A. Stepanova, V. S. Stepanov, A. Larionov, E. Salnikova, A. Samsonov, P. Azimov, S. Egorova, I. I. Babarina, Y. Larionova, M. A. Sukhanova, A. Kervinen, O. Maksimov
Abstract Geological, geochemical, isotopic and geochronological data for Paleoproterozoic mafic intrusions and dykes indicate that distinct magmatic events dated at c. 2.50, 2.45, 2.40, 2.30, 2.23 and 2.12 Ga can be distinguished in the Belomorian Province, Eastern Fennoscandian Shield. The similarity of Paleoproterozoic magmatic barcodes for the Belomorian Province and the Karelian Craton in the c. 2.5–2.1 Ga interval suggests a neighbouring position of these crustal segments in an Archean continent. Intensive tectonic and metamorphic reworking of mafic intrusions and dykes in the Belomorian Province during the c. 2.0–1.8 Ga Lapland–Kola Orogeny produced differences in mineral assemblages and tectonic position in comparison with the Karelian Craton.
{"title":"Relicts of Paleoproterozoic LIPs in the Belomorian Province, eastern Fennoscandian Shield: barcode reconstruction for a deeply eroded collisional orogen","authors":"A. Stepanova, V. S. Stepanov, A. Larionov, E. Salnikova, A. Samsonov, P. Azimov, S. Egorova, I. I. Babarina, Y. Larionova, M. A. Sukhanova, A. Kervinen, O. Maksimov","doi":"10.1144/SP518-2021-30","DOIUrl":"https://doi.org/10.1144/SP518-2021-30","url":null,"abstract":"Abstract Geological, geochemical, isotopic and geochronological data for Paleoproterozoic mafic intrusions and dykes indicate that distinct magmatic events dated at c. 2.50, 2.45, 2.40, 2.30, 2.23 and 2.12 Ga can be distinguished in the Belomorian Province, Eastern Fennoscandian Shield. The similarity of Paleoproterozoic magmatic barcodes for the Belomorian Province and the Karelian Craton in the c. 2.5–2.1 Ga interval suggests a neighbouring position of these crustal segments in an Archean continent. Intensive tectonic and metamorphic reworking of mafic intrusions and dykes in the Belomorian Province during the c. 2.0–1.8 Ga Lapland–Kola Orogeny produced differences in mineral assemblages and tectonic position in comparison with the Karelian Craton.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"122 1","pages":"101 - 128"},"PeriodicalIF":0.0,"publicationDate":"2021-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88132470","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The 1.1 Ga Midcontinent Rift System (MRS) of North America comprises a series of Mesoproterozoic flood basalts and intrusive rocks emplaced in the Lake Superior region. The mafic rocks preserved on the NW flank of Lake Superior offer insights into the early development of the rift. New geochemical data collected from intrusive rocks in the Logan Basin, coupled with improved constraints on timing relationships between units, allow for a better understanding of the geochemical evolution of intrusive rocks therein. The extensive dataset suggests many previously unrecognized relationships between MRS intrusive rocks, indicating multiple, distinct mantle-source characteristics with highly variable crustal contamination histories, implying a complicated magma plumbing system. The data presented here suggest that five geochemically distinct mantle source regions were involved in the emplacement of the Logan Igneous Suite, each with its own distinct contamination history and perhaps different degrees of partial melting. The geochemical variations could suggest either a progressive, relative depletion in the mantle source over time or heterogeneity of the source region. However, based on the model for MRS magmatism presented here, we suggest that units related to the Logan Igneous Suite were tapping a heterogeneous mantle source that varied over time.
