Xin Chen, H. Schertl, A. Cambeses, Emma Hart, Chenggui Lin, Rongke Xu, Youye Zheng
The most significant mass transfer processes at a convergent plate boundary are tectonic accretion and fluids/melts released from sites of generation to sites of accumulation. However, some crucial questions remain with regards to the source, timescale, and evolution of such anatectic processes, for example, single or multistage anatexis of deeply subducted continental crust. To better understand the processes involved in anatexis, we have quantified the timescale and nature of formation and evolution processes of multistage felsic veins within retrograde eclogite using zircon, monazite, and xenotime geochemistry and geochronology, whole-rock composition, and Sr-Nd-Hf isotope analysis from the Lüliangshan, North Qaidam orogen. The U–Pb dating of coexisting zircon, monazite, and xenotime gives three groups of ages at ca. 441 to 435, ca. 425, and ca. 413 to 409 Ma, respectively, which record at least three episodes of pulsed melts. The first stage of zircon formation is characterized by not only the absence of oscillatory zoning of different zircons in cathodoluminescence images but also some of them with flat HREE and without Eu anomalies, indicating they may form in anatectic melts under eclogite-facies conditions. The second and third phases of melts may have occurred under granulite- and amphibole-facies conditions during exhumation. Furthermore, two classes of felsic veins within the eclogite show wide variations of whole-rock composition, (87Sr/86Sr)i, εNd (t), and εHf (t) values, which demonstrate that they were derived from fluid-present dehydration partial melting of different proportions of subducted gneiss and eclogite during different periods. These findings show that melts have systematic differences in chemical and isotopic signatures resulting from lithological diversity and depth of partial melting. Thus, small-scale melts released from the source can excellently explain the variability in whole-rock composition, accessory mineral growth zoning, and prominent isotope variability in syn-collisional heterogeneous granites. An additional implication is that as these melts escape their adjacent area of formation, they migrate and mix along channelized melt pathways, resulting in melt-rock and crust-mantle interaction and the triggering of syn- and post-collisional magmatism.
{"title":"Cyclicity of multistage anatexis of deeply subducted continental crust during the North Qaidam orogeny: Tracing the source, timescale, and evolution of pulsed melts","authors":"Xin Chen, H. Schertl, A. Cambeses, Emma Hart, Chenggui Lin, Rongke Xu, Youye Zheng","doi":"10.2475/02.2022.05","DOIUrl":"https://doi.org/10.2475/02.2022.05","url":null,"abstract":"The most significant mass transfer processes at a convergent plate boundary are tectonic accretion and fluids/melts released from sites of generation to sites of accumulation. However, some crucial questions remain with regards to the source, timescale, and evolution of such anatectic processes, for example, single or multistage anatexis of deeply subducted continental crust. To better understand the processes involved in anatexis, we have quantified the timescale and nature of formation and evolution processes of multistage felsic veins within retrograde eclogite using zircon, monazite, and xenotime geochemistry and geochronology, whole-rock composition, and Sr-Nd-Hf isotope analysis from the Lüliangshan, North Qaidam orogen. The U–Pb dating of coexisting zircon, monazite, and xenotime gives three groups of ages at ca. 441 to 435, ca. 425, and ca. 413 to 409 Ma, respectively, which record at least three episodes of pulsed melts. The first stage of zircon formation is characterized by not only the absence of oscillatory zoning of different zircons in cathodoluminescence images but also some of them with flat HREE and without Eu anomalies, indicating they may form in anatectic melts under eclogite-facies conditions. The second and third phases of melts may have occurred under granulite- and amphibole-facies conditions during exhumation. Furthermore, two classes of felsic veins within the eclogite show wide variations of whole-rock composition, (87Sr/86Sr)i, εNd (t), and εHf (t) values, which demonstrate that they were derived from fluid-present dehydration partial melting of different proportions of subducted gneiss and eclogite during different periods. These findings show that melts have systematic differences in chemical and isotopic signatures resulting from lithological diversity and depth of partial melting. Thus, small-scale melts released from the source can excellently explain the variability in whole-rock composition, accessory mineral growth zoning, and prominent isotope variability in syn-collisional heterogeneous granites. An additional implication is that as these melts escape their adjacent area of formation, they migrate and mix along channelized melt pathways, resulting in melt-rock and crust-mantle interaction and the triggering of syn- and post-collisional magmatism.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45762784","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}
Zhen Wang, Yuruo Shi, Tianshui Yang, J. Anderson, Chenyang Hou, Yuelan Kang, Wenxiao Peng, Yiming Ma, W. Bian
In this contribution, we report new U-Pb SHRIMP zircon ages and geochemical data for volcanic rocks from the Dianzhong Formation. The unit represents the lower part of the Linzizong volcanic succession located in the Shiquanhe area, western part of the Gangdese belt. Zircon U-Pb dating of three trachytes yields 206Pb/238U crystallization ages of 71.5±0.6 Ma, 70.8±1.0 Ma and 68.9±1.0 Ma. Whole rock major and trace element analyses indicate a main trend of calc-alkalic to high-potassic calc-alkalic, as well as an enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HFSEs), with negative Nb, Ta and Ti anomalies. In addition, these volcanic rocks are enriched in LREE and depleted in HREE without a clear Eu anomaly. These geochemical features are similar to those of active continental margin volcanic rocks. In combination with previously published zircon U-Pb ages and geochemical data of the Dianzhong Formation, we suggest that the Linzizong volcanism started as early as the late Cretaceous (∼71 Ma) and the volcanic rocks of the Dianzhong Formation in the Shiquanhe area are the product of rollback of the Neo-Tethyan oceanic plate.
