METASOMATIC CHANGES IN ROCKS OF SEDIMENTARY COMPLEXES IN THE CARPATHIAN OIL AND GAS PROVINCE AS AN INDICATOR OF CARBOHYDRATE MIGRATION

A field and laboratory investigation of sedimentary rocks in Carpathian oil and gas province was curried out. The theoretical and practical aspects of the peculiarities of the development of metasomatic process during the migration of fluids at the postsedimentation stage of rock formation were investigated. Based on detailed field researches, a consistent pattern of mineral aggregates’ and their crystalloid individuals developing was defined. The arguments for developing a new geochemical model of oil deposits indication in Carpathian oil and gas province were provided.

Geochemical - geology characteristics implicating original sources and copper - deposit type in Kon Ra ore - field

Based on the research results on petrographic - mineralogical characteristics, tectonic structural features, geochemistry of major and trace elements of the bedrock, alternative rock, ore, soil, mineralogical geochemistry, mineral facies, inclusions, the origin of ore formation related to oxidized granite and skarnoid - typed metasomatic process in Kon Ra copper ore field have been identified. Petrological and mineral characteristics indicate the process of transitional metasomatism between the skarn and hornfels, also known as bimetasomatic stage (skarnoid deposit type). Diopxite represents the Progade skarnoid stage. Tremolite, actinolite, quartz, chlorite, magnetite, molybdenite, less of chalcopyrite, pyrrhotite, and pyrite indicate the retrogade skarnoid stage. The following is sulfide - quartz stage (major minerals include: quartz, chalcopyrite, pyrite, pyrrhotite, molybdenite). This result is also consistent with the formation temperature 210÷270 0C and the geochemical zoning of elements from intrusive blocks through the outer contact zone that contains the ore and surrounding rocks are as follows: Cu, Zn, Ca (the zone has lime-rich formations), Fe3+, Mo increases in the outer contact zone containing ore closed to acid intrusive rocks. Inversely, the ratios of Pb/Cu, Zn/Cu, and As content increased in the alteration from this zone to the outer one. In addition, uranium mineralization is associated with a later magma stage (pegmatite granite in endo-contact is high uranium radiation: U = 0.17÷0.2%, 3,420,000÷8,020,000 µR/h and contains uraninite).

Zircons of fenites of Ilmeno-Vishnevogorsky Complex (Southern Urals)

Research subject. U-Pb zircon dating, as well as a petrological and geochemical study of pyroxene-amphibole-, pyroxeneamphibole- biotite- and biotite-bearing fenites from the Central Alkaline Band Ilmeno-Vishnevogorsky Complex.Methods. The age of zircons was determined by an ion mass spectrometer (SHRIMP II, Centre of Isotopic Research VSEGEI). The content of REE and trace elements was estimated by secondary ion mass spectrometer methods (CAMECA IMS-4F, Valiev Institute of Physics and Technology RAS).Results. The mineralogical and geochemical (U, Th, REE) features of zircons, as well as fenites, reflect their polygenic-polychronous nature. Most zircon crystals have a metastable matrix and are characterized by averaged REE contents between igneous and hydrothermal types. These crystals are distinguished from magmatic zircons by high LREE contents and low values of Ce anomalies, and from hydrothermal zircons – by differentiated REE distribution spectra. Three ages of zircon were established: 2066–1686 (PR1), 425–404 (S2) and 284–266 (P1) Ma. PR1 zircons reflect the primary features and the degree of changes in the fenite substrate. S2 zircons, limited only to the biotite- bearing fenite, correspond to the age of the miaskite formation process. The P1 zircons clearly reflect the metasomatic process of fenitization initiated by late shear deformations. The temperature of the phenitization processes (based on the Ti content in zircons) was estimated at 630–670°C for S2 and ≤ 600°C for P1 fenites, respectively.Conclusions. Central Alkaline Band fenites were formed by the metasomatic process of PR1 substrate fenitization in the late stage (P1) of shear strains, which are widely expressed in the Ilmeno-Vishnevogorsky Complex.

