Small-scale heterogeneities in depleted mantle sources: near-ridge seamount lava geochemistry and implications for mid-ocean-ridge magmatic processes

Three seamounts close to the south end of the Pratt-Welker Seamount Chain, Gulf of Alaska, have been sampled to test whether or not mantle plume-related volcanism extends south of Bowie Seamount. Lavas recovered from Oshawa, Drifters, and Graham seamounts are weathered, Mn-encrusted pillow lavas and sheet-flow fragments, commonly with glassy rims. The glasses and holocrystalline rocks are tholeiitic basalts, with light rare earth element depleted to flat primitive mantle normalized incompatible element patterns and radiogenic isotope compositions within the ranges of mid-ocean ridge and near-ridge seamount basalts from the Explorer and northern Juan de Fuca ridges. Chemically, the seamount lavas strongly resemble older, "shield-phase" tholeiitic rocks dredged from the flanks of southern Pratt-Welker seamounts, but are distinct from the younger alkaline intraplate lavas that cap Pratt-Welker edifices. The weathered, encrusted basalts were most likely erupted in a near-ridge environment, adjacent to Explorer Ridge, between 11 and 14 Ma. No evidence of plume-related activity is found in this area. Compared with northeast Pacific mid-ocean ridge and alkaline intraplate basalts, Graham seamount lavas have anomalously high 206Pb/204Pb, which does not appear to be a function of sea-floor alteration, magma contamination, or mixing between previously identified mantle components. All near-ridge seamounts in the northeast Pacific exhibit isotopic heterogeneity that does not correlate with major or trace element composition, suggesting that the mantle sources of all near-ridge seamounts have been variably depleted by prior, but recent melting events.

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Sr–Nd–Pb–Hf Isotopic Constraints on the Mantle Heterogeneities beneath the South Mid-Atlantic Ridge at 18–21°S

Minerals ◽

10.3390/min10111010 ◽

2020 ◽

Vol 10 (11) ◽

pp. 1010

Author(s):

Yun Zhong ◽

Xu Zhang ◽

Zhilei Sun ◽

Jinnan Liu ◽

Wei Li ◽

...

Keyword(s):

Isotopic Data ◽

The South ◽

Mantle Heterogeneities ◽

Depleted Mantle ◽

Mid Ocean Ridge ◽

Trace Elemental ◽

Heterogeneous Mantle ◽

Mid Atlantic Ridge ◽

St Helena ◽

Ocean Ridge

In an attempt to investigate the nature and origin of mantle heterogeneities beneath the South Mid-Atlantic Ridge (SMAR), we report new whole-rock Sr, Nd, Pb, and Hf isotopic data from eight basalt samples at four dredge stations along the SMAR between 18°S and 21°S. Sr, Nd, and Pb isotopic data from SMAR mid-ocean ridge basalts (MORBs) at 18–21°S published by other researchers were also utilized in this study. The SMAR MORBs at 18–21°S feature the following ratio ranges: 87Sr/86Sr = 0.70212 to 0.70410, 143Nd/144Nd = 0.512893 to 0.513177, 206Pb/204Pb = 18.05 to 19.50, 207Pb/204Pb = 15.47 to 15.71, 208Pb/204Pb = 37.87 to 38.64, and 176Hf/177Hf = 0.283001 to 0.283175. The 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, and 176Hf/177Hf ratios of these MORBs varied considerably along the SMAR axis. The variable compositions of the Sr–Nd–Pb–Hf isotopes, combined with the corresponding whole-rock major and trace elemental abundances reported in previous studies, suggest that the SMAR MORBs at 18–21°S were probably derived from a heterogeneous mantle substrate related to a mixture of depleted mantle (DM) materials with a small amount (but variable input) of HIMU (high-μ, where μ = 238U/204Pb)- and enriched (EMII)-type materials. The HIMU-type materials likely originated from the proximal St. Helena plume and may have been transported through “pipe-like inclined sublithospheric channels” into the SMAR axial zone. The EMII-type materials possibly originated from a recycled metasomatized oceanic crust that may have been derived from the early dispersion of other plume heads into the subcontinental asthenosphere prior to the opening of the South Atlantic Ocean. In addition, the contributions of subducted sediments, continental crust, and subcontinental lithospheric mantle components to the formation of the SMAR MORBs at 18–21°S may be nonexistent or negligible.

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The influence of small-scale mantle heterogeneities on Mid-Ocean Ridge volcanism: Evidence from the southern Mid-Atlantic Ridge (7°30′S to 11°30′S) and Ascension Island

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2010.05.009 ◽

2010 ◽

Vol 296 (3-4) ◽

pp. 299-310 ◽

Cited By ~ 31

Author(s):

H. Paulick ◽

C. Münker ◽

S. Schuth

Keyword(s):

Small Scale ◽

Mantle Heterogeneities ◽

Ascension Island ◽

Mid Ocean Ridge ◽

Mid Atlantic Ridge ◽

Ocean Ridge

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Identification of chondritic krypton and xenon in Yellowstone gases and the timing of terrestrial volatile accretion

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2003907117 ◽

2020 ◽

Vol 117 (25) ◽

pp. 13997-14004 ◽

Cited By ~ 2

Author(s):

Michael W. Broadley ◽

Peter H. Barry ◽

David V. Bekaert ◽

David J. Byrne ◽

Antonio Caracausi ◽

...

