Defining the composition of the deep mantle and the primordial He inventory of the Afar plume

Mapping Intimacies ◽

10.5194/egusphere-egu21-10891 ◽

2021 ◽

Author(s):

Finlay Stuart ◽

Ugur Balci ◽

Jean-Alix Barrat

Keyword(s):

Trace Element ◽

Red Sea ◽

Incompatible Trace Element ◽

Planetary Science ◽

Basaltic Rocks ◽

The North ◽

Prevailing Paradigm ◽

Deep Mantle ◽

Mantle Component ◽

Basalt Glasses

Basaltic rocks generated by upwelling mantle plumes display a range of trace element and isotope compositions indicative of strong heterogeneity in deep material brought to Earth surface.&#160; Helium isotopes are an unrivalled tracer of the deep mantle in plume-derived basalts. &#160;It is frequently difficult to identify the composition of the deep mantle component as He isotopes rarely correlate with incompatible trace element and radiogenic isotope tracers. It is supposed that this is due to the high He concentration of the deep mantle compared to degassed/enriched mantle reservoirs dominating the He in mixtures, although this is far from widely accepted.&#160; The modern Afar plume is natural laboratory for testing the prevailing paradigm.The 3He/4He of basalt glasses from 26&#176;N to 11&#176;N along the Red Sea spreading axis increases systematically from 7.9 to 15 Ra. Strong along-rift relationships between 3He/4He and incompatible trace element ratios are consistent with a binary mixture between moderately enriched shallow asthenospheric mantle in the north and plume mantle evident in basalts from the Gulf of Tadjoura, Djibouti (the Ramad enriched component of Barrat et al. 1990). &#160;The high-3He/4He basalts have trace element-isotopic compositions that are similar, but not identical, to the high 3He/4He (22 Ra) high Ti (HT2) flood basalts erupted during the initial phase of the Afar plume volcanism (Rogers et al. in press). This suggests that the deep mantle component in the modern Afar plume has a HIMU-like composition. From the hyperbolic 3He/4He-K/Th-Rb/La mixing relationships we determine that the upwelling deep mantle has 3-5 times higher He concentration than the asthenosphere mantle beneath the northern Red Sea.Barrat et al. 1990. &#160;Earth and Planetary Science Letters 101, 233-247.

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Mantle source characteristics of Triassic alkaline lavas within the Antalya Nappes, SW Turkey

10.5194/egusphere-egu2020-6775 ◽

2020 ◽

Author(s):

Ercan Aldanmaz ◽

Aykut Güçtekin ◽

Özlem Yıldız-Yüksekol

Keyword(s):

Trace Element ◽

Partial Melting ◽

Mantle Source ◽

Carbonate Platform ◽

Incompatible Trace Element ◽

Late Triassic ◽

Radiogenic Isotope ◽

Basaltic Rocks ◽

Sw Turkey ◽

End Members

The Late Triassic basaltic rocks that are dispersed as several lava sheets in a number of different tectonic slices within the Antalya nappes in SW Turkey represent the remnants of widespread oceanic magmatism with strong intra-plate geochemical signatures. The largest exposures are observed around the Antalya Bay, where pillow structured or massif lava flows are interlayered with Upper Triassic pelagic or carbonate platform sediments. Based on bulk-rock geochemical characteristics, the rocks mostly classify as alkaline basalts and display distinctive OIB-type trace element distributions characterized by significant enrichments in LILE and HFSE abundances, as well as LREE/HREE ratios, with respect to average N-MORB. Quantitative modeling of trace element data suggest that the primary melts that produced the alkaline lavas are largely the products of variable proportions of mixing between melts generated by variable, but generally low (<10) degrees of partial melting of more than one compositionally distinct mantle source. The samples, as a whole, display large variations in radiogenic isotope ratios with 87Sr/86Sr = 0.703021&#8211;0.70553, 143Nd/144Nd = 0.51247&#8211;0.51279, 206Pb/204Pb = 18.049&#8211;20.030, 207Pb/204Pb = 15.544&#8211;15.723 and 208Pb/204Pb = 38.546&#8211;39.530. Such variations in isotopic ratios correlate with the change in incompatible trace element relative abundances and reflect the involvement of a number of compositionally distinct mantle end-members. These include EMI and EMII type enriched mantle components both having lower 143Nd/144Nd than typical depleted MORB source with their contrasting low and high 206Pb/204Pb and 207Pb/204Pb ratios respectively, as well as a high time-integrated 238U/204Pb component with high 206Pb/204Pb at relatively low 87Sr/86Sr and &#949;Nd values. The results from trace element and radiogenic isotope data are consistent with the view that the initial melt generation was likely related to partial melting of the shallow convecting upper mantle in response to Triassic rifting events, while continued mantle upwelling resulted in progressively increased melting of mantle lithosphere that contained compositionally contrasting lithological domains with strong isotopic heterogeneities.

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Trace Element and Isotopic Evidence for Recycled Lithosphere from Basalts from 48 to 53°E, Southwest Indian Ridge

Journal of Petrology ◽

10.1093/petrology/egaa068 ◽

2020 ◽

Author(s):

Jixin Wang ◽

Huaiyang Zhou ◽

Vincent J M Salters ◽

Henry J B Dick ◽

Jared J Standish ◽

...

