scholarly journals Elemental constraints on the amount of recycled crust in the generation of mid-oceanic ridge basalts (MORBs)

2020 ◽  
Vol 6 (26) ◽  
pp. eaba2923 ◽  
Author(s):  
Shuying Yang ◽  
Munir Humayun ◽  
Vincent J. M. Salters
Keyword(s):  
Mantle Plumes ◽  
Oceanic Ridge ◽  
Element Abundances ◽  
Incompatible Elements ◽  
Low Degree ◽  
Mantle Sources

Mid-oceanic ridge basalts (MORBs) are depleted in incompatible elements, but ridge segments far from mantle plumes frequently erupt chemically enriched MORBs (E-MORBs). Two major explanations of E-MORBs are that these basalts are generated by the melting of entrained recycled crust (pyroxenite) beneath ridges or by the melting of refertilized peridotites. These two hypotheses can be discriminated with compatible element abundances from Sc to Ge, here termed the ScGe elements. Here, we demonstrate that E-MORBs have systematically lower Ge/Si and Sc contents and slightly higher Fe/Mn and Nb/Ta ratios than depleted MORBs (D-MORBs) due to the mixing of low-degree pyroxenite melts. The Ge/Si ratio is a new tracer that effectively discriminates between melts derived from peridotite sources and melts derived from mixed pyroxenite-peridotite sources. These new data are used to estimate the distribution of pyroxenite in the mantle sources of global MORB segments.

Le terrane de Slide Mountain (Cordillères canadiennes) : une lithosphère océanique marquée par des points chauds

2003 ◽  
Vol 40 (6) ◽  
pp. 833-852 ◽  
Author(s):  
M Tardy ◽  
H Lapierre ◽  
D Bosch ◽  
A Cadoux ◽  
A Narros ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Oceanic Island ◽  
Light Rare Earth ◽  
Isotopic Compositions ◽  
Incompatible Elements ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
British Colombia ◽  
Ultramafic Cumulates ◽  
Back Arc

The Slide Mountain Terrane consists of Devonian to Permian siliceous and detrital sediments in which are interbedded basalts and dolerites. Locally, ultramafic cumulates intrude these sediments. The Slide Mountain Terrane is considered to represent a back-arc basin related to the Quesnellia Paleozoic arc-terrane. However, the Slide Mountain mafic volcanic rocks exposed in central British Colombia do not exhibit features of back-arc basin basalts (BABB) but those of mid-oceanic ridge (MORB) and oceanic island (OIB) basalts. The N-MORB-type volcanic rocks are characterized by light rare-earth element (LREE)-depleted patterns, La/Nb ratios ranging between 1 and 2. Moreover, their Nd and Pb isotopic compositions suggest that they derived from a depleted mantle source. The within-plate basalts differ from those of MORB affinity by LREE-enriched patterns; higher TiO2, Nb, Ta, and Th abundances; lower εNd values; and correlatively higher isotopic Pb ratios. The Nd and Pb isotopic compositions of the ultramafic cumulates are similar to those of MORB-type volcanic rocks. The correlations between εNd and incompatible elements suggest that part of the Slide Mountain volcanic rocks derive from the mixing of two mantle sources: a depleted N-MORB type and an enriched OIB type. This indicates that some volcanic rocks of the Slide Mountain basin likely developed from a ridge-centered or near-ridge hotspot. The activity of this hotspot is probably related to the worldwide important mantle plume activity that occurred at the end of Permian times, notably in Siberia.

scholarly journals Feldspar megacrysts and anorthosite xenolith-bearing dykes in the Narssarssuaq area, South Greenland

1992 ◽  
Vol 154 ◽  
pp. 49-59
Author(s):  
T Winther
Keyword(s):  
Open Systems ◽  
Early Stage ◽  
Rift System ◽  
Magma Chambers ◽  
Degree Of Contamination ◽  
Magma Reservoirs ◽  
Incompatible Elements ◽  
Low Degree ◽  
Alkaline Magmas ◽  
Compositional Gradients

