Neodymium and strontium isotope study of ophiolite and orogenic lherzolite petrogenesis |
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| Authors: | Pierre Richard Claude J Allegre |
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| Institution: | 1. Laboratoire de Géochimie et Cosmochimie, Institut de Physique du Globe de Paris, Universitéde Paris VI, 4, Place Jussieu, 75230 Paris Cedex 05 France;2. Département des Sciences de la Terre, Universitéde Paris VII, 4, Place Jussieu, 75230 Paris Cedex 05 France |
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| Abstract: | Neodymium isotopic analyses have been measured on nine ophiolites and four orogenic lherzolites. εNd varies from +12 to +3 in the ophiolites and from +18 to +2 in the orogenic lherzolites. The majority of the analyses plot on a εNd-εSr correlation line as defined by Nd and Sr isotopic analyses of oceanic basalts. However, certain ophiolitic and lherzolitic samples exhibit high87Sr/86Sr ratios and as such lie to the right of the correlation line towards seawater compositions.From these data one can postulate several origins for ophiolites including that of mid-ocean ridges and ocean islands. If the orogenic lherzolites are interpreted as representative of the mantle occurring below active ridges a more complex model is required involving mantle heterogeneity and multi-episodic chemical fractionation starting prior to 2 Ga ago. |
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