scholarly journals Alteration, fractional crystallization, partial melting, mantle properties from trace elements in basalts recovered in the North Atlantic

1979 ◽  
pp. 352-368 ◽  
Author(s):  
Henri Bougault ◽  
Jean-Louis Joron ◽  
Michel Treuil
Keyword(s):  
Trace Elements ◽  
Partial Melting ◽  
Fractional Crystallization ◽  
North Atlantic ◽  
The North ◽  
The North Atlantic

Halogens in the mantle beneath the North Atlantic

1980 ◽  
Vol 297 (1431) ◽  
pp. 147-178 ◽  
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Partial Melting ◽  
North Atlantic ◽  
Low Pressure ◽  
The North ◽  
Mid Atlantic Ridge ◽  
Ionic Size ◽  
The North Atlantic ◽  
Incompatible Trace Elements

F, Cl and Br contents of tholeiitic volcanic glasses dredged along the Mid-Atlantic Ridge from 53° to 28° N, including the transect over the Azores Plateau, are reported. The halogen variations parallel those of 87 Sr/ 86 Sr, La/Sm or other incompatible elements of varying volatility. The latitudinal halogen variation pattern is not obliterated if only Mg-rich lavas are considered. Variations in extent of low-pressure fractional crystallization or partial melting conditions do not appear to be the primary cause of the halogen variations. Instead, mantle-derived heterogeneities in halogens, with major enrichments in the mantle beneath the Azores, are suggested. The Azores platform is not only a ‘hotspot’ but also a ‘wetspot’, which may explain the unusually intense Azores volcanic activity. The magnitude of the halogen and incompatible element enrichments beneath the Azores appear strongly dependent on the size of these anions and cations, but independent of relative volatility at low pressure. The large anions Cl and Br behave similarly to large cations Rb, Cs and Ba, and the smaller anion F similarly to Sr and P. Processes involving crystal and liquid (fluid and/or melt), CO 2 rather than H 2 O dominated, seem to have produced these largescale mantle heterogeneities. Geochemical ‘anomalies’ beneath the Azores are no longer apparent for coherent element pair ratios of similar ionic size. Values of such ‘unfractionated’ coherent trace element ratios provide an indication of the mantle composition and its nature before fractionation event (s) which produced the inferred isotopic and trace element heterogeneities apparently present beneath the North Atlantic. The relative trace element composition of this precursor mantle does not resemble that of carbonaceous chondrites except for refractory trace element pairs of similar ionic size. It is strongly depleted in halogens, and to a lesser extent in large alkali ions Rb and Cs relative to refractory Ba. These relative depletions are comparable within a factor of 5 to Ganapathy & Anders’s estimates for the bulk Earth, with the exception of Cs. There is also evidence for removal of phosphorus into the iron core during its formation. With the exception of San Miguel, alkali basalts from the Azores Islands appear to have been derived from the same mantle source as tholeiitic basalts from the ridge transect over the Azores Platform but by half as much degree of partial melting. The Azores subaerial basalts seem to have been partly degassed in Cl, Br and F, in decreasing order of intensity. A working model involving metasomatism from release of fluids at phase transformation during convective mantle overturns is proposed to explain the formation of mantle plumes or diapirs enriched in larger relative to smaller halogen and other incompatible trace elements. The model is ad hoc and needs testing. However, any other dynamical model accounting for the 400 -1000 km long gradients in incompatible trace elements, halogens and radiogenic isotopes along the Mid-Atlantic Ridge should, at some stage, require either (1) some variable extent of mixing or (2) differential migration of liquid relative to crystals followed by re-equilibration (or both), as a diffusion controlled mechanism over such large distances is clearly ruled out, given the age of the Earth.