Numerous dyke intrusions are found in the Narssarssuaq area of the Gardar province, a Mid-Proterozoic intracontinental rift system. Ten to fifteen percent of these dykes, which range in composition from trachybasalt to phonolite and rhyolite, contain significant proportions of feldspar megacrysts and occasionally anorthosite xenoliths. Two groups of dykes are distinguished; the older group is more alkaline, richer in incompatible elements and contains more anorthosite xenoliths than the younger. It is probable that the main reason for the differences is variation in magma production through time and from one area to another. Chemical zonation in the dykes reflects compositional gradients in the feeding magma reservoirs; the magma reservoirs acting as open systems in which crystal fractionation was an important controlling process. The anorthosite xenoliths are not strictly cognate with their hosts, but were derived from comparable alkaline magmas with a composition roughly corresponding to the most primitive of the dykes. The plagioclase megacrysts were presumably formed at an early stage of the development of the magma chambers. Rb-Sr dating of one of the dykes from the older group of dykes gives an age of 1206 ± 20 Ma and an initial 87Sr/86Sr ratio of 0.7028 ± 0.0001 supporting a low degree of contamination with upper crustal Sr.

Chapter 5.3b Mount Early and Sheridan Bluff: petrology

2021 ◽  
pp. M55-2019-2 ◽  
Author(s):  
Kurt S. Panter ◽  
Jenna Reindel ◽  
John L. Smellie
Keyword(s):  
Volcanic Field ◽  
Rift System ◽  
The West ◽  
Simultaneous Generation ◽  
Element Abundances ◽  
West Antarctic ◽  
Mantle Sources ◽  
West Antarctic Rift System ◽  
Ocean Ridge ◽  
West Antarctic Rift

AbstractThis study discusses the petrological and geochemical features of two monogenetic Miocene volcanoes, Mount Early and Sheridan Bluff, which are the above-ice expressions of Earth's southernmost volcanic field located at c. 87° S on the East Antarctic Craton. Their geochemistry is compared to basalts from the West Antarctic Rift System to test affiliation and resolve mantle sources and cause of melting beneath East Antarctica. Basaltic lavas and dykes are olivine-phyric and comprise alkaline (hawaiite and mugearite) and subalkaline (tholeiite) types. Trace element abundances and ratios (e.g. La/Yb, Nb/Y, Zr/Y) of alkaline compositions resemble basalts from the West Antarctic rift and ocean islands (OIB), while tholeiites are relatively depleted and approach the concentrations levels of enriched mid-ocean ridge basalt (E-MORB). The magmas evolved by fractional crystallization with contamination by crust; however, neither process can adequately explain the contemporaneous eruption of hawaiite and tholeiite at Sheridan Bluff. Our preferred scenario is that primary magmas of each type were produced by different degrees of partial melting from a compositionally similar mantle source. The nearly simultaneous generation of lower degrees of melting to produce alkaline types and higher degrees of melting forming tholeiite was most likely to have been facilitated by the detachment and dehydration of metasomatized mantle lithosphere.

scholarly journals Mantle Plumes and Mantle Sources

Science ◽  
1992 ◽  
Vol 258 (5083) ◽  
pp. 821-821 ◽  
Author(s):  
K. A. Farley ◽  
H. Craig
Keyword(s):  
Mantle Plumes ◽  
Mantle Sources

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

2020 ◽  
Author(s):  
He Li ◽  
Richard Arculus ◽  
Osamu Ishizuka ◽  
Rosemary Hickey-Vargas ◽  
Gene Yogodzinski ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Philippine Sea Plate ◽  
Island Arcs ◽  
Element Abundances ◽  
Mid Ocean Ridge ◽  
Mantle Sources ◽  
Backarc Basins ◽  
Mariana Arc ◽  
Ocean Ridge ◽  
Aluminous Spinel

Abstract The character of magmatism associated with the early stages of subduction zone and island arc development is unlike that of mature systems, being dominated in the Izu-Bonon-Mariana (IBM) case by low-Ti-K tholeiitic basalts and boninites. Basalts recovered by coring the basement of the Amami Sankaku Basin (ASB), located west of the oldest remnant arc of the IBM system (Kyushu-Palau Ridge; KPR), were erupted at ~49 Ma, about 3 million years after subduction inception. The chain of stratovolcanoes defined by the KPR is superimposed on this basement. The basalts were sourced from upper mantle similar to that tapped following subduction inception, and represented by forearc basalt (FAB) dated at ~52-51 Ma. The mantle sources of the ASB basalt basement were more depleted by prior melt extraction than those involved in the vast majority of mid-ocean ridge (MOR) basalt generation. The ASB basalts are low-Ti-K, aluminous spinel-olivine-plagioclase-clinopyroxene-bearing tholeiites. We show this primary mineralogy is collectively distinct compared to basalts of MOR, backarc basins of the Philippine Sea Plate, forearc, or mature island arcs. In combination with bulk compositional (major and trace element abundances plus radiogenic isotope characteristics) data for the ASB basalts, we infer the upper mantle involved was hot (~1400oC), reduced, and refractory peridotite. For a few million years following subduction initiation, a broad region of mantle upwelling accompanied by partial melting prevailed. The ASB basalts were transferred rapidly from moderate pressures (1-2 GPa), preserving a mineralogy established at sub-crustal conditions, and experienced little of recharge-mix-tap-fractionate regimes typical of MOR or mature arcs.

scholarly journals Siderophile element constraints on the origin of the Moon

2014 ◽  
Vol 372 (2024) ◽  
pp. 20130258 ◽  
Author(s):  
Richard J. Walker
Keyword(s):  
The Moon ◽  
Element Abundances ◽  
Giant Impact ◽  
The Earth ◽  
Precision Determination ◽  
Mantle Sources ◽  
Volcanic Glasses ◽  
High Precision Determination ◽  
Origin Of The Moon

Discovery of small enrichments in 182 W/ 184 W in some Archaean rocks, relative to modern mantle, suggests both exogeneous and endogenous modifications to highly siderophile element (HSE) and moderately siderophile element abundances in the terrestrial mantle. Collectively, these isotopic enrichments suggest the formation of chemically fractionated reservoirs in the terrestrial mantle that survived the putative Moon-forming giant impact, and also provide support for the late accretion hypothesis. The lunar mantle sources of volcanic glasses and basalts were depleted in HSEs relative to the terrestrial mantle by at least a factor of 20. The most likely explanations for the disparity between the Earth and Moon are either that the Moon received a disproportionately lower share of late accreted materials than the Earth, such as may have resulted from stochastic late accretion, or the major phase of late accretion occurred prior to the Moon-forming event, and the putative giant impact led to little drawdown of HSEs to the Earth's core. High precision determination of the 182 W isotopic composition of the Moon can help to resolve this issue.

V. Petrogenesis and discussion

1971 ◽  
Vol 268 (1192) ◽  
pp. 707-725 ◽  
Keyword(s):  
Partial Melting ◽  
Upper Mantle ◽  
Experimental Studies ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Magma Genesis ◽  
Element Abundances ◽  
Incompatible Elements ◽  
Basaltic Magmas ◽  
Velocity Zone

Basaltic magmas are formed by partial melting of a source rock of peridotitic composition (pyrolite) under upper mantle conditions. Experimental studies of the mineralogy of pyrolite and the melting relations of various basaltic magmas under high-pressure conditions are integrated in an attempt to present an internally consistent model of source composition, derived liquid compositions and residual mantle compositions. The role of a small (0.1 %) content of water in the upper mantle is treated in some detail. The presence of the low velocity zone in the upper mantle is attributed to a small (< 5 %) degree of melting of pyrolite containing approximately 0.1% water. The small liquid fraction present in the low-velocity zone is highly undersaturated olivine nephelinite or olivine melilite nephelinite. Other magma types of direct upper mantle derivation ranging from olivine trachybasalt to olivine melilitite and to tholeiitic picrite are assigned to a genetic grid expressing the depth (pressure) of magma segregation, the degree of partial melting of the source pyrolite, the water content and approximate temperature of the magma. While this genetic model can account for variations in major element abundances and normative mineralogy among basalts, there are variations in abundances of the incompatible elements, particularly K, Rb, Ba, and the rare earths, which are inconsistent with a model invoking a constant source composition for all mantle-derived basalts. Additional factors producing source inhomogeneity, particularly in incompatible element abundances, include the possibility of two-stage melting and of chemical zoning within the low-velocity zone. It is suggested that vertical migration of a fluid or incipient melt phase, enriched in H 2 O, CO 2 and incompatible elements, occurs within the low-velocity zone. The evolution of continental and oceanic rift systems and of the Hawaiian volcanic province is discussed in relation to the depths and conditions of magma genesis derived from the models of magma genesis.

