Concentrations Of Lithophile Elements Research Articles

Recognition of geochemical anomalies based on geographically weighted regression: A case study across the boundary areas of China and Mongolia

The identification of stream sediment geochemical anomalies related to mineralization from background is critically needed for mineral exploration using data processing method in the diverse lithological background and complex regolith terrains. In this research, a method based on geographically weighted regression (GWR) was presented for the identification of stream sediment geochemical anomalies. The concentrations of rock-forming oxides, lithophile elements, organic carbon and total carbon were taken as proxies for parent lithology and regolith type to adjust for variations in background of trace element geochemical patterns. Robust principal component analysis (RPCA) was conducted, and then the principal components were taken as spatially independent variables. The metallogenic elements were taken as dependent variables in GWR model, and the geochemical residuals were used to indicate local anomalies. The 1:1,000,000 stream sediment geochemical data across the boundary areas of China and Mongolia were analyzed, and the result of GWR was compared with that of a traditional method. It is found that the efficiency of GWR was highly improved compared with that of the traditional method, indicating that the proposed method can model and eliminate the background differences of elements due to lithological settings and landscapes. Anomalies identified by GWR had stronger spatial association with the known deposits, and thus can be used as guides to new exploration targets.

Evolution and tectonic setting of the Malani – Nagarparkar Igneous Suite: A Neoproterozoic Silicic-dominated Large Igneous Province in NW India-SE Pakistan

The Neoproterozoic Malani Igneous Suite (MIS) in NW India, along with analogous magmatic rocks from the adjoining Nagarparkar region in SE Pakistan can be collectively classified as a Silicic-dominated Large Igneous Province (SLIP). This magmatic event includes bimodal (predominantly felsic) volcanism, granite emplacement and felsic and mafic dyke intrusions. Felsic rocks have typical A-type affinity as indicated by high abundance of silica, alkali, high field strength and large ion lithophile element concentrations and low CaO and MgO contents. Their Nb negative anomalies and Zr-saturation parameters indicate significant crustal input and high temperature melting. Mafic volcanics and dykes show geochemical homogeneity and derivation from a depleted continental mantle source without any significant crustal contamination (low U and Th contents and no visible Nb anomaly). The region extending from the Mount Abu batholith in the east to Jaswantpura in the west (2700 km2), representing a transition from the metamorphic Sirohi terrane to the undeformed MIS, was evaluated through an integrated structural (including satellite image analysis), geochemical and geochronological study. During the initial stage (prior to 760 Ma) the granitic basement (Erinpura granites) and overlying Sirohi metasediments behaved in a brittle manner that led to development of linear fractures and NNE trending rift structures, and bimodal volcanic activity. Emplacement of voluminous granitic bodies in response to progressive extension of the crust is inferred during the more evolved second stage (younger than 760 Ma). Mirpur Granite, a representative of this younger granitic suite (Jalor type pink granite) has yielded 753 ± 9 Ma zircon, U-Pb, crystallization age. Granitic plutons mark regions of crustal extension, as seen in parallel alignment of plutonic bodies (Jaswantpura granitic belt) and parallel mafic dyke swarms (340°) transecting the granites. Structural analysis further identified an episode of crustal convergence which is documented in folding and faulting of the Sindreth Basin sequence and in tectonic overprint of early stage mafic rocks. Rifting and bimodal magmatic activity in MIS is coeval with similar rock types in Nagarparkar in SE Pakistan, further traceable into the Seychelles microplate and Central Madagascar. Considering the Neoproterozoic paleogeography and our observations, an extensional setting and an active continental margin position for MIS is inferred.

Seasonal and spatial variations in the chemical components and the cellular effects of particulate matter collected in Northern China

The health effects of airborne particulate matter (PM) are likely to be strongly influenced by its components. The relationship between the composition of PM and its biological effects has been investigated in vitro/vivo, but more studies are needed to achieve a better understanding of the relationship. Such studies are limited in Northern China, where severe air pollution causes significant health impacts. In this study, we analyzed seasonal PM10 (PM, aerodynamic diameter less than 10μm) samples from five typical cities in Northern China for their physicochemical properties and their in vitro effects on A549 (human lung epithelial cell line) and RAW264.7 (murine monocyte macrophage) cells, including cytotoxicity, oxidative stress and inflammatory effects. Principal component analysis and multiple linear regressions were used to investigate the relationship between the PM components and the cellular responses. The cellular responses of A549 cells were more closely related to the endotoxin content and the levels of polycyclic aromatic hydrocarbons (PAHs) and their derivatives, while the cellular responses of RAW264.7 cells were largely related to PM10-bound metals, and the chalcophile elements (Pb, Cu, Zn, Cd) were more related to the PM-induced oxidative stress, whereas the lithophile and siderophile elements (Al, Fe, Mg, Co, V, Mn, Ca) were more related to PM-induced inflammation and cytotoxicity. As PM compositions changed seasonally, more intense cellular responses were seen when A549 cells were exposed to winter samples that contained higher levels of those components. The autumn and winter samples induced higher levels of oxidative stress in RAW264.7 cells, possibly due to higher contents of chalcophile elements, whereas the spring and/or summer samples were more cytotoxic and proinflammatory, possibly due to higher contents of lithophile and siderophile elements. The study suggests that the evaluation of health impacts induced by air pollution should take into account different physiochemical properties other than the mass concentration, and that public health would benefit greatly from effective, prioritized control of the sources that are the major producers of the central species.

