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1.
Steshenko E. N. Nikolaev A. I. Bayanova T. B. Drogobuzhskaya S. V. Chashchin V. V. Serov P. A. Lyalina L. M. Novikov A. I. Elizarov D. V. 《Doklady Earth Sciences》2018,479(1):366-370
Doklady Earth Sciences - The rocks and minerals of the Kolvitsa massif are studied by complex isotopic–geochronological and geochemical (U–Pb, Sm–Nd, REE contents of zircons)... 相似文献
2.
The geology of the basal-structural Loypishnyun low-sulfide Pt–Pd deposit is characterized, including its mineral composition and the peculiarities of its PGE and chalcophile-element distribution in ore. The deposit is situated in the northeastern part of the Monchetundra basic massif and is localized in its lower norite–orthopyroxenite zone, intensely injected with late gabbroic rocks. Two ore zones are distinguished within the deposit. Ore zone 1 has been traced by drilling for about 1.5 km at a thickness from 10–15 to 120 m and incorporates from two to nine separate lenticular–sheetlike orebodies 0.5–25 m in thickness. Ore zone 2 has been traced for 550 m and is represented by one orebody 5–35 m thick. The internal structure of the orebodies is characterized by alternation of low-grade (Pt + Pd = 0.5–0.9 gpt), ordinary (Pt + Pd = 1.0–1.9 gpt), and high-grade (Pt + Pd > 2 gpt) interlayers of various thickness. The ores are spatially and genetically related to sulfide mineralization (pentlandite–chalcopyrite–pyrrhotite) in an amount of 1–5 vol %. The PGE distribution in ores normalized to primitive mantle is characterized by fractionation of easily fusible platinoids with a positive Pd anomaly. The spectra of chalcophile elements normalized to primitive mantle are notable for elevated Te, Bi, As, and Se contents with respect to Sn, Hg, and Pb, which reflects the significant contribution of Te, Bi, and As in the formation of platinum group minerals (PGM), whereas Se, which is devoid of proper mineral phases, most likely is an admixture in the composition of sulfides. The S/Se value in ore of the Loypishnyun deposit varies from 31 to 814. The platinum group elements (PGE) in ore are represented by 45 noble metal minerals. Ore zone 1 is characterized by lateral mineral zoning, which is expressed as replacement of a bismuthotelluride–sulfide PGM assemblage by an assemblage of copper–PGE compounds and alloys. In ore zone 2, a mineral assemblage of tellurides, copper–PGE compounds and alloys predominates, with native gold, silver, and palladium, as well as sulfides and bismuthotellurides, playing a subordinate role. The formation of PGM ore proceeded under variable sulfur fugacity conditions, beginning with the late magmatic stage at temperatures of 900–700°C and ending with hydrothermal transformation at a temperature of <500°C. 相似文献
3.
V. P. Simanenko S. V. Rasskazov T. A. Yasnygina A. I. Malinovskii A. A. Chashchin 《Russian Journal of Pacific Geology》2007,1(3):265-275
The Early Cretaceous volcanic rocks of the Mariisky sequence and Early Cenozoic extrusive-vent rocks of Cape Mary are exposed at the northwestern extremity of Schmidt Peninsula, north Sakhalin. In chemical composition, all the rocks are subdivided into four groups. Three groups include the volcanic rocks of the Mariisky sequence, which consists, from bottom to top, of calc-alkaline rocks, transitional calc-alkaline-tholeiite rocks, and incompatible element-depleted tholeiites. These rocks show subduction geochemical signatures and are considered as a fragment of the Moneron-Samarga island arc system. Trace-element modeling indicates their derivation through successive melting of garnet-bearing mantle and garnet-free shallower mantle sources containing amphibole; pyroxene; and, possibly, spinel. The mixed subduction and within-plate characteristics of the extrusive vent rocks of Cape Mary attest to their formation in a transform continental margin setting. 相似文献
4.
Doklady Earth Sciences - The results of studying of the deep-seated platinum-bearing xenolith discovered in the Volchetundra gabbro-anorthosite massif in the Kola Region are presented. It is shown... 相似文献
5.
