Plate tectonic characteristics during the early paleozoic in Beishan near the Sino-Mongolian border region, China

Tectonophysics, Elsevier

385

188 (1991) 385-392

Science Publishers

B.V., Amsterdam

Plate tectonic characteristics during the early Paleozoic in Beishan near the Sino-Mongolian border region, China Zuo Guochao

a, Zhang Shuling

a, He Guoqi

b and Zhang Yang

b

a Institute of Geologic and Mineral Resource of Gansu Province, Hongxing Street I70, L.anrhou, People’s Rep. of China b Department

of Geology, Peking University, Zhongguancun, Beijing. People’s Rep. of China (Received

January

22,199O;

revision

accepted

July 13,199O)

ABSTRACT Zuo, G., Zhang, S., He, G. and Zhang, Y., 1991. Plate tectonics border region, China. Tectonophysics, 188: 385-392.

during

the early Paleozoic

in Beishan

near the Sino-Mongolian

The tectonic units during the Early Paleozoic in the Beishan area comprise the northern margin of the eastern end of the Tarim Plate and the northern flank of the Mingshui-Hanshan microplate. These two paleoplates were separated by an ophiolitic melange belt. All of them underwent the tectonic evolution typical of the continental margins of Atlantic, Andean and west Pacific Ocean types. The continental margin was an open continental shelf and a continental slope from the Early Cambrian to the Early Ordovician. At the southern flank of the continental shelf an isolated shallow sea basin developed separated from the shelf by an upwarping zone. Its northern flank, Shibanjing-Xiaohuangshan, is an ocean basin. North of this ocean basin is the Mingshui-Hanshan microcontinent or microplate. This area is situated in a tensional tectonic environment, it shows the characteristics of a passive, Atlantic-type margin. During the middle and late parts of the Early Ordovician the continental crust on the southern fringe of the shallow sea basin was pulled open, and a narrow, ocean rift formed. In the mid-Ordovician, this area underwent a period of considerable development, in which extension and subduction existed simultaneously. The southern fringe of the continental margin came to the end of the passive margin. On its northern side, a marginal volcanic zone, with talc-alkali volcanism, formed. In the Late Ordovician-Silurian, the oceanic crust was folded and subducted southward, and the Hengluanshan-Xichanjing marginal basin developed into an interarc basin, where the Hongliuhe-Niujuazi backarc basin and the BaiyunshanDongqiyishan volcanic arc had formed, with associated granitic magma. At the beginning of the Devonian, the Tarim Plate finally came into collision with the Mingshui-Hanshan microplate and the ocean basin closed, forming the Mingshui-Shibanjing-Xiaohuangshan suture belt. There were volcanic molasse basins on both sides of this erogenic zone. From the Late Paleozoic the Beishan area was incorporated into an intraplate mobile zone.

its environs”.

In this paper, we use mobilism to explain the tectonic evolution of this area during the Early Paleozoic.

Introduction The Beishan area is situated in the northwestem border area of Gansu Province and the westem part of the Nei-Mongol Autonomous Region of China. The Shule and Ruoshui rivers are the boundaries in the south and east, respectively, and

Tectonic units Using the evolutional characteristics of each geologic period during the Early Paleozoic in Beishan, we think that the following tectonic units

the western neighbor is the Xinjiang Autonomous Region. The area is about 125,000 km*. This is part of ,a project supported by the National Science Foundation of China: “research on Paleozoic lithospheric formation and evolution in the Chinese Xingmong-northern Xinjiang and 0040-1951/91/$03.50

0 1991 - Elsevier Science Publishers

may be defined in this area as follows: continental, transitional and oceanic domain. Each of these can be subdivided into secondary tectonic units (Fig. 1). B.V.

