Pub Date : 2023-04-28DOI: 10.1017/S0016756823000262
Chaozong Liu, P. Cózar, I. Coronado, Tian Liang, Xiaoxiao Liu, Hao Chen, Xin Li, Haihua An, Fukai Zhang
Abstract The Viséan–Serpukhovian boundary is poorly defined in South China, hampering regional and global stratigraphical correlations. The foraminiferal and conodont distribution of the Baping Formation in the carbonate-slope Danlu section permits the recognition of an interval from the middle Viséan to the uppermost Serpukhovian in a continuous succession. The base of the Serpukhovian in Danlu is recognized by the first occurrences of Janischewskina delicata, Howchinia subplana and questionable ‘Millerella’ tortula. At a slightly younger level, the conodont Lochriea ziegleri is first recorded. A calibration on the first occurrence of L. ziegleri in different basins at a global scale has been revised compared to auxiliary markers within the ammonoids and foraminifers. The late occurrence of L. ziegleri in the Danlu section also supports a lack of synchronicity in the global first occurrence of this taxon. This study calls for the recognition of a new base for the Serpukhovian under a far better correlation between different zonal schemes and fossil groups.
{"title":"Foraminifers and conodonts in the Danlu section, South China: implications for the Viséan–Serpukhovian boundary (Mississippian)","authors":"Chaozong Liu, P. Cózar, I. Coronado, Tian Liang, Xiaoxiao Liu, Hao Chen, Xin Li, Haihua An, Fukai Zhang","doi":"10.1017/S0016756823000262","DOIUrl":"https://doi.org/10.1017/S0016756823000262","url":null,"abstract":"Abstract The Viséan–Serpukhovian boundary is poorly defined in South China, hampering regional and global stratigraphical correlations. The foraminiferal and conodont distribution of the Baping Formation in the carbonate-slope Danlu section permits the recognition of an interval from the middle Viséan to the uppermost Serpukhovian in a continuous succession. The base of the Serpukhovian in Danlu is recognized by the first occurrences of Janischewskina delicata, Howchinia subplana and questionable ‘Millerella’ tortula. At a slightly younger level, the conodont Lochriea ziegleri is first recorded. A calibration on the first occurrence of L. ziegleri in different basins at a global scale has been revised compared to auxiliary markers within the ammonoids and foraminifers. The late occurrence of L. ziegleri in the Danlu section also supports a lack of synchronicity in the global first occurrence of this taxon. This study calls for the recognition of a new base for the Serpukhovian under a far better correlation between different zonal schemes and fossil groups.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"1131 - 1143"},"PeriodicalIF":2.3,"publicationDate":"2023-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43925690","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2023-04-27DOI: 10.1017/S0016756823000237
Pallabi Basumatary, A. Saikia, Tribujjal Prakash, Bibhuti Gogoi
The Paleo-Mesoproterozoic Shillong Basin of the Assam-Meghalaya Gneissic Complex is exposed in parts of Northeast India. The studied metadolerites are from the volcano-sedimentary sequence of Shillong Basin from the Borjuri area in the Mikir Massif. This episode of mafic magmatism can be correlated with the Columbia supercontinent formation and bears significance to its reconstruction. The present work discusses the field, petrography and geochemical characteristics of the metadolerites, which occur in close association with the quartzites of the Shillong Group of rocks (metasedimentary rocks of the Shillong Basin). Our data show distinctive characteristics of subduction-related magmatism exhibiting high LREE/HREE, large ion lithophile element/high field strength element ratios and pronounced negative Nb anomaly. Elemental ratios such as Zr/Ba (0.21–0.46), La/Nb (1.23–2.32) and Ba/Nb (30.08–56.90) point to a fluid-enriched lithospheric mantle source in a subduction regime. Metadolerites plot in the field of ‘back-arc basin basalts’ in tectonic discrimination diagrams reinforcing a subduction zone tectonic setting. The mafic rocks correspond to a 6–10 % partial melting of a mantle source incorporating spinel+garnet lherzolite. The metamorphic P-T of the metadolerites estimated from plagioclase-hornblende geothermobarometer (7–8 kbar, 664 °C) is indicative of amphibolite facies metamorphism in a medium P-T zone. Based on the comparative analysis of field observation, petrography, geochemistry and geological ages given by previous workers, we infer that the Shillong Basin represents a back-arc rift region and is the eastern continuation of the Bathani volcano-sedimentary sequence of the Chotanagpur Granite Gneiss Complex marking continuation of the Central Indian Tectonic Zone to the Mikir Massif.
