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, Available online , doi: 10.31035/cg2021034
Abstract:
The 1∶1000000 geochemical mapping of Zambia provides catchment sediment geochemical data for 58 elements including Au from 746 sediment samples at 736 sampling sites, corresponding to a sampling density of about one site per 1000 km2. Under strict quality control using field duplicates, certified reference materials, and analytical replicate samples, the Au was determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The detection limit of Au was 0.20 × 10−9. The 95% range (2.5%–97.5%) of Au concentrations was from 0.24 × 10−9 to 1.36 × 10−9, and the median value was 0.40 × 10−9. The most noticeable Au distribution patterns shown on the map are mainly located between Lusaka and Ndola (Lufilian Arc Belt). In addition, several high Au value areas occurred in Mansa, Muyombe, Chipata, and Livingstone. The spatial distribution patterns of Au in tectonic units, drainage basins, and geomorphological landscapes could be related to the Lufilian Arc Belt and Bangweulu Block. The Au concentrations show metallogenic belts between Muyombe and Mbala areas, between Mansa and Ndola areas, and between Lusaka and Kasempa areas.
The 1∶1000000 geochemical mapping of Zambia provides catchment sediment geochemical data for 58 elements including Au from 746 sediment samples at 736 sampling sites, corresponding to a sampling density of about one site per 1000 km2. Under strict quality control using field duplicates, certified reference materials, and analytical replicate samples, the Au was determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The detection limit of Au was 0.20 × 10−9. The 95% range (2.5%–97.5%) of Au concentrations was from 0.24 × 10−9 to 1.36 × 10−9, and the median value was 0.40 × 10−9. The most noticeable Au distribution patterns shown on the map are mainly located between Lusaka and Ndola (Lufilian Arc Belt). In addition, several high Au value areas occurred in Mansa, Muyombe, Chipata, and Livingstone. The spatial distribution patterns of Au in tectonic units, drainage basins, and geomorphological landscapes could be related to the Lufilian Arc Belt and Bangweulu Block. The Au concentrations show metallogenic belts between Muyombe and Mbala areas, between Mansa and Ndola areas, and between Lusaka and Kasempa areas.
, Available online , doi: 10.31035/cg2021024
Abstract:
The granite collected from the Yinshan Mountain and kaolinite has been selected for the leaching and adsorption experiment, respectively, aiming to clarify the enrichment processes of Li and Ga during the deposition. Results suggest both Li and Ga could be leached out from granite by using different acid solutions of different pH and kaolinite can adsorb Li and Ga with varying degrees. Lithium and Ga had the highest leaching ratio when pH = 1. Special geological events (e.g. volcanic eruptions and wildfires), which could result in very low pH values of water in peatland, may have accelerated the release of Li and Ga from the source rocks. Kaolinite has the highest adsorption fraction was obtained at pH = 8. The different characteristics of Li and Ga displayed in the leaching and adsorption experiments probably result from the different occurrences and enrichment processes of Li and Ga in the coals. Lithium was probably enriched before the Li carriers (e.g. kaolinite) had been transported into paleomires because of its high leaching ratio and high adsorption fraction under neutral and alkaline conditions, whereas Ga was more likely concentrated by kaolinite and other carriers after it had been transported into the peat mires.
The granite collected from the Yinshan Mountain and kaolinite has been selected for the leaching and adsorption experiment, respectively, aiming to clarify the enrichment processes of Li and Ga during the deposition. Results suggest both Li and Ga could be leached out from granite by using different acid solutions of different pH and kaolinite can adsorb Li and Ga with varying degrees. Lithium and Ga had the highest leaching ratio when pH = 1. Special geological events (e.g. volcanic eruptions and wildfires), which could result in very low pH values of water in peatland, may have accelerated the release of Li and Ga from the source rocks. Kaolinite has the highest adsorption fraction was obtained at pH = 8. The different characteristics of Li and Ga displayed in the leaching and adsorption experiments probably result from the different occurrences and enrichment processes of Li and Ga in the coals. Lithium was probably enriched before the Li carriers (e.g. kaolinite) had been transported into paleomires because of its high leaching ratio and high adsorption fraction under neutral and alkaline conditions, whereas Ga was more likely concentrated by kaolinite and other carriers after it had been transported into the peat mires.
