The rare Earth geochemistry of the Troodos Ophiolite Complex

Kay, Robert W.; Senechal, Ronald G.

doi:10.1029/jb081i005p00964

Cited by 157 publications

(30 citation statements)

References 47 publications

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“…These low concentrations support the hypothesis that the harzburgite is the residual mantle remaining after extraction of midocean ridge basalt magmas, although owing to the serpentinized nature of these samples, details of the interpretation are not clear. Available data on harzburgites from other ophiolites show that they also have very low REE concentrations Montigny et al, 1973;Kay and Senechal, 1976]. However, their Sm and Nd concentrations are lower by only a factor of -300 in relation to overlying basalts and dolerites.…”

Section: L Element Patternsmentioning

confidence: 99%

“…Analyses of other ophiolites show the same pattern of REE, K, Rb, Sr, and Ba contents [Allegre eta/., 1973;Kay and Senechal, 1976] for basalts, dolerites, and gabbros as those of the Bay of Islands Complex. Allegre et al [1973] have shown that these typical REE patterns for the pillow lavas, dolerites, and cumulate gabbros of ophiolites can be modeled by closed system fractional crystallization using the observed cumulate assemblages in the gabbros.…”

Section: L Element Patternsmentioning

confidence: 99%

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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: L Element Patternsmentioning

confidence: 99%

Section: L Element Patternsmentioning

confidence: 99%

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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“…, Cameron [1985], Hebert and Laurent [1990], Kay and Senechal [1976], Kidd and Cann [1974], Laurent [1990], Malpas [1990], Malpas and Langdon [1984], Malpas et al [1990], McCulloch and Cameron [1983], Miyashiro [1973Miyashiro [ , 1975aMiyashiro [ , 1975b, Moores [1975], Rautenschlein et al [1985], Robertson [1977], Robinson and Malpas [1990], Robinson et al [1983], Schmincke et al [1983], Schmincke and Bednarz [1990], Staudigel et al [1999], Taylor [1990] Semail (Oman) Alabaster et al [1982], Benn et al [1988], Bernoulli et al [1990], Boudier and Coleman [1981], Nicolas [1988, 1995] Robertson [1989], , Schiffman et al [1991], Shervais [1990], Kimbrough [1985a, 1985b] …”

mentioning

confidence: 99%

Birth, death, and resurrection: The life cycle of suprasubduction zone ophiolites

Shervais

2001

Geochem Geophys Geosyst

461

275

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[1] Abstract: Suprasubduction zone (SSZ) ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites. This sequence includes the following: (1) birth, which entails the formation of the ophiolite above a nascent or reconfigured subduction zone; this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex; (2) youth, during which is continued melting of refractory asthenosphere (depleted during birth) occurs in response to fluid flux from the subducting slab, with extensional deformation of the older plutonic suite, eruption of refractory lavas, and the intrusion of wehrlite-pyroxenite; (3) maturity, with the onset of semistable arc volcanism, typically calc-alkaline, as the subduction zone matures and stabilizes, and the intrusion of quartz diorite and eruption of silicic lavas; and (4) death, which is the sudden demise of active spreading and ophiolite-related volcanism, which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis; expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites; (5) resurrection, with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction. The early stages (1± 3) may be diachronous, and each stage may overlap in both time and space. The existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the SSZ tectonic setting.

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“…778A clasts could not be measured for Zr and Y, be cause insufficient quantity of material was avail able for this study. Kay and Senechal (1976 A1203 and Ti02 are believed to be immobile during hydrous alteration under the condition in which the 778A clasts were metamorphosed (200 250°C and 5-6 kb: Pearce, 1975;Pearce and Cam, 1973), though higher solubility of A1203 is re ported in an aqueous fluid under high P-T condi tions. Such immobile elements are useful for de termining the eruptive environment of altered ba saltic rocks such as the 778A clasts.…”

Section: Major Elements and Clinopyroxene Chemistrymentioning

confidence: 99%

Origin of blueschist-facies clasts in the Mariana forearc, Western Pacific.

et al. 1995

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In the Mariana forearc region, blueschist-facies metabasite clasts have been recovered from a serpentinite seamount during Ocean Drilling Program Leg 125. To clarify the origin of these metamorphic clasts, major and rare earth elements (REE), Ba, and Sr were measured in seven blueschist-facies metabasite clasts. Two out of seven clasts have zig-zag REE patterns reflecting the lanthanide tetrad effect, suggesting intense interaction with sea water. The other five clasts, however, show REE patterns with light REE depletion similar to N-type mid-ocean ridge basalts. Barium and Sr enrichments, relative to light REE abundances, are not conspicuous and most clasts show Sr and/or Ba depletions, indicating that they have chemical affinity with mid-ocean ridge basalt. This result is supported by the similarity of the Ti02-A1203 systematics of the clasts to those of mid-ocean ridge basalts.These MORB-like clasts metamorphosed under blueschist-facies conditions must have been taken into uprising serpentinite diapir at a depth where materials from oceanic crust extensively accreted. Two possible sources for the MORB-like protolith of blueschist-facies clasts are considered: (1) the oceanic crust of the subducted Pacific plate, (2) oceanic crust trapped within the area between trench axis and volcanic front when the subduction of the Pacific plate started. The second possibility is likely because the subducting Pacific plate crust is overlain by 600-800 m of oceanic sediment which is not represented in the clast population. It is proposed that the clasts provide evidence of tectonic erosion of oceanic crust which was trapped in the Mariana forearc at the initiation of subduction.

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The rare Earth geochemistry of the Troodos Ophiolite Complex

Cited by 157 publications

References 47 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

Birth, death, and resurrection: The life cycle of suprasubduction zone ophiolites

Origin of blueschist-facies clasts in the Mariana forearc, Western Pacific.

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