ZUO

386

Geologic features of the tectonic units

Liuyan-Chuanshanxun paleocontinental margin (I-1, Fig. I). At the northern margin of the eastern end of the Tarim Plate is a regional unconformity. Underlying this unconformity are lower Proterozoic strata, i.e., the Prechangcheng system. They comprise migmatitic gneisses, schists and marbles, whereas overlying strata are marbles, metamorphosed sandstones and metamorphosed volcanic rocks (a plagiohomblendite at Huangjianqiu has a Rb-Sr isochronous metamorphic age of 584 Ma). Some parts of the unconformity were found to contain migmatites. The stromatolites, Jurusania f: and Baicalia jI, have been found in the marbles of Chuanshanxun. We estimate the age to be mid

I /---. mkm

40

ET AL

to late Proterozoic or the Jixian to Qingbaikou systems. In consequence, there is a Baikalian fold belt in the northern margin of the Tarim Paleocontinent.

Northern margin of the eastern Tarim Plate

0

GUOCHAO

Huaniushan-Baishantang continental margin rift (l-2, Fig. I) The Huaniushan-Baishantang continental margin rift on the north of the Liuyan-Chuanshanxun paleocontinental margin was a shallow sea basin from the Sinian to the Early Cambrian. In the earliest Ordovician, a rift basin grew up along the western edge bounded by NWW-trending faults 200 km long. Its northern side was the Fanshankou-Shuangyinshan shelf sea. It is bounded on the south by a deep fault (or a strike ductile shear zone). The middle and upper Proterozoic formations appear on the southern flank of this fault. The basin basement is composed of

_..

i_

MONGOLIA

-y---~7.._.__

J

Fig. 1. Sketch map of the tectonic Plate.

continental

murgin

area:

units of the Early Paleozoic

Baishantang

continental

Trnnsirionul

domain: 2-1 = Hongliuhe-Niujuanzi

(Cambrian-Ordovician),

margin

= South

Hongshishan

Hanshan continental

(Ordovician-Silurian). Xiaohuangshan; Xichangjing;

backarc

arc (Silurian)

marginal

Shibanjing-Xiaohuangshan 4-I

rift (Cambrian-Ordovician);

island

Hengluanshan-Xichangjing

in Beishan.

1-I = Liuyan-Chuanshanxun

and volcanic

basin;

I-3

margin

zone on an oceanic

8 = Hongliuhe; 1.5 = Yushishan; 21=

9 = Lebaquan; 16 = Niujuanzi; Dundunshan;

ZZ = The Hanshan

sea (Ordovician-Silurian); Transitional

2 = Dananshan;

domain:

I7 = Yingzuihongshan;

of the eastern

Proterozoic?);

part of the Tarim

I-2 = Huaniushan-

shelf sea (Cambrian-Ordovician).

margin

(late Ordovician).

volcanic

arc

microplate

(late

II = Baiyungshan; I8 = Fanshankon;

23 = Baishantang;

24 = Ati;

flank.

microcontinent

4-4 = Danashan-Yuanbaoshan 4 = Mingshui;

continental Oceanic

domain:

Ordovician-Silurian);

in the northern

4-2 = Mingshui-Hanshan

3 = Yuabaoshan;

10 = Gongpoquan;

22 = Liuyuan;

margin (early

2-2 = Pochengshan-Yingzuihongshan

3-2 = Baiyunshan-Dongqiyishan

shelf sea? (Ordovician?).

1 = Hongshishan;

margin

= Fangshankou-Shuangyinshan

basin (Silurian);

ocean basin (Cambrian-Silurian). continental

Z = The northern

paleocontinental

active

5 = Shibanjiang;

I2 = Dongqiyishan; 19 = Shuangyinshan; 25 = Tiancang.

slope 3-l

=

3-3 =

Conrinentnl

urea:

(AnC?);

4-3 =

continental 6 = Hanshan;

I3 = Yueyashan;

margin 7= I4 =

20 = Huaniushan;

EARLY

PALEOZOIC

PLATE

TECTONIC

CHARACTERISTICS

387

IN BEISH AN

Hongliuhe-Niujuanzi

Fig. 2. The Late Devonian serpentine

schists

volcanic

($) and showing

tion (Jinchanggou

rocks

(Pzz) overlying

their unconformable

the rela-

on the east of Dundunshan).

