cenozoic rifting and volcanism in eastern china: a mantle...

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Tectonophysics 393

Cenozoic rifting and volcanism in eastern China:

a mantle dynamic link to the IndoAsian collision?

Mian Liua,*, Xiaojun Cuia,1, Futian Liub

aDepartment of Geological Sciences, University of Missouri, Columbia, MO 65211, USAbInstitute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100101, China

Accepted 21 April 2004

Available online 15 September 2004

Abstract

The IndoAsian continental collision is known to have had a great impact on crustal deformation in south-central Asia, but

its effects on the sublithospheric mantle remain uncertain. Studies of seismic anisotropy and volcanism have suggested that the

collision may have driven significant lateral mantle flow under the Asian continent, similar to the observed lateral extrusion of

Asian crustal blocks. Here we present supporting evidence from P-wave travel time seismic tomography and numerical

modeling. The tomography shows continuous low-velocity asthenospheric mantle structures extending from the Tibetan plateau

to eastern China, consistent with the notion of a collision-driven lateral mantle extrusion. Numerical simulations suggest that, at

the presence of a low-viscosity asthenosphere, continued mass injection under the IndoAsian collision zone over the past ~50

My could have driven significant lateral extrusion of the asthenospheric mantle, leading to diffuse asthenospheric upwelling,

rifting, and widespread Cenozoic volcanism in eastern China.

D 2004 Elsevier B.V. All rights reserved.

Keywords: IndoAsian collision; Tibetan plateau; Tomography; Volcanism; Eastern China

1. Introduction

Following the initial IndoAsia collision ~5070

My ago, tectonic evolution in western China has been

dominated by crustal compression (Yin and Harrison,

0040-1951/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.tecto.2004.07.029

* Corresponding author. Tel.: +1 573 882 3784; fax: +1 572

882 5458.

E-mail address: [email protected] (M. Liu).1 Present address: Department of Earth and Ocean Sciences,

University of British Columbia, Vancouver, BC, Canada V6T 1Z4.

2000). The continued post-collisional plate conver-

gence has telescoped N2000 km of crust, leading to

the present HimalayanTibetan plateau, rejuvenating

the Tien Shan orogen, and affecting regions as far

north as the Baikal rift (Molnar and Tapponnier, 1975;

1977; Taponnier and Molnar, 1979; Taponnier et al.,

1982) (Fig. 1). Consequently, western China has been

characterized by crustal shortening and mountain

building throughout the Cenozoic (Allegre et al.,

1984; Dewey and Burke, 1973; Harrison et al., 1992;

Hu et al., 2000; Molnar and Tapponnier, 1977; Owens

and Zandt, 1997; Yin and Harrison, 2000).

(2004) 2942

Fig. 1. Topographic relief and simplified tectonic features of China and the neighboring regions. Legends are: 1main volcanic fields with

ages: EEocene, NNeogene, and QQuaternary; 2strike-slip faults and shear directions; 3rifts; 4direction of plate convergence; 5

major spreading centers; 6historic seismicity in northeastern China. Data are from Liu et al. (2001), Logatchev and Zorin (1992), Tian et al.

(1992), Yin (2000), Zhou and Armstrong (1982), Ma (1989), Tapponnier and Molnar (1977), and Ye et al. (1987).

M. Liu et al. / Tectonophysics 393 (2004) 294230

In contrast, eastern China has been dominated by

widespread rifting and basaltic volcanism through the

Cenozoic (Deng et al., 1997; Liu et al., 1983; Tian et

al., 1992; Ye et al., 1987; Zhou et al., 1988). The North

China Plain rift system was reactivated in Eocene

along a series of major Mesozoic-originated NNE and/

or NE faults, and widespread subsidence developed

over the area since early Miocene (Gilder et al., 1991;

Tian et al., 1992; Ye et al., 1987). Some of the rifts

developed after the IndoAsia collision and are active

today, such as the YinchuanHetao rift and the Shanxi

rift system (Xu and Ma, 1992; Zhang et al., 1998) (Fig.

1). Prevalent Cenozoic basalts have occurred along

many riftgraben systems (Fig. 1). Paleogene olivine

tholeiites and tholeiites occurred mainly in the North

China Plain rift zones and the Subei basins. Neogene

alkali olivine and phonolitic basanites occurs mainly

along major fault system in eastern China, and

Quaternary alkaline basalts had a wide, dispersive

distribution in northeast and southern China (Liu et al.,

1983, 2001; Tian et al., 1992; Zhou et al., 1988). The

present eastern China is characterized by abnormally

thin crust (~3035 km) and lithosphere (as thin as 70

km), low elevation (b500 m), elevated heat flow (~60

80 mWm2), and high seismicity (Hu et al., 2000; Ma,

1989; Ma and Wu, 1987).

