Incompatible element

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

Petrogenesis of Proterozoic carbonatites and alkaline magmas from Ihouhaouene : In Ouzzal terrane, Western Hoggar, Algeria

Abstract: The In Ouzzal Archaean craton represents a succession of intrusive and metamorphic events since Eburnean, and an important marker of geodynamic processes through geological time. The Ihouhaouene area located in the N-W of In Ouzzal terrane in Algeria is unique by the presence of Proterozoic carbonatite intrusions associated with silica-saturated alkaline rocks. These intracontinental carbonatites are among the oldest and exceptional because of their diversity and the presence of unusual rare earth minerals. Carbonatites are pegmatitic or brecciated with fragments of syenite. They are calciocarbonatites with calcite (> 50 vol.%), apatite, clinopyroxene and wollastonite and are associated with red or white syenites in massive outcrops. Syenites are composed of alternating light levels of red alkaline feldspar or wollastonite associated with white feldspar and dark levels of apatite and clinopyroxene. Carbonatites and syenites form a cogenetic suite characterized by an increase in silica and decrease in calcium and CO2 content. The carbonatites have silica content ranging from 5 to 35 wt.%, 28 to 53 wt.% CaO, and 11 to 36 wt.% CO2. Syenites have high K2O (12 wt.%) and low Na2O content (1 wt.%). Carbonatites and syenites have high incompatible element concentrations with high REE content (7000*chondrites and 1000*chondrites, respectively) and high U, Pb, Sr and Th content. Trace elements (eg. Rare Earths, Nb-Ta, Zr-Hf) in magmatic minerals (apatite-pyroxene) of carbonatites and syenites reveal complex magmatic processes at the origin of these rocks involving several stages of fractional crystallization and immiscibility from a CO2-rich melilititic magma. Silica-rich carbonatites and white syenites are characterized by high Nb/Ta, Y/Zr and Rb/Sr ratios, typical of carbonate-rich magmas by immiscibility. The red syenites have characteristics of immiscible differentiated silicate melt. Silica-poor carbonatite minerals have variable subchondritic Nb/Ta (<10) indicating crystallization from highly evolved liquids and the presence of late carbonatitic magmas. Apatites, in particular, record various magmatic and supergene processes. They present, in some rocks, redistribution and enrichment in rare earth elements, which are characterized by exsolutions of britholite in silica-rich carbonatites and monazite-quartz-calcite inclusions in silica-poor carbonatites. These minerals reflect local sub-solidus re-equilibration with late-magmatic fluids rich in Cl-Th-REE for the exsolution of britholite and S-Ca-P-CO2 for monazite inclusions. The apatite and zircon present in these alkaline and carbonatite rocks, allow determination of the syn-metamorphic crystallization age of the Ihouahouene magmatic complex at 2100 Ma and confirm the pan-African age of its exhumation. The petrological, geochemical and geochronological study of Ihouhaouene carbonatites and syenites highlights the magmatic origin of these rocks and constrains the fluid-rock interactions at sub-solidus conditions leading to REE-enrichment. The carbonatites and syenites result from a low partial melting rate of a CO2-rich Precambrian mantle. Several fractional crystallization and immiscibility stages allowed the genesis of these hybrid magmas, trapped along large shear-zones during the Archean/Eburnean transition period in the In Ouzzal terrane, characterized by extensive deformation in ultra-high-temperature granulitic environment.

Geochemistry and petrogenesis of the volcanic rocks from Bagh complex, northern Balochistan, Pakistan

