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Journal of the Geological Society, London, Vol. 161, 2004, pp. 799812. Printed in Great Britain.

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Nested strike-slip duplexes, and other evidence for Late CretaceousPalaeogene

transpressional tectonics before and during IndiaEurasia collision, in Thailand,

Myanmar and Malaysia

C . K . M O R L E YDepartment of Petroleum Geosciences, Universiti Brunei Darussalam, Tunku Link, Bandar Seri Begawan,

Brunei Darussalam (e-mail: [email protected])

Abstract: The Late CretaceousPalaeogene structural and tectonic events in the northern region of Sundaland

represent a poorly known, but potentially important orogenic development in SE Asia. Extensive Late

Cretaceous S-type granites extending from Malaysia through Thailand to Myanmar have long been used to

infer an episode of crustal thickening, an inference supported by the presence of late Cretaceous Eocene

ophiolites in Myanmar. However, structural evidence for a well-developed associated fold and thrust belt has

been lacking. Apatite and zircon fission-track studies of Thailand indicate a broad regional uplift from about

80 Ma to 40 Ma, suggesting an episode of crustal thickening, but the uplift amount is modest, and not that

expected for a major fold and thrust belt. Left lateral motion on major NWSE-trending strike-slip fault zones

(Mae Ping and Three Pagodas faults) in Myanmar and Thailand has been attributed to HimalayanTibetan

escape tectonics. This paper demonstrates that the fault zones are considerably more complicated than just

NW SE trends. They are a network of branching faults with important north south trends as well as NW SEtrends, they form large-scale, nested strike-slip duplex structures and affect a region over 1000 km long and

up to 250 km wide. This diffuse, branching network of strike-slip fault trends may represent a substantial Late

CretaceousPalaeogene transpressional belt. Himalayan escape tectonics represent later increments of

deformation with both Oligocene sinistral and late OligoceneRecent dextral reactivation.

Keywords: Mae Ping, Indochina, transpression, duplexes, orogeny.

Major strike-slip faults radiate from the eastern corner of theHimalayan syntaxis. The first models to explain these faults

proposed that they underwent hundreds of kilometres ofdisplacement and permitted the lateral displacement (escape) oflarge crustal blocks away from the Himalayan collision zone

during the Tertiary (e.g. Tapponnier et al. 1986). Regionalmodels of strike-slip escape tectonics in SE Asia focused

particularly on the Red River Fault in Vietnam (e.g. Leloup etal. 1995, 2001; Wang et al. 2001; Replumaz & Tapponnier2003). The role of large-displacement, but essentially second-ary faults (Mae Ping, Three Pagodas) is regarded as lesscritical in plate reconstructions (e.g. Lee & Lawver 1995; Hall

1996, 2002) (Fig. 1). However, in one respect the Mae PingFault is critical to the escape tectonics model. The fault isused to link extrusion displacement with the NW BorneoPalawan trough in an attempt to avoid the necessity of

subducting proto South China Sea oceanic crust below Borneo(Leloup et al. 2001).

The other major strike-slip fault in the region is the north

south dextral Sagaing Fault, which has probably undergonebetween 150 and 300 km displacement from the Late Miocene toRecent (see review by Bertrand & Rangin 2003). This fault has

accommodated perhaps 6070% of the northwards motion ofIndia relative to Indochina (Bertrand & Rangin 2003). The MaePing and Three Pagodas faults are typically shown as single

NW SE-striking faults that meet the northsouth-striking Saga-ing Fault (Fig. 1). The nature of this meeting is problematic

because of both timing and sense of motion incompatibilities:the dextral Sagaing Fault is thought to be kinematically linked

with opening of the Andaman Sea (Late MioceneRecent; e.g.Curray et al. 1979; Hall 2002), whereas left lateral motion on the

Mae Ping and Three Pagodas faults ended in the late Oligocene(Lacassin et al. 1997; Morley 2002).

There is no record onshore of large-scale Palaeogene EarlyMiocene sinistral motion on the Sagaing Fault. The recordedmotion on the northsouth-trending Sagaing Fault is consistentlydextral (e.g. Curray et al. 1979; Hall 2002; Bertrand & Rangin

2003), whereas NESW-trending segments of the Three Pagodasand Mae Ping faults underwent sinistral motion until the late

Oligocene (Lacassin et al. 1997). A minimum of 300 km com-bined left lateral offset was estimated for the Mae Ping andThree Pagodas faults by Tapponnier et al. (1986) and Lacassin etal. (1993, 1997) from granite offsets and shear zone geometry in

Thailand. From the latest OligoceneEarly Miocene onwardsthese two fault zones have episodically undergone minor dextralmotion (Polachan et al. 1991; Morley 2002; Bertrand & Rangin2003).

Whereas the Late Miocene and younger dextral slip history ofthe Sagaing, Mae Ping and Three Pagodas faults is temporallyand kinematically compatible, the older history appears different

and raises two questions that have not been part of regionalmodels to date. (1) Did the Sagaing Fault zone have an older,sinistral history that can kinematically link it with the Palaeogeneleft lateral motions on the Mae Ping and Three Pagodas fault

zones? (2) If there is no kinematic link with the Sagaing Fault,just how was the estimated 300 km left lateral offset across the

Three Pagodas and Mae Ping faults in Thailand accommodatedfurther to the NW in Myanmar?

