Geochemistry International最新文献

The geochemical characteristics (REE, trace elements) and Sr and Nd isotopic composition of apatite from corundum-bearing metasomatites of the Khitoostrov occurrence (Belomorian Mobile Belt), associated plagioclasites, and host rocks represented by garnet amphibolites and kyanite–garnet–biotite gneisses of the Chupa sequence have been studied. Apatites from the corundum-bearing metasomatites and kyanite–garnet–biotite gneisses are enriched in medium REE and have a negative Eu anomaly (Eu/Eu* 0.20–0.35). Apatite from the corundum-bearing rocks differs from apatite from the gneisses of the Chupa sequence in the increased content of Sr, LREE, decreased content of HREE, as well as a lower ⁸⁷Sr/⁸⁶Sr(t) ratio and an increased ɛ_Nd(T) value: 0.70 865–0.70 896 and –9.3 ± 0.2 compared to 0.72 533 and –8.1, respectively. Apatite from the garnet amphibolites is enriched in MREE, lacks Eu-anomaly (Eu/Eu* 0.98), and has a low ɛ_Nd(T) = –9.3 and the lowest ⁸⁷Sr/⁸⁶Sr(t) ratio of 0.70 560. The Sm-Nd age estimate of apatite is 1.80 ± 0.15 Ga, which coincides with the Svecofennian metamorphism in the Belomorian Mobile Belt. The geochemical features of the apatite and ⁸⁷Sr/⁸⁶Sr(t) ratios indicate that the metasomatic alteration of the gneisses was caused by the lower crustal fluid and was accompanied by the influx of LREE and the removal of HREE. The slightly lower Eu anomaly and higher Ce vs Th and REE vs La/Sm relations reflect the fact that apatite from the corundum-bearing metasomatic rocks was formed in a more oxidizing environment than apatite from host rocks. Neither the corundum-bearing metasomatites and plagioclasites, nor the host rocks revealed any Sr-isotopic and REE-geochemical traces of interaction with surface (meteoric) waters.

The first data on the composition of organic compounds in thermal waters have been obtained from deep boreholes in the Paratunka geothermal field in Kamchatka. A variety of organic compounds belonging to eleven homological series were identified by capillary gas chromatography–mass spectrometry and solid phase extraction. The thermal waters were found out to be strongly dominated by aromatic and aliphatic hydrocarbons (HC), which were formed in relation to both thermogenic processes (transformation of organic residues under the effect of high temperatures and pressures) and bacterial activity. The Karymshina thermal waters are characterized by a specific molecular mass distribution of HC and contain only even-normal alkanes. It is shown that the composition of organic compounds of medium volatility in the Paratunka geothermal field is similar to the composition of organic matter (OM) in other thermal water occurrences of the Kamchatka Peninsula (Mutnovka and Uzon geothermal fields), which have been previously studied using the same methodology: all the waters are characterized by the prevalence of aliphatic and aromatic HC over other identified compounds.

Several pelagic sections in North-Eastern/Central Tunisia and neighboring basins have recently been the subject of detailed δ¹³C and δ¹⁸O stratigraphy. These studies have been utilized to create a composite Mesozoic (Triassic to Cretaceous) δ¹³C and δ¹⁸O curves, which is useful for high-resolution stratigraphic correlation. The long-term trend of the created composite δ¹³C and δ¹⁸O profiles change on variable time scales (100’s of years), and show the major δ¹³C positive and negative excursions around the key Mesozoic timelines: the Carnian, Toarcian, Barremian-Aptian, Cenomanian-Turonian, upper Cretaceous and Cretaceous/Paleogene. Short-term fluctuations vary also on time scales of similar magnitudes, and dominated the δ¹³C signal in the Mid-Cretaceous. Generally, the observed changes in the Carbon-isotopic record have commonly been attributed to changes in the organic carbon flux to the sedimentary reservoir in response to eustatic sea-level change. However, it is also suggested that carbonate production and burial rate may have influenced the δ¹³C signal. During Triassic and Jurassic, increased inorganic carbon burial led to a shift towards more negative values in the ¹³C/¹²C ratio, which is probably linked to the expansion of pelagic carbonate deposits in epicontinental seas (e.g. Carnian and Toarcian carbonate). However, short-term variations in δ¹³C could either be due to local sea-level changes in the North African epicontinental sea or changes in oceanic ¹²C storage due to variations in different water properties circulation. In addition, oxygen isotopic data can serve as a useful tool for estimating paleotemperatures in instances where diagenesis is not a hindrance. These data can record changes in paleoclimate associated with cooling or warming during the Mesozoic.