{"title":"Constraints on the rollback of the Neo-Tethyan oceanic plate: Geochronology and geochemistry of volcanic rocks from the Dianzhong Formation, western Gangdese belt (Tibetan Plateau)","authors":"Zhen Wang, Yuruo Shi, Tianshui Yang, J. Anderson, Chenyang Hou, Yuelan Kang, Wenxiao Peng, Yiming Ma, W. Bian","doi":"10.2475/02.2022.10","DOIUrl":"https://doi.org/10.2475/02.2022.10","url":null,"abstract":"In this contribution, we report new U-Pb SHRIMP zircon ages and geochemical data for volcanic rocks from the Dianzhong Formation. The unit represents the lower part of the Linzizong volcanic succession located in the Shiquanhe area, western part of the Gangdese belt. Zircon U-Pb dating of three trachytes yields 206Pb/238U crystallization ages of 71.5±0.6 Ma, 70.8±1.0 Ma and 68.9±1.0 Ma. Whole rock major and trace element analyses indicate a main trend of calc-alkalic to high-potassic calc-alkalic, as well as an enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HFSEs), with negative Nb, Ta and Ti anomalies. In addition, these volcanic rocks are enriched in LREE and depleted in HREE without a clear Eu anomaly. These geochemical features are similar to those of active continental margin volcanic rocks. In combination with previously published zircon U-Pb ages and geochemical data of the Dianzhong Formation, we suggest that the Linzizong volcanism started as early as the late Cretaceous (∼71 Ma) and the volcanic rocks of the Dianzhong Formation in the Shiquanhe area are the product of rollback of the Neo-Tethyan oceanic plate.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45886308","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}
C. Heubeck, N. Drabon, G. Byerly, Isabelle Leisgang, U. Linnemann, D. Lowe, R. Mertz‐Kraus, Alejandra Gonzalez-Pinzón, T. Thomsen, A. Zeh, Y. Rojas‐Agramonte, A. Kröner
Sandstones of the 3.22 Ga Archean Moodies Group represent one of the world's oldest quartz-rich sedimentary sequences. The provenance of this unit is unresolved because its quartz and common microcline can be sourced both from either now eroded or covered granitoid plutons outside the Barberton Greenstone Belt (BGB) or, alternatively and perhaps more controversially, (rhyo-)dacitic (sub-)volcanic rocks within the BGB. We compiled 31 detrital zircon data sets (n = 2588) from sandstones, reworked tuffs and conglomerate of the Moodies Group in order to constrain its age and provenance. After selection using quality criteria, the remaining zircons (n = 1621) in nearly all samples show a distribution corresponding to the four known major pulses of felsic magmatism in the BGB: 1) the ca. 3550 to 3530 Ma Theespruit and Sandspruit Formations at the base of the Onverwacht Group; 2) the ca. 3440 to 3410 Ma rhyo-dacites of the upper Hooggenoeg Formation, Onverwacht Group; 3) the ca. 3300 to 3280 Ma thin felsic tuffs in the Mendon Formation; and 4) the ca. 3260 to 3215 Ma felsic volcanic and shallow intrusive rocks of the Auber Villiers, Bien Venue and Schoongezicht Formations of the upper Fig Tree Group and the Moodies Group as well as their co-magmatic plutonic counterparts. Almost all data sets also contain near-concordant younger zircons as young as 2820 Ma, which can be attributed to one of six tectonic or magmatic events affecting the young Kaapvaal Craton in post-BGB time, causing the partial or complete resetting of the U-Pb system in some grains. The youngest (near-)concordant zircon clusters yield ages of ca. 3220 Ma in most locations, and the youngest discordant group of zircons from a reworked tuff near the top of the Moodies Group at 3212 ± 13 Ma agrees well with previous estimates of the maximum depositional age. With very few exceptions, the oldest zircons (ca. 3564 Ma) are only slightly older than the oldest rocks in the BGB stratigraphy (ca. 3550 Ma). Subtle regional and stratigraphic differences in age spectra may indicate localized or nearby sediment sources within a synorogenic setting. Preliminary age spectra along vertical stratigraphic profiles show little systematic variation, possibly indicating that intrabasinal recycling was dominant over considerable time periods of the basin's evolution. Extra-basinal plutonic sources of similar age and composition as the intra-BGB sources appear to be required to provide quartz and some feldspar to Moodies Group sandstones, although zircon age spectra, limited zircon Hf isotope data, sandstone petrography, facies analysis, and the high variability in Moodies conglomerate clast composition are consistent with uplift, deformation and erosion of several intra-BGB sources, but in particular from the region of the Onverwacht Anticline. Zircon populations, conglomerate clasts, and sandstone composition show no evidence that high-grade metamorphic rocks from the adjacent Ancient Gneiss Complex (AGC) co
3.22 Ga太古宙穆迪群的砂岩代表了世界上最古老的富含石英的沉积序列之一。该单元的来源尚未确定，因为其石英和常见的微斜长石既可以来源于Barberton Greenstone Belt（BGB）外现已被侵蚀或覆盖的花岗质深成岩体，也可以来源于BGB内的（rhyo-）英安质（亚）火山岩。我们从穆迪组的砂岩、改造凝灰岩和砾岩中汇编了31个碎屑锆石数据集（n=2588），以限制其年龄和物源。在使用质量标准进行选择后，几乎所有样品中的剩余锆石（n=1621）显示出与BGB中长英质岩浆作用的四个已知主脉冲相对应的分布：1）Onverwacht群底部的约3550至3530 Ma Theespruit和Sandspruit组；2） Onverwacht群Hooggenoeg组上部的约3440至3410 Ma rhyo英安岩；3） Mendon组中约3300至3280 Ma的薄长英质凝灰岩；和4）上部无花果树群和穆迪群的Auber Villiers、Bien Venue和Schongezicht组的约3260至3215 Ma长英质火山岩和浅侵入岩，以及它们的同岩浆深成岩对应物。几乎所有的数据集都包含年龄为2820 Ma的近乎一致的年轻锆石，这可归因于后BGB时期影响年轻Kaapvaal火山口的六个构造或岩浆事件之一，导致一些颗粒中的U-Pb系统部分或完全重置。最年轻（接近）的一致锆石群在大多数位置产生的年龄约为3220 Ma，最年轻的不一致锆石群来自穆迪群顶部附近的改造凝灰岩，在3212±13 Ma，与之前对最大沉积年龄的估计非常一致。除了极少数例外，最古老的锆石（约3564 Ma）仅比BGB地层中最古老的岩石（约3550 Ma）略老。年龄谱中细微的区域和地层差异可能表明同造山带环境中的局部或附近沉积物来源。沿垂直地层剖面的初步年龄谱显示出很少的系统变化，这可能表明在盆地演化的相当长的一段时间内，盆地内的再循环占主导地位。尽管锆石年龄谱、有限的锆石Hf同位素数据、砂岩岩石学、相分析以及穆迪砾岩碎屑组成的高度变异性与隆起一致，但似乎需要与BGB内部来源具有相似年龄和成分的盆地外深成岩体来源来为穆迪群砂岩提供石英和一些长石，几个BGB内部源的变形和侵蚀，特别是来自Onverwacht背斜区域的。锆石种群、砾岩碎屑和砂岩成分没有证据表明邻近古片麻岩杂岩（AGC）的高级变质岩对穆迪群有重大贡献。
