New Zealand Journal of Geology and Geophysics abstracts
Pliocene-Quaternary deformation and mechanisms of near-surface strain close to
the eastern tip of the Clarence Fault, northeast Marlborough, New Zealand
D. B. TOWNSEND
T. A. LITTLE
Geology Department
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand
Abstract In coastal northeast Marlborough, New Zealand, the
termination of the dextral strike-slip Clarence Fault requires a mechanism for
the accommodation of strain about its tip. The Awatere Block, to the northeast
of the tip, is inferred to be undergoing a clockwise vertical-axis rotation as
mid-lower crustal simple shear is transmitted upward into an upper crustal
rigid-body rotation. Clockwise vertical-axis rotation of the Awatere Block of
up to 44deg. has previously been constrained by paleomagnetic data in Pliocene
rocks, and the deflection of near-vertical bedding in Torlesse Terrane basement
rocks suggests a rotation of up to c. 55deg.. The attitude and slip
direction of mesoscopic faults in coastal exposures of late Miocene-Pliocene
rocks allow directions of faulting-related maximum instantaneous strain to be
deduced. These directions swing from east-west in the north of the Awatere
Block to southeast-northwest in the south of the block as the style of faulting
changes from oblique-normal to strike-slip to thrust. This changing pattern of
strain is inferred to be due to a clockwise rotation of the Awatere Block.
The London Hill Fault forms an eastern boundary to the rotating Awatere Block.
Gouge-zone foliation and stratigraphic data reveal that the London Hill Fault
is currently a reverse fault that reactivates an Eocene(?) normal fault.
Post-Pliocene dip-slip on the London Hill Fault is in the order of 2 km.
New radiocarbon dating of a marine terrace to the southwest of Cape Campbell
requires a rate of uplift of 1.7-2.5 mm/yr over the last 5500 yr,
much faster than other rates nearby. This difference in rate is inferred to be
due to active folding of the adjacent Cape Campbell Syncline. Regional Holocene
northeast tilting of the Awatere Block is inferred from stream piracy patterns
and tilted fluvial and coastal marine terraces. Local tilting patterns are more
complex and indicate surface deformation near currently active fault and fold
structures.
Keywords Awatere Block; block rotation; Clarence Fault;
London Hill Fault; Marlborough; mesoscopic faults; Miocene; Pliocene;
Quaternary; uplift; tectonics
New Zealand Journal of Geology & Geophysics, 1998, Vol. 41:
401-417
0028-8306/98/4104-0401 $7.00/0 (c) The Royal Society of New Zealand
1998
PDF file of entire paper: medium quality (4512K); (scanned from paper original: notes about this process)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
