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Produced by the NASA Center for Aerospace Information (CASI)
(NASA-CI-175617) CHSTIL LINIMICS STULIkS N85-222E5

IN CHIH1 Final Report (State Univ. of New

York) 62 6 hC 104/MF lu1 CSCL 08G

ULClaS

G3/46 14704

Final Report

NAG5-240

Crustal Dynamics Studies in China r

ti

r

Principal Investigator:

Francis T. Wu

Department of Geological Sciences

State University of New York at Binghamton

Binghamton, N.Y. 13901

March 31, 1985

►n ►,^ p

C%L ` W

. r

1^ M
Final Report for NGS- 5-240

-------------- Geodynamics of China -------°-

Under NGS-240 the following research has been performed:

(1) the tectonics along the Tanlu fault in eastern China.

(2) tectonics in the Taiwan Strait behind the collision zone in

Taiwan.

(3) analysis of faulting in the vicinity of the Altyn Tagn fault.

The major conclusions.are:

I. Tanlu fault zone.

-- A major fault zone that extends from Dabie Mountains in Anhui

Province in eastern China to the Bohai Gulf and then onto Amur

River Valley in Siberia and disappears in the Okhotsk Sea.

-- The recent motion is definitely right-lateral from field

evidence of stream offsets and focal mechanisms of small

earthquakes along the fault. The stream offsets indicate that in

the section of Tanlu in Southern Shantung Province the

right-lateral offset amount to 25 meters. An offset of the old

Yellow River channel at the town of Shouqian at the point where

there are ample evidence of the presence of the Tanlu fault, the

total right-lateral offset is about 25 kilometers.

1 -- Immediately south of the Yantze River south of the Dabie

Mountains, the only evidence of the Tanlu fault is the

right-lateral offset of a Ordovician/Silurian limestone unit; the

total offset is less than ten kilometers.

-- The existence of the fault can be traces back to at least

Jurassic with the deposition of conglomerate sandstones in the

troungh along the present Tanlu fault branches in ti,c: Shantung

Province. The Tanlu fault could be a part of the old plate

boundary however; the wrap-around _)f the "Southern China Massif"

at the southern end of the Tanlu fault is probably related to the

left-lateral motion along the fault. If that is so then the

G left-lateral motion occurred in late Mesozoic and perhaps early

wr Cenozoic and, judging from the left-lateral drag of the Dabie

i

r

JW
;b;V

Mountain metamorphics along the fault the total displacement can

i ° amount to 200-300 kilometer.

******* A partially completed manuscript is attached ******

II. Tectonic3 in the Taiwan Strait behind the collision zone.

Taiwan is known to be the product of collision between the

Philippine plate and the Asian plate. This collision is strong

enough that its effect is felt in the Taiwan Strait and most

probably across the Strait in Southeast China.

In the Strait young normal faulting striking nearly perpendicular

to the trend of the Island is found.

In Southeast China, young basins bounded by NW striking normal

faults started their existence in late Pliocene when Taiwan began

to rise out of the ocean.

  A partially completed manuscript is attached ** ***

III. Tectonics of Altyn Tagh Fault in n3rthwest China. Altyn

Tagh is a major fault bounding the northern edge of the Tibetan

Plateau. The main branch has a length of about 1500 km. The

eastern end of the fault is evidently left-lateral from stream

offsets (Allen, 1981; Molnar and Tapponier, ).

By correlating with the 1:4,000,000 geology map of China, we are

able to identify the stratigraphic units correspond to most of

the major features on the 1:750:000 LANDSAT false color images

made with funds from this grant. By correlating a geological

unit that appears on both sides of the fault, we estimate that

the maximum displacement is on the order of 300 km.

There are a number of faults around the main branch. In ge-pral

the formation of rhomboidal basins and the presence of push-ups

at bends around the bends of the main branch along the part east

of 82 east longitude are consistent with a left-lateral motion.

However, near 80 east longitude the motion becomes dominantly

compressional as shown by the presence of high ranges. Further

to the west, the motion becomes right lateral.

j It is interesting that in the western part of the Tarim basin,

directly north of the area where Altyn Tagh fault becomes
compressional, there is a major thrust in the Basin that is on

top of a bulge under the basin. There some Late Paleozoic rocks,

probably part of the basement of the Basin, is actually exposed.

This structure in the middle of the Basin results evidently from

the collision of Indian and the Asian plates.

**^* Xerox copies c; the LANDSAT images and their *****

  interpretations are attached ** ***

1
The Tanlu Fault of Eastern China

By

Francis T. Wu

^f Department of Geological Sciences

State University of New York

Binghamton, New York 13901

Zhang Yuming, Fang Zhongjing and Zhang Shiliang

Institute of Geology

State Seismological Bureau

Beijing, China

Introduction

Since Late Cretaceous and Early Cenozoic, there had been a

notable change in the tectonics of Eastern China, most probably

due to the impingement of India on Asian Continent and the

subouction activities on the western side of the Pacific plate.

