B. Bomou, G. Suan, J. Schlögl, Anne-Sabine Grosjean, B. Suchéras-Marx, T. Adatte, J. Spangenberg, S. Fouché, Axelle Zacaï, Corentin Gibert, Jean-Michel Brazier, V. Perrier, P. Vincent, Kévin Janneau, J. Martin
Abstract The Early Jurassic was marked by several episodes of rapid climate change and environmental perturbation. These changes culminated during the Toarcian Oceanic Anoxic Event (T-OAE), an episode of global warming that led to the widespread deposition of organic-rich shales. The Toarcian shales of NW Europe have also yielded exceptionally preserved fossils of marine vertebrates and invertebrates, but the potential links between the occurrences of these exceptionally preserved fossils and the T-OAE remain poorly investigated. Palaeontological excavations realized in Toarcian strata near Lodève (Hérault, southern France) have yielded several specimens of marine vertebrates and abundant invertebrate fauna. We have developed a multiproxy approach (ammonite biostratigraphy, X-ray diffraction-bulk mineralogy, Rock-Eval pyrolysis, stable isotopes, trace element, phosphorus and mercury contents) to place these findings in a well-defined temporal and palaeoenvironmental context, and hence constrain the factors that led to their remarkable preservation. The Jenkyns Event interval, unambiguously identified at the base of the Toarcian organic-rich shales by a 5‰ negative carbon isotope excursion, records higher mercury fluxes, which suggest a causal link with intense volcanic activity of the Karoo–Ferrar large igneous province. This interval is very condensed and unfossiliferous, and might have been deposited under abnormally low-salinity conditions. Our data show that the deposition of the vertebrate-yielding horizons post-dated the T-OAE by several hundreds of ka, and took place during a prolonged period of widespread oxygen-deficiency and elevated carbon burial. Our results indicate that the unusual richness in vertebrates of the studied site can be explained by a combination of regional factors such as warming-induced, prolonged seafloor anoxia, and more local factors, such as extreme condensation owing to reduced dilution by carbonate and detrital input.
{"title":"The palaeoenvironmental context of Toarcian vertebrate-yielding shales of southern France (Hérault)","authors":"B. Bomou, G. Suan, J. Schlögl, Anne-Sabine Grosjean, B. Suchéras-Marx, T. Adatte, J. Spangenberg, S. Fouché, Axelle Zacaï, Corentin Gibert, Jean-Michel Brazier, V. Perrier, P. Vincent, Kévin Janneau, J. Martin","doi":"10.1144/SP514-2021-16","DOIUrl":"https://doi.org/10.1144/SP514-2021-16","url":null,"abstract":"Abstract The Early Jurassic was marked by several episodes of rapid climate change and environmental perturbation. These changes culminated during the Toarcian Oceanic Anoxic Event (T-OAE), an episode of global warming that led to the widespread deposition of organic-rich shales. The Toarcian shales of NW Europe have also yielded exceptionally preserved fossils of marine vertebrates and invertebrates, but the potential links between the occurrences of these exceptionally preserved fossils and the T-OAE remain poorly investigated. Palaeontological excavations realized in Toarcian strata near Lodève (Hérault, southern France) have yielded several specimens of marine vertebrates and abundant invertebrate fauna. We have developed a multiproxy approach (ammonite biostratigraphy, X-ray diffraction-bulk mineralogy, Rock-Eval pyrolysis, stable isotopes, trace element, phosphorus and mercury contents) to place these findings in a well-defined temporal and palaeoenvironmental context, and hence constrain the factors that led to their remarkable preservation. The Jenkyns Event interval, unambiguously identified at the base of the Toarcian organic-rich shales by a 5‰ negative carbon isotope excursion, records higher mercury fluxes, which suggest a causal link with intense volcanic activity of the Karoo–Ferrar large igneous province. This interval is very condensed and unfossiliferous, and might have been deposited under abnormally low-salinity conditions. Our data show that the deposition of the vertebrate-yielding horizons post-dated the T-OAE by several hundreds of ka, and took place during a prolonged period of widespread oxygen-deficiency and elevated carbon burial. Our results indicate that the unusual richness in vertebrates of the studied site can be explained by a combination of regional factors such as warming-induced, prolonged seafloor anoxia, and more local factors, such as extreme condensation owing to reduced dilution by carbonate and detrital input.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"11 1","pages":"121 - 152"},"PeriodicalIF":0.0,"publicationDate":"2021-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75982423","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}
M. Reolid, M. Soussi, J. Reolid, W. Ruebsam, Ilef Belhaj Taher, E. Mattioli, M. Saidi, L. Schwark
Abstract The flooding of the Lower Jurassic shelf in the North Gondwana Palaeomargin during the early Toarcian occurred on a fragmented and irregular topography affected by differential subsidence – owing to the activity of listric faults along the North–South Axis of Tunisia – that favoured lateral changes in facies and thickness at a kilometric scale. The onset of Toarcian sedimentation (Polymorphum ammonite Zone, NJT5c nannofossil Subzone) in two adjacent sections was characterized by the deposition of limestones under high-energy conditions. The Châabet El Attaris section was located in a depressed sub-basin, and recorded restricted environmental conditions owing to water stagnation and an oxygen-depleted sea bottom. Therefore, dark mudstones developed, with increased total organic carbon contents and enhanced accumulation of redox-sensitive elements. The sedimentation of limestones bearing gutter cast structures is related to gravity flows probably linked to storm activities. These processes favoured the remobilization of sediments at the seafloor, as well as oxygen input to bottom waters, as shown by the record of trace fossils including Zoophycos, Ophiomorpha, and secondarily, Chondrites and Diplocraterion. The thinly interbedded dark mudstones are locally rich in thin-shelled bivalves that re-colonized the sea bottom after the sedimentation of these high-energy deposits, and subsequently underwent mass mortality related to the return of oxygen-depleted conditions. The Kef El Hassine section is located in the upper part of a tilted, less subsident block, as indicated by its reduced thickness compared with the Châabet El Attaris section; the absence of dark mudstones implies oxic conditions. The Polymorphum Zone consists of limestones showing evidence of sedimentation under high-energy conditions, along with hardgrounds. The occurrence of Zoophycos (deep-tiers) in the upper part of some limestone beds of the Polymorphum Zone is linked to minor erosive processes. The top of the high-energy sequence – below the deposits of a marly interval corresponding to the Levisoni Zone – is interpreted as a hardground given the high content of belemnites and Arenicolites, some of them boring on the eroded Zoophycos and Thalassinoides. This study shows that the sedimentary expression of the Jenkyns Event is not uniform across Tunisia, supporting the importance of local conditions in determining the development of anoxic conditions.
