Compatible Elements Research Articles

Petrogenesis of the Huili Paleoproterozoic leucogranite in the Jiaobei Terrane of the North China Craton: A highly fractionated albite granite forced by K-feldspar fractionation

A Paleoproterozoic leucogranite has been identified petrologically as highly fractionated granite near Huili in the Jiaobei Terrane of the North China Craton. This granite occurs as a 3×10km pluton in the metamorphic Paleoproterozoic Jingshan Group and was dated at 1.86Ga using zircon LA-ICP-MS U-Pb ages. The Huili leucogranite can be subdivided into three groups: groups I and II have normal leucogranite abundances with 2.22–2.57wt.% Na2O, 6.10–6.92wt.% K2O, and 71.68–73.07wt.% SiO2 and group III has a remarkably high Na2O concentration of 6.45–7.23wt.%, a low K2O content of 0.82–1.05wt.%, and 74.21–74.79%wt.% SiO2. Moreover, group III leucogranite comprises slightly lower Th, U, and Sr contents and considerably lower K-feldspar compatible elements, such as Rb, Ba, Pb, and Cs than those of groups I & II. All of these features strongly indicate the K-feldspar fractionation during the magma evolution from groups I and II to group III, which is strongly supported by the Pb isotope analysis. Group III leucogranite has a notably high U/Pb ratio of 0.30 to 0.45 with a normal U content of 1.42 to 2.21ppm and very low Pb content of 4 to 5ppm, indicating a significant K-feldspar fractionation of the magma. Group III leucogranite has high radiogenic Pb isotopes (i.e., 206Pb/204Pb=37.407–116.31), demonstrating that the rocks must have existed in a high U-Pb system for a notably long time. Fortunately, the whole rock Pb isotope values roughly define the Pb-Pb isochrons, not only when all three groups of samples are considered together but also when any individual group is considered. The ages are very close to the formation time of ~1.86Ga indicating the high U/Pb system required by these Pb isotopes must have been initiated during the formation of the Huili leucogranite, which has perfectly confirmed the K-feldspar fractionation during the magma evolution.All samples have consistent εNd values (t=1.86Ga) of −4.0 to −6.2 with two-stage Nd model ages (TDM2) of 2.67 to 2.85Ga. It is concluded that the 1.86Ga Huili leucogranite is highly fractionated, derived from ancient crustal material extracted from the depleted mantle at 2.7–2.8Ga, and experienced significant fractionation of K-feldspar in association with biotite and monazite fractionation during the magmatic evolution. Group III leucogranite is albite granite with albite phenocrysts, whereas groups I & II are K-feldspar granites with K-feldspar phenocrysts. It is here argued that the Huili albite granite (group III leucogranite) is derived from a highly differentiated residual melt separated from the K-rich magma represented by groups I and II leucogranite due to Kf fractionation during magma evolution.

A Silurian-early Devonian slab window in the southern Central Asian Orogenic Belt: Evidence from high-Mg diorites, adakites and granitoids in the western Central Beishan region, NW China

The Beishan orogenic belt is a key region for deciphering the accretionary processes of the southern Central Asian Orogenic Belt. Here in this paper we present new zircon U–Pb ages, bulk–rock major and trace element, and zircon Hf isotopic data for the Baitoushan, and Bagelengtai plutons in the western Central Beishan region to address the accretionary processes.The Baitoushan pluton consists of quartz diorites, monzonites and K-feldspar granites, with zircon LA–ICP–MS U–Pb ages of 435Ma, 421Ma and 401Ma, respectively. The Baitoushan quartz diorites and quartz monzonites exhibit relatively high MgO contents and Mg# values (63–72), display enrichments in LILEs and LREEs, and exhibit high Ba (585–1415ppm), Sr (416–570ppm) and compatible element (such as Cr and Ni) abundances, which make them akin to typical high-Mg andesites. The Baitoushan quartz diorites and quartz monzonites were probably generated by the interaction of subducted oceanic sediment-derived melts and mantle peridotites. The Baitoushan K-feldspar granites are ascribed to fractionated I-type granites with peraluminous and high-K calc-alkaline characteristics. They exhibit positive εHf(t) values (2.43–7.63) and Mesoproterozoic–Neoproterozoic zircon Hf model ages (0.92–1.60Ga). Those early Devonian granites, including Baitoushan K-feldspar granite and Gongpoquan leucogranites (402Ma), are derived from melting of the mafic lower crust and/or sediments by upwelling of hot asthenospheric mantle. The Bagelengtai granodiorites exhibit similar geochemical signatures with that of typical adakites, with a zircon SHRIMP U-Pb age of 435Ma. They exhibit relatively high Sr (502–628ppm) and Al2O3 (16.40–17.40wt.%) contents, and low MgO (1.02–1.29wt.%), Y (3.37–6.94ppm) and HREEs contents, with relatively high Sr/Y and (La/Yb)N ratios. The Bagelengtai granodiorites were derived from partial melting of subducted young oceanic crust, with significant contributions of subducted sediments, subsequently hybridized by the mantle peridotite.On the basis of our data and combined with previous data, we conclude that a Silurian–early Devonian slab window model accounts for all geological records in the western segment of the Central Beishan. We further propose that magmatic events associated with a slab window played an important role in crustal growth of the Central Asian Orogenic Belt.

