Mesozoic (125 Ma) Fangcheng basalts from Shandong Province contain clearly zoned olivines that are rare in terrestrial samples and provide first evidence for the replacement of lithospheric mantle from high-Mg peridot...Mesozoic (125 Ma) Fangcheng basalts from Shandong Province contain clearly zoned olivines that are rare in terrestrial samples and provide first evidence for the replacement of lithospheric mantle from high-Mg peridotites to low-Mg per-idotites through peridotite-melt reaction.Zoned olivines have compositions in the core (Mg#=87.2—90.7) similar to those olivines from the mantle peridotitic xenoliths entrained in Ceno-zoic basalts from the North China craton and in the rim (Mg#=76.8—83.9) close to olivine henocrysts of the host basalts (75.7—79.0). These compositional features as well as rounded crystal shapes and smaller grain sizes (30—800 μm) demon-strate that these zoned olivines are mantle xenocrysts, i.e. disag-gregates of mantle peridotites. Their core compositions can represent those of olivines of mantle peridotites. The zoned texture of olivines was formed through rapid reaction between the olivine xenocryst and the host basalt. This olivine-basaltic melt reaction could have been ubiquitous in the Mesozoic lithospheric mantle beneath the North China craton, i.e. an important type of the replacement of lithospheric mantle. The reaction resulted in the transformation of the Paleozoic refractory (high-Mg) peridotites to the late Mesozoic fertile (Iow-Mg) and radiogenic isotope-enriched peridotites, leading to the loss of old lithospheric mantle.展开更多
It has been proposed that the North China Craton(NCC)was thinned up to a thickness of>100 km during the Phanerozoic,and underwent an associated craton destruction.Evidently,it is an important topic worthy of future...It has been proposed that the North China Craton(NCC)was thinned up to a thickness of>100 km during the Phanerozoic,and underwent an associated craton destruction.Evidently,it is an important topic worthy of future study to understanding the mechanism of cratonic destruction and its role played in the continental evolution.After synthesized the global cratons of India,Brazil,South Africa,Siberia,East Europe(Baltic)and North America,we found that lithospheric thinning is common in the cratonic evolution,but it is not always associated with craton destruction.Most cratons was thinned by thermal erosion of mantle plume or mantle upwelling,which,however,may not cause craton destruction.Based on the studies of the North American and North China Cratons,we suggest that oceanic subduction plays an important role in caton destruction.Fluids or melts released by dehydration of the subducted slabs metasomatize the mantle wedge above and trigger extensive partial melting.More importantly,the metasomatized mantle lost its original rigidity and make craton easier to be deformed and then to be destoyed.Therefore,we suggest that the widespread crust-derived granite and large-scale ductile deformation within the continental crust can be regarded as the petrological and structural indicators of craton destruction,respectively.展开更多
This paper presents an overview of recent studies dealing with different ages of mantle peridotitic xenoliths and xenocrysts from the North China Craton, with aim to provide new ideas for further study on the destruct...This paper presents an overview of recent studies dealing with different ages of mantle peridotitic xenoliths and xenocrysts from the North China Craton, with aim to provide new ideas for further study on the destruction of the North China Craton. Re-Os isotopic studies suggest that the lithospheric mantle of the North China Craton is of Archean age prior to its thinning. The key reason why such a low density and highly refractory Archean lithospheric mantle would be thinned is changes in composition, thermal regime, and physical properties of the lithospheric mantle due to interaction of peridotites with melts of different origins. Inward subduction of circum craton plates and collision with the North China Craton provided not only the driving force for the destruction of the craton, but also continuous melts derived from partial melting of subducted continental or oceanic crustal materials that resulted in the compositional change of the lithospheric mantle. Regional thermal anomaly at ca. 120 Ma led to the melting of highly modified lithospheric mantle. At the same time or subsequently lithospheric exten- sion and asthenospheric upwelling further reinforced the melting and thinning of the lithospheric mantle. Therefore, the destruction and thinning of the North China Craton is a combined result of peridotite-melt interaction (addition of volatile), enhanced regional thermal anomaly (temperature increase) and lithospheric extension (decompression). Such a complex geological process finally produced a "mixed" lithospheric mantle of highly chemical heterogeneity during the Mesozoic and Cenozoic. It also resulted in significant difference in the composition of mantle peridotitic xenoliths between different regions and times.展开更多
