Emplacement Mechanism And Tectonic Significance Of The Late Triassic Laocheng And Yanzhiba Granitic Pluton In South Qinling

The origin, formation and dynamic background of late Triassic granites in Qinling orogeny belt is still controversy, there are different understandings, such as subduction, syn-collision and post-collision, and the views of pluton’s emplacement mechanism are contradictory, existing understanding of compression and extensiona. This paper obtains from the perspective of granite pluton structure, Choose Laocheng and Yanzhiba pluton located in the central of Qinling orogenic belt, Conducted the comprehensive research the internal fabric characteristics of pluton to illustrate the emplacement process and mechanism of pluton. The results show that the the magnetic fabric of Laocheng pluton is mainly from the contribution of MD magnetite and paramagnetic minerals, can be used to reflect the characteristics of the internal fabric of pluton. The characteristics of internal fabric of Laocheng pluton (AMS) shows regularity obviously, the magnetic foliation shows the irregular concentric rings, magnetic lineation plunge to west in low angle. The features of macro, micro structure and scalar value of magnetic fabric all shows that the magnetic foliation and lineation of Laocheng pluton are obtain in the early stage of its magmatic emplacement and cooling. The magnetic fabric of Yanzhiba pluton is mainly controlled by paramagnetic minerals, can be used to reflect the features of the pluton’s internal fabric, accurately. The general features of magnetic fabric in Yanzhiba pluton is magnetic lineation plunge to west in middle-low angle and magnetic foliation dip to south or north. The features of macro, micro structure and scalar value of magnetic fabric all shows that the magnetic foliation and lineation of Yanzhiba pluton are formed on the stage of magma emplacement. Combined with regional tectonic indicate that the features of internal fabric in Laocheng and Yanzhiba pluton are consistent with regional shear strike-slip tectonic phase of late Triassic collision orogeny. The emplacement of two plutons are on the late stage of collision orogeny.