Evidence for the Superposition of Tectonic Systems in the Northern Songliao Block, NE China, Revealed by a 3‐D Electrical Resistivity Model. Issue 4 (3rd April 2022)

• Record Type: Journal Article
• Authors: Wang, Tianqi; Ma, Guoqing; Comeau, Matthew J.; Becken, Michael; Zhou, Zikun; Liu, Wenyu; Kang, Jianqiang; Han, Jiangtao
• Is Part Of: Journal of geophysical research. Volume 127:Issue 4(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-04-03
• Subjects: Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB022827
• Languages: English
• ISSNs: 2169-9313

Abstract

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. Plain Language Summary: The Songliao Block, Northeast China, which contains the Songliao Basin region that is rich in energy resources, is known to have a complex history of formation. In order to understand the influence of the surrounding tectonic environment on the Songliao Block, we collected magnetotelluric measurements, which can determine the electrical properties of underground structures. These measurements allowed us to build a three‐dimensional electrical resistivity model, to depths of 60 km, in the north of the Songliao Block. Analysis of the model showed various low‐resistivity features with different explanations: upper‐crustal features correlated with a network of fault systems and rift basins; mid‐lower crustal features were attributed to melts; a deep feature was interpreted to be a mantle upwelling near the center of the Songliao Block. Combined with evidence from other geophysical and geological studies, we proposed that the superposition of past tectonic systems may have produced weak tectonic zones and increased subsurface heating. The deep structure of the Songliao block is important to understand because it can help to track the source of energy resources and facilitate the development of energy exploration. Key Points: A 3‐D electrical resistivity model of the subsurface beneath the northern Songliao Block was generated from 138 magnetotelluric sites Low‐resistivity features are attributed to rift and fault systems, mid‐lower crustal partial melts, and an asthenospheric upwelling Past tectonic events, for example, collisions of blocks due to ocean closures, may have produced weak zones allowing for the ascent of melt