摘要
Unlike most Precambrian cratons that have thick sub-continental lithospheric roots,the Archean lithosphere beneath the North China Craton is thin (reduced from 200 km to about 80 km),and has been replaced by a geochemically juvenile lithospheric mantle.This is a unique regional geological event,which has attracted worldwide attention.In the North China Block,Late Mesozoic extensional tectonics is evident by low-angle detachment faults,syntectonic plutons bounded by ductile faults,metamorphic core complexes (MCC) and widespread Jurassic to Cretaceous half-grabens filled by continental terrigenous deposits and volcanic rocks.At a regional scale,these structures share the same NW-SE extensional direction,while maintaining their own individual kinematics.In other words,the MCC feature a top-to-the-NW sense of shear,and syntectonic plutons are typified by a top-to-the-SE shearing deformations.Geochronological results indicate that the extensional structures were formed between 130-120 Ma.These extensional events lead to magmatic rock emplacement,distributed at the footwall of the detachment faults.Two different exhumation stages can be identified based on regional structural and magmatic interpretation:a Jurassic slow or negligible exhumation and a Cretaceous fast one assisted by normal faulting.These two cooling stages correspond to distinct geodynamic processes that occurred during the Jurassic and Cretaceous.Extensional tectonics appear to have been insignificant before the Early Cretaceous,and the process may be demonstrated by partial melting of the crust.The second stage,dominated by an extensional regime,developed after ca 120 Ma,and is tentatively correlated with crustal extension caused by lithospheric removal of the North China Craton.
Unlike most Precambrian cratons that have thick sub-continental lithospheric roots,the Archean lithosphere beneath the North China Craton is thin （reduced from 200 km to about 80 km）,and has been replaced by a geochemically juvenile lithospheric mantle.This is a unique regional geological event,which has attracted worldwide attention.In the North China Block,Late Mesozoic extensional tectonics is evident by low-angle detachment faults,syntectonic plutons bounded by ductile faults,metamorphic core complexes （MCC） and widespread Jurassic to Cretaceous half-grabens filled by continental terrigenous deposits and volcanic rocks.At a regional scale,these structures share the same NW-SE extensional direction,while maintaining their own individual kinematics.In other words,the MCC feature a top-to-the-NW sense of shear,and syntectonic plutons are typified by a top-to-the-SE shearing deformations.Geochronological results indicate that the extensional structures were formed between 130-120 Ma.These extensional events lead to magmatic rock emplacement,distributed at the footwall of the detachment faults.Two different exhumation stages can be identified based on regional structural and magmatic interpretation：a Jurassic slow or negligible exhumation and a Cretaceous fast one assisted by normal faulting.These two cooling stages correspond to distinct geodynamic processes that occurred during the Jurassic and Cretaceous.Extensional tectonics appear to have been insignificant before the Early Cretaceous,and the process may be demonstrated by partial melting of the crust.The second stage,dominated by an extensional regime,developed after ca 120 Ma,and is tentatively correlated with crustal extension caused by lithospheric removal of the North China Craton.
基金
supported by the Innovative Project of the Chinese Academy of Sciences (Grant No. KZCX2-YW-Q05-05-03)
the National Natural Science Foundation of China (Grants Nos. 90714007,40872142)