The Volch??etundrovsky Massif occupies the middle part of the autonomous anorthosite complex of the Main Range, has a sheet morphology and marks the tectonic suture between the Kola block and the Belomorian mobile belt. The massif is characterized by homogenous structure and consists of the volumetrically dominant Main Zone including leucogabbro, leucogabbronorites, and anorthosites, and Marginal Zone made up of leuconorites and gabbronorites with subordinate plagioclasites and orthopyroxenites. Chemically, the rocks of the Volch??etundrovsky Massif are ascribed to the normal (tholeiitic and calc-alkaline) petrochemical series with typomorphic high Al2O3 contents (11.71?C29.32 wt %). With Al2O3 increase in the leuconorite-anorthosite series, the SiO2 and TiO2 contents show weak variations, CaO and alkalis insignificantly increase, whereas the MgO and FeO contents sharply decrease. The rocks of the Volch??etundrovsky Massif reveal significant REE fractionation and increase in total REE content in the leuconorite-anorthosite series, most approximating the Paleoproterozoic (Sumian) anorthosites of the Kola region. The anorthosites and leucogabbro are characterized by flat HREE, while the leuconorites is strongly depleted in HREE due to garnet fractionation. All rocks of the massif have significant positive Eu anomalies caused by the plagioclase accumulation. Zircons are characterized by LREE depletion and enrichment in HREE. This defines the steep positive slope of the plots complicated by the negative Eu and positive Ce (in zircons from leucogabbro) anomalies, which is typical of the REE distribution patterns in the unaltered zircons from igneous rocks. In zircons from anorthosites, the Ce anomaly is weak to absent. The trace-element distribution in the rocks of the Volch??etundrovsky Massif show positive Ba, Ta, Pb, Sr, Sc, and V anomalies, being controlled by the mineral specifics of the massif and the presence of definite accessory minerals. New U-Pb zircon data on the rocks of the Volch??etundrovsky Massif indicate that the leuconorites from the Marginal Zone were formed 2473 ± 7 Ma and 2463 ± 2.4 Ma ago, and the leucogabbro from the Main Zone, 2467 ± 8 Ma. These rocks have negative ?Nd(T) from -1.54 up to -3.10, which indicates their derivation from enriched mantle reservoir variably contaminated by crustal material. The anorthosites of the Main Zone define an U-Pb age of 2407 ± 3 Ma and ?Nd(T) = ?3.78, which presumably reflect the timing of hydrothermal-metasomatic alterations in the upper part of the magmatic chamber accompanied by significant crustal contamination. 相似文献
6.
V. P. Simanenko S. V. Rasskazov T. A. Yasnygina L. F. Simanenko A. A. Chashchin 《Russian Journal of Pacific Geology》2011,5(1):26-46
The variations of petrogenic oxides and trace elements have been studied in the Cretaceous volcanic rocks recovered by a deep
borehole from the depth interval of 1253–4011 m on Moneron Island. The volcanic section is subdivided into two complexes:
the Early Cretaceous and Late Cretaceous. The rocks of the Early Cretaceous Complex occur below 1500 m. Chemically, they belong
to low-potassium island arc tholeiites, and their trace element distribution suggests their formation in a suprasubduction
mantle wedge under the influence of water fluids that were subsequently released from subducted sediments and oceanic plate
during the dehydration of subducted sedimentary rocks and oceanic basalts and, finally, mainly from basalts. The Early Cretaceous
basalts from the borehole are interpreted as ascribing to the frontal part of the Moneron-Samarga island arc system. The volcanic
rocks of the Late Cretaceous Complex are situated at depths above 1500 m. They also were formed in a suprasubduction setting,
but already within the East Sikhote-Alin continental-margin volcanic belt that was initiated after the accretion of the Moneron-Samarga
island arc system to the Asian continent. The island-arc section of the Moneron borehole contains basaltic andesite dikes,
which are geochemically comparable with the Early-Middle Miocene volcanic rocks of Southwestern Sakhalin. 相似文献
7.
A. N. Filippov G. I. Govorov A. A. Chashchin T. A. Punina 《Russian Journal of Pacific Geology》2010,4(4):289-303
This paper reports new data on the mineralogical-petrographical composition, genetic types of sedimentary rocks, and geochemical
features of the volcanic rocks of the Snarsky area of the Nizhneussuriisk segment of the Kiselevka-Manoma accretionary complex,
which is developed on the right bank of the lower reaches of the Ussuri River. The Middle Jurassic-Aptian sedimentary rocks
of the area are represented by pelagic radiolarian cherts, semipelagic siliceous-clayey deposits, subordinate shallow limestones,
volcanomictic conglomerates, and turbidite sandstones. The basalts of the area are represented by alkaline basalts resembling
within-plate ocean-island basalts and N-MORB-type tholeiitic basalts. Rock associations of two physicogeographical and geodynamic
settings are distinguished: the pelagic setting with within-plate alkaline volcanic rocks and the hemipelagic one with volcanic
edifices of spreading basalts. 相似文献
8.
