Element Distribution Patterns Research Articles

Concentrations of major and trace elements in soil profiles developed over granites across a climosequence in northeastern Brazil

Soils formed from granites are distributed worldwide, therefore, studies regarding their geochemical signature on tropical soils are important to understand key processes of soil weathering and soil chemistry. This paper reports the effect of S- and I-type granitic rocks on the content and distribution of trace and major elements in soil profiles developed across a climosequence in Northeastern Brazil. In general, soils developed from I-types show greater trace and major element concentrations than those originated from S-types, due to their higher proportion of accessory and mafic minerals. Geochemical mass balance and enrichment factor data suggest that climatic effects showed a less evident effect on the distribution pattern of trace and major elements from soil profiles underlain by S-type granitic rocks. The highest enrichment factor results evidenced in soils formed on I-types are explained by the rock mineralogy, which imparts higher CEC values and proportion of clay to soils. Trace elements were less leached than major elements during chemical weathering, except for Al, Fe, and P. Geochemical mass balance showed that, regardless of the granite type, the highest depletion of trace and major elements in the pedosphere took place in the humid zones as a consequence of weathering intensity. In this zone, except for quartz, the primary minerals were altered to form secondary minerals, giving rise to kaolinitic soils. These results can be used as reference contents of trace and major elements developed from different granitic rocks in environments with tropical climate. Besides, this research sheds some light on the effect of contrasting granites and a climosequence on soil geochemistry.

Distribution pattern and geochemical analysis of rare earth elements in deep-ocean sediments

The content and distribution pattern of rare earth elements (REEs) in surface sediments from the Eastern and Western Pacific Ocean, the Northern and Southern Atlantic Ocean, and the Southwestern Indian Ocean were explored and the resources and geochemical characteristics of REEs in deep-ocean sediments from different oceans were studied. The total REE abundances (∑REE) in the different oceans ranged as follows:Eastern Pacific, 56.88-500.02 μg/g; Western Pacific, 290.68-439.94 μg/g; Northern Atlantic, 55.33-154.90 μg/g; Southern Atlantic, 40.83-69.30 μg/g; and Southwestern Indian Ocean, 20.24-64.76 μg/g. Their corresponding LREE (La-Eu)/HREE (Gd-Lu) average values were 5.18, 5.86, 9.01, 5.21, and 4.59, which indicated that the light REEs were all evidently enriched. δEu and δCe showed slight Eu-negative anomalies and significant Ce-positive anomalies in all sediments. Although the contents of REEs in the sediments varied among the different oceans, the distribution patterns of REEs were similar, and the correlation coefficient was greater than 0.929 0. In the Eastern Pacific sediments, ΣREE showed a significantly positive correlation with Co, Cu, Zn, Mn, Mo and a weak correlation with Fe. In the Western Pacific and Southern Atlantic sediments, ΣREE presented no obvious correlation and a weakly negative correlation with Co, Cu, Zn, Mn, Mo and Fe, respectively. ΣREE in the Southwestern Indian Ocean sediments positively correlated with Cu, Zn, Mn, Mo, Fe, and had a weakly negative correlation with Co.

Geochemical record of rapid climate change and chemical weathering in a semi-arid area, northeastern Tibetan Plateau

Lacustrine deposits can provide insight into chemical weathering and climate change. Based on the analysis of the element concentrations and parameters of the acid-leaching residual fractions (AR) in the lacustrine deposits of the Qaidam Basin (QB), chemical weathering and paleoclimate changes in the northeastern Tibetan Plateau (NETP) have been studied. The results show that the characteristics of trace element concentrations exhibit two kinds of patterns by normalized element arbitrary units (a.u.). The rare earth element (REE) distribution patterns are moderately rich in light rare earth elements (LREEs) with slightly right-tilting and negative Eu anomalies. Triangular plots of the REEs and (La/Yb)n-ΣREE suggest that the sediments have a similar source. The geochemical records of climate proxies indicated warm-wet climate stages during 45.1–31.6 cal. ka BP., further proving that a megalake stage existed in the semi-arid area in marine isotope stage (MIS) 3. Strong evaporation resulted in a high paleolake level history in the northeastern Tibetan Plateau after the late period of MIS 3. Meanwhile, the geochemical records of the Qaidam Basin are synchronous with the global records.

