Origin of volcanism on the flanks of the Pacific‐Antarctic ridge between 41°30′S and 52°S

Abstract

[1] Non-hot spot, intraplate volcanism is a common feature near the East Pacific Rise or Pacific-Antarctic ridge. Volcanic ridges and seamount chains, tens to hundreds of kilometers long, are asymmetrically distributed about the ridge axis, with most volcanic features occurring on the Pacific plate. Their origins remain controversial. We have analyzed off-axis volcanic ridges near the Pacific-Antarctic ridge from bathymetry, backscatter, gravity, and geochemistry data of the Pacantarctic 2 cruise. K/Ar dating of samples dredged on these structures reveals a contrast of up to 3 Ma between the volcanoes and the underlying crust. The volcanic activity, as suggested by the strong backscatter in sonar images, appears to be limited to areas of seafloor younger than about 3 Ma. All surveyed ridges north of the Menard transform fault (TF) show recent activity close to the ridge axis and are not affected by faults. The off-axis volcanic ridges south of the Menard TF show recent volcanic flows in their center and are affected by N-S extension. Two different types of volcanoes can be characterized: conical, flat-topped ones and rough, elongated ones associated with narrow, E-W trending volcanic ridges, some of them showing strong backscattering on the EM12 imagery. From the morphology of the seamount chains and the ages of the lava samples, we infer that the magma source for the volcanic ridges is related to the feeding of the ridge axis through three-dimensional mantle convective circulation. We suggest that a change in the relative plate motion since about 5 Ma might have induced an offset of the mantle upwelling circulation under the ridge axis so that anomalously hot mantle rises under the Pacific ridge flank. The kinematic change is also likely responsible for the tectonic deformation in the young lithosphere south of Menard TF.

Contrasted hydrothermal activity along the South‐East Indian Ridge (130°E–140°E): From crustal to ultramafic circulation

“…East of the AAD, a variety of observations suggests the presence of an area probably as anomalous as the AAD itself. The shallow residual basement depth [e.g., Marks et al ., ; Whittaker et al ., ], off‐axis volcanism, and the presence of westward propagators [ Phipps Morgan and Sandwell , ; Sempéré et al ., ; Briais et al ., ] suggest that the magma production under the South Tasmania SEIR section is not only larger than the cold AAD area, but also abnormally high compared to other sections of intermediate‐spreading MORs such as the Juan de Fuca Ridge [ Briais et al ., ].…”

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

“…The number of seamounts > 1.5 km in height currently on the ocean floor is estimated to be more than 13 000 based on satellite altimetry (Wessel et al, 2010), and these numerous features often alter subduction zone by blocking the subducting interface or causing uplift in the accretionary prism . Seamounts can be formed by various processes: they can be the result of upper mantle mini-convection cells under mid-ocean ridges or transforms (Buck and Parmentier, 1986), deep mantle upwellings, short-lived hotspot volcanism, upper asthenospheric upwelling, and lithospheric cracking (Forsyth et al, 2006;Briais et al, 2009;Sandwell and Fialko, 2004). The geochemical signature of mafic accreted terranes is important in helping to determine if the accreted terrane was originally a plume-derived oceanic plateau, hot spot track submarine ridge, or the product of excess upper mantle magmatism.…”

Sr‐Nd‐Hf isotopes along the Pacific Antarctic Ridge from 41 to 53°S

“…Major, trace element and Sr‐Nd‐Hf isotope data reveal tight and coherent geochemical variations along segments (Figure 2). Along axis geochemistry can be disturbed by local phenomena like the presence of nearby seamounts as seen in S2 and N2 (Figure 1) [ Briais et al , 2009]. These segments are the shortest and the less robust of the studied area.…”