Murihiku-Maitai terrane boundary, South East Otago

Simpson, Brent Andrew.

This project examines the boundary between the Murihiku and Dun Mountain - Maitai Terranes, as well as the intervening strata of the Kaka Point Structural Belt, South-East Otago. Strata ofthe Murihiku and Dun Mountain -Maitai Terranes can be correlated with previously mapped units found inland, whereas the Kaka Point Structural Belt lacks clear correlatives. The Kaka Point Structural Belt shows both similarities and differences to both the Murihiku and Dun Mountain -Maitai Terranes, with previous authors provisionally including it within the Dun Mountain -Maitai Terrane. However, based on evidence from this field area, the Kaka Point Structural Belt is interpreted as a separate, "suspect" terrane. Within this field area the Dun Mountain -Maitai Terrane is represented by ophiolitic sea floor that was metamorphosed (Otanomomo Complex), then brecciated (Telford Breccia), and overlain by sedimentary rocks derived from a volcanic arc. Sedimentary features indicate deposition via storm-generated currents. The Kaka Point Structural Belt represents the deformed remnants of a turbidite filled basin, with the volcanic arc derived sediment originating from the east. Sediments were deposited either in a forearc or backarc basin setting. The Murihiku Terrane represents a large turbidite filled basin in which a regressive wedge propagated from southeast (arcwards) to the northeast (trenchwards). Most evidence favours a forearc basin setting although some evidence suggests it may have been a backarc basin. Outcrops of the Dun Mountain -Maitai Terrane and Kaka Point Structural Belt appear to be structurally controlled, with the structure developed during terrane amalgamation. Terrane amalgamation is responsible for the large scale folding of the Southland Syncline. Minor faulting and folding may also be the result of this terrane amalgamation during the Rangitata Orogeny. Evidence is also presented from mineral assemblages that suggest far greater burial depths for the Murihiku Terrane than for the adjacent Kaka Point Structural Belt and Dun Mountain -Maitai Terrane, thus implying a "boundary fault" is present between the Murihiku Terrane and the Kaka Point Structural Belt.

ix, 144 leaves : ill. (some col., some folded), maps (some col, some folded) ; 30 cm.

2002Simpson_B

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