Tracking the Australian plate motion through the Cenozoic: Constraints from ⁴⁰Ar/³⁹Ar geochronology

Abstract

[1] Here we use geochronology of Australian intraplate volcanoes to construct a high-resolution plate-velocity record and to explore how tectonic events in the southwest Pacific may have influenced plate motion. Nine samples from five volcanoes yield ages from 33.6 ± 0.5 to 27.3 ± 0.4 Ma and, when combined with published ages from 30 to 16 Ma, show that the rate of volcanic migration was not constant. Instead, the results indicate distinct changes in Australian plate motion. Fast northward velocities (61 ± 8 and 57 ± 4 km/Ma) prevailed from 34 to 30 (±0.5) and from 23 to 16 (±0.5) Ma, respectively, with distinct reductions to 20 ± 10 and 22 ± 5 km/Ma from 30 to 29 (±0.5) Ma and from 26 to 23 (±0.5) Ma. These velocity reductions are concurrent with tectonic collisions in New Guinea and Ontong Java, respectively. Interspersed between the periods of sluggish motion is a brief 29-26 (±0.5) Ma burst of atypically fast northward plate movement of 100 ± 20 km/Ma. We evaluate potential mechanisms for this atypically fast velocity, including catastrophic slab penetration into the lower mantle, thermomechanical erosion of the lithosphere, and plume-push forces; none are appropriate. This period of fast motion was, however, coincident with a major southward propagating slab tear that developed along the northeastern plate margin, following partial jamming of subduction and ophiolite obduction in New Caledonia. Although it is unclear whether such an event can play a role in driving fast plate motion, numerical or analogue models may help address this question.

Holocene-Neogene volcanism in northeastern Australia: Chronology and eruption history

“…There are, however, known gaps and analytical issues in the existing age dataset, so to fully and reliably evaluate the eruption frequency and volcanic hazard requires further chronologic investigation of this region. (Wellman and McDougall, 1974;Cohen et al, 2013a . The Undara flow is outlined in purple, Murronga in black, Kinrara in orange, and Toomba in red, while all other volcanic units are outlined in grey.…”

“…The central volcanoes become progressively younger from 34 Ma at Cape Hillsborough in central Queensland to 6 Ma at Macedon in Victoria, indicating passage over a hotspot or hotspots (Wilson, 1963), which represents Earth's longest continental hotspot track ( Fig. 1) (Wellman and McDougall, 1974;Knesel et al, 2008;Cohen et al, 2013a;Davies et al, 2015). The leucitites also become younger to the south, at a rate matching the central volcanoes .…”

Late Cenozoic intraplate faulting in eastern Australia

“…These included (1) the initiation of oblique convergence between the Melanesian arc system and the Ontong Java Plateau (OJP) (Petterson et al, 1997(Petterson et al, , 1999; (2) arc-continent collision at the northern margin of New Guinea (Hall, 2002;Hill and Hall, 2003); and (3) ophiolite obduction (Schellart, 2007) and the inception of highly oblique convergence in New Zealand (Kamp, 1986;Schellart et al, 2006). The response of the Australian continent to the OJP oblique collision may have resulted in an abrupt deceleration of the Australian plate motion at~26e23 Ma, as indicated by the spatiotemporal distribution of hotspot-related volcanic rocks in southeast Queensland Cohen et al, 2013). Similarly, the onset of oblique convergence along the northeastern boundary of Australian plate resulted in a westward offset in Cenozoic seamount chains in the Tasman Sea Cohen et al, 2013), possibly due to a possible EeW direction of S Hmax .…”

The geometry, kinematics, and reactivation history of major fault systems in eastern Australia: implications for deformation phases from the Permian to Cenozoic

“…These included (1) the initiation of oblique convergence between the Melanesian arc system and the Ontong Java Plateau (OJP) (Petterson et al, 1997;Petterson et al, 1999); (2) arc-continent collision at the northern margin of New Guinea (Hall, 2002;Hill and Hall, 2003); and (3) ophiolite obduction (Schellart, 2007) and the inception of highly oblique convergence in New Zealand (Kamp, 1986;Schellart et al, 2006). The response of the Australian continent to the OJP oblique collision may have resulted in an abrupt deceleration of the Australian plate motion at ~26-23 Ma, as indicated by the spatio-temporal distribution of hotspot-related volcanic rocks in southeast Queensland Cohen et al, 2013). Similarly, the onset of oblique convergence along the northeastern boundary of Australian plate resulted in a westward offset in Cenozoic seamount chains in the Tasman Sea Cohen et al, 2013), possibly due to a possible E-W direction of SHmax.…”

“…The response of the Australian continent to the OJP oblique collision may have resulted in an abrupt deceleration of the Australian plate motion at ~26-23 Ma, as indicated by the spatio-temporal distribution of hotspot-related volcanic rocks in southeast Queensland Cohen et al, 2013). Similarly, the onset of oblique convergence along the northeastern boundary of Australian plate resulted in a westward offset in Cenozoic seamount chains in the Tasman Sea Cohen et al, 2013), possibly due to a possible E-W direction of SHmax. A numerical paleostress model of the early Miocene shows a dominant ~WNW-ESE direction of SHmax over southeast Queensland at that time (Dyksterhuis et al, 2005a;Muller et al, 2012), possibly as a result of obduction and collision in New Zealand (Figures 6.13a,b).…”