Geoscience Frontiers xxx (2016) 1e9

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China University of Geosciences (Beijing)

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Research paper

Middle Jurassiceearly Cretaceous radiolarian assemblages of thewestern Yarlung Zangbo Suture Zone: Implications for the evolution ofthe Neo-Tethys

Hanting Zhong a,b, Jingen Dai a,*, Chengshan Wang a, Yalin Li a, Yushuai Wei a

a State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences and Resources, Research Center for Tibetan Plateau Geology,China University of Geosciences (Beijing), Beijing 100083, Chinab Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, China

a r t i c l e i n f o

Article history:Received 27 February 2016Received in revised form12 September 2016Accepted 26 September 2016Available online xxx

Keywords:Radiolarian chertJurassicCretaceousYarlung Zangbo Suture Zone

* Corresponding author.E-mail address: djgtibet@163.com (J. Dai).Peer-review under responsibility of China University

http://dx.doi.org/10.1016/j.gsf.2016.09.0061674-9871/� 2016, China University of Geosciences (Belicense (http://creativecommons.org/licenses/by-nc-nd/

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a b s t r a c t

Cherts in the Zhongba mélange of the western Yarlung Zangbo Suture Zone (YZSZ) contain well pre-served radiolarian assemblages. These radiolarian assemblages indicate that the Zhongba mélange hasmiddle Jurassiceearly Cretaceous remnant, are coeval with those from the central and eastern parts ofthe YZSZ. Cherts from the Najiu area yield Aalenian to Aptian radiolarians, while cherts interbedded withsiliceous mudstones from the Bielongjiala area yield Aptian radiolarians, indicating that terrigenous-derived sediments were deposited during early Aptian. The above observations indicate that the entireYZSZ have a similar geochronological framework and thus they underwent similar geological evolution:(1) during the Jurassic, the Neo-Tethys was a wide ocean with pelagic sediments distal from continents;(2) during the Cretaceous (around 130e120 Ma), the Neo-Tethys started to subduct along the southernmargin of the Lhasa block, and terrigenous-derived siliceous mudstone began deposition.

� 2016, China University of Geosciences (Beijing) and Peking University. Production and hosting byElsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

1. Introduction

The Yarlung Zangbo Suture Zone (YZSZ) in the southern Tibetrepresents remnants of Neo-Tethyan oceanic lithosphere (Hébertet al., 2012). Existing isotopic geochronological studies on theophiolites reveal that they were formed around 130e120 Ma (Daiet al., 2013; Wu et al., 2014). These ages are much younger thanthe timing of the Neo-Tethys opening (as early as late Permian toearly Triassic) (Garzanti et al., 1999). This paradox might beexplained by facts that these isotopically dated rocks were formedin a supra-subduction zone at the southern margin of the Asia (Daiet al., 2013; Xiong et al., 2016). Therefore, their ages may onlyrepresent the initial subduction of the Neo-Tethys rather than thespreading of the ocean.

The radiolarians from the mélange provide robust constraintson the whole history of the ocean from its initiation at mid-ocean

of Geosciences (Beijing).

ijing) and Peking University. Produc4.0/).

., et al., Middle Jurassiceearlyof the Neo-Tethys, Geoscienc

ridge to subduction at a trench because oceanic materials can beaccreted into the mélange by off scrapping of the lower plate(Wakita and Metcalfe, 2005). The radiolarians have been widelyused to investigate the occurrence of deep marine sediments andthe duration of the Neo-Tethys in the Indus-Yarlung Zangbo SutureZone (Figs. 1 and 2; Baxter et al., 2011). The radiolarian assemblagesindicate that the duration of the deep marine environment rangefrommiddle Triassic to early Eocene (Fig. 2; Wu,1984; Kojima et al.,2001; Matsuoka et al., 2002; Wang et al., 2002; Ding, 2003; Ziabrevet al., 2003, 2004; Aitchison et al., 2007; Li et al., 2007, 2009;Zyabrev et al., 2008; Baxter et al., 2010; Baxter et al., 2011; Lianget al., 2012; Li et al., 2013). Most of the above data are from thecentral and eastern segments of the YZSZ. However, very little isknown about the western segment.

Here we report assemblages of well-preserved and clearlyimaged radiolarians from the Zhongba mélange, the westernsegment of the YZSZ. These radiolarian assemblages indicate thatthe deep marine environment occurred in the western part of theYZSZ during middle Jurassic to early Cretaceous.

tion and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND

Cretaceous radiolarian assemblages of the western Yarlung Zangboe Frontiers (2016), http://dx.doi.org/10.1016/j.gsf.2016.09.006

