Ruo-Xi Zhang, Shuiyuan Yang, Shao-Yong Jiang, Bin Fu, Ji-Qiang Cui
Mafic microgranular enclaves (MMEs), commonly found in granitoid intrusions, can provide unique perspectives on the nature of magma sources and evolution, physicochemical properties of magmas, and geotectonic dynamic evolution. However, their origin and generation remain under debate. In this paper, the Cretaceous Tongkeng pluton with MME occurrence located in the Xiaojiang area of Zhejiang Province, SE China, was examined. Zircon U-Pb dating indicates that the gabbroic diorite, MMEs, and their host quartz diorite all crystallized at 107−106 Ma. All samples from the Tongkeng pluton show a comparable range of initial 87Sr/86Sr values (0.70746−0.70841), εNd(t) values (−4.9 to −2.9), and zircon εHf(t) values (−7.3 to −2.9) with the peak value of −6 to −4. In addition, Pb isotope compositions are fairly consistent. Petrology, geochemical and isotopic compositions, and geochemical modeling suggest that the gabbroic diorite, MMEs, and their host rock were cognate and their primary magma was derived from the mixing between a mantle-derived magma and a crustal magma. The “magma differentiation and convection” model, proposed in this paper to improve our understanding of the origin of the MMEs and their host rock, suggests that the gabbroic and quartz dioritic magmas were formed by cognate magma differentiation, and the MME magma is a portion of the gabbroic dioritic magma that is incorporated into and mingled with the quartz dioritic magma. Misjudgment in the origin and generation of MMEs leads to an erroneous understanding of mantle properties, the genesis of granitoids, and therefore, many other geological processes. Hence, caution is needed when considering the relationship between the host granitoid and its associated MMEs with similar chemical and isotopic compositions, particularly for those exposed in areas where mafic rocks are absent (or undiscovered).
{"title":"Differentiation and convection in a magma chamber: Novel insights on the origin of mafic microgranular enclaves in the Tongkeng pluton, Xiaojiang area, SE China","authors":"Ruo-Xi Zhang, Shuiyuan Yang, Shao-Yong Jiang, Bin Fu, Ji-Qiang Cui","doi":"10.1130/b37056.1","DOIUrl":"https://doi.org/10.1130/b37056.1","url":null,"abstract":"Mafic microgranular enclaves (MMEs), commonly found in granitoid intrusions, can provide unique perspectives on the nature of magma sources and evolution, physicochemical properties of magmas, and geotectonic dynamic evolution. However, their origin and generation remain under debate. In this paper, the Cretaceous Tongkeng pluton with MME occurrence located in the Xiaojiang area of Zhejiang Province, SE China, was examined. Zircon U-Pb dating indicates that the gabbroic diorite, MMEs, and their host quartz diorite all crystallized at 107−106 Ma. All samples from the Tongkeng pluton show a comparable range of initial 87Sr/86Sr values (0.70746−0.70841), εNd(t) values (−4.9 to −2.9), and zircon εHf(t) values (−7.3 to −2.9) with the peak value of −6 to −4. In addition, Pb isotope compositions are fairly consistent. Petrology, geochemical and isotopic compositions, and geochemical modeling suggest that the gabbroic diorite, MMEs, and their host rock were cognate and their primary magma was derived from the mixing between a mantle-derived magma and a crustal magma. The “magma differentiation and convection” model, proposed in this paper to improve our understanding of the origin of the MMEs and their host rock, suggests that the gabbroic and quartz dioritic magmas were formed by cognate magma differentiation, and the MME magma is a portion of the gabbroic dioritic magma that is incorporated into and mingled with the quartz dioritic magma. Misjudgment in the origin and generation of MMEs leads to an erroneous understanding of mantle properties, the genesis of granitoids, and therefore, many other geological processes. Hence, caution is needed when considering the relationship between the host granitoid and its associated MMEs with similar chemical and isotopic compositions, particularly for those exposed in areas where mafic rocks are absent (or undiscovered).","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"24 8","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139010335","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Carbonatite hosts the most important rare earth resources in the world, but the precise timing, ore-forming history, and mechanism of rare earth mineralization in carbonatite systems are still in debate. Here, we report a rare corona texture of monazite-allanite-fluorapatite from the Huangjiagou carbonatite in the Lesser Qinling of central China, and demonstrate that the U-Th-Pb dating, trace elements, and Sr-Nd isotopes of these minerals in the corona are useful tools to unravel multiple-stage events for rare earth element (REE) mineralization and mobilization. The first mineralization event took place at ca. 219 Ma as revealed by the monazite U-Pb age, the same as regional carbonatite forming ages, but the Th-Pb age has been disturbed, which shows a negative correlation with Th contents. The second mineralization event occurred at ca. 128 Ma, as