--> ABSTRACT: Synthesis of Arc-Derived DSDP (ODP) Modal Sand Compositions Using Multivariate Analyses, by Kathleen M. Marsaglia, Raymond V. Ingersoll, Bonnie M. Packer, and Leslie D. Gergen; #91038 (2010)

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Synthesis of Arc-Derived DSDP (ODP) Modal Sand Compositions Using Multivariate Analyses

Kathleen M. Marsaglia, Raymond V. Ingersoll, Bonnie M. Packer, Leslie D. Gergen

In contrast to ancient sequences, sands derived from Quaternary and late Tertiary arc systems can be directly correlated with the tectonic setting of the marine basin in which they were deposited (trench, arc-trench gap, back arc, etc), adjacent arc type (continental margin versus intraoceanic; dissected versus undissected), and degree of arc/basin development at the time of deposition. Rigorous compositional classifications of these sediments are useful in interpreting tectonic settings of ancient sandstones of unknown or speculative origin. Representative arc-related sand samples from DSDP (ODP) sites form the basis of this investigation; regions sampled include the Mariana, Japan, Aleutian, North American, Middle American, Southwestern Pacific, Caribbean, and Mediterra ean arc-related basins. Petrographic data were uniformly gathered using the Gazzi-Dickinson point-counting method.

Modal sand compositions for each arc are unique, but marked differences along certain arc systems reflect the variable tectonic history of individual arc segments. Quartzo-feldspathic sands from the Mexican segment of the Middle American trench system sharply contrast with volcanic-rich sands from the Central American segment; more subtle changes occur along the sands from the Central American segment; more subtle changes occur along the Japan and North American arc systems. In general, multivariate analyses of petrographic data indicate (1) modal compositions of sands from magmatic-arc settings can be subdivided into intraoceanic arcs, continental arcs, and intraoceanic arcs with continental influence and (2) the percentage of continental components including potassium feldspar, quar z, mica, and sedimentary and metamorphic lithic grains increases toward continental margins. This synthesis represents the most complete study of modern arc sand compositions and provides information essential to studies of ancient arc-related sandstones.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.