The Humber Margin of Newfoundland preserves the most distal exposures of Proterozoic basement in northeastern Laurentia. Age uncertainty has permitted a range of hypotheses for its origin and links to subsequent tectonic events. One hypothesis has proposed large-scale orogen-parallel displacement between basement blocks in western Newfoundland. The apparent absence of Grenville- (∼1250–950 Ma sensu lato) or Taconic-aged (∼480–450 Ma) magmatism or metamorphism on the Corner Brook Lake Block (CBLB), which are defining features of the Humber Margin, has been reconciled by restoring the CBLB to a pre-Taconic position in Labrador with >400 km of post-Taconic dextral motion along the Humber River Fault. To test this model and better define the basement and Paleozoic rifted margin of North America, we conducted a geochronological study of the CBLB and the basement of the adjacent Humber Margin at Indian Head Range using tandem in situ and isotope dilution U-Pb zircon and titanite geochronology. These basement blocks, separated by the Humber River Fault, consist of ∼1500 and ∼1250 Ma protoliths, 1140 to 1135 Ma magmatism, 1000 to 970 Ma metamorphism, and ∼607 Ma intraplate magmatism. These basement blocks are also overlain by similar late Ediacaran to Cambrian siliciclastic successions with similar detrital zircon age spectra. From this set of geological data, we conclude that the Humber River Fault did not accommodate significant orogen-parallel displacement. New basement ages and a revised compilation of detrital zircon ages from overlying rift-related deposits contribute to a geochronologic cratonic reference datum for western Newfoundland's crystalline basement, whose protolith has a restricted age range from circa 1500 to 950 Ma. New age constraints for metasedimentary rocks are also used to document a 1250 to 1135 Ma succession at Indian Head Range and a ∼1000 Ma succession on the CBLB associated with Grenvillian orogenesis. Protracted late Grenvillian tectono-thermal events are inferred from cores and metamorphic overgrowths of ∼990 to 920 Ma detrital titanite in late Ediacaran conglomerate overlying CBLB basement.
{"title":"A Laurentian cratonic reference from the distal Proterozoic basement of Western Newfoundland using tandem in situ and isotope dilution U-pb zircon and titanite geochronology","authors":"E. Hodgin, F. Macdonald, J. Crowley, M. Schmitz","doi":"10.2475/07.2021.02","DOIUrl":"https://doi.org/10.2475/07.2021.02","url":null,"abstract":"The Humber Margin of Newfoundland preserves the most distal exposures of Proterozoic basement in northeastern Laurentia. Age uncertainty has permitted a range of hypotheses for its origin and links to subsequent tectonic events. One hypothesis has proposed large-scale orogen-parallel displacement between basement blocks in western Newfoundland. The apparent absence of Grenville- (∼1250–950 Ma sensu lato) or Taconic-aged (∼480–450 Ma) magmatism or metamorphism on the Corner Brook Lake Block (CBLB), which are defining features of the Humber Margin, has been reconciled by restoring the CBLB to a pre-Taconic position in Labrador with >400 km of post-Taconic dextral motion along the Humber River Fault. To test this model and better define the basement and Paleozoic rifted margin of North America, we conducted a geochronological study of the CBLB and the basement of the adjacent Humber Margin at Indian Head Range using tandem in situ and isotope dilution U-Pb zircon and titanite geochronology. These basement blocks, separated by the Humber River Fault, consist of ∼1500 and ∼1250 Ma protoliths, 1140 to 1135 Ma magmatism, 1000 to 970 Ma metamorphism, and ∼607 Ma intraplate magmatism. These basement blocks are also overlain by similar late Ediacaran to Cambrian siliciclastic successions with similar detrital zircon age spectra. From this set of geological data, we conclude that the Humber River Fault did not accommodate significant orogen-parallel displacement. New basement ages and a revised compilation of detrital zircon ages from overlying rift-related deposits contribute to a geochronologic cratonic reference datum for western Newfoundland's crystalline basement, whose protolith has a restricted age range from circa 1500 to 950 Ma. New age constraints for metasedimentary rocks are also used to document a 1250 to 1135 Ma succession at Indian Head Range and a ∼1000 Ma succession on the CBLB associated with Grenvillian orogenesis. Protracted late Grenvillian tectono-thermal events are inferred from cores and metamorphic overgrowths of ∼990 to 920 Ma detrital titanite in late Ediacaran conglomerate overlying CBLB basement.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"321 1","pages":"1045 - 1079"},"PeriodicalIF":2.9,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46391078","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}
T. Bristow, A. Derkowski, D. Blake, G. Berlanga, P. Deckker
Clay mineral-bearing mudstones are a prominent component of ancient fluvial-lacustrine deposits, 100s of meters thick, documented by the Mars Science Laboratory (MSL) rover, in Gale crater, Mars. Most of the clay minerals documented by MSL are hypothesized to have formed in situ, at or close to the time of deposition ∼3.5 Ga ago, by aqueous alteration of basaltic detritus. Here we study the mechanisms, controls, and timescales of clay mineral authigenesis in a series of lakes with a wide range of water chemistries from the Western Volcanic District, Victoria, SE Australia, as an analog to the Gale crater mudstones. X-ray diffraction (XRD) analysis reveals that the sediments of most of the Western Volcanic District lakes studied contain mixtures of kaolinite, illite, mixed-layer illite-smectite (I-S), and dioctahedral smectite clay minerals. Comparisons of this mineral assemblage with regional soils and creek bedload material confirm previous assertions of significant inputs of detrital clay minerals into the lakes. A trioctahedral clay mineral phase is also detected, making up to 39 wt.