The critical area to answering these questions is the politicallysensitive region of the Karen in Myanmar; an area where

geological data are sparse (as reviewed by Mitchell et al. 2002).Hence existing data, data from adjacent areas in Thailand, and


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satellite images are the main sources of information that areavailable to answer these questions. The aims of this paper are:

(1) to demonstrate that the prior emphasis on the importantNW SE-striking segments of the Mae Ping Fault has ignored thesignificance of NNW SSE- to northsouth-trending segments;

(2) to propose a working model that unifies the entire Mae PingFault geometry (northsouth and NWSE segments) with recent

published and unpublished data on the timing of metamorphism

and uplift in Thailand. From these data it is suggested that theMae Ping and Three Pagodas faults form the main strands of amajor Late CretaceousPalaeogene transpressional orogenic belt.

Previous work that indicates Late Cretaceous Palaeogene

orogenic activity is presented first. Then the geometry and roleplayed by the Mae Ping and Three Pagodas faults in accommo-

dating orogenic strain is discussed and described. Understandingof this orogenic belt is at an early stage; consequently, thedifferent fragments of data are drawn together to present whatcan only be a tentative tectonic model for the belt.

Evidence for late CretaceousPalaeogene orogenicactivity

Similar to the Late PalaeozoicMesozoic history of the western

North American margin, the Jurassic and Cretaceous history ofthe Meso- and Ceno-Tethys south of Eurasia is thought to bemarked by small microplate collisions along the Eurasian margin(Charusiri et al. 1993;Metcalf 1998; Mitchell et al. 2002). One

of the last putative collisions occurred in the late Cretaceousbetween the West Burma Plate (which today lies west of theSagaing Fault) and the ShanThai block (e.g. Hutchison 1975,

1996; Zaw 1990; Charusiri et al. 1993; Mitchell 1993; Lee &Lawver 1995; Fig. 1).

One of the key pieces of evidence for the Late CretaceousPalaeogene continental collision between the Burma plate and

the ShanThai block is the extensive string of 9550 Ma, tin-bearing, high initial strontium ratio, S-type or ilmenite seriesgranites (with subordinate I-type) that are well documented from

western Thailand and Myanmar(Mitchell 1977; Beckinsale et al.1979; Cobbing et al. 1986, 1992; Darbyshire & Swainbank 1988;Mahawat et al. 1990; Zaw 1990; Nakapadungrat & Putthapiban

1992; Putthapiban 1992, 2002; Charusiri et al. 1993; Barley etal. 2003). S-type granites are thought to be mostly derived frommelting of sedimentary protoliths in continental crust as a resultof crustal thickening (as reviewed by Barbarin 1999), hence a

similar inference has been made for those in Indochina (e.g. Zaw1990; Charusiri et al. 1993; Hutchison 1996). However, the viewthat S-type granites are dominant has been questioned, and thegranite belt may contain a more important subduction-related

component than is the prevalent perception (Pollard et al. 1995;Barley et al. 2003).

Nevertheless, late Cretaceous orogenesis and crustal thicken-

ing is supported by monazite ages of 84

2 Ma and 72

1 Mafrom a high-temperaturelow-pressure amphibolite-facies meta-morphic event in orthogneisses from western Thailand(Dunning

et al. 1995), and by evidence for late Cretaceous anatexis in

Northern Malaysia and Thailand (Cobbing et al. 1992). Barley etal. (2003) have recorded 4347 Ma ages in rims to Jurassiczircons in some intrusions within the Mogok Metamorphic Belt.

They interpreted the distinctive low-Th domains as recrystalliza-tion during Eocene high-grade metamorphism. In southernPeninsular Thailand Rb Sr Late TriassicEarly Jurassic dates

for the Khao Phanom Bencha pluton contrast with discordant KAr age date peaks around 55 Ma, which have been interpreted byHutchison (1996) to be due to fault activity and hydrothermalcirculation. A similar situation appears to exist west of Bangkok,

where KAr biotite dates of 76 and 58 Ma were obtained fromLate TriassicEarly Jurassic granites in the Hua Hin andPranburi areas (Hutchison 1996).

Beyond the western belt of granites discussed above, Cretac-

eous granites with low initial Sr ratios are known from wellpenetrations in the Gulf of Thailand South China Sea area; thedates range between 116 and 80 Ma (Hutchison 1996). As

reviewed by Hutchison (1996), these granites, a few late Cretac-eous granitoids from Peninsular Malaysia and 10040 Ma gran-itoids from southern Vietnam are attributed to high regional heat

flow and widespread rifting. However, there seems to be amarked age gap between the Cretaceous ages and onset of riftingin the Eocene.

Fig. 1. Key elements indicating a Late CretaceousPalaeogene orogenic

belt on a digital elevation image of SE Asia (with inset of regional

setting). Mica cooling ages (in Ma) for the gneiss belts are from Ahrendt

et al. (1996), Lacassin et al. (1997), Barr et al. (2002) andBertrand &

Rangin (2003).

C . K . M O R L E Y800


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In Myanmar, a string of ultramafic rocks of Late CretaceousEocene age containing high-pressure metamorphic facies runalong and adjacent to the trend of the Sagaing Fault (Hughes etal. 2000). They include the famous jade mines of the Hpakan

Tawmaw jade tract. Hutchison (1975) and Charusiri et al. (1993)interpreted these rocks as Late Cretaceous ophiolites marking thecollision zone of the West Burma Plate and the ShanThai block

(Fig. 1). Jadeite dykes are intruded within serpentinites and arethe metasomatic products of crystallization from hydrous fluids

reacting with the serpentinites (Hughes et al. 2000). There is astriking similarity between the jadeite habitat in Myanmar andGuatamala. In Guatamala, jadeite occurs as dykes in serpenti-nites along the left lateral Motagua strike-slip fault zone thatforms the boundary between the North American and Caribbean

plates (e.g. Johnson & Harlow 1999; Guzman-Speziale &Meneses-Rocha 2000). A similar transform setting for theHpakanTawmaw jade tract would explain both why the suturezone is so cryptic and difficult to identify south of the jade tract,

and the location of the Sagaing Fault precisely along the terraneboundary.

