3D magnetotelluric inversion reveals the superposition of tectonic
systems in the northern Songliao Basin
Abstract
The creation and evolution of the Songliao Basin is closely related to
the closure of the Paleo-Asian Ocean and the Mongolia-Okhotsk Ocean, and
the subduction of the Paleo-Pacific Ocean. In an attempt to demonstrate
the various attributes of the lithospheric structure under structural
superimposition and transformation of the Songliao Basin, this work used
full impedance 3D inversion to obtain a 3D electrical structural model
of the northern Songliao Basin for the first time. The results showed
there are NE-trending high-resistance anomalies and sporadic
low-resistance anomalies at the depth of less than 10 km. At 15-30 km,
there are several NE- and NW-trending high-conductivity anomalies and
there is a large area of SN-oriented high conductor at 50 km. The
outcomes of the investigation demonstrate: 1) The high-resistance
anomalies found in the NE direction of the upper crust are consistent
with the position of the volcanic rocks predicted by the reflection
earthquake, whereas the low-resistance anomalies correspond to the
distribution of shallow faults and rifts. They constitute the main
components of the upper crust of the Songliao Basin; 2) The high
conductivity anomalies occurring at the intersection of the central
depression zone and the north plunge zone represent the thinnest
position of the lithosphere in the Songliao Basin; 3) The high-conductor
anomalies in crust-mantle can be attributed to the paleo-shear zones
which were generated in the collage of micro-continents during the
Paleo-Asian Ocean closure, and reactivated under the continuous
transformation of the Mongolia-Okhotsk and the Paleo-Pacific tectonic
systems in the later period.