Variable depths of magma genesis in Eastern Asia inferred from
teleseismic P wave attenuation
Abstract
Eastern Asia is a prime location for the study of intracontinental
tectono-magmatic activity. For instance, the origin of wide-spread
intraplate volcanism has been one of the most debated aspects of East
Asian geological activity. Measurements of attenuation of teleseismic
phases may provide additional constraints on the source regions of
volcanism by sampling the upper mantle. This study uses data from three
seismic arrays to constrain lateral variations in teleseismic P-wave
attenuation beneath the Central Orogenic Belt and the North China
Craton. We invert relative observations of attenuation for a 2-D map of
variations in attenuation along with data and model uncertainties by
applying a Hierarchical Bayesian method. As expected, low attenuation is
observed beneath the Ordos block. High attenuation is observed beneath
most of the volcanoes (e.g., the Middle Gobi volcano, the Bus Obo
volcano and the Datong volcano) in the study area, and estimated
asthenospheric Qp values span from 95 to 200. These values are within
the range of globally average asthenosphere. We infer that these
volcanoes may tap melt from ambient asthenosphere and occur where the
lithosphere is thin, which is consistent with previous petrologic
studies. More complex mantle drivers of volcanism are not rejected but
are not needed to explain eruptions in this area. In contrast, at the
Xilinhot-Abaga volcanic site, the observed low attenuation (as low as
beneath the Ordos block) excludes a typical shallow melting column.
Fluids from the subducted Pacific plate may initiate the deep melting
and would be consistent with petrological constraints.