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SCIENCE CHINA Earth Sciences, Volume 61, Issue 9: 1204-1220(2018) https://doi.org/10.1007/s11430-017-9223-5

Upper Cretaceous trench deposits of the Neo-Tethyan subduction zone: Jiachala Formation from Yarlung Zangbo suture zone in Tibet, China

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  • ReceivedOct 10, 2017
  • AcceptedMay 7, 2018
  • PublishedJul 18, 2018

Abstract

The history of convergence between the India and the Asia plates, and of their subsequent collision which triggered the Himalayan orogeny is recorded in the Yarlung Zangbo suture zone. Exposed along the southern side of the suture, turbidites of the the Jiachala Formation fed largely from the Gangdese arc have long been considered as post-collisional foreland-basin deposits based on the reported occurrence of Paleocene-early Eocene dinoflagellate cysts and pollen assemblages. Because magmatic activity in the Gangdese arc continued through the Late Cretaceous and Paleogene, this scenario is incompatible with U-Pb ages of detrital zircons invariably older than the latest Cretaceous. To solve this conundrum, we carried out detailed stratigraphic, sedimentological, paleontological, and provenance analyses in the Gyangze and Sajia areas of southern Tibet, China. The Jiachala Formation consists of submarine fan deposits that lie in fault contact with the Zongzhuo Formation. Sandstone petrography together with U-Pb ages and Hf isotope ratios of detrital zircons indicate provenance from the Gangdese arc and central Lhasa terrane. Well preserved pollen or dinoflagellate cysts microfossils were not found in spite of careful research, and the youngest age obtained from zircon grain was ~84 Ma. Based on sedimentary facies, provenance analysis and tectonic position, we suggest that the Jiachala Formation was deposited during the Late Cretaceous (~88–84 Ma) in the trench formed along the southern edge of Asia during subduction of Neo-Tethyan oceanic lithosphere.


Acknowledgment

We thank Wang Chengshan, Wu Fuyuan, Li Xianghui, Wan Xiaoqiao and Li Jianguo for constructive discussion and suggestions, Bian Lizeng and Roger Tremain for help in palynological processing, Zhou Bo for assistance in the field, and Lai Wen and Xue Weiwei for help in Hf isotopic analysis. We are grateful to the reviewers for their constructive comments. This work was supported by the National Natural Science Foundation of China (Grant Nos. 41525007, 41602115).


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  • Figure 1

    Geological map of the Himalaya (modified after Pan et al., 2004). ① and ② Zhaguo and Enba formations (Najman et al., 2010; Hu et al., 2012; Li et al., 2015); ③ Quxia and Jialazi formations (Hu et al., 2016a); ④ Sangdanlin and Zheya formations (Wang et al., 2011; DeCelles et al., 2014; Wu et al., 2014; Hu et al., 2015); ⑤ Padana Formation (An et al., 2014); ⑥ Ngamring Formation (An et al., 2014); ⑦ Xiukang mélange (An et al., 2017); ⑧ and ⑨ Jiachala Formation. GCT, Great Counter Thrust; STDZ, South Tibet Detachment Zone; MCT, Main Central Thrust; MBT, Main Boundary Thrust.

  • Figure 2

    Geological map of the studied area (a), with details for the Padu village (b) and Jiachala Mountain (c). (a) is modified after Pan et al. (2004); (b) and (c) are after Wan and Liu (2005)1), Hu et al. (2006), and our field observations.

    Wan X Q, Liu W C. 2005. 1: 250000 Gyangze Geological Map. Beijing: National Geological Archives of China.

  • Figure 3

    Lithostratigraphy of the four measured sections. Locations are shown in Figure 2, and facies codes in Table 1.

  • Figure 4

    Field photographs (locations shown in Figures 2 and 3). (a)–(d) Fault contact between the Zongzhuo Formation and the overlying Jiachala Formation, with yellow lines indicating strata and red lines indicating the faulted boundary; (e) sandstones intercalated with dark shales (L1); (f) thin sandstones interbedded with dark shales (L2); (g) thick massive sandstones (L3); (h) folded dark shales including limestone and sandstone blocks (L4), interpreted as slump features; (i) flute casts in deep-water turbidites, with white arrows indicating paleocurrent direction. Scale: geologists are ~1.7 m-tall, hammer is ~ 0.4 m-long, and the pencil is ~12 cm-long.