Figure 1. Map of the Himalayan region showing the location of Indus, YarlungeZangbo and NagaeAndaman sutures zones (after Baxter et al., 2011). The highlighted numbers are thirteen regions where radiolarians have been reported.Location 1, Shergol mélange (Kojima et al., 2001); Location 2, Spongtang arc (Baxter et al., 2010); Location 3, Nidar ophiolite (Kojima et al., 2001; Zyabrev et al., 2008); Location 4, Zhongba mélange (Liang et al., 2012; Li et al., 2013; thisstudy); Location 5, Sangdanlin (Ding, 2003; Li et al., 2007); Location 6, Saiqu mélange (Li et al., 2009); Location 7, Chongdui chert (Wu, 1984); Location 8, Xialu chert (Matsuoka et al., 2002); Location 9, Dazhuqu terrane (Ziabrev et al.,2003); Location 10, Bainang terrane (Ziabrev et al., 2004); Location 11, Zongzhuo Formation (Li et al., 2009); Location 12, Zedong mélange (Wang et al., 2002; Aitchison et al., 2007); Location 13, Naga ophiolite (Baxter et al., 2011). YZSZ,Yarlung Zangbo Suture Zone; BNSZ, Bangong Nujiang Suture Zone; JSSZ, Jinshajiang Suture Zone.

H.Zhong

etal./

Geoscience

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inpress

as:Zhong,H

.,etal.,M

iddleJurassice

earlyCretaceous

radiolarianassem

blagesof

thewestern

YarlungZangbo

SutureZone:

Implications

forthe

evolutionof

theNeo-Tethys,G

eoscienceFrontiers

(2016),http://dx.doi.org/10.1016/j.gsf.2016.09.006

InduanO

lenekianA

nisian

LadinianC

arnian

Norian

Rhaetian

Hettangian

Sinem

urian

Pliensbachian

Toarcian

Aalenian

Bajocian

Bathonian

Callovian

Oxfordian

Kim

meridgian

Berriasian

ValanginianH

auterivian

Barrem

ian

Aptian

Albian

Cenom

anianTuronianC

oniacianS

antonian

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panian

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Danian

Selandian

Thanetian

YpresianLutetianB

artonian

Priabonian

Early Middle Late Early Middle Late

Jurassic Cretaceous Paleogene

Early LatePale-ocene

Triassic

Ma

Shergol ophiolite (Kojima et al., 2001)

Spongtang arc (Baxter et al., 2010)

Nidar ophiolite (Kojiama et al., 2001; Zyabrev et al., 2008)

Zhongba mélange (Liang et al., 2012)

Zhongba mélange (this study)

Zhongba mélange (Li et al., 2013)

Zheba Group (Ding et al., 2003)

Sangdanlin mélange (Li et al., 2007)

Saiqu mélange (Li et al., 2009)

Chongdui chert (Wu., 1984)

Xialu chert (Matsuoka et al., 2002)

Dazhuqu terrane (Ziabrev et al., 2003)

Zongzhuo Formation (Li et al., 2009)

Bainang chert (Ziabrev et al., 2004)

Zedong mélange (Aitchison et al., 2007)

Naga ophiolite (Baxter et al., 2011)

Eocene

Tithonian

250

Jinlu chert (Wang et al., 2002)

240

230

220

210

200

190

180

170

160

150

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130

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100 90 80 70 60 50 40

Figure 2. Chronostratigraphic chart summarising the age constraints of deep-water sedimentation in the Neo-Tethyan Ocean (see Fig. 1 caption for references).

H.Zhong

etal./

Geoscience

Frontiersxxx

(2016)1e9

3

Pleasecite

thisarticle

inpress

as:Zhong,H

.,etal.,M

iddleJurassice

earlyCretaceous

radiolarianassem

blagesof

thewestern

YarlungZangbo

SutureZone:

Implications

forthe

evolutionof

theNeo-Tethys,G

eoscienceFrontiers

(2016),http://dx.doi.org/10.1016/j.gsf.2016.09.006

0 2 4

km

N

Quaternary sediments

Cretaceous sandstone

Jurassic quartz sandstone,chert, siliceous mudstone

Limestone block

Basalt block

Diabase

Mélange

Sample location

Q

K

J

29°55′N

83°25′E 83°35′E

Bielongjiala

YDB

YDA

Py

Pyz

29°50′N

J2-K1

Najiu, Bielongjiala

Najiu

Figure 3. Geological map of the Najiu-Bielongjiala area in the Zhongba mélange, western Yarlung Zangbo Suture Zone, showing the sample locations.

H. Zhong et al. / Geoscience Frontiers xxx (2016) 1e94

2. Geologic setting

The Tibetan Plateau is an amalgamation of several blocksseparated by major suture zones including A’nemaqin-Kunlun,Jinshajiang, Bangong-Nujiang, and YZSZ (Yin and Harrison, 2000).The southernmost YZSZ is the youngest suture zone and has beenwidely considered to mark the collision zone between India andEurasia following the latest early Cretaceouseearly Paleogeneclosure of the Neo-Tethys (Allegre et al., 1984; Hébert et al., 2012;Dai et al., 2013).

The YZSZ roughly parallels the Yarlung Zangbo River forming anarrow EeW-trending belt. Towards the west, it connects with theNW-trending Indus suture, while towards the east it crosses theYarlung Zangbo River in Medog County and extends furthersouthward into Burma and Thailand (Yin and Harrison, 2000). Fourbasic tectonic units are related to the YZSZ: (1) the Gangdese arc,(2) the Xigaze forearc basin, (3) the Yarlung Zangbo ophiolite, and(4) the accretionary prism (Wang et al., 2012; Dai et al., 2013).