Nature of mantle heterogeneity in the North Atlantic: evidence from deep sea drilling

1980 ◽  
Vol 297 (1431) ◽  
pp. 179-202 ◽  
Keyword(s):  
Partial Melting ◽  
North Atlantic ◽  
Subduction Zones ◽  
Alkali Basalts ◽  
Upward Migration ◽  
The North ◽  
Subduction Zone Processes ◽  
Wide Range ◽  
Mantle Sources ◽  
The North Atlantic

Studies of dredged and drilled samples from the North Atlantic ocean have revealed that basalts with a wide range of major and trace element compositions have been generated at the Mid-Atlantic Ridge (M.A.R.). Many of the basalts erupted between latitudes 30° and 70° N do not have the geochemical characteristics of normal mid-ocean ridge basalts (m.o.r.b.) depleted in the more-hygromagmatophile (hyg.) elements. Drilling along mantle flow lines transverse to the ridge has shown that different segments of the M.A.R. have produced basalts with a distinct compositional range for tens of millions of years. As more data have become available, the nature and scale of this variation have been established and tighter constraints can now be placed on the petrogenetic processes involved. The rare earth elements are used to test quantitatively the effects of open and closed system fractional crystallization, equilibrium partial melting (including continuous melting), zone refining and mantle mixing processes on basalt chemistry. When evaluated in terms of the more-hyg. elements, the results show that major heterogeneities must exist in the mantle sources feeding the M.A.R. Ratios of many of the more-hyg. elements remain consistent in space and time in basalts erupted at a particular ridge segment, but vary widely between different ridge segments. These ratios are not significantly modified by the processes of basalt generation. The hyg. element relations provide a major constraint on the nature of heterogeneity in the Earth’s mantle and the processes producing it. The mantle sources of anomalous ridge segments can be best explained in terms of variable veining of a hyg. element depleted host by a hyg. element enriched liquid or fluid generated by very small degrees of partial melting. Such incipient melting, as well as subduction zone processes, may be viable mechanisms for changing hyg. element ratios in the mantle source regions on the scale observed. These processes can be integrated into a model for mantle evolution which involves (1) upward migration of incipient melts to provide a hyg. element enriched source for alkali basalts and a hyg. element depleted source for normal m.o.r.b., and (2) extraction of continental crust and recycling of the depleted residue into the mantle at subduction zones. Also, some recycling of continental material into the mantle may be required to explain Pb isotope patterns.

Trace elements in the atmosphere over the North Atlantic

1995 ◽  
Vol 100 (D1) ◽  
pp. 1199-1213 ◽  
Author(s):  
R. Arimoto ◽  
R. A. Duce ◽  
B. J. Ray ◽  
W. G. Ellis ◽  
J. D. Cullen ◽  
...  
Keyword(s):  
Trace Elements ◽  
North Atlantic ◽  
The North ◽  
The North Atlantic

Trace elements in the North Atlantic troposphere: Shipboard results of precipitation and aerosols

1990 ◽  
Vol 4 (4) ◽  
pp. 431-443 ◽  
Author(s):  
T. M. Church ◽  
A. Véron ◽  
C. C. Patterson ◽  
D. Settle ◽  
Y. Erel ◽  
...  
Keyword(s):  
Trace Elements ◽  
North Atlantic ◽  
The North ◽  
The North Atlantic

Pristine Arctic: Background mapping of PAHs, PAH metabolites and inorganic trace elements in the North-Atlantic Arctic and sub-Arctic coastal environment

2014 ◽  
Vol 493 ◽  
pp. 719-728 ◽  
Author(s):  
Hrönn Ólína Jörundsdóttir ◽  
Sophie Jensen ◽  
Ketil Hylland ◽  
Tor Fredrik Holth ◽  
Helga Gunnlaugsdóttir ◽  
...  
Keyword(s):  
Trace Elements ◽  
North Atlantic ◽  
Coastal Environment ◽  
Pah Metabolites ◽  
The North ◽  
The North Atlantic

scholarly journals Inputs and processes affecting the distribution of particulate iron in the North Atlantic along the GEOVIDE (GEOTRACES GA01) section

2018 ◽  
Author(s):  
Arthur Gourain ◽  
Hélène Planquette ◽  
Marie Cheize ◽  
Nolwenn Lemaitre ◽  
Jan-Lukas Menzel Barraqueta ◽  
...  
Keyword(s):  
Trace Elements ◽  
Trace Metal ◽  
North Atlantic ◽  
Thermohaline Circulation ◽  
Labrador Sea ◽  
Elemental Ratios ◽  
The North ◽  
Particulate Iron ◽  
The North Atlantic ◽  
Iberian Margin

