scholarly journals Investigating influences on the Pb pseudo-isochron using three-dimensional mantle convection models with a continental reservoir

2021 ◽  
Author(s):  
James Panton ◽  
J. Davies ◽  
Tim Elliott ◽  
Morten Andersen ◽  
Donald Porcelli ◽  
...  
Keyword(s):  
Mantle Convection ◽  
Plate Tectonics ◽  
Three Dimensional ◽  
Isotope Ratios ◽  
Pb Isotope ◽  
Ocean Island Basalts ◽  
Mid Ocean Ridge ◽  
Subducted Oceanic Crust ◽  
Ocean Ridge ◽  
Relative Change

For mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs), measurements of Pb isotope ratios show broad linear correlations with a certain degree of scatter. In 207Pb/204Pb - 206Pb/204Pb space, the best fit line defines a pseudo-isochron age (τPb) of ~1.9 Gyr.Previous modelling suggests a relative change in the behaviours of U and Pb between 2.25-2.5 Ga, resulting in net recycling of HIMU (high U/Pb) material in the latter part of Earth's history, to explain the observed τPb. However, simulations in which fractionation is controlled by a single set of partition coefficients throughout the model runs fail to reproduce τPb and the observed scatter in Pb isotope ratios. We build on these models with 3D mantle convection simulations including parameterisations for melting, U recycling from the continents and preferential removal of Pb from subducted oceanic crust.We find that both U recycling after the great oxygenation event (GOE) and Pb extraction after the onset of plate tectonics, are required in order to fit the observed gradient and scatter of both the 207Pb/204Pb - 206Pb/204Pb and 208Pb/204Pb - 206Pb/204Pb arrays. Unlike much previous work, our model does not require accumulations of subducted oceanic crust to persist at the CMB for long periods of time in order to match geochemical observations.

scholarly journals Preliminary results are in from mid-ocean ridge three-dimensional seismic reflection survey

Eos ◽  
1999 ◽  
Vol 80 (16) ◽  
pp. 181 ◽  
Author(s):  
S. C. Singh ◽  
M. C. Sinha ◽  
A. J. Harding ◽  
G. M. Kent ◽  
P. J. Barton ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Three Dimensional ◽  
Preliminary Results ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Origin of the Indus ophiolite linked to the mantle transition zone (410–660 km)

2021 ◽  
Author(s):  
Souvik Das ◽  
Asish R. Basu
Keyword(s):  
Transition Zone ◽  
Plate Tectonics ◽  
Tectonic Setting ◽  
Ultrahigh Pressure ◽  
Historical Contingency ◽  
Mantle Transition Zone ◽  
Contingency Model ◽  
Mid Ocean Ridge ◽  
Consistent Change ◽  
Ocean Ridge

ABSTRACT The southeast Ladakh (India) area displays one of the best-preserved ophiolite sections in this planet, in places up to 10 km thick, along the southern bank of the Indus River. Recently, in situ, ultrahigh-pressure (UHP) mineralogical evidence from the mantle transition zone (MTZ; ∼410–660 km) with diamond and reduced fluids were discovered from two peridotite bodies in the basal mantle part of this Indus ophiolite. Ultrahigh-pressure phases were also found by early workers from podiform chromitites of another coeval Neo-Tethyan ophiolite in southern Tibet. However, the MTZ phases in the Indus ophiolite are found in silicate peridotites, but not in metallic chromitites, and the peridotitic UHP phases show systematic and contiguous phase transitions from the MTZ to shallower depth, unlike the discrete UHP inclusions, all in Tibetan chromitites. We observe consistent change in oxygen fugacity (fO2) and fluid composition from (C-H + H2) to (CO2 + H2O) in the upwelling peridotitic mantle, causing melting to produce mid-ocean-ridge basalt (MORB). At shallow depths (<100 km) the free water stabilizes into hydrous phases, such as pargasitic amphibole, capable of storing water and preventing melting. Our discoveries provide unique insights into deep sub-oceanic-mantle processes, and link deep-mantle upwelling and MORB genesis. Moreover, the tectonic setting of Neo-Tethyan ophiolites has been a difficult problem since the birth of the plate-tectonics concept. This problem for the origin of ophiolites in mid-ocean-ridge versus supra-subduction zone settings clearly confused the findings from Indus ophiolites. However, in this contribution, we provide arguments in favor of mid-ocean-ridge origin for Indus ophiolite. In addition, we venture to revisit the “historical contingency” model of E.M. Moores and others for Neo-Tethyan ophiolite genesis based on the available evidence and have found that our new results strongly support the “historical contingency” model.

