Element fractionation in the petrogenesis of ocean island basalts
Analytical techniques have been developed to measure the very small [230ThP32Th] atomic ratios (3-8x10-6) typical of basaltic lavas using a single focussing mass spectrometer. Compared to conventional alpha-counting methods, the technique presented typically gives a 2-5 fold improvement in reproduci...
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ftopenunivgb:oai:oro.open.ac.uk:57323 2023-06-11T04:13:13+02:00 Element fractionation in the petrogenesis of ocean island basalts Elliott, Timothy Richard 1992 application/pdf https://oro.open.ac.uk/57323/ https://oro.open.ac.uk/57323/1/541703.pdf https://doi.org/10.21954/ou.ro.0000dfeb unknown https://oro.open.ac.uk/57323/1/541703.pdf Elliott, Timothy Richard (1992). Element fractionation in the petrogenesis of ocean island basalts. PhD thesis The Open University. Thesis Public PeerReviewed 1992 ftopenunivgb https://doi.org/10.21954/ou.ro.0000dfeb 2023-05-28T05:58:16Z Analytical techniques have been developed to measure the very small [230ThP32Th] atomic ratios (3-8x10-6) typical of basaltic lavas using a single focussing mass spectrometer. Compared to conventional alpha-counting methods, the technique presented typically gives a 2-5 fold improvement in reproducibility of 230 Th/232Th ratios, and furthermore uses -5x less sample, has a simpler chemical prepartion and a data aquisition time -100x shorter. The above technique was used in investigating a suite of historic (<1000a) basanites from La Palma, Canaries. The lavas have undergone significant post melt segregration processes, involving residence in deep (>4kbar) magma chambers, that are inferred to persist for at least 30ka. The basanites show geochemical variations related to differences in the degree of partial melting, that are estimated to be between 0.3-2%. Rare earth element (REE) modelling suggests clinopyroxene, rather than garnet control during melting, contrary to expectations from recent geophysical models (McKenzie & O'Nions, in press). The La Palma mantle source is inferred to be LREE enriched, K& Rb depleted, and shows many incompatible element ratios characteristic of 'himu' basalts (Weaver 1991). In contrast, the 206pb/204pb ratios of the La Palma basanites (19.6±0.05) are lower than the isotopically defined'high p' basalts (Zindler & Hart 1986) which suggests that the La Palma source is geochemically similar, but younger than a typical 'high t' source. A suite of young (<10,000a) high MgO tholeiites from Iceland show order of magnitude variations in highly incompatible element concentrations that correlate with FeO contents. Variations within these lavas is primarily attributable to sampling of instantaneous melts from different depths within a dynamic melting column. However, additional correlations of radiogenic isotope ratios with major and trace element contents highlights mixing of various plume melts with some 20% mid-ocean ridge basalt, derived from melting of upper mantle ... Thesis Iceland Ocean Island The Open University: Open Research Online (ORO) Weaver ENVELOPE(-153.833,-153.833,-86.967,-86.967) |
institution |
Open Polar |
collection |
The Open University: Open Research Online (ORO) |
op_collection_id |
ftopenunivgb |
language |
unknown |
description |
Analytical techniques have been developed to measure the very small [230ThP32Th] atomic ratios (3-8x10-6) typical of basaltic lavas using a single focussing mass spectrometer. Compared to conventional alpha-counting methods, the technique presented typically gives a 2-5 fold improvement in reproducibility of 230 Th/232Th ratios, and furthermore uses -5x less sample, has a simpler chemical prepartion and a data aquisition time -100x shorter. The above technique was used in investigating a suite of historic (<1000a) basanites from La Palma, Canaries. The lavas have undergone significant post melt segregration processes, involving residence in deep (>4kbar) magma chambers, that are inferred to persist for at least 30ka. The basanites show geochemical variations related to differences in the degree of partial melting, that are estimated to be between 0.3-2%. Rare earth element (REE) modelling suggests clinopyroxene, rather than garnet control during melting, contrary to expectations from recent geophysical models (McKenzie & O'Nions, in press). The La Palma mantle source is inferred to be LREE enriched, K& Rb depleted, and shows many incompatible element ratios characteristic of 'himu' basalts (Weaver 1991). In contrast, the 206pb/204pb ratios of the La Palma basanites (19.6±0.05) are lower than the isotopically defined'high p' basalts (Zindler & Hart 1986) which suggests that the La Palma source is geochemically similar, but younger than a typical 'high t' source. A suite of young (<10,000a) high MgO tholeiites from Iceland show order of magnitude variations in highly incompatible element concentrations that correlate with FeO contents. Variations within these lavas is primarily attributable to sampling of instantaneous melts from different depths within a dynamic melting column. However, additional correlations of radiogenic isotope ratios with major and trace element contents highlights mixing of various plume melts with some 20% mid-ocean ridge basalt, derived from melting of upper mantle ... |
format |
Thesis |
author |
Elliott, Timothy Richard |
spellingShingle |
Elliott, Timothy Richard Element fractionation in the petrogenesis of ocean island basalts |
author_facet |
Elliott, Timothy Richard |
author_sort |
Elliott, Timothy Richard |
title |
Element fractionation in the petrogenesis of ocean island basalts |
title_short |
Element fractionation in the petrogenesis of ocean island basalts |
title_full |
Element fractionation in the petrogenesis of ocean island basalts |
title_fullStr |
Element fractionation in the petrogenesis of ocean island basalts |
title_full_unstemmed |
Element fractionation in the petrogenesis of ocean island basalts |
title_sort |
element fractionation in the petrogenesis of ocean island basalts |
publishDate |
1992 |
url |
https://oro.open.ac.uk/57323/ https://oro.open.ac.uk/57323/1/541703.pdf https://doi.org/10.21954/ou.ro.0000dfeb |
long_lat |
ENVELOPE(-153.833,-153.833,-86.967,-86.967) |
geographic |
Weaver |
geographic_facet |
Weaver |
genre |
Iceland Ocean Island |
genre_facet |
Iceland Ocean Island |
op_relation |
https://oro.open.ac.uk/57323/1/541703.pdf Elliott, Timothy Richard (1992). Element fractionation in the petrogenesis of ocean island basalts. PhD thesis The Open University. |
op_doi |
https://doi.org/10.21954/ou.ro.0000dfeb |
_version_ |
1768389972993245184 |