Evidence for the Superposition of Tectonic Systems in the Northern Songliao Block, NE China, Revealed by a 3‐D Electrical Resistivity Model

Abstract

The creation and evolution of the Songliao Block, Northeast China, is believed to be related to the closure of the Paleo‐Asian and Mongol‐Okhotsk oceans, and to the subduction of the Paleo‐Pacific Ocean. Geochemical and geophysical data indicate a complex tectonic history that may have left signatures of the superposition of separate tectonic events. However, the relationship between the current lithospheric structure of the Songliao Block and those tectonic events is not clear. In order to shed light on this question, a three‐dimensional electrical resistivity model of the crust and mantle was generated from 138 magnetotelluric sites. The results show a heterogenous lithosphere with anomalous low‐resistivity zones (∼10 Ω·m). The position of upper‐crustal features (<10 km) correlates with a network of fault systems and rift basins. Based on estimates of high crustal temperatures, mid‐lower crustal features (15–35 km), some of which appear near seismic reflectors, are attributed to partial melts (∼5%) containing moderate‐high water contents (4.5 wt. %). A deep (>45 km) feature is interpreted as an asthenospheric upwelling near the center of the Songliao Block, where seismic evidence indicates a thin lithosphere. It is proposed that the collision, convergence, and suturing of blocks caused by the closure of the Paleo‐Asian Ocean and the bidirectional convergence between the Mongol‐Okhotsk and Paleo‐Pacific Ocean may have produced weak tectonic zones throughout the lithosphere. They provided a structural basis for the later upward movement of fluids and melt, likely due to hydrous upwellings caused by the subduction of the Paleo‐Pacific system.

Insights Into the Structure of the Mongol‐Okhotsk Suture Zone, Adaatsag Ophiolite, and Tectonic Boundaries of the Central Asian Orogenic Belt (Mongolia) From Electrical Resistivity Imaging and Seismic Velocity Models

“…MT data are especially sensitive to the quantity and composition of low-resistivity materials in the subsurface, such as fluids, when they are interconnected (rather than isolated). The MT technique is well-suited to image the structure of fault zones, as well as suture zones and tectonic boundaries, which are regions of deformed and/or weakened and fractured crust due to past tectonic activity (with implications for rheology), in addition to other lithospheric structures (e.g., Heinson et al, 2005;Sheng et al, 2021;Türkoğlu et al, 2008;Wang et al, 2022;Wannamaker et al, 2002Wannamaker et al, , 2008.…”