Precambrian rocks. The lower part of the basin consists of abyssal or bathyal sediments, the upper part contains turbidites of the lower and middle Ordovician). The upper Ordovician is made up of metamorphosed fine-grained sandstones, intermediate-acidic volcanic rocks and crystalline limestones. The Caledonian melanocratic basement, which comprises ultramafites which have undergone extreme serpentinization, frequently come to light along the fault as lenses of serpentine. Unconformably overlying these are the Late Devonian volcanic rocks (Fig. 2). This area was originally situated in an aulacogen, but later the environment changed from one of extension to compression. Fanshankou-Shuangyinshan

sherf sea (I-3,

Fig.

1)

In the Fanshankou-Shuangyinshan area a sea basin existed which gradually spread to the east until it was about 150 km wide. The Cambrian system is composed of sandy slates and quartzites, including some lenticular marbles in the Fanshankou region. The Cambrian system contains phosphorus, vanadium and uranium. The depth of this sea basin increases from Shuangyinshan to the south of Mazongshan. Ordovician deposits are elastic rocks and siliciliths. Whether it is true or not, it has been implied that there were thick terrigenous sediments and a turbulent sedimentary environment in this shelf sea.

backarc basin (2-1, Fig. 1)

This backarc basin lies on the northern margin of the shelf sea. The oceanic crust at the Hengluashan-Xichangjing interarc basin subducting to the south, lead to backarc spreading to form this backarc basin. The middle and upper Silurian system unconformably overlap the Sinian and Cambrian. An ophiolite suite is well developed in the Hongliuhe-Yushishan region. Its main elements are: (1) metamorphic peridotites; (2) accumulated ultramafic rocks; (3) accumulated gabbros-anorthosites-potassium-poor granites; (4) diabases; (5) other volcanic rocks and pillow lavas overlain with pelagic deposits. This ophiolite suite, which has a prominent cumulate texture extends from the northern side of Mazongshan eastwards to Niujuanzi.

Pochengshan- Yingzuihongshan continental sIope, island arc and oceanic margin volcanic zone (2-2, Fig. I)

The Pochengshan-Yingzuihongshan area broke off from the southern paleocontinental margin in the Silurian. Its basement is made up of elastic rocks and carbonate rocks from the middle and upper Proterozoic complexes. The Silurian system of the northern slope (Lebaquan) of the island arc comprises submarine volcanic deposits of an island arc belt. On the northern flank of the island arc, the Sinian system comprises glacioaqueous deposits and the Lower Cambrian turbidites. Abyssal grit detrital rocks were uplifted and deposited on a continental rise at Pochenshan. This area underwent several cycles of uplift and submergence, leading to the formation of a sedimentary assemblage of turbidites and hemipelagic deposits. The sedimentary material came from the paleocontinent on its southern side. At the southem flank of Hengluanshan the Jixian was overlain by Ordovician elastic rocks. It is obvious that there was an underwater high with a volcano on it. Then, in the middle Ordovician a marginal volcanic zone (that is, a talc-alkali series) developed in an peripheral oceanic belt on the northern margin of the continental slope. The depth of the subduction zone is about 150 km.

ZUO

388

Baiyunshan-Dongqiyishan

GUOCHAO

ET AL

volcanic arc (3-2, Fig.

1) This volcanic arc, comprising rocks of the calcalkali series, developed on the Late Ordovician oceanic crust. It is an underwater volcanic arc, trending NWW. It is mainly of Silurian age and has a thickness of more than 4000 m. Shibanjing-Xiaohuanshan

Fig. 3. Cumulate

ultramafites

at Yueyashan.

