From Subduction to LLSVP: The Core‐Mantle Boundary Heterogeneities Across North Atlantic. (4th January 2022)

• Record Type: Journal Article
• Authors: Fan, An; Sun, Xinlei; Zhang, Zhou; Zhang, Peng; Zong, Jianye
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 23:Number 1(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-04
• Subjects: Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2021GC009879
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: The distribution of Ultra‐low Velocity Zones (ULVZs) is generally associated with the Large Low Shear Velocity Zones (LLSVPs). However, subducted slabs may be important for the characteristics of the ULVZs as well. Here we use ScS precursor (SdS) and postcursor (ScscS) phases, as well as Scd phases recorded by USArray to investigate the lowermost mantle structure across the north Atlantic, which spans the African LLSVP and the subducted Farallon slab. Our results show a ULVZ located near the edge of the African LLSVP, with thicknesses ranging from 11–16 km and S wave velocity reductions of 12%–24%. At the same time, a thin high‐velocity layer (HVL) with thicknesses of 20–30 km, Vs increases of 3%–4%, is also detected outside the LLSVP in the northwest region. Further west there is a clear D" layer at 250 km above the core mantle boundary (CMB), overlaid by a low velocity layer with Vs reduction of 3%. This transition profile from D" to HVL to ULVZ provides an excellent opportunity for us to understand the heterogeneities near the CMB region. We propose that interactions between the subducted Farallon slab with ambient mantle and LLSVP material, together with thermal effects, may result in this transition between different seismic structures along the CMB. Key Points: A structural transition from D" layer to a high‐velocity layer and Ultra‐low Velocity Zones is found from mid‐Atlantic to the northwest boundary of the African Large Low Shear Velocity Zones (LLSVP) These core mantle boundary heterogeneities are very likely from interactions of paleo‐subducted Farallon slab with ambient mantle and LLSVP material The low velocity layer at the top of D" discontinuity may be caused by compositional change from subducted slab