The present Tanlu fault, cutting across much of China, was

possibly the locus of tectonic activities since later PreCambrian.

But the fault-controlled features are much clearer in the

Post-Cretaceous rocks. With the occurrence of ma,or earthquakes

along this fault, the clear Quarternar , geomorphic development,

r

and the continuous occurrence of microearthquakes here, this is

evidently a mojor structure in Eastern China.

Il

The fault was not "discovered" until the late 1950's (Ministry of

1

Geology, 1957; Xu, 1957). In the 1970's it became the center of

attention in the study of the tectonics of Eastern China (Fang,

i

a1I
t^

b • '. 1979; Fang et al., 1979; Huang, 1977; Xu, 1980). But there are

i

still many unsolved problems concerning the fault. The exact

be nature of its past activities, its extension to the north and the

south and the total amount of displacement are all problems under

continuous research.

This report provides an outline of the knowledge concerning this

fault.

Location and Genera Geology

The geology of North China is markedly different from that of

South China in several ways. It has long been for example that

North China (Fig. 1) has a rather continuous sedimentary series

prior to mid-Ordovician. Essentially no Devonian and Silurian

rocks can be found there. The Sinian (PreCambrian) strata are

commonly very extensive ar.d thick limestone beds. And after

mid-Ordovician scattere.l continental strata were formed. In

contrast, the equivalent Sinian beds are mainly silty sandstones

in South China. And Cambrian and Ordovian strata in South China

were somewhat intermittent and from Silurian onward the

near-shore deposits were laid down; only after Triassic did the

marine sedimentation stop and replaced by sporadic continental

sedimentation.

The section of the fault that has been studied in detail extends

from the Bohai Gulf in Shantung Province to the eastern end of

the Dabie Mountains in Anhui Province (Fig. 1) for a length of

1300km. Tl, e northern half of this section lies within North

China, but the South China block wraps around the southern end of

J
the fault. The fault evidently continues northward; it

eastern boundary of the broad Northeastern China Plain i

Liaoniag, Jiling and Heilungjiang (Fig. 1). Northward, there is

a major fault that seems to link up with the Tanlu fault from

Amur to the Okhotsk Sea according to available Russian reports().

Its southern extension is much more problematical, a number of

tectonic interpretations (e.g.,Tectonic Map of China, 1980)

depicts the fault as continuing across the Changjiang (Yantze

River), through the South China block to end up in Gulf of

Tonkin; however, this interpretation is nct accepted by all.

Thus the probable total length of the fault from Anhui Province

to Okhotsk Sea is on the order of 2500 km.

Maximum Left-lateral Displacement Alo- ►g Tanli Fault

Because of the fact that the area has been uplifted above the sea

level since late Paleozoic and the continental sedimentary cover

either stripped from time to time or never had existed, it is

difficult to piece together a complete story as is the case with

the San Andreas fault. Such reconstruction has been attempted by

Xu (1979 for example) ; but the correlation of strata across the

fault is never certain and therefore the conclusion that the

left-lateral movement of 700 km might have taken place during the

MesoLoic has been subjected to much discussion (Fang et al.,1979;

Wu et al., 1981 among others).

That Tanlu is an old boundary is clearly shown by the fact that

the rocks on two sides of the fault in North China are not

correlatable even allowing major horizontal movementR. Thus the
Dabie metamaorphics near the southern end of the fault is butting

against rocks of the "South China Platform", and the Archaen

rocks of western Shandong are compositionally different from the

metamurphics in eastern Shandong. The post Mesozoic sedimentary

I

basin in eastern Shandong have not counterpa,Ls in western

Shandong. But whether we could define this generalized boundary

to have always been the Tanlu fault is questionable. As shown by !

McElhinny et al. (1982) that during Permian the North China block

and the South China block may+ be totally apart and both were near

the equator.

The existence of the Tanlu fault in North China since Mesozoic is

certain. It is marked by the presence of two clear narrow

valleys in which very characteristic Late Jurrassic and early

Cretaceous strata were found. These arr: conglomeratic sandstones

and coarse sandstones. The presence of these rift valleys

implies tensile stresses normal to the fault.

The left — lateral movement has taken place is supported by

several geological observations. The Dabie metamorphic complex

for example is very very characteristic in the region. It is

mainly found along the trend of the Dabie Mountains. However,

it is found strewn along the Tanlu fault in Central A.-ihui

Province. The farthest distance wheLe the Dabie Mountain complex

is found is about 200 km from the Dabie site. Actually,

Neotectonics and Seismicity

Neotectonic feature along portions of the Tanlu fault is very
in

clear. Figures x-x show typical outcrop along the ShandongJiangsu section of the fault. This is also the location

suposedly of the 1686 M-8 earthquake.

Fig. shows typical outcrops of the fault in Shandong Province

near the _own of Juxian. Left-lateral stream offsets amount to

20 m can be seen o1 the ground and in the airphotos. Some

thrusting is also evident in some outcrops (Fig. ).