revealed by in situ U-Pb dating of allanite, coeval with the intrusions of neighboring I-type granite. The initial Sr-Nd isotope ratios of allanite show a downtrend from the center to the rim of monazite-allanite-apatite coronas to approach the ratios of neighboring granite, indicating an increasing effect by the metasomatism of magmatic-hydrothermal fluids during the growth of these REE-mineral coronas. Therefore, a two-episode REE mineralization was recognized with the replacement of ca. 219 Ma monazite by ca. 128 Ma allanite-apatite coronas on the function of magmatic-hydrothermal fluid metasomatism, and this process accompanies the disturbance of Th/Pb geochronology in monazite. Allanite as the product of monazite dissolution can represent the later-stage REE mineralization tracing the REE reworking processes under the hydrothermal conditions in carbonatite systems. Our study highlights the implication of monazite-allanite-fluorapatite coronas on the REE remobilization and mineralization in carbonatite systems.
{"title":"U-Th-Pb dating, trace elements, and Sr-Nd isotopes of monazite and allanite as recorders for multi-stage rare earth element mineralization and remobilization in carbonatite dike systems","authors":"Hao-Xiang Zhang, Shao-Yong Jiang, Si-Qi Liu, Feng Yuan, Wei Chen, Huimin Su","doi":"10.1130/b36931.1","DOIUrl":"https://doi.org/10.1130/b36931.1","url":null,"abstract":"Carbonatite hosts the most important rare earth resources in the world, but the precise timing, ore-forming history, and mechanism of rare earth mineralization in carbonatite systems are still in debate. Here, we report a rare corona texture of monazite-allanite-fluorapatite from the Huangjiagou carbonatite in the Lesser Qinling of central China, and demonstrate that the U-Th-Pb dating, trace elements, and Sr-Nd isotopes of these minerals in the corona are useful tools to unravel multiple-stage events for rare earth element (REE) mineralization and mobilization. The first mineralization event took place at ca. 219 Ma as revealed by the monazite U-Pb age, the same as regional carbonatite forming ages, but the Th-Pb age has been disturbed, which shows a negative correlation with Th contents. The second mineralization event occurred at ca. 128 Ma, as revealed by in situ U-Pb dating of allanite, coeval with the intrusions of neighboring I-type granite. The initial Sr-Nd isotope ratios of allanite show a downtrend from the center to the rim of monazite-allanite-apatite coronas to approach the ratios of neighboring granite, indicating an increasing effect by the metasomatism of magmatic-hydrothermal fluids during the growth of these REE-mineral coronas. Therefore, a two-episode REE mineralization was recognized with the replacement of ca. 219 Ma monazite by ca. 128 Ma allanite-apatite coronas on the function of magmatic-hydrothermal fluid metasomatism, and this process accompanies the disturbance of Th/Pb geochronology in monazite. Allanite as the product of monazite dissolution can represent the later-stage REE mineralization tracing the REE reworking processes under the hydrothermal conditions in carbonatite systems. Our study highlights the implication of monazite-allanite-fluorapatite coronas on the REE remobilization and mineralization in carbonatite systems.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"1 4","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138980784","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Nonesuch Formation and related sedimentary units of the Oronto Group, southern Lake Superior region, midwestern United States, are commonly held to have been deposited in a lacustrine rift basin within interior continental Laurentia. Here, we present new sedimentologic and stratigraphic evidence that shows a marine influence on deposition. Tidally influenced shallow-marine sandstone and evaporitic, sandy and muddy tidal flat facies pass upward into fine-grained estuarine and sandy turbidite deposits, which are sharply overlain by mixed sandy and muddy tidal flat and floodplain deposits. These observations are evidence that the lower Oronto Group was deposited in an epeiric seaway, one of several such seaways that developed during the final amalgamation of Rodinia at a time of globally high sea level. Retrogradational-aggradational-progradational-degradational stratal architecture records changes in the relative balance between generation of accommodation space and sedimentation rates, which we interpret to reflect the combined influence of Grenvillian Ottawan phase tectonic subsidence and thermal subsidence from earlier Midcontinent Rift magmatism. We use this revised stratigraphic framework to show that the geochemical proxies of the Nonesuch Formation are tied closely to sedimentary facies and reflect intrabasinal redox heterogeneity rather than global anoxia at the end-Mesoproterozoic. Further, our sedimentology shows that the microfossils recovered from the Nonesuch rocks are primarily associated with tidal flat facies. The combined influence of marine and local nonmarine conditions must be considered when invoking the Nonesuch Formation, or similar marine-influenced interior basin deposits, as global analogues.