{"title":"The geochemical evolution of the Logan Igneous Suite, Ontario, Canada: new insights from the Logan Basin and implications for the genesis of the Mesoproterozoic Midcontinent Rift System","authors":"R. Cundari, P. Hollings, M. Smyk, Christian Carl","doi":"10.1144/SP518-2021-6","DOIUrl":"https://doi.org/10.1144/SP518-2021-6","url":null,"abstract":"Abstract The 1.1 Ga Midcontinent Rift System (MRS) of North America comprises a series of Mesoproterozoic flood basalts and intrusive rocks emplaced in the Lake Superior region. The mafic rocks preserved on the NW flank of Lake Superior offer insights into the early development of the rift. New geochemical data collected from intrusive rocks in the Logan Basin, coupled with improved constraints on timing relationships between units, allow for a better understanding of the geochemical evolution of intrusive rocks therein. The extensive dataset suggests many previously unrecognized relationships between MRS intrusive rocks, indicating multiple, distinct mantle-source characteristics with highly variable crustal contamination histories, implying a complicated magma plumbing system. The data presented here suggest that five geochemically distinct mantle source regions were involved in the emplacement of the Logan Igneous Suite, each with its own distinct contamination history and perhaps different degrees of partial melting. The geochemical variations could suggest either a progressive, relative depletion in the mantle source over time or heterogeneity of the source region. However, based on the model for MRS magmatism presented here, we suggest that units related to the Logan Igneous Suite were tapping a heterogeneous mantle source that varied over time.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"298 1","pages":"43 - 65"},"PeriodicalIF":0.0,"publicationDate":"2021-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77018024","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ángela Fraguas, J. J. Gómez, A. Goy, M. J. Comas-Rengifo
Abstract Quantitative analysis performed on latest Pliensbachian–early Toarcian calcareous nannofossil assemblages from the Camino section (Basque Cantabrian Basin) allowed their response to the environmental changes recorded during this time interval to be deciphered, characterized by an extinction event. The results were introduced within a principal component analysis and compared with the stable isotope and total organic carbon curves. During the latest Pliensbachian, the Mirabile and the lowermost part of the Semicelatum Ammonite Subzones, Schizosphaerella, Bussonius prinsii, Biscutum finchii, Calcivascularis jansae and Similiscutum avitum, taxa that probably thrived in rather cold waters, dominated the calcareous nannofossil assemblages. Coinciding with warmer and wetter conditions, which probably led to an increase in surface water fertility, recorded slightly below the extinction boundary, the mesotrophic taxa B. novum, L. hauffii and Calyculus spp. were dominant. Nevertheless, T. patulus and C. jansae, which became extinct just below the extinction boundary, show preferences for oligotrophic conditions. Salinities similar to those of modern oceans have been inferred around the extinction boundary, considering the coupling between the abundances of Calyculus spp. and the species richness together with the absence of black shales. After the extinction boundary, nannofossil assemblages were dominated by the deep-dwelling C. crassus and the shallow-dwelling Lotharingius species, interpreted as opportunistic taxa. This work confirms that calcareous nannofossils are a really useful tool for palaeoceanographic and palaeoenvironmental reconstructions, especially in terms of climatic changes.
{"title":"The response of calcareous nannoplankton to the latest Pliensbachian–early Toarcian environmental changes in the Camino Section (Basque Cantabrian Basin, northern Spain)","authors":"Ángela Fraguas, J. J. Gómez, A. Goy, M. J. Comas-Rengifo","doi":"10.1144/SP514-2020-256","DOIUrl":"https://doi.org/10.1144/SP514-2020-256","url":null,"abstract":"Abstract Quantitative analysis performed on latest Pliensbachian–early Toarcian calcareous nannofossil assemblages from the Camino section (Basque Cantabrian Basin) allowed their response to the environmental changes recorded during this time interval to be deciphered, characterized by an extinction event. The results were introduced within a principal component analysis and compared with the stable isotope and total organic carbon curves. During the latest Pliensbachian, the Mirabile and the lowermost part of the Semicelatum Ammonite Subzones, Schizosphaerella, Bussonius prinsii, Biscutum finchii, Calcivascularis jansae and Similiscutum avitum, taxa that probably thrived in rather cold waters, dominated the calcareous nannofossil assemblages. Coinciding with warmer and wetter conditions, which probably led to an increase in surface water fertility, recorded slightly below the extinction boundary, the mesotrophic taxa B. novum, L. hauffii and Calyculus spp. were dominant. Nevertheless, T. patulus and C. jansae, which became extinct just below the extinction boundary, show preferences for oligotrophic conditions. Salinities similar to those of modern oceans have been inferred around the extinction boundary, considering the coupling between the abundances of Calyculus spp. and the species richness together with the absence of black shales. After the extinction boundary, nannofossil assemblages were dominated by the deep-dwelling C. crassus and the shallow-dwelling Lotharingius species, interpreted as opportunistic taxa. This work confirms that calcareous nannofossils are a really useful tool for palaeoceanographic and palaeoenvironmental reconstructions, especially in terms of climatic changes.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"3 1","pages":"31 - 58"},"PeriodicalIF":0.0,"publicationDate":"2021-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89319931","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This Special Publication combines results obtained by interdisciplinary groups from numerous academic institutions working on Paleoproterozoic formations to decipher the origins of the main mineralization resources in the West African Craton (WAC) and their impacts on African economic development. Structural, geophysical, sedimentological, stratigraphical, geochemical, petrophysical and mineralogical analyses have been used to highlight the complexities involved in mineralization emplacement and its origin and evolution within the WAC. Fourteen articles contribute to new knowledge in mineral research. They show that the geodynamic evolution of the WAC is complex from one area to another: it involves subduction, collision and obduction during several deformation phases ranging from Birimian (2.3–2.0 Ga) to Pan-African (650–450 Ma) events. Various modelling techniques, when integrated, help in understanding the mechanisms of mineralization emplacement, some of which are still a matter of debate. The challenge for further studies is mitigation for sustainable development that can be appropriately used to minimize such damage.
