Why was flood volcanism on submerged continental platforms so common in the Precambrian?

Many Archean and Proterozoic greenstone belts contain volcanic rocks that e rupted subaqueously but interacted with continental crust on their way to t he surface. This points to emplacement in a tectonic setting that was rare to absent throughout the Phanerozoic - the eruption of flood basalts onto s ubmerged continental platforms. To explain the situation requires that sea levels were high during periods of flood volcanism, perhaps because the oce an basins were partially filled by extensive, active and high-standing ocea nic ridges or by oceanic plateaus. The common preservation of crust-contami nated submarine basalts, even in the oldest supracrustal sequences, may ind icate that continental crust was voluminous even at an early stage in Earth history. (C) 1999 Elsevier Science B.V. All rights reserved.