Pub Date : 2024-05-13DOI: 10.1134/s1028334x24602037
Iv. Iv. Nikulin, N. M. Boeva, N. S. Bortnikov
Abstract
Clay minerals formed as a result of hydrothermal activity within kimberlite pipes are redeposited into the horizons of the Lower Jurassic diamondiferous sedimentary rocks of proximal provenance. The mineral composition of the Lower Jurassic Dyakhtar Formation, composed of paleodeluvial and paleokarst deposits, has been studied in the immediate proximity and at a distance from kimberlite pipes. Mixed-layer minerals with structural heterogeneities, in which an increased concentration (up to 0.1 wt %) of lithium is noted, are found in sections of erosion plumes of weathered varieties of kimberlite rocks. The thickness of sediments with such minerals decreases sharply at distances of more than 2 km from the sought kimberlite body. The identified features in the mineral composition of the sedimentary rocks overlying kimberlite pipes can be used as new prospecting signs of the diamond potential during geological exploration of primary sources of diamonds.
{"title":"Structural Heterogeneities of Lithium-Bearing Layered Silicates of Paleokarst Near Kimberlites and Their Prospecting Value (Middle Markha Diamond-Bearing Region, Western Yakutia)","authors":"Iv. Iv. Nikulin, N. M. Boeva, N. S. Bortnikov","doi":"10.1134/s1028334x24602037","DOIUrl":"https://doi.org/10.1134/s1028334x24602037","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>Clay minerals formed as a result of hydrothermal activity within kimberlite pipes are redeposited into the horizons of the Lower Jurassic diamondiferous sedimentary rocks of proximal provenance. The mineral composition of the Lower Jurassic Dyakhtar Formation, composed of paleodeluvial and paleokarst deposits, has been studied in the immediate proximity and at a distance from kimberlite pipes. Mixed-layer minerals with structural heterogeneities, in which an increased concentration (up to 0.1 wt %) of lithium is noted, are found in sections of erosion plumes of weathered varieties of kimberlite rocks. The thickness of sediments with such minerals decreases sharply at distances of more than 2 km from the sought kimberlite body. The identified features in the mineral composition of the sedimentary rocks overlying kimberlite pipes can be used as new prospecting signs of the diamond potential during geological exploration of primary sources of diamonds.</p>","PeriodicalId":11352,"journal":{"name":"Doklady Earth Sciences","volume":"16 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140929692","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}
Pub Date : 2024-05-13DOI: 10.1134/s1028334x24601895
V. V. Zuev, E. S. Savelieva
Abstract
The dynamic characteristics of the stratospheric polar vortices at the levels from 100 to 1 hPa (minimum vortex area, minimum mean wind speed along the vortex edge, and the minimum wind speed at which there is a dynamic barrier is maintained) are presented for the first time. These parameters were obtained with the use of the vortex delineation method with the geopotential on the basis of the ERA5 reanalysis data. Seasonal changes and the average winter vertical profiles of the vortex area, mean wind speed along the vortex edge, and mean temperature inside the vortex for the Antarctic and Arctic polar vortices were obtained. The average daily probability of the dynamic barrier weakening along the vortex edge in winter was determined on the basis of data for 1979–2021 over the Arctic and Antarctic. It was shown that the lowest probability of the dynamic barrier weakening (and possible breakdown of the polar vortex) in winter can be traced at levels from 30 to 3 hPa and reaches less than 50% in the Arctic and less than 1% in the Antarctic. At the level of 50 hPa, the probability of the dynamic barrier weakening is 53.7% in the Arctic and 1.4% in the Antarctic.
