EARLIEST PART OF EARTHS STRATIGRAPHIC RECORD - A REAPPRAISAL OF THE GREATER-THAN-3.7 GA ISUA (GREENLAND) SUPRACRUSTAL SEQUENCE

Investigations of the Isua supracrustal rocks in West Greenland allow us to identify the protoliths and alteration history for most Isua roc ks, The protoliths consisted of alternating basalt and banded iron for mation. This sequence was invaded by dunitic sills, metamorphosed, and later intruded by felsic gneisses. Pervasive carbonation and K metaso matism produced a sequence of lithologies, mimicking those found in mo dern platform deposits, However, the protoliths could have originated in a purely oceanic environment with no sialic detrital components, Th e Isua sequence probably consists of several tectonic panels, some of which are cut by >3810 Ma felsic intrusive rocks.