{"title":"Detrital zircon provenance of the Archean Moodies Group, Barberton Greenstone Belt, South Africa and Eswatini","authors":"C. Heubeck, N. Drabon, G. Byerly, Isabelle Leisgang, U. Linnemann, D. Lowe, R. Mertz‐Kraus, Alejandra Gonzalez-Pinzón, T. Thomsen, A. Zeh, Y. Rojas‐Agramonte, A. Kröner","doi":"10.2475/02.2022.01","DOIUrl":"https://doi.org/10.2475/02.2022.01","url":null,"abstract":"Sandstones of the 3.22 Ga Archean Moodies Group represent one of the world's oldest quartz-rich sedimentary sequences. The provenance of this unit is unresolved because its quartz and common microcline can be sourced both from either now eroded or covered granitoid plutons outside the Barberton Greenstone Belt (BGB) or, alternatively and perhaps more controversially, (rhyo-)dacitic (sub-)volcanic rocks within the BGB. We compiled 31 detrital zircon data sets (n = 2588) from sandstones, reworked tuffs and conglomerate of the Moodies Group in order to constrain its age and provenance. After selection using quality criteria, the remaining zircons (n = 1621) in nearly all samples show a distribution corresponding to the four known major pulses of felsic magmatism in the BGB: 1) the ca. 3550 to 3530 Ma Theespruit and Sandspruit Formations at the base of the Onverwacht Group; 2) the ca. 3440 to 3410 Ma rhyo-dacites of the upper Hooggenoeg Formation, Onverwacht Group; 3) the ca. 3300 to 3280 Ma thin felsic tuffs in the Mendon Formation; and 4) the ca. 3260 to 3215 Ma felsic volcanic and shallow intrusive rocks of the Auber Villiers, Bien Venue and Schoongezicht Formations of the upper Fig Tree Group and the Moodies Group as well as their co-magmatic plutonic counterparts. Almost all data sets also contain near-concordant younger zircons as young as 2820 Ma, which can be attributed to one of six tectonic or magmatic events affecting the young Kaapvaal Craton in post-BGB time, causing the partial or complete resetting of the U-Pb system in some grains. The youngest (near-)concordant zircon clusters yield ages of ca. 3220 Ma in most locations, and the youngest discordant group of zircons from a reworked tuff near the top of the Moodies Group at 3212 ± 13 Ma agrees well with previous estimates of the maximum depositional age. With very few exceptions, the oldest zircons (ca. 3564 Ma) are only slightly older than the oldest rocks in the BGB stratigraphy (ca. 3550 Ma). Subtle regional and stratigraphic differences in age spectra may indicate localized or nearby sediment sources within a synorogenic setting. Preliminary age spectra along vertical stratigraphic profiles show little systematic variation, possibly indicating that intrabasinal recycling was dominant over considerable time periods of the basin's evolution. Extra-basinal plutonic sources of similar age and composition as the intra-BGB sources appear to be required to provide quartz and some feldspar to Moodies Group sandstones, although zircon age spectra, limited zircon Hf isotope data, sandstone petrography, facies analysis, and the high variability in Moodies conglomerate clast composition are consistent with uplift, deformation and erosion of several intra-BGB sources, but in particular from the region of the Onverwacht Anticline. Zircon populations, conglomerate clasts, and sandstone composition show no evidence that high-grade metamorphic rocks from the adjacent Ancient Gneiss Complex (AGC) co","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44237442","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}
Bingqing Xu, Guochun Zhao, Jinlong Yao, Peng Wang, Yanhong He, Yigui Han, H. Zhou, Bo Wang
The closure time of the Hegenshan Ocean and its suturing scenario is debated, which hinders our understanding of the architecture and tectonic evolution of the southeastern Central Asian Orogenic Belt. We present an integrated study of in-situ zircon U-Pb isotopic ages and Hf isotope compositions, whole-rock geochemistry and Sr-Nd isotopes on the less-studied Erenhot granitic pluton in central Inner Mongolia. The ca. 303 to 300 Ma Erenhot pluton is composed of monzogranites, which are high-K calc-alkaline rocks and show I-type affinities. Moreover, positive correlation between Ba and Sr, along with the notably positive Rb and Pb anomalies, negative δEu and depletion in Ba, Eu, Nb and Ti, imply crystal fractionation played an important role in the magma evolution. The pluton also shows relative enrichment in light rare earth elements and large ion lithophile elements and depletion in high field strength elements, typical features of subduction-related magma. Isotopically, predominantly positive whole-rock εNd(t) (0.9–3.8) and zircon εHf(t) (4.50–13.66) values indicate a dominant juvenile crustal source with minor older crustal contamination. Given the mostly Proterozoic model ages (1318–543 Ma) and the presence of xenocrystic zircons, we infer that the Erenhot pluton probably was formed in a continental arc setting. Combined with the available published data, it is proposed that an east-west trending continental arc developed and was accreted onto the Uliastai Continental Margin in the Carboniferous, resulting from the northward subduction of the Hegenshan Ocean. The late Carboniferous continental arc-related magmatism (ca. 303–300 Ma) at Erenhot probably witnessed the waning stage of Hegenshan oceanic lithosphere subduction beneath the Uliastai Continental Margin.
