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Showing papers on "Incompatible element published in 2004"


Journal ArticleDOI
TL;DR: The Ethiopian plateau is made up of several distinct volcanic centres of different ages and magmatic affinities as discussed by the authors, and the three main types of magma have very different major and trace element characteristics ranging from compositions low in incompatible elements in the tholeiites [e.g. 10 ppm La at 7 wt % MgO (=La7), La/εb = 4.2], moderate in the alkali basalts (La7 = 24, La/β = 9.2), and very high in the magnesian alkaline magmas (
Abstract: The Ethiopian plateau is made up of several distinct volcanic centres of different ages and magmatic affinities. In the NE, a thick sequence of 30 Ma flood basalts is overlain by the 30 Ma Simien shield volcano. The flood basalts and most of this shield volcano, except for a thin veneer of alkali basalt, are tholeiitic. In the centre of the province, a far thinner sequence of flood basalt is overlain by the 22 Ma Choke and Guguflu shield volcanoes. Like the underlying flood basalts, these shields are composed of alkaline lavas. A third type of magma, which also erupted at 30 Ma, is more magnesian, alkaline and strongly enriched in incompatible trace elements. Eruption of this magma was confined to the NE of the province, a region where the lava flows are steeply tilted as a result of deformation contemporaneous with their emplacement. Younger shields (e.g. Mt Guna, 10·7 Ma) are composed of Si-undersaturated lavas. The three main types of magma have very different major and trace element characteristics ranging from compositions low in incompatible elements in the tholeiites [e.g. 10 ppm La at 7 wt % MgO (=La7), La/Υb = 4.2], moderate in the alkali basalts (La7 = 24, La/Υb = 9.2), and very high in the magnesian alkaline magmas (La7 = 43, La/Υb = 17). Although their Nd and Sr isotope compositions are similar, Pb isotopic compositions vary considerably; 206Pb/204Pb varies in the range of ∼17·9-18·6 in the tholeiites and ∼19·0-19·6 in the 22 Ma shields. A conventional model of melting in a mantle plume, or series of plumes, cannot explain the synchronous eruption of incompatible-element-poor tholeiites and incompatible-element-rich alkali lavas, the large range of Pb isotope compositions and the broad transition from tholeiitic to alkali magmatism during a period of continental rifting. The lithospheric mantle played only a passive role in the volcanism and does not represent a major source of magma. The mantle source of the Ethiopian volcanism can be compared with the broad region of mantle upwelling in the South Pacific that gave rise to the volcanic islands of French Polynesia. Melting in large hotter-than-average parts of the Ethiopian superswell produced the flood basalts; melting in small compositionally distinct regions produced the magmas that fed the shield volcanoes. © Oxford University Press 2004; all rights reserved.

380 citations


Journal ArticleDOI
01 Sep 2004-Lithos
TL;DR: In this paper, the abundances of the mildly incompatible elements Al, Cr, V, Sc and Yb in more than 1700 mantle peridotite bulk rock analyses are interpreted in the light of a fractional melting model based on experimentally measured partition coefficients (D) and melting reaction stoichiometries.

172 citations


Journal ArticleDOI
19 Feb 2004-Nature
TL;DR: It is shown that partitioning of calcium between the grain interiors and grain boundaries of olivine in natural and synthetic Olivine-rich aggregates follows a thermodynamic model for equilibrium grain-boundary segregation, which provides a mechanism for the selective extraction of incompatible elements in the Earth's mantle.
Abstract: The concentrations and locations of elements that strongly partition into the fluid phase in rocks provide essential constraints on geochemical and geodynamical processes in Earth's interior. A fundamental question remains, however, as to where these incompatible elements reside before formation of the fluid phase. Here we show that partitioning of calcium between the grain interiors and grain boundaries of olivine in natural and synthetic olivine-rich aggregates follows a thermodynamic model for equilibrium grain-boundary segregation. The model predicts that grain boundaries can be the primary storage sites for elements with large ionic radius—that is, incompatible elements in the Earth's mantle. This observation provides a mechanism for the selective extraction of these elements and gives a framework for interpreting geochemical signatures in mantle rocks.

