An assessment of the relative roles of crust and mantle in magma genesis: an elemental approach

1984 ◽  
Vol 310 (1514) ◽  
pp. 549-590 ◽  
Keyword(s):  
Subduction Zones ◽  
Published Data ◽  
Flood Basalts ◽  
Continental Flood Basalts ◽  
Ocean Island Basalts ◽  
Mid Ocean Ridge ◽  
Source Mantle ◽  
Mantle Reservoir ◽  
Mafic Magmas ◽  
Ocean Ridge

The elemental compositions of terrestrial igneous rocks are reviewed with special emphasis on those elements that partition strongly into the liquids in mafic and ultramafic systems. Published data are supplemented by 79 new major- and trace-element analyses. The magmatism of ocean basins is considered in terms of a model that has the following main features: (i) density layering in the sub-lithospheric upper mantle, so that the more fertile source of ocean-island basalts (o.i.b.) underlies the less fertile source of mid-ocean ridge basalts (m.o.r.b.); (ii) the genesis of all mantle-derived magmas restricted to very small degrees of partial fusion; (iii) genesis of m.o.r.b. source mantle as residuum from the loss of a melt fraction (forming o.i.b. magmas and lithospheric veins) from o.i.b.-source mantle; (iv) subduction of o.i.b;- veined lithosphere, with a thin veneer of m.o.r.b. and sediments, to the 670 km seismic discontinuity, followed by re-heating of these components and their buoyant upwelling into the o.i.b.-source reservoir; (v) very little chemical communication across the 670 km discontinuity. All continental anorogenic magmatism (distant from subduction zones in space and time) seems to be related ultimately to the o.i.b.-source mantle reservoir, which therefore must extend beneath the lithospheric roots of continents. The minor sodic-alkalic magmatism of continents is effectively identical in composition to o.i.b. Some continental flood basalts are similar but the majority contain minor contamination (rarely more than 15%) from fusible sialic rocks. Although substantial amounts of sediments appear to be subducted, only a small proportion of them seems to re-appear in the products of island-arc and Cordilleran magmatism. Much larger sediment fractions enter the sparse ultrapotassic magmatism that occurs far behind some subcontinental subduction zones and also characteristically follows the subduction related magmatism of collisional orogenies. The remaining subducted sediments finally pass into the o.i.b.-mantle source reservoir. It is well established that, during and immediately after collisional orogeny, the fusion of sialic crust contributes substantially (or even occasionally exclusively) to batholithic magmatism. Nevertheless, the elemental variation in such magmas implies that the role of fractional crystallization in their genesis has tended to be underestimated in recent years. Mantle-derived mafic to ultramafic magmas appear to be directly or indirectly (as heat sources) involved at deep crustal levels in the parentage of most batholithic intermediate and acid magams. These mantle-derived liquids are subduction-related before continental collisions and then change to o.i.b., several million years after subduction ceases. Enhanced subduction of terrigenous sediments during the final stages of ocean closure leads to the large subducted sialic fractions which re-emerge in the ultrapotassic mafic magmas that characteristically appear immediately after a continental collision.

Lead- and strontium-isotope geochemistry of the Karmutsen Formation, Vancouver Island, British Columbia

1989 ◽  
Vol 26 (5) ◽  
pp. 908-919 ◽  
Author(s):  
Anne Andrew ◽  
Colin I. Godwin
Keyword(s):  
Isotope Geochemistry ◽  
Island Arcs ◽  
Flood Basalts ◽  
Continental Flood Basalts ◽  
Ocean Island ◽  
Mid Ocean Ridge ◽  
Isotopic Mixing ◽  
Ocean Ridge ◽  
Island Basalt ◽  
Basalt Type

Lead-isotope whole-rock ratios of the Triassic flood basalts of the Karmutsen Formation are heterogeneous, with 206Pb/2MPb = 18.72–21.51, 207Pb/204Pb = 15.56–15.77, and 208Pb/204Pb = 38.16–40.15. Whole-rock lead initial ratios are coincident with galena analyses having 206Pb/204Pb = 18.1–19.0, 207Pb/204Pb = 15.53–15.60, and 208Pb/204Pb = 38.2–38.6. Lead, uranium, and thorium concentrations are greater than for mid-ocean-ridge basalts, less than for island arcs, but similar to those in ocean-island and continental flood basalts. Isotopic similarities exist between the Columbia River – Chilcotin continental flood basalts and the Karmutsen Formation, suggesting similar origins for these basalts. The heterogeneity in whole-rock ratios can be explained in terms of isotopic mixing between a lead-rich average crustal lead type and an ocean-island basalt-type mantle source. Thus the Karmutsen Formation displays evidence for sediment contamination of the mantle.