The maximum right-lateral displacement that can be conjectured is

about 25 km from tre offset of one of the old Yellow River

channels that crossed the fault in Jiangsu Province near the town

of Shuqian (Fig. ).

The effect of the ria`.c-lateral displacement is also clearly

displayed by the post-Cenozoic deep graben east of the Dabie

Mountain, along the Yantze River.

Conclusion

-- A major fault zone that extends from Dabie Mountains in Anhui

Province in ee.stern China to the Bohai Gulf and then onto Amur

River Valley in Siberia and disappears in the Okhotsk Sea.

-- The recent motion is definitely right-lateral from field

evidence of stream offsets and focal mechanisms of small

earthquakes along the fault. The stream offsets indicate that in

the section of Tanlu in Southern Shantung Province the

0
right-lateral offset amount to 25 meters. Aa offset of the old

Yellow River channel at the town of Shouqian at the point where

there are ample evidence of the presence of the Tanlu fault, the

total right-lateral offset is about 25 kilometers.

-- Immediateiy south of the Yantze River south of the Dabie

Mountains, the only evidence of the Tanlu fault is the

right-lateral offset of a Ordovician/Silurian limestone unit; the

total offset is less than ten kilometer;..

-- The existence of the fault can be traces back to at least

Jurassic with the deposition of conglomerate sandstones in the

troungh along the present Tanlu fault branches in the Shantung

Province. The Tanlu fault could be a part of the old plate

boundary however; the wrap-around of the "Southern China Massif"

at the southern end of the Tanlu fault is probably related to the

left-lateral motion along the fault. If that is so then the

left-lateral motion occurred in late Mesozoic and perhaps early

Cenozoic and, judging from the left-lateral drag of the Dabie

Mountain metamorphics along the fault the total displacement can

amount to 200-300 kilometer.

References

f

1

i

Figure Captions
M.

Recent Collision and Its Effects In Taiwan and Its Vicinity

by

Francis T. Wu, State University of New York at Binghamton, N.Y.,

USA

C. C. Biq, Centeal Geological Survey, Taipei, Taiwan, ROC

Introduction

Taiwan is situated in the Western Pacific in between the Ryukyus

and Lhe Philippines. As it has been pointed out by many authors

that Taiwan, unlike its island nei.ghborsin the Ryukyus and the

Philippines, is in a collision regime (see for example, Biq,1971;

I Chai, 1972; Wu, 1978;Bowin et al., 1978; Lin and Tsai, 1982). It

• is a rather young collision; the high (3000-4000m) range q formed

from Paleogene and Neogene sediments along the axis of the

island, recent seismicity, and the rapid modern day uplifting of

the marine terraces all &test to the vigor of this young

collision process. Even with sach a young geological phenomenon,

however, there are still disagreements among the geologists and

i the geophysicists as to the location of the suture line, the

configuration of the plate boundaries and the detailed

interpretation of the tectonic environment before the collision.

Much new geological and seismological data have come into

existence in the last ten years and further refinement in the

tectonic picture of Taiwan based on these data is useful in our

understanding of mountain-building processes in general.

Much of the plains and the foothills areas have been mapped on

1:25,000 scale cnd drilling as well as geophysical profiling have

been done through petroleum exploration works. However, the

Mountainous areas, oue to the inaccessibility and the lack of

easily identifiable horizons, have not yet been studied in great

detail; the main features are known but the boundaries of units

are subjected to change as more work is done there. The gerLogy

of the eastern part of the Taiwan Strait has been studied

t"ioroghly by the Petroleum Company on Taiwan, but only one

report has been published (Sun, 1982).

It is not uncommon to apply the classic geosyncline theory to the

study of tectonics of Taiwan (see discussions in Ho, 1982) and

this interpretation is sometimes pitted against the plate

' tectonic interpretation. Actually, being a very young tectonic

VI
belt, Taiwan is an ideal place to study some of the details of

mountain building processes; the sedimentary record is relatively

complete and the forces that caused the mountains to rise are

p robably still at work.

This paper is directed at the (1) interpretation of parts of the

sedimentary record in terms of our knowledge of the recent

passive margin and the deformation in the forearc area, (2) a

further look at the seismicity through stereoscopic diagrams and

(3) interpretation of structures in the Taiwan strait and across

the strait on the mainland side as a consequence of collision of

the Ph!'.ippine Plate with the Eurasian Plate in Taiwan.

Geological Environment

Reviews of the geology of Taiwan can be found in Ho(1982),

Big(1984) and others. Since most of the papers on the geology

there are not widely available outside of Taiwan, we shall

summarize here the pertinent geological data germaine to our

discussions.

Geographically, Taiwan can be divi,'ed into four distinctive

sub-areas along nearly north-south lines. A narrow Longitudinal

Valley divides the main part of the island from the Coastal

Ranges on the east. These are wages of about 1000 m in i

elevation and ringed on the east side, facing the Pacific, with

raised marine terraces. To the west of Valley, the land slopes

rapidly upward iato the Central Mountains. Within a distance of

about 30 km, the main ridge, much of it above 3000m, is reached,

and the highest peak on the ridge has an elevation approaching

4000m. The Central Mountains grade into the Foothills to the

west and then to the flood plain. The Taiwan Strait between the

island and the Chinese Mainland is fairly shallow at an average

depth of 20 meters; the depth increases rather rapidly south of

the Pescadores, a group of basaltic islands.

