Mud Volcanic Fluids of the Kerch–Taman Region: Geochemical Reconstructions and Regional Trends. Communication 1: Geochemical Features and Genesis of Mud-Volcanic Waters

Lithology and Mineral Resources - The chemical and isotopic characteristics (δ18O and δ2H) of water from 42 mud volcanoes of the Kerch–Taman region (Crimean–Caucasus district)...     

Geochemical Characteristics and Metallogenesis of Volcanic Rocks as Exemplified by Volcanic Rocks in Ertix,Xinjiang

Volcanic rocks in Ertix,Xinjiang,occurring in the collision zone between the Siberia Plate and the Junggar Plate,are distributed along the Eritix River Valley in northern Xinjiang.The volcanic rocks were dated at Late Paleozoic and can be divided into the spilite-keratophyre series and the basalt-andesite series.The spilite-keratophyre series volcanic rocks occur in the Altay orogenic belt at the southwest margin of the Siberia Plate.In addition to sodic volcanic rocks.There are also associated potassic-sodic volcanic rocks and potassic volcanic rocks.The potassic-sodic volcanic rocks occur at the bottom of the eruption cycle and control the distribution of Pb and Zn deposits.The potassic volcanic rocks occur at the top of the eruption cycle and are associated with Au and Cu mineralizations.The sodic volcanic rocks occur in the middle stage of eruption cycle and control the occurrence of Cu(Zn) deposits.The basalt-andesite series volcanic rocks distributed in the North Junggar orogenic belt at the north margin of the Junggar-Kazakstan Plate belong to the potassic sodic volcain rocks.The volcanic rocks distributed along the Ulungur fault are relatively rich in sodium and poor in potassium and are predominated by Cu mineralization and associated with Au mineralization.Those volcanic rocks distributed along the Ertix fault are relatively rich in K and poor in Na,with Au mineralization being dominant.     

REE Geochemical Characteristics of Volcanic Rocks in Zhejiang and Jiangxi Provinces and Their Gological Significance

Based on the data of 64 samples ,the REE geochemical characteristics of volcanic rocks in northern Zhejiang and eastern Jiangxi provinces are discussed in this paper.The REE distribution patterns in acid and intermediate-acid volcanic rocks in these areas display some similarities,as indicated by rightward-inclined V-shaped curves with negative Eu anomalies,which are parallel to earch other.In addi-tion,their REE parameters(ΣREE,ΣLREE/ΣHREE,δEu,Ce/Yb,La/Sm,La/Yb,etc)also va-ry over a narrow range with small deviations.HREE are particularly concentrated in the volcanic rocks as-sociated with uranium mineralization.The initial ^87Sr/^86Sr ratio in the volcanic rocks is about 0.7056-0.7139.All these features in conjunction with strontium isotopic data indicate that the rock-forming materials come from the sialic crust.The REE distribution patterns and REE geochemical parameters of the volcanic rocks ,as well as La/Sm-La and Ce/Yb-Eu/Yb diagrams may be applied to the sources of rock-forming and ore-forming materials.     

Sr Isotope Composition of Mud Volcanic Waters in the Kerch–Taman Province

Doklady Earth Sciences - Waters at seventeen mud volcanoes of the Kerch–Taman province in the Northwestern Cis-Caucasus region have been analyzed for Sr isotope composition. The 87Sr/86Sr...     