{"title":"End-Mesoproterozoic (ca. 1.08 Ga) epeiric seaway of the Nonesuch Formation, Wisconsin and Michigan, USA","authors":"Esther K. Stewart, Ann M. Bauer, A. Prave","doi":"10.1130/b37060.1","DOIUrl":"https://doi.org/10.1130/b37060.1","url":null,"abstract":"The Nonesuch Formation and related sedimentary units of the Oronto Group, southern Lake Superior region, midwestern United States, are commonly held to have been deposited in a lacustrine rift basin within interior continental Laurentia. Here, we present new sedimentologic and stratigraphic evidence that shows a marine influence on deposition. Tidally influenced shallow-marine sandstone and evaporitic, sandy and muddy tidal flat facies pass upward into fine-grained estuarine and sandy turbidite deposits, which are sharply overlain by mixed sandy and muddy tidal flat and floodplain deposits. These observations are evidence that the lower Oronto Group was deposited in an epeiric seaway, one of several such seaways that developed during the final amalgamation of Rodinia at a time of globally high sea level. Retrogradational-aggradational-progradational-degradational stratal architecture records changes in the relative balance between generation of accommodation space and sedimentation rates, which we interpret to reflect the combined influence of Grenvillian Ottawan phase tectonic subsidence and thermal subsidence from earlier Midcontinent Rift magmatism.\u0000 We use this revised stratigraphic framework to show that the geochemical proxies of the Nonesuch Formation are tied closely to sedimentary facies and reflect intrabasinal redox heterogeneity rather than global anoxia at the end-Mesoproterozoic. Further, our sedimentology shows that the microfossils recovered from the Nonesuch rocks are primarily associated with tidal flat facies. The combined influence of marine and local nonmarine conditions must be considered when invoking the Nonesuch Formation, or similar marine-influenced interior basin deposits, as global analogues.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"93 7","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138586355","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Rodríguez-Mustafa, Adam C. Simon, Robert M. Holder, Holly Stein, A. Kylander‐Clark, B. Jicha, Daniel Blakemore, Edson L. B. Machado
Iron oxide−copper−gold (IOCG) and iron oxide−apatite (IOA) deposits are important sources of Cu and Fe, respectively. They contain abundant Fe-oxides and may contain Au, Ag, Co, rare earth elements (REEs), U, Ni, and V as economically important by-products. In Peru, the Mina Justa IOCG deposit is located next to the giant Marcona IOA deposit. Constraining the timing of Fe and Cu mineralization at Mina Justa is fundamental to understanding the duration and type of processes that generated this mineral deposit, and ultimately to testing the genetic link with other deposits in the area. Previous authors used alteration minerals to indirectly date Cu mineralization at Mina Justa at around 100 Ma. We report Ar/Ar dates of actinolite, U-Pb dates of magnetite, apatite, and titanite collected by in situ laser-ablation−multicollector−inductively coupled plasma−mass spectrometry, and Re-Os thermal ionization mass spectrometry dates for sulfides. These results indicate that Cu mineralization at Mina Justa occurred at ca. 160 Ma and that Fe mineralization is older and coeval with the neighboring Marcona IOA deposit, consistent with Cu mineralization overprinting IOA-style mineralization at Mina Justa.
