Truong Son Research Articles

Geological setting and gold mineralisation characteristics at the Me Xi, Vinh Linh, Quang Tri, Vietnam

The Me Xi gold deposit is located in Vinh Linh, Quang Tri, Truong Son Fold Belt, Vietnam, about 45 km to the east of the Sepon Mineral District, Laos PDR. Gold mineralisation at Me Xi is predominantly hosted in siltstone and subordinate calcareous siltstone, sandstone, shale, black shale and calcareous shale of Ordovician - Early Silurian Long Dai formation that were metamorphosed at greenschist facies. The igneous rocks that are closest to Me Xi deposit include undated porphyritic dolerite and mafic dykes. Two gold mineralisation zones consisting of eight mineralised bodies have been recorded, in which the main zone is ~ 640 m long and ~10÷60 m wide. The largest gold mineralisation body has a length of ~220 m and a width of ~0.5÷3 m. Gold mineralisation occurred mainly as stockwork quartz-sulphide veins that were typically characterised by the brittle deformation of host rocks. At least four hydrothermal stages were observed at the deposit, of which gold was accumulated in the stage 2 veins and possibly stage 3 veins that has similar mineralogical assemblage and alteration patterns to those of the stage 2. These stockwork stages 2 and 3 veins predominantly consist of pyrite and minor chalcopyrite, gold, arsenopyrite, pyrrhotite and galena in association with strong silicification, chloritisation, sericitisation and subordinate decalcification. The pre-Au stage 1 veins are rarely observed, but this hydrothermal stage records an initial deformation of the host sequence. The post-Au stage 4 is characterised by carbonate-rich quartz stockwork veins with local patches of sulphides.

Using compositions of zircon to reveal fertile magmas for the formation of porphyry deposits in the Loei and Truong Son fold belts, northern Laos

The Loei and Truong Son fold belts are well known as being the most geologically important and highly mineralized magmatic arc-related terranes in mainland southeast Asia. Numerous studies have examined the geology, geochemistry, and geochronology but only a few metallogenic and detailed deposit characterizations have been undertaken. This study of zircon geochemical analyses uses laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to provide U-Pb ages and magmatic fertility of felsic to intermediate volcanic and plutonic rocks from ten prospects in the Loei and Truong Son fold belts, in the northwest Laos region. The geochemical and geochronological analyses suggest at least three episodes of magmatism occurred: Silurian-Devonian (434–411 Ma), Early to Middle Permian (299–277 Ma), and Late Permian to Middle Triassic (253–243 Ma). The variable ranges of ɛHf values (−12 to + 12) suggest that mantle-derived and crustal contamination signatures are related to the history of subduction and arc magmatism in this region. Key trace elements and ratios associated with oxygen fugacity of magmas (e.g., Eu/Eu*, Dy/Yb, Ce/Nd, ΔFMQ) imply that the Phu Kham and the west of Vientiane along the Mekong River are likely to be fertile for porphyry copper deposits. In contrast, the Pha Gnai and other suites are less fertile. Using zircon as a fertility indication can be a valuable tool to distinguish between fertile and barren magmatic suites in this area.

Identification of the active faults and seismotectonic zonation of Laos territory

In this study, the main active faults in the territory of Laos were identified by analyzing the spatial relationship between the distributions of neo-tectonic faults and earthquake epicenters. The map of neo-tectonic faults was built by integrating the results of neo-tectonic faults research using geological-geomorphological data together with the lineament map obtained from remote sensing analysis. Nontectonic lineaments were eliminated by correlating the spatial distribution of the lineament field with a topographic map, DEM, and geological-geomorphological data. The earthquake data, including 4416 events in Laos and its surroundings, were collected from different sources: the International Seismological Center (ISC), the earthquakes recorded by the local seismic network in Laos, the seismic data in Vietnam, and the earthquake catalog provided by the Thailand Meteorological Department (TMD). Among these, 820 events were located using the hypocenter method, and the local network recorded the data. The magnitude conversion was applied to get a unified scale Mw. The catalog of 1617 main shocks obtained after eliminating foreshocks and aftershocks using the declustering technique was used for a spatial correlation with the neotectonic fault distribution to identify active faults. A total of 14 main active fault zones in the Laos territory were defined. Most are also seismogenic faults with Mw ≥ 5.0 occurring along their trace. Considering the characteristics of seismic activity and the active and neotectonic faults, the territory of Laos can be divided into six seismotectonic zones according to the decreasing level of seismic activity: the Western, the Northeastern Samnua, the Phongsali, the South Truong Son, the North Truong Son, and the Khorat zones. Each zone is characterized by relative homogeneity in the seismic activity and the characteristics of active and neotectonic faults.

