Massive carbon storage in convergent margins initiated by subduction of limestone

Michael W. Förster,Yongsheng Liu,Chunfei Chen,Stephen F. Foley

doi:10.1038/s41467-021-24750-0

Abstract

Remobilization of sedimentary carbonate in subduction zones modulates arc volcanism emissions and thus Earth’s climate over geological timescales. Although limestones (or chalk) are thought to be the major carbon reservoir subducted to subarc depths, their fate is still unclear. Here we present high-pressure reaction experiments between impure limestone (7.4 wt.% clay) and dunite at 1.3–2.7 GPa to constrain the melting behaviour of subducted natural limestone in contact with peridotite. The results show that although clay impurities significantly depress the solidus of limestone, melting will not occur whilst limestones are still part of the subducting slab. Buoyancy calculations suggest that most of these limestones would form solid-state diapirs intruding into the mantle wedge, resulting in limited carbon flux to the deep mantle (< ~10 Mt C y−1). Less than 20% melting within the mantle wedge indicates that most limestones remain stable and are stored in subarc lithosphere, resulting in massive carbon storage in convergent margins considering their high carbon flux (~21.4 Mt C y−1). Assimilation and outgassing of these carbonates during arc magma ascent may dominate the carbon flux in volcanic arcs.

Highlights

Remobilization of sedimentary carbonate in subduction zones modulates arc volcanism emissions and Earth’s climate over geological timescales
Tectonic activity has been invoked as the driver of icehousegreenhouse intervals because variations of volcanic emissions in convergent margins exert considerable control on atmospheric CO2 levels and climate on timescales of millions of years[1,2]
The carbonate dissolution and hydrous melting of carbonate-bearing crustal materials were advocated as two potential pathways for transferring subducted carbon to the mantle wedge at subarc depths[9,10,11]

Summary

Introduction

Remobilization of sedimentary carbonate in subduction zones modulates arc volcanism emissions and Earth’s climate over geological timescales. Less than 20% melting within the mantle wedge indicates that most limestones remain stable and are stored in subarc lithosphere, resulting in massive carbon storage in convergent margins considering their high carbon flux (~21.4 Mt C y−1). Its H2O content is similar to those of subducted marbles (Fig. 1c) These reaction experiments can be used to constrain the melting behaviour of limestone in contact with peridotite at the slab-mantle interface and of limestone diapirs during their rise through the peridotite mantle wedge. The present study suggests that most of these limestones will not melt in subduction zones or in the mantle wedge but will form limestone diapirs that are stored in arc lithosphere in the solid-state, resulting in massive carbon storage in convergent margins

Methods

Results

Conclusion