文摘Mesozoic (125 Ma) Fangcheng basalts from Shandong Province contain clearly zoned olivines that are rare in terrestrial samples and provide first evidence for the replacement of lithospheric mantle from high-Mg peridotites to low-Mg per-idotites through peridotite-melt reaction.Zoned olivines have compositions in the core (Mg#=87.2—90.7) similar to those olivines from the mantle peridotitic xenoliths entrained in Ceno-zoic basalts from the North China craton and in the rim (Mg#=76.8—83.9) close to olivine henocrysts of the host basalts (75.7—79.0). These compositional features as well as rounded crystal shapes and smaller grain sizes (30—800 μm) demon-strate that these zoned olivines are mantle xenocrysts, i.e. disag-gregates of mantle peridotites. Their core compositions can represent those of olivines of mantle peridotites. The zoned texture of olivines was formed through rapid reaction between the olivine xenocryst and the host basalt. This olivine-basaltic melt reaction could have been ubiquitous in the Mesozoic lithospheric mantle beneath the North China craton, i.e. an important type of the replacement of lithospheric mantle. The reaction resulted in the transformation of the Paleozoic refractory (high-Mg) peridotites to the late Mesozoic fertile (Iow-Mg) and radiogenic isotope-enriched peridotites, leading to the loss of old lithospheric mantle.
基金supported by National Natural Science Foundation of China(Grant Nos.41130313 and 91014007)
文摘It has been proposed that the North China Craton(NCC)was thinned up to a thickness of>100 km during the Phanerozoic,and underwent an associated craton destruction.Evidently,it is an important topic worthy of future study to understanding the mechanism of cratonic destruction and its role played in the continental evolution.After synthesized the global cratons of India,Brazil,South Africa,Siberia,East Europe(Baltic)and North America,we found that lithospheric thinning is common in the cratonic evolution,but it is not always associated with craton destruction.Most cratons was thinned by thermal erosion of mantle plume or mantle upwelling,which,however,may not cause craton destruction.Based on the studies of the North American and North China Cratons,we suggest that oceanic subduction plays an important role in caton destruction.Fluids or melts released by dehydration of the subducted slabs metasomatize the mantle wedge above and trigger extensive partial melting.More importantly,the metasomatized mantle lost its original rigidity and make craton easier to be deformed and then to be destoyed.Therefore,we suggest that the widespread crust-derived granite and large-scale ductile deformation within the continental crust can be regarded as the petrological and structural indicators of craton destruction,respectively.
基金Supported by National Natural Science Foundation of China (Grant Nos. 40534022 and 90714008) the Chinese Academy of Sciences (Grant No. KZCX2-YW-103)
文摘This paper presents an overview of recent studies dealing with different ages of mantle peridotitic xenoliths and xenocrysts from the North China Craton, with aim to provide new ideas for further study on the destruction of the North China Craton. Re-Os isotopic studies suggest that the lithospheric mantle of the North China Craton is of Archean age prior to its thinning. The key reason why such a low density and highly refractory Archean lithospheric mantle would be thinned is changes in composition, thermal regime, and physical properties of the lithospheric mantle due to interaction of peridotites with melts of different origins. Inward subduction of circum craton plates and collision with the North China Craton provided not only the driving force for the destruction of the craton, but also continuous melts derived from partial melting of subducted continental or oceanic crustal materials that resulted in the compositional change of the lithospheric mantle. Regional thermal anomaly at ca. 120 Ma led to the melting of highly modified lithospheric mantle. At the same time or subsequently lithospheric exten- sion and asthenospheric upwelling further reinforced the melting and thinning of the lithospheric mantle. Therefore, the destruction and thinning of the North China Craton is a combined result of peridotite-melt interaction (addition of volatile), enhanced regional thermal anomaly (temperature increase) and lithospheric extension (decompression). Such a complex geological process finally produced a "mixed" lithospheric mantle of highly chemical heterogeneity during the Mesozoic and Cenozoic. It also resulted in significant difference in the composition of mantle peridotitic xenoliths between different regions and times.
