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.

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.

Platinum-group element geochemistry of intraplate basalts from the Aleppo Plateau, NW Syria

2012 ◽  
Vol 150 (3) ◽  
pp. 497-508 ◽  
Author(s):  
GEORGE S.-K. MA ◽  
JOHN MALPAS ◽  
JIAN-FENG GAO ◽  
KUO-LUNG WANG ◽  
LIANG QI ◽  
...  
Keyword(s):  
Partial Melting ◽  
Middle Miocene ◽  
Primitive Mantle ◽  
Element Geochemistry ◽  
Alkali Basalts ◽  
Melt Extraction ◽  
Mid Ocean Ridge ◽  
Order Of Magnitude ◽  
Platinum Group ◽  
Ocean Ridge

AbstractEarly–Middle Miocene intraplate basalts from the Aleppo Plateau, NW Syria have been analysed for their platinum-group elements (PGEs). They contain extremely low PGE abundances, comparable with most alkali basalts, such as those from Hawaii, and mid-ocean ridge basalts. The low abundances, together with high Pd/Ir, Pt/Ir, Ni/Ir, Cu/Pd, Y/Pt and Cu/Zr are consistent with sulphide fractionation, which likely occurred during partial melting and melt extraction within the mantle. Some of the basalts are too depleted in PGEs to be explained solely by partial melting of a primitive mantle-like source. Such ultra-low PGE abundances, however, are possible if the source contains some mafic lithologies. Many of the basalts also exhibit suprachondritic Pd/Pt ratios of up to an order of magnitude higher than primitive mantle and chondrite, an increase too high to be attributable to fractionation of spinel and silicate minerals alone. The elevated Pd/Pt, associated with a decrease in Pt but not Ir and Ru, are also inconsistent with removal of Pt-bearing PGE minerals or alloys, which should have concurrently lowered Pt, Ir and Ru. In contrast, melting of a metasomatized source comprising sulphides whose Pt and to a lesser extent Rh were selectively mobilized through interaction with silicate melts, may provide an explanation.

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.

scholarly journals Extreme mantle heterogeneity in mid‐ocean ridge mantle revealed in lavas from the 8°20' N near‐axis seamount chain

2020 ◽  
Author(s):  
Molly Anderson ◽  
V. Dorsey Wanless ◽  
Michael Perfit ◽  
Ethan Conrad ◽  
Patricia Gregg ◽  
...  
Keyword(s):  
Mantle Heterogeneity ◽  
Mid Ocean Ridge ◽  
Seamount Chain ◽  
Ocean Ridge

Reply by the authors to the discussion by A. J. Calvert

Geophysics ◽  
1998 ◽  
Vol 63 (1) ◽  
pp. 318-318
Author(s):  
A. J. Calvert
Keyword(s):  
Sea Floor ◽  
Scattered Energy ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

The authors of “Suppression of sea‐floor‐scattered energy using a dip‐moveout approach—Application to the mid‐ocean ridge environment” chose not to reply to the discussion by.