% of bulk sediments. The abundance of trioctahedral clay minerals correlates with contemporary lake hydrology and proxies for past lake water Mg concentration. This indicates in situ formation of trioctahedral clay minerals by the uptake of Mg and Si from lake waters and pore fluids at rates determined by local physico-chemical conditions. Examination of crater lake sediments, where detrital clay mineral input is minimized, demonstrate that neoformed trioctahedral clay minerals are poorly crystalline trioctahedral smectites. Neoformation of trioctahedral smectites also occurs in lakes where detrital clay minerals are more abundant. However, an additional authigenic transformation process is indicated by the proportions of Mg and Si added to detrital clay minerals as well as evidence for the uptake of K from lake waters. The transformation process probably involved the incorporation of Mg into the octahedral sheets of detrital clay minerals, leading to irreversible uptake of K into interlayer sites (illitization). The distribution of trioctahedral smectites and radiocarbon ages from sediment cores show that clay mineral authigenesis occurred before sediment consolidation, on timescales of years to 100s of years. These results support syndepositional interpretations of analogous Mg-rich clay minerals documented by MSL, and their use as proxies for chemical conditions in ancient Gale lakes. In comparison with the Western Volcanic District lakes, clay mineral-bearing lacustrine mudstones from Gale crater exhibit only modest chemical weathering of basaltic detrital materials and rarely contain carbonate minerals in quantities detectable by XRD. These observations highlight significant differences in weathering regimes and regolith mineralogy on ancient Mars that could be linked to lake catchment geomorphology, climate, atmospheric CO2 content, and the absence of biotic
{"title":"A comparative study of clay mineral authigenesis in terrestrial and martian lakes; an Australian example","authors":"T. Bristow, A. Derkowski, D. Blake, G. Berlanga, P. Deckker","doi":"10.2475/07.2021.03","DOIUrl":"https://doi.org/10.2475/07.2021.03","url":null,"abstract":"Clay mineral-bearing mudstones are a prominent component of ancient fluvial-lacustrine deposits, 100s of meters thick, documented by the Mars Science Laboratory (MSL) rover, in Gale crater, Mars. Most of the clay minerals documented by MSL are hypothesized to have formed in situ, at or close to the time of deposition ∼3.5 Ga ago, by aqueous alteration of basaltic detritus. Here we study the mechanisms, controls, and timescales of clay mineral authigenesis in a series of lakes with a wide range of water chemistries from the Western Volcanic District, Victoria, SE Australia, as an analog to the Gale crater mudstones. X-ray diffraction (XRD) analysis reveals that the sediments of most of the Western Volcanic District lakes studied contain mixtures of kaolinite, illite, mixed-layer illite-smectite (I-S), and dioctahedral smectite clay minerals. Comparisons of this mineral assemblage with regional soils and creek bedload material confirm previous assertions of significant inputs of detrital clay minerals into the lakes. A trioctahedral clay mineral phase is also detected, making up to 39 wt.% of bulk sediments. The abundance of trioctahedral clay minerals correlates with contemporary lake hydrology and proxies for past lake water Mg concentration. This indicates in situ formation of trioctahedral clay minerals by the uptake of Mg and Si from lake waters and pore fluids at rates determined by local physico-chemical conditions. Examination of crater lake sediments, where detrital clay mineral input is minimized, demonstrate that neoformed trioctahedral clay minerals are poorly crystalline trioctahedral smectites. Neoformation of trioctahedral smectites also occurs in lakes where detrital clay minerals are more abundant. However, an additional authigenic transformation process is indicated by the proportions of Mg and Si added to detrital clay minerals as well as evidence for the uptake of K from lake waters. The transformation process probably involved the incorporation of Mg into the octahedral sheets of detrital clay minerals, leading to irreversible uptake of K into interlayer sites (illitization). The distribution of trioctahedral smectites and radiocarbon ages from sediment cores show that clay mineral authigenesis occurred before sediment consolidation, on timescales of years to 100s of years. These results support syndepositional interpretations of analogous Mg-rich clay minerals documented by MSL, and their use as proxies for chemical conditions in ancient Gale lakes. In comparison with the Western Volcanic District lakes, clay mineral-bearing lacustrine mudstones from Gale crater exhibit only modest chemical weathering of basaltic detrital materials and rarely contain carbonate minerals in quantities detectable by XRD. These observations highlight significant differences in weathering regimes and regolith mineralogy on ancient Mars that could be linked to lake catchment geomorphology, climate, atmospheric CO2 content, and the absence of biotic ","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"321 1","pages":"1080 - 1110"},"PeriodicalIF":2.9,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49461942","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}
Qian Liu, T. Tsunogae, Guochun Zhao, Jianhua Li, Jinlong Yao, Yigui Han, Peng Wang
Early Paleozoic ophiolitic mélanges in the Altyn Tagh Orogen, southeastern Tarim, yield a large range of formation ages and geochemical affinities. This study focused on the Hongliugou ophiolitic mélange in the North Altyn Tagh subduction-accretion belt and involved mineral chemical, zircon geochronological, and whole-rock elemental and isotopic investigations of the ultramafic and mafic rocks. In the studied lherzolite samples, Cr-spinel, olivine, and pyroxene show mineral chemistry akin to that of abyssal peridotite. Subhedral-anhedral Cr-spinel grains with high Cr# values (100*Cr/[Cr+Al] of 30–40) and negative oxygen fugacity (fO2) values represent original spinel formed during mid-ocean ridge basalt (MORB) melt extraction. Other subhedral-anhedral and euhedral Cr-spinel with low Cr# values of < 30 to 20 display a wide range of negative to positive fO2 values, indicating interaction of peridotite with MORB magma. New zircon U-Pb dating results record ages of ca. 490 Ma for gabbro and ca. 486 Ma for diabase in the Hongliugou ophiolitic mélange. Whole-rock geochemical compositions suggest that the gabbro and diabase samples are tholeiitic and show MORB affinities or transitional affinities between MORB and island arc tholeiite. These mafic rocks might have been derived from a depleted MORB-source mantle that was variably metasomatized by subduction-induced fluids based on their variable Th/Yb, high La/Nb, low Th/Nb, and depleted isotopes (initial 87Sr/86Sr ratios of 0.703073 to 0.703385 and εNd(t) values of +6.2 to +6.3). New results, when integrated with previous work, clarify that ca. 520 to 510 Ma ophiolites formed in the initial subduction setting and ca. 490 to 480 Ma ophiolites in a back-arc setting. Minor ca. 450 Ma ophiolite probably represents a late phase of ophiolite formation due to the presence of a very minor remnant ocean.