{"title":"Dynamic Characteristics of the Stratospheric Polar Vortices","authors":"V. V. Zuev, E. S. Savelieva","doi":"10.1134/s1028334x24601895","DOIUrl":"https://doi.org/10.1134/s1028334x24601895","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The dynamic characteristics of the stratospheric polar vortices at the levels from 100 to 1 hPa (minimum vortex area, minimum mean wind speed along the vortex edge, and the minimum wind speed at which there is a dynamic barrier is maintained) are presented for the first time. These parameters were obtained with the use of the vortex delineation method with the geopotential on the basis of the ERA5 reanalysis data. Seasonal changes and the average winter vertical profiles of the vortex area, mean wind speed along the vortex edge, and mean temperature inside the vortex for the Antarctic and Arctic polar vortices were obtained. The average daily probability of the dynamic barrier weakening along the vortex edge in winter was determined on the basis of data for 1979–2021 over the Arctic and Antarctic. It was shown that the lowest probability of the dynamic barrier weakening (and possible breakdown of the polar vortex) in winter can be traced at levels from 30 to 3 hPa and reaches less than 50% in the Arctic and less than 1% in the Antarctic. At the level of 50 hPa, the probability of the dynamic barrier weakening is 53.7% in the Arctic and 1.4% in the Antarctic.</p>","PeriodicalId":11352,"journal":{"name":"Doklady Earth Sciences","volume":"95 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140929679","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}
Pub Date : 2024-05-13DOI: 10.1134/s1028334x24601937
E. P. Bazarova, O. I. Kadebskaya, E. A. Tsurikhin, A. M. Kononov
Abstract
A cave formed in the course of sulfuric acid speleogenesis was explored in Uzbekistan. Evidence of the sulfuric acid speleogenesis includes the characteristic morphology of this cave, an upward flow of warm chloride–sulfate sodium–calcium groundwater with the release of hydrogen sulfide, a widespread development of the ascending passage, the presence of biomats in water, and characteristic secondary minerals. Based on the chemical composition and values of stable isotopes of oxygen and hydrogen, it is concluded that groundwater of the cave was formed by mixing of infiltration fresh and marine sedimentogenic waters. The cave is an example of active sulfuric acid speleogenesis in Uzbekistan.
{"title":"The First Study Results for Sulfuric Acid Speleogenesis in Uzbekistan (Central Asia)","authors":"E. P. Bazarova, O. I. Kadebskaya, E. A. Tsurikhin, A. M. Kononov","doi":"10.1134/s1028334x24601937","DOIUrl":"https://doi.org/10.1134/s1028334x24601937","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>A cave formed in the course of sulfuric acid speleogenesis was explored in Uzbekistan. Evidence of the sulfuric acid speleogenesis includes the characteristic morphology of this cave, an upward flow of warm chloride–sulfate sodium–calcium groundwater with the release of hydrogen sulfide, a widespread development of the ascending passage, the presence of biomats in water, and characteristic secondary minerals. Based on the chemical composition and values of stable isotopes of oxygen and hydrogen, it is concluded that groundwater of the cave was formed by mixing of infiltration fresh and marine sedimentogenic waters. The cave is an example of active sulfuric acid speleogenesis in Uzbekistan.</p>","PeriodicalId":11352,"journal":{"name":"Doklady Earth Sciences","volume":"96 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140929693","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}
Pub Date : 2024-05-13DOI: 10.1134/s1028334x24601913
U. S. Efremova, T. V. Donskaya, D. P. Gladkochub, A. M. Mazukabzov, A. V. Ivanov, N. V. Bryansky
Abstract
U–Pb (LA-ICP-MS) geochronological studies of detrital zircon from rocks of the Early Proterozoic Khargitui Formation of the Sarma Group, distributed in the central part of the Baikal uplift of the Siberian craton basement and included into the structure of the Sarma zone of the Akitkan orogenic belt, are carried out. It is established that the Khargitui Formation comprises the rocks formed in different time intervals: >2.7, 2.15–1.95, and <1.7 Ga. It is shown that Meso- and Neoarchean age peaks (2.7–3.1 Ga) are characteristic of zircon from leucocratic gneisses, which indicates the formation of gneiss protoliths after 2.7 Ga due to the destruction of Archean granitoids in the Sarma zone of the Akitkan orogenic belt and igneous rocks in the Anabar superterrane basement of the Siberian craton. The time interval of 2.15–1.95 Ga corresponds to the accumulation of protoliths of mica–quartz schists, which is substantiated by the age of the youngest zircon grains of 2150 Ma and the age of metamorphism of these rocks of 1.95 Ga. The presence of an age peak at 1833 Ma and younger zircon grains aged in the range of 1675–1785 Ma in the sample of mica–quartz schist taken from another area of rock outcrops assigned to the Khargitui Formation indicates that the protoliths of these rocks accumulated after the formation of the Akitkan orogenic belt and the South Siberian postcollisional magmatic belt. The results obtained indicate that the rocks assigned to the Khargitui Formation of the Sarma Group of the Western Baikal region cannot be considered as a single stratigraphic unit, since they formed at different stages of the evolution of the Akitkan orogenic belt. It is shown that, based on recent data, the deposits of the Khargitui Formation should be divided into complexes of different ages (stratigraphic units), each of which corresponds to a certain stage of the geological evolution of the territory.
