The sub-continental lithosphere mantle(SCLM)represents a mechanical barrier that separate the convecting mantle from the exosphere,and possesses the ability to sequester and release volatiles,making it an integral par...The sub-continental lithosphere mantle(SCLM)represents a mechanical barrier that separate the convecting mantle from the exosphere,and possesses the ability to sequester and release volatiles,making it an integral part in deep volatile cycling.Here we explore the SCLM in modulating F and Cl cycling through a case study from the Early Cretaceous Dabeigou basalts in the North China Craton(NCC).These lavas are associated with decratonization of the NCC,a process involving significant removal and replacement of the ancient SCLM.The Dabeigou basalts,characterized by arc magma-like trace element signatures,evolved initial^(87)Sr/^(86)Sr(0.70574–0.70578),ε_(Nd)(t)(-11.2–-11.1),andε_(Hf)(t)(-13.7–-13.4)values,along with high Fe/Mn ratios,Ni contents,andδ^(18)O values(5.8‰–6.8‰)of olivine phenocrysts,are compatible with their origination from a veined,pyroxene-rich source formed through the infiltration and interaction of hydrous silicate melts from the subducting Pacific slabs with ambient SCLM.Olivine-hosted melt inclusions of the Dabeigou basalts have compositions similar to the whole rocks,indicating that they record pre-eruptive melt compositions forming the whole rocks.The melt inclusions exhibit high F(1371–2316 ppm)and moderate Cl(688–900 ppm)contents,with high F/Cl ratios of 2.1±0.3(1σ).The F and Cl signatures of the Dabeigou basalts are different from those of typical arc magmas,which are commonly characterized by high Cl contents(median of~1200 ppm)and low F/Cl ratios(<1).The observed differences can be attributed to chromatographic reaction that fractionates elements of different compatibility in the metasomatic agents,with amphibole as the main mineral phase for fractionating and preserving F and Cl.That is,amphibole crystallization prefers to retain F rather than Cl,making the metasomes in vein enriched in F and exhibiting elevated F/Cl ratios compared to original metasomatic agents.It is further suggested that the scenario inferred from the Dabeigou basalts might be common for crystallization of hydrous minerals during chromatographic metasomatism,which causes significant heterogeneity with respect to F and Cl in the SCLM,and might have played a crucial role in regulating F and Cl cycling within the SCLM environments.展开更多
The diverse clam shrimp Nestoria-Keratestheria fauna is widely distributed in the Dabeigou Formation in northern Hebei and eastern Inner Mongolia of China. Its important component genus Magumbonia from the Dabeigou Fo...The diverse clam shrimp Nestoria-Keratestheria fauna is widely distributed in the Dabeigou Formation in northern Hebei and eastern Inner Mongolia of China. Its important component genus Magumbonia from the Dabeigou Formation in the Luanping Basin, northern Hebei, China, is revised on the basis of a scanning electron microscope （SEM） examination of the type species M.jingshangensis Wang, 1984, which revealed morphological features not recognized previously. These include coarse reticulation on the umbo and prominent growth lines ornamented with densely spaced, small tubercles and fine lirae.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.42288201,42003029,42322203,42303027,and 42073034)。
文摘The sub-continental lithosphere mantle(SCLM)represents a mechanical barrier that separate the convecting mantle from the exosphere,and possesses the ability to sequester and release volatiles,making it an integral part in deep volatile cycling.Here we explore the SCLM in modulating F and Cl cycling through a case study from the Early Cretaceous Dabeigou basalts in the North China Craton(NCC).These lavas are associated with decratonization of the NCC,a process involving significant removal and replacement of the ancient SCLM.The Dabeigou basalts,characterized by arc magma-like trace element signatures,evolved initial^(87)Sr/^(86)Sr(0.70574–0.70578),ε_(Nd)(t)(-11.2–-11.1),andε_(Hf)(t)(-13.7–-13.4)values,along with high Fe/Mn ratios,Ni contents,andδ^(18)O values(5.8‰–6.8‰)of olivine phenocrysts,are compatible with their origination from a veined,pyroxene-rich source formed through the infiltration and interaction of hydrous silicate melts from the subducting Pacific slabs with ambient SCLM.Olivine-hosted melt inclusions of the Dabeigou basalts have compositions similar to the whole rocks,indicating that they record pre-eruptive melt compositions forming the whole rocks.The melt inclusions exhibit high F(1371–2316 ppm)and moderate Cl(688–900 ppm)contents,with high F/Cl ratios of 2.1±0.3(1σ).The F and Cl signatures of the Dabeigou basalts are different from those of typical arc magmas,which are commonly characterized by high Cl contents(median of~1200 ppm)and low F/Cl ratios(<1).The observed differences can be attributed to chromatographic reaction that fractionates elements of different compatibility in the metasomatic agents,with amphibole as the main mineral phase for fractionating and preserving F and Cl.That is,amphibole crystallization prefers to retain F rather than Cl,making the metasomes in vein enriched in F and exhibiting elevated F/Cl ratios compared to original metasomatic agents.It is further suggested that the scenario inferred from the Dabeigou basalts might be common for crystallization of hydrous minerals during chromatographic metasomatism,which causes significant heterogeneity with respect to F and Cl in the SCLM,and might have played a crucial role in regulating F and Cl cycling within the SCLM environments.
基金supported by the Project of China Geological Survey (No.1212010610421)the Major Basic Research Projects of the Ministry of Science and Technology,China (National 973 Project No.2006CB701403)+3 种基金the National Natural Science Foundation of China (No.40572005,40632010,J0630967)JSPS Fellowship (ID No.L09522)State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing (No.073106,20082103) (SKLPS)The SEM micrographs were taken through the courtesy of the LEO 1530 VP facility of SKLPS.
文摘The diverse clam shrimp Nestoria-Keratestheria fauna is widely distributed in the Dabeigou Formation in northern Hebei and eastern Inner Mongolia of China. Its important component genus Magumbonia from the Dabeigou Formation in the Luanping Basin, northern Hebei, China, is revised on the basis of a scanning electron microscope （SEM） examination of the type species M.jingshangensis Wang, 1984, which revealed morphological features not recognized previously. These include coarse reticulation on the umbo and prominent growth lines ornamented with densely spaced, small tubercles and fine lirae.
