Weak Vertical Surface Movement Caused by the Ascent of the Emeishan Mantle Anomaly

Jiang Zhu,Ronghao Pan,Marc K Reichow,Zhaochong Zhang,Hongbo Li,Wenchang Cai

doi:10.1002/2017jb015058

Abstract

AbstractPrevailing mantle plume models reveal that the roles of plume‐lithosphere interactions in shaping surface topography are complex and controversial, and also difficult to test. The exposed and complete strata in the Emeishan large igneous province (LIP) recorded abundant paleoenvironmental information associated with preeruptions and syneruptions, attracting numerous workers to this province to test these models. Despite intensified research these models are still strongly debated. This study represents an extensive field investigation combining new and previously published data from the Emeishan LIP to further seek information on plume‐induced topographic variations. Our results indicate that there are inconspicuous vertical motions of the surface topography during the ascent of mantle plume, and a significant surface subsidence occurred at the early stage of the volcanism that has a significantly positive correlation with the thickness of local lavas, and the topographic uplift emerged in the late stage of the volcanism. Our studies provide key geological and geochemical evidence that the ascent of the Emeishan plume is unable to drive a significant surface uplift, owing to the plume containing numerous entrained bodies of dense recycled oceanic crust (10–20%) that can significantly reduce plume buoyancy. The significant surface subsidence maybe linked to a significant loss of thermal buoyancy due to the release of heat, which, accompanied by rapid loading of numerous dense erupted lava and a strong lithospheric flexure, also lead to a later synchronous and significant surface subsidence in the Emeishan LIP.

Highlights

Large igneous provinces (LIPs) form as a result of vast outpourings of predominantly basaltic lava onto the Earth’s surface (Bryan & Ernst, 2008), and their formation is linked by many geologists to mantle plume activity (e.g., Richards et al, 1989)
Our results indicate that there are inconspicuous vertical motions of the surface topography during the ascent of mantle plume, and a significant surface subsidence occurred at the early stage of the volcanism that has a significantly positive correlation with the thickness of local lavas, and the topographic uplift emerged in the late stage of the volcanism
The coastal to tidal flat environments recorded in the Emeishan LIP of Liangshan stage (Early Permian) transformed into a shallow sea carbonate platform at the beginning of the Qixia stage

Summary

Introduction

Large igneous provinces (LIPs) form as a result of vast outpourings of predominantly basaltic lava onto the Earth’s surface (Bryan & Ernst, 2008), and their formation is linked by many geologists to mantle plume activity (e.g., Richards et al, 1989). Classic mantle plume models predict that a hot, buoyant plume head should cause kilometer scale surface uplift prior to the onset of volcanic eruptions in these LIPs (Campbell & Griffiths, 1990; Richards et al, 1989; White & McKenzie, 1989). In many LIPs the predicted kilometer scale uplift is difficult to be verified from the geological record or even disputed (e.g., Czamanske et al, 1998). The Emeishan LIP was thought to be the best example of a continental LIP where plume-driven kilometer scale uplift occurred based on supposedly differential erosion from the center to the outer zone of the province and providing strong support for the classic mantle plume model (He et al, 2003, 2006; Xu et al, 2004). Several subsequent investigations revealed prevolcanic subsidence or no to insignificant uplift in the Emeishan LIP, rather than the proposed central kilometer scale lithospheric doming (e.g., Jerram et al, 2016; Sun et al, 2010; Ukstins-Peate et al, 2011; Ukstins-Peate & Bryan, 2008; Wignall et al, 2009; Zhu et al, 2014)

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