O. Dzyuba, B. Shurygin, O. Izokh, A. Kuznetsov, I. Kosenko
–The Middle Jurassic sedimentary strata of Siberia remain poorly studied chemostratigraphically. We contribute to the knowledge with pioneering C, O, and Sr isotopic data for carbonate material of belemnites from the Yuryung-Tumus Peninsula and the lower reaches of the Lena River, as a basis for comprehensive description of the north Siberian Bajocian and lower Bathonian. The obtained chemostratigraphic constraints, with new 87Sr/86Sr ratios and previous δ13C and δ18O estimates, also include data for the lower Bathonian in the Sokur section (Central Russia). Despite the limited amount of material, chemostratigraphy, along with the available biostratigraphic data, allows reliable correlation of the Boreal sections with the primary standard of Northwest Europe, which is impossible for these strata with any of the two methods alone. The δ13C, δ18О, and 87Sr/86Sr patterns correlate with the records of eustatic, climatic, tectonic, and paleogeographic events. The new δ18O data and the inferred paleotemperatures for the latest early Bajocian and the Bajocian/Bathonian boundary reveal two excursions of notable seawater warming near the Siberian Arctic coast, which were synchronous with episodes of global sealevel rise. It was presumably during the eustatic events that the N–S Komi Strait (first naming) opened twice in the territory of the Russian Plate. The strait connected the Boreal and Tethyan seas and thus changed the oceanic circulation patterns. Specifically, it opened a gateway for a warm current from the south to northern Siberia responsible for the high seawater temperatures recorded in the δ18О patterns of belemnites.
{"title":"C, O, and Sr Isotope Compositions of Belemnites from the Bajocian–Bathonian of Arctic Siberia: Implications for Global Correlations and Paleogeographic Reconstructions","authors":"O. Dzyuba, B. Shurygin, O. Izokh, A. Kuznetsov, I. Kosenko","doi":"10.2113/rgg20234613","DOIUrl":"https://doi.org/10.2113/rgg20234613","url":null,"abstract":"\u0000 –The Middle Jurassic sedimentary strata of Siberia remain poorly studied chemostratigraphically. We contribute to the knowledge with pioneering C, O, and Sr isotopic data for carbonate material of belemnites from the Yuryung-Tumus Peninsula and the lower reaches of the Lena River, as a basis for comprehensive description of the north Siberian Bajocian and lower Bathonian. The obtained chemostratigraphic constraints, with new 87Sr/86Sr ratios and previous δ13C and δ18O estimates, also include data for the lower Bathonian in the Sokur section (Central Russia). Despite the limited amount of material, chemostratigraphy, along with the available biostratigraphic data, allows reliable correlation of the Boreal sections with the primary standard of Northwest Europe, which is impossible for these strata with any of the two methods alone. The δ13C, δ18О, and 87Sr/86Sr patterns correlate with the records of eustatic, climatic, tectonic, and paleogeographic events. The new δ18O data and the inferred paleotemperatures for the latest early Bajocian and the Bajocian/Bathonian boundary reveal two excursions of notable seawater warming near the Siberian Arctic coast, which were synchronous with episodes of global sealevel rise. It was presumably during the eustatic events that the N–S Komi Strait (first naming) opened twice in the territory of the Russian Plate. The strait connected the Boreal and Tethyan seas and thus changed the oceanic circulation patterns. Specifically, it opened a gateway for a warm current from the south to northern Siberia responsible for the high seawater temperatures recorded in the δ18О patterns of belemnites.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":" ","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47399587","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
—This study continues analysis of the new seismic tomographic structure of the suprasubduction complex of the central zone of Kamchatka, obtained from the dense local networks data of 2018–2020, and is devoted to the analysis of the velocity structure in the Malko-Petropavlovsk fracture zone margins and around them. The seismic tomographic model involves about 98,000 P- and S-wave travel times from 2963 local earthquakes from August 2018 to July 2020. The resolution of this model makes it possible to trace the feeding systems of volcanoes of the South Kamchatka and East Volcanic Belt to the slab surface, as well as to identify subvertical structural faults. To construct the orientations of the compression and extension axes we used the foci mechanisms of 41 earthquakes with М ≥ 4.5 from the catalog of the International Seismological Center for the period 1979–2019. Along the Malko-Petropavlovsk fracture zone, the Avacha transform fault is clearly traced in the geometry and mutual arrangement of velocity anomalies almost throughout the entire depth of the model. Comparison of seismic anomalies with a map of the directions of the compression and extension axes distribution from the earthquake foci mechanisms showed the correlation between the change in the value of the velocity anomalies along the Avacha transform fault with the axes direction change by almost 180°. A near-surface low-velocity anomaly to the depths of 25–35 km was found along the western border of the Malko-Petropavlovsk zone under the southern tip of the Sredinny Ridge. This anomaly probably marks the axes junction zone boundary of the ancient volcanic front along the Sredinny Ridge and the modern active Eastern Volcanic Belt, which formed as a result of the Kronotsky paleoarc accretion. To the west from the Sredinny Ridge southern tip, another low-velocity anomaly was revealed. This anomaly was traced to a depth of ~150 km, has a contrasting southern boundary confirmed by the distribution of the compression and extension axes directions by the earthquake foci mechanisms and apparently marks the southern boundary of the West Kamchatka block.