本特刊结合了来自众多研究古元古代构造的学术机构的跨学科小组的成果，以破译西非克拉通(WAC)主要矿化资源的起源及其对非洲经济发展的影响。构造、地球物理、沉积学、地层学、地球化学、岩石物理和矿物学分析已被用来强调矿化侵位及其在WAC内的起源和演化的复杂性。14篇文章贡献了矿物研究的新知识。它们表明，WAC的地球动力学演化是复杂的，在briimian (2.3-2.0 Ga)到pan - africa (650-450 Ma)的几个变形阶段，WAC经历了俯冲、碰撞和逆冲。各种建模技术综合起来，有助于理解矿化侵位的机制，其中一些仍然是一个有争议的问题。进一步研究面临的挑战是，可以适当地利用减轻影响促进可持续发展，以尽量减少这种损害。
{"title":"About this title - Mineralization and Sustainable Development in the West African Craton: From Field Observations to Modelling","authors":"T. Aïfa","doi":"10.1144/sp502","DOIUrl":"https://doi.org/10.1144/sp502","url":null,"abstract":"This Special Publication combines results obtained by interdisciplinary groups from numerous academic institutions working on Paleoproterozoic formations to decipher the origins of the main mineralization resources in the West African Craton (WAC) and their impacts on African economic development. Structural, geophysical, sedimentological, stratigraphical, geochemical, petrophysical and mineralogical analyses have been used to highlight the complexities involved in mineralization emplacement and its origin and evolution within the WAC. Fourteen articles contribute to new knowledge in mineral research. They show that the geodynamic evolution of the WAC is complex from one area to another: it involves subduction, collision and obduction during several deformation phases ranging from Birimian (2.3–2.0 Ga) to Pan-African (650–450 Ma) events. Various modelling techniques, when integrated, help in understanding the mechanisms of mineralization emplacement, some of which are still a matter of debate. The challenge for further studies is mitigation for sustainable development that can be appropriately used to minimize such damage.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"11 1","pages":"NP - NP"},"PeriodicalIF":0.0,"publicationDate":"2021-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83100569","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ricardo L. Silva, M. Ruhl, Cillian Barry, M. Reolid, W. Ruebsam
Abstract Detailed assessment of high-resolution elemental and isotopic geochemical datasets collected from the marl–limestone alternations cropping out at La Cerradura (Subbetic domain of the Betic Cordillera, Spain) and chrono- and chemostratigraphic correlation with the reference Mochras borehole (Cardigan Bay Basin, UK) unveiled valuable new insights into understanding of late Pliensbachian–early Toarcian palaeoenvironmental dynamics in a key geographical area between the northern European seaway and the Tethys Ocean. This study shows that deposition in the study area took place under dominantly oxic water column conditions, indicated, for example, by the generalized lack of enrichment in organic matter and redox metals typically associated with anoxia and euxinia. Carbon isotope stratigraphy (δ13CTOC) allowed recognition of the spinatum (=emaciatum in the Submediterranean Province), Pliensbachian–Toarcian, and early Toarcian Oceanic Anoxic Event negative carbon isotopic excursions and the late Pliensbachian positive carbon isotopic excursion. It is here suggested that the observed periodic changes in lithology and sedimentary geochemistry occur at orbital frequencies (i.e. long and short eccentricity and, tentatively, precession), hinting at an astronomical control of the local–regional climate and environment during the Pliensbachian and Toarcian in the mid- to low-latitude South Iberian palaeomargin area.