In situ LA–ICP-MS and EPMA trace element characterization of Fe–Ti oxides from the phoscorite–carbonatite association at Phalaborwa, South Africa

In situ laser ablation inductively coupled plasma mass spectrometry (LA–ICP-MS) and electron probe microanalysis (EPMA) are used to characterize magnetite and ilmenite of the phoscorite–carbonatite association at Phalaborwa. We trace the behavior of the compatible elements for two different generations of magnetite related to (1) a magmatic stage, with variable Ti–V content, which pre-dates the copper mineralization, and (2) a late hydrothermal, low-Ti, low-temperature event, mostly post-dating sulfide formation. Magnetite is shown to be a robust petrogenetic indicator; no influence on its chemical composition is detected from the intergrowth with the accompanying phases, including the interaction with coexisting sulfides. High spatial resolution EPMA characterize the tiny late-stage hydrothermal magnetite veins, as well as the ilmenite granular and lamellar exsolutions mostly developed in the magnetite from the phoscorite. By combining geochemical data with geothermo-oxybarometry calculations for magnetite–ilmenite pairs, we infer that the most primitive magnetite probably formed at oxygen fugacity above the nickel nickel oxide (NNO) buffer, revealing an evolutionary trend of decreasing temperature and oxygen fugacity. Geochemical similarity exists between magnetite from phoscorite and carbonatite, thus supporting a common mantle source for the phoscorite–carbonatite association.

Origin of lamprophyres from the northern margin of the North China Craton: implications for mantle metasomatism

Abundant lamprophyre dykes occur near the northern margin of the North China Craton and offer a unique opportunity to study the nature of the mantle source. The dykes are minettes composed of phlogopite, sanidine and calcite. 40 Ar/ 39 Ar dating yields ages of 234 ± 2 and 222 ± 6 Ma. The lamprophyres are near-primary, mantle-derived ultrapotassic melts, having low SiO 2 (31.0 – 41.5 wt%) and high K 2 O (4.40 – 7.12 wt%) contents, high Mg# (62 – 84) and high contents of compatible elements. They are characterized by fractionated rare earth element patterns, radiogenic Sr and unradiogenic Nd isotope compositions ( 87 Sr/ 86 Sr i = 0.7070 – 0.7075; ε Nd ( t ) = −12.8 to −9.2). A small amount of mafic crustal rocks (<4.4%) may have been assimilated during magma ascent, as revealed by 187 Os/ 188 Os i ratios of 0.4548 – 0.8068. These data suggest that the lamprophyres originated from a low degree of partial melting of an enriched subcontinental lithospheric mantle source with abundant phlogopite, clinopyroxene and carbonate. The source has been metasomatized by carbonate- and potassium-rich fluids derived from carbonated sediments recycled via subduction of Palaeo-Mongolian oceanic slab beneath the North China Craton. Supplementary material: Microprobe analyses of biotite, feldspar and carbonate, 40 Ar– 39 Ar analytical data, and 36 Ar/ 40 Ar v. 39 Ar/ 40 Ar inverse isochron diagrams for phlogopite phenocrysts and groundmass from the Datong lamprophyres are available at https://doi.org/10.6084/m9.figshare.c.3574265 .

Origin of the Eocene porphyries and mafic microgranular enclaves from the Beiya porphyry Au polymetallic deposit, western Yunnan, China: Implications for magma mixing/mingling and mineralization

The origin of magmas with high H2O, S and metals that are linked to porphyry economic mineralization in continental collisional belts is controversial. In this paper, we studied the host porphyries and associated microgranular enclaves (MMEs) including gabbroic enclaves and dioritic enclaves from the large Beiya porphyry Au deposit in Jinshajiang-Ailaoshan mineralization belt, which provide first hand evidence of crust–mantle hybridization in the formation of fertile magma for porphyry deposit. Zircon LA-ICPMS U–Pb ages indicate coeval formation for the MMEs and the felsic porphyries in Eocene time (~36Ma). The MMEs show spheroidal shapes, acicular apatites, and oscillatory zoning with repeated resorption surfaces in plagioclases, which suggest that the MMEs are globules of a more mafic magma that was injected into and mingled with the host felsic magma. One gabbroic enclave sample exhibits high MgO (5.6wt.%), high TiO2 (1.7wt.%), enriched in large-ion lithophile element (LILE) and depleted in high field strength element (HFSE), with negative Nb, Ta and Ti anomalies. This indicates that the gabbroic enclave is similar to those of the coeval potassic mafic rocks in the Western Yunnan, which originated from the enriched mantle metasomatized by the slab-derived fluids. The dioritic enclave exhibit both potassic and adakitic-like features, and are characterized by high contents of MgO (4.4–4.9wt.%), K2O (6.4–7.4wt.%), and compatible trace elements (e.g. Ni: 115–142ppm; Cr: 214–291ppm), as well as by high Sr/Y ratios. The dioritic enclave samples yield εHf (t) values (−1.9 to +3.6) similar to those of the host porphyries. Petrographic, elemental, and isotopic evidence suggests that the Beiya dioritic enclave were formed by mixing between potassic mafic and adakitc-like melts, derived from metasomatized lithospheric mantle and lower crust, respectively. In contrast, the Beiya host porphyries are characterized by high SiO2 (66.9–71.9wt.%) and Al2O3 (13.8–15.9wt.%) contents, high Sr/Y ratios (35–79), low compatible element contents (e.g. Ni=0.9–7.2ppm; Cr =1.0–8.2ppm), low Mg# values (0.19–0.35), positive LILE anomalies, marked negative high HFSE anomalies, negative εNd(t) values (−6 to −2), and high (87Sr/86Sr)i values (0.7071–0.7081). These features indicate that the host porphyries were mainly formed by partial melting of subduction-modified lower crust with a certain assimilation of mafic melts represented by MMEs. MMEs hosted in the Beiya porphyries, formed from a hydrous, mafic magma although they formed in a non-arc setting. High magmatic water content is probably related to an enriched mantle metasomatized by fluids from a Proterozoic subducted oceanic slab. High Cu (341–626ppm) and Au contents of the MMEs suggest they crystallized from a metal-rich mafic melt. Complex assemblages of pyrite–chalcopyrite–apatite–rutile with hornblende are observed in the least altered MME. We suggest that the mafic melt probably supplied part of water, and metal to the Beiya porphyry Au system.