{"title":"The Boundary Areas Structure of the Malko-Petropavlovsk Fracture Zone from Local Seismic Tomography and Earthquake Foci Mechanisms Data","authors":"N. Bushenkova, O. Kuchay","doi":"10.2113/rgg20234573","DOIUrl":"https://doi.org/10.2113/rgg20234573","url":null,"abstract":"\u0000 —This study continues analysis of the new seismic tomographic structure of the suprasubduction complex of the central zone of Kamchatka, obtained from the dense local networks data of 2018–2020, and is devoted to the analysis of the velocity structure in the Malko-Petropavlovsk fracture zone margins and around them. The seismic tomographic model involves about 98,000 P- and S-wave travel times from 2963 local earthquakes from August 2018 to July 2020. The resolution of this model makes it possible to trace the feeding systems of volcanoes of the South Kamchatka and East Volcanic Belt to the slab surface, as well as to identify subvertical structural faults. To construct the orientations of the compression and extension axes we used the foci mechanisms of 41 earthquakes with М ≥ 4.5 from the catalog of the International Seismological Center for the period 1979–2019. Along the Malko-Petropavlovsk fracture zone, the Avacha transform fault is clearly traced in the geometry and mutual arrangement of velocity anomalies almost throughout the entire depth of the model. Comparison of seismic anomalies with a map of the directions of the compression and extension axes distribution from the earthquake foci mechanisms showed the correlation between the change in the value of the velocity anomalies along the Avacha transform fault with the axes direction change by almost 180°. A near-surface low-velocity anomaly to the depths of 25–35 km was found along the western border of the Malko-Petropavlovsk zone under the southern tip of the Sredinny Ridge. This anomaly probably marks the axes junction zone boundary of the ancient volcanic front along the Sredinny Ridge and the modern active Eastern Volcanic Belt, which formed as a result of the Kronotsky paleoarc accretion. To the west from the Sredinny Ridge southern tip, another low-velocity anomaly was revealed. This anomaly was traced to a depth of ~150 km, has a contrasting southern boundary confirmed by the distribution of the compression and extension axes directions by the earthquake foci mechanisms and apparently marks the southern boundary of the West Kamchatka block.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":" ","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44582244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Kirdyashkin, A. Kirdyashkin, V. Simonov, M. M. Buslov, A. Kotlyarov
—In the Bouvet Island region (South Atlantic), a hotspot operates in the region of the triple junction of midocean ridges. On the basis of laboratory modeling data, the structure of the conduit of a thermochemical plume melting out in the mantle from the core–mantle boundary is presented. The thermal power of the Bouvet thermochemical plume is determined from the volume of uplifted and erupted rocks above the lower topographic level. To determine the mass flow rate of the melt for the plume, a topographic profile is used in a section perpendicular to the Bouvet hotspot trajectory and passing through the Bouvet plume. The thermal power of the Bouvet plume is 1.7 · 1010 W. Based on the obtained power, the plume diameter is d = 10–13 km. The Bouvet plume belongs to intermediate-power plumes. Such plumes are diamondiferous, because their eruption on the surface transports the melt from a depth of >150 km, at which diamond is stable. The Bouvet plume trajectory originates in South Africa. Initially, the melt erupted on the cratonic surface through a diatreme. Next, the plume was preserved in the region of the drifting oceanic lithosphere and became no longer diamondiferous. The following morphostructures of the triple junction region with contrasting types of magmatic systems are distinguished according to petrological and geochemical data: MOR and the Bouvet volcanic island, which results from the plume activity. For the Bouvet region, K2О (0.5%) and Н2О (up to 0.9%) are identified in the composition of the deep magmatic melt. There is enrichment in H2 up to 100 ppm (up to 50 ppm in the Mid-Atlantic Ridge (MAR)) and in CH4 up to 12 ppm (up to 1 ppm in the MAR). Thus, it is suggested by the specific features of the melt composition that the Bouvet Island plume is thermochemical. This paper also presents a diagram showing free-convective flows in the asthenosphere in the Bouvet Triple Junction region. Sections are constructed on which the association between the convective structure and bottom morphostructures in the Bouvet region is identified. Large-scale asthenospheric flows are responsible for the formation of MOR. Convective rolls at the top of the asthenosphere account for the formation of the Bouvet and Moshesh transform faults. The Bouvet plume is under the influence of the ascending upper-mantle flow confined to the MOR axis and locally intensifies the ascending flows of the asthenospheric rolls.
