Strehlow, Karen , Kutterolf, Steffen , Freundt, Armin and Kwasnitschka, Tom (2010) Pliocene to Quaternary Central American tephrostratigraphy based on marine Tephras from ODP and DSDP sites - first comprehensive study. [Poster] In: AGU Fall Meeting 2010. , 13.-17.12.2010, San Francisco, USA .

Abstract

The Central American Volcanic Arc (CAVA) is, and has been, one of the most active volcanic regions and generated numerous Plinian eruptions along his 1200 km extension. The best preserved archive of this volcanism can be found as ash layers in the marine sediments downwind from the volcanic sources on the Pacific floor. Numerous ash layers up to 8 Mio old, which occur in ODP and DSDP cores of Legs 66, 67, and 202, originated in Central America and southern Mexico. The cores lie across the ash distribution areas expected from dominant wind directions as identified by mapped fallout deposits. We have chosen 145 ash layers of all three Legs for first detailed analysis of these sites to built up a data base for upcoming IODP cruise 334: Costa Rica Seismogenesis Project. The ash layers commonly have sharp contacts at the bottom and diffuse transitions to terrigenous and pelagic sediments at the top. Ash layer thickness ranges from 0.5 to 60 cm with typical grain sizes from medium silt to coarse sand. The mineral assemblages are typical for arc volcanism (plagioclase, pyroxene, hornblende, and olivine). The most evolved tephras also contain biotite. Electron microprobe analyses of 1300 glass shards yield compositions ranging from basaltic andesite to rhyolite and trachyte. Felsic ashes can be divided into seven compositional groups by means of silica and potassium contents. Correlations between marine ashes and on-land tephras are constrained by petrographical and stratigraphical criteria, major element geochemistry of glasses and minerals, and trace element data from LA-ICP-MS analyses. Due to limited exposure on land, such correlations with individual tephras are only possible for deposits of late Pleistocene to Holocene age. Older ash layers, however, can be correlated with regional arc segments making use of systematic along-arc variations of trace-element characteristics (Zr/Nb, Ba/La, Ce/Yb, La/Yb and Ba/Zr) of the arc rocks. Results show that source areas of the ash layers are distributed along the entire CAVA, as well as at the Southern Mexican Arc. The marine tephra record provides important data for ongoing studies of CAVA volcanism: (a) dating of undated land tephra by correlation with marine ashes and the ages derived by sedimentation rates; (b) stratigraphic correlations along the entire arc can be traced much more completely in the marine sediment cores than by limited onshore outcrops alone; (c) long-term changes in magmatic evolution of volcanic complexes can be reconstructed by using the marine archive of ash layers.

Actions (login required)

View Item