Taiwan deformat.pdf

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Tectonophysics 466 (2009) 395 – 408

www.elsevier.com/locate/tecto

Polyphase deformation in a newly emerged accretionary prism: Folding,

faulting and rotation in the southern Taiwan mountain range

Chung-Pai Chang a,b,

⁎ , Jacques Angelier c , Chia-Yu Lu d

a Center for Space and Remote Sensing Research, National Central University, Chungli, Taiwan

b Department of Earth Sciences and Institute of Geophysics, National Central University, Chungli, Taiwan

c Observatoire Océanologique de Villefrance-Géosciences Azur, Université Pierre-et-Marie-Curie, Villefrance/Mer, France

d Department of Geosciences, National Taiwan University, Taipei, Taiwan

Available online 17 November 2007

Abstract

In Taiwan, the oblique late Cenozoic collision of the Eurasian Plate with the Luzon arc provides an opportunity to observe the development of

arc – continent collision. However, analyses of tectonic structures demonstrate that a simple ESE – WNW compression, as induced by the arc –

continent collision, fails to explain all aspects of the Taiwan Mountain building processes. This is the case for the rapid uplift and exhumation of

the metamorphic rocks, the east – west trending fold-and-thrust systems in southeastern Taiwan, the tectonic rotation of the Hengchun peninsula,

the escape phenomenon in the Ilan and Pingtung Plains, which are difficult to interpret using a “ simple collision mechanism ” . In this paper we

focus on the structural record of southern Taiwan mountain range, in order to clarify the process of deformation in the growing accretionary prism.

In view of geological stratigraphy, the southern Taiwan is underlain by thick series of Miocene deposits, including dark gray argillites, flysch

deposits with occasional interbeds of gray compact sandstone and disseminated marly nodules. Field works have been done to reconstruct the

main tectonic paleostress and deformation events of this region. Polyphase brittle and fold structures are largely distributed in this area, which

allows us to determine the tectonic history in terms of nature, direction, importance and relative chronology of the main deformation events of the

Late Cenozoic. These results provide an important key to reconstruct the in situ geotectonic history of the southern Taiwan region, which can be

discussed in terms of four main stages. The stage 0 corresponds to the Early to Middle Miocene time, with WNW – ESE extension. The stage I

corresponds to the Late Miocene to Pliocene time, when the study area were incorporated into the accretionary prism by west-verging thrust faults.

The stage II is Pliocene in age, with continuing compression between the volcanic arc and the continental margin producing series of east-verging

backthrusts. During the Plio-Pleistocene time, arc – continent collision occurred in Taiwan, as stage III in our study area, which produced

conspicuous transpressional structures in the southern Central Range. A new mountain building model, involving limited counterclockwise

rotation in the transition zone between incipient collision and mature collision, is also proposed to explain the recent deformation mechanism of

the southern Taiwan range.

Keywords: Polyphase deformation; Accretionary prism; Southern Taiwan

1. Introduction

Northern Luzon Arc and the Chinese continental margin has

been estimated as 8.2 cm/yr in the N54°W direction ( Yu et al.,

1997 ), the original trend of the Northern Luzon Arc is N10°W

and the Chinese continental margin trends about N60°E.

Because of this oblique geometry, the arc

The Taiwan mountain belt, located at the boundary between

the Philippine Sea plate and the Eurasian Plate, is a product of

arc

continental collision

and the mountain belt of Taiwan propagate southward ( Suppe,

1984 ). This provides a good opportunity for Earth Scientists to

study the structural evolution by moving from north to south

along the Taiwan mountain belt.

As a newly emerged accretionary prism, the southernmost

Central Range provides exceptional opportunity to study the

–

⁎ Corresponding author. Center for Space and Remote Sensing Research,

National Central University, Jungli 320, Taoyuan, Taiwan.

E-mail address: cpchang@csrsr.ncu.edu.tw (C.-P. Chang).

doi: 10.1016/j.tecto.2007.11.002

continent collision ( Chai, 1972; Biq, 1973; Bowin et al.,

1978 ) and is one of the most active and youngest mountain belts

on the Earth ( Fig. 1 ). The convergent velocity between the

–

396

C.-P. Chang et al. / Tectonophysics 466 (2009) 395 – 408

Fig. 1. On left: Tectonic framework of the Taiwan collision belt between the Eurasian continent and the Philippine Sea plate. Large black arrow shows convergence

between the volcanic arc and the continental margin ( Yu et al., 1997 ). On right: Major stratigraphic units of the Taiwan island. The study area of this paper is shown as a

small rectangular frame ( Fig. 2 ).

early history of the Taiwan orogeny. In this paper, we take

advantage of this situation to carry out detailed field study in the

emerged area. We mainly focus on the polyphase folding and

faulting of this area, in order to clarify the structural evolution

in the oblique growing mountain belt. Moreover, through a

systematic back-tilting restoration, the original orientations of

paleostress could be recognised. Except for the dominant E

SSW,

especially in the Hengchun peninsula south of Fongkang

( Fig. 2 ), and submerges as the Hengchun Ridge at about

21°21

–

S instead of NNE

–

. This segment can be regarded as the proto-Taiwan

accretionary prism.

Before presenting our tectonic investigation, the stratigraphy

of the southern Central Range deserves examination ( Fig. 2 ).

