Cretaceous felsic volcanism in New Zealand and Lord Howe Rise (Zealandia) as a precursor to final Gondwana break-up

Abstract

We report new, highly precise, U -Pb and Ar/Ar ages for seven Cretaceous rhyolites, tuffs and granites from across Zealandia spanning a 30 Ma period from arc magmatism to continental break-up. Combined with previously published data, these reveal a strong episodicity in Cretaceous silicic magmatism outside the Median Batholith. 112 Ma tuffs are known only from the Eastern Province in association with a Cretaceous normal fault system. Both 101 and 97 Ma groups of rhyolites and tuffs occur across the entire width and half the length of Zealandia from near the palaeotrench to the continental interior, indicating widespread and effectively instantaneous extension. We attribute an increase in A-type character with time (112-101-97-88-82 Ma) to the progressive thinning of the Zealandia continental crust whereby, with time, there is less opportunity for crustal contamination. Extension directions associated with 101, 97 and 82 Ma magmatism and associated core complex exhumation across Zealandia are all oriented c. 308 oblique to the margin. These observations suggest Zealandia rifting was controlled by either .83 Ma capture of Zealandia by the Pacific Plate and/or ,83 Ma Zealandia-West Antarctica spreading, rather than by laterally migrating triple junctions, slab windows or plume heads.

Magmatism during Gondwana break-up: new geochronological data from Westland, New Zealand

“…Additionally, post-110 Ma felsic (e.g. Phillips et al 2005;Tulloch et al 2009) andmafic (e.g. Nathan 1978;Randall 2004;Timm et al 2010;Ryland 2011) magmatic rocks occur sporadically throughout south Westland.…”

“…In New Zealand, the earliest stages of thinning (c. 110-100 Ma) were associated with the formation of metamorphic core complexes (e.g. Tulloch & Kimbrough, 1989;Spell et al 2000), accompanied by emplacement of granitoid plutons Waight et al 1997Waight et al , 1998aTulloch et al 2009). Progressive extension is expressed in the deposition of terrestrial Pororari Group sediments in extensional grabens across central Westland (e.g.…”

Structure of the Blue Lake Fault Zone, Otago Schist, New Zealand

“…This event resulted in exhumation of the core of the schist belt via normal faults on the margin of the belt, and was active on the northeast side of the belt c. 112 Ma (Gray & Foster 2004;Mitchell et al 2009;Tulloch et al 2010). The major deformation in the Blue Lake Fault Zone, which formed the gouge zones, was probably part of that regional event.…”

Stratigraphy, provenance, and diagenesis of the Cretaceous Horse Range Formation, east Otago, New Zealand

“…it is notable that the Shag Valley ignimbrite is distinctly older than the Stitts Tuff in the Hawks crag Breccia sequence (Fig. 2) (Muir et al 1997;Tulloch et al in press). The cretaceous evolution of the eastern and western sides of the South island is broadly similar, but there are significant differences in timing (Fig.…”

“…1, 2). These sediments are important because they preserve the oldest record of exhumation and associated erosion that occurred during the earliest stages of a major period of tectonic extension that affected New Zealand and the southwest Pacific between the Cretaceous and the middle Tertiary (Carter 1988;Landis et al 2008;Tulloch et al in press).…”