北冈瓦纳古边缘下侏罗统陆架早陶拉纪时期的洪水发生在一个破碎和不规则的地形上，受突尼斯南北轴线上的盘状断层活动的不同沉降影响，这有利于在千米尺度上的横向相和厚度变化。相邻两个剖面的多态氨岩带(NJT5c纳米化石亚带)的起积以高能条件下灰岩沉积为特征。chabet El Attaris段位于一个凹陷的次盆地，由于水停滞和海底缺氧，记录到的环境条件受到限制。因此，暗色泥岩发育，总有机碳含量增加，氧化还原敏感元素富集。灰岩的沉积与重力流有关，重力流可能与风暴活动有关。这些过程有利于海底沉积物的再活化，也有利于向底水输入氧气，这一点可以从植藻、蛇藻、次生球粒陨石和复盖纪等微量化石的记录中得到证明。薄互层的深色泥岩在局部富含薄壳双壳类，这些双壳类在这些高能沉积物沉积后重新定居海底，随后经历了与缺氧条件返回相关的大规模死亡。Kef El Hassine段位于一个倾斜、下沉较少的区块的上部，与ch abet El Attaris段相比，其厚度较小;暗色泥岩的缺失意味着氧化条件。多态带由石灰石组成，显示出在高能条件下沉积的证据，以及硬地。在多形带的一些石灰岩层的上部，植藻(深层)的出现与轻微的侵蚀作用有关。高能量层序的顶部——位于与利维索尼带相对应的灰岩层段沉积物下方——被解释为硬地层，因为它含有高含量的菱铁矿和砂粒石，其中一些在被侵蚀的植生岩和海生岩上钻出。该研究表明，詹金斯事件的沉积表现在突尼斯各地并不统一，支持当地条件在决定缺氧条件发展中的重要性。
{"title":"The onset of the Early Toarcian flooding of the Pliensbachian carbonate platform of central Tunisia (north–south axis) as inferred from trace fossils and geochemistry","authors":"M. Reolid, M. Soussi, J. Reolid, W. Ruebsam, Ilef Belhaj Taher, E. Mattioli, M. Saidi, L. Schwark","doi":"10.1144/SP514-2021-10","DOIUrl":"https://doi.org/10.1144/SP514-2021-10","url":null,"abstract":"Abstract The flooding of the Lower Jurassic shelf in the North Gondwana Palaeomargin during the early Toarcian occurred on a fragmented and irregular topography affected by differential subsidence – owing to the activity of listric faults along the North–South Axis of Tunisia – that favoured lateral changes in facies and thickness at a kilometric scale. The onset of Toarcian sedimentation (Polymorphum ammonite Zone, NJT5c nannofossil Subzone) in two adjacent sections was characterized by the deposition of limestones under high-energy conditions. The Châabet El Attaris section was located in a depressed sub-basin, and recorded restricted environmental conditions owing to water stagnation and an oxygen-depleted sea bottom. Therefore, dark mudstones developed, with increased total organic carbon contents and enhanced accumulation of redox-sensitive elements. The sedimentation of limestones bearing gutter cast structures is related to gravity flows probably linked to storm activities. These processes favoured the remobilization of sediments at the seafloor, as well as oxygen input to bottom waters, as shown by the record of trace fossils including Zoophycos, Ophiomorpha, and secondarily, Chondrites and Diplocraterion. The thinly interbedded dark mudstones are locally rich in thin-shelled bivalves that re-colonized the sea bottom after the sedimentation of these high-energy deposits, and subsequently underwent mass mortality related to the return of oxygen-depleted conditions. The Kef El Hassine section is located in the upper part of a tilted, less subsident block, as indicated by its reduced thickness compared with the Châabet El Attaris section; the absence of dark mudstones implies oxic conditions. The Polymorphum Zone consists of limestones showing evidence of sedimentation under high-energy conditions, along with hardgrounds. The occurrence of Zoophycos (deep-tiers) in the upper part of some limestone beds of the Polymorphum Zone is linked to minor erosive processes. The top of the high-energy sequence – below the deposits of a marly interval corresponding to the Levisoni Zone – is interpreted as a hardground given the high content of belemnites and Arenicolites, some of them boring on the eroded Zoophycos and Thalassinoides. This study shows that the sedimentary expression of the Jenkyns Event is not uniform across Tunisia, supporting the importance of local conditions in determining the development of anoxic conditions.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"613 1","pages":"213 - 238"},"PeriodicalIF":0.0,"publicationDate":"2021-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80427180","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}
N. J. Reis, W. Teixeira, M. S. D’Agrella-Filho, J. Bettencourt, Richard E. Ernst, L. E. Goulart
Abstract This paper overviews the Proterozoic large igneous provinces (LIPs) of the Amazonian Craton, characterized by large volumes of extrusive and intrusive magmatic rocks. We reassess the geologic, geochronological and geochemical information to stablish three intracontinental felsic volcanic–plutonic igneous belts (i.e. SLIPs), namely: Orocaima (1.98–1.96 Ga), Uatumã (1.88–1.87 Ga) and Alta Floresta (1.80–1.79 Ga). The Avanavero LIP (1.79–1.78 Ga), as well as the Rincón del Tigre-Huanchaca LIP (1.11 Ga) are also revisited. The relationships of these events to intraplate settings through time and space are apparent. We examine the main characteristics of each magmatic event in light of the U–Pb zircon and baddeleyite ages and coupled isotopic–geochemical constraints, the geodynamic significance and metallogenetic potential. The Uatumã and Alta Floresta SLIPs host the most important mineral resources within the Amazonian Craton. Global barcode matches of the Proterozoic SLIP/LIP events of Amazonia are also addressed, as well as their possible links with geological timescale periods: the Orosirian, Statherian and Stenian boundaries. We also evaluate the available palaeomagnetic data to address issues related to the barcode match of such SLIP/LIP events in the context of supercontinent cycles.