The Zhongba ophiolitic mélange is located in the western part ofthe YZSZ. It consists of various chaotic blocks of mantle peridotite(Dai et al., 2011b), late Devonian gabbro (Dai et al., 2011a), earlyCretaceous diabase (Dai et al., 2012), purplish red and greenish graybedded chert, massive and pillow basalt, limestone, and beddedsiliceous mudstone with a heterogeneous and variously deformedmatrix (Fig. 3). The matrix is composed mainly of shale, mudstone,sandstone and basalt. The lithofacies assemblages indicate thatthey are typical ophiolitic mélange (Raymond, 1975; Festa et al.,2012).

Here we report new radiolarians from four localities (Fig. 3).They are Py (29�56.800N, 83�18.580E) and Pyz (29�58.580N,83�18.870E) located in the Najiu area, YDA (29�47.340N, 83�44.740E)and YDB (29�47.330N, 83�43.320E) located in the Bielongjiala area.

Please cite this article in press as: Zhong, H., et al., Middle JurassiceearlySuture Zone: Implications for the evolution of the Neo-Tethys, Geoscienc

In the locations of YDA and YDB, the siliceous mudstone and shaleare interbedded with the chert.

3. Materials and methods

Forty-six potentially radiolarian-bearing samples were collectedfrom purplish red or greenish gray chert and siliceous mudstone inthese four locations. The samples were processed in biostratigraphylaboratory of Nanjing Institute of Geology and Palaeontology, Chi-nese Academy of Sciences. Each sample was broken into 2e3 cm3

pieces, suspended in a plastic beaker and immersed in 4e5% hy-drofluoric acid for 24 h. Acid residues were sieved, with microfos-sils concentrated in 61e380 mm. Samples were then dried and theresidues were collected. The process from immersing to collectingwas repeated 10 times for each sample to obtain enoughspecimens.

Radiolarians were picked by stereoscopic microscope andmounted onto aluminium stubs, coated with Ti-Au alloy-coatedthen photographed using a scanning electron microscope (SEM).More than 800 SEM photomicrographs were taken in AustralianCentre for Microscopy & Microanalysis (ACMM) in the University ofSydney.

4. Age assignment

Highly diverse and well-preserved radiolarians were collectedfrom purplish red chert and siliceous mudstone (Figs. 4 and 5).Identification of taxa and age assignment for middle Jurassic toearly Cretaceous radiolarian assemblages were based on detailedradiolarian taxonomic and biostratigraphic studies in the Tethys(Jud, 1994; O’Dogherty, 1994; Baumgartner et al., 1995; De Weveret al., 2001; O’Dogherty et al., 2009). The zonal scheme

Cretaceous radiolarian assemblages of the western Yarlung Zangboe Frontiers (2016), http://dx.doi.org/10.1016/j.gsf.2016.09.006

Figure 4. Composite plate of representative radiolarians from the Zhongba sample locations (all scale bars represent 100 mm). Sample Py-0-f9: (1) Archaeodictyomitra gifuensisTakemura; (2) Homoeoparonaella sp. aff. H. elegans (Pessagno); (3) Laxtorum(?) sp.; (4) Parahsuum(?) magnum Takemura; (5) Stichocapsa convexa Yao; Sample Py-0-f14: (6) Par-ahsuum(?) grande Hori & Yao; Sample Py-0-f15: (7) Parvicingula dhimenaensis sp. A; (8) Stichocapsa robusta Matsuoka; (9) Transhsuum maxwelli gr. (Pessagno); (10) Tricolocapsatetragona Matsuoka; Sample Py-0-f12: (11) Hiscocapsa(?) sp.; (12) Napora deweveri Baumgartner; (13) Parvicingula dhimenaensis Baumgartner; (14) Podobursa(?) aff.P. quadriaculeata (Steiger); (15) Protunuma japonicus Matsuoka & Yao; (16) Zhamoidellum ovum Dumitrica; Sample Pyz-1-f3: (17) Angulobracchia(?) portmanni portmanni Baum-gartner; (18) Loopus nuda (Schaaf); (19) Sethocapsa(?) zweilii Jud; (20) Tethysetta boesii gr. (Parona); (21) Xitus sp.; Sample Pyz-5-f5: (22) Podobursa typica (Rüst); (23) Squinabollumasseni (Tan); (24) Zhamoidellum(?) sp.

