Journal of Asian Earth Sciences 111 (2015) 350–364

Contents lists available at ScienceDirect

Journal of Asian Earth Sciences

journal homepage: www.elsevier .com/locate / jseaes

Late Triassic paleomagnetic result from the Baoshan Terrane, WestYunnan of China: Implication for orientation of the East Paleotethyssuture zone and timing of the Sibumasu-Indochina collision

http://dx.doi.org/10.1016/j.jseaes.2015.06.0331367-9120/� 2015 Elsevier Ltd. All rights reserved.

⇑ Corresponding author at: School of Earth and Space Sciences, Peking University,No. 5, Yiheyuan Road, Haidian District, Beijing 100871, China.

E-mail address: bchuang@pku.edu.cn (B. Huang).

Jie Zhao a,b, Baochun Huang c,⇑, Yonggang Yan a,b, Donghai Zhang c

a State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, Chinab University of Chinese Academy of Sciences, Beijing 100049, Chinac Key Laboratory of Orogenic and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China

a r t i c l e i n f o

Article history:Received 22 February 2015Received in revised form 27 June 2015Accepted 30 June 2015Available online 2 July 2015

Keywords:Baoshan TerranePaleomagnetismTriassicSoutheast AsiaPaleotethysPaleogeography

a b s t r a c t

In order to better understand the paleogeographic position of the Baoshan Terrane in the northernmostpart of the Sibumasu Block during formation of the Pangea supercontinent, a paleomagnetic study hasbeen conducted on Late Triassic basaltic lavas from the southern part of the Baoshan Terrane in theWest Yunnan region of Southwest China. Following detailed rock magnetic investigations and progressivethermal demagnetization, stable characteristic remanent magnetizations (ChRMs) were successfully iso-lated from Late Triassic Niuhetang lava flows. The ChRMs are of dual polarity and pass fold and reversaltests with magnetic carriers dominated by magnetite and subordinate oxidation-induced hematite; wethus interpret them as a primary remanence. This new paleomagnetic result indicates that theBaoshan Terrane was located at low paleolatitudes of �15�N in the Northern Hemisphere during LateTriassic times. Together with available paleomagnetic data from the Baoshan Terrane and surroundingareas, a wider paleomagnetic comparison supports the view that the East Paleotethys Ocean separatedthe Sibumasu and Indochina blocks and closed no later than Late Triassic times. We argue that the cur-rently approximately north-to-south directed Changning-Menglian suture zone is very likely to havebeen oriented nearly east-to-west at the time of the Sibumasu-Indochina collision.

� 2015 Elsevier Ltd. All rights reserved.

1. Introduction

The Sibumasu (comprising the Sino-Burma-Malaysia-SumatraBlock forming the eastern part of the Cimmerian continent) andIndochina blocks are the main tectonic units in Southeast Asia(Fig. 1a). Their collision has been related to closure of the easternbranch of the Paleotethys Ocean and resulted in the amalgamationof East Asia during formation of the Pangea supercontinent(Sengör, 1987; Brookfield, 1996; Metcalfe, 1996; Acharyya, 1998).Thus the timing of collision and the position of the ophiolitic beltare key issues for understanding the evolution of this sector ofthe Paleotethys and the paleogeographic reconstruction of EastAsia, and hence their relationship with the main body of thePangea supercontinent. In general, the Cimmerian continent hasbeen considered to have drifted from Gondwana, the southern partof Pangea, in the Early Permian and subsequently collided with

Laurasia, the northern sector of Pangea by Jurassic times(Metcalfe, 1996; Wang et al., 2001a,b, 2010; Sone and Metcalfe,2008). However, the timing of collision between the Sibumasuand Indochina blocks is still debated due to the scarcity of reliablequantitative paleogeographic constraints such as high-qualitypaleomagnetic results for the terranes and blocks comprising theSoutheast Asia collage (Collins, 2003; Scotese, 2004; Metcalfe,2013; Stampfli, 2013). Some studies argue for an Early to earlyMiddle Triassic collision based on thermotectonic activity inVietnam dated �258 to 242 Ma (Carter et al., 2001; Nam et al.,2001; Jian et al., 2009) although it is suspected to be related tothe collision between the Indochina and South China blocks(Lepvier et al., 2004; Maluski et al., 2005) or closure of back-arcbasin between the Sukhotai arc and the Indochina Block (Soneand Metcalfe, 2008) and paleontological affinities between thetwo blocks (Shi and Archbold, 1998; Ueno, 2003). In contrast aMiddle to Late Triassic collision has been suggested from the evi-dence of the youngest pelagic sediments from theChangning-Menglian Suture Zone (Liu et al., 1993; Sone andMetcalfe, 2008), ages of the collision-correlated Lincang granite

Fig. 1. (a) Schematic tectonic map of Eurasia showing the Cimmerian continent after Sengör (1987); (b) the structural map around the Baoshan area modified from Leloupet al. (1995) and Shen et al. (2005). XLGSZ: Xuelongshan shear zone, DCSSZ: Diancangshan shear zone, CSSZ: Chongshan shear zone, SGF: Sagaing fault, MMB: Mogokmetamorphic zone, CMS: Changning-Menglian Suture zone, 1: Biwu granite, 2: Linong granite, 3: Lunong granite, 4: Xin’anzhai monzogranite, 5: Tongtiange leucogranites, 6:Xiaodingxi and Manghuihe basaltic rocks, 7: Lincang granite, 8: Metamorphic rocks from Kannack complex.

J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364 351

(Dong et al., 2013), and post-collisional basaltic rocks which cropout in the Lancangjiang Tectonic Zone (Wang et al., 2010).

Paleomagnetic study is the only approach able to providefully-quantitative paleogeographic data for these continentalblocks. Unfortunately this area has experienced strongpost-collisional deformation and intense magmatism especiallyfollowing the India-Asia collision (Tapponnier et al., 1990;Morley, 2002; Otofuji et al., 2012), which produced a pervasiveremagnetization in pre-Cenozoic rocks (Yang and Besse, 1993).For this reason only a few Late Paleozoic to Early Mesozoic paleo-magnetic data from Southeast Asia can meet minimal require-ments satisfying paleomagnetic reliability criteria (e.g. Van derVoo, 1990); this is in spite of many reconnaissance paleomagneticinvestigations performed over the past three decades (Chan et al.,1984; Fang et al., 1989; Huang and Opdyke, 1991; Yang and

Besse, 1993; Li et al., 2004; Ali et al., 2013; Kornfeld et al., 2014).Correspondingly, the scarcity of available Late Paleozoic to EarlyMesozoic paleomagnetic poles from Southeast Asia has alsoresulted in serious disagreement between paleogeographic recon-structions of East Asia during formation of the Pangea superconti-nent (Collins, 2003; Scotese, 2004; Golonka, 2007; Stampfli, 2013).

In this paper, we report a paleomagnetic study of Late Triassicbasaltic lavas from the southern area of the Baoshan Terrane inthe northernmost part of the Sibumasu Block. Together with avail-able paleomagnetic constraints from the Baoshan Terrane and thesurrounding region, the results enable us to reconstruct the orien-tation of the East Paleotethys suture zone prior to intra-continentaldeformation related mainly to the Cenozoic India-Asia collision.This further enables us to estimate the timing and position forthe Sibumasu and Simao-Indochina collision and evaluate the

352 J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364

paleogeographic setting of the Southeast Asian terranes within themain body of the Pangean supercontinent.

2. Geological setting and sampling

The northern part of Sibumasu, the Baoshan Terrane (Wopfner,1996; Ueno, 2003) is located in southwest China. It is bounded bythe Gaoligong Suture Zone (GLGSZ) to the west, the ChongshanSuture Zone (CSSZ) and the Changning-Menglian Belt to the east(Fig. 1b). In common with other parts of the Cimmerian continent,it is believed to have formed a part of the GondwanaSupercontinent before the middle Early Permian (Metcalfe, 1996;Jin, 2002; Wang and Sugiyama, 2002; Huang et al., 2008b; Soneand Metcalfe, 2008) and accreted to the Simao-Indochina Blockduring the early Mesozoic (Metcalfe, 2006; Wang et al., 2010).Subsequent major deformation is considered to be related tointra-continental strike-slip faulting and thrusting caused byCenozoic penetration of India into the Asian collage (Tapponnieret al., 1990; Tanaka et al., 2008; Otofuji et al., 2010; Cao et al.,2011a,b).

Late Cambrian to Jurassic platform carbonates and clastics arewell developed in the Baoshan Terrane and intervening volcanicepisodes occurred in the Early Permian, Late Triassic, and sparselyduring the Middle Jurassic and Cenozoic (Shi and Archbold, 1998;Wang et al., 2001a, 2002; Jin, 2002; Ueno, 2003; Jin et al., 2011).In general, Middle and Late Triassic rocks overlie the Permian plat-form carbonates and clastics with angular unconformity, and aredisconformably overlain by Middle Jurassic clastics. The TriassicSystem is composed, in ascending order, of the MiddleTriassic Hewanjie Formation (limestones) and the Upper TriassicNiuhetang Formation (volcanics and intercalated sediments) suc-ceeded by the (Upper Triassic) Dashuitang and Nanshuba forma-tions (clastic sediments); the Lower Triassic is regionally absent.The Upper Triassic Niuhetang Formation has a wide distributionin the southern part of the Baoshan Terrane. As shown inFig. 2a, d–e, this formation unconformably overlies the MiddleTriassic Hewanjie limestones but is overlain by the Dashuitangand Nanshuba clastics by a disconformity (YBGMR, 1984).Furthermore, this formation can be subdivided into three mem-bers. The lower member consists chiefly of basalts and intercalatedandesites; the middle member consists chiefly of rhyolites; whilstthe upper member is composed mainly of basalts intercalated withterrestrial sediments. Plant fossils such as Equisetites cf. sarrani(Zeiller) Harris, E. sp., Dictyophyllum aff. nathorsti Zeiller,Dorathophyllum sp., Neocalamites carrerei (Zeiller) Halle, ?N. carrerei(Zeiller) Halle, Podozamites aff. lanceolatus (L. et. H.), P. sp., Sinoctenissp., Taeniopteris sp., T.? sp., Petrophyllum ptilum Harris have beenfound in the intercalations, indicating a Late Triassic age and anintraplate setting for the basaltic eruption (YBGMR, 1984). Sincethe basaltic lavas have lower and upper portions showingalmond-shaped vesicular textures, the basalt succession can bereadily subdivided into different lava flow units in the field(Fig. 2c). In addition, the underlying Middle Triassic HewanjieFormation is composed primarily of limestones and contains anabundant conodont, brachiopod and lamellibranch fauna includingCostatoria cf. radiata hsuei Chen, Entolium discites Schlotheim,Posidonia wengensis Wissmann, Placunopsis., Daonella? Sp.,Maxillirhynchia? Sp., Ninglangothyris sp. indicative of a MiddleTriassic age. The paleontology, lithofacies and contact relationshipsindicate a Late Triassic age for the Dashuitang and Nanshuba clas-tic facies which are in contact the underlying Niuhetang Formationfollowing a short time break (YBGMR, 1984).

