Spatial And Temperal Distribution Of Unexposed Permian Igneous Rocks In The Tarim Basin And Model Of Structural-magmatic Activities:

Currently,spatial and temporal distribution of the Tarim Basin Permian Large Igneous Province(LIP)are intensively studied in the edge of the basin,whilst the distribution of the LIP within the basin is poorly known as thick sediments cover the LIP.Recently,the technology of seismic imaging of igneous rocks provides a novel way to observe three-dimensional(3d)geometry and spatial and temporal distribution of igneous intrusions and extrusions in a sedimentary basin.Combined with borehole data,this paper uses systematic 2d and 3d high resolution seismic data from the Tazhong and adjacent area to reveal the spatial and temporal distribution of igneous intrusions and extrusions in the Tarim Basin and its mutual relationship with the structure.Conclusions are as follow:(1)Fault characteristics in the Tazhong and adjacent area are proposed systematically.Based on their structural styles and planar distribution,faults are classified into 5 groups,including NW trending transcompressional faults distributed mainly in the Katake uplift,NE trending detachment faults distributed in the southern slope of the Tazhong,NNE trending strike-slip faults lying in the Katake uplift and in the northern slope of the Tazhong,NNW trending high-angle reverse faults located in the Shuntuoguole low uplift and intrusion-related faults that have a curved shape in plane.These faults have different evolution histories,formation mechanisms and contrast contrains on magmatic activities.(2)Characteristics of seismic reflection of igneous intrusions and extrusions in the Tazhong and adjacent area are identified.The seismic reflections of igneous intrusions are of high amplitude,abrupt terminations,transgression and display a saucer shape.In some cases,the seismic reflections have steps.The seismic reflection of igneous extrusions commonly has a mound shape.Seismic reflections within the mounds downlap the base,and reflections above the mound onlap the top.(3)Quantities of Permian igneous intrusions are revealed in the Tazhong and adjacent area.Their 3d geometries and spatial and temporal distributions are also identified based on seismic reflection data.Geometries of sills can be classified into three types including saucer,planar and concave-upward,among which the saucer is the dominant type.The base of sills is mainly developed along the base of the upper Ordovician strata and the top of sills is terminated within the upper Ordovician strata.Sills are mainly distributed in the north part of the studied area.Deformation of the host rocks indicates that sills were formed primarily in the middle Permian time and secondarily in the latter Permian time.(4)Quantities of Permian igneous extrusions are indentifed in the Tazhong and adjacent.Their geometries and spatial and temporal distribution are also suggested by seismic data.Volcanoes can be divided into shield volcano,eye-shaped volcano and so on.In plane view,volcanoes were aligned along the NW trending transcompressional faults and the NNE trending strike-slip faults.Combined with borehole data,it is concluded that volcanoes are mostly composed of basalt and tuff.The contact relationship between the volcanoes and surrounding strata indicates that volcanoes dominantly formed in the middle Permian time and secondarily in the latter Permian time.(5)The mutual relationship between magmatic activities and structural deformation is revealed.Furthermore a model involving structural-magmatic activities of the Tarim basin and an improved model of formation of saucer-shaped sill are built.Magmatic activities are significantly controlled by structural features.The disconformity at the base of the upper Ordovician acts as emplacement surface that controls the magma emplacement and the 3d geometry of igneous intrusions.Strike-slip faults and transcompressional faults act as magma pathways that control the location of volcanoes.Magmatic activities also impact structural deformations.Cover rocks were uplifted above igneous intrusions and normal faults were formed within the strata above volcanoes.The model of structural-magmatic activities restores the magma emplacement in the Tarim basin in more detail,which improves the current study of Tarim basin Large Igneous Province...