ISSN 0866 - 7381

Jo u rn a l of

Series BNo 15-16

2000

DEPARTMENT OF GEOLOGY & MINERALS OF VIỆT NAMHÀ NỘI

Journal of GEOLOGY EDITORIAL OFFICESeries B, No 15-16/2000 6 Phạm Ngũ Lão. Hà Nội

(Năm thứ bốn mươi) Tel: 8 241 659. 8 352 319Fax 84. 4. 8 254 734

EDITORIAL BOARD

Editor- in - chief: TRAN VÃN TRỊ

Members: LÊ ĐỨC AN, LÊ VÃN TRẢO, NGUYEN GIAO, NGUYEN KHÁC VINH, NGUYỄN NGHIÊM MINH, NGUYEN TIÊN THÀNH, NGUYÊN TRỌNG YÊM. NGUYỄN XUÂN BAO, PHẠM VĂN AN, PHAN c ự TIÊN, PHAN TRƯỜNG THỊ.TẢNG MƯỜI, TỐNG DUY THANH, TRAN m i n h t h ế , v õ c ô n g n g h i ệ p .VŨ KHÚC (Deputy Editor-in-chief), v ũ NGỌC HẢI (Deputy Editor-in-chief).

Secretary: BÙI ĐỨC THẮNG

CONTENTSPage

1. Tống Duy Thanh, Vũ Khúc, Nguyễn Văn Vượng. The possible relationship between Phanerozoic volcano-sedimentary formations on thetwo sides of the Red River Zone and the activity history of this fault zone ... 1

2. Doãn Đình Lâm, W.E. Boyd. Holocene coastal stratigraphy and a model for the sedimentary development of the Hải Phòng area in the Red River Delta, North Việt Nam........................................... ...................... .......................... 18

3. Trần Đình Tô, M. Becker, Nguyễn Trọng Yêm, Dương Chí Công,Vy Quốc Hải. Result of GPS measurement of the Red River Fault Zone atBa Vì - Tam Đảo area................................................................................................... 29

4. Cao Đình Triều. Seismic activity in the Indochinese Peninsula and itsadjacent areas........................................................................................................... 3S

5. Nguyễn Kinh Quốc. Late Cretaceous Paleogene iron-high subalkalinebasalt - andesite association of Lạng Sơn area, Việt Nam.................................. 49

6. Trần Trọng Hoà, Trần Tuấn Anh, Ngô Thị Phượng, Phan Lưu Anh. Hoàng Hữu Thành. Origin of ultramafic rocks in the Red River Zone on the basisof new results of mineralogical, geochemical and isotopic analyses.................. 62

7. Nguyen Văn Bách, Nguyễn Tiến Hải, Phạm Việt Nga. Effect ofartificial lakes on the conveyance of Red River sediment load to the East Sea 76

8. T rần Tuấn Anh. Mineralogy of major minerals in lamproite ofNorthwest Việt Nam................................................................................................ 84

9. Võ Công Nghiệp. The spa tourism potentialities of Việt Nam...................... 98

10. Nguyễn Quang Miên, Lê Khánh Phồn. Some results of '*c dating in investigation on Quaternary geology and Geomorpholoav in Nam Định -Ninh Bình area, Việt Nam....................................................................................... 106

SCIENTIFIC COMMUNICATION

11. Trịnh Dánh. First record of Placodontia (Reptile) fossil in Việt Nam .... 110

•Journal of GEOLOGY. Series B. No. 15-16/20(K). p. 1 -18

THE POSSIBLE RELATIONSHIP BETWEEN PHANEROZOIC VOLCANO-SEDIMENTARY FORMATIONS OF THE TWO

SIDES OF THE RED RIVER ZONE AND THE ACTIVITY HISTORY OF THIS FAULT ZONE*

TỐNG DUY THANH', v ũ KHÚC2, NGUYEN VÃN VƯỢNG'

1 University o f Science (Vietnam National University, Hà Nội)2 Department o f Geology and Minerals o f Việt Nam

Abstract: Although there was horizontal displacement o f hundreds kilometers caused by the Red River Fault for adjacent areas, North Việt Nam and South China areas still pertained to a sedimentaiy basin through geological limes. Facial and faunal components show that in West and East Bắc Bộ - the two skies o f the Red River - almost all Paleozoic formations are similar with each other. The differentiation o f geological formations in these two areas began to appear only since Late Permian and during Triassic. However, there are not enough evidences for proving that the Red River Fault was formed at that rime, especially the Middle and Upper Triassic sediments were discovered recently on metanwi-phic rocks o f the Red River Fault Zone. The characters o f Tertian' sediments and their distribution in the Hà Nội Depression as well as along this fault zone and other faults o f the same NW-SE direction indicate that a "Red River boundaiy " could appear after Norian-Rhaetian and before Paleocene limes.

INTRODUCTION

In many works on regional geology, the Red River Fault Zone (RRFZ) usually regarded as a natural geological boundary of the region, because of that the two side areas of this boundary were thought as in different structure and geological development history during the whole geological history, at least since Phanerozoic. Although the important role of the RRFZ in the regional geological structure is undoubted-, but this role existed only after the coming into being of RRFZ itself. Therefore the homogeneity or differentiation of geological formations in

the two sides of RRFZ will supply with important materials for discussing on the appearance time and the activity of this fault system.

Despite the displacement amplitude caused by the RRFZ reaching hundreds kilometers, the results of facio- paleogeographical and paleontological researches have been showing clearly that during different geological periods the whole present Bắc Bộ and South China (Yunnan, Guangxi) regions have similar geological conditions of a same sedimentary basin. Only after the appearance of the RRFZ as a great geological boundary, the differentiation of

This paper was com pleted in the fram ework o f the Basic Research Project which is financially supported by the Ministry o f Sciences, Technology and Environment (Natural Sciences Council).

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the geological conditions in its two sides was formed, that is expressed by the facial composition of geological formations.

An evident example on the undifferentiation of the geological conditions in the two sides of the RRFZ is expressed by Devonian and Carboniferous- Permian sedimentary formations. During Early Devonian in the all East Bắc Bộ, West Bắc Bộ and Yunnan were formed similar sedimentary formations, which consist of terrigeno-carbonate sediments bearing the same faunal assemblage; they are followed by homogeneous Middle- Upper Devonian carbonate sequences distributed in the whole extensive Bắc Bộ and South China areas. Recently, fish fossils of littoral facies of Bắc Bộ - South China type were found in West Bắc Bộ, that has an important significance, because this fish assemblage belongs to an endemic fauna and adapts only to limited environmental conditions. At the meantime, the differentiation in Devonian in South China area is expressed in two different facial assemblages, namely Nandan deep-sea facies and Xiangzhou shallow-water facies. The first of them has been observed in West Yunnan, and its equivalent facies has been seen in the west of Sông Mã Structure (Upper Lao, West Điện Biên, West Nghệ An). As for the equivalent of the second Xiangzhou facies, it is clearly expressed in Devonian sediments in Guangxi and the major part of Bắc Bộ up to the northeast margin of the Sông Mã structure.