Using this precise stratigraphic control the Late TriassicNiuhetang volcanic rocks were chosen for paleomagnetic sampling.In general, eight to twelve individual cores were drilled from each

sampling site with each one distributed within a different lavaflow. In total, sixteen lava flows were collected from two sections(Fig. 2a, d–e) with twelve, one, and three flows selected from thelower (site YY045-050 and YZ196-201), middle (site YY054), andupper (site YY051–YY053) members of the formation respectively.Bedding attitudes define a plunging fold axis dipping 29.7� towardsN148.9�E (a95 = 5.1�, N = 10, Fig. 2b). All the core samples were col-lected using a portable gasoline-powered drill and orientated usinga sun compass. Where possible cores were orientated by both sunand magnetic compasses in order to identify any local magneticeffects on the magnetic compass. The average difference betweenreadings of sun and magnetic compasses was of �0.99� ± 5.1�(n = 60,2r), which is generally consistent with local declination(�359.0�) calculated from the International GeomagneticReference Field (IGRF) model for the sampling locality at 24.0�N,99.0�E. Thus magnetic compass readings can be used with a�1.0� correction for local declination in this study.

3. Rock magnetic investigations

Field core samples were cut into cylindrical specimens�2.0–2.2 cm in length and some selected fresh end materials weresubjected to rock magnetic analysis. Following sample preparation,eleven samples were subject to magnetic experiments comprisingacquisition of isothermal remanent magnetization (IRM),back-field demagnetization of saturated IRM (SIRM), hysteresisloops, and thermomagnetic analysis in order to better understandmagnetic mineralogy. The acquisition of IRM, back-field demagne-tization of SIRM, and hysteresis loops were performed using aMicromag 3900 alternating gradient magnetometer.Magnetization versus temperature curves (J–T curves) were mea-sured by a VFTB in an equivalent DC field of �1.0 T. Rock magneticmeasurements and subsequent paleomagnetic experiments wereperformed in the Paleomagnetism and Geochronology Laboratory(PGL) of the Institute of Geology and Geophysics, ChineseAcademy of Sciences.

Rock-magnetic measurements on 11 pilot samples can be clas-sified into two categories. The first category (including 9 samples)is characterized by approximately reversible J–T curve withunblocking temperatures of �580 �C (Fig. 3a). Together with typi-cal low-coercivity (�32.0 mT) subtracted from the IRM acquisitionand back-field demagnetization of SIRM curves (Fig. 3b–c), mag-netite is identified as the main magnetic mineral. The hysteresisparameters for 9 pilot samples (Fig. 4) show that the magnetic par-ticles are resident in the pseudo-single-domain (PSD) range (Dayet al., 1977; Dunlop, 2002). The second group also exhibits approx-imately reversible J–T curves during the heating–cooling run butwith the unblocking temperature of remanence above �650�(Fig. 3e). The IRM acquisition and back-field demagnetizationcurves (Fig. 3f–g) show significant presence of two magnetic com-ponents: a low coercivity component with B1/2 of �56.0 mT and ahigh coercivity component with B1/2 of �708.0 mT and distributionwidth (DP) of 0.35 (Kruiver et al., 2001). Together with the signif-icant wasp-waisted hysteresis loop (Fig. 3h) we speculate that thissample is ferromagnetically-dominated by both magnetite andhematite.

4. Paleomagnetic results and analysis

Following evaluation of rock magnetic behaviors resolved frompilot samples, all the 149 specimens were subjected to progressivethermal demagnetization using a TD-48 thermal demagnetizerwith residual magnetic field minimized to less than 10 nT insidethe cooling chamber. Demagnetization intervals were 50–100 �Cat lower temperatures, and subsequently reduced to increments

(a)

(b) (c)

(d)

scale

(e)

Fig. 2. (a) Geological map of southern Baoshan Terrane in West Yunnan (Metcalfe, 1996, 2002, 2013; Sone and Metcalfe, 2008; Wang et al., 2010); (b) lower hemisphereequal-area projection for bedding attitudes of the sampled sites defining a fold axis plunging 29.7� towards N148.9�E; (c) photograph showing field outcrops in the studiedsection in which individual lava flow could be readily identified by almond-shaped vesicular textures; (d, e) composite cross section of the Niuhetang Formation in Zhenkangand Yongde showing stratified units and distribution of sampling sites. T2h, T3n and T3d represent the Hewanjie, Niuhetang and Dashuitang formations, respectively.

J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364 353

as small as 5 �C at higher temperatures as the maximum unblock-ing temperatures of the remanence carriers were approached. Allremanence measurements were performed on a 2G-755 cryogenicmagnetometer. Both demagnetizer and magnetometer areinstalled in a magnetically shielded space with the field inside

minimized to less than 300 nT. Demagnetization results are plottedonto orthogonal diagrams (Zijderveld, 1967) and stereographicprojections with the former used to resolve components by princi-ple component analysis (Krischvink, 1980); mean directions werecalculated using standard Fisher statistics (Fisher, 1953) or the

0 100 200 300 400 500 600 7000

2

4

6

8YY200-8

Temperature (oC)

J(A

m2 /k

g)

0 100 200 300 400 500 600 7000

0.1

0.2

0.3YY050-4

Temperature (oC)0.5 1 1.5

0

0.2

0.4

0.6

0.8

1

-0.3 -0.2 -0.1 00 1 2 3 4

0

0.2

0.4

0.6

0.8

1

-0.8 -0.4 0 0.4 0.8-2

-1

0

1

2

-0.4 -0.2 0 0.2 0.4-800

-400

0

400

800

Field (T)

0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

-0.1 -0.05 0

Field (T)

Field (T)Field (T)

J(A

m2 /k

g)

IRM

/SIR

MIR

M/S

IRM

J (A

m2 )

J (A

m2 )

(a) (b) (d)

(e) (f) (g) (h)

grad

ient

10Log Applied field (mT)

0 1 2 30

0.02

0.04

0.06

0.08

0.1 (c)

10Log Applied field (mT)

grad

ient

Fig. 3. Rock magnetic results for representative samples from the Niuhetang Formation: (a,e) J–T curves for pilot samples, all the measurement were conducted in an airatmosphere; (b, f) acquisition curves of isothermal remanent magnetization (IRM) and back-field demagnetization curves of saturated IRM; (c,g) examples of IRM componentanalyses (open circle: raw data, red line: Comp.1, green line: Comp.2); (d,h) hysteresis loops for pilot samples collected from the Late Triassic Niuhetang Formation, Baoshanarea of West Yunnan. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

001011 050302532

Bcr/Bc

0.01

0.1

1

0.02

0.03

0.05

0.2

0.3

0.5

0.005

Mrs/Ms

MD

PSD

SD

SP+SD

SD+MD

100%100%

30nm

25nm

15nm10nm

20nm

95%

90%

80%

60%

40%

20%

00

20%

40%

60%

80%

90%

95%

7nm

Fig. 4. The Day diagram for pilot samples from the Niuhetang basaltic lavas, in which Mr and Ms are saturation remanence and saturation magnetization; Bc and Bcr arecoercivity and coercivity of remanence; SD: single domain, PSD: pseudo single domain, MD: multi domain; nm: nanometer. Numbers along curves are volume fractions of thesoft component (SD or MD) in mixtures with SD grains.

354 J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364

method of combined remagnetization circles and direction obser-vations (McFadden and McElhinny, 1988).

From demagnetization results exhibited on the orthogonal dia-grams (Zijderveld, 1967), all the demagnetized specimens could be

classified into three groups. The first group contains 127 specimensand all these specimens identify a high-temperature characteristicremanent magnetization (ChRM) after removal of a viscouscomponent in the initial stage of demagnetization and/or a

J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364 355

low-temperature component by demagnetization temperatures upto �250–300 �C (Fig. 5a–c, f). The high-temperature characteristiccomponent was generally unblocked by temperatures 550–600 �C(Fig. 5b–f), and in a minority of specimens at higher temperaturesup to �650 �C (Fig. 5a). This behavior suggests that the ChRM iscarried by magnetite and subordinate hematite, which is concor-dant with rock magnetic results for the pilot samples (Fig. 3).Noticeably, thermal demagnetization for specimens from siteYZ201 showed some differences, in which the low-temperaturecomponent was completely removed by temperatures as high as450–520 �C. Correspondingly, the high-temperature ChRM wassubtracted either between 400/450 �C and 575/580 �C in 4 out of8 demagnetized specimens or between 450/540 �C and675/680 �C in the remaining 4 specimens (Fig. 5g). The secondgroup contains 12 out of 149 specimens demagnetized. These spec-imens exhibited a high-temperature demagnetization trajectory

N,N

E,Up

Fig. 5. Typical orthogonal and stereographic vector plots illustrating progressive thermaYongde and Zhenkang areas. Orthogonal directions (Zijderveld, 1967) are plotted in-situ;symbols represent endpoints projected onto horizontal or vertical planes, respectively.

following a great circle permitting ChRM isolation by a remagneti-zation great circle between temperatures of 80/100 �C and500/525 �C (Fig. 5d–e). Site-mean directions of these four sitesare therefore calculated by the McFadden and McElhinny (1988)method (Table 1). The remaining 10 specimens formed the thirdgroup in which thermal demagnetization exhibited an erratichigh-temperature demagnetization behavior following removal ofthe viscous and/or low-temperature overprints so that no mean-ingful characteristic component could be isolated.

