Computer‐aided interpretation of side‐looking sonar images from the eastern intersection of the Mid‐Atlantic Ridge with the Kane Transform

Approximately 600 km2 of Deep-Tow side-looking sonar data were collected at the eastern intersection of the Mid-Atlantic Ridge with the Kane Transform. The merged digital image mosaic provides a synoptic view of the oceanic crust exposed across major escarpments at this ridge-transform intersection (RTI). We characterized this large acoustic data set using textural attributes extracted from the backscatter image by means of a gray level co occurrence matrix method and Fourier fractal analysis. False-color texture attribute maps created from these methods aid in the interpretation and discrimination of surficial deposits and bedrock units on the seafloor. Principal components analysis performed on the textural attributes reduced the dimensionality of the textural feature vector and optimized imago texture discrimination. The textural attributes were calibrated to ground truth geologic data and extrapolated to regions with no ground data. The resultant texture and classification maps are consistent with the results of submersible studies but reveal more details of the seafloor geology than the conventional visual interpretation of the backscatter image and ground geologic observations. The inferred distribution of gabbros, basalts, surficial sediments, and rubble deposits shown in the classification map provides new constraints on seafloor geology at the eastern Kane RTI. Over 60% of the southern transform valley wall is covered by pelagic sediments and talus or rubble deposits, with intermittent exposures of coarse-grained gabbroic rocks and basaltic volcanic rocks. The western rift valley wall is classified as mainly massive outcrops of gabbroic rocks. The contact between the gabbroic outcrops on the western rift valley wall and the pillow basalt terrane on the rift valley floor can be traced for several kilometers along the base of the median valley wall. This new perspective supports the interpretation of the “inside-corner massif” as an “oceanic core complex” which is being degraded by mass wasting along tectonically active escarpments of the bounding median valley and transform valley walls.

[1]  Eldridge M. Moores,et al.  The Troodos Massif, Cyprus and other ophiolites as oceanic crust: evaluation and implications , 1971, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[2]  Jian Lin,et al.  A geological model for the structure of ridge segments in slow spreading ocean crust , 1994 .

[3]  B. Wernicke Low-angle normal faults in the Basin and Range Province: nappe tectonics in an extending orogen , 1981, Nature.

[4]  P. J. Fox,et al.  Geologic Investigations in the Cayman Trough: Evidence for Thin Oceanic Crust along the Mid-Cayman Rise , 1981, The Journal of Geology.

[5]  P. Blondel Segmentation of the Mid-Atlantic Ridge south of the Azores, based on acoustic classification of TOBI data , 1996, Geological Society, London, Special Publications.

[6]  R. Hékinian,et al.  Oceanic fracture zones do not provide deep sections in the crust , 1976 .

[7]  John A. Richards,et al.  Remote Sensing Digital Image Analysis , 1986 .

[8]  Robert M. Haralick,et al.  Textural Features for Image Classification , 1973, IEEE Trans. Syst. Man Cybern..

[9]  N. Pace,et al.  Machine Classification of Sedimentary Sea Bottoms , 1979, IEEE Transactions on Geoscience Electronics.

[10]  Jian Lin,et al.  Mid-Atlantic Ridge volcanism from deep-towed side-scan sonar images, 25 °–29 °N , 1995 .

[11]  K. Whipple,et al.  A submersible study in the western Blanco fracture Zone, N.E. Pacific: Structure and evolution during the last 1.6 Ma , 1995 .

[12]  P. J. Fox,et al.  The morphology and tectonics of the Mark area from Sea Beam and Sea MARC I observations (Mid-Atlantic Ridge 23° N) , 1988 .

[13]  P. J. Fox,et al.  The geology of the Oceanographer Transform: The ridge-transform intersection , 1984 .

[14]  A. C. Campbell,et al.  Along-axis variations in seafloor spreading in the MARK area , 1987, Nature.

[15]  G. Lister,et al.  The origin of metamorphic core complexes and detachment faults formed during Tertiary continental extension in the northern Colorado River region, U.S.A. , 1989 .

[16]  Kim A. Kastens,et al.  Structural and volcanic expression of a fast slipping Ridge-Transform-Ridge-Plate Boundary: Sea MARC I and photographic surveys at the Clipperton Transform Fault , 1986 .

[17]  J. Karson,et al.  Along-axis variations in tectonic extension and accommodation zones in the MARK Area, Mid-Atlantic Ridge 23°N latitude , 1992, Geological Society, London, Special Publications.

[18]  D. L. Turcotte,et al.  Fractal mapping of digitized images: Application to the topography of Arizona and comparisons with synthetic images , 1989 .

[19]  J. Karson,et al.  Structural Processes at Slow-Spreading Ridges , 1992, Science.

[20]  D. J. Miller,et al.  Proceedings of the Ocean Drilling Program, 153 Initial Reports , 1995 .

[21]  J. Henriet,et al.  Observation of sections of oceanic crust and mantle cropping out on the southern wall of Kane FZ (N. Atlantic) , 1994 .

[22]  D. Tamsett Sea-bed characterisation and classification from the power spectra of side-scan sonar data , 1993 .

[23]  H. Schouten,et al.  Kane Fracture Zone , 1988 .

[24]  Textural analysis and structure-tracking for geological mapping: applications to sonar images from Endeavour Segment, Juan de Fuca Ridge , 1993, Proceedings of OCEANS '93.

[25]  M. Cannat Emplacement of mantle rocks in the seafloor at mid‐ocean ridges , 1993 .

[26]  T. Reed,et al.  Digital image processing techniques for enhancement and classification of SeaMARC II side scan sonar imagery , 1989 .

[27]  J. Karson,et al.  Tectonic window into gabbroic rocks of the middle oceanic crust in the MARK area near Sites 921-924 , 1997 .

[28]  E. Bonatti,et al.  Sections of the Earth's crust in the equatorial Atlantic , 1976 .

[29]  K. W. Bjerde,et al.  Seabed classification from multibeam echosounder data using statistical methods , 1993, Proceedings of OCEANS '93.

[30]  J. Karson,et al.  Emplacement of deep crustal and mantle rocks on the west median valley wall of the MARK area (MAR, 23°N) , 1991 .

[31]  N. Mitchell A model for attenuation of backscatter due to sediment accumulations and its application to determine sediment thicknesses with GLORIA sidescan sonar , 1993 .

[32]  D. Bideau,et al.  Direct observation of a section through slow-spreading oceanic crust , 1989, Nature.

[33]  John E. Hughes Clarke,et al.  Classification of seafloor geology using multibeam sonar data from the Scotian Shelf , 1994 .

[34]  Z. Reut,et al.  Computer classification of sea beds by sonar , 1985, Nature.

[35]  J. Karson,et al.  Tectonics of ridge-transform intersections at the Kane fracture zone , 1983 .