Studies of the marine crustal magnetization at intermediate wavelengths

The data can be filtered at intermediate wavelengths to provde a data set which complements the satellite fields of MAGSAT, TSS and GRM. The filtered marine data set provides a high resolution data set which is closer to the source bodies than satellite survey data. However, the GRM and TSS could provide the necessary resolution to match the filtered sea surface field. The added resolution determines the nature of crustal magnetizations which give rise to the intermediate wavelength field. It is found that remanent magnetization is an important component over the oceans. Crustal deformation and plate motions result in magnetization vectors which differ significantly from the present day field directions. Induced magnetization or GRM are important components over the oceanic plateaus and spreading centers

New Constraints on Plate Tectonic Puzzle of the SW Pacific

A long-standing problem in the tectonics of the southwest Pacific has been the lack of closure of the plate circuit linking the Antarctic, Australia, Lord Howe Rise, and Pacific plates in late Cretaceous and early Tertiary time [Molnar et al., 1975]. Avoiding unacceptable overlaps and underlaps in reconstructions of these plates requires invoking relative motion on one or more nebulous plate boundaries somewhere along the plate circuit, such as between East and West Antarctica, within West Antarctica [Stock and Molnar, 1987], or perhaps between the Lord Howe Rise and Challenger Plateau in the Tasman Sea [Lawver and Gahagan, 1994]. This problem is of more than mere local interest since the motion of the Pacific plate relative to the rest of the globe is constrained through its connection with West Antarctica

Extension in the western Ross Sea region-links between Adare Basin and Victoria Land Basin

Spreading in the Adare Basin off north-western Ross Sea (43–26 Ma) and extension in the Victoria Land Basin (VLB, > 36 Ma) are used to constrain the pole of rotation for the Adare Basin, providing a rifting model for the region for the past 45 Ma. The offset from Northern Basin to VLB at about 74°S coincides with the linear Polar-3 magnetic anomaly, inferred to be caused by a major 48 - 34 Ma igneous intrusion. The style of extension apparently changed at about 34 Ma, with the end of intrusion at the Polar-3 anomaly, a change from highly asymmetric extension in Adare Basin, and the onset of major subsidence on the flanks of VLB. Ductile lower crustal and lithospheric flow is proposed as the cause of the inferred thick crust underlying southern Adare Basin, and a result of the constraining of extension to the adjacent contiguous Northern Basin

Comment on "Tectonic Rotations in Extensional Regimes and Their Paleomagnetic Consequences for Ocean Basalts" by Kenneth L. Verosub and Eldridge M. Moores

One of the more intriguing results from palcomagnetic studies of Deep Sea Drilling Project (DSDP) basalts is that a surprisingly large number of samples have inclinations that deviate significantly from expected values. Vetosub and Moores [1981] sought to account for what appear to be systematic departures of mean inclination at several DSDP basement sites in terms of tectonic rotations along listtic normal faults. Such rotations, about horizontal axes perpendicular to the extension direction and typically amounting to 30ø-50 ø but as large as 70 ø to 90 ø, were suggested to be characteristic of an extensional tectonic regime such as near an ocean spreading ridge system. There is a clear implication that large tectonic rotations are a characteristic process associated with ocean crust formation

Revised Eocene-Oligocene kinematics for the West Antarctic rift system

Past plate motion between East and West Antarctica along the West Antarctic rift system had important regional and global implications. Although extensively studied, the kinematics of the rift during Eocene-Oligocene time still remains elusive. Based on a recent detailed aeromagnetic survey from the Adare and Northern Basins, located in the northwestern Ross Sea, we present the first well-constrained kinematic model with four rotations for Anomalies 12o, 13o, 16y, and 18o (26.5–40.13 Ma). These rotation poles form a cluster suggesting a stable sense of motion during that period of time. The poles are located close to the central part of the rift implying that the local motion varied from extension in the western Ross Sea sector (Adare Basin, Northern Basin, and Victoria Land Basin) to dextral transcurrent motion in the Ross Ice Shelf and to oblique convergence in the eastern end of the rift zone. The results confirm previous estimates of 95 km of extension in the Victoria Land Basin

Mapping Geomagnetic Field Variations with Unmanned Airborne Vehicles

Unmanned airborne vehicles (UAVs) are increasingly being used for a variety of commercial and research applications. The small (wingspan ~3 meters), fully autonomous aircraft are well suited for use in remote areas or dangerous settings. UAVs that are launched and recovered on land are being used for atmospheric chemistry and surface imaging studies and for aeromagnetic surveys [Curry et al., 2004; Ramanathan et al., 2007; Funaki et al., 2007]. We report here on the first deployment of UAVs launched from a marine research vessel. The UAVs mapped fluctuations in the magnetic field in a remote area of the southwestern Pacific Ocean

Constraints on the proposed Marie Byrd Land-Bellingshausen Plate Boundary from seismic reflection data

Single-channel and multichannel marine seismic data off the coast of West Antarctica collected during two Nathaniel B. Palmer cruises (NP92-8 and NP96-2) in the vicinity of 65°S to 71°S, 220°E to 250°E, reveal a NNW trending graben. We interpret this graben to be part of the paleodivergent plate boundary between the Marie Byrd Land and Bellingshausen plates. This graben coincides with a −520 nT magnetic anomaly to the NNW and a −720 nT anomaly to the SSE, as well as a 20 mGal negative gravity anomaly. Seismic profiles subparallel to the graben (22 km/Ma half-spreading rate) reveal greater seafloor roughness to the NE, where seafloor spreading was slower, than to the SW (27 km/Ma half-spreading rate). These data allow the position of the Marie Byrd Land-Bellingshausen plate boundary to be constrained more precisely than has previously been possible, with a trend of N17°W from 68.52°S, 233.65°E to 68.41°S, 233.56°E. The sediment-filled graben has normal separation of sedimentary layers varying from 740±30 m to 580±20 m imaged in seafloor of age A33y (74 Ma)

Mesozoic subducted slabs under Siberia

Recent results from seismic tomography demonstrate that subducted oceanic lithosphere can be observed globally as slabs of relatively high seismic velocity in the upper as well as lower mantle(1,2). The Asian mantle is no exception, with high-velocity slabs being observed downwards from the west Pacific subduction zones under the Kurile Islands, Japan and farther south(3-5), as well as under Asia's ancient Tethyan margin. Here we present evidence for the presence of slab remnants of Jurassic age that were subducted when the Mongol-Okhotsk and Kular-Nera oceans closed between Siberia, the combined Mongolia-North China blocks and the Omolon block(6-8). We identify these proposed slab remnants in the lower mantle west of Lake Baikal down to depths of at least 2,500 km, where they join what has been interpreted as a 'graveyard'(9) of subducted lithosphere at the bottom of the mantle. Our interpretation implies that slab remnants in the mantle can still be recognized some 150 million years or more after they have been subducted and that such structures may be useful in associating geodynamic to surface-tectonic processes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62524/1/397246a0.pd