A New Record of Bufo gargarizans Complex (Bufonidae, Anura) from Truong Son Mounts, Ha Tinh and Ha Giang Provinces, Vietnam Based on Molecular Evidence with a Description of a New Species

Based on a combination of molecular and morphological data, we herein report a new species within the bufonid Bufo gargarizans species complex. This is a widespread species complex with distribution from eastern Russia and the Korean Peninsula to China and the Ryukyu Islands of Japan. Records of this species have been documented in the Guangxi and Yunnan Provinces near the border with Vietnam and, for the first time from Vietnam, in Ha Giang Province. The new record of Bufo cf. gargarizans from Vietnam is from Ha Tinh Province. This species has never been reported from Vietnam so far south, about 550 km south from the previously known locality in Ha Giang Province. The female specimen was found in the Ha Tinh Province, Vu Quang National Park of central Vietnam and two specimens (male and female) were found Ha Giang Province. They are clearly distinguished from B. gargarizans and all the mentioned species by a specific color pattern on the belly and creamy-yellowish throat with large, bright red speckles. Genetic divergences of three Vietnam specimens from Ha Giang and Ha Tinh Provinces in the ND2 gene sequences between the В. sp. nov. and all other congeners ranged from 4.3% (with B. andrewsi) to 7.0% (with B. stejnegeri). We give a description of the morphological characters and coloration of the new record and provide an expanded diagnosis.

Early Paleozoic tectonic evolution in the central Vietnam: evidence from geochronological and geochemical constraints

ABSTRACT Magmatic rocks distributed along the western part of the Po Ko fault, which documented tectono-thermal evolution of the Indochina block, when and how they formed are less constrained. Our new geochronological and geochemical data reveal that they were generated at 488–457 Ma and display a variety of SiO2 concentrations (SiO2 = 50.7–72.8 wt%). They also generally show slightly negative Eu anomalies (Eu/Eu* = 0.65–0.98) and enrich in LILEs (e.g. Rb and K) but deplete in HFSEs (e.g. Nb and Ta), consistent with arc-related signatures. Combined with their relatively high Mg# values (Mg# = 56–40) and initial87Sr/86Sr ratios (0.7085–0.7167) but negative εNd(t) values (−2.5 to −3.7), we consider those magmatic rocks originated from an enriched mantle source (e.g. EMII), which was metasomatized in the past. In comparing our data with tectono-thermal events in the southern Truong Son belt, we infer that there existed an ocean (a branch of the proto-Tethys Ocean) between the Truong Son belt and the Kontum massif during Late Cambrian, which subsequently underwent southeast subduction beneath the Kontum mass if initiated at ~488 Ma and terminated at ~457 Ma.

Influence of Foehn Winds of Truong Son Mountains on the High Temperatures Observed in North-Central Vietnam during 31 May–5 June 2017