In summary, the low-temperature component was isolatedfrom 67 out of 149 demagnetized specimens. This componenthas an in-situ mean direction of D = 7.5�, I = 39.3� (k = 45.4,a95 = 2.6�) with significant deterioration of data grouping after tiltcorrection (ks/kg = 0.27) producing a negative fold test. We inter-pret this low-temperature component as a recent overprinting inthe light of conformity to the Present Geomagnetic Field (PGF).

l demagnetization structures for basaltic rocks from the Niuhetang Formation in thewhilst stereographic directions are plotted in stratigraphic coordinates. Solid/open

Table 1Summary of characteristic remanent magnetizations from Late Triassic Niuhetang Formation, Baoshan area of West Yunnan.

Site ID ks (�N) us (�E) Strike/dip n/n0 Dg (�) Ig (�) Db (�) Ds (�) Is (�) j a95 (�) up (�E) kp (�N)

Upper member of the formationYY051 23.94 99.31 5.5/41 10/10 326.3 �53.1 305.3 313.9 �20.8 260.1 3.0 337.0 33.2YY052 23.94 99.31 5.5/41 8(2)/8 319.3 �51.6 302.3 310.9 �17.3 86.2 6.0 340.9 31.9YY053 23.94 99.31 5.5/41 6(4)/9 323.2 �55.6 302.3 310.9 �21.9 55.2 9.1 338.6 30.4

Middle member of the formationYY054 23.95 99.24 2/38 7/7 159.6 60.9 125.3 133.7 35.1 300.4 3.2 149.5 �27.5

Lower member of the formationYY045 23.94 99.30 5/48 12/12 142.5 57.3 119.6 129.8 17.0 259.2 2.7 161.8 �31.1YY046 23.94 99.30 5/48 10/10 134.9 65.2 111.8 122 21.6 121.5 4.4 164.3 �23.3YY047 23.94 99.30 5/48 11/11 147.3 62.6 118.2 128.4 22.6 926.3 1.5 159.9 �28.2YY048 23.94 99.30 5/48 8/10 145.2 60.2 119.0 129.2 20.1 767.3 2.0 160.6 �29.7YY049 23.94 99.30 5/48 3/8 143.4 59.7 118.5 128.7 19.2 719.0 4.6 161.4 �29.6YY050 23.94 99.30 5/48 10/10 143.4 61.6 117.4 127.5 20.7 1036.8 1.5 161.4 �28.1YZ196 23.72 99.15 79/36 10(4)/10 66.5 55.5 113.9 110.7 47.6 78.1 5.5 154.6 �5.2YZ197 23.73 99.15 79/36 8/8 91.0 46.1 117.5 114.4 29.9 251.3 3.5 163.9 �14.6YZ198 23.73 99.15 84/35.5 10(2)/10 65.1 41.4 98.7 94.9 42.8 191.4 3.5 164.5 5.6YZ199 23.73 99.15 84/35.5 10/10 84.9 40.5 111.0 107.1 31.5 320.9 2.7 166.5 �8.0YZ200 23.73 99.15 67/22 8/8 95.0 42.3 108.3 107.5 29.6 213.3 3.8 167.4 �8.9YZ201a 23.73 99.15 67/22 8/8 86.7 1.1 85.8 85.0 �6.2 26.3 11.0 194.0 3.3

Sub-mean Normal (12/13) 112.8 59.2 14.3 11.9115.2 28.3 51.2 6.1

120.3 28.6 32.5 7.7Reversal (3/3) 322.9 �53.5 767.0 4.5

303.3 �20.0 780.6 4.4311.9 �20.0 780.6 4.4

Formation-mean (15/16) 119.8 58.6 15.9 9.9117.0 26.6 53.5 5.3 160.9 �21.7

122.8 26.9 34.3 6.6 K = 39.9 A95 = 6.1

Abbreviations are: site ID, site identification; Strike/dip, strike azimuth and dip of bed; n/n0, number of samples used for the calculation/demagnetized, numbers showing inthe parentheses indicate number of remagnetization circles used; Dg, Ig (Db,Ds, Is), declination and inclination of direction in-situ (declination after general tilt-correction,declination and inclination after tilt-correction with plunging fold axis (N148.9�E, 29.7� with a95 = 5.1�); ks, us, latitude and longitude of the sampling site; kp, up, latitude andlongitude of corresponding virtual geomagnetic pole (VGP) after tilt-correction with plunging fold axis.

a Site-mean direction discarded from further calculation due to large deviation to the formation mean.

356 J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364

The high-temperature ChRM is of dual polarity and can be welldetermined from all the 16 sampling sites. Excluding considerationof site-mean observation from site YZ201 which deviates markedlyfrom the other results both before and after tilt correction (Fig. 6a–c), the remaining 15 sites yield a formation mean of D = 119.8�,I = 58.6� (a95 = 9.9�, k = 15.9) before and D = 117.0�, I = 26.6�(a95 = 5.3�, k = 53.5) after tilt correction (Table 1 and Fig. 6a–b).The application of a two-step unfolding procedure (Stewart andJackson, 1995) to correct for the plunging fold axis (N148.9�,29.7� with a95 = 5.1�, Fig. 2b) before unfolding about a horizontalaxis yields a corrected mean direction of D = 122.8�, I = 26.9� withk = 34.3 and a95 = 6.6� (Fig. 6c). Although this grouping by two-stepunfolding yields a grouping of site-mean directions with slightlydiminished grouping compared to the result from single tilt adjust-ment (Table 1), the Watson and Enkin (1993) fold test presents anoticeably increased optimal concentration of the ChRMs from84.8 ± 3.8 following tilt adjustment to 92.5 ± 4.1 percent unfoldingafter tilt-correction with plunging fold axis. This suggests that thetwo-step unfolding correction is the proper procedure for the dataset from this study. The traditional McElhinny (1964) fold test ispositive at the 95% confidence level with the ratio ks/kg = 2.16,larger than the statistical threshold of 1.84. The reversal test(McFadden and McElhinny, 1990) is positive with an angular dif-ference of 13.6� between the two-step unfolding corrected direc-tions of each polarity, which is smaller than the threshold of15.6� and yields a class C reversal test result.

5. Discussions

5.1. Origin of the high-temperature characteristic remanence

Both rock magnetic experiments and thermal demagnetizationindicate that the high-temperature ChRM is carried by magnetite

in a majority of samples and by both magnetite and hematite ina minority. The Day plot (Day et al., 1977; Dunlop, 2002) for pilotsamples dominated by magnetite reveals that this mineral residesmostly in a PSD state. On the other hand, the high-temperatureChRM yields both a positive fold test (McElhinny, 1964; Watsonand Enkin, 1993) and reversal test (McFadden and McElhinny,1990). This indicates a pre-folding origin for the ChRM, namelyprior to the two main regional folding phases comprising theYanshanian and Himalayan recognized in the study area (Huangand Opdyke, 1991; Liao et al., 2003). The corresponding paleomag-netic pole derived from the two-step unfolding-correctedhigh-temperature ChRMs is located at 160.9�E, 21.7�S withA95 = 6.1�, and is significantly different from Jurassic andOligocene paleopoles from the Baoshan Terrane (Huang andOpdyke, 1993; Kornfeld et al., 2014). We therefore conclude thatthe high-temperature ChRM is a primary remanence acquired atthe time of eruption of the Late Triassic Niuhetang basaltic lavas.

The corresponding paleomagnetic pole of the high-temperaturecomponent has a VGP dispersion of about 12.8�, which is compara-ble with distributions predicted from global paleosecular variation(PSV) models during the last 5 Ma at latitudes of 10–20� (Johnsonet al., 2008). Using the analytical method from Deenen et al.(2011), the 119 available VGPs yield an A95 = 2.2�, which falls intothe range of A95max = 4.04, A95min = 1.77 for N = 119 and suggeststhat PSV has been approximately averaged by this collection.Meanwhile, the ChRM was isolated from all the lower (11 sites),middle (1 site), and upper (3 sites) members of the Niuhetangbasaltic lavas and records at least one polarity reversal event(Table 1). In addition, as shown in Fig. 2c, all the sampling sitesin our study were drilled from individual lava flow and in particu-lar the three members of the Niuhetang Formation are distin-guished by either different lithological associations or terrestrialsediment layers with typical plant and gastropod fossils (YBGMR,

84.8%[81.3%,88.2%]

0001005-

%150

Unfolding percent(%)

kmax

k

(d)

k

kmax

Unfolding percent(%)

(e)

tilt-corrected =122.8D=26.9I=34.5kα95=6.6N=15

=53.0

=117.0D=26.6I

kα95=5.3N=15

tilt-corrected

95

in-situ=119.8D=58.6I=15.9k=9.9α

N=15

(a)

92.5%[88.4%,96.6%]

Fig. 6. Equal-area projections of site-mean observations from the Niuhetang Formation (a) before and (b) after tilt correction; (c) equal-area projection of the site-meanobservations after a two-step unfolding correction; (d, e) incremental unfolding analysis using Watson and Enkin (1993) for general tilt-corrected (d) and two-step unfolding-corrected (e) site-mean observations, respectively.

