Rare earth elements and Rb–Sr and Sm–Nd systematics in the peat bog iron ore and moss of the NW East European Platform

Spectra of the REE distribution in the Quaternary–Recent peat bog ore of southern Karelia and Leningrad region are characterized by La_N/Yb_N < 1.0, presence of positive Eu and negative Ce anomalies, and higher Y enrichment (relative to Ho and Dy) because of the REE sorption by Fe-bearing minerals in acid boggy waters. The ⁸⁷Sr/⁸⁶Sr ratio is 0.7175 in iron oxyhydroxides of the Somino deposit (Leningrad region) and 0.7283 in the Polovinkino ore (southern Karelia). The ¹⁴³Nd/¹⁴⁴Nd ratio in them is 0.511844 and 0.511617, respectively.     

Sm‐Nd and Rb‐Sr dating of Archaean gneisses,eastern Yilgarn Block,Western Australia

Sm‐Nd and Rb‐Sr isotopic data for Archaean gneisses from three localities within the eastern Yilgarn Block of Western Australia indicate that the gneisses define a precise Rb‐Sr whole rock isochron age of 2780 ± 60 Ma and an initial ⁸⁷Sr/⁸⁶Sr of 0.7007 ± 5. The Sm‐Nd isotopic data do not correspond to a single linear array, but form two coherent groups that are consistent with a c. 2800 Ma age of crust formation, with variable initial Nd. These results indicate that the gneiss protoliths existed as continental crust for a maximum period of only c. 100 Ma, and probably for a much shorter time, prior to the formation of the 2790 ±30 Ma greenstones.     

Sources of Ore Substance of Carbonatite Complexes of the Ural Fold Belt: Rb–Sr and Sm–Nd Isotope Data

The results of study of the Nd and Sr isotope compositions of the Nb ore minerals (pyrochlore and aeschynite groups) and rocks from the Ilmenogorsk–Vishnevogorsk and Buldym carbonatite complexes of the Ural Fold Belt are presented. It has been established that pyrochlores of the early stages of ore formation and the IVC miaskite-carbonatite rocks have a single substance source corresponding to a mantle moderately depleted source according to isotope parameters. The crustal components, along with mantle, participate in the processes of ore formation within the Buldym complex.     

Timing of eclogite facies metamorphism in the southernmost Scandinavian Caledonides by Lu–Hf and Sm–Nd geochronology

The Scandinavian Caledonides contain several non-cogenetic eclogite-bearing terranes that were metamorphosed before the main orogenic stage in Scandian time (430–395 Ma). Although petrological and geochronological data from these terranes have provided essential information on the geodynamic history of the Caledonian orogenic cycle, the general picture is still patchy. To refine existing geodynamic models, we have dated the eclogite occurrence in the Jæren nappe, SW Norway, by Lu–Hf and Sm–Nd geochronology. Five out of the six studied samples provide a weighted mean Lu–Hf age of 469.9 ± 1.2 Ma (±2σ). One sample provided a significantly younger age of 457.9 ± 2.4 Ma. Garnet from the younger sample grew exclusively at eclogite facies conditions. In contrast, garnet from the other samples comprises prograde cores and peak metamorphic rims. Age estimates that take Lu-contributions of each zone into account provide an age of 471.0 ± 0.9 Ma for the cores and suggest a ca. 455 Ma age for the rims, which is identical to the bulk-garnet age of the younger sample. The same pattern is indicated by Sm–Nd ages, although these are relatively imprecise and reflect isotopic disturbance during thermal overprinting upon exhumation. The data define a new high-pressure age population for the Scandinavian Caledonides, which allows more detailed insight into the subduction history that affected the Baltoscandian margin before Scandian continental collision. Furthermore, this study highlights the potential complexities involved in garnet geochronology and shows the strength of Lu–Hf dating for unraveling the geochronological record of HP rocks.     

Geochemical and Sr–Nd isotope evidences of the suprasubduction nature of mesozoic magmatism in the Mongol–Okhotsk Sector of the Pacific Fold Belt

In this article we present geochemical and isotope characteristics of rocks of the Unerikan, Selitkan and Aezop–Yamalin volcano–plutonic zones of the eastern termination of the Mongol–Okhotsk Orogenic Belt. The obtained data demonstrate that the Mesozoic igneous rocks of the Mongol–Okhotsk sector of the Pacific Folded Belt were formed due to the melting of the continental crust in a tectonic setting corresponding to a suprasubduction one.     