{"title":"The Bouvet Plume: Parameters, Evolution, and Interaction with the Triple Junction of Midocean Ridges in the South Atlantic","authors":"A. Kirdyashkin, A. Kirdyashkin, V. Simonov, M. M. Buslov, A. Kotlyarov","doi":"10.2113/rgg20234568","DOIUrl":"https://doi.org/10.2113/rgg20234568","url":null,"abstract":"\u0000 —In the Bouvet Island region (South Atlantic), a hotspot operates in the region of the triple junction of midocean ridges. On the basis of laboratory modeling data, the structure of the conduit of a thermochemical plume melting out in the mantle from the core–mantle boundary is presented. The thermal power of the Bouvet thermochemical plume is determined from the volume of uplifted and erupted rocks above the lower topographic level. To determine the mass flow rate of the melt for the plume, a topographic profile is used in a section perpendicular to the Bouvet hotspot trajectory and passing through the Bouvet plume. The thermal power of the Bouvet plume is 1.7 · 1010 W. Based on the obtained power, the plume diameter is d = 10–13 km. The Bouvet plume belongs to intermediate-power plumes. Such plumes are diamondiferous, because their eruption on the surface transports the melt from a depth of >150 km, at which diamond is stable. The Bouvet plume trajectory originates in South Africa. Initially, the melt erupted on the cratonic surface through a diatreme. Next, the plume was preserved in the region of the drifting oceanic lithosphere and became no longer diamondiferous. The following morphostructures of the triple junction region with contrasting types of magmatic systems are distinguished according to petrological and geochemical data: MOR and the Bouvet volcanic island, which results from the plume activity. For the Bouvet region, K2О (0.5%) and Н2О (up to 0.9%) are identified in the composition of the deep magmatic melt. There is enrichment in H2 up to 100 ppm (up to 50 ppm in the Mid-Atlantic Ridge (MAR)) and in CH4 up to 12 ppm (up to 1 ppm in the MAR). Thus, it is suggested by the specific features of the melt composition that the Bouvet Island plume is thermochemical. This paper also presents a diagram showing free-convective flows in the asthenosphere in the Bouvet Triple Junction region. Sections are constructed on which the association between the convective structure and bottom morphostructures in the Bouvet region is identified. Large-scale asthenospheric flows are responsible for the formation of MOR. Convective rolls at the top of the asthenosphere account for the formation of the Bouvet and Moshesh transform faults. The Bouvet plume is under the influence of the ascending upper-mantle flow confined to the MOR axis and locally intensifies the ascending flows of the asthenospheric rolls.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":" ","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46600550","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
––The geochemical and mineralogical aspects of the distribution of rare-earth elements (REE) in ferruginous deposits (FD) and bottom sediments of the southeastern Laptev Sea are analyzed. The FD are dominated by biomorphs developed after polychaete tubes. The REE patterns depend on the proportion of ore and non-ore substances. The ore substance is represented mainly by iron hydroxides (limonite). It is a product of suboxic diagenesis enhanced by bioturbation and determines the slight enrichment of FD in MREE and cerium deficiency (Cean = 0.94). The non-ore substance comes from terrigenous sediments and has an (alumino)silicate composition. It controls the scandium content and is the source of REE mineral grains, among which monazite-(Ce) prevails. The sediments demonstrate a common similarity in REE patterns to shales and suspended material transported to the Laptev Sea by the Lena River, with elevated LREE and MREE contents and the value of Ce anomaly almost equal to unity (Cean = 1.06). In the sediments, REE minerals occur mostly in the silt fraction (<63 μm in size). The high content of organic matter (Corg of up to 2.15%) of predominantly terrigenous origin (OMter of up to 85%) in the sediments explains the oxygen deficiency and weak diagenetic mineral formation with low accumulation of trace elements, including REE, in the FD. The total REE content in the FD is lower than that in the sediments (on average, 173 ppm against 206 ppm).
