No abstract

We report Sr-, Nd-and Pb-isotopic compositions for the lavas of Mauritius, the second youngest volcanic island in the Re ´union hotspot. The lavas of the Older Series (7Á8-5Á5 Ma) have identical isotopic compositions ( 87 Sr/ 86 Sr ¼ 0Á70411 to 0Á70422, 143 Nd/ 144 Nd ¼ 0Á512865 to 0Á512854, and 206 Pb/ 204 Pb ¼ 19Á016 to 19Á041) to those of Re ´union, where the center of volcanic activity is currently located. The lavas of the Intermediate Series (3Á5-1Á9 Ma) and Younger Series (0Á70-0Á17 Ma) are shifted to lower Sr-isotopic compositions (0Á70364-0Á70394, with 143 Nd/ 144 Nd ¼ 0Á512813 to 0Á512948 and 206 Pb/ 204 Pb ¼ 18Á794 to 18Á984). The Intermediate Series lavas have similar trace-element characteristics (e.g. Zr-Nb, Ba-Y) to those of Rodrigues, in both cases requiring the involvement of an enriched mantlelike component in the mantle source. During the volcanic history of Mauritius, the magmas lost the principal isotopic characteristics of the Re ´union hotspot with time, and became gradually imprinted with the isotopic signature of a shallower mantle source that produced the Central Indian Ridge basalts.

ABSTRACT:Blends of polyamide-6 (PA6) with syndiotactic polystyrene (sPS) were prepared using a series of styrene/glycidyl methacrylate (SG) copolymers as compatibilizers. These copolymers are miscible with sPS, and the epoxide units in SG are capable of reacting with PA6 end groups. These copolymers thus have the potential to form SGg-PA6 graft copolymers at the PA6/sPS interface during melt processing. This study focuses on the effects of functionality and concentration of the compatibilizer on the morphological, mechanical and crystallization behaviors of the blends. In general, SG copolymers are effective in reducing the sPS domain size and improving the interfacial adhesion. About 5 wt% glycidyl methacrylate (GMA) is the optimum content in SG copolymer that produces the best compatibilization. Both the strength and modulus of the blend have been improved on addition of the SG copolymers, accompanying a loss in toughness when higher concentration copolymer is added. Incorporation of SG compatibilizers to PA6/sPS blend has little influence on the crystallization behavior of PA6 component but resulted in a steady reduction in intensity of crystallinity peak of sPS and simultaneous crystallization of sPS with PA6 is observed.