Evidence for multiple sources for inorganic components in the Tucheng coal deposit, western Guizhou, China and the lack of critical-elements

Terrigenous materials from sediment-source regions are important controls on the types and concentrations of inorganic components in coal. The Kangdian Upland (dominated by the Emeishan basalts) is the dominant terrigenous supplier for most of the Late Permian coals, as well as for their associated host rocks (roof and floor strata) in southwestern China. The high volatile bituminous coals (Nos. 3 and 6 coals) are the two major minable coal seams in the Tucheng coal deposit in southwestern China. Unlike most Late Permian coals in this region that are characterized by elevated concentrations of the element assemblage Sc-V-Cr-Co-Ni-Cu-Zn-Se, these two coals are not enriched in this assemblage although Se is slightly concentrated.The mineralogical (e.g., relatively abundant quartz and mixed-layer illite/smectite) and elemental distribution patterns (e.g., spider diagrams of rare earth elements, discrimination diagrams of Al2O3-TiO2 and Zr/TiO2-Nb/Y, and elemental assemblages) indicate that the inorganic components in the two coal seams were mainly derived from unidentified volcanic arc and/or distal orogens, while the clastic components in the roof and floor strata of the two coal seams were mainly supplied by the high-Ti Emeishan basalts. The two partings in the two coal seams, identified as tonsteins, were probably derived from the final (rejuvenated) activity of the Emeishan plume. Critical elements in the two coals and associated non-coal horizons (partings, roof and floor strata) are economically unpromising, indicating that prospecting for Late Permian coal-hosted critical metal ore deposits in the vicinity of the Emeishan plume in southwestern China, should not be focused on coals with inorganic components derived mostly from distal volcanic arcs and orogens and high-Ti Emeishan basalts, and a minor contribution of volcanic ashes resulting from the final rejuvenated activity of the Emeishan plume.

Prospectivity of Mesoproterozoic magmatism in the northern Karbi Hills, NE India for porphyry copper mineralization

The Kuthori porphyry copper prospect in the Mesoproterozoic Kaziranga magmato-sedimentary domain of the northern Karbi Hills of Shillong Plateau, NE India, is a recently discovered granitoid-hosted Cu-Fe-S occurrence. We present here a preliminary geological account to appraise the petrography, geochronology and bulk geochemistry of the occurrence, and propose a geological model for copper mineralization in the Precambrian granitiods of Karbi Hills. These largely anorogenic (A-type) granitoids show evidences of multiple injections of magma of varying compositions ranging from granite-granodiorite-quartz monzonite. The granitoids have undergone hydrothermal alteration, resulting in the development of alteration mineral zones characterized by a central zone of potassic alteration, containing quartz–K-feldspar-biotite-sericite, followed by phyllic and argillic alteration showing typomorphic mineral growth away from the central alteration zone. The granitoids have wide range of silica contents (54.69–73.07%); are dominantly metaluminous and calc-alkaline; contain high total alkalis and Fe-rich biotite; and show high abundances of Y, Nb, Zr, high FeO/(FeO + MgO) ratios and low CaO, MgO and Sr abundances. The incompatible trace element distribution pattern, positive zircon εHf(t) (+3.2 to + 9.7), initial whole rock 87Sr/86Sr ratio (0.703) and sulphide minerals with 34S/32S ratio (+4.5 ± 0.05‰), indicate magma and sulphide derivation from an enriched mantle source at varying temperatures (828 °C-688 °C). The overall evidence suggests that granitoid magma production and emplacement took place in postcollision back arc basin, creating avenues for ore deposition due to a rapid diapiric rise of magma, sudden decrease in pressure and temperature, resurgent boiling marked by crackle brecciation and increase in the oxidation state of magma.

Occurrence of Liddicoatite-Bearing LCT Pegmatites in Sirohi Region, Northwest India and their Rare Metal Potentiality

Rare and trace element study of pegmatites around Sibagaon area of Sirohi region, Rajasthan, India revealed that the pegmatites are of rare element class and LCT (Li–Cs–Ta) type. Rare metal concentration in these pegmatites is notably high against crustal abundance, with Li ranging from 1007 to 10785 ppm, Rb from 1285 to 9147 ppm, Cs from 36 to 1142 ppm, Ta from 12 to 386 ppm, Sn from 54.22 to 2283.61 ppm and F from 2724 to 48,275 ppm. Integration of EPMA and LA-ICPMS analyses indicated that the main Li-bearing mineral in pegmatites is lepidolite with Li ranging from 21,599 to 28,178 ppm, which is economically worthwhile to process for Li, followed by elbaite and rare mineral liddicoatite, which has not been reported so far in India. Rare earth element (REE) distribution pattern shows enrichment of LREEs than HREEs, indicating that pegmatites are fractionated and thus causing enrichment of rare metals. This reporting of liddicoatite-bearing LCT pegmatites from Sirohi region with high anomalous values of rare metals can therefore be a good prospect for rare metal exploration in India in the present economic scenario. These pegmatites have indicated a syn-collisional signature and may be related to the accretion of Marwar craton with greater Indian land mass along the Phulad Shear zone.