摘要 对分布在西伯利亚克拉通基底贝加尔隆起带中部、被纳入阿基坦造山带萨玛区构造的萨玛组早新生代哈尔吉图地层岩石中的锆英石碎片进行了U-Pb（LA-ICP-MS）地质年代研究。研究确定，哈尔吉图地层由不同时间段形成的岩石组成：2.7、2.15-1.95 和 1.7 Ga。研究表明，白云母片麻岩中的锆石具有中、新元古代年龄峰值（2.7-3.1 Ga）的特征，这表明片麻岩原岩是在 2.7 Ga 之后由于阿基坦造山带萨尔马区的阿基坦花岗岩和西伯利亚克拉通阿纳巴尔超基底的火成岩的破坏而形成的。2.15-1.95Ga的时间间隔与云母石英片岩原岩的堆积相对应，最年轻的锆石颗粒的年龄为2150Ma，这些岩石的变质年龄为1.95Ga，这些都证实了这一点。在另一个属于哈尔吉图地层的岩石露头地区采集的云母石英片岩样本中，出现了一个 1833 Ma 的年龄峰值和年龄在 1675-1785 Ma 之间的较年轻的锆石颗粒，这表明这些岩石的原岩是在阿基坦造山带和南西伯利亚碰撞后岩浆带形成之后堆积的。研究结果表明，西贝加尔湖地区萨玛组哈尔吉图地层的岩石不能被视为单一地层单元，因为它们形成于阿基坦造山带演化的不同阶段。研究表明，根据最新数据，哈尔吉图地层的沉积物应划分为不同时代的复合体（地层单元），每个复合体对应于该地区地质演变的某一阶段。
{"title":"Division of the Early Proterozoic Khargitui Formation of the Sarma Group (Akitkan Orogenic Belt, Siberian Craton) into Different Age Sequences Based on the Results of U–Pb Isotopic Analysis of Zircon","authors":"U. S. Efremova, T. V. Donskaya, D. P. Gladkochub, A. M. Mazukabzov, A. V. Ivanov, N. V. Bryansky","doi":"10.1134/s1028334x24601913","DOIUrl":"https://doi.org/10.1134/s1028334x24601913","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>U–Pb (LA-ICP-MS) geochronological studies of detrital zircon from rocks of the Early Proterozoic Khargitui Formation of the Sarma Group, distributed in the central part of the Baikal uplift of the Siberian craton basement and included into the structure of the Sarma zone of the Akitkan orogenic belt, are carried out. It is established that the Khargitui Formation comprises the rocks formed in different time intervals: >2.7, 2.15–1.95, and <1.7 Ga. It is shown that Meso- and Neoarchean age peaks (2.7–3.1 Ga) are characteristic of zircon from leucocratic gneisses, which indicates the formation of gneiss protoliths after 2.7 Ga due to the destruction of Archean granitoids in the Sarma zone of the Akitkan orogenic belt and igneous rocks in the Anabar superterrane basement of the Siberian craton. The time interval of 2.15–1.95 Ga corresponds to the accumulation of protoliths of mica–quartz schists, which is substantiated by the age of the youngest zircon grains of 2150 Ma and the age of metamorphism of these rocks of 1.95 Ga. The presence of an age peak at 1833 Ma and younger zircon grains aged in the range of 1675–1785 Ma in the sample of mica–quartz schist taken from another area of rock outcrops assigned to the Khargitui Formation indicates that the protoliths of these rocks accumulated after the formation of the Akitkan orogenic belt and the South Siberian postcollisional magmatic belt. The results obtained indicate that the rocks assigned to the Khargitui Formation of the Sarma Group of the Western Baikal region cannot be considered as a single stratigraphic unit, since they formed at different stages of the evolution of the Akitkan orogenic belt. It is shown that, based on recent data, the deposits of the Khargitui Formation should be divided into complexes of different ages (stratigraphic units), each of which corresponds to a certain stage of the geological evolution of the territory.</p>","PeriodicalId":11352,"journal":{"name":"Doklady Earth Sciences","volume":"2014 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140929677","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}
Pub Date : 2024-05-13DOI: 10.1134/s1028334x24601408
E. V. Agasheva, L. V. Zyryanova, A. M. Agashev, N. G. Soloshenko, N. P. Pokhilenko
Abstract
Recent data on the bulk and isotopic (Sr, Nd) composition of kimberlites from the low-diamondiferous TsNIGRI–Arkhangelskaya pipe, located in the Kepino field of the Arkhangelsk diamondiferous province, are presented. It is shown that the kimberlites belong to the moderate titanium type of kimberlites of the province and differ significantly from the previously studied kimberlites of the Kepino field in the lower concentrations of TiO2, Ba, high field strength, and light rare earth elements. Among all the kimberlites of the province, the kimberlites from the TsNIGRI–Arkhangelskaya pipe have the most radiogenic Sr composition (87Sr/86Sr t from 0.7068 to 0.7089), which may be related to a combination of several factors. It has been established that the kimberlites from the pipe are represented by two varieties, having differences both in the concentrations of major and trace elements and in the Sr and Nd isotopic composition. The Nd isotopic composition (εNd from 0 to –0.6) for type-I kimberlites indicates their enriched source in the lithospheric mantle. The type-II kimberlites have a less radiogenic Nd composition (εNd from –3.5 to –4.9), which is interpreted ambiguously: their formation from an even more ancient enriched source inside the lithospheric mantle compared to type-I kimberlites cannot be excluded.