Abstract North-central Vietnam often experiences high temperatures. Foehn winds originating from the Truong Son Mountains (also known as Laos winds) are believed to contribute to abnormally high temperatures; however, no quantitative research has focused on foehn warming in Vietnam. In this study, we conducted numerical simulations using the Weather Research and Forecasting (WRF) Model to investigate the contribution of foehn warming to abnormally high temperatures in north-central Vietnam in early June 2017. Generally, May–June is the monsoon period in Vietnam. Consequently, foehn warming during this season is thought to be mainly caused by latent heating and precipitation mechanism. However, the primary factor in the cases covered in this study was foehn warming with an isentropic drawdown mechanism. Diabatic heating with turbulent diffusion and sensible heat flux from mountain slopes also plays significant roles. The warming effect of the foehn winds on the temperatures during the events was approximately 2°–3°C. It was concluded that the high temperature events from 31 May to 5 June 2017 were caused by synoptic-scale warm advection and foehn warming. Sensitivity experiments were conducted on the WRF Model, utilizing three atmospheric boundary layer turbulence schemes (YSU, ACM2, and MYNN), consistently yielding results for simulated temperature and relative humidity. The wind speed bias for the MYNN scheme was found to be lower than that of the other schemes. However, this study did not delve into the underlying reasons for these differences. The optimal performance of each scheme remains an open question. Significance Statement It was hypothesized that north-central Vietnam often experiences high temperatures owing to foehn winds (also known as Laos winds) descending from the Truong Son Mountains. This study conducted numerical experiments to validate this hypothesis and investigate the associated mechanisms of foehn winds in this region. Surprisingly, despite the monsoon season, the isentropic drawdown mechanism without precipitation effects provides the primary explanation for the high temperatures caused by foehn winds in north-central Vietnam, and not the latent heating and precipitation mechanism with precipitation effects that researchers expected. The results of this study contribute to better prediction of high temperatures in this region and improve our understanding of foehn winds in tropical monsoon climate zones.

The Petrographic Characteristics and U-Pb Zircon Isotope Age of Felsic Extrusive Rocks in the Western Thanh Hoa Area, Song Ma Suture Zone

Felsic extrusive rocks are widely distributed in the western region of Thanh Hoa, primarily comprising rhyolite and rhyolitic tuff formations. They show porphyritic textures, and are composed of 15–25% phenocrysts and 75–85% groundmass. Phenocrysts are mainly euhedral–subhedral plagioclase (5-10 vol.%), K-feldspar (5-10 vol.%) and quartz (5-10 vol.%). The groundmass consists of plagioclase (30-45 vol.%), K-feldspar (25-40 vol.%), quartz (30-40 vol.%), and minor biotite with random distribution. In terms of geological context, these extrusive rocks overlie Silurian-Devonian sequences of sandstone and siltstone interbedded with shale and limestone lenses, and were intruded by the Early Triassic granite of the Song Ma complex. Zircons selected from rhyolite were LA-ICP-MS U-Pb dated, yielding an age of 253 Ma. This age is the timing of the magma crystallization, corresponding to the Late Permian - Early Triassic Indosinian tectonomagmatic event. These findings together with historical study results, prove that the Indosinian magmatic event widely occurred in the Truong Son belt, the Song Ma domain and the Kon Tum area. The eruption of the rhyolite is linked to the amalgamation between the South China and Indochina blocks.

Enrichment Factors and Metallogenic Models of Critical Metals in Late Permian Coal Measures from Yunnan, Guizhou, and Guangxi Provinces

The Late Permian coal measures in eastern Yunnan, western Guizhou, and central Guangxi are significantly enriched in critical metals that could serve as important supplements to conventional critical metal deposits in China. This study collected previous geochronological and geochemical data from the Late Permian coal measures to evaluate the distribution characteristics and enrichment factors of critical metals. Moreover, metallogenic models for critical metals were also developed. The results showed that Late Permian coal measures in Yunnan, Guizhou, and Guangxi provinces exhibited abnormal enrichment in Nb, Zr, and rare earth elements (REY, or REE if Y is excluded). The Emeishan mafic rocks and intermediate-felsic volcanic ash from the Truong Son orogenic belt underwent chemical weathering, with Nb and Zr selectively preserved in situ in the form of heavy minerals (e.g., rutile, zircon, and anatase), which subsequently led to the enrichment of Nb and Zr in bauxite and Al-claystone at the bottom of the Late Permian coal measures. Intermediate-felsic volcanic ash from the Emeishan large igneous province (ELIP) and the Truong Son orogenic belt supplied Nb, Zr, and REY for the middle and upper parts of the Late Permian coal measures. The intermediate-felsic mineral material of the coal measures in the intermediate zone, outer zone, and outside zone of ELIP are derived mainly from the ELIP, the mixture from ELIP and the Truong Son orogenic belt, and the Truong Son orogenic belts, respectively. Nb, Zr, and REY were leached by acidic aqueous solutions and from the parting and roof into underlying coal seams, where they deposited as authigenic minerals or adsorbed ions on organic matter during early coalification.