A petrologic, geochemical and Sr–Nd isotopic study on contact metamorphism and degassing of Devonian evaporites in the Norilsk aureoles, Siberia

Devonian evaporites and associated sedimentary rocks in the Norilsk region were contact metamorphosed during emplacement of mafic sills that form part of the end-Permian (~252 Ma) Siberian Traps. We present mineralogical, geochemical and Sr–Nd isotopic data on sedimentary rocks unaffected by metamorphism, and meta-sedimentary rocks from selected contact aureoles at Norilsk, to examine the mechanisms responsible for magma-evaporite interaction and its relation to the end-Permian environmental crisis. The sedimentary rocks include massive anhydrite, rock salt, dolostone, calcareous siltstones and shale, and the meta-sedimentary rocks comprise calcareous hornfels, siliceous hornfels and minor meta-anhydrite and meta-sandstone. Contact metamorphism took place at low pressure and at maximum temperatures corresponding to the phlogopite-diopside stability field. Calcareous hornfels have high CaO, MgO, CΟ₂, SΟ₃, low SiO₂ and initial Sr isotopic ratios of 0.7079–0.7092, features indicative of calcareous siltstone protoliths. Siliceous hornfels, in contrast, have high SiO₂, Al₂O₃, Na₂O, low in other major element oxides and initial Sr isotopic ratios of 0.7083–0.7152, consistent with pelitic or shaley protoliths. Loss of CO₂ in a subset of calcareous hornfels can be explained by decarbonation reactions during metamorphism, but release of SO₂ from evaporites cannot be accounted for by a similar mechanism. Occurrences of wollastonite and a variety of hydrous minerals in the calcareous hornfels are consistent with equilibration with hydrous fluid, which was capable of leaching large quantities of anhydrite in the presence of dissolved NaCl. In this way, substantial sediment-derived sulfur could have been mobilized, incorporated into the magmatic system and released to the atmosphere. The release of CO₂ and SO₂ from Siberian evaporites added to the variety of toxic gases generated during metamorphism of organic matter, coal and rock salt, contributing to the end-Permian environmental crisis.     

Paleoproterozoic gabbro–diorite–granite magmatism of the Batomga Rise (NE Aldan Shield): Sm–Nd isotope geochemical evidence

The geochemical similarity and almost simultaneous (2055–2060 Ma) formation of Utakachan gabbro-amphibolite, Jagdakin granodiorite-diorite, Khoyunda granitoid, and Tygymyt leucogranite complexes, which inruded metamorphic formations of the Batomga Group are evidence of their formaton from unified magmatic source. All this makes it possibble to combine aforementioned complexes into the unified Early Proterozoic diferentiated gabbro-diorite-granite complex.     

Coupled Lu–Hf and Sm–Nd geochronology constrains blueschist-facies metamorphism and closure timing of the Qilian Ocean in the North Qilian orogen

The Qilian–Qaidam orogenic belt at the northern edge of the Tibetan Plateau has received increasing attention as it recorded a complete history from continental breakup to opening and closure of ocean basin, and to the ultimate continental collision in the time period from the Neoproterozoic to the Paleozoic. Determining a geochronological framework of the initiation and termination of the fossil Qilian Ocean subduction in the North Qilian orogenic belt plays an essential role in understanding the whole tectonic process. Dating the high-pressure metamorphic rocks in the North Qilian orogenic belt, such as blueschist and eclogite, is the key in this respect. A blueschist from the southern North Qilian orogenic belt was investigated with a combined metamorphic P–T and U–Pb, Lu–Hf, and Sm–Nd multichronometric approaches. Pseudosection modeling indicates that the blueschist was metamorphosed under peak P–T conditions of 1.4–1.6 GPa and 530–550 °C. Zircon U–Pb ages show no constraints on the metamorphism due to the lack of metamorphic growth of zircon. Lu–Hf and Sm–Nd ages of 466.3 ± 2.0 Ma and 462.2 ± 5.6 Ma were obtained for the blueschist, which is generally consistent with the U–Pb zircon ages of 467–489 Ma for adjacent eclogites. Lutetium and Sm zoning profiles in garnet indicate that the Lu–Hf and Sm–Nd ages are biased toward the formation of the garnet inner rim. The ages are thus interpreted to reflect the time of blueschist-facies metamorphism. Previous ⁴⁰Ar/³⁹Ar ages of phengitic muscovite from blueschist/eclogite in this area likely represent a cooling age due to the higher peak metamorphic temperature than the argon retention temperature. The differences of peak metamorphic conditions and metamorphic ages between the eclogites and adjacent blueschists indicate that this region likely comprises different tectonic slices, which had distinct P–T histories and underwent high-pressure metamorphism at different times. The initial opening of the Qilian Ocean could trace back to the early Paleozoic, and the ultimate closure of the Qilian Ocean was no earlier than c. 466 Ma.     

