合肥盆地位于华北板块东南缘,形成于华南、华北板块碰撞过程中。合肥盆地形成时表现为大别造山带向北逆冲形成的前陆挠曲盆地,早白垩世在区域伸展背景下转变为断陷盆地。中侏罗统圆筒山组是合肥盆地前陆挠曲阶段的沉积地层之一,主要表...合肥盆地位于华北板块东南缘,形成于华南、华北板块碰撞过程中。合肥盆地形成时表现为大别造山带向北逆冲形成的前陆挠曲盆地,早白垩世在区域伸展背景下转变为断陷盆地。中侏罗统圆筒山组是合肥盆地前陆挠曲阶段的沉积地层之一,主要表现为湖泊相沉积,与下伏的防虎山组典型的河流相沉积明显不同。为了获得圆筒山组更详细的物源信息,对肥西地区出露的圆筒山组紫红色粉砂岩开展了碎屑锆石LA-ICP MS U-Pb定年。定年结果显示,两个粉砂岩样品均获得了约2.0Ga和约770 Ma两个主要峰值以及约2.4Ga次要峰值。该特征与扬子板块锆石年龄分布特征几乎完全一致,指示圆筒山组物源应来自扬子板块。考虑到盆地地层的物源不应来自其周边隆起区分水岭的另一侧,因而推测圆筒山组物源应来自张八岭隆起中侏罗世时地表出露岩石。在燕山运动A幕影响下,下扬子地区发生逆冲-褶皱活动,张八岭隆起发生明显隆升,上部岩石被剥蚀殆尽,仅保留现今出露的新元古代张八岭群及肥东杂岩,被剥蚀的岩石搬运沉积于合肥盆地内,形成圆筒山组。展开更多
Two grabens were developed in the Yi-Shu segment of the Tan-Lu fault zone (TLFZ) during its extensional activities, and are now confined by four major NNE-trending normal faults and filled with Cretaceous sediments. T...Two grabens were developed in the Yi-Shu segment of the Tan-Lu fault zone (TLFZ) during its extensional activities, and are now confined by four major NNE-trending normal faults and filled with Cretaceous sediments. These faults were developed due to their reactivities, containing gouge and cutting the graben sediments. Detailed fieldwork demonstrates that the faults experienced sinistral transtensional moment related to regional NE-SW extension during the reactivity. X-ray diffraction (XRD) analysis of the finest gouge samples gives illite crystallinity values higher than 0.42°Δ2θ, indicating temperatures experienced by the gouge samples were less than 150°C. From the relation between K-Ar data and proportions of detrital illite in different size fractions of the gouge samples, we conclude that refaulting for the western boundary fault of the TLFZ, abbreviated to F4, took place at ca. 90 Ma and for the eastern boundary fault, abbreviated to F1, happened from 70 to 60 Ma. During the two phases of reactivity imposed by the same NE-SW extension, the TLFZ experienced uplifting and no sediments were deposited in the two grabens. It is suggested that the TLFZ experienced extension during the Late Cretaceous, which supports the inference that lithospheric thinning was still undergoing in the east of the North China Craton during the Late Cretaceous magmatic hiatus.展开更多
大别造山带内部零星出露有浅变质岩,其与造山带其他单元内高级变质岩的共生状态可以为造山带的演化过程提供信息。北大别单元东北缘沈桥地区出露有浅变质岩。为了获取该浅变质岩的形成时间、物源信息及与北大别单元岩石之间的接触关系,...大别造山带内部零星出露有浅变质岩,其与造山带其他单元内高级变质岩的共生状态可以为造山带的演化过程提供信息。北大别单元东北缘沈桥地区出露有浅变质岩。为了获取该浅变质岩的形成时间、物源信息及与北大别单元岩石之间的接触关系,在详细的野外观察基础上,对出露于沈桥地区的浅变质岩进行了详细的显微鉴定和碎屑锆石LA-ICP MS U-Pb定年。研究发现,沈桥地区浅变质岩具有与佛子岭群诸佛庵岩组一致的岩石学特征,碎屑锆石的最小年龄为431 Ma,年龄频谱特征与佛子岭群变沉积岩一致,表明沈桥地区浅变质岩为佛子岭群的一部分。显微鉴定表明,沈桥变沉积岩中石英动态重结晶型式均表现为完全的亚颗粒旋转(SGR)重结晶,黑云母具有明显的生长边,表明在其形成过程中曾经历了绿帘—角闪岩相变质—变形事件;变沉积岩在露头上显示的韵律层在沉积岩原岩形成时就已经存在,之后经过浅变质作用,岩石中的矿物相发生了改变:原岩中的泥质层变质为颜色较深的层状黑云母,砂质层变质为颜色较浅的动态重结晶石英。展开更多
