Isotopic composition of lead in oceanic basalt and its implication to mantle evolution

Tatsumoto, M.

doi:10.1016/0012-821x(78)90126-7

Cited by 515 publications

(188 citation statements)

References 86 publications

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“…This is similar to differentiation ages derived from mantle isochrons (Sun and Hanson, 1975;Sun and Jahn, 1975;Brooks et al, 1916a, b;Church and Tatsumoto, 1975;Tatsumoto, 1978] for both MORB and ocean island basalts. This would suggest that the widespread formation of continental crust -1.8 aeons ago is coincident with the formation of the MORB source reservoir.…”

Section: Significance Of Differentiation Ages For the Morb Sourcesupporting

confidence: 87%

Nd and Sr isotopic study of the Bay of Islands Ophiolite Complex and the evolution of the source of midocean ridge basalts

Jacobsen¹,

Wasserburg²

1979

J. Geophys. Res.

224

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Two Sm-Nd internal isochrons for pyroxene gabbros of the Bay of Islands Ophiolite Complex give well-defined ages of508 ± 6 m.y. and 501 ± 13 m.y. with initial 143 Nd/ 144 Nd of ENd= +7.7 + 0.1 and ENd = +7.5 + 0.2, respectively. Total rock samples from pillow basalts, sheeted dikes, trondhjemites, hornblende gabbros, pyroxene gabbros, and an orthopyroxenite layer from the harzburgite give initial ENd in the range from +6.5 to +8.1 with an average value of +7.6. The initial 87 Sr/ 86 Sr obtained on a pyroxenegabbro is Esr = -19.3 ± 0.3, which is typical of oceanic samples. However, the initial 87 Sr/ 86 Sr within the different phases of the complex is found to be highly variable (-52 E units) and shows the effect of sea water alteration. The ENd values demonstrate a clear oceanic affinity for the Bay of Islands complex and support earlier interpretations made on the basis of structure and geochemistry. The magnitudes of the initial ENd values (+7.6) are somewhat smaller than for typical present-day midocean ridge basalts (MORB) ( + 10). This is most likely due to differential evolution over the past 0.5 aeon of the oceanic mantle relative to the bulk earth. The observed shift is quantitatively whllt should be expected for a simple single-stage evolution. For a model with a single differentiation event at time T 0 to produce the depleted mantle, both Sm-Nd and Rb-Sr data for MORB and the Bay oflslands Complex give T 0 ::::: 1.8 aeons. This age is, however, interpreted as the mean age of the MORB source and does not refer to a unique event. The total time for producing this source by a uniform process would be of the order of 3.6 aeons. The Nd isotopic signature of oceanic crust is clearly present in this Paleozoic ophiolite and suggests that typical high-ENd reservoirs are sources of oceanic crust through the Phanerozoic. This implies relatively rapid turnover between oceanic crust and mantle sources and a good mixing of oceanic mantle for the past 1.0 aeon, including contributions from recycled continental materials. These data indicate that the major distinction between oceanic basalts and continental basalts observed in recent rocks is also preserved through the Phanerozoic. These isotopic differences clearly imply a long time distinction between the magma sources of these basalt types. It should be possible to apply the distinctive ENd values of oceanic crust and mantle to identify old obducted oceanic segments on continental blocks.

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Section: Significance Of Differentiation Ages For the Morb Sourcesupporting

confidence: 87%

Nd and Sr isotopic study of the Bay of Islands Ophiolite Complex and the evolution of the source of midocean ridge basalts

Jacobsen¹,

Wasserburg²

1979

J. Geophys. Res.

224

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“…The linear correlations of the Pb ratios for oceanic island basalts on the 207pb;204pb versus 206pb;204pb diagram and on the 208pb;204pb versus 206pb;204pb diagram can be interpreted as if they were isochrons with an age of about 1.8 b.y. [Church and Tatsumoto, 1975;Tatsumoto, 1978;Chase, 1981]. This apparent age is corroborated by Rb-Sr isotope systematics which implies an age of 1.6 b.y.…”

