Fracture Patterns in the Southland Synclinorium.


Scadden, PG


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Fracture patterns were studied on the Owaka Anticline and Southland Syncline of the Southland Synclinorium. Jointing was found to be dominated by two sets, both at right angles to bedding. J1 is perpendicular to the Synclinorium axis, while J2 is parallel. J3, thought to represent conjugate shear joints, is also important. 5 other joint sets were recognised. A possible origin is proposed relating jointing to interaction between the probable external and residual stress fields during the deformation, uplift and relaxation cycle.
Comparison of faults shown on existing maps with the lineament pattern obtained from a study of LANDSAT imagery resulted in 6 fault sets being recognised. 3 are thought to be the result of an extensional, block-faulting regime in the late Cretaceous, while 2 others are postulated to result from bending of the Synclinorium in the Kaikoura Orogeny. An accord between a mathematical model for bending of the Synclinorium and the observed fracture pattern is demonstrated. The final fault set is a lineament grouping only and its origin is unknown.
From existing maps and from this study, a structurHl synthesis is attempted. The Southland Synclinorium if; a non-cylindrical, asymmetrical synclinorium, plunging S.E. with an axial trend ranging 105-ยท130. The folds are probably near concentric with tightness varying along its length. Folding took place in the Rangitata Orogeny but has been modified during the Kaikoura Orogeny. Flexural s1ip/flow is thought to have been the dominant process of folding though longitudinal tangential strain may have been important in the hinge zone. There is some evidence that the principal compressive stress was not quite perpendicular to the axis.
Finally a possible tectonic history of the Synclinorium is given.

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86 leaves. Diagms, photos, 30 cm.


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Scadden, PG, “Fracture Patterns in the Southland Synclinorium.,” Otago Geology Theses, accessed July 23, 2019,