E.Gusev

New Insight on the Knipovich Ridge tectonic position



 

Knipovich Ridge is the northernmost member of the mid-ocean ridge system of the Norwegian-Greenland basin. The last one is traditionally interpreted as the transition zone between Atlantic and Arctic oceans. According plate tectonic model of the Northern Greenland Sea evolution [Talwani and Eldholm, 1977], transform motion of Northern American and Eurasian plates took place during first stage (since 24 magnetic anomaly) since Oligocene (13 anomaly) structural replacement occurred and the opening of the northernmost Greenland Sea has started. New data are in contradiction with accepted model; consequently investigators attempted to newly reconstructed geodynamics of this region [Skogseid et al., 2000].

Interpretation of sonar survey and bottom coring data obtained from Knipovich ridge rift valley as well as previously obtained materials (MCS and HRS, magnetic data, etc.) constrains the evidence of complicated tectonic position of modern spreading center. Sonar survey carried out in the rift valley during 19th cruise of R/V "Professor Logachev" confirm the main lineaments directions established previously by wide-scan sonar survey [Crane et al., 1995]. Prevailing northern-eastern orientation of lineament coincides to tectonic displacements and volcanic rises which form the boundaries of ridge segments. But north-western directions are also recognized in the composition of crest zone creating "rhombus" structures. Major past of rises in rift valley and its displacements are not of transform origin. Dredging of the bottom and flanks of rift valley of Knipovich ridge show rather irregular distribution of fresh and ancient basalt floods along the main ridge axe direction. In 750 N area increased thicknesses of sediments (up to 2 km) were observed [Shkarubo, 1996] in rift valley. Sedimentary cover also fills rift valley in the northernmost part of the ridge (78020'N) adjacent to transform Molloy fault [Baturin,1993].

Correspondence of seismic horizons on profiles crossing rift valley in its northern part to ODR data [Thiede et al., 1995] allows to recognize distribution of ancient (Oligocene) sedimentary units up to the slope of rift valley [Gusev, Shkarubo, 2000]. Dense lithified argillites were obtained by dredging of the western slope of rift valley during 19th Cruise of R/V "Professor Logachev" near 77052' N [Cruise Report "Knipovich-2000"]. These facts scarcely could be interpreted from the point of view of consequent transform-rift evolution of Knipovich Ridge. Suggestion of replacement of Knipovich Ridge axe from the central part of Greenland sea to its eastern edge seems to be more reasonable. In this case presence of ancient sedimentary rocks near modern spreading center is understandable. Moreover new magnetic data [Olesen et al., 1997] make it possible to establish north-eastern orientation of linear magnetic anomalies system. Position of Knipovich ridge is slanting oriented in compare with more ancient anomalies being reformed on the original structure of the oceanic basin. The main problem is the time of this replacement. Norwegian researches data this event by 7 anomaly time [Skogseid et al., 2000].

Localization of the Knipovich Ridge oceanic rift in the eastern part of Norwegian-Greenland basin adjacent to west Spitsbergen margin occurred during Miocene time. This was concluded on the base of seismic sections analyses corresponded stratigraphically to ODR wells sections characterized by fauna assemblages.

Knipovich Ridge is the active modern center of spreading with clear morphology of rift valley, numerous active submarine volcanoes, and hydrothermal activity; but there is no evidence of distinguishable spreading of oceanic floor. Processes of extension are characterized by variable directions and cyclicity: impulses of sharp strengthening of tectonic and magmatic activity are alternated by long epochs of calm tectonic regime. Impulses of extension accompanying by forming of normal and-listric faults and penetration of basalt extrusions tone place not simultaneously in various segments of the ridge rift valley.



References

1. Baturin Ju.G. Structure of sedimentary cover and development of Spitsbergen continental margin. – In: Sedimentory cover of West Arctic metaplatform (tectonics and seysmic stratigraphy). Murmansk, 1993, p. 35-47 (in Russian).

2. Gusev E. & Shkarubo S. Anomalous structure of Knipovich Ridge. Russian Journal of Earth Scinces, Vol. 3, № 2, p. 145–161, 2001, http://rjes.agu.org/v03/tje01056/tje01056.htm

3. Shkarubo S.I. Regularities of spreading in the northern part of Norwegian – Greenland basin. – In: Geological-geophysical characteristics of Arctic region lithosphere. SPb., VNIIO, 1996, p. 101-114 (in Russian).

4. Cherkashev G.A., Poroshina I.M., Shilov V.N., Crone K., Cherrington S. First data on the Knipovich Ridge hydrothermal activity. – In: Marine geology, abstracts of XII Int. Marine Geology School, vol. 2, 1997, Moscow, "GEOS", p. 190-191 (in Russian).



Reference:

 

Gusev E. New Insight on the Knipovich Ridge tectonic positions. Geology and Geophysics of the Knipovich Ridge. Abstracts of the K2K post-cruise meeting, p.13–14, St.Petersburg, November 01–03, 2001.



 


 

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