Geomorphological and Spatial Characteristics of Underwater Volcanoes in the Easternmost Australian-Antarctic Ridge

Abstract

Underwater volcanoes and their linear distribution on the flanks of mid-ocean ridges are common submarine topographic structures at intermediate- and fast-spreading systems, where sufficient melt supplies are often available. Such magma sources beneath the seafloor located within a few kilometers of the corresponding ridge-axis tend to concentrate toward the axis during the upwelling process and contribute to seafloor formation. As a result, seamounts on the flanks of the ridge axis are formed at a distance from the spreading axis and distributed asymmetrically about the axis. In this study, we examined three linearly aligned seamount chains on the flanks of the KR1 ridge, which is the easternmost and longest Australian-Antarctic Ridge (AAR) segment. The AAR is an intermediate-spreading rate system located between the Southeast Indian Ridge and Macquarie Triple Junction of the Australian-Antarctic-Pacific plates. By inspecting the high-resolution shipboard multi-beam bathymetric data newly acquired in the study area, we detected 20 individual seamounts. The volcanic lineament runs parallel to the spreading direction of the KR1 segment. The geomorphologic parameters of height, basal area, volume, and summit types of the identified seamounts were individually measured. We also investigated the spatial distribution of the seamounts along the KR1 segment, which exhibits large variations in axial morphology with depth along the ridge axis. Based on the geomorphology and spatial distribution, all the KR1 seamounts can be divided into two groups: the subset seamounts of volcanic chains distributed along the KR1 segment characterized by high elevation and large volume, and the small seamounts distributed mostly on the western KR1. The differences in the volumetric magnitude of volcanic eruptions on the seafloor and the distance from the given axis between these two groups indicate the presence of magma sources with different origins.

Magnetic Constraints on Off‐Axis Seamount Volcanism in the Easternmost Segment of the Australian‐Antarctic Ridge

“…The longest formation time was identified from the seamount E group, that is, ∼830 kyrs (e.g., seamount E1 formed during 0.16–0.55 Ma, E2 during 0.55–0.72 Ma, and E3 during 0.87–1.14 Ma), whereas the other seamounts exhibited formation times of less than 600 kyrs (Figure 8a and Table 1). For example, seamount A, the tallest edifice (∼1.6 km tall) in segment KR1, required ∼530 kyrs for its formation processes, whereas seamount H1, the most voluminous (∼131 km 3 ) (Choi et al., 2021), was formed within ∼500 kyrs (Figure 8a and Table 1). The duration of seamount formation was estimated by projecting the basal width of a given seamount to the adjusted or seafloor geomagnetic polarity sequence (e.g., Figure 4), assuming that the seamount formation occurred progressively with seafloor spreading.…”

“…In particular, the full-spreading rates of 60-67 and 66-70 mm/yr for segments KR1 and KR2, respectively, were estimated directly from shipboard magnetic data (Choi et al, 2017). According to the classifications of the full-spreading rate (Dick et al, 2003;Macdonald, 2001;Supak et al, 2007), the AAR is an intermediate-spreading ridge with full-spreading rates of 50-80 mm/yr (Choi et al, 2017 The 300-km-long segment KR1 exhibits a relatively rapid transition from an axial valley in the east to an axial high in the west (Choi et al, 2013;Choi et al, 2021;Kim et al, 2015;Park et al, 2014). Difference in axial morphology is primarily modulated by the thickness of the axial lithosphere, which in turn is controlled by the axial heat flux of magma delivered to the axis (Dick et al, 2003;Macdonald, 2001;Phipps Morgan & Chen, 1993).…”

“…Here we present magnetically constrained ages of off‐axis seamounts located in the vicinity of segment KR1, the eastern end of the Australian‐Antarctic Ridge (AAR), using the shipboard magnetic anomalies (Figure 1). These three off‐axis seamount chains oriented perpendicular to the ridge provide unique opportunities to constrain the spatial and temporal variation of the off‐axis volcanism in the study area (Choi et al., 2021). A 2‐D forward magnetic modeling method (Mendel et al., 2005) is used to determine the magnetization polarity sequence of the off‐axis seamounts at the time of their formation.…”

“…The 300‐km‐long segment KR1 exhibits a relatively rapid transition from an axial valley in the east to an axial high in the west (Choi et al., 2013; Choi et al., 2021; Kim et al., 2015; Park et al., 2014). Difference in axial morphology is primarily modulated by the thickness of the axial lithosphere, which in turn is controlled by the axial heat flux of magma delivered to the axis (Dick et al., 2003; Macdonald, 2001; Phipps Morgan & Chen, 1993).…”

Dating volcanic materials through biochronostratigraphic methods applied to hosting strata (example from the Iberian Chain, eastern Spain)

“…Typical off-axis magmatism develops over oceanic crust on the faulted flanks of mid-ocean ridges [e.g., Sohn and Sims, 2005, Toomey, 2012, Choi et al, 2021. Off-axis magmatism has been reported as occurring up to 20 km beyond the ridge axis in the East Pacific Rise [Turner et al, 2011], up to 40 km in the Gulf of Aden [Guillard et al, 2021], or by more than 200 km in the volcanic fields of the Kamar-Daban, the Udokan and the Vitim Plateau [Yang et al, 2018].…”