{"title":"Geochemical constraints on the petrogenesis of mafic rocks (metadolerites) from the Proterozoic Shillong Basin, Northeast India: implications for growth of the Greater Indian Landmass","authors":"Pallabi Basumatary, A. Saikia, Tribujjal Prakash, Bibhuti Gogoi","doi":"10.1017/S0016756823000237","DOIUrl":"https://doi.org/10.1017/S0016756823000237","url":null,"abstract":"\u0000 The Paleo-Mesoproterozoic Shillong Basin of the Assam-Meghalaya Gneissic Complex is exposed in parts of Northeast India. The studied metadolerites are from the volcano-sedimentary sequence of Shillong Basin from the Borjuri area in the Mikir Massif. This episode of mafic magmatism can be correlated with the Columbia supercontinent formation and bears significance to its reconstruction. The present work discusses the field, petrography and geochemical characteristics of the metadolerites, which occur in close association with the quartzites of the Shillong Group of rocks (metasedimentary rocks of the Shillong Basin). Our data show distinctive characteristics of subduction-related magmatism exhibiting high LREE/HREE, large ion lithophile element/high field strength element ratios and pronounced negative Nb anomaly. Elemental ratios such as Zr/Ba (0.21–0.46), La/Nb (1.23–2.32) and Ba/Nb (30.08–56.90) point to a fluid-enriched lithospheric mantle source in a subduction regime. Metadolerites plot in the field of ‘back-arc basin basalts’ in tectonic discrimination diagrams reinforcing a subduction zone tectonic setting. The mafic rocks correspond to a 6–10 % partial melting of a mantle source incorporating spinel+garnet lherzolite. The metamorphic P-T of the metadolerites estimated from plagioclase-hornblende geothermobarometer (7–8 kbar, 664 °C) is indicative of amphibolite facies metamorphism in a medium P-T zone. Based on the comparative analysis of field observation, petrography, geochemistry and geological ages given by previous workers, we infer that the Shillong Basin represents a back-arc rift region and is the eastern continuation of the Bathani volcano-sedimentary sequence of the Chotanagpur Granite Gneiss Complex marking continuation of the Central Indian Tectonic Zone to the Mikir Massif.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"1114 - 1130"},"PeriodicalIF":2.3,"publicationDate":"2023-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43358322","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2023-04-11DOI: 10.1017/S0016756823000183
F. Narduzzi, M. Ponton, Michele Marello, Marco Paulo de Castro, G. Queiroga, A. De Min
Abstract We investigated olivine minette dykes from the Rio Colan Valley of the Julian Alps (NE Italy) to provide new constraints on the mantle geochemistry underneath this extreme sector of the Italian Southern Alps. Petrographic observations, high Mg#s, high Cr and Ni contents, low Dy/YbCN ratios and flat heavy rare earth element (REE) profiles imply these are primary magmas derived from a depleted peridotite with olivine and garnet as possible residual phases. However, high K2O and incompatible trace element contents, coupled with superchondritic Nb/Ta ratios, suggest that the source was modified into a rutile–phlogopite-bearing carbonated peridotite by multiple metasomatic events such as recycling of crustal material and carbonatitic metasomatism related to an old orogenic event and rutile-rich metasomatism linked to the Pangaea break-up. Laser ablation – multi-collector – inductively coupled plasma – mass spectrometer (LA-MC-ICP-MS) U–Pb geochronology of apatites from two dykes yielded differences between unforced and forced discordia ages up to ∼45 Ma, likely due to the initial 207Pb/206Pb correction adopted. Nonetheless, because forced discordia and 206Pb/238U weighted mean ages are overall similar within the uncertainty, our preferred interpretation is that olivine minettes intruded and crystallized at ∼67 Ma. The age and anorogenic signature of these magmas are consistent with the regional extensional tectonics in the Julian Alps due to the advance of the external Dinaric front following Adria plate eastward subduction. Eventually, we show also that Rio Colan magmas are geochemically hybrid products between lamprophyres and lamproites compared with similar Italian and Western Mediterranean volcanics.
