Igneous Rock Associations 18. Transition Metals in Oceanic Island Basalt: Relationships with the Mantle Components

Greenough, John D.; MacKenzie, Kevin

doi:10.12789/geocanj.2015.42.071

Cited by 5 publications

(5 citation statements)

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“…In the case of the North Island Complex, it is unlikely that the parental magma was tholeiitic. The total alkali (Na 2 O+K 2 O wt%) content of the syenitic rocks of this study exceeds 11 wt%, the contemporaneous basaltic rocks reported from North Island and Silhouette are alkaline, and the most calcic plagioclase in the North Island gabbroic rocks is An37 which is common for the late crystallization stages of alkali basalt (Dickin et al, 1986;Greenough et al, 2005;Owen-Smith et al, 2013). Yet, the North Island Complex is metaluminous rather than peralkaline.…”

Section: Implications For the Tectonomagmatic Evolution Of The North ...contrasting

confidence: 51%

Petrogenesis of the Early Paleogene North Island Syenite Complex, Seychelles

Shellnutt,

Lee,

Iizuka

et al. 2024

American Journal of Science

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The Early Paleogene (63.65 ± 0.52 Ma, 63.11 ± 0.45 Ma) North Island syenitic complex of the Seychelles microcontinent is composed principally of diorite (SiO2 ≈ 57 wt%), syenite (SiO2 = 61–65 wt%), and microsyenite (SiO2 = ∼70 wt%). The rocks are metaluminous, ferroan, and alkalic, and are compositionally similar to the A1-type granitoids. The trace element compositions of the syenitic rocks show minor spatial variability between the eastern (Congoment, Bernica) and western portions (Grand’Anse, Mt. Des Cèdres) of the island. The whole rock Sr-Nd (87Sr/86Sri = 0.704095–0.707533; εNd(t) = +1.2–+1.9) and zircon Hf ( εHf(t) = +2.1–+8.4) isotopes are indicative of a juvenile magma source. The low Th/NbPM (0.3–1.5) and high Nb/U (30.9–109) ratios do not indicate a crustal origin of the rocks nor do they suggest crustal contamination was significant. Hydrous fractional crystallization modeling shows that a mafic alkaline parental magma can yield residual liquid compositions similar to the diorites and syenites under reducing conditions ( ΔFMQ = −1) at a pressure of 0.3 GPa. However, feldspar accumulation likely occurred as some rocks have elevated Eu/Eu* (>1.1) values. The emplacement of the North Island complex is contemporaneous with the eruption of the Deccan Traps and rifting of the Seychelles microcontinent from India. Rifting and magmatism was likely related to the passage of the Indian plate over the Réunion hotspot. The modeling results of the study demonstrate that crystallization pressure has an influence on whether basalt-derived A-type granitoids will evolve to metaluminous or peralkaline compositions.

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Section: Implications For the Tectonomagmatic Evolution Of The North ...contrasting

confidence: 51%

Petrogenesis of the Early Paleogene North Island Syenite Complex, Seychelles

Shellnutt,

Lee,

Iizuka

et al. 2024

American Journal of Science

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“…The total alkalis versus silica diagram ( Figure 42; see List of Figures), higher Nb/Y ratios ( Figure 43), and steeper slopes of Wells Gray sideromelane on chondrite-normalized rare earth element (REE) diagrams (Figures 48 and 49) confirm that, for samples analyzed in this study, those from Wells Gray are more alkaline than those from Helgafell. Sideromelane analyses from the two Helgafell outcrops appear to have distinguishable characteristics with those low in the stratigraphic section showing subtly higher Nb/Y ratios ( Figure 43) consistent with higher percentages of melting (Condie, 2003;Floyd & Winchester, 1975;Greenough & MacKenzie, 2015;Greenough & Ya'acoby, 2013) as well as subtly lower Zr/TiO 2 ( Figure 43) indicative of slightly less differentiation (Hastie et al, 2007;Motoki et al, 2015;Murphy, 2007). The eruption that produced the unit may have been precipitated by the arrival of a new batch of magma to the magma chamber.…”

Section: Sideromelane Compositionsmentioning

confidence: 93%

“…Any two samples plotting close together on a MDS diagram have highly correlated element concentrations. The spread of geochemical analyses along the X and Y axes of MDS diagrams are thought to reflect the dominant processes that affected the samples; variation along dimension 1 should reflect the more dominant process (Greenough et al, 2010;Greenough & MacKenzie, 2015;Greenough & Ya'acoby, 2013). Thus, the observation that palagonite and sideromelane from each locality plot at a common dimension 1 value (Figures 52 and 53; see…”

