Melt volume at Atlantic volcanic rifted margins controlled by depth-dependent extension and mantle temperature

Gang Lu,Ritske S Huismans

doi:10.1038/s41467-021-23981-5

Abstract

Breakup volcanism along rifted passive margins is highly variable in time and space. The factors controlling magmatic activity during continental rifting and breakup are not resolved and controversial. Here we use numerical models to investigate melt generation at rifted margins with contrasting rifting styles corresponding to those observed in natural systems. Our results demonstrate a surprising correlation of enhanced magmatism with margin width. This relationship is explained by depth-dependent extension, during which the lithospheric mantle ruptures earlier than the crust, and is confirmed by a semi-analytical prediction of melt volume over margin width. The results presented here show that the effect of increased mantle temperature at wide volcanic margins is likely over-estimated, and demonstrate that the large volumes of magmatism at volcanic rifted margin can be explained by depth- dependent extension and very moderate excess mantle potential temperature in the order of 50–80 °C, significantly smaller than previously suggested.

Highlights

Breakup volcanism along rifted passive margins is highly variable in time and space
Rifted margins in terms of the thickness of early oceanic crust can to first order be characterised with three magmatic modes (Fig. 1). (1) Margins with a sharp transition from the continent-ocean boundary (COB) to normal thickness (4–8 km) magmatic oceanic crust[3,4] can be termed normal-magmatic (Mode 1). (2) Margins where magmatic productivity exceeds that expected from decompression melting at normal mantle temperature, expressed in high volumes of extruded volcanics deposited as seaward-dipping sequences (SDRs), over-thickened intruded continental and oceanic crust and regions of magmatic underplating[11] can be considered excess-magmatic margins (Mode 2). (3) Magma-poor (a-magmatic) margins (Mode 3) have little syn-rift magmatism, in some cases exhibiting a broad zone of exhumed mantle with little to no magmatism at the sea floor preceding formation of mature oceanic crust[12]
By combining forward models and published observations, we provide a new conceptual and quantitative framework explaining the volume of decompression melting accreted to rifted passive margins as a function of margin width and mantle potential temperature

Summary

Introduction

Breakup volcanism along rifted passive margins is highly variable in time and space. The factors controlling magmatic activity during continental rifting and breakup are not resolved and controversial. While a variety of mechanisms, including low mantle potential temperature[13], low spreading rate[3] and counterflow of depleted lithospheric mantle[14,15], have been suggested as an explanation for the absence of magmatism on magma-poor margins, what controls the volume, distribution and timing of magmatism at normal- to excess-magmatic margins is incompletely understood. Similar removal of mantle lithosphere is observed in the Basin and Range wide rift system, where syn-extensional magmatism over a wide range has been identified[31] These contrasting styles of rifting are to first order controlled by crustal rheology[14,15,32,33]

Methods

Results

Conclusion