J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364 357

1984). We therefore believe that our sampling of the Niuhetangbasaltic lavas has embraced a time interval larger than at least amillion years so that the PSV should have been adequately aver-aged by this collection.

This newly-obtained Late Triassic paleomagnetic pole suggestsa paleolatitude of �15�N for the southern part of the BaoshanTerrane during eruption of the Niuhetang basaltic lavas.

5.2. Orientation of the East Paleotethys Suture Zone

As shown in Fig. 1b, the Changning-Menglian-Inthanon (CMI)ophiolite belt separating the Sibumasu and Indochina blocks (e.g.Sone and Metcalfe, 2008) extends nearly north-to-south in presentgeographic coordinates. Noting that substantial paleomagneticdata have shown that the terranes in west Yunnan have experi-enced a clockwise (CW) rotation relative to the stable EurasianPlate ranging from �20� to 135� due to the India-Asia collision(Li et al., 2012 and references therein; Tong et al., 2013; Kornfeldet al., 2014). This post-India-Asia collisional large-scale rotationalmotion is compatible with the observed southeastward escape ofupper-crustal blocks (e.g. Chen et al., 2000; Shen et al., 2005;Gan et al., 2007). Therefore, the question of whether the CMI ophi-olite belt suffered significant India-Asia collision-induced vertical

axis rotation is a key issue for late Paleozoic to early Mesozoic pale-ogeographic reconstruction of the Sibumasu and Indochina blocks.

Since no available paleomagnetic data have been obtaineddirectly from the CMI ophiolite belt where structural complexitiesare in any case likely to render such an approach difficult, we con-sider the available Devonian to Jurassic paleomagnetic results fromthe Sibumasu and Indochina blocks (Table 2). Firstly, Fang et al.(1989) reported a Devonian paleomagnetic pole from limestonesin the northern part of the Baoshan Terrane. This pole is definedby positive fold and reversal tests and indicates a high paleolati-tude of �42�S for the Devonian Baoshan Terrane, which seems tobe compatible with Early Permian paleolatitudes reported byHuang and Opdyke (1991) and Ali et al. (2013). However, a com-parison between this preliminary paleomagnetic pole and theEarly Permian pole (Huang and Opdyke, 1991) suggests a vastCW rotation of �169� for northern Baoshan during Devonian toEarly Permian times. This vast rotation is more than twice theamount of that observed from west Australia of East Gondwanaduring the period between 390–380 Ma and 290–280 Ma(e.g. Torsvik et al., 2012) and considered to be of local rather thenregional significance. Secondly, Huang and Opdyke (1991) reporteda paleomagnetic study for the Early Permian Woniusi Formationfrom both northern and southern parts of the Baoshan Terrane. It

Table 2Summary of Late Paleozoic to Cenozoic paleomagnetic data from the Baoshan-Sibumasu, Simao-Indochina and South China blocks.

ID Sampling information Age N Test Observed direction Paleomagnetic pole Rotation Ref. Reference

Locality Lat.(�N)

Lon. (�E) Dec.(�)

Inc.(�)

a95 Lat.(�N)

Lon.(�E)

A95 (�) (�)

Northern part of Baoshan, Sibumasu1 Baoshan 26.0 98.9 Oli 12 42.2 47.0 7.8 52.6 175.7 10.1/

6.542.2 PGF Kornfeld et al. (2014)

2 Baoshan 25.2 99.3 Pl 13 F 29.2 �61.0 6.7 17.2 257.5 9.3 �13.1 1 Huang and Opdyke(1991)

3 Baoshan 25.0 99.0 D 7 R 198.0 �62.0 5.8 �66.5 313.8 7.0/9.0

169.6 2 Fang et al., (1989)

Southern part of Baoshan, Sibumasu4 Luxi 24.3 98.4 Jm 6 99.7 35.2 11.3 �0.5 166.6 12.2 99.7 PGF Huang and Opdyke

(1993)5 Yongde 23.9 99.1 Tu 15 F, R 122.8 26.9 6.6 �21.7 160.9 6.1 22.2 ± 10.6 4 This study6 Yongde 23.9 99.2 Pl 6 114.5 �63.9 7.8 �33.9 229.6 11.6 �7.5 ± 13.1 5 Huang and Opdyke

(1991)

Shan State, Sibumasu7 Kalaw 20.7 96.5 J–K 13 F 44.7 23.4 6.1 47.2 190.6 4.8 44.7 PGF Richter and Fuller

(1996)

Simao, Indochina8 Yunlong 25.8 99.4 Km 20 F 40.2 49.9 3.9 54.6 171.3 4.4 40.2 PGF Sato et al. (1999)9 Yunlong 25.8 99.4 Km 29 F, R 38.3 50.7 3.4 56.7 170.1 4.0 38.3 PGF Yang et al. (2001)10 Xiaguan 25.6 100.2 Km 9 F, R 6.9 47.7 8.6 83.6 152.7 10.0 6.9 PGF Huang and Opdyke

(1993)11 Weishan 25.4 100.2 Ju 5 7.3 25.3 10.4 76.3 250.0 10.4 7.3 PGF Huang and Opdyke,

199312 Yongping 25.5 99.5 Kl 12 F 42.0 51.1 15.7 50.9 167.3 20.6 42.0 PGF Funahara et al.,

(1993)13 Jingdong 24.5 100.8 Kl–m 13 F 8.3 48.8 7.7 81.2 145.8 8.9 8.3 PGF Tanaka et al. (2008)14 Jinggu 23.6 100.5 Jm 10 83.3 36.8 5.4 14.0 173.6 4.2 83.3 PGF Chen et al. (1995)15 Jinggu 23.4 100.4 Kl 3 84.4 39.6 17.8 13.6 171.5 - 84.4 PGF Chen et al. (1995)16 Jinggu 23.4 100.5 Km 7 F 115.8 36.0 6.3 �13.9 161.3 - 115.8 PGF Chen et al. (1995)17 Jinggu 23.4 100.9 Km 8 79.4 43.3 9.1 18.9 170.0 8.9 79.4 PGF Huang and Opdyke

(1993)18 Zhenyuan 24.1 101.1 Kl–m 7 F 61.8 46.1 8.1 34.7 172.7 8.1 61.8 PGF Tanaka et al. (2008)19 West Zhenyuan 24.1 101.1 Kl–m 4 F 144.2 49.4 6.4 �25.7 135.2 7.7 144.2 PGF Tanaka et al. (2008)20 Pu’er 23.0 101.0 Kl–m 25 F 59.9 45.2 5.1 35.8 173.1 5.6 59.9 PGF Sato et al. (2007)21 Mengla 21.6 101.4 Km 10 60.8 37.8 7.6 33.7 179.3 8.2 60.8 PGF Huang and Opdyke

(1993)22 South Mengla 21.4 101.6 Kl–m 14 F 51.2 46.4 5.6 43.6 172.1 6.1 51.2 PGF Tanaka et al. (2008)23 Nan 19.2 101.0 Jl–u 11 F 32.2 33.3 12.2 60.1 186.5 11.7 32.2 PGF Aihara et al. (2007)24 Phong Saly 21.6 101.9 Ju–Kl 19 F 28.8 32.1 8.8 63.4 193.9 7.4 28.8 PGF Takemoto et al.

(2009)

Central and southern part of Indochina25 Lai Chau 22.3 103.4 Ku 5 F 12.2 40.1 4.7 78.7 188.0 5.1 12.2 PGF Takemoto et al.

(2005)26 Yen Chau 21.0 104.4 Ku 8 F 3.2 26.7 12.9 83.2 255.6 10.8 3.2 PGF Takemoto et al.

(2005)27 Borikhanxay 18.5 103.8 Ju–Kl 18 F 42.1 46.9 7.9 50.7 169.7 8.7 42.1 PGF Takemoto et al.

(2009)28 Amphoe Bung

Kuan18.2 103.9 Km 14 31.8 28.7 3.5 59.4 190.8 3.5 31.8 PGF Charusiri et al. (2006)

29 Nam Nao 16.5 103.0 Kl 10 28.1 40.5 2.4 62.7 173.3 2.4 28.1 PGF Yang and Besse(1993)

30 Nam Nao 16.5 103.3 Ju 10 31.8 28.7 3.5 64.8 178.1 2.3 31.8 PGF Yang and Besse(1993)

31 Muan SakonNakhon

16.5–17.2

102.5–104.1

Km 8 31.4 27.1 9.4 59.7 192.7 9.4 31.4 PGF Charusiri et al. (2006)

32 Muan SakonNakon

16.5–17.2

102.5–104.1

Kl 4 F 31.8 38.3 5.7 59.7 178.2 5.7 31.8 PGF Charusiri et al. (2006)

33 Muang Phin 16.5 106.0 J (Km) 23 30.8 39.9 3.0 60.5 178.6 3.0 30.8 PGF Takemoto et al.(2009)

34 Da Lat 10.4–12.5

105.0–109.4

J–K 21 14.5 33.3 6.3 74.2 171.1 5.9 14.5 PGF Chi and Dorobek(2004)

35 16.7 101.8 Jl 8 F 39.5 46.3 7.1 54.4 175.5 7.3 39.5 PGF Yang and Besse(1993)

36 16.7 101.8 Tu/Jl 13 F 40.4 47.8 4.7 53.6 173.3 4.9 40.4 PGF Yang and Besse(1993)

37 16.7 101.8 Tu 5 F 42.2 50.2 6.7 52.1 169.8 7.3 42.2 PGF Yang and Besse(1993)

358 J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364

Table 2 (continued)

ID Sampling information Age N Test Observed direction Paleomagnetic pole Rotation Ref. Reference

Locality Lat.(�N)

Lon. (�E) Dec.(�)

Inc.(�)

a95 Lat.(�N)

Lon.(�E)

A95 (�) (�)

South China38 Jl–m 79.9 221.8 6.3 Yang and Besse

(2001)39 Tu 52.0 187.3 – Huang et al. (2008a)40 Tm 50.8 227.7 5.2 Su et al. (2005)41 Pm–Tl 42.7 215.9 3.3 Su et al. (2005)42 P/T 48.8 227.7 3.1 Yang and Besse

(2001)43 Pm 52.7 246.4 9.1 Yang and Besse

(2001)44 Pl 65.3 265.2 6.5 Lin and Fuller (1990)

# Abbreviations are: Lat./Long., latitude and longitude of sampling area; N, number of sites used in paleomagnetic statistics; Dec. and Inc., declination and inclination; a95 andA95, radius of circle of 95 percent confidence of observed direction and paleomagnetic pole; F and R, reversal and fold test; PGF, Present Geomagnetic Field; Rotationaldifference is evaluated by comparing observed paleomagnetic declination with that expected from reference pole (Ref.), positive and negative values represent CW and CCWrotation, respectively; D, C, P, T, J and Oli represent Devonian, Carboniferous, Permian, Triassic and Oligocene, respectively with l = Early, m = Middle, and u = Late.

