The Australian plate is one of the most imposing and older ones on Earth and is in contact with 17 other plates and micro-plates. On its southeast boundary, the plate has been subducting under the Pacific plate along the Puysegur trench at a rate of 5 ± 0.8 mm yr-1 [ 3] since 5-10 Ma[ 4] towards the northeast direction. The active configuration generates earthquakes of M4-M7.9 on both plates and at their interface [ 5].The Australian slab gradually steepens from south to north along the subduction zone until becoming nearly vertical. The plate boundary abruptly converts to the Alpine Fault (linear dextral transpressive transform fault) which transects the New Zealand since 6.5-10 Ma[ 3]. Furthemore, the Australian plate subducts under the Pacific plate further north, near the Solomon islands, since 10 Ma at a rate of 52 ± 4 mm yr-1[ 4].
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The Southeast Indian ridge appeared during the separation of the Gondwana continent (34 Ma) and it lies on the southern boundary of the Australian plate, which diverges from the Antartic plate at a rate of 60-70 mm yr-1 towards the northeast direction [6]. The mid-ocean ridge is separated by transformation faults and two propagating rifts, and at its eastern end lies the Australia-Antarctica Discordance where the temperature is remarkably low conforming with the observed sea-floor deep levels [ 7]. |
The southwest plate boundary begins at the Rodrigues Triple Junction which marks a common point between the Australian, the Antarctic, and the African (Somalian) plates and exists since 65 Ma [9]. The Australia-African intersection is marked by the Central Indian Ridge, where the Australian is drifting towards the northeast direction at a rate of 40 mm yr-1 conserved for the last 0-4 Myr. An increase of seismici is observed at less magmatic sections corresponding to the transform faults intersecting the ocean ridge [8]. Moreover, the Indo-Australian plate was considered to be united until recently, since theoretical plate configurations and motions do not coincide with observations. Thus, it is proposed that the hypothetical Capricorn plate has been forming for the last 11 Ma [10] from the Central Indian Ridge, and has a diffuse western plate boundary with Australia [6]. The India-Australian plate boundary is also diffuse, having an oceanic spreading ridge and an oceanic convergent boundary[1].
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On the nothern plate boundary, the Australian plate subducts under the Sunda plate along the Java Trench towards the northeast at a rate of 71± 2 mm yr-1 [11] since 80 Ma [12]. The Pacific Ring of Fire along the subduction zone presents a great volcanic activity and earthquake incidence, the biggest earthquake being of magnitude M9 in 2004. |
On the northeast side, the Australian plate is in contact with younger micro-plates where the plate boundaries are of varying nature [1]. |
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Furthermore, the plate encloses the Australian continent which is under compression stress due to the multiple plate boundaries. This situation generates a lot of earthquake activity drive by major fault displacements, mainly in the southern region of Australia (Flinders seismic zone) which is on a heat zone anomaly. On the eastern side of the continent lies the Newer Volcano Group (dormant volcanoes) where the soil is fertile and rich in gemstones. Moreover, there are seamount chains in the Tasman Sea, exposing the passage of the Australian plate over a mantle plume. At the west, pre-cambrian rocks can be traced on a great fraction of the continent and the soil is sandy, acidic, and not very fertile. The center of Australia has no major mountain building [6].
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The Australian plate encloses a significant water area such as the Indian sea where lies the aseismic Ninety East Ridge with singular basalt composition [13], the Tasman Sea comprising the Resolution ridge which is a geologic boundary between sedimentary deposition corresponding to different ages [14], the Coral Sea characterized by its complex bathymetry[15], the Timor Sea which is rich in fishing and hydorcarbon ressources [16], and the Arafura Sea. |
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Bibliography
- USGS. Dynamic Earth. Google Earth file for Elementary Earth Physics course.
- National Earthquake Information Center, 2004, M7.1 Puysegur Trench Earthquake of 22 November 2004, US Geological Survey, scale 1:1,300,00.
- Beavan, John, and John Haines. "Contemporary Horizontal Velocity and Strain Rate Fields of the Pacific-Australian Plate Boundary Zone through New Zealand." Journal of Geophysical Research 106.B1 (2001): 741-70. Print.
- Lebrun, Jean-Frédéric. "Subduction Initiation at a Strike-slip Plate Boundary: The Cenozoic Pacific-Australian Plate Boundary, South of New Zealand." Journal of Geophysical Research 108.B9 (2003): n. pag. Print.
- Tregoning, Paul, Francis Tan, John Gilliland, Herbert McQueen, and Kurt Lambeck. "Present‐day Crustal Motion in the Solomon Islands from GPS Observations." Geophysical Research Letters 25.19 (1998): 3627. Print.
- Blewett, Richard. "Australia in Time and Space." Shaping a Nation: A Geology of Australia. Canberra: Geoscience Australia and ANU E-Press, 2012. 47-119. Print.
- Sempere, J.-C., B. P. West, and L. Geli. "The Southeast Indian Ridge between 127 and 132 40'E: Contrasts in Segmentation Characteristics and Implications for Crustal Accretion." Geological Society, London, Special Publications 118.1 (1996): 1-15. Print.
- Kamesh Raju, K.A., Kiranmai Samudrala, R.K. Drolia, Dileep Amarnath, Ratheesh Ramachandran, and Abhay Mudholkar. "Segmentation and Morphology of the Central Indian Ridge between 3°S and 11°S, Indian Ocean." Tectonophysics 554-557 (2012): 114-26. Print.
- Mendel, Véronique, Daniel Sauter, Philippe Patriat, and Marc Munschy. "Relationship of the Central Indian Ridge Segmentation with the Evolution of the Rodrigues Triple Junction for the past 8 Myr." Journal of Geophysical Research 105.B7 (2000): 16563-6575. Print.
- Conder, James A, and Donald W Forsyth. "Sea£oor Spreading on the Southeast Indian Ridge over the Last One Million Years: A Test of the Capricorn Plate Hypothesis." Earth and Planetary Science Letters 188.1-2 (2001): 91-105. Print.
- Tregoning, P., F. K. Brunner, Y. Bock, S. S. O. Puntodewo, R. McCaffrey, F. Genrich, E. Calais, J. Rais, and C. Subarya. "First Geodetic Measurement of Convergencea Cross the Java Trench." Geophysical Research Letters 21.19 (1994): 2135-138. Print.
- Lebrun, Jean-Frédéric. "Subduction Initiation at a Strike-slip Plate Boundary: The Cenozoic Pacific-Australian Plate Boundary, South of New Zealand." Journal of Geophysical Research 108.B9 (2003): n. pag. Print.
- Hekinian, Roger. "Petrology of the Ninety East Ridge (Indian Ocean) Compared to Other Aseismic Ridges." Contributions to Mineralogy and Petrology 43.2 (1974): 125-47. Print.
- Mortimer, N., P. B. Gans, F. Hauff, and D. H. N. Barker. "Paleocene MORB and OIB from the Resolution Ridge, Tasman Sea." Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia 59.6 (2012): 953-64. Print.
- Landmesser, Charles W., James E. Andrews, and Gordon H. Packham. "Aspects of the Geology of the Eastern Coral Sea and the Western New Hebrides Basin." Annual Progress Report, Contract N00014-70-A-0016-0001, Between the Office of Naval Research, Ocean Science and Technology Branch, and the Hawaii Institute of Geophysics, University of Hawaii 70.27 (1975): 647-62. Print.
- Environment and Development Division. "Geology and Mineral Resources of Timor-Leste."Atlas of Mineral Resources of the ESCAP Region 17 (2004): 1-36. Print.