H. Zhong et al. / Geoscience Frontiers xxx (2016) 1e9 5

Please cite this article in press as: Zhong, H., et al., Middle Jurassiceearly Cretaceous radiolarian assemblages of the western Yarlung ZangboSuture Zone: Implications for the evolution of the Neo-Tethys, Geoscience Frontiers (2016), http://dx.doi.org/10.1016/j.gsf.2016.09.006

Figure 5. Composite plate of representative radiolarians from the Zhongba sample locations (all scale bars represent 100 mm). Sample YDA03: (1) Cryptamphorella gilkeyi(Dumitrica); (2) Cryptamphorella sp.; (3) Holocryptocanium barbui Dumitrica; (4) Pseudodictyomitra sp. cf. P. lodogaensis Pessagno; (5) Rhopalosyringium fossile (Squinabol); (6)Stichomitra japonica (Nakaseko & Nishimura); (7) Tethysetta boesii gr. (Parona); (8) Thanarla brouweri (Tan); (9) Xitus sp. aff. X. spicularius (Aliev); (10) Xitus clava (Parona); SampleYDA05: (11) Acaeniotyle diaphorogona gr. Foreman sense Baumgartner; (12) Podobursa typica (Rüst); (13) Xitus clava (Parona); Sample YDA13: (14) Pseudodictyomitra lancelotiSchaaf; (15) Pseudodictyomitra lodogaensis Pessagno; (16) Thanarla lacrimula (Foreman); (17) Xitus elegans (Squinabol); Sample YDB10: (18) Crolanium puga (Schaaf); (19) Hol-ocryptocanium barbui Dumitrica; (20) Stichomitra mediocris (Tan); (21) Thanarla brouweri (Tan); (22) Thanarla lacrimula (Foreman); (23) Thanarla sp.; (24) Xitus clava (Parona); (25)Xitus spicularius (Aliev).

H. Zhong et al. / Geoscience Frontiers xxx (2016) 1e96

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H. Zhong et al. / Geoscience Frontiers xxx (2016) 1e9 7

established in Japan and the western Pacific (Matsuoka, 1995a,b)was also referenced. The stratigraphic positions of the fossiliferoussediments were assigned with Unitary Association (UA) zonescorrelated to the geological time scale of Gradstein et al. (2012).Forty-six species belonging to 28 genera were identified (Fig. 6).

Sample Py-0-f9 contains abundant and moderately preservedradiolarian shells assigned to five species within four genera(Fig. 6). Among them, Homoeoparonaella sp. aff. H. elegans (Pes-sagno) appears in UAZones 1e3, Stichocapsa convexa Yao appears inUAZones 1e11, Parahsuum(?) magnum Takemura appears inUAZones 2e5 (Fig. 4; Baumgartner et al., 1995). The overlapping agerange of these species suggests a late Aalenian to early Bajocian(UAZones 2e3) age range.

Sample Py-0-f14 yields rare radiolarian shells assigned to 5species (Fig. 6). Among theses Jurassic radiolarians, Parahsuum(?)grande Hori & Yao and Parahsuum(?) natorense (El Kadiri) appear inUAZones 1e3, S. convexa Yao appears in UAZones 1e11, Transhsuummaxwelli gr. (Pessagno) appears in UAZones 3e10 (Baumgartneret al., 1995). Co-occurrence of them suggests an early Bajocian(UAZones 3) age.

Py-0-f9 Py-0-f12 Py-0-f1

chert chert chert

Acaeniotyle diaphorogona gr. Foreman sense BaumgartnerArchaeodictyomitra gifuensis Takemura ●

Angulobracchia (?) portmanni portmanni BaumgartnerCrolanium puga (Schaaf)Cryptamphorella gilkeyi (Dumitrica,1972)Cryptamphorella sp.Hiscocapsa (?) sp. ●

Holocryptocanium barbui DumitricaHomoeoparonaella sp. aff. H. elegans (Pessagno) ●

Laxtorum (?) sp. ●

Loopus nuda (Schaaf)Napora deweveri Baumgartner ●

Parahsuum (?) grande Hori & Yao ●

Parahsuum (?) magnum Takemura ●

Parahsuum (?) natorense (El Kadiri) ●

Parvicingula dhimenaensis Baumgartner ●

Parvicingula dhimenaensis sp. APodobursa (?) sp. aff. P. quadriaculeata (Steiger) ●

Podobursa sp.Podobursa typica (Rüst)Protunuma japonicus Matsuoka & Yao ●

Pseudodictyomitra lanceloti SchaafPseudodictyomitra lodogaensis PessagnoPseudodictyomitra sp. cf. P. lodogaensis PessagnoRhopalosyringium fossile (Squinabol)Sethocapsa (?) zweilii JudSquinabollum asseni (Tan)Stichocapsa convexa Yao ● ●

Stichocapsa robusta MatsuokaStichomitra mediocris (Tan)Stichomitra japonica (Nakaseko & Nishimura)Tethysetta boesii gr. (Parona)Thanarla brouweri (Tan)Thanarla lacrimula (Foreman)Thanarla sp. ●

Transhsuum maxwelli gr. (Pessagno) ●

Triactoma blakei (Pessagno) ●

Tricolocapsa tetragona MatsuokaTritrabs rhododactylus Baumgartner ●

Xitus clava (Parona)Xitus elegans (Squinabol)Xitus spicularius (Aliev)Xitus sp.Xitus sp. aff. X. spicularius (Aliev)Zhamoidellum ovum Dumitrica ●

Zhamoidellum (?) sp.Unitary Association (Baumgartner et al., 1995) 2-3 9-11 3Unitary Association (O'Dogherty, 1994)

Age late Aalen.to early Baj.

late Oxford.to early Tith. early Ba

SampleSpecies list

Figure 6. Occurrence of radiolarian species in Zhongba area and the ag

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Sample Py-0-f15 contains Parvicingula dhimenaensis sp. A, T.maxwelli gr. (Pessagno), Tricolocapsa tetragona Matsuoka, and Sti-chocapsa robustaMatsuoka (Fig. 4). T. tetragonaMatsuoka existed ina relatively short age range which constrains the sample’s ageranging from late Bajocian to early Bathonian (UAZones 5).

