209 



The Na20 docs not vary systematically with the CaO, and MgO -! FeO varia- 

 tions in the analyzed greenstones. This further reflects the distinction between meta- 

 morphic difiercntiation effects, which are important only on a hand specimen lc\el, 

 and changes in the bulk composition of the rocks as a whole. 



A small decrease in FeO/FeoOa compared to fresh abyssal basalts is evident. 

 However, 2-5 has a high ratio compared to most oceanic tholeiites. As with the 

 MgO + FeO to CaO ratio, the ferrous/ferric ratio is about inversely proportional 

 to the amount of epidote present. 



The comparison with analyses of fresh basalts suggests that the bulk SiOi and 

 AI2O3 has not been greatly altered, although AI2O3 is lower than that of many 

 abyssal basalts. The relative enrichment in H2O of the greenstones and the slightly 

 higher Si02 content suggest that some slight enrichment of Si02 may ha\e occurred. 

 This is in accord with the abundance of quartz-rich veins in some of the greenstones, 

 particularly those from dredge 2. The normati\e quartz in 2-5 and .^-2 is a further 

 contrast between the greenstones and abyssal basalts. Normati\e quartz is rare in 

 fresh abyssal basalts. 



Introduction of sulfur is also evident in the greenstones {3-6, Table VI). Pyrite 

 is common in many of the unanalyzed 22"N greenstones, particularly as euhedral 

 crystals in chloritized olivine phenocrysts (Fig. 8). 



Trace and minor element data are also of interest in a comparison of the 22''N 

 greenstones with fresh abyssal basalts. Such data are presently being obtained and 

 will be reported separately. 



Contrast with continental greenschist fades rocks 



Small amounts of the potassian phases, stilpnomelane or biotite, are common in con- 

 tinental greenschist facies rocks of basaltic composition (Hutton, 1938). The occur- 

 rence of biotite rather than stilpnonielane is one of the features which distinguishes 

 the quartz-albite-biotite subfacies from the quartz-albite-muscovite-chlorite subfacics 

 of TuRNUR and Vi;riioogln (1960). Because of the very low K2O contents of the 

 22'N greenstones such potassian phases do not occur, and it is difllcult to place the 

 greenstones in an appropriate subfacies. 



The low K2O content of the 22 N greenstones may account for the abundance of 

 nontronite in the dredge 2 greenstones. Celadonitc, a potassian iron-rich illitc, has 

 been described from continental zeolite facies basic rocks, but was not noted in the 