The oldest rocks in Taiwan are exposed on the eastern side of the

Central Mountains. These include shists, gneisses, metamorphosed

limestone and amphibolites. The parent rocks of these

metamorphic rocks are limestones, clastic sediments and igneous

rocks. Greenschist, serpentinite and amphibolite bodies in the

eastern part of this belt have been recently studied by Ernst et

al.(1981) and Liou(1981) among others. The ages of these

metamorphic rocks is certainly pre-Tertiary, but the their ages

have not yet been accurately determined. Based on available
data, the oldest rocks have an age of 86 m.y.(Yen. ). But a

few deformed amonites found in these rocks place them in Permian.

Of course it should be pointed out here that at Permian time, the

area in q uestion could have beer in an y ntirely differert place

and it has since drifted (McElhinny, 1981) for ' Stances up to

3000 ka to reach the present location. These rocks most probably

form the basement of tht northern part of the main Island.

Overlain the metamorphic basement are the thick slightly

metamorphosed marine argillacco•a sediments that form the high

ridges o° the Central MouAtains and their western flank. The

metamorphic grades of rocks in this belt increases generally from

west to east. They are Eocene to Miocene in age. It is common

practice to discuss the geology of the Island in term of a

east-wear profile. But there are significant north-south

differences, and these argillaceous rocks demonstrate this well.

In the north, this Tertiary indtirated to metamorphosed argillite

belt consists of actually two belts, the western belt includes

sandstone members and carbonaceous layers and interbedded

basaltic flows, tuffaceous sediments and so on. But thj eastern

belt contains limestone or marly intecbeds and -:nri:ular

conglomerate beds, althosgh these are of limited occurrecice. In

the south, unly the the argillaceous strata are found; they are

judged to be of similar nature as the eastern belt in northern

Taiwan. The boundary between the north and south sub-provinces

it marked on the map, but due to the lack of work in that area,

the exact location is frc from certain. It is interesting to

observe that the boundaries of the eastern argillite belt in

northern Taiwan fullows the faults well, but the internal

boundaries of the w-stern belt inters(ct the western limit of the

belt. These rocks do not appear in southern Taiwan, but the

basement rocks under the Coastal Plain are perhaps the extensior

of these units (Chiu, 1975). In the south, the Eoceno slate also

is found to the east of the Pre-Tertiary metamorphic rocks west

of the Longitudinal Valley.

The mechanically incompetent rocks in the eastern slate belt is

severely faulted and folded with extensive development of slaty

cleavage. The fold axes trend in the north-northeast direction.

The rocks in the western belt however are markedly lees deformed.

That these two sedimentologically and structurally different rock

units are juxtaposed means that the eastern belt was probably

placed there after significant horizontal displacement and that

the boundary is probably a fault, the Lishan fault, alt1i-ugh the

existence of this fault is not undisputed(Chen, ).

0
M

To the west of the Central Mountains, a suite of Middle Miocene

to early Pliocene shallow marine to shelf-elastics form the bulk

of the foothills. Alternating sandstone and shaly layers

dominate. In general the sediments contains more fine muddy

matrix as one goes south and the strata are much thicker. Lenses

of tuffaceous rocks, resulting from submarine pyroclastic

eruptions of basalt, are present. The total thickness of the

sedimentary rock reach 8000m to the east and decreases to less

than 1000m in the west. In northern Taiwan, there are several

coal-bearing layers; these are absent in the south, and the rocks

contain a high proportion of mud. There is a drastic increase in

the thickness of late Miocene to Pliocene strata south of 23.5

latitude (Ho, 1981), marking probably the position of the

contnental margin before the collision.

The eastern edge of the Coastal Plain is festooned by a chain of

terraces formed from sandstones/shale and conglomerates. These

Pleistocene to Holocene deposits represent tectonic molasse.

Detailed studies of sedimentary structures reveal that while the

sediments deposited prior to late Pliocene were supplied from

sources to the west, those after that period were supplied by

sources to the east(Chou, 1973).

The rocks in the Coastal Ranges on the eastern side of the island

are quite distinctive from those on the rest of the island. The

oldest rocks that crop out Miocene volcanics, mainly andesitic

flows and pyroclastics. One magmatic suite seems to be an old

eruptive center to the two islands, Lutao and Lanhsu off-shore to

the southeast (Figure ). Indeed, this center appears to line up

with the two islands along an undersea ridge (figure ),

indicating perhaps that at one time they were all active and had

the same role in the tectonic regime. A layer of agglomerates,

tuff, and tuffaceous sediments underlies much of the Coastal

Range, in the north and the south; the age of these rocks range

from early Miocene to Miocene/Pliocene as determined from

nanofossils and planktons contained in the limestone lenses

occuring near the top of the formation.

