach also identifies the nature of source and residual mantle materials from which such magma segregation may have occurred. The LTZ group show uniformly shallow pressures (ca. 13–15 kb) of magma segregation and the HTZ group show a range of pressures (10 kb to > 30 kb) of segregation. In the HTZ group a range of K₂O, TiO₂ and Zr contents is observed, with greater concentrations in picrites which have segregated at higher pressures (high-NaK# HTZ picrites) relative to a low-NaK# HTZ picrite group (NaK#=[Na/₂O+K₂O][Na₂O+K₂O+CaO]). If we measure the refractory character of a mantle source peridotite by its CaO and Al₂O₃ content then it is shown that the LTZ picrites have segregated from sources which are more refractory than MORB or OIB sources and which lack the strong K, Ti and Zr enrichments of HTZ sources. Mixing of at least two mantle components is required to fully explain the major element and isotopic data in the HTZ group and is combined with variations in composition produced by different depths of magma segregation. Consideration of the major element phase relations coupled with trace element abundances and isotope data leads us to suggest that one component is the Kaapvaal lithospheric mantle (incompatible element enriched but relatively refractory with respect to basaltic components) and the other is asthenospheric mantle. This lithospheric mantle component is most evident in the high-NaK# HTZ picrite end-member which has segregated at a greater depth (ca. 18–32 kb). The asthenospheric component is most closely represented by the low-NaK# HTZ picrites which have segregated at pressures of 10–22 kb. The LTZ source, more refractory mantle than MORB, is inferred to be the shallow sub-continental lithospheric mantle which may also be the source of the low-MgO tholeiites related to these picrites, and therefore the source for the main phase of Karoo basaltic eruptions.  相似文献   

Acute toxicity of the water-soluble fraction of Cook Inlet crude oil to the Manila clam     

Pepsi Nunes  Pete E. Benville  Jr. 《Marine pollution bulletin》1978,9(12):324-331

Recognition of the inherent complexities of oil bioassays prompted the development of several apparatuses designed to deliver uniform solutions of the water-soluble components of crude oil and capable of system equilibration for both static and continuous-flow bioassays without the loss of the more volatile compounds and without the formation of emulsions. Clams from a relatively contaminated area exhibited greater resistance to the water-soluble fraction of Cook Inlet crude oil than specimens from a more pristine area. Behaviour was altered below lethal levels suggesting the possibility of using behavioural modifications as a concommitant criterion of toxicity with mortality. An increase in mortality with a longer exposure period and a significant rate of latent mortalities following the end of the 96-h exposure period suggest that future bioassays with bivalves should be determined over a longer exposure period.  相似文献   

FARM BILL MAY MEAN FUNDS FOR GEOGRAPHICAL RESEARCH     

Pete Sorenson 《The Professional geographer》1978,30(2):199-201

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A New Single Vacuum Furnace Design for Cosmogenic 3He Dating     

Laurent Zimmermann  Pierre Henri Blard  Pete Burnard  Sarah Medynski  Raphael Pik  Nicolas Puchol 《Geostandards and Geoanalytical Research》2012,36(2):121-129

Helium‐3 is a stable cosmogenic isotope that can be used to determine the time interval during which a rock sample has been at or close to the Earth’s surface. As a result of the high production rate of ‘cosmogenic’³He (≈ 130 at g^?1 year^?1) and the low detection limit of modern mass spectrometers, it is possible to date exceptionally young surfaces (≈ 1000 years). The precision and accuracy of cosmogenic ³He measurements depend critically on the passive helium blank (produced by the metalwork of the extraction furnace) which can be significant relative to the sample signals. We have developed and constructed, at the CRPG (Nancy, France), a new high temperature furnace (< 1500 °C) to extract helium in minerals such as apatite, pyroxene and olivine at 1050, 1350 and 1450 °C, respectively. The furnace demonstrated an excellent helium extraction yield (> 99% for olivine and pyroxene for heating times of 20–30 min and temperatures in the range 1050–1450 °C) and low residual helium contributions (the blank, obtained under the same analytical conditions as for sample extraction: 1 × 10^?15 mole ⁴He and < 4 × 10^?21 mole ³He). This is approximately an order of magnitude lower than those reported by other laboratories using conventional furnaces.  相似文献   

Developing carbon budgets for UK agriculture, land-use, land-use change and forestry out to 2022   总被引：1，自引：0，他引：1  

Dominic Moran  Michael MacLeod  Eileen Wall  Vera Eory  Alistair McVittie  Andrew Barnes  R. M. Rees  Cairistiona F. E. Topp  Guillaume Pajot  Robin Matthews  Pete Smith  Andrew Moxey 《Climatic change》2011,105(3-4):529-553