The Late Miocene turbidite sequences, as the so-called Mutan

Formation, crop out in the southernmost portion of this range

( Sung, 1991; Chang et al., 2003 ). The Mutan Formations is

composed of alternated sandstones and shales, with numerous

lenticular bodies of sandstone and conglomerates at variety of

scales. These lenticular bodies represent typical deposits of

submarine channels or canyons and deep sea fans from the

continental slope to the base of the slope ( Pelletier and Stephan,

1986; Sung, 1991 ). Sedimentological analyses of pebbles and

lithic fragments revealed low-grade metamorphism, suggesting

that the Mutan Formation may be derived from the rifted Asian

continent margin to the northwest ( Page and Lan, 1983 ). Until

now, no evidence has been found to support that sediments

came from the Taiwan mountain belt; it is thus reasonable to

believe that this formation is pre-tectonic.

North of the Hengchun peninsula, the southern Central Range

shows large outcrops of thick series of Miocene to Pliocene

accretionary wedge deposits. These deposits contribute the

trending compressional stress related to the direction of arc

–

S trending transpressional stress is

also largely distributed in this area, which is an important key to

reconstruct in situ the geotectonic history. We finally propose a

new mountain building model to explain the recent deformation

mechanism in the southern Taiwan Island.

–

2. General geological setting

The Taiwan island consists of five morphotectonic units,

which are from west to east the Coastal Plain, Western Foothills,

Hsüeshan Range, Central Range and Coastal Range ( Fig. 1 ).

From the tectonic point of view, the former four units belong

to the emerged accretionary prism; the latter unit belongs to

the collided volcanic arc; between these two groups, the

Longitudinal Valley is the most obvious onshore plate boundary

between the Eurasian plate and the Philippine Sea plate

( Tsai, 1986; Ho, 1986 ). West of this boundary, the general

morphology of the NNE

–

SSW trending Central Range

gradually descends and anticlockwise rotates southward. Fur-

ther south, this range thus trends N

′

continental collision, the N

C.-P. Chang et al. / Tectonophysics 466 (2009) 395 – 408

397

Fig. 2. General geological map of the southern Central Range (original data after Central Geological Survey). Location of Figs. 3, 4, 5, 7 are indicated. Main

stratigraphic formations indicated. Topography clearly shows the well-aligned en-échelon structure pattern in the eastern flank of the Central Range.

pumpel-

lyite to lower greenschist facies during the Taiwan mountain

building processes ( Chen et al., 1983 ) ; they exhibit intense layer

parallel shearing with or without slaty cleavage ( Pelletier and

Hu, 1984 ). Because at this latitude the Northern Luzon arc is still

located at a large distance east of our study area, these strata have

probably been exposed and exhumed before the mature arc

a limited area and do not play an important role in reconstructing

the regional tectonic history since the late Miocene time, they

will not be discussed in this paper.

From the point of view of stratigraphy, the main formations

of the southern Central Range are composed of metasediments

that belonged to a very thick deep sea fan sequence. The clastic

material was transported and deposited in the continental slope

and ocean basin by turbidity currents ( Hu and Tsan, 1984 ). On

the other hand, the structural geology records seem complex

( Fisher et al., 2002 ), giving rise to apparently contradictory

observations. In this paper, we show that this complexity re-

sults from polyphase evolution, not from chaotic structure. For

instance, the topography of the study area shows an intriguing

pattern of ENE trending en-échelon ridges and valleys ( Fig. 2 ),

–

continental collision ( Fig. 1 ). To the north, the metamorphic

rocks, including the Eocene metasandstone and the Mesozoic

schist and marble, are distributed in elongated, belt parallel

zones. Because the high-grade metamorphic formations occupy

Chaochu and Lushan Formations, including dark gray argillites,

and flysch deposits with occasional interbeds of gray compact

sandstone and disseminated marly nodules ( Hu et al., 1981 ).

These strata were metamorphosed under the prehnite

–

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C.-P. Chang et al. / Tectonophysics 466 (2009) 395 – 408

which in fact is related to large regional structures (faults

and folds). This topographic pattern and structures are unusual

in southern Taiwan, where most major structures trend ap-

proximately N

3. Monophase and polyphase structures

S. The presence of such contrasting struc-

tural grains reveals a polyphase tectonic history of folding and

faulting.

–

The general structural geological map and profiles of the

western flank of the southern Central Range are shown in Fig. 3 .

As could be expected on the west flank of the Taiwan belt, most

faults and folds are west-verging. This N

–

S trending structural

Fig. 3. General geological map and cross-sections of the eastern flank of the western Central Range. The N – S trending structural pattern suggests that most of the

deformation resulted from an E – W directed compressional tectonic regime during the period of tectonic uplift. Stereoplots involve lower hemisphere, equal area

projection. Location in Fig. 2 . Fault slip data analysis in Fig. 10 .

C.-P. Chang et al. / Tectonophysics 466 (2009) 395 – 408

399

pattern of this area suggests that most of the deformation result

from an E

hereafter. However, some structural evidences of polyphase

tectonism are present, such as the eastern verging backthrusts,

the western dipping cleavages and the E

–

W striking strata (the

Fig. 4. General geological map and cross-sections of the eastern flank of the southern Central Range. Location in Fig. 2 . Fault slip data analysis in Fig. 10 .

W directed compressional tectonic regime during the

period of tectonic uplift, which we name deformation Phase 1

–

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