Compositional evolution of the upper continental crust through time, as constrained by ancient glacial diamictites

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• 作者：Richard M. Gaschnig^a ; ; Roberta L. Rudnick^a ; ¹ ; William F. McDonough^a ; Alan J. Kaufman^b ; John W. Valley^c ; Zhaochu Hu^d ; Shan Gao^d ; ² ; Michelle L. Beck^e
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2016
• 出版时间：1 August 2016
• 年：2016
• 卷：186
• 期：Complete
• 页码：316-343
• 全文大小：4905 K

文摘

The composition of the fine-grained matrix of glacial diamictites from the Mesoarchean, Paleoproterozoic, Neoproterozoic, and Paleozoic, collected from four modern continents, reflects the secular evolution of the average composition of the upper continental crust (UCC). The effects of localized provenance are present in some cases, but distinctive geochemical signatures exist in diamictites of the same age from different localities, suggesting that these are global signatures. Archean UCC, dominated by greenstone basalts and to a lesser extent komatiites, was more mafic, based on major elements and transition metal trace elements. Temporal changes in oxygen isotope ratios, rare earth elements, and high field strength elements indicate that the UCC became more differentiated and that tonalite–trondhjemite–granodiorite suites became less important with time, findings consistent with previous studies. We also document the concentrations of siderophile and chalcophile elements (Ga, Ge, Cd, In, Sn, Sb, W, Tl, Bi) and lithophile Be in the UCC through time, and use the data for the younger diamictites to construct a new estimate of average UCC along with associated uncertainties.