The Hongzhen metamorphic core complex is situated in the Yangtze plate to the east of the Dabie oro- genic belt. Its ductile detachment zone in the foot wall overprints on the metamorphic complex of the Proterozoic Do...The Hongzhen metamorphic core complex is situated in the Yangtze plate to the east of the Dabie oro- genic belt. Its ductile detachment zone in the foot wall overprints on the metamorphic complex of the Proterozoic Dongling Group. The present profile of the ductile shear zone with consistent SW-dipping mineral elongation lineation shows antiform and reversed S-shape from northeast to southwest respectively. Exposure structures, microstructures and quartz C-axis fabric all indicate top-to-SW movement for the ductile shear zone. Recrystallisation types of quartz and feldspar in the mylonites demonstrate that the shear zone was developed under the amphibolite facies condition and at mid-crust levels. The metamorphic core complex formed in the Early Cretaceous with a muscovite plateau age of 124.8±1.2 Ma. Regional NE-SW extension along a SW-dipping, gentle detachment zone was responsible for formation of the core complex. Intrusion of the Hongzhen granite with a biotite plateau age of 124.8±1.2 Ma rendered the ductile shear zone curved, uplifted and final localization of the core complex. The Hongzhen metamorphic core complex suggests that the Early Cretaceous magma- tism in this region took place under the condition of regional extension and the eastern Yangtze plate also experienced lithospheric thinning.展开更多
基金中国地质调查局发展研究中心课题“安徽省宣城矿集区深部找矿预测”(编号:DD2019057004)安徽省公益性地质工作项目“1∶50000洪镇(H50 E 009012)+1 种基金安庆市幅(H50 E 009013)深部矿产地质调查”(编号:2023-g-1-3)国家自然科学基金项目“数据驱动与相似度推理知识嵌入的可扩展岩石图像识别研究”(编号:42372342)联合资助。
文摘合肥盆地位于华北板块东南缘,形成于华南、华北板块碰撞过程中。合肥盆地形成时表现为大别造山带向北逆冲形成的前陆挠曲盆地,早白垩世在区域伸展背景下转变为断陷盆地。中侏罗统圆筒山组是合肥盆地前陆挠曲阶段的沉积地层之一,主要表现为湖泊相沉积,与下伏的防虎山组典型的河流相沉积明显不同。为了获得圆筒山组更详细的物源信息,对肥西地区出露的圆筒山组紫红色粉砂岩开展了碎屑锆石LA-ICP MS U-Pb定年。定年结果显示,两个粉砂岩样品均获得了约2.0Ga和约770 Ma两个主要峰值以及约2.4Ga次要峰值。该特征与扬子板块锆石年龄分布特征几乎完全一致,指示圆筒山组物源应来自扬子板块。考虑到盆地地层的物源不应来自其周边隆起区分水岭的另一侧,因而推测圆筒山组物源应来自张八岭隆起中侏罗世时地表出露岩石。在燕山运动A幕影响下,下扬子地区发生逆冲-褶皱活动,张八岭隆起发生明显隆升,上部岩石被剥蚀殆尽,仅保留现今出露的新元古代张八岭群及肥东杂岩,被剥蚀的岩石搬运沉积于合肥盆地内,形成圆筒山组。
基金Supported by National Natural Science Foundation of China (Grant Nos. 90714004, 40672131)
文摘Two grabens were developed in the Yi-Shu segment of the Tan-Lu fault zone (TLFZ) during its extensional activities, and are now confined by four major NNE-trending normal faults and filled with Cretaceous sediments. These faults were developed due to their reactivities, containing gouge and cutting the graben sediments. Detailed fieldwork demonstrates that the faults experienced sinistral transtensional moment related to regional NE-SW extension during the reactivity. X-ray