This paper is aiming to supply with materials for comparing geological formations in the two sides of RRFZ, basing on that the role of this fault zone in the geological history of the region, and the appearing time of RRFZ will be well founded.

TECTONIC FRAMEWORK OF THE RED RIVER FAULT ZONE

1. Role in Cenozoic tectonics of RRFZ

The RRFZ stretches on 1,200 km, from Northeast Syntax (Myanmar) through Yunnan (China) to Bắc Bộ (Việt Nam), and disappears in the offshore of Bắc Bộ Gulf. This fault zone can be divided into 3 sections from northwest to southeast, such as: section 1 corresponding to theXiaohou Fault, which stretches from Xiaguan northwestward, section 2 developed between Jianchuan and Midu, section 3 stretching from Midu Depression to Bắc Bộ Gulf. Along the RRFZ many Miocene basins of coarse­grained sediments are developed, such as South Jiangchuan, Midu, Lao Cai, and Phú Thọ basins. Materials from neotectonic and geomorphologic researches have been showing that the the RRFZ operates in accordance with the dextral strike-slip mechanics during Pliocene and Quaternary up to present days (GEODYSEA Programme). The dextral displacement rate has been determined by geomorphological studies in Yunnan as 5 mm/yr with a total displacement amplitude of about 50 km.

Before the dextral displacement, the RRFZ was subjected to strong deformation and metamorphism, magmatic intrusion and effusion during Cenozoic. These activities are resulted from the India-Eurasia collision process happening 50 Ma ago. The appearance of sinistral strike-slip began 15 Ma. after the collision. On the present structural plan, the RRFZ is a fault zone, which controls linear, deformed metamorphic mountain ranges of NW-SE direction, composed of 4 discontinuously exposed main mountain bands. These are the Xulunshan, Diencangshan, Ailaoshan and Núi Con Voi Ranges. Their width varies about 10 - 12 km. The studies on the characteristics of deformation and metamorphism carried out by Tapponnier p. since the ’80 have demonstrated that these ranges are the

result of sinistral strike-slip andmetamorphism during Cenozoic. The results of many studies on the deformation age and metamorphism by different methods have been supporting the published data of Tapponnier and hiscolleagues. The results of recentgeochemical isotope and geochronological studies have been showing that the magmatism and sinistral strike-slipsimultaneously happened from the end of Eocene to Oligocene (from 33 to 22 Ma.). By this violent displacement, the RRFZ has been regarded as a tectonic boundary, separating the Sundaland Plate with the South China Plate during the Cenozoic period of tectonic activity. During the process of displacement of Sundaland Plate along the RRFZ a series of Tertiary depositional basins took shape, such as Red River, Bắc Bộ Gulf, and especially Biển Đông (South China Sea) Basins. However the opening mechanism and the beginning time of spreading still exist as an object of many international discussions.

2. Displacement amplitude of the RRFZ during Cenozoic

The data, of different authors have been giving similar results on the beginning time point and the prolongation in time of the sinistral stike-slip. However, the discussible problem on the RRFZ is its role on the Cenozoic tectonics in SE Asia region, especially the opening mechanism of Biển Đông. This problem is related to the displacement amplitude along the RRFZ, and its end in the Bắc Bộ Gulf. The different approaches and different studied localities along this fault zone have been giving different results. According to published results, the displacement amplitude differs from one another, from 80 km to 1500 km. The process of exposure of Cenozoic metamorphic rocks in above-cited mountain ranges is not simultaneous, and the mechanism of this process has not

been touched upon in details and satisfactorily. After Harrison et al. (1996) the transitional strike-slip - . spreading stage began earlier in the southeastern end, 25 Ma. ago, and ended later in the north-northwest end, 17 Ma. ago. The paleomagnetic studies carried out in Late Mesozoic sediments and volcanogenic rocks on the Shan-Thai Plateau, in the Khorat Depression and red-bed basins of the same age in South China have been giving very different conclusions, even contradictory, on the“ displacement amplitude. It is worthy to note that, the paleomagnetic studies carried out in red- beds have been showing a large displacement during Cenozoic, but those carried out in effusive rocks did not confirm this large amplitude. In the other side, the studies on forming mechanism of Cenozoic depressions along the coast of Central and South Việt Nam have been showing that the amplitude of sinistral strike-slip along the RRFZ of the Sundaland Block lessened strongly since 26 Ma ago. The studies on the uplift of highly metamorphic rocks forming above said mountain ranges have been showing that this whole process is not simultaneous. These above-mentioned materials show that there exist many unclarified points in the forming mechanism and role of RRFZ in only the Cenozoic stage. The published data on the different displacement amplitude and uplift rate of RRFZ have been showing that the Sundaland Plate did not only simply displace along this fault zone.

3. Pre-Cenozoic deformation of the RRFZ

Did have many Pre-Cenozoic deformation phases in the RRFZ, so far there is no answer on this question.

The studies on the age of deformation and metamorphism carried out along metamorphic mountain ranges of the RRFZ have been suggesting only that the

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rocks subjected to Cenozoic deformation have an inherited composition from older rocks. However, the studies on tectonic phases carried out along other deformation-fault zones in Việt Nam have been showing that one of the strongest tectonic phases in the Indochina Block and the South China Plate is just the Indosinian deformation phase happened in Permiaii-Triassic. The main characteristic feature of this phase is expressed by the dextral strike-slip along the deformation zones lying parallel with the Red River Zone. The age of these deformation activities lies in the limit of 250-200 Ma. The studies on this deformation let see that all deformation zones in Indosinian reactivated in further stages, especially in Cenozoic. However, the deformation intensity along these zones is weak, and the deformation was not accompanied by metamorphism. This shows that, possibly, the deformation and metamorphism of high temperature happened in Cenozoic had effaced all traces of the former deformation phases. The preliminary data on isotopic dating analysis (of zircon by U/Pb method) realized by us in collaboration with the research group of B. Hasen and Kl. Wemmer from the Goettingen University have been giving an age of 2,386 Ma. (non published data yet) to amphibole gneiss from Hưng Khánh, about 20 km southwest of the Red River Zone. The results of study on the Sông Chảy Block by Maluski et al. (1999) and Leloup et al. (1999) let see that this block was subjected also to the impact of Indosinian and Jurassic-Cretaceous deformation phases. Thus, both the sides of RRFZ were subjected to the impact of Indosiniart and Jurassic-Cretaceous deformation phases. All these above- mentioned data allow coming to the judgement that the RRFZ, possibly, is a multiphase deformation zone as other deformation phases of the same direction in Việt Nam.

