A compilation and characterisation of lithics in kimberlite and common maar-diatremes and tephra ring deposits

M K Fitzgerald,J D L White

doi:10.1038/s41598-021-03307-7

Abstract

Maar-diatreme volcanoes are the second-most common type on land, occurring in volcanic fields within all major tectonic environments. Their deposits typically contain an abundance of lithic fragments quarried from the substrate, and many contain large, deep-sourced lithic fragments that were erupted to the surface. Primary volcaniclastic deposits fill the diatreme structure formed during eruption. There is negligible inelastic deformation of diatreme-adjacent country rock, indicating that country rock is removed to create the diatreme structures, either by being shifting downward below observable levels, ejected upward to contribute to surficial deposits, or dissolved and hidden in magma erupted or intruded at depth. No previous study has systematically reviewed and analysed the reported lithic fragments of maar-diatreme systems. We present a comprehensive compilation from published work of lithic characteristics in maar ejecta rings and in diatreme deposits of both common and kimberlite maar-diatremes. For maar-diatremes and their tephra ring deposits, we find no correlations among lithic clast sizes, shapes, depositional sites, and excavation depths. This is difficult to reconcile with models involving systematic diatreme deepening coupled with tephra-ring growth, but consistent with those involving chaotic explosions and mixing. Larger amounts of data are needed to further examine how these types of volcanoes operate.

Highlights

Maar-diatreme volcanoes are the second-most common type on land, occurring in volcanic fields within all major tectonic environments
Researchers have increasingly recognized the role of lithic fragments as potential indicators of fragmentation sites and transport processes and histories
Of the original depth observations, 53.5% were given in metres or in specific stratigraphic context, and 46.5% were inferred from information gleaned regarding the published geological setting and lithic description

Summary

Introduction

Maar-diatreme volcanoes are the second-most common type on land, occurring in volcanic fields within all major tectonic environments Their deposits typically contain an abundance of lithic fragments quarried from the substrate, and many contain large, deep-sourced lithic fragments that were erupted to the surface. There is negligible inelastic deformation of diatreme-adjacent country rock, indicating that country rock is removed to create the diatreme structures, either by being shifting downward below observable levels, ejected upward to contribute to surficial deposits, or dissolved and hidden in magma erupted or intruded at depth. The country rock missing, in the volume occupied by the diatreme deposits, could either be dropped downward, below levels of observation, ejected upward, to form parts of the ejecta ring or other surficial deposits, or hidden by dissolution into magma that is erupted or intruded at depth (Fig. 1).

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Conclusion