Showing papers on "Incompatible element published in 1983"
TL;DR: In this paper, the authors proposed a plum pudding model for the upper mantle, which best accommodates geochemical coherence of OIB and IAV, and the presence of a MORB-type source at back arc spreading centers.
372 citations
TL;DR: In this paper, it was shown that the Gorge Creek Group samples, characterized by muscovite-quartzchlorite mineralogy, are enriched in incompatible elements (K, Th, U, LREE) by factors of about two, when compared to younger Archean shales from the Yilgarn Block.
297 citations
TL;DR: In this article, the major and trace element abundances and Nd and Sr isotopic compositions have been determined for boninites from the Bonin Islands, Cape Vogel (Papua New Guinea) and New Caledonia and for similar lavas from Cyprus and New Zealand.
201 citations
TL;DR: In this article, the authors show that these samples are not genetically related by different degrees of melting of a compositionally homogeneous source of basalt from Loihi Seamount.
171 citations
TL;DR: In this article, the authors investigated the nature of the metasomatic processes and the character of the kimberlitic fluid or liquid and that generating the MARID samples.
171 citations
TL;DR: In this article, the chemical variation within the Laacher See magma chamber prior to eruption with a highly fractionated phonolite at the top and a more mafic phonolitic at its base was analyzed by instrumental neutron activation.
Abstract: Twenty six whole rocks, seven matrix and fifty three mineral separates from the compositionally zoned late Quaternary Laacher See tephra sequence (East Eifel, W Germany) were analyzed by instrumental neutron activation. These data document the chemical variation within the Laacher See magma chamber prior to eruption with a highly fractionated phonolite at the top and a more mafic phonolite at its base as derived from other data. Incompatible elements such as Zn, Zr, Nb, Hf, U, light and heavy rare earths are extremely enriched towards the top whereas compatible elements (e.g. Sr, Sc, Co, Eu) are strongly depleted. Semicompatible elements (Ta and some middle REE) are depleted at intermediate levels. This chemical variation is shown by whole rock and matrix data indicating the phonolite liquid was compositionally zoned regardless of phenocryst content. Hybrid rocks (phonolite-basanite) show the largest concentrations for compatible elements. All elements (except Rb) display continuous compositional variations with regard to the stratigraphic position of pumice samples. From these data we are able to distinguish three main units: An early erupted highly fractionated magma, the main volume of evolved phonolite and a mafic phonolite as the final products.
158 citations
TL;DR: In this article, a mass balance approach was used to estimate the composition of the primitive mantle (54 elements) by a mass-balance approach that does not make a priori assignments of basalt: peridotite ratios or LIL contents of these components.
Abstract: The composition of primitive mantle (54 elements) is estimated by a mass balance approach that does not make a priori assignments of basalt:peridotite ratios or LIL contents of these components. It is also not necessary to assume that such ratios as Rb/Sr and K/U are the same as in the crust. Primitive upper mantle is treated as a four-component system: crust, peridotite, LIL-depleted basalt (MORB), and an LIL-enriched component. These are combined to give chondritic ratios of the oxyphile refractory trace elements. The composition of the whole mantle is estimated by requiring chondritic ratios of the major elements as well. In this way one can estimate the volatile and siderophile content of the mantle. The primitive mantle has K = 152 ppm, U = 0.020 ppm, Th = 0.078 ppm, K/U = 7724, and Rb/Sr = 0.025. The ratios are significantly less than previous estimates. The inferred steady state heat flow, 0.9 μ cal/cm^2s, implies a substantial contribution of cooling to the observed heat flow. The crust and upper mantle may contain most of the terrestrial inventory of the incompatible elements, including K, U, and Th. There is no evidence that the chalcophiles are strongly partitioned into the core.
149 citations
TL;DR: This article showed that the chemistry of lavas is a direct consequence of the presence of the cold, thick lithospheric edge of Nazca plate exposed at the intersection with the Inca transform, which has resulted in excess magmatism and the eruption of only FeTi basalts.
