Тектоническая эволюция южной части Центрального Вьетнама и прилегающей территории

Interpretations of seismic, gravity and magnetic anomalies and structural data on the coastal zone of southern part of Central Viet Nam (SCVN) and the adjacent Tertiary basins suggest several phases in the tectonic evolution of the study region since the Late Cretaceous to Quaternary. In this paper, we try to clarify the tectonic evolution of SCVN and the adjacent continental margin. The Cretaceous – Paleocene tectonic phase commenced after cessation of the West Pacific plutonic magmatic activity that produced numerous diabases and aplite dykes of mainly sub-meridian orientation. It was characterized by N–S compression and E–W extension. The geomorphology and geology ofSE Asiawere considerably changed during the Neotectonic phases caused by collision between the Indian plate and the Eurasian continent. Two tectonic phases – Early and Late Neotectonic – are separated by a regional unconformity represented by a boundary surface between below strongly deformed strata (synrift) and above less deformed formations (post-rift). The Early Neotectonic phase was related to the left-lateral movement of the Red River Fault Zone (RRFZ) and includes two tectonic sub-phases: Eocene – Oligocene (NW–SE compression), and Oligocene – Miocene (E–W compression). Activity in the Oligocene-Miocene sub-phase gave birth to rift basins in the continental margin of the SCVN. The Late Neotectonic phase began since the RRFZ stopped left-lateral movement and the East Viet Nam (orSouth China) Sea stopped spreading. The Late Neotectonic phase is also divided into two tectonic sub-phases: Late Early Miocene (sub-meridian compression), and Late Miocene – Pliocene (NE–SW compression). The Late Miocene – Pliocene sub-phase is characterized by vertical movements that caused episodic uplifting of the onland terrains, and subsidence of the offshore Phu Khanh basin. Besides, Miocene – Pliocene-Quarternary basaltic eruptions were widespread all over the southern Indosinian terrain and the continental margin.Путем интерпретации данных о сейсмических, гравитационных и магнитных аномалиях, а также данных о структуре прибрежной зоны южной части Центрального Вьетнама и прилегающих к нему третичных впадин можно выделить несколько этапов тектонической эволюции изучаемого региона, с позднего мелового до четвертичного периода. Цель статьи – получить более точную картину тектонической эволюции южной части Центрального Вьетнама и прилегающей территории. Тектоническая фаза, датируемая как мел – палеоцен, началась после прекращения глубинного магматизма в западной части Тихого океана, приведшего к образованию многочисленных диабазов и аплитовых даек, ориентированных в основном субмеридионально. В течение этой фазы происходило меридиональное сжатие (С-Ю) и расширение в широтном направлении (З-В). В геоморфологическом и геологическом отношении ЮЗ Азия значительно изменилась в течение неотектонических фаз вследствие столкновения между Индийской плитой и Евразийским континентом. Ранняя и поздняя неотектонические фазы разделены региональным несогласием, которое установлено как поверхность, разграничивающая сильнодеформированные толщи (синрифтовые) и перекрывающие, менее деформированные формации (пострифтовые). Ранняя неотектоническая фаза, связанная с левосторонним смещением в зоне разлома Ред-Ривер, может быть разделена на две тектонические подфазы: эоцен – олигоцен (сжатие в СЗ-ЮВ направлении) и олигоцен – миоцен (широтное сжатие, В-З). В течение подфазы, датируемой как олигоцен – миоцен, возникли рифтовые впадины на континентальной окраине южной части Центрального Вьетнама. Поздняя неотектоническая фаза началась после прекращения сдвигового смещения в зоне разлома Ред-Ривер и прекращения расширения Восточного (Южно-Китайского) моря. Поздняя неотектоническая фаза также может быть разделена на две тектонические подфазы: поздний ранний миоцен (субмеридиональное сжатие) и поздний миоцен – плиоцен (сжатие в СВ-ЮЗ направлении). В течение подфазы, датируемой как поздний миоцен – плиоцен, происходили вертикальные движения, приведшие к формированию ряда поднятий на суше, а также опускания в районе морской впадины Фухань. При этом по всей южной части Индокитая и на континентальной окраине широко распространены миоцен-плиоцен-четвертичные базальтовые извержения