Geology of the Taiwan Strait is not yet well-known. The

petroleum exploration in the eastern half of the Strait has

produced detailed seismic and drilling data. However, so far

only very generalized cross sections have been published (Sun,

1^ '). According to Sun, widespread unconformity exists between

Eocene and Oligocene and between Pliocene and Pleistocene strata.
Throughout Tertiary, several basins can be identified with local

ridges separating the basins from each other. Growth faults have

also been found to accompany the deposition. Major faults are

sub-parallel to the zxis of the present Taiwan while the recent

normal faults are often nearly east-west in orientation. The

NNE-SSW block faults resemble those that are found on other

continental shelves (see for example, Poag, 1982). Little has

been said about the more recent (Pliocene-Pleistocene)

environm, nt in the Strait, although apparently the structural

trends differ from those in the earlier basins and the intensity

of tectonic movement decreases toward the west.

The foregoing discussion can be surmarised in two schematic

cross-sections, one for the north acid one for south Taiwan are

shown in figs re together with a reconstruction of might have

been before the mountain building. The Tertiary sediments in the

Central Mountains and the foothills were deposited in basins on

wi,at was at the time a passive continental margin, a 200 or so

kilometers wide shelf. As shown in figure , the shelf in early

Tertiary probably went through the present day midpoint of the

Island. In other words, the northern half of the Island was on

the shelf, and the southern half of Taiwan was then the

continental slope and part of the abyssal plain. The rocks in

the eastern slate belt, phyllites and slates with limy

components, may actually be mainly slope and apron sediments that

were subsequently tectonically emplaced onto the shelf next to

the shelf-deposited western belt(see further discussion later). 4-

Geologic Structures of the Island

Off-shore Geologic Strizztures in the Taiwan Strait

We have mentioned the older structures in the last section. The

multi-channel data must contain rich information concerning the

neotectonics in the Strait. However, the data is not available

for study. Lee (1973) however, has reported on the

single-channel reflection profiles in the eastern half of the

Taiwan Strait. Two nearly parallel reflection lines were run.

It is evident that some of the on-shore faults are extenued into

the strait. But it is also clear that there are two basins, the

Taichung basin and the Hsinchu Basin that are bounded by a number

of normal faults that cut through the youngest sediments and are

probably still active. The faults on the northern and southern

edges of the Penghu platform are particularly clear. As we shall

see that the Strait has infrequent, but very large earthquakes,

P
and some of these faults are probably related to the seismicity.

Seismicity

The area under consideration is seismically very active.

Katsumata and Sykes(1969), Wu(1970,1978) among others studied

teleseismic data compiled by USCGS, NOAA, USGS and ISC and

interpreted the data in terms of modern-day plate tectonics in

the area. Recent maps published by Tsai and others(e.g., Tsai et

al., 1982; Lin and Tsai, 1982) use data from the Taiwan

telemetered network; although the main picture emerges from the

regional network remains the same, the data provides more details

in the immediate vicinity of Taiwan, especially in clarifying the

relation of the Benioff zone under the andesitic volcanoes in the

extreme north of the island and the thickness of the seismically

active layer.

The spatial distribution of hypocenters( data from the USGS PDE

tape and the ISS Bulletins) can be seen in a series of

stereoscopic perspective plots(figure ). Clearly, no Benioff

zone exists in the section of Taiwan between the northern and the

southern ends of the Longitudinal Valley. On the other hand, the

dipping seismic zone continues from the Ryukyus to the region

northeast of the island. It is shown clearly in Lin and Tsai

(1982) that this zone extends under the northern tip of the

Taiwan island under the group of young andesitic volcanoes.

In figure the historical seismicity of the Taiwan and the

continent across the Strait is plotted. It is interesting to

note that several major earthquakes occurred in or off-shore of

Fujian area. All along the eastern shore of China has been

populated throughout the recorded history, thus the lack of large

historical events elsewhere is not due to a lack of recorded

history of those areas. Only magnitude six or smaller events

have been reported elsewhere along the coast (Geophysical

Institute).

Focal Mechanism solutions and Interpretation

A compilation of the available focal mechanism solutions is shown

in Table 1.

Plate Configuration in the Taiwan Area

Figure depicts the plate configuration in the vicinity of
Taiwan as implied by geology, seismicity and focal mechanisms

presented in the last sections. The main features are: (1) a

collision boundary exists along the coastal range, the Philippine

Sea plate exerts stress perpendicular to the boundary as well as

slips along this boundary in a left lateral sense, (2) the

Philippine sea plate

Faulting Behind the Collision Front

We have discussed so far several types of recent faulting west of

the Longitudinal Valley. These represent faulting activities

behind the collision boundary. The thrust faulting in the

foothills is easy to understand as they are consistent with the

direction of the tectonic stress that cause the uplifting and

east-west deformation on the isla d. The repeated strike-slip

faulting (e.g. associated with the 1935 Hsinchu and the 1906 and

the 1946 Chiayi earthquakes) along nearly east-west trending

faults, and the nearly east-west trending normal faults in the

Strait are features that demand explanation.

Recent Faulting and Basin Formation in SE Fujian

No marine geology or seismic data in the western half of the

Taiwan Strait is now available. However, there are some recent

land data in Fujian Province across the Strait that indicates

some young structural .-activities are taking place that may be a

result of the intense collision in Taiwan. Figure shows the

locations of several young basin in the coastal area (Zhang,

1982;Chen et al., 1980). These basins are controlled by

north-west oriented normal faults. The Fouzhou graben is one of

the largest basins in Fujian; according to drilling data, the

subsie..ence started in MiO- to Late-Pleistocene and has now

reached 100 meters or so, i.e. subsiding at an average rate of

0.3-0.7 mm/yr(Zhang, 1982). The 1604 earthquake, with an

estimated magnitude 8 occurred in the Strait near Fouzhou.

The Santou basin further to the southwest is also controlled

mainly by the rorthwes' oriented faults; the basin contains

vertebrate fossils of Late Mid-Pleistocene, stone-age tools etc.

It is clear that during Quarternary, this area has undergone

several episodes of rapid subsidence; the earthquake of 1918

(4-7.5) was apparently related to a NW oriented fault (Zhang,

1982).

Until marine seismic data in the Taiwan Strait becomes available,
(41

the continuity of tectonic fabrics from Taiwan to Fujian cannot

be ascertained. However, the occurrence of large earthquakes in

the Strait, the presence of east-rest to northwest oriented

faults on both sides of the strait, and the presence of numerous

normal faults in the eastern half of the Strait (Lee, 1974) all

point to the possibility that these structures are genetically

related. These faults, at high angles, with the colission

boundary, have been observed at several places. Molnar and

Tapponier (197 ) have particularly point out the pres,-nce of

such a structure behind the Himalayas in southern Tibe:.

Discussion

The recency of the orogeny that is found on Taiwan affords us a

chance to examine some of the details of tectonic processes that

had taken place. With the general agreement that collision is

responsible for the conversion of a continental margin into an

impressive mountain range does not preclude disagreement

regarding the collision boundary nor does it imply that the major

geological observations have been adequately understood in terms

of plate tectonics. We shall attempt here to offer explanations

for some of them.

The argillite belts in the Central Mountains have been

interpreted as the result of marine transgression into the

"Taiwan Geosyncline". But the juxtapositioning of two very

diverse sedimentary units, the eastern belt that contains limy

and marly layers and the western belt that contains carbonaceous

sandstones, implies that major tectonic action had brought them

together.

The Philippine Sea was most probably an expanding basin in early

Tertiary (e.g. Lee and Hilde, 1982; ), although the exact

location of the ridge and mode of spreading is not yet totally

clear. Thus the continental shelf of southeastern Asia ar that

time could resemble the Atlantic margin during late Cre^aceous

and the present-day Atlantic margin can be viewed ad a model of

the pre-collision depositional basin in Taiwan area (figure ).

From Eocene to early Pliocene, the edge of the shelf probably

subsided continuously and the sediments lapped farther and

farther onto the adjacent floor (figure ). As the island arc

approached the shelf, the depositional basin deepened. But the

sediments on the ocean floor were compressed and pushed toward

the shelf (figure ). Since part of the sediments are on the

oceanic crust and we know that the continental crust has now been

is

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thrusted up into mountains, with the island arc next to it, the

sediments must have been telescoped onto the continental crust.

And the eastern argillite belt could actually be these shelf edge

to abysal sediments (figure ). In fact, the "Cretaceous or

early Eocene" corals found in the conglomerate bed intercalated

—i the lower part of the slate sequence in northeastern Taiwan

(Ho, 1982) could very well be steep reef corals on the edge of

the shelf that were plucked off by flow loaded with sediments.

Judging from (1) the positions of the Miocene volcanic complex in

the Coastal Range and the offshore Miocene andesitic islands as

well as the undersea ridge that connects these points, and (2)

the existence of a dipping seismic zone under these islands, the

collision of the island arc with the continental shelf started

in the northern portion of the Longitudinal Valley and the

collission in the southern half of the Coastal Range has not yet

come into full force. Thus we expect that Lutao and Lanhsu to

converge onto the eastern coast of Taiwan in the future.

Because of the oblique orientation of the continental shelf with

respect to the approaching island arc, there is a distinctive

difference between northern and southern Taiwan. In terms of the

metamorphosed paleogene sedimentary rocks, in the northern part

of the island we find shelf facies rocks, alternating sandstone

and shale strata with carbonaceous layers, in the southern part

we find deeper water facies, fine grained shale with marly

nodules. Also, the Eocene slates appear only on the western side

of the Paleozoic/Mesozoic metamorphic rocks in the northern half,

a long strip can be found on the eastern side of the metamorphics

in the south. In other words, projecting into the future, one

could expect the further convergence of the rest of the island

arc, now marked by the positions of Lutao and Larhsu, and the

southern portion of Taiwan.

Conclusions

Taiwan came into being because of a former island arc (the

current Coastal Range)

Under Luzon a similar "reversed Benioff zone" exists, but Luzon

does not have intense shortening — because there is nothing to

collide with.

The collision forces are so intense nea: Taiwan that it is
transmitted to areas west of Taiwan. In the Taiwan Strait, there

are normal faulting perpendicular to the axis of Taiwan due ..o

tensile stress behind Taiwan perpendicular to the direction of

collision. Across the Taiwan Strait on the Fujian Province side

there are a number of nearly northwest oriented basins that

evidently started to subside at the time Taiwan rose out of the

water to become an island.

At present, the island of Taiwan represents a cross-section as

follows:

East of the Longitudinal Valley — Island arc and melange

complex.

West of the Valley -- trench sediments thrusted over the edge of

the old continental shelf (the Eocene argillites) and the

miogeosynclinal sediments on the former shelf.

References
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FAULTING IN SOUTHERN XINJIANG PROVINCE, CHINA

-- a Study based on LANDSAT ime, , es ---
The original figures are color false LANDSAT images. These have

been processed at the JPL Image Processing Laboratory by Joseph

Preisig, a graduate student in the Department of Geological

Sciences, at SUNY Binghamton, under the guidance of Dr. Alan

Gillespie. The numbers at ,-ached to each frame can be located on

the index map.

The geology along the fault is obtained by comparison with the

1:4,000,000 Geology Map of China (1976, Ministry of Geology of

People's Republic of China).

According to most Chinese geologists, the Altyn Tagh mountain

ranges represent the site of a Paleozoic collision. There are

many ultra-basic rock bodies on the Geology Map.

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Figure 1. (189 on the index map.) This frame is located at the

end of the Altyn Tagh fault, in the Province of Gansu. While

Altyn Tagn fault is evidently a strike-slip fault west of this

point (approximately at longitude 97 degrees E., the Qiliang

fault to the southeast is dominanatly a thrust fault, leading to

mountains with elevations reaching more than 5000 meters. The

main city in the area is Yumen. The Sule River comes from the

west into the frame AND fanned out before it becomes one and

crosses the fault. At the fault the river valley has a clear

left-lateral displacement, amount to about four to five

kilometers. The 1932 Changma (the name of a small town)

earthquake was located at the juncture of the Qiliang Mountains

and the Altyn Tagh fault (39.7 N, 97.0 E, M-7.5). There is no

evidence that the Altyn Tagh fault extends further to the

northeast, beyond 98 degrees or so. This implies that the

left-lateral motion is transformed into thrust motion here

resulting in mountain-building.

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Figure 2. (224 on the index map). The most impressive features

on this frame is the presence of prominant curvature along the

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fault trace. As a r_sult of the curvature, the Altyn Tagh, or

the Altyn Mountain 'the name sake of the fault) rises to a height

of 5792 meters as result of the presence of a curvature at this

point in such a way that the left lateral motion results in 1

compression in the NE-SW direction. The Altyn Tagh is capped by

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ultrabasic bodies according to the Geology 4ap of China. {

The southeast corner of the frame is still dominat.c by the

Qilian Range. The Range is comp osed mainly of Paleozoic

sedimentary rocks.

To the southwest, it is a part of the Qaidam Basin. It has an

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average elevation of 2500 m or so, somewhat higher than the Tarim

Basin to the west-northwest. It is considered to be a "rigid

block" in the Chinese literature. It is interesting that -._file

the Altyn Tagh fault in contact with the northwestern boundary f ,

this fault is fairly straight, the segment at the northeaast

corner of this block is curved, perhaps consonant with the idea

that Qa i dam behives like a block in the overall deformation of

the region.

To the northeast corner of the frame is a Paleozoic stratus. that

is of common occurrence along the fault. 4owever it is very

remarka r le that this stratum for a distance of about 300 km

appears only on the south side of the fault. See discussions on

Fig. 3.

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Figure 3. (223 on the index map). Remarkable dragging of the

strata can be seen here (as indicated by . lines). The sense

of the dragging is consistent with the left-lateral displacement.

The Pzl starata appear first on the northern side of the fault.

It shows severe dragging. If this is correlatable with the Pzl

strata south of the fault in Figure 2, then the total

left-lateral displacement of the fault amounts to about 250 km.

Although there are strata marked as Pzl on the Geology of China

Map, which are identified in the LANDSAT image, the northern and

southern units are evidently not continuous.

There are a number of other faults and faulted blocks in this

frame. In particular, on the northern side of the fault, near

' the middle of the figure.

The southwestern corner of the frame where the Neogene strata

i appears marks the w-stern termination of the Qaidam Basin.

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Figure 4. (222 and 221) Faulting is becoming much more complex

here than in Figure 3. The Altyn Tagh fault in the eastern

portion of this figure is straddled by a granite body. Faulting

seems to spread over a width of about seventy kilometers.

