Effects of sedimentation on rift segment evolution and rift interaction in orthogonal and oblique extensional settings: Insights from analogue models analysed with 4D X-ray computed tomography and digital volume correlation techniques

Abstract

Please cite this article as: Frank Zwaan, Guido Schreurs, Jürgen Adam , Effects of sedimentation on rift segment and transfer zone evolution in orthogonal and oblique extension settings: Insights from analogue models analysed with 4D X-ray computed tomography and digital volume correlation techniques. AbstractDuring the early evolution of rift systems, individual rift segments often develop along preexisting crustal weaknesses that are frequently non-continuous and laterally offset. As extension progresses, these initial rift segments establish linkage in order to develop a continuous rift system that might eventually lead to continental break-up. Previous analogue and numerical modelling efforts have demonstrated that rift interaction structures are influenced by structural inheritances, detachment layers, magma bodies, rate and direction of extension, as well as distance between rift segments on rift interaction structures. Yet to date, the effects of syn-tectonic sediments have been largely ignored or only modelled in 2D.In this study we therefore assess the influence of sedimentation on rift segment and rift transfer zone evolution in orthogonal and oblique extension settings, by means of 3D brittleductile analogue models, analysed with 4D X-ray computed tomography (XRCT or CT) methods and 3D digital volume correlation (DVC) techniques.Our models show that syn-rift sedimentation does not significantly influence the large-scale evolution of rift and transfer zone structures. Nevertheless, syn-rift sedimentation can strongly affect rift-internal structures: sedimentary loading reinforces the rift wedge, decreasing rift wedge faulting and increases subsidence within the rift basin. These effects are strongest in areas where most accommodation space is available, that is, along the main rift segments. In contrast, rift segments that undergo high degrees of oblique extension develop less accommodation space and are therefore less influenced by sedimentary loading. Rift interaction structures are least affected by sediment influx, as they experience ACCEPTED MANUSCRIPT extension promotes the formation of oblique rift-internal structures (Fig. 4c).The above-mentioned general features also occur in models with syn-rift sedimentation (Fig. 4g-j). However, the regular filling of the rift basins results in significantly less pronounced rift topography. In models without sedimentation the seed below the rift segments rises towards the model surface as is visible after sand removal ( Fig. 4d-e). In models with sedimentation the same "diapirism" occurs but an additional trough structure develops within the seed, which continues partially into the propagating rift branch (Fig. 4i, j). CT-analysisThe use of X-Ray CT techniques allows a more detailed analysis of our models (Figs. 5-7).Almost immediately after experiment initiation faults localize above the seed (Figs. 6d, j, 7d, ACCEPTED MANUSCRIPT

An Inside Perspective on Magma Intrusion: Quantifying 3D Displacement and Strain in Laboratory Experiments by Dynamic X-Ray Computed Tomography

“…The slow rotation speeds (26 s for one 3D image) and large voxel sizes (1 mm) used by Rincón et al (2018) make imaging complex intrusion geometries and overburden faulting patterns difficult and DVC application impossible. Image noise was sufficiently low in our case and, in contrast to the existing analog CT studies (Adam et al, 2013;Zwaan et al, 2018), imaging several times at each time step and stacking CT images to improve image texture proved unnecessary. Instead, the sufficiently small voxel sizes and the high frequency of image acquisition (1 s) at our wide beam CT set-up enabled a complete 4D (3D + time) view of the growth of analog intrusions and the development of deformation structures induced in the granular host material.…”

“…The short detectors of standard CT scanners (4-8 cm) require minute-long helical scanning, during which the model deformation has to be paused. This can be done with tectonic laboratory models which involve externally forced deformation (Schreurs et al, 2003;Adam et al, 2013;Zwaan et al, 2018), but it is impracticable once analog magma intrusion has initiated. That is why Poppe et al (2015) used radiographs, rather than 3D CT scans, to monitor their laboratory model development.…”

“…While high-resolution micro-CT scanners only allow imaging of the final model geometry (Kervyn et al, 2010;Poppe et al, 2015), medical scanners can acquire a time-series of 3D CT images at any desirable time interval, but at the cost of lower spatial resolutions (Schreurs et al, 2003). This technique has been used to image structural geometries in sandbox models simulating tectonic compression (Adam et al, 2013) or extension (Holland et al, 2011;Zwaan et al, 2018), or viscous magma intrusion in a sand-plaster cone (Rincón et al, 2018). Standard CT scanners have narrow X-ray detectors and only allow for "helical scanning" by moving the model box through the X-ray gantry while experimental deformation has to be arrested (Schreurs et al, 2003).…”

“…Standard CT scanners have narrow X-ray detectors and only allow for "helical scanning" by moving the model box through the X-ray gantry while experimental deformation has to be arrested (Schreurs et al, 2003). The recent development of Digital Volume Correlation (DVC) techniques enables one to quantify displacement and strain in 4D throughout the entire laboratory model volume (Adam et al, 2013;Zwaan et al, 2018).…”

Rift propagation in rotational versus orthogonal extension: Insights from 4D analogue models

“…This 191 extension velocity is chosen to prevent strong brittle-viscous coupling and associated 192 distributed rifting effects, since we aim to analyze the development and propagation of a 193 single well-constrained rift basin. No sedimentation is implemented in this study, which is 194 permissible since we are not focusing on detailed rift-internal structures but on first-order 195 tectonics processes that are not significantly affected when surface processes are excluded 196 (Zwaan et al 2018a horizontal displacements and deformation of the model surface at high precision (<1 mm). 208…”