PHANEROZOIC SEDIMENTARY AND VOLCANOGENIC FORMATIONS IN THE TWO

SIDES OF RED RIVER FAULT ZONE

1. Cambrian-Ordovician-Silurian formations (Fig.l)

1.1. East Bắc Bộ. Middle Cambrian is composed of two Hà Giang and Mỏ Đồng Formations which correspond to the shallow-water - continental shelf facies. The Hà Giang Formation is distributed around the Sông Chảy Dome and in small strips in Bắc Hà and Mường Khương, consisting mainly of limestone, clayey limestone interbedded with clay shale in the upper part. These sediments bear fossils of algae, trilobites and brachiopods. The Mỏ Đồng Formation is exposed in the Mỏ Đồng Stream, Thần Sa and Bồ Cu (Thái Nguyên) areas, composed of chocolate clay shale and siltstone interbedded with violetish-red sandstone.

Upper Cambrian is composed also of two Chang Pung and Thần Sa Formations which correspond to the shallow-water - continental shelf facies. The Chang Pung Formation binds the edge of Sông Chảy Dome and is exposed along the China- Vietnamese border in Hà Giang and Lao Cai. It is composed of sandstone, siltstone, and clay shale yielding trilobites and brachiopods. The Thần Sa Formation includes sandstone, siltstone, clay shale bearing also trilobites and brachiopods, distributed in Thần Sa - Bồ Cu (Thái Nguyên) and Hạ Lang, Trùng Khánh and Đông Khê areas (Cao Bằng).

Ordovician sediments have been divided into two formations of shallow- water - continental shelf facies, namely Lutxia and Nà Mọ Formations, and one formation of deep-sea facies, namely Phú Ngữ one. The Lutxia Formation is exposed in Đồng Văn (Hà Giang) and North Bắc Cạn, composed mainly of limestone: with interbeds of siltstone in the

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NORTH WEST NORTH EAST

" X T T T 1 1 1 1 1 1 1 1 1 11 1 1 1 1

I I 1.. I" T 1 1 1 [.1 . J . .1. .1.. 1. t • 1 • a À A Jo a la Bala

Fig.l. Sketch o f Paleozoic facies in North 'Việt NamL E G E N D

- Z -Shallow water facies

Bauxite bearing facies

• 0 oo ^ 0 • o •

Deep water facies

Conglomerate

Shelf continental

facies

Continental facies

Deep waterJ j carbonate facies

a. Acid ic and alkaline effusive rocks

b. Mafic effusive rocks

The Upper Silurian Kiến An Formation of shallow-water facies is distributed in the neighborhood of the same name town, composed of limestone, marl interbedded with siltstone, sandstone yielding brachiopods of the Retziella weberi Assemblage and corals.

1.2. West Bắc Bộ. The Cam Đường Formation of Early Cambrian age is exposed in over 100 km long strips along the Fan Si Pan Zone, composed of basal conglomerate, sandstone, marlaceous shale with phosphorite seams. The Sông Mã Formation of the same age is exposed in the middle and lower course of the Mã River, composed of clayey-sericite shale interbedded with marbleized limestone, marble, thin interbeds of sandstone bearing inarticulate brachiopods and

trilobites in the upper part of the formation, which indicate the shallow- water - continental shelf conditions. It is possible to compare the Sông Mã Formation with the Hà Giang one of East Bắc Bộ. The Hàm Rồng Formation of Late Cambrian age is exposed in the middle and lower course of Mã River, consisting of limestone with fossils of trilobites and inarticulate brachiopods. It is the equivalent of Chang Pung Formation in East Bắc Bộ.

The Bến K hế Formation of Late Cambrian - Early Ordovician age is distributed nearly along the lower course of Đà River, including sandstone, clay shale, quartzite interbedded with some marl and limestone which sometimes have stripped structure. Based on the

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lithological composition and bedding character of the sediments the described formation, maybe, corresponds to the deep-sea facies.

The Đông San Formation of Early Ordovician age is distributed in the lower course of Mã River, lying conformably upon the Hàm Rồng Formation. It is composed of sandstone, siltstone and clay shale bearing trilobites, brachiopods, molluscs and conoids, which characterize the shallow-water - > continental shelf facies. The Sinh Vinh Formation of Late Ordovician - Silurian age is distributed in the lower course of Đà River, belonging also to the same facies. It includes limestone bearing Late Ordovician corals in its lower part, and Late Silurian corals in its upper part.

The Bó Hiêng Formation Late Silurian in age, appears to an equivalent of Kiến An Formation in East Bac Bộ, exposed in the lower course of Đà River, and composed of clay shale, marl', stripped limestone yielding the Retziella weberi Assemblage.

1.3. Remarks. Although there are some diferences in the Cam Đường, Bến Khế Formations in West Bắc Bộ (WBB) and Phú Ngữ, Nà Mọ Formations in East Bắc Bộ (EBB), but the equivalent character of Lower Paleozoic sediments in West and East Bắc Bộ is clearly seen. One can regard the equivalent formation couples, such as Sông Mã (WBB) - Hà Giang (EBB), Hàm Rồng (WBB) - Chang Pung (EBB), Đông Sơn (WBB) - Lutxia (EBB), and Bó Hieng (WBB) - Kiến An (EBB) as equivalent stratigraphic bodies, formed in the same depositional basin.

2. Devonian formations

2.1. East Bắc Bộ. The Sông Cẩu Group of Early Devonian age occurs in north Hà Giang, Cao Bằng, Lạng Sơn, Thái Nguyên, etc. areas, with two Si Ka (red continental facies) and Bắc Bun (littoral facies) Formations. They are composed of basal conglomerate bearing lenses of chocolate and greenish-gray siltstone, chocolate and bluish-gray clay shale, marlaceous shale (Si Ka Formation)', clay shale, silty sandstone, sandstone

interbedded with calcareous shale and limestone, locally arkosic sandstone (Bắc Bun Formation). Fish fossils and the Howittia wangi Assemblage from this group are endemic forms of the Yunnan - Bắc Bộ paleogeographic region.

The Mia Lé Formation Early Devonian in age consists of shallow-water facies exposed largely in East Bắc Bộ. It composes of clay shale, marlaceous shale, siltstone with limestone lenses bearing in abundance fossils of the Euryspirifer tonkinensis Assemblage well known in Bắc Bộ and South China. The Lược Khiêu Formation of the same age is distributed in the Hạ Lang Structure (Cao Bằng), consists of only terrigenous sediments yielding brachiopods of the Euryspirifer tonkinensis Assemblage. The Dưỡng Động Formation, distributed in the northeast coastal zone, consist of sandstone, siltstone, and clay shale interbedded with limestone lenses in its upper part. Fossils from its lower part correspond to those of the Mia Lé Formation, as for these of the upper part they indicate the Eifelian or early Givetian age sediments.

