Surface and mantle records reveal an ancient slab tear beneath Gondwana

Guido M Gianni,Silvana Spagnotto,César Navarrete

doi:10.1038/s41598-019-56335-9

Abstract

Vertical slab-tearing has been widely reported in modern convergent settings profoundly influencing subduction and mantle dynamics. However, evaluating a similar impact in ancient convergent settings, where oceanic plates have been subducted and the geological record is limited, remains challenging. In this study, we correlate the lower mantle structure, which retained the past subduction configuration, with the upper-plate geological record to show a deep slab rupture interpreted as a large-scale tearing event in the early Mesozoic beneath southwestern Gondwana. For this purpose, we integrated geochronological and geological datasets with P-wave global seismic tomography and plate-kinematic reconstructions. The development of a Late Triassic-Early Jurassic slab-tearing episode supports (i) a slab gap at lower mantle depths, (ii) a contrasting spatiotemporal magmatic evolution, (iii) a lull in arc activity, and (iv) intraplate extension and magmatism in the Neuquén and Colorado basins. This finding not only has implications for identifying past examples of a fundamental process that shapes subduction zones, but also illustrates an additional mechanism to trigger slab-tearing in which plate rupture is caused by opposite rotation of slab segments.

Highlights

Tear in subducting plates, linked to vertical or horizontal slab ruptures, are outstanding tectonic features described in some modern subduction[1,2] and collisional[3] settings
Slab gaps created by slab tears differ from those produced by subduction of spreading centers, which result from continued sublithospheric divergence of oceanic plate boundaries leaving a geological fingerprint widely detected in ancient settings
We drew on the work of Navarrete et al for our reconstruction, but focused on a previously overlooked slab gap. This approach is based on overlapping the reconstructed positions of southwestern Gondwana in Mesozoic times[31] by using the GPlates 2.0 software[32] with tomographic slices at lower mantle depths from the UU-P07 P-wave global seismic tomography model[33]

Summary

Introduction

Tear in subducting plates, linked to vertical or horizontal slab ruptures, are outstanding tectonic features described in some modern subduction[1,2] and collisional[3] settings. Geological consequences of this process include acceleration of trench retreat[13,20], creation of slab gaps and consequent mantle flow[21], anomalous arc-backarc magmatism[2,10], thermal perturbations[22], and upper-plate segmentation and extension[13].

Results

Conclusion