Petrology of Jurassic and Cretaceous basaltic formations from the Parnaíba Basin, NE Brazil: correlations and associations with large igneous provinces

Abstract The basaltic Mosquito and Sardinha formations in the Parnaíba Basin are related to the opening of the Atlantic Ocean at the Triassic–Jurassic boundary and in the early Cretaceous, respectively. The Mosquito Formation consists of tholeiitic flows with both high-Ti (>1.5 wt%) and low-Ti (<1.5 wt%) compositions and the petrogenetic characteristics of enriched mantle reservoirs. The Mosquito Formation basalts have an initial 87 Sr/ 86 Sr isotopic composition of 0.70296–0.70841 and a low Nd isotopic composition (0.512245–0.512677) associated with an enrichment in large ion lithophile and high field strength elements relative to primitive mantle compositions. The Sardinha Formation is composed of high-Ti and low-Ti tholeiitic dykes with subordinate alkali basalts. The Sardinha Formation rocks have trace element and isotopic features associated with enriched mantle end-members. The initial isotopic compositions range from 0.702859 to 0.706703 and 0.512184 to 0.512671 for 87 Sr/ 86 Sr and 143 Nd/ 144 Nd, respectively. The concentrations of large ion lithophile and high field strength elements are elevated relative to primitive mantle values. Although the Mosquito and Sardinha formations share some similarities, they can be differentiated by their unique petrographic characteristics and trace element concentrations. These differences allow the discrimination of the basaltic magmatism in the Parnaíba Basin and their association with large igneous provinces, such as the Central Atlantic Magmatic Province or the Paraná–Etendeka Magmatic Province. Supplementary material: Microprobe analyses for clinopyroxene (Table A1), plagioclase (Table A2) and olivine (Table A3) for the Mosquito and Sardinha formations, along with mixing calculation parameters for the geochemical model (Table A4) are available at: https://doi.org/10.6084/m9.figshare.c.3985437

Eocene magmatism from the Liemai intrusion in the Eastern Tethyan Himalayan Belt and tectonic implications

AbstractMultistage magmatic thermal events occurred in the Yardoi Dome and contain important information on the tectonomagmatic processes. The dome has played a crucial role in understanding the collisional evolution of the Tethyan Himalayan. We present new geochronological and geochemical data for muscovite-granite exposed in the Liemai area, Eastern Tethyan Himalayan Belt. Liemai muscovite-granite is strongly peraluminous, with A/CNK values characterized by evolved geochemical composition with high contents of SiO2-enriched large-ion lithophile elements, and is depleted of high-field-strength elements. These geochemical features indicate that granites possibly derived from partial melting of metasedimentary rocks and plagioclase fractional crystallization probably played a critical role in production of peraluminous granitic melts. Zircon U–Pb dating from muscovite-granite yielded ages of approximately 48.5 ± 1.1 Ma, representing its crystallization ages. This age is the oldest age of Tethyan Himalayan leucogranite from the Yardoi Dome and adjacent areas. However, the inherited zircon cores have ages of 135.7–3339.2 Ma. The εHf(t) values of all zircons vary from –6.4 to –2.3 and have varying Hf-isotope crustal model ages of 731–839 Ma. The geochemical and isotopic compositions indicate that magma of the Liemai granite can most likely be interpreted as products of the break-off related to thermal perturbation along the break-off window associated with the subduction of Neo-Tethyan slab. These magmas were derived mainly from the anatexis of ancient crustal materials under contraction and thickening conditions due to subduction of the Indian continent beneath southeastern Tibet.

Origin, baseline contents, and vertical distribution of selected trace lithophile elements in soils from nature reserves, Russian Far East

Despite extensive studies, little is known about the natural trace lithophile element contents and the relationship between contents of these elements and soil properties in the natural environment. The objectives of this study are as follows: (i) to quantify the natural baseline total trace lithophile element contents in soils, (ii) to identify the main factors controlling the vertical distribution and accumulation of elements, and (iii) to evaluate the anthropogenic influence on the soils in the territory of reserves. In this work, we collected 42 soil samples from conditionally pollution-free Dystric Cambisols of three large natural reserves on the coast of the Russian Far East. Soil samples were analyzed for total trace lithophile elements (Ga, Rb, Sr, V, Y, and Zr), total oxides of some major elements (Si, Al, Fe, and Mn), pH(KCl), organic C, total H, and clay content. The total contents of elements were determined via energy dispersive X-ray fluorescence spectroscopy. The correlations between soil properties and contents of the trace lithophile elements were analyzed. Estimation of additional inputs of trace lithophile elements from external sources was assessed by using corrected technogenic index (Tg) of the elements. Natural baseline total element contents (mg kg−1) were as follows: Ga (5.77–7.27), Rb (68.72–113.55), Sr (56.14–154.70), V (106.90–168.99), Y (18.02–20.98), and Zr (189.74–249.28). Rubidium and Y in soils from all reserves include additions from external sources. These elements tended to accumulate in the upper parts of the soil profiles. Contents of Rb and Y were dependent largely on organic C content, total H content, and Mn-containing compounds of soil. In the territories with the maximum levels of Tg, we identified increased associations of total soil Ga and Sr with organic C content and Mn-Fe-containing compounds, Zr with Fe-containing compounds. Distribution and accumulation of V were mainly controlled by natural soil-forming factors and were mostly dependent on Al2O3 and SiO2 contents in soils. The levels of trace lithophile element contents in the soils from natural reserves depend on the mixed influence of natural environmental conditions (main soil-forming factors, peculiar geographic area) and additional inputs of elements originating from atmospheric deposition of long-distance transported pollutants. Technogenic index (Tg) indicated progressive contamination of soils from all reserves by Rb and Y, and local contamination of soils by Ga, Sr, and Zr. In our study, V was an uncontaminated element.

Geochronology and geochemistry of Early Devonian intrusions in the Qimantagh area, Northwest China: evidence for post-collisional slab break-off

ABSTRACTThe Qimantagh area of Northwest China lies in the western part of the East Kunlun Orogenic Belt and is characterized by extensive magmatism, particularly in the Triassic. However, recent research has shown that Devonian magmatism was also widespread in this area and has a genetic relationship with mineralization. This article presents a detailed study of three types of Early Devonian intrusions: high-K calc-alkaline granites, A-type granites, and mafic intrusions, all from the Qimantagh region. These rocks were subjected to precise zircon U–Pb dating, major and trace element analyses, and Sr–Nd isotope measurements, focusing on the Lalingzaohuo (eastern Qimantagh) and Yemaquan (central Qimantagh) monzogranites, as well as the coeval Tanbeixuefeng (western Qimantagh) mafic dike swarm. To better understand the Early Devonian igneous activity in the Eastern Kunlun, data for other coeval granitoids were compared with our data. The Yemaquan monzogranite yielded a mean zircon U–Pb age of 400.5 ± 1.4 Ma. These rocks are metaluminous to slightly peraluminous, with Al2O3 contents of 13.10–14.16 wt.%, high alkali contents (total K2O + Na2O) of 6.89–7.68 wt.%, relatively low Sr contents (79–192 ppm), and high (La/Yb)N ratios, all of which indicate an I-type granite affinity. The Lalingzaohuo monzogranites yielded mean zircon U–Pb ages of 396.2–402.2 Ma. These rocks have higher SiO2 and alkali contents than the Yemaquan monzogranite, with high 10,000 Ga/Al ratios, high Zr + Nb + Ce + Y contents, high Fe2O3T/MgO ratios, and high Y contents, indicating an A-type granite affinity. These two monzogranites have initial 87Sr/86Sr ratios of 0.703–0.706 and εNd(t) values of –0.1 to –0.7. The Sr–Nd isotopic data require a significant input of a mantle component in the petrogenesis of these granites. The Tanbeixuefeng diabase dikes formed at ~396 Ma and have a continental tholeiitic affinity, as evident from small Ti–Nb–Ta anomalies and high contents of light rare earth and large-ion lithophile elements. We propose that post-collisional slab break-off was responsible for the generation of these Early Devonian intrusions in the Qimantagh area.

Petrogenesis of an Early Cretaceous lamprophyre dike from Kyoto Prefecture, Japan: Implications for the generation of high-Nb basalt magmas in subduction zones

We studied a 107Ma vogesite (a kind of lamprophyre with alkali-feldspar>plagioclase, and hornblende±clinopyroxene±biotite) dike in the Kinki district of the Tamba Belt, Kyoto Prefecture, SW Japan, using petrography, mineralogy, K–Ar ages, and geochemistry to evaluate its petrogenesis and tectonic implications. The dike has the very specific geochemical characteristics of a primitive high-Mg basalt, with 48–50wt.% SiO2 (anhydrous basis), high values of Mg# (67.3–72.4), and high Cr (~431ppm), Ni (~371ppm), and Co (~52ppm) contents. The vogesite is alkaline and ne-normative with high concentrations of large ion lithophile elements (LILEs: Sr=1270–2200ppm, Ba=3910–26,900ppm), light rare earth elements (LREEs) [(La/Yb)n=58–62), and high field strength elements (HFSEs: TiO2=1.5–1.8wt.%, Nb=24–33ppm, Zr=171–251ppm), and the vogesite can be classified as a high-Nb basalt (HNB). The vogesite was formed by the lowest degree of melting of metasomatized mantle in the garnet stability field, and it may also have been formed at higher melting pressures than other Kyoto lamprophyres. The low degree of melting is the primary reason for the high-Nb content of the vogesite, not mantle metasomatism, and a higher degree of melting would have changed the primary magma composition from a HNB to a Nb-enriched basalt (NEB). The vogesite magma was contaminated at an early stage of its development by melts derived from sediments drawn down a subduction zone, as indicated by some geochemical indices and the initial Nd isotope ratios. The vogesite exhibits positive correlations between εSr(107 Ma) values (5.4–50.9) and its high Ba and Sr concentrations, and it has a limited range of εNd(107 Ma) values (+0.97 to +2.4). The fact that the vogesite contains centimeter-sized xenoliths of chert, which are composed of polycrystalline quartz, calcite, barite, pyrite, and magnetite, indicates that the barium contamination took place during the ascent of the lamprophyric magma through the upper crust. The episode of magmatism at c. 107Ma extended regionally from the Kinki district, through the Chugoku district and North Kyushu in SW Japan, to Korea as a result of slab roll-back at the eastern margin of Asia.

Evidence for a chondritic impactor, evaporation-condensation effects and melting of the Precambrian basement beneath the ‘target’ Deccan basalts at Lonar crater, India

The ∼1.88km diameter Lonar impact crater formed ∼570ka ago and is an almost circular depression hosted entirely in the Poladpur suite of the ∼65Ma old basalts of the Deccan Traps. To understand the effects of impact cratering on basaltic targets, commonly found on the surfaces of inner Solar System planetary bodies, major and trace element concentrations as well as Nd and Sr isotopic compositions were determined on a suite of selected samples composed of: basalts, a red bole sample, which is a product of basalt alteration, impact breccia, and impact glasses, either in the form of spherules (<1mm in diameter) or non-spherical impact glasses (>1mm and <1cm). These data include the first highly siderophile element (HSE) concentrations for the Lonar spherules. The chemical index of alteration (CIA) values for the basalts and impact breccia (36.4–42.7) are low while the red bole sample shows a high CIA value (55.6 in the acid-leached sample), consistent with its origin by aqueous alteration of the basalts. The Lonar spherules are classified into two main groups based on their CIA values. Most spherules show low CIA values (Group 1: 34.7–40.5) overlapping with the basalts and impact breccia, while seven spherules show significantly higher CIA values (Group 2: >43.0). The Group 1 spherules are further subdivided into Groups 1a and 1b, with Group 1a spherules showing higher Ni and mostly higher Cr compared to the Group 1b spherules. Iridium and Cr concentrations of the spherules are consistent with the admixture of 1–8wt% of a chondritic impactor to the basaltic target rocks. The impactor contribution is most prominent in the Group 1a and Group 2 spherules, which show higher Ni/Co, Ni/Cr and Cr/Co ratios compared to the target basalts. In contrast, the Group 1b spherules show major and trace element compositions that overlap with those of the impact breccia and are characterized by high EFTh (Enrichment Factor for Th defined as the Nb-normalized concentration of Th relative to that of the average basalt) as well as fractionated La/Sm(N), and higher large ion lithophile element (LILE) concentrations compared to the basalts. The relatively more radiogenic Sr and less radiogenic Nd isotopic composition of the impact breccia and non-spherical impact glasses compared to the target basalts are consistent with melting and mixing of the Precambrian basement beneath the Deccan basalt with up to 15wt% contribution of the basement to these samples. Variations in the moderately siderophile element (MSE) concentration ratios of the impact breccia as well as all the spherules are best explained by contributions from three components – a chondritic impactor, the basaltic target rocks at Lonar and the basement underlying the Deccan basalts. The large variations in concentrations of volatile elements like Zn and Cu and correlated variations of EFCu-EFZn, EFPb-EFZn, EFK-EFZn and EFNa-EFZn, particularly in the Group 1a spherules, are best explained by evaporation-condensation effects during impact. While most spherules, irrespective of their general major and trace element composition, show a loss in volatile elements (e.g., Zn and Cu) relative to the target basalts, some spherules, mainly of Group 1, display enrichments in these elements that are interpreted to reflect the unique preservation of volatile-rich vapour condensates resulting from geochemical fractionation in a vertical direction within the vapour cloud.

Petrology, geochemistry and zircon U–Pb geochronology of the Jurassic porphyry dykes in the Dehua gold field, Southeast China: Genesis and geodynamics

The widespread tectonic and magmatic events in Southeast China during the Mesozoic were accompanied by large‐scale metallogenesis. Here, we investigate the petrology, geochemistry, and zircon U–Pb age of the porphyry dykes in relation to the gold mineralization at Dongyang deposit in the Fujian Province. The geochemical data show silica‐rich and Mg‐ and Ca‐poor A‐type granite affinity for the dykes. The rocks have high concentrations of Light Rare Earth Elements (LREE) and Large Ion Lithophile Elements (LILE) and relatively low contents of Heavy Rare Earth Elements (HREE) and High Field Strength Element (HFSE). They display (La/Yb)N and (La/Sm)N values in the range of 5.7 to 31.4 and 6.0 to 8.3, respectively, with negative anomalies of Ba, Nb, Ta, Sr, Zr, Eu, and Ti and positive Ce anomaly. The source magma for the dykes was derived from a mixture of partially melted Al‐rich crustal material, with an input of mantle components. We present sensitive high‐resolution ion microprobe zircon U–Pb data from the dykes, which show emplacement ages in the range of 158 to 162 Ma, coinciding with the onset of the Yanshanian magmatism in Southeast China. Integrating the data obtained from studies on geology, geochronology and petro‐geochemistry, we suggest that the dykes played role in controlling the gold mineralization, and the magmatism and gold mineralization are the response of continental lithosphere thinning in Southeast China triggered by the subduction of the ancient Pacific Ocean Plate.

SHRIMP U–Pb zircon ages and whole-rock geochemistry for the Şapçı volcanic rocks, Biga Peninsula, Northwest Turkey: implications for pre-eruption crystallization conditions and source characteristics

ABSTRACTPalaeogene and Neogene volcanic rocks are widespread on the Biga Peninsula of Northwest Turkey. These rocks were formed during the Eocene, Oligocene–Miocene, and late Miocene, and the early Miocene Şapçı volcanic rocks in the Balıkesir area consist of andesitic lava flows and associated pyroclastics. Temperatures, pressures, and oxygen fugacities calculated for the hornblendes in these andesitic rocks are 903–930°C, 3.3–4.8 kbar, and –9.91 to –11.88, respectively, and for the biotites they are 755–788°C, 1.30–1.74 kbar, and –14.88 to –13.98, respectively. SHRIMP U–Pb dating of zircons from three andesite samples gave ages of 22.72 ± 0.19, 22.97 ± 0.23, and 18.72 ± 0.17 Ma (early Miocene), and these are regarded as crystallization ages. Geochemical analyses show that the volcanic rocks are mainly high-K and calc-alkaline, and have high contents of large-ion lithophile elements and low contents of high-field strength elements, revealing that they evolved from parental magmas that were derived from an enriched subcontinental lithospheric mantle source. The chondrite-normalized rare earth element patterns of the rocks are concave upwards with LaCN/LuCN = 11.9–21.2 and EuCN/Eu* = 0.84–0.92, implying significant fractional crystallization of hornblende during their evolution. According to the petrological data with regional geology, Neogene magmatic activity on the Biga Peninsula has a post-collisional feature, and was closely related to slab break-off geodynamic model after collision of Tauride–Anatolide Block and Sakarya continent.

Elemental variations in glacier cryoconites of Indian Himalaya and Spitsbergen, Arctic

Cryoconite samples were collected from two different climatic domains i.e., the Sutri Dhaka glacier, western Himalaya India and Svalbard glaciers, the Spitsbergen, Arctic, to understand the elemental source and elemental deposition patterns. The data of geochemical analysis suggest that the Himalayan cryoconite samples accumulate higher concentrations as compared to the cryoconite samples of the Arctic glaciers. The concentration of lithophile elements (Cs, Li, Rb and U) was recorded higher in the cryoconite holes of the Himalayas, especially, in the lower to the higher parts of the glacier, whereas, lower concentrations were recorded in the Arctic samples. Chalcophile elements in the Himalayan cryoconites are enriched in As and Bi while the Arctic cryoconite samples show a higher concentration of Bi, Pb and As. The higher concentrations are responsible for influencing the ecosystem and in human health related issues. Siderophile elements (Co, Fe, Mn and Ni) show high concentrations in the Himalayan samples, whereas, the Arctic samples show minor variations and low elemental concentration in these elements, respectively. In addition, a few elements, such as Ag, Mg, and Ca show higher concentration in the Himalayan glacier samples. Ca also occurs in high concentrations in Arctic glacier samples. R-mode factor analysis of the Himalayas (Arctic) samples indicate that the elements are distributed in four (three) factors, explaining 89% (90%) of the variance in their elemental distribution. The Factor 1 suggests statistically significant positive loadings for most of the lithophile, chalcophile and siderophile elements of the “Himalayan” and the Arctic cryoconite samples. The sample-wise factor score distribution shows a considerable variation in the sampling locations along the glaciers of both the regions. Factors 2 and 3, demonstrate insignificant loading for most of the elements, except statistically significant positive loading in some of the elements of the both, Himalayan and Arctic “cryoconites”. The higher elemental concentration in the cryoconites of the Himalayan region may be an indicator of the natural processes and/or attributed to the rapid industrialization in the Asian countries.

Subduction-related Late Cretaceous high-K volcanism in the Central Pontides orogenic belt: constraints on geodynamic implications