The contrasting Cenozoic tectonics between west-

ern and eastern Chinamay be genetically linked. Part of

the N2000 km plate convergence (Molnar and Tappon-

nier, 1975) following the initial IndoAsian collision

has been accommodated by large-scale eastward

southeastward lateral bescapeQ of Asian continent

Table 1

M. Liu et al. / Tectonophysics 393 (2004) 2942 31

along numerous strike-slip faults (Avouac and Tap-

ponnier, 1993), which may have transmitted the colli-

sional stresses to eastern China and contributed to the

rifting (Taponnier et al., 1982; Tapponnier and Molnar,

1977). Previous studies of the far-field effects of the

IndoAsia collision have focused on stress trans-

mission through the lithosphere (Kong et al., 1997;

Taponnier et al., 1982), but the dynamic effects of the

IndoAsian collision may have extended much deeper.

Seismic anisotropy under the Tibetan plateau shows a

strained mantle extending to N200 km depth (Lave et

al., 1996; McNamara et al., 1994). The orientation of

the polarized fast S-wave is consistent with the strain

field in the Tibetan crust, suggesting coherent defor-

mation in the mantle (Holt, 2000). Owens and Zandt

(1997) interpreted the seismic anisotropy under the

northern Tibetan plateau, where the mantle is hot and

weak, as indicative of an EW directed lateral mantle

flow. The lateral extend of suchmantle flow is not clear.

Based on the geochemistry of the dispersive Cenozoic

volcanic rocks in eastern China and southeastern Asia,

a large-scale, collision-driven lateral mantle extrusion

under the Asian continent has been speculated (Basu et

al., 1991; Flower et al., 1998).

The collision-driven, large-scale lateral mantle flow

under the Asian continent, similar to the observed

escaping lithospheric blocks, may help to explain the

broad and dispersive mantle upwelling under eastern

China indicated by seismic tomography (Liu and Jin,

1993; Zhang, 1998) and the Cenozoic volcanism

(Basu et al., 1991; Liu et al., 1994; Zhou et al.,

1988). Here we test this hypothesis by firstly inves-

tigating the mantle structure under Asia using P-wave

seismic tomography. The results show continuous low-

velocity asthenospheric mantle structure extending

from the Tibetan plateau to eastern China, consistent

with collision-driven lateral mantle extrusion. We then

explore the feasibility and conditions for such lateral

mantle extrusion using numerical modeling.

Reference velocity model

Depth (km) Velocity (km s1

0 5.80

45o 6.70

45+o 8.00

110 8.15

220 8.47

400 9.15

600 10.10

800 10.35

2. Seismic tomography of mantle structure

We derived the three-dimensional mantle structure

under China and surrounding regions using P-wave

travel time tomography. The inversion used P-wave

arrival times from 745 Chinese seismic stations and the

global data set from the International Seismological

Center (Fig. 2). The rays were selected from 3712 local

events and 4623 teleseismic events from year 1978 to

1995. A total of 217,569 rays was used in the study, a

significant improvement over the b100,000 rays used

in the study by Liu and Jin (1993). As a result, the

spatial resolution is much improved. Under eastern

China where stations are dense, the spatial resolution is

better than 50 km. Table 1 shows the reference velocity

model used in this study, based on an averaged

velocity structure of the Chinese continent and

adjacent regions (Liu and Jin, 1993). The average

crustal thickness is taken to be 45 km. The depth 45o

and 45+o in Table 1 represent the interface immediately

above and below the reference Moho depth. The

analytical procedures and the algorithm used for

inversion of the velocity perturbations were described

in previous papers (Liu and Jin, 1993; Liu et al., 1990).

Fig. 2 shows velocity perturbations at 110 and 220

km depths, within the typical depth ranges of litho-

sphere and asthenosphere, respectively. As usual for

seismic tomography, velocity structures near the

margins of the model domain are not well constrained

by the data. At the 110 km depth (Fig. 2a), a major

velocity low is found in the North China Plain,

consistent with thin lithosphere and high heat flow

there (Hu et al., 2000; Ma, 1989). Other significant

velocity lows includes those under the northern rim of

the Tibetan plateau and the eastern end of the

SongpangGanzi fold-thrust belt near the northeastern

margin of the Tibetan plateau. Major velocity highs are

found under the Himalayas, the Tarim basin, and the

Siberian shield surrounding west China and Mongolia,

the Sichuan basin and the core of the South China

block. The low-velocity belt to the east of the Chinese

coast underlies the continental shelf and back arc

regions. Major velocity-highs correlate well with the

)

Fig. 2. P-wave travel time seismic tomography of China and the surrounding regions. (a) P-wave velocity perturbation at 110 km depth. The dashed

line indicates the approximate direction and dimension of the model domain in Figs. 37, and the solid white lines show the directions and

dimensions of the two vertical sections in (c) and (d). (b) P-wave velocity perturbation at 220 km depth. (c) Avertical section of the P-wave velocity

structure across northern China (line 1 in (a)). (d) A vertical section of the P-wave velocity structure across southern China (line 2 in (a)).


Fig. 2 (continued).


Himalayas and south Tibet, the Tarim basin and Tian

Shan mountain ranges, the Sichuan basin and the

QinglingDabie orogenic belt. Recent study by Xu et

al. (2002) using regional events recorded in China and

Kyrgyzstan seismic networks reveals more detailed

structures in northwestern China, but the broad patterns

are similar.

