The Yarlung suture mélange, Lopu Range, southern Tibet

Provenance of sandstone blocks and transition from oceanic subduction to continental collision

Kathryn Metcalf, Paul A Kapp

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

With the aim of better understanding the history of ocean closure and suturing between India and Asia, we conducted a geologic investigation of a siliciclastic matrix tectonic mélange within the western Yarlung suture zone of southern Tibet (Lopu Range region, ~ 50 km northwest of Saga). The siliciclastic matrix mélange includes abundant blocks of ocean plate stratigraphy and sparse blocks of sandstone. Metapelite and metabasite blocks in the mélange exhibit lower greenschist facies mineral assemblages, indicating that they were not deeply subducted. We obtained detrital zircon U-Pb geochronologic and sandstone petrographic data from sandstone blocks in the mélange and sandstone beds from Tethyan Himalayan strata exposed to the south of the suture. The sandstones from both units are all similar in U-Pb detrital zircon age spectra and petrography to the nearby Tethyan Cretaceous–Paleocene Sangdanlin section, which records the earliest appearance (at ~ 59 Ma) of arc-affinity strata deposited conformably on Indian-affinity strata. Two Paleocene sandstones, one of which is a schistose block incorporated in the siliciclastic matrix mélange, yielded indistinguishable maximum depositional ages of ~ 59 Ma. Mesozoic Asian-affinity sandstone blocks previously documented in the siliciclastic matrix mélange 200–500 km along strike to the east are notably absent in the Lopu Range region. We documented a gradational transition in structural style from the block-in-matrix mélange in the northeast to the south-vergent Tethyan thrust belt in the southwest. Blocks of Tethyan Himalayan strata increase in size and the volumetric proportion of matrix decreases from northeast to southwest. We conclude that no arc-affinity sandstone blocks were incorporated into the subduction complex until India-Asia collision at ~ 59 Ma when the Xigaze forearc basin became overfilled and Tethyan Himalayan strata entered the trench. As collision progressed, there was a gradual transition in structural style from block-in-matrix mélange formation to imbricate-style thrust belt formation.

Original languageEnglish (US)
Pages (from-to)15-33
Number of pages19
JournalGondwana Research
Volume48
DOIs
StatePublished - Aug 1 2017

Fingerprint

continental collision
provenance
subduction
sandstone
matrix
zircon
thrust
collision
metabasite
metapelite
forearc basin
suture zone
ocean
greenschist facies
petrography
Paleocene
trench
stratigraphy
tectonics
mineral

Keywords

  • Accretion
  • Mélange
  • Southern Tibet
  • Subduction
  • Suture zone

ASJC Scopus subject areas

  • Geology

Cite this

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title = "The Yarlung suture m{\'e}lange, Lopu Range, southern Tibet: Provenance of sandstone blocks and transition from oceanic subduction to continental collision",
abstract = "With the aim of better understanding the history of ocean closure and suturing between India and Asia, we conducted a geologic investigation of a siliciclastic matrix tectonic m{\'e}lange within the western Yarlung suture zone of southern Tibet (Lopu Range region, ~ 50 km northwest of Saga). The siliciclastic matrix m{\'e}lange includes abundant blocks of ocean plate stratigraphy and sparse blocks of sandstone. Metapelite and metabasite blocks in the m{\'e}lange exhibit lower greenschist facies mineral assemblages, indicating that they were not deeply subducted. We obtained detrital zircon U-Pb geochronologic and sandstone petrographic data from sandstone blocks in the m{\'e}lange and sandstone beds from Tethyan Himalayan strata exposed to the south of the suture. The sandstones from both units are all similar in U-Pb detrital zircon age spectra and petrography to the nearby Tethyan Cretaceous–Paleocene Sangdanlin section, which records the earliest appearance (at ~ 59 Ma) of arc-affinity strata deposited conformably on Indian-affinity strata. Two Paleocene sandstones, one of which is a schistose block incorporated in the siliciclastic matrix m{\'e}lange, yielded indistinguishable maximum depositional ages of ~ 59 Ma. Mesozoic Asian-affinity sandstone blocks previously documented in the siliciclastic matrix m{\'e}lange 200–500 km along strike to the east are notably absent in the Lopu Range region. We documented a gradational transition in structural style from the block-in-matrix m{\'e}lange in the northeast to the south-vergent Tethyan thrust belt in the southwest. Blocks of Tethyan Himalayan strata increase in size and the volumetric proportion of matrix decreases from northeast to southwest. We conclude that no arc-affinity sandstone blocks were incorporated into the subduction complex until India-Asia collision at ~ 59 Ma when the Xigaze forearc basin became overfilled and Tethyan Himalayan strata entered the trench. As collision progressed, there was a gradual transition in structural style from block-in-matrix m{\'e}lange formation to imbricate-style thrust belt formation.",
keywords = "Accretion, M{\'e}lange, Southern Tibet, Subduction, Suture zone",
author = "Kathryn Metcalf and Kapp, {Paul A}",
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T1 - The Yarlung suture mélange, Lopu Range, southern Tibet

