poster - tectonic evolution taiwan 2010

7/29/2019 Poster - Tectonic Evolution Taiwan 2010

1/16

Workshop on

Tectonic

Evolutionof Taiwan

.

Sciences

Sinica

Conveners: Bor-ming Jahn & Tzen-Fu Yui

[email protected]

[email protected]

Time: Friday, March 26, 2010

9:00 - 17:00

Venue: Institute of Earth

Academia

Agenda:

1. Review of existing models2. Geophysical constraints3. Petrological, geochemical

and age constraints4. New results from marine

and land studies5. Perspectives6. Cooperation opportunities7. Summary


2/16

Program and Abstracts

Workshop on

Tectonic Evolution of Taiwan

26 March, 2010

Institute of Earth Sciences

Academia Sinica


3/16

09:00-09:15 Registration

09:15-09:30 Welcome

09:30-10:00 Louis S. Teng - Deformation and Exhumation of the Taiwan Orogenic Wedge:

10:00-10:30 John Suppe - Deep and Shallow Structure of the Taiwan Arc-Continent Collisi10:30-11:00 Char-Shine Liu - Seismic Imaging of the Tectonic Features Offshore Taiwan: A

11:00-11:30 Coffee Break

11:30-12:00 Cheng-Horng Lin - Continental Subduction and Active Crustal Exhumation in

12:00-12:30 Francis T. Wu - Recent Results of Geophysical Imaging of Taiwan and Implica

12:30-14:00 Lunch

14:00-14:30 Chia-Yu Lu - The Paradox of an Ocean-dipping Benioff Zone - Example from

14:30-15:00 J. Bruce H. Shyu - A Tale of Two Sutures: An Alternative Point of View on the

15:00-15:30 Borming Jahn - The Crustal Development of Taiwan in the Late-Paleozoic to

the Tectonic Evolution of Taiwan

15:30-16:00 Coffee Break

16:00-17:00 Discussion


4/16

The Crustal Development of Taiwan in the Late-Paleozoic to Early Cenozoic:

Implications for the Tectonic Evolution of Taiwan

Bor-ming Jahn

Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan

The purpose of this communication is to address the problem of crustal and

tectonic evolution of Taiwan, particularly the earliest crustal development of Taiwan

in the Permo-Triassic time.

The oldest rocks of Taiwan occur in the Tananao Metamorphic Complex, and

are composed of a thick marble sequence and associated metasedimentary rocks

including greenschist, blackschist, metachert, and metasandstone. The still older

basement rocks underlying the oldest rocks are not exposed but they could be

hypothesized to have Proterozoic ages as inferred from the geology of SE China. It is

important to agree for further discussion that the crustal development of Taiwan began

with the deposition of the oldest rocks occurring in the Tananao Complex.

The time of the oldest geologic event of Taiwan has been established by Sr-Pb

isotopic dating of carbonate rocks from (1) Tailuko of the Tananao Complex in

eastern Taiwan, and (2) Chia-Li Well No. 1 of Peikang High in western Taiwan. Sr

isotope analyses of marbles from both localities yielded a nearly identical range of87

Sr/

86

Sr ratios (0.7069 to 0.7078), and the lower limit of the ratios (0.7069) was takento determine an age of about 250 Ma for the time of carbonate deposition (Jahn et al.,

1984, 1992). In fact, the Sr isotope age data is consistent with the inferred late

Permian age by Yen et al. (1951) based on the fusulinid fauna of the Cathaysina

affinity. This period coincided with the most spectacular mass extinction and volcanic

eruption (Siberian Trap and Emeishan Basalt LIPs)

On the other hand, Pb isotope analyses on the Chia-Li marbles gave a Pb-Pb

isochron age of 242 22 (2) Ma, with 1 = 8.33 (Jahn et al., 1992); and on the

Tailuko marbles an age of 193 15 Ma (2) Ma with 1 = 8.29, updaded with

additional data from the earlier published age data of 166 33 Ma (Jahn, 1988). The

Pb-Pb isochron ages of recrystallized carbonates constrain the times of the early

Mesozoic thermal (metamorphic) events at 240 and 190 Ma. In fact, the 190 Ma event

has been identified by a zircon dating of a granite stock occurring in the southern part

of the Tailuko Belt of the Tananao Complex (Yui et al., 2009).