{"title":"Late carboniferous continental arc magmatism in the southeastern Central Asian Orogenic Belt: insights from the Erenhot granitic pluton, Inner Mongolia","authors":"Bingqing Xu, Guochun Zhao, Jinlong Yao, Peng Wang, Yanhong He, Yigui Han, H. Zhou, Bo Wang","doi":"10.2475/02.2022.08","DOIUrl":"https://doi.org/10.2475/02.2022.08","url":null,"abstract":"The closure time of the Hegenshan Ocean and its suturing scenario is debated, which hinders our understanding of the architecture and tectonic evolution of the southeastern Central Asian Orogenic Belt. We present an integrated study of in-situ zircon U-Pb isotopic ages and Hf isotope compositions, whole-rock geochemistry and Sr-Nd isotopes on the less-studied Erenhot granitic pluton in central Inner Mongolia. The ca. 303 to 300 Ma Erenhot pluton is composed of monzogranites, which are high-K calc-alkaline rocks and show I-type affinities. Moreover, positive correlation between Ba and Sr, along with the notably positive Rb and Pb anomalies, negative δEu and depletion in Ba, Eu, Nb and Ti, imply crystal fractionation played an important role in the magma evolution. The pluton also shows relative enrichment in light rare earth elements and large ion lithophile elements and depletion in high field strength elements, typical features of subduction-related magma. Isotopically, predominantly positive whole-rock εNd(t) (0.9–3.8) and zircon εHf(t) (4.50–13.66) values indicate a dominant juvenile crustal source with minor older crustal contamination. Given the mostly Proterozoic model ages (1318–543 Ma) and the presence of xenocrystic zircons, we infer that the Erenhot pluton probably was formed in a continental arc setting. Combined with the available published data, it is proposed that an east-west trending continental arc developed and was accreted onto the Uliastai Continental Margin in the Carboniferous, resulting from the northward subduction of the Hegenshan Ocean. The late Carboniferous continental arc-related magmatism (ca. 303–300 Ma) at Erenhot probably witnessed the waning stage of Hegenshan oceanic lithosphere subduction beneath the Uliastai Continental Margin.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48444665","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}
X. Cui, M. Sun, Guochun Zhao, Jinlong Yao, Yunying Zhang, Yigui Han
High-grade gneisses are widespread in the Chinese segment of the Altai orogen, but their nature is not yet well-constrained with interpretations varying from Precambrian basement to Paleozoic meta-sediments. Such a controversy has hindered our understanding of the early Paleozoic geologic history of the Altai orogen. This study presents whole-rock geochemistry, zircon U-Pb and Hf isotopic data for paragneisses from the Qiongkuer Domain of the southern Chinese Altai, aiming to reveal their sedimentary and metamorphic history and shed light on the geodynamics of the Altai orogen. The paragneisses contain detrital zircons with mostly euhedral shapes, which, together with their weak HREE fractionation and Zr-Hf depletion relative to continental crust, may imply short-distance transport and low maturity of the sediments. In addition, these rocks have felsic compositions, high Rb contents and negative Eu anomalies, as well as low La/Sc and high Co/Th ratios, possibly indicating an acidic-intermediate igneous provenance. Our results show that the detrital zircons from the paragneisses are dominantly ca. 535 to 435 Ma old, some have Neoproterozoic ages, and only a few have Mesoproterozoic or Archean ages. Since the youngest detrital zircon population record an early Silurian weighted mean age of 441 Ma, and an early Devonian (411 Ma) granite intruded these paragneisses, we infer that their protoliths were deposited in the Silurian. The cumulative distribution curves of zircon age spectra of the paragneisses are comparable to those of sediments at convergent continental margins. The large spread of εHf(t) values (−9.5 to +12.9) of the predominant Paleozoic zircons also reflects possible active margin settings which contain both juvenile and reworked materials in the source. Therefore, the protoliths of the studied paragneisses were immature sediments mostly deposited at an active continental margin during the early Paleozoic and sourced mainly from proximal igneous rocks. Similar detrital zircon age spectra of early Paleozoic sequences from the Chinese Altai, Mongolia Altai, and Khovd Zone support the existence of a large accretionary wedge developed along the western margin of the Ikh-Mongol Arc system, resulting from continuous northeast-dipping oceanic subduction.
{"title":"An early Paleozoic active continental margin basin along the southern Chinese Altai: Evidence from high-grade paragneisses in the Fuyun region","authors":"X. Cui, M. Sun, Guochun Zhao, Jinlong Yao, Yunying Zhang, Yigui Han","doi":"10.2475/02.2022.04","DOIUrl":"https://doi.org/10.2475/02.2022.04","url":null,"abstract":"High-grade gneisses are widespread in the Chinese segment of the Altai orogen, but their nature is not yet well-constrained with interpretations varying from Precambrian basement to Paleozoic meta-sediments. Such a controversy has hindered our understanding of the early Paleozoic geologic history of the Altai orogen. This study presents whole-rock geochemistry, zircon U-Pb and Hf isotopic data for paragneisses from the Qiongkuer Domain of the southern Chinese Altai, aiming to reveal their sedimentary and metamorphic history and shed light on the geodynamics of the Altai orogen. The paragneisses contain detrital zircons with mostly euhedral shapes, which, together with their weak HREE fractionation and Zr-Hf depletion relative to continental crust, may imply short-distance transport and low maturity of the sediments. In addition, these rocks have felsic compositions, high Rb contents and negative Eu anomalies, as well as low La/Sc and high Co/Th ratios, possibly indicating an acidic-intermediate igneous provenance. Our results show that the detrital zircons from the paragneisses are dominantly ca. 535 to 435 Ma old, some have Neoproterozoic ages, and only a few have Mesoproterozoic or Archean ages. Since the youngest detrital zircon population record an early Silurian weighted mean age of 441 Ma, and an early Devonian (411 Ma) granite intruded these paragneisses, we infer that their protoliths were deposited in the Silurian. The cumulative distribution curves of zircon age spectra of the paragneisses are comparable to those of sediments at convergent continental margins. The large spread of εHf(t) values (−9.5 to +12.9) of the predominant Paleozoic zircons also reflects possible active margin settings which contain both juvenile and reworked materials in the source. Therefore, the protoliths of the studied paragneisses were immature sediments mostly deposited at an active continental margin during the early Paleozoic and sourced mainly from proximal igneous rocks. Similar detrital zircon age spectra of early Paleozoic sequences from the Chinese Altai, Mongolia Altai, and Khovd Zone support the existence of a large accretionary wedge developed along the western margin of the Ikh-Mongol Arc system, resulting from continuous northeast-dipping oceanic subduction.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47204862","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}
