Other
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.v22c..07c&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #V22C-07
Other
1025 Composition Of The Mantle, 1026 Composition Of The Moon, 1155 Extinct Radionuclide Geochronology, 5410 Composition (1060, 3672), 5455 Origin And Evolution
Scientific paper
Variations in the 142Nd/144Nd ratio of terrestrial, lunar, martian and asteroidal materials caused by the decay of 103 Myr half-life 146Sm show that early differentiation of the silicate portions of planetary objects is the rule rather than the exception. On the Earth, old mafic rocks from Isua, Greenland have a 142Nd/144Nd ratio approximately 15 ppm higher than found in most other terrestrial rocks, which, in turn, are about 18 ppm higher than ordinary chondrites. High 142Nd/144Nd is a signature of an early-formed source with high Sm/Nd, a sign of incompatible element depletion. The Isua result suggests that the early-Earths mantle was even more depleted than the post-3.8 Ga mantle. A very depleted early Earth mantle is supported by new 142Nd data for 11 lunar samples where we find, in contrast to recent results reported by Rankenburg et al. (Science 31, 2006), but similar to the results of Nyquist et al. (GCA 59, 1995), that ancient lunar rocks have an initial 142Nd/144Nd even higher than the terrestrial value. For example, a two-point 146Sm-142Nd isochron for crustal rocks 60025 and 78236 provides an age of 4432 Ma, within error of previous 147Sm-143Nd isochrons for these samples, and an initial 142Nd/144Nd that is 6 ppm higher than terrestrial Nd. These results are consistent with data for KREEP and both low-Ti and high-Ti basalts. The lunar data suggest that the Moon formed with a 147Sm/144Nd of between 0.227 and 0.241, which is on the low side of previous estimates based on the elevated initial 143Nd/144Nd of lunar crustal rocks (e.g. Borg et al., GCA 63, 1999). An originally chondritic reservoir that was depleted to a 147Sm/144Nd = 0.227 30 Myr after solar system formation would have a present day 142Nd/144Nd 18 ppm higher than the terrestrial standard, similar to that measured in Isua. This result may suggest that the Moon formed preferentially from an early-formed, strongly incompatible element depleted, terrestrial mantle. The decrease in 142Nd/144Nd from the high at Isua to the value measured for most post-3.8 Ga terrestrial rocks suggests that this initially strongly depleted terrestrial mantle became less depleted through limited remixing with an early-formed complementary enriched reservoir.
Boyet M. M.
Carlson Richard W.
No associations
LandOfFree
Evidence for a Strongly Depleted Early Earth does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Evidence for a Strongly Depleted Early Earth, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Evidence for a Strongly Depleted Early Earth will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-963099