Some of the high-velocity structures extend to the

asthenosphere, notably those under the Himalayas, the

Tarim basin, and the Siberian shield surrounding

western China and northern Mongolia. These results

are similar to those from previous studies (Cipar et al.,

1993; Liu and Jin, 1993; Lyon-Caen, 1986). The main

feature in Fig. 2b, however, is the diffuse velocity lows

in eastern China and northern Tibet, connected by two

broad low velocity channels, one runs through northern

China and southern Mongolia and another through

southern China. The relatively high velocity regions


under central Chinamay reflect lithospheric roots of the

Mesozoic QinlingDabie orogenic belt (Fig. 1).

Fig. 2c and d show vertical sections of the mantle

structure crossing northern and southern China,

respectively. In both sections the asthenospheric

layer, indicated by the low velocity zone in the

depth range of ~150350 km, is well defined.

Obviously, these results depend on the reference

velocity model. The reference model used here

(Table 1) is based on the average velocity structure

of the Chinese continents and the neighboring

regions, which may be biased by the abnormally

low velocities under eastern China and the back-arc

basins. If we choose the velocity structure of the

stable Chinese continent as the reference, the

velocity values would be higher than the reference

model in Table 1. Consequently, the velocity highs

in Fig. 2 would be weakened, but the low-velocity

asthenospheric channel would be enhanced.

Although some of the velocity perturbations may

result from compositional variations, we believe that

the results in Fig. 2 reflect primarily temperature

perturbations, because similar structures were derived

from surface-wave tomography (Zhang, 1998; Zhang

and Tanimoto, 1993), which are more sensitive to

temperature perturbations than P-waves.

Fig. 3. Model geometry, initial thermal structure and boundary conditions

an initially thickened Tibetan lithosphere. The imposed velocity boundary

The continuous low-velocity asthenospheric mantle

extending from the Tibetan plateau to eastern China

cannot prove lateral mantle flow under Asia, but it is

consistent with the notion of collision-driven lateral

mantle extrusion. Furthermore, we show below that

the low-velocity asthenosphere channels in Fig. 2

make large-scale lateral mantle extrusion mechanically

feasible.

3. Numerical modeling

The N2000 km post-collisional convergence

between the India and Eurasian plates implies that

large volumes of mantle lithospheric material was

injected under Tibet in the past 5070 My. Did all the

convergent mantle lithospheric material sink into the

deep mantle, or could some of the mass injection have

been accommodated by lateral mantle flow, presum-

ably in the asthenosphere? Here we test the feasibility

of collision-driven large-scale lateral asthenospheric

flow in a two-dimensional (2-D) finite element model

(Fig. 3). The model domain encompasses the crust,

mantle lithosphere, asthenosphere and underlying

mantle regions with different viscosity for each layer

(Table 2). The initial Tibetan lithosphere is assumed to

of the numerical model. The thick thermal boundary layer represents

conditions are used in the cases in Figs. 5 and 6.

Table 2

Model parameter

Parameter Value

Thermal expansivity (a) 2.5105 K1Thermal diffusivity (k) 1.5106 m2 s1Crustal density (q) 2900 kg m3

Mantle density (q) 3700 kg m3

Viscosity of crust (l) 1024 Pa sViscosity of mantle lithosphere (l) 1022 Pa sViscosity of asthenosphere (l) 51019 Pa sViscosity of sub-asthenospheric mantle (l) 10221023 Pa s


be thicker and weaker than the lowland Asian

continent (Fig. 3). With the Boussinesq approxima-

tion, the mantle flow and thermal evolution were

described by the coupled mass, heat, and momentum

equations:

jS Yu 0 1

BT

Bt Yu SjT kj2T 0 2

qYu SjYu lj2 Yu jP aq T T0 Yg 03

where Yu is velocity vector, T is temperature, T0 isreference temperature at bottom of the lithosphere, t is

time, k is thermal diffusivity, q is density, P is fluidpressure, l is viscosity, a is thermal expansivity, andYg is gravity. The values of model parameters used inthis study are given in Table 2.

The crust and mantle were approximated as viscous,

incompressible Newtonian fluids. The model domain

approximates a roughly SWNE vertical section across

China (see Fig. 2a). Although continental deformation

and mantle structures in south-central Asia are three-

dimensional in nature, the 2-D model as first order

approximation is justifiable because of the tectonic

boundary conditions around the Tibetan plateau. As

shown in Fig. 2 and suggested by other seismic studies

(Cipar et al., 1993; Lyon-Caen, 1986; Zhang, 1998),

the Tibetan plateau is surrounded by deep (N250 km),

cold mantle structures on all sides except the east. The

major outlet for mass injected into the collision zone is

downward and to the east and southeast, where a

relatively free boundary may be assumed because of

the observed continental extrusion and the presence of

back-arc spreading centers along the eastern Asian

continental margins throughout the Cenozoic (North-

rup et al., 1995; Tapponnier and Molnar, 1977).