ĐẶC ĐIỂM ĐỊA HÓA THẠCH HỌC ĐÁ MAGMA BAZAN VÀ ĐẶC ĐIỂM NGUỒN MANTI KHU VỰC BIỂN ĐÔNG VÀ LÂN CẬN TRONG KAINOZOI

The East Vietnam Sea is one of the largest marginal basins in western Pacific Ocenan, formed by breaking of continental margin in the Late Mesozoic. Geochemical data of the Miocene - Pleistocene bazanic samples collected in the East Sea and neighboring areas show two major eruption trends that reflect the formation and development of the region. The early eruption event is characterized by low alkaline, TiO2, Na2O, K2O and P2O5, and high SiO2 group, comprising olivine and tholeiitic bazans. The later eruption demonstrates high alkaline, TiO2, Na2O, K2O and P2O5, and low SiO2 group, mainly generated by central-type volcanic eruptions, consisting of alkaline olivine and olivine bazans. Distinctive geochemistry of the volcanic rocks within the East Vietnam Sea and adjacent areas is illustrated by wide range of Magnesium index (Mg#= 35-75). At the values of Mg#>65, the relation between Mg# and major oxides is unclear. In contrast, Mg#65 (Olivine differentiation) the isotope ratios start changing. The primitive components are computed based on the principle of olivine compensation. The computed results show that the critical pressure for Tholeiite melting was estimated from ~11.97-20.33 Kb (ca. 30 - 60 km deep) and the Alkaline melting pressure varies from ~16.87-34.93 Kb (corresponding to the depths of ~60 km to 100 km). The continuous range of melting pressures suggests two trends of tholeiitic and alkaline eruptions occurr at various depths in the same magmatic source. Hight temperature and melting pressure of the primitive magma are dependent on partial melting pressure. Possibly, this process was triggered by the asthenosphere intrusion resulted from the closure of the Neo-Tethys following the India - Eurasia collision. This event has not only made the mantle hotter and easily melted but also triggered the opening of the marginal seas, including the East Vietnam Sea.Biển Đông là một trong những biển rìa lớn nhất thuộc rìa tây Thái Bình Dương hình thành do phá vỡ một bộ phận của rìa lục địa vào cuối Mesozoi. Kết quả thành phần địa hóa các đá bazan tuổi Miocen - Pleitocen khu vực Biển Đông và lân cận cho thấy hai xu thế phun trào chính phản ánh quá trình hình thành và phát triển khu vực. Xu thế phun trào sớm có đặc điểm thấp Kiềm, TiO2 và P2O5 và cao SiO2 chủ yếu là các Tholeit, Olivin bazan. Xu thế phun trào muộn thường cao Kiềm, TiO2 và P2O5 và cao SiO2, chủ yếu tập trung tại các khu vực phun trào kiểu trung tâm, thành phần là các bazan Olivin và Nephenin. Đặc trưng địa hóa của đá núi lửa khu vực Biển Đông và lân cận là sự phân bố rộng của chỉ số Magie (Mg#=35-75). Tại giá trị Mg#>65, quan hệ giữa Mg# và các hợp phần oxit chính là không rõ ràng. Ngược lại, tại giá trị Mg

Vietnam geographical exploitation under the United Nations Convention on the Law of the Sea in 1982 (UNCLOS 1982)

As an active member of the United Nations Convention on the Law of the Sea - UNCLOS, Vietnam has completed 3 Reports on the Limits of the Continental Shelf and has submitted two of them to the Commission on the Limits of the Continental Shelf - CLCS, before the deadline 13-5-2009. Those are: (1) Outer Limits of the Vietnam’s Extended Continental Shelf: North Area (VNM-N); (2) Outer Limits of the Vietnam’s Extended Continental Shelf: Middle Area (VNM-M) and (3) Vietnam - Malaysia Joint Continental Shelf Submission. The VNM-M has not yet been submitted but it was mentioned to the CLCS and will be submitted in the appropriate time.Vietnam’s submissions were highly appreciated by CLCS; although the CLCS has not yet organized a special sub-committee to look at our reports, the secretariat of CLCS has already posted the executive reports of our submissions, with our principle claims on the continental shelf, on the website of the CLCS since May 2009. This paper presents shortly the UNCLOS and its application in Vietnam case

