Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.684749
Title: The role of the oceanic crust in the genesis of volcanic arc magmas
Author: Freymuth, Heye
ISNI:       0000 0004 5922 384X
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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Abstract:
Volcanic arc magmas are usually thought to receive components from three different sources: the subarc mantle, fluids derived from the subducted oceanic crust and lithospheric mantle, and melts derived from subducted sediments. This thesis re-evaluates this model based on isotopic data for magmas from the Izu, New Britain and Mariana arcs. High (230Th/232Th) ratios of up to 2.5 and U excess over Th in samples from the Izu and New Britain arcs are shown to be inconsistent with a derivation from subducted sediments or the sub-arc mantle and are instead argued to reflect a contribution of a melt of the mafic oceanic crust. In addition to Th, the magmas require a number of incompatible elements to be added to the sub-arc mantle. Many of these elements have traditionally been interpreted to be derived from a melt of subducted sediments. Yet, radiogenic Nd and Hf isotopes in these samples do not indicate the presence of a sediment melt. In order to explain this discrepancy, a model is presented in which the component previously identified as sediment melt is a mixture of a sediment melt and a melt of the mafic oceanic crust. Mo isotopes are suggested as a novel tracer for subduction components in volcanic arc magmas and a potential tracer for deep recycling of material transported into the mantle beyond subduction zones. Mo isotope ratios are presented for samples from oceanic sediments, the altered top part of the mafic oceanic crust, and volcanic arc magmas from the Mariana arc, thus defining input and output parameters for a subduction zone. Mo is shown to be preferentially transported in an isotopically distinct fluid derived from the subducted slab. Fluid addition leads to values of 0'98Mo in the Mariana arc lavas ~0.1-0.3 %0 higher than in MORB.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.684749  DOI: Not available
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