RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES4001, doi:10.2205/2005ES000181, 2005

Geological Overview

2005ES000181-fig01
Figure 1
2005ES000181-fig02
Figure 2
[6]  The axial MAR segment described in this paper lies between the Bogdanov Fracture Zone (7o 10 primeN) and 5o00primeN [Pushcharovskii et al., 2002; Skolotnev et al., 2003a], near the Sierra Leone Fracture Zone (Figure 1). The local seafloor has a highly dissected topography, which is characterized by the absence of transform faults and the variable strike of the rift valley, which consists here of graben-shaped depressions up to 4-5 km deep, such as the Markov depression (Figure 2). This MAR segment also differs from adjacent areas in having lower seismicity.

[7]  The results of dredging during Cruise 10 of the R/V Akademik Ioffe in 2001-2002 and Cruise 22 of the R/V Professor Logachev in 2003 suggest that long ( > 300 km) segments of both walls of the rift valley consist of plutonic rocks, including serpentinized peridotites, various gabbroids, cataclasites and mylonites developing after mafic and ultramafic rocks, and various metasomatic rocks. Strongly altered and tectonized basalts and dolerites crop out in the floor of the valley, its northern and southern flanks, and in the upper parts of its walls. Fresh basalts with crusts of volcanic glass were found on valley floor and on the slopes of neovolcanic rises.

[8]  In spite of the uneven character of the sampling, it can be definitely concluded that both walls of the valley contain similar rock complexes that characterize the whole sequence of the oceanic crust. Judging from the results of remote sensing (conducted with the use of a MAK marine acoustic complex during Cruise 22 of the R/V Professor Logachev in 2003), the local crust is clearly layered. This suggests that most of the rocks discussed in this paper compose a layered complex, which is analogous to those in ophiolitic associations like Monviso in the Western Alps [Lombardo et al., 2002].

[9]  The abundance of sediments in the axial valley and the wide occurrence of ultramafics and gabbro indicate that the modern extension of the oceanic crust in this MAR segment proceeded at the predominance of tectonic over magmatic processes. All of the examined and sampled neovolcanic ridges are variably shifted to the east relative to the rift axis.


RJES

Citation: Sharkov, E. V., N. S. Bortnikov, T. F. Zinger, and A. V. Chistyakov (2005), Silicic Fe-Ti-oxide series of slow-spreading ridges: petrology, geochemistry, and genesis with reference to the Sierra Leone segment of the Mid-Atlantic Ridge axial zone at 6° N, Russ. J. Earth Sci., 7, ES4001, doi:10.2205/2005ES000181.

Copyright 2005 by the Russian Journal of Earth Sciences

Powered by TeXWeb (Win32, v.2.0).