Éditeur(s) : HAL CCSD
Résumé : International audience
The core of South East Asia is composed of a mosaic of continental blocks, among which the Indochina and theSouth China blocks (present day northern Vietnam), amalgamated during the Permian and/or the Triassic. LatePermian to Late Triassic geodynamic evolution of these two blocks remains controversial. The main discussionpoints concern the existence and the closure of an oceanic domain separating the Indochina and the South Chinablocks during this period. Especially, the polarity and the timing of the subduction zone that led to the collisionbetween the blocks as well as the present location of the suture delimiting them are a matter of debate. Despite thevaluable information they can provide, the sedimentary basins from northern Vietnam have been neglected in theprevious studies dealing with the geodynamic evolution of South East Asia.To determine the geodynamic evolution of the area, the basins of Sam Nua and Song Da, presently locatedin North Vietnam, have been investigated using a combined approach involving sedimentology, geochronology(U-Pb/zircon) and geochemistry (whole-rock major and trace elements composition of both volcanic and volcaniclasticrocks). The palaeoenvironment evolution, the main unconformities, their age and the tectonic affinitiesof the interbedded volcanic and volcaniclastics series have been characterized for these two basins. Our resultsdemonstrate (i) that the Song Da Basin exhibits a palaeogeographic affinity with the South China block, (ii) theoccurrence of extensive calk-alkaline volcanism and associated volcaniclastic deposits in the Sam Nua Basin,related to the existence of an active magmatic arc during the Early and the lower Middle Triassic, (iii) a Southdipping (present day coordinate) oceanic lithosphere beneath the Indochina block, deduced from the location ofthe magmatic arc south of the potential suture zones, (iv) that an angular unconformity postdates the lower MiddleTriassic volcaniclastic deposits in the Sam Nua basin. This unconformity, crosscutting the subduction relateddeposits, is interpreted as the result of the collision between the Indochina and the South China blocks.
European Geoscience Union General Assembly 2015
Vienne, Austria

insu-01137675
https://hal-insu.archives-ouvertes.fr/insu-01137675

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
U-Pb zircon and Ar-Ar amphibole and biotite ages from rocks of the West Congo Belt of Angola indicate that this area underwent two main deformation events of amphibolite facies grade at c. 540 and 490 Ma, which were followed by tectonically assisted exhumation during eastward thrusting of the hinterland domain onto the foreland domain. High-grade conditions in the West Congo Belt are 20-40 Ma younger than in the Ribeira-Araçuai Belt of Brazil, its South American counterpart, or than in the westernmost Kaoko Belt of Namibia, its African correlative. In the present state of knowledge, a more appropriate counterpart to the southern part of the West Congo Belt may be restricted to the Cabo Frio Terrane in the eastern Ribeira Belt, which yields a broadly similar evolution.
ISSN: 0954-4879

hal-00716463
https://hal.archives-ouvertes.fr/hal-00716463
DOI : 10.1111/j.1365-3121.2012.01060.x

Éditeur(s) : HAL CCSD
Résumé : International audience
Sedimentary basins, through the sedimentary successions and the nature of the deposits, reflect the geology of thearea from which the sediments were derived and thus provide valuable record of hinterland tectonism. As the collisionbetween the South China and the Indochina blocks (i.e. the Indosinian orogeny) is still the object of a numberof controversies regarding, for instance, its timing and the polarity of the subduction, the sedimentary basins associatedwith this mountain belt are likely to provide clues to reconstruct its geodynamic evolution. However, boththe Sam Nua Basin (located to the south of the inner zones of the Indosinian orogeny and the Song Ma ophiolites)and the Song Da Basin (located to the north of the inner zones), northern Vietnam, are still lacking importantinformation regarding the depositional environments and the ages of the main formations that they contain.Using sedimentological and dating analyses (foraminifers biostratigraphy and U-Pb dating on detrital zircon), weprovide a new stratigraphic framework for these basins and propose a geodynamic evolution of the present-daynorthern Vietnam.During the Early Triassic, the Sam Nua Basin was mainly supplied by volcaniclastic sediments originating froman active volcanic activity. Geochemical investigations, combined with sedimentological and structural analyses,support an arc-related setting for this magmatism. This magmatic arc resulted from the subduction of a south dippingoceanic slab that once separated the South China from the Indochina blocks. During the Middle to the LateTriassic, the Sam Nua Basin underwent erosion that lead to the formation of a major unconformity, termed theIndosinian unconformity. This unconformity is interpreted to result from the erosion of the Indosinian mountainbelt, built after the continental collision between the South China and the Indochina blocks. Later, during the LateTriassic, the Sam Nua Basin experienced the deposition of very coarse material, emplaced under continental settingand representing the product of the erosion of the Indosinian mountain belt.To the North, the Song Da Basin is characterized by strongly diachronous deposits over a basal unconformitydeveloped at the expense of volcanic and volcaniclastic deposits related to the Emeishan Large Igneous Province.The sedimentary succession indicates a foreland setting during the Early to the Middle Triassic, which contrastswith the commonly assumed rift setting for these sediments. Thus, the Song Da Basin documents the formation ofthe Indosinian thrust belt, located immediately to the South of the basin.
European Geosciences Union General Assembly 2017
Vienne, Austria

insu-01510331
https://hal-insu.archives-ouvertes.fr/insu-01510331