C. Ishwar-Kumar, K. Sajeev, M. Satish‐Kumar, I. Williams, S. Wilde, T. Hokada, B. Windley
In this study we present field relations, petrology, whole-rock major, trace and rare earth element geochemistry, zircon U-Pb ages, whole-rock Sr and Nd isotopes, and in situ zircon Hf and O isotopes from the Karwar block, western peninsular India. The rocks consist predominantly of tonalite-trondhjemite-granodiorite (TTG), granite and amphibolite. The felsic rocks are grouped into three: 1. TTG-I characterised by low K2O, high Na2O and Al2O3, low Sr/Y and La/Yb ratios, slightly enriched HREEs, negative Sr, Eu and Ti anomalies, a 3.2 Ga crystallisation age, and 3.60 Ga and 3.47 Ga inherited zircons; 2. TTG-II with lower SiO2, higher Sr/Y and La/Yb ratios, stronger REE fractionation with no HREE enrichment, negative Nb and Ta anomalies, a 3.2 Ga crystallisation age, but no inheritance; 3. Granites with high SiO2 and K2O, low Na2O and Al2O3, very low Sr/Y and La/Yb ratios, weak REE fractionation with enriched REEs, negative Sr, Eu and Ti anomalies and a 2.94 Ga crystallisation age. The TTG-I formed from a mantle source, but with a significant component of older crustal material, whereas the TTG-II originated mostly from a mantle-derived juvenile magma. The granite evolved from an enriched source containing a relatively large amount of older crustal material. The precursors of TTG-I and -II are similar to mid-ocean ridge basalts (MORB), whereas the granites are similar to volcanic arc/within-plate sources and the amphibolites are remnants of gabbros/basalts. An initial 3.6 Ga crust likely formed by the underplating of an accreted oceanic plateau-like or island arc-like crust. TTG-I was produced by subduction and slab melting at a moderate depth, induced melting of mafic lower crust and older upper crust at 3.2 Ga. TTG-II formed at 3.2 Ga by subduction and with a higher degree of slab melting at a greater depth than TTG-1, together with more effective mixing with mantle peridotite, followed by intrusion and induced melting of mafic lower crust. Basaltic magmatism at 3.0 Ga and subsequent metamorphism to amphibolite resulted in extensive and thicker crust. Assimilation and melting of TTG crust at a shallow depth during the emplacement of a mantle-derived magma produced the 2.94 Ga granites. The presence of inherited zircons, combined with whole-rock major and trace elements, Nd isotopes and in situ zircon Hf and O isotopes, indicates that older crustal material was incorporated into the source magma of TTG-I and that the Karwar block originally contained 3.60 to 3.47 Ga crust that was subsequently reworked during the Paleo- and Mesoarchean.
{"title":"Paleo- to Mesoarchean crustal growth in the Karwar block, southern India: Constraints on TTG genesis and Archean tectonics","authors":"C. Ishwar-Kumar, K. Sajeev, M. Satish‐Kumar, I. Williams, S. Wilde, T. Hokada, B. Windley","doi":"10.2475/02.2022.02","DOIUrl":"https://doi.org/10.2475/02.2022.02","url":null,"abstract":"In this study we present field relations, petrology, whole-rock major, trace and rare earth element geochemistry, zircon U-Pb ages, whole-rock Sr and Nd isotopes, and in situ zircon Hf and O isotopes from the Karwar block, western peninsular India. The rocks consist predominantly of tonalite-trondhjemite-granodiorite (TTG), granite and amphibolite. The felsic rocks are grouped into three: 1. TTG-I characterised by low K2O, high Na2O and Al2O3, low Sr/Y and La/Yb ratios, slightly enriched HREEs, negative Sr, Eu and Ti anomalies, a 3.2 Ga crystallisation age, and 3.60 Ga and 3.47 Ga inherited zircons; 2. TTG-II with lower SiO2, higher Sr/Y and La/Yb ratios, stronger REE fractionation with no HREE enrichment, negative Nb and Ta anomalies, a 3.2 Ga crystallisation age, but no inheritance; 3. Granites with high SiO2 and K2O, low Na2O and Al2O3, very low Sr/Y and La/Yb ratios, weak REE fractionation with enriched REEs, negative Sr, Eu and Ti anomalies and a 2.94 Ga crystallisation age. The TTG-I formed from a mantle source, but with a significant component of older crustal material, whereas the TTG-II originated mostly from a mantle-derived juvenile magma. The granite evolved from an enriched source containing a relatively large amount of older crustal material. The precursors of TTG-I and -II are similar to mid-ocean ridge basalts (MORB), whereas the granites are similar to volcanic arc/within-plate sources and the amphibolites are remnants of gabbros/basalts. An initial 3.6 Ga crust likely formed by the underplating of an accreted oceanic plateau-like or island arc-like crust. TTG-I was produced by subduction and slab melting at a moderate depth, induced melting of mafic lower crust and older upper crust at 3.2 Ga. TTG-II formed at 3.2 Ga by subduction and with a higher degree of slab melting at a greater depth than TTG-1, together with more effective mixing with mantle peridotite, followed by intrusion and induced melting of mafic lower crust. Basaltic magmatism at 3.0 Ga and subsequent metamorphism to amphibolite resulted in extensive and thicker crust. Assimilation and melting of TTG crust at a shallow depth during the emplacement of a mantle-derived magma produced the 2.94 Ga granites. The presence of inherited zircons, combined with whole-rock major and trace elements, Nd isotopes and in situ zircon Hf and O isotopes, indicates that older crustal material was incorporated into the source magma of TTG-I and that the Karwar block originally contained 3.60 to 3.47 Ga crust that was subsequently reworked during the Paleo- and Mesoarchean.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41368151","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}
Liangbo Li, W. Xiao, B. Windley, He Yang, Xiaoliang Jia, Miao Sang, Nijiati Abuduxun, Yin Liu
