Extensional faulting and caldera collapse in the axial region of fast spreading ridges: Analog modeling

Abstract

Abstract. The axial high of the East Pacific Rise (EPR) is bounded by ridge-parallel lateral grabens that develop 2-8 km off-axis. These troughs appear to lengthen away from the ridge crest, suggesting that tectonics is active at least 10 km away from the axis. Along 15-20% of the length of the ridge the axial high is notched by a summit trough 500 to 1800 m wide. These large axial troughs represent elongated collapse calderas that form when the EPR magma reservoir (comprising the melt lens and the underlying crystal mush zone) deforms and compacts during periods of waning magma supply under continuous stretching. We report the results of analog experiments performed in order to constrain the tectonic-magmatic evolution of the crestal region of fast spreading ridges and more particularly the possible link that may exist between the development of axial caldera and the creation of lateral grabens along the crestal region. We used inflatable elongated balloons filled with water as an analog of the magma reservoir. The balloon is capped with a silicone layer representing hot rocks below the brittle-ductile transition and is covered by a sand layer representing the brittle crust. The sand surface was given a dome shape that approximates the morphology of a fast spreading ridge. Mobile walls activated by a stepping motor allowed us to conduct the deflation experiments during continuous extension. Combination of deflation and extension leads to the creation of two lateral depressions and one axial trough. The lateral depressions are controlled by normal faults, while the central trough is delineated by reverse faults. During balloon deflation, tectonic extension is accommodated away from the axis due to the presence of the ductile silicone layer, whereas the deflation of the axial reservoir is accommodated by the collapse of the overlaying brittle crust. This accounts (1) for the development of axial troughs as collapse calderas, and (2) for the ubiquitous formation of lateral grabens of the flanking tectonic province in response to the deformation of the crystal mush.

Recent volcanic events and the distribution of hydrothermal venting at the Lucky Strike hydrothermal field, Mid‐Atlantic Ridge

“…[36] The Lucky Strike lava lake contains flat lavas and lava pillars similar to those observed at the axis of the intermediate and fast spreading ridges [Ballard, 1979;Francheteau et al, 1979;Auzende et al, 1996;Gregg and Chadwick, 1996;Gregg et al, 2000;Lagabrielle et al, 2001;Chadwick, 2003;Tanaka et al, 2007]. Lava pillars have also been reported at the Mid-Atlantic Ridge south of the Oceanographer transform [Bideau et al, 1998].…”

A review of analogue modelling of geodynamic processes: Approaches, scaling, materials and quantification, with an application to subduction experiments

“…(Munteanu et al, 2013, gravity spreading (Hatzfeld et al, 1997;Gautier et al, 1999;Martinod et al, 2000;Schellart and Lister, 2005), rifting (e.g. Vendeville et al, 1987;Allemand and Brun, 1991;Benes and Davy, 1996;Bonini et al, 1997;Lagabrielle et al, 2001;Michon and Sokoutis, 2005;Autin et al, 2010), and core complexes (Malavieille, 1993;Brun et al, 1994). In this approach, materials used to model the viscous layers include silicone polymers and syrups (Table 2).…”

Giant Dike Swarms: Earth, Venus, and Mars

“…Figure 5b depicts a mechanism for surface collapse on Mars involving both remote stress and pressure drop above a magma chamber within the framework of volcanic rifting (Mège et al 2000). This mechanism is inspired by interpretations of tectonic stretching and magmatic activity at terrestrial rift zones such as at the East Pacific Rise (Lagabrielle & Cormier 1999;Lagabrielle et al 2001) and Iceland (e.g. Forslund & Gudmundsson 1991), where ambient crustal extension is accom modated by magma reservoir emplacement at depth, dike dilation at middle depth, and purely tectonic stretching at surface.…”

“…Graben formation may be linked to driving stress during dike intrusion (Pollard & Holzhausen 1979;Mastin & Pollard 1988;Rubin 1992Rubin , 1993Rubin , 1995 and may be enhanced by subsurface pressure drop (Mège et al 2000, Lagabrielle et al 2001. Possible remote stress sources may include tectonic extension owing to remote regional stresses and gravitational spreading associated with domal uplift (Koenig & Pollard 1998, van Wyk de Vries & Merle 1996, Merle & Borgia 1996.…”