Ideal Element Distribution Pattern and Characteristics of Primary Halo in the Fault-Controlled Ore Zone of the Yidinan Gold Deposit, Gansu Province, China

A mineral deposit forms because of a combination of complex geologic processes, and this makes it difficult to confirm effectively the presence of ore bodies below the surface. Primary haloes are commonly utilized in mineral exploration as an indicator of the presence of blind ore bodies. Three basic types of zoning occur in primary haloes of mineral deposits, namely axial, longitudinal and transversal. The study of axial zoning is particularly important for deep ore prospecting because it is usually linked to the flow direction of ore-bearing fluids. In this study, multi-element geochemical data were used to analyze the axial variation of primary halos in the Yidinan gold deposit, and a future prospecting target was proposed. A novel method is proposed that combines a correlation matrix and cluster analysis to characterize correlations among various elements. In addition, Gregorian's method was used to calculate the axial zonality series, and the contrast coefficient of the elements on the 14 different elevations of the No. 4 gold-bearing quartz vein was used to study the axial variations of indicator elements. It is proposed that the front halo elements of ore bodies are As, Sb, Bi and Hg, the near-ore halo elements are Au, Ag, Cu, Pb, Zn and Sn, and the tail halo elements are Ti, Co, V, Ni, Mo and W. Finally, based on the zonal concentration of each element and the axial variation of the contrast coefficient of each element with depth, it is speculated that four ore-enrichment regions are present in the No. 4 gold-bearing quartz vein. The study showed that the formation of a primary halo with an ideal element distribution occurred after the establishment of two main metallogenic stages and that other processes that cause strong superimposition of mineralization may occur at depth of the deposit.

Bioaccumulation of vanadium (V), niobium (Nb) and tantalum (Ta) in diverse mangroves of the Indian Sundarbans

Vanadium (V), niobium (Nb), and tantalum (Ta), recognized as Technology-Critical Element (TCE), are highly growing in demand for industrial development. Despite their economic relevance, little is known about their environmental concentrations, especially in marine ecosystems like mangroves. This paper describes concentrations and distribution patterns of Group Va elements (V, Nb and Ta) in plant organs and sediments from diverse mangroves of the Indian Sundarbans. Sediment cores and plant organs of eight dominant mangrove species were sampled and analyzed for V, Nb and Ta by ICP-MS. Stable carbon isotope (δ13C) in mangrove leaves were analyzed by EA-IRMS. Mean concentrations (mg kg−1) of V, Nb and Ta decreased in the order V (84.7 ± 12.5) > Nb (37.5 ± 4) > Ta (3 ± 0.8) in the sediment and V (0.6 ± 0.6) > Nb (0.02) > Ta (0.002) in the mangrove plants. Species-specific variability in bioaccumulation factor (V: 0.012–0.035; Nb: 0.001–0.003; Ta: 0.001–0.005), translocation factor (V: 0.5–5.1; Nb: 0.26–7.06; Ta: 0.22–2.56) and enrichment factor (V: 0.008–0.027; Nb: 0.0002–0.001; Ta: 1.0 × 10−5-3.0 × 10−6) indicated different partitioning of Group Va elements within the plant organs and varying degree of mangrove uptake efficiency. Results showed a general decrease in V, Nb and Ta concentrations with their increasing atomic weight. Their total concentrations in plants were related to the degree of enrichment of substrate sediments. The phytoextraction capacity varied amongst mangrove species depending on their CO2 uptake efficiency. Given increased demand for TCEs, results may have important implications for bioremediation processes.

Quantifying the Distribution Characteristics of Geochemical Elements and Identifying Their Associations in Southwestern Fujian Province, China

The distribution of geochemical elements in the surficial media is the end product of geochemical dispersion under complex geological conditions. This study explored the frequency and spatial distribution characteristics of geochemical elements and their associations. It quantifies the frequency distribution via mean, variance, skewness and kurtosis, followed by measuring the spatial distribution characteristics (i.e., spatial autocorrelation, heterogeneity and self-similarity) via semivariogram, q-statistic and multifractal spectrum, and further identify the elemental associations based on these distribution parameters using hierarchical clustering. A criterion was defined to identify the importance of parameters in the clustering procedure. A case study processing a geochemical dataset of stream sediment samples collected in southwestern Fujian province of China was carried out to illustrate and validate the procedure. The results indicate that studies of the frequency and spatial distribution characteristics of geochemical elements can enhance the knowledge of geochemical dispersions. The associations identified based on the frequency and spatial distribution parameters are different from those obtained by conventional cluster analysis. Spatial distribution characteristics cannot be neglected when investigating the distribution patterns of geochemical elements and their associations. The findings can enhance the knowledge of the geochemical dispersion in the study area and might benefit the following-up mineral exploration.

Trace and Rare Earth Element Distribution and Mobility During Diagenetic Alteration of Volcanic Ash to Bentonite in Eastern Iranian Bentonite Deposits

AbstractThe chemical composition of the source magma along with the physiochemical conditions of the depositional environment are the main controlling factors in determining the behavior and mobility of trace elements and rare earth elements (REEs) during the transformation of volcanic ash to bentonite. The purpose of the present study was to determine the distribution pattern and mobility of trace elements and REEs in several bentonite deposits formed by diagenetic alteration of volcanic ash in shallow alkaline water in eastern Iran. Using geochemical and statistical data, the degree of weathering in the parent rocks and the distribution and mobility of trace elements and REEs during the alteration process at seven deposits (Chah-Taleb, Chah-Keshmir, Chah-Golestan, Chah-Pirouz, Gholeh-Gelia, Kharman-Sar, and Khal-Kooh) were studied. None of the parent rocks showed an advanced degree of depositional reworking and, therefore, their chemical composition is representative of the volcanic ash from which the bentonites were formed. In the chondrite-normalized REE patterns of both parent rocks and bentonites, the light rare earth elements (LREEs) were found to be enriched relative to the heavy rare earth elements (HREEs). The variation in δEu and δCe values suggested a high-temperature (<200°C), suboxic, aquatic environment in which the conversion of volcanic ash to bentonite occurred. In the bivariate correlation analysis, Si showed a strong inverse relationship with Al and LREEs, while large ion lithophile elements (LILEs), high field strength elements (HFSEs), HREEs, and LREEs displayed a positive correlation between the elements of their respective groups. The R2 values in the binary diagram of potential immobile elements against Al suggest a qualitative classification in which Ti, Gd, Ga, Pr, Tb, Nd, Sm, Ce, and Nb are considered immobile, and U, Dy, In, Sc, Hf, Zr, La, and Eu are considered to have had poor mobility during formation of the Eastern Iranian bentonite deposits.

Subcellular Chemical Imaging: New Avenues in Cell Biology.

To better understand the physiology and acclimation capability of the cell, one of the great challenges of the future is to access the interior of a cell and unveil its chemical landscape (composition and distribution of elements and molecules). Chemical imaging has greatly improved in sensitivity and spatial resolution to visualize and quantify nutrients, metabolites, toxic elements, and drugs in single cells at the subcellular level. This review aims to present the current potential of these emerging imaging technologies and to guide biologists towards a strategy for interrogating biological processes at the nanoscale. We also describe various solutions to combine multiple imaging techniques in a correlative way and provide perspectives and future directions for integrative subcellular imaging across different disciplines.

Oligocene-Miocene high Sr/Y magmatism and implications for deep processes of Qulin pluton in Gangdese batholith, southern Tibet

曲林岩体位于冈底斯带中段的南缘，为渐新世-中新世复合岩体，主体为粗粒花岗斑岩，被后期煌斑质、花岗闪长质和花岗质岩脉切割，是多期岩浆作用的产物，出露面积约8km²。花岗斑岩两组样品（T0849-PG和T0849-G）的锆石U-Pb定年结果分别为29.7±0.1Ma和30.0±0.2Ma。花岗斑岩为高钾，准铝质，低MgO，高度富集轻稀土元素（LREE）和大离子亲石元素（LILE），亏损重稀土元素（HREE）和高场强元素（HFSE）。此外具有高Sr、Sr/Y、（La/Yb）_N；低Y和Yb，弱Eu负异常等特征。岩体内发育一系列近南北向展布的花岗闪长玢岩脉，其中两组样品的锆石U-Pb定年结果分别为15.5±0.1Ma（T0848-PY）和14.4±0.1Ma（T0850）。两条花岗闪长玢岩脉具有与岩体主体相似的稀土和微量元素分布模式，同样富集轻稀土及大离子亲石元素，亏损重稀土及高场强元素。花岗斑岩的⁸⁷Sr/⁸⁶Sr_（i）=0.706102~0.706202，ε_Nd（t）=-0.6~+0.6，锆石ε_Hf（t）=+4.9~+7.9；花岗闪长玢岩脉的⁸⁷Sr/⁸⁶Sr_（i）=0.705429~0.705474，ε_Nd（t）=-1.4~-0.2，锆石ε_Hf（t）=+2.6~+7.6。本文数据和文献数据结果表明：曲林花岗斑岩与花岗闪长玢岩脉均来源于加厚南拉萨下地壳的部分熔融，很可能与增厚的深部岩石圈的拆沉或俯冲印度岩石圈的撕裂诱发软流圈上涌有关。;The Qulin pluton is located at the southern edge of the middle part of Gangdese belt. As an Oligocene-Miocene pluton, its main body is coarse-grained granite porphyry, which was later staged by lamproitic, granodioritic, and granitic dikes which are the products of multi-stage magmatism, with an exposed area of about 8km². The zircon U-Pb dating results of two samples of granite porphyry are ~30Ma. Whole rock geochemical studies show that granite porphyry is high potassium and quasi-aluminum, characterized by low MgO together with enriched light rare earth elements (LREE) and large ion lithophile elements (LILE), depleted heavy rare earth elements (HREE) and high field strength elements (HFSE). In addition, it has the characteristics of high Sr, Sr/Y, (La/Yb)_N; low Y and Yb, and weak Eu negative anomaly. A series of nearly N-S trending granodiorite porphyrite dikes occur in the pluton, among which the zircon U-Pb dating results of two samples are 15.5±0.1Ma and 14.4±0.1Ma, respectively. They have similar distribution patterns of rare earth and trace elements as the main body of pluton. And they are also rich in LREE and LILE, along with depleting HREE and HFSE. The ⁸⁷Sr/⁸⁶Sr_(i) values of granite porphyry range from 0.706102 to 0.706202, ε_Nd(t) of which from -0.6 to +0.6, and zircon ε_Hf(t) of which from +4.9 to +7.9; while for granodiorite porphyrite dikes, the ⁸⁷Sr/⁸⁶Sr_(i) values range from 0.705429 to 0.705474, ε_Nd(t) from -1.4 to -0.2, and zircon ε_Hf(t) from +2.6 to +7.6. The new data and literature data results show that: both the granite porphyry and granodiorite porphyrite dikes of the Qulin pluton origined from the partial melting of the thickened lower crust beneath Lhasa terrane, possibly related to the upwelling of asthenosphere induced by delamination of thickened lithosphere or tearing of the Indian lithospheric slab.

Early Jurassic Mafic Intrusions in the Southern Youjiang Basin, SW China: Petrogenesis, Tectonic and Metallogenic Implications

A suite of mafic intrusions, composed of diabase and micro-gabbro outcrops in the Jingxi area of southern Youjiang Basin, SW China. This study conducts geochronological, geochemical, and Sr–Nd isotopic analyses on the mafic intrusions in Jingxi with the aim of determining their petrogenesis, tectonic setting, and metallogenic implications. Zircon U–Pb dating for the mafic intrusions yielded an age of 183 ± 3 Ma (MSWD = 2.3), which is coeval with the Carlin-like gold mineralization in the Youjiang Basin. The mafic intrusions are alkaline in composition and characterized by low TiO2 (1.25–1.87 wt %) contents and low Ti/Y ratios (410–550). They exhibit OIB-like patterns of trace element distribution and they have low (87Sr/86Sr)i ratios of 0.704341 to 0.705677, slightly negative εNd(t) values of −0.30 to −2.16, low La/Ta (11.57–15.66) and La/Nb (0.77–1.06) ratios, with [La/Yb]N = 6.52–10.63. The geochemical characteristics, combined with regional considerations, suggest that the mafic intrusions originated from partial melting of upwelling asthenosphere within the garnet-spinel transition zone, as a result of intracontinental back-arc extension triggered by the steep subduction of the Paleo-Pacific plate beneath the South China Block. Moreover, the new data not only suggest Early Jurassic magma was a possible heat source, but also support a magmatism-related model for the Carlin-like gold mineralization in the Youjiang Basin.