This paper derives a notional future carbon budget for UK agriculture, land use, land use change and forestry sectors (ALULUCF). The budget is based on a bottom-up marginal abatement cost curve (MACC) derived for a range of mitigation measures for specified adoption scenarios for the years 2012, 2017 and 2022. The results indicate that in 2022 around 6.36 MtCO₂e could be abated at negative or zero cost. Furthermore, in the same year, over 17% of agricultural GHG emissions (7.85 MtCO₂e) could be abated at a cost of less than the 2022 Shadow Price of Carbon (£34 (tCO₂e)^???1). The development of robust MACCs faces a range of methodological hurdles that complicate cost-effectiveness appraisal in ALULUCF relative to other sectors. Nevertheless, the current analysis provides an initial route map of efficient measures for mitigation in UK agriculture.  相似文献   

The importance of population,climate change and CO2 plant physiological forcing in determining future global water stress     

Andrew Wiltshire  Jemma Gornall  Ben Booth  Emily Dennis  Pete Falloon  Gillian Kay  Doug McNeall  Carol McSweeney  Richard Betts 《Global Environmental Change》2013,23(5):1083-1097

Future levels of water stress depend on changes in several key factors including population, climate-change driven water availability, and a carbon dioxide physiological-forcing effect on evaporation and run-off. In this study we use an ensemble of the HadCM3 climate model forced with a range of future emissions scenarios combined with a simple water scarcity index to assess the contribution of each of these factors to the projected population living in water stress over the 21st century.Population change only scenarios increase the number of people living in water stress such that at peak global population 65% of people experience some level of water stress. Globally, the climate model ensemble projects an increase in water availability which partially offsets some of the impacts of population growth. The result is 1 billion fewer people living in water stress by the 2080s under the high end emissions scenarios than if population increased in the absence of climate change.This study highlights the important role plant-physiological forcing has on future water resources. The effect of rising CO₂ is to increase available water and to reduce the number of people living in high water stress by around 200 million compared to climate only projections. This effect is of a similar order of magnitude to climate change.  相似文献   

Genesis of late carboniferous granitoid intrusions in the Dayinsu area,West Junggar,Northwest China: evidence of an arc setting for the western CAOB     

Dayu Zhang  Feng Yuan  Noel White  Pete Hollings  Wenjiao Xiao 《International Geology Review》2017,59(9):1082-1096

ABSTRACT

The Dayinsu area is located in the northern part of the West Junggar district near the border between China and Kazakhstan and is an important component of the Central Asian Orogenic Belt (CAOB). The Dayinsu area hosts numerous granitoid plutons in Devonian–Carboniferous volcano–sedimentary strata. The older Laodayinsu and Kubei (345–330 Ma) plutons are located in the west with the younger Bayimuzha and Qianfeng (330–325 Ma) plutons in the east. The whole-rock SiO₂ contents of the four granitoid plutons range from 52.22 to 68.42 wt.% and total alkaline contents (K₂O + Na₂O) range from 4.94 to 9.16 wt.%. The granites are enriched in large ion lithophile elements and light rare earth elements with depletions in Nb, Ta, Ce, Pr, P, and Ti. The plutons are metaluminous with I-type signatures. The geochemistry of the intrusions suggests that they formed in a subduction zone setting, and subsequently underwent fractional crystallization during emplacement, with higher degrees of fractionation in the eastern sector than in the west. Similarities in the geochronology and geochemical characteristics of the granitoid plutons in Dayinsu to those in the Tabei district (west to Dayinsu area) suggest that both districts are part of the Carboniferous Tarbagatay Mountain intrusive event. The early Carboniferous (345–324 Ma) granitoid intrusions in the Tarbagatay Mountain likely formed in an island arc subduction setting during the evolution of the CAOB.  相似文献   

花岗质岩浆和矿化之间的关系:重要概念和关键特征   总被引：1，自引：0，他引：1  

ZUREVINSKI Shannon  HOLLINGS Pete  周涛发  王世伟 《岩石学报》2017,33(5):1541-1553

最近对与花岗岩相关的锂、稀土金属和贱金属(例如Cu和Mo)矿产需求重新激发了人们对其成矿作用研究的兴趣。本文综述了不同类型花岗质岩石及与其相关的矿床:1)与高分异花岗岩有关的浸染状稀有金属矿化;2)热液型锡和钨矿化(如:矽卡岩型矿床);3)伟晶岩型稀有元素矿化;4)斑岩型矿化。虽然花岗岩和相关矿化作用之间(特别是斑岩系统相对于稀有金属)的联系还没有明确,但最近这些成矿系统的相关研究进展为探讨两者之间的关系提供了条件。本文重点回顾了与花岗岩相关成矿作用的主要特征,以及与不同类型矿化有关的花岗质岩浆的多样性,并论述了不同类型矿床的成矿模式。尽管长英质侵入岩浆系统复杂多样,但近来与这些矿化系统有关的研究进展可望能够作为找矿勘探的指示。地球化学特征可以揭示岩浆系统的氧化还原状态,进而可以判断斑岩系统的成矿潜力,它还可以与其他找矿勘探指标如矿物的同位素和微量元素分析联合使用。本文还讨论了通过熔融包裹体分析,研究微量元素在硅酸盐岩浆与挥发分体系中的行为。  相似文献   

Noble gases in submarine pillow basalt glasses from the Lau Basin: Detection of a solar component in backarc basin basalts     

