Plate tectonics of East Qinling Mountains, China

25

Tecronophysics, 181 (1990) 25-30 Elsevier

Science

Publishers

B.V., Amsterdam

Plate tectonics of East Qinling Mountains, China Yangshen Department

Shi, Chengzhao

Jia, Dong Jia and Lingzhi Guo

of Earth Sciences, Nanjing University, Nunjing 210008 (People’s Republic of China) (Received

May 6,1989;

revision accepted

November

3.1989)

ABSTRACT Shi, Y., Jia, C., Jia, D. and Guo, L., 1990. Plate tectonics of the East Qinling Mountains, China. In: M. Kono and Burchfiel (Editors), Tectonics of Eastern Asia and Western Pacific Continental Margin. Tecronophysics, 181: 25-30.

B.C.

This paper presents the first detail study of the tectonic evolution and the petrologic and geochemical characteristics of the eastern Qinling Mountains of Central China and their relation to plate tectonics theory. The field investigations and petrological and geochemicaf studies have verified that the plate tectonic regime of the East Qinhng Mountains resulted from the middle-late Proterozoic evolution of the continental margins of the North China and Yangtze plates, and the iate Paleozoic-Triassic collision of the two plates.

logical boundary between South and North China. In these mountains the tectonic deformations and associated magmatic activity record more than 1000 Ma history of plate movements from the

Introduction

The Qinling Mountains in Central China form a geological, geographical, biological, and climato-

H CHINE

YANCTZE

PLATE

,

1 Fig. 1. Map

PLATE

showing

the middle-late

B, = Guandaokou-Lianchen

fore-arc -the

oo40-1951/90/%03.50

Proterozoic basin;

tectonic

B, = Ruyiang-loya

Hon~~pu-Erl~gping-Maban

0 1990 - Elsevier Science

Publishers

elements back-arc ophiolite

B.V.

of the East Qinhng basin;

C = Kuanpin

belt; E = Central

I

Mountains

A = Xionger

subduction Qinling

istands.

complex;

volcanic

arc;

L) = suture

zone

Y. SHI ET AL.

26

middle-late evolution

Proterozoic of the southern

the northern early

and

Yangtze

Mesozoic

the early

North

China

Paleozoic plate

and

plate to the late Paleozoic-

collision

between

the two plates

(Fig. I). It is one of the key areas for studying tectonics

of continental

plates

in China

the

and East

Asia. The plate tectonic

evolution,

1000 Ma, of the East Qinling divided during cludes

covering

more than

Mountains

can be

into three stages: (I) the pre-collision middle-late

Proterozoic

and Andean-type

time

continental

stage

which

margin

in-

along

experienced construction include,

intense tectonic disruption, but a reby Lin et al. (1984) showed that they

from the bottom

peridotite,

a cumulate

mafic pillow overlain

upwards,

complex,

metamorphic

diabase

dikes, and

lava mixed with radiolaria

by flysch. A whole-rock

obtained

from

the mafic

ophiolite

yielded

isochron

from

volcanic

isochron

rocks

an age of 681 158 a biotite-quartz

silicolites

Rb-Sr

in the

Ma and an

schist

yielded

an

age of 744 + 32 Ma. The radiolaria

Liosphaeridue

indeterminate

indeterminate

and

of Cambrian-Devonian

Stylosphaeridae

age were recovered

from

the southern part of the North China plate and a terrane accretion-type continental margin along

cherts. Thus we regard the age of the ophiolite suite as Sinian to early Paleozoic (700-500 Ma),

the northern part of the Yangtze plate; (2) the collision stage during late Paleozoic and early Mesozoic time which is characterized by thrusts,

The Andean-type continental margin of middle-(ate Proterozoic age on the southern margin of the North

nappes, and detachment structures which resulted from closing of the ancient Qinling Ocean be-

China plate

tween

A comprehensive tectonic shows that an Andean-type

the two plates;

and

(3) the post-collision

stage which is characterized by large-scale A-type subduction along the 1000 km length and the 100 km width

of the suture

zone

after

the collision

was present

along

and petrologic study continental margin

the southern

flank

of North

China plate during Middle-Late Proterozoic The Andean-type continental margin resulted

time. from

between the North China and the Yangtze plates. This evolutionary history was developed during an intensive study from 1981 to 1096 that included field, petrological, and geochemical investigation of rocks from the East Qinling Mountains.

the subduction of ancient Qinling oceanic crust beneath the continental crust of the North China plate. Rocks forming this Andean margin are north of the Honghuapu-Erlangping-Maban ophiolite

Geological evidence for the tectonic evolution East Qinling Mountains

belt (i.e. the suture zone), and can be divided into four tectonic units, from south to north (Fig. 1): (1) the Kuanpin subduction complex, (2) the

of

Guandaokou-Lianchuan The tectonics of the suture zone between the North China and Yangtze plates

Xionger back-arc active

fore-arc

basin;

(3) the

volcanic arc, and (4) the Ruyian-Loyu basin. Identification of the Andean-type continental

margin

of Middle-Late

Pro-

The collisional suture zone between the Yangtze and North China plates is marked by the Honghuapu-Erlangping-Maban ophiolitic suite of rocks that forms a belt extending from Feng

terozoic age on the south flank of North China plate is based on the presence of the volcanic arc in the Xionger Mountains which consists of calcalkaline volcanic rocks composed predominantly

County, Shanxi Province, through Xixia County to the north end of Xingyang city, Henan Province. This suture zone separated the southern

of andesites and dacite (the Xionger Group). The volcanic rocks are distributed roughly in a WNW direction along the southern margin of the North

margin of the North China plate from the geological units of northern margin of the Yang&e plate before collision. Both sides of the ophiolitic belt are marked by large-scale thrusts. The belt is characterized by intense structural deformation and appears to be rootless. The ophiolitic rocks

China plate. The Xionger Group of volcanic rocks overlies Archean units (Taihua Group) that consist of highly metamorphosed rocks which form the basement of the ancient continental crust of the North China plate. Hence the volcanic arc of Xionger Mountains was constructed on a base-

PLATE

TECTONICS

OF EAST OlNLfNG

MOUNTAINS.

27

CHINA

and those of the Aleutian within A

The

DZ values DZ values

Xionger

island

of 35-65

for the volcanic

Group

are concentrated

and 90 and belong

with continental

lands

than a volcanic

arcs rather peaks

rock

associated

volcanic

rocks series with However,

rocks of Xionger

are too high in comparison

with the volcanic may

Cascades.

Range. are

built

This on

rock

and is-

of

Cascade

of

DZ = 34

margins

with rifts.

DZ values for the volcanic

peak.

series

between

to a talk-alkaline

series associated double

arc are associated

with no double

be

a very

the

Group

because

primitive

rock the crust

whereas the Xionger Group are built on an older, more mature continental basement.

n

The Kuanping subduction complex is distributed in a belt a few to tens of kilometers wide and more 600 km long. The ophiolitic suture zone between the North China and Yangtze plates lies

261

E I

10

~

IO

35

50

70

DIFFERENTIATION

Fig. 2. Diagram volcanic

statistics

rock series (after Condie,

(Ethiopia). margin

showing

B. Oeanic

(Cascades).

INDEX

of differential

subduction indexes

1982). A. Continental

ridge (Iceland).

D. Volcanic

south of the subduction complex and the volcanic arc of Xionger Mount~ns (Fig. 1). The Kuanping

9ODI

C. Active

island

of rift

continental

arcs (Aleutians).

E.

Xionger voIcanic arc.

ment of ancient continental crust. The volcanic rock series was dated by the whole-rock Rb-Sr method and yielded an age of 1717 Ma (Sun et al.,

semblage consists plicated mainly

complex with

is a tectono-petrologic

extremely

complex

of mutually parallel folds. The subduction low-grade

structure.

asIt

thrusts and comcomplex contains

greywacke

flysch

mixed

with

abundant blocks of metamorphic mafic and ultramafic rocks and marbles, and exhibits the characteristics of a melange. This assemblage was probably derived from oceanic crust by tectonic accumulation in a subduction zone when the ultramafic rocks of the lower oceanic crust and the