Lithium isotopic compositions of post-collisional mafic–ultramafic rocks from Dabieshan, China: Implications for recycling of deeply subducted continental crust

Lithium (Li) isotopes are potential tracers of processes related to crust–mantle interaction and recycled crustal materials. Previous studies have reported that Li isotopic compositions of island arc lavas are similar to those of fresh mid-ocean-ridge basalts (MORBs), although the former are expected to record high slab-derived δ7Li values caused by fluid metasomatism. However, it is unclear whether Li isotopic signatures of subducted continental crust were transported to mantle depths and preserved there. For clarification, we determined whole-rock major and trace element, and Li isotopic compositions of post-collisional mafic–ultramafic rocks from northern Dabieshan, China. The analyzed samples have high MgO (up to 20.67 wt%) and low SiO2 (41.06–56.20 wt%) contents, and arc-like trace element distribution patterns, suggesting derivation by partial melting of fertile mantle sources. The samples have δ7Li values of −2.9 to +7.2‰ (average = +2.7‰, n = 42) and Li concentrations of 2.50 to 28.1 μg/g (average = 9.20 μg/g), both of which are beyond the relatively limited ranges of mantle values (δ7Li = +2.9 to +4.3‰, average = +3.5 ± 1.0‰, and Li = 1.20 ± 0.10 μg/g). Excluding possible effects of wall-rock assimilation and contamination, magmatic crystallization, and Li isotopic fractionation during subduction–exhumation processes, the observed Li isotopic heterogeneity is most likely related to the recycling of crustal materials. Based on a comparison with Li isotopic compositions of ultrahigh-pressure (UHP) metamorphic rocks from the Dabie–Sulu orogenic belt and terrestrial sediments, we suggest that the recycled continental crustal materials likely comprised gneisses, sediments, eclogites, and/or minor carbonate rocks (i.e., marbles). Our study demonstrates that Li isotopes may provide a novel means of tracing deeply subducted continental materials.

Integrated major and trace element study of clinopyroxene in basic, intermediate and acidic volcanic rocks from the middle Okinawa Trough: Insights into petrogenesis and the influence of subduction component

Magmatism is very common in the Okinawa Trough. However, the influence of magmatic processes, including fractional crystallization and magma mixing, on the petrogenesis of volcanic rocks is poorly understood. The in situ major and trace element compositions of clinopyroxene in co-genetic basalts, andesites, trachyandesites and rhyolites from the Iheya Ridge in the middle Okinawa Trough are examined to determine their petrogenesis and the influence of slab subduction. Regarding the types of mineral zoning, in basalt and andesite, clinopyroxene phenocrysts are unzoned. In trachyandesite, the clinopyroxene phenocrysts can be classified into three groups: normal zoned, oscillatory zoned and unzoned. Similarly, unzoned and reverse zoned clinopyroxene phenocrysts are the two main structures in rhyolites. According to the major element contents and distinct distribution patterns of rare earth elements (REEs), we identify various clinopyroxene domains in their host volcanic rocks. Type 1 clinopyroxene domains in basalts and trachyandesites are dark, have high Mg# values and are strongly depleted in light REEs (LREEs) with no significant Eu anomalies. The Type 2 clinopyroxene domains in basalts and trachyandesites and all clinopyroxene phenocrysts in andesites are bright, have low Mg# values and are strongly depleted in LREEs and have significant negative Eu anomalies. Clinopyroxene domains in rhyolites have significant negative Eu anomalies and can be divided into two types: Type 1 clinopyroxene domains are characterized by strong depletion in LREEs, Sr, P and high field strength elements (HFSEs), while Type 2 clinopyroxene domains are slightly depleted in LREEs and have small negative P anomalies. The continuously changing major element composition and parallel distribution of trace element spider diagrams suggest that all these clinopyroxene phenocrysts in the studied volcanic rocks were derived from co-genetic magmas and the compositional transition of clinopyroxene from basalts to rhyolites attributed to different extents of fractional crystallization of various minerals (e.g., clinopyroxene, orthopyroxene, plagioclase and apatite). The oscillatory zoned and reversed zoned clinopyroxene phenocrysts show that magma mixing and recharge events with co-genetic magmas are common in the middle Okinawa Trough magma system. The origin of clinopyroxene phenocrysts involves contributions from subducted sedimentary components of 2.5% sediment melts and 1.5% sediment fluids and is deduced based on the equilibrium melts of clinopyroxene phenocrysts in basalts. The geochemical study of clinopyroxene provides evidence for the contributions of magmatic processes and slab subduction to the petrogenesis of Okinawa Trough volcanic rocks.

