Resurgent Toba—field, chronologic, and model constraints on time scales and mechanisms of resurgence at large calderas

Frontiers in Digital Humanities

de Silva, Shanaka L.¹  Gregg, Patricia M.¹  Mucek, Adonara E.²  Pratomo, Indyo² 

[1] College of Earth, Ocean, and Atmospheric Science, Oregon State University, Corvallis, OR, USA;Earth Observatory of Singapore, Nanyang Technological University, Singapore, Singapore

关键词: Toba Caldera;    resurgence;    lake sediments;    C14 dating;    Numerical modeling;    magmastatic equilibrium;    remnant magma;    magmatic rebound;    Recharge;   

DOI  :  10.3389/feart.2015.00025

学科分类：社会科学、人文和艺术（综合）

来源: Frontiers

【 摘 要 】

New data reveal details of the post-caldera history at the Earth’s youngest resurgent supervolcano, Toba caldera in Sumatra. Resurgence after the caldera-forming ~74 ka Youngest Toba Tuff eruption uplifted the caldera floor as a resurgent dome, Samosir Island, capped with 100m of lake sediments. 14C age data from the uppermost datable sediments reveal that Samosir Island was submerged beneath lake level (~900m a.s.l) ~33.7 ky. Since then, Samosir experienced 700m of uplift as a tilted block dipping to the west. Using 14C ages and elevations of sediment along a transect of Samosir reveal that minimum uplift rates were ~4.9 cm/yr from ~33.7 to 22.5 ka, but diminished to ~0.7 cm/yr after 22.5ka. Thermo-mechanical models informed by these rates reveal that detumescence does not produce the uplift nor the uplift rates estimated for Samosir. However, models calculating the effect of volume change of the magma reservoir within a temperature-dependent viscoelastic host rock reveal that a single pulse of ~475 km3 of magma produces a better fit to the uplift data than a constant flux. Reproducing the uplift rates require more sophisticated models. Motivation for resurgent uplift of the caldera floor is rebound of remnant magma as the system re-established magmastatic and isostatic equilibrium after the caldera collapse. Previous assertions that the caldera floor was apparently at 400m a.s.l or lower requires that uplift must have initiated between sometime between 33.7 ka and 74 ka at a minimum average uplift rate of ~1.1 cm/ year. The change in uplift rate from pre-33.7 ka to immediately post-33.7 ka suggests a role for deep recharge augmenting rebound. Average minimum rates of resurgent uplift at Toba are at least an order of magnitude slower than net rates of "restlessness" at currently active calderas. This connotes a distinction between resurgence and “restlessness” controlled by different processes, scales of process, and controlling variables.

【 授权许可】

CC BY