The Thrust Deformation Of Pluton

The author analyzes the thrust deformation features of the Jinfosi pluton in the eastern Jiuquan Basin which were controlled by the effect of later regional structure, based on investigating the field deformation features and interpreting the seismic profiles which passed the pluton, and finds that Jinfosi pluton had been distorted many times, especially in the long-distance effect of the collision between India plate and Eurasian plate in Neogene Period, the pluton, which formed in the late Caledonian, experienced fierce distortion and controlled the deformation and deposit of northeastern Yiner depression. This is different to predecessors' opinions that the large-scale Jinfosi pluton, rooted from deep earth, was similar to a perpendicularly fixed sphenoid of large scale, and the thrust action of Qilianshan had been blocked here.The author finds that Jinfosi pluton had been distorted four times since it has been refrigerated from Silurian Period, based on investigating the field deformation features and studying the geological history of the pluton. The first event of the distortion was happened in the period between last stage of Silurian Period and Devonian Period. The second was happened in last stage of Triassic Period. The third was happened in the period between last stage of Cretaceous Period and the forepart of Paleogene Period. The fourth was happened in Neogene Period. And the author will detailedly discuss Cenozoic deformation of the pluton in this paper.During Neogene Period, the area of Jinfosi pluton had been unitarily thrust from south to north because of the thrust action of large scale, and formed a thrust structure with three different layers: upper layer, middle layer, and down layer. The pluton, which was the middle deformation layer, was controlled by a main thrust fault with a middle-angle, and developed a series of secondary thrust faults and many fault-propagation folds. The average distance of thrust is 14.2km, based on interpreting the time migration data and depth migration data. The author considers that Jinfosi thrust belt was a typical deformation of basement-involved compressive deformation by comparing the feature of Jinfosi thrust belt with the deformation feature of typical thrust belt, and presents basic deformation mode of the pluton.The fourth event of the distortion was happened in Neogene Period, for granite and the stratums after paleogene Baiyang river series had been entangled into the fold at the profile of Qilian community, and the stratums of N- Q₃ under theâ‘ main thrust fault had a feeble phenomena of growth stratum in seismic profiles.In the northeast of the pluton, there is a Cenozoic foreland sag with some thrust faults, controlled byâ‘ main thrust fault, which shows the deformation of Yiner depression has not been weakened, based on interpreting the time migration data and depth migration data. It also shows the pluton had covered a large-scale fault basin of Mesozoic, which greatly enlarges the area of exploring gas and oil. The structural shape of Mesozoic and Cenozoic stratums under the main thrust fault was fault-propagation fold, which promotes the prospect of oil and gas exploration in this area.