Abstract: Glassy to sparsely phyric submarine lavas were recovered from nine Alvin dive sites located along the eastern Galapagos rift and at the intersection with the Inca transform. Samples include quartz-normative tholeiitic basalts (MORB), numerous Fe- and Ti-enriched basalts (FeTi basalts) and a smaller number of oceanic andesites (55.9–64.3 wt % SiO2). MORB have light rare earth element (REE) and large ion lithophile (LIL) element depletions but exhibit slight REE fractionation (CeN/YbN 0.6–1.0) and increasing negative Europium anomalies (0.96–0.66) with progressive differentiation. Andesites have sixfold to tenfold enrichments of incompatible elements and volatiles compared to the least fractionated (Mg number < 60) basalt recovered. REE and LIL enrichments in the FeTi basalts and andesites are up to 70% greater than those predicted from closed-system fractional crystallization models computed using major and trace element data. Trace element data indicate that extreme fractional crystallization of MORB liquids (40–65%) has occurred in order for the most evolved FeTi basalt to be generated and further crystallization (40–50%) of FeTi basalt residual liquid is required to produce andesites. Magma mixing has occurred on a small scale in the evolved liquids and can partially explain the chemical characteristics of basaltic andesites. All data point to extensive amounts of fractional crystallization during the evolution of these lavas; however, mantle heterogeneity and other processes such as partial melting, open-system fractional crystallization, and convection-driven thermogravitational diffusion may also play minor roles in influencing magmatic evolution. The principal tectonic controls which influence magmatic evolution along this accretionary boundary are (1) the presence of the cold, thick lithospheric edge of Nazca plate exposed at the intersection with the Inca transform, and (2) attempted rift propagation across the Inca transform intersection, which has resulted in excess magmatism and the eruption of only FeTi basalts. Three subrift, accretionary magmatic domains result from the interplay of transform effects and attempted propagation. The chemistry of lavas is a direct consequence of the magmatic domain that prevails along an accretionary boundary.
133 citations
TL;DR: In this article, the authors analyzed 18 Cenozoic melilitite samples from Spain, France, West Germany and Czechoslovakia for major and trace elements (including REE) together with their Sr and Nd isotopic compositions.
Abstract: Eighteen Cenozoic melilitite samples from Spain, France, West Germany and Czechoslovakia have been analyzed for major and trace elements (including REE) together with their Sr and Nd isotopic compositions. Leaching experiments produced significant shifts of their87Sr/86Sr ratio indicative of a contamination by a crustal component. Most samples fall within the Sr-Nd mantle array with ɛNd values in the 1.5–6 range. These values are considered as minimum for the melilitite mantle source hence demonstrating its time integrated LRE depletion. The Ni and Cr contents of the samples are typical of primary magmas and exclude extensive crystallization of olivine and pyroxene in a closed system. However, the chemical relationships suggest that dilution of the liquids by mafic minerals of the conduits during their ascent has been important. The REE patterns show some variations which are interpreted by this dilution effect. Once normalized to Yb they are closely similar and perfectly distinguishable from those of alkali basalts and kimberlites. All of these rocks have Ce/Yb ratios which are high but distinctive for each rock type: 40 to 200 times the chondritic ratio for kimberlites, 20 to 30 for melilitites, 8 to 15 for alkali basalts. As contamination is likely to have modified somewhat the isotopic characteristics of most of these rocks, there is no overwhelming evidence that their source is chemically different. The Ba and Rb contents together with the REE patterns of the melilitites would constrain the degree of melting to be very small (<0.2%). The calculation of batch melting and steady zone refining models suggests that kimberlites, melilitites and alkali basalts may have been derived by equilibration of deep melts with different upper mantle levels characterized by decreasing garnet/clinopyroxene ratios. The strongly incompatible elements are enriched in the melt during its ascent by leaching of the wall rocks. For the steady zone refining model, the degree of melting concept loses its significance and the difficult requirement of extracting small liquid fractions from a molten source disappears. Within the frame of this model, the preenrichment of the kimberlite, melilitite and alkali basalts source in incompatible elements by metasomatic fluids is no longer necessary.
122 citations
TL;DR: In this paper, the calc-alkalic chemical trends characteristic of arc volcanic rocks mainly result from three mechanisms which act additively: (1) fractional crystallization involving separation of titanomagnetite, (2) selective concentration of plagioclase phenocrysts, and (3) mixing of magmas on continuous fractionation trends.
84 citations
TL;DR: In this article, a suite of dredged and drilled samples from the Walvis Ridge have been analyzed to determine their rare earth element (REE) contents in order to investigate the origin and evolution of this major structural feature in the South Atlantic Ocean.
TL;DR: In this paper, the relative and absolute abundance of LIL-incompatible trace elements (K, Rb, Cs, Sr, and Ba) and isotopic compositions (18 O 16 O, 87 Sr 86 Sr, and 143 Nd 144 Nd ) are summarized for fresh samples from active and dormant volcanoes of the Volcano and Mariana island arcs.