Depletion, metasomatism and refertilisation in the Sub-Continental Lithospheric Mantle beneath northern Victoria Land (Antarctica): a review

<p>Assessing the nature and evolution of the Sub-Continental Lithospheric Mantle (SCLM) is crucial to understand the dynamics of Earth’s interior and the global scale tectono-magmatic processes. The study of ultramafic xenoliths brought to the surface in specific context, such as northern Victoria Land (Antarctica), is a key to investigate how the SCLM bear witness of large-scale geodynamic episodes. Indeed, the Antarctica lithosphere was involved into three main tectono-magmatic episodes since Paleozoic, i.e. the 550-110 Ma Ross subduction, the Jurassic (~182 Ma) Ferrar magmatism and the Cenozoic alkaline magmatism responsible for the opening of the West Antarctic Rift System (WARS).</p><p>In this study, a review of the petrological and geochemical features of >200 mantle-derived and cumulate xenoliths brought to the surface at Baker Rocks, Greene Point, Handler Ridge, Harrow Peaks, Browning Pass and Mount Overlord enabled us to reconstruct the main depletion and enrichment processes that took place in the Antarctica SCLM. Strong depletion is recorded by Greene Point lherzolites and harzburgites (18-21%), which likely began melting in the garnet facies and terminated in the spinel facies (Perinelli et al. 2006), whereas mild melt extraction in the spinel stability field was hypothesized at Baker Rocks and Handler Ridge (12-16% and 7-13% melting, respectively). The onset of the Jurassic Ferrar large magmatic event is testified by both the refertilisation in Greene Point-Baker Rocks peridotites and the appearance of cumulate orthopyroxenites/olivine-websterites at Harrow Peaks and Baker Rocks. Late enrichment process/es took place in concomitance with the Cenozoic alkaline magmatism of the WARS, resulting in both cryptic and modal metasomatism and overprinting earlier chemical modifications. This metasomatism was particularly effective at Baker Rocks, as shown by the increase of clinopyroxene abundance, its trace element enrichment and the formation of amphibole disseminated and in veins. Clinopyroxene composition in Cenozoic cumulate rocks matches the enrichment path observed in the peridotites, supporting the link between the last metasomatic process and the recent alkaline magmatism.</p><p>Among mantle xenoliths populations, Greene Point record the highest T-P (870-1059 °C; 0.8-1.6 GPa) and the least oxidized conditions (fO<sub>2</sub> down to -2/-3 ΔFMQ). Cumulate rocks yield the highest fO<sub>2</sub> (up to +1.5 ΔFMQ), at T varying between 900 and 1150°C, approximating the conditions of crystallizing melts. No discrepancies in fO<sub>2</sub> emerged between amphibole-bearing and amphibole-free peridotites, ruling out a strict correlation between amphibole stability, H<sub>2</sub>O activity and fO<sub>2</sub>. Nevertheless, the alkaline metasomatic event, which led to amphibole formation, caused a remarkable increase in the H<sub>2</sub>O content of the system. In fact, anhydrous peridotites preserve bulk H<sub>2</sub>O contents ≤128 ppm, while lherzolites with disseminated amphibole and hornblendites have H<sub>2</sub>O contents as up to 354-1120 ppm and 1.42 wt%, respectively.</p><p> </p><p>Perinelli, C., et al. 2006. Geochemical and O-isotope constraints on the evolution of lithospheric mantle in the Ross Sea rift area (Antarctica). Contributions to Mineralogy and Petrology, 151(3), 245-266.</p>

Rodingitization of mafic rocks from Central Evia (Greece) associated with serpentinite exhumation: Evidence from Petrological, Geochemical and Isotopic data