{"title":"Geochemistry and Mineralogy of Rare-Earth Elements in Ferruginous Deposits and Bottom Sediments of the Laptev Sea","authors":"O. Kolesnik, A. Kolesnik, A. Astakhov","doi":"10.2113/rgg20234491","DOIUrl":"https://doi.org/10.2113/rgg20234491","url":null,"abstract":"\u0000 ––The geochemical and mineralogical aspects of the distribution of rare-earth elements (REE) in ferruginous deposits (FD) and bottom sediments of the southeastern Laptev Sea are analyzed. The FD are dominated by biomorphs developed after polychaete tubes. The REE patterns depend on the proportion of ore and non-ore substances. The ore substance is represented mainly by iron hydroxides (limonite). It is a product of suboxic diagenesis enhanced by bioturbation and determines the slight enrichment of FD in MREE and cerium deficiency (Cean = 0.94). The non-ore substance comes from terrigenous sediments and has an (alumino)silicate composition. It controls the scandium content and is the source of REE mineral grains, among which monazite-(Ce) prevails. The sediments demonstrate a common similarity in REE patterns to shales and suspended material transported to the Laptev Sea by the Lena River, with elevated LREE and MREE contents and the value of Ce anomaly almost equal to unity (Cean = 1.06). In the sediments, REE minerals occur mostly in the silt fraction (<63 μm in size). The high content of organic matter (Corg of up to 2.15%) of predominantly terrigenous origin (OMter of up to 85%) in the sediments explains the oxygen deficiency and weak diagenetic mineral formation with low accumulation of trace elements, including REE, in the FD. The total REE content in the FD is lower than that in the sediments (on average, 173 ppm against 206 ppm).","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":" ","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48538601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. Pushkarev, A. V. Lavrenchuk, I. Gottman, E. Sklyarov
––The paper presents new data on the chemical and mineral compositions of ultramafic rocks and various gabbro of the Birkhin massif in the Ol’khon region. Porphyric phenocrysts and zoned grains of clinopyroxene have been first found and studied in gabbronorite, which made it possible to reconstruct the entire melt crystallization trend from ultramafic to gabbro parageneses. Similar clinopyroxene trends have been established for clinopyroxenites and subvolcanic ankaramites, whose bodies and dikes have been recently discovered within the massif and in its environment. The total petrological data show that the magnesian high-Ca ankaramite melt corresponds in composition to the assumed primary melt for the Birkhin massif.