T2 - Provenance of sandstone blocks and transition from oceanic subduction to continental collision

AU - Metcalf, Kathryn

AU - Kapp, Paul A

PY - 2017/8/1

Y1 - 2017/8/1

N2 - With the aim of better understanding the history of ocean closure and suturing between India and Asia, we conducted a geologic investigation of a siliciclastic matrix tectonic mélange within the western Yarlung suture zone of southern Tibet (Lopu Range region, ~ 50 km northwest of Saga). The siliciclastic matrix mélange includes abundant blocks of ocean plate stratigraphy and sparse blocks of sandstone. Metapelite and metabasite blocks in the mélange exhibit lower greenschist facies mineral assemblages, indicating that they were not deeply subducted. We obtained detrital zircon U-Pb geochronologic and sandstone petrographic data from sandstone blocks in the mélange and sandstone beds from Tethyan Himalayan strata exposed to the south of the suture. The sandstones from both units are all similar in U-Pb detrital zircon age spectra and petrography to the nearby Tethyan Cretaceous–Paleocene Sangdanlin section, which records the earliest appearance (at ~ 59 Ma) of arc-affinity strata deposited conformably on Indian-affinity strata. Two Paleocene sandstones, one of which is a schistose block incorporated in the siliciclastic matrix mélange, yielded indistinguishable maximum depositional ages of ~ 59 Ma. Mesozoic Asian-affinity sandstone blocks previously documented in the siliciclastic matrix mélange 200–500 km along strike to the east are notably absent in the Lopu Range region. We documented a gradational transition in structural style from the block-in-matrix mélange in the northeast to the south-vergent Tethyan thrust belt in the southwest. Blocks of Tethyan Himalayan strata increase in size and the volumetric proportion of matrix decreases from northeast to southwest. We conclude that no arc-affinity sandstone blocks were incorporated into the subduction complex until India-Asia collision at ~ 59 Ma when the Xigaze forearc basin became overfilled and Tethyan Himalayan strata entered the trench. As collision progressed, there was a gradual transition in structural style from block-in-matrix mélange formation to imbricate-style thrust belt formation.

AB - With the aim of better understanding the history of ocean closure and suturing between India and Asia, we conducted a geologic investigation of a siliciclastic matrix tectonic mélange within the western Yarlung suture zone of southern Tibet (Lopu Range region, ~ 50 km northwest of Saga). The siliciclastic matrix mélange includes abundant blocks of ocean plate stratigraphy and sparse blocks of sandstone. Metapelite and metabasite blocks in the mélange exhibit lower greenschist facies mineral assemblages, indicating that they were not deeply subducted. We obtained detrital zircon U-Pb geochronologic and sandstone petrographic data from sandstone blocks in the mélange and sandstone beds from Tethyan Himalayan strata exposed to the south of the suture. The sandstones from both units are all similar in U-Pb detrital zircon age spectra and petrography to the nearby Tethyan Cretaceous–Paleocene Sangdanlin section, which records the earliest appearance (at ~ 59 Ma) of arc-affinity strata deposited conformably on Indian-affinity strata. Two Paleocene sandstones, one of which is a schistose block incorporated in the siliciclastic matrix mélange, yielded indistinguishable maximum depositional ages of ~ 59 Ma. Mesozoic Asian-affinity sandstone blocks previously documented in the siliciclastic matrix mélange 200–500 km along strike to the east are notably absent in the Lopu Range region. We documented a gradational transition in structural style from the block-in-matrix mélange in the northeast to the south-vergent Tethyan thrust belt in the southwest. Blocks of Tethyan Himalayan strata increase in size and the volumetric proportion of matrix decreases from northeast to southwest. We conclude that no arc-affinity sandstone blocks were incorporated into the subduction complex until India-Asia collision at ~ 59 Ma when the Xigaze forearc basin became overfilled and Tethyan Himalayan strata entered the trench. As collision progressed, there was a gradual transition in structural style from block-in-matrix mélange formation to imbricate-style thrust belt formation.

KW - Accretion

KW - Mélange

KW - Southern Tibet

KW - Subduction

KW - Suture zone

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DO - 10.1016/j.gr.2017.03.002

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