{"title":"Integrated Re-Os, Ar/Ar, and U-Pb geochronology directly dates the timing of mineralization at the Mina Justa and Marcona deposits, Peru","authors":"M. Rodríguez-Mustafa, Adam C. Simon, Robert M. Holder, Holly Stein, A. Kylander‐Clark, B. Jicha, Daniel Blakemore, Edson L. B. Machado","doi":"10.1130/b36904.1","DOIUrl":"https://doi.org/10.1130/b36904.1","url":null,"abstract":"Iron oxide−copper−gold (IOCG) and iron oxide−apatite (IOA) deposits are important sources of Cu and Fe, respectively. They contain abundant Fe-oxides and may contain Au, Ag, Co, rare earth elements (REEs), U, Ni, and V as economically important by-products. In Peru, the Mina Justa IOCG deposit is located next to the giant Marcona IOA deposit. Constraining the timing of Fe and Cu mineralization at Mina Justa is fundamental to understanding the duration and type of processes that generated this mineral deposit, and ultimately to testing the genetic link with other deposits in the area. Previous authors used alteration minerals to indirectly date Cu mineralization at Mina Justa at around 100 Ma. We report Ar/Ar dates of actinolite, U-Pb dates of magnetite, apatite, and titanite collected by in situ laser-ablation−multicollector−inductively coupled plasma−mass spectrometry, and Re-Os thermal ionization mass spectrometry dates for sulfides. These results indicate that Cu mineralization at Mina Justa occurred at ca. 160 Ma and that Fe mineralization is older and coeval with the neighboring Marcona IOA deposit, consistent with Cu mineralization overprinting IOA-style mineralization at Mina Justa.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"37 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138593940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Unconformity-bounded rift sequences in Terreneuvian−Miaolingian strata of the Caledonian Highlands, Atlantic Canada: Comment","authors":"E. Landing, Gerd Geyer, S. Westrop, Thomas Wotte","doi":"10.1130/b37005.1","DOIUrl":"https://doi.org/10.1130/b37005.1","url":null,"abstract":"","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"125 42","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138599215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. J. Álvaro, Susan C. Johnson, S. Barr, Sören Jensen, T. Palacios, De Wet van Rooyen, C. White
{"title":"Unconformity-bounded rift sequences in Terreneuvian−Miaolingian strata of the Caledonian Highlands, Atlantic Canada: Reply","authors":"J. J. Álvaro, Susan C. Johnson, S. Barr, Sören Jensen, T. Palacios, De Wet van Rooyen, C. White","doi":"10.1130/b37173.1","DOIUrl":"https://doi.org/10.1130/b37173.1","url":null,"abstract":"","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"124 37","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138599208","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The generation and modification of silicic magma systems are essential processes in resolving the differentiation of continental crust. This understanding motivated the geochronological and geochemical study of the early Permian Hongliujing granite complex, consisting of quartz monzonite, granite, and leucogranite in the Central Tianshan microcontinent of the southern Central Asian Orogenic Belt. Laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) zircon U-Pb dating of the Hongliujing complex rock units revealed almost identical ages (279 ± 2 Ma to 270 ± 2 Ma). The high-silica leucogranite and granite are characterized by positive Rb and negative Eu anomalies and Ba, Sr, P, and Ti depletions. The zircon trace elements are characterized by relatively low Ti and Th/U and high Yb/Gd. In contrast, the quartz monzonite and its mafic microgranular enclaves display minor negative Ba, Sr, P, Ti, and Eu anomalies, while the zircon trace elements are characterized by relatively high Ti and Th/U and low Yb/Gd. The complex has similar zircon Hf and whole-rock Nd isotopic compositions, with Hf and Nd model ages younger than 1.4 Ga, suggesting that their magmas were derived from an isotopically depleted mantle, with some contributions from crustal melts. The leucogranites further showed relatively large variations of εHf(t) and lower εNd(t) values, implying that their magma was affected by higher amounts of crustal contamination. We suggest that crystal-melt segregation was the major mechanism responsible for the evolution of the magmatic system, and that the early Permian magmatism represents a crust-forming episode triggered by slab rollback of the subducting South Tianshan oceanic plate beneath the eastern Central Tianshan microcontinent. Thus, our study reveals that microcontinents with Precambrian crustal basement were major sites of juvenile continental growth during the accretionary evolution of the Central Asian Orogenic Belt.