{"title":"Calcium-Rich Ultramafites, Ankaramites, and Clinopyroxene–Porphyric Gabbro of the Birkhin Massif in the Ol’khon Region: Solution of the Problem of Primary Melt and Formation of Intrusion","authors":"E. Pushkarev, A. V. Lavrenchuk, I. Gottman, E. Sklyarov","doi":"10.2113/rgg20234571","DOIUrl":"https://doi.org/10.2113/rgg20234571","url":null,"abstract":"\u0000 ––The paper presents new data on the chemical and mineral compositions of ultramafic rocks and various gabbro of the Birkhin massif in the Ol’khon region. Porphyric phenocrysts and zoned grains of clinopyroxene have been first found and studied in gabbronorite, which made it possible to reconstruct the entire melt crystallization trend from ultramafic to gabbro parageneses. Similar clinopyroxene trends have been established for clinopyroxenites and subvolcanic ankaramites, whose bodies and dikes have been recently discovered within the massif and in its environment. The total petrological data show that the magnesian high-Ca ankaramite melt corresponds in composition to the assumed primary melt for the Birkhin massif.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":" ","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43408300","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
—Preservation of soft-bodied organisms as casts is common in the Ediacaran fossil record and extremely rare in Cambrian rocks. Among the factors, limiting fossilization of soft tissues, there is bioturbation–sediment disturbance by burrowing organisms. It is the emergence of burrowing metazoans and associated sediment bioturbation that is thought to be one of the major causes for the disappearance of Ediacaran soft-bodied organisms from the fossil record around ~540 Ma. Here, we study an assemblage of fossils preserved as casts in the Fortunian carbonates of the Olenek Uplift (northeastern Siberian Platform) in association with a typical Fortunian ichnoassemblage. The overall morphology and preservation of the fossils reveal that they comprise microbially induced sedimentary structures and soft-bodied holdfasts. The latter are vaguely reminiscent of some Ediacaran holdfasts, though it is unlikely that they include their phylogenetic descendants. Three-dimensional preservation of the studied fossils was caused by authigenic crystallization of calcite and its further early-diagenetic dolomitization. Our study confirms the critical importance of specific environmental conditions ensuring preservation of soft-bodied organisms as three-dimensional molds and casts. This unique interplay of environmental factors became rare in the Cambrian Period, which was caused by intensification and expansion of bioturbation in marine basins.
{"title":"Preservation of Soft-Bodied Organisms in Early Cambrian Carbonates","authors":"V. Marusin, N. Bykova","doi":"10.2113/rgg20234595","DOIUrl":"https://doi.org/10.2113/rgg20234595","url":null,"abstract":"\u0000 —Preservation of soft-bodied organisms as casts is common in the Ediacaran fossil record and extremely rare in Cambrian rocks. Among the factors, limiting fossilization of soft tissues, there is bioturbation–sediment disturbance by burrowing organisms. It is the emergence of burrowing metazoans and associated sediment bioturbation that is thought to be one of the major causes for the disappearance of Ediacaran soft-bodied organisms from the fossil record around ~540 Ma. Here, we study an assemblage of fossils preserved as casts in the Fortunian carbonates of the Olenek Uplift (northeastern Siberian Platform) in association with a typical Fortunian ichnoassemblage. The overall morphology and preservation of the fossils reveal that they comprise microbially induced sedimentary structures and soft-bodied holdfasts. The latter are vaguely reminiscent of some Ediacaran holdfasts, though it is unlikely that they include their phylogenetic descendants. Three-dimensional preservation of the studied fossils was caused by authigenic crystallization of calcite and its further early-diagenetic dolomitization. Our study confirms the critical importance of specific environmental conditions ensuring preservation of soft-bodied organisms as three-dimensional molds and casts. This unique interplay of environmental factors became rare in the Cambrian Period, which was caused by intensification and expansion of bioturbation in marine basins.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":" ","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45750735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. N. Kungulova, P. Tishin, D. Lychagin, A. Tomilenko, E. Moskvichev
—The behavior of fluids during plastic deformation is studied from the morphology and distribution of fluid inclusions in quartz grains of different microstructure types from a vein system controlled by thrusting and strike-slip faulting in the eastern Sayan–Baikal fold area. The analytical work includes electron backscatter diffraction (EBSD) for quartz microstructure and crystallography, as well as Linkam heating-and-freezing analysis and Raman spectroscopy for the composition of fluid inclusions. The studied fluid inclusions are of seven types that differ in morphology and position in the deformed quartz structure. A model is suggested to describe successive structural changes of quartz aggregates during dislocation sliding and subsequent creep-related recrystallization associated with redistribution of fluid. Fluid inclusions undergo qualitative and quantitative changes due to water leakage at all stages of plastic deformation. The changes occur by two main mechanisms: (i) mass transfer during dislocation sliding at medium temperatures and strain rates and (ii) diffusion creep at low strain rates and high temperatures. The contribution of creep increases gradually with temperature, which maintains the interaction of inclusions with migrating grain boundaries.