The subduction of Indian plate oceanic crust during theMesozoicPalaeogene offers a long-term regional mechanism for

crustal deformation and magmatism in an Andean-type setting.

Determining the significance of the long-term subduction-relatedtectonic processes as opposed to collisions by small microconti-nents for the magmatic and tectonic evolution of SE Asiaremains ambiguous.

Evidence for collision-related uplift in Myanmar, northernand western Thailand

Although the geochemistry of S-type granites points to a

collisional event, structural evidence for a corresponding foldand thrust belt is much harder to find. The ShanThai blockhas been affected by several Palaeozoic collisional events,culminating in the Indosinian Orogeny (Bunopas 1981;

Cooper et al. 1989; Hutchison 1996). Most of the exposedrocks of the ShanThai block are moderate- to low-grademetamorphic PalaeozoicTriassic sediments and volcanic

rocks, and smaller areas of ortho- and para-gneisses thattypically display peak metamorphic ages focused around200 10 Ma (Ahrendt et al. 1993, 1997; Barr et al. 2002;Hansen et al. 2002). Triassic and Cretaceous granite intru-

sions are abundant.Even the youngest Triassic rocks are strongly folded, in places

by isoclinal, recumbent folds. The region is typically covered injungle and outcrops are discontinuous. Consequently, correlating

units, mapping out large structures, and determining the age of

folds and thrusts can be problematic. In western Thailand andeastern Myanmar, Mesozoic rocks are scattered and discontin-uous, and outcrops of Palaeogene rocks are very rare. No classicLate CretaceousPalaeogene fold and thrust belt is present, andstructural timing for a collisional event using synkinematic

sedimentary rocks is not well constrained. One possible remnant,however, exists in southern Peninsular Thaland from KrabiChumphon, in the vicinity of the Ranong and Khlong Maruistrike-slip fault zones. There, four major (up to 55 km wide and

150 km long) northsouth- to NNE-striking east-verging folds inJurassic Cretaceous rocks have been identified (Kanjanapayont

et al. 2002).Whereas older references discussed Palaeogene thickening

(e.g. Zaw 1990; Charusiri et al. 1993; Mitchell 1993), later work

has emphasized the importance of older collisions in creating themain thrust and fold features east of the Sagaing Fault. Early

Jurassic and late Early Cretaceous events were identified in theShan Plateau of Myanmar by Mitchell et al. (2002). However,

the geology of the Shan Plateau in Myanmar is poorly known. InThailand, an extensive regional apatite fission-track (AFT) study

by Upton (1999) showed widespread evidence for maximumburial or onset of cooling between 70 and 50 Ma (Figs 13). For

10 samples collected in western Thailand the range in centralages derived from AFT dating lay between 34 2 Ma and80 6 Ma (Upton et al. 1997; Upton 1999; Fig. 3). Four zirconfission-track ages between 52 and 40 Ma were also obtained

(Upton 1999; Fig. 3). One sample (location a, Fig. 3) showsprogressive cooling from the late Cretaceous (K Ar) through theEocene (zircon fission-track) to the early Miocene (apatitefission-track, Upton 1999).

Fig. 2. Map showing some of the key

northsouth and NWSE and NESW

fault trends that were probably active during

Late CretaceousPalaeogene transpression.

Cooling ages from apatite fission-track dataindicate extensive Late Cretaceous

Palaeogene uplift in northern Thailand.

Radiometric ages from Ahrendt et al.

(1993, 1997) indicate prograde

metamorphic events. Thrusts shown by bold

black lines indicate possible major oblique

reverse faults, which have restraining

geometries under left lateral motion on

NW SE-striking strike-slip faults. Fault a is

the Paunglaung Fault and its probable

southern extension. (See Fig. 1 for

location.)

T R AN S PR E S SI O NA L T EC TO N IC S I N S E A S IA 801


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Mesozoic Palaeogene uplift in eastern ThailandYunnan

An extensive belt of uplifted, folded and eroded Mesozoic rocksand underlying Palaeozoic metasediments runs from the easternhalf of Thailand (LoeiPetchabun fold belt) through Laos (PakLay fold belt) into the Yunnan province of China (Lanping

Saimo fold belt; Fig. 2). This fold belt shows evidence for LateJurassic compression in Laos (Stokes et al. 1996) and importantLate Jurassic metamorphism in northern Thailand (Ahrendt et al.1993). Other folds in the LoeiPetchabun fold belt are younger,

involving Cretaceous units. Ahrendt et al. (1993) found evidencefor younging of metamorphic events to the east or SE inThailand (Fig. 2). They subdivided northern Thailand into three

main thrust-bounded blocks. Two of these blocks, the Long andPhrae, display an internal eastwards younging of progrademetamorphic events (Long block 22092 Ma, Phrae block 122

63 Ma). However, the last high-grade overprint occurred around200 Ma. For the eastern margin of the Phrae block, at the Sirkitdam, where Ahrendt et al. (1997) have a prograde metamorphic

date of 63 3 Ma, Upton (1999) obtained a 73 7 Ma AFT age(Fig. 2). Ahrendt et al. (1997) interpreted a significant east- toSE-verging thrusting event around 70 Ma in the vicinity of the

Nan Uttardit suture. However, Upton (1999) found no convin-

cing evidence for large-scale Mesozoic thrust structures, fromgeological relationships or from AFT data.

