Citation

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Crawford, A.J. & von Rad, U., 1994. The petrology, geochemistry and implications of basalts dredged from the Rowley Terrace-Scott Plateau and Exmouth Plateau margins, northwestern Australia. AGSO Journal of Australian Geology and Geophysics  15:1:43-54. Australian Geological Survey Organisation, Canberra.

Abstract

We report major and trace-e lement compositions of 14 basalts and dolerites dredged from seven sites along the outer rifted margin of northwestern Australia. Lavas from the margin of the Scott Plateau-Rowley Terrace, of interpreted Callovian-Oxfordian age, are evolved basalts and ferrobasalts with Zr/ Nb from 5-17, and LREE-enriched REE patterns [(La/ Yb)N from 3.4 to 8], and are T-MORB transitional to more P-MORB from the SW Indian Ridge and the Red Sea-Afar rift zone. They are significantly different from the unusually depleted N-MORB drilled less than 100 km farther west on the Argo Abyssal Plain at ODP Site 765. T- to P-MORB were also dredged at the foot of the southwestern corner of the Exmouth Plateau. This dredge site is only 80 km from ODP Site 766, which also yielded N-MORB. Basalts very similar to those drilled at ODP Site 766 were also dredged at a site only 20 km east of Site 766. The evolved, mainly ferrobasaltic nature of the Rowley Terrace-Scott Plateau margin basalts, their T- to P-MORB compositional signatures, and their close spatial association with strongly depleted N-MORB resemble in many ways the lava pile formed during the last 4 m.y. along the southern Red Sea-Gulf of Aden-Asal-Afar region. Although the latter region is associated with the effects of the long-lived (~40 m.y.) Afar plume, a plume origin for the northwest Australian margin basalts is less easily demonstrated. Problems with the plume hypothesis for this region include (1) the remarkably rapid change from plume-influenced MORB along the Rowley Terrace margin to depleted N-MORB at the foot of this margin at the eastern end of the Argo Abyssal Plain, requiring a sudden switch-off of the hypothetical plum; (2) the apparent recurrence of this same pattern of T-MORB to depleted N-MORB basalts 400 km farther south on the same margin some 20-25 m.y. later (Valanginian); and (3) the occurrence of perhaps more convincingly plume-related basalts that constitute the Wallaby Plateau, which formed as part of interpreted plume head eruptions of the Kerguelen plume around 115 Ma, and were apparently erupted onto Cuvier Abyssal Plain oceanic crust only probably 30-40 m.y. old.
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1994

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Earth Sciences

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English

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2015-05-19

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