Incompatible element

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

Geochemical constraints on petrogenic processes on Venus

Abstract: Abundances of three incompatible elements (K, U, Th) have been determined by robotic spacecraft in five surface materials on Venus. We present these data normalized to terrestrial normal mid-ocean ridge basalt (NMORB) derived from the depleted mantle. Relative to NMORB, all of the Venus materials studied are enriched in all of these elements. The moderately enriched (Venera 9 and 10, Vega 1 and 2) basaltic rocks are similar to one another in the sense of their enrichment trends (U N > K N ) but differ from the highly enriched Venera 8 material, where the trend is K N > U N . This difference implies that the enrichment pattern for the basaltic materials is not controlled by crystallization of an NMORB-like magma or by contamination of such a magma by highly enriched Venera 8 material within the crust, and the Venera 8 material cannot have evolved from the magma of any of the basaltic rocks. Our calculations show the K-U-Th pattern for any of the Venus rocks analyzed was not controlled by batch partial melting of primitive mantle. The Venera 8 material could be produced as a partial melt from eclogitic tholeiite, but none of the basaltic materials could be because the sense of their U N > K N trends is opposite to the enrichment trends in calculated models (K N > U N ). The Venus basalts differ from fresh terrestrial rocks (NMORBs and oceanic island-arc volcanics) in having nearly constant K/U ratios, while terrestrial rocks have nearly constant Th/U ratios. This may suggest an unusual composition of mantle source(s) of the Venus basalts and/or unusual fractionation process(es) on that planet.

Magmatic and metamorphic evolution of the oceanic crust in the western flank of the MAR crest zone at 15°44′N: Investigation of cores from sites 1275B and 1275D, JOIDES resolution Leg 209

Abstract: This paper reports the results of an investigation of a representative collection of samples recovered by deep-sea drilling from the oceanic basement 10 miles west of the rift valley axis in the crest zone of the Mid-Atlantic Ridge at 15°44′N (sites 1275B and 1275D). The drilling operations were carried out during Leg 209 of the drilling vessel JOIDES Resolution within the framework of the Ocean Drilling Program (ODP). The oceanic crust was penetrated to a depth of 108.7 m at Site 1275B and 209 m at Site 1275D. We reconstructed the following sequence of magmatic and metamorphic events resulting in the formation of a typical oceanic core complex of slow-spreading ridges: (1) formation of a strongly fractionated (enriched in iron and titanium) tholeiitic magmatic melt parental to the gabbroids under investigation in a large magma chamber located in a shallow mantle and operating for a long time under steady-state conditions; (2) transfer of the parental magmatic melt of the gabbroids to the base of the oceanic crust, its interaction with the host mantle peridotites, and formation of troctolites and plagioclase peridotites; (3) intrusion of enriched trondhjemite melts as veins and dikes in the early formed plutonic complex, contact recrystallization of the gabbro, and development in the peridotite-gabbro complex of enriched geochemical signatures owing to the influence of the trondhjemite injections; (4) emplacement of dolerite dikes (transformed to diabases); (5) metamorphism of upper epidoteamphibolite facies with the participation of marine fluids; and (6) rapid exhumation of the plutonic complex to the seafloor accompanied by greenschist-facies metamorphism. The distribution patterns of Sr and Nd isotopes and strongly incompatible elements in the rocks suggest contributions from two melt sources to the magmatic evolution of the MAR crest at 15°44′N: a depleted reservoir responsible for the formation of the gabbros and diabases and an enriched reservoir from which the trondhjemites (granophyres) were derived.

The petrology and geochemistry of mantle-derived basic and ultrabasic rocks from the Szklary massif in the Fore-Sudetic Block (SW Poland)

Abstract: This paper presents the results of petrological investigations of rocks from the Szklary serpentinite massif in the eastern margin of the Gory Sowie Block. Among the weakly serpentinised ultrabasites present, harzburgites, lherzolites and pyroxenites have been distinguished. Small enclaves of metabasites within the serpentinites represent low-Ti varieties and - like rodingites - they developed from initial gabbroides or picrites. They reveal a characteristic depletion in incompatible elements. This feature is reminiscent of high-Mg (boninite) basic magmas formed in island arc or back-arc basin environments. Plagiogranites, present within the serpentinites, most probably represent trondhjemites - more acid derivates formed during the fractional crystallisation of the same initial basic magma. On the basis of the petrological investigation results, the hypothesis was put forward that - with regard to their initial composition - the ultrabasites of the Szklary massif may represent heterogeneous spinel residual peridotites impregnated with pyroxenite veins. Enclaves of metabasites and plagiogranites, having the properties of mafic cumulates and/or fractional differentiates, may reflect a stage of further magmatic processes which took place in a zone of lithospheric plate convergence.