Near-ridge seamount volcanism in the easternmost segment of the
Australian-Antarctic Ridge: Distribution, morphology, and magnetism
Abstract
The Australian-Antarctic Ridge (AAR) is the intermediate spreading
system located between the Southeast Indian Ridge and Macquarie Triple
Junction of the Australian-Antarctic-Pacific plates. KR1 is the
easternmost and longest AAR segment and exhibits unique axial morphology
and various volcanic structures. Within it, we identified three linearly
aligned volcanic seamount chains positioned parallel to the seafloor
spreading direction. We found that the seamount chains had formed
asymmetrically and had developed through near-ridge volcanism at some
distance away from the KR1 axis. Based on high-resolution bathymetric
data, we identified the spatial distribution, morphology, and summit
types of the isolated volcanic structures composing the seamount chains.
The magnetic constraints on the age of the identified seamounts indicate
that most had a formation time of less than ~600 kyrs,
which primarily occurred during four distinct volcanic pulses from
0.3-0.8 Ma, 0.9-1.1 Ma, 1.6-2.1 Ma, and 2.2-2.7 Ma (or two major
distinct pulses from 0.3-1.1 Ma and 1.6-2.7 Ma). When inconsistency
existed between the observed and modeled ages of volcanic structures,
volcanos were found to have a temporal gap of 200-650 kyrs between their
formation and that of the underlying seafloor. Such volcanos are thought
to have developed due to off-axis volcanism at a distance of 7-20 km.
Considering the scale of off-axis volcanism and thickening lithosphere
of such areas of ~20 km away from the axis of the
intermediate spreading ridge, we propose that the seamounts originated
from a deep plume source beneath the oceanic lithosphere.