Keyword(s):

Mantle Plume ◽

Noble Gases ◽

Noble Gas ◽

Mid Ocean Ridge ◽

Mantle Sources ◽

Source Mantle ◽

Morb Source ◽

Protosolar Nebula ◽

Ocean Ridge ◽

Yellowstone Caldera

Identifying the origin of noble gases in Earth’s mantle can provide crucial constraints on the source and timing of volatile (C, N, H2O, noble gases, etc.) delivery to Earth. It remains unclear whether the early Earth was able to directly capture and retain volatiles throughout accretion or whether it accreted anhydrously and subsequently acquired volatiles through later additions of chondritic material. Here, we report high-precision noble gas isotopic data from volcanic gases emanating from, in and around, the Yellowstone caldera (Wyoming, United States). We show that the He and Ne isotopic and elemental signatures of the Yellowstone gas requires an input from an undegassed mantle plume. Coupled with the distinct ratio of129Xe to primordial Xe isotopes in Yellowstone compared with mid-ocean ridge basalt (MORB) samples, this confirms that the deep plume and shallow MORB mantles have remained distinct from one another for the majority of Earth’s history. Krypton and xenon isotopes in the Yellowstone mantle plume are found to be chondritic in origin, similar to the MORB source mantle. This is in contrast with the origin of neon in the mantle, which exhibits an isotopic dichotomy between solar plume and chondritic MORB mantle sources. The co-occurrence of solar and chondritic noble gases in the deep mantle is thought to reflect the heterogeneous nature of Earth’s volatile accretion during the lifetime of the protosolar nebula. It notably implies that the Earth was able to retain its chondritic volatiles since its earliest stages of accretion, and not only through late additions.

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Discerning asthenospheric, lithospheric, and crustal influences on the geochemistry of Quaternary basalts from the Iskut–Unuk rivers area, northwestern British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e95-117 ◽

1995 ◽

Vol 32 (9) ◽

pp. 1451-1461 ◽

Cited By ~ 5

Author(s):

Brian L. Cousens ◽

Mary Lou Bevier

Keyword(s):

Volcanic Rocks ◽

Volcanic Belt ◽

Volcanic Field ◽

Northwest Pacific ◽

Small Range ◽

Geochemical Composition ◽

Basaltic Rocks ◽

Depleted Mantle ◽

Mid Ocean Ridge ◽

Ocean Ridge

Pleistocene- to Holocene-age basaltic rocks of the Iskut–Unuk rivers volcanic field, at the southern terminus of the Stikine Volcanic Belt in the northern Canadian Cordillera, provide information on the geochemical composition of the underlying mantle and processes that have modified parental magmas. Basaltic rocks from four of the six eruptive centres are moderately evolved (MgO = 5.7–6.8%) alkaline basalts with chondrite-normalized La/Sm = 1.6–1.8, 87Sr/86Sr = 0.70336–0.70361, εNd = +4.4 to +5.9, and 206Pb/204Pb = 19.07–19.22. The small range of isotopic compositions and incompatible element ratios imply a common "depleted" mantle source for the basalts, similar to the sources of enriched mid-ocean ridge basalts from northwest Pacific spreading centres or alkali olivine basalts from the western Yukon. Positive Ba and negative Nb anomalies that increase in size with increasing SiO2 and 87Sr/86Sr indicate that the basalts are contaminated by Mesozoic-age, arc-related, Stikine Terrane crust or lithospheric mantle through which the magmas passed. Lavas from a fifth volcanic centre, Cinder Mountain, have undergone greater amounts of fractional crystallization and are relatively enriched in incompatible elements, but are isotopically identical to least-contaminated Iskut–Unuk rivers basalts. Iskut–Unuk rivers lavas share many of the geochemical characteristics of volcanic rocks from other Stikine Belt and Anahim Belt centres, as well as alkali olivine basalts from the Fort Selkirk volcanic centres of the western Yukon.

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Basalt derived from highly refractory mantle sources during early Izu-Bonin-Mariana arc development

10.21203/rs.3.rs-89845/v1 ◽

2020 ◽

Author(s):

He Li ◽

Richard Arculus ◽

Osamu Ishizuka ◽

Rosemary Hickey-Vargas ◽

Gene Yogodzinski ◽

...

Keyword(s):

Upper Mantle ◽

Philippine Sea Plate ◽

Island Arcs ◽

Element Abundances ◽

Mid Ocean Ridge ◽

Mantle Sources ◽

Backarc Basins ◽

Mariana Arc ◽

Ocean Ridge ◽

Aluminous Spinel

Abstract The character of magmatism associated with the early stages of subduction zone and island arc development is unlike that of mature systems, being dominated in the Izu-Bonon-Mariana (IBM) case by low-Ti-K tholeiitic basalts and boninites. Basalts recovered by coring the basement of the Amami Sankaku Basin (ASB), located west of the oldest remnant arc of the IBM system (Kyushu-Palau Ridge; KPR), were erupted at ~49 Ma, about 3 million years after subduction inception. The chain of stratovolcanoes defined by the KPR is superimposed on this basement. The basalts were sourced from upper mantle similar to that tapped following subduction inception, and represented by forearc basalt (FAB) dated at ~52-51 Ma. The mantle sources of the ASB basalt basement were more depleted by prior melt extraction than those involved in the vast majority of mid-ocean ridge (MOR) basalt generation. The ASB basalts are low-Ti-K, aluminous spinel-olivine-plagioclase-clinopyroxene-bearing tholeiites. We show this primary mineralogy is collectively distinct compared to basalts of MOR, backarc basins of the Philippine Sea Plate, forearc, or mature island arcs. In combination with bulk compositional (major and trace element abundances plus radiogenic isotope characteristics) data for the ASB basalts, we infer the upper mantle involved was hot (~1400oC), reduced, and refractory peridotite. For a few million years following subduction initiation, a broad region of mantle upwelling accompanied by partial melting prevailed. The ASB basalts were transferred rapidly from moderate pressures (1-2 GPa), preserving a mineralogy established at sub-crustal conditions, and experienced little of recharge-mix-tap-fractionate regimes typical of MOR or mature arcs.

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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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