Coupled major and trace elements as indicators of the extent of melting in mid-ocean-ridge peridotites

Nature ◽  
2001 ◽  
Vol 410 (6829) ◽  
pp. 677-681 ◽  
Author(s):  
Eric Hellebrand ◽  
Jonathan E. Snow ◽  
Henry J. B. Dick ◽  
Albrecht W. Hofmann
Keyword(s):  
Trace Elements ◽  
Major And Trace Elements ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Petrogenetic insights from chromite in ultramafic cumulates of the Xiarihamu intrusion, northern Tibet Plateau, China

2020 ◽  
Vol 105 (4) ◽  
pp. 479-497 ◽  
Author(s):  
Xie-Yan Song ◽  
Kai-Yuan Wang ◽  
Stephen J. Barnes ◽  
Jun-Nian Yi ◽  
Lie-Meng Chen ◽  
...  
Keyword(s):  
Trace Elements ◽  
Major And Trace Elements ◽  
Tibet Plateau ◽  
Ultramafic Rocks ◽  
Sulfide Deposit ◽  
Northern Tibet ◽  
Mid Ocean Ridge ◽  
Ultramafic Cumulates ◽  
Positive Correlations ◽  
Ocean Ridge

Abstract Chromite is one of the earliest crystallized minerals from mafic melts and has been used as an important “petrogenetic indicator.” Its composition may be modified by interaction with intercumulate melt and adjacent minerals. Thus, chromite in mafic-ultramafic rocks contains clues to the geochemical affinity, evolution, and mantle source of its parent magmas. The Devonian Xiarihamu intrusion, located in the East Kunlun Orogenic Belt in the northern Tibet Plateau, China, hosts a very large disseminated Ni-Co sulfide deposit. This study focuses on geochemistry of the chromite enclosed in olivine of ultramafic rocks of the intrusion. Enrichments in Mg and Al in the rim of the chromite indicate only minor effects of alteration on the compositions of the chromite. The chromites enclosed in the olivines with forsterite percentage (Fo) lower than 87 are characterized by large variations in major and trace elements, such as large ranges of Cr·100/(Cr+Al) (Cr# = 15–47), Mg·100/(Mg+Fe2+) (Mg# = 41–65), and Al2O3 (= 26–53 wt%) as well as 380–3100 ppm V, 70–380 ppm Ga, and 1100–16300 ppm Zn. The chromites display positive correlations between Cr/(Cr+Al) and Ti, Mn, V, Ga, and Sc, inconsistent with fractional crystallization but indicative of an interaction between the chromites, intercumulate melts and hosting minerals. In contrast, chromites hosted in olivine with Fo > 87 in harzburgite have small variations in Cr# (ranging from 37 to 41), Mg# (48 to 51), and Al2O3 (30 to 35 wt%) as well as restricted variation in trace elements, indicating relatively weak interaction with trapped liquid and adjacent phases; these compositions are close to those of the most primitive, earliest crystallized chromites. The most primitive chromite has similarities with chromite in mid-ocean ridge basalt (MORB) in TiO2 and Al2O3 contents (0.19–0.32 and 27.9–36.3 wt%, respectively) and depletion of Sc and enrichment of Ga and Zn relative to MORB chromite. The geochemistry of the chromite indicates a partial melting of the asthenospheric mantle that was modified by melts derived from the subduction slab at garnet-stable pressures.

The origin of compositional variation in basalts recovered by submersible drill from Mount Glooscap, Mid-Atlantic Ridge at 36°25′N

1984 ◽  
Vol 21 (8) ◽  
pp. 934-948 ◽  
Author(s):  
James A. Walker ◽  
Patrick J. C. Ryall ◽  
Marcos Zentilli ◽  
Ian L. Gibson ◽  
Jarda Dostal
Keyword(s):  
Trace Elements ◽  
Low Temperature ◽  
Carbonate Rocks ◽  
Compositional Data ◽  
Major And Trace Elements ◽  
Compositional Variation ◽  
Mid Ocean Ridge ◽  
Mid Atlantic Ridge ◽  
Large Peak ◽  
Ocean Ridge