Comparative geochemical study of the cherty rocks of the Taukha terrane (Sikhote-Alin) and its paleogeodynamic significance

The article presents the results of a comparative geochemical study of cherts and siliceous–clayey rocks composing the tectono-sedimentary complexes of various structural levels of the Taukha terrain of the Sikhote-Alin Late Jurassic–Early Cretaceous accretionary prism. The data obtained show that the same-aged parts of the cross-sections of the cherty–terrigenous sequences of the terrane lower and middle structural levels are characterized by significantly different contents and distribution patterns of major petrogenic oxides, trace, and rare-earth elements due to their accumulation in various facies of oceanic zones. The set of geochemical data indicates that the formation of both tectono-sedimentary complexes was carried out differently, gradually replacing each others’ facies oceanic zones, and started in the near-spreading ridge area, then in the pelagial, and completed in the continental-margin deposition environment. Based on the time interval of the facies conditions changing for each complex (i.e., time of transition from one facies zone to another), the speeds of a paleo-oceanic plate motion (and, correspondingly, the speeds of spreading) for individual intervals of the Jurassic were calculated. Differences in the spreading speeds at various sites of a paleorift zone caused the turning of a paleocontinent margin contour and spreading ridge axis at the perpendicular position, which in turn caused change of the geodynamic mode on the eastern margin of the Paleo-Asian continent at the Jurassic–Cretaceous transition.

Epigenetic geochemical dynamics and driving mechanisms of distribution patterns of chemical elements in soil, Southwest China

Epigenetic geochemical dynamics and driving mechanisms of distribution patterns of chemical elements in soil, Southwest China

Trace element associations in magnetite and hydrothermal pyrite from the Geita Hill gold deposit, Tanzania

Gold mineralization in the Geita Hill deposit is associated with pyrite formed along microfracture networks and sulfidation fronts together with K-feldspar and biotite. The sulfidation fronts are best developed in magnetite-bearing ironstone. The gold is present mainly as electrum and gold tellurides along grain boundaries, and as inclusions in pyrite, quartz, biotite and K-feldspar. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of pyrite and magnetite grains reflect complex fluid-host rock interactions. Magnetite textures and chemistry change with alteration intensity, indicating the progression of the alteration front into the host rock. Pyrite textures are uniform across all rock types and reflect late-tectonic growth linked to multi-staged infiltration of hydrothermal fluids. Trace element distribution patterns in pyrite are locally complex and influenced by host rock chemistry.Gold distribution patterns in pyrite correlate closely with Te, Ag, Bi and Pb, indicating that gold occurs in micro- and nano-inclusions of telluride minerals. This is especially so for gold in quartz veins, whereas gold in ironstone and diorite also occurs as electrum with an average Au/Ag ratio of 0.41. As, Co and Ni in pyrite are lattice bound and occur in high concentrations in ironstone and diorite where they show characteristic growth zoning patterns. Pyrite in quartz veins has As, Co and Ni concentrations that are low and variable. Cr, Cu, Mo, Mn and Zn are present in all rock types in isolated inclusions in pyrite grains, whilst Pb, Bi and Sb occur in more dispersed patches of fine clustered inclusions. The Se content in pyrite is typical for Archean gold deposits, and reflects an average temperature of ~340 °C for the mineralizing fluid. The Co/Ni ratio of pyrite grains varies between 0 and 5.2 in ironstone and diorite, and most likely reflects the equilibration Co/Ni ratio of the host rock. The Co/Ni ratio of pyrite grains in quartz veins varies between 1 and 12, and is consistent with a magmatic-hydrothermal origin for the ore fluid. Trace element distribution patterns in magnetite and pyrite indicate that As, Ni, Co, Cr, Mn and Cu were mostly locally derived, and remobilised into the pyrite during sulfidation of the host rock. The concentrations of these elements are strongly lithologically controlled, and they are not consistently incorporated into the pyrite after initial stages of growth. Au, Ag, Te, Bi and Pb were externally derived, and closely correlate in all varieties of pyrite as well as strongly altered magnetite. The alteration footprint of the Geita Hill deposit is limited in extent, and does not involve As and Sb that are typically enriched in Archaean lode-gold systems. Instead, Te and Bi are most characteristic for the deposit and could be of use as path finder elements together with altered magnetite grains.

