The Yunmeng Shan metamorphic core complex （MCC） is composed of the lower plate, the upper plate and the detachment zone. The detachment zone consists of ductile shear zone （mylonite zone）, chloritized microbreccia...The Yunmeng Shan metamorphic core complex （MCC） is composed of the lower plate, the upper plate and the detachment zone. The detachment zone consists of ductile shear zone （mylonite zone）, chloritized microbreccias zone and the brittle fault plane. The ductile shear zone contains mylonitic rocks, protomylonites, and mylonites. Finite strain measurements of feldspar porphyroclasts from those rocks using the Rf/φ method show that the strain intensities increase from mylonitic rocks （Es=0.66-0.72） to protomylonites （Es=0.66-0.83）, and to mylonites （Es=0.71-1.2）. The strain type is close to flatten strain. Kinematic vorticity estimated by Polar Mohr diagrams suggest that foliations and lineation of mylonite （0.47〈Wk〈0.85） record a bulk simple-dominated general shearing at the initial evolution stage of the Yunmeng Shan MCC＇s detachment zone; and the extensional crenulation cleavage（ecc） （0.34〈Wk〈0.77） recorded a bulk pure-dominated general shearing at the later stage of the evolution. Kinematic vorticity measurements also show that the Yunmeng Shan MCC detachment zone is a result of a combination of simple-dominated general shearing caused by crustal extension at the early stage and pure-dominated general shearing caused by MCC uplifting at the late stage. The ductile thinning estimated by finite strain measurements and estimation of Kinematic vorticity ranges from 52% to 82%, which is the minimum thining estimation. Our studies provide new evidence for mechanisms of the Yunmeng Shan MCC detachement zone.展开更多
The studies on the paleo-fluid in the OrdovicianeSilurian detachment zone in the MiddleeUpper Yangtze area focus on the origin of highdensity methane inclusions and the evolution process of formation pressure,but rare...The studies on the paleo-fluid in the OrdovicianeSilurian detachment zone in the MiddleeUpper Yangtze area focus on the origin of highdensity methane inclusions and the evolution process of formation pressure,but rarely deal with the significance of paleo-fluid to shale gas preservation.In this paper,the relationship between fracture formation and detachment zone was analyzed by observing the OrdovicianeSilurian outcrops in western HunaneHubei area and by investigating the geological characteristics of fracture veins in the drilling cores.Then,the significance of paleo-fluid forming environment and detachment zone to shale gas preservation was studied by using inclusion compositions of fracture veins and homogenization temperature test data.Finally,accumulationedispersion modes of shale gas in the detachment zone were established.The following results were obtained.First,the detachment zone is lithologically composed of silicite with intercalated shale at the OrdovicianeSilurian interface.In the detachment zone,rocks are broken and small crumples are developed.The conjugate-vertical joints are relatively developed in the silicite above and below the detachment zone.Second,multi-stage and multi-type inclusions,especially the aqueous inclusions,are developed in the veins of the detachment zone.Third,the infiltration depth of ancient meteoric water along the detachment zone in the study area is over 4000 m.High-density overpressure methane inclusions were captured in the detachment zone during early stage,while normal-pressure methane and nitrogen inclusions were captured during late stage.Fourth,the ionic constituents of inclusions recording the fluid activity during the late stage was characterized by high sodium-chloride coefficient,high desulfurization coefficient and low metamorphic coefficient,and it is indicated that the sealing capacity of the shale in the detachment zone gets worse.Fifth,the accumulation and dispersion of shale gas in the detachment zone within the study area is divided into three modes,i.e.,syncline,broad anticline and closed anticline.In conclusion,the detachment zone in the study area is permeable.Synclines and closed anticlines developed in detachment structures are unfavorable for the accumulation of shale gas,while broad anticlines are favorable.展开更多
