Vastly Different Heights of LLVPs Caused by Different Strengths of Historical Slab Push. Issue 17 (3rd September 2022)

• Record Type: Journal Article
• Authors: Yuan, Qian; Li, Mingming
• Is Part Of: Geophysical research letters. Volume 49:Issue 17(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-03
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL099564
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Two large low velocity provinces (LLVPs) are observed in Earth's lower mantle, beneath Africa and the Pacific Ocean, respectively. The maximum height of the African LLVP is ∼1, 000 km larger than that of the Pacific LLVP, but what causes this height difference remains unclear. LLVPs are often interpreted as thermochemical piles whose morphology is greatly controlled by the surrounding mantle flow. Seismic observations have revealed that while some subducted slabs are laterally deflected at ∼660–1, 200 km, other slabs penetrate into the lowermost mantle. Here, through geodynamic modeling experiments, we show that rapid sinking of stagnant slabs to the lowermost mantle can cause significant height increases of nearby thermochemical piles. Our results suggest that the African LLVP may have been pushed more strongly and longer by surrounding mantle flows to reach a much shallower depth than the Pacific LLVP, perhaps since the Tethys slabs sank to the lowermost mantle. Plain Language Summary: Seismic observations have revealed the two large low velocity provinces (LLVPs) beneath Africa and the Pacific Ocean in Earth's lowest mantle. Growing evidence indicates that the maximum height of the African LLVP is up to ∼1, 000 km taller than that of the Pacific LLVP, but the underlying cause of such a large difference in height remains uncertain. Geodynamic modeling studies have shown that the morphology of LLVPs is greatly controlled by their interactions with surrounding mantle flow which is mainly driven by subduction of cold slabs. Seismic observations have shown that while some subducted slabs flatten or stagnate at ∼660–1, 200 km, other slabs arrive at the deepest mantle. With geodynamic modeling experiments, we show that catastrophic sinking of subducted slabs into the lower mantle can cause strong upwelling flows that in turn greatly increase the height of nearby LLVP‐like piles, while other piles can be less affected. This work suggests that the African LLVP may be enduring stronger nearby mantle flow to rise by the slab‐driven surrounding mantle flow than the Pacific LLVP. The African LLVP may start rising since the sinking of the Tethys slabs to the lowermost mantle. Key Points: Continuous sinking of voluminous subducted slabs to the lower mantle can push nearby large low velocity province (LLVP)‐like piles to rise significantly Episodic large increase of height is only possible for piles that are nearly neutrally buoyant and are relatively unstable The African LLVP may have been strongly pushed by the Tethys slabs and reach a much larger height than the Pacific LLVP