Hengluanshan-Xichan@ng (interarc) marginal basin (3-1, Fig. 1) This basin is situated between PochengshanYingzuihongshan (its southern flank) and Baiyunshan-Dongqiyishan volcanic arc (its northern flank). At first this region was a marginal basin, but later it turned into an interarc basin. The present remnant, being principally oceanic crust, consists of parts of an ophiolite suite. The remnant oceanic crust includes chiefly: (1) red jasper, siliceous shales, and tuffaceous siltstones; (2) pillow basalts; (3) diabase dyke swarm, potassium-poor granites and metamorphosed ultramafites (Fig. 3). The remnants of the ophiolitic suite highlight the tectonic sheets found in this area (Fig. 4). This association of rocks has a genetic relationship and BEE patterns show that they belong to the tholeiite series. Late Ordovician turbidites overlie pelagic deposits (parts of which are allochthonous olistoliths). It is clear that this basin has been subject to convergence and compression and the detrital sediments deposited come from the island arcs on both its flanks. The total thickness of the detrital sediments is about 1000 m.

ocean basin (3-3, Fig.

1) This ocean basin is located between the Tarim Plate and the Hanshan microplate. At present, it appears in the form of a suture belt. The earlier oceanic ophiolite suite has lost its primary sequence. The drilling data show that it is a set of nappes forming an imbricate structure dipping to the south or north. All the ultramafites at the fault zone were strongly altered by serpentinization, mylonitization or chromitization. There are clear cumulate textures in the gabbros. The Hanshan microplate of the northern flank The continental margin sea south of Hanshan (4-1, Fig. I) Terrigenous elastic rocks, volcanic rocks and marbles are found in the area north of Shibanjing-Xiaohuangshan suture belt and south of Hanshan. These deposits are the remainder of the Ordovician-Silurian and are over 1000 m thick. This area may have been a passive margin at an early period and have changed into an active margin later in its development. Mingshui-Hanshan microcontinent (4-2, Fig. I) A middle Proterozoic metamorphic rock series, has been brought to light in Mingshui, Hanshan and Weiboshan. In this rock series there are a large number of metasediments which have under-

N-

Fig. 4. Sketch map of the fault scarp in the eastern B, = pillow basalt;

Q = medium-coarse

flank 3 km. north

bedded

siliceous rock;

of Xichangjing. + = carbonatites;

M = ophiokitic

melange;

S = thin bedded

B, = massive

tuffaceous

phyllite.

basalt;

EARLY

PALEOZOIC

PLATE

TECTONIC

CHARACTERISTICS

gone iron mineralization.

Diagonal

389

IN BEISHAN

bedding

in

flank was a passive margin or a miogeosyncline.

middle Ordovician turbidites on the northern flank

The depth of the sedimentary

of Yuanbaoshan

increased, and to the north the littoral sea changed

indicates that there was a paleo-

continent on its southern side.

into a shallow sea. There are turbidites on a continental slope, or rise, in the Pochengshan zone Fig.

(Fig. 5B).

1) This is thought to have existed because of the

Middle-late

Hongshishan

continental

basin continually

shelf sea (?) (4-3,

Early Ordovician

neighbouring tectonic situation. During Dananshan-

Yuanbaoshan

active

continental

margin (4-4, Fig. 1) This

is situated

on the northern

slope of the Mingshui-Hanshan

microcontinent.

It belongs to an active continental had a lot of volcanicity

continental margin that

from the middle Ordovi-

cian to the late Silurian.

this time a tensile

throughout

Xiaohuangshan

Beishan.

environment The

per-

Shibanjing-

ocean basin continued extending.

On its southern flank, the Huaniushan region, the continental

crust basement

was faulted,

forming

of the earlier period

a rift basin

and primary

oceanic crust was generated on the flanks of the continental margin. Turbidites developed on both sides of the Hanshan microcontinent

Tectonic evolution Sinian-earliest

sisted

(Fig. 5C).

