November 1999 AGSO Research Newsletter 31

Tectonic provinces of the Lord Howe Rise ‘Law of the Sea’ study has implications for frontier hydrocarbons Howard M.J. Stagg1, Irina Borissova1, Mark Alcock1, & Aidan M.G. Moore1 Australia’s 200-n-mile Exclusive siliceous and carbonate oozes. To the segmentation of the Lord Howe Rise. Economic Zone (EEZ) and ‘extended con- east, the basement of the New Cal- The most prominent of these linea- tinental shelf’ beyond Lord Howe and edonia Basin is about 5 km deeper and ments extends for about 1800 km north- Norfolk Islands in the Tasman Sea takes of uncertain crustal affinity, and the east from east of Jervis Bay — across the in an area of about 1.4 million km2, simi- western boundary of the platform is Tasman Sea, Dampier Ridge, Lord Howe lar to that of the State of Queensland. defined by a Cretaceous hinge. Rise, and New Caledonia Basin — as far Despite its vast size and long-term hy- •A central rifted province character- as the Norfolk Ridge. This lineament (the drocarbon potential, the Lord Howe Rise ised by a series of poorly defined Barcoo–Elizabeth–Fairway Lineament), region is one of the most poorly known basement blocks, normally has gravity and seismic expression as: parts of Australia’s marine jurisdiction. downfaulted to the west, with 2–4 km • the boundary between the orthogonal Recent studies for AGSO’s ‘Law of the of Upper Cretaceous and Cainozoic seafloor spreading in the south Sea’ project, in support of defining syn- and post-rift section. This prov- Tasman Sea and the highly segmented, Australia’s jurisdiction, have provided ince includes the newly named Moore oblique spreading pattern in the north new insights into the tectonic framework Basin in the south, and the Faust Ba- Tasman Sea; and long-term resource potential of this sin in the north. • an offset in the Dampier Ridge and the enormous feature. •A western rift province separated major offset between the Lord Howe The rise extends from the Bellona from the central rift by a broad fault and Middleton Basins; Trough and Challenger Plateau, west of zone across which basement is • a 130-km offset in the western edge of New Zealand, to southwest of New Cal- downfaulted to the west. Basement the Lord Howe Platform, and a com- edonia, and lies at water depths gener- and water depths are considerably mensurate northward narrowing of ally deeper than 1000 m. It is underlain by deeper than in the central rift, and the that province; continental crust which detached from syn- and post-rift sediments are • southward termination of the Fairway eastern Australia during the breakup of thicker. This province includes the Trough and Fairway Ridge; and eastern Gondwana leading to the forma- newly named Monawai Basin in the • a northward constriction, and a corre- tion of the oceanic Tasman Basin from south, and the Capel Basin in the sponding change in structural style, 85–52 Ma. north. Near Lord Howe Island, the of the New Caledonia Basin. During 1999, ‘Law of the Sea’ project central and western rifts cannot be The northwest–southeast lineaments scientists carried out a framework geo- separated, and the combined rift has are mainly restricted to the structural prov- logical study to provide background in- been referred to as the Gower Basin. inces east of Lord Howe Rise, although formation pertinent to the definition of •A western bounding complex ridge they may also have overprinted some of Australia’s seabed jurisdiction in this re- system of continental origin. In the the older structuring on the rise. These gion. Owing to the paucity of geophysi- north, the Dampier Ridge is separated lineaments are most strongly expressed cal data, the project has made extensive from the western rift province by the in the segments of the Vening Meinesz use of satellite gravity data to in-fill the Lord Howe and Middleton Basins, Fracture Zone, north of New Zealand, and interpretation between widely separated which may in part be underlain by by the parallel Cook Fracture Zone, some seismic lines. Geological samples are highly extended lower continental 600–700 km farther north. equally sparse, being limited to several crust. Farther south, where crustal Deep Sea Drilling Project (DSDP) holes, extension is less extreme, the Frontiers of hydrocarbon drilled in the 1970s and 1980s, and a few Monawai Ridge forms an intact outer potential samples dredged from the flanks of Lord margin to the Monawai Basin. The possibility of unconventional hydro- Howe Rise and Dampier and Norfolk carbon resources in the Lord Howe Rise Ridges. Regional lineaments of the region, in the form of gas hydrates, already Lord Howe Rise has been reported (Exon et al. 1998: PESA Provinces of the Lord Howe Rise Regional crustal lineaments are inter- Journal 26, 148–158). Our study suggests An important early output from this work preted to be an important factor in the that these resources may be more wide- has been a map of the major tectonic prov- present-day structural divisions of the spread than originally envisaged. By inces in the region (Fig. 36) — the first Lord Howe Rise region. These lineaments identifying sedimentary basins that such product for this remote part of Aus- are aligned along two principal trends: extend for much of the length of the rise, tralia’s jurisdiction. northeast–southwest, parallel to the it also confirms the long-term potential of The 400–600-km-wide rise consists of Cretaceous–early Cainozoic Tasman Sea the region for conventional hydro- four subparallel provinces that extend for spreading direction; and northwest– carbons. The most prospective areas are much of its length. From east to west, southeast, resulting from the late the central and western rift provinces of these provinces comprise: Cainozoic formation of the ridge-and- Lord Howe Rise, the eastern flank of the • Shallow, planated, probably basin complex between Norfolk Ridge and rise adjacent to the New Caledonia Basin, Palaeozoic basement of the Lord the Tonga–Kermadec Trench. The north- and possibly in the New Caledonia Basin Howe Platform, overlain by a few east–southwest lineaments are particu- itself, where the sediment thickness hundred metres of mainly Cainozoic larly important to the structural exceeds 4 km.