摘要 本文介绍了位于阿尔汉格尔斯克金刚石矿区克皮诺矿田的低菱锰矿TsNIGRI-Arkhangelskaya矿管金伯利岩的块状成分和同位素（Sr、Nd）成分的最新数据。研究表明，这些金伯利岩属于该省的中等钛型金伯利岩，与之前研究过的克皮诺矿田金伯利岩在二氧化钛、钡、高场强和轻稀土元素含量方面有很大不同。在该省的所有金伯利岩中，来自 TsNIGRI-Arkhangelskaya 管道的金伯利岩的放射性 Sr 成分最高（87Sr/86Sr t 从 0.7068 到 0.7089），这可能与多种因素的综合作用有关。已经确定，来自该管道的金伯利岩有两个品种，在主要元素和微量元素的浓度以及硒和钕的同位素组成方面都存在差异。I 型金伯利岩的钕同位素组成（εNd 从 0 到 -0.6）表明其富源于岩石圈地幔。II型金伯利岩的钕同位素组成（εNd从-3.5到-4.9）的辐射性较低，对其解释含糊不清：与I型金伯利岩相比，不能排除它们是由岩石圈地幔内更古老的富集源形成的。
{"title":"Recent Data on the Isotope–Geochemical Composition of Kimberlites in the TSNIGRI-Arkhangelskaya Pipe, Arkhangelsk Diamondiferous Province (Northern East European Platform)","authors":"E. V. Agasheva, L. V. Zyryanova, A. M. Agashev, N. G. Soloshenko, N. P. Pokhilenko","doi":"10.1134/s1028334x24601408","DOIUrl":"https://doi.org/10.1134/s1028334x24601408","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>Recent data on the bulk and isotopic (Sr, Nd) composition of kimberlites from the low-diamondiferous TsNIGRI–Arkhangelskaya pipe, located in the Kepino field of the Arkhangelsk diamondiferous province, are presented. It is shown that the kimberlites belong to the moderate titanium type of kimberlites of the province and differ significantly from the previously studied kimberlites of the Kepino field in the lower concentrations of TiO<sub>2</sub>, Ba, high field strength, and light rare earth elements. Among all the kimberlites of the province, the kimberlites from the TsNIGRI–Arkhangelskaya pipe have the most radiogenic Sr composition (<sup>87</sup>Sr/<sup>86</sup>Sr t from 0.7068 to 0.7089), which may be related to a combination of several factors. It has been established that the kimberlites from the pipe are represented by two varieties, having differences both in the concentrations of major and trace elements and in the Sr and Nd isotopic composition. The Nd isotopic composition (ε<sub>Nd</sub> from 0 to –0.6) for type-I kimberlites indicates their enriched source in the lithospheric mantle. The type-II kimberlites have a less radiogenic Nd composition (ε<sub>Nd</sub> from –3.5 to –4.9), which is interpreted ambiguously: their formation from an even more ancient enriched source inside the lithospheric mantle compared to type-I kimberlites cannot be excluded.</p>","PeriodicalId":11352,"journal":{"name":"Doklady Earth Sciences","volume":"27 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140929684","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}
Pub Date : 2024-05-13DOI: 10.1134/s1028334x24601251
Nong Thi Quynh Anh, Tran Van Xuan, Pham Trung Hieu, Pham Minh, Nguyen Tuan, Nguyen Xuan Kha, Truong Quoc Thanh
Abstract
Late Mesozoic granitoids in the Dalat Zone are widely accepted to be formed in two main stages of magmatism corresponding to Paleo-Pacific subduction and post-orogenic regimes. This study focuses on the transitional phase (ca. 20 Ma interval) between these two stages with representatives of the Deoca granitoids and Ankroet granite in the southern Dalat Zone, mainly along the coastal line from Vung Tau to Binh Thuan. The Deoca rock suite comprises coarse- to medium-grained granites, fine-grained granophyric granite, and dyke phases while the Ankroet suite mainly comprises medium- to fine-grained granite. Although the whole-rock chemical characteristics of these two rock suites to some extent overlap each other with the peraluminous and calc-alkaline signatures and the similarities in element abundance yet exhibit distinction. Rocks of the Deoca suite are characterized by typical arc-like affinities with strong positive anomalies of Rb, Th, U, Pb, and Nd, and negative anomalies of Ba, Nb, Sr, P, Eu, and Ti. The Ankroet granite is especially more depleted in Sr, P, Eu, and Ti and enriched in Rb, Th, U, Ta, and Pb in comparison with the Deoca rock suite and can be categorized as “within-plate” granite formed in the following extensional stage. Zircon U–Pb geochronology of the two rock suites distinguishes two magmatic stages, 93.6 ± 1.3 Ma for the Deoca rocks and 73.3 ± 1.8 Ma for the Ankroet rocks. Zircon Hf isotopic compositions indicate the similarities in