硅质岩浆体系的生成和变质是解决大陆地壳分异的重要过程。这一认识推动了中亚造山带南缘天山中微大陆早二叠世红流井花岗岩杂岩的年代学和地球化学研究，该杂岩由石英二长岩、花岗岩和浅花岗岩组成。激光烧蚀-电感耦合等离子体-质谱(LA-ICP-MS)锆石U-Pb测年结果显示，红柳井杂岩单元的年龄(279±2 Ma ~ 270±2 Ma)几乎一致。高硅白花岗岩体和花岗岩具有Rb正、Eu负异常和Ba、Sr、P、Ti亏缺的特征。锆石微量元素具有较低的Ti、Th/U和较高的Yb/Gd的特征。石英二长岩及其基性微颗粒包体呈现少量负Ba、Sr、P、Ti、Eu异常，锆石微量元素表现为较高的Ti、Th/U和较低的Yb/Gd。该杂岩具有相似的锆石Hf和全岩Nd同位素组成，Hf和Nd模型年龄小于1.4 Ga，表明它们的岩浆来自于同位素衰竭的地幔，并有地壳熔体的贡献。浅花岗岩的εHf(t)变化较大，而εNd(t)变化较小，表明其岩浆受较大的地壳污染影响。本文认为，结晶-熔体分离是岩浆系统演化的主要机制，早二叠世岩浆活动是由俯冲的南天山洋板块在中天山微大陆东部下方的板块回滚引发的地壳形成事件。因此，具有前寒武纪地壳基底的微大陆是中亚造山带增生演化中幼年大陆发育的主要场所。
{"title":"Petrogenesis of the early Permian Hongliujing granite complex in the Chinese Eastern Tianshan orogen: Evidence for crustal growth in the Central Tianshan microcontinent","authors":"Zhen‐Yu He, R. Klemd, T. Lu, Lili Yan, Hua Xiang","doi":"10.1130/b36970.1","DOIUrl":"https://doi.org/10.1130/b36970.1","url":null,"abstract":"The generation and modification of silicic magma systems are essential processes in resolving the differentiation of continental crust. This understanding motivated the geochronological and geochemical study of the early Permian Hongliujing granite complex, consisting of quartz monzonite, granite, and leucogranite in the Central Tianshan microcontinent of the southern Central Asian Orogenic Belt. Laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) zircon U-Pb dating of the Hongliujing complex rock units revealed almost identical ages (279 ± 2 Ma to 270 ± 2 Ma). The high-silica leucogranite and granite are characterized by positive Rb and negative Eu anomalies and Ba, Sr, P, and Ti depletions. The zircon trace elements are characterized by relatively low Ti and Th/U and high Yb/Gd. In contrast, the quartz monzonite and its mafic microgranular enclaves display minor negative Ba, Sr, P, Ti, and Eu anomalies, while the zircon trace elements are characterized by relatively high Ti and Th/U and low Yb/Gd. The complex has similar zircon Hf and whole-rock Nd isotopic compositions, with Hf and Nd model ages younger than 1.4 Ga, suggesting that their magmas were derived from an isotopically depleted mantle, with some contributions from crustal melts. The leucogranites further showed relatively large variations of εHf(t) and lower εNd(t) values, implying that their magma was affected by higher amounts of crustal contamination. We suggest that crystal-melt segregation was the major mechanism responsible for the evolution of the magmatic system, and that the early Permian magmatism represents a crust-forming episode triggered by slab rollback of the subducting South Tianshan oceanic plate beneath the eastern Central Tianshan microcontinent. Thus, our study reveals that microcontinents with Precambrian crustal basement were major sites of juvenile continental growth during the accretionary evolution of the Central Asian Orogenic Belt.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" 6","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138610269","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M.E. Smith, H. Gregorich, L. Gipson, R.C. Krueger, A.R. Carroll, E.C. Parrish, A.P. Walters, S. Honig, C. Schwaderer, S. Meyers, B.S. Singer, T.K. Lowenstein, W. Arnuk
The Green River Formation of Wyoming, USA, is host to the world’s largest known lacustrine sodium carbonate deposits, which accumulated in a closed basin during the early Eocene greenhouse. Alkaline brines are hypothesized to have been delivered to ancient Gosiute Lake by the Aspen paleoriver that flowed from the Colorado Mineral Belt. To precisely trace fluvial provenance in the resulting deposits, we conducted X-ray fluorescence analyses and petrographic studies across a suite of well-dated sandstone marker beds of the Wilkins Peak Member of the Green River Formation. Principal component analysis reveals strong correlation among elemental abundances, grain composition, and sedimentary lithofacies. To isolate a detrital signal, elements least affected by authigenic minerals, weathering, and other processes were included in a principal component analysis, the results of which are consistent with petrographic sandstone modes and detrital zircon chronofacies of the basin. Sandstone marker beds formed during eccentricity-paced lacustrine lowstands and record the migration of fluvial distributary channel networks from multiple catchments around a migrating depocenter, including two major paleorivers. The depositional topography of these convergent fluvial fans would have inversely defined bathymetric lows during subsequent phases of lacustrine inundation, locations where trona could accumulate below a thermocline. Provenance mapping verifies fluvial connectivity to the Aspen paleoriver and to sources of alkalinity in the Colorado Mineral Belt across Wilkins Peak Member deposition, and shows that the greatest volumes of sediment were delivered from the Aspen paleoriver during deposition of marker beds A, B, D, and I, each of which were deposited coincident with prominent “hyperthermal” isotopic excursions documented in oceanic cores.