The Pia Phương Formation of Early Devonian age is exposed in the Lô-Gâm Structural Zone, with sericite-clay shale, marlaceous shale, calcareous phyllite interbedded with clayey limestone bearing carbonaceous matter, dolomitic limestone, calcareous siltstone, marbleized bituminous limestone, cherty clay limestone, cherty-calcareous manganese- bearing silty sandstone, interbeds of rhyolitic tuffs and albitophyre1.

The Bản Páp Formation2 Emsian- Givetian in age lying conformably upon the Mia Lé Formation, and upon the Dưỡng Động Formation in the northeast

1 The presence o f effusives in the Pia Phương Formation needs further studies; preliminary analyses o f isotopic age have been showing that they, possibly, belong to Triassic effusive phases as the major part o f effusives in Bắc Bộ ("The authors).

2 Formerly, in EBB the Bản Pcip Formation was described as Tràng Kênh, Lỗ Sơn, or Nà Quản Formations; the Bân Cải Formation as Tốc Tát Formation (The authors)..

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coastal zone is composed of limestone bearing corals, which prove its shallow- water - continental shelf forming conditions. The Bản Cải Formation of Late Devonian age is largely distributed in Cao Bằng and Hà Giang with cherty limestone, thin-stripped limestone interbedded with cherty shale. Cherty sediments and conodont fossils demonstrate the deep-sea forming conditions of this formation.

2.2. West Bắc Bộ. Devonian deposits in this area consists of from Lower to Upper Devonian, and fairly corresponds to the Devonian sequences in East Bắc Bộ, differing only by the absence of continental red-beds at the base of their sections.

The Sông Mua Formation of Early- Devonian age is composed of black clay shale interbedded with sandstone in its lower part, and limestone lenses and sandstone in its upper part. Brachiopod and bivalve fossils from the upper part correspond to the level of Bắc Bun Formation from East Bắc Bộ. The Bản Nguồn Formation, largely exposed in the middle and lower course of Đà River, consists of sandstone, siltstone interbedded with clay shale and limestone lenses in the lower part, bearing brachiopods of the Euryspirifer tonkinensis Assemblage. The sections of Nậm Pia Formation consist of basal conglomerate and gritstone, sandstone, black-gray clay shale, marlaceous shale, limestone lenses, distributed along the east part of Sông Mã Structural Zone. Brachiopod, coral and fish fossils described from this formation belong to the same association of Bắc Bun and Mia Lé Formations. The Bản Páp and Bản Cải Formations consist of Middle and Upper Devonian identical stratigraphic bodies in both East and West Bắc Bộ.

2.3. Remarks. Devonian formations in East (EBB) and West Bắc Bộ (WBB) are

generally similar with one another. The similarity between these two regions is shown clearly in the formations' bearing Howittia wangi (Bắc Bun in EBB, lower part of Nậm Pia Formation and upper part of Sông Mua Formation in WBB), bearing Euryspirifer tonkinensis (Bản Nguồn, Mia Lé and Lược Khiêu Formations), and then the Bản Páp and Bản Cải Formations are distributed in both regions. The similarity of sediment facies and fossils let see that in Devo.nian the whole Bắc Bộ region belonged to a same depositional basin, and there was not any difference between its east and west parts.

3. Lower Carboniferous - Middle Permian formations (Fig.l)

East Bắc Bộ. Lower Carboniferous - Middle Permian carbonate formations of continental shelf facies are largely distributed not only in EBB, but also in WBB and North Trung Bộ. Lũng Nậm Formation of Early Carboniferous age exposed mainly in Cao Bằng province, and Cát Bà Formation of the same age - in Hải Phòng City and Quảng Ninh province, both are composed of carbonate sediments bearing coral and foraminifer fossils, interbedded with cherty shale, cherty limestone bearing conodonts. Đá Mài Formation1 of Carboniferous - Early Permian age is largely distributed in EBB with light gray, thick-bedded to massive limestone, locally oolitic or interbedded with cherty limestone. Foraminifers play the main dating role for this formation; in addition, there are corals, brachiopods, etc.

West Bắc Bộ. In this region, Lower Carboniferous - Middle Permian sediments are largely exposed in Sơn La, Lai Châu, Hoà Bình and Thanh Hoá provinces with

1 This Formatiion in the former publications was described as the Bắc Sơn one, according to the “Stratigraphic Codex of Việt Nam (1994)”, it should be renamed as Đá Mài Formati on (The authors).

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similar to EBB limestone composition of the Đá Mài Formation, bearing the same fossil assemblage. There is only a difference in the composition of these sequences, which consists of the presence of effusives in the Bản Diệt Formation of Late Permian age. It is composed of clay shale, limestone, marl interbedded with sandstone, tuffaceous sandstone and mafic effusives in the middle part of the formation, which is distributed in small bands in Sơn La, Lai Châu and Hoà Bình provinces. Limestone and marl yield brachiopods, bivalves and foraminifers fossils.

4. Upper Permian - Upper Triassic (Carnian) formations (Fig. 2)

East Bắc Bộ. In EBB Permian Triassic sedimentary and volcanogenic formations have been grouped in three series: 1) Upper Permian, composed of Đồng Đăng and Bãi Cháy Formations of shallow- water carbonate facies; 2) Lower Triassic, composed of Lạng Sơn, Bắc Thuỷ, Sông Hiến and Hồng Ngài Formations of terrigenous facies in the An Châu Depression, and terrigeno-volcanic or carbonate shallow-water facies in the Sông Hiến Depression, and; 3) Middle- Upper Triassic (Carman), which begun by felsic volcanogenic formation, then terminated the depositional process, or graded upward to marine sediments, and terminated by a continental formation, composed of Khôn Làng, Bình Liêu, Lân Pảng, Yên Bình, Nà Khuất and Mẫu Sơn Formations.

Đồng Đăng Formation of Late Permian age, distributed in Lạng Sơn, Cao Bằng and Hà Giang provinces, includes foraminifer-bearing limestone interbedded with chert, cherty limestone and pisolitic bauxite, unconformable overlying the Đá Mài Formation, and underlying the Lạng Sơn Formation. Bãi Cháy Formation of the same age, forming narrow bands in the coastal zone of Quảng Ninh province,

is composed of sandstone, siltstone, coaly shale, thin-bedded cherty limestone, limestone lenses, bearing brachiopods and foraminifers.