Keyword(s):

Trace Element ◽

Southwest Indian Ridge ◽

Isotopic Compositions ◽

Depleted Mantle ◽

Bone Segment ◽

Mid Ocean Ridge ◽

Mantle Component ◽

Indian Ridge ◽

Basalt Glasses ◽

Ocean Ridge

Abstract Mantle source heterogeneity and magmatic processes have been widely studied beneath most parts of the Southwest Indian Ridge (SWIR). But less is known from the newly recovered mid-ocean ridge basalts from the Dragon Bone Amagmatic Segment (53°E, SWIR) and the adjacent magmatically robust Dragon Flag Segment. Fresh basalt glasses from the Dragon Bone Segment are clearly more enriched in isotopic composition than the adjacent Dragon Flag basalts, but the trace element ratios of the Dragon Flag basalts are more extreme compared with average mid-ocean ridge basalts (MORB) than the Dragon Bone basalts. Their geochemical differences can be explained only by source differences rather than by variations in degree of melting of a roughly similar source. The Dragon Flag basalts are influenced by an arc-like mantle component as evidenced by enrichment in fluid-mobile over fluid-immobile elements. However, the sub-ridge mantle at the Dragon Flag Segment is depleted in melt component compared with a normal MORB source owing to previous melting in the subarc. This fluid-metasomatized, subarc depleted mantle is entrained beneath the Dragon Flag Segment. In comparison, for the Dragon Bone axial basalts, their Pb isotopic compositions and their slight enrichment in Ba, Nb, Ta, K, La, Sr and Zr and depletion in Pb and Ti concentrations show resemblance to the Ejeda–Bekily dikes of Madagascar. Also, Dragon Bone Sr and Nd isotopic compositions together with the Ce/Pb, La/Nb and La/Th ratios can be modeled by mixing the most isotopically depleted Dragon Flag basalts with a composition within the range of the Ejeda–Bekily dikes. It is therefore proposed that the Dragon Bone axial basalts, similar to the Ejeda–Bekily dikes, are sourced from subcontinental lithospheric Archean mantle beneath Gondwana, pulled from beneath the Madagascar Plateau. The recycling of the residual subarc mantle and the subcontinental lithospheric mantle could be related to either the breakup of Gondwana or the formation and accretion of Neoproterozoic island arc terranes during the collapse of the Mozambique Ocean, and is now present beneath the ridge.

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An evaluation of major element heterogeneity in the mantle sources of basalts

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1980.0223 ◽

1980 ◽

Vol 297 (1431) ◽

pp. 383-407 ◽

Cited By ~ 134

Keyword(s):

Trace Elements ◽

Trace Element ◽

Major Element ◽

Major Elements ◽

Element Abundances ◽

Ocean Island ◽

Basaltic Rocks ◽

The North ◽

Mantle Sources ◽

Incompatible Trace Elements

Understanding the evolution of the mantle requires a knowledge of the relative variations of the major elements, trace elements and isotopes in the mantle. Most of the evidence for mantle heterogeneity is based on variations in the trace element and isotopic ratios of basaltic rocks. These ratios are presumed to reflect variations in the mantle sources. To compare major element heterogeneities with trace element and isotopic heterogeneities, it is necessary that the major element abundances in basalts also reflect variations in the mantle sources. Probably the only major element for which this is so is iron. If a basalt has only undergone fractional crystallization of olivine, then the abundance of FeO in the basalt reflects the FeO/MgO ratio of the mantle source, the degree of melting, and the pressure at which melting occurs. Relative pressures and degrees of melting can often be constrained, so that variations in the abundances of FeO can be used to obtain information about variations in the FeO/MgO ratio of the mantle sources of basalts. Comparison of FeO contents with trace element and isotopic contents of basalts shows some striking correlations and leads to the following conclusions. 1. Parental magmas for Kilauean basalts from Hawaii may be related by different degrees of melting of a homogeneous, garnet-bearing source. 2. Mid-ocean ridge basalts from the North Atlantic show a negative correlation of La/Sm with FeO, suggesting that the sources that are most enriched in incompatible trace elements are most depleted in FeO relative to MgO, and are probably also depleted in the other components of basalt. This correlation does not apply to the entire suboceanic mantle. 3. A comparison of tholeiites from near the Azores and from Hawaii shows that sources with similar Nd and Sr isotope ratios may have undergone distinctly different histories in the development of their major and trace element abundances. 4. Ocean island tholeiites tend to be more enriched in FeO than ocean floor tholeiites. Either the ocean island sources have greater FeO/MgO ratios, or melting begins at significantly greater pressures beneath ocean islands than beneath ocean ridges. 5. Major element variations in the mantle are controlled mainly by tectonics and the addition or removal of silicate melts. Trace element variations, however, may be controlled by the addition or removal of fluids as well. Thus major elements, trace elements and isotopes may each give a different perspective important to the understanding of the evolution of the mantle.

