Deep Electrical and Crustal Structures of the Raohe Complex

Abstract:

The Raohe complex is located on the eastern Center Asian Orogenic Belt, which is belong to the Nadanhada terrane being the Chinese part of the Mino-Sikhote-Alin. The raohe complex contains a typical accretionary complex related to Paleo-Pacific plate subduction accretion. Their affinity, evolution and contact relationship is highly controversial. Although its petrology, isotope chronology have a large number of studies, the magnetotelluric researches are seldom.To better understand their tectonic nature, the influence of Paleo-Pacific plate subduction on them, magnetotelluric (MT) investigation was carried out with site spacing of 500m cross through the Raohe complex. The two-dimensional (2-D) inversion modeling in TM modes is used to determine the electrical structure.

The study shows that Raohe Complex has many discontinuous high resistivity bodies increasing gradually from west to east in the upper crust. The Pelagic sediments has the high resistivity bodies with different occurrences, and the intrusive rocks and Ultramafic-mafic rocks has the stable high resistivity body, which having obvious thrust characteristics from east to west. The nappe structure was caused by the multi-stage subduction of the paleo pacific plate. There are the east inclined high conductors in the upper crust, a continuous low resistivity layer in the lower crust and the upper mantle, a local high resistance in the lower crust. There are many factors causing high conductivity, considering the exposed surface Cenozoic basalts, we believe that the upwelling of mantle derived materials is most likely.Since Cenozoic, the subduction of the Pacific plate turned to roll back, further causing back arc spreading of the Japan Sea. Then mantle derived material upwelling to the upper crust along deep faults in the Raohe complex in the compressional tectonic stress environment.