{"title":"Multiphase ophiolite formation in the Northern Altyn Tagh Orogen, southeastern Tarim","authors":"Qian Liu, T. Tsunogae, Guochun Zhao, Jianhua Li, Jinlong Yao, Yigui Han, Peng Wang","doi":"10.2475/06.2021.05","DOIUrl":"https://doi.org/10.2475/06.2021.05","url":null,"abstract":"Early Paleozoic ophiolitic mélanges in the Altyn Tagh Orogen, southeastern Tarim, yield a large range of formation ages and geochemical affinities. This study focused on the Hongliugou ophiolitic mélange in the North Altyn Tagh subduction-accretion belt and involved mineral chemical, zircon geochronological, and whole-rock elemental and isotopic investigations of the ultramafic and mafic rocks. In the studied lherzolite samples, Cr-spinel, olivine, and pyroxene show mineral chemistry akin to that of abyssal peridotite. Subhedral-anhedral Cr-spinel grains with high Cr# values (100*Cr/[Cr+Al] of 30–40) and negative oxygen fugacity (fO2) values represent original spinel formed during mid-ocean ridge basalt (MORB) melt extraction. Other subhedral-anhedral and euhedral Cr-spinel with low Cr# values of < 30 to 20 display a wide range of negative to positive fO2 values, indicating interaction of peridotite with MORB magma. New zircon U-Pb dating results record ages of ca. 490 Ma for gabbro and ca. 486 Ma for diabase in the Hongliugou ophiolitic mélange. Whole-rock geochemical compositions suggest that the gabbro and diabase samples are tholeiitic and show MORB affinities or transitional affinities between MORB and island arc tholeiite. These mafic rocks might have been derived from a depleted MORB-source mantle that was variably metasomatized by subduction-induced fluids based on their variable Th/Yb, high La/Nb, low Th/Nb, and depleted isotopes (initial 87Sr/86Sr ratios of 0.703073 to 0.703385 and εNd(t) values of +6.2 to +6.3). New results, when integrated with previous work, clarify that ca. 520 to 510 Ma ophiolites formed in the initial subduction setting and ca. 490 to 480 Ma ophiolites in a back-arc setting. Minor ca. 450 Ma ophiolite probably represents a late phase of ophiolite formation due to the presence of a very minor remnant ocean.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"321 1","pages":"788 - 821"},"PeriodicalIF":2.9,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42451255","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}
J. Cárdenas-Párraga, A. Garcia‐Casco, I. Blanco-Quintero, Y. Rojas‐Agramonte, K. N. Cambra, G. Harlow
A U-Pb zircon date of ∼113 Ma revealed that a variety of jadeitites and related omphacitite, chloritite and albite-rich rocks from the subduction-related Sierra del Convento block-in-serpentinite-matrix mélange (eastern Cuba) formed nearly synchronously with MORB metabasite-derived anatectic trondhjemitic liquids at high-temperature and pressure in a hot subduction environment. Field, petrologic and geochemical data indicate hydrothermal/metasomatic processes triggered by juvenile fluids likely evolved from the crystallizing hydrous trondhjemitic melts. These fluids, variably mixed with sediment-derived fluids and channelized along fractures in the supra-slab mantle, precipitated relatively pure jadeitite with geochemical patterns depleted in REE and HFSE and epidote-rich jadeitite with LILE- (notably Ba) enriched compositions with respect to N-MORB. The crystallization of jadeitite veins was accompanied by formation of chloritite blackwalls at the vein-ultramafic rock contact and omphacititic patches at the outer parts of the veins, denoting wall rock-fluid interactions. Further pervasive flow of external fluid within the rock bodies triggered modal and cryptic (geochemical) metasomatic transformation of earlier jadeitite, producing mica-rich jadeitite and albite-epidote (-chlorite) rocks. Altogether these rocks document a discrete episode of massive flow of fluid in the supra-slab mantle roughly coeval with hydrous melting of subducted MORB metabasite.