详细评估了La Cerradura(西班牙Betic Cordillera的亚北洋域)的泥灰岩蚀变所收集的高分辨率元素和同位素地球化学数据集，并与参考Mochras钻孔(Cardigan Bay Basin)进行了年代和化学地层对比。在欧洲北部海道和特提斯洋之间的一个关键地理区域，英国)揭示了对pliensbachia - Toarcian早期古环境动力学的有价值的新见解。该研究表明，研究区域的沉积主要发生在含氧水柱条件下，例如，有机质和氧化还原金属普遍缺乏富集，通常与缺氧和缺氧有关。碳同位素地层(δ13CTOC)识别了spinatum(亚地中海省=emaciatum)、Pliensbachian - Toarcian和Toarcian早期海洋缺氧事件的负碳同位素偏移和Pliensbachian晚期的正碳同位素偏移。本文认为，观测到的岩性和沉积地球化学的周期性变化发生在轨道频率上(即长、短偏心率和暂定的岁差)，暗示了中低纬度南伊比利亚古边缘地区Pliensbachian和Toarcian时期局地气候和环境的天文控制。
{"title":"Pacing of late Pliensbachian and early Toarcian carbon cycle perturbations and environmental change in the westernmost Tethys (La Cerradura Section, Subbetic zone of the Betic Cordillera, Spain)","authors":"Ricardo L. Silva, M. Ruhl, Cillian Barry, M. Reolid, W. Ruebsam","doi":"10.1144/SP514-2021-27","DOIUrl":"https://doi.org/10.1144/SP514-2021-27","url":null,"abstract":"Abstract Detailed assessment of high-resolution elemental and isotopic geochemical datasets collected from the marl–limestone alternations cropping out at La Cerradura (Subbetic domain of the Betic Cordillera, Spain) and chrono- and chemostratigraphic correlation with the reference Mochras borehole (Cardigan Bay Basin, UK) unveiled valuable new insights into understanding of late Pliensbachian–early Toarcian palaeoenvironmental dynamics in a key geographical area between the northern European seaway and the Tethys Ocean. This study shows that deposition in the study area took place under dominantly oxic water column conditions, indicated, for example, by the generalized lack of enrichment in organic matter and redox metals typically associated with anoxia and euxinia. Carbon isotope stratigraphy (δ13CTOC) allowed recognition of the spinatum (=emaciatum in the Submediterranean Province), Pliensbachian–Toarcian, and early Toarcian Oceanic Anoxic Event negative carbon isotopic excursions and the late Pliensbachian positive carbon isotopic excursion. It is here suggested that the observed periodic changes in lithology and sedimentary geochemistry occur at orbital frequencies (i.e. long and short eccentricity and, tentatively, precession), hinting at an astronomical control of the local–regional climate and environment during the Pliensbachian and Toarcian in the mid- to low-latitude South Iberian palaeomargin area.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"514 1","pages":"387 - 408"},"PeriodicalIF":0.0,"publicationDate":"2021-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81631183","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Silcock, M. Huuse, M. Bowman, A. Hurst, S. Cobain
Sand injectites form during shallow-crustal deformation. Short periods of elevated pore-fluid pressure, which developed regionally, triggered formation of hydrofracture networks into which sand was sometimes injected. Sand injection complexes preserve a record of this process and sandstone intrusions are significant reservoirs in many petroleum systems. Most known subsurface sand injection complexes are from offshore NW Europe and associated with Paleogene strata. Outcrop occurrence is global. Sand injection into unconventional host rocks, including granitoid and metamorphic basement and coal seams, raises awareness of the breadth of geological environments in which sand injection may occur. Discordance between sandstone intrusions and sedimentary hosts occurs on a scale from millimetres to kilometres and is a fundamental diagnostic of intrusions. Microscale textural characterization provides new opportunities to establish possible additional criteria for differentiating intrusions from depositional sandstone. The significance of sand injection complexes in shallow crustal evolution is exemplified by the wide range of lithological hosts and diverse tectonostratigraphic settings documented in this volume. Potential for original research still remains.