Late-Mesozoic tectonic evolution and magmatic history of the Zhe-Gan-Wan region, SE China: evidence from the Shiling rhyolite and other Yanshanian granitoids

Yanshanian granitoids (178–120 Ma, Jurassic to Cretaceous), which intruded into Precambrian crystalline base- ment and Paleozoic strata, are widely distributed at the junction of the Zhejiang, Jiangxi and Anhui provinces (the ZGW region) in southern China, along with coeval volcanic rocks. This paper summarizes zircon U–Pb age data, geochemi- cal characteristics and Sr-Nd isotopic characteristics of the Late Jurassic to Middle Cretaceous granitoids and volcanic rocks from the ZGW region. We demonstrate that members of the Shiling rhyolite formed during two different periods of magmatic activity at 154.7 ± 2.5 Ma and 139–134 Ma and that igneous rocks from the different periods have distinct geochemical characteristics. Jurassic igneous rocks of the ZGW region have relatively low SiO2and high Al 2O3contents, and show enrichment of large ion lithophile elements (LILEs) and depletion of high field strength elements (HFSEs). They are strongly enriched in LREE and depleted in HREEs with weakly negative Eu anomalies and strongly negative Nb, Ta anomalies. Rb and Y concentrations follow the trends of I-type and S-type granites. By contrast, Cretaceous igneous rocks of this region are characterized by high SiO2and low Al2O3contents with negative Eu anomalies. They have typical wing- shaped rare earth element (REE) distribution patterns and show enrichment of Rb, Th, U, Nb, Ta and depletion of Ba, Sr, P and Ti. They have affinity to A-type peraluminous granites or highly-fractionated felsic rocks. Overall, the igneous rocks evolved from high-Sr low-Yb to low-Sr high-Yb, which might reflect the evolution of the tectonic setting from subduction to lithospheric extension/thinning, i. e., a transition from a continental margin subduction setting during the Late Jurassic to a within-plate extensional setting during the Early Cretaceous, at c. 142 ± 3 Ma. The repeated alternation between lava extrusion and extension and extensional fault kinematics in the late Mesozoic is related to the changes of direction and rate of plate movement of the Izanagi and Pacific plates.

Tectonic transition from oceanic subduction to continental collision: New geochemical evidence from Early-Middle Triassic mafic igneous rocks in southern Liaodong Peninsula, east-central China

AbstractIn contrast to the widespread occurrence of mafic arc magmatism during oceanic subduction, there is a general lack of such magmatism during continental subduction. This paradigm is challenged by the discovery of Early-Middle Triassic mafic igneous rocks from the southeastern margin of the North China Block (NCB), which was subducted by the South China Block (SCB) during the Triassic. Zircon U-Pb dating for these mafic rocks yields 247 ± 2–244 ± 5 Ma for their emplacement, coeval with the initial collision between the two continental blocks. These Triassic mafic rocks generally exhibit ocean island basalt (OIB)-like trace element distribution patterns, intermediate (87Sr/86Sr)i ratios of 0.7057–0.7091, weakly negative εNd(t) values of –1.2 to –3.8, and εHf(t) values of –1.3 to –3.2. Such geochemical features indicate origination from a metasomatic mantle source with involvement of felsic melts derived from dehydration melting of the previously subducting Paleo-Tethyan oceanic crust. The syn-magmatic zircons of Triassic age show variable Hf-O isotopic compositions, indicating that the crustal component was composed of both altered basaltic oceanic crust and terrigenous sediment. High Fe/Mn and Zn/Fe ratios suggest that the mantle source would mainly consist of ultramafic pyroxenites. The melt-mobile incompatible trace elements were further fractionated relative to melt-immobile trace elements during partial melting of these pyroxenites, giving rise to basaltic melts with OIB-like geochemical signatures. The mafic magmatism may be caused by tectonic extension due to rollback of the subducting Paleo-Tethyan oceanic slab in response to the initial collision of the NCB and SCB in the Early Triassic. Therefore, the syn-subduction mafic magmatism provides new geochemical evidence for tectonic transition from oceanic subduction to continental collision in east-central China.