Incompatible element

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

Geochemistry and Platinum-group Elements of Ultramafic Rocks from the Songshugou Area in the Eastern Qinling:Constraints on Petrogenesis

Abstract: Ultramafites in the Songshugou area, Shangnan county, Shaanxi Province, to the north of the Shangzhou—Danfeng fault is the largest Alpine-type ultramafic massif in China. Covering an area of about 20 km2,and it is contact with the Qinling Group as intrusions. The rockbody is composed mainly of fine-grained dunite, medium dunite and harzburgite. Geochemical characteristics show ultramafites are depleted, while rocks from the Songshugou dunite body display clear enrichment of highly incompatible elements (Rb to Nb) and LREE compared HREE. The PGE concentrations of dunite are lower than harzburgite obviously. Compared with ophoplitic mantle peridotite, we propose that the Songshugou body is the product of peridotite with melt through melt percolation.

18 – the composition of late stage kimberlite liquids as revealed by nucleated autoliths

Abstract: Nucleated spheroids of kimberlite have been recognized in ten kimberlite pipes in Lesotho, the Northern Cape, the Transvaal and South West Africa. These structures have been termed nucleated autoliths and are believed to represent crystallization of kimberlite magma around a solid nucleus, and as such may provide useful information concerning the chemical composition of these kimberlitic liquids. Major element compositions were determined for a total of twenty-six autoliths from the Wesselton Mine and various localities in Lesotho, and a cluster analysis technique has been used to compare the chemistry of the autoliths with kimberlites and other alkaline ultramafic rocks associated in space and time. The major element chemistry of the autoliths does not indicate any unique composition but groups with two of the four kimberlite cluster groups. Compared to kimberlites in the remaining cluster groups the autoliths are enriched in the incompatible elements Ti, P and Mn, and impoverished in Mg. In the CMAS tetrahedron (O′HARA, 1968) kimberlites lie on a fairly well defined olivine control line trending sub–parallel to the CAM plane. Autoliths have compositions which plot near the extremity of the kimberlite trend, and would consequently appear to have fractionated more olivine than more Mg–rich varieties of kimberlite. These CMAS sub-projections provide support for O′HARA's (1970) suggestion that kimberlites have major element compositions consistent with their derivation as partial melts of a four–phase garnet lherzolite rock at depth equivalents of more than 40 kbar. 87Sr/86Sr ratios of 0.7040 for two Lesotho autoliths provide confirmatory evidence that these autoliths are largely uncontaminated with crustal material and represent magma which has erupted from great depths in the mantle. A microprobe study of ilmenites and spinels present in the groundmass of the autoliths has shown that these minerals are predominantly of late generation, and are compositionally different from those of deep mantle origin. The presence of these late–stage minerals in the autoliths further suggests that these structures formed by magmatic rather than accretionary processes.

Plume Related (?) Acid Volcanic Activity in St. Mary's Island, South Kanara District, Karnataka

Abstract: Metaluminous (Alumina Saturation Index A/CNK < 1.04), acid volcanic rocks ranging in composition from rhyolite to dacite occur in St Mary's island. The rocks are rich in SiO, (68.58-71.27%), high field strength elemenls, moderately rich in AI 2 O 3 , (1 1.78-15.02%), and low in CaO, MgO. V, Cr, and Ni. They are characterized by fractionated light rare earth elements (La/Sm=6.8) and a flat heavy rare earth elements pattern with a large negative Eu anomaly (0.48). Variation in bulk- rock major and trace element composition together with mineral data on clinopyroxene composition, suggest a basaltic precursor and a cause related to rifting. The enrichments of incompatible elements point to an EM-I type mantle source. From the over all geochemical characteristics, it is inferred that the Marion plume caused the lower part of the basaltic crust to soften, stretch and rift in an extensional setting. The rise in the geotherm caused by the rising asthenosphere and the pressure change resulting from rifting lowered the solidus temperature and resulted in partial melting of the basaltic crust. Subsequent fractionation produced dacitic to rhyolitic magma, which was emplaced in a rift setting.

Geochemical characteristics and the provenance of Cretaceous basic dikes in Zhongdong area of Xiazhuang uranium ore field

Abstract: The NWW-extending Cretaceous amphibolic diabase dikes are developed in Xiazhuang uranium ore field,Northern Guangdong province.Geochemical characteristics and the provenance of Cretaceous amphibolic diabases from Xiazhuang area have been studied from the aspects of major and trace elemental geochemistry.It can be concluded that the amphibolic diabases formed at internal plate tectonic setting with less crustal rocks assimilation during their intrusion and evolution,which mostly represent the primary magma from the mantle.The rocks are enriched in LREE,LILE,incompatible elements(K、Rb、Ba、Th、Ta、Ce et al),have no Nb,Ta,Zr and Hf anomalies and Eu depletion compared with that of OIB basalts.Trace elements ratios and discrimination diagrams indicate that the amphibolic diabases came from the enriched mantle(EMI and EMII)and related to activities of Cretaceous hotspots(mantle plume) in Xiazhuang district.