, Available online , doi: 10.31035/cg2021035
Abstract:
Source rock assessment is a key step in any petroleum exploration activity. The results of Rock-Eval analysis showed that Sarchahan Formation was in the late oil window, while the Faraghun and Zakeen Formations were just in the early stages of the oil window. Furthermore, Sarchahan, Zakeen and Faraghun Formations exhibited different kerogen types (types-Ⅱ, types-Ⅲ and type-Ⅲ, respectively). Refining the kinetic parameters using the OPTKIN software, the error function returned error values below 0.1, indicating accurate optimization of the kinetic parameters. Based on the obtained values of activation energy, it was clear that Sarchahan Formation contained type-Ⅱ kerogen with an activation energy of 48–52 kcal/mol, while Zakeen and Faraghun Formations contained type-III kerogen with activation energies of 70–80 kcal/mol and 44–56 kcal/mol, respectively. The geographical distribution of the samples studied in this work, it was found that the organic matter (OM) quantity and quality increased as one moved toward the Coastal Fars in Sarchahan Formation. The same trend was observed as one moved from the southern coasts of Iran toward the shaly and coaly portions of Faraghun Formation in the center of the Persian Gulf.
Source rock assessment is a key step in any petroleum exploration activity. The results of Rock-Eval analysis showed that Sarchahan Formation was in the late oil window, while the Faraghun and Zakeen Formations were just in the early stages of the oil window. Furthermore, Sarchahan, Zakeen and Faraghun Formations exhibited different kerogen types (types-Ⅱ, types-Ⅲ and type-Ⅲ, respectively). Refining the kinetic parameters using the OPTKIN software, the error function returned error values below 0.1, indicating accurate optimization of the kinetic parameters. Based on the obtained values of activation energy, it was clear that Sarchahan Formation contained type-Ⅱ kerogen with an activation energy of 48–52 kcal/mol, while Zakeen and Faraghun Formations contained type-III kerogen with activation energies of 70–80 kcal/mol and 44–56 kcal/mol, respectively. The geographical distribution of the samples studied in this work, it was found that the organic matter (OM) quantity and quality increased as one moved toward the Coastal Fars in Sarchahan Formation. The same trend was observed as one moved from the southern coasts of Iran toward the shaly and coaly portions of Faraghun Formation in the center of the Persian Gulf.
, Available online , doi: 10.31035/cg2021026
Abstract:
Archaeanthus is a famous Cretaceous angiosperm from the Albian-Cenomanian of Kansas, the USA documented by Dilcher and Crane in 1984. Its seeds/ovules were interpreted as arranged along the adaxial (ventral) suture of the fruits. This interpretation used to sound plausible, especially under the light of the then-dominating doctrine of angiosperm evolution. However, Dilcher and Crane’s interpretation of seed/ovule insertion was not fully supported even by their own evidence. Considering the early age, importance, and influence of Archaeanthus in palaeobotany and angiosperm systematics, it is necessary to ascertain the seed/ovule position in Archaeanthus. New observation on the type materials of Archaeanthus indicates that at least some ovules/seeds in Archaeanthus are attached to the abaxial (dorsal) margin of the fruit. This information undermines the former assumed Magnoliaceous affinity of Archaeanthus and falsifies its support to the then-dominating speculation of carpel homology and origin of angiosperms. Analysis of the common reason underlying the misinterpretations of early fossil angiosperms (including Archaeanthus, Archaefructus, and others) indicates that the speculation of Arber and Parkin deviated much from the botanical reality.
Archaeanthus is a famous Cretaceous angiosperm from the Albian-Cenomanian of Kansas, the USA documented by Dilcher and Crane in 1984. Its seeds/ovules were interpreted as arranged along the adaxial (ventral) suture of the fruits. This interpretation used to sound plausible, especially under the light of the then-dominating doctrine of angiosperm evolution. However, Dilcher and Crane’s interpretation of seed/ovule insertion was not fully supported even by their own evidence. Considering the early age, importance, and influence of Archaeanthus in palaeobotany and angiosperm systematics, it is necessary to ascertain the seed/ovule position in Archaeanthus. New observation on the type materials of Archaeanthus indicates that at least some ovules/seeds in Archaeanthus are attached to the abaxial (dorsal) margin of the fruit. This information undermines the former assumed Magnoliaceous affinity of Archaeanthus and falsifies its support to the then-dominating speculation of carpel homology and origin of angiosperms. Analysis of the common reason underlying the misinterpretations of early fossil angiosperms (including Archaeanthus, Archaefructus, and others) indicates that the speculation of Arber and Parkin deviated much from the botanical reality.