source materials of these two rock suites, but they might have been influenced by different geodynamics and magma differentiation processes. Zircon Hf isotopic compositions of the studied rocks are compared to those from the adjacent area (Cambodia, Datlat-Kratie Belt) and suggest that Carboniferous-Permian magmas generating inherited zircons in Cambodia are most likely the source materials of Late Mesozoic plutonic rocks in the Dalat Zone/Cambodia (Dalat-Kratie Belt). This study highlights the distinction of these two rock suites by new observations on zircon morphology and composition. Although they are both enriched in heavy REE relative to light REE, enriched in Ce and depleted in Eu and typical for magmatic zircons, samples of the Ankroet suite tend to be more enriched in REEs compared to those of the Deoca suite, except Eu with strong Eu anomaly. This may indicate the higher involvement of hydrothermal processes on Ankroet granite that is supported by common CL-dark rims of zircon.
{"title":"Two Stages of Late Mesozoic Magmatism in Southern Dalat Zone Associated with Paleo-Pacific Subduction Constrained by Whole-Rock Chemistry and Geochronology Combined with New Findings on Zircon Chemical Composition","authors":"Nong Thi Quynh Anh, Tran Van Xuan, Pham Trung Hieu, Pham Minh, Nguyen Tuan, Nguyen Xuan Kha, Truong Quoc Thanh","doi":"10.1134/s1028334x24601251","DOIUrl":"https://doi.org/10.1134/s1028334x24601251","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>Late Mesozoic granitoids in the Dalat Zone are widely accepted to be formed in two main stages of magmatism corresponding to Paleo-Pacific subduction and post-orogenic regimes. This study focuses on the transitional phase (ca. 20 Ma interval) between these two stages with representatives of the Deoca granitoids and Ankroet granite in the southern Dalat Zone, mainly along the coastal line from Vung Tau to Binh Thuan. The Deoca rock suite comprises coarse- to medium-grained granites, fine-grained granophyric granite, and dyke phases while the Ankroet suite mainly comprises medium- to fine-grained granite. Although the whole-rock chemical characteristics of these two rock suites to some extent overlap each other with the peraluminous and calc-alkaline signatures and the similarities in element abundance yet exhibit distinction. Rocks of the Deoca suite are characterized by typical arc-like affinities with strong positive anomalies of Rb, Th, U, Pb, and Nd, and negative anomalies of Ba, Nb, Sr, P, Eu, and Ti. The Ankroet granite is especially more depleted in Sr, P, Eu, and Ti and enriched in Rb, Th, U, Ta, and Pb in comparison with the Deoca rock suite and can be categorized as “within-plate” granite formed in the following extensional stage. Zircon U–Pb geochronology of the two rock suites distinguishes two magmatic stages, 93.6 ± 1.3 Ma for the Deoca rocks and 73.3 ± 1.8 Ma for the Ankroet rocks. Zircon Hf isotopic compositions indicate the similarities in source materials of these two rock suites, but they might have been influenced by different geodynamics and magma differentiation processes. Zircon Hf isotopic compositions of the studied rocks are compared to those from the adjacent area (Cambodia, Datlat-Kratie Belt) and suggest that Carboniferous-Permian magmas generating inherited zircons in Cambodia are most likely the source materials of Late Mesozoic plutonic rocks in the Dalat Zone/Cambodia (Dalat-Kratie Belt). This study highlights the distinction of these two rock suites by new observations on zircon morphology and composition. Although they are both enriched in heavy REE relative to light REE, enriched in Ce and depleted in Eu and typical for magmatic zircons, samples of the Ankroet suite tend to be more enriched in REEs compared to those of the Deoca suite, except Eu with strong Eu anomaly. This may indicate the higher involvement of hydrothermal processes on Ankroet granite that is supported by common CL-dark rims of zircon.</p>","PeriodicalId":11352,"journal":{"name":"Doklady Earth Sciences","volume":"65 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140929581","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}