Regional Geochemical Division—A Tool for Delineating Geochemical Block

INTRODUCTIONGeochemists need to study the spatial distribution of theassociations of the geochemical elements(AGE) to delineatethe geochemical blocks or recognize geochemical anomalies inregional geochemical exploration.Regional geochemical divi-sion (RGD) is a mapping technique for the division of thestudy area into slices where the natural AGEs are relativelysimple and uniform.A practical approach to RGD is to digital-ly devide the collected geochemical samples into groups bymeans o…     

Geochemical Characteristics and Tectonic Setting of Ore-hosted Volcanic Rocks in Yindonggou Copper Ore Deposit, Gansu Province

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Geochemical Characteristics of Mid-oceanic Ridge Volcanic Glass from Lau Basin: Evidence from the Major Elements Variation

Orientale size craters are not recognized on Earth nor expected for Phanerozoic and Proterozoic eons from conventional crater size frequency distributions (Ivanov et al., 2002). Here suggested are three such Phanerozoic craters, modified by plate tectonics, and tentatively correlated with extinction and “ophiolite obduction” events. Hypothesis testing is proposed and plate tectonics implications are discussed. Such basins might manifest:

• circular to elliptical rims (or rim segments), with exposed lithospheric mantle, as strain markers for plate boundary motion;
• thick ejecta near rim expressed as “ophiolitic melange”;
• power law decay of ejecta thickness with radial distance from rim (McGetchin et al., 1973) and/or systematic azimuthal variation of ejecta thickness for low angle impacts (Schultz, 1999);
• weathering resistant shocked mantle minerals (Bohor et al., 1990) in ejecta;? global spherule layer with PGE anomalies (Alvarez et al., 1980);
• rim structures consistent with cratering mechanics (Melosh, 1989; Kenkmann, 2014);
• impact melt basement (Grieve et al., 1992; Pierazzo et al. 2000) recording uniform cooling age and Earth's magnetic polarity of the time. Tentatively suggested Phanerozoic impact basins:
• Yucatan Basin: Greater Antilles ophiolite rim – KPg Boundary? Maastrichtian ophiolite obduction in southeast Cuba (Iturralde‐Vinent et al., 2006).
• Sulu Sea Basin: Palawan, Sabah etc. ophiolite rim – Middle Miocene Disruption? MM ophiolitic mélange emplacement in Sabah (Clennell, 1991).
• Loyalty Basin: New Caledonia ophiolite and d'Entrecasteaux ridge rim – EO Boundary? EO ophiolite obduction in New Caledonia (Cluzel et al., 2012).

     

Chronological and Geochemical Characterisitics of Volcanic Rocks of the Yingcheng Formation in the Southern Songliao Basin: Constraints on the Early Cretaceous Evolution of the Songliao Basin

The discoveries of oil and gas reservoirs in the volcanic rocks of the Songliao Basin(SB) have attracted the attention of many researchers. However, the lack of studies on the genesis of the volcanic rocks has led to different opinions being presented for the genesis of the SB. In order to solve this problem, this study selected the volcanic rocks of the Yingcheng Formation in the Southern Songliao Basin(SSB) as the research object, and determined the genesis and tectonic setting of the volcanic rocks by using LA-ICP-MS zircon U-Pb dating and a geochemical analysis method(major elements, trace elements, and Hf isotopes). The volcanic rocks of the Yingcheng Formation are mainly composed of rhyolites with minor dacites and pyroclastic rocks. Our new zircon U-Pb dating results show that these volcanic rocks were erupted in the Early Cretaceous(113–118 Ma). The primary zircons from the rhyolites have εHf(t) values of +4.70 to +12.46 and twostage model age(TDM2) of 876–374 Ma. The geochemical data presented in this study allow these rhyolites to be divided into I-type rhyolites and A-type rhyolites, both of which were formed by the partial melting of the crust. They have SiO2 contents of 71.62 wt.%–75.76 wt.% and Al2 O3 contentsof 10.88 wt.% to 12.92 wt.%. The rhyolites have distinctively higher REE contents than those of ordinary granites, with obvious negative Eu anomalies. The light to heavy REE fractionation is not obvious, and the LaN/YbN(average value = 9.78) is less than 10. The A-type rhyolites depleted in Ba, Sr, P, and Ti, with relatively low Nb/Ta, indicating that the rocks belong A2 subtype granites formed in an extensional environment. The adakitic dacites are characterized by high Sr contents(624 to 1,082 ppm), low Y contents(10.6 to 12.6 ppm), high Sr/Y and Sr/Yb ratios, and low Mg# values(14.77 to 36.46), indicating that they belong to "C" type adakites. The adakitic dacite with high Sr and low Yb were likely generated by partial melting of the lower crust under high pressure conditions at least 40 km depth. The I-type rhyolites with low Sr and high Yb, and the A-type rhyolites with very low Sr and high Yb, were formed in the middle and upper crust under low pressure conditions, respectively. In addition, the formation depths of the former were approximately 30 km, whereas those of the latter were less than 30 km. The geochemical characteristics reveal that the volcanic rocks of Yingcheng Formation were formed in an extensional environment which was related to the retreat of subducted Paleo-Pacific Plate. At the late Early Cretaceous Period, the upwelling of the asthenosphere mantle and the lithosphere delamination caused by the retreat of the subducted Paleo-Pacific Plate, had resulted in lithosheric extension in the eastern part of China. Subsequently, a large area of volcanic rocks had formed. The SB has also been confirmed to be a product of the tectonic stress field in that region.     