{"title":"Morphology and Composition Changes in Fluid Inclusions from Quartz under Progressive Deformation: Case Study of a Vein System in the Western Kelyan-Irokinda Fold Zone (Western Transbaikalia)","authors":"E. N. Kungulova, P. Tishin, D. Lychagin, A. Tomilenko, E. Moskvichev","doi":"10.2113/rgg20234546","DOIUrl":"https://doi.org/10.2113/rgg20234546","url":null,"abstract":"\u0000 —The behavior of fluids during plastic deformation is studied from the morphology and distribution of fluid inclusions in quartz grains of different microstructure types from a vein system controlled by thrusting and strike-slip faulting in the eastern Sayan–Baikal fold area. The analytical work includes electron backscatter diffraction (EBSD) for quartz microstructure and crystallography, as well as Linkam heating-and-freezing analysis and Raman spectroscopy for the composition of fluid inclusions. The studied fluid inclusions are of seven types that differ in morphology and position in the deformed quartz structure. A model is suggested to describe successive structural changes of quartz aggregates during dislocation sliding and subsequent creep-related recrystallization associated with redistribution of fluid. Fluid inclusions undergo qualitative and quantitative changes due to water leakage at all stages of plastic deformation. The changes occur by two main mechanisms: (i) mass transfer during dislocation sliding at medium temperatures and strain rates and (ii) diffusion creep at low strain rates and high temperatures. The contribution of creep increases gradually with temperature, which maintains the interaction of inclusions with migrating grain boundaries.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":" ","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47488713","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Barkov, A. A. Nikiforov, V. Korolyuk, R. Martin
—In this paper, we present a description of the characteristics of the Lotmvara-II sill, which is a representative of the Serpentinite Belt (SB) composed of a series of shallowly emplaced ultrabasic intrusive bodies. The Paleoproterozoic SB complexes were derived from a large-scale mantle plume of komatiitic melt. The sill consists predominantly of fine-grained (locally nearly micrograined) harzburgites with subordinate zones of dunites and orthopyroxenites, located in the central and marginal parts, respectively. It formed from an Al-undepleted komatiitic magma of extremely high Mg content and may represent a near-surface laccolithic “ridge.” In general, the sill is comparatively homogeneous and does not have distinct zoning in the distribution of Mg# values in rock compositions (Mg# = 84.2–88.9, average 86.7). Detailed studies show that olivine, chromian spinel, and ilmenite are the most strongly magnesian in the central part of the body. The maximum values of Mg# equal to 90.7–91.4 in the compositions of olivine at the center of the sill are interpreted as “centers of initial crystallization”. The low values of Mg# equal to 73.4–76.4 are attributed to manifestations of the recurrent generation of olivine. The values of Mg# of orthopyroxene in the sill are within the range 84.6 to 92.3. Orthopyroxene grains in a porphyritic texture are surrounded by a rim of calcic amphibole (autometasomatic in origin); they do not differ compositionally from normal grains. The Zn content of the chromian spinel generally decreases toward the marginal parts of the sill. There is an insignificant degree of magmatic differentiation in the sill with respect to the principal components, but incompatible elements (REE and HFSE) locally show increased levels of their relative enrichment, which is reflected in the nature of the mineral associations described. Thus, the sill has a cryptic zonal structure, which is consistent with its overall crystallization from the center to the edges. The data gathered suggest the presence and significant development of volatile components, halogens, CO2, and especially magmatic H2O, which are capable of strongly lowering the liquidus and reducing the density and viscosity of the high-magnesium melt, thereby improving its mobility during ascent from the mantle to the near-surface level of the crust. An increase in fO2 is observed during in situ subvolcanic crystallization of the sill, as noted earlier in the related complexes of the belt. The relatively small volume of the komatiitic magma in the sill crystallized fairly quickly, resulting in unusual mineral intergrowths. Thus, the Lotmvara-II sill is a novel member in the Serpentinite Belt–Tulppio Belt (SB–TB) in the Paleoproterozoic SB–TB megastructure of the Fennoscandian Shield.