diffraction (XRD) analysis of the finest gouge samples gives illite crystallinity values higher than 0.42°Δ2θ, indicating temperatures experienced by the gouge samples were less than 150°C. From the relation between K-Ar data and proportions of detrital illite in different size fractions of the gouge samples, we conclude that refaulting for the western boundary fault of the TLFZ, abbreviated to F4, took place at ca. 90 Ma and for the eastern boundary fault, abbreviated to F1, happened from 70 to 60 Ma. During the two phases of reactivity imposed by the same NE-SW extension, the TLFZ experienced uplifting and no sediments were deposited in the two grabens. It is suggested that the TLFZ experienced extension during the Late Cretaceous, which supports the inference that lithospheric thinning was still undergoing in the east of the North China Craton during the Late Cretaceous magmatic hiatus.
文摘大别造山带内部零星出露有浅变质岩,其与造山带其他单元内高级变质岩的共生状态可以为造山带的演化过程提供信息。北大别单元东北缘沈桥地区出露有浅变质岩。为了获取该浅变质岩的形成时间、物源信息及与北大别单元岩石之间的接触关系,在详细的野外观察基础上,对出露于沈桥地区的浅变质岩进行了详细的显微鉴定和碎屑锆石LA-ICP MS U-Pb定年。研究发现,沈桥地区浅变质岩具有与佛子岭群诸佛庵岩组一致的岩石学特征,碎屑锆石的最小年龄为431 Ma,年龄频谱特征与佛子岭群变沉积岩一致,表明沈桥地区浅变质岩为佛子岭群的一部分。显微鉴定表明,沈桥变沉积岩中石英动态重结晶型式均表现为完全的亚颗粒旋转(SGR)重结晶,黑云母具有明显的生长边,表明在其形成过程中曾经历了绿帘—角闪岩相变质—变形事件;变沉积岩在露头上显示的韵律层在沉积岩原岩形成时就已经存在,之后经过浅变质作用,岩石中的矿物相发生了改变:原岩中的泥质层变质为颜色较深的层状黑云母,砂质层变质为颜色较浅的动态重结晶石英。
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40272094 and 40672131)
文摘The Hongzhen metamorphic core complex is situated in the Yangtze plate to the east of the Dabie oro- genic belt. Its ductile detachment zone in the foot wall overprints on the metamorphic complex of the Proterozoic Dongling Group. The present profile of the ductile shear zone with consistent SW-dipping mineral elongation lineation shows antiform and reversed S-shape from northeast to southwest respectively. Exposure structures, microstructures and quartz C-axis fabric all indicate top-to-SW movement for the ductile shear zone. Recrystallisation types of quartz and feldspar in the mylonites demonstrate that the shear zone was developed under the amphibolite facies condition and at mid-crust levels. The metamorphic core complex formed in the Early Cretaceous with a muscovite plateau age of 124.8±1.2 Ma. Regional NE-SW extension along a SW-dipping, gentle detachment zone was responsible for formation of the core complex. Intrusion of the Hongzhen granite with a biotite plateau age of 124.8±1.2 Ma rendered the ductile shear zone curved, uplifted and final localization of the core complex. The Hongzhen metamorphic core complex suggests that the Early Cretaceous magma- tism in this region took place under the condition of regional extension and the eastern Yangtze plate also experienced lithospheric thinning.
