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Research about Vietnam

Source-linked reports with geographic coverage including Vietnam.

8 recordsLinked to original sources
USGS2023

Extrusion tectonism of Indochina reassessed: constraints from 40Ar/39Ar geochronology from the Day Nui Con Voi metamorphic massif, Vietnam

The extrusion tectonic model for the southeastern margin of the Himalayan orogeny links the crustal shear activity along the Red River Shear Zone (RRSZ) to the opening of the South China Sea (SCS). The Day Nui Con Voi (DNCV) metamorphic massif in northern Vietnam strikes NW-SE, is bounded by the RRSZ to the south and continues along the strike where it meets the SCS. The DNCV is thus a critical area to document thermotectonic history in order to advance our understanding of the tectonic evolution of Indochina extrusion and its relationship to the opening of the SCS. Our new 40 Ar/ 39 Ar data combined with microstructural and petrological analyses constrained the timing of the left-lateral shearing of the RRSZ and revealed the thermal evolution of the DNCV metamorphic massif. Three ductile deformation events were observed. D 1 formed NNW-SSE striking upright folds under granulite to upper amphibolite facies conditions. D 2 was a horizontal to sub-horizontal folding event that occurred at amphibolite facies conditions. D 3 was a doming event that formed NW-SE striking up-right folds bounded by left-lateral shearing mylonite belts along the two limbs. The S/C fabrics were defined by muscovite fish, quartz + albite + K-feldspar aggregates, and muscovite folia. The D 3 doming event exhumed the DNCV metamorphic massif from amphibolite facies conditions to the lower greenschist facies conditions. The 40 Ar/ 39 Ar ages obtained from amphibole (∼26 Ma), phlogopite (∼25 Ma), muscovites (∼24-23 Ma), biotite (∼25-23 Ma), and K-feldspars (∼25-22 Ma) from different structural domains of the DNCV metamorphic massif indicated a rapid exhumation ∼26–22 Ma. We interpreted this as the time period for the D 3 event, with the onset of left-lateral shearing occurring around 24 Ma based on ages obtained from syn-kinematic muscovites. This age was much younger than the initiation of sea-floor spreading of the SCS (since 32 Ma) but coincided with the age for the ridge jump event in the SCS. Based on these new data, we proposed that extrusion tectonism cannot be the cause for the initial opening of the SCS. Rather, the extrusion of the Indochina block was temporally correlative with the southward ridge jump event of the already opened SCS.

Day Nui Con Voi massif↗
USGS2017

Assessment of forest degradation in Vietnam using Landsat time series data

Landsat time series data were used to characterize forest degradation in Lam Dong Province, Vietnam. We conducted three types of image change analyses using Landsat time series data to characterize the land cover changes. Our analyses concentrated on the timeframe of 1973–2014, with much emphasis on the latter part of that range. We conducted a field trip through Lam Dong Province to develop a better understanding of the ground conditions of the region, during which we obtained many photographs of representative forest sites with Global Positioning System locations to assist us in our image interpretations. High-resolution Google Earth imagery and Landsat data of the region were used to validate results. In general, our analyses indicated that many land-use changes have occurred throughout Lam Dong Province, including gradual forest to non-forest transitions. Recent changes are most marked along the relatively narrow interfaces between agricultural and forest areas that occur towards the boundaries of the province. One important observation is that the most highly protected national reserves in the region have not changed much over the entire Landsat timeframe (1972–present). Spectral changes within these regions have not occurred at the same levels as those areas adjacent to the reserves.

Forests↗
USGS2015

High influx of carbon in walls of agglutinated foraminifers during the Permian-Triassic transition in global oceans

The Permian – Triassic mass extinction is postulated to be related to the rapid volcanism that produced the Siberian flood basalt (Traps). Unrelated volcanic eruptions producing several episodes of ash falls synchronous with the Siberian Traps are found in South China and Australia. Such regional eruptions could have caused wildfires, burning of coal deposits, and the dispersion of coal fly ash. These eruptions introduced a major influx of carbon into the atmosphere and oceans that can be recognized in the wall structure of foraminiferal tests present in survival populations in the boundary interval strata. Analysis of free specimens of foraminifers recovered from residues of conodont samples taken at a Permian – Triassic boundary section at Lung Cam in northern Vietnam has revealed the presence of a significant amount of elemental carbon , along with oxygen and silica, in their test wall structure, but an absence of calcium carbonate . These foraminifers , identified as Rectocornuspira kalhori , Cornuspira mahajeri , and Earlandia spp. and whose tests previously were considered to be calcareous, are confirmed to be agglutinated , and are now referred to as Ammodiscus kalhori and Hyperammina deformis . Measurement of the 207 Pb/ 204 Pb ratios in pyrite clusters attached to the foraminiferal tests confirmed that these tests inherited the Pb in their outer layer from carbon -contaminated seawater. We conclude that the source of the carbon could have been either global coal fly ash or forest fire-dispersed carbon , or a combination of both, that was dispersed into the Palaeo-Tethys Ocean immediately after the end- Permian extinction event.

Ha Giang Province↗
USGS2015

Conodont biostratigraphy of the Permian-Triassic boundary sequence at Lung Cam, Vietnam

The occurrences of a few specimens of Clarkina and many specimens of Hindeodus at the Permian-Triassic boundary section at Lung Cam, Vietnam allow accurate graphic correlation to the P-T boundary stratotype at Meishan, China. One species of Clarkina, ten species and two subspecies of Hindeodus, and the apparatuses of Hindeodus latidentatus and Merrillina ultima are described and illustrated.

Micropaleontology↗
USGS2012

Bathymetry of the Hong and Luoc River Junction, Red River Delta, Vietnam, 2010

The U.S. Geological Survey, in collaboration with the Water Resources University in Hanoi, Vietnam, conducted a bathymetric survey of the junction of the Hong and Luoc Rivers. The survey was done to characterize the channel morphology of this delta distributary network and provide input for hydrodynamic and sediment transport models. The survey was carried out in December 2010 using a boat-mounted multibeam echo sounder integrated with a global positioning system. A bathymetric map of the Hong and Luoc River junction was produced which was referenced to the datum of the Trieu Duong tide gage on the Luoc River.

Hong River;Luoc River;Red River Delta↗
USGS1967

Age, composition, and tectonic setting of the granite island, Hon Trung Lon, off the coast of South Vietnam

Hon Trung Lon , a granite island off the coast of South Vietnam , is composed solely of a unique, extremely differentiated, high-silica alkali granite of Cretaceous age . An adjacent island , Hon Trung Nho, is composed solely of rhyolitic rock of similar composition . The Hon Trung Nho rhyolite may be a fine-grained equivalent of the granite . Whole-rock potassium-argon analysis suggests that the age of the Hon Trung Lon granite is greater than 70 m.y. and less than 100 m.y. This age implies a previously unrecognized period of intrusion for the zone of granitic rocks outcropping along the northeast side of the Gulf of Thailand. Extensive investigation of the Mesozoic and Tertiary igneous rocks of Southeast Asia, particularly Indochina, including reliable geochronological work, is needed to trace the geologic events that produced the complicated structural features and orogenic history of this region. Existing data suggest that Southeast Asia has been the site of active orogeny since the Paleozoic and that the Hon Trung Lon granite was emplaced through a sialic crust which has been evolving in this area for at least the last 400 m.y.

south Vietnam Islands↗