  • Figure 5

    Standard palynological laboratory treatment revealed that Jiachala Formation samples contain abundant dark to black particles, degraded terrestrial phytoclasts and detrital minerals, but well-preserved dinoflagellate cyst and spores/pollen were not recognized. Scale bar = 20 μm.

  • Figure 6

    Micrographs of Jiachala sandstones. Lithic fragments consist of intermediate to felsic volcanic grains with minor sedimentary and metamorphic grains. Abbreviations of minerals and lithic fragments are explained in Table 2.

  • Figure 7

    Ternary diagrams showing the petrographic composition of Jiachala sandstones. Qt, total quartz, Qt= Qm+Qp; F, feldspar; L, lithic fragment; L= Lv+Ls+Lm. Abbreviations of minerals and lithic fragments are explained in Table 2.

  • Figure 8

    U-Pb relative age vs. probability density diagrams for detrital zircons in the Jiachala Formation.

  • Figure 9

    U-Pb age of detrital zircons versus εHf(t) plots. The εHf(t) values of Mesozoic zircons in the Jiachala Formation compare well with those in the Gangdese arc (Chu et al., 2006; Lee et al., 2007; Zhang et al., 2007b; Ji et al., 2009; Zhu et al., 2009, 2011), central Lhasa terrane (Chu et al., 2006; Zhang et al., 2007a; Zhu et al., 2011), and Upper Cretaceous strata and blocks found along the Yarlung Zangbo suture zone. Note that zircons yielding negative εHf(t) are much less abundant in Paleogene sandstones.

  • Figure 10

    U-Pb age spectra of detrital zircons and sandstone petrography of the Jiachala Formation compared with Upper Cretaceous to Paleogene strata and blocks. Note the marked differences with Paleogene strata and similarity with Upper Cretaceous units, including the lack of 84–50 Ma ages and common pre-Mesozoic zircons.

  • Figure 11

    Comparison of zircon age spectra in Jiachala sandstones versus other Upper Cretaceous to Paleogene strata and blocks. (a) Cumulative distributions; (b) K-S test. The P value increases with increasing similarity.

  • Figure 12

    Paleogeographic scenario for the Jiachala Formation. Detritus shed from the Gangdese arc and central Lhasa terrane bypassed the Xigaze forearc basin, reached the trench, and was transported axially before final deposition. Trench deposits similar to the Jiachala Formation (a) are documented to the west: sandstone blocks within the Xiukang mélange (b) and Luogangcuo Formation (c).

  • Figure 13

    Age spectra of detrital zircons and sandstone petrography for the Jiachala, Zongzhuo and Luogangcuo formations. The Jiachala Formation is exposed from Gyangze to Langkazi; classification of group of blocks is from Zhou et al. (2018) . Age spectra of Jiachala sandstones are clearly different with Zongzhuo or Luogangcuo formations, although detrital modes are similar for the Jiachala sandstones and matrix and first group of blocks contained in the Zongzhuo Formation.

  • Table 1   Sedimentary facies identified in the Jiachala Formation and corresponding depositional environment

    Facies code

    Description

    Interpretation

    F1

    Grey green to black shale 5–15 cm thick

    Low density turbidity currents

    F2

    Grey to black shale with chaotic deformation, including folded sandstone layers and limestone blocks

    Submarine slides

    S1

    Fine- to medium-grained, poorly sorted sandstones with flute casts in 0.1–2 m-thick beds

    Turbidity currents

    S2

    Fine- to medium-grained, poorly sorted massive sandstones in > 2 m-thick beds

    Highly concentrated turbidity currents

    S3

    Thin (< 0.2 m) beds of fine-grained, poorly sorted sandstones interbedded with shale

    Low density turbidity current deposits

    S4

    Thin (0.1–0.3 m) sandstone lenses

    Channel deposits

    Modified after Mutti and Ricci Lucchi (1978), Thornburg and Kulm (1987), and Underwood and Moore (1995).