Geochemical Characteristics of Cenozoic Basaltic High-K Volcanic Rocks from Maguan Area, Eastern Tibet

The major element, trace element and Nd-Sr isotopic composition of Cenozoic basaltic volcanic rocks from the Maguan area, eastern Tibet, indicates that the volcanic rocks are enriched in alkalis, especially K (K2O up to 3.81%) and depleted in Ti (TiO2 = 1.27%-2.00%). These rocks may be classified as two groups, based on their Mg# numbers: one may represent primary magma (Mg# numbers from 68 to 69), and the other, the evolved magma(Mg# numbers from 49 to 57). Their REE contents are very high (∑REE = 155.06-239.04μg/g). Their REE distribution patterns are of the right-inclined type, characterized by LREE enrichment [(La/Yb)N =12.0-19.2], no Ce anomaly (Ce/Ce*=1.0), and weak negative Eu anomaly (Eu/Eu*=0.9). The rocks are highly enriched in Rb, Sr and Ba (59.5-93.8μg/g, 732-999 μg/g, and 450-632 g/g, respectively), high in U and Th (1.59-2.31μg/g and 4.73-8.16 μg/g, respectively), and high in Nb, Ta, Zr and Hf (70-118 μg/g,3.72-5.93 μg/g, 215-381 μg/g, and 5.47-9.03 μg/g, respectively). In the primitive mantle-normalized incompatible element spidergram, Nb, Ta, Zr, Hf and P show positive anomalies, whereas Ba, Ti and Y show negative anomalies. The 87Sr/86Sr ratios range from 0. 704029 to 0.704761; 143Nd/144Nd from 0. 512769 to 0. 512949; and εNd from 2.6 to 6.1. These geochemical features might suggest that the potential source of the basaltic high-K volcanic rocks in the Maguan area is similar to the OIB-source mantle of Hawaii and Kergeulen volcanic rocks.     

Geochemical survey of Portugal: Comparative analysis of data from soils and stream sediments

This study reports some results of a low density geochemical survey covering the entire country, taking both topsoils and active stream sediments as the sampling media. Standardized methods for sampling, sample preparation, analysis and analytical quality…     

Geochemical Characteristics of the Cenozoic Volcanic Rocks in Central Qiangtang, Tibet: Relation with the Uplift of the Qinghai Tibet Plateau

1. Introduction The uplift and evolution of the Qinghai Tibet Plateau has been the most important projects for studying the dynamic process of the plateau, and the uplift mechanism and history are the essential problems. Researches have been done extensively in terms of tectonics, sedimentology, geophysics, paleontology, paleoclimate and paleomagnetism for several tens of years. Many evolution models have been suggested but so far none of them have been explained perfectly. In recent years,…     

Geochemical Characteristics of Volcanic Rocks of the Laochang Ag Polymetallic Deposit,Lancang,Yunnan Province,China