{"title":"High-resolution X-ray fluorescence-based provenance mapping of Eocene fluvial distributary fans that fed ancient Gosiute Lake, Wyoming, USA","authors":"M.E. Smith, H. Gregorich, L. Gipson, R.C. Krueger, A.R. Carroll, E.C. Parrish, A.P. Walters, S. Honig, C. Schwaderer, S. Meyers, B.S. Singer, T.K. Lowenstein, W. Arnuk","doi":"10.1130/b37207.1","DOIUrl":"https://doi.org/10.1130/b37207.1","url":null,"abstract":"The Green River Formation of Wyoming, USA, is host to the world’s largest known lacustrine sodium carbonate deposits, which accumulated in a closed basin during the early Eocene greenhouse. Alkaline brines are hypothesized to have been delivered to ancient Gosiute Lake by the Aspen paleoriver that flowed from the Colorado Mineral Belt. To precisely trace fluvial provenance in the resulting deposits, we conducted X-ray fluorescence analyses and petrographic studies across a suite of well-dated sandstone marker beds of the Wilkins Peak Member of the Green River Formation. Principal component analysis reveals strong correlation among elemental abundances, grain composition, and sedimentary lithofacies. To isolate a detrital signal, elements least affected by authigenic minerals, weathering, and other processes were included in a principal component analysis, the results of which are consistent with petrographic sandstone modes and detrital zircon chronofacies of the basin. Sandstone marker beds formed during eccentricity-paced lacustrine lowstands and record the migration of fluvial distributary channel networks from multiple catchments around a migrating depocenter, including two major paleorivers. The depositional topography of these convergent fluvial fans would have inversely defined bathymetric lows during subsequent phases of lacustrine inundation, locations where trona could accumulate below a thermocline. Provenance mapping verifies fluvial connectivity to the Aspen paleoriver and to sources of alkalinity in the Colorado Mineral Belt across Wilkins Peak Member deposition, and shows that the greatest volumes of sediment were delivered from the Aspen paleoriver during deposition of marker beds A, B, D, and I, each of which were deposited coincident with prominent “hyperthermal” isotopic excursions documented in oceanic cores.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" 47","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138616800","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Y. Najman, Guangsheng Zhuang, Andrew Carter, Lorenzo Gemignani, Ian Millar, Jan Wijbrans
For sedimentary archives to be used as a record of hinterland evolution, the factors affecting the archive must be known. In addition to tectonics, a number of factors, such as changes in climate and paleodrainage, as well as the degree of diagenesis, influence basin sediments. The Indus River delta-fan system of South-Central Asia records a history of Himalayan evolution, and both the onshore and offshore sedimentary repositories have been studied extensively to research orogenesis. However, a number of unknowns remain regarding this system. This paper seeks to elucidate the paleodrainage of the Indus River, in particular when it took on its modern drainage configuration with respect to conjoinment of the main Himalayan (Punjabi) tributary system with the Indus trunk river. We leverage the fact that the Punjabi tributary system has a significantly different provenance signature than the main trunk Indus River, draining mainly the Indian plate. Therefore, after the Punjabi tributary system joined the Indus River, the proportion of Indian plate material in the repositories downstream of the confluence should have been higher than in the upstream repository. We compared bulk Sr-Nd data and detrital zircon U-Pb data from the Cenozoic upstream peripheral foreland basin and downstream Indus delta and Indus Fan repositories. We determined that throughout Neogene times, repositories below the confluence had a higher proportion of material from the Indian plate than those above the confluence. Therefore, we conclude that the Indus River took on its current configuration, with the Punjabi tributary system draining into the Indus trunk river in the Paleogene, early in the history of the orogen. The exact time when the tributary system joined the Indus should correlate with a shift to more Indian plate input in the downstream repositories only. While the upstream repository records no change in Indian plate input from Eocene to Neogene times, a shift to increased material from the Indian plate occurs at the Eocene−Oligocene boundary in the delta, but sometime between 50 Ma and 40 Ma in the fan. Though further work is required to understand the discrepancy between the two downstream repositories, we can conclude that the tributary system joined the Indus trunk river at or before the start of the Oligocene.