{"title":"Large igneous provinces of the Amazonian Craton and their metallogenic potential in Proterozoic times","authors":"N. J. Reis, W. Teixeira, M. S. D’Agrella-Filho, J. Bettencourt, Richard E. Ernst, L. E. Goulart","doi":"10.1144/SP518-2021-7","DOIUrl":"https://doi.org/10.1144/SP518-2021-7","url":null,"abstract":"Abstract This paper overviews the Proterozoic large igneous provinces (LIPs) of the Amazonian Craton, characterized by large volumes of extrusive and intrusive magmatic rocks. We reassess the geologic, geochronological and geochemical information to stablish three intracontinental felsic volcanic–plutonic igneous belts (i.e. SLIPs), namely: Orocaima (1.98–1.96 Ga), Uatumã (1.88–1.87 Ga) and Alta Floresta (1.80–1.79 Ga). The Avanavero LIP (1.79–1.78 Ga), as well as the Rincón del Tigre-Huanchaca LIP (1.11 Ga) are also revisited. The relationships of these events to intraplate settings through time and space are apparent. We examine the main characteristics of each magmatic event in light of the U–Pb zircon and baddeleyite ages and coupled isotopic–geochemical constraints, the geodynamic significance and metallogenetic potential. The Uatumã and Alta Floresta SLIPs host the most important mineral resources within the Amazonian Craton. Global barcode matches of the Proterozoic SLIP/LIP events of Amazonia are also addressed, as well as their possible links with geological timescale periods: the Orosirian, Statherian and Stenian boundaries. We also evaluate the available palaeomagnetic data to address issues related to the barcode match of such SLIP/LIP events in the context of supercontinent cycles.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"30 1","pages":"493 - 529"},"PeriodicalIF":0.0,"publicationDate":"2021-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90599377","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. Tappe, Azhar M. Shaikh, Allan H Wilson, A. Stracke
Abstract Orangeites are a significant source of diamonds, yet ambiguity surrounds their status among groups of mantle-derived potassic rocks. This study reports mineralogical and geochemical data for a c. 140 Ma orangeite dyke swarm that intersects the Bushveld Complex on the Kaapvaal craton in South Africa. The dykes comprise distinctive petrographic varieties that are linked principally by olivine fractionation, with the most evolved members containing minor amounts of primary carbonate, sanidine and andradite garnet in the groundmass. Although abundant groundmass phlogopite and clinopyroxene have compositions that are similar to those of cratonic lamproites, these phases show notable Ti-depletion, which we consider a hallmark feature of type orangeites from the Kaapvaal craton. Ti-depletion is also characteristic of bulk rock compositions and is associated with strongly depleted Th–U–Nb–Ta contents at high Cs–Rb–Ba–K concentrations. The resultant high large ion lithophile element/high field strength element ratios of orangeites suggest that mantle source enrichment occurred by metasomatic processes in the proximity of ancient subduction zones. The Bushveld-intersecting orangeite dykes have strongly enriched Sr–Nd–Hf isotopic compositions (initial 87Sr/86Sr = 0.70701–0.70741; εNd = −10.6 to −5.8; εHf = −14.4 to −2.5), similar to those of other orangeites from across South Africa. Combined with the strong Ti–Nb–Ta depletion, this ubiquitous isotopic feature points to the involvement of ancient metasomatized mantle lithosphere in the origin of Kaapvaal craton orangeites, where K-rich metasomes imparted a ‘fossil’ subduction geochemical signature. Previous geochronology studies identified ancient K-enrichment events within the Kaapvaal cratonic mantle lithosphere, possibly associated with collisional tectonics during the 1.2–1.1 Ga Namaqua–Natal orogeny of the Rodinia supercontinent cycle. It therefore seems permissible that the cratonic mantle root was preconditioned for ultrapotassic magma production by tectonomagmatic events that occurred along convergent plate margins during the Proterozoic. However, reactivation of the K-rich metasomes had to await establishment of an extensional tectonic regime, such as that during the Mesozoic breakup of Gondwana, which was accompanied by widespread (1000 × 750 km) small-volume orangeite volcanism between 200 and 110 Ma. Although similarities exist between orangeites and lamproites, these and other potassic rocks are sufficiently distinct in their compositions such that different magma formation processes must be considered. In addition to new investigations of the geodynamic triggers of K-rich ultramafic magmatism, future research should more stringently evaluate the relative roles of redox effects and volatile components such as H2O–CO2–F in the petrogeneses of these potentially diamondiferous alkaline rocks.
