Geochemical Constraints on Mantle Melting and Magma Genesis at Pohnpei Island, Micronesia

The lithospheric mantle is of paramount importance in controlling the chemical composition of ocean island basalts (OIBs), influencing partial melting and magma evolution processes. To improve the understanding of these processes, the pressure–temperature conditions of mantle melting were investigated, and liquid lines of descent were modelled for OIBs on Pohnpei Island. The studied basaltic samples are alkalic, and can be classified as SiO2-undersaturated or SiO2-saturated series rocks, with the former having higher TiO2 and FeOT contents but with no distinct trace-element composition, suggesting melting of a compositionally homogenous mantle source at varying depths. Both series underwent sequential crystallization of olivine, clinopyroxene, Fe–Ti oxides, and minor plagioclase and alkali feldspar. Early magnetite crystallization resulted from initially high FeOT contents and oxygen fugacity, and late feldspar crystallization was due to initially low Al2O3 contents and alkali enrichment of the evolved magma. The Pohnpei lavas formed at estimated mantle-melting temperatures of 1486–1626 °C (average 1557 ± 43 °C, 1σ), and pressures of 2.9–5.1 GPa (average 3.8 ± 0.7 GPa), with the SiO2-undersaturated series forming at higher melting temperatures and pressures. Trace-element compositions further suggest that garnet rather than spinel was a residual phase in the mantle source during the melting process. Compared with the Hawaiian and Louisville seamount chains, Pohnpei Island underwent much lower degrees of mantle melting at greater depth, possibly due to a thicker lithosphere.

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Major- and trace-element composition of REE-rich turkestanite from peralkaline granites of the Morro Redondo Complex, Graciosa Province, south Brazil

Mineralogical Magazine ◽

10.1180/minmag.2010.074.4.645 ◽

2010 ◽

Vol 74 (4) ◽

pp. 645-658 ◽

Cited By ~ 6

Author(s):

F. C. J. Vilalva ◽

S. R. F. Vlach

Keyword(s):

Trace Element ◽

Inductively Coupled Plasma ◽

Alkali Feldspar ◽

Trace Element Composition ◽

Inductively Coupled ◽

Coupled Substitution ◽

Plasma Mass Spectrometry ◽

Compositional Variations ◽

End Members ◽

South Brazil

AbstractTurkestanite, a rare Th- and REE-bearing cyclosilicate in the ekanite–steacyite group was found in evolved peralkaline granitesfrom the Morro Redondo Complex, south Brazil. It occurswith quartz, alkali feldspar and an unnamed Y-bearing silicate. Electron microprobe analysis indicates relatively homogeneous compositions with maximum ThO2, Na2O and K2O contentsof 22.4%, 2.93% and 3.15 wt.%, respectively, and significant REE2O3 abundances(5.21 to 11.04 wt.%). The REE patterns show enrichment of LREE over HREE, a strong negative Eu anomaly and positive Ce anomaly, the latter in the most transformed crystals. Laser ablation inductively coupled plasma mass spectrometry trace element patterns display considerable depletions in Nb, Zr, Hf, Ti and Li relative to whole-rock sample compositions. Observed compositional variations suggest the influence of coupled substitution mechanisms involving steacyite, a Na-dominant analogue of turkestanite, iraqite, a REE-bearing end-member in the ekanite–steacyite group, ekanite and some theoretical end-members. Turkestanite crystals were interpreted as having precipitated during post-magmatic stages in the presence of residual HFSE-rich fluidscarrying Ca, the circulation of which wasenhanced by deformational events.

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Sr, Nd, and Pb isotopic and trace element geochemical constraints for a veined-mantle source of magmas in the Michoacan-Guanajuato Volcanic Field, west-central Mexican Volcanic Belt

GEOCHEMICAL JOURNAL ◽

10.2343/geochemj.38.43 ◽

2004 ◽

Vol 38 (1) ◽

pp. 43-65 ◽

Cited By ~ 32

Author(s):

Surendra P. Verma ◽

Toshiaki Hasenaka

Keyword(s):

Trace Element ◽

Mantle Source ◽

Volcanic Belt ◽

Volcanic Field ◽

West Central ◽

Mexican Volcanic Belt ◽

Geochemical Constraints

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Major element chemistry of ocean island basalts — Conditions of mantle melting and heterogeneity of mantle source

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2009.11.027 ◽

2010 ◽

Vol 289 (3-4) ◽

pp. 377-392 ◽

Cited By ~ 110

Author(s):

Rajdeep Dasgupta ◽

Matthew G. Jackson ◽

Cin-Ty A. Lee

Keyword(s):

Mantle Source ◽

Major Element ◽

Mantle Melting ◽

Ocean Island ◽

Ocean Island Basalts ◽

Major Element Chemistry ◽

Element Chemistry

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

10.5194/egusphere-egu21-14475 ◽

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).&#160; 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>

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