Late Pleistocene to present day eruptive history of the Changbaishan- Tianchi Volcano, China/DPRK: New field, geochronological and chemical constraints

摘要

Volcanic unrest during 2002-2006 renewed attention on Changbaishan-Tianchi volcano as the source of the powerful explosive eruption (VEI 6 to 7) Millennium Eruption of 946 CE (Common Era). However, progress in understanding the potential risk is complicated by discordant accounts of the most recent, explosive eruptive history. Several eruptions since the Late Pleistocene, such as the Tianwenfeng (TWF), Qixiangzhan (QXZ), Millennium (ME), Baguamiao (BGM), Liuhaojie (LHj), 1403 CE event (1403), and even a 1903 CE event have been proposed, but the stratigraphic order, ages, distributions, and even the very existence of some of these, are still not fully ratified. Based on recent detailed stratigraphic logs of over 100 surface exposures and three deep trenches, coupled with new geochronologic and petrochemical data (including trace elements on glass and pyroxene), we can now clarify these relationships.Herein we propose that the 946 CE Millennium eruption, be formally re-named the Generalized Millennium Eruption (GME) to avoid entrenched confusion and to formally acknowledge the composite comenditetrachyte nature of the eruption. Thus three eruptions, the TWF, QXZ and the GME are confirmed. The TWF eruption is the first powerful explosive eruption at Changbaishan-Tianchi and we find evidence that this eruption may have initiated the Tianchi caldera. It produced an extensive fallout pumice deposit, that on the basis of new Optically Stimulated Luminescence (OSL) and radiocarbon (C-14 ages) of overlying sedimentary strata indicates an eruption age 42 ka. This new age constraint coupled with geochemical fingerprints confirms a correlation to the similar to 50.6 kyr B-J ash in Japan Sea. The next eruption was the predominately effusive QXZ that produced a clastogenic lava flow down the north slope of the edifice. An age of similar to 4-8 ka is proposed based on new radiocarbon (C-14) ages of charcoal at the base and from overlying sediment. Although the age of the GME is well established as late 946 CE, there are some intriguing details in historical records of ash falls in Japan that indicate two separate events on Nov 3, 946 CE and Feb 7, 947 CE. We speculate that these correspond to the comendite and trachyte stages of the GME respectively. Subsequent to the GME, no evidence of any post-GME eruptions have been found. These findings clarify and refine the history of the explosive stage of the Changbaishan-Tianchi volcano that began similar to 51 kyr. This improved understanding should serve as a basis for further studies at Changbaishan-Tianchi and inform a better-constrained assessment of volcano hazard. (C) 2020 Elsevier B.V. All rights reserved.