{"title":"Evolution of ultrapotassic volcanism on the Kaapvaal craton: deepening the orangeite versus lamproite debate","authors":"S. Tappe, Azhar M. Shaikh, Allan H Wilson, A. Stracke","doi":"10.1144/SP513-2021-84","DOIUrl":"https://doi.org/10.1144/SP513-2021-84","url":null,"abstract":"Abstract Orangeites are a significant source of diamonds, yet ambiguity surrounds their status among groups of mantle-derived potassic rocks. This study reports mineralogical and geochemical data for a c. 140 Ma orangeite dyke swarm that intersects the Bushveld Complex on the Kaapvaal craton in South Africa. The dykes comprise distinctive petrographic varieties that are linked principally by olivine fractionation, with the most evolved members containing minor amounts of primary carbonate, sanidine and andradite garnet in the groundmass. Although abundant groundmass phlogopite and clinopyroxene have compositions that are similar to those of cratonic lamproites, these phases show notable Ti-depletion, which we consider a hallmark feature of type orangeites from the Kaapvaal craton. Ti-depletion is also characteristic of bulk rock compositions and is associated with strongly depleted Th–U–Nb–Ta contents at high Cs–Rb–Ba–K concentrations. The resultant high large ion lithophile element/high field strength element ratios of orangeites suggest that mantle source enrichment occurred by metasomatic processes in the proximity of ancient subduction zones. The Bushveld-intersecting orangeite dykes have strongly enriched Sr–Nd–Hf isotopic compositions (initial 87Sr/86Sr = 0.70701–0.70741; εNd = −10.6 to −5.8; εHf = −14.4 to −2.5), similar to those of other orangeites from across South Africa. Combined with the strong Ti–Nb–Ta depletion, this ubiquitous isotopic feature points to the involvement of ancient metasomatized mantle lithosphere in the origin of Kaapvaal craton orangeites, where K-rich metasomes imparted a ‘fossil’ subduction geochemical signature. Previous geochronology studies identified ancient K-enrichment events within the Kaapvaal cratonic mantle lithosphere, possibly associated with collisional tectonics during the 1.2–1.1 Ga Namaqua–Natal orogeny of the Rodinia supercontinent cycle. It therefore seems permissible that the cratonic mantle root was preconditioned for ultrapotassic magma production by tectonomagmatic events that occurred along convergent plate margins during the Proterozoic. However, reactivation of the K-rich metasomes had to await establishment of an extensional tectonic regime, such as that during the Mesozoic breakup of Gondwana, which was accompanied by widespread (1000 × 750 km) small-volume orangeite volcanism between 200 and 110 Ma. Although similarities exist between orangeites and lamproites, these and other potassic rocks are sufficiently distinct in their compositions such that different magma formation processes must be considered. In addition to new investigations of the geodynamic triggers of K-rich ultramafic magmatism, future research should more stringently evaluate the relative roles of redox effects and volatile components such as H2O–CO2–F in the petrogeneses of these potentially diamondiferous alkaline rocks.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"33 1","pages":"17 - 44"},"PeriodicalIF":0.0,"publicationDate":"2021-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80912434","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}
L. Krmíček, T. Magna, Ashutosh Pandey, N. C. Chalapathi Rao, J. Kynický
Abstract Our pilot study reveals potential Li isotope fingerprints recorded in the Mesoproterozoic (c. 1.4–1.1 Ga) kimberlites, lamproites and lamprophyres from the Eastern Dharwar Craton and Paleocene (62 Ma) orangeite from the Bastar Craton in India. The new data are interpreted in the context of available Li isotope composition of lamproitic to lamprophyric rocks occurring in Variscan (Bohemian Massif) and Alpine–Himalayan (SW Tibet) orogenic belts formed in response to Gondwana–Pangea amalgamation and break-up. As a result of the development of supercontinents, kimberlites from the Eastern Dharwar Craton and ‘orangeite’ from the Bastar Craton show clear presence of a component with a heavy Li isotope signature (δ7Li up to 9.7‰) similar to ancient altered oceanic crust, whereas the Eastern Dharwar Craton lamproites (2.3–6.3‰) and lamprophyres (3.3–6.7‰) show Li isotope signatures indicative of a dominant contribution from heterogeneous lithospheric mantle. Variscan lamprophyric to lamproitic rocks and post-collisional mantle-derived (ultra)potassic volcanic rocks from SW Tibet, i.e. rocks from the orogenic belts outside the cratonic areas, are characterized by a clear Li isotope shift towards an isotopically lighter component (δ7Li as low as –9.5‰) comparable with the involvement of evolved continental crust and high-pressure metamorphic rocks in their orogenic mantle source. Such components with isotopically light Li are strikingly missing in the source of cratonic kimberlites, lamproites and lamprophyres.
