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Meade FC, Troll VR, Ellam RM, Freda C, Font L, Donaldson CH, Klonowska I. Bimodal magmatism produced by progressively inhibited crustal assimilation. Nat Commun 2014; 5:4199. [PMID: 24947142 DOI: 10.1038/ncomms5199] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Accepted: 05/22/2014] [Indexed: 11/09/2022] Open
Abstract
The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose 'progressively inhibited crustal assimilation' (PICA) as a major cause of bimodality in continental volcanism.
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Affiliation(s)
- F C Meade
- Department of Earth Sciences, CEMPEG, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden
| | - V R Troll
- 1] Department of Earth Sciences, CEMPEG, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden [2] Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, 00143 Rome, Italy
| | - R M Ellam
- Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride, G75 0QF Scotland, UK
| | - C Freda
- Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, 00143 Rome, Italy
| | - L Font
- Department of Petrology, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands
| | - C H Donaldson
- School of Geography and Geosciences, University of St Andrews, North Street, St Andrews, KY16 9AL Scotland, UK
| | - I Klonowska
- Department of Earth Sciences, CEMPEG, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden
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Ellam RM, Hawkesworth CJ, Menzies MA, Rogers NW. The volcanism of southern Italy: Role of subduction and the relationship between potassic and sodic alkaline magmatism. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/jb094ib04p04589] [Citation(s) in RCA: 128] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Ellam RM. The graphical presentation of lead isotope data for environmental source apportionment. Sci Total Environ 2010; 408:3490-3492. [PMID: 20434757 DOI: 10.1016/j.scitotenv.2010.03.037] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2010] [Revised: 03/18/2010] [Accepted: 03/22/2010] [Indexed: 05/27/2023]
Abstract
Lead isotope ratios are widely used to identify original sources of Pb in the environment. Such source apportionment depends on the ability to distinguish potential sources on the basis of their isotopic composition. However, almost all terrestrial Pb is co-linear in some of the plots i.e. (206)Pb/(208)Pb versus (206)Pb/(207)Pb and (206)Pb/(204)Pb versus (206)Pb/(207)Pb commonly presented in the literature. These diagrams are unable to distinguish more than two sources of environmental Pb. Linear trends in such plots are an inevitable consequence of the co-linearity of terrestrial leads and should not be taken necessarily to indicate simple binary mixing of sources. A more reliable test for multiple source mixing can be obtained from plots involving (206)Pb/(204)Pb, (207)Pb/(204)Pb and (208)Pb/(204)Pb and therefore requires measurements of the minor (204)Pb isotope.
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Affiliation(s)
- R M Ellam
- Scottish Universities Environmental Research Centre, Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride, G75 8DZ, United Kingdom.
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Pichevin LE, Reynolds BC, Ganeshram RS, Cacho I, Pena L, Keefe K, Ellam RM. Enhanced carbon pump inferred from relaxation of nutrient limitation in the glacial ocean. Nature 2009; 459:1114-7. [PMID: 19553996 DOI: 10.1038/nature08101] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2008] [Accepted: 04/23/2009] [Indexed: 11/09/2022]
Abstract
The modern Eastern Equatorial Pacific (EEP) Ocean is a large oceanic source of carbon to the atmosphere. Primary productivity over large areas of the EEP is limited by silicic acid and iron availability, and because of this constraint the organic carbon export to the deep ocean is unable to compensate for the outgassing of carbon dioxide that occurs through upwelling of deep waters. It has been suggested that the delivery of dust-borne iron to the glacial ocean could have increased primary productivity and enhanced deep-sea carbon export in this region, lowering atmospheric carbon dioxide concentrations during glacial periods. Such a role for the EEP is supported by higher organic carbon burial rates documented in underlying glacial sediments, but lower opal accumulation rates cast doubts on the importance of the EEP as an oceanic region for significant glacial carbon dioxide drawdown. Here we present a new silicon isotope record that suggests the paradoxical decline in opal accumulation rate in the glacial EEP results from a decrease in the silicon to carbon uptake ratio of diatoms under conditions of increased iron availability from enhanced dust input. Consequently, our study supports the idea of an invigorated biological pump in this region during the last glacial period that could have contributed to glacial carbon dioxide drawdown. Additionally, using evidence from silicon and nitrogen isotope changes, we infer that, in contrast to the modern situation, the biological productivity in this region is not constrained by the availability of iron, silicon and nitrogen during the glacial period. We hypothesize that an invigorated biological carbon dioxide pump constrained perhaps only by phosphorus limitation was a more common occurrence in low-latitude areas of the glacial ocean.
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Affiliation(s)
- L E Pichevin
- School of Geosciences, Grant Institute, University of Edinburgh, West Main Road, EH10 3JW, Edinburgh, UK.
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Tudhope AW, Chilcott CP, McCulloch MT, Cook ER, Chappell J, Ellam RM, Lea DW, Lough JM, Shimmield GB. Variability in the El Niño-Southern Oscillation through a glacial-interglacial cycle. Science 2001; 291:1511-7. [PMID: 11222850 DOI: 10.1126/science.1057969] [Citation(s) in RCA: 730] [Impact Index Per Article: 31.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The El Niño-Southern Oscillation (ENSO) is the most potent source of interannual climate variability. Uncertainty surrounding the impact of greenhouse warming on ENSO strength and frequency has stimulated efforts to develop a better understanding of the sensitivity of ENSO to climate change. Here we use annually banded corals from Papua New Guinea to show that ENSO has existed for the past 130,000 years, operating even during "glacial" times of substantially reduced regional and global temperature and changed solar forcing. However, we also find that during the 20th century ENSO has been strong compared with ENSO of previous cool (glacial) and warm (interglacial) times. The observed pattern of change in amplitude may be due to the combined effects of ENSO dampening during cool glacial conditions and ENSO forcing by precessional orbital variations.
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Affiliation(s)
- A W Tudhope
- Department of Geology & Geophysics, Edinburgh University, Edinburgh, EH9 3JW, UK. mail:
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Ellam RM, Padbury JM. Base catalysed dehydration of α-alkoxybenzyl hydroperoxides: applications to zwitterion trapping reactions in ozonolysis. ACTA ACUST UNITED AC 1972. [DOI: 10.1039/c39720001086] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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