Crustal evolution of Paleozoic-Mesozoic granitoid in Dakrong-A Luoi area, Truong Son belt, central Vietnam: evidence from zircon U-Pb geochronology, geochemistry, and Hf isotope composition

ABSTRACT The Dakrong-A Luoi area is located in the South Truong Son belt in the Indochina block and has been affected by multiple stages of magmatic-metamorphic events. In this paper, Paleozoic-Mesozoic granitoids from the Dakrong-A Luoi area were studied using LA ICP-MS U-Pb zircon geochronologies, Hf isotopes on zircon and whole-rock geochemistry of the Paleozoic to examine the tectonic-magmatic history of the Southern Truong Son belt. The magmatism history of the area can be divided into three phases, at ~ 452 Ma (Ordovician), ~259 Ma (Permian), and ~ 243 Ma (Triassic). The Ordovician granites were exposed in the narrow belt of NW-SE trending, while the later two granite phases were exposed in E-W trending. The Ordovician granites show consistent LA-ICP-MS zircon ꜪHf(t) values from + 6.2 to + 8.3. Their corresponding Hf model ages (TDM2) from 0.9 Ga to 1.0 Ga suggest that the Ordovician granite was derived from the partial melting of ancient crustal rocks, which is related to the subduction of the Tam Ky-Phuoc Son (TKPS) ocean beneath the Truong Son belt. The Permian granites have Hf isotopic natures (ꜪHf(t)=-1.6 to 1.3, TDM2 = 1.2–1.3 Ga) of partial melting from ancient mantle components with minor Paleoproterozoic ancient continental crust The Triassic granites have negative ɛHf(t) values ranging from −11.9 to −7.0 and Hf model ages of 1.7–2.0 Ga suggesting that they were a product of partial melting from the Paleoproterozoic crust, corresponding to subduction/collision of the Paleo-Tethys ocean beneath the Indochina block along the Song Ma suture.

Applying TOPSIS to selecting business accounting software: A case study at Truong Son Technology Development Investment Joint Stock Company

This study aimed to build a model and set of criteria to evaluate and select business accounting software providers for Truong Son Technology Investment and Development Joint Stock Company. The study helped choose the most suitable supplier that meets the criteria that the company desired. The research proposed the Technique of Order Preference Similarity to the Ideal Solution (TOPSIS) model and was also applied in the case of selecting accounting software suppliers for Truong Son Technology Investment and Development Joint Stock Company. There were 5 business accounting software packages considered: Misa business accounting software, Bravo accounting software, FAST Accounting software, Effect accounting software, and Gamma accounting software. The ranking results of accounting software providers at Truong Son Technology Investment and Development Joint Stock Company were as follows: A1 (Misa Business Accounting Software) was the best supplier, second-ranking was A3 (FAST Accounting software), followed by A2 (Bravo Accounting Software) in third place. The findings of this study could be used as a valuable reference for businesses to choose the best supplier.

Differences in Geochemical Characteristics and Tectonic Settings between Hai Van Granitic Rocks in Da Nang Province and Van Canh Plutonic Rocks in Quang Nam Province, Central Vietnam

Research was conducted on plutonic rocks, previously referred to as the Hai Van granitic rocks, distributed in Da Nang and Quang Nam provinces in Central Vietnam. The granitic rocks in Da Nang Province have low magnetic susceptibilities and have geochemical signatures typical of S-type. Additionally, a negative Eu anomaly suggests that the source rock is an organic matter-bearing sedimentary rock. The granitic rocks were likely formed during the collision between the Indochina and South China blocks. In contrast, plutonic rocks in Quang Nam Province have high magnetic susceptibilities and have geochemical signatures of I-type. No Eu anomaly was observed, and they are adakitic rocks in nature. Based on these findings, the plutonic rocks in Quang Nam Province are distinctly different from the Hai Van granitic rocks in Da Nang Province, but they are Van Canh plutonic rocks. The Hai Van granitic rocks in Da Nang Province and the Van Canh plutonic rocks in Quang Nam Province are located in the Truong Son Fold Belt. The Van Canh plutonic rocks are located farther away from the Song Ma Suture Zone than the Hai Van granitic rocks. The Van Canh plutonic rocks were generated due to the subduction of the hot Song Ma Ocean beneath the Indochina Block. The Hai Van granitic rocks are understood to have been generated in a compressional field where the Song Ma Ocean was pushing against the Indochina Block; however, the Van Canh plutonic rocks are supposed to have been generated in an extensional field, like in a back-arc-like environment generated by the subduction of the Song Ma Ocean beneath the Indochina Block.

