EVALUATING GEOCHEMICAL RELATIONSHIPS AMONG YOUNG COMENDITES AT CHANGBAISHAN VOLCANO, CHINA

In order to assess the hazards that large, highly-explosive volcanic eruptions pose, the number and timing of these eruptions must be determined. Currently, the number and timing of recent eruptions at Changbaishan volcano is controversial. Changbaishan is a polygenetic intraplate stratovolcano on the China/North Korea border and has had several large, comenditic eruptions in the last ~ 4 ka, including the Tianwenfeng (TWF), the Qixiangzhan (QIX), the 946 CE Millennium eruption (M.E.), which was one of the largest in the last 2000 years, and the 1702 CE Wuhaojie eruption. This study assesses whole-rock major and trace element geochemistry, whole-rock Sr, Nd, and Pb isotope compositions, and single crystal Sr and Pb isotope compositions of the 1702 CE eruption to evaluate potential geochemical and isotopic relationships with the other comendite deposits.

Whole-rock major element concentrations for the M.E., QIX, and 1702 CE deposits are indistinguishable; however, the TWF deposit has higher FeO* (5.9-4.2 wt.%), K₂O (4.98-4.70 wt.%) and Al₂O₃ (13.14-11.80 wt.%) concentrations than other Changbaishan comendites. Moreover, the TWF deposit has higher Zr concentrations, lower Sr concentrations, and lower Nb/Zr ratios than other comendite deposits (Dunlap, 1996). Whole-rock ⁸⁷Sr/⁸⁶Sr ratios from the 1702 CE and M.E. deposits (0.705050-0.705451) are consistently less radiogenic than the TWF (0.706890 - 0.707620). Single sanidine crystal ⁸⁷Sr/⁸⁶Sr ratios from the M.E. (0.70450-0.705252) and 1702 CE deposits (0.704549-0.705123) are also less radiogenic than TWF sanidine (0.705312-0.705933). Based on these characteristics, the 1702 CE deposits appear to be related to the M.E. and QIX, and likely unrelated to the older TWF comendite. It is possible that magma chambers imaged beneath Changbaishan (Choi et al., 2013) still contain highly explosive comendite magma that erupted in 946 CE and again in 1702 CE, posing an additional risk for another highly explosive eruption.