J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364 359

is noteworthy that this study found a large declinational differenceof �85� between the northern and southern parts of the BaoshanTerrane, suggesting a CW rotation of the southern Baoshan of�85� since the Early Permian.

For the northern Baoshan Terrane, comparison between EarlyPermian (Huang and Opdyke, 1991) and Oligocene poles(Kornfeld et al., 2014) indicates little or no significant counter-clockwise (CCW) rotation (13.1�) between Early Permian andOligocene times followed by a CW rotation of 42.2� relative to pre-sent geomagnetic field (PGF) after Oligocene times. The later signif-icant CW rotation is likely to have resulted from the India-Asiacollision. For the southern Baoshan Terrane however, a paleomag-netic comparison between Early Permian (Huang and Opdyke,1991), Late Triassic (this study), and Jurassic (Huang and Opdyke,1993) poles indicates a CCW rotation of 7.5� ± 13.1� betweenEarly Permian and Late Triassic times, a CW rotation of22.2� ± 10.6� from Late Triassic to Jurassic times, and a CW rotationof 99.7� (relative to PGF) after Jurassic times. Although someremarkably large rotations are identified here, neither northernnor southern part of the Baoshan Terrane appear to have been sub-jected to large-scale vertical-axis rotational motion betweenPermian and Jurassic times. In other words, the large-scalepost-Permian CW rotation of the southern Baoshan Terrane rela-tive to the northern Baoshan Terrane (Huang and Opdyke, 1991)should have occurred later than the Jurassic and is most probablyrelated to crustal rotational deformation around the East HimalayaSyntaxis (Huang and Opdyke, 1993; Yang and Besse, 1993; Otofujiet al., 2010; Tong et al., 2013; Kornfeld et al., 2014).

More broadly, differential India-Asia collision-induced CW rota-tions have also been observed between the northern and southernparts of the Simao Terrane of the Indochina Block. As shown inFig. 8, available Jurassic and Cretaceous paleomagnetic data fromthe Jinggu (Huang and Opdyke, 1993; Chen et al., 1995),Zhenyuan (Tanaka et al., 2008), Mengla (Huang and Opdyke,1993; Tanaka et al., 2008), and Pu’er (Sato et al., 2007) areas ofsouthern Simao indicate large-scale Cenozoic CW rotation rangingfrom �50� to 144� (Table 2). Meanwhile, Tanaka et al. (2008) fur-ther argue for a Cenozoic CW rotation of �90� relative to the PGFresulting in an approximately easterly-deflected Jurassic–Cretaceous declination for southern Simao. However, Cretaceouspaleomagnetic data from the Yunlong (Sato et al., 1999; Yanget al., 2001) and Yongping (Funahara et al., 1993) areas of northernSimao suggest relatively smaller Cenozoic CW rotation of �38� to42�, and even little or no significant rotation (�7–8�) in theXiaguan, Weishan (Huang and Opdyke, 1993), and Jingdong areas,any small magnitude rotations here could have a local tectonicexplanation (Tanaka et al., 2008).

For the other parts of the Sibumasu and Indochina blocks, theCenozoic rotation pattern is a little more complicated. As summa-rized by Otofuji et al. (2012), preliminary Jurassic–Cretaceous pale-omagnetic results from the Kalaw area of East Myanmar (Richterand Fuller, 1996) yielded a Cenozoic CW rotation of �45� (relativeto PGF) for the Shan State Terrane; while the Cretaceous paleomag-netic results from the Khorat Basin (Yang and Besse, 1993;Charusiri et al., 2006; Takemoto et al., 2009) implied a CenozoicCW rotation (relative to PGF) of �30� for the central part of theIndochina Block. However, only little or marginal significantCenozoic CW rotation of �11� (relative to PGF) was observed fromthe Da Lat area of southeastern tip of the Indochina Peninsula(Otofuji et al., 2012). For this noticeable divergence in rotationalmotion, the original authors interpreted it in terms of a secondphase CCW rotation of 27� ± 10� of the Kontum Terrane relativeto the Khorat Basin and it most probably resulted from the32–17 Ma sinistral movement of the Kontum Terrane along theEast Vietnam Boundary Fault.

In summary, with the exception of the Kontum Terrane insoutheastern tip of the Indochina Block, large-scale Cenozoicvertical-axis CW rotations have been observed from different ter-ranes located on both sides of the CMI belt. In particular, relativelyabundant Jurassic to Cretaceous paleomagnetic data from theBaoshan and Simao terranes suggest that the northern part of thesetwo terranes experienced a Cenozoic CW rotation of �40� (relativeto PGF); whereas the southern part may have been subjected to amuch larger Cenozoic CW rotation of �90� relative to the PGF(Fig. 8). Therefore, when we make a rotational motion correctionto the northern and southern segments of theChangning-Menglian suture according to the above differentialCenozoic CW rotation observed in the northern and southern partsof the Baoshan and Simao terranes respectively, the currentlyNW–SE to NE–SW directed Changning-Menglian suture will havean orientation of approximately east-to-west extended (Fig. 8).This implies that the eastern branch of the Paleotethys Ocean islikely to have subducted northward and closed along a nearlyeast-to-west directed suture zone. As a result, direct comparisonof paleolatitudes of the terranes/blocks located on both sides ofthe East Paleotethys Ocean should provide robust constraints onthe timing and location of the closure of the East Paleotethys Ocean.

5.3. The closure of the East Paleotethys Ocean

Based on available paleopoles from the Sibumasu, Indochinaand South China blocks (Table 2), the South China and Indochinablocks (reference site: Lincang, 100.1�E, 23.9�N) is constrained tohave moved from a paleolatitude near the paleo-equator to a

360 J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364

higher paleolatitude around �20�N in the Northern Hemisphere inthe Early Permian to Late Triassic with little vertical-axis rotationalmotion. However, the Baoshan Terrane of the Sibumasu Block for-merly occupied a paleolatitude as high as �42�S in the SouthernHemisphere during the Early Permian (Ali et al., 2013; Huangand Opdyke, 1991), and moved rapidly northward to low latitudesaround �15�N in the Northern Hemisphere by Late Triassic times.As shown in Fig. 7, the Late Triassic to Jurassic paleomagnetic polesfrom the Sibumasu, Indochina and South China blocks are dis-tributed along a small circle centered on the reference site ofLincang. This is the paleomagnetic signature of regional block rota-tion and indicates that these blocks occupied similar paleolatitudesduring Late Triassic to Jurassic times; they may have collided witheach other by the Late Triassic.

The view that the Sibumasu, Indochina, and South China blockshad collided by the Late Triassic is consistent with substantial geo-logical evidence suggesting the main East Paleotethys Ocean hadclosed by the Late Triassic. Firstly, the 200–230 Ma Lincang graniteon the east fringe of the Changning-Menglian suture zone indicatesa continent–continent collision between the Baoshan and Simaoterranes no later than the Late Triassic (Dong et al., 2013).Secondly, the chronostratigraphic range of pelagic sediments inthe CMI suture zone ranges from Middle Devonian to Late

Fig. 7. Equal area projections of the Late Paleozoic to Mesozoic paleomagnetic poles of thof expected declination from reference site.

Anisian/Early Ladinian stages of the Middle Triassic in which theyoungest horizon is represented by the Triassocampe deweveri radi-olarian assemblage (Feng et al., 1999; Feng, 2002). In contrast theMae Sariang Group in the Inthanon suture zone, consisting ofMiddle–Late Triassic radiolarian cherts and turbiditic clastics, isnon-pelagic and represents deposits more proximate to theSibumasu margin (Kamata et al., 2002). Geochemical andgeochronological study (Wang et al., 2010) of the Xiaodingxi(214 ± 7 Ma) and Manghuihe (210 ± 22 Ma) volcanic sequences,representative of the Lancangjiang igneous zone and dominatedby alkaline basalts and basaltic andesites, indicates that theLancangjiang igneous zone was erupted in a post-collisional exten-sional setting, confirming again the commencement of theBaoshan-Simao collision should have occurred at least prior to for-mation of this igneous zone. Thirdly, paleontological studies (Fang,1994; Hisada et al., 2001; Jin, 2002; Wang and Sugiyama, 2002)show that the Sibumasu Block fauna exhibits a progressive transi-tion to non-marine provinciality from the peri-GondwananIndoralian Province (i.e. the Asselian Bandoproductus–Punctocyrtella–Tomiopsis brachiopod assemblage) in the EarlyPermian to an endemic Sibumasu Province in the MiddlePermian and then into an equatorial Cathaysian Province in theLate Permian.

e Baoshan Terrane and surrounding blocks. The dashed gray line shows the direction

GLG

SZ

SCSZ

ALSRRSZ

18

19

1

2

3?