170 citations


Journal ArticleDOI
TL;DR: In this paper, Cenozoic basalts from both sides of the Daxin'anling-Taihang gravity lineament that separates the Sino-Korean craton into western and eastern parts have been studied.
Abstract: Cenozoic basalts from both sides of the Daxin’anling‐Taihang gravity lineament that separates the Sino‐Korean craton (SKC) into western and eastern parts have been studied. In the western SKC, magmas evolved from xenolith‐bearing alkali basalts of Late Eocene–Oligocene age to coexisting alkali and tholeiitic basalts of Late Miocene–Quaternary age. This change in basalt type is accompanied by a decrease in La/Yb and an increase in Yb content. Sr‐Nd isotopic ratios and relative abundances on incompatible elements are consistent with a prevailing asthenospheric origin, although lithospheric mantle may have also contributed to these basalts. This temporal variation in basalt geochemistry is interpreted as reflecting progressive lithospheric thinning in the western SKC during the Cenozoic. An opposite trend is observed for Cenozoic basalts from the eastern SKC, suggesting lithospheric thickening during this time period. This thickening was probably related to regional thermal decay following peak magm...

161 citations


Journal ArticleDOI
TL;DR: In this paper, major and trace element compositions of lavas from the entire 3098 m stratigraphic section sampled by phase-2 of the Hawaii Scientific Drilling Project are presented.
Abstract: [1] This paper presents major and trace element compositions of lavas from the entire 3098 m stratigraphic section sampled by phase-2 of the Hawaii Scientific Drilling Project. The upper 245 m are lavas from Mauna Loa volcano, and the lower 2853 m are lavas and volcanoclastic rocks from Mauna Kea volcano. These intervals are inferred to represent about 100 ka and 400 ka respectively of the eruptive history of the two volcanoes. The Mauna Loa tholeiites tend to be higher in SiO2 and lower in total iron, TiO2, alkalis, and incompatible elements at a given MgO content than Mauna Kea lavas. The transition from Mauna Loa to Mauna Kea lavas is all the more pronounced because the Mauna Loa tholeiites overlie a thin sequence of postshield Mauna Kea alkalic to transitional tholeiitic lavas. The Mauna Loa tholeiites display welldeveloped coherent trends with MgO that are indistinguishable in most respects from modern lavas. With depth, however, there is a slight decline in incompatible element abundances, and small shifts to depleted isotopic ratios. These characteristics suggest small changes in melt production and source components over time, superimposed on shallow melt segregation. The Mauna Kea section is subdivided into a thin, upper 107 m sequence of postshield tholeiites, transitional tholeiites and alkali basalts of the Hamakua volcanics, overlying four tholeiitic magma types that are intercalated throughout the rest of the core. These four magma types are recognized on the basis of MgO-normalized SiO2 and Zr/Nb values. Type-1 lavas (high SiO2 and Zr/Nb) are ubiquitous below the postshield lavas and are the dominant magma type on Mauna Kea. They are inter-layered with the other three lava types. Type-2 lavas (low SiO2 but high Zr/Nb) are found only in the upper core, and especially above 850 m. Type-3 lavas (low SiO2 and Zr/Nb) are very similar to tholeiites from Loihi volcano and are present only below 1974 m. There are only 3 discrete samples of type-4 lavas (high SiO2 and low Zr/Nb), which are present in the upper and lower core. The differences between these magma types are inferred to reflect changes in melt production, depth of melt segregation, and differences in plume source components over about 400 ka of Mauna Kea’s eruptive history. At the start of this record, eruption rates were high, and two distinct tholeiitic magmas (type-1 and 3) were erupting concurrently. These two magmas require two distinct source components, one similar to that of modern Loihi tholeiites and the other close to that of Kilauea magmas. Subsequently, the Loihilike source of the type-3 magmas was exhausted, and these lavas are absent from the remainder of the core. For the next 200 ka or so, the eruptive sequence consists of inter-layered type-1 and -2 lavas that are derived from a common Mauna Kea source, the major difference between the two being the depth at which the melts segregated from the source. At around 440 ka (corresponding with the transition in the core from submarine to subaerial lavas) eruption rates began to decline and low-MgO lavas are suddenly much more abundant in the record. Continuing gradual decline in melting and eruption rates was accompanied by a decline in normalized SiO2 content of the type-1 magmas, and the eventual onset of postshield magmatism. Components: 30,168 words, 16 figures, 4 tables.

160 citations


Journal ArticleDOI
01 Sep 2004-Geology
TL;DR: The Tatara-San Pedro complex is characterized by xenocrysts and microxenoliths of olivine, augite, and plagioclase derived from solidified cumulates, wide but poorly correlated ranges of incompatible and compatible major and trace elements, and limited isotopic variability as discussed by the authors.
Abstract: At long-lived arc volcanic centers, open-system interactions between new magma and the plutonic roots of the arc will increase with time relative to interactions with older crust. Assimilative recycling of mafic plutonic arc roots will have different isotopic consequences than incorporation of aged continental crust. In the Tatara–San Pedro complex, 30 comagmatic basaltic lavas are characterized by xenocrysts and microxenoliths of olivine, augite, and plagioclase derived from solidified cumulates, wide but poorly correlated ranges of incompatible and compatible major and trace elements, and limited isotopic variability. This mineralogical-chemical signature reflects assimilation wherein grain-boundary melting and disaggregation of xenoliths led to blending of incompatible element– enriched melts derived mainly from hornblende, phlogopite, and plagioclase in combination with variable retention of xenocrysts, hence variable but high compatible element concentrations.