The initial thermal gradient was conductive within

the lithosphere, and adiabatic within the sub-litho-

spheric mantle (Fig. 3). The temperature is fixed at the

top and bottom boundaries; the left and right edges of

the model domain are insulated from horizontal heat

flux. To focus on collision-induced mantle flow,

possible internal heat was excluded from the model.

For the velocity field, the bottom of the model is

permeable, allowing vertical flow. Various velocity

boundary conditions were applied to simulate the

effects of plate collision and crustal rift on the mantle

flow (see blow). The governing equations were solved

using the finite element method based on the

DIFFPACK library codes (Langtangen, 1996). The

numerical grid for most simulations is 20 by 60,

corresponding to vertical and horizontal spatial

resolution of 35 km. Results using a finer 40120mesh differ by b8%.

To better understand the effects of mass injection

associated with the IndoAsian collision, we present

first a reference model where no external velocity is

imposed on the boundaries of the model domain. Fig.

4 shows the sequential snapshots of the predicted

thermal and velocity fields. During the first 30 My or

so the major feature was downwelling mantle flow

beneath the initially thickened Tibetan lithosphere

(Fig. 3), similar to results of previous studies

(England, 1993; Houseman et al., 1981). The

downwelling flow and the induced small-scale

upwelling flows work together to thin the Tibetan

lithosphere. This process has been proposed as a

major cause of volcanism and accelerated uplift in

central and north Tibet (Molnar et al., 1993). By ~50

My most of the Tibetan lithosphere has been

significantly thinned, and some small convection

cells within the asthenosphere started under eastern

China. However, the convection was weak, the

thermal structure of the lithosphere in eastern China

was hardly perturbed.

The results are significantly different when mass

injection associated with the IndoAsian collision was

considered (Fig. 5). The mass injection was simulated

with a linear velocity profile imposed on the left side

of the model domain (Fig. 3). Considering possible

mantle flow not contained in the model plane, we used

only a fraction (up to 2 cm year1) of the total

Fig. 4. Sequential snapshots of the simulated thermal and velocity fields for the reference case at 12 My (a), 28 My (b), and 52 My (c). The

mantle flow results from gravitational instability of the thickened lithosphere. Zero velocity is imposed on the surface and the two vertical edges,

and the bottom is permeable to vertical flow. The scale of velocity is shown on the top left corner of each panel.


Fig. 5. Sequential snapshots of the simulated thermal and velocity fields resulting from gravitational instability of the thickened lithosphere and

continued mass injection into the collision zone. The imposed velocity boundary conditions are shown in Fig. 3. (a), (b), and (c) show the

temperature and velocity fields at 12, 28, and 52 My, respectively. See text for discussion.



convergence rate (~5 cm year1). The velocity

boundary condition on the right side of the model is

used to be consistent with the back-arc spreading

along eastern China continental margins throughout

the Cenozoic (Fig. 1). In this case we also imposed a

horizontal velocity field on the top left boundary to

simulate the distributed crustal contraction in western

China (England and Molnar, 1997), and a velocity

field on the top right boundary to simulate the effects

of crustal rifting in eastern China (see Fig. 3).

Although the predominantly NWSE extension in

eastern China (Fig. 1) cannot be fully represented in

the NESW model section, the model nonetheless

helps to illustrate the physical effects of crustal rifting

on mantle dynamics.

Fig. 5 shows a downwelling mantle flow devel-

oping from the gravitational instability of the

thickened Tibetan lithosphere during the first few

million years, similar to that in Fig. 4. However,

because of the continued mass injection under Tibet,

the downwelling flow spread out eastward within the

asthenosphere, driving asthenospheric upwelling and

causing lithospheric thinning under eastern China.

The combined free convection resulting from gravita-

tional instability of the thickened Tibetan lithosphere

and forced flow from mass injection into the collision

zone produced a complicated mantle flow pattern

over time. Part of the Tibetan lithosphere is thinned

by small-scale upwelling flow, while a large-scale

lateral mantle flow extended to eastern China (Fig.

5b). By ~50 My small-scale asthenosphere plumes

formed under eastern China, producing diffuse

mantle thermal perturbations and significant litho-

spheric thinning (Fig. 5c). The results are comparable

to the observed mantle structure under eastern China

(Fig. 2).

4. Discussion and conclusions

It is well known that lithospheric deformation may

induce significant mantle flow. However, such flow

is often predominantly vertical, resulting from

thermally induced buoyancy forces (England, 1993;

Houseman et al., 1981; Liu and Zandt, 1996). The

evidence for large-scale lateral mantle flow has been

inferred mainly from seismic anisotropy (Owens and

Zandt, 1997; Russo and Silver, 1994), but interpre-

tation of seismic anisotropy is not unique (Holt,

2000; Savage, 1999). Our seismic tomography shows

that the mantle structure beneath China and the

neighboring regions is consistent with the notion of

collision-driven lateral mantle extrusion, and our

numerical results suggest that, at the presence of

well-developed low-viscosity asthenospheric chan-

nels, it is feasible for the IndoAsian collision to

have driven large lateral mantle extrusion. This

process could have led to broad asthenospheric

upwelling under eastern China, contributing to the

Cenozoic rifting and basaltic volcanism in eastern

China and southeast Asia.