New geological, geochemical, and geochronological (U-Pb zircon) data obtained on the greenstone rocks of the Kichany structure from the Archean Tiksheozero greenstone belt made it possible to clarify and supplement the previously proposed stratification schemes. The composition of the identified sequences, the order and duration of their formation have been specified. The Archean supracrustal rocks are divided into three sequences. The lower sequence (previously not identified) is represented by a bimodal series: tholeiitic metabasalts and felsic metavolcanics, with subordinate metagraywackes. It has been formed for over 20 million years (from 2788 ± 5 to 2766 ± 9 Ma). Sm–Nd data obtained on basaltic metaandesites (Sm–Nd model age 2.86 Ga and ε_Nd = 2.92) indicate their mantle nature. Metarhyolites from the lower sequence with a Sm–Nd model age of 2.89 Ga and ε_Nd = 2.59 were generated from a source with a short residence time. The differentiated volcanic series of the upper sequence (from basalts to dacites) has been also formed for about 20 million years (2738 ± 7–2716 ± 7 Ma). The parental melts for the intermediate–felsic metavolcanics of the upper sequence are variably enriched in ancient crustal matter. The oldest rocks with a Sm–Nd model age of 2.84 Ga and ε_Nd = 2.67 were formed during the Early Neoarchean crust-forming event. The younger rocks have a different contribution of ancient crustal material: significant contribution for dacites (Sm–Nd model age of 3 Ga and ε_Nd = 0.4) and less significant contribution for dacitic andesites (Sm–Nd model age of 2.89 Ga and ε_Nd = 1.73). In the Paleoproterozoic (from 1786 ± 11 to 1796 ± 6 Ma), the supracrustal rocks of the Kichany structure underwent metamorphic transformations.

An original database compiled by the authors on volatile components of mineral-hosted fluid inclusions currently includes 12 470 analyses from 480 publications and was used to calculate the average gas phase composition of fluids that formed hydrothermal deposits throughout the Earth’s geological evolution, from the Archean to Cenozoic. The paper reviews the methods used in the study, their potential errors, and limitations. Characteristics of the gas composition of fluids are traced for more than 300 ore deposits of Au, Sn, W, Cu, Cu, Pb, Zn, Sb, Mo, and U. The dominant volatile component of natural mineralizing fluids in the Earth’s crust is carbon dioxide, regardless of the geologic age. The fluids contain subordinate amounts of reduced carbon species (methane) and nitrogen, as well as minor amounts of hydrogen sulfide and some other gases. The Cenozoic fluids commonly contain more nitrogen than methane. These relations are occasionally also found in the Precambrian fluids. The CO₂/CH₄ ratio as an indicator of the redox state of the system notably increased over the Earth’s geological history.

The paper presents newly obtained and summarizes preexisting data of long-term geochronological and isotope studies of orogenic mesothermal gold deposits in the world’s largest Lena metallogenic province and reviews interpretations of their genesis. Geochronologic data indicate that the gold mineralization was formed during three ore-forming Paleozoic events. The early Late Ordovician–Early Silurian (450–430 Ma) event produced the abundant veinlet—disseminated gold–sulfide mineralization in Neoproterozoic carbonaceous terrigenous–carbonate rocks of the Baikal–Patom foldbelt (BPB). The mineralization was formed simultaneously with regional metamorphic processes. The rejuvenation of hydrothermal activity in the BPB resulted in gold-bearing quartz veins, which was produced in the Middle Carboniferous (340–330 Ma) in relation to postcollisional granitoid magmatism. The latest ore-forming event occurred in the Early Permian (290–280 Ma) and affected exclusively in Precambrian structures of the Baikal-Muya foldbelt (BMB). It was synchronous with the development of intraplate alkaline and subalkaline magmatism in the region. Newly obtained and preexisting isotopic-geochemical (⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, Pb–Pb, and δ³⁴S) data indicate that the mesothermal ore-forming systems of northern Transbaikalia were heterogeneous in their isotopic characteristics, which distinguishes them from the ore–magmatic (intrusion-related type) systems. Comparison of the Sr, Nd, and Pb isotopic composition of the ores and rocks, including magmatic rocks coeval with the gold mineralization, indicates that the Precambrian continental crust was the dominant source of mineral-forming components for the hydrothermal systems of the gold deposits. The contribution of the magmatic source to the genesis of the orogenic gold mineralization was limited and is identifiable only for the Early Permian ore-forming systems of the BMB, for which the input of metals from alkaline mafic melts was suggested.