{"title":"Lithium isotopes in kimberlites, lamproites and lamprophyres as tracers of source components and processes related to supercontinent cycles","authors":"L. Krmíček, T. Magna, Ashutosh Pandey, N. C. Chalapathi Rao, J. Kynický","doi":"10.1144/SP513-2021-60","DOIUrl":"https://doi.org/10.1144/SP513-2021-60","url":null,"abstract":"Abstract Our pilot study reveals potential Li isotope fingerprints recorded in the Mesoproterozoic (c. 1.4–1.1 Ga) kimberlites, lamproites and lamprophyres from the Eastern Dharwar Craton and Paleocene (62 Ma) orangeite from the Bastar Craton in India. The new data are interpreted in the context of available Li isotope composition of lamproitic to lamprophyric rocks occurring in Variscan (Bohemian Massif) and Alpine–Himalayan (SW Tibet) orogenic belts formed in response to Gondwana–Pangea amalgamation and break-up. As a result of the development of supercontinents, kimberlites from the Eastern Dharwar Craton and ‘orangeite’ from the Bastar Craton show clear presence of a component with a heavy Li isotope signature (δ7Li up to 9.7‰) similar to ancient altered oceanic crust, whereas the Eastern Dharwar Craton lamproites (2.3–6.3‰) and lamprophyres (3.3–6.7‰) show Li isotope signatures indicative of a dominant contribution from heterogeneous lithospheric mantle. Variscan lamprophyric to lamproitic rocks and post-collisional mantle-derived (ultra)potassic volcanic rocks from SW Tibet, i.e. rocks from the orogenic belts outside the cratonic areas, are characterized by a clear Li isotope shift towards an isotopically lighter component (δ7Li as low as –9.5‰) comparable with the involvement of evolved continental crust and high-pressure metamorphic rocks in their orogenic mantle source. Such components with isotopically light Li are strikingly missing in the source of cratonic kimberlites, lamproites and lamprophyres.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"22 1","pages":"209 - 236"},"PeriodicalIF":0.0,"publicationDate":"2021-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88304706","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}
A. Dongre, P. Dhote, P. Zamarkar, S. Sangode, G. Belyanin, D. Meshram, S. Patil, Aaheri Karmakar, Lokant Jain
Abstract Available geochronological information on Deccan indicates prolonged (started at 68.5 Ma) alkaline magmatism related to the Réunion mantle plume based on the 40Ar/39Ar ages from Sarnu-Dandali and Mundwara alkaline complexes. We studied in detail an alkaline lamprophyre, from the Sarnu-Dandali Complex, rich in groundmass (magmatic) as well as xenocrystic phlogopites and clinopyroxenes. 40Ar/39Ar age determinations of the phlogopites from this lamprophyre reveal two distinct ages of 65.44 ± 1.5 Ma and 68.17 ± 1 Ma. However, palaeomagnetic results show a VGP at 32.31° N and 298.52° E concordant with that of the Deccan Super Pole at 65.5 Ma and support the younger eruption age at c. 65.44 ± 1.5 Ma. Analysed phlogopites lack any signs of retention of excess radiogenic Ar and yield similar inverse isochron ages, which suggests that the older age of c. 68.17 ± 1 Ma belongs to the crystallization of xenocrystic phlogopite during mantle metasomatism. Trace element compositions support derivation of lamprophyre magma from an OIB-type enriched (metasomatized) mantle source with an involvement of phlogopite. This finding suggests that the pre-Deccan ages of c. 68–69 Ma reported previously may reflect the timing of metasomatism of the subcratonic lithospheric mantle during the separation of Greater-Seychelles from India at c. 68.5 Ma. The absence of pre-Deccan alkaline rocks therefore indicates the short duration (between 67–65 Ma) of alkaline as well as small-volume, volatile-rich magmatism directly related to the Réunion (Deccan) plume.