Petrogenesis of cogenetic silica-oversaturated and -undersaturated syenites of Abu Khruq ring complex, South Eastern Desert, Egypt

The upper Cretaceous Abu Khruq ring complex (ARC) is located in the South Eastern Desert of Egypt displays concentric zonation of syenitic rocks from quartz-rich syenite at the margin, through alkali feldspar syenite to nepheline syenite in the centre. The syenitic rocks occur with nepheline monzogabbro, volcanic rocks (phonolite and trachyte) and the quartz- and nepheline-bearing pegmatites. Rocks of contrasting composition (mafic and salic) exhibit sophisticate geometric relationships. The nepheline monzogabbroic rocks have pillowy xenoliths forms within the salic (nepheline syenite and quartz alkali feldspar syenite) rocks, suggesting synchronous emplacement of the mafic and salic magmas. Clinopyroxene analysis of mafic and salic plutonic rocks of the ARC revealed that the overall pyroxene trend suggesting that fractionation involved a late, progressive increase in Na, in a reaction of the type Ca Mg Fe2+↔Na Fe3+. The chemistry of the analysed amphiboles are compositionally similar to those from typical differentiated peralkaline suites. Geochemically, the complex is enriched in the LILE, HFSE and REE. The concentrations of the compatible elements (V, Sr and Ba) generally decrease with increasing silica, consistent with fractional crystallization. A generalised increase in the Nb/Ta from the nepheline monzogabbro to nepheline syenite compositions is attributed to titanite fractionation. All the rock samples show relative increment of the LREE content than the HREE indicating weak to steep fractionated REE patterns (La/Yb) from 9.43 to 10.86, and thus retaining the geochemical characteristics of anorogenic suites. The magma sources of ARC are not derived from normal primitive mantle. The early stages of differentiation involved extensive olivine and pyroxene fractionation, the fractionation of amphibole, titanite, magnetite, apatite and feldspar may have been involved in the genesis of the salic differentiated compositions. The deviation towards silica-oversaturated members attributed to crustal assimilation and associated with fractional crystallization of the basic magma at a relatively early stage during the development of the complex. The whole complex is deduced to have originated from alkali basaltic to basanitic magma of OIB-like character. The general increasing of the amphibole and biotite among the different rocks of the complex reflects the hydrous nature of ARC magmas.

Middle Jurassic MORB-type gabbro, high-Mg diorite, calc-alkaline diorite and granodiorite in the Ando area, central Tibet: Evidence for a slab roll-back of the Bangong-Nujiang Ocean

Mesozoic intrusions, including MORB-type gabbros, high-Mg diorites, calc-alkaline diorites and granodiorites, were exposed in the Ando microcontinent that is bounded between the Qiangtang and Lhasa terranes. Discoveries of these Mesozoic intrusions have provided new petrogenetic constraints on our understanding of Bangong-Nujiang ocean evolution. Zircon U–Pb dating shows that these intrusions formed in the early-middle Jurassic (174–177Ma). The gabbros have relatively flat REE distribution patterns, which is analogous to the geochemical features of MORB. Their positive εNd(t) values (εNd(t)=4.4–5.5) are consistent with those of ophiolites along the Bangong-Nujiang suture zone. These gabbros are also characterized by enrichments of fluid-sensitive elements and negative to positive Nb anomalies, indicative of the influence of subduction-related compositions in their mantle source. These features suggest that the gabbros were most likely originated from asthenosphere-derived melts metasomatized by enriched lithospheric mantle during the upwelling. The high-Mg diorites are characterized by typical features of high compatible elements (MgO=8.3–10.24wt%, Cr=400–547ppm, Ni=120–152ppm), high Mg# (70–74) and low Sr/Y ratios. Their high initial 87Sr/86Sr isotopic ratios and negative εNd(t) values (−10.5 to −10.8), together with their sanukitic characteristics, imply that the high-Mg diorites were probably produced by partial melting of mantle peridotites metasomatized by slab-derived melts and aqueous fluids. The calc-alkaline diorites have relatively high MgO (4.04–5.50wt%), Cr, Ni contents and Mg# (56–59), as well as high (86Sr/87Sr)i ratios and negative εNd(t) values (−7.5 to −7.3), suggesting that they were most likely formed by partial melting of the Ando basement rocks with significant input of mantle components. The granodiorites are peraluminous and have higher (86Sr/87Sr)i ratios and more negative εNd(t) values (−10.6 to −10.8), similar to those of the granitic gneisses of the Ando basement, suggesting partial melting of the Ando basement. Taking into account the spatial and temporal distribution of the Mesozoic magmatic rocks in the Southern Qiangtang terrane, we suggest that the formation of the Early-Middle Jurassic magmatic “flare-up” in the Southern Qiangtang terrane was related to the asthenospheric upwelling triggered by the roll-back of the subducted Bangong–Nujiang oceanic slab.