Paired uraninite and molybdenite dating of the K?nigshain granite: implications for the onset of late-Variscan magmatism in the Lausitz Block

We present geochronological data for late-Variscan magmatism in the Lausitz Block of the Saxo-Thuringian Zone, Germany. The Th–U–total Pb age of uraninite and the Re–Os age of molybdenite from the composite biotite–monzogranite pluton of K?nigshain overlap at the 2σ confidence limit: 328.6 ± 1.9 Ma (uraninite), and 327.0 ± 1.3 Ma and 327.6 ± 1.3 Ma (molybdenite), indicating that crystallization of magmatic uraninite and deposition of molybdenite were nearly contemporaneous. These data imply that magmatic processes in this part of the Variscan orogen already started in latest Visean time, about 10 Ma earlier than previously assumed (315–320 Ma). The new ages correspond to ages for plutonic rocks in the Elbe Zone immediately west of the Lausitz (around 335–325 Ma) and the bulk of late-Variscan igneous rocks in the Saxo-Thuringian Zone (335–320 Ma).     

Isotope (U–Pb,Sm–Nd,Rb–Sr) geochronology of alkaline basic plutons of the Kuznetsk Alatau

On the northeastern slope of the Kuznetsk Alatau, small differentiated alkaline basic intrusive massifs form an isometric area ~ 100 km across. They are composed of subalkalic and alkali gabbroids, basic and ultrabasic foidolites, nepheline and alkali syenites, and carbonatites. Results of complex (U–Pb, Sm–Nd, and Rb–Sr) isotope dating suggest that alkaline basic magmatism developed at two stages, in the Middle Cambrian–Early Ordovician (~ 510–480 Ma) and in the Early–Middle Devonian (~ 410–385 Ma). Finding of accessory zircons (age 1.3–2.0 Ga) in alkaline rocks suggests that the ascent of mantle plume was accompanied by the melting of fragments of Proterozoic mature continental crust composing the basement of the Caledonian orogen of the Kuznetsk Alatau. Probably, parental Cambrian–Ordovician alkaline mafic melts initiated metasomatism and lithosphere erosion. During the next melting of lithosphere substrate in ~ 100 Myr, this caused the generation of magmas of similar composition with inherited isotope parameters (ε_Nd(T) ≈ + 4.8 to + 5.7, T_Nd(DM) ≈ 0.8–0.9 Ga) pointing to the similar nature of their matter sources in the moderately depleted mantle.     

147sm–143Nd and 87Rb–87Sr ages of the eucrite Piplia Kalan

Prompted by the finding that the eucrite Piplia Kalan could have retained Pu fission Xe earlier than the eucrites so far studied and hence be very ancient, we have measured a precise internal ¹⁴⁷Sm–¹⁴³Nd isochron for this meteorite. The age and initial Nd ratio relative to CHUR are 4.570 ± 0.023 Ga and −1.3 ± 0.7 ϵu, respectively. A Rb–Sr whole rock (clast) isochron for this meteorite corresponds to an age of 3.963 ± 0.119 Ga and initial ⁸⁷Sr/⁸⁶Sr ratio of 0.69902 ± 3. But initial ⁸⁷Sr/⁸⁶Sr ratio calculated for an age of 4.57 Ga is 0.698956 ± 25, which is indistinguishable from 0.698970 ± 15 reported for the angrites LEW and ADOR dated at 4.5578 ± 0.0005 Ga. These results indicating that Piplia Kalan could have formed within only a few million years of the earliest condensates in the Solar System are strongly supported by the recent discovery of live ²⁶Al in it.     

Mantle and crustal processes in the magmatism of the Campania region: inferences from mineralogy, geochemistry, and Sr–Nd–O isotopes of young hybrid volcanics of the Ischia island (South Italy)