Geochemical constraints on the evolution of the early continental crust

1981 ◽  
Vol 301 (1461) ◽  
pp. 423-442 ◽  
Keyword(s):  
Trace Element ◽  
Continental Crust ◽  
Lower Crust ◽  
Plate Tectonics ◽  
Tectonic Setting ◽  
Mantle Plumes ◽  
Element Abundances ◽  
Ocean Island ◽  
Rock Types ◽  
Greenstone Belts

The most important process affecting both major and trace-element concentrations in the mantle and crust is melting producing silicate liquids which then migrate. Another process whose effects are becoming more apparent is the transport of elements by CO 2 - and H 2 O-rich fluids. Due to the relatively small amounts of fluids involved they have but little effect on the major-element abundances but may severely affect minor- and trace-element abundances in their source and the material through which they travel. The Archaean crust was a density filter which reduced the possibility of komatiite or high FeO melts with relative densities greater than about 3.0 from reaching the surface. Those melts retained in the lower crust or at the crust-mantle boundary would have enhanced the possibility of melting in the lower crust. The high FeO melts may have included the Archaean equivalents of alkali basalt whose derivatives may form an important component in the Archaean crust. The occurrence of ultramafic to basic to alkaline magmas in some Archaean greenstone belts is an assemblage most typical of modern ocean-island suites in continental environments. The rock types in the assemblage were modified by conditions of higher heat production during the Archaean and thus greater extents of melting and melting at greater depths. If modern ocean-island suites are associated with mantle plumes, which even now may be an important way to transport heat upward from the deeper mantle, it is suggested that during the Archaean mantle plumes were an important factor in the evolution of the continental crust. It appears that the Archaean continental crust was of comparable thickness to that of the present based on geobarometeric data. If the freeboard concept applied then, this would suggest that plate tectonics was also an active process during the Archaean. If so, it is probably no more realistic to assume that all Archaean greenstone belts had a similar tectonic setting than to assume that all modern occurrences of basic rocks have a common tectonic setting.

Volcanism from fissure zones and the Caldeira central volcano of Faial Island, Azores archipelago: geochemical processes in multiple feeding systems

2013 ◽  
Vol 150 (3) ◽  
pp. 536-555 ◽  
Author(s):  
VITTORIO ZANON ◽  
ULRICH KUEPPERS ◽  
JOSÉ MANUEL PACHECO ◽  
INÊS CRUZ
Keyword(s):  
Fractional Crystallization ◽  
Central Volcano ◽  
Geochemical Processes ◽  
Magma Reservoirs ◽  
Incompatible Elements ◽  
Mantle Sources ◽  
Mafic Magmas ◽  
Multiple Feeding ◽  
Atlantic Area ◽  
Feeding Systems

AbstractMagmas in Faial Island, Azores (Portugal), were mostly erupted from two fissure zones and the Caldeira central volcano during overlapping periods. The fissure zones follow extensional trends oriented WNW and ESE and erupted nepheline- to hypersthene-normative basalts and hawaiites. The Caldeira central volcano builds the central part of the island, which is cut by the fissure zones. Ne-normative basalts show similar high-field-strength element (HFSE) concentrations but higher large ion lithophile element (LILE) concentrations than hy-normative equivalents. Primitive melts were generated by small (3–5%) degrees of partial melting of garnet-bearing peridotite, variably enriched in incompatible elements. Overall, basalts from Faial show relatively higher LILE abundances and LILE/HFSE ratios than those of the other islands of the Azores and of many other volcanoes in the Atlantic area. This feature indicates the existence of chemical heterogeneities in the mantle sources characterized by variable degrees of metasomatism, both at local and regional scales. Hawaiites evolved from basalts through 30–40% fractional crystallization of mafic phases plus some plagioclase, in deep reservoirs, at about 430–425 MPa (~ 15 km). The Caldeira central volcano rocks range from basalts to trachytes. Basalts, produced under similar conditions as fissure basalts, evolved to trachytes through large degrees of polybaric fractional crystallization (100–760 MPa; i.e. ~ 3.6–26 km), involving olivine, clinopyroxene, feldspar and minor quantities of amphibole, biotite, apatite and oxides. In contrast, mafic magmas from the fissure zones were erupted directly onto the surface from magma reservoirs mainly located at the crust–mantle boundary.

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.

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