{"title":"Short-lived alkaline magmatism related to the Réunion plume in the Deccan Large Igneous Province: inferences from petrology, 40Ar/39Ar geochronology and palaeomagnetism of lamprophyre from the Sarnu-Dandali Alkaline Igneous Complex","authors":"A. Dongre, P. Dhote, P. Zamarkar, S. Sangode, G. Belyanin, D. Meshram, S. Patil, Aaheri Karmakar, Lokant Jain","doi":"10.1144/SP513-2021-34","DOIUrl":"https://doi.org/10.1144/SP513-2021-34","url":null,"abstract":"Abstract Available geochronological information on Deccan indicates prolonged (started at 68.5 Ma) alkaline magmatism related to the Réunion mantle plume based on the 40Ar/39Ar ages from Sarnu-Dandali and Mundwara alkaline complexes. We studied in detail an alkaline lamprophyre, from the Sarnu-Dandali Complex, rich in groundmass (magmatic) as well as xenocrystic phlogopites and clinopyroxenes. 40Ar/39Ar age determinations of the phlogopites from this lamprophyre reveal two distinct ages of 65.44 ± 1.5 Ma and 68.17 ± 1 Ma. However, palaeomagnetic results show a VGP at 32.31° N and 298.52° E concordant with that of the Deccan Super Pole at 65.5 Ma and support the younger eruption age at c. 65.44 ± 1.5 Ma. Analysed phlogopites lack any signs of retention of excess radiogenic Ar and yield similar inverse isochron ages, which suggests that the older age of c. 68.17 ± 1 Ma belongs to the crystallization of xenocrystic phlogopite during mantle metasomatism. Trace element compositions support derivation of lamprophyre magma from an OIB-type enriched (metasomatized) mantle source with an involvement of phlogopite. This finding suggests that the pre-Deccan ages of c. 68–69 Ma reported previously may reflect the timing of metasomatism of the subcratonic lithospheric mantle during the separation of Greater-Seychelles from India at c. 68.5 Ma. The absence of pre-Deccan alkaline rocks therefore indicates the short duration (between 67–65 Ma) of alkaline as well as small-volume, volatile-rich magmatism directly related to the Réunion (Deccan) plume.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"23 1","pages":"381 - 411"},"PeriodicalIF":0.0,"publicationDate":"2021-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88916752","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. Kostrovitsky, D. Yakovlev, I. Sharygin, D. Gladkochub, T. V. Donskaya, I. Tretiakova, A. Dymshits, A. P. Sekerin, V. Malkovets
Abstract Ingashi lamproite dykes are the only known primary sources of diamond in the Irkutsk district (Russia) and the only non-kimberlitic one in the Siberian craton. The Ingashi lamproite field is situated in the Urik-Iya graben within the Prisayan uplift of the Siberian craton. The phlogopite-olivine lamproites contain olivine, talc, phlogopite, serpentine, chlorite, olivine, garnet, chromite, orthopyroxene, clinopyroxene as well as Sr-F-apatite, monazite, zircon, armolcolite, priderite, potassium Mg-arfvedsonite, Mn-ilmenite, Nb-rutile and diamond. The only ultramafic lamprophyre dyke is composed mainly of serpentinized olivine and phlogopite in the talc-carbonate groundmass and is similar to Ingashi lamproites accessory assemblage with the same major element compositions. Trace element and Sr-Nd isotopic relationships of the Ingashi lamproites are similar to classic lamproites. Different dating methods have provided the ages of lamproites: 1481 Ma (Ar-Ar phlogopite), 1268 Ma (Rb-Sr whole rock) and 300 Ma (U-Pb zircon). Ingashi lamproite ages are controversial and require additional study. The calculated pressure of 3.5 GPamax for clinopyroxenes indicates that lamproite magma originated deeper than 100 km. A Cr-in-garnet barometer shows a 3.7–4.3 GPamin and derivation of Ingashi lamproites deeper than 120 km in depth. Based on the range of typical cratonic geotherms and the presence of diamonds, the Ingashi lamproite magma originated at a depth greater than 155 km.
