Focusing of relative plate motion at a continental transform fault: Cenozoic dextral displacement >700 km on New Zealand's Alpine Fault, reversing >225 km of Late Cretaceous sinistral motion

Abstract

The widely accepted 450 km Cenozoic dextral strike-slip displacement on New Zealand's Alpine Fault is large for continental strike-slip faults, but it is still less than 60% of the Cenozoic relative plate motion between the Australian and Pacific plates through Zealandia, with the remaining motion assumed to be taken up by rotation and displacement on other faults in a zone up to 300 km wide. We show here that the 450 km total displacement across the Alpine Fault is an artifact of assumptions about the geometry of New Zealand's basement terranes in the Eocene, and the actual Cenozoic dextral displacement across the active trace is greater than 665 km, with more than 700 km (and <785 km since 25 Ma) occurring in a narrow zone less than 10 km wide. This way, the Alpine Fault has accommodated almost all (>94%) of the relative plate motion in the last 25 Ma at an average rate in excess of 28 mm/yr. It reverses more than 225 km (and <300 km) of sinistral shear through Zealandia in the Late Cretaceous, when Zealandia lay on the margin of Gondwana, providing a direct constraint on the kinematics of extension between East and West Antarctica at this time.

Variations in Seismogenic Thickness Along the Central Alpine Fault, New Zealand, Revealed by a Decade's Relocated Microseismicity

“…The western margin of the Southern Alps orogen is delineated by a major strike-slip reverse fault, the Alpine Fault (Norris & Cooper, 2001;Wellman & Willett, 1942). During the Cenozoic, the strike-slip motion of the Alpine Fault has produced a cumulative offset of at least 450 km (Sutherland, 1999) and possibly as much as 700 km (Lamb et al, 2016).…”

Terrane Boundary Reactivation, Barriers to Lateral Fault Propagation and Reactivated Fabrics: Rifting Across the Median Batholith Zone, Great South Basin, New Zealand

“…Subduction ceased during the Early Cretaceous (~105 Ma) as the buoyant Hikurangi Plateau collided along the margin (Davy et al, 2008;Uruski, 2015). Since the Cenozoic, these terranes have been offset along the Alpine Fault, a major plate boundary and strike-slip fault located along the spine of the South Island that has accommodated >450 km, and potentially >700 km, offset (Cooper et al, 1987;Lamb et al, 2016;Sutherland et al, 2000;Wellman, 1953). Due to this offset, the basement terranes of the South Island are also present beneath the North Island ( Figure 1) (Collanega et al, 2018;Mortimer et al, 2002;Muir et al, 2000).…”

Microseismicity in Southern South Island, New Zealand: Implications for the Mechanism of Crustal Deformation Adjacent to a Major Continental Transform

“…This diffuse microseismicity defines a triangular zone >100 km wide, which narrows to the NE, (Figure a). However, virtually all the moment release of seismicity (Figure a) and more than 90% of the Cenozoic surface finite strain (Lamb et al, ) are constrained to a much narrower (10–20 km wide) zone close to the Alpine Fault and offshore thrusts in the Puysegur subduction zone, in contrast to simple models of a wide fluid‐like channel of distributed deformation (e.g., Moore et al, ).…”

“…The Alpine Fault has accommodated ~700 km of dextral shear since 25 Ma (Lamb et al, ) and ruptures in large to great ( M w > 7–8) earthquakes (Okaya et al, ; Sutherland et al, ). Paleoseismic studies (Berryman et al, ; Cochran et al, ) indicate remarkably regular ruptures with a mean recurrence interval of 291 ± 23 years for the southern onshore section, suggesting rupturing in response to a specific amount of strain accumulation and that the fault is late in its seismic cycle (the last known event occurred in 1717 CE (De Pascale & Langridge, ; Wells et al, )).…”