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

Differentiation and source of the Nipissing Diabase intrusions, Ontario, Canada

1993 ◽  
Vol 30 (6) ◽  
pp. 1123-1140 ◽  
Author(s):  
P. C. Lightfoot ◽  
H. de Souza ◽  
W. Doherty
Keyword(s):  
Trace Element ◽  
Crustal Contamination ◽  
Primitive Mantle ◽  
Magma Source ◽  
Magma Type ◽  
Ni Content ◽  
Chemical Signatures ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Major and trace element data are presented for 2.2 Ga Proterozoic diabase sills from across the Nipissing magmatic province of Ontario. In situ differentiation of the magma coupled with assimilation of Huronian Supergroup roof sediments is responsible for the variation in composition between quartz diabase and granophyric diabase seen within many of the differentiated intrusions. Uniform trace element and isotope ratio signatures, such as La/Sm (2.8 – 3.7) and εNdCHUR (−2.7 to −5.9) characterize chilled margins and undifferentiated quartz diabases. These chemical signatures suggest the existence of a single magma source that was parental to intrusions throughout the magmatic province; this magma has higher La/Sm and lower Ti/Y than primitive mantle and is displaced towards the composition of shales. Most chilled diabases and quartz diabases have a similar Mg# (0.64 and 0.60) and Ni content (98 and 127 ppm), and it is argued that the magma differentiated at depth and was emplaced as a uniform low-Mg magma. The Wanapitei intrusion and Kukagami Lake sill are an exception in that although the quartz diabase has La/Sm similar to the Nipissing magma type, which suggests that they came from the same source, the Mg# (0.68–0.71) and Ni content (130–141 ppm) are higher, which may suggest that they are either slightly more primitive examples of the normal Nipissing magma or that cumulus hypersthene has been resorbed. The light rare earth element enriched signature of the Nipissing magmas was perhaps introduced from the continental crust as the magma migrated from the mantle to the surface, but a remarkably constant and large amount (>20%) of crustal contamination would be required. An addition of 1 –3% shale to the source of a transitional mid-ocean ridge basalt type magma can broadly reproduce the compositional features of the Nipissing magma type. The source characteristics were perhaps imparted during subduction accompanying the terminal Kenoran orogeny.

scholarly journals Radiogenic isotopes in enriched mid-ocean ridge basalts from Explorer Ridge, northeast Pacific Ocean

2017 ◽  
Vol 213 ◽  
pp. 63-90 ◽  
Author(s):  
Brian Cousens ◽  
Dominique Weis ◽  
Marc Constantin ◽  
Steve Scott
Keyword(s):  
Pacific Ocean ◽  
Radiogenic Isotopes ◽  
Northeast Pacific ◽  
Mid Ocean Ridge ◽  
Ocean Ridge ◽  
Northeast Pacific Ocean

Isotopic and trace element constraints on the genesis of a boninitic sequence in the Thetford Mines ophiolitic complex, Quebec, Canada

1997 ◽  
Vol 34 (9) ◽  
pp. 1258-1271 ◽  
Author(s):  
Valérie Olive ◽  
Réjean Hébert ◽  
Michel Loubet
Keyword(s):  
Trace Element ◽  
Trace Element Composition ◽  
Nd Isotope ◽  
Geodynamic Environment ◽  
The Pacific ◽  
Geochemical Study ◽  
Mid Ocean Ridge ◽  
Isochron Diagram ◽  
Component C ◽  
Ocean Ridge

The Mont Ham Massif (part of the Thetford Mines ophiolite, south Quebec) represents a magmatic sequence made up of tholeiitic and boninitic derived products. A geochemical study confirms the multicomponent mixing models that have been classically advanced for the source of boninites, with slab-derived components added to the main refractory harzburgitic peridotite. An isochron diagram of the boninitic rocks is interpreted as a mixing trend between two components: (i) a light rare earth element (LREE) enriched component (A), interpreted as slab-derived fluid–melts equilibrated with sedimentary materials (εNd = −3, 147Sm/144Nd = 0.140), and (ii) a LREE-depleted component (B) (0.21 < 147Sm/144Nd < 0.23), interpreted as slab-derived fluid–melt equilibrated with recycled Iapetus oceanic crust and equated to the Nd-isotope characteristics of the Iapetus mantle (εNd = 9). A multicomponent source is also necessary to explain the Nd-isotope and trace element composition of the tholeiites, which are explained by the melting of a more fertile, lherzolitic mantle and (or) mid-ocean ridge basalt source (component C), characterized by a large-ion lithophile element depleted pattern and an Iapetus mantle Nd isotopic composition (εNd = 9), mixed in adequate proportions with the two previously infered slab-derived components (A and B). The genesis of the boninites of Mont Ham is not significantly different from those of boninites located in the Pacific. An intraoceanic subduction zone appears to be an appropriate geodynamic environment for the Mont Ham ophiolitic sequence.

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