{"title":"Geochemical characterization, U–Pb apatite geochronology, and geodynamic significance of olivine minette dykes from the Julian Alps, NE Italy","authors":"F. Narduzzi, M. Ponton, Michele Marello, Marco Paulo de Castro, G. Queiroga, A. De Min","doi":"10.1017/S0016756823000183","DOIUrl":"https://doi.org/10.1017/S0016756823000183","url":null,"abstract":"Abstract We investigated olivine minette dykes from the Rio Colan Valley of the Julian Alps (NE Italy) to provide new constraints on the mantle geochemistry underneath this extreme sector of the Italian Southern Alps. Petrographic observations, high Mg#s, high Cr and Ni contents, low Dy/YbCN ratios and flat heavy rare earth element (REE) profiles imply these are primary magmas derived from a depleted peridotite with olivine and garnet as possible residual phases. However, high K2O and incompatible trace element contents, coupled with superchondritic Nb/Ta ratios, suggest that the source was modified into a rutile–phlogopite-bearing carbonated peridotite by multiple metasomatic events such as recycling of crustal material and carbonatitic metasomatism related to an old orogenic event and rutile-rich metasomatism linked to the Pangaea break-up. Laser ablation – multi-collector – inductively coupled plasma – mass spectrometer (LA-MC-ICP-MS) U–Pb geochronology of apatites from two dykes yielded differences between unforced and forced discordia ages up to ∼45 Ma, likely due to the initial 207Pb/206Pb correction adopted. Nonetheless, because forced discordia and 206Pb/238U weighted mean ages are overall similar within the uncertainty, our preferred interpretation is that olivine minettes intruded and crystallized at ∼67 Ma. The age and anorogenic signature of these magmas are consistent with the regional extensional tectonics in the Julian Alps due to the advance of the external Dinaric front following Adria plate eastward subduction. Eventually, we show also that Rio Colan magmas are geochemically hybrid products between lamprophyres and lamproites compared with similar Italian and Western Mediterranean volcanics.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"1098 - 1113"},"PeriodicalIF":2.3,"publicationDate":"2023-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47111940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2023-04-05DOI: 10.1017/S001675682300016X
Nan Gao, Yingkui Xu, Dan Zhu, Yang Li, Xiongyao Li, Jianzhong Liu, Jincheng Luo
Abstract We report high-precision K isotopes, apatite U–Pb ages, whole-rock elements and Sr–Nd isotopes for the Saima nephelite syenite in the North China Craton. Trace-element and Sr–Nd–Hf–O isotope data indicate the presence of subducting sediments in the source region, while K isotopic compositions show a narrow range between –0.54 ‰ and –0.28 ‰, with an average of –0.41 ± 0.06 ‰, identical to the value of the asthenosphere. The nearly identical K isotopic compositions are low probability events compared with the K isotopic compositions of island arc lavas reported previously (–1.55 ‰ to +0.2 ‰). Although crustal contamination is consistent with the Sr–Nd–K isotopic data, alternatively we propose that the isotopic data also reconcile with the interaction between cratonic roots and the underlying convective asthenosphere, if this interaction is over prolonged periods of time. Numerical simulations successfully reproduced the observed data, if the metasomatism of the lithospheric mantle root, the source of the Saima alkaline rocks, occurred 500 Ma ago. Our study reveals that the isotopic compositions of fast-diffusion components in a lithospheric mantle metasomatized by ancient subducting melts can be effectively homogenized by convective asthenosphere through diffusion over a long time interval.
