Incompatible element

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

Origin of the xiugugabu ophiolite massif,sw tibet:evidence from petrology and geochemistry

Abstract: The Daba-Xiugugabu ophiolite massif is situated in the western portion of the Yalung Zangbo Suture Zone (YZSZ), composed mainly of mantle peridotites and of mafic dikes that intruded the mantle peridotites. The mafic dikes show similar geochemical features to back-arc basin basalts, characterized by LREE depletion with (La/Yb)N between 0.39 to 0.55, and clear negative anomalies of Ti and Nb and positive anomalies of Sr and Ba. Sr and Nd isotope systematics indicates an origin from a depleted upper mantle source modified by fluid released from the subducting oceanic slab. Sm-Nd isotopic data of four mafic dike samples yielded an isochron age of 126.2±9.1Ma (MSWD=0.44), representing the emplacement age of the mafic magma. The mantle peridotites have two types of REE patterns: spoon-shaped and U-shaped. The spoon-shaped peridotites display slightly LREE-enriched to roughly flattened patterns and have low and limited range of spinel Cr# values, features of mantle peridotites in back-arc extentional basins. Such trace element characteristics reflect lower degrees of partial melting (15%~20%) and moderate to low extent of metasomatism. By contrast, the peridotites having U-type REE patterns show significant LREE enrichment, and have higher and variable spinel Cr# values (0.40~0.77), implying that they experienced higher degrees of partial melting (25%~30%) and the following extensive incompatible element enrichment by melt/fluid metasomatism. Combined geochemical data of the mafic and ultramafic components of the Daba-Xiugugabu ophiolite massif suggests that the ophiolites were probably formed in an intraoceanic arc.

Petrogenesis of alkalic and calcalkalic volcanic rocks of Mormon Mountain Volcanic Field, Arizona

Abstract: The Cenozoic Mormon Mountain Volcanic Field (MMVF) of northern Arizona is situated in the transition zone between the Basin and Range and the Colorado Plateau. It is composed of alkalic to sub-alkalic basalts and calcalkalic andesites, dacites, and rhyodacites. Despite their spatial and temporal association, the basalts and the calcalkalic suite do not seem to be co-genetic. The petrogenesis of primitive MMVF basalts can be explained as the result of different degrees of partial melting of a relatively homogenous, incompatible element-enriched peridotitic source. The variety of evolved basalt types was the result of subsequent fractional crystallization of olivine, spinel, and clinopyroxene from the range of primitive basalts. Crustal contamination seems to have occurred, but affected only the highly incompatible element abundances. The formation of MMVF calcalkalic rocks is most readily explained by small to moderate amounts of partial melting of an amphibolitic lower crust. This source is LREE-enriched but depleted in Rb and relatively unradiogenic Sr (87Sr/86Sr ∼0.7040). Calcalkalic rhyodacites may also be derived from andesitic parents by fractional crystallization. The overall petrogenesis of the MMVF complex is the result of intra-plate volcanism where mantle-derived magmas intrude and pass through thick continental crust.

High μ (HIMU) ocean island basalts in southern Polynesia: new evidence for whole mantle scale recycling of subducted oceanic crust

Abstract: Major elements, trace elements, and Pb isotopic compositions were determined for ocean island basalts (OIBs) from Polynesia in the southern Pacific in order to document the chemical characteristics of OIB sources and to understand their origin. High μ (HIMU: μ=238U/204Pb) basalts, which have distinctly high Pb isotopic ratios, have systematically different compositions from non-HIMU basalts; HIMU basalts are more enriched in Fe2O3*, MnO, and CaO and more depleted in SiO2, K2O, P2O5, Ni and incompatible trace elements than non-HIMU, except for Nb. Major element characteristics of HIMU basalts suggest that the HIMU source is more fertile, i.e., more enriched in a basaltic component, than non-HIMU sources. This is consistent with the suggestion that subducted oceanic crust may contribute to the formation of the HIMU reservoir. Relative depletion of incompatible trace elements in HIMU is consistent with involvement of sedimentary components in non-HIMU sources. However, enrichment of Nb relative to other incompatible elements in HIMU cannot be explained by simple addition of the crustal component nor partial melting processes in the upper mantle, implying that lower mantle processes may contribute to the formation of the HIMU source.

Geochemistry and Petrogenesis of Amphibolites from the Southern Part of Gadag Greenstone Belt, Karnataka

Abstract: Gadag Greenstone Belt (GGB) is the northern continuation of Chitradurga Greenstone Belt (CGB) It consists of a variety of metavolcanic and metasedimentary rocks Two types of metavolcanic assemblages are found in this terrane (l) the tholeute-calc-alkaline island arc bimodal assemblage and (u) the tholeute-high-Mg basalt assemblage The tholente-calc-alkaline assemblage is exposed in the central and northern parts, whereas the tholentic-high-Mg basaltic assemblage is found in the southwestern part of the belt Tholente-high-Mg basalts are represented by the coarse-grained amphibolites formed under lower amphibolite facies conditions REE and HFSE data along with major element compositions confirm that these coarse-grained amphibolites are tholentic basalts derived from an intraoceanic island arc setting The REE patterns are coherent, flat to slightly LREE depleted (La/Yb n =079 to 120, La/Sm n =084-097, Gd/Yb n =107-150) with no Eu anomaly Relationship between compatible and incompatible elements suggests least effects of alteration and no crustal contamination or fractional crystallization The mixing calculations indicate that these rocks are derived by partial melting of a depleted mantle source, with source composition in between that of the N-MORB and high-Mg basalts