, Available online , doi: 10.31035/cg2021033
Abstract:
The A-type granites with highly positive εNd(t) values in the West Junggar, Central Asian Orogenic Belt (CAOB), have long been perceived as a group formed under the same tectonic and geodynamic setting, magmatic source, and petrogenetic model. Geological evidence shows that these granites occurred at two different tectonic units related to the southeastern subduction of Junggar oceanic plate: the Hongshan and Karamay granites emplaced in the southeast of West Junggar in the Baogutu continental arc; whereas the Akebasitao and Miaoergou granites formed in the accretionary prism. Here the authors present new bulk-rock geochemistry and Sr-Nd isotopes, zircon U-Pb ages and Hf-O isotopes data on these granites. The granites in the Baogutu continental arc and accretionary prism contain similar zircon εHf(t) values (+10.9 to +16.2) and bulk-rock geochemical characteristics (e.g., high SiO2 and K2O contents, enriched LILEs (except Sr), depleted Sr, Ta, and Ti, and negative anomalies in Ce and Eu). The Hongshan and Karamay granites in the Baogutu continental arc have older zircon U-Pb ages (range: 315 Ma to 305 Ma) and moderate 18O enrichments (δ18Ozircon=+6.41‰–+7.96‰); whereas the Akebasitao and Miaoergou granites in the accretionary prism have younger zircon U-Pb ages (range: 305 Ma to 301 Ma) with higher 18O enrichments (δ18Ozircon=+8.72‰–+9.89‰). The authors deduce that the elevated 18O enrichments of the Akebasitao and Miaoergou granites were probably inherited from low-temperature altered oceanic crusts. The Akebasitao and Miaoergou granites were originated from partial melting of low-temperature altered oceanic crusts with juvenile oceanic sediments below the accretionary prism. The Hongshan and Karamay granites were mainly derived from partial melting of basaltic juvenile lower crust with mixtures of potentially chemical weathered ancient crustal residues and mantle basaltic melt (induced by hot intruding mantle basaltic magma at the bottom of the Baogutu continental arc). On the other hand, the Miaoergou charnockite might be sourced from a deeper partial melting reservoir under the accretionary prism, consisting of the low-temperature altered oceanic crust, juvenile oceanic sediments, and mantle basaltic melt. These granites could be related to the asthenosphere's counterflow and upwelling, caused by the break-off and delamination of the subducted oceanic plate beneath the accretionary prism Baogutu continental arc in a post-collisional tectonic setting.
The A-type granites with highly positive εNd(t) values in the West Junggar, Central Asian Orogenic Belt (CAOB), have long been perceived as a group formed under the same tectonic and geodynamic setting, magmatic source, and petrogenetic model. Geological evidence shows that these granites occurred at two different tectonic units related to the southeastern subduction of Junggar oceanic plate: the Hongshan and Karamay granites emplaced in the southeast of West Junggar in the Baogutu continental arc; whereas the Akebasitao and Miaoergou granites formed in the accretionary prism. Here the authors present new bulk-rock geochemistry and Sr-Nd isotopes, zircon U-Pb ages and Hf-O isotopes data on these granites. The granites in the Baogutu continental arc and accretionary prism contain similar zircon εHf(t) values (+10.9 to +16.2) and bulk-rock geochemical characteristics (e.g., high SiO2 and K2O contents, enriched LILEs (except Sr), depleted Sr, Ta, and Ti, and negative anomalies in Ce and Eu). The Hongshan and Karamay granites in the Baogutu continental arc have older zircon U-Pb ages (range: 315 Ma to 305 Ma) and moderate 18O enrichments (δ18Ozircon=+6.41‰–+7.96‰); whereas the Akebasitao and Miaoergou granites in the accretionary prism have younger zircon U-Pb ages (range: 305 Ma to 301 Ma) with higher 18O enrichments (δ18Ozircon=+8.72‰–+9.89‰). The authors deduce that the elevated 18O enrichments of the Akebasitao and Miaoergou granites were probably inherited from low-temperature altered oceanic crusts. The Akebasitao and Miaoergou granites were originated from partial melting of low-temperature altered oceanic crusts with juvenile oceanic sediments below the accretionary prism. The Hongshan and Karamay granites were mainly derived from partial melting of basaltic juvenile lower crust with mixtures of potentially chemical weathered ancient crustal residues and mantle basaltic melt (induced by hot intruding mantle basaltic magma at the bottom of the Baogutu continental arc). On the other hand, the Miaoergou charnockite might be sourced from a deeper partial melting reservoir under the accretionary prism, consisting of the low-temperature altered oceanic crust, juvenile oceanic sediments, and mantle basaltic melt. These granites could be related to the asthenosphere's counterflow and upwelling, caused by the break-off and delamination of the subducted oceanic plate beneath the accretionary prism Baogutu continental arc in a post-collisional tectonic setting.