In terms of major element, trace element and REE geochemical characteristics ofvolcanic rocks in the area studied and by making use of the TiO2-K2O-P2O5,The-Hf-Ta and Zr-Nb-Y trianglar diagrams and the environmental discrimination diagrams of incompatible ele-ment distribution pattems,the authors have drawn some conclusions that are different from those by previous workers.It is concluded that volcanic rocks in the Laochang Ag polymetallic deposit at Lancang,Yunnan belong to continental within-plate alkali basalts, and that their geotectonic setting seems to be at the northeastern margin of East Gondwana Land.     

Geochemical Features of the Two Early Paleozoic Ophiolitic Zones and Volcanic Rocks in the Central —Southern Tianshan Region ,Xinjiang

This paper deals with the geochemical features of the two Early Paleozoic ophiolite zones in the central-southem Tianshan region and the central Tianshan igneous rock belt between them.Study results suggest that the central Tianshan belt was an Ordovician volcanic arc with an affinity of continental crust, and the Kumux-Hongluhe ophiolitic zone that is located on the southern margin of central Tianshan has a crustal affinity to back-arc marginal sea.The Aqqikkudug-Weiya ophiolitic zone is an accretionary boundary between the Tuha continental block and the central Tianshan volcanic arc during Late Silurian to Devoniann;Ordovician ophi-olitic blocks,Silurian flysch sequence and HP metamorphic rock relics are distributed along the Aqqikkudug-Weiya zone.Geochemically,ophiolitic rocks in the Aqqikkudug-Weiya zone have an affinity to oceanic crust,reflecting a tectonic setting of paleo-trench or subduction zone .The Early Carboniferous red molasses were deposited unconformably on the pre-Carboniferous meta-mrophosed and ductile sheared volcanic and flysch rocks,providing an upper limit age of the central and southern Tianshan belts.     

Compositional Variation of Hydrothermally Altered Volcanic Rocks in Hishikari Gold Epithermal System: A Useful Geochemical Indicator of Gold–Silver Epithermal Mineralization

The hydrothermally altered andesite hosting the Hishikari gold-silver vein deposits in southern Kyushu, Japan, is analyzed with respect to the spatial variation in chemical composition. The (CaO + Na₂O) content is found to be inversely correlated with the K₂O content as it progresses away from the site of mineralization. It was found that analytical data plotted on a (CaO + Na₂O) − K₂O diagram cannot be explained only by addition of K⁺ from the hydrothermal solution to the original rock and release of Ca²⁺ and Na⁺ from the original rock (K- alteration). Addition of Ca²⁺ and Na⁺ from the hydrothermal solution to the rock and release of K⁺ from the rock but release of K⁺, Ca²⁺, and Na⁺ to the hydrothermal solution (advanced argillic alteration) is important for causing the wide variations in K₂O, CaO, and Na₂O contents on the (CaO + Na₂O) − K₂O diagram. These variations can be explained by superimposed potassic, advanced argillic and calcium alterations. The altered rocks in the Honko-Sanjin area, Yamada area, and Masaki area analyzed by this study are characterized by their intermediate K₂O content and variable CaO content, high K₂O content and low CaO content, and low K₂O content and low CaO content, respectively. The K₂O, Na₂O and CaO contents and oxygen isotopic composition of altered andesite, in conjunction with the solubility of gold as a thio complex, suggest that both gold deposition and the observed compositional variation of altered andesite are the result of mixing between acidic groundwater and neutral gold-bearing hydrothermal solution. The present results indicate that the compositional variation of hydrothermally altered rocks may represent a useful geochemical indicator of epithermal gold–silver mineralization.     

