The Indosinian orogeny: A perspective from sedimentary archives of north Vietnam

Abstract

The Triassic stratigraphic framework for the Song Da and the Sam Nua basins, north Vietnam, suffers important discrepancies regarding both the depositional environments and ages of the main formations they contain. Using sedimentological analyses and dating (foraminifer biostratigraphy and U-Pb dating on detrital zircon), we provide an improved stratigraphic framework for both basins. A striking feature in the Song Da Basin, located on the southern margin of the South China Block, is the diachronous deposition, over a basal unconformity, of terrestrial and marine deposits. The sedimentary succession of the Song Da Basin points to a foreland setting during the late Early to the Middle Triassic, which contrasts with the commonly interpreted rift setting. On the northern margin of the Indochina Block, the Sam Nua Basin recorded the activity of a proximal magmatic arc during the late Permian up to the Anisian. This arc resulted from the subduction of a southward dipping oceanic slab that separated the South China block from the Indochina block. During the Middle to the Late Triassic, the Song Da and Sam Nua basins underwent erosion that led to the formation of a major unconformity, resulting from the erosion of the Middle Triassic Indosinian mountain belt, built after an ongoing continental collision between the South China and the Indochina blocks. Later, during the Late Triassic, as syn-to post-orogenic foreland basins in a terrestrial setting, the Song Da and Sam Nua basins experienced the deposition of very coarse detrital material representing products of the mountain belt erosion.

Early Paleoproterozoic magmatism in the Yangtze Block: Evidence from zircon U-Pb ages, Sr-Nd-Hf isotopes and geochemistry of ca. 2.3 Ga and 2.1 Ga granitic rocks in the Phan Si Pan Complex, north Vietnam

“…The Yangtze Block extends into north Vietnam as far south as the Song Ma Suture Zone, where it is generally divided into the NW and NE parts by the Cenozoic Ailaoshan-Red River shear zone (Figs. 1 and 2; Rossignol et al, 2018). Precambrian rocks in north Vietnam mainly crop out in the Phan Si Pan Complex and the Neoproterozoic Nam Co unit (Fig.…”

New insights into the Triassic sedimentary environment of the eastern parts of the Song Da and Sam Nua basins alongside the Indosinian Song Ma suture, Northern Vietnam

“…These platforms provide important information that can be used to document the global environmental evolution and biotic recovery after the end-Permian mass extinction (Algeo et al, 2007;Son et al, 2007, Komatsu et al, 2010Metcalfe, 2012). However, the precise stratigraphic framework for the Northern Vietnam Triassic carbonate platforms is still incompletely characterized (Shi and Shen, 1998;Martini et al, 1998;Tri and Khuc, 2011;Thanh and Khuc, 2012;Rossignol et al, 2016Rossignol et al, , 2018, making it difficult to make correlations and comparisons with other platforms of similar age worldwide and in Southeast Asia.…”

“…The Early and Middle Triassic carbonate platforms of Northern Vietnam developed in foreland basins associated with the onset and growing of the Indosinian orogen from the Early to the Late Triassic (Lepvrier et al, 2008;Vuong et al, 2013;Faure et al, 2014Faure et al, , 2016Roger et al, 2014;Halpin et al, 2015;Rossignol et al, 2018). The studied areas concern the Song Da Basin, located to the southwest of the Indosinian orogen, and the Sam Nua Basin, bordering the orogen to the northeast.…”

“…1). The collision between these two blocks probably occurred during the Triassic (Lepvrier et al, 2004(Lepvrier et al, , 2008Liu et al, 2012;Zhang et al, 2013;Kamvong et al, 2014;Faure et al, 2014;Roger et al, 2014;Halpin et al, 2015;Hieu et al, 2017;Rossignol et al, 2018;Thanh et al, 2019), even though various other ages such as Silurian-Devonian (Thanh et al, 1996;Findlay and Trinh, 1997;Thanh et al, 2011) or Carboniferous (Metcalfe, 2011(Metcalfe, , 2012 have been proposed.…”

“…A general stratigraphic framework for the Song Da and Sam Nua basins has been presented by Rossignol et al (2018), in which the carbonate deposits of these two basins were succinctly described. The present study, based on 16 cross-sections located in the eastern part of the Song Da and Sam Nua basins, focuses on the structural, stratigraphic, and sedimentological characteristics of these marine Triassic formations, with a particular emphasis on the carbonate platform deposits.…”