HR: 0800h
AN: V51C-0712    [Abstracts]
TI: Evaluating the Timing of Volcanism at Baitoushan Volcano (North Korea/China) in the Context of Open-system Effects: Insights from Sr, Nd, and Pb Isotopes at the Single Grain Scale
AU: * Ramos, F C
EM: ramos@geology.cwu.edu
AF: Central Washington University, 101 Lind Hall 400 E University Way, Ellensburg, WA 98926-7418, United States
AU: Gill, J B
EM: jgill@pmc.ucsc.edu
AF: University of California, Santa Cruz, EM&S Building 1156 High Street, Santa Cruz, CA 95064, United States
AU: Rodgers, S L
EM: rodgerssa@cwu.edu
AF: Central Washington University, 101 Lind Hall 400 E University Way, Ellensburg, WA 98926-7418, United States
AB: Baitoushan volcano, located along the North Korean-China border, is responsible for one of the largest caldera- forming rhyolitic eruptions in the northern hemisphere in the last 2000 years. In addition to an ~1000AD eruption, additional activity occurred at ~0AD and ~2000BC. These eruptions ejected large volumes of comenditic airfall and pyroclastic materials in addition to a small pantelleritic airfall deposit. We are at the initial stage of evaluating the sources of isotope variations, including whether these systems are open or closed, in order to evaluate the timing and residence of highly alkaline rhyolitic magma systems. Initial whole-rock isotope ratios suggest that young (<10ka) Baitoushan satellite basalts generally have slightly lower 87Sr/86Sr and higher 143Nd/144Nd than similarly young comendites, while the pantellerite has 143Nd/144Nd ratios similar to basalts. Sr isotopes in basalt hosted plagioclase crystals are generally higher than both whole rock hosts and accompanying clinopyroxene crystals, suggesting isotopic modification of basalts at crustal depths. These plagioclase 87Sr/86Sr ratios are similar to those in comendites and are consistent with early crustal inputs of either a limited amount of regional Archean basement or more extensive assimilation of Baitoushan "root" rocks with similar isotopic ratios. If limited, elevated Rb/Sr ratios in these rocks and resulting 87Sr/86Sr ratios in the comendites should be able to date magmatic residence while Nd and Pb isotopes remain constant. Such evaluations will be undertaken at the single grain scale where any potential of "open-ness" of the system can be constrained. Results will aid in determining the extent to which chronometric information is degraded by open-system processes leading up to large volume rhyolite eruptions.
DE: 1036 Magma chamber processes (3618)
DE: 1040 Radiogenic isotope geochemistry
DE: 1115 Radioisotope geochronology
DE: 3618 Magma chamber processes (1036)
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting