Different Characteristics Between Syntectonic Magmatic Flow And Magmatic Intrusion In An Intracontinental Setting

Granitic magma plays a vital role in the formation of the continent.In recent years,geologists have done a lot of researches on the structural geology and fundamental tectonic framework of the Yanshan tectonic belt in the northern part of North China Craton.However,there are few studies on the dynamic environment of the emplacement of granite.In this thesis,Daguangding granodiorite and Panshan granite in the northern margin of the North China Craton have been selected as the main research objects.Through field geological investigations and lab analysis,two different rock masses have been analyzed in terms of structure,minerals and petrologic genesis.The difference of the two granitic plutons,combined with electron probe experimental analysis,mineralogical characteristics analysis,temperature and pressure conditions of the Daguangding rock mass during magmatic flow process have been evaluated.And then tectonic environment under different dynamic background in the northern North China has been discussed.The Daguangding granodiorite has the same deformation characteristics on the outcrop scale.The fold axis dips in low-angle to the north,and the dark minerals such as amphibole and biotite are oriented,parallel to the long axis of the inclusion and fold axis.Parallel to the flow surface,the dark-colored mineral such as hornblende and biotite on the microscopic scale have obvious directional alignment characteristics,and the mineral particles do not undergo plastic deformation,showing a rock mass formed by magmatic flow.The ductile shear deformation developed at the late stage and on the plutonic edges.In the Panshan granitic pluton,under the microscopic scale,the mineral arrangement in the Panshan rock mass has no directional characteristics,and it is a granitic body intruded in a stable intracontinental environment.The marble produced by the thermal contact around the pluton and the contact zone between the rock mass and the surrounding rock is not deformed.The inclusion body in the rock mass are also not deformed,and the emplaced rock mass is hardly subjected to regional compression.According to the analysis of mineralogical characteristics,the minerals in thenorthern part of the Daguangding rock mass first crystallize,and the magma flows to the south.Due to the influence of the late hydrothermal fluid,the mineral composition changes,while the edge of the Panshan rock mass crystallizes first,and the central part of the rock mass crystallizes.In the process of upward emplacement,the composition begins to change.The crystallization pressure of the hornblende in the Daguangding mass is estimated to be 3.62~5.64 kbar using hornblende all-aluminum pressure thermalmetry and the emplacement depth is 12.86~22.99 km.It is crystallized in the upper crust and the middle crust.During the Late Paleozoic period,tectonic magma flow occurred in the northern margin of North China,and the lower crust material flowed from north to south.During the period of 320-300 Ma,the lower crust remelted in the middle to the lower part of the northern margin of North China,and flows horizontally within the earth's crust,forming a large light-topped rock mass with magma flow.The Early Mesozoic magma of the Panshan rock mass in the northern margin of the North China Craton was formed during the transition from compression deformation to relatively quiet period after intense cratonic reactivation.