Abstract - Precursor monoclines or fault propagation folds are commonly associated with normal faults. Many previous studies have analysed these structures at outcrop or in analogue models but there are few natural examples which have been studied in detail in 3D. Here we present the results of analysis of two monoclines imaged in a 3D seismic reflection survey in the Taranaki Basin, offshore New Zealand. The monoclines formed in response to Miocene-Recent extensional reactivation of underlying basement normal faults of Cretaceous age. The Miocene structures have associated growth strata that allow their geometrical evolution to be established. The two monoclines initiated at the same time (~ 3.4 Ma). The smaller of the two monoclines has only limited associated faulting while the larger structure was cross-cut by upward propagation of the basement fault as a segmented array of normal faults. Variations in fold amplitudes and fault displacements within the growth strata associated with the larger structure record the progressive transition from folding to faulting, with folding limited to the relay zones between fault segments in the later stages of growth. This structure demonstrates spatial and temporal complementary relationships between folding and faulting so that together they define a single kinematically coherent structure. Although the monoclines widen upwards with geometries consistent with the trishear model of forced folding, there is also a positive correlation between monocline amplitude and wavelength measured along the length of the structure which suggests that the wavelengths of these structures increased as they grew.
Tectonophysics, doi.org/10.1016/j.tecto.2017.06.036, 2017.