The numerical results are dependent on model

parameters; some of them, especially the viscosities,

are poorly constrained. We have explored the effects

of major model parameters and boundary conditions

with numerical experiments; our results indicate that

the most critical condition for the predicted lateral

mantle extrusion is a well-developed low-viscosity

asthenospheric layer. Without this layer the litho-

spheric material injected into the collision zone would

flow predominantly downward because of its rela-

tively low temperature, and the Tibetan lithosphere

may be thickened further by the mass injection (Fig.

6). The upwelling flow in the right half of the model

domain in Fig. 6 results from the imposed mass

conservation in the rectangular model domain. In the

real Earth, the descending mantle flow under Tibet

would not require an equal amount of upwelling

mantle flow under eastern China.

Our seismic tomography (Fig. 2) indicates that

well-developed asthenosphere channels exist beneath

the Asian continent at present, and we may assume

that a hot and weak asthenosphere existed throughout

much of the Cenozoic time when volcanism and

continental deformation were active in east and

southeast Asia. With such a low-viscosity astheno-

sphere, the IndoAsian collision could have driven

large-scale lateral mantle flow under Asian continent.

The predicted rates and scale of the lateral mantle

flow correlate positively with the rate of mass

injection and are affected by the viscosity of the

model asthenosphere and its contrast with that of the

rest part of the upper mantle. Viscosity values used in

this study are typical for the mantle (Cathles, 1975).

The viscosity of 51019 Pa s for the model astheno-sphere is probably a conservative estimate. It has been

Fig. 6. Simulated temperature and velocity fields at time=52 My. The model parameters and boundary conditions are same to those in Fig. 5 but

without the low-viscosity asthenosphere. In this case the mantle flow is dominated by a thick downwelling flow beneath the thickened

lithosphere, which is further thickened by the mass injection associated with plate convergence.


suggested that the effective asthenospheric viscosity

could be as low as 1018 Pa s beneath young oceanic

and active continental regions (Buck and Parmentier,

1986). We tested a broad range of mantle viscosity

values and found that, within typical ranges of

viscosity for the asthenosphere (10181020 Pa s) and

the upper mantle (10211023 Pa s), significant lateral

mantle flow beneath Asia is predictable.

The causative relationship between crustal rifting

and mantle upwelling under eastern China has been

controversial. Some workers suggested that the broad

mantle upwelling beneath eastern China resulted

directly from crustal rifting (Ma and Wu, 1987; Xu

and Ma, 1992), others suggested active role of mantle

upwelling in inducing crustal rifting (Liu, 1987; Ye et

al., 1987; Yin, 2000). We imposed a surface velocity

gradient in eastern China to simulate the effects of

crustal rifting (Fig. 5) and find the effects minimal

we obtained essentially identical results as those in

Fig. 5 without imposing the surface velocity gradient.

The broad and dispersive velocity lows in the upper

mantle under eastern China (Fig. 2) would be

explained better by active mantle upwelling. Such

mantle upwelling more likely originated from the

asthenospheric mantle, rather than deep-rooted mantle

plumes as some workers have suggested (Deng et al.,

1998), because our tomography (Fig. 2) as well as

those from other studies (Zhang, 1998) all indicate

that the low-velocity structures under eastern China

are limited to the upper mantle, above the transition

zone.

Many studies have linked Cenozoic rifting and

volcanism in eastern China to the rollback of the

subducting Pacific plate away from the Eurasian

continent (Allen et al., 1998; Northrup et al., 1995;

Ye et al., 1987). The supporting evidence includes

(1) that the early Tertiary reactivation of eastern

China rift system predates the IndoAsia collision at

~50 Ma (Ye et al., 1987) and (2) the timing of

extension correlates to the change of converging rate

between the Eurasia and Pacific plates (Northrup et

al., 1995). The low-velocity mantle structures to the

east of the Chinese coast (Fig. 2) would be best

explained by subduction-induced mantle upwelling

in the back-arc setting. However, the diffuse mantel

upwelling under much of eastern China (Fig. 2a,b)

and many of the rifts in eastern China, located

thousands of kilometers from the EurasianPacific


plate boundary, cannot be readily linked to the

subduction of the Pacific plate.

We suggest that both the IndoAsian collision and

subduction of the Pacific plate played important roles

in the Cenozoic rifting and volcanism in eastern

China. Our results indicate that, in addition to the

observed crustal bescapingQ, the IndoAsian collisionmay have also driven significant lateral extrusion of

the mantle asthenosphere. Such lateral mantle flow

would help to explain many features of Cenozoic

tectonics in eastern China, including (1) the reactiva-

tion of the pre-existing NNE trending and basin-

bounding faults and the resurgence of basaltic

volcanism along these faults during Neogene and

Quaternary (Tian et al., 1992), (2) the rifting migra-

tion along the Pliocene Shanxi rift and the extensive

Quaternary eruption of basalts (Tapponnier and

Molnar, 1977), (3) the high heat flow and high

historical seismicity in the North China Plain basin

(Hu et al., 2000; Ma, 1989), and (4) the presently

elevated asthenosphere and thinned crust and litho-

sphere in northern and northeastern China (Fig. 2).