, Available online , doi: 10.31035/cg2021006
Abstract:
The newly discovered medium-scale Huangling uranium deposit is located in the Shuanlong area of southeast Ordos Basin. Here, the authors present the systematic geochemistry and zircon U-Pb studies on the Zhiluo Formation sandstone in the Huanling area. These data plays an important role in deducing its provenance and tectonic setting of the source rocks. The results show that the lower part of the Zhiluo Formation is mainly composed of felsic sedimentary rocks. The tectonic setting of source rocks can be defined as a continental island arc environment. U-Pb ages of detrital zircons can be roughly divided into three groups: 170‒500 Ma, 1600‒2050 Ma, and 2100‒2650 Ma. Based on the characteristics of trace and rare earth elements (REE) and the zircon U-Pb dating results, it is considered that the Cryptozoic Edo provenance of the Zhiluo Formation is mainly derived from magmatic rocks including granodioritic intrusions and metamorphic rocks such as gneiss and granulite in the orogenic belt of the northern margin of North China Plate and the Alxa Block. Based on the results of sedimentology and petrology, it is concluded that the direction of provenance supply of clastic sediments during the Zhiluo period is from north to south. The preconcentration of uranium in the Lower Zhiluo Formation of Huangling area is relatively low, and the paleocurrent system in the sedimentary period is inconsistent with the ore-bearing flow field in the mineralization period, which restricts the formation of large-scale and super large-scale uranium deposits and ore zones in the southeast of Ordos Basin. The recognition on provenance supply direction might provide crucial reference to prototype recovery, paleo-geomorphology and prediction of potential uranium reservoir of Ordos Basin in Jurassic period.
The newly discovered medium-scale Huangling uranium deposit is located in the Shuanlong area of southeast Ordos Basin. Here, the authors present the systematic geochemistry and zircon U-Pb studies on the Zhiluo Formation sandstone in the Huanling area. These data plays an important role in deducing its provenance and tectonic setting of the source rocks. The results show that the lower part of the Zhiluo Formation is mainly composed of felsic sedimentary rocks. The tectonic setting of source rocks can be defined as a continental island arc environment. U-Pb ages of detrital zircons can be roughly divided into three groups: 170‒500 Ma, 1600‒2050 Ma, and 2100‒2650 Ma. Based on the characteristics of trace and rare earth elements (REE) and the zircon U-Pb dating results, it is considered that the Cryptozoic Edo provenance of the Zhiluo Formation is mainly derived from magmatic rocks including granodioritic intrusions and metamorphic rocks such as gneiss and granulite in the orogenic belt of the northern margin of North China Plate and the Alxa Block. Based on the results of sedimentology and petrology, it is concluded that the direction of provenance supply of clastic sediments during the Zhiluo period is from north to south. The preconcentration of uranium in the Lower Zhiluo Formation of Huangling area is relatively low, and the paleocurrent system in the sedimentary period is inconsistent with the ore-bearing flow field in the mineralization period, which restricts the formation of large-scale and super large-scale uranium deposits and ore zones in the southeast of Ordos Basin. The recognition on provenance supply direction might provide crucial reference to prototype recovery, paleo-geomorphology and prediction of potential uranium reservoir of Ordos Basin in Jurassic period.
, Available online , doi: 10.31035/cg2021005
Abstract:
The Nan Suture and Sukhothai Arc Terrane are products of the eastward subduction of the Paleotethyan Ocean during the Late Carboniferous to Triassic. However, their footprints in northwestern Laos are poorly constrained. New geochronological and geochemical data presented in this study demonstrate a Late Permian origin for the andesitic rocks from the B.Xiengnou area rather than Late Triassic. The breccia-bearing andesitic tuff from the B.On ultramafic complex yield a zircon U-Pb age of 260 ± 1.4 Ma, geochemically displaying a MORB-like signature. The andesitic tuff from the B.Kiophoulan-B.Houayhak belt gave the U-Pb age of 254 ± 1.3 Ma, with arc-like geochemical affinity. By combining geochronological and geochemical data from the Nan Suture and Sukhothai Arc Terrane, the authors suggest that the andesitic rocks from the B.On ultramafic complex formed in a back-arc basin background, which connected the Jinghong and Nan back-arc basin during the Permian; while the andesitic tuff from the B.Kiophoulan-B.Houayhak belt erupted in the Sukhothai continental island arc setting.