TL;DR: In this article, four submarine volcanoes in the southern and central Mariana arc were dredge-sampled and the recovered lavas were analyzed for major and trace-element abundances, including rare-earth elements (REE), mineral compositions, and Sr and Nd isotopic ratios.
Abstract: Four submarine volcanoes in the southern and central Mariana arc were dredge-sampled. The recovered lavas were analyzed for major- and trace-element abundances, including rare-earth elements (REE), mineral compositions, and Sr and Nd isotopic ratios. The samples exhibit a great range of chemical and mineral compositions relative to subaerial exposures in the central arc. Zealandia Bank produces high magnesium basalts (MgO = 8–9 wt %) enriched in Ni and with forsteritic olivine, as much as Fo 88 . This lava composition is probably parental to more fractionated basalts and basaltic andesites exposed on the adjacent islands of Guguan and Sarigan. The southernmost seamounts in the Mariana arc (south of lat. 15°N) produce dacitic pumice, a composition that is not common in the active arc. REE data preclude their derivation from a basaltic parent by fractional crystallization. They may be derived by direct partial mantle melting under water-saturated conditions at low pressure. Nd and Sr isotopic data ( 143 Nd/ 144 Nd = 0.5130–0.5131; 87 Sr/ 86 Sr = 0.7032–0.7035) indicate a mantle source for the Mariana arc lavas similar in isotopic characteristics to sources for ocean islands. Significant contributions to these arc magmas from subducted oceanic crust or sediment are not evident. A spatial distribution in magmatic characteristics coincides with a structural break in the arc near 16°N. South of this, submarine seamounts produce incompatible element–enriched lavas with relatively high 87 Sr/ 86 Sr (0.7034–0.7035). These lavas were produced by a relatively low degree of partial melting (5%–15%) of a shallow (spinel-bearing) mantle. To the north, Zealandia Bank and the central arc islands are characterized by lower incompatible element abundances and lower 87 Sr/ 86 Sr (0.7032–0.7033). These lavas were produced by higher degrees of partial melting (15%–25%) of a deeper (garnet-bearing) mantle.
TL;DR: The trace element systematics of the Main Volcanic Series of Santorini volcano, Greece are consistent with the crystal fractionation of observed phenocryst phases from a parental basaltic magma as the dominant mechanism involved in generating the range of magmatic compositions as mentioned in this paper.
Abstract: Trace element systematics throughout the cal-calkaline high alumina basalt — basaltic andesite — andesite — dacite — rhyodacite lavas and dyke rocks of the Main Volcanic Series of Santorini volcano, Greece are consistent with the crystal fractionation of observed phenocryst phases from a parental basaltic magma as the dominant mechanism involved in generating the range of magmatic compositions. Marked inflection points in several variation trends correspond to changes in phenocryst mineralogy and divide the Main Series into two distinct crystallisation intervals — an early basalt to andesite stage characterised by calcic plagioclase+augite+olivine separation and a later andesite to rhyodacite stage generated by plagioclase augite+hypersthene+magnetite+apatite crystallisation. Percent solidification values derived from ratios of highly incompatible trace elements agree with previous values derived from major element data using addition-subtraction diagrams and indicate that basaltic andesites represent 47–69%; andesites 70–76%; dacites ca. 80% and rhyodacite ca. 84% crystallisation of the initial basalt magma. Least squares major element mixing calculations also confirm that crystal fractionation of the least fractionated basalts could generate derivative Main Series lavas, though the details of the least squares solutions differ significantly from those derived from highly incompatible element and addition-subtraction techniques. Main Series basalts may result from partial melting of the mantle asthenosphere wedge followed by limited olivine+pyroxene+Cr-spinel crystallisation on ascent through the sub-Aegean mantle and may fractionate to more evolved compositions at pressures close to the base of the Aegean crust. Residual andesitic to rhyodacite magmas may stagnate within the upper regions of the sialic Aegean crust and form relatively high level magma chambers beneath the southern volcanic centres of Santorini. The eruption of large volumes of basic lavas and silicic pyroclastics from Santorini may have a volcanological rather than petrological explanation.
TL;DR: The Proterozoic Arendal metabasites are minor intrusions which possess wholly metamorphic textures and mineral assemblages as mentioned in this paper, and they are similar to many destructive plate margin basalts.