A large peak in the crestal mountains of the Mid-Atlantic Ridge, about 16 km west of the AMAR rift valley at 36°25′N, was sampled for basalt with a submersible electric rock core drill on a comparable surficial scale as the FAMOUS area. Twenty-eight basalt samples from seven drilling stations have been analyzed for major and trace elements. Many of the samples come from flows lying under a cover of carbonate rocks and therefore could not have been sampled by a submersible or a dredge.Through comparisons with published compositional data, it appears that, unlike "FAMOUS-generated" basalts, "AMAR-generated" basalts are, on average, more evolved and are always LREE enriched. Most of the in- and between-hole compositional variation can be accounted for by low-temperature alteration, accumulation of phenocrysts, and low-pressure, relatively low-temperature fractional crystallization. A source heterogeneous in trace elements or undergoing variable degrees of partial melting is necessary to explain the remaining compositional variation. If the large peak can be interpreted as a single volcano, it may be that lavas become progressively more differentiated with time at mid-ocean ridge volcanoes as they commonly do at subduction zone volcanoes.

Trace elements in anatectic products at the roof of mid-ocean ridge magma chambers: An experimental study

2017 ◽  
Vol 456 ◽  
pp. 43-57 ◽  
Author(s):  
Martin Erdmann ◽  
Lydéric France ◽  
Lennart A. Fischer ◽  
Etienne Deloule ◽  
Jürgen Koepke
Keyword(s):  
Experimental Study ◽  
Trace Elements ◽  
Magma Chambers ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

scholarly journals Geochemistry of Basalts from Southwest Indian Ridge 64° E: Implications for the Mantle Heterogeneity East of the Melville Transform

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 175
Author(s):  
Zhen Dong ◽  
Chunhui Tao ◽  
Jin Liang ◽  
Shili Liao ◽  
Wei Li ◽  
...  
Keyword(s):  
Trace Elements ◽  
Continental Crust ◽  
Major And Trace Elements ◽  
Southwest Indian Ridge ◽  
Spinel Lherzolite ◽  
Lower Continental Crust ◽  
Heavy Rare Earth Elements ◽  
Indian Ridge ◽  
Incompatible Trace Elements ◽  
Ocean Ridge

As one of the regional, magmatic, robust, axial ridge segments along the ultraslow-spreading Southwest Indian Ridge (SWIR), the magmatic process and mantle composition of the axial high relief at 64° E is still unclear. Here, we present major and trace elements and Sr-Nd-Pb isotope data of mid-ocean ridge basalts (MORBs) from 64° E. The basalts show higher contents of Al2O3, SiO2, and Na2O and lower contents of TiO2, CaO, and FeO for a given MgO content, and depletion in heavy rare-earth elements (HREE), enrichment in large-ion lithophile elements, and lower 87Sr/86Sr, 143Nd/144Nd and higher radiogenic Pb isotopes than the depleted MORB mantle (DMM). The high Zr/Nb (24–43) and low Ba/Nb (3.8–7.0) ratios are consistent with typical, normal MORB (N-MORB). Extensive plagioclase fractional crystallization during magma evolution was indicated, while fractionation of olivine and clinopyroxene is not significant, which is consistent with petrographic observations. Incompatible trace elements and isotopic characteristics show that the basaltic melt was formed by the lower partial melting degree of spinel lherzolite than that of segment #27 (i.e., Duanqiao Seamount, 50.5° E), Joseph Mayes Mountain (11.5° E), etc. The samples with a DMM end-member are unevenly mixed with the lower continental crust (LCC)- and the enriched mantle end-member (EM2)-like components, genetically related to the Gondwana breakup and contaminated by upper and lower continental crust (or continental mantle) components.

scholarly journals A Disequilibrium Reactive Transport Model for Mantle Magmatism