Fieldwork and geophysical observations indicate mid-Cretac-

eous inversion (Lovatt-Smith et al. 1996) in the Khorat region ofeastern Thailand and Laos. However, AFT studies do not recordthis event, suggesting that it was too minor to perturb the relativedepth of the apatite partial annealing zone (Upton 1999). For

eastern Thailand, Upton et al. (1997) determined inversionbetween 73.5 and 39 Ma, with data clustering between 64 and39 Ma. Tectonic uplift rates were estimated to be slow tomoderate (6835 m Ma1). Cooling rates from western Thailand

(1.85 0.55 8C Ma1) and the Khorat Group (1.5

0.5 8C Ma1) in eastern Thailand were similar (Upton 1999).In addition to the fold belt deformation in eastern Thailand,

anticlines within the Khorat Plateau have resulted from inversionof Triassic rift basins at various times, including the Palaeogene(e.g. Cooper et al. 1989; Sattayarak et al. 1989). In the eastern

Khorat area, AFT results indicate that a prominent region ofinversion of Triassic basins called the Phu Phan Uplift (Fig. 1)led to between 2.9 and 4.0 km of denudation during the Late

CretaceousEarly Tertiary (c. 7050 Ma) (Racey et al. 1997;Upton 1999). Mouret et al. (1993) provided several corroboratinggeological observations that support basin inversion during theEarly Palaeocene (c. 65 Ma). During inversion of eastern Thai-

land, several hundred metres of conglomerates were deposited asalluvial fans derived from tectonic uplift in the LoeiPetchabun

Fig. 3. Apatite fission-track central age

(Upton et al. 1997; Upton 1999) and other

isotopic ages (Lacassin et al. 1997; Barr et

al. 2002) provide evidence for a north

south-trending belt of Late Oligocene

Early Miocene uplift that extended from

northern Thailand to the Thai peninsula

south of the Three Pagodas Fault. (See Fig.

1 for location.) Graph shows cooling of

three samples from the northsouth trend,

showing that within the northsouth trend

older cooling (hence inferred uplift) events

can be discerned.

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fold and thrust belt and the Uttaradit fault zone, Nam PatProvince (Heggemann 1994; Heggemann et al. 1994). In thefrontal monocline and LoeiPetchabun fold belt, the amount of

post-Khorat Group (Jurassic Cretaceous) overburden thickness

removed since inversion is estimated at about 2.34.4 km,depending on the geothermal gradient used (25 8C km1,Mouret

et al. 1993; 35 8C km1, Racey et al. 1997).

The LanpingSaimo fold belt lies on the western side of theRed River Fault zone (Wang & Burchfiel 1997; Wang et al.

2001; Figs 1 and 2). Considerable non-rigid deformation isindicated by variable palaeomagnetic rotations derived from theregion (Geissman et al. 2001; Sato et al. 2001). Wang et al.(2001) suggested a Palaeogene age for some of the folds andthrusts in the LanpingSimao fold belt. Accompanying the

deformation is a phase of volcanism (4224 Ma) interpreted asforming by partial melting accompanying local continentalsubduction along the northeastern margin (Wang et al. 2001).The northeastern margin is now defined by the Red River shear

zone, but dating of synkinematic garnets indicates that sinistralshear may have commenced only at about 34 Ma (Gilley et al.2003). The extensive Mesozoic fold belt stretching from Yunnanto Thailand is the clearest evidence for Mesozoic Palaeogene

orogenic activity, but multiple episodes of deformation make

determination of the amount of shortening attributable to thedifferent episodes difficult.

Late CretaceousPalaeogene transpressionaldeformation in the ShanThai block

As described above, there is a belt of MesozoicPalaeogene

folding that can be traced from the eastern half of Thailand toYunnan, but no comparable belt of deformation has been

described in western Thailand and Myanmar. This sectionexplores the possibility that an important belt of transpressionaldeformation is located in western Thailand and Myanmar related

to motion on the Mae Ping and Three Pagodas fault zonesamongst others.

Mae Ping Fault zone

Evidence for motion on the Mae Ping Fault zone has beendescribed by Lacassin et al. (1997) and reviewed and updated byMorley et al. (2001) and Morley (2002), and so is only brieflyoutlined here. The shear zone exposed at Lang San National Park

(Fig. 4), as described by Lacassin et al. (1993), displays goodevidence for ductile sinistral displacement (in particular, rolledstructures and SC fabrics), which, from reconstruction of

rotated, boudinaged veins, requires a minimum of 40 km sinistraldisplacement. 40Ar/39Ar ages from biotites and K-feldspar dateuplift at the end of sinistral motion between 40 and 30 Ma(Lacassin et al. 1997; Fig. 5). AFT data for the Mae Ping and

Three Pagodas faults area are consistent with rapid coolingthrough the partial annealing zone during the Late Oligocene toEarly Miocene (Upton 1999; Fig. 4). These data require that

substantial uplift (from temperatures around 300 8C, i.e. depthsof 8 10 km) to near surface occurred in the Late Oligoceneearliest Miocene.