The Chia-Li marbles from western Taiwan and the Tailuko marbles from eastern

Taiwan share the same geochemical and Sr-Pb-C-O isotopic characteristics.

Consequently, it is reasonable to suggest that the two carbonate sequences were

formed coevally in late Permian, in the same depositional environment, and


5/16

underwent similar processes of C-O re-equilibrium and U-Th fractionation. This, in

turn, suggests a widespread carbonate deposition in a vast epeiric platform, and in a

warm climatic condition. It is well documented that the lithofacies of late Permian to

early Triassic (Changxing Stage) in SE China is dominated by carbonate rocks (Wang,

1985, 1986). Consequently, it is highly probable that the carbonate deposits of Taiwan

were a part of the vast expanse of the Permo-Triassic carbonate formations in SE

China.

The oldest rocks of Taiwan were intruded by Cretaceous granitoid plutons at

about 90 Ma. The granitoids were emplaced in the same period as the numerous

granitic plutons occurring in the coastal areas of SE China. Besides, in terms of

chemical and Sr-Nd isotopic compositions, the granitic rocks (granitic gneisses

included) of Taiwan are indistinguishable from that of the coastal areas of Fujian and

Guangdong. Such similarity in age and composition is not expected for the granitoid

suites separated by 350 km (perpendicular to the subduction axis) if they were

generated in the same subduction system.

The occurrences of late Permian carbonates and Cretaceous granitoids in Taiwan

could be best interpreted in a tectonic framework in which the proto-Taiwan was

initially formed as the southern extension of the South China Craton. The Tailuko Belt

could be correlated with the Gunanhai Melange, as suggested by Hs et al. (1990), in

coastal Fujian, where metamorphosed oceanic crust (= amphibolite, greenschists) and

pelagic sediments (= black schists) also occur. A crustal segment (proto-Taiwan),composed of a carbonate sequence, mlange deposits and granitic intrusions, was then

translated northeastward to the present position by a sinistral strike-slip fault. The

process must have taken place after the emplacement of the Cretaceous granites, and

more likely after the generation of andesitic rocks in Huayu (Penghu Islands) in early

Cenozoic or Paleocene (65 60 Ma; Chen et al., 2007).

The tectonic scenario has been supported by two recent works. First, based on the

extensive measurement of monazite Th-Pb ages (ca. 5000; by EPMA) for Tertiary and

Quaternary sandstones in Taiwan and Recent sands from six drainage basins in eastern

China and South Korea, Yokoyama et al. (2007) concluded that the sediments of the

Hsueshan Range (Eocene) were derived from the drainage basin of Zhujiang

(Guangdong). Second, the zircon dating (by LA-ICP-MS) of andesites from Huayu

yielded a magmatic event at 65-60 Ma. Chen et al. (2007) interpreted these rocks as

the surface exposure of a magmatic belt reflected by the high magnetic anomalies.

These ages support the idea that this magmatic belt was a continuation of the SCMB

(Southeast Coast Magmatic Belt) in origin, but offset or split apart by a left-lateral

fault.

The proposed tectonic evolution of Mesozoic Taiwan (Jahn et al., 1992; this work)


6/16

could be better appreciated if it is to be compared with that of the Japanese Islands

(Maruyama et al., 1977; Sengor and Natalin, 1996). The late Paleozoic to Mesozoic

accretionary complexes of Japan are composed, in significant proportion, of recycled

ancient (Proterozoic) continental crust, probably of the Yantse craton. The bulk

composition of Japan, as inferred from Sr-Nd isotopic data, is quite similar to that of

Taiwan and of the crustal segments in SE China, but is vastly different from that of

the Central Asian Orogenic Belt (= the Altaids) or the Arabian-Nubian Shield.