4

56

8 9

13

14

1516 17

20

21

12

10

11

Cha

ngni

ng-M

engl

ian

sutu

re

22

Sampling site

Fig. 8. Sketch geological map showing major units and faults in the Baoshan area modified after Wang et al. (2006). Arrows represent declination deviations (rotations aboutvertical axes) from the present-day meridian (dashed lines). The long blue/orange rectangle shows orientations of the East Paleotethys Suture Zone at present/before theIndia-Asia collision-induced rotational deformation. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364 361

362 J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364

On the other hand, substantial geological evidence suggests thatthe Jinshajiang-Ailaoshan-Song Ma-Song Chay Ocean (Faure et al.,2014), separating the Indochina Block in the south from the SouthChina Block in the north (c.f. Section 5.2), should have closed atleast by the Late Triassic. Recent geochronological and geochemicalstudy of the Xin’anzhai monzogranite (251.6 ± 2.0 Ma) and theTongtiange leucogranite (247.5 ± 2.2 Ma) in the Ailaoshan suturezone indicates that emplacement of these igneous intrusionsmarked the termination of accretion of Indochina to the SouthChina Block and commencement of the Indosinian Orogeny (Liuet al., in press). This in turn suggests that the northern branch ofthe East Paleotethys may have closed by latest Permian to earliestTriassic times. Meanwhile, as summarized by Lai et al. (2014), theMiddle Triassic regional unconformity, supported by detrital U–Pbzircon ages from West Ailaoshan sandstones and the Middleto Late Triassic post-collisional granitoids along the Jinshajiang(ca. 235–230 Ma, Zhu et al., 2011) and Truong Son(ca. 230–200 Ma; Liu et al., 2012) regions, implies that theJinshajiang-Ailaoshan-Song Ma Ocean should have completelyclosed by the Late Triassic. Furthermore, field structuralobservations and systematic analysis of published data in NorthVietnam indicated a Middle Triassic age for the South ChinaBlock-Indochina collision, which is strongly supported by a LateTriassic regional unconformity, postorogenic stitching granitoids,and a Early–Middle syntectonic metamorphism (see Faure et al.,2014 for details).

6. Conclusions

A paleomagnetic study of the Late Triassic Niuhetang basalticlavas from the Baoshan Terrane of the Sibumasu Block yields apaleomagnetic pole at 160.9�E, 21.7�S (A95 = 6.1�) with positive foldand reversal tests. Together with a significant deviation fromyounger paleopoles from this terrane and a compatible VGP disper-sion (12.8�) to the global PSV model during the last 5 Ma, this indi-cates that the time-averaged geomagnetic field has beenadequately sampled. We therefore believe that this pole is a repre-sentative record of the paleomagnetic field during the time oferuption of the Niuhetang basaltic lavas.

The new Late Triassic paleomagnetic pole suggests that theBaoshan Terrane was situated in the Northern Hemisphere around�15�N during eruption of these lavas. Further comparison withavailable paleomagnetic results from the Baoshan Terrane suggeststhat this terrane experienced little or non-significant CCW rotationduring the Early Permian/Late Triassic to Jurassic interval; but amore important observation is that the southern part of the terraneexperienced a post-Jurassic CW rotation of �90� relative to thenorthern sector. The significant differential Cenozoic CW rotationalmotion between northern and southern parts of the Baoshan andSimao terranes indicates that the currently nearly north-to-southdirected East Paleotethys suture zone is very likely to haveextended approximately west to east during the suturing of theEast Paleotethys Ocean. Therefore paleolatitudinal overlap of theBaoshan and Indochina blocks is a key issue for identifying the tim-ing and position of the East Paleotethys Ocean. The Late Triassicpaleomagnetic pole suggests that the Baoshan Terrane occupiedsimilar paleolatitudes to the South China and Indochina blocksduring the Middle to Late Triassic thus indicating that the EastPaleotethys Ocean closed no later than the Late Triassic at low lat-itudes of �15�N.

Acknowledgments

This work was financially supported by a National NaturalScience Foundation of China (NSFC) project (41190071) of Major

NSFC Program (41190070) ‘‘Reconstruction of East Asian Blocksin Pangaea’’. We are grateful to Jinjiang Zhang and John D.A.Piper for their constructive discussions and suggestions and toLiwei Chen and Jianjun Li for field assistance. We are also greatlyindebted to Michel Faure, Yo-ichiro Otofuji and another anony-mous reviewer for careful reviews that greatly improved themanuscript.

References

Acharyya, S.K., 1998. Break-up of the greater Indo-Australian continent andaccretion of blocks framing South and East Asia. J. Geodyn. 26, 149–170.

Aihara, K., Takemoto, K., Zaman, H., Inokuchi, H., Miura, D., Surinkum, A., Paiyarom,A., Phajuy, B., Chantraprasert, S., Panjasawatwong, Y., Wongpornchai, P., Otofuji,Y., 2007. Internal deformation of the Shan-Thai block inferred frompaleomagnetism of Jurassic sedimentary rocks in Northern Thailand. J. AsianEarth Sci. 30, 530–541.

Ali, J.R., Cheung, H.M.C., Aitchison, J.C., Sun, Y.D., 2013. Palaeomagnetic re-investigation of Early Permian rift basalts from the Baoshan Block, SW China:constraints on the site-of-origin of the Gondwana-derived eastern Cimmerianterranes. Geophys. J. Int. 193 (2), 650–663. http://dx.doi.org/10.1093/gji/ggt012.

Brookfield, M.E., 1996. Reconstruction of western Sibumasu. J. Geol., 65–80Cao, S.Y., Liu, J.L., Leiss, B., Neubauer, F., Genser, J., Zhao, C.Q., 2011a. Oligo-Miocene

shearing along the Ailao Shan-Red River shear zone: constraints from structuralanalysis and zircon U/Pb geochronology of magmatic rocks in the DiancangShan massif, SE Tibet, China. Gondwana Res. 19, 975–993.

Cao, S.Y., Neubauer, F., Liu, J.L., Genser, J., Leiss, B., 2011b. Exhumation of theDiancang Shan metamorphic complex along the Ailao Shan-Red River belt,southwestern Yunnan, China: evidence from 40Ar/39Ar thermochronology. J.Asian Earth Sci. 42, 525–550.

Carter, A., Roques, D., Bristow, C., Kinny, P., 2001. Understanding Mesozoic accretionin Southeast Asia: significance of Triassic thermotectonism (Indosinianorogeny) in Vietnam. Geology 29, 211–214.

Chan, L.S., Wang, C.Y., Wu, X.Y., 1984. Paleomagnetic results from some Permian-Triassic rocks from southwestern China. Geophys. Res. Lett. 11, 1157–1160.

Charusiri, P., Imsamut, S., Zhuang, Z., Ampaiwan, T., Xu, X., 2006. Paleomagnetism ofthe earliest Cretaceous to early Late Cretaceous sandstones, Khorat Group,Northeast Thailand: implications for tectonic plate movement of the Indochinablock. Gondwana Res. 9, 310–325.

Chen, H., Dobson, J., Heller, F., Hao, J., 1995. Paleomagnetic evidence for clockwiserotation of the Simao region since the Cretaceous: a consequence of India-Asiacollision. Earth Planet. Sci. Lett. 134, 203–217.

Chen, Z., Burchfiel, B.C., Liu, Y., King, R.W., Royden, L.H., Tang, W., Wang, E., Zhao, J.,Zhang, X., 2000. Global positioning system measurements from eastern Tibetand their implications for India/Eurasia intercontinental deformation. J.Geophys. Res.: Sol. Earth 105, 16215–16227.

Chi, C.T., Dorobek, S.L., 2004. Cretaceous palaeomagnetism of Indochina andsurrounding regions: Cenozoic tectonic implications, In: Malpas, J., Fletcher,C.J.N., Ali, J.R. (Eds.), Aspects of the Tectonic Evolution of China, GeologicalSociety Special Publication No. 226, pp. 273–287.

Collins, W.J., 2003. Slab pull, mantle convection, and Pangaean assembly anddispersal. Earth Planet. Sci. Lett. 205, 225–237.

Day, R., Fuller, M., Schmidt, V.A., 1977. Hysteresis properties of titanomagnetites:grain-size and compositional dependence. Phys. Earth Planet. In. 13, 260–267.

Deenen, M.H.L., Langereis, C.G., van Hinsbergen, D.J.J., Biggin, A.J., 2011.Geomagnetic secular variation and the statistics of palaeomagnetic directions.Geophys. J. Int. 186, 509–520.

Dong, G.C., Mo, X.X., Zhao, Z.D., Zhu, D.C., Goodman, R.C., Kong, H.L., Wang, S., 2013.Zircon U–Pb dating and the petrological and geochemical constraints onLincang granite in Western Yunnan, China: implications for the closure of thePaleo-Tethys Ocean. J. Asian Earth Sci. 62, 282–294.

Dunlop, D.J., 2002. Theory and application of the Day plot (Mrs/Ms versus Hcr/Hc) 1.Theoretical curves and tests using titanomagnetite data. J. Geophys. Res.: Sol.Earth 107, EPM 4-1–EPM 4-22.

Fang, Z.J., 1994. Biogeographic constraints on the rift-drift-accretion history of theSibumasu block. J. SE Asian Earth Sci. 9, 375–385.

Fang, W., Van der Voo, R., Liang, Q.Z., 1989. Devonian paleomagnetism of YunnanProvince across the Shan Thai-South China Suture. Tectonics 8, 939–952.

Faure, M., Lepvrier, C., Nguyen, V.V., Vu, T.V., Lin, W., Chen, Z., 2014. The South Chinablock-Indochina collision: where, when, and how? J. Asian Earth Sci. 79 (Part A),260–274.