{"title":"About this title - Subsurface Sand Remobilization and Injection","authors":"S. Silcock, M. Huuse, M. Bowman, A. Hurst, S. Cobain","doi":"10.1144/sp493","DOIUrl":"https://doi.org/10.1144/sp493","url":null,"abstract":"Sand injectites form during shallow-crustal deformation. Short periods of elevated pore-fluid pressure, which developed regionally, triggered formation of hydrofracture networks into which sand was sometimes injected. Sand injection complexes preserve a record of this process and sandstone intrusions are significant reservoirs in many petroleum systems. Most known subsurface sand injection complexes are from offshore NW Europe and associated with Paleogene strata. Outcrop occurrence is global. Sand injection into unconventional host rocks, including granitoid and metamorphic basement and coal seams, raises awareness of the breadth of geological environments in which sand injection may occur. Discordance between sandstone intrusions and sedimentary hosts occurs on a scale from millimetres to kilometres and is a fundamental diagnostic of intrusions. Microscale textural characterization provides new opportunities to establish possible additional criteria for differentiating intrusions from depositional sandstone. The significance of sand injection complexes in shallow crustal evolution is exemplified by the wide range of lithological hosts and diverse tectonostratigraphic settings documented in this volume. Potential for original research still remains.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"33 1","pages":"NP - NP"},"PeriodicalIF":0.0,"publicationDate":"2021-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84863038","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract China has a rich record of Holocene volcanism that is relatively little known outside the country. It is encountered in large stratovolcanoes in the NE, linked to subduction of the Pacific plate (e.g. Changbaishan), in smaller volcanoes on the Tibetan margin, associated with the collision of India and Eurasia (e.g. Tengchong, Ashishan), and in more isolated centres, possibly resulting from mantle upwelling (e.g. volcanoes in Hainan island). This makes China a natural laboratory for studies of intraplate volcanism, and significant progress in understanding its nature and origins has been made over the past quarter century. Here, we introduce the first publication in English to provide a comprehensive survey of the state of knowledge and research highlights. Accordingly, we provide an overview of the dynamics, geology, geochemistry, volcanic histories and geophysical studies of 14 volcanic areas associated with the Holocene documented thus far. The special publication represents a benchmark reference on the topic but, as importantly, we hope that it will stimulate new, international collaborations aimed at deepening our understanding of the origins, history, hazards and associated risks of China's volcanoes.
{"title":"Perspectives on the active volcanoes of China","authors":"Jiandong Xu, C. Oppenheimer, J. Hammond, H. Wei","doi":"10.1144/SP510-2021-87","DOIUrl":"https://doi.org/10.1144/SP510-2021-87","url":null,"abstract":"Abstract China has a rich record of Holocene volcanism that is relatively little known outside the country. It is encountered in large stratovolcanoes in the NE, linked to subduction of the Pacific plate (e.g. Changbaishan), in smaller volcanoes on the Tibetan margin, associated with the collision of India and Eurasia (e.g. Tengchong, Ashishan), and in more isolated centres, possibly resulting from mantle upwelling (e.g. volcanoes in Hainan island). This makes China a natural laboratory for studies of intraplate volcanism, and significant progress in understanding its nature and origins has been made over the past quarter century. Here, we introduce the first publication in English to provide a comprehensive survey of the state of knowledge and research highlights. Accordingly, we provide an overview of the dynamics, geology, geochemistry, volcanic histories and geophysical studies of 14 volcanic areas associated with the Holocene documented thus far. The special publication represents a benchmark reference on the topic but, as importantly, we hope that it will stimulate new, international collaborations aimed at deepening our understanding of the origins, history, hazards and associated risks of China's volcanoes.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"12 1","pages":"1 - 14"},"PeriodicalIF":0.0,"publicationDate":"2021-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81325934","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Yakovlev, S. Kostrovitsky, B. Fosu, I. Ashchepkov
Abstract Petrographic, geochemical and mineralogical characteristics of diamond deposits from the Upper Muna field have been investigated. Geochemically, diamondiferous kimberlites from Upper Muna belong to the most widespread Fe–Mg-rich rocks in the Yakutian kimberlite province (average FeOtotal = 8.4 wt%, MgO = 32.36 wt%, TiO2 = 1.6 wt%). Striking mineralogical features of Upper Muna kimberlites are: (1) abundance of monticellite and perovskite in the groundmass; (2) rare occurrence of Mg-ilmenite; (3) abundance of phlogopite megacrysts (up to 8 cm across); and (4) coexistence of low-Cr (0.1–4 wt% Cr2O3, with 0.8–1.2 wt% TiO2) and high-Cr (3–8 wt% Cr2O3, with 0.1–0.6 wt% TiO2) garnet megacrysts with contrasting rare earth element patterns. The compositional features of groundmass minerals, the relatively low CaO and CO2 contents in kimberlites and few deuteric alteration in Upper Muna kimberlites suggest high-temperature melt crystallization during pipe emplacement. Based on the compositional data of garnet and Cr-diopside from megacrysts and peridotites, we suggest a poor Cr dunite–harzburgitic and lherzolitic mantle source beneath the Upper Muna field where Cr-diopside crystallized within a wide pressure and temperature range (40–65 kbar and 900–1350°С). The mineral geochemistry, trace element distribution and Sr–Nd isotope variations of Upper Muna kimberlites are typical for group I kimberlites and reflect a deep-seated asthenospheric (convective mantle) source for the kimberlites.