The complex physical and chemical properties and geochemical characteristics of crude oils in the Chepaizi area have long made the types and sources of crude oils controversial, plus biodegradation widely exists in crude oils, thus, triaromatic steroid series with strong biodegradation resistance and source significance can be used for oil-oil and oil-source correlation in the Chepaizi area. The saturated and aromatic fractions in crude oils and source rocks in the Chepaizi area were analyzed by gas chromatography-mass spectrometry. The results show that triaromatic steroid series are detected in all investigated oils and four sets of source rocks from the Chepaizi area. Based on the considerable differences in their compositional features, three families of crude oils are distinguished. Family I crude oils show the highest ratio of C₂₆/C₂₈ 20S TAS and abundant triaromatic dinosteroids, which are sourced from Qingshuihe Formation of Lower Cretaceous. Oil Family II has the lowest C₂₆/C₂₈ 20S TAS, C₂₇/C₂₈ 20R TAS and C₂₆ + C₂₇/C₂₈ TAS ratios and highest 4-MTSI ratio, considering to be related to Jurassic source rocks. Oil Family III displays very similar distribution characteristics of C₂₆–C₂₈ triaromatic steroids and C₂₇–C₂₉ methyltriaromatic steroids to Permian source rocks, and can be subdivided into two subtypes based on C₂₆/C₂₈ 20S TAS, C₂₇/C₂₈ 20R TAS and C₂₆ + C₂₇/C₂₈ TAS ratios, both of these two subtypes are mainly originated from Permian Fengcheng Formation source rocks due to the lack of triaromatic dinosteriods, while Family III-1 possibly mixed with a minor contribution from Wuerhe Formation because of the coexistence of n-alkanes with 25-norhopanes. The studied oil samples are found to be mainly in the mature and high mature stage based on the triaromatic steroid series parameters. The findings of this paper suggest that triaromatic steroid series may provide valuable molecular marker evidence for geochemical study in complex oil and gas exploration fields, at least be well applied in the Chepaizi area.

Geothermal Resource as a kind of renewable energy is widely distributed in tectonically active regions. Using hot springs along the Red River fault zone as an example, this study attempts to analyze the recharge source, recharge elevation, reservoir temperature, circulation depth, mixing of cold groundwater, and heat source through ions, stable hydrogen and oxygen isotopes, and data in previous studies to determine the characteristics and formation mechanism of geothermal resources in tectonically active regions. The findings show that whereas the non-thermal groundwater is abundant in ({text{HCO}}_{3}^{ - })–Ca²⁺, the hot springs in the Red River Fault are predominantly of the ({text{HCO}}_{3}^{ - })–Na⁺ type. The stable hydrogen and oxygen isotopes indicate that the geothermal water is derived from local meteoric precipitation, with a positive excursion in the oxygen isotope indicating that the geothermal water has undergone the strong water-rock interaction under high reservoir temperature. The recharge area is located in the mountainous regions on both sides of the Red River Fault, with recharge elevations ranging from 2252 and 3482 m. The reservoir temperature varies from 67.4 to 173.42°C calculated by the SiO₂ geothermometer, and the associated circulation depth is between 1601.18–5134.12 m. Furthermore, the data of previous studies suggest that the primary heat sources in the study area are mantle-derived heat, crust-derived heat, and radioactive heat, while the composition ratio of various heat sources is different from north to south because of the influence of structural development. The primary determinants of geothermal resources in tectonically active regions are the composition of the heat source and the scale and number of large faults, which in turn affect the temperature of geothermal resources.