Sample Py-0-f12 yields abundant and well-preserved radio-larian shells referred to eight species (Fig. 6). Among them, Naporadeweveri Baumgartner appears in UAZones 7e11, P. dhimenaensisBaumgartner appears in UAZones 3e11, Podobursa(?) sp. aff.P. quadriaculeata (Steiger) appears in UAZones 9e17, ProtunumajaponicusMatsuoka & Yao appears in UAZones 7e12, Zhamoidellumovum Dumitrica appears in UAZones 9e11 (Fig. 4; Baumgartneret al., 1995). The overlapping age range of these species indicatesa late Oxfordian to early Tithonian (UAZones 9e11) age range.

Sample Pyz-1-f3 contains abundant and moderately preservedradiolarian shells including Angulobracchia(?) portmanni portmanniBaumgartner, Loopus nuda (Schaaf), Tethysetta boesii gr. (Parona),Sethocapsa(?) zweilii Jud, and Xitus sp (Fig. 4). These species appearin UAZones 13e22, UAZones 12e16, UAZones 9e22, UAZones14e19 respectively (Baumgartner et al., 1995; Matsuoka et al.,

4 Py-0-f15 Pyz-1-f3 Pyz-5-f5 YDA03 YDA05 YDA13 YDB10

chert chert chert siliceousmudstone chert chert siliceous

mudstone

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5 14-164 4-5 4 4 6

j. late Baj. toearly Bath.

Berr. toearly Val. early Aptian early Aptian early Aptian early Aptian mid Aptian

es of radiolarian assemblages with respect to Unitary Associations.

Cretaceous radiolarian assemblages of the western Yarlung Zangboe Frontiers (2016), http://dx.doi.org/10.1016/j.gsf.2016.09.006

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2002). The overlapping age range of these species indicates a Ber-riasian to early Valanginian (UAZones 14e16) age range.

Abundant and moderately preserved radiolarians from samplePyz-5-f5 are assigned to six species within five genera (Fig. 6).Based on Unitary Associations of mid-Cretaceous, Podobursa typica(Rüst) appears in U.As. 1e4, Rhopalosyringium fossile (Squinabol)appears in U.As. 4e12, Squinabollum asseni (Tan) appears in U.As.1e10, Thanarla brouweri (Tan) appears in U.As. 1e11 (O’Dogherty,1994). The overlapping age range of these species suggests anearly Aptian (Turbocapsula Zone, Verbeeki Subzone) age.

Abundant, well-preserved and diversified radiolarians extractedfrom sample YDA03 are identified as 11 species within nine genera(Fig. 6). According to Unitary Associations of mid-Cretaceous(O’Dogherty, 1994), the co-occurrence of T. boesii gr. (Parona) andR. fossile (Squinabol) indicates an early Aptian (Turbocapsula Zone,Verbeeki Subzone) age.

Sample YDA05 yields moderately preserved radiolarian shellsassign to seven species within seven genera (Fig. 6). Among them, P.typica (Rüst) appears in U.As. 1e4, while Pseudodictyomitra lodo-gaensis Pessagno appears in U.As. 4e9. The co-occurrence of thesetwo species suggests an early Aptian (Turbocapsula Zone, VerbeekiSubzone) age.

Sample YDA13 contains abundant and moderately preservedradiolarian shells assigned to nine species within six genera (Fig. 6).P. typica (Rüst) appears in U.As. 1e4, while P. lodogaensis Pessagnoappears in U.As. 4e9 (O’Dogherty, 1994). The co-occurrence ofthese two species suggests an early Aptian (Turbocapsula Zone,Verbeeki Subzone) age.

Moderately to well-preserved radiolarian shells obtained fromsample YDB10 are assigned to eight species within five genera(Fig. 6). Thanarla lacrimula (Foreman) appears in U.As. 1e6, whileXitus spicularius (Aliev) appears in U.As. 6e19 (O’Dogherty, 1994).The co-occurrence of these two species suggests a mid Aptian(Turbocapsula Zone, Costata Subzone) age.

5. Discussion

5.1. Age constraints for the Indus-Yarlung Zangbo Suture Zone

Liang et al. (2012) has reported late Paleocene radiolarian faunafrom Jiazhu Village in the Zhongba mélange, while within the samemélange. Li et al. (2013) presented a late Jurassic radiolarianassemblage which is the oldest radiolarian age in this region(Fig. 2). Our studies reveal that the pelagic deposits of the chertsequence existed from at least the early middle Jurassic (Aalenian)to late early Cretaceous (Aptian) (Fig. 2).