1982). A petrochemical analysis on 261 specimens from the volcanic rocks of Xionger Group showed

tholeiite of the upper oceanic crust were detached during the subduction of the oceanic plate. Be-

include andesite

that nearly 80% of the rocks are talc-alkaline and rhyolite, dacite, andesite and basaltic as well as 20% weakly alkaline rocks that

Kuanping subduction complex long ancient forearc basin

include latite, trachyte and alkalic basalt. It was proposed by Martin and Piwinskii (1972) and Condie (1982) that the Differential Index (DI) can be used to identify volcanic rock series for

Lianchuan which terozoic carbonate

different types of plate margins (Fig. 2). Figure 2 shows that the volcanic rock series of continental rifts and oceanic ridges are associated with DI values concentrated in two areas, DI = 35-75 and DZ = 95, characterized by typical double peak distribution in a frequency histogram. However, the continental margin volcanic rocks of the Cascade Range in the Cordillera of western North America

tween

the ancient

Xionger

volcanic

consists flysch.

Ruyang-Luoyu back-arc north side of the volcanic

arc and

the

is the narrow and of Guandaokou-

of Middle-Late ProThe contemporaneous basin is present on the arc. It consists of a suite

of terrestrial coarse detrital rocks (i.e. the Ruyan and Luoyu Groups of Middle-Late Proterozoicage), mainly deposited in a back-arc basin on a continental basement. An important question in Precambrian geology and plate tectonics is when plate tectonics characterized by the Wilson cycle began (Kroner, 1982). The recent

proposals

for the beginning

of

Y. SHI ET AL.

28

anic plate. The Doubling complexity metamorphosed

terrane consists of a opbiolite suite associ-

zoic (Zhu, 1983). The evidence from the Xionger

ated with metamorphosed

elastic rocks and also

volcanic arc (dated at 1800 Ma) and the Kuanping

include

subduction

serpentine,

Wilson cycles include late Archean (Taylor, 1986), middle Proterozoic

(Guo et al., 1980) and Meso-

complex

support a time of at least

1800 Ma for the begining of plate tectonics.

It

should be pointed out that tectonic events at the this time area of a global significance. tectonic

events

are present

Similar

as the Harson

of

plagioclase-amphibolite, etc. The Hannan

metamorphosed Late

Proterozoic

geochemical

(800

Ma) age. Petrologic

analyses of metamorphosed

rocks demonstrate

developed as an oceanic

that the Hannan

terrane is composed of a Precambrian

acid volcanic rocks dated at 1800-2000 Ma. Therefore we believe that out data supports a

ultramafic

Proterozoic

by at least Middle

time and resulted in a global peak of

intermediate-acid

eruptions at about 1800 Ma B.P.

Middle-Late Proterozoic terrane accretion-type active continental margin along the northern margin of the Yangtze plate

and

volcanic

terrane was

island arc. The Bikou

it is associated with abundant and intermediate-

for plate tectonics

of

and flysch deposits of marine facies, which are of

the Transmazonian

begining

and

volcanic rocks of island arc type

Penokean erogenic cycle in North America and as cycle in South America where

gneiss

terrane consists

ophiolite assemblage

mafic and

which includes a

series of intermediate-acid rocks. Sun (1986) has shown the ultramafic rocks are of Alpine type and are associated with gabbro-diabase

sheeted dykes,

spilite keratophyre and abyssal sediments that are nearly 10,000 m thick. These rocks are interpreted as residul fragments of the ancient Sonpan-Ganzi