{"title":"Isotopic decoupling of K from Sr and Nd in the Saima alkaline complex, NE China: interactions of cratonic roots and asthenosphere","authors":"Nan Gao, Yingkui Xu, Dan Zhu, Yang Li, Xiongyao Li, Jianzhong Liu, Jincheng Luo","doi":"10.1017/S001675682300016X","DOIUrl":"https://doi.org/10.1017/S001675682300016X","url":null,"abstract":"Abstract We report high-precision K isotopes, apatite U–Pb ages, whole-rock elements and Sr–Nd isotopes for the Saima nephelite syenite in the North China Craton. Trace-element and Sr–Nd–Hf–O isotope data indicate the presence of subducting sediments in the source region, while K isotopic compositions show a narrow range between –0.54 ‰ and –0.28 ‰, with an average of –0.41 ± 0.06 ‰, identical to the value of the asthenosphere. The nearly identical K isotopic compositions are low probability events compared with the K isotopic compositions of island arc lavas reported previously (–1.55 ‰ to +0.2 ‰). Although crustal contamination is consistent with the Sr–Nd–K isotopic data, alternatively we propose that the isotopic data also reconcile with the interaction between cratonic roots and the underlying convective asthenosphere, if this interaction is over prolonged periods of time. Numerical simulations successfully reproduced the observed data, if the metasomatism of the lithospheric mantle root, the source of the Saima alkaline rocks, occurred 500 Ma ago. Our study reveals that the isotopic compositions of fast-diffusion components in a lithospheric mantle metasomatized by ancient subducting melts can be effectively homogenized by convective asthenosphere through diffusion over a long time interval.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"1090 - 1097"},"PeriodicalIF":2.3,"publicationDate":"2023-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47242611","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2023-04-04DOI: 10.1017/S0016756822001303
Hao Xing, C. Xue, Xiaobo Zhao, Dta Symons, Peng Niu
Abstract In the Yili terrane at Awulale mountain, most shoshonitic lavas are related to post-collision extension and were extruded during the Late Carboniferous to Early Permian (310–280 Ma). Herein, we evaluate a small-volume occurrence of shoshonitic magmas in the southern Yili terrane formed c. 346 Ma ago. The high MgO (Mg#) and positive Hf isotope values of the shoshonitic magmas indicate the input of juvenile mantle-derived material. Still, their high Ba–Sr signatures were likely inherited from the partial melting of previously metasomatized lithospheric mantle. We argue the shoshonitic magmatic activity recorded a syn-subduction extensional history in the Yili terrane. This interpretation is consistent with the magmatic records from Early Carboniferous A-type granite and magnesian andesite found in the Zhaosu–Adentao–Dahalajunshan area of the southern Yili terrane. Combined with the geological development in this area, we propose that the emergence of the shoshonitic rocks records either the retreat of the trench or the rollback of the Junggar oceanic slab that occurred at or before the 346.1 ± 3.1 Ma age of the rocks.
{"title":"Petrogenesis and tectonic implications of the Early Carboniferous shoshonitic to calc-alkaline magmatic rocks of the southern Yili terrane, western Tianshan","authors":"Hao Xing, C. Xue, Xiaobo Zhao, Dta Symons, Peng Niu","doi":"10.1017/S0016756822001303","DOIUrl":"https://doi.org/10.1017/S0016756822001303","url":null,"abstract":"Abstract In the Yili terrane at Awulale mountain, most shoshonitic lavas are related to post-collision extension and were extruded during the Late Carboniferous to Early Permian (310–280 Ma). Herein, we evaluate a small-volume occurrence of shoshonitic magmas in the southern Yili terrane formed c. 346 Ma ago. The high MgO (Mg#) and positive Hf isotope values of the shoshonitic magmas indicate the input of juvenile mantle-derived material. Still, their high Ba–Sr signatures were likely inherited from the partial melting of previously metasomatized lithospheric mantle. We argue the shoshonitic magmatic activity recorded a syn-subduction extensional history in the Yili terrane. This interpretation is consistent with the magmatic records from Early Carboniferous A-type granite and magnesian andesite found in the Zhaosu–Adentao–Dahalajunshan area of the southern Yili terrane. Combined with the geological development in this area, we propose that the emergence of the shoshonitic rocks records either the retreat of the trench or the rollback of the Junggar oceanic slab that occurred at or before the 346.1 ± 3.1 Ma age of the rocks.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"855 - 873"},"PeriodicalIF":2.3,"publicationDate":"2023-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44368909","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2023-04-03DOI: 10.1017/S0016756823000134
R. Chandra, N. Kowser, M. Brookfield, M. Satyanarayanan, D. Stöckli
Abstract The Shyok Suture Zone is an oceanic remnant of the Neo-Tethyan ocean sandwiched between the Ladakh Batholiths to the south and Karakoram Batholith to the north. The Tirit granitoids in this suture are dark-coloured, relatively rich in ferromagnesian minerals and range from granodiorite–tonalite to gabbro–diorite in composition. Mafic igneous enclaves are quite common and they are intruded by NW–SE parallel doleritic and aplitic dykes. The Tirit granitoids have a wide range of major oxide compositions (SiO2 = 52.1–72.11 wt %, TiO2 = 0.21–1.23 wt %, Al2O3 = 11.42–13.52 wt %, MgO = 1.69–10.69 wt % and CaO = 3.24–9.31 wt %) and show calc-alkaline, metaluminous, I-type characteristics, transitional between primitive and mature arc continental plutons. Rare earth elements (REE) show considerable enrichment in light REE (LREE) as compared to the heavy REE (HREE). Late Cretaceous U/Pb dates (74–68 Ma) show that they formed during the pre-collision northward movement of India. The Tirit dykes are only slightly younger and probably part of the same episode.