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 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

scholarly journals Evidence for a dominantly reducing Archaean ambient mantle from two redox proxies, and low oxygen fugacity of deeply subducted oceanic crust

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Sonja Aulbach ◽  
Alan B. Woodland ◽  
Richard A. Stern ◽  
Prokopiy Vasilyev ◽  
Larry M. Heaman ◽  
...  
Keyword(s):  
Oxygen Fugacity ◽  
Published Data ◽  
Low Oxygen ◽  
Efficient Reduction ◽  
Mid Ocean Ridge ◽  
Subducted Oceanic Crust ◽  
Carbon Recycling ◽  
Oxygen Buffer ◽  
Significant Pathway ◽  
Ocean Ridge

AbstractOxygen fugacity (ƒO2) is an intensive variable implicated in a range of processes that have shaped the Earth system, but there is controversy on the timing and rate of oxidation of the uppermost convecting mantle to its present ƒO2 around the fayalite-magnetite-quartz oxygen buffer. Here, we report Fe3+/ΣFe and ƒO2 for ancient eclogite xenoliths with oceanic crustal protoliths that sampled the coeval ambient convecting mantle. Using new and published data, we demonstrate that in these eclogites, two redox proxies, V/Sc and Fe3+/ΣFe, behave sympathetically, despite different responses of their protoliths to differentiation and post-formation degassing, seawater alteration, devolatilisation and partial melting, testifying to an unexpected robustness of Fe3+/ΣFe. Therefore, these processes, while causing significant scatter, did not completely obliterate the underlying convecting mantle signal. Considering only unmetasomatised samples with non-cumulate and little-differentiated protoliths, V/Sc and Fe3+/ΣFe in two Archaean eclogite suites are significantly lower than those of modern mid-ocean ridge basalts (MORB), while a third suite has ratios similar to modern MORB, indicating redox heterogeneity. Another major finding is the predominantly low though variable estimated ƒO2 of eclogite at mantle depths, which does not permit stabilisation of CO2-dominated fluids or pure carbonatite melts. Conversely, low-ƒO2 eclogite may have caused efficient reduction of CO2 in fluids and melts generated in other portions of ancient subducting slabs, consistent with eclogitic diamond formation ages, the disproportionate frequency of eclogitic diamonds relative to the subordinate abundance of eclogite in the mantle lithosphere and the general absence of carbonate in mantle eclogite. This indicates carbon recycling at least to depths of diamond stability and may have represented a significant pathway for carbon ingassing through time.

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.

A Silurian U–Pb age for the Cape St. Mary's sills, Avalon Peninsula, Newfoundland, Canada: implications for Silurian orogenesis in the Avalon Zone

1993 ◽  
Vol 30 (8) ◽  
pp. 1607-1612 ◽  
Author(s):  
John D. Greenough ◽  
Sandra L. Kamo ◽  
Thomas E. Krogh
Keyword(s):  
Sedimentary Rocks ◽  
Geochemical Data ◽  
Mobile Belt ◽  
Ridge Basalt ◽  
Tectonic Environment ◽  
Mid Ocean Ridge ◽  
Mafic Magmas ◽  
Ocean Ridge ◽  
Avalon Peninsula ◽  
Orogenic Events

Mafic sills from Cape St. Mary's on the Avalon Peninsula of Newfoundland give an U–Pb baddeleyite age of 441 ± 2 Ma. This age corresponds with the earliest ages recorded for the climactic Silurian orogenic event that dominantly affected rocks of the Central Mobile Belt in Newfoundland. The age is consistent with but in no way necessitates that the Avalon and Gander zones were juxtaposed during the Silurian. Because sills tend to form in poorly lithified and undeformed sedimentary rocks, it is unlikely that Cambrian sediments hosting the sills were affected by Ordovician orogenic events that strongly affected central Newfoundland. Negative Nb and Ti anomalies on mid-ocean-ridge basalt normalized diagrams show that the sill geochemistry is consistent with formation in a transpressional tectonic environment. Mafic magmas clearly associated with the Silurian event share these chemical and tectonic affinities. Thus both the age and geochemical data are consistent with but do not require a link between the Gander and Avalon zones during the Silurian. If the two zones were joined prior to the Silurian then the Avalon must have been distal to both the Ordovician and Silurian orogenic activity. Further, considerable post-Silurian movement would have had to occur along the bounding Hermitage–Dover fault to account for contrasts in the intensity of metamorphism, plutonism, and deformation between the Gander and Avalon zones.

