An estimate of the Nd isotopic composition of Iapetus seawater from ca. 490 Ma metalliferous sediments |
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| Authors: | PJ Hooker PJ Hamilton RK O&#x;Nions |
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| Institution: | Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge England |
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| Abstract: | Well-preserved metalliferous sediments and pillow basalts of Lower Ordovician age (ca. 490 Ma) have been studied in an attempt to specify the Nd isotopic composition of Iapetus seawater. Initial143Nd/144Nd ratios of the pillow basalts are indistinguishable from published initial ratios for the 505-Ma Bay of Islands ophiolite complex and are within the anticipated range for MORB-type basalts 500 Ma ago. Metalliferous sediments occur both interstitial to basalt pillows and as well-developed sedimentary accumulations. The initial143Nd/144Nd ratios for the non-interstitial variety range from 0.511851 to 0.511712 (εNd = ?2.7to?5.4) and are considered to provide an estimate of143Nd/144Nd in Iapetus seawater. The interstitial metalliferous sediments show evidence for a significant basalt-derived Nd component. Although volcanic activity occurred at the margin of Iapetus essentially contemporaneous with the formation of the metalliferous sediments, it is clear that arc-type volcanic material was not a major source of Nd in Iapetus seawater. Rather the source of Nd was from continental regions with a similar average age to those supplying material to the present-day Atlantic Ocean. |
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