Two-stage rifting of Zealandia-Australia-Antarctica: Evidence from 40Ar/39Ar thermochronometry of the Sisters shear zone, Stewart Island, New Zealand

Tectonics of the West Antarctic rift system: new light on the history and dynamics of distributed intracontinental extension

“…The ages correspond to the time of initiation of seafloor spreading between Campbell Plateau (NZ) and WANT (Figure 1) at 83-79 Ma (chron 33r) (McAdoo and Laxon, 1997;Larter et al, 2002;Stock and Cande, 2002;Eagles et al, 2004), suggesting that the second AFT cooling pulse was triggered by the lithospheric separation (Figure 9c) (Siddoway et al, 2004a;Kula et al, 2007). There is a good correspondence in timing and tectonic history of MBL localities with detachment structures in New Zealand (Kula et al, 2007).…”

“…HT metamorphism and exhumation of deep crustal rocks on detachment structures are documented over a wide region proximal to the Gondwana margin arc in New Zealand and MBL Fitzgerald and Baldwin, 1997;Forster and Lister, 2003;Siddoway et al, 2004b;Kula et al, 2007), suggesting pervasive middle to lower crustal flow and advection of magmatic heat (Ehlers, 2005) over a large region (Figures 8 and 9). The existing geochronological and thermochronological data reviewed above suggest a comparatively short and dynamic development of the Fosdick gneiss dome and other strike slip shear zones active in the eastern WARS in Cretaceous time.…”

“…The timing of fault activity determined from U-Pb zircon geochronology, 40 Ar/ 39 Ar, and AFT thermochronology corresponds with the time of development of the eastern WARS. The younger phase of rapid cooling at ~75 Ma reflects regional uplift and cooling, coincident in time with and attributable to modest denudation in response to onset of seafloor spreading and separation between WANT and New Zealand, upon a new divergent plate boundary that continued in to the Tasman Sea ( Figure 3a) (Gaina et al, 1998;Sutherland, 1999;Kula et al, 2007). The observation that rapid cooling occurred first upon discrete WARS fault zones (101-92 Ma) suggests a localized landscape response, reflected in the thermochronology cooling histories data.…”

“…Nd isotope data indicate FIGURE 3 Tectonic correlation between terranes of north Victoria Land, West Antarctica, and New Zealand/Campbell Plateau, compiled from Bradshaw (1989) and Bradshaw et al (1997). Reconstruction of the Cretaceous East Gondwana margin is based on Gaina et al (1998) and Kula et al (2007), with oceanic plates confi guration based on Sutherland and Hollis (2001) and Larter et al (2002). Representation of oceanic plateaus is based on Taylor (2006) and Hoernle et al (2004) a Ford Granodiorite source for the leucogranites (Saito et al, 2007) at T, P conditions of 820-870°C and 6.5-7.5 kbar determined from mineral equilibria modeling (Korhonen et al, 2007a,b).…”

Kinematic, finite strain and vorticity analysis of the Sisters Shear Zone, Stewart Island, New Zealand

“…For those grains where tracks-lengths were measured Dpar values were also determined, which range between 1.74 and 2.36 mm (Table 2). Kula et al (2007Kula et al ( , 2009 Reiners et al (2004) reported a single 40 Ar/ 39 Ar K-feldspar age spectrum, and zircon, apatite and titanite (U-Th)/He ages of 76.8e87.6 Ma, 54.5e60.4 Ma and 85.4e92.7 Ma, respectively (Fig. 2).…”