Abstract. The GEOVIDE cruise (May–June 2014, R/V Pourquoi Pas?) aimed to provide a better understanding on trace metal biogeochemical cycles in the North Atlantic. As particles play a key role in the global biogeochemical cycle of trace elements in the ocean, we discuss the distribution of particulate iron (PFe), in light of particulate aluminium (PAl), manganese (PMn) and phosphorus (PP) distributions. Overall, 32 full vertical profiles were collected for trace metal analyses, representing more than 500 samples. This resolution provides a solid basis for assessing concentration distributions, elemental ratios, size-fractionation, or adsorptive scavenging processes in key areas of the thermohaline circulation. Total particulate iron (PFe) concentrations ranged from as low as 9 pmol L−1 in surface Labrador Sea waters to 304 nmol L−1 near the Iberian margin, while median PFe concentrations of 1.15 nmol L−1 were measured over the sub-euphotic ocean interior. At most stations over the Western, the relative concentrations of total PFe and aluminium (PAl) showed the near-ubiquitous influence of crustal particles in the water column. Overall, the lithogenic component explained more than 87 % of PFe variance along the section. Within the Irminger and Labrador basins, the formation of biogenic particles led to an increase of the PFe / PAl ratio (up to 0.7 mol mol−1) compared to the continental crust ratio (0.21 mol mol−1), Margins provide important quantities of particulate trace elements (up to 10 nmol L−1 of PFe) to the open ocean, and in the case of the Iberian margin, advection of PFe was visible more than 250 km away from the margin. Additionally, several benthic nepheloid layers spreading over 200m above the seafloor were encountered along the transect, especially in the Icelandic, Irminger and Labrador basins, delivering particles with high PFe content, up to 89 nmol L−1 of PFe. Finally, remineralisation processes are also discussed, and showed different patterns among basins and elements.

scholarly journals Inputs and processes affecting the distribution of particulate iron in the North Atlantic along the GEOVIDE (GEOTRACES GA01) section

2019 ◽  
Vol 16 (7) ◽  
pp. 1563-1582 ◽  
Author(s):  
Arthur Gourain ◽  
Hélène Planquette ◽  
Marie Cheize ◽  
Nolwenn Lemaitre ◽  
Jan-Lukas Menzel Barraqueta ◽  
...  
Keyword(s):  
Trace Elements ◽  
Trace Metal ◽  
Continental Crust ◽  
North Atlantic ◽  
Molar Ratio ◽  
Surrounding Water ◽  
The North ◽  
Particulate Iron ◽  
The North Atlantic ◽  
Iberian Margin

Abstract. The aim of the GEOVIDE cruise (May–June 2014, R/V Pourquoi Pas?) was to provide a better understanding of trace metal biogeochemical cycles in the North Atlantic Ocean. As marine particles play a key role in the global biogeochemical cycle of trace elements in the ocean, we discuss the distribution of particulate iron (PFe), in relation to the distribution of particulate aluminium (PAl), manganese (PMn), and phosphorus (PP). Overall, 32 full vertical profiles were collected for trace metal analyses, representing more than 500 samples. This resolution provides a solid basis for assessing concentration distributions, elemental ratios, size fractionation, and adsorptive scavenging processes in key areas of the thermohaline overturning circulation. Total particulate iron concentrations ranged from as low as 9 pmol L−1 in surface waters of the Labrador Sea to 304 nmol L−1 near the Iberian margin, while median PFe concentrations of 1.15 nmol L−1 were measured over the sub-euphotic ocean interior. Within the Iberian Abyssal Plain, the ratio of PFe to PAl was identical to the continental crust molar ratio (0.21 mol mol−1), indicating the important influence of crustal particles in the water column. Overall, the lithogenic component explained more than 87% of PFe variance along the section. Within the Irminger and Labrador basins, the formation of biogenic particles led to an increase in the PFe∕PAl ratio (up to 0.64 mol mol−1) compared to the continental crust ratio. Continental margins induce high concentrations of particulate trace elements within the surrounding water masses (up to 10 nmol L−1 of PFe). For example, horizontal advection of PFe was visible more than 250 km away from the Iberian margin. Additionally, several benthic nepheloid layers were observed more than 200 m above the seafloor along the transect, especially in the Icelandic, Irminger, and Labrador basins, suspending particles with high PFe content of up to 89 nmol L−1.

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