Geochemical Characters of Selenium，Fluorine and Human Health

通过研究中国土壤、水系沉积物、浅层地下水、粮食、人发中硒和氟的丰度特征，探讨了氧化还原电位、酸碱度等环境参数及母质的元素组分对硒、氟元素迁移、转化、赋存状态的影响，得出硒、氟等不同元素组合与克山病、大骨节病及肝癌等疾病有关的结论。关键词硒氟环境地球化学     

Negative Haloes and Geochemical Field Systems of Hydrothermal Deposits

Primary haloes of hydrothermal deposits were previously considered as positive haloes. Although it has been recently suggested that primary haloes incude positive and negative ones, almost all the research work on primary haloes has still focused on positive haloes for various reasons. In order to understand the source of ore substances a number of large hydrothermal deposits related to magmatism including porphyry, skarn and vein type deposits have been studied. It has been found that negative haloes exist on the peripheries of positive haloes of a mineral deposit. On the basis of the study the authors propose the concept of the geochemical field system of ore-forming elements of hydrotherreal deposits, i. e., with the orebody as the centre outwards there occur the mineralized field, positive halo field, depleted field and background field successively.     

Geochemical Characteristics and Sedimentary Environment of the Salawusu Section

The chemical compositions of and the contents of CaCO3, free Fe2O3 and REE in the sediments of the Salawusu section have been analyzed to investigate the geochemical features of different sedimentary facies and explore their sedimentary enironmetnts during the Late Pleistocene.The con-tents of CaCO3, free Fe2O3 and ∑REE in lacustrine deposits of the middle part of the section are higher than those in the other parts ,except SiO2 which shows an opposite trend.According to the distribution characteristics of the components mentioned above, the section may be divided into four parts which are equivalent to those divided in terms of lithologic characters and sedimentary facies.More remarkable characteristics were observed with respect to the distribution of CaCO3, free Fe2O3,∑REE and SiO2/Al2O3 and FeO/Fe2O3 ratios, which can be adopted as the geochemical indices for paleoclimate division.From the above, four paleoclimate stages have been distinguished for the deposition process.The first stage ,dated at 0.20-0.15Ma, is characterized by a dry and cold climate,the second stage, ranging from 0.15 to 0.07 Ma ,by a warm and slightly dry climate,the third stage ,about 0.07-0.01Ma ,by a cold and humid climate;and prevailing in the last ten thorsand years is the fourth stage,with the climate changing graduall from warm-humid to warm-dry.     

Geochemical and Petrological Characteristics of the Kale (Gümüshane) Volcanic Rocks: Implications for the Eocene Evolution of Eastern Pontide Arc Volcanism,Northeast Turkey

The Kale (Gumushane) volcanic rocks crop out in the southern zone of the eastern Pontide arc, and consist mainly of agglomerate, andesite, minor basalt, and tuff associated with sediments (limestone, marl, siltstone, sandstone) deposited in a shallow basin environment. The volcanites show mainly porphyritic, hyalo-porphyritic, and rare fluidal and glomeroporphyritic textures. These volcanic rocks consist predominantly of plagioclase, augite, hornblende, and lesser biotite, magnetite, and quartz, and secondary products of chloritization, carbonation, sericitization, and epidotization. In general, they show disequilibrium textures, possibly reflecting magma-mixing processes.

The volcanic rocks are mainly calc-alkaline in composition, and show moderate potassium enrichment. Most of the major- and trace-element variations reflect the significant role of fractional crystallization during the evolution of the volcanic suite. The fractionating phases are dominantly hornblende and augite, minor plagioclase, and magnetite. The rocks have high LILE and LREE enrichments, but are relatively depleted in HFSE relative to MORB. Moreover, incompatible trace-element distributions show similarities to those of an E-type MORB source. The rocks have moderately fractionated REE patterns with (La/Lu)_N = 2–12. Geochemical data suggest that the volcanites evolved by shallow-level fractional crystallization and magma-mixing contamination of a parental magma derived from metasomatized upper mantle by partial melting after thickening of the Pontide arc during the Paleocene-Eocene. Furthermore, differentiation took place in a magma chamber situated in the thickened arc crust within an extensional tectonic regime.