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Abstract-Electron paramagnetic resonance (EPR) signals of Bi2+ ions have been detected in the EPR spec trum of manganese , bismuth , and tin doped PbWO 4 single crystals irradiated by xenon and mercury lamps at 100 K. The parameters of the Zeeman, hyperfine, and superhyperfine interactions and the localization of Bi 2+ ions have been determined.

SUMMARY Rapid onset of subduction tectonics across the western Pacific convergent margins in the early Eocene was followed by a slower phase of margin growth of the proto Tonga-Kermadec subduction system north of Zealandia during a middle Eocene phase to tectonic adjustment. We present new age constraints from International Ocean Discovery Program Expedition 371 borehole data on deformation events in northern Zealandian sediments that document the formation of the convergent margin boundary northwest of New Zealand. The deformation shows a shortening event that lasted up to 20 myr and acted over distances of ∼1000 km inboard of the evolving plate margin, just northwest of New Zealand. Multichannel seismic profiles tied to our new borehole sites show shortening occurred predominantly between 45 Ma and 35 Ma with some deformation related to slope failure continuing into the Oligocene. The termination of shortening is linked to opening of the backarc basins of the southwest Pacific and the migration of the Tonga-Kermadec Trench to the east which may have removed the structural evidence of the Eocene plate margin. Paleogene deformation observed inboard of the evolving proto Tonga-Kermadec subduction system indicates that the lithosphere of northern Zealandia, a region of thin continental crust, was strong enough to act as a stress guide. Compressive stresses that caused intra plate folding and faulting developed behind the initiating subduction system with the finite period of deformation indicating the time frame over which an active convergent margin lay along the northern margin of Zealandia.

The results of electron paramagnetic resonance (EPR) studies of Dy 3+ ions in lead thiogallate PbGa 2 S 4 single crystals have been presented. It has been shown that the ground state of these ions corre sponds to the lowest Stark sublevel Γ 6 of the term 6 H 15/2 . The spectra are well described by the axially sym metric spin Hamiltonian with the effective spin S = 1/2 with the factors g || = 15.06 and g ⊥ = 2.47. The Dy 3+ ions substitute Pb 2+ ions in the crystal lattice of PbGa 2 S 4 . The observed hyperfine structure has allowed to unambiguously interpret the EPR spectra. The hyperfine interaction constants of two odd isotopes of dyspro sium in lead thiogallate single crystals have been found to be A || = 675 × 10 -4 cm -1 and A ⊥ = 111 × 10 ⎯4 cm -1 for 163 Dy and A || = 472 × 10 -4 cm -1 and A ⊥ = 77 × 10 -4 cm -1 for 161 Dy.

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