Feng, Q.-L., 2002. Stratigraphy of volcanic rocks in the Changning-Menglian Belt insouthwestern Yunnan, China. J. Asian Earth Sci. 20, 657–664.

Feng, Q.L., Ge, M.C., Xie, D.F., Ma, Z.D., Jiang, Y.S., 1999. Stratigraphic sequence andtectonic evolution in passive continental margin, Jinshajiang belt, northwesternYunnan Province, China. Earth Sci.-J. China Univ. Geosci. 24, 553–557 (inChinese).

Fisher, R., 1953. Dispersion on a sphere. Proc. Roy. Soc. Lond. A217, 295–305.Funahara, S., Nishiwaki, N., Murata, F., Otofuji, Y., Wang, Y.Z., 1993. Clockwise

rotation of the Red River fault inferred from paleomagnetic study of Cretaceousrocks in the Shan-Thai-Malay block of western Yunnan, China. Earth Planet. Sci.Lett. 117, 29–42.

J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364 363

Gan, W.J., Zhang, P.Z., Shen, Z.K., Niu, Z.J., Wang, M., Wan, Y.G., Zhou, D.M., Cheng, J.,2007. Present-day crustal motion within the Tibetan Plateau inferred from GPSmeasurements. J. Geophys. Res.: Sol. Earth 112, B08416.

Golonka, J., 2007. Late Triassic and Early Jurassic palaeogeography of the world.Palaeogeogr. Palaeoclimatol. Palaeoecol. 244, 297–307.

Hisada, K.-I., Ueno, K., Sugimaya, T., Nagai, K., Wang, X.D., 2001. Confirmation ofDropstones in the Dingjiazhai Formation of the Gondwana-Derived BaoshanBlock, West Yunnan. Gondwana Res. 4, 630–631.

Huang, K.N., Opdyke, N.D., 1991. Paleomagnetic results from the UpperCarboniferous of the Shan-Thai-Malay Block of Western Yunnan, China.Tectonophysics 192, 333–344.

Huang, K.N., Opdyke, N.D., 1993. Paleomagnetic results from Cretaceous andJurassic rocks of South and Southwest Yunnan: evidence for large clockwiserotations in the Indochina and Shan-Thai-Malay terranes. Earth Planet. Sci. Lett.117, 507–524.

Huang, B.C., Zhou, Y.X., Zhu, R.X., 2008a. Discussions on Phanerozoic evolution andformation of continental China, based on paleomagnetic studies. Earth Sci.Front. 15, 348–359 (in Chinese).

Huang, H., Jin, X.C., Shi, Y.K., Yang, X.N., 2008b. Middle Permian Western TethyanFusulinids from Southern Baoshan Block, Western Yunnan, China. J. Paleontol.83, 880–896.

Jian, P., Liu, D.Y., Kröner, A., Zhang, Q., Wang, Y.Z., Sun, X.M., Zhang, W., 2009.Devonian to Permian plate tectonic cycle of the Paleo-Tethys Orogen insouthwest China (I): geochemistry of ophiolites, arc/back-arc assemblages andwithin-plate igneous rocks. Lithos 113, 748–766.

Jin, X.C., 2002. Permo-Carboniferous sequences of Gondwana affinity in southwestChina and their paleogeographic implications. J. Asian Earth Sci. 20, 633–646.

Jin, X.C., Huang, H., Shi, Y.K., Zhan, L.P., 2011. Lithologic boundaries in Permian post-glacial sediments of the Gondwana-affinity Regions of China: typical sections,age range and correlation. Acta Geol. Sin. – Engl. Ed. 85, 373–386.

Johnson, C.L., Constable, C.G., Tauxe, L., Barendregt, R., Brown, L.L., Coe, R.S., Layer, P.,Mejia, V., Opdyke, N.D., Singer, B.S., Staudigel, H., Stone, D.B., 2008. Recentinvestigations of the 0–5 Ma geomagnetic field recorded by lava flows. G-Cubed9. http://dx.doi.org/10.1029/2007GC001696.

Kamata, Y., Hisada, K., Nakornsri, N., Charusiri, P., Sashida, K., Ueno, K., 2002. Triassicradiolarian faunas from the Mae Sariang area, northern Thailand and theirpaleogeographic significance. J. Asian Earth Sci. 20, 491–506.

Kornfeld, D., Eckert, S., Appel, E., Ratschbacher, L., Pfänder, J., Liu, D.L., Ding, L., 2014.Clockwise rotation of the Baoshan Block due to southeastward tectonic escapeof Tibetan crust since the Oligocene. Geophys. J. Int. 197 (1), 149–163. http://dx.doi.org/10.1093/gji/ggu009.

Krischvink, J.L., 1980. The least-squares line and plane and the analysis ofpalaeomagnetic data. Geophys. J. Roy. Astron. Soc. 62, 699–718.

Kruiver, P.P., Dekkers, M.J., Heslop, D., 2001. Quantification of magnetic coercivitycomponents by the analysis of acquisition curves of isothermal remanentmagnetisation. Earth Planet. Sci. Lett. 189, 269–276.

Lai, C.-K., Meffre, S., Crawford, A.J., Zaw, K., Xue, C.-D., Halpin, J.A., 2014. TheWestern Ailaoshan Volcanic Belts and their SE Asia connection: a new tectonicmodel for the Eastern Indochina Block. Gondwana Res. 26, 52–74.

Leloup, P.H., Lacassin, R., Tapponnier, P., Schärer, U., Zhong, D.L., Liu, X.H., Zhang,L.S., Ji, S.C., Trinh, P.T., 1995. The Ailao Shan-Red River shear zone (Yunnan,China), Tertiary transform boundary of Indochina. Tectonophysics 251, 3–84.

Lepvier, C., Maluski, H., Vu, V.T., Leyreloup, A., Phan, T.T., Nguyen, V.V., 2004. TheEarly Triassic Indosinian orogeny in Vietnam (Truong Sone Belt and KontumMassif); implications on the geodynamic evolution of Indochina.Tectonophysics 393, 87–118.

Li, P.W., Gao, R., Cui, J.W., Ye, G., 2004. Paleomagnetic analysis of eastern Tibet:implications for the collisional and amalgamation history of the Three RiversRegion, SW China. J. Asian Earth Sci. 24, 291–310.

Li, S.H., Huang, B.C., Zhu, R.X., 2012. Paleomagnetic constraints on the tectonicrotation of the southeastern margin of the Tibetan Plateau. Chin. J. Geophys. 55(1), 76–94. http://dx.doi.org/10.6038/j.isn.0001-5733.2012.01.008 (in Chinese).

Liao, Z.T., Chen, Y.K., Wei, Z.H., Li, M.H., 2003. Tectonic evolution sine LatePalaeozoic Era in West Yunnan. J. Tongji Univ. 31, 1029–1033 (in Chinese).

Lin, J.L., Fuller, M., 1990. Palaeomagnetism, North China and South China Collision,and the Tan-Lu Fault. Philos. Trans. Roy. Soc. A331, 589–598. http://dx.doi.org/10.1098/rsta.1990.0091.

Liu, B.P., Feng, Q.L., Fang, N.Q., Jia, J.H., He, F.X., 1993. Tectonic evolution of Paleo-Tethys Poly-Island-Ocean in Changning-Menglian and Lancangjiang Belts,Southwestern Yunnan, China. Earth Sci.-J. China Univ. Geosci. 18, 529–539 (inChinese).

Liu, J., Tran, M.-D., Tang, Y., Nguyen, Q.-L., Tran, T.-H., Wu, W., Chen, J., Zhang, Z.,Zhao, Z., 2012. Permo-Triassic granitoids in the northern part of the Truong Sonbelt, NW Vietnam: geochronology, geochemistry and tectonic implications.Gondwana Res. 22, 628–644.

Liu, H.C., Wang, Y.J., Cawood, P.A., Fan, W.M., Cai, Y.F., Xing, X.W., 2015. Record ofTethyan ocean closure and Indosinian collision along the Ailaoshan suture zone(SW China). Gondwana Res. (in press). http://dx.doi.org/10.1016/j.gr.2013.12.013.

Maluski, H., Lepvrier, C., Leyreloup, A., Vu, V.T., Phan, T.T., 2005. 40Ar-39Argeochronology of the charnockites and granulites of the Kan Nack complex,Kon Tum Massif, Vietnam. J. Asian Earth Sci. 25, 653–677.

McElhinny, M.W., 1964. Statistical significance of the fold test in palaeomagnetism.Geophys. J. Roy. Astron. Soc. 8, 338–340.

McFadden, P.L., McElhinny, M.W., 1988. The combined analysis of remagnetizationcircles and direct observations in palaeomagnetism. Earth Planet. Sci. Lett. 87,161–172.

McFadden, P.L., McElhinny, M.W., 1990. Classification of the reversal test inpalaeomagnetism. Geophys. J. Int. 103, 725–729.

Metcalfe, I., 1996. Gondwanaland dispersion, Asian accretion and evolution ofeastern Tethys. Aust. J. Earth Sci. 43, 605–623.

Metcalfe, I., 2002. Permian tectonic framework and palaeogeography of SE Asia. J.Asian Earth Sci. 20, 551–566.

Metcalfe, I., 2006. Paleozoic and Mesozoic tectonic evolution and palaeogeographyof East Asian crustal fragments: the Korean Peninsula in context. GondwanaRes. 9, 24–46.

Metcalfe, I., 2013. Tectonic evolution of the Malay Peninsula. J. Asian Earth Sci. 76,195–213.

Morley, C.K., 2002. A tectonic model for the Tertiary evolution of strike–slip faultsand rift basins in SE Asia. Tectonophysics 347, 189–215.

