Macroscopic structural features in Deep Sea Drilling Project cores from forearc regions
Neil Lundberg, J. Casey Moore, 1986. "Macroscopic structural features in Deep Sea Drilling Project cores from forearc regions", Structural Fabrics in Deep Sea Drilling Project Cores From Forearcs, J. Casey Moore
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DSDP cores from active margins show a range of structural features, including bedding dips, semi-penetrative secondary fabrics, and faults. We have collected data on the distribution and orientation of structural features in all DSDP cores recovered to date in forearcs, and have carried out topical studies on selected fabrics. Graphic structural logs, compiled from a consistently acquired data set, show the distribution of structural features margin by margin, and allow comparisons to be drawn between margins. Most sediments cored in forearcs are in situ slope deposits, and bedding dips constitute a fundamental strain indicator. Histograms of bedding dips in slope deposits document a distinction between 1) actively deforming forearc regions underlain by Neogene and Quaternary accretionary wedges, and 2) less-deformed sedimentary sequences that overlie rigid basement terranes.
Structural fabrics in active-margin cores include stratal disruption and cataclastic fabrics, scaly foliation, spaced foliation, vein structure, kink bands, crenulation folds, web structure, and fissility. The distribution of structural fabrics in active-margin cores serves to distinguish between different structural regimes in forearc regions. Cores from upper-slope sites tend to be dominated by structures indicative of layer-parallel extension, which may have formed during postulated bedding-parallel shear in gravity-induced downslope movement of upper sediment layers. Cores from lower-slope sites tend to be dominated by compressional structures, presumably due to overall horizontal shortening resulting from plate convergence.