P and S velocity structure of the upper mantle beneath the Transantarctic Mountains, East Antarctic craton, and Ross Sea from travel time tomography

Abstract

[1] P and S wave travel times from teleseismic earthquakes recorded by the Transantarctic Mountains Seismic Experiment (TAMSEIS) have been used to tomographically image upper mantle structure beneath portions of the Transantarctic Mountains (TAM), the East Antarctic (EA) craton, and the West Antarctic rift system (WARS) in the vicinity of Ross Island, Antarctica. The TAM form a major tectonic boundary that divides the stable EA craton and the tectonically active WARS. Relative arrival times were determined using a multichannel cross-correlation technique on teleseismic P and S phases from earthquakes with m b ! 5.5. 3934 P waves were used from 322 events, and 2244 S waves were used from 168 events. Relative travel time residuals were inverted for upper mantle structure using VanDecar's method. The P wave tomography model reveals a low-velocity anomaly in the upper mantle of approximately dVp = À1 to À1.5% in the vicinity of Ross Island extending laterally 50 to 100 km beneath the TAM from the coast, placing the contact between regions of fast and slow velocities well inland from the coast beneath the TAM. The magnitude of the low-velocity anomaly in the P wave model appears to diminish beneath the TAM to the north and south of Ross Island. The depth extent of the low-velocity anomaly is not well constrained, but it probably is confined to depths above $200 km. The S wave model, within resolution limits, is consistent with the P wave model. The low-velocity anomaly within the upper mantle can be attributed to a 200-300 K thermal anomaly, consistent with estimates obtained from seismic attenuation G 3

Tectonic history of mid-Miocene to present southern Victoria Land Basin, inferred from seismic stratigraphy in McMurdo Sound, Antarctica

“…Inversion of Rayleigh wave show that the upper mantle (40 -160 km depth) shear wave velocities beneath the Terror Rift are up to 6% slower compared to standard reference earth model (Bannister et al, 2000). P and S wave tomography images (Watson et al, 2006) also reveal a low-velocity region, interpreted as a 200-300 K thermal anomaly, within the upper mantle centred beneath Ross Island. The presence of the thermal anomaly is corroborated by present-day active volcanism (LeMasurier, 1990) at Mt Melbourne, at the northern end of the Terror Rift (Fig.1), and Mt Erebus, at the southern limit.…”

Glimpses of East Antarctica: Aeromagnetic and satellite magnetic view from the central Transantarctic Mountains of East Antarctica

“…The seismic data show that there is only a small crustal root beneath the TAM (≤5 km) and that the Moho is uniformly flat, extending more than 1300 km inland. Seismic velocity and body wave tomography data also indicate that a prominent transition between high-and low-velocity lithospheric mantle underlies the TAM between about 50-150 km inboard of the present-day range front [Watson et al, 2006;Lawrence et al, 2006b].…”

“…North of the transfer zone, the seismic boundary is not offset and generally follows the center and east side of the Wilkes Subglacial Basin (Figure 9). Local tomography studies suggest that high-velocity, thick lithosphere extends farther east nearly to the coast at ∼75°S [Lawrence et al, 2006a[Lawrence et al, , 2006bWatson et al, 2006]. The difference between the magnetically delineated and seismically delineated edges of the undeformed craton is puzzling and unusual.…”

Heat Flow and Hydrologic Characteristics at the AND-1B borehole, ANDRILL McMurdo Ice Shelf Project, Antarctica

“…The high heat fl ow may be a direct manifestation of a thermal anomaly within the upper mantle and beneath Ross Island (Watson et al, 2006), and also is typical of the effects of crustal extension and thinning on temperatures within rift basins (Jaupart and Mareschal, 2007). For example, high heat fl ow values greater than The most reliable determinations are from repeat temperature logs recorded in deep boreholes, shown in boldface type.…”