Toward an understanding of chemical and isotopic heterogeneity in the Earth's mantle
- 出版日期：2004.
- 页数：1 v. :
- 第一责任说明：James Brewster Kellogg.
- 分类号：a240 ; a270
- ISBN：0496791206(ebk.) :
MARC全文
02h0029752 20120628145756.0 cr un||||||||| 120628s2004 xx ||||f|||d||||||||eng | 3131880 0496791206(ebk.) : CNY371.35 NGL NGL NGL a240 ; a270 Kellogg, James Brewster. Toward an understanding of chemical and isotopic heterogeneity in the Earth's mantle [electronic resource] / James Brewster Kellogg. 2004. 1 v. : digital, PDF file. Adviser: O'Connell, Richard J. Thesis (Ph.D.)--Harvard University, 2004. We present models of the evolution of isotopic heterogeneity in the Earths mantle to develop an understanding of the relationship between modern geochemical observables and physical processes through time. Our basic model is an extension of the conventional geochemical reservoir model for the evolution of the Earths crust-mantle system in which we calculate not only the mean isotopic ratios, but also the distribution of those ratios within the reservoirs. Owing to low chemical diffusion rates, subreservoirs that are created by mass transport into and out of the mantle effectively exist as distinct geochemical entities for all time. By tracking these subreservoirs, we obtain a model of the full range of isotopic values represented in the mantle. Using results from numerical calculations of mixing, we also track the length scales associated with each subreservoir. Applying simple statistics, we obtain the distribution of expected measurements as a function of the stirring time, effective melt fraction, sampling volume, and mass transport history. In developing the model, we focus on the samarium-neodymium and rubidium-strontium parent-daughter systems, as these are the best behaved of the commonly-used systems. We then focus on the uranium-thorium-lead system, which introduces a significant degree of complexity not present in the simpler systems. We find that the removal of lead from the oceanic crust by subduction zone processes is critical in obtaining the observed slopes in lead-isotopic space. We derive an internally consistent model of the Earths isotopic evolution both in the bulk and statistical sense. We obtain a model of the Earths mantle, heterogeneous on all length scales, which successfully reproduces the spectrum of heterogeneity observed in mid-ocean ridge basalts. This model leads us to a new version of the plum-pudding mantle in which relatively young, <；1 Gyr) depleted residua from continental crustal extraction form the plums and everything else mixes to form the pudding. This latter component may be identified with FOZO or C, the intermediate mixing endmember suggested previously by other authors. Earth ; Geochemistry. Mantle. Electronic dissertations. aeBook. aCN bNGL http://pqdt.bjzhongke.com.cn/Detail.aspx?pid=7Wsb8jjWyto%3d NGL Bs1624 rCNY371.35 ; h1 bs1204