In conclusion, the crustal history of Taiwan began in the late Permian. The

proto-Taiwan was initially formed as the southern extension of SE China. It

underwent at least two periods of thermal events at ca. 190 Ma and ca. 90 Ma.

Metamorphic recrystallization and associated crustal deformation would have

occurred prior to the large-scale strike-slip faulting. In this scenario, the

metamorphism and deformation of the Tananao Complex was unrelated to the late

Cenozoic arc-continent collision as incorrectly envisaged by many existing tectonic

models. However, the collision event is expected to accentuate the deformation and

uplift of the Central Range.


7/16

Continental Subduction and Active Crustal Exhumation in Central Taiwan

Cheng-Horng Lin

Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan

Abstract

The island of Taiwan is located at one part of the convergence zones between the

Eurasian Plate (EUP) and the Philippine Sea Plate (PSP). To the northeast of Taiwan,

the PSP subducts beneath the EUP while the EUP underthrusts the PSP to the south.

However, the strong convergence behavior between the two plates in central Taiwan

has long remained unclear due to the absence of reliable deep structures image in the

past. Recently, several different seismic observations show that the EUP has beensubducted beneath Central Taiwan (Chen et al., 2004; Wang et al., 2006; Lin, 2009).

Although there is no earthquake to show the Wadati-Benioff zone in the Central

Taiwan between the Latitudes of 23oN and 24

oN, the eastward subduction of velocity

anomalies has been consistently imaged from seismological data. Such a result

provides an important evidence to examine all of the proposed models in the past.

Among them, the tectonic model of Continental Subduction and Active Crustal

Exhumation proposed by Lin et al., (1998) and Lin (2002) might be one of the

suitable models to explain the tectonic mechanism for Taiwan Orogeny.


8/16

Seismic Imaging of the Tectonic Features Offshore Taiwan: An Overview

Char-Shine Liu

Institute of Oceanography, National Taiwan University, Taipei, Taiwan

Situated at the juncture of two flipped subduction systems, morpho-structural

features observed on land and offshore Taiwan shed lights on the tectonic processes of

an arc-continent collision (the Luzon subduction system) off southern Taiwan and the

Ryukyu subduction-collision system off eastern Taiwan. Multichannel seismic

reflection profiles have revealed structural and sedimentary characters of the upper

crust in the past two decades, deep seismic reflection profiles collected during the

1995 TAICRUST and 2009 TAIGER surveys help to image the structures of the deep

crust. This paper presents an overview of the morpho-tectonic features offshore

southern and eastern Taiwan as imaged by seismic reflection profiles.

The area offshore southern Taiwan is the place where the Luzon subduction

complex transforms into an incipient arc-continent collision complex near Taiwan.

Morphologically, the subduction complex shows a classic trench (Manila Trench) -

accretionary wedge (Hengchun Ridge) - forearc basin (North Luzon Trough) -

volcanic arc (Luzon Arc) system north of the Luzon Island. The accretionary wedge

expanded toward north, the forearc basin was closed north of 21.5oN offshore SE

Taiwan while the frontal portion of the accretionary wedge encroached on the passive

China continental margin off SW Taiwan. A prominent out-of-sequence thrust was

developed that divides the accretionary wedge into an upper slope domain and a lower

slope domain. The closure of the forearc basin near Taiwan has been attributed to the

development of a back thrust system along the rare side of the accretionary wedge.

However, strike-slip faulting and block rotation due to oblique arc-continent collision

also played significant roles in creating the present morphology off SE Taiwan. At the

frontal portion of the accretionary wedge, folds and thrusts are the prominent

structural features in the lower slope domain. The distances between the

fault-bend-folds increase north of 21.5oN, the sediment thickness also increases

northward, from about 1000 m thick at 20.5oN to about 4000 m thick at 21.5

oN. The

upper slope domain consists of highly deformed accretionary wedge material that was

uplifted probably due to under-plating processes. The deep seismic images from the

TAIGER survey have shown that there are some west-dipping deep reflections,


9/16

interpreted as Moho reflections, lie underneath the thick accretionary wedge material

offshore SW Taiwan, suggesting thickening of the crust toward China continental

margin.

The Ryukyu forearc region offshore eastern Taiwan is the area where the Ryukyusubduction zone terminates against the Taiwan island. Extremely active seismicity

with frequently occurred large earthquakes (M > 6.5) makes this area a potential

earthquake hazard zone. Morphotectonic features of this trench-accretionary

wedge-forearc region have been studied quite extensively, but deep structures of the

seismogenic zone are still unclear. Based on the different structural styles, the

southernmost section of the Ryukyu arc-trench system can be divided into three zones.

The first zone lies to the east of 123oE. It presents structures of a typical oblique

subduction zone with frontal accretion of trench sediments, imbricated thrusts and

folds in the accretionary wedge (the Yaeyama Ridge), and slightly folded forearc

basin strata. A prominent right-lateral strike-slip fault has developed at the rear of the

accretionary wedge which accounts for, at least particially, the lateral component of

the oblique plate convergence. The second zone lies between 123oE and 122o10E.

The active frontal accretion may have ceased, and strong shearing is observed in the

accretionary wedge. The forearc basin here (the Nanao Basin) undergoes

trench-parallel tension, as demonstrated by series of normal faults that cut through

very thick (up to 4 s twt) basin strata. Between zone 1 and zone 2 at 123oE, a

subducted asperity, the Gagua Ridge, has uplifted the basement of the forearc basin,

and created a prominent reentrant at the frontal portion of the accretionary wedge. The

third zone lies to the west of 122o10E where the Ryukyu subduction system is

terminated by the Luzon volcanic arc and the Taiwan mountain belt. Series of NW-SE

trending shear faults cut through the thrusted and folded ridges in the accretionary

wedge. A NW-SE trending forearc basin (the Hoping Basin) lies between the

accretionary wedge and the Ryukyu arc. Seismic reflection profiles show that

underneath the young Hoping Basin strata, there is a thick (up to 3 s twt) old

sedimentary layer (the Suao basin strata) lies above the Ryukyu arc basement. ThisSuao basin strata are tilted but otherwise little deformed in the northern Hoping Basin,

however, in the southern Hoping Basin, they are highly folded and probably thrusted

in a SW direction. The Hoping Basin strata display mainly submarine depositional

and erosional structures, such as channel cut and fill and slumping deposits. The

structures in the studied forearc region are mainly controlled by the high obliquity of

convergence between the Philippine Sea and Eurasia plates, and by the collision of the

Luzon arc with the Eurasia continental margin that terminates the Ryukyu subduction

system to the west. Furthermore, the subduction of asperities and active submarinesedimentary processes have also played important roles in shaping the structures of


10/16

the accretionary wedge and forearc basins here.


11/16

The Paradox of an Ocean-dipping Benioff Zone - Example from Taiwan

Chia-Yu Lu

Institute of Geosciences, National Taiwan University, Taipei, Taiwan

In Taiwan, the Paleozoic/ Mesozoic basement is regarded as a rifted continental

margin by back-arc spreading from the southeastern coast of the China mainland. The

Backbone Range Slate Belt is interpreted as a part of the Miocene accretionary wedge.

The Lishan Fault is referred to as the suture between the Philippine Sea plate and the

Eurasia. Following the concept of tectonic facies in an archipelago model of intraplate

orogenesis, a back-arc basin collapse orogenesis model is proposed to interpret the

ocean-dipping Benioff zone of Taiwan. The back-arc basin collapse orogenesis model

explains the mechanism, which transforms continental-dipping into oceanic-dipping

Benioff zone as well as oceanic subduction into continental subduction.


12/16

A Tale of Two Sutures: An Alternative Point of View on the Tectonic Evolution of

Taiwan

J. Bruce H. Shyu

Institute of Geosciences, National Taiwan University, Taipei, Taiwan

Taiwans numerous active faults and folds demarcate distinct eastern and western

neotectonic belts. The western belt results from the attachment and subsequent

detachment of a sliver of continental lithosphere to the Eurasian continental margin.

The eastern belt is the product of the same continental sliver docking with and then

separating from the Luzon volcanic arc. Thus, the active Taiwan orogen can be

viewed as a tandem suturing and tandem disengagement of a volcanic arc and a

continental sliver to and from the Eurasian continental margin. This progressive

suturing and separation is a superb, living demonstration of the fundamental weakness

of lithospheric sutures.


13/16

Deep and Shallow Structure of the Taiwan Arc-Continent Collision

John Suppe1, Yih-Min Wu

1, Sara Carena

2and Kamil Ustaszewski

3

1Department of Geosciences, National Taiwan University. Taipei, Taiwan

2Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universitt,

Luisenstr. 37, 80333 Mnchen, Germany3Lithospheric Dynamics 3.1, GFZ Helmholtz Zentrum, D-14473 Potsdam, Germany

The on-going oblique arc-continent collision in Taiwan between the Luzon arc and

the Eurasian continental margin provides a classic spatial view of the temporal

evolution of the collision. In addition Taiwan is a well-known site of critical-taper

wedge mechanics and erosional forcing of deformation, leading to a mountain belt

that is approximately in topographic steady state, with erosion balancing the

compressive flux. This classic picture, based largely on surface and upper-crustal data,

is now being illuminated at lower crustal and upper mantle levels with high-resolution

local seismic tomography and earthquake locations. These new data document in 3D

that the deep structure is remarkably independent of the shallow thinned-skinned

mountain belt. Here we show that the lower crust and upper mantle of the Eurasian

plate undergoes a transition from normal subduction and accretionary-wedge tectonics

south of Taiwan to a strongly localized progressively bent geometry with a vertical to

overturned plate interface. The lower crust and Moho of the Eurasian plate is verticalto overturned to depths of 70-80 km under central and northern Taiwan. In this region

the deep plate shortening is accomplished by folding of both the Eurasian and

Philippine-Sea lower lithospheres without a classic active subduction zone, whereas

the crust of both plates above the main detachment is mechanically and kinematically

separated from this deep shortening.


14/16

Deformation and Exhumation of the Taiwan Orogenic Wedge:

A View from the East

Louis S. Teng1

and En-Chao Yeh2

1Institute of Geosciences, National Taiwan University, Taipei, Taiwan2Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan

The eastern Taiwan orogenic wedge comprises the Tananao Metamorphic

Complex (TMC) and overlying slate formations that represent the deepest-buried rock

suites ever exhumed during the late Cenozoic collisional orogeny. These rocks exhibit

a whole gamut of petrological and structural features that help unraveling the

deformation and exhumation history of the Taiwan mountain belt.

Before the collision took place in late Miocene, TMC was part of the

pre-Cenozoic basement of the outer China continental margin and the slate formations

were the sedimentary cover. During the collision, these rocks were first pulled into the

deep subduction zone, underplated into the orogenic wedge, stacked up by continued

underplating, and then exhumed and exposed by erosion. Compilation of petrological

data of TMC shows a clockwise P-T path with a maximum metamorphism of low- to

medium-greenschist facies. Field mapping and shear sense analyses indicate that

TMC and overlying slate formations have undergone an early-stage west-vergent,

left-lateral transpressional deformation followed by a late-stage east-vergentbackfolding and thrusting with minor normal faulting. Coupled with available

geochronological data, the metamorphic history of the eastern Taiwan orogenic wedge

can be interpreted to reflect an early-stage wedge thickening and heating followed by

rapid uplift and exhumation around 3 Ma.

