The sulfur content of Archean volcanic rocks and a comparison with ocean floor basalts

Abstract

In this paper we report the sulfur contents of 1056 basalts, andesites, dacites and rhyolites of known major element composition from the Rankin–Ennadai, Birch Lake – Uchi Lake, Lake of the Woods – Wabigoon Lake, Timmins and Skead Archean greenstone belts of the Canadian Shield. The sulfur contents of 299 ocean floor basalts and 68 sub-aerial or shallow water extrusive rocks are also reported. Sulfur contents for rocks of a given class are highly variable, ranging from near zero to several thousand parts per million (ppm). However, when averages for each of the rock classes are examined, the data from the two best documented of the Archean greenstone belts exhibit the same positive correlation between sulfur and total Fe content of the rocks. The trend for the Rankin–Ennadai belt coincides almost exactly with that reported earlier for the Blake River Group, approximating that expected if the rocks were saturated in sulfide at the time of extrusion. Rocks from the Lake of the Woods – Wabigoon Lake, Timmins and Skead areas seem to be somewhat poorer in sulfur than those from the Rankin–Ennadai and Blake River belts.Despite the fact that all evidence in the literature for fresh glassy pillow rims indicates that modern ocean floor basalts are saturated in sulfide, our average values for these ocean floor rocks are much lower than the predicted saturation levels, suggesting that the rocks have lost one-half to three-fourths of their sulfur, presumably through reaction with sea water. It is suggested that the reason for the Archean basalts retaining most of their sulfur despite the extensive redistribution that has occurred, whereas modern ocean floor basalts lose so much, may be due to the Archean rocks accumulating much more quickly and being exposed to direct interaction with sea water for a much shorter time than the modern rocks.