Transgressive sills and lateral lava flows: On the visual observation of igneous sheets in rugged terrains and the optical illusion factor

This is a Preprint and has not been peer reviewed.

Downloads

Download Preprint

Authors

Jogvan Hansen

Abstract

Abstract
Transgressive sills are of common occurrences in rift-related offshore and onshore sedimentary settings worldwide and have been reported in onshore volcanic settings in e.g. flood basalt provinces as well. General geometries of individual sills and of entire sill complexes too are well documented from seismic images in many offshore sedimentary settings of exploration interest, but limitations in seismic resolution may inhibit correct interpretations when it comes to small-scale structures and evidences on sill intrusion modes. Hence, relevant and important details and clues on intrusion mechanisms during emplacement of sheet intrusions, which may be unclear or missing in seismic images from offshore sedimentary basins, can to some degree be clarified by means of thorough visual examination and measurements on exposed onshore sills and sill complexes. In the actual study, relevant visual observations and measurements of the Streymoy Sill and its feeders in particular and to a lesser degree the Eysturoy Sill of the Faroe Islands, as well as some local lava flows, are scrutinised in order to demonstrate the importance of correct and detailed mapping, associated measurements and interpretations at exposed sill margins.
The actual study chiefly focuses on potential optical illusion factors, not uncommon for sheet intrusions in rugged mountainous terrain, and potential associated misinterpretations. It is shown that unless due care is taken in assuring that sub-horizontal visual observations from some distance in such terrains are duly accompanied by other observations in the sub-vertical and/or sub-lateral plane at other angles as well, i.e. proper 3-D considerations, noticeable errors could result, when it comes to interpretations on intrusion mechanisms and possible regional stresses that prevailed during emplacement of such sheet-like igneous bodies.

DOI

https://doi.org/10.31223/osf.io/vjwsp

Subjects

Earth Sciences, Geology, Physical Sciences and Mathematics

Keywords

Faroe Islands; Basaltic rocks; Transgressive sills; Flood basalts; Sill Intrusion; Structural geology.

Dates

Published: 2020-07-22 16:30

Older Versions
License

Academic Free License (AFL) 3.0

Additional Metadata

Data Availability (Reason not available):
There are no external data associated with this preprint

Add a Comment

You must log in to post a comment.


Comments

There are no comments or no comments have been made public for this article.