The orogenic history interpreted above can be further substantiated by the

sedimentary records of the northern Coastal Range where a complete Luzon forearc

basin sequence is exposed. The dominance of arc-derived andesitic fragments in the

Miocene lower forearc sequence shows that the thickening orogenic wedge had

remained submerged and was not uplifted as a hilly terrane until 5 Ma. Afterwards the

wedge rapidly grew to a high mountain chain that supplied an increasing amount of

sediment to the forearc basin, as shown by the coarse-grained orogenic detritus in the

Plio-Pleistocene upper forearc sequence. The successive appearances of slate and

schist fragments in the forearc sequence indicate that the slate formations and TMC

were consecutively exhumed to the surface at 3 and 0.4 Ma.


15/16

Recent Results of Geophysical Imaging of Taiwan and Implications

Francis T. Wu1, Kuo-Chen, Hao

1and Taiwan TAIGER teams

1SUNY Binghamton, US

Based on recently derived subsurface structures we can distinguish clearly the

collision/subduction characteristics between northern (north of ~23.7ON), central

(between ~23ON and ~23.7

ON) and southern (south of ~23

ON). In central Taiwan full

collision is taking place, with distinctive lower crust and upper mantle structures

suggesting arrested subduction. Northern Taiwan is subjected to collision of a

subducting indenter, with diminishing collision toward the north as subduction

deepens. In the south, active subduction is taking place. Do all these subsurface

processes have corresponding identifiable surface structures? Certainly the northern

Taiwan bight (bend) has long been associated with the geometry of the subduction

zone. Simple elastic models indicate that the recent deformation of northern Taiwan

agree with that of subducting indenter. However, one of the most puzzling features is

the boundary around 23ON, between the well-defined subduction and the collision

zone; although the subsurface feature is clear, in terms of deep seismicity, the overall

plate tectonic environment, GPS measurements etc., a geological boundary has not

been identified.

One of the properties that the Taiwan orogen clearly shares with mountain rangesof the world is the pattern of S-wave splitting. As is true with South Island, New

Zealand, Tibet, Tienshan etc., the fast direction of the S waves are parallel to the

structural trend the delay times between the fast and slow S-waves are around 2

seconds. The source of these splits is usually ascribed to be anisotropy owing to the

lattice-preferred-orientation of minerals. LPO can occur as a result of shearing or of

flow. Although, the metamorphic rocks in the eastern Central Range is highly foliated

and isotropic the measured crustal delay time has a maximum of about 0.3 seconds.,

so the source for S-splitting must reside in the upper mantle, down to 200-300

kilometers. No precise way is currently available to invert the S-splitting

measurements for 3-D anisotropy. We do have limited information in Taiwan of how

extensive the anisotropic zone is perpendicular to strike by using scant broadband

OBS data to the east and using pattern of S-split delays across Taiwan for data from

the eastern and western back-azimuths, it is mainly limited to Taiwan.

Intriguing magnetotelluric profiles across Taiwan obtained recently show a feature

that could perhaps be explored in terms of dehydration in metamorphism, strength of

foliated rocks etc. Both profiles in Central Taiwan (~24ON) and southern Taiwan

(Southern Cross-Island highway) show a remarkable (vertical) high resistivity zone


16/16

(>500 -m). It is bordered by a low resistivity zone to the west, generally under the

Lishan fault. The Eastern Central Range is undergoing the most rapid uplift (Ching et

al., 2010, personal communication; Hu et al., 2010, personal communication). The

expectation is that water would be needed to facilitate deformation. But high

resistivity implies that, 1) water may be present in significant quantity but they are not

connected, then the effective pressure effect would not operate, or 2) the water has

been expelled during metamorphism (Ferry, 1994) and the foliated rocks are weak.

Understanding the metamorphism, deformation and erosion in the Central Range will

advance the knowledge of Taiwan orogeny.

Orogeny involves complex processes. Taiwan orogen, being compact and variable,

remains to be one of the best locations for further data acquisition, modeling and

testing for the basic processes of mountain building.

poster - tectonic evolution taiwan 2010

Documents