Mineral chemistry, major and trace elements, 40Ar/39Ar age and Sr–Nd–Pb isotopic data are presented for the Late Cretaceous Hamsilos volcanic rocks in the Central Pontides, Turkey. The Hamsilos volcanic rocks mainly consist of basalt, andesite and associated pyroclastics (volcanic breccia, vitric tuff and crystal tuff). They display shoshonitic and high-K calc-alkaline affinities. The shoshonitic rocks contain plagioclase, clinopyroxene, alkali feldspar, phlogopite, analcime, sanidine, olivine, apatite and titanomagnetite, whereas the high-K calc-alkaline rocks contain plagioclase, clinopyroxene, orthopyroxene, magnetite / titanomagnetite in microgranular porphyritic, hyalo-microlitic porphyritic and glomeroporphyritic matrix. Mineral chemistry data reveal that the pressure condition of the clinopyroxene crystallisation for the shoshonitic rocks are between 1.4 and 6.3 kbar corresponds to 6–18-km depth and the high-K calc-alkaline rocks are between 5 and 12 km. 40Ar/39Ar age data changing between 72 ± .5 Ma and 79.0 ± .3 Ma (Campanian) were determined for the Late Cretaceous Hamsilos volcanic rocks, contemporaneous with the subduction of the Neo-Tethyan Ocean beneath the Pontides. The studied volcanic rocks were enriched in the large-ion lithophile and light rare earth element contents, with pronounced depletion in the contents of high-field-strength elements. Chondrite-normalised rare earth element patterns (LaN/LuN = 6–17) show low to medium enrichment, indicating similar sources of the rock suite. Initial 87Sr/86Sr values vary between .70615 and .70796, whereas initial 143Nd/144Nd values change between .51228 and .51249. Initial 206Pb/204Pb values vary between 18.001 and 18.349, 207Pb/204Pb values between 15.611 and 15.629 and 208Pb/204Pb values between 37.839 and 38.427. The main solidification processes involved in the evolution of the volcanic rocks consist of fractional crystallisation, with minor amounts of crustal contamination ± magma mixing. According to geochemical evidence, the shoshonitic melts in the Hamsilos volcanic rocks were possibly derived from the low degree of partial melting of a subcontinental lithospheric mantle (SCLM), while the high-K calc-alkaline melts were derived from relatively high degree of partial melting of SCLM that was enriched by fluids and/or sediments from a subduction of oceanic crust.

Porphyry Cu mineralizations related with the small Tertiary volcanic intrusions in the Bučim ore deposit, Eastern Macedonia

The paper presents data about geology, geochemistry, structure, genesis and specific features of the Bucim, porphyry Cu deposit with active mining in Macedonia. The porphyry mineralization (0.3 % Cu, 0.3-0.5 ppm Au) is spatially and temporarily associated with Tertiary subvolcanic intrusions of latitic and latitic-andesitic composition. The intrusions took place during Oligo-Miocene time (24 to 27 Ma), a period of intensive tectono-magmatic and ore-forming processes.. The latest results of this study to an array of major ore (hypogen) minerals such chalcopyrite, pyrite, magnetite, hematite, cubanite, valleriite, native Au and bornite and secondary enrichment zone minerals (within Cukar ore body) chalcocite, covellite, tenorite, native Cu, malachite, azurite etc added minerals such calaverite, krennerite, electrum, petzite and bismuth±selenium minerals (bismuthinite, galenobismutite, krupkaite, friedrichite, emplectite, cosalite, laitakarite and native bismuth). Variations of the δ34S values for the whole Bucim ore deposit ranged from +0.2 ‰ to +2.5 ‰ while δ13C‰ and δ18O‰ isotope values ranged from -10.8 to -3.8‰ and from +14.0 to +22.7 ‰, respectively. In regards to fluid inclusions it was confirmed that beside dominated gas-liquid, two-phase inclusions, there are also three-phase fluid inclusions (gas + liquid + solid phase). Also, recent Sr and Nd isotope ratios (87Sr/86Sr 0.70666-0.70741 and 143Nd/144Nd 0.512487–0.512489) indicated slight contamination of the magmatic products by continental crust material, due to a partial melting of the deep parts of continental crust underthrusted by collision of continental blocks. In direction were results from the REE data, manifested through high contents of large ion lithophile elements (LILE), high Ba/Nb ratio (116.72-190.72) and depletion in high field strength elements (HFSE) and Europium negative anomaly (0.68893-0.91251).

Detrital zircon geochronology and geochemistry of metasediments from the Vorontsovka terrane: implications for microcontinent tectonics

ABSTRACTThe Vorontsovka terrane (VT) is an important component of the East Sarmatian Orogen (ESO) which divides the Precambrian cores of the Sarmatian and Volgo-Uralia segments of the East European Craton (EEC). The tectonic framework of the VT remains controversial due to poor constraints from geochemical and geochronological studies. In this article we present detrital zircon U–Pb ages and geochemical features of the Precambrian meta-sedimentary rocks from the VT, which occur interlayered with calc-silicate rocks and metabasites. Most of the zircons from metasediments possess oscillatory zoning and high Th/U ratios (>0.2), indicating magmatic provenance. Their 207Pb/206Pb ages cluster around 2093 ± 7, 2126 ± 7, 2158 ± 12, 2189 ± 16, and 2210 ± 31 Ma, correlating with the ages of magmatic zircon cores from the surrounding igneous suites, and reflecting a single tectono-magmatic cycle (~2200–2100 Ma) in the source area. Age of the youngest detrital zircon grain from the metasedimentary rocks and the cores of zircon grains from igneous suites show 207Pb/206Pb ages at 2094 and 2106 Ma, respectively. Together with the largest age clusters of 2126 ± 7 and 2158 ± 12 Ma of the magmatic cores of the detrital zircons, the timing of sedimentation is inferred as ~ 2100–2170 Ma.The metapelites display strong rare earth element fractionation with variable Eu anomalies ((La/Yb)N = 7.0–14.5, Eu/Eu* = 0.49–1.23). In contrast, the calc-silicate rocks and metabasites lack Eu anomalies ((La/Yb)N = 5.2–11.5, Eu/Eu* = 0.87–1.00). The large-ion lithophile (LILE) and high field strength element (HFSE) concentrations of most samples are comparable with those of the upper continental crust (UCC). The rocks possess negative anomalies of Th, Nb, Sr, and Zr relative to UCC. Their high Index of Compositional Variability (0.85–1.32, up to 1.8 in metabasites) and relatively low Chemical Index of Alteration (46.1–70.4) indicate that the metapelitic sediments were immature to weakly immature and probably underwent minor chemical weathering. The protoliths of the metabasites are interpreted as interlayered volcano-sedimentary and pyroclastic material. Relict clastic textures of the VT rocks, their geochemical features, and the grain morphology of detrital zircons suggest that the sediments were derived from intermediate and felsic provenances, which were most likely deposited in an environment with active volcanism. We envisage an active continental margin setting in the southwestern part of the Volgo-Uralia segment of the EEC related to the assembly of the Palaeoproterozoic Columbia supercontinent. Combined with recent data from surrounding terranes of the ESO, our results suggest that the VT represents an accretionary prism along a continental arc within the Sarmatia and Volgo-Uralia oceanic realm in the Palaeoproterozoic.