Capitalism and the media: moral economy, well-being and capabilities

This article aims to contribute to the renewal of consideration of media and culture under capitalism, by seeking solid normative foundations for critique via various compatible elements: moral economy, well-being understood as flourishing and Sen and Nussbaum’s capabilities approach. Insufficient attention has been paid to normative and conceptual issues concerning capitalism, media and culture. Moral economy approaches might help fill this gap by valuably providing a richly critical ethics-based approach, drawing on political economy, cultural studies and social theory. Two further concepts, compatible with moral economy, can reinvigorate and renew critique of capitalism, media and culture. The first is a particular (Aristotelian) conception of well-being, understood as flourishing. This is outlined, and its potential contribution to critique of media and culture under capitalism is explicated. The second concept is capabilities, which can provide a basis for dealing with different understandings of flourishing. The article outlines the capabilities approach, analyses rare applications of it to media and culture, and explains how these applications might be built upon, by developing Nussbaum’s work in a way that could ground critique in an understanding of the potential value of media and culture in contributing to people’s flourishing.

The Kuradawe Granitic Pegmatite From the Mawat Ophiolite, Northeastern Iraq: Anatomy, Mineralogy, Geochemistry, and Petrogenesis

Abstract The highly evolved Kuradawe granitic pegmatite dike is hosted in a harzburgite-dunite succession of the Mawat ophiolite in northeastern Iraq. It consists mainly of quartz, orthoclase, albite, tourmaline, and muscovite. Accessory minerals include cordierite, andalusite, monazite-(Ce), biotite, zircon, Nb-rich rutile, chlorapatite, chlorite, Sc-bearing columbite-(Fe), uraninite, U-rich thorite, and xenotime-(Y). The internal structure of the pegmatite consists of border, wall, intermediate, and core zones. Plagioclase composition increases from Ab 92 to Ab 97 towards the core. Whole rock major oxides such as MgO, Al 2 O 3 , and CaO decrease and SiO 2 increases toward the core. Na 2 O, K 2 O, and total FeO are enriched in specific zones. Among the trace elements, incompatible elements such as Sr, Ba, and Zr decrease and the compatible elements Ni and Cr slightly increase toward the core. The pegmatite is characterized by the dominance of tourmaline; muscovite as the dominant mica; normative corundum; high contents of SiO 2 , Al 2 O 3 , A/CNK, and Rb; low contents of CaO and Sr; and a high total FeO/MgO ratio in biotite. These features suggest an affinity with calc-alkaline peraluminous S-type granite in a subduction-related, syncollisional setting. The pegmatite is classified as beryl-columbite subtype of the LCT family. The restricted occurrence of high-temperature cordierite in the border zone may suggest that the pegmatite was overprinted by modal metasomatism during intrusion into the mantle rocks. Zircon saturation geothermometry indicates inward crystallization at temperatures of 782 °C in the border zone, 717 °C in the wall zone, and 550 °C in the intermediate zones. Geochemical data suggest that inward crystallization typified the formation of the pegmatite.

Melt/rock reaction at oceanic peridotite/gabbro transition as revealed by trace element chemistry of olivine

Several recent studies have documented that reactions between melt and crystal mush in primitive gabbroic rocks (via reactive porous flow) have an important control in the formation of the lower oceanic crust and the evolution of MORBs. In this context, olivine-rich rocks can form either by fractional crystallization of primitive melts or by open system reactive percolation of pre-existing (possibly mantle-derived) olivine matrix. To address this question, we performed in-situ trace element analyses (by LA-ICP-MS) of olivine from the Erro-Tobbio ophiolite Unit (Ligurian Alps), where mantle peridotites show gradational contacts with an hectometer-scale body of troctolites and plagioclase wehrlites, and both are cut by later decameter-wide lenses and dykes of olivine gabbros. Previous studies inferred that troctolites and olivine gabbros represent variably differentiated crystallization products from primitive MORB-type melts. Olivines in the three rock types (mantle peridotites, troctolites, olivine gabbros) exhibit distinct geochemical signature and well-defined elemental correlations. As expected, compatible elements (e.g. Ni) show the highest concentrations in peridotites (2580–2730ppm), intermediate in troctolites (2050–2230ppm) and lowest in gabbros (1355–1420ppm), whereas moderate incompatible elements (e.g. Mn, Zn) show the opposite behaviour. By contrast, highly incompatible elements like Zr, Hf, Ti, HREE are variably enriched in olivines of troctolites, and the enrichment in absolute concentrations is coupled to development of significant HFSE/REE fractionation (ZrN/NdN up to 80). AFC modelling shows that such large ZrN/NdN ratios in olivines are consistent with a process of olivine assimilation and plagioclase crystallization at decreasing melt mass, in agreement with textural observations. In-situ trace element geochemistry of olivine, combined with microstructural investigations, thus appears a powerful tool to investigate reactive percolation and the origin of olivine-rich rocks in the lower oceanic crust.