Lạng Sơn Formation of Induan age, lying unconformably upon Upper Permian limestone in the vicinities of Lạng Sơn Town, Bản Thí, Đồng Mỏ, Chợ Bai and Hữu Lũng, includes medium-grained sandstone rhythmically interbedded with thin-banded siltstone and clay shale, bearing Claraia and ammonoids. Bắc Thuỷ Formation, lying conformably upon the Lạng Sơn one in the west of Lạng Sơn Town, is composed of marl, calcareous siltstone, siltstone interbedded with clay shale, sandstone bearing bivalves and ammonoids.

Sông Hiến Formation of Early Triassic age is distributed rather largely in Đồng Văn, Yên Minh (Hà Giang province), Cao Bằng, and Bình Gia (Lạng Sơn province) areas. It begins by from felsic (porphyritic rhyolite, felsite) to mafic effusives (spilite, diabase) grading upward to tuffaceous sandstone and siltstone, clay shale, siltstone, locally with some interbeds of limestone, bearing Claraia in its lower part and ammonoids in the upper one. Hồng Ngài Formation of the same age, distributed in Hồng Ngài, Phó Bảng, Táp Ná and Nhị Tảo areas, includes marl, black-gray limestone, oolitic limestone, bearing Claraia and foraminifers.

Lân Pang Formation of Anisian age, distributed rerestrictively in Lạng Sơn and Bắc Cạn provinces, is composed of gravelstone, gritstone, siltstone, clay shale and limestone bearing shallow-water bivalves. Khôn Làng Formation of the same age, distributed in Lạng Sơn province, begins by basal conglomerate, tuffs, porphyritic rhyolite, porphyritic rhyodacite grading upward to tuffaceous sandstone and siltstone, clay shale, of the An Châu Depression, has the same terrigeno-volcanic composition as the

NORTH WEST RED RIVER ZONE NORTH EAST

Fig.2. Sketch o f Mesozoic - Cenozoic facies in North Việt NamLEGEND

sShallow

water facies

. 1 1 / \ / r r r

i'i ' % / V r f r

/ S / r r r

v r T fContinental coal a. A c id ic and a lka line b M afic bearing facies effusive rocks e ffusive rocks

Khôn Làng Formation, but the sedimentary beds in the lower part of the formation is thicker. Nà Khuất Formation of Middle Triassic age, distributed largely in Lạng Sơn (east of Mẫu Sơn Range, Hữu Lũng), Bấc Giang and Thái Nguyên provinces, includes large lenses of clayey limestone at the base grading upward to calcareous siltstone, siltstone, clay shale, sandstone bearing ammonoids and shallow-water bivalves. In the Lô-Gâm zone, the Yên Bình Formation of Anisian age, distributed rerestrictively in Yên Bình area, comprises gravelstone, sandstone, claystone, siltstone, some interbeds of felsic effusives and tuffaceous sandstone, bearing rare ammonoids.

Mẫu Sơn Formation of Carnian age, distributed mainly in the Mẫu Sơn mountainous area, An Châu, Kép, Nhã Nam, Ba Chẽ and Yên Tử areas, is composed of red continental sediments, such as: quartzitic sandstone, siltstone, claystone, marl, calcareous sandstone, bearing fresh-water bivalves.

West Bắc Bộ. Permian-Triassic sedimentary and volcanogenic formations in WBB are distributed mainly in the Sông Đà Rift, and a bit in Fan Si Pan and Mường Tè Zones. In the Sông Đà Rift, Upper Permian consists of cẩm Thuỷ and Yên Duyệt Formations, while Lower Triassic includes Cò Nòi Formation and its equivalent - Viên Nam and Tân Lạc Formations. Middle-Upper Triassic

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comprises Đồng Giao, Nậm Thẳm, Mường Trai, Nậm Mu, Pác Ma and Sông Bôi Formations.

Cẩm Thuỷ Formation of Late Permian age, distributed mainly in Hoà Bình, Vạn Yên and Sơn La, is composed of basalt, porphyrite, porphyritic hyalobasalt, tuffs, tuffaceous silty sandstone, some tuffaceous breccia, locally limestone lenses bearing fusulinids. Yên Duyệt Formation of late Late Permian age, lying conformably upon cẩm Thuỷ one, includes clay shale, marlaceous shale, limestone, cherty limestone, cherty shale and thin seams of iron ore and anthracite, bearing brachiopods, ammonoids and plant remains.

Cò Nòi Formation of Early Triassic age, distributed in narrow bands in Lan Nhị Thăng and Tà Phin Plateaux, Sơn La, Mộc Châu, Hoà Bình, Vụ Bản, Rịa and Kiểu areas, is composed of basal conglomerate, chocolate sandstone, siltstone, locally thin interbeds of mafic effusives, arkosic sandstone, tuffaceous siltstone grading upward to bedded marl and clayey limestone, bearing Claraia, other bivalves and ammonoids. Corresponding to this formation, there are two Viên Nam and Tân Lạc Formations, distributed in Hoà Bình, Ninh Bình and Hà Tây. Viên Nam Formation of Induan age includes aphyric basalt, trachyte, porphyritic trachyte, interbedded with rhyotrachyte, porphyritic rhyolite, agglomerate tuff, felsitic tuff. Tân Lạc Formation of Olenekian age is composed of sandstone, tuffaceous sandstone, tuffite, chocolate siltstone and clay shale, grading upward to bedded marl and clayey limestone bearing bivalves and ammonoids.

Đổng Giao Formation of Anisian age, distributed in large bands in the Lan Nhi Thãng Plateau, Sơn La, Mộc Châu, Hoà Bình, Cúc Phương, Đồng Giao, Tam Điệp and Thanh Hoá areas, includes thin- to

medium-bedded limestone bearing brachiopods, bivalves and rare ammonoids. Nậm Thẳm Formation of Early Ladinian age, distributed in narrow bands in Sơn La, Nậm Thẳm, Mộc Châu, Vụ Bản and Bỉm Sơn areas, is composed of clay shale, marl, siltstone, interbeds of sandstone and limestone bearing deep-sea bivalves. Mường Trai Formation of Late Ladinian age, distributed in Thuận Châu, Nậm Mu, Phong Thổ, and along the Đà River from Quỳnh Nhai to Vạn Yên, is composed of tuffaceous sandstone, mafic effusives (?), marl, limestone, siltstone, sandstone, clay shale bearing shallow- water bivalves in its lower part, and deep- sea bivalves and ammonoids in its upper part. Lai Châu Formation of Ladinian- Carnian age, distributed in a narrow band along the Điện Biên - Lai Châu Fault, includes clay shale, siltstone, a little sandstone and coaly shale bearing deep- sea bivalves. Nậm Mu Formation of Carnian age, distributed in Nậm Mu, Phong Thổ and west Vạn Yên areas, is composed of clay shale, slate, siltstone and, in the upper part, thick interbeds of sandstone bearing deep-sea bivalves and ammonoids. Pác Ma Formation of Late Carnian age, rerestrictively distributed in Pác Ma and north Yên Châu areas, includes pink and gray reef limestone grading upward to marl, clay shale and calcareous siltstone bearing corals, algae, brachiopods and rare ammonoids. Sông Bôi Formation of Ladinian-Carnian age, equivalent to the three Mường Trai, Nậm Mu and Pác Ma Formations, distributed mainly in Hoà Bình and Ninh Bình areas, is composed of basal conglomerate, sandstone, clay shale, siltstone and a little coaly shale bearing deep-sea bivalves.