~ 113 Ma的U-Pb锆石表明，在俯冲相关的Sierra del Convento地块蛇纹岩基msamulange(古巴东部)，在高温高压的热俯冲环境下，与MORB变质岩衍生的闪辉质流体几乎同时形成了多种硬玉岩及其相关辉长岩、绿泥岩和富含钠长岩的岩石。野外、岩石学和地球化学资料表明，幼流体引发的热液/交代过程可能是由含水岩浆熔体结晶演化而来的。这些流体与沉积流体的混合程度不同，并沿着上板块地幔的裂缝形成通道，沉淀出相对纯净的翡翠岩和富含绿帘石的翡翠岩，这些翡翠岩的地球化学模式缺乏REE和HFSE，而相对于N-MORB，富含LILE-(特别是Ba)成分。翡翠脉的结晶过程伴随着脉与超镁铁质岩石接触处绿泥岩黑壁的形成和脉外侧红辉质斑块的形成，表明了围岩与流体的相互作用。岩体内部外部流体的进一步普遍流动触发了早期翡翠岩的模态和隐式(地球化学)交代转化，生成了富云母的翡翠岩和钠长绿帘石(-绿泥石)岩石。总的来说，这些岩石记录了上板块地幔中大量流体流动的离散事件，大致与俯冲的MORB变质岩的含水熔融同时发生。
{"title":"A Highly dynamic hot hydrothermal system in the subduction environment: Geochemistry and geochronology of jadeitite and associated rocks of the Sierra del Convento mélange (eastern Cuba)","authors":"J. Cárdenas-Párraga, A. Garcia‐Casco, I. Blanco-Quintero, Y. Rojas‐Agramonte, K. N. Cambra, G. Harlow","doi":"10.2475/06.2021.06","DOIUrl":"https://doi.org/10.2475/06.2021.06","url":null,"abstract":"A U-Pb zircon date of ∼113 Ma revealed that a variety of jadeitites and related omphacitite, chloritite and albite-rich rocks from the subduction-related Sierra del Convento block-in-serpentinite-matrix mélange (eastern Cuba) formed nearly synchronously with MORB metabasite-derived anatectic trondhjemitic liquids at high-temperature and pressure in a hot subduction environment. Field, petrologic and geochemical data indicate hydrothermal/metasomatic processes triggered by juvenile fluids likely evolved from the crystallizing hydrous trondhjemitic melts. These fluids, variably mixed with sediment-derived fluids and channelized along fractures in the supra-slab mantle, precipitated relatively pure jadeitite with geochemical patterns depleted in REE and HFSE and epidote-rich jadeitite with LILE- (notably Ba) enriched compositions with respect to N-MORB. The crystallization of jadeitite veins was accompanied by formation of chloritite blackwalls at the vein-ultramafic rock contact and omphacititic patches at the outer parts of the veins, denoting wall rock-fluid interactions. Further pervasive flow of external fluid within the rock bodies triggered modal and cryptic (geochemical) metasomatic transformation of earlier jadeitite, producing mica-rich jadeitite and albite-epidote (-chlorite) rocks. Altogether these rocks document a discrete episode of massive flow of fluid in the supra-slab mantle roughly coeval with hydrous melting of subducted MORB metabasite.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"321 1","pages":"822 - 887"},"PeriodicalIF":2.9,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43159474","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}
Tsung-Pin Chen, Chih-Lung Lin, Kuo-Chin Fan, Wanzun Lin
This is the second of three issues of American Journal of Science in which the papers have been submitted by friends and colleagues as a mark of respect to Alfred Kroner, who passed away just a few months before his 80 birthday in 2019. Alfred has left an indelible mark on the geoscience community, with his boundless energy and dedication, and especially his application of detailed fieldwork and microanalysis to solve the bigger issues. As the subtitle ‘From Cratons to Orogens’ indicates, Alfred was always cognizant of how his work related to global events, and this is reflected by the nine papers that constitute this volume. The first paper by Allen Nutman and co-workers presents an overview of the 3.8 Ga Outer Arc of the Isua Greenstone Belt in West Greenland. This forms an integral part of the oldest and best-preserved volcano-sedimentary sequence on Earth. Utilizing rare low-strain zones, accompanied by new and published geochronology, the authors endeavor to unravel the stratigraphy of the arc. The lowermost mafic unit contains pillow lavas, indicating a subaqueous depositional environment. The overlying formation commences with a unit of fuchsitic quartzite, overlain by various carbonate and silicate units; some with relict sedimentary structures. There is an upward transition to chemical sediments and then into units showing a greater influx of felsic volcanic components. The uppermost unit is felsic, with both lavas and pyroclastic rocks, interpreted as forming in an arc. The authors therefore support a plate tectonic scenario and not a stagnant lid environment for the early Eoarchean of Greenland. Xiao Wang and co-workers investigate Archean/Paleoproterozoic rocks in the Khondalite Belt, which marks the Paleoproterozoic collision zone between the Yinshan and Ordos blocks, and is located in the western block of the North China Craton. The authors describe TTG rocks of I-type affinity in the Daqingshan Complex, whose ages straddle the Archean/Proterozoic boundary and define oceanic subduction beneath the southern margin of the Yinshan Block. Docking of the Ordos Block led to closure of the ocean with the TTG rocks undergoing high-grade metamorphism between 1.95-1.85 Ga. In a companion paper, Xiao Wang and co-workers analyze and date high-grade metamorphic rocks of the Daqingshan Complex, interpreted as bimodal volcanics that formed in a back arc setting prior to the collision of the Yinshan and Ordos block, as detailed above. The volcanic rocks formed between 2.47-2.40 Ga and were metamorphosed at high grade between 1.95-1.85 Ga, similar to the TTG rocks in the complex. This latter event is one of the global collisions marking assembly of Colombia/Nuna. In another paper on the North China Craton where Alfred worked extensively, Yue-Lan Kang and co-workers investigate the late Mesozoic granitoids to the east and west of the Tan-Lu Fault, one of the most significant late Phanerozoic structures in China. In the Taihang Mountains to the west,
