Late Cretaceous oceanic plate reorganization and the breakup of Zealandia and Gondwana
Graphical abstract
Introduction
The SW Pacific region (Fig. 1) underwent major tectonic and geological change in the Cretaceous Period (145–66 Ma). For much of the Mesozoic, the continent-ocean margin between SE Gondwana and the crust of the paleo-Pacific was convergent and characterised by the development of Cordilleran batholiths and accretionary complexes (Mortimer et al., 2014). Sometime between 110 and 85 Ma this tectonic regime was interrupted and/or replaced by a passive margin and widespread intracontinental rifting and volcanism (Bradshaw, 1989; Luyendyk, 1995; Tulloch et al., 2009). This intracontinental rifting culminated in the breakup of Gondwana, such that by 83 Ma (anomaly 34ny; Seton et al., 2014) new oceanic crust had started to form between the continents of Australia, Antarctica and Zealandia (Stock and Cande, 2002; Wright et al., 2016; Mortimer et al., 2017). Meanwhile, in the ocean basins the eruption of 125–115 Ma large igneous provinces (LIPs) such as Ontong Java, Manihiki and Hikurangi Plateaus took place, likely as a single superplateau (Taylor, 2006; Davy et al., 2008; Hoernle et al., 2010; Timm et al., 2011; Chandler et al., 2012; Hochmuth et al., 2015).
There has been much speculation on the cause and effect between rapid Cretaceous spreading, LIP eruption, LIP collision, and the change in continental tectonic regime (Luyendyk, 1995; Mortimer et al., 2006; Downey et al., 2007; Davy et al., 2008; Tulloch et al., 2009; Davy, 2014; Hochmuth and Gohl, 2017). Satellite gravity maps (Sandwell and Smith, 1997) have provided extremely useful insights into kinematic aspects of oceanic crust tectonics. But the dearth of sampled rocks, particularly from the widespread oceanic crust of Cretaceous Normal Superchron (121–83 Ma) age (Fig. 1), has hindered our ability to date the age of events, and hence define spreading rates and tectonic events.
This paper increases our knowledge of SW Pacific tectonics by providing new 40Ar/39Ar ages of igneous rocks, particularly in the parts of the large and difficult-to-access oceanic crust northeast and east of Zealandia (Fig. 1). The direct dating provides a critical check on oceanic crust ages inferred from magnetic reversals. This paper is relevant to, and develops, themes of Ontong Java Nui Large Igneous Province (LIP) breakup and collision (Larson et al., 2002; Taylor, 2006; Davy et al., 2008; Hoernle et al., 2010; Chandler et al., 2012; Hochmuth and Gohl, 2017; Barrett et al., 2018), SW Pacific volcanism (Mortimer et al., 2006, Mortimer et al., 2018; Tulloch et al., 2009; Timm et al., 2010; van der Meer et al., 2016), and SW Pacific-Zealandia-Antarctica Cretaceous tectonics (Luyendyk, 1995; Sutherland and Hollis, 2000; Larter et al., 2002; Eagles et al., 2004; Wright et al., 2016). Our data clarify the age and rate of breakup of the Hikurangi Plateau part of the Ontong Java Nui LIP and our tectonic model emphasises the role of LIP collision in controlling subsequent continental and oceanic magmatic and tectonic events. This is a companion paper to Homrighausen et al. (2018) in which trace element and isotopic data for some of the dated samples are described and discussed.
Section snippets
Oceanic crust east of Zealandia
Lying east of the Kermadec Trench, the Osbourn Trough is an east-west trending fossil spreading ridge that split the once contiguous Hikurangi and Manihiki Plateau LIPs (Fig. 1; Billen and Stock, 2000; Taylor, 2006, Downey et al., 2007). Rocks dredged from the Osbourn Trough axial valley and drilled at International Ocean Discovery Program (IODP) Site U1365 are altered lavas of normal mid-ocean ridge basalt (N-MORB) composition (Worthington et al., 2006; Zhang et al., 2012). All or most of the
Samples and methods
Samples were obtained from several sources including Sonne 168 dredges, the International Ocean Discovery Programme core repository, newly collected onland samples and existing samples in the GNS Petrology Collection (Table 1; Fig. 2). All samples prefixed “P” refer to the GNS Science Petrology Collection. Sample data are lodged in the PETLAB database (http://pet.gns.cri.nz; Strong et al., 2016).
