Tectonic significance of ductile deformation in low-grade sandstones in the mesozoic Otago subduction wedge, New Zealand

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ID: 302796
2011
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Abstract
This study demonstrates how ductile strain measurements can determine the tectonic evolution of a large and long-lived subduction wedge. We provide a synthesis of the geology of the South Island of New Zealand, with an emphasis on a wedge tectonics perspective that contrasts with a traditional view that interprets New Zealand geology in the context of terrane collision and accretion. We argue that the Otago subduction wedge evolved in a steady fashion throughout its 290 to 105 Ma history in response to accretion of trench-fill and abyssal-plain sediments, and slow erosion of a subaerially-exposed forearc high. Maximum temperatures for rocks in the flanks of the forearc high were no greater than 150 to 300 °C, with solution mass-transfer active as the dominant ductile mechanism. The 54 studied samples provide information about the absolute ductile strains acquired all along their flow-path, from the site of accretion to exhumation in the forearc high. We use tensor-averages to estimate strain at a regional scale. These show plane-strain uniaxial flattening, given that the tensor-averages for Sy and Sx are close to one. On average, Sz is approximately 0.77, and this is balanced by a mass loss of about 23 percent. The average Z direction is sub-horizontal in the prowedge and moderately plunging in the retrowedge, a difference attributed to spatial variations in the mode of accretion. We infer that rocks presently in the pro-side of the Otago high were sourced by frontal accretion, and those in the retro-side were underplated. This result highlights the important role of accretion in determining the style of within-wedge deformation, and also demonstrates the benefit of using a tensor-averaging approach to examine regional strain.
Reference Key
openalex_W2055239297 Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors Jeffrey M. Rahl, M. T. Brandon, Hagen Deckert, Uwe Ring, N. Mortimer
Journal american journal of science
Year 2011
DOI
10.2475/01.2011.02
URL
https://doi.org/10.2475/01.2011.02
Keywords Keywords not found

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