The Nan Suture and Sukhothai Arc Terrane are products of the eastward subduction of the Paleotethyan Ocean during the Late Carboniferous to Triassic. However, their footprints in northwestern Laos are poorly constrained. New geochronological and geochemical data presented in this study demonstrate a Late Permian origin for the andesitic rocks from the B.Xiengnou area rather than Late Triassic. The breccia-bearing andesitic tuff from the B.On ultramafic complex yield a zircon U-Pb age of 260 ± 1.4 Ma, geochemically displaying a MORB-like signature. The andesitic tuff from the B.Kiophoulan-B.Houayhak belt gave the U-Pb age of 254 ± 1.3 Ma, with arc-like geochemical affinity. By combining geochronological and geochemical data from the Nan Suture and Sukhothai Arc Terrane, the authors suggest that the andesitic rocks from the B.On ultramafic complex formed in a back-arc basin background, which connected the Jinghong and Nan back-arc basin during the Permian; while the andesitic tuff from the B.Kiophoulan-B.Houayhak belt erupted in the Sukhothai continental island arc setting.
, Available online , doi: 10.31035/cg2021004
Abstract:
The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area, central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks, which are closely related to the early tectonic evolution of the Earth. However, its formation era, sedimentary filling sequence, and geotectonic characteristics have always been in dispute. In this study, several rhyolitic tuffaceous slate interlayers with a centimeter-level thickness were found in the previously determined Heishan Formation of the Dongchuan Group located to the western part of Yimen-Luoci fault zone. This paper focuses on the study of the rhyolitic tuffaceous slate in Qifulangqing Village, Tongchang Township, Yimen County. LA-ICP-MS zircon dating was conducted, achieving the crystallization age of magma of 2491 ± 15 Ma (MSWD = 1.19, n = 31) and the metamorphic ages of about 2.3 Ga, 2.0 Ga, and 1.8 Ga for the first time. Meanwhile, according to in-situ Hf isotope analysis, the zircon εHf(t) values were determined to range from -3.0 to 7.6, with an average of 2.7. Furthermore, the first-stage Hf model age (TDM1) was determined to be 2513−2916 Ma, indicating that the provenance of the rhyolitic tuffaceous slate is the depleted mantle or juvenile crust between the Middle Mesoarchean and the Late Neoarchean. Therefore, it is believed that the strata of the slate were deposited in the Late Neoarchean, instead of the Mesoproterozoic as determined by previous researchers. Accordingly, it is not appropriate to group the strata into the Mesoproterozoic Dongchuan Group. Instead, they should be classified as the Maolu Formation of the Neoarchean Puduhe Group given the lithologic association and regional information. Furthermore, the magma ages of 2491 ± 15 Ma are highly consistent with the eras of the large-scale Late Neoarchean orogenic magmatic activities on the northern margin of the Yangtze Craton, and thus reflect the orogenic process consisting of subduction and collision from Late Neoarchean to Early Paleoproterozoic. The magmatic activities during this period were possibly caused by the convergence of the supercontinent Kenorland. Meanwhile, the metamorphic ages of 2.3 Ga, 2.0 Ga, and 1.8 Ga are highly consistent with three metamorphic ages of 2.36 Ga, 1.95 Ga, and 1.85 Ga of the northern margin of the Yangtze Craton, indicating that the strata experienced Paleoproterozoic tectonic-thermal events. The study area is located on the eastern margin of Qinghai-Tibet Plateau, and thus was possibly re-transformed by magmatism subjected to the subduction of the Meso-Tethys Ocean during the Early Cretaceous. The discoveries made in this study will provide strong petrological and chronological evidence for analyzing the early crustal evolution of the Yangtze block.