<p>In Central Evia island (Aegean-Greece) serpentinized ultramafic rocks appear as elongated thrust sheets or in the form of olistostromes incorporated within Maestrichtian-Paleocene flysch. These are crosscut by well-developed rodingite dykes that were derived from four main protoliths that include i) Boninites, ii) Island-arc Tholeiitic Basalts and Gabbros, iii) Alkaline basalts and iv) Calc-alkaline basalts. They mainly comprise of minerals that include (hydro)garnet + chlorite + clinopyroxene ± vesuvianite. Accessory minerals include spinel ± calcite ± prehnite ± amphibole ± orthopyroxene ± olivine ± quartz ± opaque Fe-Ti oxides. Rodingites that were formed at the expense of boninites and island-arc tholeiitic rocks were likely formed within a single rodingitization stage, since garnet is mainly grossular-rich and relict primary clinopyroxene has been preserved. The rodingitization of the alkaline and calc-alkaline basalts seems to have occurred as a multi-stage metasomatic process that occurred during the exhumation of the mafic-ultramafic mantle wedge complex. This resulted in the development of late-stage andradite, vesuvianite and in some cases of chlorite during derodingitization. In this case, successive reaction zones with variability in the participating mineral phases were developed.  Geochemical results reveal remarkable rare earth element (REE) enrichments, especially in the inner zones, likely being the result of successive diffusion and element transfer. Few rodingites are characterized as calcite-bearing, whose stable <sup>13</sup>C-<sup>18</sup>O isotopic data points to the restricted involvement of late-stage mixed hydrothermal and seawater-related carbonation processes.</p>

Mineralogical and geochemical features of volcanics from the pre-Jurassic basement of the western part of Yamal

Relevance of the work. The Arctic part of the West Siberian megabasin is the main source of oil and gas in Russia, therefore, the study of the geological structure of this region is extremely important. Recently, Russia has lodged an application to extend its territory in the Arctic Ocean along the ridges that stretch from the continental shelf. Unfortunately, at the same time, we know little about the geological structure of the Arctic in the region of Western Siberia, where the thickness of the sedimentary cover is very high (about 3–4 km), therefore, the study of the basement of the Yamal Peninsula seems to be extremely urgent. The purpose of this work is mineralogical, petrological and geochemical study of dolerites from the pre-Jurassic basement of the Bovanenkovskaya area (well No. 114) within the territory of the gas condensate field of the same name, located in the western part of the Yamal Peninsula. Scope of the work. This work can be useful in constructing geological maps of the pre-Jurassic basement of the Yamal Peninsula. Results and conclusions. We have studied the mineralogical and geochemical features of dolerites from the pre-Jurassic basement of the Bovanenkovskaya area (well No. 114, sampling depth – 3210 m) of the West Siberian megabasin. The mineralogy of the rocks is represented by augite, diopside, albite, magnesian chamosite, ferrous hornblende, calcite, siderite, dolomite, anorthoclase, grossular, zeolite (gmelenite-K), pyrite, chalcopyrite, and rare lead chloride – cotunnite. The rocks underwent minor transformations in the conditions of the lower greenschist metamorphism, as well as secondary alterations in the form of superimposed propylitization. As a result of this low-temperature metasomatic process, zeolite, carbonate (calcite, dolomite, and siderite) and sulfide mineralization composed of pyrite and chalcopyrite, as well as cotunnite, which apparently replaced the dissemination of galena, were formed in the rock. Judging by geological position of the region, these dolerites are most likely formed at shallow depths during continental rifting. Remelting of the Paleozoic island arc substrate during the Early Triassic rifting and volcanism provided some closeness to the island arc trend in the geochemical features of these rift volcanics.

Geochemistry of sillimanite-magnetite-kaolinite of metasomatic rocks of the island of Great Tyuters (gulf of Finland, Russia)

Among the secondary quartzites of the island of the Great Tyuters there are extended linear zones with a capacity of up to 3 meters, clearly visible in detailed satellite images. They are composed of sillimanite-magnetite-kaolinite metasomatites discovered for the first time. The formation of metasomatites is associated with fragmentation of quartzites and the subsequent introduction of fluids of a substance saturated with various components. Metasomatites are enriched with Al2O3 (16–23 wt.%), in contrast to 2–5 wt. per cent of this oxide is present in their substrate – quartzite. In metasomatic rocks dominated by iron oxide, quartzite – ferrous. The rocks do not contain any alkaline and alkaline-earth elements. They are enriched with Zr (146–199 g/t) and a number of other elements, including impurities and rare earth, among which prevail Ce (34 g/t) and La (17 g/t). REE of both breeds is characterized by a small and close degree of fractionation ((La/Yb)n=6.55 and 6.17). Metasomatites on a set of minerals do not differ from quartzites, but differ in their quantitative ratios and composition. Of particular interest is the magnetite of metasomatites. It contains many quartz inclusions with kaolinite edges. Quartz inclusions, in turn, contain inclusions of titanium magnetite crystals. In the formation of metasomatites, there were several stages of the metasomatic process with a changing composition of fluids and different acidity-alkalinity of the mineral formation medium. The development of metasomatites in linear zones, the disintegration of their substrate, the high content of kaolinite – all this gives them a similarity with weathering cows. However, the same set of minerals in metasomatite and its substrate, the complete absence of sulfides and sulfur, the presence of magnetite with double mineral inclusions – such features distinguish these rocks from the classical weathering crust.

