Paleomagnetic evidence for time of emplacement of the early Paleozoic terranes in New Zealand

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Oliver, P.J.; Mumme, T.C.; Cooper, R.A. 1996 Paleomagnetic evidence for time of emplacement of the early Paleozoic terranes in New Zealand . Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 96/22 60 p.

Abstract: Paleomagnetic directions derived from the Early Devonian Baton Formation (eastern Takaka Terrane) and Reefton Group (western Buller Terrane) sedimentary sequences yielded stable single component remanent magnetisation directions after alternating field and thermal demagnetisation removed minor secondary overprinted components. These results are from the oldest New Zealand rocks yet tested successfully for paleomagnetism, and provide encouragement that the perceived problem of a New Zealand wide Cretaceous magnetic overprint is not insurmountable. These stable remanent magnetisation directions are distinct from mid to late Mesozoic, Tertiary, or present day directions. The possibility of post middle to late Mesozoic resetting of the magnetisation directions is therefore positively excluded. The magnetisation directions are interpreted to be a late Devonian remagnetisation acquired on folding in the earliest phase of tectonic uplift of the sediments, rather than a primary depositional remanent magnetisation. The remanent magnetisation directions obtained are different from those for Late Devonian poles from the Gondwana Apparent Polar Wander Path. The late Devonian stable single-component remanent magnetisation directions, uncorrected for tectonic tilt, are similar for both the Baton Formation and the Reefton Group. This is interpreted as indicating that little or no significant relative rotational tectonic movement has occurred between the two areas since the late Paleozoic. The western Buller Terrane was therefore in juxtaposition with the eastern Takaka Terrane by late Devonian time, although some subsequent lateral movement between the two Terranes may have occurred since the Devonian. (auth)