The ductile shear zone geometry of the Mae Ping is mostprominently displayed NW of Lang San National Park (Fig. 4).SE of Lang San the fault zone broadens out to form a strike-slipduplex geometry (Morley 2002). This has a restraining bend

geometry under sinistral motion, and so might be expected toshow some of the greatest uplift and erosion in the region. Yetthe rocks in the area of the duplex appear to be mostly of

Palaeozoic age, with no uplift and exposure of rocks from deeperin the crust (such as those seen at Lang San National Park).

Whereas the exposed units within the Chainat Ridge duplex arelow-grade metasediments, the western margin of the duplex is

Fig. 4. Map of northern Sundaland (Myanmar, Laos, Thailand,

Cambodia, China) showing the significant extensional and strike-slipfaults and associated basins, which indicate significant internal

deformation of the Sundaland block during escape tectonics (based on

satellite images, surface mapping and seismic reflection data). The Mae

Ping and Three Pagoadas fault systems display numerous branching,

splaying and duplex geometries, and affect a large area (unlike the more

discrete Sagaing and Red River faults), possibly indicating a

transpressional setting during the Palaeogene.



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bounded by ortho- and para-gneisses and Triassic granites (Fig.4). Upton (1999) obtained a zircon fission-track age of 473 Ma and an apatite fission-track age of 40 2 Ma from the

gneisses (location b, Fig. 3); hence uplift of the crystalline rockscould be associated with the formation of the duplex. If so, to

produce the typical thrust older over younger rock relationship

the duplex is probably composed of steep, west-dipping obliquethrust faults.

A regional transpressional pop-up in northern Thailand?

Previous work on the Mae Ping Fault zone has focused ondeformation along the NWSE-striking trend of the fault zone.Many regional maps show only the NW SE orientation, andextend the fault right up to the Sagaing Fault (e.g. Le Dain et al.

1984). However, compilation of all the faults that splay off theMae Ping Fault zone from regional geological maps and satelliteimages shows that this picture is significantly oversimplified

(Figs 1 and 4). Usually on regional maps, the two fault zones arerepresented by simple NWSE trends, whereas the faultsactually splay and strike-slip duplex geometries appear common

at a variety of scales (Fig. 4). The northsouth trends arenumerous and 100300 km long (Fig. 4). These faults aresometimes shown in regional compilations (e.g. Le Dain et al.

1984; Lacassin et al. 1997, 1998) yet are given much lessemphasis in terms of their regional significance than the NWSE trends. The dimensions of the region affected by the principal

fault zones and their splays is considerable: the main ThreePagodas Fault zone itself is up to 50 km wide, and where theMae Ping and Three Pagodas faults lie parallel, the zone affected

by the main faults and their splays is 250 km wide.The north south-striking fault zone splays show significant

variations in the ages of exposed rocks juxtaposed across thefaults. Across the two largest north south trends, north of the

main NW SE-trending segment of the Mae Ping Fault zone(Fig. 2, faults b and c), consistently older rocks (Lower

Fig. 5. Regional Landsat image showingthe major Tertiary fault trend in the region

of northern Thailand and central Myanmar

between the Sagaing Fault and the Chiang

Mai basin. MCC, metamorphic core

complex. (See Fig. 4 for location.)

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Palaeozoic) are juxtaposed against PermianMesozoic rocks.The oldest, most uplifted rocks are exposed on the eastern sideof the northsouth faults, consistent with the northsouth trendsacting as oblique-slip high-angle reverse faults during sinistral

motion. The long northsouth faults have restraining bendorientations for sinistral motion on NWSE strike-slip faults.The linear nature of the fault zones suggests that they are

composed of high-angle faults. Differences in the age andmetamorphic grade between units juxtaposed across the faults

are not very great, suggesting that thrust displacements are nogreater than c. 510 km.

Figure 2 shows an interpretation of potentially key Palaeogenefaults, within northern Thailand forming a large-scale pop-upstructure between east-dipping oblique thrusts to the west (faults

b and c), and west- to NW-dipping oblique thrusts to the east(faults d and e). The putative NNESSW-striking, west-dippingfault (Fig. 2, fault d) marks the boundary between extensivegneisses and granites to the west and PalaeozoicMesozoic

sedimentary and metasedimentary units to the east. A string oflate Tertiary rift basins follows the trend. This trend is also theIndosinian terrane boundary between the Shan Terrane to thewest and the Sukhotahi Terrane to the east (Barr & Macdonald

1991). The NESW-striking oblique thrust (Fig. 2, fault e)

follows the NanUttaradit suture zone (Macdonald & Barr1984), where predominantly NW-dipping Indosinian structureshave been described (Singharajwarapan & Berry 1993). Itseparates predominantly Palaeozoic Mesozoic units in the hang-

ing wall from Mesozoic rocks in the footwall to the SE.

Strike-slip faults in central and eastern Thailand

The major strike-slip zones in Thailand are well exposed on the

western side of the country and are generally poorly exposed inthe central and eastern parts. There is little pronounced topogra-

phy associated with the traces of the Mae Ping and Three

Pagodas faults in eastern Thailand, and three AFT dates thoughtto represent uplift associated with the Mae Ping Fault haveyielded ages between 36 and 40 Ma (Upton 1999).

