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Science 2 November 2007:
Vol. 318. no. 5851, p. 746
DOI: 10.1126/science.1144148
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Technical Comments

Comment on "A Vestige of Earth's Oldest Ophiolite"

Allen P. Nutman1* and Clark R. L. Friend2

1 Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037, China.
2 45 Stanway Road, Headington, Oxford OX3 8HU, UK.


Figure 1 Fig. 1. Geological sketch map of part of the western end of the Isua supracrustal belt. Only the thickest, most continuous areas of cover moraine are shown. Mapping compiled from (6, 7). Zircon dating results constraining the ages of supracrustal rocks in the southwest to ≥3.8 Ga and in the northeast to ≤3.7 Ga are shown. The localities 1, 2, and 3 are from (1). The belt is partitioned by Eoarchaean shear zones. The likely position of the break between the ~3.8 and 3.7 Ga sequences is presently known only within 200 m (7). [View Larger Version of this Image (81K GIF file)]
 

Figure 2 Fig. 2. About 1:10,000 scale mapping by A. P. Nutman in August 1980 of the area thought to cover the Furnes et al. localities 2 and 3, by using their low-resolution sketch map [figure 1C in (1)]. Numerous amphibolitized dikes cut all lithologies and are oriented subconcordant to the lithological layering. [View Larger Version of this Image (38K GIF file)]
 

Figure 3 Fig. 3. Pillow lavas at Furnes et al. locality 1. The shape of the pillows indicates facing to the south (left of picture), and hence toward the proposed sheeted dikes. IPH is the interpillow hyaloclastite shown by Furnes et al.; T and B are the top and base, respectively, of some pillows. The pillows have been flattened orthogonal to their original orientation. [Photo by A. P. Nutman] [View Larger Version of this Image (137K GIF file)]
 

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Science. ISSN 0036-8075 (print), 1095-9203 (online)