Incompatible element

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

Geochemistry of ultramafic xenoliths and their host alkali basalts from Tallante, southern Spain

Abstract: Ultramafic xenoliths enclosed in Plio- Quaternary alkali basalts from Tallante near Cartagne (southern Spain) are composed mainly of spinel lherzo- lites which are probably upper mantle residues. In many xenoliths, the spinel lherzolite is cut by pyroxenite or gabbroic anorthosite veinlets generally 0.2-3 cm thick. The clinopyroxenite veinlets were formed by high-pressure crystal-liquid segregation from alkali basalt magmas formed earlier than the host basalts, whereas mantle metasomatism played a role in the genesis of gabbroic anorthosites. Close to the contact with the veinlets, the spinel lherzolites are enriched in Ca, Fe, and some incompatible elements including light REE due to the migration of a fluid from the veinlets into the surrounding lherzolites. The host alkali basalts were derived from a heterogeneous, incompatible element-enriched upper- mantle source probably similar in composition and nature to the composite xenoliths, but were formed in a garnet stability field.

Geochemistry of Shoshonitic Volcanic Rocks in the Luzong Basin,Anhui Province(Eastern China):Constraints on Cretaceous Lithospheric Thinning of the Lower Yangtze Region

Abstract: The volcanic-subvolcanic rocks in the Luzong basin are characterized by high-K and rich in alkali,belonging to typical shoshonite series.These rocks is obvious depletion in high-field-strong-elements(HFSE)such as Nb and Ta,and rich in strong incompatible elements such as Rb,Th,U and K as well as light rare earth elements(LREE).Nd and Sr isotope compositions of the rocks are similar roughly to those of the enriched subcontinental lithospheric mantle in the Yangtze craton,implying that their parental magma came mainly from partial melting of the enriched subcontinental lithospheric mantle.Geochemical variations of the volcanic-subvolcanic rocks show that the shoshonitic original magma had undergone high-pressure(higher than the stabilization pressure of plagioclase, 1.5 GPa)fractional crystallization,dominant Cpx and Ti-Fe oxide fractionation.But low-pressure( GPa)fractional crystallization and upper crustal contamination process are inconspicuous.These rocks are partially similarly the shoshonite series in intra-oceanic island arcs in geochemistry(such as Ce/Yb),possibly because lithospheric thinning has allowed upwelling of asthenospheric mantle to relatively shallow depths where a greater proportion of spinel-facies melting can contribute to magma generation.Although may being "thermal erosion" partially(such as western margin of the basin near the Tailu deep fault),we favor delamination as the main model for lithospheric thinning of the region(and the whole lower Yangtze region).

President Jackson Seamounts, northern Gorda Ridge: Tectonomagmatic relationship between on‐ and off‐axis volcanism

Abstract: Basaltic lavas and hyaloclastites dredged from the President Jackson Seamounts, a 65-km-long, linear volcanic chain starting near latitude 42°20'N west of the northern Gorda Ridge, are normal mid-ocean ridge basalt (MORB), with compositions ranging from highly depleted (0.07% K 2 O, 0.54 La/Sm N ) to moderately enriched in incompatible elements (0.24% K 2 O, 0.86 La/Sm N ). The seamount lavas are similar in many respects to those erupted at the adjacent ridge but have some important geochemical differences. Seamount lavas are concentrated toward primitive compositions with higher MgO contents (to 9.3%, Mg number 69.5) than most of the nearby ridge lavas. They also have systematically lower TiO 2 and FeO and higher CaO, Na 2 O, and Sr at comparable MgO content than adjacent ridge basalts. Seamount basalts contain phenocrysts in equilibrium with the melt and lack compositionally diverse glass inclusions and compositional zoning common in phenocrysts of most ridge basalt. Minor and trace element variability at a given MgO content indicates complex petrogenetic processes. Radiogenic isotopic ratios indicate somewhat less depleted sources than for basalt from the adjacent ridge axis. The higher Pb isotopic ratios of some lavas trend toward enriched MORB. The seamounts typically have multiple, nested calderas or pit craters, stepping downward toward the ridge axis, indicating formation in the active, near-ridge, extensional environment. The predominantly primitive nature of the lavas suggests that they pass through crustal magma reservoirs, presumably underlying the calderas, very rapidly. The lack of evidence for magma mixing suggests that batches of magma are delivered to the seamounts episodically and either solidify or are drained into ridge-parallel faults before the next batch arrives. In contrast, lavas from the ridge axis show evidence for magma mixing involving more fractionated melts that show evidence for clinopyroxene fractionation. Despite a lack of seismic evidence for magma chambers under slow spreading centers, continuous melt zones must be present under the Gorda Ridge axis to give the ubiquitous imprint of magma mixing.