HR: 15:25h
AN: T33G-08    [Abstracts]
TI: Arctic Lena Trough -- NOT a Mid-Ocean Ridge
AU: * Snow, J E
EM: jesnow@uh.edu
AF: University of Houston, Department of Geosciences 315 S&R 1, Houston, TX 77204-5007 United States
AU: * Snow, J E
EM: jesnow@uh.edu
AF: Max-Planck Institute for Chemistry, Postfach 3060, Mainz, 55020 Germany
AU: Hellebrand, E
EM: ehelle@mpch-mainz.mpg.de
AF: Max-Planck Institute for Chemistry, Postfach 3060, Mainz, 55020 Germany
AU: Handt, A v
EM: avdh@mpch-mainz.mpg.de
AF: Max-Planck Institute for Chemistry, Postfach 3060, Mainz, 55020 Germany
AU: Nauret, F
EM: fnauret@eos.ubc.ca
AF: University of British Columbia, Earth and Ocean Sciences, Vancouver, V6T 1Z4 Canada
AU: Gao, Y
EM: yongjungao@uh.edu
AF: University of Houston, Department of Geosciences 315 S&R 1, Houston, TX 77204-5007 United States
AU: Feig, S
T33G-08 AF: Universitaet Hannover, Callinstr., Hannover, 30167 Germany
AU: Jovanovic, Z
T33G-08 AF: Max-Planck Institute for Chemistry, Postfach 3060, Mainz, 55020 Germany
AB: The North American-Eurasian plate boundary traverses the Atlantic and Arctic oceans. Over most of that length, it is a Mid-Ocean Ridge that spreads between about 23 mm/yr (MAR) and 10 mm/yr (Gakkel Ridge) full rate. The northern MAR and the Gakkel ridge are connected by a deep linear feature called Lena Trough. Until about 10 million years ago, Lena Trough was not an oceanic domain at all, but a continental shear zone through a narrow isthmus of continental crust that connected the American and Eurasian plates. Its opening was, significantly, the most recent and final event in the separation of the North American from the Eurasian continent, and opened the gateway for deep water circulation between the Arctic and North Atlantic oceans. Models for the tectonic configuration of Lena Trough have until now differed only in the number and length of fracture zones and spreading segments thought to be present. Lena Trough is a deep fault-bounded basin with depths of 3800-4200m, and irregular, steep valley sides that are oblique to the spreading direction. Basement horst structures outcrop as sigmoidal ridges with steeply dipping sides project out of the valley floor, but these are not traceable to any parallel structures on either side. Ridge-orthogonal topography is simply absent (ie no segments trending parallel nor fracture zones perpendicular to Gakkel Ridge). Most faults trend approximately SSE-NNW, an obliquity with respect to Gakkel Ridge (SW-NE) of about 55 degrees. The basement ridges are composed nearly entirely of mantle peridotite, as are the valley walls. Only at the northern and southern extremities of Lena Trough do basalts appear at all. The Northern basalts show strong chemical affinities to those of Gakkel Ridge, and can be considered a part of the Gakkel volcanic system. The rare southernmost basalts, however, are quite unique. They are alkali basalts with K2O up to 2 weight percent, highly incompaitble element enriched and occupy a corner of isotope space known as EM1 (See abstract in the Stan Hart Symposium), and bear more resemblance to alkaline rift magmas than to mid-ocean ridge volcanics. Thus Lena Trough is not a Mid-Ocean Ridge (in any event there is no ridge there), but represents a recent transition form between a continental rift and an oceanic one. The Lena Trough is also the only known modern analog of the Iberia Margin, the conjugate Newfoundland Margin, as well as the ophiolite complexes of the Western Alps. It is significant that there is no evidence for low-angle detachment at Lena Trough. Instead, the thick lithosphere at Lena Trough results in decidedly thick-skinned rift tectonics, with steeply dipping fault surfaces and relatively narrow basement blocks.
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8140 Ophiolites (3042)
DE: 8178 Tectonics and magmatism
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
DE: 9315 Arctic region (0718, 4207)
SC: Tectonophysics [T]
MN: Fall Meeting 2005