Tephrochronology, petrology and geochemistry of Late-Holocene pyroclastic deposits from Volcan de Colima, Mexico

Volcan de Colima in Western Mexican Volcanic Belt is the most active volcano in North America. We present a detailed tephrochronological study of its Holocene proximal tephra-fall, pyroclastic surge and pyroclastic flow deposits based on 98 new stratigraphic sections, 183 new dendrocalibrated radiocarbon [C-14] age determinations, 209 new geochemical analyses of pumice and ash, >50 texture and mineral (point-counting) mode determinations and 230 grain-size analyses. These results provide a much clearer understanding of the explosive eruptive behavior of Volcan de Colima during the past 10,000 years. Our data reveals that only one of the many eruptions described in historic documents has been large enough to be preserved. We discuss the major and trace element geochemistry and petrology of the Holocene tephra and compare it with the currently erupting calc-alkaline andesites and alkaline minettes and basanites from the adjacent cinder cones. It appears that several of the oldest (similar to 12,000-6000 yrs BP) samples of the Holocene tephra may record the last episodes of calc-alkaline and alkaline magma mixing as first described in the pioneering work of Luhr and Carmichael (1981). Finally, the tephrochronological record from the northern, downwind side of the Colima Volcanic Complex is compared with the extensive, radiocarbon-constrained, record of Holocene debris-avalanche deposits on the south side of the complex, to build a more integrated picture of its past volcanic activity. (C) 2009 Elsevier B.V. All rights reserved.