Section: Large-scale Recyclingsupporting

confidence: 55%

Mixing in numerical models of mantle convection incorporating plate kinematics

Gurnis¹,

Davies²

1986

J. Geophys. Res.

128

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Abstract.The process by which subducted lithosphere is mixed by mantle convection is investigated in numerical calculations.The results show that the observed isotopic heterogeneity of mantle sources and their ancient (1-2 b.y.) apparent ages are consistent with convective mixing.Passive tracers, which are introduced below "trenches," are efficiently dispersed, but nonetheless, heterogeneities in tracer density with a large range of length scales are observed to persist for 40 or more transit times (one transit time is the time to travel the fluid depth with the boundary velocity). In particular, there is a strong tendency to form high-density folds of the tracer strings, which persist much longer than simple shearing indicates. The folds persist because there is a strong tendency for material that enters the flow at the margins of cells to be transferred to adjacent cells, where it is "unmixed."When the simulations are scaled to the whole mantle, the tight clumps (folds) of tracers are shown to persist for up to 1-2 b .y. There is also a tendency for large-scale convection cells to remain isolated from recycled material for 1-2 b.y. These results are consistent with the significant chemical heterogeneity of the mantle as revealed by isotopic studies of oceanic basalts. Despite the spatial heterogeneity in tracer density, the average time tracers remain in the box from subduction at trenches to sampling at ridges (i.e., the residence time) is well constrained and within 20% of the mean residence time expected from an analytic model in which tracers are assumed to be sampled randomly. Model ages of the mantle that explicitly incorporate increased convection rates in the past and assume random sampling of heterogeneities bracket the -2 b.y. apparent Pb-Pb and Rb-Sr isochrons of midocean ridge basalts and oceanic island basalts. The conclusion of persistent spatial heterogeneity is different from the conclusions drawn from other studies. The different conclusions result, primarily, from our emphasis on the details of spatial variations as opposed to some average of the mixing, from a difference in flow unsteadiness, and from the different ways tracers have been introduced into the flow.

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“…As discussed below, however, the Sr isotopic composition of the source region for the Emperor Seamounts is different from that of the Hawaiian Ridge. Tatsumoto (1978) No. …”

Section: Discussionmentioning

confidence: 99%

“…Paleomagnetic evidence cited earlier requires the Hawaiian melting anomaly to have been relatively near its present latitude for the past 65 m.y. The significant variations in the isotopic compositions of Sr and Pb in oceanic basalts (for example, Tatsumoto, 1978) require that the oceanic mantle be heterogeneous in Rb/Sr and U/Pb ratios. If the melting anomaly is replenished by sampling a heterogeneous mantle, then the heterogeneities probably would carry through into the derivative basalts, though the sampling mechanism might tend to homogenize the source region.…”

Section: Discussionmentioning

confidence: 99%

Rb-Sr Systematics of Basalts from the Hawaiian-Emperor Volcanic Chain

Lanphere¹,

Dalrymple²,

Clague³

1980

Initial Reports of the Deep Sea Drilling Project

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RubidiumSr and Rb/Sr for basalts of the Hawaiian-Emperor chain. These data do not support the concept of a mantle isochron indicating a time when the source region for the basalts was established.The source regions for basalts of the Hawaiian-Emperor chain probably lie within the lithospheric plate; the Hawaiian hot spot or melting anomaly is probably an energy source that produced melting in the overlying plate. Variations in Sr isotopic composition within individual volcanoes and between volcanoes indicate that the source regions for basalt are quite heterogeneous in detail.

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Isotopic composition of lead in oceanic basalt and its implication to mantle evolution

Cited by 515 publications

References 86 publications

Nd and Sr isotopic study of the Bay of Islands Ophiolite Complex and the evolution of the source of midocean ridge basalts

Nd and Sr isotopic study of the Bay of Islands Ophiolite Complex and the evolution of the source of midocean ridge basalts

Mixing in numerical models of mantle convection incorporating plate kinematics

Rb-Sr Systematics of Basalts from the Hawaiian-Emperor Volcanic Chain

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