Geological Structures and Age of the Magmatic Rocks Related to Primary Gold in Vietnam

The research on gold in Vietnam has been interesting to many authors. So far, studies on Geology-Minerals on the territory of Vietnam have determined that there are hundreds of gold mineralization. The structures related to primary gold in Vietnam have identified as Truong Son Fold Belt/ East Indochina Block and Sino-Vietnam composit Terran corresponding to Mountain belt internal contents early Paleozoic and Areas with high metamorphism. The magma formations associated with the mineralization zone contain gold mainly in the P3-T1 period, primary gold in Vietnam is closely related to the folding structure. Primary gold in Vietnam is an ore type of quartz-polymetallic sulfide-gold (silver) and quartz-sulfur-gold. Our research results have contributed to orienting the search for primary gold in Vietnam.

Runoff and erosion from three unpaved road segments in northern Vietnam

Study regionTruong Son Commune, Luong Son District, Hoa Binh Province in north Vietnam. Study focusRunoff and erosion from three road surface and three adjacent cutslope plots in a young plantation forest to evaluate how unpaved forest roads affect runoff and erosion. New hydrologic insights for the regionThe 10-m long road surface plots generated similar amounts of runoff with runoff coefficients of 24–32 % over 24 rainstorms divided into an initial wetter period followed by a relatively drier period. Runoff coefficients for the two monitoring periods were not statistically different, and the relatively low runoff coefficients compared to previous studies were due to infiltration outside the narrow compacted tracks created primarily by motorbike traffic. Runoff from the base of the cutslopes varied by a factor of three, associated with the topographic convergence of the hillslopes. Road surface erosion over the two monitoring periods was consistent among the three plots and storm-based sediment production was strongly correlated with both storm precipitation and surface runoff. The amounts of runoff and sediment collected at the base of the cutslopes increased with increasing hillslope convergence, and the mass of collected sediment was 52–97 % of the corresponding amounts from the road surface plots. The results provide data on the extent of unpaved road runoff and erosion in this seasonally wet tropical environment, and the need to consider topographic convergence in road design and drainage.

On the keeled box turtle (Cuora mouhotii) from reforested land in Vietnam

The keeled box turtle (Cuora mouhotii Gray, 1862) is endangered and native to Bangladesh, Bhutan, China, India, Laos, Myanmar, Thailand and Vietnam. First described in 1862 by Gray, its numbers have declined by 50-80% in the past 75 years, particularly in China due to harvesting. Other research has also shown that C. mouhotii is very rare in Myanmar and at risk in Laos. In Vietnam, C. mouhotii has been found in the mountainous areas from North Central to Central Vietnam such as Cuc Phuong National Park, Nghe An, Ha Tinh and Quang Binh provinces, as well as in the Truong Son mountains as far as Quang Nam province in Central Vietnam. However, the population of C. mouhotii in Vietnam has also decreased significantly because of overexploitation and habitat destruction.

Tadpole of the Vietnamese jelly-nest tree frog, Feihyla palpebralis (Anura: Rhacophoridae): external morphology and chondrocranium.

The genus Feihyla Frost, Grant, Faivovich, Bain, Haas, Haddad, de S, Channing, Wilkinson, Donnellan, Raxworthy, Campbell, Blotto, Moler, Drewes, Nussbaum, Lynch, Green & Wheeler was established relatively recently (Frost et al. 2006), but to date its composition has changed several times due to the extremely confusing and labile systematics of small rhacophorids (e.g., Grosjean et al. 2008; Hertwig et al. 2013; Biju et al. 2020). It embeds rather miniature, delicate tree frogs and currently comprises six species (Frost 2023). The type species, Feihyla palpebralis (Smith 1924), was described from Mount Langbian in the southern part of the Truong Son Range (Annamite Mountains) and was long considered endemic to Vietnam; recent reports that it is also distributed in China can be based on misidentification and need reliable confirmation (Biju et al. 2020).

Truongsonia (Arecaceae: Arecoideae: Truongsonieae)—a new palm genus and tribe from Vietnam

A genus and species of palm from the Truong Son Range in Vietnam, Truongsonia lecongkietii, is described as new to science. Phylogenomic analysis strongly supports the placement of the new taxon in subfamily Arecoideae as sister to the African endemic tribe Podococceae, which comprises a single genus Podococcus. A new tribe Truongsonieae is also described to accommodate Truongsonia in the current phylogenetic classification of palms. Truongsonia is a dwarf, acaulescent, clump-forming palm bearing entire, bifid leaves with a fibre-like extension of the rachis through the sinus of the two lobes of the leaf. The interfoliar inflorescence is exserted on a long peduncle with 3­–4 tightly sheathing peduncular bracts and rachillae presented at the apex only. The ovary is triovulate-tricarpellate, but fruits are single-seeded. Truongsonia is Critically Endangered, with surveys locating only 10–15 plants in the wild. Swift conservation action is required to secure the future of this remarkable and phylogenetically isolated lineage of palms.

Tectonic evolution of the Red river basin and adjacent area (Vietnam) in Cenozoic era

Basing on the structural and tectonophysic analysis of data collected from outcrops around Tonkin Gulf and the results of analysis of seismic setions of the Red river basin, the fourmain successivetectonic phases with specific paleostress fields since beginning of Cenozoic era have been established. The first middle Eocene-early Miocene (45-15.97 my) tectonic phase, with sub-latitudinal compression and sub-longitudinal extension, was accompanied by large scale sinistral displacement of the Red river fault, the extension centers of the Red river basin andseafloor spreading of East Vietnam Sea. The second middle-late of middle Miocene (13, 82-7, 25 my) tectonic phase, with sub-longitudinal compression and sub-latitudinal extension, has created a local depocenter N-S orientation; right-lateral strike slip of the Red river fault and first inversion of the basin. The third late Miocene (~7.25-5.33 my BP) tectonic phase, with NE-SWcompression, has caused strongest inversion in the Red river basin with strong uplift of some blocks and significant shrinkage of the RRB up to 15–20%. The fourth Quaternary-to-Recent tectonic phase, with NW-SE compression and NE-SW extension, is appeared in form of existing of the recent grabens of NW-SE direction, earthquakes and GPS data. Formation and development of the Red river basin was controlled by the tectonic activities and closely connected to NW-SE trending fault system of regional scale such as the Red river fault, Chay river fault, Lo river faults as well the local faults such as Ca river fault, Rao Nay river fault, Thakhek-Da Nang fault. Some spectacular examples for tectonic activity can be seen in form of geographic features of Vietnam, Laos and Thailand, in particular the mountain ranges, such as Truong Son (or Viet-Laos) belt. The Red river fault when comes to the sea becomes less active, while the other faults of the RRFS like Chay river and Lo river had played the main role in development of the Red river basin.

P–T–t conditions of Early Palaeozoic low‐P high‐T granulite facies metamorphism in the southern Truong Son Belt, Central Vietnam