Middle Ordovician

Cambrian

In the Precambrian, there may have been two plate tectonic units in Beishan. The tectonic framework at this stage is characterized by the

During the middle Ordovician there was an abrupt change from the early Paleozoic crustal evolution in Beishan. In this stage extension and

separation of the two plates by an ocean basin. The basement of the southern paleocontinent is

subduction existed simultaneously. The sea domain on the northern flank of the Huaniushan-

made up of the lower Proterozoic pre-Changcheng system and the middle-upper Proterozoic granite-metamorphic rocks. The Jixian and Qingbai-

Xiaocaohu

kou systems, comprising sediments of the stable platform type, can be compared with the northern margin of Tarim in Xinjiang. It can be seen that they belong to the periphery of the Tarim Plate. The earliest folding is found in the middle Proterozoic Changcheng system, a mesothermal metamorphic rock formation. At the southern paleocontinental

margin, Sinian glacial carbonate

sedi-

ments unconformably overlie the basement rocks. At the bottom of the Cambrian system are littoral-shallow sea siliciliths, carbonate rocks and glacial rocks. Glacial sediments were found on both sides of an upwarping zone (Fig. 5A). Middle Early Cambrian-earliest

Ordovician

From the beginning of the Paleozoic this area was situated in an environment of tectonic tension. The paleocontinent margin at the southern

Baishantang paleocontinent margin closed and this was associated with acidic volcanic activity (the stock has a Rb-Sr

isochron age of 479

Ma); there was also volcanic activity on the southem flank of this ocean basin. In keeping with extension in the Shibanjing-Xiaohuangshan oceanic region, the southern flank of the continental margin encountered the end of the passive margin. A marginal volcanic zone comprising talc-alkali series rocks was formed to the north of the continental slope. There was a typical marginal basin at Hengluanshan-Xichangjing, lying on the southern side of the oceanic region. There was a continental shelf sea sedimentary environment on the southern margin of the continent’s northern flank. At the northern margin of the continent’s northem flank (the Dananshan-Yuanbaoshan region) turbidites of a stable continental marginal type had formed in the beginning of the middle Ordovician. A neutral-basic volcanic eruption at the end of the middle Ordovician, was the precursor to the area becoming a mobile margin. (Fig. 5D).

ZUO

390

L I

H

Du

I

I

HO

X

Xi

I

ET AL

LU

M.Ha

I

I

GUOCHAO

I

I

F

I.

I I

I I

90

I I

I

L

H

I

I

I

x,i

I

I

I

I

F

H

L O-”

Xi

Le

Ho

H I I

I /

F. Sh

I I

I I

M.Ha

s;x /

I

I

I

I

1 I

I I

D.yu I I

M*Ha

SX

I

I I

M.Ha

s.x

P;Y

D.yu

I I I

D.Yu

I I

c H-B e:-

0:

I 1

F.Sh

I I

sex

P;Y

I I

I

M-Ha

I I

B H

z-et

I I

P-Y I I

Fig. 5. Sketch showing the structural evolution during the Early Paleozoic in Beishan. I = pre-Sinian basement; 2 = glacial strata; 3 = terrigenous elastic sediment; 4 = shallow sea sediment; 5 = continental slope sediment; 6 = molasse type deposit; 7 = neutralacidic volcanic deposit; 8 = neutral-basic volcanic deposit; 9 = neutral-acidic volcanic deposit; 10 = volcanic island arc; 11 = granitic rocks; 12 = strata deformed by folding; 13 = oceanic crust (arrow points out subduction direction); I4 = ophiolite and ophiolite melange; 15 = ocean basin spreading; 16 = fault. H = Huaniushan; P = Pochengshan; B = Baishantang; F = Panshankou; Xi = Xichanejing; Ho = I-fongliuhe; ,!,e = Y = Yingzuihongshan; Sh = Shuangyinshan; S = Shibanjing; X= Xiaohuangshan; Lebaquan; Do = Dongqiyishan; Du = Dundunshan; Lu = Luchojing; L = Liuyan-Chuanshanxuan).