Dating of most samples was done at GEOMAR, Kiel using step heating and single crystal laser fusion 40
Osbourn MORB lava
Whole rock chemical analysis of DSDP 595A sample P63853 confirms a Pacific N-MORB composition that matches other samples from the plate between the Osbourn Trough and Manihiki Plateau (Fig. 1; Saunders, 1987; Thomas, 2002; Worthington et al., 2006; Castillo et al., 2009; Zhang et al., 2012). This is especially evident in Fig. 3 where the basalt is seen to be subalkaline and with the moderate Ti/V of MORBs.
Our dated DSDP595 samples P63853 and 63854 are from basalt unit 2 (Saunders, 1987). This
Osbourn Trough spreading system
DSDP 595 is in a sparsely surveyed region (Fig. 1). Available nearby multibeam bathymetry, single channel seismic reflection lines and satellite gravity maps indicate tectonic continuity, and no identifiable fracture zones, between the DSDP 595 site and the Osbourn Trough. DSDP 595 is c. 200 km off-axis from the main Osbourn Trough and knowledge of the age of the DSDP 595 basalts provide a date on the later spreading history of the ridge system. A 78.8 ± 1.3 Ma age from Osbourn Seamount at the
Tectonic model
Our new age data require changes to previous tectonic models of the region (e.g., Bradshaw, 1989; Weaver et al., 1994; Luyendyk, 1995; Sutherland and Hollis, 2000; Larter et al., 2002; Eagles et al., 2004). Key new points in Fig. 7 are a potentially relatively young (c. 79 Ma) cessation of spreading at the Osbourn Trough and demonstration of an area of pre-83 Ma oceanic crust between the West Wishbone Scarp and magnetic anomaly C34ny.
The Ontong Java Nui superplateau formed in the Pacific Ocean
Conclusions
New geochronological data from Late Cretaceous igneous rocks in the SW Pacific-New Zealand region highlight regional changes in tectonomagmatic regime from subduction to a rift and intraplate setting to stable seafloor spreading. Cessation of long-lived subduction at the SE Gondwana margin is reasonably attributed to collision of the Hikurangi Plateau at 110–100 Ma. Widespread but low-volume intraplate volcanic rocks erupted in the interval 99–78 Ma across Gondwana/Zealandia continental
Acknowledgments
We thank the Captain and crew of F/S Sonne 168 “Zealandia” cruise for dredged rocks and the IODP/DSDP core repository for providing the DSDP 595 samples. The New Zealand Ministry of Foreign Affairs and Trade gave permission to use the data obtained from Bollons Gap. We also thank John Simes, Belinda Smith Lyttle and Jenny Black for technical assistance, and Karsten Gohl, Bryan Davy and Hamish Campbell for discussions. An earlier version of the manuscript was improved by comments from Quinten
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2023, Earth-Science ReviewsCitation Excerpt :Through extrapolation of spreading rates, they proposed that Osbourn Trough spreading may have continued until ∼79 Ma (Mortimer et al., 2019), implying that spreading may indeed have continued after the Cretaceous Quiet Zone as suggested by Billen and Stock (2000). However, the 84.4 Ma age is a tentative age, as the effects of seawater alteration could not be entirely ruled out (Mortimer et al., 2019). On the other hand, Zhang and Li (2016) suggested that spreading at the Osbourn Trough ceased around 101 Ma, which would require ultrafast spreading rates of 19 cm/yr.