Glass‐bearing inclusions in Shergotty and Chassigny: Consistent samples of a primary trapped melt?

AbstractGlass‐bearing inclusions hosted by different mineral phases in SNC meteorites provide important information on the conditions that prevailed during formation of early phases and/or on the composition of the primary trapped liquids/melts of these rocks. Although extensive previous work has been reported on such inclusions, several questions are still unresolved. We performed a chemical and petrographic study of the constituents (glasses and mineral assemblage) of glassy and multiphase inclusions in Shergotty and Chassigny. We focused on obtaining accurate trace element contents of glasses and co‐existing minerals and discussing their highly variable REE contents. Our results reveal an unusual geochemistry of trace element contents that appear to be independent of their major element compositions. Chemical equilibrium between phases inside inclusions as well as between glasses and host minerals could not be established. The LREE contents of glasses in glass inclusions can vary by up to two orders of magnitude. The depletion in trace element abundances shown by glasses seem to be inconsistent with these phases being residual melts. The light lithophile element contents of glasses are highly variable with enrichment in incompatible elements (e.g., Be, Sr, Ba, and LREE) indicating some processes involving percolation of fluids. All of these features are incompatible with glass‐bearing inclusions in the host minerals acting as closed systems preserving unmodified primary liquids/melts. Glass‐bearing inclusions in Shergotty and Chassigny appear to have been altered (as was the rock itself) by different postformational processes (e.g., shock, metamorphism, metasomatic [?] fluids) that affected these meteorites with different degree of intensity. Our results indicate that these inclusions could not preserve a reliable sample of the primary trapped melt.

Late Cretaceous lithospheric extension in SE China: Constraints from volcanic rocks in Hainan Island

Petrological, geochemical and in-situ zircon U–Pb dating and Hf-isotope analyses have been carried out on a suite of basalt–andesite–rhyolite volcanic rocks exposed in the Liuluocun area, Hainan Island, SE China. Zircon analyses show that these volcanic rocks crystallized in the Early Cretaceous (ca. 102Ma). The basalts are characterized by low MgO contents and mg-numbers but high rare earth element, high field strength element and large ion lithophile element contents and Nb–Ta negative anomalies. They have relatively uniform Sr–Nd isotope compositions with εNd(t) values of −4.09 to −3.63. The andesites show enrichment of high field strength element and rare earth element with negligible Eu anomalies. They have εNd(t) values of −2.35 to −3.88 and εHf(t) values of −9.73 to −1.13. The rhyolites have high K2O and SiO2 contents. They are characterized by prominent Eu, P and Ti negative anomalies and enrichment in large ion lithophile element, and show εHf(t) values of −7.51 to +0.47 and εNd(t) values of −2.49 to −2.69. Petrogenetic analysis indicates that the Liuluocun volcanic rocks were produced by incomplete reaction of the mantle wedge peridotite with felsic melts derived from partial melting of subducted sediment. All these characteristics, combined with geological observations, suggest that their formation was related to regional lithospheric extension in the South China Craton during the Early Cretaceous, which may have been caused by subduction of the Paleo-Pacific plate beneath the continental plate of China.

Mineralogy and geochemical anomalies of Lower Cretaceous marine oil shale from Changshe Mountain West, northern Tibet, China