{"title":"Diamondiferous kimberlites from recently explored Upper Muna Field (Siberian Craton): petrology, mineralogy and geochemistry insights","authors":"D. Yakovlev, S. Kostrovitsky, B. Fosu, I. Ashchepkov","doi":"10.1144/SP513-2021-9","DOIUrl":"https://doi.org/10.1144/SP513-2021-9","url":null,"abstract":"Abstract Petrographic, geochemical and mineralogical characteristics of diamond deposits from the Upper Muna field have been investigated. Geochemically, diamondiferous kimberlites from Upper Muna belong to the most widespread Fe–Mg-rich rocks in the Yakutian kimberlite province (average FeOtotal = 8.4 wt%, MgO = 32.36 wt%, TiO2 = 1.6 wt%). Striking mineralogical features of Upper Muna kimberlites are: (1) abundance of monticellite and perovskite in the groundmass; (2) rare occurrence of Mg-ilmenite; (3) abundance of phlogopite megacrysts (up to 8 cm across); and (4) coexistence of low-Cr (0.1–4 wt% Cr2O3, with 0.8–1.2 wt% TiO2) and high-Cr (3–8 wt% Cr2O3, with 0.1–0.6 wt% TiO2) garnet megacrysts with contrasting rare earth element patterns. The compositional features of groundmass minerals, the relatively low CaO and CO2 contents in kimberlites and few deuteric alteration in Upper Muna kimberlites suggest high-temperature melt crystallization during pipe emplacement. Based on the compositional data of garnet and Cr-diopside from megacrysts and peridotites, we suggest a poor Cr dunite–harzburgitic and lherzolitic mantle source beneath the Upper Muna field where Cr-diopside crystallized within a wide pressure and temperature range (40–65 kbar and 900–1350°С). The mineral geochemistry, trace element distribution and Sr–Nd isotope variations of Upper Muna kimberlites are typical for group I kimberlites and reflect a deep-seated asthenospheric (convective mantle) source for the kimberlites.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"40 1","pages":"71 - 102"},"PeriodicalIF":0.0,"publicationDate":"2021-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90881761","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Di Capua, P. Bobrowsky, S. Kieffer, C. Palinkas
This is the second volume focused on geoethics published by the Geological Society of London. This is a significant step forward in which authors address the maturation of geoethics. The field of geoethics is now ready to be introduced outside the geoscience community as a logical platform for global ethics that addresses anthropogenic changes. Geoethics has a distinction in the geoscientific community for discussing ethical, social and cultural implications of geoscience knowledge, research, practice, education and communication. This provides a common ground for confronting ideas, experiences and proposals on how geosciences can supply additional service to society in order to improve the way humans interact responsibly with the Earth system. This book provides new messages to geoscientists, social scientists, intellectuals, law- and decision-makers, and laypeople. Motivations and actions for facing global anthropogenic changes and their intense impacts on the planet need to be governed by an ethical framework capable of merging a solid conceptual structure with pragmatic approaches based on geoscientific knowledge. This philosophy defines geoethics.