Lute Ordovician-Silurian

In the late Ordovician, both the southern and northern rifts of the Huaniushan-Baishantang had

further withered away and were substituted by a shallow sea basin associated with granitic igneous activity (K-Ar ages around 457 Ma are recorded from the Wufengshan granite). As a consequence

EARLY

PALEOZOIC

PLATE

of the subduction ocean

basin

TECTONIC

of the Shibanjing-Xiaohuashan

southward,

the

Baiyunshar-Dongqiyishan possesses

391

IN BEISH LAN

CHARACTERISTICS

lower

volcanic

neutral-basic

volcanics

part

of the

arc,

which

and greenschist

facies rocks, was also subducted southwards, forming a double subduction zone (Fig. 5E). There was no continental the nous

margin

volcanic

Hengluanshan-Xichangjing sediments

occurred

Dananshan-Yuabaoshan flank,

region; in the region,

an active continental

rock series in region.

terrigeIn

the

on the northern

margin

continued

de-

veloping. In the early Silurian, this oceanic region continued subducting southward, an embryonic form of Hongliuhe-Niujuanzi back-arc basin had formed, the Hengluanshan-Xichangjing marginal basin evolved into an interarc basin, the Baiyunshan-Dongqiyishan volcanic arc came to maturity. The middle and late Silurian are the last periods of the Early Paleozoic geosyncline found in our research area, while the Jianquanzi molasse volcanic

basin

was

formed.

The

Hongliuhe-

Niujuanzi back-arc basin on the northern flank of this area began a period of great liveliness, forming an ophiolite suite. The continental margin was broken, due to back-arc spreading, subjected to folding and metamorphism, and developed into an island upwarping zone, the basement of which is continental crust. There was a submarine volcanic eruption of an island arc type and talcalkali rocks developed at Lebaquan and Gongpoquan. In the late Silurian, the Early Paleozoic ocean basin talc-alkali

closed volcanic

and was covered deposits

by abundant

of the island

arc type.

Fig. 6. Serpenttied

mylonite

belt to the south of Hanshan.

(which have a Rb-Sr isochron age of 398 Ma), monzonitic granite occurred in the form of stocks in the Huangjianqiu region. There of plagioclase granites (with Rb-Sr

are intrusions isochron ages

of 397 Ma) in the form of batholiths at Xinchang. Plagioclase granites to the west of Xiaohuangshan are probably

the product

of the final

stage. In the Dananshan-Yuanbaoshan association of volcanics and molasse

erogenic region an developed

which is associated with large-scale granitic sions at the beginning of the Devonian. The geotectonic its environs

intru-

relationship between Beishan and

In studying Asian geology, scholars from the Soviet Union have mentioned a Middle Asian foldbelt that contains an entirely Paleozoic folded region from the Tarim-Sino-Korean Platform to the Siberian

Platform.

In view of its geotectonic

Lute Silurian-Devonian

position, the Middle Asian foldbelt should include the Beishan area which lies in the neighborhood of

In this stage the Tarim Plate finally came into collision with the Hanshan microplate and the Mingshui-Shibanjmg-Xiaohuangshan suture belt was formed (Fig. 6). The volcanic-molasse associ-

the southern branch of the foldbelt. Peive et al. (1980) discussed in detail the evolution features of the Middle Asian foldbelt and divided into several stages as follows. In the oceanic stage, the Early Cambrian,

ation was widely affected by metamorphism and magmatism on both sides of the erogenic zone. In the process of subduction and closing the Xichangjing ophiolite melange was formed. Large-scale magmatism affected the internal flank of the Liuyan-Chuanshanxun paleocontinental margin. There were intrusions of quartz diorites,

paleo-oceans and microcontinents existed together in the foldbelt. The Mongolia microcontinent is the microcontinent nearest to Beishan that preserves the Archaeozoic metamorphic basement. In the Vendian-Early Cambrian, the paleo-oceanic tectonics became rather complicated. There were three types of crust (new oceanic crust, oceanic

