Late Carboniferous to Early Permian A-type granites are extensively distributed throughout the West Junggar region, NW China, and the Akebasitao pluton is extremely distinguished among these plutons. In this paper, we...Late Carboniferous to Early Permian A-type granites are extensively distributed throughout the West Junggar region, NW China, and the Akebasitao pluton is extremely distinguished among these plutons. In this paper, we reported new anisotropy of magnetic susceptible (AMS) data combine with detailed field study and audio magnetotelluric (AMT) sounding to assess the three-dimensional shape and magmatic emplacement mechanism of the Akebasitao pluton. The geological features and the AMT sounding indicate that the pluton had a slightly oblique movement of magma from northwest to southeast, which was most likely to correspond to an asymmetrical torch with a laccolith-shaped upper part, and a lower part formed by sub-vertical "root" that was located within its northwestern part, probably controlled by the NE-trending Anqi fault. The AMS fabrics of all the specimens reveal a low Pj value (mean of 1.02) and a low T value (mean of -0.024), suggesting that the deformation of the AMS ellipsoid is relatively weak. The specimens exhibit both oblate and prolate shapes of the AMS ellipsoid. Magnetic lineations and foliations are randomly distributed throughout the pluton without any preferred orientation. These AMS patterns indicate that the pluton formed in a relatively stable structural environment with no regional extrusion. Therefore, we propose a complex emplacement process in which the magmas reached the shallower crust levels via deep-faults and subsequently occupied the room created by doming, accompanied by stoping near the pluton roof. Additionally, the regional tectonic setting was relatively stable during the emplacement of the Akebasitao pluton, indicating the termination of compressional orogeny during the late Late Carboniferous in the West Junggar region. This conclusion perfectly coincides with the regional tectonic paleogeography, magmatic system, and paleostress field.展开更多
The forming time of the Yangtze River Three Gorges is considered as one of keys in the research on the Yangtze River,also is one of the most disputed hotspots.In order to solve the difficult problem,the authors adopt ...The forming time of the Yangtze River Three Gorges is considered as one of keys in the research on the Yangtze River,also is one of the most disputed hotspots.In order to solve the difficult problem,the authors adopt the internationally recognized thoughts and methods of substance tracing from source to sink.The lithologic characteristics,magnetic parameters and magnetic mineral characteristics of deposits in 2 bores are analyzed,which are both sampled from the sedimentary center of the Jianghan Plain.The results are as follows:At about 110 m depth of the core,the contents of coarse materials and stable magnetic mineral both increase significantly.Meanwhile,the magnetic susceptibility of sediment,saturation isothermal remanent magnetization and magnetic susceptibility values of anhysteretic remanent magnetism increase suddenly,which all reflect that at about 110 m depth,the important adjustment has appeared in water system of the Jianghan Plain,and the sedimentary environment and material composition have changed greatly.And it may be the horizon where the Yangtze River Three Gorges formed,its forming time reflected by the paleomagnetic dating is between 1.17 and 1.12Ma B.P.展开更多
基金funded by the China Geological Survey(Grant Nos.1212011120502,1212011220245)
文摘Late Carboniferous to Early Permian A-type granites are extensively distributed throughout the West Junggar region, NW China, and the Akebasitao pluton is extremely distinguished among these plutons. In this paper, we reported new anisotropy of magnetic susceptible (AMS) data combine with detailed field study and audio magnetotelluric (AMT) sounding to assess the three-dimensional shape and magmatic emplacement mechanism of the Akebasitao pluton. The geological features and the AMT sounding indicate that the pluton had a slightly oblique movement of magma from northwest to southeast, which was most likely to correspond to an asymmetrical torch with a laccolith-shaped upper part, and a lower part formed by sub-vertical "root" that was located within its northwestern part, probably controlled by the NE-trending Anqi fault. The AMS fabrics of all the specimens reveal a low Pj value (mean of 1.02) and a low T value (mean of -0.024), suggesting that the deformation of the AMS ellipsoid is relatively weak. The specimens exhibit both oblate and prolate shapes of the AMS ellipsoid. Magnetic lineations and foliations are randomly distributed throughout the pluton without any preferred orientation. These AMS patterns indicate that the pluton formed in a relatively stable structural environment with no regional extrusion. Therefore, we propose a complex emplacement process in which the magmas reached the shallower crust levels via deep-faults and subsequently occupied the room created by doming, accompanied by stoping near the pluton roof. Additionally, the regional tectonic setting was relatively stable during the emplacement of the Akebasitao pluton, indicating the termination of compressional orogeny during the late Late Carboniferous in the West Junggar region. This conclusion perfectly coincides with the regional tectonic paleogeography, magmatic system, and paleostress field.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 90411005,40472151and40672206)the National Basic Research Program of China (Grant No. 2004CB720204)
文摘The forming time of the Yangtze River Three Gorges is considered as one of keys in the research on the Yangtze River,also is one of the most disputed hotspots.In order to solve the difficult problem,the authors adopt the internationally recognized thoughts and methods of substance tracing from source to sink.The lithologic characteristics,magnetic parameters and magnetic mineral characteristics of deposits in 2 bores are analyzed,which are both sampled from the sedimentary center of the Jianghan Plain.The results are as follows:At about 110 m depth of the core,the contents of coarse materials and stable magnetic mineral both increase significantly.Meanwhile,the magnetic susceptibility of sediment,saturation isothermal remanent magnetization and magnetic susceptibility values of anhysteretic remanent magnetism increase suddenly,which all reflect that at about 110 m depth,the important adjustment has appeared in water system of the Jianghan Plain,and the sedimentary environment and material composition have changed greatly.And it may be the horizon where the Yangtze River Three Gorges formed,its forming time reflected by the paleomagnetic dating is between 1.17 and 1.12Ma B.P.