Early mantle heterogeneities in the Réunion hotspot source inferred from highly siderophile elements in cumulate xenoliths

Ultramafic cumulate rocks form during intrusive crystallization of high-MgO magmas, incorporating relatively high abundances of compatible elements, including Cr and Ni, and high abundances of the highly siderophile elements (HSE: Os, Ir, Ru, Pt, Pd, Re). Here, we utilize a suite of cumulate xenoliths from Piton de la Fournaise, La Réunion (Indian Ocean), to examine the mantle source composition of the Réunion hotspot using HSE abundances and Os isotopes. Dunite and wherlite xenoliths and associated lavas from the Piton de la Fournaise volcanic complex span a range of MgO contents (46 to 7 wt.%), yet exhibit remarkably homogeneous 187Os/188Os (0.1324±0.0014, 2σ), representing the Os-isotopic composition of Réunion hotspot primary melts. A significant fraction of the xenoliths also have primitive upper-mantle (PUM) normalized HSE patterns with elevated Ru and Pd (PUM-normalized Ru/Ir and Pd/Ir of 0.8–6.3 and 0.2–7.2, respectively). These patterns are not artifacts of alteration, fractional crystallization, or partial melting processes, but rather require a primary magma with similar relative enrichments. Some highly olivine-phyric (>40 modal percent olivine) Piton de la Fournaise lavas also preserve these relative Ru and Pd enrichments, while others preserve a pattern that is likely related to sulfur saturation in evolved melts.The estimate of HSE abundances in PUM indicates high Ru/Ir and Pd/Pt values relative to carbonaceous, ordinary and enstatite chondrite meteorite groups. Thus, the existence of cumulate rocks with even more fractionated HSE patterns relative to PUM suggests that the Réunion hotspot samples a yet unrecognized mantle source. The origin of fractionated HSE patterns in Réunion melts may arise from sampling of a mantle source that experienced limited late accretion (<0.2% by mass) compared with PUM (0.5–0.8%), possibly involving impactors that were distinct from present-day chondrites, or limited core–mantle interactions. Given the remarkably homogeneous Os, Pb, and noble-gas isotopic signatures of Réunion, which plot near the convergence point of isotopic data for many hotspots, such a conclusion provides evidence for an early differentiated and subsequently isolated mantle domain that may be partially sampled by some ocean island basalts.

Orthogonal apartments in Hilbert Grassmannians

Let H be a complex Hilbert space. Denote by Gk(H) the Grassmannian consisting of k-dimensional subspaces of H. Every orthogonal apartment of Gk(H) is defined by a certain orthogonal base of H and consists of all k-dimensional subspaces spanned by subsets of this base. Orthogonal apartments can be characterized as maximal sets of mutually compatible elements of Gk(H). In the case when H is infinite-dimensional, we prove the following: if f is a bijective transformation of Gk(H) such that f and f−1 send orthogonal apartments to orthogonal apartments (in other words, f preserves the compatibility relation in both directions), then f is induced by an unitary or antiunitary operator on H. Suppose that dim⁡H=n is finite and not less than 3. For n≠2k (except the case when n=6 and k is equal to 2 or 4) we show that every bijective transformation of Gk(H) sending orthogonal apartments to orthogonal apartments is induced by an unitary or antiunitary operator on H. Our third result is the following: if n=2k≥8 and f is a bijective transformation of Gk(H) such that f and f−1 send orthogonal apartments to orthogonal apartments, then there is an unitary or antiunitary operator U such that for every X∈Gk(H) we have f(X)=U(X) or f(X) coincides with the orthogonal complement of U(X).

Magnetite Chemistry As A Provenance Indicator In Archean Metamorphosed Sedimentary Rocks

