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Incompatible element

About: Incompatible element is a research topic. Over the lifetime, 2420 publications have been published within this topic receiving 154052 citations.


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TL;DR: In particular, the 1-2-Ga Sr age and the 780-Ma Nd age can be regarded as minimum ages of differentiation as discussed by the authors, which is the most suitable geodynamic mechanism to account for the exposure of huge bodies of subcontinental orogenic spinel Iherzolites from the western Mediterranean area.
Abstract: Mantle peridotites of the External Liguride (EL) units (Northern Apennines) represent slices of subcontinental lithospheric mantle emplaced at the surface during early stages of rifting of the Jurassic Ligurian Piemontese basin. Petrological, ion probe and isotopic investigations have been used to unravel the nature of their mantle protolith and to constrain the timing and mechanisms of their evolution. EL peridotites are dominantly fertile spinel Iherzolites partly recrystallized in the plagioclase Iherzolite stability field. Clinopyroxenes stable in the spinelfacies assemblage have nearly flat REE patterns (Ce-s/ SmN = 0-6-0-8) at (10-16) xCl and high Na, Sr, Ti and %r contents. Kaersutitic—Ti-pargasitic amphiboles also occur in the spinelfacies assemblage. Their LREE-depleted REE spectra and very low Sr, %r and Ba contents indicate that they crystallized from hydrous fluids with low concentrations of incompatible elements. Thermometric estimates on the spinelfacies parageneses yield lithospheric equilibrium temperatures in the range 1000-1100°C, in agreement with the stability of amphibole, which implies T<1100°C. Sr and Nd isotopic compositions, determined on carefully handpicked clinopyroxene separates, plot within the depleted end of the MORB field CSr/Sr = 0 • 70222-0 • 70263; Nd/Nd = 0 -5130470 -513205) similar to many subcontinental orogenic spinel Iherzolites from the western Mediterranean area (e.g. Ivrea Z and Lanzo N). The interpretation of the EL Iherzolites as subcontinental lithospheric mantle is reinforced by the occurrence of one extremeh depleted isotopic composition (Sr/Sr-0-701736; Nd/Nd = 0-513543). Sr and Nd model ages, calculated assuming both CHUR and DM mantle sources, range between 2-4 Ga and 780 Ma. In particular, the 1-2-Ga Sr age and the 780-Ma Nd age can be regarded as minimum ages of differentiation. The transition from spinelto plagioclase-fades assemblage, accompanied by progressive deformation (from granular to tectonite—mylonite textures), indicate that the EL Iherzolites experienced a later, subsolidus decompressional evolution, starting from subcontinental lithospheric levels. Sm/Nd isochrons on plagioclase—clinopyroxene pairs furnish ages of ~165 Ma. This early Jurassic subsolidus decompressional history is consistent with uplift by means of denudation in response to passive and asymmetric lithospheric extension. This is considered to be the most suitable geodynamic mechanism to account for the exposure of huge bodies of subcontinental lithospheric mantle during early stages of opening of an oceanic basin.

177 citations

Journal ArticleDOI
01 Mar 2003-Geology
TL;DR: This paper showed that fluxing of the wedge with an H 2 O-rich component from the subducted slab is important in formation of large ion lithophile (LILE) and light rare earth (LREE) elements relative to high field strength elements (HFSE).
Abstract: Although there is a growing body of data on H 2 O in arc magmas, there is still considerable uncertainty about the relationship between H 2 O and various incompatible elements during enrichment of the mantle wedge by subduction processes. We report data for H 2 O, other volatiles (CO 2 , S, Cl), and trace elements in olivine-hosted melt inclusions from high-Mg basalts in central Mexico that exhibit varying degrees of subduction-related enrichment. Most melt inclusions were trapped at low pressure, but rare inclusions (Mg# 65-78, olivine hosts Fo 8 5 - 9 0 ) trapped at upper to middle crustal pressures (1-6 kbar) contain high CO 2 (250-2120 ppm). The high-pressure inclusions indicate magmatic H 2 O contents from 1.3 to 5.2 wt%. Enrichment of H 2 O relative to Nb correlates positively with K/Nb, Ba/Nb, and La/Nb, indicating a clear link between H 2 O) and trace element enrichment of the mantle wedge. Our results show that fluxing of the wedge with an H 2 O-rich component from the subducted slab is important in formation of magmas that are enriched in large ion lithophile (LILE) and light rare earth (LREE) elements relative to high field strength elements (HFSE). In contrast, magmas with low LILEs and LREEs relative to HFSEs have relatively low H 2 O, and must have formed largely by decompression melting of unmodified mantle. Our data for volcanoes <50 km apart show evidence of significant variability in the composition of H 2 O-rich subduction components that are added to the mantle wedge beneath central Mexico.

176 citations

Journal ArticleDOI
TL;DR: In this paper, a crystallization age of 474 ± 11 Ma and an initial eNd143 value of +36.6 ± 0.8 were derived from a source region that had a slightly greater incompatible enrichment than the QUE94201 source region.

176 citations

Journal ArticleDOI
01 Apr 1996-Lithos
TL;DR: Gorgona Island, Colombia is remarkable not only because it contains the only Phanerozoic komatiites, but also because it has mafic to ultramafic lavas with a wide range of compositions, from moderately enriched to extremely depleted (relative to Bulk Earth) as mentioned in this paper.

175 citations

Journal ArticleDOI
TL;DR: In this article, a model for polybaric magma evolution in the West Eifel is proposed, where primitive alkali basaltic lava rises through the upper mantle precipitating Al-augite en route It stagnates and differentiates near the crust/mantle boundary crystallizing Fe-rich fassaitic augites.
Abstract: The Quaternary foidites and basanites of the West Eifel (Germany) contain optically and chemically heterogeneous clinopyroxenes, some of which occur as discrete zones within individual crystals: Most clinopyroxene phenocrysts are made up of a core and a normally zoned comagmatic titanaugite mantle Most cores are greenish pleochroic and moderately resorbed (fassaitic augite) Some are pale green and strongly resorbed (acmitic augite) Cores of Al-augite composition and of Cr-diopside derived from peridotite xenoliths are rare The fassaitic augites are similar in trace element distribution pattern to the titanaugites, but are more enriched in incompatible elements The acmitic augites, in contrast, are clearly different in their trace element composition and are enriched in Na, Mn, Fe and depleted in Al, Ti, Sr, Zr A model for polybaric magma evolution in the West Eifel is proposed: Primitive alkali basaltic magma rises through the upper mantle precipitating Al-augite en route It stagnates and differentiates near the crust/mantle boundary crystallizing Fe-rich fassaitic augites The magma differentiated at high pressure is subsequently mixed with new pulses of primitive magma from which the rims of pyroxene are crystallized Sporadic alkali pyroxenite xenoliths are interpreted to represent cumulates of cognate phases formed within the crust and not metasomatized upper mantle material (Lloyd and Bailey 1975)

175 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20237
202216
202157
202056
201960
201851