Geochemistry, Geochronology, and Hf-S-Pb Isotopes of the Akechukesai IV Mafic-Ultramafic Complex, Western China

The Akechukesai IV mafic–ultramafic complex, located in the western segment of the eastern Kunlun orogenic belt (EKOB), represents a newly-discovered complex, containing Ni ores at grades of up to 0.98% Ni. It is dominated by olivine pyroxenite, pyroxenite, and gabbro units. The gabbros are enriched in lithophile elements (e.g., Rb, U, and K) and light rare-earth elements (LREE), with negative anomalies in high field-strength elements, except Zr, Ta. Nb/Ta(∼5) and Zr/Hf (∼10) ratios lower than the primitive mantle and chondrites, respectively, indicate the influence of the mantle metasomatic process or fractionation of accessory mineral phases. Zircon U–Pb dating of the gabbro yielded an age of 423.9 ± 2.6 Ma, indicating that the complex formed contemporaneously with the Xiarihamu Ni deposit (423 ± 1 Ma). The gabbro has negative εHf(t) values (−11.3 to −1.2) with corresponding TDM1 ages of 1535–1092 Ma. The vein-like and disseminated mineralization (i.e., pyrite and pyrrhotite) have δ34S values of 13.1‰–13.4‰ and 5.0‰–8.5‰, respectively, suggesting that the magmas that formed the complex assimilated crustal sulfur. They yield 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 17.323–18.472, 15.422–15.626, and 37.610–38.327, respectively, indicating Pb derived from multiple sources (i.e., mantle crustal sources). Geochemical and Hf–S–Pb isotopic characteristics suggest that the complex formed from a primitive magma derived by partial melting of a spinel- and garnet-bearing lherzolite mantle at variable degree of 5%–10%. This source region was geochemically enriched by previous interaction with slab-related fluids. Tectonic reconstruction suggests that the Akechukesai IV complex was generated in a post-collisional extensional environment.

Origin of Skarns at Migmatization on Ol’khon Island, Lake Baikal, Russia

Migmatites on the western shore of Ol’khon Island host unusual rocks: zoned lenses of hedenbergite–garnet–epidote–anorthite metasomatites coupled with the migmatites. No intrusive granites were found nearby. The skarn-forming process operated at the interface of the granite gneiss and skarn protolith (perhaps, carbonate rocks). The composition of the metasomatites is analogous to that of calcic skarns with high Al2O3, FeO, and CaO concentrations. The compositions and relations of the minerals provide evidence of the successive development of the hedenbergite–anorthite outer zone, dominantly anorthite–garnet main zone, and quartz-enriched inner zone, with all of the zones parallel to contact with the granite gneiss. The granite gneiss itself is also likely of metasomatic nature, as follows from its supraeutectic concentration of potassic feldspar in the leucosome and low crystallization temperatures. A minimum of the Gibbs free energy (calculated with the SELECTOR-C program package) was reached at 8 kbar and temperatures of 600– 625°C. These parameters are lower than the melting temperature of the granite eutectic, and the absence of melt is confirmed by the absence of melt inclusions in minerals of the granite gneisses. This indicate that the driving force of the process was migmatizing silicic–potassic solutions. The P–T parameters of the skarns are close to the foregoing values. The very high Sr and Ca and low Mg concentrations suggest that the protolith of the skarns was calcite marble. The enrichment of the skarns in the granitophile elements suggests that the skarns were produced simultaneously with and in genetic relation to the migmatization processes. The metasomatites were formed before the partial melts were derived, early in the course of the granite-forming processes and provide important information for better understanding the metasomatic process responsible for the exchange of chemical elements between the rocks.