Field, geochronological, geochemical and Sr-Nd isotopic analyses are applied to late Paleozoic gabbro-diorites and monzogranites in the Hulugou-Miaoergou regions, Harlik arc, in order to provide constraints on the tectonic evolution of the Eastern Tianshan orogen in the late Paleozoic. LA-ICP-MS zircon U-Pb ages show that the first pulse of gabbroic magmatism occurred at 348 ± 4 Ma, accompanied by simultaneous dioritic (342 ± 3 Ma) and monzogranitic (343 ± 5 Ma) magmatism, and the second pulse of gabbroic magmatism was at 334 ± 3 Ma. Most of the gabbros are medium- to high- K calc-alkaline in composition, and show enrichments in light rare earth elements (LREE) and large ion lithophile elements (LILE), but depletions in high field strength elements (HFSE, especially Nb and Ta). In combination with their juvenile isotopic signature (initial 87Sr/86Sr = 0.70345–0.70380, εNd(t) = 4.5–6), the geochemical features suggest that both pulses of gabbroic magmatism were likely derived from partial melting of asthenosphere facilitated by a flux from a subducting slab. The diorites also display the arc-related geochemical characteristics and juvenile isotopic signature (initial 87Sr/86Sr = 0.70355–0.70358, εNd(t) = 4.3–4.7), coupled with their intimate relationship with the gabbros indicate that they formed by fractional crystallization of clinopyroxene, plagioclase and amphibole from the first pulse of gabbroic magmatism. The monzogranites have relatively high A/CNK values (1.04–1.1) and are weakly to moderately peraluminous. Considering the presence of zircon xenocrysts dated at 510 to 450 Ma in the monzogranites, and their moderate molar Al2O3/(MgO+FeOT) and molar CaO/(MgO+FeOT) ratios, partial melting of supracrustal rocks of probable late Ordovician age was most likely the cause of their genesis and heterogeneity. These three different magmas (gabbroic, dioritic and monzogranitic) were probably extracted from a deep crustal hot zone. The primitive basaltic magmas continuously intruded the deep crust where they solidified, fractionated, assimilated, and heated the crust, generating in turn the peraluminous and A-type granitoids, similar to the magmas in the Lachlan orogen that intruded during progressive slab rollback. Based on all available evidence, we propose that southward slab rollback of the subducting Paleo-Asian Ocean in the early Carboniferous was responsible for the progressive emplacement of these different magmas, which eventually resulted in rifting of the Harlik arc.
{"title":"Early carboniferous rifting of the Harlik arc in the Eastern Tianshan (NW China): Response to rollback in the southern Altaids?","authors":"Liangbo Li, W. Xiao, B. Windley, He Yang, Xiaoliang Jia, Miao Sang, Nijiati Abuduxun, Yin Liu","doi":"10.2475/02.2022.07","DOIUrl":"https://doi.org/10.2475/02.2022.07","url":null,"abstract":"Field, geochronological, geochemical and Sr-Nd isotopic analyses are applied to late Paleozoic gabbro-diorites and monzogranites in the Hulugou-Miaoergou regions, Harlik arc, in order to provide constraints on the tectonic evolution of the Eastern Tianshan orogen in the late Paleozoic. LA-ICP-MS zircon U-Pb ages show that the first pulse of gabbroic magmatism occurred at 348 ± 4 Ma, accompanied by simultaneous dioritic (342 ± 3 Ma) and monzogranitic (343 ± 5 Ma) magmatism, and the second pulse of gabbroic magmatism was at 334 ± 3 Ma. Most of the gabbros are medium- to high- K calc-alkaline in composition, and show enrichments in light rare earth elements (LREE) and large ion lithophile elements (LILE), but depletions in high field strength elements (HFSE, especially Nb and Ta). In combination with their juvenile isotopic signature (initial 87Sr/86Sr = 0.70345–0.70380, εNd(t) = 4.5–6), the geochemical features suggest that both pulses of gabbroic magmatism were likely derived from partial melting of asthenosphere facilitated by a flux from a subducting slab. The diorites also display the arc-related geochemical characteristics and juvenile isotopic signature (initial 87Sr/86Sr = 0.70355–0.70358, εNd(t) = 4.3–4.7), coupled with their intimate relationship with the gabbros indicate that they formed by fractional crystallization of clinopyroxene, plagioclase and amphibole from the first pulse of gabbroic magmatism. The monzogranites have relatively high A/CNK values (1.04–1.1) and are weakly to moderately peraluminous. Considering the presence of zircon xenocrysts dated at 510 to 450 Ma in the monzogranites, and their moderate molar Al2O3/(MgO+FeOT) and molar CaO/(MgO+FeOT) ratios, partial melting of supracrustal rocks of probable late Ordovician age was most likely the cause of their genesis and heterogeneity. These three different magmas (gabbroic, dioritic and monzogranitic) were probably extracted from a deep crustal hot zone. The primitive basaltic magmas continuously intruded the deep crust where they solidified, fractionated, assimilated, and heated the crust, generating in turn the peraluminous and A-type granitoids, similar to the magmas in the Lachlan orogen that intruded during progressive slab rollback. Based on all available evidence, we propose that southward slab rollback of the subducting Paleo-Asian Ocean in the early Carboniferous was responsible for the progressive emplacement of these different magmas, which eventually resulted in rifting of the Harlik arc.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44976771","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}
W. Fu, H. Hou, R. Gao, Haiyan Wang, Lei Guo, Jianbo Zhou, Jin Yang, R. Guo, Zongdong Pan
The final closure of the Paleo-Asian Ocean (PAO) and its tectonic characteristics have been debated for several decades owing to a lack of high-resolution information on the lithosphere structure. Scholars have been attempting to explain deep tectonic evolutionary processes while studying continental growth at the southern margin of the Mongolian Terrane. In a bid to provide a new interpretation of the deep structure with a higher resolution, we study two reprocessed deep seismic reflection profiles. We studied the northern part (210 km long) of the 630-km-long deep seismic reflection profile extending across the North China Craton (NCC) margin to the northern Sino-Mongolia border in the west; and a parallel profile (80 km long) in the east near the Sino-Mongolia border. Both profiles are characterized by consistently north-dipping layered reflections projecting from the lower crust to the upper mantle, with an estimated thickness of 3.6 to 6 km between adjacent reflections beneath the Uliastai and Hegenshan belts. Arched reflections are observed in the middle and lower crust; these may have been caused by later magmatic activities. In addition, the Moho reflection is observed to be fairly continuous and flat in most parts of these two profiles. The layered lower crust reflections and mantle reflections serve as important evidence that northward subduction occurred during the closure of the Paleo-Asian Ocean at the southeastern margin of the Mongolian Terrane. We propose a detailed model of the evolutionary processes from the early Paleozoic to early Mesozoic. The proposed model explains how these deep reflections were formed.
