Caught between a rock and a hard place: Microplate ...

Caught between a rock and a hard place: Microplate dynamics on the northern Australian plate margin. Robert Holm and Simon Richards School of Earth and Environmental Sciences James Cook University

GSA SGTSG, Waratah Bay, 2012 Cause and effects of deformation in the lithosphere

Introduction • Tectonic setting • Previous work • New geological concepts in PNG • New tectonic reconstructions • Discussion and conclusions

Tectonic Setting

Previous Reconstructions • Almost without exception, previous reconstructions are based on the assumption that the Trobriand trough has accommodated significant convergence throughout the Miocene.

15 Ma; Honza et al., 1987

10 Ma, Late Miocene; Hall, 2002

We want to test an alternative hypothesis. Northward advance of the Australian plate during the Miocene is primarily accommodated at the Pocklington trough rather than the Trobriand trench.

Grasberg (3 Ma) 2,480 Mt @1.05 g/t Au & 1.13% Cu

Frieda River (14–11 Ma) 1,103 Mt @ 0.32 g/t Au & 0.61% Cu Porgera (~5.9 Ma) 23.5 Moz Au

Ok Tedi (1.2–1.1 Ma) 700 Mt @ 0.64 g/t Au & 0.64% Cu

Ladolam, Lihir (0.6–0.5 Ma) 48.5 Moz Au @ 2.35 g/t Panguna (3.5 Ma) 1,415 Mt @ 0.57 g/t Au & 0.46% Cu

Wafi-Golpu (~14 Ma) Wafi: 6.51 Moz Au; Golpu: 63 Mt @ 0.6 g/t Au & 1.08% Cu Cooke et al., 2005; Gauthier, 2010; Kavanamur, 2010; Lihir Gold Limited, 2010

The Maramuni arc, Lagaip fault zone and the Papuan Accretionary Complex

Constructing a Slab Model

Earthquake data from USGS NEIC

Slab Model Ladolam, Lihir (0.6–0.5 Ma) 48.5 Moz Au @ 2.35 g/t

Fitting a surface to subduction related earthquake hypocenters allows us to visualize a subducted slab at depth and associated slab structure.

Pre 24 Ma •West-directed subduction of Pacific plate beneath the Outer Melanesian arc. •Owen Stanley Terrane a continental ribbon rifted from northern Australia; equivalent to Lord Howe Rise or Norfolk Ridge. •Solomon and Caroline plates

24 – 20 Ma •Onset of increased convergence at the Australian-Pacific plate boundary (Schellart et al., 2006). •Obduction of back arc complex to the Owen Stanley Terrane. •Initiation of north-directed subduction of the Australian plate at the Pocklington trough.

20 – 16 Ma •Initial collision of the Australian continental margin with Owen Stanley Terrane (and Louisiade Plateau with the Pocklington trough). •The impinging lateral Australian continental margin shears the Owen Stanley Terrane propogating through the Solomon and Caroline Seas on extinct transform structures. •Dilational dextral shear of the Caroline plate results in magma outpouring forming the early Euripik Rise. •Initial offset of Lagaip fault zone and adjacent crust due to bouyant indentor (Porgera Transfer).

16 – 12 Ma •Full collision of Australian continent and Louisiade Plateau cause cessation of subduction at the Pocklington trough.

Frieda River (14–11 Ma) 1,103 Mt @ 0.32 g/t Au & 0.61% Cu

Wafi-Golpu (~14 Ma) Wafi: 6.51 Moz Au; Golpu: 63 Mt @ 0.6 g/t Au & 1.08% Cu

•Initiation of north-directed subduction at the New Britain trench to accommodate convergence. •Uplift and cooling of Mobile Belt @ 12 Ma (Hill and Raza, 1999); cessation of sedimentation in the Aure trough with initial accretionary complex growth. (Tcherepanov et al., 2010). •Shearing associated with Porgera Transfer propagates through to Euripik Rise.

12 – 8 Ma •Initial “soft docking” of the Ontong Java Plateau with the Solomon Islands (Mann and Taira, 2004). •OJP collision increases westward convergence through the Solomon Sea to induce westdirected subduction of the Solomon Sea plate at the Trobriand trench.