153 citations


Journal ArticleDOI
TL;DR: In this article, major elements, trace elements including highly siderophile elements (HSE) and Re-Os isotope ratios were analysed in situ on individual sulfide grains and one Fe metal grain enclosed in fresh xenocrystic olivine and pyroxenes from kimberlites in the Lac de Gras area, central Slave Craton.

147 citations


Journal ArticleDOI
01 Sep 2004-Lithos
TL;DR: Garnet peridotite xenoliths from the Sloan kimberlite (Colorado) are variably depleted in their major magmaphile (Ca, Al) element compositions with whole rock Re-depletion model ages generally consistent with this depletion occurring in the mid-Proterozoic as discussed by the authors.

138 citations


Journal ArticleDOI
01 Jul 2004-Lithos
TL;DR: In this paper, the authors show that peridotites in the spinel-to-plagioclase stability field of the Betic Cordillera of southern Spain can be attributed to at least two metasomatizing agents with distinct chemical and isotopic compositions.

117 citations


Journal ArticleDOI
TL;DR: The 2.7 Ga Ramagiri-Hungund composite greenstone belt (RHST) is one of a series of volcanic dominated supracrustal belts in the eastern Dharwar craton.

92 citations


Journal ArticleDOI
TL;DR: Jeju plume magmas can be divided into three series, based on major and trace element abundances: high-alumina alkalic, low-aluminant alkalics, and sub-alkalic as mentioned in this paper.
Abstract: The incompatible element signatures of volcanic rocks forming Jeju Island, located at the eastern margin of the Asian continent, are identical to those of typical intraplate magmas. The source of these volcanic rocks may be a mantle plume, located immediately behind the SW Japan arc. Jeju plume magmas can be divided into three series, based on major and trace element abundances: high-alumina alkalic, low-alumina alkalic, and sub-alkalic. Mass-balance calculations indicate that the compositional variations within each magma series are largely governed by fractional crystallization of three chemically distinct parental magmas. The compositions of primary magmas for these series, using inferred residual mantle olivine compositions, suggest that the low-alumina alkalic and subalkalic magmas are generated at the deepest and shallowest depths by lowest and highest degrees of melting, respectively. These estimates, together with systematic differences in trace element and isotopic compositions, indicate that the upper mantle beneath Jeju Island is characterized by an increased degree of metasomatism and a change in major metasomatic hydrous minerals from amphibole to phlogopite with decreasing depth. The original plume material, having rather depleted geochemical characteristics, entrained shallower metasomatized uppermost mantle material, and segregated least-enriched low-alumina alkalic, moderately enriched high-alumina alkalic, and highly enriched sub-alkalic magmas, with decreasing depth.

Journal ArticleDOI
11 Nov 2004-Nature
TL;DR: Evidence that KREEP magmatism extended for an additional 1 Gyr is presented, based on analyses of the youngest dated lunar sample.
Abstract: Primordial solidification of the Moon (or its uppermost layer) resulted in the formation of a variety of rock types that subsequently melted and mixed to produce the compositional diversity observed in the lunar sample suite. The initial rocks to crystallize from this Moon-wide molten layer (the magma ocean) contained olivine and pyroxene and were compositionally less evolved than the plagioclase-rich rocks that followed. The last stage of crystallization, representing the last few per cent of the magma ocean, produced materials that are strongly enriched in incompatible elements including potassium (K), the rare earth elements (REE) and phosphorus (P)--termed KREEP. The decay of radioactive elements in KREEP, such as uranium and thorium, is generally thought to provide the thermal energy necessary for more recent lunar magmatism. The ages of KREEP-rich samples are, however, confined to the earliest periods of lunar magmatism between 3.8 and 4.6 billion years (Gyr) ago, providing no physical evidence that KREEP is directly involved in more recent lunar magmatism. But here we present evidence that KREEP magmatism extended for an additional 1 Gyr, based on analyses of the youngest dated lunar sample.