The collision-driven mantle extrusion may also help

to account for the DUPAL-like composition of most

Cenozoic basalts in eastern China (Flower et al.,

1998). Such a mantle flow was speculated to have

triggered the opening of Japan Sea (Okamura et al.,

1998), and, in conjunction with intraplate stress

associated with the IndoAsia collision, contributed

to the Cenozoic rifting and magmatism in the Baikal

Fig. 7. A sketch of the suggested relationship between IndoAsia collision

discussion.

rift zone (Logatchev and Zorin, 1992; Molnar and

Tapponnier, 1975).

Fig. 7 summarizes our preferred model of mantle

dynamics for Cenozoic rifting and volcanism in

eastern Asia. Continued injection of voluminous

lithospheric material under Tibet associated with

N2000 km IndoAsian convergence, facilitated by

the low-viscosity asthenospheric channels under

Asian continent and the convective instability of the

thickened lithosphere in western China, have driven a

lateral mantle extrusion. Because of the deep cratonic

roots west and north of the Tibetan plateau, mantle

extrusion has been predominately eastward, similar to

the observed lateral crustal extrusion in Asia. Such

mantle extrusion, together with extensional stresses

induced by rolling back of the Pacific plate (Northrup

et al., 1995), may have driven a broad asthenospheric

upwelling under eastern China, reactivated preexisting

rifting systems and produced widespread volcanism.

Both the seismic tomography and numerical results

presented here are meant to illustrate this conceptual

model and to test its physical feasibility. Further

investigation of the impacts of the IndoAsian

collision on mantle dynamics would lead to a better

understanding of many key observations in east and

southeast Asia, including significant lithospheric

thinning during the Cenozoic (Liu, 1987), opening

of the South China sea (Taponnier et al., 1982), broad

regions of low-velocity upper mantle, isotopically

anomalous asthenosphere, and dispersed Cenozoic

and Cenozoic extension and volcanism in eastern China. See text for


basalts derived from upwelling asthenosphere (Basu

et al., 1991; Flower et al., 1998).

Acknowledgements

We thank Peter Nabelek, An Yin, Mike Murphy,

Martin Flower, Seth Stein, Bill Holt, and Ray Russo

for helpful comments on the early versions of this

paper. R.J. McCabe and J.F. Dengs review improved

the manuscript. This work is supported by NSF grant

EAR-9805127, EAR-0207200, grant #40228005 from

the Chinese NSF and the Research Board of the

University of Missouri system.

References

Allegre, C.J., Courtillot, V., Tapponnier, P., Hirn, A., Mattauer,

M., Coulon, C., Jaeger, J.J., Achache, J., Schaerer, U.,

Marcoux, J., Burg, J.P., Girardeau, J., Armijo, R., Gariepy,

C., Goepel, C., Li, T., Xiao, X., Chang, C., Li, G., Lin, B.,

Teng, J.W., Wang, N., Chen, G., Han, T., Wang, X., Den, W.,

Sheng, H., Cao, Y., Zhou, J., Qiu, H., Bao, P., Wang, S.,

Wang, B., Zhou, Y., Ronghua, X., 1984. Structure and

evolution of the HimalayaTibet orogenic belt. Nature (Lond.)

307 (5946), 1722.

Allen, M.B., Macdonald, D.I.M., Xun, Z., Vincent, S.J., Brouet,

M.C., 1998. Transtensional deformation in the evolution of the

Bohai Basin, northern China. In: Holdsworth, R.E., Strachan,

R.A., Dewey, J.F. (Eds.), Continental transpressional and

transtensional tectonics. Geological Society Special Publica-

tions. Geological Society of London, London, pp. 215229.

Avouac, J.-P., Tapponnier, P., 1993. Kinematic model of active

deformation in Central Asia. Geophys. Res. Lett. 20 (10),

895898.

Basu, R., Wang, J., Huang, W., Xie, G., Tatsuboto, M., 1991. Major

element, REE, and Pb, Nd and Sr isotopic geochemistry of

Cenozoic volcanic rocks of eastern China: implications for their

origin from suboceanic-type mantle reservoirs. Earth Planet. Sci.

Lett. 105, 149169.

Buck, W.R., Parmentier, E.M., 1986. Convection beneath young

oceanic lithosphere: implications for thermal structures and

gravity. J. Geophys. Res. 91, 19611974.

Cathles, L.M., 1975. The Viscosity of the Earths Mantle. Princeton

Press, Princeton.

Cipar, J.J., Priestley, K., Egorkin, A.V., Pavlenkova, N.I., 1993. The

Yamal PeninsulaLake Baikal deep seismic sounding profile.

Geophys. Res. Lett. 20, 16311634.

Deng, J., Mo, X., Zhao, H., Luo, Z., Wu, Z., 1997. Geotectonic

units of China continent on a lithospheric scale since Cenozoic.

