کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
10121377 | 1641621 | 2005 | 22 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Early crust on top of the Earth's core
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
فیزیک زمین (ژئو فیزیک)
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چکیده انگلیسی
Mass balance considerations and preliminary results of geochemical modelling of the above scenario (similar to that performed by Tolstikhin and Marty [Tolstikhin, I.N., Marty, B., 1998. The evolution of terrestrial volatiles, A view from helium, neon, argon and nitrogen isotope modeling. Chem. Geol. 147, 27-52]) show the potential geochemical importance of Dâ³. (1) Modelling of Pu-U-I-Xe isotope systematics predicts formation of this reservoir early in Earth history, â¼100 Ma after formation of the Solar system. (2) The total amount of heat-generating U, Th, K (and other highly incompatible elements) in Dâ³ exceeds 20% of the Earth inventory, and a similar portion of terrestrial heat is being transferred from the core + Dâ³ into the base of the overlying convecting mantle. (3) Dâ³ is enriched in solar implanted rare gases because the small (re)-accreting debris with high surface/mass ratios will have been subjected to intense radiation by the early sun. (4) Rare gases diffuse from Dâ³ into the overlying mantle and are then transferred into upwelling plumes, which originate above Dâ³. In addition, small amounts of Dâ³ material may be entrained by the mantle convective flow as was recently discussed by Schott et al. [Schott, B., Yuen, D.A., Braun, A., 2002. The influences of composition and temperature-dependent rheology in thermal-chemical convection on entrainment of the Dâ³ layer. Physics Earth Planet. Inter. 129, 43-65]. From the rare-gas modelling it follows that initially (â¼4500 Ma ago) Dâ³ could have been more massive by a factor of â¼1.2 than at present (about 2 à 1026 g). The present-day mass flux from Dâ³ into the convecting mantle is estimated to be â¤0.05 à 1016 g yearâ1, a factor of â¼100 less than the rate of ridge magmatism. This small contribution of Dâ³ material makes it difficult to trace fingerprints of Dâ³ even using such sensitive tracers as Pb isotope ratios. (5) The density contrast that stabilizes Dâ³ is maintained by its higher intrinsic density due to the iron-rich chondrite-like component. Subduction of this material, its entrainment by convective mantle flow and mixing could also account for the preservation of the chondritic relative abundances of siderophile elements in the mantle. If Dâ³ is partially molten, the density contrast may be caused by a high-density melt fraction.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Physics of the Earth and Planetary Interiors - Volume 148, Issues 2â4, February 2005, Pages 109-130
Journal: Physics of the Earth and Planetary Interiors - Volume 148, Issues 2â4, February 2005, Pages 109-130
نویسندگان
Igor Tolstikhin, Albrecht W. Hofmann,