{"title":"Foreword","authors":"Tsung-Pin Chen, Chih-Lung Lin, Kuo-Chin Fan, Wanzun Lin","doi":"10.2475/06.2021.11","DOIUrl":"https://doi.org/10.2475/06.2021.11","url":null,"abstract":"This is the second of three issues of American Journal of Science in which the papers have been submitted by friends and colleagues as a mark of respect to Alfred Kroner, who passed away just a few months before his 80 birthday in 2019. Alfred has left an indelible mark on the geoscience community, with his boundless energy and dedication, and especially his application of detailed fieldwork and microanalysis to solve the bigger issues. As the subtitle ‘From Cratons to Orogens’ indicates, Alfred was always cognizant of how his work related to global events, and this is reflected by the nine papers that constitute this volume. The first paper by Allen Nutman and co-workers presents an overview of the 3.8 Ga Outer Arc of the Isua Greenstone Belt in West Greenland. This forms an integral part of the oldest and best-preserved volcano-sedimentary sequence on Earth. Utilizing rare low-strain zones, accompanied by new and published geochronology, the authors endeavor to unravel the stratigraphy of the arc. The lowermost mafic unit contains pillow lavas, indicating a subaqueous depositional environment. The overlying formation commences with a unit of fuchsitic quartzite, overlain by various carbonate and silicate units; some with relict sedimentary structures. There is an upward transition to chemical sediments and then into units showing a greater influx of felsic volcanic components. The uppermost unit is felsic, with both lavas and pyroclastic rocks, interpreted as forming in an arc. The authors therefore support a plate tectonic scenario and not a stagnant lid environment for the early Eoarchean of Greenland. Xiao Wang and co-workers investigate Archean/Paleoproterozoic rocks in the Khondalite Belt, which marks the Paleoproterozoic collision zone between the Yinshan and Ordos blocks, and is located in the western block of the North China Craton. The authors describe TTG rocks of I-type affinity in the Daqingshan Complex, whose ages straddle the Archean/Proterozoic boundary and define oceanic subduction beneath the southern margin of the Yinshan Block. Docking of the Ordos Block led to closure of the ocean with the TTG rocks undergoing high-grade metamorphism between 1.95-1.85 Ga. In a companion paper, Xiao Wang and co-workers analyze and date high-grade metamorphic rocks of the Daqingshan Complex, interpreted as bimodal volcanics that formed in a back arc setting prior to the collision of the Yinshan and Ordos block, as detailed above. The volcanic rocks formed between 2.47-2.40 Ga and were metamorphosed at high grade between 1.95-1.85 Ga, similar to the TTG rocks in the complex. This latter event is one of the global collisions marking assembly of Colombia/Nuna. In another paper on the North China Craton where Alfred worked extensively, Yue-Lan Kang and co-workers investigate the late Mesozoic granitoids to the east and west of the Tan-Lu Fault, one of the most significant late Phanerozoic structures in China. In the Taihang Mountains to the west, ","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"321 1","pages":"xii - xiii"},"PeriodicalIF":2.9,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41823830","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}
In the Late Mesozoic, the North China Craton (NCC) underwent significant lithospheric thinning and destruction, especially in the eastern part, but the mechanism and timing related to this process are still contentious. The Taihang Mountains (TH) are located in the western part of the eastern NCC and the Tan-Lu Fault (TLF) is in the eastern part, which are two essential magmatic areas that reveal deep processes of magma origin. We investigated the spatial-temporal distribution of igneous rocks from these two areas to constrain the tectonic setting and magmatic sources. SHRIMP zircon U-Pb ages of the granitoids within the Fangshan pluton in northern TH area range from 136 to 128 Ma. Their εHf(t) values and δ18O values show ranges of −27.7 to −18.5 and 6.68 to 7.26 permil, respectively. Hence, we conclude that the rocks were formed by mixing between underplating magma and the melts from the lower crust. The O-Hf isotopic compositions of six granitoid samples from the Yunmengshan complex in northern TH are also reported. In combination with previous studies, we propose that the geochemical characteristics of the magmatic rocks from the TH area had insignificant changes during late Mesozoic time, but the rocks from the TLF area varied greatly. The difference between those two areas may reflect the diverse impact of the Paleo-Pacific subduction process. The high Mg# adakitic rocks (HMA) from TLF area have higher Mg# values than the HMA rocks from TH area. Our conclusion is that the HMA rocks in the TLF area were mainly formed by delaminated lower crust interacting with mantle materials and that the Paleo-Pacific subduction had limited impact on TH magmas. Based on chronology and geochemical characteristics, we recognize three stages: 1) ∼166 to 140 Ma, multi-directional compression resulted in crustal shortening and thickening in the NCC, accompanied by regional partial melting of the crust and underplating of mafic magmas, 2) 140 to 125 Ma, the TLF underwent left-lateral strike-slip movement. Subsequent delamination of the lower crust around the fault and the NCC evolved into an extensional tectonic environment, 3) after 125 Ma, a large-scale extension of the NCC occurred likely due to stress relaxation after delamination. The TLF acted as a favorable channel for transporting mantle material and fluids, which implies that the large-scale fault zone was a key factor of the NCC lithosphere destruction.