Abstract: The Bagh complex is an assemblage of igneous and sedimentary rocks containing many lithologic units which are bounded by layered parallel thrusts. The volcanic rocks from basalt-chert unit (Bbc) and hyaloclastite-mudstone unit (Bhm) are comprised of pillowed and bedded basalt, hyaloclastite and reworked sediments. Petrography and geochemistry of the basalt from Bbc shows that these rocks are basaltic trachy-andesite, trachy-andesite and foidite with tholeiitic charecter. While those from Bhm are tephrite-basanite, basalt and picro-basalt having alkaline nature. N-MORB-normalized diagram of the tholeiitic rocks have flat pattern of HFS-elements. In contrast enrichment of LIL-elements with the REE having almost flat pattern between 10X and 20X chondritic which are typical of N-MORB. The enrichment of LIL-elements, especially Th and depletion of Nb relative to other incompatible elements are depicting the addition of subduction zone component to a depleted mantle source. The multi element normalised plots of the volcanic rocks from Bhm show a similar pattern to that of OIB. Theese show a marked enrichment in the LIL-elements, depletion in some of the HFS-elements enrichments in LREEs and a marked depletion in the HREEs as compared to NMORB. The geochemical features on tectonic discrimination diagram of tholiiete from Bbc and alkaline rocks from Bhm suggest supra-subduction zone and oceanic-island arc tectonic settings respectively. These rocks were possibly erupted during Cretaceous period in the area which extends from the continental margin of the Indian subcontinent over the Neo-Tethys Ocean floor, and then were obducted with the Muslim Bagh ophiolite over the Indian subcontinent.

The Geochemical Characteristics of the Early Riphean Navysh Volcanic Complex (Southern Urals)

Abstract: The Navysh volcanic complex, which is an integral part of the Ai Formation (Lower Riphean), overlies Archean–Early Proterozoic formations of the Taratash metamorphic complex. It is represented mainly by trachybasalts, as well as by dacites and metasomatic bostonites. The Navysh complex is subdivided for the first time here into several volcanic series, which differ in their contents of TiO2 and several incompatible elements. The metasomatic nature of the bostonites has been proven. Reasons are given for excluding dacites from the composition of the Navysh complex.

Genesis and Metallogenesis of Alkaline Complexes in China Mainland

Abstract: This paper presents the recent research results on the occurrence,distribution,geological and geochemical characteristics,genesis and metallogenesis of alkaline complexes in China mainland. The petrographic and isotopic characteristics indicate that silica-undersaturated alkaline complex is mostly the product of original magma emplacement,which mainly comes from low-degree partial melting mantle. However,silica-saturated or silica-supersaturated alkaline complex is mostly the product of deep source magma contaminated by continental crust. Low-degree partial melt of mantle source led to the enrichment of rare earth elements,large ion lithophile elements and other incompatible elements,while the volatile material enriched in the same time constitutes mineralizer,which has an important controlling role in mineralization. Deep faults control the output of alkaline complex,accompanied by significant geological events in geological history. Alkaline complex zones controlled by deep faults in China mainland include nine major alkaline complex zones,such as the Tancheng-Lujiang alkaline complex zone,Panxi alkaline complex zone and Ailaoshan-Jinsha River alkaline complex zone.

Adcumulate mafic dykes in layered intrusions: a case study of a late-stage dyke in the Bayantsagaan layered intrusion, Mongolia

Abstract: We have discovered an adcumulate late-stage dyke in the Bayantsagaan layered intrusion. The 11-cm-thick dyke is composed of fresh troctolite with no signs of chilling against the host leucotroctolite. Texturally, both the dyke and its host are medium-grained plagioclase-olivine-magnetite cumulates. The dyke is however finer grained and contains less interstitial material. Two geochemical features characterize the dyke: it is compositionally more evolved than the host, as indicated by its lower real and normative An-content in plagioclase, whole-rock Cr and Mg-number; and it is highly depleted in all incompatible components (e.g. K 2 O, Y and rare earth elements or REEs) that have much lower concentrations than in the host. The depletion in REEs is extreme and has not been reported earlier for any troctolitic rocks. It has an internal reverse zonation with an inwards increase in compatible MgO and TiO 2 and a decrease in all incompatible elements, suggesting an inwards decrease in the amount of trapped melt. We interpret this late-stage dyke as having formed from a residual melt that was channelled along a fissure in solidifying cumulates. The flow of the melt resulted in the very efficient removal of a boundary layer of evolved liquid from crystals growing on the walls of the dyke. This resulted in an almost perfect adcumulate that is extremely depleted in incompatible components.