Journal ArticleDOI
01 Jun 2004-Lithos
TL;DR: The Uintjiesberg kimberlite diatreme as mentioned in this paper is a group I, calcite kimbersite that has an emplacement age of ∼100 Ma.

Journal ArticleDOI
TL;DR: Sr-Nd-Os-O isotope and major and trace element data from ~62 Ma picrites from Baffin Island constrain the composition of mantle sources sampled at the inception of North Atlantic Igneous Province (NAIP) magmatism as mentioned in this paper.
Abstract: Sr-Nd-Os-O isotope and major and trace element data from ~62 Ma picrites from Baffin Island constrain the composition of mantle sources sampled at the inception of North Atlantic Igneous Province (NAIP) magmatism. We recognize two compositional types. Depleted (N-type) lavas have low 87Sr/86Sri (0.702990–0.703060) and 187Os/188Osi (0.1220–0.1247) and high 143Nd/144Ndi (0.512989–0.512999) and are depleted in incompatible elements relative to primitive mantle. Enriched (E-type) lavas have higher 87Sr/86Sri (0.703306–0.703851) and 187Os/188Osi (0.1261–0.1303), lower 143Nd/144Ndi (0.512825–0.512906), and incompatible element concentrations similar to, or more enriched than, primitive mantle. There is also a subtle difference in oxygen isotope composition; E-type lavas are marginally lower in δ18Oolivine value (5.16–4.84‰) than N-type lavas (5.15–5.22‰). Chemical and isotopic variations between E- and N-type lavas are inconsistent with assimilation of crust and/or subcontinental lithospheric mantle and appear to instead reflect mixing between melts derived from two distinct mantle sources. Strontium-Nd-O isotope compositions and incompatible trace element abundances of N-type lavas suggest these are largely derived from the depleted upper mantle. The 187Os/188Osi ratios of N-type lavas can also be explained by such a model but require that the depleted upper mantle had γOs of approximately −5 to −7 at 62 Ma. This range overlaps the lowest γOs values measured in abyssal peridotites. Baffin Island lava compositions are also permissive of a model involving recharging of depleted upper mantle with 3He-rich material from the lower mantle (Stuart et al., Nature, 424, 57–59, 2003), with the proviso that recharge had no recognizable effect on the lithophile trace element and Sr-Nd-Os-O isotope composition. The origin of the enriched mantle component sampled by Baffin Island lavas is less clear but may be metasomatized and high-temperature-altered recycled oceanic lithosphere transported within the proto Iceland plume. Differences between Baffin Island lavas and modern Icelandic basalts suggest that a range of enriched and depleted mantle sources have been tapped since the inception of magmatism in the province. Similarities between Baffin Island lavas erupted and those of similar age from East and West Greenland also suggest that the enriched component in Baffin Island lavas may have been sampled by lavas erupted over a wide geographic range.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the trace element chemistry of a melt from a recycled component and performed trace element partitioning experiments in the simple systems CMAS (CaO-MgO-Al2O3-SiO2), NCMAS (Na2O-CMAS) and TiO2 -CMAS (TiO2-CS) at 3 GPa and 1298-1500°C using analogue eclogitic compositions.

Journal ArticleDOI
TL;DR: The South Auckland Volcanic Field is a Pleistocene (1 59 − 0 51Ma) basaltic intraplate, monogenetic field situated south of Auckland City, North Island, New Zealand as mentioned in this paper.
Abstract: The South Auckland Volcanic Field is a Pleistocene (1 59– 0 51Ma) basaltic intraplate, monogenetic field situated south of Auckland City, North Island, New Zealand. Two groups of basalts are distinguished based on mineralogy and geochemical compositions, but no temporal or spatial patterns exist in the distribution of various lava types forming each group within the field: Group A basalts are silica-undersaturated transitional to quartz-tholeiitic basalts with relatively low total alkalis (3 0–4 6 wt %), Nb (7–29 ppm), and (La/Yb)N (3 4–7 6); Group B basalts are strongly silicaundersaturated basanites to nepheline-hawaiites with high total alkalis (3 3–7 9 wt %), Nb (32–102 ppm), and (La/Yb)N (12–47). Group A has slightly higher Sr/Sr, similar eNd, and lower Pb/Pb values compared with Group B. Contrasting geochemical trends and incompatible element ratios (e.g. K/Nb, Zr/Nb, Ce/Pb) are consistent with separate evolution of Groups A and B from dissimilar parental magmas derived from distinct subcontinental lithospheric mantle sources. Differentiation within each group was controlled by olivine and clinopyroxene fractionation. Group B magmas were generated by <8% melting of an ocean island basalt (OIB)-like garnet peridotite source with high U/Pb mantle (HIMU) and enriched mantle (EMII) characteristics possibly inherited from recycled oceanic crust. Group A magmas were generated by <12% melting of a spinel peridotite source also with HIMU and EMII signatures. This source type may have resulted from subduction-related metasomatism of the sub-continental lithosphere modified by a HIMU plume. These events were associated with Mesozoic or earlier subductionand plume-related magmatism when New Zealand was at the eastern margin of the Gondwana supercontinent.

