Upper crustal recycling in southern Britain; evidence from Nd and Sr isotopes

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doi: 10.1016/0012-821X(85)90045-7
Authors:Davies, Gareth; Gledhill, Andy; Hawkesworth, Chris
Author Affiliations:Primary:
Open Univ., Dep. Earth Sci., Milton Keynes, United Kingdom
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 75(1), p.1-12. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:1985
Note:In English. 42 refs.; illus. incl. 3 tables, geol. sketch map
Summary:Analyses of representative rocks from southern Britain are used to examine the evolution of this segment of continental crust. The vast majority of late Precambrian basement rocks have unradiogenic 87Sr/86Sr ratios and model 023tNdDM ages of approx 1300 m.y., although locally the Rosslare complex and the Rushton schists have model 023tNdDM ages of approx 1700 m.y., identifying for the first time an 'old' component in the basement of southern Britain. Following the closure of the Iapetus Ocean, sediments exhibit a progressive increase in model 023tNdDM ages of approx 1350 in the Lower Palaeozoic to 1750 m.y. in the Jurassic. This variation demonstrates the southerly transport of detritus 029tNdDM >2000 m.y.) from the mixed Archaean/Proterozoic terrains of N Europe and America. The granitic rocks have significantly higher epsilonNd than those of contemporaneous sediments and thus yield a different Nd isotope evolution curve when considered in isolation. The majority of rocks analysed have model 023tSrDM ages in the range 1200 to 460 m.y., with youngest sediments generally recording the lowest model ages. Therefore, with time, the sediments record a striking increase in the model ratio of model Nd to model Sr age. The data suggest that the Rb/Sr ratios of the crustal rocks increased by a factor of approx 2 every 900 m.y., implying that on average the British upper crust was reworked by erosion and sedimentation every 600 m.y. Nd and Sr isotope results for 51 upper crustal rocks and 15 Leinster and SW England granite batholiths are presented. [P.Br.]
Subjects:Absolute age; Alkaline earth metals; Basement; Cambrian; Continental crust; Crust; Dates; Geochemistry; Gneisses; Granites; Iapetus; Igneous rocks; Isotopes; Jurassic; Mesozoic; Metals; Metamorphic rocks; Nd-144/Nd-143; Neodymium; Paleozoic; Plutonic rocks; Precambrian; Proterozoic; Rare earths; Sedimentary rocks; Sr-87/Sr-86; Stable isotopes; Strontium; Upper crust; Upper Precambrian; Europe; Great Britain; United Kingdom; Western Europe; Rosslare Complex; Rushton schists; Southern Great Britain
Abstract Numbers:86M/1881
Record ID:1986015123
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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