{"title":"Chronological and geochemical variations of the late Mesozoic granitoids in the Taihang Mountains and middle-southern Tan-Lu Fault: Implications for lithosphere destruction of the North China Craton","authors":"Yuelan Kang, Yuruo Shi, J. Anderson","doi":"10.2475/06.2021.04","DOIUrl":"https://doi.org/10.2475/06.2021.04","url":null,"abstract":"In the Late Mesozoic, the North China Craton (NCC) underwent significant lithospheric thinning and destruction, especially in the eastern part, but the mechanism and timing related to this process are still contentious. The Taihang Mountains (TH) are located in the western part of the eastern NCC and the Tan-Lu Fault (TLF) is in the eastern part, which are two essential magmatic areas that reveal deep processes of magma origin. We investigated the spatial-temporal distribution of igneous rocks from these two areas to constrain the tectonic setting and magmatic sources. SHRIMP zircon U-Pb ages of the granitoids within the Fangshan pluton in northern TH area range from 136 to 128 Ma. Their εHf(t) values and δ18O values show ranges of −27.7 to −18.5 and 6.68 to 7.26 permil, respectively. Hence, we conclude that the rocks were formed by mixing between underplating magma and the melts from the lower crust. The O-Hf isotopic compositions of six granitoid samples from the Yunmengshan complex in northern TH are also reported. In combination with previous studies, we propose that the geochemical characteristics of the magmatic rocks from the TH area had insignificant changes during late Mesozoic time, but the rocks from the TLF area varied greatly. The difference between those two areas may reflect the diverse impact of the Paleo-Pacific subduction process. The high Mg# adakitic rocks (HMA) from TLF area have higher Mg# values than the HMA rocks from TH area. Our conclusion is that the HMA rocks in the TLF area were mainly formed by delaminated lower crust interacting with mantle materials and that the Paleo-Pacific subduction had limited impact on TH magmas. Based on chronology and geochemical characteristics, we recognize three stages: 1) ∼166 to 140 Ma, multi-directional compression resulted in crustal shortening and thickening in the NCC, accompanied by regional partial melting of the crust and underplating of mafic magmas, 2) 140 to 125 Ma, the TLF underwent left-lateral strike-slip movement. Subsequent delamination of the lower crust around the fault and the NCC evolved into an extensional tectonic environment, 3) after 125 Ma, a large-scale extension of the NCC occurred likely due to stress relaxation after delamination. The TLF acted as a favorable channel for transporting mantle material and fluids, which implies that the large-scale fault zone was a key factor of the NCC lithosphere destruction.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"321 1","pages":"739 - 787"},"PeriodicalIF":2.9,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43722269","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}
A. Nutman, C. Friend, V. Bennett, M. V. Kranendonk, A. Chivas
The arcuate, 35 km long Isua supracrustal belt (ISB, southern West Greenland) contains the world's largest remnants of Eoarchean volcanic and sedimentary sequences. The ISB is broadly divided into: (i) the northern Inner Arc Group of 3720 to 3690 Ma rocks, and (ii) the southern Outer Arc Group of ca. 3800 Ma rocks which is bounded on its northern side by the highly tectonized ca. 3750 Ma Dividing Sedimentary Unit. The boundary between the two groups is a mylonite formed between 3685 and 3660 Ma. Despite the generally high strain, amphibolite facies metamorphism and layer-parallel dislocations that can thin or altogether excise some units, domains of lower deformation comprising ≪1% (qualitative assessment) of the Outer Arc Group contain relict sedimentary and igneous structures. Combined with zircon U-Pb geochronology and whole rock geochemistry, this enables the Outer Arc Group lithological sequence and geodynamic setting to be reconstructed. The lower part of the Outer Arc Group is dominated by metabasaltic amphibolites of the Mafic Volcanic formation in which rarely-preserved pillow structures indicate both their predominantly subaqueous eruption and also their stratigraphic facing. They erupted >3800 Ma, because they were first intruded by subconcordant sheets of fine-grained hypabyssal tonalite dated at 3803±3 Ma (Crowley, 2003) and then by coarser-grained 3795 to 3791 Ma tonalite-granodiorite, which forms a large deformed pluton along the south side of the ISB. This formation is succeeded by the Sedimentary formation whose base consists of discontinuous rare, thin fuchsitic quartzites with 3890 to 3805 Ma detrital zircons. Overlying is a diverse package of dolostones, marls and siliceous rocks. Although they are extensively modified by metamorphism and metasomatism, producing widespread growth of talc or tremolite, relict graded sedimentary layering, chemical and isotopic signatures indicate originally sedimentary protoliths. Detrital zircons in these rocks range in age from ca. 3820 to 3805 Ma. This unit shows an upwards transition from ‘pure' chemical sedimentary rocks with distinct seawater-like trace element signatures into lithologies increasingly contaminated by felsic material that is locally preserved as graded layers, which are interpreted as an increasing volcanogenic input. Succeeding the sedimentary rocks is the Felsic Volcanic formation, an extensive unit of mostly schistose 3807 to 3802 Ma felsic potassic-altered rocks with carbonate-rich interludes and veins. Locally-preserved andesitic units with graded layering, massive vesicular lavas, polymict breccias, resorbed quartz phenocrysts and fiammé, attest to volcanic and volcano-sedimentary protoliths. Whole rock geochemistry and oxygen isotope analyses on these rocks and their zircons indicate predominantly felsic volcanic protoliths that experienced massive alteration in a surficial environment, probably following subaerial eruption. Massive volcanic rocks are commonest in th