{"title":"North-dipping relict subduction of the Paleo-Asian Ocean at the southeastern margin of the Mongolian Terrane: Study of two parallel deep seismic profiles","authors":"W. Fu, H. Hou, R. Gao, Haiyan Wang, Lei Guo, Jianbo Zhou, Jin Yang, R. Guo, Zongdong Pan","doi":"10.2475/02.2022.09","DOIUrl":"https://doi.org/10.2475/02.2022.09","url":null,"abstract":"The final closure of the Paleo-Asian Ocean (PAO) and its tectonic characteristics have been debated for several decades owing to a lack of high-resolution information on the lithosphere structure. Scholars have been attempting to explain deep tectonic evolutionary processes while studying continental growth at the southern margin of the Mongolian Terrane. In a bid to provide a new interpretation of the deep structure with a higher resolution, we study two reprocessed deep seismic reflection profiles. We studied the northern part (210 km long) of the 630-km-long deep seismic reflection profile extending across the North China Craton (NCC) margin to the northern Sino-Mongolia border in the west; and a parallel profile (80 km long) in the east near the Sino-Mongolia border. Both profiles are characterized by consistently north-dipping layered reflections projecting from the lower crust to the upper mantle, with an estimated thickness of 3.6 to 6 km between adjacent reflections beneath the Uliastai and Hegenshan belts. Arched reflections are observed in the middle and lower crust; these may have been caused by later magmatic activities. In addition, the Moho reflection is observed to be fairly continuous and flat in most parts of these two profiles. The layered lower crust reflections and mantle reflections serve as important evidence that northward subduction occurred during the closure of the Paleo-Asian Ocean at the southeastern margin of the Mongolian Terrane. We propose a detailed model of the evolutionary processes from the early Paleozoic to early Mesozoic. The proposed model explains how these deep reflections were formed.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43550411","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}
Zaili Tao, Jiyuan Yin, W. Xiao, R. Seltmann, Wen Chen, M. Sun, Tao Wang, C. Yuan, S. Thomson, Yuelong Chen, X. Xia
Peraluminous granitoids have aluminum saturation indices (A/CNK) higher than 1.0, which overlap to some extent between S- and I-type granitoids. However, their source and petrogenesis are still disputed. For example, whole-rock compositions alone are not always a valid way to discriminate the sources of peraluminous granitoids. To identify the geochemical affinities, source and petrogenesis of the peraluminous granitoids, we present new geochemical data, in situ zircon U-Pb ages and Hf-O isotopic data, and whole-rock Sr-Nd isotopic data for the peraluminous granitoids in the South Tianshan Orogen Belt (STOB), Northwesten China. Zircon U-Pb ages suggest that these peraluminous granitoids were emplaced in the latest Carboniferous (ca. 299 Ma). They contain the diagnostic mineral muscovite and have high δ18OZrn values (>8.0 ‰) demonstrating a close affinity with S-type granitoids. Their low εNd(t) values (−5.3 to −7.6), combined with variable zircon εHf(t) values (−0.35 to −10.18), indicate that these S-type granitoids were likely derived from partial melting of metasedimentary rocks. In addition, inherited zircon cores from the S-type granitoids have variable δ18O values (6.34–10.5 ‰) and zircon εHf(t) values (−4.3 to +6.3), with age populations (ca. 400 to 500 Ma) similar to those of detrital zircons from late Carboniferous metasedimentary rocks in the region. These data show that the S-type granitoids were dominantly derived from late Carboniferous metasedimentary rocks rather than Precambrian crustal materials. The studied granitoids have a transitional composition between I- and S-type granitoids, which could be related to low compositional maturity of the late Carboniferous metasedimentary source. According to the spatial and temporal distribution and petrogenesis of the Carboniferous intrusive rocks in the STOB, we propose that a slab roll-back model can account for the generation of late Carboniferous S-type granitoids in the STOB.