Earth Sci.-J. China Univ. Geosci. 22, 227232.

Deng, J., Zhao, H., Luo, Z., Guo, Z., Mo, Z., 1998. Mantle plumes

and lithosphere motion in east Asia. In: Flower, F.J.M., Chung,

S.-L., Lo, C.-H., Lee, T.-Y. (Eds.), Mantle Dynamics and Plate

Interactions In East Asia, Geodynamics Series. American

Geophysical Union, Washington, DC, pp. 5966.

Dewey, J.F., Burke, K., 1973. Tibetan, Variscan and Precambrian

basement reactivation: products of continental collision. J. Geol.

81, 683692.

England, P., 1993. Convective removal of thermal boundary layer of

thickened continental lithosphere: A brief summary of the Tibetan

Plateau and surrounding regions. Tectonophysics 223, 6773.

England, P., Molnar, P., 1997. The field of crustal velocity in Asia

calculated from Quaternary rates of slip on faults. Geophys. J.

Int. 130 (3), 551582.

Flower, M., Tamaki, K., Hoang, N., 1998. Mantle Extrusion: A

model for dispersed volcanism and DUPAL-like asthenosphere

in East Asia and the western Pacific. In: Flower, M.F.J., Chung,

S.-L., Lo, C.-H., Lee, T.-Y. (Eds.), Mantle Dynamics and Plate

Interactions in East Asia, Geodynamics Series. American

Geophysical Union, Washington, DC, pp. 6788.

Gilder, S.A., Keller, G.R., Luo, M., Goodell, P.C., 1991. Timing and

spatial distribution of rifting in China. Tectonophysics 197,

225243.

Harrison, T.M., Copeland, P., Kidd, W.S.F., Yin, A., 1992. Raising

Tibet. Science 255, 16631670.

Holt, W.E., 2000. Correlated crust and mantle strain fields in Tibet.

Geology 28, 6770.

Houseman, G.A., McKenzie, D.P., Molnar, P., 1981. Convective

instability of a thickened boundary layer and its relevance for

the thermal evolution of continental convergent belts. J. Geo-

phys. Res. 86, 61156132.

Hu, S., He, L., Wang, J., 2000. Heat flow in the continental area of

China: a new data set. Earth Planet. Sci. Lett. 179, 407419.

Kong, X., Yin, A., Harrison, T.M., 1997. Evaluating the role of

preexisting weakness and topographic distributions in the Indo

Asian collision by use of a thin-shell numerical model. Geology

25, 527530.

Langtangen, H.P., 1996. A diffpack module for scalar convection

diffusion equations. WWW document: Diffpack V1.4 Report

Series. SINTEF and University of Oslo. URL: http//www.oslo.

sintef.no/diffpack/reports.

Lave, J., Avouac, J.P., Lacassin, R., Tapponnier, P., Montagner, J.P.,

1996. Seismic anisotropy beneath Tibet: evidence for eastward

extrusion of the Tibetan lithosphere? Earth Planet. Sci. Lett.

140, 8396.

Liu, G., 1987. The Cenozoic rift system of North China Plain and

the deep internal process. Tectonophysics 133, 277285.

Liu, F., Jin, A., 1993. Seismic tomography of China. In: Iyer, H.M.,

Hirahara, K. (Eds.), Seismic Tomography: Theory and Practice.

Chapman & Hall, New York, pp. 299310.

Liu, M., Zandt, G., 1996. Convective thermal instabilities in the

wake of the migrating Mendocino triple junction, California.

Geophys. Res. Lett. 23, 15731576.

Liu, R., Sun, J., Chen, W., 1983. Cenozoic basalts in North China

their distribution, geochemical characteristics and tectonic

implications. Geochemistry 2, 1733.

Liu, F.-t., Wu, H., Liu, J.-h., Hu, G., Li, Q., Qu, K.-x., 1990. 3-D

velocity images beneath the Chinese continent and adjacent

regions. Geophys. J. Int. 101, 379394.

http:http//www.oslo.sintef.no/diffpack/reports


Liu, C.-Q., Masuda, A., Xie, G.-H., 1994. Major- and trace-element

compositions of Cenozoic basalts in eastern China: petrogenesis

and mantle source. Chem. Geol. 114, 1942.

Liu, J., Han, J., Fyfe, W., 2001. Cenozoic episodic volcanism and

continental rifting in northeast China and possible link to Japan

Sea development as revealed from KAr geochronology.

Tectonophysics 339, 385401.

Logatchev, N.A., Zorin, Y.A., 1992. Baikal rift zone: structure and

geodynamics. Tectonophysics 208, 273286.

Lyon-Caen, H., 1986. Comparison of the upper mantle shear

wave velocity structure of the Indian shield and the Tibetan

plateau and tectonic implications. Geophys. J. R. Astron. Soc.

86, 727749.

Ma, X., 1989. Lithospheric Dynamics Altas of China. China

Cartographic, Beijing.

Ma, X., Wu, D., 1987. Cenozoic extensional tectonics in China.