Abstract: Conventional provenance studies of high grade (e.g., amphibolite facies) metamorphic sandstone are limited due to intense recrystallization, destruction of original minerals, and growth of new minerals. Magnetite is a heavy mineral common in a wide range of sedimentary rocks. It can originate from a wide range of rock sources from high-temperature to low-temperature magmatic, metamorphic, or hydrothermal environments. Laser ablation (LA)-ICP-MS and electron microprobe analytical techniques allowed determination of a wide range of trace elements at sub ppm levels in magnetite to identify the provenance of two Archean sedimentary formations in Eeyou Istchee Baie-James, Quebec, Canada. Results were plotted on multi-element diagrams. The most compatible elements in magnetite were identified as the most discriminant elements to differentiate four potential different rock sources for the Magin Formation. Overlap between the spectra of the Magin and Keyano formations substantiate the existence of a common source. Interbedded conglomerate magnetite-bearing clasts were examined to determine potential source-rocks. Mafic clasts apparently do not contain magnetite. Detrital magnetites analyzed have low Ti values that would support either felsic (to intermediate) plutonic or a hydrothermal source. The trace-element spectra of detrital magnetite from the sandstone beds were compared to magnetite spectra from conglomerate clasts of banded iron formation and felsic to intermediate plutonic rocks. Only magnetites from felsic plutonic rocks have a signature similar to those from the sandstone. To further substantiate a felsic plutonic source, a detailed study of magnetite chemistry from ten felsic and intermediate regional plutons from a regional databank allowed us to recognize that each of these plutons has a particular signature on the basis of wide variations in Ni and Cr. From this data base, four individual plutons were identified as potential sources for the Magin Formation. Recently published magnetite discrimination diagrams proposed for mineral deposits can be applied to sedimentary magnetite provenance. However, our database shows the importance of identifying low-Ti magnetite from felsic rocks since these could be misidentified as low-Ti magnetite from hydrothermal mineral deposits. Thus, we propose improvement to these diagrams by differentiating magnetite from felsic magmatic (low Ni/Cr) and hydrothermal (high Ni/Cr) sources before applying the mineral-deposit discrimination diagrams.

Petrological, Geochemical and Sr–Nd–O Isotopic Constraints on the Origin of Garnet and Spinel Pyroxenites from the Moldanubian Zone of the Bohemian Massif

Garnet pyroxenites, spinel pyroxenites, and eclogites in the Moldanubian Zone of the Bohemian Massif form layers and lenses in mantle-derived peridotites that are enclosed by migmatitic gneisses and granulites. We have analysed major and trace elements, and Sr, Nd and oxygen isotopes for a suite of pyroxenites, which vary in composition and origin, from nine localities (Becvary, Horni Bory, Drahonin, Nihov, Mohelno, Nove Dvory, Horni Kounice, Karlstetten and Meidling-im-Tal) in the Gfohl Unit and Kutna Hora Complex. Based on conventional geothermobarometry, most pyroxenites yield a restricted range of temperatures (similar to 875-975 degrees C) over a wide span of pressures (similar to 1.0-3.0 GPa). The pyroxenite suite exhibits large variations in elemental and isotopic compositions, reflecting its complex origin and evolution. Based on the rare earth element (REE) compositions of clinopyroxene (Cpx), three types of pyroxenite can be distinguished: Type A with a light REE (LREE)-depleted patterns, Type B with an LREE-enriched pattern and Type C with a convex-upward REE pattern. Such REE patterns reflect derivation of the melts from depleted (Type A) and enriched (Types B and C) mantle sources. Pyroxenites from eight localities originated as high-pressure crystal cumulates from transient basaltic melts migrating through the lithospheric mantle. In contrast, pyroxenites at the Becvary locality represent fragments of metamorphosed gabbroic cumulates from oceanic crust. For the pyroxenite suite as a whole, a positive correlation between Sr/Nd and Eu/Eu*, radiogenic Sr-87/Sr-86 and negative epsilon(Nd) values in clinopyroxene, and variable delta O-18 values in coexisting garnet argue for the presence of a crustal component in the parental pyroxenite melts. Variations in compatible elements (Ni, Sc, and Co) indicate that combined assimilation and fractional crystallization was important in the evolution of most of the pyroxenite parental melts, although fractional crystallization alone is recorded by the fragments of oceanic crust, perhaps reflecting their pre-subduction crystallization history.

A comparative study of two modes for mapping felsic intrusions using geoinformatics

Identifying felsic intrusions is an essential task in support of mineral exploration because the intrusions can be a source of energy and metals for magmatic-hydrothermal mineralization. In this paper, two models for mapping felsic intrusions are compared based on regional geochemical and geophysical data. Geochemical data as a type of compositional data which carry relative information should be preprocessed using log-ratio transformation. The first model, a factor ratio (F2/F1) model, was developed based on the chemical characteristics of the felsic intrusions, which are rich in K2O and high field strength elements (F2), but poor in Fe2O3 and compatible elements (F1). The second model, a hybrid model that combines principal component analysis and local singularity analysis, was based on the chemical and physical properties of the felsic intrusions. The results showed that (1) raw geochemical data should be processed using log-ratio transformation prior to multivariate data analysis to avoid spurious correlations between variables, and (2) the hybrid model performed better than the ratio of factors model for inferring felsic intrusions in the study area. The felsic intrusions mapped in this study provide information that can support further mineral exploration in the Dong Ujimqin Fe–Cu polymetallic district, Inner Mongolia, northern China.