{"title":"Contrasting styles of peraluminous S-type and I-type granitic magmatism: Identification and implications for the accretionary history of the Chinese South Tianshan","authors":"Zaili Tao, Jiyuan Yin, W. Xiao, R. Seltmann, Wen Chen, M. Sun, Tao Wang, C. Yuan, S. Thomson, Yuelong Chen, X. Xia","doi":"10.2475/02.2022.06","DOIUrl":"https://doi.org/10.2475/02.2022.06","url":null,"abstract":"Peraluminous granitoids have aluminum saturation indices (A/CNK) higher than 1.0, which overlap to some extent between S- and I-type granitoids. However, their source and petrogenesis are still disputed. For example, whole-rock compositions alone are not always a valid way to discriminate the sources of peraluminous granitoids. To identify the geochemical affinities, source and petrogenesis of the peraluminous granitoids, we present new geochemical data, in situ zircon U-Pb ages and Hf-O isotopic data, and whole-rock Sr-Nd isotopic data for the peraluminous granitoids in the South Tianshan Orogen Belt (STOB), Northwesten China. Zircon U-Pb ages suggest that these peraluminous granitoids were emplaced in the latest Carboniferous (ca. 299 Ma). They contain the diagnostic mineral muscovite and have high δ18OZrn values (>8.0 ‰) demonstrating a close affinity with S-type granitoids. Their low εNd(t) values (−5.3 to −7.6), combined with variable zircon εHf(t) values (−0.35 to −10.18), indicate that these S-type granitoids were likely derived from partial melting of metasedimentary rocks. In addition, inherited zircon cores from the S-type granitoids have variable δ18O values (6.34–10.5 ‰) and zircon εHf(t) values (−4.3 to +6.3), with age populations (ca. 400 to 500 Ma) similar to those of detrital zircons from late Carboniferous metasedimentary rocks in the region. These data show that the S-type granitoids were dominantly derived from late Carboniferous metasedimentary rocks rather than Precambrian crustal materials. The studied granitoids have a transitional composition between I- and S-type granitoids, which could be related to low compositional maturity of the late Carboniferous metasedimentary source. According to the spatial and temporal distribution and petrogenesis of the Carboniferous intrusive rocks in the STOB, we propose that a slab roll-back model can account for the generation of late Carboniferous S-type granitoids in the STOB.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45710910","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}
S. Wilde, Shoujie Liu, Y. Rojas‐Agramonte, Guochun Zhao
It is now over eleven years' ago, in November 2010, that the American Journal of Science published the first of two volumes marking the 70 birthday of Alfred Kroner. We, his friends and colleagues, planned to mark Alfred's 80 birthday with another special issue of the American Journal of Science, designed to showcase the scientific advances that had been made over the past decade in those areas of geoscientific endeavor that were closest to Alfred's heart. Sadly, Alfred passed away on 22 May 2019, less than four months before his 80 birthday (8 September). This is the third and final volume compiled to celebrate his tremendous contribution to geoscientific research. In the Preface to American Journal of Science, volume 310, number 9 of November 2010, a comprehensive outline of Alfred's career up until that date was presented (kindly outlined and supplemented by Alfred) and the reader is referred to this for more details of his earlier career. In the Preface to the first of these special issues (volume 321, numbers 1,2 of January-February 2021), we focused on the last ten years, outlining Alfred's major contributions, where his work was principally focused, and the key activities he undertook. We include this information below: Alfred's long association with Prof Liu Dunyi and the Beijing SHRIMP Center continued throughout the last decade of his life and resulted in a fruitful cooperation that was especially beneficial to young Chinese geoscientists. Alfred would spend several months every year based at the SHRIMP Laboratory, although he made many journeys both within China to deliver invited lectures and short courses at numerous institutions and universities, as well as undertaking many fieldtrips both in China and neighboring countries. In particular, his work on the Central Asian Orogenic Belt (CAOB) was ongoing in Mongolia, Kyrgyzstan and Russia. As Chairman of the International Precambrian Research Center of China (IPRCC), Alfred also organized a series of lectures, workshops and fieldtrips every year; many designed principally for students. The first of these was in May 2010, when the field workshop “Early Crustal Evolution of the SE Kaapvaal Craton in South Africa and Swaziland” was organized and attended by a large contingent from China. In October that year, the 5 SHRIMP Workshop and a workshop on “Advances in high-resolution SIMS and LA-ICP-MS Geochronology and Application to Geological Processes” were held in Beijing and Alfred took an active part in their organization. These were followed by a field excursion to Inner Mongolia to investigate Paleoproterozoic ultra-high temperature rocks of the Khondalite Belt. Also organized during this period was a training course in zircon geochronology including SHRIMP analytical techniques, which was run for the benefit of higher degree students from universities and institutions all over China. This course was presented by Ian Williams, Robert Pidgeon, Lutz Nasdala, William Griffin, Fernando Corf
{"title":"THIS IS THE THIRD ISSUE DEDICATED TO THE MEMORY OF DISTINGUISHED SCIENTIST ALFRED KRONER WHO SADLY PASSED AWAY ON 22 MAY 2019","authors":"S. Wilde, Shoujie Liu, Y. Rojas‐Agramonte, Guochun Zhao","doi":"10.2475/02.2022.11","DOIUrl":"https://doi.org/10.2475/02.2022.11","url":null,"abstract":"It is now over eleven years' ago, in November 2010, that the American Journal of Science published the first of two volumes marking the 70 birthday of Alfred Kroner. We, his friends and colleagues, planned to mark Alfred's 80 birthday with another special issue of the American Journal of Science, designed to showcase the scientific advances that had been made over the past decade in those areas of geoscientific endeavor that were closest to Alfred's heart. Sadly, Alfred passed away on 22 May 2019, less than four months before his 80 birthday (8 September). This is the third and final volume compiled to celebrate his tremendous contribution to geoscientific research. In the Preface to American Journal of Science, volume 310, number 9 of November 2010, a comprehensive outline of Alfred's career up until that date was presented (kindly outlined and supplemented by Alfred) and the reader is referred to this for more details of his earlier career. In the Preface to the first of these special issues (volume 321, numbers 1,2 of January-February 2021), we focused on the last ten years, outlining Alfred's major contributions, where his work was principally focused, and the key activities he undertook. We include this information below: Alfred's long association with Prof Liu Dunyi and the Beijing SHRIMP Center continued throughout the last decade of his life and resulted in a fruitful cooperation that was especially beneficial to young Chinese geoscientists. Alfred would spend several months every year based at the SHRIMP Laboratory, although he made many journeys both within China to deliver invited lectures and short courses at numerous institutions and universities, as well as undertaking many fieldtrips both in China and neighboring countries. In particular, his work on the Central Asian Orogenic Belt (CAOB) was ongoing in Mongolia, Kyrgyzstan and Russia. As Chairman of the International Precambrian Research Center of China (IPRCC), Alfred also organized a series of lectures, workshops and fieldtrips every year; many designed principally for students. The first of these was in May 2010, when the field workshop “Early Crustal Evolution of the SE Kaapvaal Craton in South Africa and Swaziland” was organized and attended by a large contingent from China. In October that year, the 5 SHRIMP Workshop and a workshop on “Advances in high-resolution SIMS and LA-ICP-MS Geochronology and Application to Geological Processes” were held in Beijing and Alfred took an active part in their organization. These were followed by a field excursion to Inner Mongolia to investigate Paleoproterozoic ultra-high temperature rocks of the Khondalite Belt. Also organized during this period was a training course in zircon geochronology including SHRIMP analytical techniques, which was run for the benefit of higher degree students from universities and institutions all over China. This course was presented by Ian Williams, Robert Pidgeon, Lutz Nasdala, William Griffin, Fernando Corf","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48861780","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}
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