Discovery of thrust klippen, northwest of Mary Kathleen, Mt Isa Inlier, Australia

Abstract

In the northeastern part of the Mary Kathleen 1:100 000 sheet, a thick pile of Early to Middle Proterozoic metasediments, metavolcanics and intrusive rocks were deformed by an early thrusting event and later by east‐west shortening. D₁ produced a thrust complex, containing imbricate stacks of thrust sheets and a sequence of foliations, changing in orientation and style: S_1A is a phyllonitic fabric on the major thrusts; Sib is the axial‐plane foliation to west‐verging folds in the immediate vicinity of the major thrusts; and S_1C is the axial‐plane foliation of northeast‐southwest upright folds, locally developed within the thrust sheets, caused by shortening parallel to the transport direction. Two thrust systems have been studied in detail. In the first, in the Deighton area, the geometry of the imbricates, the extension lineations on S_1A and the orientation of D_1C folds all point towards a westward or northwestward movement direction. In contrast, the West Leichhardt imbricates may have moved southward. After thrusting, both systems underwent east‐west shortening during D₂, causing the alignment of elongate doubly plunging klippen, separated from each other by underlying steepened imbricate stacks. These results require a revision of the significance of the current lithostratigraphic column: the possibility that a major tectonic repetition rather than a sedimentary repetition occurs in the cover sequences cannot be excluded at present.

Key words:

• Mt Isa
• Proterozoic mobile belts
• Queensland
• structural geology
• thrusting