TL;DR: The Shuksan schist comprises a structurally coherent, metabasaltic member of the Easton Formation, the uppermost allochthon (Shuksan thrust plate) in the thrust system of the western North Cascades of Washington State as discussed by the authors.
Abstract: The Shuksan schist comprises a structurally coherent, metabasaltic member of the Easton Formation, the uppermost allochthon (Shuksan thrust plate) in the thrust system of the western North Cascades of Washington State. Late Jurassic metamorphism at moderately high P/T produced interlayering of actinolite-bearing greenschist assemblages with blue amphibole-bearing rocks. Major and trace element analyses of twelve greenschist and blueschist samples have been used to establish similarities between the basaltic protolith and moderately to strongly fractionated Type I MORB, to distinguish the effects of seafloor alteration superimposed on the primary igneous chemistry, and to evaluate the origin and nature of the chemical controls which produced the two mineral assemblages. The twelve analyzed samples exhibit moderate to strong LREE depletion, and characteristically low concentrations of other non-labile trace elements such as Nb, Th and Hf. The highly to moderately incompatible elements Ti, P, Nb, Zr, Hf, Y, Sc, and the REE vary by factors of 1.5 to 3.5 within the suite in a systematic pattern, increasing smoothly with increasing total iron. The relative enrichments of these elements are inversely proportional to bulk partition coefficients estimated for fractionation of basaltic magmas. The magnitude of the negative europium anomaly increases with overall incompatible element enrichment. These variations are consistent with the production of a wide spectrum of compositions by different degrees of low pressure fractionation of similar Type I MORB parent magmas. The concentrations of Sr, Rb, Na, and K vary irregularly and do not correlate with the non-labile trace elements. K and Rb are substantially elevated over typical MORB values in most samples and exhibit a consistently lower ratio (K/Rb=400 vs 1000) than fresh MORB. Concentrations of these four elements are believed to have been modified by low temperature seafloor alteration (pre-metamorphic) characterized by the formation of K-rich celadonitic clays, palagonite and minor potassium feldspar. The critical chemical variables that control the occurrence of actinolite and blue amphibole in the Shuksan schists are total iron, Fe2O3-content and Na/Ca (all high in blueschists). The chemical features were largely established by magmatic processes and inherited from the igneous parent rocks; the chemically more evolved samples are blueschists. The Fe2O3-content and Na/Ca, however, may be modified during alteration, rendering initial bulk compositions near the chemical boundary susceptible to changes which may shift rock compositions from one compatibility field to the other. Heterogeneous alteration of pillow lavas and other fragmental deposits, followed by intense flattening during metamorphism, provides a mechanism for generating blueschists and greenschists interlayered on the cm scale.
TL;DR: In this paper, the isotopic compositions of calc-alkalic volcanic rocks were determined for Quaternary calcalkalistic volcanic rocks from six volcanic rock suites in the central and western Japan arcs.
TL;DR: In this paper, the composition of the initial basalt magma in equilibrium with the residual phase is extrapolated to be FM = 0.40-0.48. And the importance of apatite introduced from the parental peridotite for the incompatible elements (REE, F and P2O5) within various basalt differentiation series is demonstrated.
TL;DR: For example, rare mafic dykes, which intrude 1000 Ma high-grade metamorphic rocks of the northern Prince Charles Mountains and the Mawson Coast area, are compositionally distinct from abundant early to middle Proterozoic tholeiite dykes as mentioned in this paper.
Abstract: Rare mafic dykes, which intrude 1000 Ma high‐grade metamorphic rocks of the northern Prince Charles Mountains‐Mawson Coast area, are compositionally distinct from abundant early to middle Proterozoic tholeiite dykes, which are confined to Archaean or early Proterozoic terrains in the southern Prince Charles Mountains and elsewhere in East Antarctica, and which have therefore proved useful as stratigraphic markers. The younger dykes (and extrusive rocks) are a composition‐ally heterogeneous group with a wide range of ages (at least Cambrian to Eocene), although most are of K‐rich alkaline composition or have alkaline affinites. Their strong enrichment in highly incompatible elements (Rb, Ba, Th, Nb, K, Pb, Th and U) relative to less incompatible elements (La, Ce and P) suggests derivation by partial melting of more enriched mantle source regions than those of most of the Proterozoic tholeiite suites. However, unlike the latter, many incompatible element ratios have been significantly affected by f...
