New Zealand Journal of abstracts
Structure of the Buller and Takaka Terrane rocks
adjacent to
the Anatoki Fault, northwest Nelson, New
Zealand
Richard Jongens*
Department of Geological Sciences
University
of Canterbury
Private Bag 4800
Christchurch, New
Zealand
r.jongens@gns.cri.nz
*Present
address: GNS Science, Private Bag 1930, Dunedin
9054, New Zealand.
Abstract Structures and
microstructures
within flanking
lithologies of the Buller and Takaka Terrane boundary, the Anatoki
Fault,
record three pre-Cenozoic deformation events in northwest Nelson. Each
deformation event recognised in the Buller Terrane has structures that
can be
matched in style, orientation, and timing of development with that in
the
adjacent Takaka Terrane. D1 is represented by
north-trending,
upright or overturned to the west, large-scale folds with an axial
planar slaty
cleavage. D1 is mid Devonian in age and relates to
amalgamation of the Buller and Takaka Terrane. D2
foliation
occurs in a zone of ductile deformation adjacent to the Anatoki Fault
near Boulder Lake.
Rb-Sr geochronology, and the
relationship between the foliation and metamorphism associated with the
adjacent c. 111 Ma Mt Olympus Pluton, suggests D2
formed in the Early Cretaceous following pluton emplacement. D3
is represented mainly by mesoscopic folds with an axial planar
crenulation
cleavage. D3 structures crenulate and refold both D1
and D2 structures and are mid Cretaceous in age.
Both D2
and D3 relate to an extremely active and changing
tectonic
period of New Zealand
in the Early to mid Cretaceous. The east-dipping Anatoki Fault in
northwest
Nelson records a complex history of ductile and brittle movement.
Tectonites from
central segments record ductile/brittle east-over-west reverse-slip
associated
with D1. To the north, D2
tectonites from
the Boulder Lake
area record Early Cretaceous ductile dextral-slip reactivation. To the
south,
tectonites from the Crow River and Mt Benson area record
ductile/brittle
dextral-normal slip which, in the Crow River area, represents
reactivation that
postdates the intrusion of the c. 137 Ma Crow Granite. From the Crow
River southwards, the
Anatoki Fault
has also undergone late Cenozoic brittle reactivation.
Keywords northwest Nelson;
Anatoki Fault;
Buller
Terrane; Takaka Terrane; Mt Olympus Pluton; Crow Granite; structure;
deformation; folds; foliation; lineations; cleavages; Paleozoic;
Cretaceous
:
443–461
0028–8306/06/4904–0443 © The Royal Society
of New Zealand
2006
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