The submarine features of the divergent marginshave a certain bilateral symmetry about the meridian halfway across Australia: complexes of marginal plat-eaus and abyssal plains are backe
Trang 1The submarine features of the divergent margins
have a certain bilateral symmetry about the meridian
halfway across Australia: complexes of marginal
plat-eaus and abyssal plains are backed by a broad shelf in
the north, and narrow margins expand into long
ap-pendages (Naturaliste Plateau and Tasmania–South
Tasman Rise) in the south This pattern extends to
the arrangement of seafloor-spreading magnetic
anomalies in that the azimuth of the anomalies off
the west coast is reflected in that off the east coast,
while the set to the south is crossed by the line of
symmetry The age of onset of spreading follows
an-other pattern, with anticlockwise propagation from
156 Ma in the north-west through 132 Ma in the
west, and 99 Ma in the south, and as back-arc
spread-ing at 83.5 Ma, 68 Ma, and 64 Ma in the south-east,
62 Ma in the north-east, and 5 Ma off eastern New
Guinea
Present Motion
Figure 27shows the velocities (azimuth and
magni-tude) from a few years of Global Positioning System
(GPS) measurements and from the NUVEL-1A
global-plate-motion model averaged over several
mil-lion years For example, the GPS estimate in western
Victoria of 58.3 mm year 1at 022approximates the
NUVEL-1A estimate of 61 mm year 1 at 019, and
that near Darwin of 67.2 mm year 1 at 034.9
matches the NUVEL-1A estimate of 71 mm year 1
at 033 Most of this motion comes from seafloor
spreading in the Southeast Indian Ocean at a full
rate of 60 mm year 1 from an almost stationary
Antarctica
The stations on mainland New Guinea, including
one near the plate boundary, record an azimuth of
ca 050, which locates them on the south-western (Australian) side of the plate boundary On the other side, the Pacific Plate is moving at a velocity of 66 mm year 1at 289, almost at a right angle to Australia’s motion, confirming the idea expressed by Alfred Wegener that the Pacific’s westerly motion has planed off the obtruding anvil of New Guinea
According to NUVEL-1A, the Eurasian Plate is moving slowly south-eastwards GPS measurements
on either side of the Flores and Wetar thrusts show that the southern Banda arc is virtually accreted to the Australian plate margin and that most of the conver-gence seems to be accommodated by left-lateral slip
at the plate boundary, suggesting that the Timor Trough is now inactive as a thrust
See Also
Antarctic Australia: Proterozoic; Tasman Orogenic Belt Gondwanaland and Gondwana New Zealand Oceania (Including Fiji, PNG and Solomons) Palaeo-climates Pangaea Plate Tectonics Tectonics: Moun-tain Building and Orogeny
Further Reading
BMR Palaeogeographic Group (1990) Evolution of a Con tinent Canberra: Bureau of Mineral Resources, Geology and Geophysics
Veevers JJ (ed.) (1984) Phanerozoic Earth History of Australia Oxford: Clarendon Press
Veevers JJ (ed.) (2000) Billion Year Earth History of Aus tralia and Neighbours in Gondwanaland Sydney: GEMOC Press
Veevers JJ (2001) Atlas of Billion Year Earth History of Australia and Neighbours in Gondwanaland Sydney: GEMOC Press
Tasman Orogenic Belt
D R Gray, University of Melbourne, Melbourne, VIC,
Australia
D A Foster, University of Florida, Gainesville, FL, USA
ß 2005, Elsevier Ltd All Rights Reserved.
Introduction
The eastern part of Australia formed along the
margin of Gondwana during the Palaeozoic due to
the accretion of oceanic platform and basinal
sequences (Figure 1) A region of eastern Australia
over 1000 km wide now consists of three distinct
orogenic belts (the Delamerian, Lachlan–Thomson, and New England orogens), which are collectively referred to as the Tasman Orogenic Belt (Figures 1 and 2) This deformed and metamorphosed tract of rocks was once part of a major orogenic system that extended some 20 000 km along the Gondwanan margin, incorporating parts of the Andes in South America (see Andes), the Cape Fold Belt in southern Africa, and the Ross Orogen in Antarctica (see Ant-arctic) (Figure 1) In eastern Australia accretion oc-curred in a stepwise fashion, with an eastward younging from the Cambrian to the Triassic, reflected
AUSTRALIA/Tasman Orogenic Belt 237