Interaction between a Late Miocene andesitic dyke swarm and wet sediment in the Szoros Valley, Eastern Borsod Basin, Northeast Hungary

Árpád Csámer

doi:10.1556/24.58.2015.3.4

Abstract

Magma/wet sediment interaction (e.g. autobrecciation, magma-sediment mingling, hyaloclastite and peperite-forming, etc.) is a common phenomenon, where hot magma intrudes into unconsolidated or poorly consolidated water saturated sediment. In the Eastern Borsod Basin (NE-Hungary) relatively small (2–30 m) subvolcanic bodies, sills and dykes with contact lithofacies zones were found generated by mechanical stress and quenching of the magma, and interacting with unconsolidated wet andesitic lapilli-tuff and tuff-breccia. Close to the contact between sediment and intrusions, thermal and mechanical effects may occur in the host sediment. Hydrothermal alteration and stratification of the host sediment were developed only locally along the contact zone, probably due to the paleo-hydrogeologic and paleo-rheological inhomogeneities of the lapilli-tuff–tuff-breccia deposits. Processes of magma/wet sediment interaction may be difficult to recognize because of limited exposure and/or certain similarities of the brecciated intrusions to the characteristics of the host sediment; hence detailed field work (geologic mapping or profiling) was required to demonstrate the subvolcanic origin of the brecciated andesite bodies.

Highlights

As early as the 1970s but mainly since the 1990s many authors have published examples of magma coming into contact with wet sediment, generating hyaloclastites, peperites, in situ breccias, etc. (i.e. Lydon 1968; Yamagishi 1991; Hanson and Hargrove 1999)
These studies make clear that phenomena of magma/wet sediment interactions are common in geologic settings where thick sediment sequences accumulate during active volcanism
This paper describes an extensive, well-exposed dyke swarm complex along the Szoros Valley where detailed geologic section recording and texture analysis was performed in the field and on carefully collected samples

Summary

Introduction

As early as the 1970s but mainly since the 1990s many authors have published examples of magma coming into contact with wet sediment, generating hyaloclastites, peperites, in situ breccias, etc. (i.e. Lydon 1968; Yamagishi 1991; Hanson and Hargrove 1999). Pyroclastic rocks (lapilli-tuff, tuff and tuffite) of rhyolitic and dacitic composition were deposited in three main phases during the Miocene (Pelikán 2005) The older of these was accumulated in a continental environment, approximately 18.5–21 Ma ago (Gyulakeszi Rhyolite Tuff Formation) (Gyalog 2005). The Dubicsány Andesite Formation (DAF) comprises thick andesite volcaniclastic sequences (i.e. lapilli-tuff, tuff and tuff-breccia) deposited in terrestrial, deltaic and near-shore environments and penetrated by subvolcanic bodies and dykes of andesitic composition. Almost the entire Late Miocene intermediate volcanic and subvolcanic succession (i.e. Dubicsány Andesite Formation), including overlying and underlying sediment sequences, is exposed in numerous outcrops along the valley. K/Ar radiometric dating, carried out on an andesite dyke sample collected from the Szoros Valley, yields an age of 13.73 ± 0.76 Ma (Late Badenian–Sarmatian) (Csámer 2007)

Analytical methods

Findings

259 Discussion