Pub Date : 2024-05-13DOI: 10.1134/s1028334x24601858
E. S. Zhitova, D. S. Mikhailenko, I. V. Pekov, A. V. Korsakov, A. A. Zolotarev
Abstract
An atypical variety of iowaite with an extremely low content of divalent cations (Mg + Fe2+)/Fe3+ of ~2.75 : 1 is identified in a late hydrothermal mineral assemblage of the Udachnaya kimberlite pipe, Yakutia. Its crystal structure is studied using a single crystal: polytype 3R, space group (Rbar {3}m), a = 3.1213(3) Å, с = 23.621(4) Å, V = 199.30(5) Å3; R1 = 0.027. Some crystals are characterized by zonation indicating a natural ion exchange, the leading schemes of which are 2Cl– → SO(_{4}^{{2 - }}) and 2Cl– → 2SO(_{4}^{{2 - }}) + Ca2+. This is the first reliable case of natural anion exchange in minerals of the hydrotalcite supergroup. The anion exchange reaction occurs with an increase of interlayer distance from 8.0 to 11.2 Å. The composition of the mineral and the character of its zonation bear information on the evolution of late hydrothermal processes.
{"title":"Iowaite from the Udachnaya Kimberlite Pipe, Yakutia: Crystal Chemistry and Postcrystallization Transformations","authors":"E. S. Zhitova, D. S. Mikhailenko, I. V. Pekov, A. V. Korsakov, A. A. Zolotarev","doi":"10.1134/s1028334x24601858","DOIUrl":"https://doi.org/10.1134/s1028334x24601858","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>An atypical variety of iowaite with an extremely low content of divalent cations (Mg + Fe<sup>2+</sup>)/Fe<sup>3+</sup> of ~2.75 : 1 is identified in a late hydrothermal mineral assemblage of the Udachnaya kimberlite pipe, Yakutia. Its crystal structure is studied using a single crystal: polytype 3<i>R</i>, space group <span>(Rbar {3}m)</span>, <i>a</i> = 3.1213(3) Å, <i>с</i> = 23.621(4) Å, <i>V</i> = 199.30(5) Å<sup>3</sup>; <i>R</i><sub>1</sub> = 0.027. Some crystals are characterized by zonation indicating a natural ion exchange, the leading schemes of which are 2Cl<sup>–</sup> → SO<span>(_{4}^{{2 - }})</span> and 2Cl<sup>–</sup> → 2SO<span>(_{4}^{{2 - }})</span> + Ca<sup>2+</sup>. This is the first reliable case of natural anion exchange in minerals of the hydrotalcite supergroup. The anion exchange reaction occurs with an increase of interlayer distance from 8.0 to 11.2 Å. The composition of the mineral and the character of its zonation bear information on the evolution of late hydrothermal processes.</p>","PeriodicalId":11352,"journal":{"name":"Doklady Earth Sciences","volume":"7 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140929688","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}
Pub Date : 2024-05-02DOI: 10.1134/s1028334x24601901
R. B. Shakirov, V. A. Luchin, E. A. Petrova
Abstract
Based on all the available oceanological information (131 286 stations carried out from 1929 to 2020), for the first time for the Sea of Okhotsk, the spatial patterns of the upper boundary distribution parameters of the methane hydrate stability zone (water temperature, salinity, depth of the upper boundary in the water column) are presented and discussed. A model of the methane hydrate stability zone is considered. We revealed that the minimum water temperature and the minimum depth of the upper boundary of the gas hydrate stability zone (less than 1°C and 300–320 m, respectively) in the Sea of Okhotsk are located near the eastern slope of Sakhalin Island. The maximum water temperature and maximum depth of the upper boundary (1.5–1.7°C and 340–350 m, respectively) are characteristic of the area adjacent to the central and northern straits of the Kuril Islands Arc, as well as above the slope of the Kamchatka Peninsula. The salinity at the upper boundary of the methane hydrate stability zone in the Sea of Okhotsk varies within a narrow range from 33.4 to 33.6 psu, which is quite close to the conditions assume for the stability of methane hydrate in seawater. An area where the thermobaric conditions in the water column not favorable for the formation of methane hydrates has been identified.