Surface sediment grain-size distribution and sediment transport in the subaqueous Mekong Delta, Vietnam

The sediment transport around the Mekong delta was clarified by using geochemical data and modeling indicating the southwestward transport of re-suspended sediments under the influence of NE monsoon. However, the detail pattern of grain-size distribution of the surface sediments in the subaqueous Mekong River delta has not been well understood. This paper presents characteristics of grain-size parameters of the surface sediments in order to interpret the sediment-transport pattern and the linkage to coastal erosion and deposition off the Mekong River delta. Surface sediments collected in the coastal water of Mekong River delta (as far south as Ca Mau Peninsula) were analyzed to determine the grain-size distribution and sediment transports in subaqueous Mekong delta.  Results indicated that the net sediment transport was southwestward to the Ca Mau peninsula and the sediments were finer from the delta topset downward the delta foreset. In contrast, the sediment particles on the adjacent inner shelf were coarser and are more poorly sorted due to the increase in carbonate shell fragments and the Early Holocene sediments. The sediment grain-size parameters were variable in different sedimentary sub-environments of the subaqueous Mekong delta and controlled by the distance of sediment transport, the hydrodynamic regime of each region and coastal erosion of the delta coast.References Anthony J.E., Brunier G., BessetM., Goichot M., Dusouillez P, Nguyen V.L., 2015. Linking repid erosion of the Mekong River delta to human activities. Scientific Reports, 1-12. Blott S.J and Pye K., 2001. Gradistat: a grain size distrubution and statistics package for the analysis of unconsolidated sediments, Technical Communication. Earth Surface Processes and Landforms, 26, 1237-1248. Dung B.V., Schimanski A., Stattegger K., Phach P.V., Tiep N.T., Hai N.T., Thanh N.T., Phi T.T., 2009. Sandwaves on the Southeast Vietnam Shelf recorded by high resolution seismic profiles: formation and mechanism. Front. Earth Sci. China, 3(1), 9-20. Dung B.V., Stattegger K., Unverricht, D., Phach P.V.,Thanh N.T.,2013. Late Pleistocene-Holocene seismic stratigraphy of the Southeast Vietnam Shelf. Global and Planetary Change 110, 156-169. Hein H., Hein B., Pohlmann T., 2013. Recent dynamics in the region of Mekong water influence. Global and Planetary Change, 110, 183-194. Folk R.L and Ward W.C., 1957. Brazos River bar: a study in the significance of grain size parameters. Journal of Sedimentary Petrology, 27, 3-26.Liu S., Lu P., Liu D., Jin P and Wang W., 2009. Pinpointing source and measuring the lengths of the principal rivers of the world.International Journal of Digital Earth, 2, 80-87. doi:10.1080/17538940902746082.Mothersill J., 1969. A grain size analysis of longshore bars and troughs, Lake Superior, Ontario. Journal of Sedimentary Petrology, 39, 1317-1324.Milliman J.D., and Meade R.H., 1983. World-wide delivery of river sediments to the ocean. Journal of Geology, 91, 1-21. Milliman J.D., Syvistski J.P.M., 1982. Geomorphic/tectonic control of sediment discharge to the oceans: the importance of small mountain rivers. Journal of Geology, 100, 525-544. Pettijohn F.G., Ridge J.D., 1932. A textural variation series of beach sands from Cedar Point, Ohio, Journal of Sedimentary Petrology, 2, 76-88. Ninh P.V (Ed.)