AbstractHigh‐grade metamorphic rocks are widely exposed along the SE–NW‐ to E–W‐trending shear zones in the Truong Son Belt, Central Vietnam, but few petrological studies have been conducted in this area. Herein, we report the occurrence of mylonitized granulites that crop out along the Dai Loc shear zone in the southernmost Truong Son Belt. Detailed petrographic analysis, geochemistry and P–T–t estimates of the evolution of two granulite samples are presented to elucidate the formation processes of these high‐grade metamorphic rocks. The results indicate that the rocks underwent two distinct metamorphic cycles. The first cycle (M1) is characterized by coarse‐grained granulite mineral assemblages, defining a tight clockwise P–T path with near‐isobaric heating to a near ultrahigh‐temperature peak at low pressure, followed by cooling. The prograde mineral assemblage (M1a) is indicated by inclusions of cordierite + sillimanite + biotite + quartz + spinel ± plagioclase in coarse‐grained garnet, orthopyroxene and cordierite. The mineral assemblage of garnet + orthopyroxene + cordierite + plagioclase + K‐feldspar + ilmenite + melt ± biotite (M1b) defines the peak P–T conditions of 5.3–6.3 kbar and 850–920°C. Post‐peak cooling (M1c) is marked by the formation of quartz + biotite symplectites around garnet and orthopyroxene. The second cycle involved medium‐pressure amphibolite facies metamorphism (M2), characterized by domainal development of fine‐grained kyanite‐bearing mineral associations. Petrographic observations indicate that these fine‐grained associations were formed during mylonitization. Zircon U–Pb dating reveals that the timing of granulite facies metamorphism appears to be coeval with the intrusion of a post‐collisional granitoid at 430–410 Ma. Granulite facies metamorphism and crustal melting were probably driven by asthenospheric mantle upwelling triggered by slab breakoff during the Early Palaeozoic. Considering previous structural and geochronological studies, the second metamorphic event likely occurred during the Triassic Indosinian orogeny.

Sand-rich Pleistocene deep-water channels and their implications for gas hydrate accumulation: Evidence from the Qiongdongnan Basin, northern South China Sea

Deep-water turbidite channels are conduits for transporting terrigenous clastic sediments into the ocean, and channel deposits can also act as high-quality hydrocarbon reservoirs. In this study, based on high-resolution 3D seismic data and logging-while-drilling data, four Pleistocene turbidite channels are identified and characterized in the deep-water area. These deep-water channels are sinuous with V- or U-shaped on the seismic profiles, and their evolutionary history can be divided into Unit 1 (Erosion-dominated stage), Unit 2 (Erosion-Deposition stage), Unit 3 (Erosion-Deposition stage), and Unit 3 (MTDs-dominated stage). The internal fillings of these channels are almost basal lags with high-amplitude reflections at the bottom, pelagic sediments with low-amplitude reflections, and mass transport deposits with translucent/transparent seismic facies. Since sand-rich sediments dominate the deep-water channel-levee systems in Unit 3 in the study area, they could act as shallow gas reservoirs and facilitate the accumulation of gas hydrates. By analyzing the source-to-sink systems around the basin, the source of the sediments within the deep-water channels is discussed, which are mainly from the Truong Son Belt. Floods, sea level fluctuations, and earthquakes are the most likely triggering mechanisms of turbidity currents in the Qiongdongnan Basin. This study provides new insights into the Quaternary deep-water sedimentary process, gas hydrate exploration, and source-to-sink systems in the northwestern South China Sea.

Geochemistry and zircon U-Pb geochronology of the Dak Krong plutonic rocks in the Kontum Massif (central Vietnam) and their petrogenetic implications

Dak Krong plutonic rocks are found in the Kontum Massif along the N-S-oriented Po Ko River and mainly within the distributive area of the Ben Giang-Que Son granitic bodies. The Hai Van complex crosscuts the Dak-Krong rocks. They are predominantly composed of plagioclase (35-47%), quartz (29-30%), K-feldspar (20-28%), and minor biotite (3-4%). Geochemically, they are characterized by meta- to peraluminous and high-K affinities and straddle I- and S-type granite fields. Zircon U-Pb dating results yielded two main magmatic stages (ca. 258 Ma and ca. 245 Ma) spanning two phases of magmatism presumably accepted as being associated with the Paleo-Tethys Ocean evolution: latest subduction to syn-collisional phases. The Hf isotope data from zircon with eHf(t) ranging between -6.4 and -0.5 indicates a crustal signature. From the results of eHf(t) values along with zircon Hf model ages (TDM2) ranging from 1165-1497 Ma, it is presumable that the Dak Krong plutonic rocks are the product of the partial melting of Mesoproterozoic crustal materials with a negligible contribution of mantle materials. Together with other Permian-Triassic magmatic complexes throughout the Kontum Massif (e.g., Ben Giang-Que Son, Hai Van, and Van Canh complexes) and other plutonic further to the north along the Truong Son Belt and the Song Ma suture zone, the Dak Krong plutonic rocks represent magmatism generated by the amalgamation of Indochina and South China during the Late Permian-Early Triassic, referred to as Indosinian orogeny.