2020 ◽  
Author(s):  
Beñat Oliveira ◽  
Juan Carlos Afonso ◽  
Romain Tilhac
Keyword(s):  
Trace Elements ◽  
Rare Earth ◽  
Trace Element ◽  
Chemical Evolution ◽  
Reactive Transport ◽  
Major Elements ◽  
Phase Changes ◽  
Scale Model ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Abstract Besides standard thermo-mechanical conservation laws, a general description of mantle magmatism requires the simultaneous consideration of phase changes (e.g. from solid to liquid), chemical reactions (i.e. exchange of chemical components) and multiple dynamic phases (e.g. liquid percolating through a deforming matrix). Typically, these processes evolve at different rates, over multiple spatial scales and exhibit complex feedback loops and disequilibrium features. Partially as a result of these complexities, integrated descriptions of the thermal, mechanical and chemical evolution of mantle magmatism have been challenging for numerical models. Here we present a conceptual and numerical model that provides a versatile platform to study the dynamics and nonlinear feedbacks inherent in mantle magmatism and to make quantitative comparisons between petrological and geochemical datasets. Our model is based on the combination of three main modules: (1) a Two-Phase, Multi-Component, Reactive Transport module that describes how liquids and solids evolve in space and time; (2) a melting formalism, called Dynamic Disequilibirum Melting, based on thermodynamic grounds and capable of describing the chemical exchange of major elements between phases in disequilibrium; (3) a grain-scale model for diffusion-controlled trace-element mass transfer. We illustrate some of the benefits of the model by analyzing both major and trace elements during mantle magmatism in a mid-ocean ridge-like context. We systematically explore the effects of mantle potential temperature, upwelling velocity, degree of equilibrium and hetererogeneous sources on the compositional variability of melts and residual peridotites. Our model not only reproduces the main thermo-chemical features of decompression melting but also predicts counter-intuitive differentiation trends as a consequence of phase changes and transport occurring in disequilibrium. These include a negative correlation between Na2O and FeO in melts generated at the same Tp and the continued increase of the melt’s CaO/Al2O3 after Cpx exhaustion. Our model results also emphasize the role of disequilibrium arising from diffusion for the interpretation of trace-element signatures. The latter is shown to be able to reconcile the major- and trace-element compositions of abyssal peridotites with field evidence indicating extensive reaction between peridotites and melts. The combination of chemical disequilibrium of major elements and sluggish diffusion of trace elements may also result in weakened middle rare earth to heavy rare earth depletion comparable with the effect of residual garnet in mid-ocean ridge basalt, despite its absence in the modelled melts source. We also find that the crystallization of basalts ascending in disequilibrium through the asthenospheric mantle could be responsible for the formation of olivine gabbros and wehrlites that are observed in the deep sections of ophiolites. The presented framework is general and readily extendable to accommodate additional processes of geological relevance (e.g. melting in the presence of volatiles and/or of complex heterogeneous sources, refertilization of the lithospheric mantle, magma channelization and shallow processes) and the implementation of other geochemical and isotopic proxies. Here we illustrate the effect of heterogeneous sources on the thermo-mechanical-chemical evolution of melts and residues using a mixed peridotite–pyroxenite source.

Basalt geochemistry of the Explorer Ridge area, northeast Pacific Ocean

1984 ◽  
Vol 21 (2) ◽  
pp. 157-170 ◽  
Author(s):  
Brian L. Cousens ◽  
R. L. Chase ◽  
J. -G. Schilling
Keyword(s):  
Trace Elements ◽  
Trace Element Content ◽  
Minor And Trace Elements ◽  
Mid Ocean Ridge ◽  
Mantle Sources ◽  
Juan De Fuca ◽  
Ridge Area ◽  
Heterogeneous Mantle ◽  
Basalt Geochemistry ◽  
Ocean Ridge

Forty-two fragments of young, fresh basalts, dredged from the Explorer Ridge, Paul Revere Ridge (Fracture Zone), and Dellwood Knolls, have been analysed for 34 major, minor, and trace elements, and 87Sr/86Sr ratios have been determined in seven of the fragments.The Explorer Ridge basalts have major element compositions similar to most mid-ocean ridge basalts (MORB), particularly to the iron-rich basalts of the southern Juan de Fuca Ridge. The basalts exhibit variability in trace element content, largely attributable to crystal fractionation at low pressure. With respect to MORB the incompatible minor and trace elements are weakly to strongly enriched in the Explorer samples, and are most strongly enriched in basalts from Explorer Deep. Adjacent ridge segments erupt basalts with variable incompatible element concentrations and ratios. This could be an indicator of a chemically heterogeneous mantle source, or may be the result of intermittent injection of enriched magmas from a hotspot beneath Explorer Deep. 87Sr/86Sr ratios are similar for both basalt types, and values are typical of most MORB.Based on their very different rare earth element patterns and 87Sr/86Sr ratios, the two Dellwood Knolls appear to have different mantle sources, one typically depleted and one chemically and radiogenically enriched.

Trace element composition of clinopyroxene in gabbros and dolerites of the Tortuga Ophiolitic Complex, southernmost Patagonia.