TL;DR: In this paper, a 128 mg sample of the Antarctic meteorite ALHA 81005 was analysed for major, and trace elements by instrumental neutron activation techniques and it was shown that the meteorite or at least its major components may represent a piece of the ancient lunar crust, before the formation of the large basins on the front-side of the Moon.
Abstract: A 128 mg sample of the Antarctic meteorite ALHA 81005 was analysed for major, and trace elements by instrumental neutron activation techniques. The meteorite, or at least its major components, may be older than 4 billion years and represent a piece of the ancient lunar crust, before the formation of the large basins on the front-side of the Moon. The evidence is derived from the low absolute content of incompatible elements and their slightly different fractionation pattern from KREEP, the dominant source for these elements on the front-side. The basically chondritic pattern of siderophile elements (Ni, Co, Ir, Au) is clearly distinguished from younger, basin related, meteoritic components.
TL;DR: In this article, it was suggested that continental tholeiites have been generated from the same source as P-type oceanic tholeite, and geochemical features such as the enrichment of some lithophile elements in many of these rocks, may be related to crustal contamination.
Abstract: Proterozoic basaltic flows (> 2000 m thick) and associated dykes and sills from the Coppermine River area, Northwest Territories have chemical compositions typical of continental tholeiites. The low Mg/Fe ratio and abundances of Ni and Cr indicate that the lavas were extensively fractionated prior to extrusion. The variations of incompatible elements such as K, Rb, REE, Y, Zr, Nb, and Th suggest that the rocks were affected by interaction with continental crust. The samples least affected by contamination have trace-element compositions very similar to those of P-type mid-ocean ridge basalts. It is suggested that continental tholeiites have been generated from the same source as P-type oceanic tholeiites, and geochemical features, such as the enrichment of some lithophile elements in many of these rocks, may be related to crustal contamination. The variations within the volcanic pile of the Coppermine River area are related to those of an exposed part of the Muskox layered intrusion.
TL;DR: In this paper, an analysis of Siluro-Devonian lavas from Fife, Scotland is presented, where the major and trace elements including REE, and Sr, Nd and Pb isotopes are reported.
TL;DR: The eastern and central Beartooth Mountains of Montana and Wyoming are composed of 2,800m.y.-old granitoids that intruded older rocks of variable age and composition as mentioned in this paper.
Abstract: The eastern and central Beartooth Mountains of Montana and Wyoming are composed of 2,800-m.y.-old granitoids that intruded older rocks of variable age and composition. The most abundant rock type among these older units is a 3,000-m.y.-old amphibolite with a major-element composition similar to modern andesites. The concentrations of the incompatible trace elements, particularly the light rare earth elements, however, are much higher than those of most modern or ancient andesites. In addition, the range in concentration of many major and trace elements is large, and strong correlations for both mobile and immobile elements are evident. This coherence suggests that the observed element-abundance patterns in these rocks are not the result of metamorphic or other postcrystallization, nonisochemical processes. The compositional features of these andesitic rocks seem to be explained most easily as the result of variable degrees of partial melting of a source enriched in incompatible elements, followed by variable extents of crystallization of the resulting magmas. The mafic compositions of these magmas and limited Sm-Nd isotopic data suggest that the magmas were of mantle origin and that they were generated with the aid of incompatible-element–rich or metasomatic fluids.
TL;DR: In this article, a metasomatic enrichment of the source is proposed to account for this discrepancy, but the timing of the enrichment event can only be constrained to less than 1 AE ago, and the isotopic composition of the premetasomatized source and the metasomating agent cannot be specified.
Abstract: Major and trace-element whole rock data, Nd and Sr isotopic data, and microprobe data have been collected from a suite of basanites, olivine nephelinites, and olivine melilite nephelinites from the Raton-Clayton volcanic field, New Mexico. Most of the lavas have geochemical characteristics that suggest they are primary upper mantle derived melts. The previously unreported occurrence of Type I and Type II ultramafic xenoliths in some of the lava flows supports this conclusion. All the lavas are strongly enriched in light REE, Sr, Ba, U, Th, and P2O5. 87Sr/86Sr ratios are 0.70394 to 0.70412 and 143Nd/144Nd ratios are equal to an epsilon value of +1.4; the data fall within the Nd-Sr correlation field. Trace-element modeling indicates that the lavas were last in equilibrium with a light-REE enriched mantle with a (La/Yb)N of two to nine. However, the Nd isotopic data indicate a source with a time integrated, chondritic normalized, Sm/Nd ratio of 1.01. To account for this discrepancy a metasomatic enrichment of the source is proposed. The timing of the enrichment event can only be constrained to less than 1 AE ago, and the isotopic composition of the premetasomatized source and the metasomatizing agent cannot be specified. However, geochemical constraints suggest a CO2-rich fluid enriched in incompatible elements as the likely metasomatizing agent
TL;DR: The Keweenawan Mamainse Point Formation of Ontario consists of a sequence of tholeiitic lavas and transitional basalt dykes, with trace-element characteristics similar to other proto-oceanic rift sequences as mentioned in this paper.