Journal ArticleDOI
TL;DR: The Nushan peridotite as discussed by the authors showed a large variation in rare earth element (LREE)-depleted or relatively flat REE patterns with only a slight depletion in high field strength elements (HFSE), consistent with 'wall-rock' metasomatism adjacent to basaltic veins.
Abstract: Distinct equilibration temperatures, deformation and trace element characteristics are observed in amphibole-bearing and amphibole-free peridotite xenoliths from Nushan, Sino-Korean Craton, eastern China. Amphibole-free peridotites are predominantly deformed, fine-grained ( 1 mm) and equilibrated at 990---1110 C. Their cpx are characterized by either light rare earth element (LREE)-depleted or relatively flat REE patterns with only a slight depletion in high field strength elements (HFSE). LREE enrichment is generally associated with Fe-rich samples, consistent with `wall-rock' metasomatism adjacent to basaltic veins. In contrast, amphibole-bearing peridotites are less deformed, coarse-grained (43 mm) and display chemical zonation in the pyroxenes suggesting cooling from 1050 to 850 C. Their cpx show a large variation in LREE (Cen ˆ 1 7---68) and almost constant heavy rare earth element (HREE) contents (Ybn ˆ 9 8---11 6). The highest LREE contents occur in cpx from amphibole-rich samples, coupled with Fe enrichment, strong enrichment in Th and U, and marked depletion in the HFSE. These characteristics may be accounted for by combined `wall-rock' and `diffuse' metasomatism involving an agent rich in volatiles and incompatible elements. As such the Nushan xenoliths could represent samples from two spatially separate metasomatic aureoles. Conversely, the cryptic and modal metasomatism could be genetically related, because the amphibole-peridotites and Fe-rich amphibole-free samples show similar Sr---Nd isotopic ranges that are indistinguishable from those of the Cenozoic basalts from eastern China. The different metasomatic assemblage and the trace element composition can be accounted for in terms of P---T control on amphibole stability and progressive chemical evolution of asthenosphere-derived melts during upward migration. Trace element signatures and metasomatic assemblages, together with the fertile composition of the Nushan peridotites, suggest an origin as newly accreted lithosphere rather than as relic cratonic mantle. Metasomatism may have occurred after late Mesozoic lithospheric thinning, which marked a dramatic change in lithospheric architecture beneath the Sino-Korean Craton.

Journal ArticleDOI
01 Jul 2004-Lithos
TL;DR: Partition coefficients for compatible and incompatible trace elements for use in modelling the origin and evolution of lamproitic and other potassic rocks are reported in this paper, based on values obtained by in situ determination using laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS) on mineral/glass pairs in examples of the Gaussberg olivine leucitite, a classic leucite lamproite.

Journal ArticleDOI
TL;DR: The Quaternary Nevado de Longavi volcano of the Andean Southern Volcanic Zone (SVZ) has erupted magmas that range in composition from basalt to low-silica dacite, although andesites are the dominant erupted magma type as mentioned in this paper.
Abstract: The Quaternary Nevado de Longavi volcano of the Andean Southern Volcanic Zone (SVZ) has erupted magmas that range in composition from basalt to low-silica dacite, although andesites are the dominant erupted magma type. Amphibole is a common phenocryst phase in andesites throughout the volcano, and it is the dominant mafic phase in Holocene dacites and their included mafic enclaves. Compositions of magmas erupted at Longavi volcano define arrays that diverge from trends delineated by neighboring frontal-arc volcanoes. Although mafic compositions at Longavi are broadly similar to basalts at other SVZ centers, Longavi intermediate and evolved magmas have systematically lower abundances of incompatible major (K 2 O, P 2 O 5 ) and trace elements (Rb, Zr, Nb, REE, Th, etc), as well as high Ba/Th, Sr/Y, and La/Yb ratios. Longavi volcano magmas define two differentiation series with regard to enrichments of Rb (and other incompatible elements) with increasing silica. A high-Rb series that includes the oldest units of the volcano comprises basalts to andesites dominated by anhydrous mineral assemblages with chemical compositions similar to other SVZ magmatic series. The series with low Rb, on the other hand, includes the Holocene units that evolved from basaltic andesites to dacites by means of fractional crystallization wherein amphibole and calcic plagioclase dominate the mineral assemblage. Magmas parental to low-Rb series are interpreted to be high-degree mantle melts, highly hydrous and oxidized, formed as a response to high fluid inputs into the subarc mantle. Enhanced water transport to the subarc mantle is a plausible effect of the subduction of the oceanic Mocha Fracture Zone that projects beneath Nevado de Longavi. Volcanoes located over oceanic fracture zones further south along the SVZ have erupted hornblende-bearing magmas that share some chemical similarities with Longavi volcano magmas.