The Three Pagodas Fault in western Thailand forms a number

of NWSE- to northsouth-striking splays from an eastwestsplay that runs through Bangkok Chonburi (Figs 1 and 4).Migmatitic gneiss is uplifted along a left lateral restraining bendgeometry within the Three Pagodas Fault zone east of Chonburi

(Fig. 1). Isotopic ages for the gneiss are uncertain because of thepossibility of multiple partial lead loss in zircons (Hansen et al.2002). However, two identified high-grade events are TriassicJurassic formation of the gneissic fabric and a late Creta-

ceous thermal event of at least 500 8C, which partly reset U/Pbages (Hansen et al. 2002). Uplift of the gneisses during the

Palaeogene is indicated by 4540 Ma cooling ages (B. T.Hansen, pers. comm.), and thus may indicate a terminal phase ofuplift on the Three Pagodas Fault. On the southern part of the

Thailand peninsula, ESE of Surat Thani, Hansen et al. (2002)found evidence for a strong early Eocene thermal event ingneisses. Granites with ages of 7273 Ma and 5558 Ma areknown from the nearby region of Phuket (Charusiri et al. 1993),indicating granite emplacement concomitant with transpression

in southern Thailand.

The western extent of the Mae Ping Fault in Myanmar

In Myanmar, distinct belts of major rock units trend NNWSSEat an acute angle to the Sagaing Fault on its eastern side(Mitchell et al. 2002, Fig. 2, fault a; Fig. 3). These distinctive

belts (Mogok Metamorphic Belt, Slate Belt, Cambro-CretaceousLimestone Plateau sequence of the ShanThai block) have beenmapped only at a regional scale (Chhiber 1934;Mitchell et al.2002). Passing northwards in Myanmar the trace of the Mae Ping

Fault zone becomes diffuse, in part running parallel to, andwithin the Mogok Metamorphic Belt and the (Palaeozoic) SlateBelt, or at the western border of the Cambro-Cretaceous Lime-stone Plateau sequence, with its distinctive karstic topography

(Fig. 4). Within the Plateau sequence, northsouth- to NNE

SSW-trending, lozenge-shaped transpression-related fault trendsare suspected. However, karstic topography and presence of olderstructures makes identification of Tertiary faults difficult in many

places. Nevertheless, several clear and important trends ofprobable Tertiary faults are present on satellite images; in

particular, the two NW SE splays and a NNWSSE trendmarked a, b and c in Figure 5. Le Dain et al. (1984) andLacassin et al. (1998) showed sketchy outlines of these trends,

but did not discuss their significance. The diffuse, branching,

widening narrowing nature of the Palaeogene strike-slip faultzone is distinctive and in marked contrast to the straight, well-defined and more recent Sagaing Fault.

The interpretations of the Mae Ping Fault in Myanmar in

Figures 5 and 6 are supported by tracing the faults back to the

well-defined segment of the Mae Ping Fault zone in Thailand.Strike-slip-related faults on the satellite images are discrete, with

distinctive sharp, straight, slightly wavy and branching patterns.Confidence that the faults represent the Mae Ping Fault zone

decreases northwards as fewer faults retain this distinctive pattern.Only Mitchell et al. (2002) have published a detailed map andaccount of the geology of any part of the region crossed by the

NNW-striking segment of the Mae Ping Fault zone in Myanmar.

This map is shown in Figure 7, and identifies the Mogokmetamorphic rocks, the Slate Belt and the Plateau Limestones as

NNW SSE-trending lithology belts, which tend to be divided byNNW SSE-trending thrusts. These thrusts may have a Jurassic or

early Cretaceous history (Mitchell et al. 2002). One of the mostimportant thrust faults is the steeply inclined Paunglaung Fault,which lies at the boundary of the Slate Belt and the PlateauLimestones. The highly deformed belt of predominantly Meso-

zoic limestones, marble, flysch and red beds in the footwall of thePaunglaung Fault is called the PaunglaungMawchi zone

(Mitchell et al. 2002). The Paunglaung Fault is a top-to-the-eastthrust, which folds Aptian limestone in its footwall. The timing ofthrusting is ambiguous: the fault may have formed exclusively inthe AptianAlbian, Late Cretaceous or Palaeogene, or been active

during any combination of these times (Mitchell et al. 2002). ANNW SSE-striking fault east of the Sagaing Fault that appearson maps of Le Dain et al. (1984), Lacassin et al. (1997) andReplumaz & Tapponnier (2003) is probably the Paunglaung Fault.

The Paunglaung Fault in the southern half of Figure 7 is adistinctive sharp, linear feature, which can be traced on satelliteimages south to the NWSE-trending segment of the Mae Ping

Fault zone (Figs 5 and 6). Northwards, the distinctive nature ofthe fault is lost in the central part of Figure 7, but can still bemapped from outcrops as a Cretaceous thrust (Mitchell et al.2002). It is uncertain whether this change in character represents

variations in weathering as a result of lithological changes, achange in nature of the fault (strike-slip in the south, greater

thrust component to the north), or age variations in timing ofactivity, where the Mae Ping Fault zone reactivated the Paun-glaung Fault during the late Tertiary in the south but not in thenorth. However, regionally there does appear to be a change in

the style of the Mae Ping Fault zone, with the extensive systemof strike-slip duplexes dying out northwards (Fig. 4).



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Fig. 6. Detail of the Mae Ping Fault zone in Myanmar on the western side of the image shown in Figure 5. The fault zone comprises two major NWSE-

striking splays and a NNWSSE-branching and -splaying broad fault zone.

Fig. 7. Detail of the Mae Ping Fault zone

in northern Myanmar (see Fig. 4 for

location), with details of a geological map

by Mitchell et al. (2002), showing the main

lithological units and structures in the area.

This region may lie at the northern extent

of the Late CretaceousPalaeogene Mae

Ping Fault zone, and displays predominantly

Early Cretaceous and older deformation, or

may be part of a Late Cretaceous

transpressional belt. Timing on the key

Paunglaung Fault is ambiguous.