{"title":"Geodynamic Environment of the ca. 3800 Ma Outer Arc Group, Isua (Greenland)","authors":"A. Nutman, C. Friend, V. Bennett, M. V. Kranendonk, A. Chivas","doi":"10.2475/06.2021.01","DOIUrl":"https://doi.org/10.2475/06.2021.01","url":null,"abstract":"The arcuate, 35 km long Isua supracrustal belt (ISB, southern West Greenland) contains the world's largest remnants of Eoarchean volcanic and sedimentary sequences. The ISB is broadly divided into: (i) the northern Inner Arc Group of 3720 to 3690 Ma rocks, and (ii) the southern Outer Arc Group of ca. 3800 Ma rocks which is bounded on its northern side by the highly tectonized ca. 3750 Ma Dividing Sedimentary Unit. The boundary between the two groups is a mylonite formed between 3685 and 3660 Ma. Despite the generally high strain, amphibolite facies metamorphism and layer-parallel dislocations that can thin or altogether excise some units, domains of lower deformation comprising ≪1% (qualitative assessment) of the Outer Arc Group contain relict sedimentary and igneous structures. Combined with zircon U-Pb geochronology and whole rock geochemistry, this enables the Outer Arc Group lithological sequence and geodynamic setting to be reconstructed. The lower part of the Outer Arc Group is dominated by metabasaltic amphibolites of the Mafic Volcanic formation in which rarely-preserved pillow structures indicate both their predominantly subaqueous eruption and also their stratigraphic facing. They erupted >3800 Ma, because they were first intruded by subconcordant sheets of fine-grained hypabyssal tonalite dated at 3803±3 Ma (Crowley, 2003) and then by coarser-grained 3795 to 3791 Ma tonalite-granodiorite, which forms a large deformed pluton along the south side of the ISB. This formation is succeeded by the Sedimentary formation whose base consists of discontinuous rare, thin fuchsitic quartzites with 3890 to 3805 Ma detrital zircons. Overlying is a diverse package of dolostones, marls and siliceous rocks. Although they are extensively modified by metamorphism and metasomatism, producing widespread growth of talc or tremolite, relict graded sedimentary layering, chemical and isotopic signatures indicate originally sedimentary protoliths. Detrital zircons in these rocks range in age from ca. 3820 to 3805 Ma. This unit shows an upwards transition from ‘pure' chemical sedimentary rocks with distinct seawater-like trace element signatures into lithologies increasingly contaminated by felsic material that is locally preserved as graded layers, which are interpreted as an increasing volcanogenic input. Succeeding the sedimentary rocks is the Felsic Volcanic formation, an extensive unit of mostly schistose 3807 to 3802 Ma felsic potassic-altered rocks with carbonate-rich interludes and veins. Locally-preserved andesitic units with graded layering, massive vesicular lavas, polymict breccias, resorbed quartz phenocrysts and fiammé, attest to volcanic and volcano-sedimentary protoliths. Whole rock geochemistry and oxygen isotope analyses on these rocks and their zircons indicate predominantly felsic volcanic protoliths that experienced massive alteration in a surficial environment, probably following subaerial eruption. Massive volcanic rocks are commonest in th","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"321 1","pages":"643 - 679"},"PeriodicalIF":2.9,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43971817","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}
Orogens that form at convergent plate boundaries typically consist of accreted rock units that form an incomplete archive of subducted oceanic and continental lithosphere, as well as of deformed lithosphere of the former upper plate. Reading the construction of orogenic architecture forms the key to decipher the pre-orogenic paleogeographic distribution of oceans and continents, as well as bathymetric and topographic features that existed thereon such as igneous plateaus, seamounts, microcontinents, or magmatic arcs. Current classification schemes of orogens divide between settings associated with termination of subduction [continent-continent collision, continent-ocean collision (obduction)] and with ongoing subduction (accretionary orogenesis), alongside intraplate orogens. Perceived diagnostic features for such classifications, particularly of collisional orogenesis, hinge on dynamic interpretations linking downgoing plate paleogeography to upper plate deformation, plate motion changes, or magmatism. Here, we show, however, that Mesozoic-Cenozoic orogens that undergo collision almost all defy these proposed diagnostic features and behave as accretionary orogens instead. To reconstruct paleogeography of subducted and upper plates, we therefore propose an alternative approach to navigating through orogenic architecture: subducted plate units comprise nappes (or mélanges) with Ocean Plate Stratigraphy (OPS) and Continental Plate Stratigraphy (CPS) stripped from their now-subducted or otherwise underthrust lower crustal and mantle lithospheric underpinnings. Upper plate deformation and paleogeography respond to the competition between absolute motions of the upper plate and the subducting slab. Our navigation approach through orogenic architecture aims to avoid a priori dynamic interpretations that link downgoing plate paleogeography to deformation or magmatic responses in the upper plate, to provide an independent basis for geodynamic analysis. From our analysis we identify ‘rules of orogenesis' that link the rules of rigid plate tectonics with the reality of plate deformation. We use these rules for a thought experiment, in which we predict orogenic architecture that will result from subducting the present-day Indian Ocean and colliding the Somali, Madagascar, and Indian margins using a published continental drift scenario for a future supercontinent as basis. We illustrate that our inferred rules (of thumb) generate orogenic architecture that is analogous to elements of modern orogens, unlocking the well-known modern geography as inspiration for developing testable hypotheses that aid interpreting paleogeography from orogens that formed since the birth of plate tectonics.