{"title":"Mineral–Geochemical and Geotectonic Features of the Lotmvara-II Ultrabasic Sill, Serpentinite Belt (Kola Peninsula)","authors":"A. Barkov, A. A. Nikiforov, V. Korolyuk, R. Martin","doi":"10.2113/rgg20234538","DOIUrl":"https://doi.org/10.2113/rgg20234538","url":null,"abstract":"\u0000 —In this paper, we present a description of the characteristics of the Lotmvara-II sill, which is a representative of the Serpentinite Belt (SB) composed of a series of shallowly emplaced ultrabasic intrusive bodies. The Paleoproterozoic SB complexes were derived from a large-scale mantle plume of komatiitic melt. The sill consists predominantly of fine-grained (locally nearly micrograined) harzburgites with subordinate zones of dunites and orthopyroxenites, located in the central and marginal parts, respectively. It formed from an Al-undepleted komatiitic magma of extremely high Mg content and may represent a near-surface laccolithic “ridge.” In general, the sill is comparatively homogeneous and does not have distinct zoning in the distribution of Mg# values in rock compositions (Mg# = 84.2–88.9, average 86.7). Detailed studies show that olivine, chromian spinel, and ilmenite are the most strongly magnesian in the central part of the body. The maximum values of Mg# equal to 90.7–91.4 in the compositions of olivine at the center of the sill are interpreted as “centers of initial crystallization”. The low values of Mg# equal to 73.4–76.4 are attributed to manifestations of the recurrent generation of olivine. The values of Mg# of orthopyroxene in the sill are within the range 84.6 to 92.3. Orthopyroxene grains in a porphyritic texture are surrounded by a rim of calcic amphibole (autometasomatic in origin); they do not differ compositionally from normal grains. The Zn content of the chromian spinel generally decreases toward the marginal parts of the sill. There is an insignificant degree of magmatic differentiation in the sill with respect to the principal components, but incompatible elements (REE and HFSE) locally show increased levels of their relative enrichment, which is reflected in the nature of the mineral associations described. Thus, the sill has a cryptic zonal structure, which is consistent with its overall crystallization from the center to the edges. The data gathered suggest the presence and significant development of volatile components, halogens, CO2, and especially magmatic H2O, which are capable of strongly lowering the liquidus and reducing the density and viscosity of the high-magnesium melt, thereby improving its mobility during ascent from the mantle to the near-surface level of the crust. An increase in fO2 is observed during in situ subvolcanic crystallization of the sill, as noted earlier in the related complexes of the belt. The relatively small volume of the komatiitic magma in the sill crystallized fairly quickly, resulting in unusual mineral intergrowths. Thus, the Lotmvara-II sill is a novel member in the Serpentinite Belt–Tulppio Belt (SB–TB) in the Paleoproterozoic SB–TB megastructure of the Fennoscandian Shield.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":" ","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46327173","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
I. Seminsky, А.K. Seminsky, А. Pospeev, F.R. Rustamova
—The Angara regional fault which is transversal to the Baikal basin totals about 150 km in length and ranks as a major strike-slip fault with the normal component in the seismically active rift zone. Given that its vicinities represent an area with high population density, the emphasis needs to be placed primarily on the study of its structural features. At this, the Angara fault has been poorly studied by geophysical methods. Results of the specialized mapping carried out in the 1990s revealed the block structure of the Angara fault zone, however without a reliable identification of the fault plane, which leaves its position still to be debatable. To establish the Angara fault plane and studying its deep structure, the integration of such geophysical methods as magnetotelluric (MT) sounding, radon emanation and fieldwalking magnetic surveys was required. Their application in the study of the deep structure of the southern parts of the Angara fault allowed revealing anomalies in all of the measured fields, accordingly. The anomaly-forming object, which the authors associate with the deep penetrated Angara fault plane, was expressed in the most distinct way by the magnetotelluric data (as a high-resistivity region (ER = 8500 Ohm∙m) relative to the host rock) and radon emanation survey (radon volumetric activity index RAI ≥ 20). The fact that the magnetic field received only minor distortions from the object may indicate either moderate magnetic characteristics of the latter or a significant occurrence depth. The identified anomaly-forming object localized within the crystalline basement tends to be more sharply expressed in the left bank of the Irkutsk Reservoir, while in the upper part of the cross-section it is overprinted by rocks of the sedimentary cover.