Low Ni olivine in silica-undersaturated ultrapotassic igneous rocks as evidence for carbonate metasomatism in the mantle

Subduction drags a large amount of CO2 into the Earth's interior, which is partly returned to the atmosphere by arc volcanism. Processes involved in the recycling of subducted carbon within the upper mantle are mainly related to mineralogical transformation. Subducted CO2 may dramatically affect the equilibria among peridotitic minerals (olivine vs. pyroxenes) changing their stability fields and hence their modal abundances. This process is accompanied by a subduction-induced change in the budget of some incompatible trace and major elements (e.g., K, Ca, HFSE), whereas it has a minimal effect on the mass balance of compatible elements (e.g., Ni). We report trace elements in olivine in subduction-related mafic alkaline ultrapotassic rocks from Italy, which are used as a proxy to define mantle wedge mineralogy and metasomatic processes. Minor element concentrations, and in particular the high Li and low Ti of all the olivines, confirm a major role for recycled sediment in the generation of Italian ultrapotassic magmas. The distinct contents of Ni, Mn, and Ca in olivine reflect the bimodal character of silica-rich and silica-poor ultrapotassic Italian rocks and constrain two distinct mineralogical reactions between metasomatic agents and peridotite. Olivine chemistry from silica-saturated rocks reflects the reaction of silicate melts with the ambient mantle, with consequent consumption of olivine in favour of orthopyroxene. In contrast, the low-Ni, high-Mn/Fe of olivine crystallised from silica-undersaturated leucitites require a mantle source enriched in olivine (and clinopyroxene) compared to orthopyroxene, as a result of the interaction between the ambient peridotitic mantle and CaCO3-rich metasomatic agents. The change from silica-oversaturated lamproites to silica-undersaturated leucitites and thus the difference in the olivine composition is due to a change in composition of the subducting sediment from pelitic to carbonate-rich. The results of this study provide new insights into how CO2 is recycled via subduction processes deep into the mantle.

Rb-Sr isotopic composition of granites in the Western Krušné hory/Erzgebirge pluton, Central Europe: record of variations in source lithologies, mafic magma input and postmagmatic hydrothermal events

The late Variscan (327–318 Ma) Western Krusne hory/Erzgebirge pluton (Czech Republic and Germany) represents a multiply emplaced intrusive sequence ranging from low-F biotite monzogranites (with rare minor bodies of gabbrodiorites and granodiorites) to high-F topaz-zinnwaldite alkali-feldspar granites. This granite suite is characterized by progressively increasing concentrations of incompatible elements (Li, Rb, F), monotonous decrease in mafic components and compatible elements (FeOtot, MgO, TiO2, CaO, Sr) with increasing silica. Consequently, this leads to extreme variations in the Rb/Sr ratios (0.52 to 59), which impose highly variable 87Rb/86Sr and 87Sr/86Sr signatures. The low-F biotite monzogranites represent isotopically heterogeneous mixture with (87Sr/86Sr)323 = 0.707–0.709 between partial melts from the Saxothuringian metasediments and mantle-derived mafic precursors. The medium-F two-mica microgranites show variable (87Sr/86Sr)323 = 0.708–0.714, indicating involvement of multiple precursors and more mature crustal protoliths. The evolved high-F topaz-zinnwaldite alkali-feldspar granites were derived from a precursor with (87Sr/86Sr)320 = 0.707–0.708 at 324–317 Ma by differentiation, which produced the extreme Rb/Sr enrichment and variations. The Li/Rb ratios remain nearly constant (~0.5), thus insensitive to the degree of geochemical differentiation. In comparison to terrestrial variations, the high Li/Rb values indicate derivation of granitic magmas from predominantly sedimentary precursors, in accord with 7Li-6Li and 143Nd-144Nd isotope composition reported previously. The Rb-Sr element variations in each granite unit are sligthly different and indicate ascent and emplacement of separate magma batches, which do not form a single liquid line of descent. We consider the enrichment of granites in incompatible elements (Li, Rb, F) and compatible depletion of ferromagnesian components, CaO and Sr as a combined effect of multiple precursors, changes in the chemical composition of crustal sources, in the degree of fractional melting and fractional crystallization, and of possibly repeated postmagmatic hydrothermal events.

Petrology, geochemistry and tectonic setting of intrusives around omam (east of guilan)

Intrusives around Omam (East of Guilan) with gabbro, monzo-gabbro-porphyry, syenite and granite compositions have intruded to upper Cretaceous lavas, sedimentary and pyroclastic rocks. The geochemical data of the mentioned intrusives on the variation diagrams show that these rocks are categorized into mafic and felsic groups and in terms of magmatic series, they are often from alkaline one. Relative continuity between most intrusive mafic rocks data on the variation diagrams and the parallel feature of their rare earth elements patterns clearly show the derivation of this group from a common origin. Based on the severity of changes in strongly compatible elements versus the strongly incompatible elements, the dominant process governing the magmatic evolution for mafic rocks is fractional crystallization. REE patterns for different types of mafic rocks are in parallel with each other and have a uniform and downward slope, while the slope of felsic varieties patterns for LREE is steep and descending and flat for HREE. Based on the La/Sm ratio, it seems that the melts forming mafic rocks are derived from the enriched mantle with spinel lherzolite composition and partial melting degree of 4 to 10 percent. On the tectonic setting discrimination diagrams, the intrusive rocks of the studied area are categorized in the territory of intracontinental rifts.