The Caldwell Group lavas of southern Quebec: MORB-like tholeiites associated with the opening of Iapetus Ocean

1999 ◽  
Vol 36 (6) ◽  
pp. 999-1019 ◽  
Author(s):  
Jean H Bédard ◽  
Ross Stevenson
Keyword(s):  
Incompatible Element ◽  
Crustal Contamination ◽  
Isotopic Data ◽  
High Field Strength ◽  
Element Abundances ◽  
Incompatible Elements ◽  
Iapetus Ocean ◽  
Mid Ocean Ridge ◽  
Source Mantle ◽  
Ocean Ridge

The Caldwell Group belongs to the Internal Nappe Domain of the Humber Zone and consists of basaltic lavas, quartzo-feldspathic sandstones, and mudslates. The lavas are clinopyroxene ± plagioclase ± olivine-phyric tholeiites, and are typically altered to epidote-, chlorite-, carbonate-, and (or) hematite-rich secondary assemblages. In most cases, the high field strength elements do not appear to have been perturbed by the alteration, and preserve magmatic signatures. Most Caldwell basalts exhibit coupled major and trace element variations compatible with low- to medium-pressure ([Formula: see text] 10 kbar, where 1 kbar = 100 MPa) fractional crystallization. Paleotectonic discriminants imply an ocean-floor or normal mid-ocean ridge basalt (N-MORB) affinity. Most basalts have flat N-MORB-normalized profiles, except for the highly incompatible elements (Ba, Th, Nb), which show slight relative enrichment. Melting models suggest that most of these lavas formed by about 20% melting from a mantle slightly less depleted than fertile MORB mantle (FMM). Subpopulations of Caldwell lavas (types 1b and 1a) are characterized by slightly higher incompatible element abundances, with similarly shaped N-MORB-normalized profiles, and can be modeled by slightly smaller degrees of melting (6-15%) of a similar source mantle. The Caldwell basalts erupted in the final stages of Iapetus rifting, when the predominant mantle source involved in melting was the depleted asthenosphere. Isotopic data preclude significant crustal contamination, yet the basalts are associated with sandstones, implying that a mature continental crust was present nearby. Nd isotopic data on the sandstones suggest erosion of an ancient Archean-Proterozoic composite terrane.

scholarly journals Basalt derived from highly refractory mantle sources during early Izu-Bonin-Mariana arc development

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
He Li ◽  
Richard J. Arculus ◽  
Osamu Ishizuka ◽  
Rosemary Hickey-Vargas ◽  
Gene M. Yogodzinski ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Spinel Peridotite ◽  
Backarc Basin ◽  
Melt Extraction ◽  
Ocean Island Basalts ◽  
Mid Ocean Ridge ◽  
Mantle Sources ◽  
Mariana Arc ◽  
Ocean Ridge ◽  
Aluminous Spinel

AbstractThe magmatic character of early subduction zone and arc development is unlike mature systems. Low-Ti-K tholeiitic basalts and boninites dominate the early Izu-Bonin-Mariana (IBM) system. Basalts recovered from the Amami Sankaku Basin (ASB), underlying and located west of the IBM’s oldest remnant arc, erupted at ~49 Ma. This was 3 million years after subduction inception (51-52 Ma) represented by forearc basalt (FAB), at the tipping point between FAB-boninite and typical arc magmatism. We show ASB basalts are low-Ti-K, aluminous spinel-bearing tholeiites, distinct compared to mid-ocean ridge (MOR), backarc basin, island arc or ocean island basalts. Their upper mantle source was hot, reduced, refractory peridotite, indicating prior melt extraction. ASB basalts transferred rapidly from pressures (~0.7-2 GPa) at the plagioclase-spinel peridotite facies boundary to the surface. Vestiges of a polybaric-polythermal mineralogy are preserved in this basalt, and were not obliterated during persistent recharge-mix-tap-fractionate regimes typical of MOR or mature arcs.

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