Ischia, one active volcano of the Phlegraean Volcanic District, prone to very high risk, is dominated by a caldera formed 55 ka BP, followed by resurgence of the collapsed area. Over the past 3 ka, the activity extruded evolved potassic magmas; only a few low-energy explosive events were fed by less evolved magmas. A geochemical and Sr–Nd–O isotope investigation has been performed on minerals and glass from products of three of such eruptions, Molara, Vateliero, and Cava Nocelle (<2.6 ka BP). Data document strong mineralogical, geochemical, and isotopic heterogeneities likely resulting from mingling/mixing processes among mafic and felsic magmas that already fed the Ischia volcanism in the past. Detailed study on the most mafic magma has permitted to investigate its origin. The mantle sector below Ischia underwent subduction processes that modified its pristine chemical, isotopic, and redox conditions by addition of ≤1 % of sediment fluids/melts. Similar processes occurred from Southeast to Northwest along the Apennine compressive margin, with addition of up to 2.5 % of sediment-derived material. This is shown by volcanics with poorly variable, typical δ¹⁸O mantle values, and ⁸⁷Sr/⁸⁶Sr progressively increasing toward typical continental crust values. Multiple partial melting of this modified mantle generated distinct primary magmas that occasionally assimilated continental crust, acquiring more ¹⁸O than ⁸⁷Sr. At Ischia, 7 % of Hercynian granodiorite assimilation produced isotopically distinct, K-basaltic to latitic magmas. A SW–NE regional tectonic structure gave these magmas coming from large depth the opportunity to mingle/mix with felsic magmas stagnating in shallower reservoirs, eventually triggering explosive eruptions.     

Shopping behaviour in the Øresund region before and after the establishment of the fixed link between Denmark and Sweden

In July 2000 the 15.5 km long fixed link across the Øresund was opened, connecting the Danish capital Copenhagen and the Swedish city of Malmö. With the decrease of the barrier an enlarged flow of shoppers was expected with Swedish customers availing themselves of the range of opportunities in the Copenhagen area and Danish customers making use of the much longer shop opening hours in Sweden. However, experience from other European border areas shows that customers tend to do their ordinary shopping in their home countries and that there must be significant differences in prices or ranges of goods to overcome the barrier of the border. Does the typical situation result from the rural nature of many border areas, and will matters be quite different in a metropolitan area? The purpose of the present paper is to describe the level and character of cross-border shopping by the residents of the Øresund region before and after the opening of the fixed link. Responses from about 4,000 people form the basis of the conclusion that a little less than a year after the opening of the fixed link the number of shopping trips across the Øresund had increased, but there was still no heavy flow of customers doing ordinary shopping in the neighbouring countries. In order to assess the level of cross-border shopping across the Øresund the findings are compared to those from surveys across the Danish-German land border.     

Areas and sources of metasedimentary rocks in the Tukuringra terrane of the Mongolian–Okhotsk mobile belt: Results of Sm–Nd isotope study

The results of Sm–Nd studies of metasedimentary rocks from the Tukuringra terrane, one of the largest units in the structure of the eastern part of the Mongolian–Okhotsk mobile belt, are reported. Metasedimentary rocks of the Algainskaya, Garmakanskaya, and Teploklyuchevskaya formations are characterized by similar model ages t_Nd(DM) = 1.5–1.1 Ga. This shows that the major protoliths of metasedimentary rocks of the terrane are characterized by Mesoproterozoic estimates of the Nd model ages. The results obtained allow us to assume that introduction of terrigenous material into the sedimentary basin mostly occurred from the continental massifs united into the Amur superterrane, since their magmatic and sedimentary complexes are characterized by identical values of the Nd model ages.     

Rhyolite–granite association in the Central Taimyr zone: evidence of accretionary-collisional events in the Neoproterozoic

The Central Taimyr accretionary belt includes two granite-metamorphic terranes: Faddey and Mamont-Shrenk, which include the oldest igneous formations of the Taimyr folded area in the Arctic framing of the Siberian craton—granitoids and granite-gneisses with U–Pb zircon ages of 900–830 Ma. The [FeO*/(FeO* + MgO)]-enriched granitoids of these terranes are products of highly fractionated I-type magmas. This paper presents results of new petrographic, geochemical, geochronological, and paleomagnetic investigations of acid rocks from a volcanic-plutonic association (in the region of the Leningradskaya River) in the Faddey terrane in the northeastern Taimyr area. These rocks formed during the final stage of continent–island arc accretion and collision that occurred at approximately 870–820 Ma. We established that the studied rocks belong to a long granitoid belt extending from Mamont-Shrenk to Faddey terrane, where all the igneous bodies are deformed and oriented uniformly. The paleomagnetic pole we calculated differs significantly from the apparent polar-wander path interval of corresponding age for Siberia. The 33.8°±5.4° angular distance between the poles indicates that the formation of this volcanic-plutonic association took place at a significant distance from the Taimyr margin of the Siberian paleocontinent.     