Section: Relict Sideromelane Signatures In Palagonitementioning

confidence: 99%

“…Multi-dimensional scaling (MDS) is a powerful exploratory multivariate statistical method used to find similarities and dissimilarities between either samples or the chemical data in two or more dimensions (Greenough & MacKenzie, 2015;Greenough & Ya'acoby, 2013). As a spatial model, MDS operates directly on dissimilarities and scales distances, not axes.…”

Section: Multi-dimensional Scalingmentioning

confidence: 99%

“…Although multi-dimensional scaling (MDS) does not provide direct information on processes or causes for observed patterns, it is an effective tool to show important relationships (similarities and differences) within geochemical data (Greenough & MacKenzie, 2015;Greenough & Ya-acoby, 2013 An MDS plot for Helgafell palagonite shows dimension 1 to generally separate basalt 1 and 2, and palagonite compositions relate to the sample from which they came ( Figure 54). (Table 11) data.…”

Section: Multi-dimensional Scaling (Mds) Statisticsmentioning

confidence: 99%

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A Comparative Study of Glaciovolcanic Palagonitization of Tholeiitic and Alkaline Sideromelane at Helgafell, Iceland and Wells Gray-Clearwater Volcanic Field, Bc Canada

Massey¹,

Greenough²,

Edwards³

2017

Geological Society of America Abstracts With Programs

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Pleistocene glaciovolcanic eruptions occurred frequently beneath continental-scale ice sheets producing vitric, fragmental volcanic deposits in Helgafell, Iceland (tholeiitic basalt) and Wells Gray, BC, Canada (alkali olivine basalt). They are highly susceptible to hydrothermal alteration that transforms sideromelane (basaltic volcanic glass) into palagonite (early amorphous material) and secondary minerals (i.e. zeolites, clays and sulfides). Compositional controls, mass transfer and geochemical-textural relationships are investigated by optical microscopy and analyses of major (12) and trace (32) elements in glass-palagonite pairs by Electron Microprobe Analysis (EMPA), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), and geochemical modelling. Helgafell's thinner (6-10 µm vs. 10-20 µm) palagonite rims demarcate highly vesicular (30.2% vs. 4.9%) sideromelane that has more secondary minerals (1.4% vs. 0.5%) than Wells Gray's microlite-rich (12.3% vs. 0.1%) sideromelane. The thicknesses of palagonite rims are similar whether the sideromelane is unaltered or completely altered. Multi-dimensional scaling confirms that sideromelane composition, reflecting igneous processes, strongly controls the chemistry of palagonite. A comparison of element behavior in the palagonite from both localities reveals a tendency for water-soluble cations (Cl, K, Na, Rb, Cu, Mn, P) to correlate with water concentrations. Plots of element ratios (Nb/Y vs La/Nd; Sc/Ta vs Zr/Th) calculated from "immobile" elements show that palagonite from Wells Gray and Helgafell are distinct, and have ratios that are similar to sideromelane that produced the palagonite. Thus some palagonite compositions reflect primary magma compositions based on immobile elements. Gresens' mass transfer calculations confirm minimal movement of these elements during palagonitization. However, the same calculations reveal a pattern of Cu, Cl, Ni, Rb and U addition and Na, Ca, Mg, P, V and Mn removal that is similar at both localities. Microprobe traverses identified eight prominent trends across the glass-palagonite interface and palagonite rim, which do not appear to be controlled by sideromelane composition. Several element concentrations decrease in palagonite, including Si (by ~3-10%), Al, Ca and Na, while Ti, Fe and Mg concentrations increase. Locally, the palagonite has an inner Ti-rich zone. The gradual increase in Mg across the palagonite rim may be indicative of changes in solubility and pH. Preface The sites chosen in Iceland and British Columbia to sample and analyze for this thesis were at the suggestion of co-supervisor, Dr. Benjamin Edwards. Sample collection, cutting and preparation was completed by the author. Stephen Wood at the University of Western Ontario cut the thin sections. Standards used during the SEM-EDS and EMPA-WDS analyses were provided by both the Smithsonian and Micro-Analysis Consultants Ltd.

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Earth’s evolving subcontinental lithospheric mantle: inferences from LIP continental flood basalt geochemistry

Greenough

McDivitt

2017

Int J Earth Sci (Geol Rundsch)

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Igneous Rock Associations 18. Transition Metals in Oceanic Island Basalt: Relationships with the Mantle Components

Cited by 5 publications

References 56 publications

Petrogenesis of the Early Paleogene North Island Syenite Complex, Seychelles

Petrogenesis of the Early Paleogene North Island Syenite Complex, Seychelles

A Comparative Study of Glaciovolcanic Palagonitization of Tholeiitic and Alkaline Sideromelane at Helgafell, Iceland and Wells Gray-Clearwater Volcanic Field, Bc Canada

Earth’s evolving subcontinental lithospheric mantle: inferences from LIP continental flood basalt geochemistry

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