In the Fan Si Pan Zone, Nghĩa Lộ Formation of supposedly Lower-Middle Triassic age is composed of basal conglomerate, siltstone and black-gray clay shale grading upward to clayey limestone and microgranular limestone

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bearing foraminifers. Sông Bôi Formation includes basal conglomerate, gritstone, siltstone, clay shale and thin interbeds of coaly shale and sandstone bearing deep- sea bivalves.

In the RRFZ, recently Hoàng Thái Sơn et al. (2000) have been finding sediments bearing Triassic fossils in Thanh Ba - Phú Thọ area, including dark-gray fine­grained limestone with lenses of violetish- brown siltstone and clay shale, supposedly attributed to the Nghĩa Lộ Formation of the adjacent Fan Si Pan Zone.

Remarks. Permian-Triassic formations in EBB and WBB have basic similar features: 1) Lower Triassic belongs to formations more or less bearing effusives, although those in WBB are of stronger level and of more mafic character; 2) Characteristic fossils from these two regions are relatively similar; 3) Middle Triassic carbonate sediments overspread the RRFZ, found in Thanh Ba area (Phú Thọ province).

However, since this period the depositional conditions began to be differentiated: 1) the depositional and volcanic cycles in these two regions was different one from another. In EBB there are 3 cycles, namely: Late Permian, Early Triassic, and Anisian-Camian; while in WBB these cycles consist of: LatePermian, Early Triassic - Early Ladinian, and Late Ladinian - Carnian; 2) there exist differences in formational facies between these cycles: 2a) Upper Permian in EBB consists of carbonate sediments, while in WBB - mafic effusive and their tuffs; 2b) Anisian in EBB begins the third cycle and is composed of felsic effusives and their tuffs associated with terrigenous sediments, while in WBB it belongs to the middle part of the second cycle, and consists of a carbonate formation; 2c) Carnian in EBB is characterized by red continental beds, while in WBB it is

composed of deep-sea sediments bearing halobiid fossils.

5. Upper Triassic (Norian) - Jurassic- Cretaceous (Fig.2)

East Bắc Bộ'. Hòn Gai Formation of Norian-Rhaetian age, distributed in large bands at Quảng Ninh, consists of a coal- bearing formation with conglomerate, gravelstone, gritstone, quartz sandstone, siltstone, clay shale, coaly shale and thick seams of anthracite. Marine bivalve fossils have been found in Trới area (Hoành Bồ), while plant remains are largely distributed in many places of the Quảng Ninh coal basin, forming the well- known Hòn Gai Flora. Văn Lãng Formation of the same age and same coal- bearing character, largely distributed in the An Châu Depression with well-known geographic names, such as Phấn Mễ, Làng Cam coal mines (Thái Nguyên), Bố Hạ, Chũ, An Châu, etc., is composed of conglomerate, black-gray marl and calcareous siltstone, coaly shale and thick seams of fat coal, bearing marine bivalves in the lower part, and plant remains of the Hòn Gai type in the upper part.

Hà Cối Formation of Early-Middle Jurassic age, largely distributed in both the Quảng Ninh and An Châu Zones, consists of continental red beds with basal conglomerate, gravelstone, sandstone, chocolate siltstone and claystone, bearing rare plant remains. Tam Lung Formation of Late Jurassic - Early Cretaceous age, distributed restrictively in southeast of Đồng Đãng and south of Lạng Sơn Town, includes basal conglomerate, gritstone, sandstone grading upward to rhyolitic tuffs, porphyritic rhyolite, rhyodacite, rhyotrachyte and tuffaceousconglomerate. Bản Hang Formation of supposedly Cretaceous age, distributed restrictively in Đình Lập area (Lạng Sơn), is composed of continental red beds with basal conglomerate, gritstone, polymictic

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sandstone and siltstone bearing calcareous concretions.

West Bắc Bộ. Norian-Jurassic- Cretaceous sedimentary and volcano- sedimentary formations are largely distributed in the Sông Đà Rift, Tú Lệ superimposed Depression, Mường Tè Zone, and restrictively in the Fan Si Pan Zone.

Suối Bàng Formation of Norian- Rhaetian age, distributed in Quỳnh Nhai, Suối Bàng, Suối Hoa, Mường Vọ and Đầm Đùn areas, consists of a coal-bearing formation with basal conglomerate, sandstone, siltstone, interbeds of coquina grading upward to coaly shale, siltstone with thin seams of meager coal bearing marine bivalves and ammonoids in the lower part, Hòn Gai Flora and brackish- water bivalves in the upper.

Nậm Thếp Formation of Early Jurassic age, distributed in the Sông Đà Rift, consists of continental red beds with sandstone, chocolate siltstone and claystone lying conformably upon and closely related in space to the Suối Bàng Formation. Nậm Pô Formation of the same age and sedimentary facies, largely distributed in the Mường Tè Zone, is composed of chocolate siltstone and claystone, quartz sandstone.

Văn Chấn Formation of Late Jurassic - Early Cretaceous age, largely distributed in the Tú Lệ Depression, consists of a volcanogeno-sedimentary formation with basal conglomerate, siltstone, some sandstone grading upward to tuffaceous siltstone and sandstone, clayey limestone, and then, tuffaceous sandstone, rhyolitic tuffs, quartz orthophyre, felsitoid orthophyre. Ngòi Thia Formation of Late Cretaceous age (79 Ma. according to isotopic dating of porphyritic rhyolite) is composed of porphyritic rhyolite of subvolcanic facies, quartz porphyre of flowage structure in the margin of the

massif, but massive structure in the center.

Yên Châu Formation of Late Cretaceous age, distributed in large bands in Ba Nậm Cúm - Quỳnh Nhai, Mộc Châu- Pa Háng areas, and Yên Châu, Mai Châu Valleys, consists of Continental red beds with conglomerate, gritstone, sandstone, chocolate siltstone and claystone, and in the section top - calcareous conglomerate with very big pebbles and boulders.

