Origin of Hawaiian Tholeiites: Trace Element Constraints

We report here geochemical studies of Hawaiian tholeiites and ultramafic xenoliths from Salt Lake Crater, Oahu. We focus attention on tholeiitic basalts that comprise the bulk of Hawaiian volcanoes. When the samples are screened to include only those lying neat the log-MgO (about 7 percent) end of olivine-control lines (Wright, 1971), tholeiites from individual volcanoes are remarkably uniform. On this basis, we show that, for tholeiites from six volcanoes, systematic geochemical differences exist that cannot be attributed to differentiation of these magmas from a common parental magma. Apparently there have been important differences in the processes of magma generation, source composition, or source mineral constitution. Partial melting calculations based on REE contents emphasize these distinctions, but unique melting models are not presented. In these models, relative REE abundances in the source material is a major uncertainty. Nd isotopic studies of Hawaiian basalts require systematic differences in Sm/Nd for the source material of each volcano. Furthermore, the time-integrated Sm/Nd of the sources must be less than that in chondrites. REE analyses of Hawaiian garnet lherzolite xenoliths show that they have chondritic to light REE-enriched relative abundances with absolute contents (for light REE) about 3 to 8 times chondrites. These data obviously conflict with interpretations of the Nd isotopic data. Several possibilities follow: (1) the available xenoliths are not parental to tholeiite, (2) our simple interpretation of the Nd isotopic data is wrong, and (3) the source regions may have been invaded at geologically recent times by a light REE-enriched phase, in which case the xenoliths may represent the course material. If the xenoliths are characteristic of the source, partial melting calculations indicate that the tholeiites may be generated by 15 to 20 percent melting of garnet lherzolite and at the sane tune conform to constraints imposed by the REE and Ni contents and the partitioning of Fe and Mg between melts and residues. We propose that the primary tholeiitic magmas contain no more than about 12 percent MgO, and that erupted magmas probably fractionated less than 10 to 15 percent of olivine during ascent and storage in high-level chambers

Werkzeugunterstuetzte Parallelisierung von Finite-Element Anwendungen (PARFEM) Abschlussbericht

Goal of the PARFEM project was the development of software tools and methods to support the efficient treatment of large sparse matrices on parallel computers. Also new algorithms for the solution of such systems should be investigated. Portability of all components was an important aspect. Finally, the algorithms and methods should be integrated in the well-known FE software package PERMAS. The parallelization concept for PERMAS is based on the exploitation of task parallelism and not on the usual mesh partitioning (or domain decomposition) technique. The solution of the sparse system leads to the execution on many tasks which operate on independent data and which can be executed in parallel. A task graph controls the data dependency. A scheduler maps those tasks to processors and tries to achieve load balance. As an alternative to the standard direct Cholesky solver parallel preconditioned cg-solvers and parallel multifrontal solvers were implemented and investigated: - Several variants of preconditioners were tested as well as different storage schemes. The optimal variants showed very good speed-up results and the execution time was shorter than the time of the standard direct solver for a large number of processors. The integration into the PERMAS code, however, lead to some loss of scalability. - A parallel multifrontal solver was integrated and parallelized using the tools developed in the project. Speedup figures on an IBM SP2 system were satisfactory. The PARFEM project was very important for the development of the PERMAS code. The tools in PARFEM made it possible to maintain one version of the code for sequential and parallel platforms. Users can use the parallel code without additional training since the user interface was not changed at all. Since portability was very important the project used PARMACS and later MPI as portability platform. The parallel approach could even be executed on workstation clusters although, due to weak communication performance, not very efficiently. (orig.)SIGLEAvailable from TIB Hannover: F98B607+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman