Investigating flat-slab subduction underneath South America using 4D numerical simulations

Flat Subduction;Craton;South America;Along-trench angle variation;numerical simulations;Nazca Plate;trench

Hermosillo, Armando ; Liu ; Lijun

关键词: Flat Subduction;    Craton;    South America;    Along-trench angle variation;    numerical simulations;    Nazca Plate;    trench;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/49663/Armando_Hermosillo.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The Nazca Plate recycling underneath South America is an ideal example of modern subduction, which provides an opportunity to study mechanisms of flat-slab subduction and the nature of mantle seismic structures. Subduction occurring at this location is characterized by along-trench variation from flat- to steep-dipping slabs, as indicated by both seismic images and geological observations. First, we will quantitatively investigate several earlier proposed conceptual mechanisms for flat-slab subduction along the South American trench. Another target of this study is to better understand the seismic structure under South America, where existing seismic imaging results including studies of seismicity distribution and tomographic inversions still show significant discrepancies. We therefore attempt to provide more constraints on the actual mantle structure by comparing different seismic images with our 4D subduction model predictions. We use forward data-assimilation models to simulate Nazca subduction from 80 Ma to the present day.The models incorporate the age of the oceanic lithosphere, kinematic plate motions through time, geometry of plate boundaries including that of the South American trench, as well as thick cratons within the continent. Preliminary results do show flat subduction and an overall match with present day tomography images within the upper ~1000 km depth. However, the fit to mantle seismic images and slab angle variation still need further improvements. Future models will progressively assimilate more realistic subduction geometry including extended trench lines to the north and over-thickened oceanic crust (oceanic plateaus or aseismic ridges) for a better prediction of mantle structures.