要将沉积档案作为腹地演变的记录，必须了解影响档案的因素。除构造作用外，气候和古排水的变化以及成岩作用的程度等多种因素也会影响盆地沉积物。中南亚的印度河三角洲-扇形系统记录了喜马拉雅山的演化史，对陆上和近海沉积物库进行了广泛研究，以研究成因。然而，该系统仍存在许多未知因素。本文试图阐明印度河的古排水系统，特别是印度河何时形成现代排水系统，喜马拉雅山（旁遮普）主要支流系统与印度河干流的汇合情况。我们利用了旁遮普支流系统与印度河主干河有着明显不同的产地特征这一事实，印度河主干河主要向印度板块排水。因此，在旁遮普支流水系与印度河汇合后，汇合点下游储层中印度板块物质的比例应高于上游储层。我们比较了新生代上游外围前陆盆地和下游印度河三角洲及印度河扇矿床的大块 Sr-Nd 数据和锆英石 U-Pb 数据。我们确定，在整个新近纪时期，汇合点以下的储层中来自印度板块的物质比例高于汇合点以上的储层。因此，我们得出结论，印度河在造山运动历史的早期，即古新世时期就形成了目前的格局，旁遮普支流系统排入印度河干流。支流系统汇入印度河的确切时间应该只与下游储层中印度板块输入量的增加有关。上游储层记录的印度板块输入量从始新世到新近纪没有变化，而在三角洲的始新世-渐新世边界，印度板块的输入量却增加了，但在扇区的 50 Ma 到 40 Ma 之间的某个时间，印度板块的输入量却增加了。虽然还需要进一步研究才能了解这两个下游储存库之间的差异，但我们可以得出结论，支流系统是在渐新世开始时或之前加入印度河干流的。
{"title":"When did the Indus River of South-Central Asia take on its “modern” drainage configuration?","authors":"Y. Najman, Guangsheng Zhuang, Andrew Carter, Lorenzo Gemignani, Ian Millar, Jan Wijbrans","doi":"10.1130/b36596.1","DOIUrl":"https://doi.org/10.1130/b36596.1","url":null,"abstract":"For sedimentary archives to be used as a record of hinterland evolution, the factors affecting the archive must be known. In addition to tectonics, a number of factors, such as changes in climate and paleodrainage, as well as the degree of diagenesis, influence basin sediments. The Indus River delta-fan system of South-Central Asia records a history of Himalayan evolution, and both the onshore and offshore sedimentary repositories have been studied extensively to research orogenesis. However, a number of unknowns remain regarding this system. This paper seeks to elucidate the paleodrainage of the Indus River, in particular when it took on its modern drainage configuration with respect to conjoinment of the main Himalayan (Punjabi) tributary system with the Indus trunk river. We leverage the fact that the Punjabi tributary system has a significantly different provenance signature than the main trunk Indus River, draining mainly the Indian plate. Therefore, after the Punjabi tributary system joined the Indus River, the proportion of Indian plate material in the repositories downstream of the confluence should have been higher than in the upstream repository. We compared bulk Sr-Nd data and detrital zircon U-Pb data from the Cenozoic upstream peripheral foreland basin and downstream Indus delta and Indus Fan repositories. We determined that throughout Neogene times, repositories below the confluence had a higher proportion of material from the Indian plate than those above the confluence. Therefore, we conclude that the Indus River took on its current configuration, with the Punjabi tributary system draining into the Indus trunk river in the Paleogene, early in the history of the orogen. The exact time when the tributary system joined the Indus should correlate with a shift to more Indian plate input in the downstream repositories only. While the upstream repository records no change in Indian plate input from Eocene to Neogene times, a shift to increased material from the Indian plate occurs at the Eocene−Oligocene boundary in the delta, but sometime between 50 Ma and 40 Ma in the fan. Though further work is required to understand the discrepancy between the two downstream repositories, we can conclude that the tributary system joined the Indus trunk river at or before the start of the Oligocene.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"108 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139200463","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shenqiang Chen, M. Fellin, Sean D. Willett, Colin Maden, M. Guillong, Hanlin Chen, Yaguang Chen