We present the results of stepwise crushing and combustion analyses for noble gases, carbon and nitrogen in Pesyanoe aubrite pyroxene lithologies, composed of grey (Px-G) and light (Px-B) enstatites differing in the degree of impact processing and the number of inclusions. Our study identifies three main noble gas endmembers in Pesyanoe: a cosmogenic component, radiogenic ⁴⁰Ar, and an endmember representing a mixture of solar wind and Q components in variable proportions. Based on petrographic and noble gas data we argue that these gases accumulated in the material during its regolith history and were later redistributed into gas inclusions/voids as the result of an impact event. During impact metamorphism, Px-G acquired its grey color and multiple gas inclusions were formed within it, more than in case of Px-B. Our study demonstrates for the first time: (1) The host phase of gases trapped during shock metamorphism are grains of rock-forming minerals, in particular Px-G, due to the formation of a large number of cracks in the direction of cleavage during brittle deformation, (2) The gas capture is associated not with the final stage of the formation of consolidated fragmental breccia, at which lithification of the fragments occurred, but with one of the intermediate impact events. High amounts of trapped and cosmogenic noble gases are released during the stepwise crushing—significantly higher than in case of any other studied aubrite. Some unusually high ³⁶Ar/¹³²Xe ratios (up to 54 780 versus 22 705 in the solar wind) were discovered during crushing of Px-G. Our preferable explanation of this phenomenon is a specific superposition of noble gas elemental fractionation processes related to the impact cratering of the Pesyanoe parent body. The carbon isotopic composition (δ¹³C = –21.2 ± 0.2‰, 1σ) is slightly heavier than that of the Bustee aubrite carbon. The combined use of different extraction methods made it possible to determine that the solar type and indigenous (δ¹⁵N_indig = –0.1 ± 3.2‰, 1σ) nitrogen components are located in the gas inclusions, whereas the extraneous nitrogen component (~+45‰) is chemically bound. The large cosmic ray exposure age variations (44 and 55 Ma in case of Px-G and Px-B, respectively) and the heterogeneous distribution of solar-type gases in Pesyanoe aubrite point to a diverse irradiation history of the material before breccia formation. Alternatively/additionally, cosmogenic gases (as well as solar and primordial) in Px-G may have became lost and/or partly redistributed into gas inclusions as a result of the impact event.

The Kyun Tso lakes are located in the climate-sensitive and tectonically active area in Ladakh, India. The terrain is an example of deciphering tectonism and provenance studies. Kyun Tso consists of twin lakes Chilling Tso and Ryul Tso. The lakes are located near the Nidar ophiolite suite at an altitude of 5500 m amsl (above mean sea level) in the arid Trans Himalayan Region. Rocks of augen gneiss or para-gneiss of Tsomoriri Gneissic Complex, graphitic schist of Rupshu Formation, metavolcanics of Kuling Lilang Formation, ultrabasic rocks of Sangeluma Formation and alluvium of Quarternary deposits from Paleo-Proterozoic to recent age surround the lakes. Lake Chilling Tso is smaller in perimeter (8 km) and area (4.5 sq. km) as compared to Lake Ryul Tso (perimeter 11 km, area 6 sq. km). The studied watershed of the area represents moderate stream frequency (2.8), mean annual rainfall, and moderate to lower runoff. Both the CIA (36 to 72) and CNK indicators suggest a range of weak to intermediate weathering. The ICV values (lake Ryul Tso ranging from 0.79 to 2.40, lake Chilling Tso ranging from 0.89 to 1.52) indicate that the sediments are compositionally immature and mature, and were likely deposited in active and cratonic tectonic settings, respectively. The results of hydrodynamic sorting and X-ray diffraction (XRD) analysis revealed that the lake sediments are predominantly quartz-dominated, with a notable presence of feldspar and a limited amount of clay minerals. The analytical values of the sediment samples demonstrate a diverse range of source rocks. The study involves weathering component and compositional variation of the sediments, their relationship with climatic conditions, geomorphic features, basin environment, and catchment lithology.