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Provenance of basaltic tephra from Vatnajökull subglacial volcanoes, Iceland, as determined by major- and trace-element analyses

The Holocene ◽

10.1177/0959683611400456 ◽

2011 ◽

Vol 21 (7) ◽

pp. 1037-1048 ◽

Cited By ~ 62

Author(s):

Bergrún Arna Óladóttir ◽

Olgeir Sigmarsson ◽

Gudrún Larsen ◽

Jean-Luc Devidal

Keyword(s):

Trace Element ◽

Inductively Coupled Plasma ◽

Major Element ◽

Element Composition ◽

Major Element Composition ◽

Volcanic System ◽

The Holocene ◽

Inductively Coupled ◽

Ice Cap ◽

The North

The Holocene eruption history of subglacial volcanoes in Iceland is largely recorded by their tephra deposits. The numerous basaltic tephra offer the possibility to make the tephrochronology in the North Atlantic area more detailed and, therefore, more useful as a tool not only in volcanology but also in environmental and archaeological studies. The source of a tephra is established by mapping its distribution or inferred via compositional fingerprinting, mainly based on major-element analyses. In order to improve the provenance determinations for basaltic tephra produced at Grímsvötn, Bárdarbunga and Kverkfjöll volcanic systems in Iceland, 921 samples from soil profiles around the Vatnajökull ice-cap were analysed for major-element concentrations by electron probe microanalysis. These samples are shown to represent 747 primary tephra units. The tephra erupted within each of these volcanic system has similar chemical characteristics. The major-element results fall into three distinctive compositional groups, all of which show regular decrease of MgO with increasing K2O concentrations. The new analyses presented here considerably improve the compositional distinction between products of the three volcanic systems. Nevertheless, slight overlap of the compositional groups for each system still remains. In situ trace-element analyses by laser-ablation-inductively-coupled-plasma-mass-spectrometry were applied for better provenance identification for those tephra having similar major-element composition. Three trace-element ratios, Rb/Y, La/Yb and Sr/Th, proved particularly useful. Significantly higher La/Yb distinguishes the Grímsvötn basalts from those of Bárdarbunga and Rb/Y values differentiate the basalts of Grímsvötn and Kverkfjöll. Additionally, the products of Bárdarbunga, Grímsvötn and Kverkfjöll form distinct compositional fields on a Sr/Th versus Th plot. Taken together, the combined use of major- and trace-element analyses in delineating the provenance of basaltic tephra having similar major-element composition significantly improves the Holocene tephra record as well as the potential for correlations with tephra from outside Iceland.

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The efficiency of trace element uptake by seagrass Cymodocea serrulata in Rabigh lagoon, Red Sea

Environmental Science and Pollution Research ◽

10.1007/s11356-021-16808-9 ◽

2021 ◽

Author(s):

Mohammed Othman Aljahdali ◽

Abdullahi Bala Alhassan

Keyword(s):

Trace Element ◽

Red Sea ◽

Element Uptake ◽

Trace Element Uptake ◽

Cymodocea Serrulata

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Geochemical morphology of the North Mid-Atlantic Ridge, 10°–24°N: Trace element-isotope complementarity

Earth and Planetary Science Letters ◽

10.1016/0012-821x(93)90256-9 ◽

1993 ◽

Vol 120 (3-4) ◽

pp. 443-462 ◽

Cited By ~ 132

Author(s):

Laure Dosso ◽

Henri Bougault ◽

Jean-Louis Joron

Keyword(s):

Trace Element ◽

The North ◽

Mid Atlantic Ridge

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Age and Geochemical Studies of the Snyder Breccia, Coastal Labrador

Canadian Journal of Earth Sciences ◽

10.1139/e75-033 ◽

1975 ◽

Vol 12 (3) ◽

pp. 361-370 ◽

Cited By ~ 4

Author(s):

Jackson M. Barton Jr. ◽

Erika S. Barton

Keyword(s):

Trace Element ◽

North Atlantic ◽

Layered Intrusion ◽

Basement Complex ◽

Fine Grained ◽

The North ◽

Isotopic Analyses ◽

The Matrix ◽

The North Atlantic ◽

Geochemical Studies

The Snyder breccia is composed of angular to subrounded xenoliths of migmatites and amphibolites in a very fine grained matrix. It is apparently intrusive into the metasediments of the Snyder Group exposed at Snyder Bay, Labrador. The Snyder Group unconformably overlies a migmatitic and amphibolitic basement complex and is intruded by the Kiglapait layered intrusion. K–Ar ages indicate that the basement complex is Archean in age (> 2600 m.y. old) and that the Kiglapait layered intrusion was emplaced prior to 1280 m.y. ago. Major and trace element analyses of the matrix of the Snyder breccia indicate that while it was originally of tonalitic composition, later it locally underwent alteration characterized by loss of sodium and strontium and gain of potassium, rubidium and barium. Rb–Sr isotopic analyses show that this alteration occurred about 1842 m.y. ago, most probably contemporaneously with emplacement of the breccia. The Snyder Group thus was deposited sometime between 2600 and 1842 m.y. ago and may be correlative with other Aphebian successions preserved on the North Atlantic Archean craton.

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