Late Cenozoic gneiss domes cover ∼30% of the surface of the Pamir salient in the northwestern end of the India−Asia collision zone. The highest peaks of the Pamir are in the east, where the ∼250-km-long, ∼N−S-trending Kongur Shan extensional system controls the topography. We combined 115 new apatite (U-Th-Sm)/He and zircon (U-Th)/He single-grain dates from 18 samples and previous thermochronologic data with three-dimensional thermokinematic models to constrain the thermo-tectonic history of the southern portion of the Muztaghata dome, one of the largest gneiss domes in the eastern Pamir. The new cooling dates from the western boundary of the southern Muztaghata dome generally increase with distance from the southern Kongur Shan fault and are related to normal faulting along the fault at near-surface levels over the last 6.5 m.y. The new dates across the central−eastern portion of the dome outline the previously recorded U-shaped date pattern at a higher spatial resolution. The modeling indicates that this pattern is most likely the result of uplift and erosion above a flat-ramp-flat thrust fault at depth over the last 7 m.y. Modeling does not resolve how topographic changes may have affected the observed distribution of cooling dates, but it indicates a faster thrust-slip rate associated with an increase in relief and a slower one associated with steady-state topography. Our results suggest that the modern topography along the southern Muztaghata dome, similar to the rest of the eastern Pamir salient, is shaped by normal faulting at shallow depth, but its growth may still be governed by contraction and crustal thickening at depth.
{"title":"Late Miocene to present synchronous extension and contraction in the eastern Pamir: Insights from inversion of thermochronologic data across the southern Muztaghata dome","authors":"Shenqiang Chen, M. Fellin, Sean D. Willett, Colin Maden, M. Guillong, Hanlin Chen, Yaguang Chen","doi":"10.1130/b36953.1","DOIUrl":"https://doi.org/10.1130/b36953.1","url":null,"abstract":"Late Cenozoic gneiss domes cover ∼30% of the surface of the Pamir salient in the northwestern end of the India−Asia collision zone. The highest peaks of the Pamir are in the east, where the ∼250-km-long, ∼N−S-trending Kongur Shan extensional system controls the topography. We combined 115 new apatite (U-Th-Sm)/He and zircon (U-Th)/He single-grain dates from 18 samples and previous thermochronologic data with three-dimensional thermokinematic models to constrain the thermo-tectonic history of the southern portion of the Muztaghata dome, one of the largest gneiss domes in the eastern Pamir. The new cooling dates from the western boundary of the southern Muztaghata dome generally increase with distance from the southern Kongur Shan fault and are related to normal faulting along the fault at near-surface levels over the last 6.5 m.y. The new dates across the central−eastern portion of the dome outline the previously recorded U-shaped date pattern at a higher spatial resolution. The modeling indicates that this pattern is most likely the result of uplift and erosion above a flat-ramp-flat thrust fault at depth over the last 7 m.y. Modeling does not resolve how topographic changes may have affected the observed distribution of cooling dates, but it indicates a faster thrust-slip rate associated with an increase in relief and a slower one associated with steady-state topography. Our results suggest that the modern topography along the southern Muztaghata dome, similar to the rest of the eastern Pamir salient, is shaped by normal faulting at shallow depth, but its growth may still be governed by contraction and crustal thickening at depth.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"438 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139211631","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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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