Ingashi煌石岩岩脉是俄罗斯伊尔库茨克地区唯一已知的主要钻石来源，也是西伯利亚克拉通中唯一的非金伯利岩岩脉。Ingashi煌斑岩田位于西伯利亚克拉通Prisayan隆起的Urik-Iya地堑内。绿云母-橄榄石煌斑岩中含有橄榄石、滑石、绿云母、蛇纹石、绿泥石、橄榄石、石榴石、铬铁矿、正辉石、斜辉石以及sr - f磷灰石、独居石、锆石、银辉石、铁辉石、钾镁铝榴石、锰钛铁矿、铌金红石和金刚石。滑石-碳酸盐地块中唯一的超镁铁质煌斑岩脉主要由蛇纹石化橄榄石和绿云母组成，与主要元素组成相同的印石煌斑岩副组合相似。印石煌斑岩的微量元素和Sr-Nd同位素关系与经典煌斑岩相似。不同的测年方法给出了煌斑岩的年龄:1481 Ma (Ar-Ar辉云母)，1268 Ma (Rb-Sr全岩)和300 Ma (U-Pb锆石)。Ingashi煌石岩年龄存在争议，需要进一步研究。斜辉石岩的计算压力为3.5 GPamax，表明煌斑岩岩浆的起源深度超过100 km。cr -in-石榴石气压计显示，在深度大于120 km的Ingashi煌斑岩中存在3.7-4.3 GPamin和衍生。根据典型克拉通地热的范围和钻石的存在，Ingashi煌石岩岩浆的起源深度大于155公里。
{"title":"Diamondiferous lamproites of Ingashi field, Siberian craton","authors":"S. Kostrovitsky, D. Yakovlev, I. Sharygin, D. Gladkochub, T. V. Donskaya, I. Tretiakova, A. Dymshits, A. P. Sekerin, V. Malkovets","doi":"10.1144/SP513-2020-274","DOIUrl":"https://doi.org/10.1144/SP513-2020-274","url":null,"abstract":"Abstract Ingashi lamproite dykes are the only known primary sources of diamond in the Irkutsk district (Russia) and the only non-kimberlitic one in the Siberian craton. The Ingashi lamproite field is situated in the Urik-Iya graben within the Prisayan uplift of the Siberian craton. The phlogopite-olivine lamproites contain olivine, talc, phlogopite, serpentine, chlorite, olivine, garnet, chromite, orthopyroxene, clinopyroxene as well as Sr-F-apatite, monazite, zircon, armolcolite, priderite, potassium Mg-arfvedsonite, Mn-ilmenite, Nb-rutile and diamond. The only ultramafic lamprophyre dyke is composed mainly of serpentinized olivine and phlogopite in the talc-carbonate groundmass and is similar to Ingashi lamproites accessory assemblage with the same major element compositions. Trace element and Sr-Nd isotopic relationships of the Ingashi lamproites are similar to classic lamproites. Different dating methods have provided the ages of lamproites: 1481 Ma (Ar-Ar phlogopite), 1268 Ma (Rb-Sr whole rock) and 300 Ma (U-Pb zircon). Ingashi lamproite ages are controversial and require additional study. The calculated pressure of 3.5 GPamax for clinopyroxenes indicates that lamproite magma originated deeper than 100 km. A Cr-in-garnet barometer shows a 3.7–4.3 GPamin and derivation of Ingashi lamproites deeper than 120 km in depth. Based on the range of typical cratonic geotherms and the presence of diamonds, the Ingashi lamproite magma originated at a depth greater than 155 km.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"2 1","pages":"45 - 70"},"PeriodicalIF":0.0,"publicationDate":"2021-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87128448","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}
Sonu, Amit Kumar, M. Satyanarayanan, Vamdev Pathak, N. Vedanti, J. Shrivastava
Abstract The Koyna borehole penetrated c. 1 km through the Deccan basalt units and into the cratonic basement beneath, thus providing a unique insight into the subsurface succession of the main Deccan province. Earlier studies focused on southwestern Deccan lava packages exposed in the Western Ghat escarpment, and resolved a well-constrained stratigraphy and key reference sections, but lacked supporting subsurface data. To construct the stratigraphy and correlate it with the main Deccan formations, we report flow-wise physical and chemical data of a c. 932 m-thick core. We document 37 lava-flow units and four lava-flow groups that have similar major-oxide contents. These groups fit into two of the recognized chemostratigraphic formations, and the transitional Poladpur–Ambenali lavas. In addition, data plots on Ba v. Sr; Ba v. Zr/Nb; Ba/Y v. Zr/Nb; and Ba, Sr, Ba/Y, Zr/Nb v. height bivariate diagrams confine them to the Poladpur and Ambenali formations. Lava flows match with the Khumbarli and Mahabaleshwar Ghat sections and Killari core. The granitoid basement–basalt and the Poladpur Formation v. Ambenali Formation contacts lie at −332.5 and c. 482 m above sea-level, respectively. Further, the new data endorse the southern overstepping of chemostratigraphic units and the asymmetry of the Deccan edifice due to the northward motion of the Indian Plate over the nascent Réunion plume (c. 67–64 Ma). For comparison, the oldest 66.4 Ma lava flow predates the Cretaceous–Paleogene boundary (KPB) (66.052 Ma) by <0.35 Ma, with much of the Wai Subgroup erupted syn-KPB or >0.55 Ma post-KPB; however, the restricted lava thickness at the contact between the Poladpur and Ambenali formations provides a reference point in the Deccan stratigraphy.
