Aspects of the sedimentology and petrology of "Torlesse" rocks, northeastern North Island, New Zealand

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dc.contributor.advisor Spörli, Bernhard en
dc.contributor.advisor Ballance, Peter F. en
dc.contributor.author Leverenz, Axel en
dc.date.accessioned 2007-06-26T01:53:57Z en
dc.date.available 2007-06-26T01:53:57Z en
dc.date.issued 1999 en
dc.identifier THESIS 99-260 en
dc.identifier.citation Thesis (PhD--Geology)--University of Auckland, 1999 en
dc.identifier.uri http://hdl.handle.net/2292/546 en
dc.description Full text is available to authenticated members of The University of Auckland only. en
dc.description.abstract The Late Jurassic to Mid-Cretaceous Waioeka subterrane of the North Island, New Zealand, considered as the youngest part of the Torlesse terrane, is interpreted as an accretionary prism complex at the Gondwana margin. These basement rocks are characterized by sedimentological and petrological monotony, scarcity of bio-and lithostratigraphic markers, and tectonic complexity. Despite the lack of lateral correlation of sedimentary sequences, use of models of facies patterns and criteria such as complexity of facies distribution, slumping of oligomict material, proximal-to-distal distribution of Bouma sequences and conglomerate fabrics, has reduced the number of possible interpretation schemes. As a result, a trench-depositional environment is suggested here, rather than an earlier postulated submarine fan setting on a basin plain, subsequently accreted at a convergent margin. The Waioeka subterrane is characterized by mud/sand- to sand-rich sediments, consisting dominantly of very thick sandstones, and alternating sandstone-mudstone sequences, and only minor conglomerates and silty/muddy deposits. Five here defined facies associations are interpreted as major and minor midfan-type channel deposits, lobe and lobe-/fan-fringe facies, and/or trench-axial channel facies, and levee/overbank facies. Overall sedimentological features suggest a depositional setting beyond a significant slope break, at the lower reaches of a turbidite system, associated with a small number of large point-sourced channels reaching the trench. Facies analysis and trace element data implies that sediment accretion was controlled by subduction décollement within thick trench-fill sedimentary sequences. Petrographic data of extrabasinal sediment clasts and their surrounding matrix from localities east and west of the Whakatane Fault, a proposed boundary between Waioeka and 'older' Torlesse subterranes, contradict existing models of large-scale dextral displacement of eastern North Island. This requires a revision of previously postulated boundaries either (a) between subterranes of the Torlesse terrane, or (b) between major North Island terranes (Waipapa and Torlesse terranes), whereby geochemical data favour the latter interpretation. However, both interpretations imply a northward termination of 'older' Torlesse rocks (Rakaia and Pahau subterranes), in contrast to a previously suggested northward tapering only of the older Rakaia subterrane. A previous subdivision of the Waioeka subterrane into an older western Waioeka and a younger eastern Omaio petrofacies, has been refined here by further dividing the former into a western and an eastern Waioeka petrofacies. Based on geochemical data and multivariate statistics, these three petrofacies have been further subdivided into eleven compositionally discrete structural blocks. Detailed petrographic and geochemical analyses reveal a rather continuous change from western intermediate, dominantly volcaniclastic, to eastern more felsic, increasingly plutonic compositions. This west-to-east trend of increasingly felsic character can be explained by progressive dissection of a continental arc massif, which appears to be the dominant tectonic setting of the source areas. In contrast, compositional changes due to increased recycling are only minor. Structural blocks identified as compositionally 'anomalous' were probably introduced laterally by strike-slip tectonics, in one case possibly derived from 'older' Torlesse sequences. All petrologic data of Waioeka subterrane rocks suggest a lack of any significant provenance link from the 'older' Torlesse terrane, except for the westernmost structural block in the area. Conversely, similarity in composition and source of recycled material, may indicate a closer affinity to the Waipapa terrane, or possibly suggests a separate terrane status. en
dc.language.iso en en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA9987127714002091 en
dc.rights Restricted Item. Available to authenticated members of The University of Auckland. en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. en
dc.rights.uri https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm en
dc.title Aspects of the sedimentology and petrology of "Torlesse" rocks, northeastern North Island, New Zealand en
dc.type Thesis en
thesis.degree.discipline Geology en
thesis.degree.grantor The University of Auckland en
thesis.degree.level Doctoral en
thesis.degree.name PhD en
dc.rights.holder Copyright: The author en


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