392

crust and microcontinent and an environment similar to a stable paleocontinental margin existed between the microcontinents and the new oceans. The Pochengshan-Yingzuihongshan continental margin in Beishan could be similar to this unit. The Shibanjing-Xiaohuangshan ocean basin began to open during this period. The intermediate stage of the Middle Asian Foldbelt lasted from the beginning of the Cambrian to the end of the Early Paleozoic era. During this stage, a granite-metamorphic rock formation took shape, the paleooceans began to close and island arc series were more fully developed. In the mean time island arcs connected with the mosaic crust to form a whole that contained oceanic crust and microcontinents, along with ancient basement. At this time Beishan was experiencing a primary stage of evolution in which island arcs, less mature than those of the corresponding unit in the Siberian Platform, developed. During the Silurian, the ancient Asian ocean gradually reduced in size until it closed. A great deal of granite and metamorphic rock was spread over the entire area of the closed Shibanjing-Xiaohuangshan ocean basin. The continental margin at the southern flank, the trench-arc-basin system of the intermediate region and the Mingshui-Hanshan microcontinent were pieced together, forming a mosaic pattern, and the intermediate stage moved towards the final stage. The Tianshan geosyncline is situated on the southern margin of the Middle Asian Foldbelt. It is spatially closely related with Beishan. According to regional geological data from recent years, the Tianshan (Chinese part) may have consisted of three parts by the end of Caledonian period. The Mingshui-Hanshan microcontinent in Beishan is an eastward extension of the middle Tianshan. Figure 7 is a sketch map showing the position of Beishan in which it can be seen, that the Liuyan-Chuanshanxun continental margin and the south region of Shibanjing-Xiaohuanshan are part of the Tarim Plate, and the area to the north of Shibanjing-Xiaohuanshan could have been a block (the Mingshui-Hanshan microcontinent) which was tom away in Baikalian period. The tectonic framework of the northern area of the

ZUO

Fig. 7. Paleoplate

tectonic

part of Asia (based tion).

Cross-hatching

paleoplate

suture;

(triangles

indicate

schematic

on Li Chunyu,

diagram

of the middle

areas;

double

= main paleoplate

subduction

ET AL

1983 with a little modifica-

= continental

fault-lines

GUOCHAO

direction);

lines =

subduction

belt

square = position

of

Beishan.

Badanjilin desert, to the east of Beishan, would belong to the same geotectonic unit as the Beishan area. Acknowledgement

This project was supported by the National Natural Science Foundation of China. References Codie,

K.C., 1982. Plate Tectonic

gamon,

and Crustal

Evolution.

Per-

New York, 2nd ed.

Peive, A.V. and Yangshen, Nauka,

Moscow

Zou Guoqing, northeast

1980. Tectonics

1988. A discovery in margin

donian

stage

of Northern

Eurasia.

(in Russian). of Tarim

of the ophiolite

suite on the

paleocontinent

in the Cale-

and its significance

in tectonics.

Univ. (Nat. Sci. ed.), 24 (1): 39-54

J. Nanjing

(in Chinese with English

Abstr.). Zuo

Guochao, Guoqi,

Jin Songqiao,

Zhang

Xie, Zhang

Shuling,

structure

and

ophiolitic

Paleozoic

ophiolite

zone

at Baiyunshan-Xichangjing

trict of Beishan

Region.

Plate Tectonics

in Northern

Guochao, 1987,

In: Contributions

Shuling,

assemblages

the Xichangjing (2): 71-77

melange

in the Early dis-

to the Project

of

China,

2, pp. 8-70 (in Chinese

Wang

Xie and Jin Songqiao,

Abstr.). Zhang

Characteristics

mentary

He

1987. A discovery

of nappe

with English Zuo

Wang

Yang and Li Hongcheng,

of the turbidite

Area of Beishan.

(in Chinese

and

of Cambrian-middle with English

Acta

volcanic-sediOrdovician

Sedimentol.

Abstr.).

in

Sin., 5