TL;DR: In this article, the abundance of thirty-five elements were determined in two bulk samples and a white clast in the Allan Hills A81005 meteorite, which is very similar to those found in most lunar highlands rocks, and provide very strong evidence that the sample is lunar in origin.
Abstract: Abundances of thirty-five elements were determined in two bulk samples and a white clast in the Allan Hills A81005 meteorite. High siderophile element content indicates that the sample is a regolith breccia. An Fe/Mn ratio of 77 in this meteorite eliminates parent bodies of known differentiated meteorites as the source of ALHA 81005. The incompatible elements are very similar to those found in most lunar highlands rocks, and provide very strong evidence that the sample is lunar in origin. The clast sample has the trace element pattern of a lunar anorthosite and is very low in KREEP and siderophile elements. It may be a fragment of a pristine lunar rock.
TL;DR: Experimental melting equilibria at 1 kbar P H2O are reported for three early Tertiary granites from Skye and one from Rhum, together with a quartz monzonite from Ardnamurchan as discussed by the authors.
Abstract: Experimental melting equilibria at 1 kbar P H2O are reported for three early Tertiary granites from Skye and one from Rhum, together with a quartz monzonite from Ardnamurchan. The Hebridean Province leucogranites show cotectic melting behaviour, whilst associated ‘primitive’ (mostly adamellitic) acid plutons have silicate liquidi ∼ 925 °C and plagioclase liquidi ∼ 875 °C. At such high temperatures the morefusible crustal rock types of the region would be almost completely molten. If the Tertiary ‘primitive’ acid magmas were simple crustal melts, they would inherit the incompatible element ratios of their sialic progenitors. This is demonstrably not so. Minor element ratios in these plutons are consistent with extensive fractional crystallization during the evolution of their magmas. But it is, in most individual instances, extremely difficult to specify, either by thermal or geochemical arguments, whether (1) fractional crystallization followed sialic contamination of basic magmas or (2) mixing occurred between fractionation residua and sialic melts. Both the minor element ratios and cotectic melting behaviour of the Hebridean Province leucogranites are consistent with the view that they are products of extreme fractional crystallization of (sial contaminated) more-basic magmas. Nevertheless, it is clear—when the sequence and timing of emplacement of acid magmas within individual intrusive centres is considered—that very complex polycyclic combinations of fusion, fractionation, and re-fusion were involved in the evolution of these granites. The solidi of the samples studied experimentally, together with published data, show a progressive rise in temperature as the compositions of the rocks diverge from the minimum melting composition in NaAlSi3O8-KAlSi3O8-SiO2 at 1 kbarH2O. This relationship is important when considering the likely nature of sialic contamination of basic to intermediate continental magmatic suites fed through reservoir systems which are swarms of dykes and, or, sills. Because salic low-solidus crustal rock types also show near-cotectic melting behaviour, the composition of the contaminant may be strongly biased towards these (usually minor) crustal units, rather than the ‘bulk’ or average crustal composition.
TL;DR: In the early stages of metamorphism, U and Th were retained together with several other incompatible elements (Zr, Nb, La and Ce) in stable secondary phases or alternatively these elements may be held in primary accessory minerals such as zircon and apatite.
Abstract: In the Paleozoic basalts of Nova Scotia (Canada) metamorphosed to a greenschist facies grade, U and Th are closely associated with immobile elements (e.g. Zr and Nb). The coherence of these elements with K, typical of igneous rocks is, however, absent, U and Th are apparently not affected by greenschist facies metamorphism as are alkali and alkali earth elements and their variation thus reflects primary magmatic processes. It seems that during the early stages of metamorphism, U and Th were retained together with several other incompatible elements (Zr, Nb, La and Ce) in stable secondary phases or alternatively these elements may be held in primary accessory minerals such as zircon and apatite.