{"title":"Nature of the Shyok (Northern) Suture Zone between India and Asia: petrology, geochemistry and origin of the Tirit granitoids and associated dykes (Nubra Valley Ladakh Himalaya, NW India)","authors":"R. Chandra, N. Kowser, M. Brookfield, M. Satyanarayanan, D. Stöckli","doi":"10.1017/S0016756823000134","DOIUrl":"https://doi.org/10.1017/S0016756823000134","url":null,"abstract":"Abstract The Shyok Suture Zone is an oceanic remnant of the Neo-Tethyan ocean sandwiched between the Ladakh Batholiths to the south and Karakoram Batholith to the north. The Tirit granitoids in this suture are dark-coloured, relatively rich in ferromagnesian minerals and range from granodiorite–tonalite to gabbro–diorite in composition. Mafic igneous enclaves are quite common and they are intruded by NW–SE parallel doleritic and aplitic dykes. The Tirit granitoids have a wide range of major oxide compositions (SiO2 = 52.1–72.11 wt %, TiO2 = 0.21–1.23 wt %, Al2O3 = 11.42–13.52 wt %, MgO = 1.69–10.69 wt % and CaO = 3.24–9.31 wt %) and show calc-alkaline, metaluminous, I-type characteristics, transitional between primitive and mature arc continental plutons. Rare earth elements (REE) show considerable enrichment in light REE (LREE) as compared to the heavy REE (HREE). Late Cretaceous U/Pb dates (74–68 Ma) show that they formed during the pre-collision northward movement of India. The Tirit dykes are only slightly younger and probably part of the same episode.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"1020 - 1039"},"PeriodicalIF":2.3,"publicationDate":"2023-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44953819","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2023-04-03DOI: 10.1017/S0016756823000055
L. Desutter‐Grandcolas, Hugo Josse, Marie Laurent, Lucas Denadai de Campos, Sylvain Hugel, C. Soriano, A. Nel, V. Perrichot
Abstract Fossils are more and more used in phylogenetic evolutionary studies either for clade calibration, or as terminals in a dataset including morphological characters. The strength of these methodological advances relies however on the quality and completeness of the fossil record. For crickets (Insecta, Orthoptera, Gryllidea), few ancient (pre-Cenozoic) well-preserved fossils are known, except for isolated wings often classified in purely fossil groups and a few fossils found in Cretaceous amber. Here, we present two remarkable fossils from mid-Cretaceous amber of France, that were imaged using X-ray synchrotron microtomography and exhibit an exquisite preservation allowing description with a precision similar to that of extant taxa. Palaeonemobius occidentalis Laurent and Desutter-Grandcolas, gen. nov., sp. nov. and Picogryllus carentonensis Josse and Desutter-Grandcolas, gen. nov., sp. nov. are the oldest representatives of the Nemobiinae and Podoscirtinae subfamilies of the Trigonidiidae and Oecanthidae families respectively. P. carentonensis Josse and Desutter-Grandcolas, gen. nov., sp. nov. is also the smallest adult male with a full stridulatory apparatus ever documented in crickets (body length 3.3 mm), and the first taxon of the cricket clade for which male genitalia can be partly described. We discuss the significance of Cretaceous fossils of crickets for future evolutionary studies of this clade.