In the RRFZ, recently Hoàng Thái Sơn et aỉ. (2000) have been describing from the Thanh Ba - Phú Thọ area a formation with sandstone, siltstone, clay shale bearing Hòn Gai Flora and oyster fossils (Ostreidae), corresponding to the coal- bearing Suối Bàng Formation in WBB and Văn Lãng Formation in EBB.

Remarks. Norian-Jurassic-Cretaceous formations in EBB and WBB have many similar features, such as: 1) Norian-Rhaetian are characterized by coal-bearing formations with marine sediments in the lower part and subcontinental coal-bearing beds in the upper; which have been found recently in the RRFZ; 2) Jurassic- Cretaceous are represented by two section types; the first one is composed of Lower or Lower-Middle Jurassic, and Late Cretaceous or undiscriminated Cretaceous continental red beds, and the second type includes Late Jurassic - Early Cretaceous volcanogenic formations; particularly in WBB there exists a Cretaceous volcanic and subvolcanic formation.

6. Tertiary volcanogeno-sedimentary formations (Fig.2)

In the two sides of the RRFZ, volcanogeno-sedimentary formations are restrictively distributed in narrow and, usually, elongated depressions, running along the faults of NW-SE direction.

East Bắc Bộ. Tertiary formations consists mainly of continental sediments, distributed along the Cao Bằng - Tiên Yên

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and Road No. 18 Faults, apart from these, along the Lô River Fault. Volcanite rocks occur rarely, and their Paleogene age is dated inferentially.

Tam Danh Formation supposedly of Paleogene age, distributed near Lạng Sơn Town as a thin cover upon Late Jurassic - Early Cretaceous felsic effusives, is composed of basalt, hyalobasalt, variolite, andesitobasalt interbedded with andesitodacite and sedimentary beds bearing tuffs and volcanic ash.

Cao Bằng Formation of Middle Miocene age, distributed near Cao Bằng Town, consists of coarse-grained sediments of detrital cone facies with conglomerate, gravelstone, gritstone with interbeds of sandstone of mixed composition; these rocks are of poor sorting and poor roundness. Nà Dương Formation of Late Miocene age, distributed in the Nà Dương Depression, consists of lacustrine sediments with basal conglomerate, sandstone, siltstone, clay shale, coaly shale and thick seams of brown coal bearing plant remains of aquatic type. Rinh Chùa Formation of Early Pliocene age, distributed in the same depression, and consisting also of the same lacustrine facies, includes only fine-grained sediments, such as siltstone, clay shale bearing big-sized siderite concretions and aquatic plant remains, fresh-water bivalves.

Đồng Ho and Tiêư Giao Formations of also Late Miocene - Early Pliocene age, distributed along the Road No. 18 in the coastal zone. The lower part of this Neogene section is composed of a thin bed of basal conglomerate which grades upward to fine-grained sediments - sandstone, siltstone, clay shale, interbedded with some thin brown coal and oil shale seams, bearing plant remains of subtropical humid forest type in the lower part, and of shrub type in the upper.

Along the Lô River, there are also formations characterizing the Late Miocene - Early Pliocene stage, namely: Phan Lương and Tuyên Quang Formations. Phan Lương Formation includes conglomerate, gravelstone, gritstone interbedded with sandstone, siltstone, some thin brown coal seams, bearing plant remains of riverine and marshy types. Tuyên Quang Formation is composed of small-grained sandstone, siltstone, and clay shale bearing moderate forest and marshy plant remains and lacustrine bivalves.

West Bắc Bộ. Tertiary sediments occur rarely in this region, consisting only of Pu Tra and Hang Mon Formations. Pit Tra Formation supposedly of Paleogene age, distributed restrictively in the Pu Tra - Cam Đường area, is composed of alkaline volcanogenic rocks with agglomerate tuffs, trachytic tuffs, tuffaceous sandstone. Hang Mon Formation of Late Miocene - Early Pliocene age, distributed restrictively in the Hang Mon area, includes lacustrine sediments with basal conglomerate which grades upward to fine-grained sediments bearing thin seams of brown coal with plant remains of humid forest, marshy types and lacustrine gastropods.

Red River Fault Zone. Tertiary sediments are largely distributed along this fault zone and in the Hà Nội Depression. Beneath the thick Quaternary and Neogene cover, deep boreholes have been finding Paleogene sediments, discriminated into Phù Tiên and Đình Cao Formations. Phù Tiên Formation of Eocene age is composed of conglomerate, gravelstone interbedded with fine-grained beds characterizing the fluvial facies. Oligocene Đình Cao Formation lies unconformably upon it, including fine-grained sediments interbedded with arkosic sandstone, greywacke and, more rarely, conglomerate, possibly, of fluvial facies.

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Neogene sediments in the Hà Nội Depression lie mainly under the Quaternary cover, and occur in some places of the depression margin with incomplete sections. They have been discriminated into 5 formations, namely: Phong Châu (of Early Miocene), Phù Cừ (of Middle Miocene), Tiên Hiừig (of Late Miocene), Vĩnh Bảo (of Pliocene), and Thái Thuỵ (of Pliocene-Pleistocene) Formations. These are continuous sequences of continental, locally coal- bearing sediments, that are interbedded with littoral or marine beds bearing foraminifers. Particularly, the Thái Thuỵ Formation is composed mainly of conglomerate, gravelstone, sandstone and some siltstone in the upper part, marking a new depositional cycle.

Along the RRFZ, Neogene section has been subdivided into Văn Yên and cổ Phúc Formations. Văn Yên Formation of Middle Miocene age, distributed in the two sides of the Red River, from Văn Yên, Văn Chấn, through Đoan Hùng, Ngòi Thia to Chí Chủ areas, is composed of boulderstone, conglomerate with some sandstone lenses of detrital cone facies. Cổ Phúc Formation of Late Miocene age, distributed from cổ Phúc area (near Yên Bái Town), through Thanh Ba, Chí Chủ, Phú Thọ to Hưng Hoá areas, comprises an intercalation of small- to medium-grained sandstone, siltstone, claystone with some lignite seams in the upper part, bearing Unio sp. and plant remains of humid tropical forest environment.

GENERAL REMARKS AND SUGGESTED PROBLEMS

1. Although the Red River Fault had displaced its surrounding area with an amplitude of hundreds kilometers, during Paleozoic, at least up to Middle Permian, the territories of Bắc Bộ (Việt Nam) and South China (Yunnan, Guangxi) belonged to an unique depositional basin. The sedimentary composition, sediment facies

and fossil assemblages of Cambrian, Ordovician, Silurian, Devonian and Carboniferous-Permian formationsdistributed in the two sides of this fault prove this remark (Fig. 1).

1.1. In Cambrian, Ordovician and Silurian, the mentioned homogeneity is expressed in the sedimentary composition and fossil assemblages of the Chang Pung, Lutxia, Kiến An Formations distributed in EBB, and corresponding Hàm Rồng, Đông Sơn, Bó Hiềng Formations in WBB.