Masahiko Honda  Desmond B. Patterson  Ian McDougall  Trevor J. Falloon 《Earth and Planetary Science Letters》1993,120(3-4):135-148

Noble gas elemental and isotopic abundances have been analysed in eight samples of youthful basaltic glass dredged from three different locations within the Lau Backarc Basin: (1) the King's Triple Junction, (2) the Central Lau Spreading Centre at 18°S and (3) the Eastern Lau Spreading Centre at 19°S. Samples from the Lau central and eastern spreading centres have MORB-like helium isotopic ratios of approximately 1.2 × 10⁻⁵ (8.5 R/R_A). In contrast, the samples from the King's Triple Junction yield helium isotopic ratios averaging 9.4 (±0.8) × 10⁻⁶ (6.7 ± 0.6 R/R_A), systematically lower than the MORB-like value, which may be reflecting the addition of radiogenic ⁴He released from the descending slab. Neon isotopic ratios are enriched in ²⁰Ne and ²¹Ne with respect to atmospheric ratios by as much as 23% and 62% respectively. These observations further confirm that non-atmospheric neon is a common characteristic of samples derived from the mantle. The helium and neon isotopic signatures in the samples can be explained by mixing of a primordial solar component, radiogenic and nucleogenic components produced by radioactive processes inside the Earth, and an atmospheric component. This reconnaissance survey of noble gases in a backarc basin indicates that current volcanism is dominated by magmas from the mantle wedge, a source similar to that from which MORBs are derived. The heavier noble gases (argon, krypton and xenon), however, show more atmosphere-like compositions, either indicating strong interaction of the magmas with the atmosphere or the presence of a recycled component derived from the underlying subducting slab.  相似文献   

The origin of island arc high-alumina basalts   总被引：5，自引：1，他引：5  

A. J. Crawford  T. J. Falloon  S. Eggins 《Contributions to Mineralogy and Petrology》1987,97(3):417-430

A detailed examination of the hypothesis that high-alumina basalts (HAB) in island arcs are primary magmas derived by 50–60% partial melting of subducted ocean crust eclogite shows that this model is unlikely to be viable. Evidence suggests that the overwhelming majority of arc HAB are porphyritic lavas, enriched in Al₂O₃ either by protracted prior crystallization of olivine and clinopyroxene, or by plagioclase phenocryst accumulation in magmas of basaltic andesite to dacite composition. Experimentally-determined phase relationships of such plagioclase-enriched (non-liquid) compositions have little bearing on the petrogenesis of arc magmas, and do not rule out the possibility that arc HAB can be derived by fractionation of more primitive arc lavas. Although models invoking eclogite-melting can match typical arc HAB REE patterns, calculations indicate that the Ni and Cr contents of proposed Aleutian primary HAB are many times lower than such models predict. In contrast, Ni vs Sc and Cr vs Sc trends for arc HAB are readily explained by olivine (+Cr-sp) and clinopyroxene-dominated fractionation from more primitive arc magmas. GENMIX major element modelling of several HAB compositions as partial melts of MORB eclogite, using appropriate experimentally (26–34 kb)-determined garnet and omphacite compositions yields exceptionally poor matches, especially for CaO, Na₂O, MgO and Al₂O₃. These mismatches are easily explained if the HAB are plagioclase-accumulative. Groundmasses of arc HAB are shown to vary from basaltic andesite to dacite in composition. Crystal fractionation driving liquid compositions toward dacite involves important plagioclase separation, resulting in development of significant negative Eu anomalies in more evolved lavas. Plagioclase accumulation in such evolved liquids tends to diminish or eliminate negative Eu anomalies. Therefore, the absence of positive Eu anomaly in a plagioclase-phyric HAB does not indicate that plagioclase has not accumulated in that lava. In addition, we show that plagioclase phenocrysts in arc HAB are not in equilibrium with the liquids in which they were carried (groundmass). Exceptional volumes of picrite and olivine basalt occur in the Solomons and Vanuatu arcs; the presence in lavas from these and other arcs (Aleutian, Tonga) of olivine phenocrysts to Fo₉₄, finds no ready explanation in the primary eclogite-derived HAB model. We suggest that most lavas in intra-oceanic arcs are derived from parental magmas with >10% MgO; fractionation of olivine (+Cr-sp) and clinopyroxene drives liquids to basalt compositions with <7% MgO, but plagioclase nucleation is delayed by their low but significant (<1%?) H₂O contents. Thus evolved liquid compositions in the basaltic andesite—andesite range may achieve relatively high Al₂O₃ contents (<17.5%). The majority of arc basalts, however, have Al₂O₃ contents in excess of 18%, reflecting plagioclase accumulation. We give new experimental data to show that HAB liquids may be generated by anhydrous, low-degree (<10%) partial melting of peridotite at P<18 kb. Relative to arc HAB, these experimental melts have notably higher Mg#(69–72) and are in equilibrium with olivine Fo_87–89. Only further detailed trace element modelling will show if they might be parental magmas for some arc HAB.  相似文献