Fluid inclusion,geochemical, Rb–Sr and Sm–Nd isotope studies on tungsten mineralized Degana and Balda granites of the Aravalli craton,NW India

Granitic plutons occurring within and to the west of the Delhi Fold Belt in the Aravalli craton, northwestern India are the result of widespread felsic magmatism during Neoproterozoic, some of which are associated with greisen and skarn tungsten deposits. In this paper, we present the result of our study on fluid inclusions, geochemistry and geochronology of two such tungsten mineralized granite plutons at Degana and Balda, and interpret the nature of ore fluid, and petrogenesis and age of these mineralized granites. Fluid inclusion study reveals coexistence of moderate and hyper-saline aqueous fluid inclusions along with aqueous-carbonic inclusions, suggesting their origin due to liquid immiscibility during fluid–rock interaction. Geochemically, the granites are peraluminous, Rb enriched, Sr and Ba depleted and highly differentiated. The Rb–Sr isotopic systematics yielded \(795\pm 11\) Ma for Balda granite and \(827\pm 8\) Ma for Degana granite. We show that major phase of widespread granitoid magmatism and mineralization during the Neoproterozoic (840–790 Ma) in NW India is coeval with breakup of the Rodinia supercontinent and infer a causal relationship between them.     

Oxygen isotope ratio of quartz veins from the auriferous Ramagiri–Penakacherla schist belt and surrounding granitoids in the Eastern Dharwar craton: A case for a possible link between gold mineralization and granite magmatism

In the Eastern Dharwar craton, among the many shear zone-hosted lode gold deposits, those at Ramagiri and Penakacherla are located near the western margin of the craton. Mineralized quartz (± sulfide ± carbonate) veins are hosted by the schistose (metavolcanic and carbonaceous metasedimentary) rocks, in close spatial association with granitoids having quartz and quartzofeldspathic veins representing hydrothermal activities associated with them. Mineralized quartz veins from the ore zones (in Ramagiri and Penakacherla regions) and quartz (or pegmatitic) veins from the surrounding granitic terrane were chosen for δ¹⁸O analysis. Samples from the schistose and granitic domains show δ¹⁸O_quartz values in the range of 10.4–14.9 and 9.3–10.9‰ respectively. The ore-zone fluids from the Ramagiri and Penakacherla regions give δ¹⁸O values of 7.9 ± 1.5 and 5.1 ± 0.8‰, calculated at pressure-corrected temperatures obtained from fluid inclusion microthermometry. The late-magmatic fluid is relatively ¹⁸O-poor with δ¹⁸O values estimated at 4.5 ± 0.7‰ and the value is closer to what is obtained for the ore zones. Based on the δ¹⁸O values reported and a possible magmatic contribution to ore fluid deciphered from fluid inclusion characteristics, a genetic relationship between granitic magmatism and gold mineralization is surmised. The observed increase in the ¹⁸O/¹⁶O ratio from the magmatic fluid to ore fluid in the shear zone is attributed to interaction of the magmatic fluid with host metasediments, that agrees well with the variation in the CO₂/CH₄ ratio of carbonic component in such fluids.     

Geochemical and Sr–Nd–Pb-Isotope Characteristics of Ice-Rafted Sediments of the Arctic Ocean

The paper discusses the geochemical and Sr–Nd–Pb-isotope data on ice-rafted sediments (IRS) from different areas of the Arctic Ocean. Samples were collected during the Cruise of R/V Polarstern between Spitsbergen and North Pole, Yermak Plateau, as well as in Fram Strait. It is shown that the studied IRS samples in terms of La_N/Yb_N and εNd values are close to the composition of suspended particulate matter (SPM) from the mouth parts of large rivers and rivers transporting the sedimentary erosion products. This also follows from their Th/Sc, Th/Co, La/Sc, La/Sm, Sc/Th ratios and Sc content and from the position of their data points in the Sc–Th/Sc, La/Sc–Th/Co, and La/Sm–Sc/Th diagrams between the average SPM compositions of the Ob and Lena rivers. The values of ²⁰⁷Pb/²⁰⁶Pb and εNd in IRS samples give grounds to suggest that the rock complexes of the European, North American, and Asian continental margins could be potential sources for this sedimentary material. In the ²⁰⁷Pb/²⁰⁶Pb–εNd diagram, the IRS samples from all three studied areas define a compact cluster and are mainly confined to the triangle with corners represented by the Mackenzie River, Okhotsk–Chukotka volcanic area, and Lena River, being closer to the latter. In the Sm/Nd–εNd diagram, IRS points also form a compact field, being located almost in the middle between the average SPM compositions of the Yenisei and Ob rivers, on the one hand, and Lena River, on the other. In all diagrams, IRS samples from the different West Arctic areas show no significant scatter. With allowance for the fact that sediments are not subjected to significant homogenization during ice rafting, sediments from all three areas were obtained from a common source. As seen from the position of IRS data points in the ⁸⁷Sr/⁸⁶Sr–εNd diagram, this source was the Asian continental margin.