Element fluxes associated with subduction related magmatism

1991 ◽  
Vol 335 (1638) ◽  
pp. 393-405 ◽  
Keyword(s):  
Trace Element ◽  
Incompatible Element ◽  
Mantle Wedge ◽  
Isotope Ratios ◽  
Noticeable Effect ◽  
Arc Magmas ◽  
Mid Ocean Ridge ◽  
Ocean Ridge ◽  
Arc Magma ◽  
Subducted Sediment

Destructive plate margin magmas may be subdivided into two groups on the basis of their rare earth element (REE) ratios. Most island arc suites have low Ce/Yb, and remarkably restricted isotope ratios of 87 Sr/ 86 Sr = 0.7033, 143 Nd/ 144 Nd = 0.51302, 206 Pb/ 204 Pb = 18.76 , 207 Pb/ 204 Pb = 15.57, and 208 Pb/ 204 Pb = 38.4. However, they also have Rb/Sr (0.03), Th/U (2.2) and Ce/Yb (8.5) ratios which are significantly less than accepted estimates for the bulk continental crust. The high Ce/Yb suites have higher incompatible element contents, more restricted heavy REE, and much more variable isotope ratios. Such rocks are found in the Aeolian Islands, Grenada, Indonesia and Philippines, and their isotope and trace element features have been attributed both to contributions from subducted sediment, and/or old trace element enriched material in the mantle wedge. It is argued that for isotope and trace element models the slab component can usefully be taken to consist of subducted sediment and altered mid-ocean ridge basalts, since these may contain ca. 80% of the water in the subducted slab, and the distinctive trace element features of arc magmas are generally attributed to the movement of material in hydrous fluids. The isotope data indicate that not more than 15% of the Sr and Th in an average arc magma were derived from subducted material, and that the rest were derived from the mantle wedge. The fluxes of elements which cannot be characterized isotopically are more difficult to constrain, but for most minor and trace elements the slab derived contribution in arc magmas is too small to have a noticeable effect on the residual slab.

scholarly journals The stable strontium isotopic composition of ocean island basalts, mid-ocean ridge basalts, and komatiites

2018 ◽  
Vol 483 ◽  
pp. 595-602 ◽  
Author(s):  
Elsa Amsellem ◽  
Frédéric Moynier ◽  
James M.D. Day ◽  
Manuel Moreira ◽  
Igor S. Puchtel ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Ocean Island ◽  
Ocean Island Basalts ◽  
Mid Ocean Ridge ◽  
Stable Strontium ◽  
Ocean Ridge

Evidence from three-dimensional seismic reflectivity images for enhanced melt supply beneath mid-ocean -ridge discontinuities

Nature ◽  
2000 ◽  
Vol 406 (6796) ◽  
pp. 614-618 ◽  
Author(s):  
G. M. Kent ◽  
S. C. Singh ◽  
A. J. Harding ◽  
M. C. Sinha ◽  
J. A. Orcutt ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Mid Ocean Ridge ◽  
Seismic Reflectivity ◽  
Ocean Ridge

Triple oxygen isotope constraints on the origin of ocean island basalts

2020 ◽  
Author(s):  
Xiaobin Cao ◽  
Huiming Bao ◽  
Yongbo Peng
Keyword(s):  
Theoretical Calculation ◽  
Oxygen Isotope ◽  
Mantle Source ◽  
Plate Tectonics ◽  
Unique Feature ◽  
Published Data ◽  
Ocean Island ◽  
Ocean Island Basalts ◽  
Geochemical Proxies ◽  
Subducted Oceanic Crust

<p> </p><p><span>Understanding the origin of ocean island basalts (OIB) has important bearings on Earth’s deep mantle. Although it is widely accepted that subducted oceanic crust, as a consequence of plate tectonics, contributes material to OIB’s formation, its exact fraction in OIB’s mantle source remains ambiguous largely due to uncertainties associated with existing geochemical proxies. We have shown, through theoretical calculation and examining published data, that unlike many known proxies, triple oxygen isotope compositions (i.e. Δ<sup>17</sup>O) in olivine samples are not affected by crystallization and partial melting. This unique feature allows olivine Δ<sup>17</sup>O values to identify and quantify the fractions of subducted ocean sediments and hydrothermally altered oceanic crusts in OIB’s mantle source. In this work, new Δ<sup>17</sup>O measurements for OIB will be presented, and the implications will be discussed.<span>  </span></span></p><p> </p>

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