. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 268 NATURE VOL. 235 FEBRUARY 4 1972 over the hot spot. To show the effect of such a jump on the seafloor isochrons, we have arbitrarily assumed a jump at 10 bp of the central rift (Fig. 3). The tendency for a hot spot to force the relocation of a spreading rift can also be observed at Iceland. This hot spot apparently causes a 175 km eastward offset of the Mid-Atlantic rift relative to an extra- polated trend connecting the Reykjanes rift direc
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 268 NATURE VOL. 235 FEBRUARY 4 1972 over the hot spot. To show the effect of such a jump on the seafloor isochrons, we have arbitrarily assumed a jump at 10 bp of the central rift (Fig. 3). The tendency for a hot spot to force the relocation of a spreading rift can also be observed at Iceland. This hot spot apparently causes a 175 km eastward offset of the Mid-Atlantic rift relative to an extra- polated trend connecting the Reykjanes rift directly to the Jan Mayen rift. Five "basement ages" in the region have been reported by tr* Deep Sea Drilling Project (JOIDES)1'•'2. These are: for leg 9, cores No. 83 and 84; and for leg 16, cores No. 155, 157 and 158. Ages of the lowermost sediments from these cores are: 11 bp at core 83; 10 bp at core 84; 15-20 bp at core 155; 10 bp at core 157; 15-20 bp at core 158. Although core 83 agrees rather closely with our isochron, all "basement dates" are somewhat younger than the basement indicated on our isochron map (Fig. 3). These data possibly Cocos nemataths are appropriately reduced in length and they both mark the absolute drift vectors of the plates on which they are imposed. Since the Nazca plate is moving parallel to the southern isochron flexure, the opening of the gore is due entirely to the drift of the Cocos plate along a bearing of 045°. The Galapagos rifts migrate northward attempting to maintain a central position with the gore. This is not achieved by the Central Galapagos rift because it tends to hug the hot spot. Fig. 5 depicts the gore 30 bp, or 10 after its birth. The gore was then very small, and the triple junction was near the hot spot. A long transform fault connected the new rift to the Middle America subduct ion zone (off the diagram). In this construction, the close fit of the Carnegie and Cocos rid
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