The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area, central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks, which are closely related to the early tectonic evolution of the Earth. However, its formation era, sedimentary filling sequence, and geotectonic characteristics have always been in dispute. In this study, several rhyolitic tuffaceous slate interlayers with a centimeter-level thickness were found in the previously determined Heishan Formation of the Dongchuan Group located to the western part of Yimen-Luoci fault zone. This paper focuses on the study of the rhyolitic tuffaceous slate in Qifulangqing Village, Tongchang Township, Yimen County. LA-ICP-MS zircon dating was conducted, achieving the crystallization age of magma of 2491 ± 15 Ma (MSWD = 1.19, n = 31) and the metamorphic ages of about 2.3 Ga, 2.0 Ga, and 1.8 Ga for the first time. Meanwhile, according to in-situ Hf isotope analysis, the zircon εHf(t) values were determined to range from -3.0 to 7.6, with an average of 2.7. Furthermore, the first-stage Hf model age (TDM1) was determined to be 2513−2916 Ma, indicating that the provenance of the rhyolitic tuffaceous slate is the depleted mantle or juvenile crust between the Middle Mesoarchean and the Late Neoarchean. Therefore, it is believed that the strata of the slate were deposited in the Late Neoarchean, instead of the Mesoproterozoic as determined by previous researchers. Accordingly, it is not appropriate to group the strata into the Mesoproterozoic Dongchuan Group. Instead, they should be classified as the Maolu Formation of the Neoarchean Puduhe Group given the lithologic association and regional information. Furthermore, the magma ages of 2491 ± 15 Ma are highly consistent with the eras of the large-scale Late Neoarchean orogenic magmatic activities on the northern margin of the Yangtze Craton, and thus reflect the orogenic process consisting of subduction and collision from Late Neoarchean to Early Paleoproterozoic. The magmatic activities during this period were possibly caused by the convergence of the supercontinent Kenorland. Meanwhile, the metamorphic ages of 2.3 Ga, 2.0 Ga, and 1.8 Ga are highly consistent with three metamorphic ages of 2.36 Ga, 1.95 Ga, and 1.85 Ga of the northern margin of the Yangtze Craton, indicating that the strata experienced Paleoproterozoic tectonic-thermal events. The study area is located on the eastern margin of Qinghai-Tibet Plateau, and thus was possibly re-transformed by magmatism subjected to the subduction of the Meso-Tethys Ocean during the Early Cretaceous. The discoveries made in this study will provide strong petrological and chronological evidence for analyzing the early crustal evolution of the Yangtze block.
, Available online , doi: 10.31035/cg2020052
Abstract:
The Cenozoic basalts with OIB-affinity in northern marginal region of the North China Craton are thought to experience minor even no crustal contamination during the magma evolution. The whole-rock Sr-Nd-Pb-Hf isotopes are attributed to a two-component mixing between depleted and enriched mantle sources, while the major element variations are controlled by the fractional crystallization of olivine and clinopyroxene. However, in this study, our new Os isotopic data proposes an opposite model for the Cenozoic basalts in northern marginal region of the North China Craton. In this model, the Jining basalts were contaminated by the Archean mafic rocks during the magma storage and ascent. The crustal contamination process is supported by (1) the highly radiogenic Os isotopic compositions, and (2) the positive correlation between 187Os/188Os and 1/Os of the Jining basalts. By modeling the Os isotopic composition of the basalts, an incorporation of < 10% mafic granulites/amphibolites to the parental magma can successfully explain the initial values of highly radiogenic Os. In contrast, the unradiogenic and uniform Os isotopic compositions of the Chifeng basalts suggest negligible crustal contamination. Os isotopic data acts as an indicator of crustal contamination during magma evolution, providing us a novel insight into the evolution of the intra-continental OIB-like basalts worldwide.
The Cenozoic basalts with OIB-affinity in northern marginal region of the North China Craton are thought to experience minor even no crustal contamination during the magma evolution. The whole-rock Sr-Nd-Pb-Hf isotopes are attributed to a two-component mixing between depleted and enriched mantle sources, while the major element variations are controlled by the fractional crystallization of olivine and clinopyroxene. However, in this study, our new Os isotopic data proposes an opposite model for the Cenozoic basalts in northern marginal region of the North China Craton. In this model, the Jining basalts were contaminated by the Archean mafic rocks during the magma storage and ascent. The crustal contamination process is supported by (1) the highly radiogenic Os isotopic compositions, and (2) the positive correlation between 187Os/188Os and 1/Os of the Jining basalts. By modeling the Os isotopic composition of the basalts, an incorporation of < 10% mafic granulites/amphibolites to the parental magma can successfully explain the initial values of highly radiogenic Os. In contrast, the unradiogenic and uniform Os isotopic compositions of the Chifeng basalts suggest negligible crustal contamination. Os isotopic data acts as an indicator of crustal contamination during magma evolution, providing us a novel insight into the evolution of the intra-continental OIB-like basalts worldwide.
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