{"title":"Integration of Geophysical Methods to Study Deep Structure of the Angara Fault, the Largest in the Baikal Rift","authors":"I. Seminsky, А.K. Seminsky, А. Pospeev, F.R. Rustamova","doi":"10.2113/rgg20234539","DOIUrl":"https://doi.org/10.2113/rgg20234539","url":null,"abstract":"\u0000 —The Angara regional fault which is transversal to the Baikal basin totals about 150 km in length and ranks as a major strike-slip fault with the normal component in the seismically active rift zone. Given that its vicinities represent an area with high population density, the emphasis needs to be placed primarily on the study of its structural features. At this, the Angara fault has been poorly studied by geophysical methods. Results of the specialized mapping carried out in the 1990s revealed the block structure of the Angara fault zone, however without a reliable identification of the fault plane, which leaves its position still to be debatable. To establish the Angara fault plane and studying its deep structure, the integration of such geophysical methods as magnetotelluric (MT) sounding, radon emanation and fieldwalking magnetic surveys was required. Their application in the study of the deep structure of the southern parts of the Angara fault allowed revealing anomalies in all of the measured fields, accordingly. The anomaly-forming object, which the authors associate with the deep penetrated Angara fault plane, was expressed in the most distinct way by the magnetotelluric data (as a high-resistivity region (ER = 8500 Ohm∙m) relative to the host rock) and radon emanation survey (radon volumetric activity index RAI ≥ 20). The fact that the magnetic field received only minor distortions from the object may indicate either moderate magnetic characteristics of the latter or a significant occurrence depth. The identified anomaly-forming object localized within the crystalline basement tends to be more sharply expressed in the left bank of the Irkutsk Reservoir, while in the upper part of the cross-section it is overprinted by rocks of the sedimentary cover.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":" ","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43115314","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
––A continuous history of annual air temperatures in the Russian Altai for the past 2000 years has been reconstructed for the first time by integrating climate archives stored in the bottom sediments of four lakes in Gorny Altai (Teletskoye, Kucherla, Lower Multa, and Middle Multa). The integrated chronology comprises all known climate events of the two milennia time span: Roman warm epoch (~200 to 500 AD), Dark Age cold epoch (~500 to 750 AD), medieval warming (~750 to 1300 AD), and Little Ice Age (~1300 to 1850 AD). The events distinguished in the integrated climate reconstruction agree perfectly in number and time with the events reconstructed from other climate proxies for the Altai and adjacent areas of West Siberia, Tyva, and West Mongolia. Therefore, the temperature patterns represent a common course of the 2000-year climate evolution over a large part of Central Asia. Similar synchronicity is observed with the available quantitative climate reconstructions for the Northern Hemisphere and its different regions. It means that the climate change in Central Asia over the past two millennia has followed the general global scenario.
{"title":"Two Millennia of Climate History for the Russian Altai: Integrated Reconstruction from Lake Sediment Data","authors":"V. V. Babich, A. Daryin, N. Rudaya, T. Markovich","doi":"10.2113/rgg20234585","DOIUrl":"https://doi.org/10.2113/rgg20234585","url":null,"abstract":"––A continuous history of annual air temperatures in the Russian Altai for the past 2000 years has been reconstructed for the first time by integrating climate archives stored in the bottom sediments of four lakes in Gorny Altai (Teletskoye, Kucherla, Lower Multa, and Middle Multa). The integrated chronology comprises all known climate events of the two milennia time span: Roman warm epoch (~200 to 500 AD), Dark Age cold epoch (~500 to 750 AD), medieval warming (~750 to 1300 AD), and Little Ice Age (~1300 to 1850 AD). The events distinguished in the integrated climate reconstruction agree perfectly in number and time with the events reconstructed from other climate proxies for the Altai and adjacent areas of West Siberia, Tyva, and West Mongolia. Therefore, the temperature patterns represent a common course of the 2000-year climate evolution over a large part of Central Asia. Similar synchronicity is observed with the available quantitative climate reconstructions for the Northern Hemisphere and its different regions. It means that the climate change in Central Asia over the past two millennia has followed the general global scenario.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":" ","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47340895","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：