Normal fault growth in layered basaltic rocks: The role of strain rate in fault evolution

Abstract

9Conceptual models for the evolution of dilatant faults in volcanic rift settings involve a step-wise 10 growth pattern, involving upward propagation of subsurface faults, surface monocline formation, 11 which are breached by subvertical, open faults. Immature, discontinuous normal faults are 12 considered representative of the early stages of mature, linked faults that accommodate extensional 13 strains. We consider the evolution of surface-breaking normal faults using a comparison of the 14 distribution and geometry of normal faults from two volcanic rift zones: the Koaʻe fault system, 15Hawaiʻi, and the Krafla fissure swarm, NE Iceland. Field mapping highlights similarities to current 16 predicted geometries, but also prominent differences that are not reconciled by current models. 17Variable deformation styles record magma supply changes within the rift zones, which drive local 18 strain rate gradients. Building on existing studies, we present a conceptual model of fault growth 19 that accounts for spatial and temporal changes in strain rate within the deforming regions. We 20propose that faults in separate rift systems may not advance through the same stages of evolution 21and that faults within individual rift systems can show differing growth patterns. Variations in 22 2 surface strains may be indicative of subsurface magmatic system changes, with important 23 implications for our understanding of volcano-tectonic coupling. 24 25Key words: normal fault; monocline; extension; basalt; volcanic rift 26 27 Introduction 28Normal fault systems comprise discontinuous, non-collinear segments, with overlaps and segment 29 linkage commonly resulting in characteristic overlapping or step-like geometries across a broad 30 range of scales (e.g. Segall and Pollard, 1980;Peacock, 2002; Long and Imber, 2011). Regional 31 extension is conserved ahead of first-order fault terminations by areas of folding and linking faults 32 and fractures (e.g. Morley et al., 1990;Faulds and Varga, 1998). The geometry and distribution of 33 structures within these domains play an important role in the tectono-stratigraphic development of 34 rift basins (e.g. Lambiase and Bosworth, 1995; Sharp et al., 2000; Hus et al., 2006), and the 35 evolving fluid flow properties of fault zones (e.g. Manzocchi et al., 2010;Seebeck et al., 2014). 36Much of our current understanding of the growth of normal fault populations and fault zone 37 architecture is derived from studies of faults in clastic sequences using combinations of: (1) fault 38 analysis and scaling relationships, based on field and seismic data-derived measurements of 39 displacement and length versus width (e.g. Ferrill and Morris, 2001;Peacock, 2002; Walsh et al., 40 2003;Nixon et al., 2014); (2) scaled-analogue modelling (e.g. Holland et al., 2006; Tentler and 41 Acocella, 2010); and (3) numerical-based modelling techniques (e.g. Crider and Pollard, 1998; 42 Maerten et al., 2002;Schöpfer et al., 2006). Many of these studies have focussed on fault 43 propagation and se...

Quantitative Constraints on Faulting and Fault Slip Rates in the Northern Main Ethiopian Rift

“…A quantitative understanding of fault networks and their kinematics including growth, reactivation, and interaction in magma‐assisted continental rifts has been hampered by a lack of chronological constraints, but studies worldwide provide a qualitative framework. In this paper we build on previous studies from Iceland (e.g., Bull et al, 2003; Grant & Kattenhorn, 2004; Tentler, 2005; Villemin & Bergerat, 2013); Hawaii (e.g., Bubeck et al, 2018; Holland et al, 2006; Kaven & Martel, 2007; Martel & Langley, 2006); the Taupo Rift Zone, New Zealand (e.g., Rowland et al, 2010; Rowland & Sibson, 2001, 2004); and the East African Rift (EAR) (Acocella et al, 2011; Casey et al, 2006; Corti, 2009; Rowland et al, 2007) by characterizing the structural style of the active Boset magmatic segment (BMS) of the northern Main Ethiopian Rift (MER). Here, previous work has provided a relative and absolute chronological framework (Abebe, Manetti, et al, 2005; Chernet et al, 1998; Siegburg et al, 2018).…”

Structure of massively dilatant faults in Iceland: lessons learned from high-resolution unmanned aerial vehicle data

“…EVZ: east volcanic zone; KR: Kolbeinsey Ridge; NVZ: north volcanic zone; RR: Reykjanes Ridge; TFZ: Tjörnes Fracture Zone; WVZ: west volcanic zone. (b) Detailed view of the Reykjanes Peninsula and WVZ; the presented faults are taken from Clifton and Kattenhorn (2006). (c) Detailed view of the geology and study areas in the NVZ.…”

“…The Vogar fissure swarm has been the scope of several field studies (Clifton and Schlische, 2003;Grant and Kattenhorn, 2004;Gudmundsson, 1986Gudmundsson, , 1987a and a remote sensing study, introducing a post-coalescence model for fault growth (Villemin and Bergerat, 2013). The geometry of the fractures of the fissure swarm has been characterized as anastomosing or sinuous (Clifton and Kattenhorn, 2006;Clifton and Schlische, 2003;Gudmundsson, 1987a).…”

“…Some examples of young volcanic eruptions include the Krafla fires (Hjartardóttir et al, 2012;Tryggvason, 1986) with nine eruptions between 1975 and 1984 (Thordarson and Larsen, 2007), the 1991 and 2000 eruptions of Hekla (Gudmundsson et al, 1992;Rose et al, 2003) or the Holuhraun eruption during 2014-2015, the largest Icelandic eruption in more than two centuries (Geiger et al, 2016;Müller et al, 2017;Schmidt et al, 2015). Published mappings of faults and fissures of the NVZ (Hjartardóttir et al, 2012) and the Reykjanes Peninsula (Clifton and Kattenhorn, 2006) were further used to identify possible sites. TanDEM-X WorldDEM ™ tiles with a resolution of 12 m were used at a later stage to complement our own DEMs, which are highly resolved but only able to cover respectively smaller areas.…”

Structure of massively dilatant faults in Iceland: lessons learned from high resolution UAV data

“…MDF guide the flux of water, magma or hydrocarbons and are therefore of interest for geo-hazard assessment, hydrocarbon 10 exploration, geothermal energy or geodynamics (Crider and Peacock, 2004;Faulkner et al, 2010;Ferrill and Morris, 2003;Grant and Kattenhorn, 2004;Gudmundsson, 1987a;Kettermann et al, 2015Kettermann et al, , 2016Rowland et al, 2007). During the past decades, MDF have been studied in the field (Bubeck et al, 2018;Gudmundsson, 1987bGudmundsson, , 1987aHjartardóttir et al, 2012;Sonnette et al, 2010;Tibaldi et al, 2016;Trippanera et al, 2015), and using analog and numerical models (Abe et al, 2011;van Gent et al, 2010;Grant and Kattenhorn, 2004;von Hagke et al, 2019;Holland et al, 2006;Kettermann et al, 2015Kettermann et al, , 2016Kettermann et al, , 15 2019Martel and Langley, 2006;Smart and Ferrill, 2018). In these studies, the surface geometries have been described including tilted blocks (i.e.…”