{"title":"Spatial Variability of the Methane Hydrate Stability Zone’s Upper Boundary Parameters in the Water Column of the Sea of Okhotsk","authors":"R. B. Shakirov, V. A. Luchin, E. A. Petrova","doi":"10.1134/s1028334x24601901","DOIUrl":"https://doi.org/10.1134/s1028334x24601901","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>Based on all the available oceanological information (131 286 stations carried out from 1929 to 2020), for the first time for the Sea of Okhotsk, the spatial patterns of the upper boundary distribution parameters of the methane hydrate stability zone (water temperature, salinity, depth of the upper boundary in the water column) are presented and discussed. A model of the methane hydrate stability zone is considered. We revealed that the minimum water temperature and the minimum depth of the upper boundary of the gas hydrate stability zone (less than 1°C and 300–320 m, respectively) in the Sea of Okhotsk are located near the eastern slope of Sakhalin Island. The maximum water temperature and maximum depth of the upper boundary (1.5–1.7°C and 340–350 m, respectively) are characteristic of the area adjacent to the central and northern straits of the Kuril Islands Arc, as well as above the slope of the Kamchatka Peninsula. The salinity at the upper boundary of the methane hydrate stability zone in the Sea of Okhotsk varies within a narrow range from 33.4 to 33.6 psu, which is quite close to the conditions assume for the stability of methane hydrate in seawater. An area where the thermobaric conditions in the water column not favorable for the formation of methane hydrates has been identified.</p>","PeriodicalId":11352,"journal":{"name":"Doklady Earth Sciences","volume":"14 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140883066","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}
Pub Date : 2024-05-02DOI: 10.1134/s1028334x24601561
S. Yu. Sokolov, A. P. Denisova, I. S. Patina
Abstract
The study of the neotectonic deformation features of the sedimentary cover and seismicity of the Charlie Gibbs twin transform fault has shown that its southern trough is developed in a transtensional mode and its northern thrust, in a transpressional mode. Signs of activity in the structure of the upper part of the sedimentary section were noted in the eastern passive parts of the fault at a distance of at least 150 km from the active rift zone of the Mid-Atlantic Ridge. Dislocations of normal fault kinematics and signs of an increased sedimentation rate and occurrence of landslide clastic deposits near the trough slopes are manifested in the sedimentary section of the southern trough. The median ridge with folded structures, overlain by sediments with angular unconformity, is established in the axial part of the northern trough. Faults located south of the ridge are interpreted as reverse faults. At the present stage, the Northern trough is accompanied by the formation of piercements of the median ridge during extrusion of deep matter and accompanying deformations of the sedimentary cover.
{"title":"Geodynamic Setting of the Passive Part of the Charlie Gibbs Twin Transform Fault (North Atlantic)","authors":"S. Yu. Sokolov, A. P. Denisova, I. S. Patina","doi":"10.1134/s1028334x24601561","DOIUrl":"https://doi.org/10.1134/s1028334x24601561","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The study of the neotectonic deformation features of the sedimentary cover and seismicity of the Charlie Gibbs twin transform fault has shown that its southern trough is developed in a transtensional mode and its northern thrust, in a transpressional mode. Signs of activity in the structure of the upper part of the sedimentary section were noted in the eastern passive parts of the fault at a distance of at least 150 km from the active rift zone of the Mid-Atlantic Ridge. Dislocations of normal fault kinematics and signs of an increased sedimentation rate and occurrence of landslide clastic deposits near the trough slopes are manifested in the sedimentary section of the southern trough. The median ridge with folded structures, overlain by sediments with angular unconformity, is established in the axial part of the northern trough. Faults located south of the ridge are interpreted as reverse faults. At the present stage, the Northern trough is accompanied by the formation of piercements of the median ridge during extrusion of deep matter and accompanying deformations of the sedimentary cover.</p>","PeriodicalId":11352,"journal":{"name":"Doklady Earth Sciences","volume":"48 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140883181","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}