Tectonophysics 133, 243255.

McNamara, D.E., Owens, T.J., Silver, P.G., Wu, F.T., 1994. Shear

wave anisotropy beneath the Tibetan Plateau. J. Geophys. Res.

99 (B7), 1365513666.

Molnar, P., Tapponnier, P., 1975. Cenozoic tectonics of Asia: effects

of a continental collision. Science 189, 419426.

Molnar, P., Tapponnier, P., 1977. Relation of the Tectonics of

eastern China to the IndiaEurasia Collision: application of slip-

line field theory to large-scale continental tectonics. Geology 5,

212216.

Molnar, P., England, P., Martinod, J., 1993. Mantle dynamics, uplift

of the Tibetan plateau, and the Indian monsoon. Rev. Geophys.

31 (4), 357396.

Northrup, C.J., Royden, L.H., Burchfiel, B.C., 1995. Motion of the

Pacific plate relative to Eurasia and its potential relation to

Cenozoic extension along the eastern margin of Eurasia.

Geology 23 (8), 719722.

Okamura, S., Arculus, J.R., Martynov, A.Y., Kagami, H., Yoshida,

T., Kawano, Y., 1998. Multiple magma sources involved in

marginal-sea formation: Pb, Sr, and Nd isotopic evidence from

the Japan Sea region. Geology 26, 619622.

Owens, T.J., Zandt, G., 1997. Implications of crustal property

veriations for models of Tibetan plateau evolution. Nature 387,

3743.

Russo, R.M., Silver, P.G., 1994. Trench-parallel flow beneath the

subducted Nazca plate from seismic anisotropy. Science 263,

11051111.

Savage, M.K., 1999. Seismic anisotropy and mantle deformation:

what have we learned from shear wave splitting? Rev. Geophys.

37 (1), 65106.

Tapponnier, P., Molnar, P., 1977. Active faulting and tectonics in

China. J. Geophys. Res. 82, 29052930.

Taponnier, P., Molnar, P., 1979. Active faulting and cenozoic

tectonics of Tien Shan, Mongolia and Baikal regions. J.

Geophys. Res. 84, 34253459.

Taponnier, P., Pelzer, G., LeDain, A.Y., Armijo, R., Cobbold, P.,

1982. Propagating extrusion tectonics in Asia: new insights

from simple plasticine experiments. Geology 10, 611616.

Tian, Z.-Y., Han, P., Xu, K.-D., 1992. The MesozoicConozic East

China rift system. Tectonophysics 208, 341363.

Xu, X., Ma, X., 1992. Geodynamics of the Shanxi Rift system,

China. Tectonophysics 208, 325340.

Xu, Y., Liu, F., Liu, J., Chen, H., 2002. Crustal and upper mantle

structure beneath western China from P wave trave time

tomography. J. Geophys. Res. 107 (B10), 2220.

Ye, H., Zhang, B., Mao, F., 1987. The Cenozoic tectonic evolution

of the Great North China: two types of rifting and crustal

necking in the Great North China and their tectonic implica-

tions. Tectonophysics 133, 217227.

Yin, A., 2000. Mode of Cenozoic eastwest extension in Tibet

suggesting a common origin of rifts in Asia during the Indo

Asian collision. J. Geophys. Res. 105, 2174521759.

Yin, A., Harrison, M., 2000. Geological Evolution of the

HimalayanTibetan orogen. Annu. Rev. Earth Planet. Sci. 28,

211280.

Zhang, Y.-S., 1998. Three-dimensional upper mantle structure be-

neath East Asia and its tectonic implications. In: Flower, M.F.J.,

Chung, S.-L., Lo, C.-H., Lee, T.-Y. (Eds.), Mantle Dynamics

and Plate Interactions in East Asia, Geodynamics Series.

American Geophysical Union, Washington, DC, pp. 1123.

Zhang, Y.-S., Tanimoto, T., 1993. High-resolution global upper

mantle structure and plate tectonics. J. Geophys. Res. 98,

97939823.

Zhang, Y.-Q., Mercier, J.L., Vergely, P., 1998. Extension in the

graben systems around the Ordos (China), and its contribution

to the extrusion tectonics of south China with respect to Gobi-

Mongolia. Tectonophysics 285, 4175.

Zhou, X.-H., Armstrong, R.L., 1982. Cenozoic volcanic rocks of

eastern ChinaSecular and geographic trends in Chemistry and

Strontium isotopic Composition. Earth Planet. Sci. Lett. 58,

301329.

Zhou, X.-H., Zhu, B.-Q., Liu, R.-X., Xhen, W.-J., 1988.

Cenozoic basaltic rocks in eastern China. In: Macdougall,

J.D. (Ed.), Continental Flood Basalts. Kluwer Academic,

Boston, pp. 311330.

Cenozoic rifting and volcanism in eastern China: a mantle dynamic link to the Indo-Asian collision?IntroductionSeismic tomography of mantle structureNumerical modelingDiscussion and conclusionsAcknowledgementsReferences

cenozoic rifting and volcanism in eastern china: a mantle...

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