8 – 4 Ma Grasberg (3 Ma) 2,480 Mt @1.05 g/t Au & 1.13% Cu

Porgera (~5.9 Ma) 23.5 Moz Au

Panguna (3.5 Ma) 1,415 Mt @ 0.57 g/t Au & 0.46% Cu

•OJP collision captures the Solomon Islands and Caroline plate for the Pacific plate. •Rifting and seafloor spreading in the Woodlark Basin from at least 6 Ma (Taylor et al., 1999) to accommodate northwestdirected component of subduction at the New Britain and Trobriand trenched. •Initiation of south-directed subduction of the Caroline plate at the New Guinea trench from 5 Ma.

4 – 0 Ma •“Hard docking” of OJP uplifts Malaita Accretionary Prism (Phinney et al., 2004). •Adelbert-Finisterre Terrane accreted to the New Guinea margin from 3.5 Ma (Abbott et al., 1994).


•The Bismarck plate, caught between New Guinea and OJP fragments into the North and South Bismarck plates with formation of the Manus Spreading Center.

Structure, Magmatism, and Mineralisation Frieda River (14–11 Ma) 1,103 Mt @ 0.32 g/t Au & 0.61% Cu


Porgera (~5.9 Ma) 23.5 Moz Au

Wafi-Golpu (~14 Ma) Wafi: 6.51 Moz Au; Golpu: 63 Mt @ 0.6 g/t Au & 1.08% Cu

References •

•

•

•

•

•

•

•

Abbott, L. D., E. A. Silver, and J. Galewsky (1994), Structural • evolution of a modern arc-continent collision in Papua New Guinea, Tectonics, 13, 1007–1034. Australian Bureau of Mineral Resources (1973), Geology of • Papua New Guinea, 1:1,000,000 map, Aus. Bur. Min. Resources. Cooke, D. R., P. Hollings, and J. L. Walshe (2005), Giant porphyry deposits: Characteristics, distribution, and • tectonic controls, Economic Geol., 100, 801–818. Gauthier, L. (2010), Porgera low sulphidation alkalic deposit, PNG, Proceedings of the Papua New Guinea Minerals Workshop, Port Moresby. • Hall, R. (2002), Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations, J. Asian Earth Sci., 20, 353–431. • Hill, K. C., and A. Raza (1999), Arc-continent collision in Papua Guinea: Constraints from fission track thermochronology, Tectonics, 18, 950–966. Honza, E., H. L. Davies, J. B. Keene, and D. L. Tiffin (1987), • Plate boundaries and evolution of the Solomon Sea region, Geo Mar. Lett., 7, 161–168. Kavanamur, B. (2010), Wafi-Golpu Project: Nambonga North and Golpu West recent discoveries, Proceedings of the Papua New Guinea Minerals Workshop, Port Moresby.

Lihir Gold Limited (2010), Update on the Ladolam Orebody, Lihir Island, Proceedings of the Papua New Guinea Minerals Workshop, Port Moresby. Mann, P., and A. Taira (2004), Global tectonic significance of the Solomon Islands and Ontong Java Plateau convergent zone, Tectonophysics, 389, 137–190, doi:10.1016/j.tecto.2003.10.024. Phinney, E. J., P. Mann, M. F. Coffin, and T. H. Shipley (2004), Sequence stratigraphy, structural style, and age of deformation of the Malaita accretionary prism (Solomon arc–Ontong Java Plateau convergent zone), Tectonophysics, 389, 221–246, doi:10.1016/j.tecto.2003.10.025. Schellart, W. P., G. S. Lister, and V. G. Toy (2006), A Late Cretaceous and Cenozoic reconstruction of the Southwest Pacific region: Tectonics controlled by subduction and slab rollback processes, Earth-Sci. Reviews, 76, 191–233. Taylor, B., A. M. Goodliffe, and F. Martinez (1999), How continents break up: Insights from Papua New Guinea, J. Geophys. Res., 104, 7497–7512. Tcherepanov, E. N., A. W. Droxler, P. Lapointe, K. Mohn, and O. A. Larsen (2010), Siliclastic influx and burial of the Cenozoic carbonate system in the Gulf of Papua, Marine Petroleum Geol., 27, 533–554.

Questions?