Pub Date : 2024-05-02DOI: 10.1134/s1028334x24601597
S. G. Soloviev, S. G. Kryazhev, D. V. Semenova, Yu. A. Kalinin, N. S. Bortnikov
Abstract
The paper presents the isotopic U–Pb study data (LA-ICP-MS method) of zircon from intrusive rocks of the Sonkul and Kokturpak plutons situated along the deep-seated fault system of the “Nikolaev Line” in the eastern Kyrgyzstan. These plutons of high-potassic rocks are spatially and genetically associated with the Kumbel and Kashkasu W–Mo–Cu–Au deposits, respectively, as well as other occurrences of W and W–Au mineralization. Together with other Au, W and Cu deposits, they are parts of the extended metallogenic belt of Tien Shan. The concordant isotopic U–Pb ages of zircon autocrysts for the consecutive intrusive phases span over the interval of approximately 303 to 283 Ma. This interval included the crystallization of olivine gabbro (299 ± 2 Ma) in the Sonkul pluton, monzonite (300 ± 3 Ma) in the Kokturpak pluton, granodiorite of the main intrusive phase (299 ± 3 Ma in the Sonkul pluton and 297 ± 4 Ma in the Kokturpak pluton), and monzogranite (289 ± 4 Ma in the Sonkul pluton and 285 ± 2 Ma in the Kokturpak pluton). Zircon antecrysts dated at 306–311 (to 323?) Ma have also been distinguished. The age data obtained correspond to the pluton emplacement in the Late Carboniferous-Early Permian initially in subduction-related and then post-collisional tectonic settings. Besides, in the Middle Tien Shan, this age interval corresponds to one of the regional pulses of high-potassic calc-alkaline and shoshonitic magmatism. A distinct metallogenic evolution corresponds to these pulses that is expressed in the change from porphyry Cu–Au–Mo deposits related to the early pulse to essentially tungsten (W–Mo–Cu–Au) and then essentially gold deposits related to younger pulses. The rocks also contain zircon xenocrysts with ancient age (in the order of 1.5–2.5 Ga) that probably represent the age of the Tarim craton basement.
{"title":"Late Paleozoic Stages of Ore Formation in the Middle Tian Shan: Isotopic U–Pb Zircon Dating (LA-ICP-MS Method) of Intrusive Rocks from the Sonkul and Kokturpak Plutons (Eastern Kyrgyzstan)","authors":"S. G. Soloviev, S. G. Kryazhev, D. V. Semenova, Yu. A. Kalinin, N. S. Bortnikov","doi":"10.1134/s1028334x24601597","DOIUrl":"https://doi.org/10.1134/s1028334x24601597","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The paper presents the isotopic U–Pb study data (LA-ICP-MS method) of zircon from intrusive rocks of the Sonkul and Kokturpak plutons situated along the deep-seated fault system of the “Nikolaev Line” in the eastern Kyrgyzstan. These plutons of high-potassic rocks are spatially and genetically associated with the Kumbel and Kashkasu W–Mo–Cu–Au deposits, respectively, as well as other occurrences of W and W–Au mineralization. Together with other Au, W and Cu deposits, they are parts of the extended metallogenic belt of Tien Shan. The concordant isotopic U–Pb ages of zircon autocrysts for the consecutive intrusive phases span over the interval of approximately 303 to 283 Ma. This interval included the crystallization of olivine gabbro (299 ± 2 Ma) in the Sonkul pluton, monzonite (300 ± 3 Ma) in the Kokturpak pluton, granodiorite of the main intrusive phase (299 ± 3 Ma in the Sonkul pluton and 297 ± 4 Ma in the Kokturpak pluton), and monzogranite (289 ± 4 Ma in the Sonkul pluton and 285 ± 2 Ma in the Kokturpak pluton). Zircon antecrysts dated at 306–311 (to 323?) Ma have also been distinguished. The age data obtained correspond to the pluton emplacement in the Late Carboniferous-Early Permian initially in subduction-related and then post-collisional tectonic settings. Besides, in the Middle Tien Shan, this age interval corresponds to one of the regional pulses of high-potassic calc-alkaline and shoshonitic magmatism. A distinct metallogenic evolution corresponds to these pulses that is expressed in the change from porphyry Cu–Au–Mo deposits related to the early pulse to essentially tungsten (W–Mo–Cu–Au) and then essentially gold deposits related to younger pulses. The rocks also contain zircon xenocrysts with ancient age (in the order of 1.5–2.5 Ga) that probably represent the age of the Tarim craton basement.</p>","PeriodicalId":11352,"journal":{"name":"Doklady Earth Sciences","volume":"21 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140883067","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}
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