Seismic probing of continental subduction zones. (1st September 2017)

• Record Type: Journal Article
• Authors: Zhao, Liang; Xu, Xiaobing; Malusà, Marco G.
• Is Part Of: Journal of Asian earth sciences. Volume 145:Part A(2017)
• Page Start: 37
• Page End: 45
• Publication Date: 2017-09-01
• Subjects: Seismic observations -- Continental subduction -- Ultra-high-pressure rock exhumation -- Mantle deformation -- Slab geometry; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2017.05.026
• Languages: English
• ISSNs: 1367-9120

Abstract

Graphical abstract: Highlights: A summary of seismic observations operated in the known continental UHP terranes worldwide. Most of the continental subduction zones with clear slab image are younger than the Late Cretaceous. Continued subduction slabs and progressive breakoff ones have similar shapes. Abstract: High-resolution images of Earth's interior provide pivotal information for the understanding of a range of geodynamic processes, including continental subduction and exhumation of ultrahigh-pressure (UHP) metamorphic rocks. Here we present a synthesis of available global seismic observations on continental subduction zones, and selected examples of seismic probing from the European Alps, the Himalaya-Tibet and the Qinling-Dabie orogenic belts. Our synthesis and examples show that slabs recognized beneath exhumed continental UHP terranes generally have shallow dip angles (<45°) at depths <100 km, to become much steeper at depths >100 km. Slabs underlined by a clear high velocity anomaly from Earth's surface to the mantle are generally Cenozoic in age. Some of these slabs are continuous, whereas other continental subduction zones are located above discontinuous high velocity anomalies possibly suggesting slab breakoff. The density of seismic stations and the quality of recordings are of primary importance to get high-resolution images of the upper mantle to be used as a starting point to provide reliable geodynamic interpretations. In some cases, areas previously indicated as possible site of slab breakoff, such as the European Alps, have been later proven to be located above a continuous slab by using higher quality travel time data from denser seismic arrays. Discriminating between oceanic and continental slabs can be challenging, but valuable information can be provided by combining teleseismic tomography and receiver function analysis. The upper mantle beneath most continental UHP terranes generally shows complex seismic anisotropy patterns that are potentially preserved even in pre-Cenozoic subduction zones. These patterns can be used to provide information on continental slabs that are no longer highlighted by a clear high-velocity anomaly.