See AGSO Research Newsletter on the WWW at URL: http://www.agso.gov.au/information/publications/resnews/ AGSO Research Newsletter 31 November 1999

1 Petroleum & Marine Division, Australian Geological Survey Organisation, GPO Box 378, Canberra, ACT, 2601; tel. +61 2 6249 9343 (HMJS), +61 2 6249 9658 (IB), +61 2 6249 9356 (MA), +61 2 6249 9583 (AMGM); email [email protected], [email protected], [email protected], [email protected].

160¡ 165¡ 170¡ 155¡ 175¡ 149¡ NHT 179¡ CHESTERFIELD NC NORTH FIJI 20¡ PLATEAU BASIN

FR

NEW

L O R D

FT NORFOLK

SOUTH FIJI 25¡ MB CB BASIN FB Cook FZ

DAMPIER

Fairway CALEDONIA MiB

LHP NORFOLK Norfolk Island

Elizabeth -H O W E RIDGE

GoB

TKR 30¡

RIDGE Lord Howe VeningBASIN LHB Island Meinesz

WNR Barcoo - Fracture MoB SB BASIN

RB Zone

MnB R I S E 35¡ MnR KT

GiB BT CHALLENGER TASMAN PLATEAU TB

BASIN 40¡

New Zealand

0 500 km 45¡ 23/OA/1019

GoB Gower Basin MoB Moore Basin Volcanics KT Kermacec Trench NC New Caledonia BT Bellona Trough LHB Lord Howe Basin NHT New Hebrides Trench CB Capel Basin LHP Lord Howe Platform RB Reinga Basin FB Faust Basin MB Maryborough Basin SB Sydney Basin FR Fairway Ridge MiB Middleton Basin TB Taranaki Basin FT Fairway Trough MnB Monawai Basin TKR Three Kings Ridge GiB Gippsland Basin MnR Monawai Ridge WNR West Norfolk Ridge

Fig. 36. Structural elements of the Lord Howe Rise region. Blue tones represent ocean basins. On the Australian continent, brown tones represent fold belts; beige, Palaeozoic–Mesozoic basins; yellow, Mesozoic–Cainozoic rift basins. On Lord Howe Rise and ridges to the east, red and deep orange tones represent high-standing basement; yellow, mustard, and pale orange tones, rift-basin elements. New Zealand elements are coloured grey.

See AGSO Research Newsletter on the WWW at URL: http://www.agso.gov.au/information/publications/resnews/