Oceanic and Continental Transform Faults

JI gal. Soc. hnd. Vol. 136, 1979, pp. 267-268. Printed in Northern Ireland.

Oceanic and continental transform faults

Editorial Note: A thematic meeting on 'Oceanic and continental transform faults', convened by Dr Brian F. Windley (Department of Geology, University of Leicester) was held at the Geological Society on 18 January 1978.

Dr Windley has provided the following Introduction to the published papers:

Transforms in perspective Sedimentary basins form along continental margins and their relationships with fracture zones in the At- Transform faults are important structures fundamental lantic are reviewed byWilson & Williams (1979). to the mechanism of sea floor spreading and plate Fracture zone end basins form in tensional rifts, frac- tectonics, and yet, since they were first defined and ture zone-parallel and fracture ridge-dammed basins explained by J. T. Wilson in 1965, they have been the occuralong sheared margins,and aulacogen basins subject of relatively little study in comparison withthe may be controlled by pre-drift continental structures. other 2 major plate boundaries:mid-oceanic ridges Continental transform plate boundaries occur today and subduction zones. To my knowledge there has particularly in the circum-Pacific region, e.g. Califor- never been an international symposiumconcerned nia(Crowell 1979), southern Alaska(Naugler & exclusively with transform faults, and for this reason Wageman1973), New Zealand (Norris et al. 1978), the one-daymeeting at the GeologicalSociety was and in the Alpine fold belt, e.g. Turkey (Sengor 1979) organized,with the aim of bringing together in a and the Dead Sea (Quennell 1958). The San Andreas comprehensive manner the diverse aspects of trans- fault system constitutes the transform boundary be- forms;this thematic set of papers resultsfrom the tween the Pacific and American plates; it originated in meeting. the early Miocene and hasa total displacement of Transforms are faults along which 2 platesmove more than 1OOOkm (Crowell 1979). The North past each other by simple shear with no creation or Anatolian transform fault forms the boundary be- destruction of lithosphere. They were first recognized tween the Black Sea and Anatolian plates that origi- in the NE Pacific (Mendocino, Murray and Pioneer nated asa result of the ArabiaIAnatolia collision fracture zones, e.g. Vacquier 1965), but recent study during the late Mimne; it has an offset of about has been concentrated on the N Atlantic, e.g. on the 85 lan (Sengor 1979). These papers provide a useful Famous (c. 37"N), Kurchatov (40.5"N), and Charlie- comparison between two types of continental trans- Gibbs (52"N) fracture zones(Searle 1979), and the form evolution. Oceanographer zone (35"N). Attention has often been While the majority of oceanic transform faults are focussed on 2 aspects: (a) the composition of the caused directly by the differential rates of sea floor igneous rocks, ranging from basalts to gabbros, and spreading, a few larger transforms owe their position serpentinized peridotites and breccias dredged from to pre-drift continental structures (Wilson 1965). Wil- the fracture mne walls (Bonatti et al. 1974); and (b) son & Williams (1979) point out that basement struc- the morphologyand structure of the zones using tural grain has influenced the location of some Atlan- bathymetric data (Searle 1979). These data provide tic ocean transforms,such as Kelvin, Canary, unique constraints on the tectonic character and Romanche and 56.5"s (the last was substantiated by evolution of these oceanic boundaries. Scrutton & Dingle 1973), and geophysical data indi- In an important link paper, DeLong et al. (1979) cate that the Hermitage-Dover fault mne inNew- present an evolutionary model for ridge-ridge trans- foundland is ancestral tothe Charlie fracture zone forms in which information from the oceanic crust is (Haworth 1977). These results are consistent with the integrated with that fromancient fracture zones in suggestion of Francheteau & Le Pichon (1972) that terrestrial ophiolite complexes, especially in W New- differential subsidence along continental margins may foundland and the Apennines. lead to faulting along old lines of weakness, so extend- 0016-7649/79/0500-0267502.00 ing the effects of oceanic transforms into continental 0 1979 The Geological Society interiors.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/136/3/267/4886287/gsjgs.136.3.0267.pdf by guest on 28 September 2021 268 B. F. Windley References BONATTJ.E., EM[LIANI, C., G., HONNOREZ,J. & continental transform boundary in southern New Zea- RYDELL, H. 1974. Ultramafic-carbonate breccias from land. J. w01. Soc. Lond. 135, 191-205. the equatorial mid-Atlantic ridge. Mar. Geol., 16, 83- QUENNEL,A. M. 1958. The structural and geomorphic evolu- 103. tion of the Dead Sea Rift. Q. X. geol. Soc. Lond. 114, CROWELL, J. C. 1979. The San Andreas fault system through 1-24. time. J. gwl. Soc. Lond. 136,293-302. SCRUTIDN,R. A. & DINGLE,R. V. 1973. Basement control DELONG.S. E., DEWEY.J. F. & Fox, P. J. 1979. Topog- over sedimentation on the continental margin west of raphic and geologic evolution of fracture zones. J. geol. southern Africa. 7tans. geol. Soc. S. Afi. 77, 253-260. Soc. Lond. 136, 303-10. S-, R. C. 1979. Side scan sonar studies of N Atlantic FRANCHEEMU, J. 8r LE PICHON, X. 1972. Marginal fracture fracture zones. I. gal. Soc. Lond. 136, 283-92. zones as structural framework of continental margins in SENG~R,A. M. C. 1979. The N Anatolian transform fault: South Atlantic ocean. Bull. Am. Ass. Petrol. Gal. 56, Its age, offset and tectonic significance. J. geol. Soc. 991-1007. Lond. 136, 269-82. HAWORTH. R. T. 1977. The continental crust northeast of VACQUIBR,V. 1965. Transcurrent faulting in the ocean floor. Newfoundland and its ancestral relationship to the Char- Phil. Tmns. R. Soc. Lond. 258A, 77-81. lie Fracture Zone. Nature 266, 246-9. Wnso~,J. T. 1965. A new class of faults and their bearing NAUGJER,F. P. & WAGEMAN,J. M. 1973. Gulf of Alaska: on continental drift. Nature 207, 343-47. magnetic anomalies, fracture zones and plate intemction. Wnso~.R. C. L. & W=, C. H. 1979. Oceanic tram- Bull. ~01.Soc. Am. 84 1575-84, form structures and the development of Atlantic conti- Nom, R. J., CARTER,R. M. & TURNBULL, I. M. 1978. nental margin sedimentary basins- review. J. gal. Soc. caiwzoic sedimentation in basins adjacent to a major Lond. l36, 311-20.

Received 1 September 1978. BRIANF. WIND-, Department of Geology, The University, Leicester LE1 7RH.

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FIG. 2A,B. Sonograph and physiogra- FIG. lA, B. Part of sonograph mosaic of FAMOUS area with phic interpretation: intersection of me- bathymetry (contour interval 500 fm (914.4m)). Broken lines indi- dian valley with Fracture Zone A in the cate spreading axes and fracture zones. FAMOUS area. After Laughton & Rusby (1975).

30'00' 29'00' 50 KM

FIG. 3A, B. Part of sonograph mosaic of Kurchatov Fracture Zone and bathymetry (contour interval 250 m). Broken lines indicate spreading axes. PLATE l 286

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32 31 30

FIGS. lA, B; 2A, B. Sections of sonograph mosaic and tectonic interpretations from Charlie-Gibbs Fracture Zone. lA, B: Southern transform fault. 2A, B: Northern transform fault. Major inferred strike-slip fault is indicated by a heavy line. Sea floor shallower than 3000 m is shaded. PLATE 2

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