The Sonid Zuoqi ductile detachment zone is located at the southeastern margin of the Central Asian orogenic belt(CAOB),striking EW and dipping to the S.The major rock type of the Sonid Zuoqi ductile detachment zone is...The Sonid Zuoqi ductile detachment zone is located at the southeastern margin of the Central Asian orogenic belt(CAOB),striking EW and dipping to the S.The major rock type of the Sonid Zuoqi ductile detachment zone is mylonite derived from granite.The sequence of mylonite features is:(1)S and C foliations of mylonite,and(2)extensional crenulation cleavage(ecc)or C′and the kinematic vorticity(Wk)value changed from 0.70 to 0.95 and from 0.37 to 0.69,respectively;the strain type of the mylonites within the Sonid Zuoqi ductile detachment zone is compressional to planar strain.The strong deformation mylonite and Halatu plutons yielded a zircon U-Pb age of 244 Ma and a zircon(U-Th)/He age of 214 Ma,respectively.Based on the strain and kinematic vorticity analysis,together with the zircon U-Pb and zircon(U-Th)/He ages and the regional tectonic background,the study area experienced three stage evolution:tangential simpleshear(244 Ma),simple-shear-dominated general shear represented by upper crustal extension(224 Ma)and pure-shear-dominated general shear represented by the Halatu pluton doming(214 Ma),which constrained the early Mesozoic NE-SW crustal extension at the southeastern margin of the CAOB.This NE-SW extension probably originated from the postorogenic extensional collapse of the CAOB,subsequent exhumation being controlled by the far afield effects of the closure of the Mongol-Okhotsk belt.展开更多
The present-day observable tectonic framework of the ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic belts in the Dabie-Sulu region was dominantly formed by an extensional process, mostly between 200 and 1...The present-day observable tectonic framework of the ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic belts in the Dabie-Sulu region was dominantly formed by an extensional process, mostly between 200 and 170 Ma, following the Triassic collision between the Sino-Korean and Yangtze cratons. The framework that controls the present spatial distribution of UHP and HP metamorphic rocks in particular displays the typical features of a Cordilleran-type metamorphic core complex, in which at least four regional-scale, shallow-dipping detachment zones are recognized. Each of these detachment zones corresponds to a pressure gap of 0.5 to 2.0 GPa. The detachment zones separate the rocks exposed in the region into several petrotectonic units with different P-T conditions. The geometry and kinematics of both the detachment zones and the petrotectonic units show that the exhumation of UHP and HP metamorphic rocks in the Dabie-Sulu region was achieved, at least in part, by non-coaxial ductile flow in the multi-layered detachment zones, and by coaxial vertical shortening and horizontal stretching in the metamorphic units, under amphibolite- to greenschist-facies conditions, and in an extensional regime. All ductile extensional deformations occurred at depths below 10 to 15 km, i.e. below the brittle/ductile deformation transition.展开更多
The Waziyu metamorphic core complex is situated at the eastern end of the Yanshan tectonic belt.The NNE-striking detachment ductile shear zone in the core complex lies between the Archean metamorphic basement and Fuxi...The Waziyu metamorphic core complex is situated at the eastern end of the Yanshan tectonic belt.The NNE-striking detachment ductile shear zone in the core complex lies between the Archean metamorphic basement and Fuxin-Yixian rift basin,dips NW gently,and shows corrugation folds.Exposure structures,microstructures,and quartz C-axis fabrics all indicate top-to-the WNW sense of shear,i.e.,ca.285°,for the shear zone.Estimates of the deformation temperatures(ca.550-250°C) demonstrate its mid-crustal origination and progressive deformation from deep to shallow levels.The northern segment of the shear zone shows relatively weak exhumation with exposures of low-temperature mylonites whereas its middle and southern segments have more intense uplifting with exposures of high-temperature mylonites.Biotite and muscovite 40 Ar/39 Ar ages,U-Pb dating results of zircon from dikes and plutons as well as formation ages of the supra-detachment basin all suggest the formation time of 135-100 Ma for the core complex.The formation was also associated with syntectonic emplacement of the Early Cretaceous Shishan pluton.The western margin of the core complex was truncated by the Sunjiawan-Shaohuyingzi brittle normal fault when it uplifted to shallow crust levels,and finally exhumed to near-surface levels.The core complex was developed by the rolling-hinge model under WNW-ESE extension during the Early Cretaceous peak destruction of the North China Craton.Ductile flow did not appear in the lower plate,therefore not supporting the low-crust gravitational collapse.展开更多
The Queshan MCC is an important example of a crustal extensional structure in the eastern Jiaodong Peninsula along the southeastern margin of the NCC in the Early Cretaceous. The MCC is a typical Cordilleran-type core...The Queshan MCC is an important example of a crustal extensional structure in the eastern Jiaodong Peninsula along the southeastern margin of the NCC in the Early Cretaceous. The MCC is a typical Cordilleran-type core complex with a three-layered structure:(1) the upper plate is constituted by the Cretaceous supradetachment basin and Paleoproterozoic basement;(2) the lower plate comprises the Neoarchean high-grade metamorphic complexes and late Mesozoic granitic intrusions; and(3) the two plates are separated by a master detachment fault. A series of late NEN-oriented brittle faults superimposed on and destructed the early MCC. Petrology, geometry, kinematics, macro- and micro-structures and quartz c-axis fabrics imply that the MCC has a progressive exhumation history from middle-lower to subsurface level(via middle-upper crustal level) under the nearly WNW-ESE regional extensional regime. We present structural and geochronological evidence to constrain the exhumation of the Queshan MCC from ca. 135 to 113 Ma. Based on the comprehensive analysis of the different patterns of extensional structures in the Jiaodong and Liaodong Peninsula, we have defined the Jiao-Liao Early Cretaceou extensional province and further divided the crustal extension of it into two stages: the first stage was the intense flow of the middle-lower crust and the second stage was the extension of the middle-upper crust. Combining the tectonic setting, the lithosphere thinning in the Jiao-Liao Early Cretaceous extensional province can be considered a typical model for the response of crust-mantle detachment faulting under regional extension in East Asia.展开更多
基金supported by National Natural Science Foundation of China(Grant No.41102129,90714006 and 41002073)the foundation of Fundamental Science on Radioactive Geology and Exploration Technology Laboratory,East China Institute of Technology(Grant No.REGT1207)+1 种基金the Deep Exploration Technology and Experimentation Program of China(Grant No.SinoProbe-08-01-03)projects of China Geological Survey(1212011120135,1212010611803,1212011085474,1212011085473)
文摘The Yunmeng Shan metamorphic core complex （MCC） is composed of the lower plate, the upper plate and the detachment zone. The detachment zone consists of ductile shear zone （mylonite zone）, chloritized microbreccias zone and the brittle fault plane. The ductile shear zone contains mylonitic rocks, protomylonites, and mylonites. Finite strain measurements of feldspar porphyroclasts from those rocks using the Rf/φ method show that the strain intensities increase from mylonitic rocks （Es=0.66-0.72） to protomylonites （Es=0.66-0.83）, and to mylonites （Es=0.71-1.2）. The strain type is close to flatten strain. Kinematic vorticity estimated by Polar Mohr diagrams suggest that foliations and lineation of mylonite （0.47〈Wk〈0.85） record a bulk simple-dominated general shearing at the initial evolution stage of the Yunmeng Shan MCC＇s detachment zone; and the extensional crenulation cleavage（ecc） （0.34〈Wk〈0.77） recorded a bulk pure-dominated general shearing at the later stage of the evolution. Kinematic vorticity measurements also show that the Yunmeng Shan MCC detachment zone is a result of a combination of simple-dominated general shearing caused by crustal extension at the early stage and pure-dominated general shearing caused by MCC uplifting at the late stage. The ductile thinning estimated by finite strain measurements and estimation of Kinematic vorticity ranges from 52% to 82%, which is the minimum thining estimation. Our studies provide new evidence for mechanisms of the Yunmeng Shan MCC detachement zone.
基金supported by the National Major Science and Technology Project“Study on high-mature shale gas occurrence mechanism and enriching law in Middle Yangtze region”(No.:2016ZX05034-001-002)the Foundation Project of China Geological Survey“Investigation and evaluation of shale gas resources in Wuling and Western Hunan-Hubei area”(No.:12120114049801).
文摘The studies on the paleo-fluid in the OrdovicianeSilurian detachment zone in the MiddleeUpper Yangtze area focus on the origin of highdensity methane inclusions and the evolution process of formation pressure,but rarely deal with the significance of paleo-fluid to shale gas preservation.In this paper,the relationship between fracture formation and detachment zone was analyzed by observing the OrdovicianeSilurian outcrops in western HunaneHubei area and by investigating the geological characteristics of fracture veins in the drilling cores.Then,the significance of paleo-fluid forming environment and detachment zone to shale gas preservation was studied by using inclusion compositions of fracture veins and homogenization temperature test data.Finally,accumulationedispersion modes of shale gas in the detachment zone were established.The following results were obtained.First,the detachment zone is lithologically composed of silicite with intercalated shale at the OrdovicianeSilurian interface.In the detachment zone,rocks are broken and small crumples are developed.The conjugate-vertical joints are relatively developed in the silicite above and below the detachment zone.Second,multi-stage and multi-type inclusions,especially the aqueous inclusions,are developed in the veins of the detachment zone.Third,the infiltration depth of ancient meteoric water along the detachment zone in the study area is over 4000 m.High-density overpressure methane inclusions were captured in the detachment zone during early stage,while normal-pressure methane and nitrogen inclusions were captured during late stage.Fourth,the ionic constituents of inclusions recording the fluid activity during the late stage was characterized by high sodium-chloride coefficient,high desulfurization coefficient and low metamorphic coefficient,and it is indicated that the sealing capacity of the shale in the detachment zone gets worse.Fifth,the accumulation and dispersion of shale gas in the detachment zone within the study area is divided into three modes,i.e.,syncline,broad anticline and closed anticline.In conclusion,the detachment zone in the study area is permeable.Synclines and closed anticlines developed in detachment structures are unfavorable for the accumulation of shale gas,while broad anticlines are favorable.
基金supported by the National Natural Science Foundation of China(Grant No.41662014)。
文摘The Sonid Zuoqi ductile detachment zone is located at the southeastern margin of the Central Asian orogenic belt(CAOB),striking EW and dipping to the S.The major rock type of the Sonid Zuoqi ductile detachment zone is mylonite derived from granite.The sequence of mylonite features is:(1)S and C foliations of mylonite,and(2)extensional crenulation cleavage(ecc)or C′and the kinematic vorticity(Wk)value changed from 0.70 to 0.95 and from 0.37 to 0.69,respectively;the strain type of the mylonites within the Sonid Zuoqi ductile detachment zone is compressional to planar strain.The strong deformation mylonite and Halatu plutons yielded a zircon U-Pb age of 244 Ma and a zircon(U-Th)/He age of 214 Ma,respectively.Based on the strain and kinematic vorticity analysis,together with the zircon U-Pb and zircon(U-Th)/He ages and the regional tectonic background,the study area experienced three stage evolution:tangential simpleshear(244 Ma),simple-shear-dominated general shear represented by upper crustal extension(224 Ma)and pure-shear-dominated general shear represented by the Halatu pluton doming(214 Ma),which constrained the early Mesozoic NE-SW crustal extension at the southeastern margin of the CAOB.This NE-SW extension probably originated from the postorogenic extensional collapse of the CAOB,subsequent exhumation being controlled by the far afield effects of the closure of the Mongol-Okhotsk belt.
基金This study was supported by the Key State Basic Research Development Project grant G1999075506the National Natural Science Foundation of China grants 49794041,49972067 and 49772146the former Ministry of Geology and Mineral Resources Project No.9501102.
文摘The present-day observable tectonic framework of the ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic belts in the Dabie-Sulu region was dominantly formed by an extensional process, mostly between 200 and 170 Ma, following the Triassic collision between the Sino-Korean and Yangtze cratons. The framework that controls the present spatial distribution of UHP and HP metamorphic rocks in particular displays the typical features of a Cordilleran-type metamorphic core complex, in which at least four regional-scale, shallow-dipping detachment zones are recognized. Each of these detachment zones corresponds to a pressure gap of 0.5 to 2.0 GPa. The detachment zones separate the rocks exposed in the region into several petrotectonic units with different P-T conditions. The geometry and kinematics of both the detachment zones and the petrotectonic units show that the exhumation of UHP and HP metamorphic rocks in the Dabie-Sulu region was achieved, at least in part, by non-coaxial ductile flow in the multi-layered detachment zones, and by coaxial vertical shortening and horizontal stretching in the metamorphic units, under amphibolite- to greenschist-facies conditions, and in an extensional regime. All ductile extensional deformations occurred at depths below 10 to 15 km, i.e. below the brittle/ductile deformation transition.
基金supported by National Natural Science Foundation of China (Grant Nos. 90714004,40828001,41072162)
文摘The Waziyu metamorphic core complex is situated at the eastern end of the Yanshan tectonic belt.The NNE-striking detachment ductile shear zone in the core complex lies between the Archean metamorphic basement and Fuxin-Yixian rift basin,dips NW gently,and shows corrugation folds.Exposure structures,microstructures,and quartz C-axis fabrics all indicate top-to-the WNW sense of shear,i.e.,ca.285°,for the shear zone.Estimates of the deformation temperatures(ca.550-250°C) demonstrate its mid-crustal origination and progressive deformation from deep to shallow levels.The northern segment of the shear zone shows relatively weak exhumation with exposures of low-temperature mylonites whereas its middle and southern segments have more intense uplifting with exposures of high-temperature mylonites.Biotite and muscovite 40 Ar/39 Ar ages,U-Pb dating results of zircon from dikes and plutons as well as formation ages of the supra-detachment basin all suggest the formation time of 135-100 Ma for the core complex.The formation was also associated with syntectonic emplacement of the Early Cretaceous Shishan pluton.The western margin of the core complex was truncated by the Sunjiawan-Shaohuyingzi brittle normal fault when it uplifted to shallow crust levels,and finally exhumed to near-surface levels.The core complex was developed by the rolling-hinge model under WNW-ESE extension during the Early Cretaceous peak destruction of the North China Craton.Ductile flow did not appear in the lower plate,therefore not supporting the low-crust gravitational collapse.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41430211, 90814006 & 91214301)Doctoral Foundation of Ministry of Education of China (Grant No. 20110022130001)
文摘The Queshan MCC is an important example of a crustal extensional structure in the eastern Jiaodong Peninsula along the southeastern margin of the NCC in the Early Cretaceous. The MCC is a typical Cordilleran-type core complex with a three-layered structure:(1) the upper plate is constituted by the Cretaceous supradetachment basin and Paleoproterozoic basement;(2) the lower plate comprises the Neoarchean high-grade metamorphic complexes and late Mesozoic granitic intrusions; and(3) the two plates are separated by a master detachment fault. A series of late NEN-oriented brittle faults superimposed on and destructed the early MCC. Petrology, geometry, kinematics, macro- and micro-structures and quartz c-axis fabrics imply that the MCC has a progressive exhumation history from middle-lower to subsurface level(via middle-upper crustal level) under the nearly WNW-ESE regional extensional regime. We present structural and geochronological evidence to constrain the exhumation of the Queshan MCC from ca. 135 to 113 Ma. Based on the comprehensive analysis of the different patterns of extensional structures in the Jiaodong and Liaodong Peninsula, we have defined the Jiao-Liao Early Cretaceou extensional province and further divided the crustal extension of it into two stages: the first stage was the intense flow of the middle-lower crust and the second stage was the extension of the middle-upper crust. Combining the tectonic setting, the lithosphere thinning in the Jiao-Liao Early Cretaceous extensional province can be considered a typical model for the response of crust-mantle detachment faulting under regional extension in East Asia.
