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 Recent alkaline lavas by lithospheric thinning beneath the northern Canadian Cordillera

Abstract: Recent alkaline lavas that have erupted across the disparate terranes of the northern Canadian Cordillera provide natural probes with which to interrogate the underlying lithosphere. The lavas range between two compositional end members, olivine nephelinite (NEPH) and hypersthene-normative olivine (Hy-NORM) basalt. The chemical signature of amphibole in the incompatible element enriched NEPH end member indicates that it is derived in the lithospheric mantle. The Hy-NORM end member is characterized by lower incompatible trace element contents but is still relatively enriched relative to primitive mantle. Although the Hy-NORM end member is always more radiogenic in Pb and Sr isotopes and less radiogenic in Nd isotopes than the NEPH end member, its isotopic signature varies with tectonic belt. In particular, Hy-NORM basalts in the Omineca Belt are strikingly more radiogenic in Sr and Pb isotopes and less radiogenic in Nd isotopes than otherwise equivalent Hy-NORM basalts in the adjacent Intermontane Belt, in...

Palaeoarchaean deep mantle heterogeneity recorded by enriched plume remnants

Abstract: The thermal and chemical state of the early Archaean deep mantle is poorly resolved due to the rare occurrences of early Archaean magnesium-rich volcanic rocks. In particular, it is not clear whether compositional heterogeneity existed in the early Archaean deep mantle and, if it did, how deep mantle heterogeneity formed. Here we present a geochronological and geochemical study on a Palaeoarchaean ultramafic–mafic suite (3.45-Gyr-old) with mantle plume signatures in Longwan, Eastern Hebei, the North China Craton. This suite consists of metamorphosed cumulates and basalts. The meta-basalts are iron rich and show the geochemical characteristics of present-day oceanic island basalt and unusually high mantle potential temperatures (1,675 °C), which suggests a deep mantle source enriched in iron and incompatible elements. The Longwan ultramafic–mafic suite is best interpreted as the remnants of a 3.45-Gyr-old enriched mantle plume. The first emergence of mantle-plume-related rocks on the Earth 3.5–3.45 billion years ago indicates that a global mantle plume event occurred with the onset of large-scale deep mantle convection in the Palaeoarchaean. Various deep mantle sources of these Palaeoarchaean mantle-plume-related rocks imply that significant compositional heterogeneity was present in the Palaeoarchaean deep mantle, most probably introduced by recycled crustal material. Deep mantle heterogeneity and large-scale deep mantle convection has been operating since the Palaeoarchaean, according to enriched plume signatures found in a 3.45-billion-year-old ultramafic–mafic suite from the North China Craton.

Petrogenesis of basalts from the Blanco Trough, northeast Pacific: Inferences for off‐axis melt generation

Abstract: Basaltic lavas recovered in a single dredge haul from the Blanco Trough, in the western portion of the Blanco Fracture Zone, demonstrate that off-axis volcanism can produce significant compositional variability in lavas that are closely related spatially. Glass compositions range from depleted in incompatible elements (0.07 wt % K2O; 35 ppm Zr) to strongly enriched (0.43 wt % K2O; 214 ppm Zr) with SiO2 contents from 48. 1 to 50.9 wt % over a limited range of MgO (9.22 to 6.82 wt %). These basalts are distinct from mid-ocean ridge basalts sampled globally at spreading centers in that they are characterized by high FeO* and Na2O at a given MgO content and low normative SiO2, a compositional signature consistent with relatively low extents of partial melting at high pressures. This results from the presence of thick lithosphere that forces melting to stop at a significantly greater depth than is the case at ridge axes. Forward models of low-pressure liquid lines of descent demonstrate that the major and trace element variations observed in these lavas cannot be explained by crystal fractionation from a single parent magma. After correcting the glass compositions to 8 wt % MgO to eliminate the effects of low-pressure crystallization, the Fe8.0-Na8.0 and Si8.0-Na8.0 variations display characteristics of both Atlantic- and Pacific-type local trends. Variable extents of partial melting and interaction with the mantle as the magmas ascended through the lithosphere can explain these systematics. A subset of the samples shows evidence for crystallization of olivine + plagioclase + high-Ca clinopyroxene at upper mantle pressures (∼400 MPa). Modeling of incompatible element variations suggests that two distinct mantle sources were involved in producing the Blanco Trough lavas. The first resembles the primitive upper mantle of Hart and Zindler (1986) with a small initial depletion (∼0.1 wt % melt extraction). The second is characterized by a significant depletion in incompatible elements (K2O, TiO2, Zr, Sr).

Evidence of mingling between contrasting magmas in a deep plutonic environment: the example of Várzea Alegre, in the Ribeira Mobile Belt, Espírito Santo, Brazil

Abstract: At the end of the geotectonic cycle that shaped the northern segment of the Ribeira Mobile Belt (Upper Proterozoic to Paleozoic age), a late to post-collisional set of plutonic complexes, consisting of a wide range of lithotypes, intruded all metamorphic units. The Varzea Alegre Intrusive Complex is a post-collisional complex. The younger intrusion consists of an inversely zoned multistage structure envolved by a large early emplaced ring of megaporphyritic charnoenderbitic rocks. The combination of field, petrographic and geochemical data reveals the presence of at least two different series of igneous rocks. The first originated from the partial melting of the mantle. This was previously enriched in incompatible elements, low and intermediate REE and some HFS-elements. A second enrichment in LREE and incompatible elements in this series was due to the mingling with a crustal granitic magma. This mingling process changed the composition of the original tholeiitic magma towards a medium-K calc-alkalic magma to produce a suite of basic to intermediate rock types. The granitic magma from the second high-K, calc-alkalic suite originated from the partial melting of the continental crust, but with strong influence of mantle-derived melts.