P-wave tomography and origin of the Changbai intraplate volcano in Northeast Asia
Institute of Crustal Dynamics, China Earthquake Administration,
Xisanqi, Haidian District, Beijing 100085, China, firstname.lastname@example.org
This webpage is a synopsis of the paper:
Lei. Jianshe & D.
Zhao, P-wave tomography and origin of the Changbai
intraplate volcano in Northeast Asia, Tectonophysics, 397,
281– 295, 2005.
Changbai volcano, also called Tianchi
or Baitoushan volcano, is located in the Changbai Mountains,
close to the boundary between NE China and North Korea
(Figure 1a). Changbai volcano erupted in BC 1120, AD
1050, 1413, 1597, 1668, and 1702 (Simkin & Siebert,
1994; Liu, 2000). However, the origin of such
intraplate volcanoes is still unclear. Some researchers
suggested that Changbai volcano originated either from
accretion processes at the craton margin since the
Mesoproterozoic or as a result of subduction processes
associated with the Pacific plate before the opening
of the Japan Sea (e.g., Zhang & O’Reilly,
1997). Turcotte & Schubert (1982) assumed
that it is a hotspot like Hawaii, while Tatsumi
et al. (1990) considered it to be a kind of back-arc
volcano. Global tomographic models are still too poorly
resolved to show the detailed structure and reveal
the origin of the Changbai intraplate volcano.
researchers have used geological, geochemical and geophysical
approaches to study Changbai volcano (e.g., Zhang & Tang,
1983; Zindler & Hart,
1986; Zhao, 1991; Basu et al., 1991; Zhang & O’Reilly,
1997; Fan et al., 1999a, b; Tang et al.,
1999; Wang et al., 2003). Magnetotelluric
soundings show that low-resistivity anomalies exist
beneath it in the crust (Tang et al., 1997,
2001). Seismic explosion experiments revealed low-velocity
anomalies in the crust and upper mantle down to a depth
of 40 km, suggesting the existence of magma chambers
(Zhang et al., 2002).
With the recent installation
of 19 portable seismic stations during seismic experiments
in NE China (Wu & Hetland,
1999), a few studies investigated the structure
under NE China. For example, receiver function techniques
were applied to the data set recorded by the portable
seismic network to study crustal structure and upper
mantle discontinuities (Ai et al., 2003; Li & Yuan,
2003; Hetland et al., 2004). These studies
showed that the crust is thicker and contains low-velocity
anomalies beneath Changbai volcano, and that the subducted
Pacific slab lies flat in the mantle transition zone
there. It has also been suggested that pieces of slab
material penetrated into the lower mantle under NE
Asia (Ai et al., 2003). However, no tomographic
study of this was made using the new data set.
The availability of abundant teleseismic data recorded
by the portable seismic network enabled us to determine
the 3-D velocity structure beneath Changbai volcano
and investigate the origin of the volcano.
Figure 1a shows the distribution
of seismic stations used in this study. The portable
seismic network contains 19 broad-band seismic stations
equipped with Guralp 3T three-component digital seismometers
(Wu & Hetland,
1999; Hetland et al., 2004). In this work,
data from 3 permanent seismic stations, MDJ, HIA, and
BJT were also used (Figure 1a). These stations
are sited adjacent to the portable seismic network
and have recorded data since 1986. The 19 temporary
seismic stations were located around Changbai volcano
and were in operation from late June to September 1998.
Ten continued recording until April 1999 (Hetland
et al., 2004). The geometry of the subducting
Pacific slab as estimated from the deep seismicity
by Gudmundsson & Sambridge (1998) is also
shown in Figure 1a.
Figure 1: (a) Locations
of 19 portable seismic stations (solid triangles) and
3 permanent stations (diamonds) used in this study.
Open triangles denote intraplate volcanoes. CB, Changbai;
LG, Longgang; XJD, Xianjindao; CUR, Ch’Uga-Ryong
(Simkin & Siebert, 1994). The dotted lines
show the depth contours of the Wadati-Benioff deep
seismic zone (Gudmundsson & Sambridge,
1998). (b) Epicentral locations of the 68 teleseismic
events (diamonds) used in this study. The triangle
denotes the center of the NE China Seismic Network.
P-wave arrival times were
hand-picked from high-quality original seismograms.
The resulting data set contains 548 high-quality P arrival
times from 68 teleseismic events (M > 4.8; Figure
1b). The events selected have a good azimuthal coverage
except in the Pacific Ocean and Russia. Except for
one event in Kamchatka that has an epicentral distance
of about 25°, all events lie in the range 30-90° from
The tomographic method of Zhao
et al. (1994)
was used to determine the 3-D P-wave velocity
(Vp) structure beneath Changbai volcano. Our
results (Figure 2) show a columnar low-velocity anomaly
extending to 400 km depth with a P-wave velocity
reduction of up to 3%. High-velocity anomalies are
visible in the mantle transition zone, and deep-focus
earthquakes occur at depths of 500-600 km beneath the
region, suggesting that the subducting Pacific slab
lies flat in the transition zone there, as imaged clearly
by global tomography (Zhao, 2004; Lei & Zhao,
2006a). Such structural features are similar to those
beneath Tengchong volcano in SW China (e.g., Lei
et al., 2009a), but different from those under
the Hainan, Hawaii and Iceland hotspots (e.g., Zhao,
2004; Lei & Zhao,
Figure 2: (a)
North-south, and (b) east-west vertical cross
sections of P-wave velocity images. Red and
blue colors denote low and high velocity anomalies,
respectively. The velocity perturbation scale is shown
below the cross sections. Black triangles in (a) and
(b) denote volcanoes. White dots show earthquakes within
100 km of the profiles. The two dashed lines denote
the 410- and 660-km discontinuities. The locations
of the cross sections are shown in the insert map (c).
Labels in (c) are the same as in Figure 1a.
These results indicate
that the active intraplate volcanoes in NE Asia are
not hotspots but a kind of back-arc volcano closely
related to the subduction process of the Pacific slab.
Low-velocity anomalies in back-arc regions are generally
associated with back-arc magmatism and volcanism caused
by the deep dehydration process of the subducting slab
and convective circulation process of the mantle wedge
(Zhao et al., 1997; Zhao,
2001b). These processes may lead to large-scale upwelling
of asthenosphere under NE Asia and cause intraplate
volcanism and continental rift systems in the region. Tatsumi
et al. (1990) first invoked asthenospheric injection
to explain the formation of Wudalianchi and Changbai
volcanoes, but they did not consider the flat Pacific
slab under the region because such a slab structure
was unknown at that time. Here we modified the model
of Tatsumi et al. (1990) to emphasize the
role of the flat Pacific slab in the formation of intraplate
volcanism in E Asia (Figure 3).
Figure 3: (a) Tectonic
features on the surface in the NW Pacific and NE Asia.
Black patches denote Cenozoic basalts. A, Baikal rift;
B, Shanxi graben; C, Tancheng-Lujiang fault zone; D,
Okinawa trough. (b) Schematic east-west vertical section
showing upper mantle structure beneath NE Asia. The
subducting Pacific slab becomes flat in the mantle
transition zone. The deep dehydration process of the
slab and convective circulation process in the mantle
wedge cause upwellings of high-temperature asthenospheric
materials, leading to the formation of the continental
rift system as well as intraplate volcanoes in NE Asia
(modified from Tatsumi et al., 1990).
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