C . K . M O R L E Y806


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A portion of the NNWSSE Mae Ping Fault trend inMyanmar is shown in Figure 8. The bending of beds and offsetof possible marker horizons suggests left lateral motion of about910 km on one of the fault strands (location a, Fig. 8). There is

also evidence for later dextral motion: a small pull-apart basin ata releasing bend is consistent only with dextral displacement(Fig. 8, location b). A small amount of dextral motion at location

a is also required. Bertrand & Rangin (2003) described someNNW SSE-striking faults in outcrop in the same vicinity as

showing brittle dextral displacement, and Mitchell et al. (2002)indicated Tertiary dextral motion on the Paunglaung Fault. Thewestern fault branch is the southerly extension of the PaunglaungFault from Figure 6, where it separates the Slate Belt from thePaunglaung Mawchi zone. In Figures 5 and 8 the Paunglaung

Fault appears to be part of Mae Ping Fault zone.The various splaying trends are very significant, because they

(and associated folds) are the means of distributing the estimatedsinistral motion of up to 300 km (Tapponnier et al. 1986) on the

more discrete NWSE-striking segments of the Mae Ping andThree Pagodas faults in western Thailand. The Mae Ping andThree Pagodas fault zones are far from being isolated, parallelstrike-slip faults. Instead, regionally there is a network of north

south-trending faults that might link the two systems and form a

very large-scale strike-slip duplex system (Figs 4 and 5). Thereis also an important network of NWSE- to northsouth-trending strike-slip faults that lie to the west and south of theThree Pagodas Fault zone that are also probably linked (Fig. 4).

Some of these faults appear to exhibit large (.10 km) dextraloffsets.

Significance of metamorphic core complexes forPalaeogene deformation

Evidence for metamorphic core-complex development in the

Late Oligocene has been presented for the Mogok gneisses eastof the Sagaing Fault and the ranges west of the Chiang Mai basin

in Thailand (Macdonald et al. 1993; Dunning et al. 1995;Rhodes et al. 1997; Bertrand et al. 1999; Barr et al. 2002). InThailand, the metamorphic core complexes lie north of the MaePing Fault zone in the middle of the region of northsouth and

NE SW splays (Dunning et al. 1995; Rhodes et al. 1997; Barr

et al. 2002) (Fig. 2). The limit of core-complex extension to thesouth is uncertain because the necessary fieldwork has not yet

been conducted.Recent U Pb dating of monazite and zircon from the Doi

Suthep mylonitic orthogneiss yielded a 40 0.5 Ma date inter-preted to be that of a syntectonic granite protolith of theorthogneiss, and an upper age for the mylonitization; lower agesare around 28 Ma (Dunning et al. 1995; Barr et al. 2002). This

mylonitization is thought to be associated with east to west

extensional shear marking the beginning of metamorphic core-complex development (Macdonaldet al. 1993; Barret al. 2002).The timing of core-complex uplift and tectonic denudation is,

however, considerably later than the EoceneOligocene mylonite

Fig. 8. Detail of the Mae Ping Fault zone in Myanmar, showing the anastamosing geometry of the fault zone along the northern part of the Mae Ping

Fault zone in Myanmar. Two areas show evidence for the sense and magnitude of motion on the fault zone. Area a shows the boundary of the massive

crystalline basement region (predominantly the Mogok gneisses) to the west with a metasedimentary region to the east (which shows extensive

karstification in places). The boundary shows both offset and bending of layers consistent with left lateral motion. However, a small triangular wedge of

metasedimentary rocks between two splaying faults suggests that later right lateral offset occurred. Area b is a rhomboidal flat depression present at a

small bend in the fault trace, compatible with it being a pull-apart depression or basin associated with right lateral motion on the fault zone. (See Fig. 4

for location.)



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solution; Polachan et al. (1991) proposed a right lateral pull-apartsolution for the Mae Ping and Three Pagodas faults. However,the northsouth-striking rift basins of the western Gulf ofThailand have undergone extension from the Oligocene to Mid-

Miocene, whereas further SE the Pattani and Malay basinsunderwent extension during the Eocene(?)Oligocene (Morley et

al. 2001). These time periods cover both sinistral and dextral

phases of strike-slip motion on the Three Pagodas and Mae Pingfault zones (Lacassin et al. 1997). On both timing and geometricgrounds, most rift basins do not appear to have evolved as pull-

apart basins along the strike-slip fault zones (Morley et al. 2001;Morley 2002). These rifts developed just to the south of theonshore traces of the Mae Ping and Three Pagodas faults.

Perhaps this extension too was related to orogenic development,and the sediments feeding the basins were partially derived fromthe uplift transpressional belt. The westwards shift of extensionduring the Oligocene from the Pattani basin to the western Gulf

of Thailand may also represent extensional collapse of thickenedcrust in the transpressional belt and the northwards passage of

India. However, a more detailed understanding of how the riftbasins relate to the Palaeogene orogeny is a subject requiringconsiderably more work.

Conclusions

The presence of extensive S-type CretaceousPalaeogene gran-

ites in Myanmar and Thailand has been used to infer synchro-nous episodes of crustal thickening (e.g. Cobbing et al. 1986,1992; Zaw 1990; Charusiri et al. 1993; Hutchison 1996). The

problem is finding the upper-crustal deformation that couldsupport the inference. One possibility is that much of the leftlateral history of the Mae Ping and Three Pagodas fault zones is

associated with Late Cretaceous Palaeogene transpression aris-ing from an oblique subduction margin setting punctuated byapproximately NE SW-directed collisions (Cretaceous Palaeo-gene Burma PlateShan Thai block collision, EoceneRecent

IndiaBurma PlateShan Thai block collision). Crustal thicken-ing and heating by intrusion of I-type granites during subduction

Fig. 9. (a) Late Cretaceous tectonic setting loosely based on Metcalf (1998), to show the possible transform fault margin setting of the West Burma block.