  • Table 2   Detrital modes of Jiachala sandstones

    Sample

    Lithology

    Qm

    Qp

    F

    Lv

    Ls

    Lm

    Total

    14QM111

    feldspatho-litho-quartzose

    234

    10

    62

    72

    18

    7

    403

    14QM113

    feldspatho-litho-quartzose

    238

    9

    70

    67

    10

    8

    402

    14QM115

    feldspatho-litho-quartzose

    229

    8

    72

    57

    29

    10

    405

    14QM116

    litho-quartzose

    299

    2

    31

    54

    10

    14

    410

    14QM119

    feldspatho-litho-quartzose

    246

    8

    60

    68

    14

    9

    405

    08JCL03

    litho-feldspatho-quartzose

    206

    3

    121

    73

    3

    4

    410

    08JCL04

    litho-feldspatho-quartzose

    199

    4

    114

    85

    1

    2

    405

    08JCL07

    feldspatho-litho-quartzose

    189

    1

    101

    110

    0

    1

    402

    08JCL13

    litho-feldspatho-quartzose

    192

    4

    134

    68

    4

    0

    402

    08JCL15

    litho-feldspatho-quartzose

    159

    5

    140

    91

    2

    3

    400

    Qm, monocrystalline quartz; Qp, polycrystalline quartz; F, feldspar; Lv, volcanic lithic fragment, Ls, sedimentary lithic fragment, Lm, metamorphic lithic fragment. The figures in the table mean grain numbers.

  • Table 3   Detrital zircon U-Pb ages of the Jiachala Formation and other Upper Cretaceous to Paleogene strata and blocks

    Unit & references

    Number

    YDZ

    (Ma)

    YSG

    (Ma)

    YPP

    (Ma)

    YC1σ(2+)

    (Ma)

    YC2σ(3+)

    (Ma)

    Jiachala Fm. (Jiachala Mountain, this study)

    197

    73.2+2/–2.6

    73±1

    86

    83.8±1.3

    (n=3)

    84.2±2.4

    (n=5)

    Jiachala Fm. (Padu village, this study)

    161

    83.7+4.3/–4.1

    84±2

    95

    86.0±2.8

    (n=2)

    109.8±5

    (n=4)

    Jiachala Fm. (Jiachala Mountain, Wu et al., 2014)

    478

    60.6+2.6/–2

    61±1

    101

    88.2±2.4

    (n=6)

    88.2±3.1

    (n=6)

    Enba and Zhaguo fms. (Hu et al., 2012; Li et al., 2015)

    679

    43.2+1.7/–1.9

    43.1±0.8

    54

    53.0±0.8

    (n=9)

    51.9±1.3

    (n=8)

    Quxia and Jialazi fms. (Hu et al., 2016a)

    205

    53.2+1.7/–3.6

    54±0.9

    54

    55.3±0.9

    (n=5)

    56.2±0.8

    (n=7)

    Sangdanlin and Zheya fms. (Wang et al., 2011; DeCelles et al., 2014)

    909

    49.2+1.4/–2.6

    49.1±0.7

    59

    54.1±1.0

    (n=7)

    55.8±0.6

    (n=15)

    Upper Ngamring and Padana fms. (Wu et al., 2010; An et al., 2014)

    490

    73.1+3.1/–4

    74±2

    81

    76.2±1.6

    (n=4)

    78.5±1.0

    (n=8)

    One group of sandstone blocks within the Xiukang mélange (An et al., 2017)

    273

    92.7+1.9/–2.6

    93±1

    99

    94.3±1.3

    (n=4)

    94.5±1.2

    (n=5)

    Number, number of zircon grains; YDZ, age calculated by the ″Youngest Detrital Zircon″ routine of Isoplot (Ludwig, 2011); YSG, youngest single detrital zircon age with 1δ uncertainty; YPP, youngest graphical detrital-zircon age peak on an age-probability plot or age-distribution curve; YC1σ(2+), weighted mean age (±1σ incorporating both internal analytical error and external systematic error) of the youngest cluster of two or more grain ages overlapping in age at 1σ; YC2σ(3+), weighted mean age (±1σ incorporating both internal analytical error and external systematic error) of the youngest cluster of three or more grain ages overlapping in age at 2σ (Dickinson and Gehrels, 2009).

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