It started with a plume - Early Archaean basaltic proto-continental crust

R. Hugh Smithies, Martin Van Kranendonk, David C. Champion

Research output: Contribution to journalArticle

111 Citations (Scopus)

Abstract

The lower part of the Pilbara Supergroup records 300 million years of voluminous basaltic magmatism from ca. 3.515 to 3.24 Ga. The basalts are divided into two compositionally distinct but contemporaneous and interbedded types. Compared to low-Ti basalts, high-Ti basalts (TiO2 > 0.8 wt.%) have relatively high concentrations of HFSE and REE, are generally more Fe-rich, have very low Al2 O3/TiO2 (18.7-8.9) and high Gd/Yb ratios (1.12-2.23). The composition of the high-Ti basalts, and their source, did not change significantly throughout the 300 m.y. period of basalt eruption. In contrast, low-Ti basalts show distinct secular trends to lower concentrations of incompatible trace elements and to lower ratios of La/Sm, La/Gd, La/Yb and Gd/Yb that reflect a source progressively more depleted than N-MORB source. Gd/Yb ratios in the younger low-Ti basalts are as low as 0.67, well below estimates for modern depleted mantle (0.98). These values reflect a strongly depleted source, and possibly also a contribution from a low Gd/Yb source component representing the garnet-bearing residue of previous high-pressure melting events. The source for the low-Ti basalts comprised the accumulated residues of plumes that produced the earliest high-Ti basalts and of plumes that produced subsequent high-Ti basalts, and was periodically modified through melt extraction. It remained isolated from the convecting asthenosphere throughout the 300 m.y. period of basaltic magmatism, but parts of it remelted each time one of a series of plumes impinged on the lithospheric mantle. It progressively formed the thick, depleted, and buoyant sub-continental lithospheric mantle (SCLM) that is complimentary to the thick pile of interbedded high- and low-Ti basalt that comprises the bulk of the Pilbara Supergroup. These interpretations support models for Palaeoarchaean protocrust formation through extensive mantle plume magmatic events, and models that suggest that the Archaean SCLM formed at the same time as early voluminous mafic magmatism.

Original languageEnglish
Pages (from-to)284-297
Number of pages14
JournalEarth and Planetary Science Letters
Volume238
Issue number3-4
DOIs
Publication statusPublished - Oct 15 2005
Externally publishedYes

Fingerprint

basalt
continental crust
plumes
Archean
crusts
plume
Earth mantle
mantle
magmatism
Bearings (structural)
asthenosphere
Garnets
Trace Elements
mantle plume
piles
mid-ocean ridge basalt
trace elements
volcanic eruptions
garnets
Piles

Keywords

  • Basalt geochemistry
  • Palaeoarchaean
  • Pilbara supergroup
  • Secular evolution
  • Sub-continental lithospheric mantle (SCLM)

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)

Cite this

It started with a plume - Early Archaean basaltic proto-continental crust. / Smithies, R. Hugh; Van Kranendonk, Martin; Champion, David C.

In: Earth and Planetary Science Letters, Vol. 238, No. 3-4, 15.10.2005, p. 284-297.

Research output: Contribution to journalArticle

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