Distribution, morphology and magnetic characteristics of near-axis seamounts along the KR1, the easternmost segment of the Australian-Antarctic Ridge

Abstract

<p>The Australian-Antarctic Ridge (AAR) is the spreading boundary between the Australian and the Antarctic plates, and extended from the Southeast Indian Ridge (SEIR) to the Macquarie Triple Junction (MTJ) of Australian-Antarctic-Pacific plates. The KR1 is the easternmost segment of AAR, with a quite large variation in axial morphology. In this study, we identified 3-volcanic seamount chains aligned linearly parallel to the spreading direction of the KR1. The spatial distribution, morphology and summit types for the isolated volcanic structures composing the seamount chains were determined. Eastern seamount chain has the 3-isolated volcanoes which are significantly steep and located at a considerable distance away from the ridge-axis. The central seamount chain is morphologically connected to the ridge-axis, and relatively small and less isolated compared to the other seamount chains. Western seamount chain shows a massive volcanic eruption with significantly large volcanic structures. In usual, a seamount is formed on pre-existing seafloor, and the observed magnetic signal of the seamount is correspond to that of the underlying seafloor when the seamount formation occurs nearly simultaneously with the formation of the underlying seafloor. However, if the observed magnetic anomalies of the seamount have a large misfit or/and reversed geomagnetic polarities with respect to the modeled magnetic anomalies of the underlying seafloor, it implies that there is a sufficiently large temporal gap between the formations of the seamount and the underlying seafloor. Applying this assumption, we forced the relatively younger geomagnetic history to move into the seamount having such misfits, and finally reduced the misfits. As a result, our magnetic model for the seamount chains shows that the isolated volcanoes were mostly originated from off-axis volcanisms of 7~20 km, and have a time span of less than ~600 kyrs to build. In particular, it is assumed that the seamount formations were intensively active during four-periods of 0.3~0.8 Ma, 0.9~1.1 Ma, 1.6~2.1 Ma and 2.2~2.7 Ma.</p>