Journal Article

The Western Segment of the Precambrian Suture Between the Yangtze and Cathaysia Blocks: Constraints From Magnetotelluric Data in Southwest China

Chen, Chaojian, Yang, Xin, Xu, Shan, Sun, Heping, Hu, Xiangyun

2023

Overview

The western segment of the suture zone between the Yangtze and Cathaysia blocks, which is the most important tectonic boundary related to the formation and rifting of south China, is enigmatic and not fully understood due to the sporadic exposure of Precambrian strata and ophiolites. Three‐dimensional electrical resistivity models derived from inversion of magnetotelluric data identified a lithospheric‐scale conductive zone extending northeastwards beneath the Youjiang basin, which was interpreted as the western segment of the suture zone. The high conductivity and coincident high magnetic anomalies closely match the location of Carlin‐type gold deposits, which can be explained by fluids and gold‐bearing sulfide minerals in a fossil suture zone. Inconsistent with the southeast‐dip resolved at the eastern segment of the suture zone (the Jiangshan‐Shaoxing fault) in the earlier study, the slightly north‐dipping geometry at the western suture zone implies the reactivation by northward subduction and closure of the Paleo‐Tethys Ocean. Plain Language Summary Suture zones are tectonic scars that mark the subduction, collision, and amalgamation of different tectonic units. Imaging suture zones is critical because they are first‐order tectonic boundaries and can play a guiding role in continental rifting and breakup. The suture zone between the Yangtze and Cathaysia blocks is the most important tectonic boundary in south China. While the eastern segment of this suture zone is agreed to be located along the Jiangshan‐Shaoxing fault, the western segment of this suture zone is under debate. This study used magnetotelluric method to image the deep earth structure beneath the western boundary of the Yangtze and Cathaysia blocks. We identified a high‐conductivity zone from the subsurface to a depth of 80 km and interpreted this zone as being caused by fluids and gold‐bearing sulfide minerals in a fossil suture zone. The conductivity pattern observed in this suture zone differs from that in the earlier study about the eastern segment of the suture zone. This implies that the western suture zone has been modified after the initial collision of the two continents, perhaps by northward subduction and closure of the Paleo‐Tethys Ocean. Key Points Magnetotelluric array data were inverted to obtain the lithospheric resistivity structure in southwestern China Three‐dimensional resistivity model images a Precambrian suture beneath the Youjiang basin The geometry resolved at the suture zone implies the reactivation by northward subduction and closure of the Paleo‐Tethys Ocean

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Dipping / Earth structure / Electrical resistivity / Fluids / Fossils / Gold / Magnetic anomalies / Magnetotelluric methods / Minerals / Oceans / Ophiolites / Paleoceanography / Precambrian / Rifting / Segments / Subduction / Subduction (geology) / Sulphides / Tectonics