Exploring the Interactions Between Rift Propagation and Inherited Crustal Fabrics Through Experimental Modeling

Abstract

Continental rifting is a geodynamic process that involves the breakup of the crust and may eventually evolve to seafloor spreading. Although it is often assumed to be a product of orthogonal divergence, continental rifting may result from oblique extension, and in several cases, it is related to the rotation of plates or crustal blocks about a vertical axis. This implies the occurrence of rifts with straight but not parallel margins and rift axis-parallel gradients in extension velocity and amount of strain. The effects of rift propagation through the continental crust has only recently started to be addressed, and even less investigated is the interaction between rift propagation and inherited crustal fabrics. We have studied this issue by carrying out a series of analog laboratory experiments. Modeling results suggest that inherited linear discontinuities in the model brittle upper crust that are oriented above a threshold angle (≥45°) from the orthogonal to the rift axis have the ability to interact with rift-related structures. Depending on their orientation, such inherited discontinuities are reactivated as either transfer zones or rift-bounding faults. We compare our models with four natural prototypes in which rift propagation is likely to have occurred (the Trans Mexican Volcanic belt, the Gofa Province, the Gulf of Suez, and the Kenya Rift). For each case study, we show how the kinematics of propagating rifts is comparable to our model results, and we provide insights into how rift-related deformation may interact with inherited crustal fabrics. Plain Language Summary When the continental Earth's crust breaks due to tensional tectonic forces, deep depressions called continental rifts form. Over geological time, these features may ultimately evolve to oceans. This process is often assumed to occur symmetrically, but it has been shown that this is rarely the case. Indeed, continental rifting is often generated by the rotation of tectonic plates, which induces changes in the extension velocity along the length of the rift. In order to understand the evolution of many natural rifts, it is also important to determine how rifting interacts with existing discontinuities in the crust (e.g., faults). This issue has only been recently addressed by laboratory experimental models, in which natural processes are simulated at reduced time and length scales, using appropriate analog materials to replicate the physical properties of natural rocks. We have performed a series of experiments that test this interaction, discovering that preexisting faults can have a strong influence on the formation and evolution of continental rifts. To verify this correlation, we have compared our models with four (Mexico, Ethiopia, Egypt, and Kenya) natural cases, finding that older faults have often influenced the rifting process and the resulting structure.

Exploring fault propagation and the role of inherited structures during caldera collapse through laboratory experiments

“…15c), in agreement with other regional structural trends (e.g., Norini et al, 2019). This structural setting may suggest that the LH caldera collapse was partly controlled by existing regional structures (Liotta and WP4 Working Group, 2019;Maestrelli et al, 2020a), and it is therefore possible to compare this caldera complex with our analogue models.…”

“…Journal Pre-proof Vasconcelos et al, 2020;Maestrelli et al, 2020a). -Monroy, 1987;Carrasco-Núñez et al, 2017;Avellán et al, 2019;García-Palomo et al, 2018;Maestrelli et al, 2020a), which may have played a role during the development of the caldera complexes and likely during caldera collapse (Bonini et al, 2021). As noted earlier, caldera-related structures, may interact with inherited discontinuities and localise the up-flow of geothermal fluids, thereby representing important exploration targets (Giordano et al, 2014;Norini et al, 2015).…”

“…Journal Pre-proof Vasconcelos et al, 2020;Maestrelli et al, 2020a). -Monroy, 1987;Carrasco-Núñez et al, 2017;Avellán et al, 2019;García-Palomo et al, 2018;Maestrelli et al, 2020a), which may have played a role during the development of the caldera complexes and likely during caldera collapse (Bonini et al, 2021).…”

“…1e). This operation causes re-orientation of particles and variation in their compaction, generating a sharp and narrow millimetric-wide weak zone, which focuses deformation during model development if favourably oriented with respect to the local stress field (e.g., Bellahsen & Daniel, 2005;Maestrelli et al, 2020a). We then varied the shape of the magma chamber by imposing one the end of the deformation, models were saturated with water, frozen and cross-sectioned for investigating the 3D caldera fault pattern.…”

Caldera collapse and tectonics along the Main Ethiopian Rift: reviewing possible relationships

“…Despite caldera collapse is generally accommodated by a system of outward-dipping reverse faults and inwarddipping normal ring faults [e.g., Acocella, 2007], existing tectonic structures may interact with calderarelated structures, and influence the eccentricity of the caldera system. Several researches claimed, in fact, an important role of tectonic structures on the evolution of such systems, indicating that both inherited (older) and rift-related structures are key factors controlling the collapse [e.g., Acocella et al, 2002, Holohan et al, 2005, 2008, Maestrelli et al, 2020, 2021a,b, Bonini et al, 2021.…”