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Abstract:
Pico de Orizaba (Mexico) had important, possibly historic, volcanic activity during the Holocene. Only a few pyroclastic flows could be C-14 dated, and for some young lava flows just their stratigraphic order is known. Two flows were recently dated by the Cl-36 method at about 1.45 ka and 3.06 ka. Comparing their paleomagnetic record, often including paleointensities, allows distinguishing flow lobes or combining them to flow means. Apart from this direct comparison, the paleomagnetic record was used for paleomagnetic dating. Preselection of potential sites and the refinement during the field work resulted in a very successful sampling: 30 sites provided mean directions with α95<5°, important for paleomagnetic dating. Combined flow means often have uncertainties α95<3°, restricting potential paleomagnetic age ranges. First paleointensities group between 35-45 µT and 50-60 µT. Many lava flows have similar paleomagnetic directions and intensities, possibly indicating that there were short periods of increased effusive activity, separated by periods of inactivity. Paleomagnetic dating supports this view, and together with stratigraphic relations and available Cl-36 age data, we propose a refined Holocene eruption history for Pico de Orizaba volcano. This right away rejects any historic effusive activity, as the youngest lava was emitted before 660 CE. The older Holocene lava flows are of approximately 1.5 to 9 ka age.