Journal ArticleDOI
01 Sep 2004-Lithos
TL;DR: In this paper, major and trace element data for a suite of rocks emplaced over an area of ∼45,000 km2 in the Eastern Goldfields Province (EGP), Yilgarn Craton, that are petrographically and mineralogically described as kimberlites, melnoites and carbonatites are obtained.

01 Dec 2004
TL;DR: In this paper, the geochemical variations of the southern Patagonia lavas are discussed in terms of different geochemical components: depleted and enriched sub-slab asthenosphere, enriched continental lithospheric mantle, continental crust and subducted materials.
Abstract: Palabras clave: Patagonia, Magmas basalticos, Retroarco, Cenozoico, Ventana astenosferica, Geoquimica, Geodinamica ABSTRACT. Huge amounts of basaltic s.l. lavas were persistently erupted along the eastern side of the Andean Cordillera, throughout Cenozoic time, forming extensive plateaus, hundreds of monogenetic scoria cones and other volcanic structures in a continental back-arc setting. The igneous products exposed in the southern sector of the extra-Andean Patagonia (44° 30' - 52° S) are dominantly mafic with minor slightly evolved compositions and rare highly differentiated products. The many published chemical analyses of these rocks, indicate that the mafic lavas range from strongly silica - undersaturated basanites to oversaturated basaltic andesites, and that most of the lavas have a typical within-plate geochemical signature. However, a number of lavas, generally erupted in the western-central sectors of Patagonia, are characterized by different distributions of the incompatible elements with high LILE/HFSE and LREE/HFSE ratios. The REE distribution modelling suggests a low degree of melting of a deep (> 70 km) garnet-bearing source for the alkaline magmas, and a higher degree of melting of the same source, or an even higher degree of melting of an enriched source, for the subalkaline magmas. The available Sr-Nd-Pb isotope compositions clearly attest to a major geographic variation: the southernmost lavas have lower 87 204 Pb ratios with respect to those erupted to the north. On the whole, the Sr-Nd-Pb isotope compositions of the southern Patagonia lavas fall within the typical range of within-plate continental magmas; in addition the Pb isotope ratios fall in the range of the Southern Hemisphere Dupal Pb isotope anomaly. The geochemical variations of the southern Patagonia lavas are discussed in terms of different geochemical components: depleted and enriched sub-slab asthenosphere, enriched continental lithospheric mantle, continental crust and subducted materials. The geodynamic significance is interpreted with in the framework of the space-time evolution of the magmatism and in the wider frame of the Cenozoic history of the Pacific margin of southern South America. The slab window openings associated with the collision between oceanic spreading ridges and the Chile Trench are the preferred geodynamic interpretation of the southern Patagonia magmatism. However, the occurrence of many volcanic formations whose age and location are not entirely compatible with the slab window model suggests that other geodynamic processes inducing mantle melting could have been active during Cenozoic time in the extra Andean Patagonia.

Journal ArticleDOI
TL;DR: In this article, secondary ion mass spectrometry was used to determine the Pb isotopic compositions of melt inclusions in olivine phenocrysts of lava samples from Mangaia and Rarotonga, Cook-Austral islands.

Journal ArticleDOI
TL;DR: In this article, an isotopic and chemical profile across a modally layered pyroxenite indicates substantial Os isotopic disequilibrium on the centimeter scale, while Nd and Sb isotopes are equilibrated or nearly equilibria.

Journal ArticleDOI
TL;DR: Using the best estimates of rare gas isotopic ratios for both Oceanic Island Basalts (OIB) and MORB sources, and knowing the incompatible element ratios between these two sources (e.g. K, U), it is therefore possible to determine the ratios between the concentrations of non-radiogenic isotopes (3He, 22Ne, 36Ar) in the lower mantle and the upper mantle as discussed by the authors.

Journal ArticleDOI
TL;DR: Spinel lherzolite and harzburgite xenoliths from the Basin and Range and Colorado Plateau Provinces in the southwestern United States (SWUS) show a broad range in incompatible element distributions from depleted to enriched, both within and between sites as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the geochemical properties of syn-opening volcanic rocks from the Hirado, Ikitsuki and Takushima islands off western Kyushu in the Taiwan-Sinzi Folded Zone.

Journal ArticleDOI
TL;DR: The Black Swan komatiite sequence is a package of dominantly olivine-rich cumulates with lesser volumes of spinifex textured rocks, interpreted as a section through an extensive komatisite lava flow field as mentioned in this paper.
Abstract: The Black Swan komatiite sequence is a package of dominantly olivine-rich cumulates with lesser volumes of spinifex textured rocks, interpreted as a section through an extensive komatiite lava flow field. The sequence hosts a number of nickel sulfide orebodies, including the Silver Swan massive shoot and the Cygnet and Black Swan disseminated orebodies. A large body of whole rock analyses on komatiitic rocks from the Black Swan area has been filtered for metasomatic effects. With the exception of mobile elements such as Ca and alkalis, most samples retain residual igneous geochemistry, and can be modelled predominantly by fractionation and accumulation of olivine. Whole rock MgO–FeO relationships imply a relatively restricted range of olivine compositions, more primitive than the olivine which would have been in equilibrium with the transporting komatiite lavas, and together with textural data indicate that much of the cumulus olivine in the sequence was transported. Flow top compositions show evidence for chromite saturation, but the cumulates are deficient in accumulated chromite. Chromite compositions are typical of those found in compound flow-facies komatiites, and are distinct from those in komatiitic dunite bodies. Incompatible trace element abundances show three superimposed influences: control by the relative proportion of olivine to liquid; a signature of crustal contamination and an overprint of metasomatic introduction of LREE, Zr and Th. This overprint is most evident in cumulates, and relatively insignificant in the spinifex rocks. Platinum and palladium behaved as incompatible elements and are negatively correlated with MgO. They show no evidence for wholesale depletion due to sulfide extraction, which was evidently restricted to specific lava tubes or pathways. The lack of correspondence between PGE depletion and contamination by siliceous material implies that contamination alone is insufficient to generate S-saturation and ore formation in the absence of sulfide in the assimilant. Contamination signatures in spinifex-textured rocks may be a guide to Ni-sulfide mineralisation, but are not entirely reliable in the absence of other evidence. The widespread vesicularity of the sequence may be attributable to assimilated water rather than to primary mantle-derived volatiles, and cannot be taken as evidence for primary volatile-rich magmas. The characteristic signature of the Black Swan Succession is the presence of highly localised disseminated sulfide within a sequence showing more widespread evidence for crustal contamination and interaction with its immediate substrate. This has important implications for the applicability of trace element geochemistry in exploration for komatiite-hosted nickel deposits.

Journal ArticleDOI
TL;DR: Two distinct groups of subduction-related granitoid rocks, one Jurassic and the other Tertiary, occur in the area between the Vardar (Axios) Zone and the Rhodope Massif in northern Greece.
Abstract: Two distinct groups of subduction-related (orogenic) granitoid rocks, one Jurassic and the other Tertiary, occur in the area between the Vardar (Axios) Zone and the Rhodope Massif in northern Greece. The two groups of granitoids differ in many respects. The first group shows evolved geochemical characters, it is not associated with mafic facies, and evidence of magmatic interaction between mantle- and crustal-derived melts is lacking. The second group has less evolved geochemical characters, it is associated with larger amount of mafic facies, and magmatic interaction processes between mantle-derived and crustal melts are ubiquitous as evidenced by mafic microgranular enclaves and synplutonic dykes showing different enrichment in K2O, Ti, and incompatible elements. This kind of magmatism can be attributed to the complex geodynamic evolution of the area. In particular, we suggest that two successive subduction events related to the closure of the Vardar and the Pindos oceans, respectively, occurred in the investigated area from Late Jurassic to Tertiary. We relate the genesis of Jurassic granitoids to the first subduction event, whereas Tertiary granitoids are associated with the second subduction. Fluids released by the two subducted slabs induced metasomatic processes generating a ‘leopard skin’ mantle wedge able to produce mafic melts ranging from typical calc-alkaline to ultra-potassic. Such melts interacted in various amounts with crustal calc-alkaline anatectic melts to generate the wide spectrum of Tertiary granitoids occurring in the study area. Copyright © 2004 John Wiley & Sons, Ltd.

