215 



(9) Much of the compositional difference between the greenstones is a result of 

 epidote enrichment on the one hand and of chlorite enrichment on the other. 



(/C) Based on heat flow measurements from the Mid-Atlantic Ridge, minimum 

 depth of burial to obtain minimum postulated greenschist temperatures is around 

 2 km. 



(//) Greenschist facies metabasalts may be common in oceanic crustal rocks 

 as a whole, particularly in the mid-ocean ridges. 



(12) The greenstones may occur in an uplifted block of the lower oceanic crust. 



ACKNOWLEDGEMENTS 



Dr. Vaughan Bowen of the Woods Hole Oceanographic Institution initiated this 

 study of the 22''N rocks, and has offered assistance and advice at all stages of the 

 study. We wish to thank Prof. Raymond Siever, Harvard University, and Prof. H. H. 

 Hess, Princeton University, for reviewing the manuscript. 



We also wish to thank the scientific party and crew of the R. V. "Chain" and 

 R. V. "Thomas Washington" who made the dredging possible. Collection of the 

 samples and much of the analytical work were supported through contracts and 

 grants with the Woods Hole Oceanographic Institution, by the following: U.S. 

 Atomic Energy Commission (contract AT (30-l)-2174); this is report number NYO- 

 2174-40); the U.S. Office of Naval Research (contract NONR 2196 (00)); and the 

 National Science Foundation (grants GP 921 and GP 1599). Participation of the 

 junior author was made possible by contract NONR 2216 (23) of the U.S. Ofiice 

 of Naval Research with Scripps Institution of Oceanography. 



Participation by the senior author was made possible by Smithsonian Research 

 Award 007 (1965). We wish to thank Dr. Kurt Fredricksson and M-. Charles Fiori 

 of the Division of Meteorites, for use of their electron microprobe laboratory; Mr. 

 Grover Moreland for preparation of specimens for microprobe analyses; Mr. Larry 

 Isham for drafting the illustrations; and Mr. Harold Banks for assistance with the 

 microprobe data calculations, and in the X-ray diffraction work, and many other 

 members of the Department of Mineral Sciences, U.S. National Museum. This is a 

 contribution of Scripps Institution of Oceanography, New Series, and contribution 

 1801 from the Woods Hole Oceanographic Institution. 