The basement along the northern margin of Yangtze plate was formed by amalgamation of a

oceanic crust. These terranes were formed in different tectonic en~ronments. The Wudang terrane may represent a residul ancient oceanic ridge. The Shennongjia terrane is obviously a microcontinent separated

series of Precambrian terranes which include the Wudang Mountains, Shennongjia, Douling, Huan-

from an ancient continent, perhaps from the North China plate. The Huangling terrane represents a

gling, Hannan terranes, the Middle Qinling island

fragment of an ancient continent characterized

arc and Dabie terrane. There are great differences in fossil content, t~tono-petrolo~c assemblages,

highly metamorposed

magmatic activity and metamorphism among these

The Doubling and the Bikou terranes are obviously fragments of oceanic crust. It is proposed

different terranes that indicates they have different origins, such as, residual ancient islands arc, fragments of the ancient continental crust or oceanic crust. Accordingly we classify each terrane according to its type of crust, either continental or oceanic crust. The Wudang terrane might represent and oceanic plateau made of bimodal volcanic rocks erupted on oceanic crust. The Shennongjia terrane is characterized by a continental crust

by

rocks. The Hannan terrane

could be an island arc developed on oceanic crust.

that these terranes were amalgamated and accreted to the northern margin of the Yangtze plate between 1000 and 800 Ma, forming a terrane-accretion-type continental margin of Middle-Late Proterozoic age. Following terrane accretion, southward subduction of an oceanic plate started disintegration of the northern margin of the Yangtze plate. The Central Qinling Mountain block sep-

overlain by very thick carbonate formations inter-

arated from the Yangtze plate and drifted north-

bedded with a minor amount of the muddy and elastic rocks of Middle Proterozoic age. The

ward in early Sinian time. The subduction zone was located on the north side of this block and

Hu~~ng terrane is mainly composed a variety of metamorphic rocks which formed an Early-Middle Proterozoic metamorphic continental basement. Consequently these terranes all formed continental fragments scattered within an ancient oce-

back-arc extension developed between the Middle Qinling Mountain block and the Yangtze plate forming a new trench-arc-back-arc basin system. The Central Qinling block formed an ancient island arc.

PLATE

TECTONICS

OF FAST

QINLING

MOUNTAINS.

29

CHINA

Fig. 4. Velocity

structure

in the crust along the Suixian

County

seismic profiles (after Wang, et al., 1988).

oped progressively processes Fig. 3. A model of the tectonic and convergence

evolution

in the East Qinling North

during

Mountains

China and Yangtze

the collision between

the

structures China

between

the

North

China

plate.

foreland

structure

the northern

boundary

of Yangtze

as terrane-accretion-type

tal margin,

followed

arc-back-arc

basin

by development system.

Both

and nappe

of the North

deformation

forms the Qinling

An intra-plate A-type Qinling Mountains

southern boundary of North China plate developed as an Andean-type active continental margin first developed

Intense

thrust

margin

with

plate

continenof a trenchbelong

erogenic

zone.

and

The North China and Yang&e plates has separate and independent tectonic evolutions. The

whereas

produced

on the southern

large-scale detachment-nappe structures formed on the northern margin of the Yangtze plate. This

plates.

complex Collision model Yangtze plates

from the east to the west. The

of collision

to the

subduction

zone in the East

An intra-plate A-type subduction long and 100 km wide developed Qinling

Mountains

the collision

during

between

zone 500 km in the East

Cretaceous

the North

China

Yangtze plates. The A-type subduction tended in a NWW direction from

time after and

the

zone exHauaxian

precollisional tectonic evolution of both North China and Yangtze plates. The North China and

County, Shanxi, the Shangdan Wuyang-Lushan

the Yangtze plates approached each other during subduction of the intervening Qinling oceanic plate, finally colliding in early Paleozoic time (Fig.

Seismic study (Wang, 1988) shows that the velocity structure of the crust is characterized by: (1) a gradual change in depth of the boundary between

3). Tectonic

upper and lower crust (from 13 to 17 km), and (2)

studies

show that the collision

was a

complex long-term process which included the initial collision dated as late Ordovician (440-480 Ma) followed by continued convergence. The initial collision was an intense tectonic event of relatively short duration that caused a large area of short-lived crustal uplift and was associated with high-pressure glaucophane-schist metamorphism. The processes of collision and convergence lasted for 200 Ma until Triassic time, and devel-

S

to Xinyang, Henan, and between fault in the south and the shallow nappe belt in the north.

Shanadan fault

Fig. 5. Model

of Cretaceous northern

A-type

East Qinling

subduction Mountains.

zone in the

30

a low-velocity zone of 3 km thickness at a depth of

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with granite

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