2021 ◽  
Author(s):  
Fernanda Torres Garcia ◽  
Mauricio Calderón ◽  
Leonardo Fadel Cury ◽  
Thomas Theye ◽  
Joachim Opitz ◽  
...  
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Partial Melting ◽  
Mantle Source ◽  
Trace Element Composition ◽  
Element Composition ◽  
Mid Ocean Ridge ◽  
Back Arc ◽  
Ocean Ridge ◽  
Ophiolitic Complex

<p>During the Upper Jurassic-Lower Cretaceous times the western margin of Gondwana in southern Patagonia experienced extreme lithospheric extension and generation of rift and marginal back-arc basins. The ophiolitic complexes of the Rocas Verdes basin comprises incomplete ophiolite pseudostratigraphy lacking ultramafic rocks. The Tortuga Ophiolitic Complex, the southernmost seafloor remnant of the Rocas Verdes basin, record the most advanced evolutionary stage of the back-arc basin evolution in a mid-ocean ridge-type setting. The base of the Tortuga Complex consists of massive and layered gabbros, most of which are two pyroxene and olivine gabbros, leucogabbros, and clinopyroxene troctolites intruded by dikes of basalt and diabase with chilled margins. We present new major and trace element composition of clinopyroxene from the gabbros and sheeted dikes complexes to assess the geochemical affinity of parental basaltic magmas. Clinopyroxene in gabbros is mostly augite and have Al contents of 0.06-0.14 a.p.f.u. and Mg# of 80-92. Clinopyroxene in dolerites in the sheeted dike unit (augite and diopside) have Al content of 0.11-0.12 a.p.f.u. and Mg# of 85-92. Some immobile trace elements (e.g. Zr, Ti, Y) are sensitive to the degree of partial melting and mantle source composition, and can be used as a proxy for distinguishing tectonic environments. The Ti+Cr vs. Ca diagram, coupled with moderate-high TiO<sub>2</sub> content of clinopyroxene (0.4-1.4 wt.%) suggests their generation in mid-oceanic ridge-type environment (cf. Beccaluva et al., 1989).  The high Ti/Zr ratios (of ~4-11) coupled with low Zr contents (~0.2-1.1) are expected for higher degrees of partial melting or for melting of more depleted mantle sources. Conversely, low Zr/Y ratios (0.05-0.13) plot between the range of arc basalts. Chondrite-normalized REE patterns in clinopyroxene display a strong depletion of LREE compared to HREE and have an almost flat pattern in the MREE to HREE with a positive Eu (Eu*= 0.9-1.1) anomaly, indicating that clinopyroxene crystallized from a strongly depleted mid-ocean-ridge-type basalt, formed by extensive fractional melting of the mantle source and/or fractional crystallization and accumulation of anhydrous phases. The general trend of the incompatible trace elements patterns exhibit depletion in LILEs, minor HFSEs depletion, positive anomaly of Rb and negative anomalies in Ba, Zr, Ti and Nb, consistent with their generation from a refractory mantle source barely influenced by subduction components derived from the oceanic slab. This agrees with basalt generation in a back-arc basin located far away from the convergent margin. This study was supported by the Fondecyt grant 1161818 and the Anillo Project ACT-105.</p>

The Geology and Geochemistry of Ophiolitic Rocks Exposed at Ming's Bight, Newfoundland

1975 ◽  
Vol 12 (5) ◽  
pp. 777-797 ◽  
Author(s):  
Ryburn E. Norman ◽  
D. F. Strong
Keyword(s):  
Pillow Lava ◽  
Major And Trace Elements ◽  
Low Oxygen ◽  
Tholeiitic Magma ◽  
Mid Ocean Ridge ◽  
Lava Sequence ◽  
Deformation Features ◽  
Ophiolitic Rocks ◽  
Ocean Ridge ◽  
Structural Blocks

The Baie Verte Group, as exposed on the peninsula between Baie Verte and Ming's Bight, consists of an ophiolite assemblage ranging from interlayered ultramafic and gabbroic rocks to sheeted diabase dikes overlain by pillow lavas and volcanic sediments. The sequence has been disrupted into five structural blocks separated by fault zones containing serpentinized peridotite and/or talc-carbonate; units within each block are separated by less significant faults. These structures and other deformation features in the Baie Verte Group are interpreted to be related to early Ordovician emplacement with some effects of later Acadian deformation.The Baie Verte Group is chemically similar, both in major and trace elements, to other ophiolite sequences such as in Oman and Papua. A low-Ti and low-K tholeiitic magma crystallized under conditions of low oxygen fugacity in the upper crust beneath a mid-ocean ridge, producing the observed peridotite–pyroxenite–gabbro–diabase–pillow lava sequence.

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