Peridotite xenoliths from the Polynesian Austral and Samoa hotspots: Implications for the destruction of ancient 187Os and 142Nd isotopic domains and the preservation of Hadean 129Xe in the modern convecting mantle

The Re–Os systematics in 13 peridotite xenoliths hosted in young (<0.39myr) rejuvenated lavas from the Samoan island of Savai’i and 8 peridotite xenoliths from 6 to 10myr old lavas from the Austral island of Tubuai have been examined to evaluate the history of the oceanic mantle in this region. Modal mineralogy, trace element compositions and 187Os/188Os ratios suggest that these peridotites are not cognate or residual to mantle plumes but rather samples of Pacific oceanic lithosphere created at the ridge. Savai’i and Tubuai islands lie along a flow line in the Pacific plate, and provide two snapshots (separated by over 40Ma in time) of Pacific mantle that originated in the same region of the East Pacific rise. Tubuai xenoliths exhibit 187Os/188Os from 0.1163 to 0.1304, and Savai’i (Samoa) xenoliths span a smaller range from 0.1173 to 0.1284. The 187Os/188Os ratios measured in Tubuai xenoliths are lower than (and show no overlap with) basalts from Tubuai. The 187Os/188Os of the Savai’i xenoliths overlap the isotopic compositions of lavas from the island of Savai’i, but also extend to lower 187Os/188Os than the lavas. 3He/4He measurements of a subset of the xenoliths range from 2.5 to 6.4Ra for Tubuai and 10.8 to 12.4Ra for Savai’i.Like abyssal peridotites and xenoliths from oceanic hotspots that sample the convecting mantle, Os isotopes from the Savai’i and Tubuai xenolith suites are relatively unradiogenic, but do not preserve a record of depleted early-formed (Hadean and Archean) mantle domains expected from earlier cycles of ridge-related depletion, continent extraction, or subcontinental lithospheric mantle erosion. The lack of preservation of early-formed, geochemically-depleted Os-isotopic and 142Nd/144Nd domains in the modern convecting mantle contrasts with the preservation of early-formed (early-Hadean) 129Xe/130Xe isotopic heterogeneities in the convecting mantle. This can be explained if the initial isotopic signatures in Re–Os and Sm–Nd systems are erased by recycling because the parent and daughter elements are retained in subducting slabs and more efficiently returned to the mantle during subduction than Xe. In this way, early-formed Os and Nd-isotopic heterogeneities could have been overprinted with, and diluted by, younger isotopic signatures. In contrast, preservation of early-formed heterogeneities in the modern convecting mantle is possible for other elements, such as Xe, that are not as efficiently recycled back into the mantle, owing to greater fluid mobility that concentrates such elements in the near-surface. Differing recycling efficiencies for Os, Nd and Xe lead to wide differences in the preservation of Hadean isotopic signatures of these elements in the modern convecting mantle. In general, incompatible elements that are fluid mobile (e.g., Xe) concentrate in surface reservoirs and are more likely to preserve Hadean geochemical signatures in the convecting mantle than compatible elements (e.g., Os) and fluid immobile incompatible elements (e.g., Nd).

Geochemical characteristics of biotite from felsic intrusive rocks around the Sisson Brook W–Mo–Cu deposit, west-central New Brunswick: An indicator of halogen and oxygen fugacity of magmatic systems

The Sisson Brook W–Mo–Cu deposit was formed by hydrothermal fluids likely related to the Nashwaak Granites (muscovite–biotite granite, Group I; and biotite granite, Group II) and related dykes (biotite granitic dykes, Group III; and a feldspar–biotite–quartz porphyry dyke, Group IV). Chemical data obtained using EPMA and LA-ICP-MS data of primary magmatic biotites were used to investigate magmatic processes and associated hydrothermal fluids.Trace element features of biotite in the Group I two-mica granite suggest other magmatic processes along with a simple fractional crystallization. The K/Rb ratios and compatible elements (Cr, Ti, Co, V, and Ba) in biotite from Groups II, III, and IV decrease, whereas incompatible elements including Ta, Tl, Ga, Cs, Li, and Sn increase with magma fractionation. No correlation of Cu, W and Mo with K/Rb ratios is evident, suggesting that partitioning of Cu, W, and Mo into biotite may not be entirely controlled by magma fractionation.Halogen fugacity of the parental magma of the Nashwaak Granites and related dykes, calculated from zircon saturation temperature shows that Group I has high fHF/fCl ratios (broadly higher than 0), similar to the plutons at the Henderson porphyry Mo deposit. The fHF/fCl ratios of the other groups are generally lower than 0, comparable to the Santa Rita porphyry Cu deposit. The fH2O/fHCl and fH2O/fHF ratios inferred from biotite in the Nashwaak Granites and related dykes range from 3 to 5 and from 4 to 5, respectively. The inferred oxygen fugacity shows that the dyke phases (Groups III and IV) have the oxygen fugacity around the nickel–nickel oxide buffer. The plutonic phases (Groups I and II) have the oxygen fugacity around the quartz–fayalite–magnetite (QFM) buffer at high temperatures and oxidized to nickel–nickel oxide buffer at lower temperatures. This oxidation process in the plutonic phases (Groups I and II) could be caused by H2 release at or near H2O vapor saturation at high H2O/Fe2+. The magma associated with the biotite dykes (Group III) is more likely the source of the hydrothermal fluids at the Sisson Brook deposit since it has the highest differentiation degree and seems to have formed in an oxidized setting, necessary for Mo to concentrate in the late stage fluids.