1.2. In Devonian and Carboniferous- Permian, this character is expressed clearer: a) in Devonian the homogeneous couples of Nậm Pìa, Sông Mua, Bản Nguồn Formations in WBB, and Bắc Bun, Mia Lé, Lược Khiêu Formations in EBB indicate that they were formed in a same depositional basin. The Devonian assemblages of littoral fishes together with Howittia wangi and Euryspirifer tonkinensis brachiopod assemblages bear the endemic character of this basin do not occur in any locality of the world, even in adjacent areas, such as in the south of Mã River Fault; b) during Middle Devonian - Carboniferous-Permian, this basin expanded into adjacent areas, such as NE Thailand, Upper and Central Lao, North Trung Bộ (Việt Nam), within it a homogeneous carbonate formation was formed. So, there are not data to prove the existence o f the “Red River Boundary" which play the controlling role for geological conditions o f Bắc Bộ Region during Paleozoic.

2. The differentiation of depositional regime and other geological conditions appeared from Upper Permian formations, and continued to express oneself in Mesozoic formations. In WBB Upper Permian consists of mafic effusive formation (cẩm Thitỷ Formation) and coal-bearing subcontinental formation {Yên Duyệt Formation), whilst in EBB it is composed of bauxite-bearing marine

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carbonate formation (Đồng Đăng Formation) and carbonate beds interbedded with chert, siltstone, clay shale {Bãi Cháy Formation) (Fig. 2).

3. During Mesozoic, there were many differences between EBB and WBB, but the most notable among them are as follows: 2.1) Anisian in EBB consists of felsic effusive formations, whilst in WBB - carbonate formation; 2.2) Camian in EBB consists of continental red beds, whilst in WBB - halobiids-bearing deep-sea formation; 2.3) during Jurassic-Cretaceous, in WBB there is large tectono-magmatic activation basin (Tú Lệ Depression) where thick volcanogenic formations were formed, whilst in EBB largely distributed continental red beds mainly occur. So, since Triassic the geological settings in the studied region had clear changes in comparing with Paleozoic, but so far there are not enough data to regard that this differentiation results from the existence of the RRFZ. Furthermore, within the RRFZ there still is the presence of a Lower- Middle Triassic marine carbonate formation and a Norian-Rhaetian subcontinental formation. If the relationship between these Triassic formations consists of an unconformity, just to Triassic there was not a “Red River Boundary” in the geological structure of Bắc Bộ Region.

4. The “Red River Boundary” expressed itself clearly in Tertiary formations of Bắc Bộ Region. They occur in the present two sides of the RRFZ, but all of them are distributed along faults of the same NW-SE direction of the RRFZ. The presence of Paleogene sediments in the Hà Nội Depression lying unconformably upon the ancient basement allows to interpret that, the RRFZ occurred at least before this time point, and possibly, after Norian-Rhaetian. In the conditions of continental deposition, the homogeneity of both sedimentary composition and distribution of Neogene

formations in Bắc Bộ Region, including those within the RRFZ, in the same NW- SE direction of the RRFZ allows to confirm the clear role of the RRFZ on the territory of Bắc Bộ in Neogene; this accords with data on the strong deformation during Neogene, that has been touched upon by many geologists when studying on the RRFZ.

Acknowledgement

This paper was completed from the first studied results of the project 7.10.1 in the framework of the Fundamental Research Program in the field of Natural Sciences. The authors express their gratitude to the Ministry of Sciences, Technology and Environment of Việt Nam for the financial support.

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N i’cty nhận bài: 25-ỉ 1 -2000

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Journal of GEOLOGY

Copyright © b y Department o f Geology and M inerals o f Việt Nam, 6 Phạm Ngũ Lão Str.. Hà Nội, Việt Nam.All right resei-vecl. No part o f this publication may be produced or transmitted in any form without permission.Printed at the Printing Enterprise No.15, Nguyên Hồng Str. Láng Hạ, Đống Đa, Hà Nội. Permission o f the Publishing Department No. 5536/BC. Com pleted at December, 2000

Tạp chí ĐỊA CHẤT

CỤC ĐỊA CHẤT & KHO ÁNG SẢN

MỤC LỤCTrang

1. Tống Duy Thanh, Vũ Khúc, Nguyễn Văn Vượng. Mối quan hệ có thể có giữa các hệ tầng trầm tích - nguồn núi lửa ở hai phía của đới Sông Hồngvà lịch sử hoạt động của đới n à v ........................................................................... 1

2. Doãn Đình Lâm, W.E. Boyd. Địa tầng Holocen vùng ven biển và một mô hình phát triển trầm tích ở vùng Hải Phòng trong châu thổ Sông Hồng,Bắc Việt N am ........................................................................................................ 18

3. T rần Đình Tô, M. Becker, Nguyễn Trọng Yêm, Dương Chí Công, Vy Quốc Hải. Kết quả đo GPS đới đút gãy Sông Hồng tại vùng Ba Vì - TamĐ ảo .....................' ....... ............................7. ........................... .................................. 29

4. Cao Đình Triều. Hoạt động địa chấn trên bán đảo Đông Dương và cácvùng lân cận............................................................................................................ 38

5. Nguỳễn Kinh Quốc. Tổ hợp bazan á kiềm - anđesit cao sắt Creata muộn -Paleogen ở vùng Lạng Sơn, Việt Nam.................................................................. 49

6. Trần Trọng Hoà, Trần Tuấn Anh, Ngô Thị Phượng, Phan Lưu Anh, Hoàng Hữu Thành. Nguồn gốc của các thành tạo siêu mafic đới sông Hồng trên cơsở các phân tích về khoáng vật, địa hoá và đồng v ị.......................................... 62

7. Nguyễn Văn Bách, Nguyễn Tiến Hải, Phạm Việt Nga. Ảnh hưởng củacác hồ nhân tạo tới sự vận chuyển tải trọng trầm tích của Sông Hồng ra biển Đông.............................. ........................................................................................... 76

8. T rần Tuấn Anh. Khoáng vật học của các khoáng vật chính tronglamproit ở Tây Bắc Bộ, Việt Nam....................................................................... 84

9. Võ Công Nghiệp. Tiềm năng du lịch suối khoáng ở Việt Nam................. 98

10. Nguyễn Quang Miên, Lê Khánh Phồn. Một số kết quả '4C trong việckhảo sát địa chất Đệ tứ vùng Nam Định - Ninh Bình, Việt Nam................... 106

SCIENTIFIC COMMUNICATION11. Trịnh Dánh. Lần đầu tiên phát hiện hoá thạch Bò sát Placođontia ởViệt N am ......................:........................................................................................... 110