The Shengli River–Changshe Mountain oil shale zone in northern Tibet represents a large marine oil shale resource in China. Thirty-four samples of oil shale were collected from the Changshe Mountain West oil shale, a new oil shale deposit discovered in this oil shale zone, to evaluate the minerals and geochemical anomalies in the oil shale. Minerals identified in the oil shale include calcite, dolomite, quartz, illite, and trace amounts of siderite, hematite, feldspar, apatite, zinc oxide, pyrite, sphalerite, barite, celestite, and Fe(Si, Al)-oxysulfate minerals. The oil shale samples are rich in trace elements compared to post-Archean average shales including Co (up to 15.8μg/g), Ni (up to 83.6μg/g), Cu (up to 101μg/g), Zn (up to 775μg/g), As (up to 255μg/g), Se (up to 6.91μg/g), Sr (up to 738μg/g), Mo (up to 87.9μg/g), Pb (up to 17.4μg/g), Cd (up to 13.0μg/g), Bi (up to 0.38μg/g), and U (up to 7.10μg/g), and to a lesser extent, Li, F, Sc, V, Cr, Ga, Sn, Hg, and rare earth elements. Trace elements of probable terrigenous origin in the oil shale were derived from two possible sources: a felsic volcanic rock source and a limestone source. High concentrations of lithophile elements (e.g., Li, Sc, Ga, and REEs) were derived from these provenances. However, the enrichment factor for these elements also is low. In addition, seawater and hydrothermal activity may have influenced the geological and geochemical compositions of the oil shale. Minerals such as calcite, dolomite, and a large proportion of pyrite are of marine origin, and the enrichment of V, Cr, Co, Ni, Cu, Se, Sr, Mo, Pb, and U in the oil shales was probably due to marine influence. Barite, celestite, sphalerite, Fe(Si, Al)-oxysulfate minerals, and fracture-filling pyrite are of hydrothermal origin, and F, Zn, and Cd were derived from hydrothermal fluids.

Sm–Nd and Rb–Sr isotope geochemistry and petrology of Abu Hamamid intrusion, Eastern Desert, Egypt: An Alaskan-type complex in a backarc setting

Alaskan-type complexes are uplifted fragments of the deep levels of island arcs. These complexes usually reveal chemical diversity that cannot be assigned to a unique setting within arcs. Here we report the petrology, Rb–Sr and Sm–Nd isotopic data of the Abu Hamamid intrusion from the Eastern Desert of Egypt as an example of Neoproterozoic backarc Alaskan-type complex. The intrusion comprises clinopyroxene dunite, olivine clinopyroxenite, amphibole clinopyroxenite and gabbro. All rock units represent cumulates crystallized from a high-MgO hydrous magma with geochemical characteristics intermediate between mid-ocean ridge basalt and island arc magmas. Slab signatures of the parental magma comprise elevated H2O, 87Sr/86Sr and large ion lithophile element contents and relative depletion in Nb. High positive initial ɛNd (+6.2 to +11.0) is consistent with the Abu Hamamid magma being extracted from a highly depleted mantle source. The parental magma was generated by 10% partial melting of a mantle source modified by 10% MORB (ecolgite) derived fluid. The Abu Hamamid Alaskan-type complex and the surrounding related volcanic rocks were formed in a Neoproterozoic backarc setting. The magmas forming the lower crust of the Arabian-Nubian shield were liberated from a depleted mantle before 900Ma.

The 2.31 Ga mafic dykes in the Karelian Craton, eastern Fennoscandian shield: U–Pb age, source characteristics and implications for continental break-up processes

Major- and trace-element geochemistry, Sm–Nd isotopic and U–Pb geochronological (ID TIMS, baddeleyite) data are presented for Paleoproterozoic mafic dykes in the Karelian Craton, eastern Fennoscandian shield. Mafic dyke swarms recognized in the Lake Upper Kuito area in the Western Karelian terrane of the Karelian Craton include (i) NE-trending ca. 2450Ma gabbronorite dykes, (ii) NW-trending ca. 2310Ma dolerite dykes, and (iii) NNW-trending ca. 2130Ma continental MORB-type tholeiitic dykes. Each swarm belongs to a distinct intraplate igneous event and indicates specific mantle melting and extensional processes.The ca. 2.31Ga doleritic dykes have high-Fe, high-Ti tholeiitic series affinity and characterized by high concentrations of lithophile trace elements. The enrichment of LREE and unfractionated HREE patterns together with depletion of Nb on multi-element diagrams and initial ɛNd values of +0.5 to +0.8 are characteristic for ca. 2.31Ga dolerites. The geochemical modelling results suggest that these features could be originated via combination of fractional crystallization and crustal contamination processes, and do not indicative of a mantle source enrichment. It also indicates long-term storage of melts in an intracrustal magma chamber and a relatively slow ascent to the surface. The primary melts of ca. 2.31Ga dolerites possibly originated by partial melting of a DM-type mantle source in the spinel peridotite stability field.In contrast to previous ca. 2.45Ga event studied ca. 2.31Ga dolerites do not indicate high-temperature mantle-plume induced mantle melting. On the other hand, the ca. 2.31Ga dykes have some similarities with syn-breakup ca. 2.13Ga continental MORB-type tholeiites, although there is no evidence for the break-up of the continental lithosphere of the Karelian Craton at ca. 2.31Ga. Thus ca. 2.31Ga dykes could indicate the existence of relatively stable extensional tectonic environment and an unsuccessful attempt of break-up of the continent.The ca. 2.31Ga dykes together with previously studied Runkaus basalts and Taivalkoski dykes could be considered as a component of distinct relatively wide-spread Kuito-Taivalkoski igneous event within the ca. 2.2–2.4Ga “crustal age gap” period in the eastern Fennoscandian shield. This probably indicate that the number and intensity of endogenous events of age 2.4–2.2Ga are greatly undervalued. This also argues against a decrease of endogenic activity and magmatic “slowdown” during ca. 2.4–2.2Ga period.