., 2003. South China Sea Monograph, Vol II-Meteorology, Marine Hydrology and Hydrodynamics, Hanoi National University Publisher., 565p., Hanoi (in Vietnamese). Nowacki D.J., Ogston A.S., Nittrouer C.A., Fricke A.T, and Tri V.P.D., 2015. Sediment dynamics in the lower Mekong River: Transition from tidal river to estuary. J.Geophys,Res, Oceans, 120, 6363-6383, doi:10.1002/2015JC010754. Kubicki, A., 2008. Large and very large subaqueous delta dunes on the continental shelf off southern Vietnam, South China Sea. Geo-Mar. Lett, 28, 229-238. Doi:10.1007/s00367-008-0103-9. Sibson R., 1981. A brief description of natural neighbor interpolation, in V. Barnett, ed., Interpreting Multivariate Data: John Wiley Sons, 21-36. Stattegger K., Tjallingii R., Saito Y., Michelli M., Thanh N.T., Wetzel A., 2013. Mid to late Holocene sea-level reconstruction of Southeast Vietnam using beachrock and beach-ridge deposits. Global and Planetary Change, 110, 214-222. Szczuciński W., Jagodziński R., Hanebuth T.J.J., Stattegger K., Wetzel A., Mitręga M., Unverricht D., Phach P.V., 2013. Modern sedimentation and sediment dispersal pattern on the continental shelf off the Mekong River delta, South China Sea. Global and Planetary Change, 110, 195-213. Ta T.K.O., Nguyen V.L., Kobayashi I., Tateishi M and Saito Y., 2001. Late Pleistocene-Holocene stratigraphy and delta progradation, the Mekong River delta, South Vietnam. Gondwana Research, 4(4), 779. Ta T.K.O., Nguyen V.L., Tateishi M., Kobayashi I., Saito Y., Nakamura T., 2002a. Sediment facies and Late Holocene progradation of the Mekong River Delta in Bentre Province, southern Vietnam: an example of evolution from a tide-dominated to a tide- and wave-dominated delta. Sedimentary Geology, 152, 313-325. Doi 10.1007/s11707-009-0002-z. Ta T.K.O, Nguyen V.L., Tateishi M., Kobayashi I., Tanabe S., Saito Y., 2002b. Holocene delta evolution and sediment discharge of the Mekong River, southern Vietnam: Quaternary Science Reviews, 21, 1807-1819. Tamura T., Saito Y., Sieng S., Ben B., Kong M., Choup S., Tsukawaki S., 2007. Depositional facies and radiocarbon ages of a drill core from the Mekong River lowland near Phnom Penh, Cambodia: evidence for tidal sedimentation at the time of Holocene maximum flooding. J. Asian Earth Sci., 29, 585-592. 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Earth Surf. Process. Landforms, 36, 296-308. Xue Z., He R., Liu J.P., Warner J.C., 2012. Modeling transport and deposition of the Mekong River sediment. Continental Shelf Research, 37, 66-78. Xue Z., Liu J.P., DeMaster D., Leithold E L., Wan S., Ge Q., Nguyen V.L., Ta T.K.O., 2014. Sedimentary processes on the Mekong subaqueous delta: Clay mineral and geochemical analysis. Journal of Asian Earth Sciences,79, 520-528. Unverricht D., Szczuciński W., Statteger K., Jagodziński R., Le X.T., Kwong L.L.W., 2013. Modern sedimentation and morphology of the subaqueous Mekong Delta, Southern Vietnam. Global and Planetary Change, 110, 223-235. Wolanski E., Nguyen N.H., Spagnol S., 1998. Sediment dynamics during low flow conditions in the Mekong River Estuary, Vietnam. Journal of Coastal Research, 14, 472-482. Wolanski E., Ngoc Huan N., Trong Dao L., Huu Nhan N., Ngoc Thuy N., 1996. Fine sediment dynamics in the Mekong River Estuary, Vietnam. Estuar. Coast. Shelf Sci, 43, 565-582

