Subsurface structure of St. Elmo submarine volcanic mound (Austin, Texas) and its volcanic conduits imaged using geophysical methods

Mustafa Saribudak

doi:10.30909/vol.02.02.253268

Abstract

Geophysical survey techniques including electrical resistivity imaging and magnetics were utilized to study the late-Cretaceous submarine volcanic mound of St. Elmo railroad cut located in south Austin, TX. The St. Elmo site cut exposes a sequence of late Cretaceous volcaniclastic rocks in contact with carbonate rocks. Resistivity imaging results provided subsurface evidence that the St. Elmo submarine mound has high resistivity limestone blocks scattered randomly within the resistivity sections. These limestone blocks are interpreted to be erratic blocks of Austin Chalk, which were probably torn from the walls of the volcanic conduits (vents) and ejected. Magnetic anomalies correlate well with the resistivity anomalies, strengthening the interpretation of the resistivity data. Resistivity results from the residential site, not far from the St. Elmo volcanic mound, are interpreted as a conduit which is similar to the conduit anomalies observed on the St. Elmo railroad cut site.

Highlights

Near-surface geophysical imaging is used in a wide range of volcanic settings to understand the internal structure of volcanic centers and the nature of volcanic deposits [e.g. Courtland et al 2012; Barde-Cabusson et al 2013; Di Giuseppe et al 2017; Saribudak and Caran 2015; Saribudak 2016; Blaikie et al 2014; Di Giuseppe et al 2015; George et al 2015; Marshall et al 2015]
Locations of the geophysical profiles are shown on a site map (Figure 6A) and on a detailed, schematic geological map of the site, which shows the locations of late Cretaceous volcaniclastic and carbonate rocks of Austin Group (Dessau Chalk) where they are in a geological contact (Figure 6B)
Elmo submarinemound has high resistivity limestone blocks scattered randomly within the resistivity sections as deep as 35 m. The distribution of these chaotic limestone blocks is more evident on the eastern resistivity profiles than the western resistivity profiles

Summary

Introduction

Near-surface geophysical imaging is used in a wide range of volcanic settings to understand the internal structure of volcanic centers and the nature of volcanic deposits [e.g. Courtland et al 2012; Barde-Cabusson et al 2013; Di Giuseppe et al 2017; Saribudak and Caran 2015; Saribudak 2016; Blaikie et al 2014; Di Giuseppe et al 2015; George et al 2015; Marshall et al 2015]. Electrical imaging has a specific capability to resolve subsurface features of the buried volcanic deposits based on electrical resistivity contrasts in some volcanic deposits. Such electrical resistivity contrasts occur in the Cretaceous strata of Austin Chalk of south-central Texas, where they contain electrically conductive (low resistivity) volcanic domes or mounds [Ormond 1984; Young et al 1982].

Results

Discussion

Conclusion