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(2006) 'Adakites without slab melting : high pressure dierentiation of island arc magma, Mindanao, the Philippines.', Earth and planetary science letters., 243 (3-4). pp. 581-593. Further information on publisher's website:http://dx.doi.org/10.1016/j.epsl.2005.12.034Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Pliocene arc lavas generated in the same subduction zone. Excepting the heavy rare earth 27 elements, the adakites and arc lavas also possess similar ratios of incompatible elements 28 suggesting that the adakites were ultimately derived from melting of the mantle wedge. 29The wide range of SiO 2 in the adakites and its strong correlation with trace element 30 concentrations and ratios indicate two possible mechanisms for generating the adakitic 31 signature. (1) Adakitic melt was produced from basaltic arc magma by fractional 32 crystallisation of a garnet-bearing assemblage. (2) Solidified basaltic rock containing 33 garnet melted to yield adakitic magma. In either case the basaltic precursor was generated 34 from fluid-modified mantle then differentiated within the garnet stability field. In Surigao 35 this requires differentiation within mantle. The Surigao example suggests that any 36 subduction zone has the potential to produce adakitic magma if basalt crystallises at 37 sufficient depth. This has important implications for the geodynamics of modern and 38 ancient subduction zones that have generated similar rocks. 39

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87Sr/ 86 Sr ratios have been determined for glasses from four production sites, dated to between the sixth and the 11th centuries, in the Eastern Mediterranean region. On the basis of elemental analyses, the glasses at each location are believed to have been melted from different raw materials. Two glass groups, from Bet Eli'ezer and Bet She'an, in Israel, are believed to have been based upon mixtures of Levantine coastal sands and natron, and have 87 Sr/ 86 Sr ratios close to 0.7090, plus high elemental strontium, confirming a high concentration of modern marine shell ( 87 Sr/ 86 Sr ~ 0.7092) in the raw materials. The isotopic compositions of these two groups of glasses differ slightly, however, probably reflecting a varying ratio of limestone to shell because the sands that were utilized were from different coastal locations. Natron-based glasses from a workshop at Tel el Ashmunein, Middle Egypt, have 87 Sr/ 86 Sr values of 0.70794-0.70798, and low elemental strontium, consistent with the use of limestone or limestone-rich sand in the batch. High-magnesia glasses based on plant ash, from Banias, Israel, have 87 Sr/ 86 , probably reflecting the isotopic composition of the soils that were parental to the plants that were ashed to make the glass. Strontium and its isotopes offer an approach to identifying both the raw materials and the origins of ancient glasses, and are a potentially powerful tool in their interpretation.

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