scholarly journals Rootless tephra stratigraphy and emplacement processes

2017 ◽  
Vol 79 (1) ◽  
Author(s):  
Christopher W. Hamilton ◽  
Erin P. Fitch ◽  
Sarah A. Fagents ◽  
Thorvaldur Thordarson
Keyword(s):  
Tephra Stratigraphy ◽  
Emplacement Processes

Unravelling magma emplacement through palaeomagnetic backstripping of an intrusion-induced forced fold: A case study from the Sandfell Laccolith, SE Iceland

2020 ◽  
Author(s):  
William McCarthy ◽  
Vincent Twomey ◽  
Craig Magee ◽  
Mike Petronis
Keyword(s):  
Ground Deformation ◽  
Test Site ◽  
Natural Remanent Magnetisation ◽  
Magma Emplacement ◽  
Emplacement Processes ◽  
Lava Pile ◽  
Forced Folding ◽  
Instance Analysis ◽  
Shallow Crust ◽  
Deformation Patterns

<p>Volcano eruption forecasting typically links ground deformation patterns to sub-surface magma movement. Injection and inflation of magmatic intrusions in the shallow crust is commonly accommodated by roof uplift, producing intrusion-induced forced folds that mimic the geometry of underlying igneous bodies. Whilst such forced folds have previously been described from field exposures, seismic reflection images, and modelled in scaled laboratory experiments, the dynamic interaction between progressive emplacement of hot magma, roof uplift, and any associated fracture/fault development remains poorly understood. For instance, analysis of ancient examples where magmatism has long-since ceased only provides information on final geometrical relationships, while, studies of active intrusions and forced folding only capture brief phases of the dynamic evolution of these structures. If we could unravel the spatial and temporal evolution of ancient forced folds, we could therefore acquire critical insights into magma emplacement processes and interpretation of ground deformation data at active volcanoes.</p><p> </p><p>We put forth and aim to test a new hypothesis suggesting that thermoremanent magnetization (TRM) records progressive deflection of the host rock during incremental laccolith construction and that these measurements can be used to measure the rate of laccolith construction. Here, we integrate palaeomagnetic techniques with semi-automated, UAV-based photogrammetric structural mapping to test: (1) whether we can identify variations in Natural Remanent Magnetisation (NRM), TRM, and magnetic mineralogy across an intrusions structural aureole; and (2) whether measured magnetic variations can be related to deflection caused by incremental sheet emplacement. Our test site is located within the basaltic lava pile of the ~800 m wide structural aureole of the rhyolitic Sandfell Laccolith in SE Iceland, which intruded <1 Km below the palaeosurface at ~11.7 Ma. We discuss whether palaeomagnetic backstripping can be an effective resource to constrain the rate and magnitude of intrusion-induced forced fold evolution, and thus an effective tool in volcanic hazard assessment.</p>

scholarly journals Tephra layers in the marine environment: A review of properties and emplacement processes

2021 ◽  
pp. SP520-2021-50
Author(s):  
Armin Freundt ◽  
Julie C. Schindlbeck-Belo ◽  
Steffen Kutterolf ◽  
Jenni L. Hopkins
Keyword(s):  
Volcanic Ash ◽  
Layer Structure ◽  
Sediment Cores ◽  
Submarine Landslides ◽  
Natural Processes ◽  
Ash Layer ◽  
Tephra Layers ◽  
Emplacement Processes ◽  
Volcaniclastic Deposits ◽  
Important Marker

AbstractThis review focusses on the recognition of volcanic ash occurrences in marine sediment cores and on using their appearance and properties to deduce their origin. Widespread marine tephra layers are important marker horizons for both volcanological as well as general geological investigations. We describe ash detection by visual inspection and logging of sediment cores. Ash layer structure and texture, particle morphologies and lithological compositions of primary volcanic deposits are summarized and processes modifying them are discussed, both natural processes acting on and in the seafloor, i.e., erosion and bioturbation, and man-made modifications during drilling/coring and core preparation. We discuss primary emplacement processes of marine fall and flow tephra deposits derived from either subaerial or submarine sources in order to identify distinguishing properties. We also elaborate on processes generating secondary, resedimented volcaniclastic layers such as submarine landslides and shelf erosion as well as fluvial input and ice-rafting, and how they can be distinguished from primary volcaniclastic deposits, which is essential in tephrostratigraphy. Finally, methods of tephra correlation between cores and on-land deposits/volcanoes are illustrated because they allow us to extend the 1-D information from single cores to 3-D distribution and facies changes of tephras and to bridge the land-sea gap.

scholarly journals Tarawera Volcanic Complex

2021 ◽  
Author(s):  
◽  
James William Cole
Keyword(s):  
General Structure ◽  
Volcanic Complex ◽  
Volcanic Centre ◽  
Residual Glass ◽  
Sequence Of Events ◽  
Field Evidence ◽  
Tephra Stratigraphy ◽  
Relationship Of ◽  
Basic Rocks ◽  
The Relationship

<p>The Tarawera Volcanic Complex is situated on the south eastern side of the Okataina Volcanic Centre, and is an association of rhyolite domes, flows and tephra, and basalt scoria. Twelve rhyolite domes are described, and using evidence obtained from the good internal sections available, the general structure of volcanic domes is discussed. Tephra stratigraphy of the Tarawera-Rerewhakaaitu region is described and by relating stratigraphy on the mountain to this tephra, four major eruptions can be recognized. A sequence of events for the Kaharoa eruption about 1020 A.D. can be postulated. The Tarawera eruption in 1886, however, was observed, and from the eye witness accounts, together with present day field evidence, a detailed account can be written. All the rocks of the Complex are described petrographically, mineralogically, and in some cases petrochemically. Twelve new full analyses; nine partial analyses of plagioclase, and eight partial analyses of residual glass are given, and the relationship of these is illustrated by variation diagrams. Finally, the origins of the acid and basic rocks of the Complex are discussed, and a hypothesis for the occurrence of the two lava types is given.</p>

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