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TL;DR: In the Youjiang Basin of the southern Yangtze block of China as mentioned in this paper, the upper Devonian (D-3) tholeiitic volcanics grading to Lower Carboniferous (C-1) alkali basalts have EM1-like Sr-Nd isotopic signatures.
Abstract: Basalts in the Youjiang Basin of the southern Yangtze block. South China, consist of Upper Devonian (D-3) tholeiitic volcanics grading to Lower Carboniferous (C-1) alkali basalts. Alkali basalts are generally enriched in incompatible elements relative to tholeiites, having higher Zr. Nb, Hf, Th, LREE, Ti and P abundances, a La/Sm-CN, range of 2.3-2.8, a La/Yb-CN range of 5.9-7.5, a Sr-87/Sr-86(i) range of 0.7050-0.7053, and epsilon(ND)(t) values of -1.4 to -0.6. Tholeiites possess a La/Sm-CN range of 1.8-2.1. a La/Yb-CN range of 3.3-4.6, a Sr-87/Sr-86(i) range of 0.7047-0.7054, and epsilon(Nd) (1) values of -3.1 to -2.2. Both basaltic suites have EM1-like Sr-Nd isotopic signatures; however, their distinctly different La/Nb, Zr/Nb, and Th/Nb values suggest heterogeneous mantle sources. Higher La/Nb (1.03-1.31), Tb/Nb (0.22-0.24) and Zr/Nb (8.2-8.5) ratios in the D-3 tholeiites indicate the importance of enriched lithospheric mantle in the petrogenesis, whereas strong OIB-type trace element signatures-e.g., low La/Nb (0.74-0.87), Th/Nb (0.14-0.15) and Zr/Nb (5.3-5.9) in the C-1 volcanics necessitates an important contribution of an OIB-type asthenosphere. Increasing epsilon(Nd)(t) and La/ Sm values coupled with decreasing La/Nb ratios grading from D-3 to C-1 basalts suggest that the D-3 tholeiites were produced at relatively larger melting degrees with higher proportions of enriched components, and that the C-1 alkali basalts were generated at smaller melting degrees with lower proportions of enriched components. Such trends reflect a continuous lithospheric thinning event attending asthenosphere-lithiosphere interaction. Progressive rifting episodes explain the petrogenesis of these Upper Paleozoic basalts, suggesting that the southern Yangtze block had become a passive continental margin following the opening and spreading of the Paleo-Tethyan Ocean.

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TL;DR: More than 100 volcanic necks in central Scania (southern Sweden) are the product of Jurassic continental rift-related mafic alkaline magmatism at the southwest margin of the Baltic Shield as mentioned in this paper.
Abstract: More than 100 volcanic necks in central Scania (southern Sweden) are the product of Jurassic continental rift-related mafic alkaline magmatism at the southwest margin of the Baltic Shield. They are mainly basanites, with rarer melanephelinites. Both rock groups display overlapping primitive Mg-numbers, Cr and Ni contents, steep chondrite-normalized rare earth element patterns (LaN /YbN = 17–27) and an overall enrichment in incompatible elements. However, the melanephelinites are more alkaline and have stronger high field strength element enrichment than the basanites. The existence of distinct primary magmas is also indicated by heterogeneity in highly incompatible element ratios (e.g. Zr/Nb, La/Nb). Trace element modelling indicates that the magmas were generated by comparably low degrees of melting of a heterogeneous mantle source. Such a source can best be explained by a metasomatic overprint of the mantle lithosphere by percolating evolved melts. The former existence of such alkaline trace element-enriched melts can be demonstrated by inversion of the trace element content of green-core clinopyroxenes and anorthoclase which occur as xenocrysts in the melanephelinites and are interpreted as being derived from crystallization of evolved mantle melts. Jurassic magmatic activity in Scania was coeval with the generation of nephelinites in the nearby Egersund Basin (Norwegian North Sea). Both Scanian and North Sea alkaline magmas share similar trace element characteristics. Mantle enrichment processes at the southwest margin of the Baltic Shield and the North Sea Basin generated trace element signatures similar to those of ocean island basalts (e.g. low Zr/Nb and La/Nb) but there are no indications of plume activity during the Mesozoic in this area. On the contrary, the short duration of rifting, absence of extensive lithospheric thinning, and low magma volumes argue against a Mesozoic mantle plume. It seems likely that the metasomatic imprint resulted from the earlier Permo-Carboniferous rifting episode which affected the entire study area and clearly was accompanied by plume activity (Ernst and Buchan in American Geophysical Union, pp 297–337, 1997). Renewed rifting in Jurassic times triggered decompression melting in the volatile-enriched lithospheric mantle and the alkaline melts generated inherited the earlier “stored” plume signature.