Abu Sharib, A.S.A.A. (2012) Foliation intersection axes (FIAs) preserved within porphyroblasts: resolving plan view orthogonal refolding, Eastern Fold Belt, Mt Isa Inlier. Australian Journal of Earth Sciences, 59 (4). pp. 571-598.

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Abstract

The relative timing of the sequence of events is problematic where deformation partitioning strongly separates zones dominated by folds that formed in different periods of orogeny. This is particularly the case where they form orthogonal to one another in plan view. A succession of foliation inflection/intersection axes (FIAs) preserved within porphyroblasts readily resolves the sequence. In situ monazite age dating of porphyroblasts preserving W–E and N–S-trending FIAs yielded ages of 1645 ± 7 and 1591 ± 10 Ma, respectively. Peaks in the distribution of the two FIA sets coincide with the trends of the axial planes of the regional folds. The succession of FIAs, as well as foliations in the matrix in the Soldiers Cap Group of the eastern Mount Isa Inlier, supported with geochronological data reveal W–E directed bulk horizontal shortening followed N–S bulk horizontal shortening. This is despite the apparent regional lack of curvature of the W–E-trending folds around those trending N–S. Furthermore, N–S and W–E-directed bulk shortening resulted in at least 2 cycles of subvertical and subhorizontal foliation development that define the W–E and N–S-trending FIAs.

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