摘要化石越来越多地用于系统发育进化研究，要么用于分支校准，要么作为包括形态特征的数据集中的终端。然而，这些方法学进步的力量取决于化石记录的质量和完整性。蟋蟀（昆虫纲、直翅目、蟋蟀总科），除了通常被归类为纯化石组的孤立翅膀和白垩纪琥珀中发现的一些化石外，几乎没有已知的古代（新生代前）保存完好的化石。在这里，我们展示了两个来自法国白垩纪中期琥珀的引人注目的化石，它们是使用X射线同步加速器显微成像技术拍摄的，保存完好，可以以与现存分类群相似的精度进行描述。Palaeonamobius occidentalis Laurent和Desutter Grandcolas，gen.nov.，sp.nov.和Picogryllus carentonensis Josse和Desutter-Grandcolas（gen.nov..，sp.nov）分别是三角藻科和Oecanthidae科的线虫亚科和足目昆虫亚科的最古老代表。P.carentonensis Josse和Desutter Grandcolas，gen.nov.，sp.nov.也是蟋蟀中有记录以来体型最小的成年雄性（体长3.3毫米），也是蟋蟀分支中第一个可以部分描述雄性生殖器的分类单元。我们讨论了蟋蟀白垩纪化石对该分支未来进化研究的意义。
{"title":"New Cretaceous crickets of the subfamilies Nemobiinae and Podoscirtinae (Orthoptera, Grylloidea: Trigonidiidae, Oecanthidae) attest the antiquity of these clades","authors":"L. Desutter‐Grandcolas, Hugo Josse, Marie Laurent, Lucas Denadai de Campos, Sylvain Hugel, C. Soriano, A. Nel, V. Perrichot","doi":"10.1017/S0016756823000055","DOIUrl":"https://doi.org/10.1017/S0016756823000055","url":null,"abstract":"Abstract Fossils are more and more used in phylogenetic evolutionary studies either for clade calibration, or as terminals in a dataset including morphological characters. The strength of these methodological advances relies however on the quality and completeness of the fossil record. For crickets (Insecta, Orthoptera, Gryllidea), few ancient (pre-Cenozoic) well-preserved fossils are known, except for isolated wings often classified in purely fossil groups and a few fossils found in Cretaceous amber. Here, we present two remarkable fossils from mid-Cretaceous amber of France, that were imaged using X-ray synchrotron microtomography and exhibit an exquisite preservation allowing description with a precision similar to that of extant taxa. Palaeonemobius occidentalis Laurent and Desutter-Grandcolas, gen. nov., sp. nov. and Picogryllus carentonensis Josse and Desutter-Grandcolas, gen. nov., sp. nov. are the oldest representatives of the Nemobiinae and Podoscirtinae subfamilies of the Trigonidiidae and Oecanthidae families respectively. P. carentonensis Josse and Desutter-Grandcolas, gen. nov., sp. nov. is also the smallest adult male with a full stridulatory apparatus ever documented in crickets (body length 3.3 mm), and the first taxon of the cricket clade for which male genitalia can be partly described. We discuss the significance of Cretaceous fossils of crickets for future evolutionary studies of this clade.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"927 - 940"},"PeriodicalIF":2.3,"publicationDate":"2023-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49553646","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2023-04-03DOI: 10.1017/S0016756823000146
M. Shirmohammadi, A. Sepahi, J. Santos, M. Maanijou, A. Torkian, Hamed Vahidpour
Abstract The Almogholagh–Dehgolan region is in the North Sanandaj–Sirjan zone of NW Iran. The granites of the region are metaluminous and display geochemical and textural characteristics of transitional granites between ferroan (A-type) and I-type granites. In geotectonic discrimination diagrams, the Almogholagh–Dehgolan granites plot mainly in the fields of within-plate granites and volcanic arc granites. With the exception of the Qalaylan granites, parts of other granites resemble A2-type granites. Granites of the Qalaylan intrusive body have petrographic and geochemical features close to I-type granites and are not A-type. Primary mantle and chondrite-normalized spider diagrams show enrichments in light rare earth elements relative to heavy rare earth elements. For an age of 150 Ma, the initial 87Sr/86Sr and 143Nd/144Nd ratios vary from 0.702769 to 0.706545 and from 0.512431 to 0.512558, respectively. Epsilon Nd values vary in a relatively limited range between −0.3 and +2.2, which corresponds to a mixed mantle–crustal source. On the basis of new geochemical and isotopic data, we suggest a geodynamic model involving partial melting of lower crustal rocks with the contribution of mantle magmas in a weakly extensional tectonic setting for the generation of the A-type granites of the region. The occurrence of ferroan (A-type) granites in this region of the Sanandaj–Sirjan zone indicates the existence of a partly extensional tectonic environment in a mainly compressional subduction-related regime in Late Jurassic time.
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