Generally, the above radiolarian assemblages in the Zhongbamélange are chronologically consistent with those from the Spon-tang massif in NW India (Baxter et al., 2010), Dazhuqu ophiolite(Ziabrev et al., 2003), Bainang terrane (Ziabrev et al., 2004), andXialu chert (Matsuoka et al., 2002) near Xigaze in the middlesegment of the YZSZ, and Naga ophiolite in NE India (Figs. 1 and 2;Baxter et al., 2011). The above observations indicate that the Neo-Tethys occurred widely during the middle Jurassic to earlyCretaceous.

5.2. Implications for the evolution of the Neo-Tethys

The radiolarian assemblages from the red cherts in the Bainangarea reveal the oldest ages of late Triassic (Ziabrev et al., 2004),indicating that the occurrence of Neo-Tethys during that time,consistent with the studies of rifting-related mafic rocks (Garzantiet al., 1999) and the Tethyan Himalayan passive margin (Jadoulet al., 1998).

Please cite this article in press as: Zhong, H., et al., Middle JurassiceearlySuture Zone: Implications for the evolution of the Neo-Tethys, Geoscienc

Ages of the radiolarian assemblages are focused on the middleJurassiceearly Cretaceous (Fig. 2), indicating this is criticallyimportant stage of the Neo-Tethys evolution. In the Beilongjialaarea, the Aptian cherts are interbedded with siliceous mudstoneand shale. Therefore, the ages of these terrigenous-derived sedi-ments were also deposited during the Aptian. In Xialu of the centralsegment of the YZSZ, Matsuoka et al. (2002) also reported thelithofacies transition from chert to siliceous mudstone occurredaround the Barremian/Aptian boundary. The occurrence ofterrigenous-derived sediments during Aptian implies that a newstage of subduction of the Neo-Tethys occurred. This conclusion isconsistent with studies from the Yarlung Zangbo ophiolites whichalso reveal one stage of subduction initiation of the Neo-Tethysoccurred around 130e120 Ma (Dai et al., 2013).

The above observations indicate that the entire YZSZ have asimilar geochronological framework and thus underwent similargeological evolution: (1) during the Jurassic, the Neo-Tethys was awide ocean with pelagic sediments far away from continents; (2)during the Cretaceous (around 130e120 Ma), the Neo-Tethys star-ted to subduct along the southern margin of the Lhasa block.

The youngest age of the radiolarians is PaleoceneeEocene (Ding,2003; Li et al., 2009; Liang et al., 2012). This indicates that theyoungest deep marine sediments were preserved in the YZSZ. Ev-idence from foraminifers and calcareous nannofossils in theTethyan Himalaya reveals that the shallow marine conditionsoccurred widely during Eocene (Jiang et al., 2016). Considering theoldest (Wang et al., 2002) and the youngest deep marine sedi-ments, the duration of the Neo-Tethys was at least more than180 m.y.

Acknowledgements

We thank Tom Savage and Sarah Kachovich for assistance in themicrofossil lab in the University of Sydney; Dr. Patrick Trimby atAustralian Centre for Microscopy & Microanalysis for his assistancein the images of microfossils. Hui Luo and Bo Xu from NanjingInstitute of Geology and Palaeontology, Chinese Academy of Sci-ences are gratefully acknowledged for their advice in radiolarianidentification. We also thank Jonathan Aitchison for his construc-tive reviews and comments on the early version of this manuscript.Finally we appreciate two anonymous reviewers for their criticalreview, and thank Vice Editor Dr. XiaoqiaoWan for his handling ourmanuscript. This researchwas supported by the Research Center forTibetan Plateau Geology, China Geological Survey (201401),the Fundamental Research Funds for the Central Universities(Grant No. 292016004), and China Geological Survey (Grant Nos.12112011086037 and 1212011221072). This is CUGB petro-geochemical contribution No. PGC-201517.

References

Aitchison, J.C., Ali, J.R., Davis, A.M., 2007. When and where did India and Asiacollide? Journal of Geophysical Research-Solid Earth 112, B05423. http://dx.doi.org/10.1029/2006JB004706.

Allegre, C.J., Courtillot, V., Tapponnier, P., Hirn, A., Mattauer, M., Coulon, C.,Jaeger, J.J., Achache, J., Scharer, U., Marcoux, J., Burg, J.P., Girardeau, J., Armijo, R.,Gariepy, C., Gopel, C., Li, T.D., Xiao, X.C., Chang, C.F., Li, G.Q., Lin, B.Y., Teng, J.W.,Wang, N.W., Chen, G.M., Han, T.L., Wang, X.B., Den, W.M., Sheng, H.B., Cao, Y.G.,Zhou, J., Qiu, H.R., Bao, P.S., Wang, S.C., Wang, B.X., Zhou, Y.X., Ronghua, X., 1984.Structure and evolution of the Himalaya-Tibet orogenic belt. Nature 307, 17e22.

Baumgartner, P.O., O’Dogherty, L., Gorican, S., Urquhart, E., Pillevuit, A., De Wever, P.,1995. Middle Jurassic to lower cretaceous radiolaria of Tethys: occurrences, sys-tematics, biochronology. Mémoires de Géologie (Lausanne) 23, iexxix, 1-1172.