Envidence to the north of the main fault is abundant. There are

several rhomboidal basins created as a result of curvature in

faults (2) and (3). The Altyn Tagh fault itself has a probably

younger branch to the north of the granitic body; although it is

clearly marked where it crosses the young alluvial features, the

offset is not very large. Going further west this seems to be

the branch that is linked to the main branch that is

geomorphically very prominant. The southern branch (1') merges

into the same fault but the not so clearly. Futher to the west

(Fig. 4b), the fault gets into another prominant bend, in such a

way that the left-lateral motion results in compression and

hence the snow-capped mountains peaking at 5810 m.
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Figure 5. (255) There are clearly several branches of Altyn Tagh

fault in this figure. The high peak along the fault at 6295 m is

again associated with a bend in the fault and the rock on the

northern side of the fault is granite and in the south Jurassic

rocks. South of the fault there are a number of high mountains

(the Mubayen Mtns, for example), and they are mostly associated

with granitic intrusives.

It is interesting that the unit marked J1-2 is a Jurrssic unit

that is clearly marked on the Geology Map and is very easy to

distinguish on the UNDSAT image.

On the northern side of the fault in the Sinian strata there are

a number of instrusive bodies and several ultra-basic bodies.

These usually appear as mountains. The northern edge of this

block is also a fault. See Fig. 6 for more discussions.
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Figure 6. (254) This is the frame in which the recent nature of

the left-lateral motion of the Altyn fault is made certain. As

is clear in the lower left quadrant of the figure that several

river have very noticeable offsets.

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Figure 7. (253) In addition to the stream offsets across the

Altyn Tagh fault, the interesting phenomenon is the presence of a

major "asperity" in the fault. With the left-lateral motion

along the fault, this asperity seems to have caused tha opposite

side of the fault to bulge up and also leaves behind it a

rhomboidal basin. It can be surmised that the whole length of

the ridge on the north side of the fault was created as the

asperity moved northeastward.
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Figure 8. (284) Here the Altyn Tagh fault has broken into two

main branches, one following a northeast-southwest trend and the

other a nearly east-west trend. The former branches further

going southwest; here an extension basin was formed. As a result

of this extension, wide-spread basaltic flows and volcanoes are

found here. This is one of the few places in Tibet where recent

vol,-an:sm has taken place.

The northern branch is at the mountain-desert (Tarim) edge.

There evidence of recent left-lateral displacement is still

abundant.

The Carboniferous strata on the eastern side of the NE-SW

trending branch Seems to be very pliable; dragging is evident

(indicated again by the _ _ _ _. lines.)
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Figure 9. (283) The southeastern corner of the figure shows the

extensive basaltic volcanic field. The SW trending continues to

the southern edge of this figure. The Northern branch enter4

from tie northeast corner of the figure and shows many

left-laterally offset channels as indicated by the dashed lines.

IL: Starting from the middle of the figure however, there is a marked

change of trend; further west, the fault is WNW-ESE trending.

The fault scarp s become steeper and the movement is dominated by

thrust faulting. The mountains are also much higher; near the

lower edge of the figure, a peak stands at 6903.
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Figure 10. (250) Here we see the fault at the juncture between

the Tarim and the Tibetan Plateau. Toward the lower left, an

impressive closed fold system is seen. The core of this fold is

composed of Paleozoic rocks the flanks are however Cretaceous and

younger rocks. Several branches of the thrust faults are clearly

displayed. No left-lateral motion along the faults can be

discerned.

Along the WNW trending section the compression is probably the

strongest as the direction is slmost perpendicular to the

direction of impingement of Indian Plate. As a matter of fact

the compression is so strong that further to the north in the

middle of the Tarim desert the basement rocks have been folded

and probably faulted to poke through the sand; these structures

have the same trend as the faults shown in this figure. Along

the northern edge of the Tarim Basin are the Kepin mountains,

where impressive fold structures are seen.
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Figure 11. (248) In this frame we can again see the thrusting of

the Tarim near the edge of the dessert. The foothills are

underlain by Neogene to Quarternary sedimentary rocks. Because

of its proximity to the dessert, the area is covered by eolian

deposits and thus have very smooth topography. However, the

downward slopes have been cut by many WNW trending faults. Here

some of the stream offsets are created probably not by the

lateral movements of the faults but by the barriers they form in

front of the streams. The fact that these faults show clearly

through areas that are subjected to rapid eolian deposition

implies that the tectonic process is extremely active. The

deeply dissected valleys and very high altitudes the mountains

attain in the northern part of the Tibetan Plateau is a part of

the same process.
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Figure 12. (247) Continuation of the last frame to the west. The

mountain chain makes a dramatic turn to the northwest. The most

interesting observation in this frame is that faults striki._Q in

NWN directions have right-lateral stream offsets across them.

Thus we have cross from dominantly left-laterally strike-slip

faulting in the eastern section of the Altyn Tagh fault, to areas

where thrust faulting is the dominant mode of deformation and

here, in between the Tibetan Plateau to the east and the Pamirs

to the west, compressional structures and NWN striking

strike-slip faults are found to coexist.
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