Crustal structure and tectonic provinces of the Riiser-Larsen Sea area (East Antarctica): results of geophysical studies |
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| Authors: | G Leitchenkov J Guseva V Gandyukhin G Grikurov Y Kristoffersen M Sand A Golynsky N Aleshkova |
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| Institution: | (1) All-Russia Research Institute for Geology and Mineral, Resources of the World Ocean (VNIIOkeangeologia), 1 Angliysky Ave, St. Petersburg, 190121, Russia;(2) Polar Marine Geosurvey Expedition (PMGE), 24 Pobeda St., Lomonosov, 189510, Russia;(3) University of Bergen, PO 7800, Prof Keysers gt. 8, Bergen, 5020, Norway;(4) Norwegian Petroleum Directorate (NPD), N-4003, Stavanger, Norway |
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| Abstract: | About 16,000 km of multichannel seismic (MCS), gravity and magnetic data and 28 sonobuoys were acquired in the Riiser-Larsen
Sea Basin and across the Gunnerus and Astrid Ridges, to study their crustal structure. The study area has contrasting basement
morphologies and crustal thicknesses. The crust ranges in thickness from about 35 km under the Riiser-Larsen Sea shelf, 26–28 km
under the Gunnerus Ridge, 12–17 km under the Astrid Ridge, and 9.5–10 km under the deep-water basin. A 50-km-wide block with
increased density and magnetization is modeled from potential field data in the upper crust of the inshore zone and is interpreted
as associated with emplacement of mafic intrusions into the continental margin of the southern Riiser-Larsen Sea. In addition
to previously mapped seafloor spreading magnetic anomalies in the western Riiser-Larsen Sea, a linear succession from M2 to
M16 is identified in the eastern Riiser-Larsen Sea. In the southwestern Riiser-Larsen Sea, a symmetric succession from M24B
to 24n with the central anomaly M23 is recognized. This succession is obliquely truncated by younger lineation M22–M22n. It
is proposed that seafloor spreading stopped at about M23 time and reoriented to the M22 opening direction. The seismic stratigraphy
model of the Riiser-Larsen Sea includes five reflecting horizons that bound six seismic units. Ages of seismic units are determined
from onlap geometry to magnetically dated oceanic basement and from tracing horizons to other parts of the southern Indian
Ocean. The seaward edge of stretched and attenuated continental crust in the southern Riiser-Larsen Sea and the landward edge
of unequivocal oceanic crust are mapped based on structural and geophysical characteristics. In the eastern Riiser-Larsen
Sea the boundary between oceanic and stretched continental crust is better defined and is interpreted as a strike-slip fault
lying along a sheared margin. |
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| Keywords: | Antarctica Continental margin Riiser-Larsen Sea Geophysical data Seismic stratigraphy Crust |
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