{"title":"Chemical stratigraphy of subsurface lava flows from the Koyna (KBH1) core and correlation with the southwestern stratigraphy of the Deccan Traps","authors":"Sonu, Amit Kumar, M. Satyanarayanan, Vamdev Pathak, N. Vedanti, J. Shrivastava","doi":"10.1144/SP518-2020-214","DOIUrl":"https://doi.org/10.1144/SP518-2020-214","url":null,"abstract":"Abstract The Koyna borehole penetrated c. 1 km through the Deccan basalt units and into the cratonic basement beneath, thus providing a unique insight into the subsurface succession of the main Deccan province. Earlier studies focused on southwestern Deccan lava packages exposed in the Western Ghat escarpment, and resolved a well-constrained stratigraphy and key reference sections, but lacked supporting subsurface data. To construct the stratigraphy and correlate it with the main Deccan formations, we report flow-wise physical and chemical data of a c. 932 m-thick core. We document 37 lava-flow units and four lava-flow groups that have similar major-oxide contents. These groups fit into two of the recognized chemostratigraphic formations, and the transitional Poladpur–Ambenali lavas. In addition, data plots on Ba v. Sr; Ba v. Zr/Nb; Ba/Y v. Zr/Nb; and Ba, Sr, Ba/Y, Zr/Nb v. height bivariate diagrams confine them to the Poladpur and Ambenali formations. Lava flows match with the Khumbarli and Mahabaleshwar Ghat sections and Killari core. The granitoid basement–basalt and the Poladpur Formation v. Ambenali Formation contacts lie at −332.5 and c. 482 m above sea-level, respectively. Further, the new data endorse the southern overstepping of chemostratigraphic units and the asymmetry of the Deccan edifice due to the northward motion of the Indian Plate over the nascent Réunion plume (c. 67–64 Ma). For comparison, the oldest 66.4 Ma lava flow predates the Cretaceous–Paleogene boundary (KPB) (66.052 Ma) by <0.35 Ma, with much of the Wai Subgroup erupted syn-KPB or >0.55 Ma post-KPB; however, the restricted lava thickness at the contact between the Poladpur and Ambenali formations provides a reference point in the Deccan stratigraphy.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"97 1","pages":"397 - 433"},"PeriodicalIF":0.0,"publicationDate":"2021-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77487702","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}
A. K. Singh, Govind Oinam, Sun‐Lin Chung, R. Bikramaditya, Hao-Yang Lee, M. Joshi
Abstract We report new U–Pb zircon ages for mafic plutonic (gabbro) and volcanic (andesite) rocks, along with the whole-rock chemistry of a mafic–felsic suite of volcanic rocks from the Siang window of the Eastern Himalayan Syntaxis, NE India. Field relationships, and mineralogical and geochemical characteristics, of the studied mafic–intermediate–felsic rocks suggest their co-magmatic linkage that was generated in an extensional tectonic environment. Incompatible trace elements and low concentrations of large ion lithophile elements (LILEs) and REE behaviour reflect both the enriched nature of the mafic rocks and the limited influence of crustal contamination in their genesis. Partial melting and fractional crystallization processes have played a major role during the genesis of these felsic volcanics from the parental mafic magma. The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb ages suggest that the mafic plutonic rock was emplaced at c. 121.18 ± 1 Ma and intermediate volcanic rock was emplaced at c. 135.48 ± 0.50 Ma during the Early Cretaceous period. The new ages are consistent with earlier reported zircon U–Pb ages (133.0 ± 1.9–130.7 ± 1.8 Ma) of felsic volcanic rocks from the present study area. Our new field observations, and mineralogical and geochemical characteristics, in conjunction with the U–Pb isotopic database suggest that the major magmatic event in the core of the Siang window of the Eastern Himalaya is coeval with the Rajmahal–Sylhet–Mikir–Shillong flood basalts of eastern and northeastern India, and the Comei–Bunbury Large Igneous Province of southeastern Tibet and SW Australia. These events are related to the break-up of eastern Gondwana and outbreak of the Kerguelen plume.
{"title":"Magmatism in the Siang window of the Eastern Himalayan Syntaxis, NE India: a vestige of Kerguelen mantle plume activity","authors":"A. K. Singh, Govind Oinam, Sun‐Lin Chung, R. Bikramaditya, Hao-Yang Lee, M. Joshi","doi":"10.1144/SP518-2021-13","DOIUrl":"https://doi.org/10.1144/SP518-2021-13","url":null,"abstract":"Abstract We report new U–Pb zircon ages for mafic plutonic (gabbro) and volcanic (andesite) rocks, along with the whole-rock chemistry of a mafic–felsic suite of volcanic rocks from the Siang window of the Eastern Himalayan Syntaxis, NE India. Field relationships, and mineralogical and geochemical characteristics, of the studied mafic–intermediate–felsic rocks suggest their co-magmatic linkage that was generated in an extensional tectonic environment. Incompatible trace elements and low concentrations of large ion lithophile elements (LILEs) and REE behaviour reflect both the enriched nature of the mafic rocks and the limited influence of crustal contamination in their genesis. Partial melting and fractional crystallization processes have played a major role during the genesis of these felsic volcanics from the parental mafic magma. The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb ages suggest that the mafic plutonic rock was emplaced at c. 121.18 ± 1 Ma and intermediate volcanic rock was emplaced at c. 135.48 ± 0.50 Ma during the Early Cretaceous period. The new ages are consistent with earlier reported zircon U–Pb ages (133.0 ± 1.9–130.7 ± 1.8 Ma) of felsic volcanic rocks from the present study area. Our new field observations, and mineralogical and geochemical characteristics, in conjunction with the U–Pb isotopic database suggest that the major magmatic event in the core of the Siang window of the Eastern Himalaya is coeval with the Rajmahal–Sylhet–Mikir–Shillong flood basalts of eastern and northeastern India, and the Comei–Bunbury Large Igneous Province of southeastern Tibet and SW Australia. These events are related to the break-up of eastern Gondwana and outbreak of the Kerguelen plume.","PeriodicalId":22055,"journal":{"name":"Special Publications","volume":"39 1","pages":"301 - 323"},"PeriodicalIF":0.0,"publicationDate":"2021-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73334797","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}
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