Abstract. Here we examine the landscape of New Zealand's
Marlborough Fault System (MFS), where the Australian and Pacific plates obliquely
collide, in order to study landscape evolution and the controls on fluvial
patterns at a long-lived plate boundary. We present maps of drainage
anomalies and channel steepness, as well as an analysis of the plan-view
orientations of rivers and faults, and we find abundant evidence of
structurally controlled drainage that we relate to a history of drainage
capture and rearrangement in response to mountain-building and strike-slip
faulting. Despite clear evidence of recent rearrangement of the western MFS
drainage network, rivers in this region still flow parallel to older faults,
rather than along orthogonal traces of younger, active strike-slip faults.
Such drainage patterns emphasize the importance of river entrenchment,
showing that once rivers establish themselves along a structural grain,
their capture or avulsion becomes difficult, even when exposed to new
weakening and tectonic strain. Continued flow along older faults may also
indicate that the younger faults have not yet generated a fault damage zone
with the material weakening needed to focus erosion and reorient rivers.
Channel steepness is highest in the eastern MFS, in a zone centered on the
Kaikōura ranges, including within the low-elevation valleys of main stem
rivers and at tributaries near the coast. This pattern is consistent with an
increase in rock uplift rate toward a subduction front that is locked on its
southern end. Based on these results and a wealth of previous geologic
studies, we propose two broad stages of landscape evolution over the last 25 million years of orogenesis. In the eastern MFS, Miocene folding above blind
thrust faults generated prominent mountain peaks and formed major transverse
rivers early in the plate collision history. A transition to Pliocene
dextral strike-slip faulting and widespread uplift led to cycles of river
channel offset, deflection and capture of tributaries draining across active
faults, and headward erosion and captures by major transverse rivers within
the western MFS. We predict a similar landscape will evolve south of the
Hope Fault, as the locus of plate boundary deformation migrates southward
into this region with time.
Spatial variations in damage zone width along strike-slip faults: An example from active faults in southwest Japan