{"title":"Deciphering paleogeography from orogenic architecture: Constructing orogens in a future supercontinent as thought experiment","authors":"Douwe J. J. van Hinsbergen,Thomas L. A. Schouten","doi":"10.2475/06.2021.09","DOIUrl":"https://doi.org/10.2475/06.2021.09","url":null,"abstract":"Orogens that form at convergent plate boundaries typically consist of accreted rock units that form an incomplete archive of subducted oceanic and continental lithosphere, as well as of deformed lithosphere of the former upper plate. Reading the construction of orogenic architecture forms the key to decipher the pre-orogenic paleogeographic distribution of oceans and continents, as well as bathymetric and topographic features that existed thereon such as igneous plateaus, seamounts, microcontinents, or magmatic arcs. Current classification schemes of orogens divide between settings associated with termination of subduction [continent-continent collision, continent-ocean collision (obduction)] and with ongoing subduction (accretionary orogenesis), alongside intraplate orogens. Perceived diagnostic features for such classifications, particularly of collisional orogenesis, hinge on dynamic interpretations linking downgoing plate paleogeography to upper plate deformation, plate motion changes, or magmatism. Here, we show, however, that Mesozoic-Cenozoic orogens that undergo collision almost all defy these proposed diagnostic features and behave as accretionary orogens instead. To reconstruct paleogeography of subducted and upper plates, we therefore propose an alternative approach to navigating through orogenic architecture: subducted plate units comprise nappes (or mélanges) with Ocean Plate Stratigraphy (OPS) and Continental Plate Stratigraphy (CPS) stripped from their now-subducted or otherwise underthrust lower crustal and mantle lithospheric underpinnings. Upper plate deformation and paleogeography respond to the competition between absolute motions of the upper plate and the subducting slab. Our navigation approach through orogenic architecture aims to avoid a priori dynamic interpretations that link downgoing plate paleogeography to deformation or magmatic responses in the upper plate, to provide an independent basis for geodynamic analysis. From our analysis we identify ‘rules of orogenesis' that link the rules of rigid plate tectonics with the reality of plate deformation. We use these rules for a thought experiment, in which we predict orogenic architecture that will result from subducting the present-day Indian Ocean and colliding the Somali, Madagascar, and Indian margins using a published continental drift scenario for a future supercontinent as basis. We illustrate that our inferred rules (of thumb) generate orogenic architecture that is analogous to elements of modern orogens, unlocking the well-known modern geography as inspiration for developing testable hypotheses that aid interpreting paleogeography from orogens that formed since the birth of plate tectonics.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"855 ","pages":"955-1031"},"PeriodicalIF":2.9,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138504451","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. Wang, Jian Zhang, C. Yin, Hai Zhou, Jin Liu, Wenxia Zhang, Shuhui Zhang, Chen Zhao, Changquan Cheng
As one of the 2.1 to 1.9 Ga orogenic belts that welded the Columbia supercontinent, the Khondalite Belt in the North China Craton is a typical continent-continent collisional orogen that formed through the collision between the Yinshan and Ordos Blocks. Previous studies mostly focused on the collisional event in the Khondalite Belt but paid little attention to how the subduction system operated before the final closure of the ocean. To address this issue, we identified a series of interlayered meta-mafic and felsic rock assemblages in the Daqingshan Complex and implemented geochemical and geochronological analyses. Petrological and geochemical studies revealed that these rocks are bimodal and include plagioclase amphibolite (Group 1) and biotite plagiogneiss (Group 2). Geochemically, Group 1 samples show tholeiitic affinity, whereas Group 2 samples belong to the high-K calc-alkaline series. Geochemical data indicate that the protolith magma of Group 1 was most likely derived from the partial melting of lithospheric mantle with minor crustal contamination, whereas Group 2 rocks represent highly differentiated magma derived from the partial melting of ancient crustal materials. All the samples show depletion of HFSEs and enrichment of LILEs, indicative of a subduction-related magmatic arc environment. Zircon U-Pb dating results show that the protoliths of Group 1 samples yield crystallization ages of ∼2.47 Ga and metamorphic ages of 1.95 to 1.85 Ga, whereas the protoliths of Group 2 samples yield crystallization ages of ∼2.40 Ga and metamorphic ages of ∼1.85 Ga. Our new results and available geochemical, petrological, and isotopic data demonstrate that the bimodal volcanic sequence of the Daqingshan Complex was developed in a 2.47 to 2.40 Ga back-arc system along the southern margin of Yinshan Block. Subsequent collision between the Ordos and Yinshan Blocks resulted in the formation of the Khondalite Belt and final amalgamation of the Western Block between 1.95 and 1.85 Ga.
{"title":"An Early Paleoproterozoic back-arc system along the southern margin of the Yinshan Block: Evidence from a newly-defined bimodal volcanic sequence in the Daqingshan Complex, Khondalite Belt","authors":"X. Wang, Jian Zhang, C. Yin, Hai Zhou, Jin Liu, Wenxia Zhang, Shuhui Zhang, Chen Zhao, Changquan Cheng","doi":"10.2475/06.2021.03","DOIUrl":"https://doi.org/10.2475/06.2021.03","url":null,"abstract":"As one of the 2.1 to 1.9 Ga orogenic belts that welded the Columbia supercontinent, the Khondalite Belt in the North China Craton is a typical continent-continent collisional orogen that formed through the collision between the Yinshan and Ordos Blocks. Previous studies mostly focused on the collisional event in the Khondalite Belt but paid little attention to how the subduction system operated before the final closure of the ocean. To address this issue, we identified a series of interlayered meta-mafic and felsic rock assemblages in the Daqingshan Complex and implemented geochemical and geochronological analyses. Petrological and geochemical studies revealed that these rocks are bimodal and include plagioclase amphibolite (Group 1) and biotite plagiogneiss (Group 2). Geochemically, Group 1 samples show tholeiitic affinity, whereas Group 2 samples belong to the high-K calc-alkaline series. Geochemical data indicate that the protolith magma of Group 1 was most likely derived from the partial melting of lithospheric mantle with minor crustal contamination, whereas Group 2 rocks represent highly differentiated magma derived from the partial melting of ancient crustal materials. All the samples show depletion of HFSEs and enrichment of LILEs, indicative of a subduction-related magmatic arc environment. Zircon U-Pb dating results show that the protoliths of Group 1 samples yield crystallization ages of ∼2.47 Ga and metamorphic ages of 1.95 to 1.85 Ga, whereas the protoliths of Group 2 samples yield crystallization ages of ∼2.40 Ga and metamorphic ages of ∼1.85 Ga. Our new results and available geochemical, petrological, and isotopic data demonstrate that the bimodal volcanic sequence of the Daqingshan Complex was developed in a 2.47 to 2.40 Ga back-arc system along the southern margin of Yinshan Block. Subsequent collision between the Ordos and Yinshan Blocks resulted in the formation of the Khondalite Belt and final amalgamation of the Western Block between 1.95 and 1.85 Ga.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"321 1","pages":"708 - 738"},"PeriodicalIF":2.9,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47874058","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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