Basalt geochemistry of the Explorer Ridge area, northeast Pacific Ocean

1984 ◽  
Vol 21 (2) ◽  
pp. 157-170 ◽  
Author(s):  
Brian L. Cousens ◽  
R. L. Chase ◽  
J. -G. Schilling
Keyword(s):  
Trace Elements ◽  
Trace Element Content ◽  
Minor And Trace Elements ◽  
Mid Ocean Ridge ◽  
Mantle Sources ◽  
Juan De Fuca ◽  
Ridge Area ◽  
Heterogeneous Mantle ◽  
Basalt Geochemistry ◽  
Ocean Ridge

Forty-two fragments of young, fresh basalts, dredged from the Explorer Ridge, Paul Revere Ridge (Fracture Zone), and Dellwood Knolls, have been analysed for 34 major, minor, and trace elements, and 87Sr/86Sr ratios have been determined in seven of the fragments.The Explorer Ridge basalts have major element compositions similar to most mid-ocean ridge basalts (MORB), particularly to the iron-rich basalts of the southern Juan de Fuca Ridge. The basalts exhibit variability in trace element content, largely attributable to crystal fractionation at low pressure. With respect to MORB the incompatible minor and trace elements are weakly to strongly enriched in the Explorer samples, and are most strongly enriched in basalts from Explorer Deep. Adjacent ridge segments erupt basalts with variable incompatible element concentrations and ratios. This could be an indicator of a chemically heterogeneous mantle source, or may be the result of intermittent injection of enriched magmas from a hotspot beneath Explorer Deep. 87Sr/86Sr ratios are similar for both basalt types, and values are typical of most MORB.Based on their very different rare earth element patterns and 87Sr/86Sr ratios, the two Dellwood Knolls appear to have different mantle sources, one typically depleted and one chemically and radiogenically enriched.

A near-ridge origin for seamounts at the southern terminus of the Pratt-Welker Seamount Chain, northeast Pacific Ocean

1999 ◽  
Vol 36 (6) ◽  
pp. 1021-1031 ◽  
Author(s):  
Brian Cousens ◽  
Jarda Dostal ◽  
T S Hamilton
Keyword(s):  
Gulf Of Alaska ◽  
Trace Element Composition ◽  
Primitive Mantle ◽  
Sea Floor ◽  
Northeast Pacific ◽  
Mid Ocean Ridge ◽  
Mantle Sources ◽  
Juan De Fuca ◽  
Seamount Chain ◽  
Ocean Ridge

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.

Trace elements in anatectic products at the roof of mid-ocean ridge magma chambers: An experimental study

2017 ◽  
Vol 456 ◽  
pp. 43-57 ◽  
Author(s):  
Martin Erdmann ◽  
Lydéric France ◽  
Lennart A. Fischer ◽  
Etienne Deloule ◽  
Jürgen Koepke
Keyword(s):  
Experimental Study ◽  
Trace Elements ◽  
Magma Chambers ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

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

Minerals ◽  
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.

Petrogenetic insights from chromite in ultramafic cumulates of the Xiarihamu intrusion, northern Tibet Plateau, China

2020 ◽  
Vol 105 (4) ◽  
pp. 479-497 ◽  
Author(s):  
Xie-Yan Song ◽  
Kai-Yuan Wang ◽  
Stephen J. Barnes ◽  
Jun-Nian Yi ◽  
Lie-Meng Chen ◽  
...  
Keyword(s):  
Trace Elements ◽  
Major And Trace Elements ◽  
Tibet Plateau ◽  
Ultramafic Rocks ◽  
Sulfide Deposit ◽  
Northern Tibet ◽  
Mid Ocean Ridge ◽  
Ultramafic Cumulates ◽  
Positive Correlations ◽  
Ocean Ridge

Abstract Chromite is one of the earliest crystallized minerals from mafic melts and has been used as an important “petrogenetic indicator.” Its composition may be modified by interaction with intercumulate melt and adjacent minerals. Thus, chromite in mafic-ultramafic rocks contains clues to the geochemical affinity, evolution, and mantle source of its parent magmas. The Devonian Xiarihamu intrusion, located in the East Kunlun Orogenic Belt in the northern Tibet Plateau, China, hosts a very large disseminated Ni-Co sulfide deposit. This study focuses on geochemistry of the chromite enclosed in olivine of ultramafic rocks of the intrusion. Enrichments in Mg and Al in the rim of the chromite indicate only minor effects of alteration on the compositions of the chromite. The chromites enclosed in the olivines with forsterite percentage (Fo) lower than 87 are characterized by large variations in major and trace elements, such as large ranges of Cr·100/(Cr+Al) (Cr# = 15–47), Mg·100/(Mg+Fe2+) (Mg# = 41–65), and Al2O3 (= 26–53 wt%) as well as 380–3100 ppm V, 70–380 ppm Ga, and 1100–16300 ppm Zn. The chromites display positive correlations between Cr/(Cr+Al) and Ti, Mn, V, Ga, and Sc, inconsistent with fractional crystallization but indicative of an interaction between the chromites, intercumulate melts and hosting minerals. In contrast, chromites hosted in olivine with Fo > 87 in harzburgite have small variations in Cr# (ranging from 37 to 41), Mg# (48 to 51), and Al2O3 (30 to 35 wt%) as well as restricted variation in trace elements, indicating relatively weak interaction with trapped liquid and adjacent phases; these compositions are close to those of the most primitive, earliest crystallized chromites. The most primitive chromite has similarities with chromite in mid-ocean ridge basalt (MORB) in TiO2 and Al2O3 contents (0.19–0.32 and 27.9–36.3 wt%, respectively) and depletion of Sc and enrichment of Ga and Zn relative to MORB chromite. The geochemistry of the chromite indicates a partial melting of the asthenospheric mantle that was modified by melts derived from the subduction slab at garnet-stable pressures.

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

2020 ◽  
Vol 117 (25) ◽  
pp. 13997-14004 ◽  
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.

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

Nature ◽  
1988 ◽  
Vol 331 (6156) ◽  
pp. 511-513 ◽  
Author(s):  
Daniel J. Fornari ◽  
Michael R. Perfit ◽  
James F. Allan ◽  
Rodey Batiza
Keyword(s):  
Small Scale ◽  
Depleted Mantle ◽  
Mid Ocean Ridge ◽  
Mantle Sources ◽  
Magmatic Processes ◽  
Ocean Ridge ◽  
Lava Geochemistry
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