Baxter, A.T., Aitchison, J.C., Ali, J.R., Zyabrev, S.V., 2010. Early cretaceous radiolariansfrom the Spongtang massif, Ladakh, NW India: implications for Neo-Tethyanevolution. Journal of the Geological Society 167, 511e517.

Baxter, A.T., Aitchison, J.C., Zyabrev, S.V., Ali, J.R., 2011. Upper Jurassic radiolariansfrom the Naga Ophiolite, Nagaland, northeast India. Gondwana Research 20,638e644.

Cretaceous radiolarian assemblages of the western Yarlung Zangboe Frontiers (2016), http://dx.doi.org/10.1016/j.gsf.2016.09.006

H. Zhong et al. / Geoscience Frontiers xxx (2016) 1e9 9

Dai, J., Wang, C., Hébert, R., Li, Y., Zhong, H., Guillaume, R., Bezard, R., Wei, Y., 2011a.Late Devonian OIB alkaline gabbro in the Yarlung Zangbo suture zone: rem-nants of the Paleo-Tethys? Gondwana Research 19, 232e243.

Dai, J., Wang, C., Li, Y., 2012. Relicts of the early cretaceous seamounts in the central-western Yarlung Zangbo suture zone, southern Tibet. Journal of Asian EarthSciences 53, 25e37.

Dai, J., Wang, C., Polat, A., Santosh, M., Li, Y., Ge, Y., 2013. Rapid forearc spreadingbetween 130 and 120 Ma: evidence from geochronology and geochemistry ofthe Xigaze ophiolite, southern Tibet. Lithos 172e173, 1e16.

Dai, J.-G., Wang, C.-S., Hébert, R., Santosh, M., Li, Y.-L., Xu, J.-Y., 2011b. Petrology andgeochemistry of peridotites in the Zhongba ophiolite, Yarlung Zangbo suturezone: implications for the early cretaceous intra-oceanic subduction zonewithin the Neo-Tethys. Chemical Geology 288, 133e148.

De Wever, P., Dumitrica, P., Caulet, J.P., Caridroit, M., 2001. Radiolarians in theSedimentary Record. Amsterdam, p. 533.

Ding, L., 2003. Paleocene deep-water sediments and radiolarian faunas: implica-tions for evolution of Yarlung-Zangbo foreland basin, southern Tibet. Science inChina, Series D: Earth Sciences 46, 84e96.

Festa, A., Dilek, Y., Pini, G.A., Codegone, G., Ogata, K., 2012.Mechanisms and processesof stratal disruption and mixing in the development of mélanges and brokenformations: redefiningandclassifyingmélanges. Tectonophysics568e569, 7e24.

Garzanti, E., Le Fort, P., Sciunnach, D., 1999. First report of Lower Permian basalts inSouth Tibet: tholeiitic magmatism during break-up and incipient opening ofNeotethys. Journal of Asian Earth Sciences 17, 533e546.

Gradstein, F.M., Ogg, G., Schmitz, M., 2012. The Geologic Time Scale 2012, 2-VolumeSet. Elsevier, pp. 1e1145.

Hébert, R., Bezard, R., Guilmette, C., Dostal, J., Wang, C.S., Liu, Z.F., 2012. TheInduseYarlung Zangbo ophiolites from Nanga Parbat to Namche Barwa syn-taxes, southern Tibet: first synthesis of petrology, geochemistry, and geochro-nology with incidences on geodynamic reconstructions of Neo-Tethys.Gondwana Research 22, 377e397.

Jadoul, F., Berra, F., Garzanti, E., 1998. The Tethys Himalayan passive margin fromLate Triassic to early cretaceous (South Tibet). Journal of Asian Earth Sciences16, 173e194.

Jud, R., 1994. Biochronology and systematics of early cretaceous radiolarian of thewestern Tethys. Mémoires de Géologie (Lausanne) 19, 1e147.

Jiang, T., Aitchison, J.C., Wan, X., 2016. The youngest marine deposits preserved insouthern Tibet and disappearance of the Tethyan Ocean. Gondwana Research32, 64e75.

Kojima, S., Ahmad, T., Tanaka, T., Bagati, T.N.,Mishra,M., Kumar, R., Islam, R., Khanna, P.,2001. Early cretaceous radiolarians from the Indus suture zone, Ladakh, northernIndia. News of Osaka Micropaleontologists, 257e270. special volume 12.

Li, G., Wan, X., Liu, W., Bucher, H., Li, H., Goudemand, N., 2009. A new cretaceous agefor the Saiqu “mélange,” southern Tibet: evidence from Radiolaria. CretaceousResearch 30, 35e40.

Li, X., Li, Y., Wang, C., Matsuoka, A., 2013. Late Jurassic Radiolarians from theZhongba Melange in the Yarlung-Tsangpo Suture Zone, Southern Tibet,pp. 23e30. Science Reports of Niigata University (Geology) 28.

Li, Y.L., Wang, C.S., Hu, X.M., Bak, M., Wang, J.J., Chen, L., 2007. Characteristics ofearly Eocene radiolarian assemblages of the Saga area, southern Tibet and theirconstraint on the closure history of the Tethys. Chinese Science Bulletin 52,2108e2114.