The setting links the inferred transform fault setting of the HpakanTawmaw jadeite tract with transpressional deformation in the ShanThai block. Themotion of India is redrawn fromLeloup (2001, and website at http://image.univ-lyon1.fr/herve/RRF1.html). IY suture, IndusYardang suture. A note of

caution regarding the hairpin path around 50 Ma: this extreme trajectory requires further work and verification before it can be considered reliable (P. H.

Leloup, pers. comm.). (b, c) The regional geological evolution of SE Asia for the Eocene and Oligocene modified from Morley (2002). Dashed lines

representing likely Shmax directions are based on the sense of motion of major thrusts, strike-slip faults, metamorphic core-complex detachments, and

faults in sedimentary basins (modified from Huchon et al. 1994).

http://image.univ-lyon1.fr/herve/RRF1.htmlhttp://image.univ-lyon1.fr/herve/RRF1.html


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could have established conditions whereby S-type granite genera-tion required only an extra increment of shortening related to theBurma PlateShanThai collision.

The analogy of the Late Cretaceous Eocene HpakanTaw-

maw jade tract to the tectonic setting of jadeite along theMotagua strike-slip fault zone in Guatamala suggests a directlink between the Mae PingThree Pagodas transpressional belt

and formation of the jadeite tract (Fig. 9). A proto-Sagaing Faultzone probably formed the westerly boundary to strands of the

Mae Ping Fault zone, and is inferred to follow a sinistraltransform plate boundary along which the HpakanTawmaw

jadeite dykes were emplaced. This model suggests that thesinistral motion on the Mae Ping and Three Pagodas fault zonescan only partially be attributed to Himalayan escape tectonics.

The northsouth extent of the transpressional fault systems isover 1000 km and remains poorly known. This paper can onlyhighlight its potential tectonic importance. The major strike-slipzones in Thailand are well exposed on the western side of the

country and are generally poorly exposed in the central andeastern parts. There is little pronounced topography associatedwith the traces of the Mae Ping and Three Pagodas faults ineastern Thailand, and three apatite fission-track dates thought to

represent uplift associated with the Mae Ping Fault have yielded

older ages (3640 Ma, Upton 1999) than mica cooling agesalong the Mae Ping Fault zone in western Thailand (Lacassin etal. 1997). Only along a northsouth zone of regional uplifttrending through western Thailand are rocks displaying ductile

strike-slip deformation exposed. Strike-slip motions might havepartly contributed to the uplift, but they are not entirely thecause. The origin of the regional northsouth uplift may berelated to northerly passage of the Himalayan syntaxis, as the

timing and age progression fit with data from the MogokMetamorphic Belt described by Bertrand & Rangin (2003).

On regional maps, the Mae Ping Fault is invariably shown as asingle major throughgoing NWSE strike-slip fault. Where the

fault zone is mapped in detail one significant feature is thenumber of northsouth-striking faults that branch off the faultzone. These linked NWSE and northsouth fault trends affect alarge region, up to 250 km wide, and form numerous splaying

and strike-slip duplex geometries. Along the NNWSSE andNW SE splays of the Mae Ping Fault zone approaching the

Sagaing Fault, approximately 50 km of the 160 km displacementestimated for western Thailand (Tapponnier et al. 1986) can bemeasured from offset of geological markers. This excludesdisplacement on potentially the largest fault in the zone, the

Paunglaung Fault, which is a high-angle, east-verging thrustseparating the Slate Belt from the Plateau Limestones (Mitchell

et al. 2002). However, timing of deformation on this fault zoneremains ambiguous; it may be exclusively AptianAlbian

(Mitchell et al. 2002). More probably, the fault zone was at leastreactivated under left lateral strike-slip during the late Cretac-eousPalaeogene, and left lateral motion may be exclusively of

that age.During the late Oligocene(?) Recent, the Paunglaung Fault

along with numerous others underwent episodic right lateralmotion (e.g. Bertrand et al. 2001; Mitchell et al. 2002; Bertrand

& Rangin 2003). Evidence for dextral displacement on NNESSW, and northsouth to NWSE faults is widespread onshore

in a northsouth-trending belt some 100150 km wide, includ-ing and east of the Sagaing Fault and west of the main Tertiaryrift basins. This belt is particularly well developed onshore southand west of the Three Pagodas Fault zone (Fig. 4).

It should be emphasized that the model presented here is basedon limited data and more work is required to test its viability. In

particular, peak metamorphism and cooling age data for thegneisses and fault zones, and fault kinematic data (especially inMyanmar) are needed.

C. Hutchison, R. Hall and D. Cunningham are thanked for detailed and

constructive reviews. A. Carter helpfully provided a copy of the thesis of

D. Upton and supported the use of much material from the thesis. P.

Leloup is thanked for permitting reproduction of his website figure in

Figure 9 and for his discussion of the figure. Thanks also go to P.

Charusiri for helpfully answering a number of questions about the

regional geology. The University of Brunei Darussalam is gratefully

acknowledged for providing funding for this study.

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Received 28 July 2003; revised typescript accepted 11 February 2004.

Scientific editing by Rob Strachan

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