V. V. Chashchin 《Geochemistry International》2007,45(1):15-31
The paper presents materials on the fabric of the western, southwestern, and southern exocontact zones of the Khibina alkaline pluton and metavolcanic rocks of the Il’mozerskaya Formation of the Paleoproterozoic Imandra-Varzuga riftogenic structure. The volcanics of the Imandra-Varzuga structure were originally metamorphosed to the greenschist facies (at temperatures of ≥300°C and pressures of ≥2.0–2.5 kbar) and were afterward metamorphosed to the pyroxene-hornfels facies under the thermal effect the Khibina pluton with the development of a hornfels zone 150–400 m thick. According to their composition, the hornfelses are subdivided into three zones: inner, intermediate, and outer. The inner zone is up to 30 m thick and consists of hornfelses of clinopyroxene-plagioclase composition with olivine as a typomorphic mineral and with variable amounts of amphibole. The intermediate zone occurs at a distance of 30–200 m from the pluton, is separated from the inner zone by the olivine isograde, and consists of amphibole-clinopyroxene-plagioclase hornfelses. The outer zone, 200–400 m away from the contact of the pluton, is made of fine-grained melanocratic hornblende hornfelses. The thermal transformations of the metavolcanics involved the gradual replacement of their low-temperature mineral assemblage (actinolite + albite) by a higher temperature one (clinopyroxene + amphibole + andesinebytownite ± olivine). Our data on the chemical composition of the rock-forming minerals of the hornfelses indicate that the olivine is ferrohortonolite-fayalite, the clinopyroxene belongs to the augite-ferroaugite series, and occasional orthopyroxene grains (which were found only in the intermediate zone) are ferrohypersthene. The amphibole in the hornfelses of the intermediate zone and the outermost (farthest from the contact) part of the inner zone is edenite, a Ca amphibole. The amphibole in hornfelses near the contact is kataphorite of the Na-Ca amphibole group. The plagioclase composition generally corresponds to andesine and bytownite and is albite-oligoclase near the contact with the pluton. The hornfelses adjacent to the contact bear rare sanidine grains. The mineral thermo-and barometry of the hornfelses yielded temperatures of 700–640°C and pressures of 1–1.5 kbar. The temperature determined for the zone exactly at the contact was approximately 700°C, which corresponds to the initial temperature of the rocks in contact with the magma and is close to the crystallization temperature of the nepheline syenites of the Khibina pluton. 相似文献
9.
A. A. Chashchin Yu. A. Martynov A. B. Perepelov N. I. Ekimova T. P. Vladimirova 《Russian Journal of Pacific Geology》2011,5(4):348-367
A detailed mineralogical and geochemical study of basic volcanic rocks from the modern edifices of the Gorely (Q34-Q44) and Mutnovsky (Q32-Q4) volcanoes, as well as the results of numerical modeling with the COMAGMAT program, made it possible to estimate the role
of fractional crystallization, the fluid regime, and geodynamic conditions in the petrogenesis of the studied basaltoids.
The specific features of the evolution of magmas of the two volcanoes give grounds to suggest that beginning from the Late
Pleistocene (Q34), all of the considered territory experienced a change in geodynamic regime, with an increasing role of extending strains
in its evolution. 相似文献
10.
A. V. Rybin A. V. Degterev E. A. Kravchunovskaya M. V. Chibisova A. S. Neroda I. V. Melekestsev N. G. Razzhigaeva S. A. Chashchin S. A. Chirkov I. G. Koroteev Kh. A. Arslanov 《Journal of Volcanology and Seismology》2012,6(5):290-300
We provide data concerning a weak phreatic eruption of Ekarma Volcano on Ekarma Island, in the Kurils, in June 2010. The ash plumes did not rise higher than 3 km above sea level. A preliminary estimate of the volume of erupted resurgent material (mostly tephra) is on order 2 × 105 m3. Reconstruction of the volcano??s history and the dynamics of its eruptive activity for the last 4500?C5000 years suggests that a larger eruption can occur during the next few decades that will discharge juvenile pyroclastics and/or lava. 相似文献