Liang, Y., Zhang, K., Xu, Y., He, W., An, X., Yang, Y., 2012. Late Paleocene radiolarianfauna from Tibet and its geological implications. Canadian Journal of EarthSciences 49, 1364e1371.

Please cite this article in press as: Zhong, H., et al., Middle JurassiceearlySuture Zone: Implications for the evolution of the Neo-Tethys, Geoscienc

Matsuoka, A., 1995a. Jurassic and lower cretaceous radiolarian zonation in Japanand in the western pacific. The Island Arc 4, 140e153.

Matsuoka, A., 1995b. Middle Jurassic-lower cretaceous radiolarian zonation in Japanand the western pacific, and age assignments based on the unitary associationsmethod. In: Baumgartner, P.O., O’Dogherty, L., Gorican, S., Urquhart, E.,Pillevuit, A., De Wever, P. (Eds.), Mémoires de Géologie (Lausanne), vol. 23,pp. 1049e1057.

Matsuoka, A., Yang, Q., Kobayashi, K., Takei, M., Nagahashi, T., Zeng, Q.G., Wang, Y.J.,2002. Jurassic-cretaceous radiolarian biostratigraphy and sedimentary envi-ronments of the Ceno-Tethys: records from the Xialu Chert in the Yarlung-Zangbo suture zone, southern Tibet. Journal of Asian Earth Sciences 20,277e287.

O’Dogherty, L., 1994. Biochronology and paleontology of mid-cretaceous radiolar-ians from northern Apennines (Italy) and Betic Cordillera (Spain). Mémoires deGéologie (Lausanne) 21, 1e415.

O’Dogherty, L., Carter, E.S., Dumitrica, P., Gorican, S., De Wever, P., Bandini, A.N.,Baumgartner, P.O., Matsuoka, A., 2009. Catalogue of Mesozoic radiolariangenera; Part 2, Jurassic-cretaceous. Geodiversitas 31, 271e356.

Raymond, L.A., 1975. Tectonite and mélangeda distinction. Geology 3, 7e9.Wakita, K., Metcalfe, I., 2005. Ocean plate stratigraphy in East and Southeast Asia.

Journal of Asian Earth Sciences 24, 679e702.Wang, C., Li, X., Liu, Z., Li, Y., Jansa, L., Dai, J., Wei, Y., 2012. Revision of the creta-

ceousepaleogene stratigraphic framework, facies architecture and provenanceof the Xigaze forearc basin along the Yarlung Zangbo suture zone. GondwanaResearch 22, 415e433.

Wang, Y.J., Yang, Q., Matsuoka, A., Kobayashi, K., Nagahashi, T., Zeng, Q.G., 2002.Triassic radiolarians from the Yarlung Zangbo suture zone in the Jinlu area,Zetang county, southern Tibet. Acta Micropalaeontologica Sinica 19 (3),215e227.

Wu, F.Y., Liu, C.Z., Zhang, L.L., Zhang, C., Wang, J.G., Ji, W.Q., Liu, X.C., 2014. YarlungZangbo ophiolite: a critical updated view. Acta Petrologica Sinica 30,293e325.

Wu, H.R., 1984. The congdu formationdcretaceous deep-sea deposits in southernXizang (Tibet) and its significance. Chinese Journal of Geology 1, 26e33 (inChinese with English abstract).

Xiong, Q., Griffin, W.L., Zheng, J.-P., O’Reilly, S.Y., Pearson, N.J., Xu, B., Belousova, E.A.,2016. Southward trench migration at w130e120 Ma caused accretion of theNeo-Tethyan forearc lithosphere in Tibetan ophiolites. Earth and PlanetaryScience Letters 438, 57e65.

Yin, A., Harrison, T.M., 2000. Geologic evolution of the Himalayan-Tibetan orogen.Annual Review of Earth and Planetary Sciences 28, 211e280.

Ziabrev, S., Aitchison, J., Abrajevitch, A., Badengzhu, Davis, A., Luo, H., 2003. Preciseradiolarian age constraints on the timing of ophiolite generation and sedi-mentation in the Dazhuqu terrane, Yarlung-Tsangpo suture zone, Tibet. Journalof the Geological Society 160, 591e599.

Ziabrev, S.V., Aitchison, J.C., Abrajevitch, A.V., Badengzhu, Davis, A.M., Luo, H., 2004.Bainang Terrane, YarlungeTsangpo suture, southern Tibet (Xizang, China): arecord of intra-Neotethyan subductioneaccretion processes preserved on theroof of the world. Journal of the Geological Society 161, 523e539.

Zyabrev, S.V., Kojima, S., Ahmad, T., 2008. Radiolarian biostratigraphic constraintson the generation of the Nidar ophiolite and the onset of Dras arc volcanism:tracing the evolution of the closing Tethys along the Indus-Yarlung-Tsangposuture. Stratigraphy 5, 99e112.

Cretaceous radiolarian assemblages of the western Yarlung Zangboe Frontiers (2016), http://dx.doi.org/10.1016/j.gsf.2016.09.006