{"title":"About this title - Geoethics: Status and Future Perspectives","authors":"G. Di Capua, P. Bobrowsky, S. Kieffer, C. Palinkas","doi":"10.1144/sp508","DOIUrl":"https://doi.org/10.1144/sp508","url":null,"abstract":"This is the second volume focused on geoethics published by the Geological Society of London. This is a significant step forward in which authors address the maturation of geoethics. The field of geoethics is now ready to be introduced outside the geoscience community as a logical platform for global ethics that addresses anthropogenic changes. Geoethics has a distinction in the geoscientific community for discussing ethical, social and cultural implications of geoscience knowledge, research, practice, education and communication. This provides a common ground for confronting ideas, experiences and proposals on how geosciences can supply additional service to society in order to improve the way humans interact responsibly with the Earth system. This book provides new messages to geoscientists, social scientists, intellectuals, law- and decision-makers, and laypeople. Motivations and actions for facing global anthropogenic changes and their intense impacts on the planet need to be governed by an ethical framework capable of merging a solid conceptual structure with pragmatic approaches based on geoscientific knowledge. This philosophy defines geoethics.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"14 1","pages":"NP - NP"},"PeriodicalIF":0.0,"publicationDate":"2021-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88227350","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Forty-two volcanic rocks of the Panjal Traps were analysed for platinum-group elements (PGEs) to investigate the magma genesis, high-temperature behaviour and exploration potential of these elements. The PGE data exhibit substantial variability and show no systematic relation to their low- or high-Ti affinity. Instead, the basalts can be subdivided into a PGE-undepleted group (group 1) that has ΣPGE >10 ppb and Cu/Pd <30 000, and a PGE-depleted group, which consists of a subgroup showing limited (group 2A) or substantial depletion in Ir-series PGEs relative to Ni (group 2B). The group 1 samples indicate an S-undersaturated history, whereas the group 2 samples might have different origins in terms of S-saturation. Fractionation of a tiny amount of sulfide melts (0.075–0.1%) from a representative group 1 sample accounts for the chalcophile element patterns observed in the group 2B samples. The relatively high Cu/Pd, unfractionated Ni/Ir and low PGE abundances observed in the group 2A samples cannot be explained by equilibration of an immiscible sulfide melt alone, and probably require decomposition of residual sulfides into sulfide melt and a monosulfide solid solution in the mantle restite. Our results question the notion that the coexistence of PGE-undepleted and -depleted magmas is prospective in the exploration of magmatic Ni–Cu–(PGE) sulfide mineralization.
{"title":"Platinum-group element geochemistry of the Panjal Traps: constraints on mantle melting and implications for mineral exploration","authors":"J. G. Shellnutt, K. Pang, L. Qi, G. Bhat","doi":"10.1144/SP518-2020-241","DOIUrl":"https://doi.org/10.1144/SP518-2020-241","url":null,"abstract":"Abstract Forty-two volcanic rocks of the Panjal Traps were analysed for platinum-group elements (PGEs) to investigate the magma genesis, high-temperature behaviour and exploration potential of these elements. The PGE data exhibit substantial variability and show no systematic relation to their low- or high-Ti affinity. Instead, the basalts can be subdivided into a PGE-undepleted group (group 1) that has ΣPGE >10 ppb and Cu/Pd <30 000, and a PGE-depleted group, which consists of a subgroup showing limited (group 2A) or substantial depletion in Ir-series PGEs relative to Ni (group 2B). The group 1 samples indicate an S-undersaturated history, whereas the group 2 samples might have different origins in terms of S-saturation. Fractionation of a tiny amount of sulfide melts (0.075–0.1%) from a representative group 1 sample accounts for the chalcophile element patterns observed in the group 2B samples. The relatively high Cu/Pd, unfractionated Ni/Ir and low PGE abundances observed in the group 2A samples cannot be explained by equilibration of an immiscible sulfide melt alone, and probably require decomposition of residual sulfides into sulfide melt and a monosulfide solid solution in the mantle restite. Our results question the notion that the coexistence of PGE-undepleted and -depleted magmas is prospective in the exploration of magmatic Ni–Cu–(PGE) sulfide mineralization.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"59 1","pages":"531 - 551"},"PeriodicalIF":0.0,"publicationDate":"2021-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87875949","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","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：