Nam, T.N., Sano, Y., Terada, K., Toriumi, M., Van Quynh, P., Dung, L.T., 2001. FirstSHRIMP U–Pb zircon dating of granulites from the Kontum massif (Vietnam)and tectonothermal implications. J. Asian Earth Sci. 19, 77–84.

Otofuji, Y., Yokoyama, M., Kitada, K., Zaman, H., 2010. Paleomagnetic versus GPSdetermined tectonic rotation around eastern Himalayan syntaxis in East Asia. J.Asian Earth Sci. 37, 438–451.

Otofuji, Y., Tung, V.D., Fujihara, M., Tanaka, M., Yokoyama, M., Kitada, K., Zaman, H.,2012. Tectonic deformation of the southeastern tip of the Indochina Peninsuladuring its southward displacement in the Cenozoic time. Gondwana Res. 22,615–627.

Richter, B., Fuller, M. 1996. Paleomagnetism of the Sibumasu and Indochina blocks:implications for the extrusion tectonic model. In: Hall, R., Blundell, D. (Eds.),Tectonic Evolution of Southeast Asia, Geological Society Special Publication No.106, pp. 203–224.

Sato, K., Liu, Y.Y., Zhu, Z.C., Yang, Z.Y., Otofuji, Y., 1999. Paleomagnetic study ofmiddle Cretaceous rocks from Yunlong, western Yunnan, China: evidence ofsouthward displacement of Indochina. Earth Planet. Sci. Lett. 165, 1–15.

Sato, K., Liu, Y., Wang, Y., Yokoyama, M., Yoshioka, S., Yang, Z., Otofuji, Y., 2007.Paleomagnetic study of Cretaceous rocks from Pu’er, western Yunnan, China:evidence of internal deformation of the Indochina block. Earth Planet. Sci. Lett.257, 1–15.

Scotese, C.R., 2004. A continental drift flipbook. J. Geol. 112, 729–741.Sengör, A.M.C., 1987. Tectonics of the Tethysides: orogenic collage development in a

collisional setting. Annu. Rev. Earth Planet. Sci. 15, 213–244.Shen, Z.K., Lü, J.N., Wang, M., Bürgmann, R., 2005. Contemporary crustal

deformation around the southeast borderland of the Tibetan Plateau. J.Geophys. Res.: Sol. Earth 110, B11409.

Shi, G.R., Archbold, N.W., 1998. Permian marine biogeography of SE Asia. In: Robert,H., Hollyway, J.D. (Eds.), Biogeography and Geological Evolution of SE Asia.Backhys Publishers, Leiden, The Netherlands, pp. 57–72.

Sone, M., Metcalfe, I., 2008. Parallel Tethyan sutures in mainland Southeast Asia:new insights for Palaeo-Tethys closure and implications for the Indosinianorogeny. C.R. Geosci. 340, 166–179.

Stampfli, G.M., 2013. Response to the comments on ‘‘The formation of Pangea’’ byD.A. Ruban. Tectonophysics 608, 1445–1447.

Stewart, S.A., Jackson, K.C., 1995. Palaeomagnetic analysis of fold closure growthand volumetrics. Geol. Soc. Lond. Spec. Publ. 98, 283–295.

Su, L., Yang, Z.Y., Sun, Z.M., Yang, T.S., Zaman, H., Takemoto, K., Otofuji, Y., 2005.Regional deformational features of the South China Block inferred from MiddleTriassic palaeomagnetic data. Geophys. J. Int. 162, 339–356.

Takemoto, K., Halim, N., Otofuji, Y., Tri, T.V., De, L.V., Hada, S., 2005. Newpaleomagnetic constraints on the extrusion of Indochina: late Cretaceousresults from the Song Da Terrane, northern Vietnam. Earth Planet. Sci. Lett. 229,273–285.

Takemoto, K., Sato, S., Chanthavichith, K., Inthavong, T., Inokuchi, H., Fujihara, M.,Zaman, H., Yang, Z.Y., Yokoyama, M., Iwamoto, H., Otofuji, Y., 2009. Tectonicdeformation of the Indochina Peninsula recorded in the Mesozoicpalaeomagnetic results. Geophys. J. Int. 179, 97–111.

Tanaka, K., Mu, C.L., Sato, K., Takemoto, K., Miura, D., Liu, Y.Y., Haider, Z., Yang, Z.Y.,Yokoyama, M., Hisanori, I., Uno, K., Otofuji, Y.-I., 2008. Tectonic deformationaround the eastern Himalayan syntaxis: constraints from the Cretaceouspalaeomagnetic data of the Shan-Thai Block. Geophys. J. Int. 175, 713–728.

Tapponnier, P., Lacassin, R., Leloup, P.H., Scharer, U., Zhong, D.L., Wu, H.W., Liu, X.H.,Ji, S.C., Zhang, L.S., Zhong, J.Y., 1990. The Ailao Shan/Red River metamorphicbelt: Tertiary left-lateral shear between Indochina and South China. Nature 343,431–437.

Tong, Y.B., Yang, Z.Y., Zheng, L.D., Xu, Y.L., Wang, H., Gao, L., Hu, X.-Z., 2013. Internalcrustal deformation in the northern part of Shan-Thai Block: new evidence frompaleomagnetic results of Cretaceous and Paleogene redbeds. Tectonophysics608, 1138–1158.

Torsvik, T.H., Van der Voo, R., Preeden, U., Niocaill, C.M., Steinberger, B., Doubrovine,B.V., van Hinsbergen, D.J.J., Domeier, M., Gaina, C., Tohver, E., Meert, J.G.,McCausland, P.J.A., Cocks, R.M., 2012. Phanerozoic polar wander,palaeogeography and dynamics. Earth Sci. Rev. 114, 325–368.

Ueno, K., 2003. The Permian fusulinoidean faunas of the Sibumasu and Baoshanblocks: their implications for the paleogeographic and paleoclimatologicreconstruction of the Cimmerian Continent. Palaeogeogr. Palaeoclimatol.Palaeoecol. 193, 1–24.

Van der Voo, R., 1990. The reliability of paleomagnetic data. Tectonophysics 184, 1–9.Wang, Y.J., Fan, W.M., Zhang, Y.H., Peng, T.P., Chen, X.Y., Xu, Y.G., 2006. Kinematics

and 40Ar/39Ar geochronology of the Gaoligong and Chongshan shear systems,western Yunnan, China: implication for early Oligocene tectonic extrusion of SEAsia. Tectonophysics 418, 235–254.

364 J. Zhao et al. / Journal of Asian Earth Sciences 111 (2015) 350–364

Wang, X.D., Sugiyama, T., 2002. Permian coral faunas of the eastern CimmerianContinent and their biogeographical implications. J. Asian Earth Sci. 20, 589–597.

Wang, X.D., Sugimaya, T., Nagai, K., 2001a. Permo-Carboniferous Coral Faunas fromPaleo-Tethys in the Changning-Menglian Belt, West Yunnan, Southwest China.Gondwana Res. 4, 818–819.

Wang, X.D., Ueno, K., Mizuno, Y., Sugiyama, T., 2001b. Late Paleozoic faunal,climatic, and geographic changes in the Baoshan block as a Gondwana-derivedcontinental fragment in southwest China. Palaeogeogr. Palaeoclimatol.Palaeoecol. 170, 197–218.

Wang, X.D., Shi, G.R., Sugiyama, T., 2002. Permian of West Yunnan, SouthwestChina: a biostratigraphic synthesis. J. Asian Earth Sci. 20, 647–656.

Wang, Y.J., Zhang, A.M., Fan, W.M., Peng, T.P., Zhang, F.F., Zhang, Y.H., Bi, X.W., 2010.Petrogenesis of late Triassic post-collisional basaltic rocks of the Lancangjiangtectonic zone, southwest China, and tectonic implications for the evolution ofthe eastern Paleotethys: geochronological and geochemical constraints. Lithos120, 529–546.

Watson, G.S., Enkin, R.J., 1993. The fold test in paleomagnetism as a parameterestimation problem. Geophys. Res. Lett. 20, 2135–2137.

Wopfner, H., 1996. Gondwana origin of the Baoshan and Tengchong terranes ofWest Yunnan, in Tectonic Evolution of Southeast Asia. In: Hall, R., Blundell, D.(Eds.), Geol. Soc. London, Special Publications, vol. 106, pp. 539–547.

Yang, Z.Y., Besse, J., 1993. Paleomagnetic study of Permian and MesozoicSedimentary-Rocks from Northern Thailand Supports the Extrusion Model forIndo-China. Earth Planet. Sci. Lett. 117, 525–552.

Yang, Z.Y., Besse, J., 2001. New Mesozoic apparent polar wander path for southChina: Tectonic consequences. J. Geophys. Res.: Sol. Earth 106, 8493–8520.

Yang, Z.Y., Yin, J.Y., Sun, Z.M., Otofuji, Y., Sato, K., 2001. Discrepant Cretaceouspaleomagnetic poles between Eastern China and Indochina: a consequence ofthe extrusion of Indochina. Tectonophysics 334, 101–113.

Yunnan Bureau of Geology and Mineral Resources (YBGMR), 1984. Geological map(1:200000) of the People’s Republic of China, Nansan sheet (F-47-III) andGengma sheet (F-47-IV).

Zhu, J.J., Hu, R.Z., Bi, X.W., Zhong, H., Chen, H., 2011. Zircon U–Pb ages, Hf–O isotopesand whole-rock Sr–Nd–Pb isotopic geochemistry of granitoids in the Jinshajiangsuture zone, SW China: constraints on petrogenesis and tectonic evolution ofthe Paleo-Tethys Ocean. Lithos 126, 248–264.

Zijderveld, J.D.A., 1967. A.C. demagnetization of rocks: analysis of results. In:Collinson, D.W., Greer, K.M., Runcorn, S.K. (Eds.), Methods on Paleomagnetism.Elsevier, Amsterdam.