Evolution of the Pacific-Antarctic Ridge South of the Udintsev Fracture Zone

Abstract

Because of the proximity of the Euler poles of rotation of the Pacific and Antarctic plates, small variations in plate kinematics are fully recorded in the axial morphology and in the geometry of the Pacific-Antarctic Ridge south of the Udintsev fracture zone. Swath bathymetry and magnetic data show that clockwise rotations of the relative motion between the Pacific and Antarctic plates over the last 6 million years resulted in rift propagation or in the linkage of ridge segments, with transitions from transform faults to giant overlapping spreading centers. This bimodal axial rearrangement has propagated southward for the last 30 to 35 million years, leaving trails on the sea floor along a 1000-kilometer-long V-shaped structure south of the Udintsev fracture zone.

T-phase Stations for the International Monitoring System of the Comprehensive Nuclear-Test Ban Treaty: A Global Perspective

“…In a more recent study (Talandier and Okal, 1996), T phases of exceptionally monochromatic character were used to identify a powerful volcanic source in the vicinity of the Eltanin fracture zone at 54~ 140~ Subsequent shipboard exploration of the area (Gdli et al, 1997;Vlastelic et al, 1998) mapped the Hollister Ridge as a massive extrusion of basaltic volcanics, 450 km long by 20 km in width at its base and reaching only 135 m below sea level, and determined that its morphology and its isotopic and trace element signatures have no known equivalent in the Pacific. Talandier and Okal (1996) suggested that the monochromatic spectrum of the Hollister Ridge T waves could express resonance of a water column populated with gaseous bubbles, resulting from geyserlike activity during the volcanic episode, made possible by the exceptionally shallow depth of the eruption.…”

Large-scale chemical and thermal division of the Pacific mantle

“…The magnitude of this time lag can be determined if the time difference is known between the onset of the d 13 C org excursion and the first maximum carbon-isotope value for organic matter. As the d 13 C excursion is synchronous for all sites 30 , data from the expanded C/Tsection of the Tarfaya basin 31,32 can be used for this calculation. An accumulation rate of ϳ120 cm ky −1 (ref.…”

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

“…The adjustment of the Pacific ridges to the changing spreading direction might have increased the component of ridge parallel tensile stresses since about 5 Ma, favoring the cracking of the young lithosphere and the emplacement of seamounts. In the southern Pacific, a change in the relative Pacific‐Antarctic plate motion at that time is responsible for extension in the right‐stepping transform faults [ Géli et al , 1997; Ondréas et al , 2001], as well as for the development of a large‐offset propagator along the Pacific‐Antarctic ridge [ Briais et al , 2002]. The changes in plate motion might also have induced an offset between the zones of mantle upwelling and the plate boundary, explaining why more off‐axis seamounts are observed on the Pacific plate than on the Antarctic one.…”

“…Numerous changes in the Pacific‐Antarctic plate motion have occurred since 70 Ma [ Cande et al , 1995; Cande and Stock , 2004; Croon et al , 2008]. The results of the Pacantarctic 1 cruise have shown the importance of these changes on morphological reorganizations of the ridge axis [ Briais et al , 2002; Géli et al , 1997; Ondréas et al , 2001]. They have also emphasized the relationships between heterogeneities in upper mantle temperature, geochemical segmentation of the upper mantle and seafloor morphology.…”