Establishing calculation method for chemical composition of primitive magma in the Cenozoic in South Central coast region and the adjacent continental shelf of Vietnam

The calculations which determine the chemical composition of the primitive magma are simple but they show changes in the temperature and pressure states of the magma source. The method is based on the addition of the chemical composition of the Olivine to the major element composition of the eruptive rocks which follows the formula: Ci = Ci-1+ 0.1 * Ci-1Ol. In accordance with the characteristics of the study area, we have made new additions to the calculation method. The calculation results are highly accurate when tested and compared with the chemical composition of the eruptive rocks. The chemical composition of the primitive magma solution is used to calculate the temperature and pressure states in the magma source. The results show that there is a difference in temperature and pressure in the source at different tectonic positions in the study area. Accordingly, the South Central coast region and the adjacent continental shelf are divided into two main types of eruptions. The first type of volcanic eruptions occurs at locations where major faults intersect and they are located north of the study area. The second type of volcanic eruptions in the form of a single volcano is located to the south of the study area and the southeastern continental shelf, and occurs in intracontinental extension structure

Late Pleistocene-Holocene sequence stratigraphy of the subaqueous Red River delta and the adjacent shelf

The model of Late Pleistocene-Holocene sequence stratigraphy of the subaqueous Red River delta and the adjacent shelf is proposed by interpretation of high-resolution seismic documents and comparison with previous research results on Holocene sedimentary evolution on the delta plain. Four units (U1, U2, U3, and U4) and four sequence stratigraphic surfaces (SB1, TS, TRS and MFS) were determined. The formation of these units and surfaces is related to the global sea-level change in Late Pleistocene-Holocene. SB1, defined as the sequence boundary, was generated by subaerial processes during the Late Pleistocene regression and could be remolded partially or significantly by transgressive ravinement processes subsequently. The basal unit U1 (fluvial formations) within incised valleys is arranged into the lowstand systems tract (LST) formed in the early slow sea-level rise ~19-14.5 cal.kyr BP, the U2 unit is arranged into the early transgressive systems tract (E-TST) deposited mainly within incised-valleys under the tide-influenced river to estuarine conditions in the rapid sea-level rise ~14.5-9 cal.kyr BP, the U3 unit is arranged into the late transgressive systems tract (L-TST) deposited widely on the continental shelf in the fully marine condition during the late sea-level rise ~9-7 cal.kyr BP, and the U4 unit represents for the highstand systems tract (HST) with clinoform structure surrounding the modern delta coast, extending to the water depth of 25-30 m, developed by sediments from the Red River system in ~3-0 cal.kyr BP.ReferencesBadley M.E., 1985. Practical Seismic Interpretation. International Human Resources Development Corporation, Boston, 266p.Bergh  G.D. 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Tectonic evolution of the southern part of Central Viet Nam and the adjacent area

Interpretations of seismic, gravity and magnetic anomalies and structural data on the coastal zone of southern part of Central Viet Nam (SCVN) and the adjacent Tertiary basins suggest several phases in the tectonic evolution of the study region since the Late Cretaceous to Quaternary. In this paper, we try to clarify the tectonic evolution of SCVN and the adjacent continental margin. The Cretaceous – Paleocene tectonic phase commenced after cessation of the West Pacific plutonic magmatic activity that produced numerous diabases and aplite dykes of mainly sub-meridian orientation. It was characterized by N–S compression and E–W extension. The geomorphology and geology ofSE Asiawere considerably changed during the Neotectonic phases caused by collision between the Indian plate and the Eurasian continent. Two tectonic phases – Early and Late Neotectonic – are separated by a regional unconformity represented by a boundary surface between below strongly deformed strata (synrift) and above less deformed formations (post-rift). The Early Neotectonic phase was related to the left-lateral movement of the Red River Fault Zone (RRFZ) and includes two tectonic sub-phases: Eocene – Oligocene (NW–SE compression), and Oligocene – Miocene (E–W compression). Activity in the Oligocene-Miocene sub-phase gave birth to rift basins in the continental margin of the SCVN. The Late Neotectonic phase began since the RRFZ stopped left-lateral movement and the East Viet Nam (orSouth China) Sea stopped spreading. The Late Neotectonic phase is also divided into two tectonic sub-phases: Late Early Miocene (sub-meridian compression), and Late Miocene – Pliocene (NE–SW compression). The Late Miocene – Pliocene sub-phase is characterized by vertical movements that caused episodic uplifting of the onland terrains, and subsidence of the offshore Phu Khanh basin. Besides, Miocene – Pliocene-Quarternary basaltic eruptions were widespread all over the southern Indosinian terrain and the continental margin