VIETNAM ACADEMY of SCIENCE and TECHNOLOGY
Institute of geological sciences
X  W
Van Duc Tung
DEVELOPMENT CHARACTERISTICS OF THE
LAI CHAU-DIEN BIEN FAULT ZONE

Major: Geotectonic
Code: 62.44.55.05 ABSTRACT OF THESIS OF DOCTORATE IN geological Ha Noi - 2011
Research finished at Department of Tectonic - Institute of Geological
Sciences-VIETNAM ACADEMY of SCIENCE and TECHNOLOGY

Supervisors:

the North-West region of Vietnam.
In the modern period, the fault active zone is quite active where
many related geological disasters have occurred along the Lai Chau -
Dien Bien fault zone such as earthquake, landslide, mudflow which
cause great damage to people of Lai Chau and Dien Bien provinces.
This fault zone has been studied by many geologists, both domestic
and overseas researchers. However, there are still many issues need to be
further clarified such as the position of tectonic center, the formation and
development of the zone. Especially, the segmentary feature of the fault
zone and the role of the segments in the formation and development of
various types of geohazards should be interpreted to provide scientific
basis for proposal of hazard prevention and mitigation solutions.
Based on the above-mentioned issues, the doctoral student had
selected study topic “Development characteristics of the Lai Chau-
Dien Bien fault zone".
The study objective: clarification of the tectonic and geodynamic
features, historical development process of the Lai Chau - Dien Bien
tectonic fault zone and the relationship between the modern activity of
the zone with some typical geological hazards.
Study tasks
- Study of formation and development history of the Lai Chau -
Dien Bien fault zone through the combination study of geotectonics and
deformation characteristics in order to clarify the environment of
geodynamics of the fault zone in each stage of its development.
- Study of the characteristics of the Lai Chau - Dien Bien fault's
segments in the modern period on the basis of differences in
characteristics such as geomorphological, geological, geological
structural, dynamic zone, movement mechanism, magnitude and
movement rate and expressions of modern activities of the fault
segments.

different scales (1:500,000; 1: 200,000; 1: 50,000; 1: 25,000)
- Special reports, doctoral and master theses and articles related to
the study contents.
Field data, results and analysis which fully or partially made by
the student since 1999:
Results of processing of 300 geological and geomorphological
survey points and tectonic fracture measurement data in 18 sections
through the Lai Chau - Dien Bien fault and adjacent; collecting and
processing of more than 735 measurements of scratches and slipping
surfaces; results of detailed study of three key areas: Lai Chau , Na Pheo
and Dien Bien on the Lai Chau - Dien Bien fault; analysis of 80 samples
for orientation and micro structure study along with petrographic
analysis; five samples for relative age analysis by the method of pollen
spores in the Quaternary Division-Institute of Geological Sciences, 4
samples for analysis of absolute age by means of LA-ICPMS U-Pb in the
laboratory of the University of Tasmania, Australia; results of detailed
study with air photos for 10 areas along the Lai Chau - Dien Bien fault.
Study object and area
The study object is the Lai Chau - Dien Bien fault zone in Vietnam
territory within the coordinates:
21
0
08’ - 22
0
41’ Latitude
102
0
48’ - 103
0
20’ Longitude

fault with 33-28 million years old; the fourth phase is characterized by a
brittle deformation mechanism and is a right-lateral strike-slip fault zone
which began after deformation phase 3 and ended about 5.3 million years
ago; the last phase is also characterized by brittle deformation
mechanism and is a left-lateral strike-slip fault with start about 5.3
million years ago and still continues to the present.
Point of view 2. The Lai Chau - Dien Bien fault zone in the Modern
period quite clearly demonstrates segmentary nature and divided into
three segments with very different characteristics and activity levels: the
first segment is Ma Lu Thang - Chan Nua with normal left-lateral strike-
slip fault with a weak modern activity; the second segment is Chan Nua -
Huoi Leng also with normal left-lateral strike-slip fault with relatively
strong modern activity; the third segment is Huoi Leng - Thin Toc with
normal left-lateral strike-slip fault with strong modern activity.
The thesis has the following structure
Introduction
Chapter 1. Overview of the past studies and study methods
Chapter 2. Characteristics of tectonical structure of the Lai Chau -
Dien Bien fault zone
Chapter 3. S
egmentary characteristics of the Lai Chau - Dien Bien
fault zone in the modern period

Chapter 4. Geotectonic development history of the Lai Chau - Dien
Bien fault zone
Chapter 5. The relationship of modern activity of the Lai Chau -
Dien Bien fault zone with typical geohazards
Conclusions and recommendations
List of published works related to the thesis
References

Studies of composition are of Pham Tich Xuan, Nguyen Trong
Yem (1999); Koszowska E. (2005, 2007, 2009); Tran Tuan Anh (2005);
Tran Trong Hoa (2008).
Studies of modern activity and its relationship with geohazards are
of Nguyen Dinh Xuyen (2004); Nguyen Ngoc Thuy (2005); Cao Đinh
Trieu (2000- 2003); Tran Trong Hue (2002, 2003).
Conclusion: Overall so far there has been no integrated work on the
formation and development of the Lai Chau - Dien Bien fault zone
throughout its development history. The division, the deformation phases
and deformation ages, mode and mechanism of deformation according to
the criteria of plate tectonics, especially for the development stages
before the Cenozoic have not been in detail and fully studied.
1.2. Study methodology and methods
1.2.1. Methodology
As it had been known that folding deformation (plastic deformation)
and fault deformation (brittle deformation) are two main types of
deformation due to tectonic movement. In areas where the continental
crust was formed and consolidated, tectonic movement has intraplate
nature and occur mainly along major fault zones which act as the
boundary dividing the architectural blocks of different sizes. Research of
deformation characteristics-the marks of tectonic activity phases in the
fault zones allows to reconstruct the sequence and characteristics of
intraplate tectonic development of the study area.
1.2.2. Study methods
Combination of the following methods have been used: 1 -
Method
of analysis of geological structures; 2 - Method of three conjugate
fracture systems, fracture belt, method of geodynamic structure,
structural dynamic method; 3 - Method of analysis of the absolute age-
LA ICPMS U-Pb, method of spore-pollen; 4-Method of analysis of

3
) is Bac Son, Ban Diec,
Pa Sa formations.
2.2.6. Tectono-stratigraphic Assemblage 5: Active continental
edge, late Paleozoic-early Mesozoic (PZ
3
-MZ
1
), is Da river, Si Phay, Na
Vang, Cam Thuy, Yen Duyet, Vien Nam, Co Noi, Tan Lac, Dong Giao,
Muong Trai, Lai Chau, Nam Mu, Dien Bien formations.
2.2.7. Tectono-stratigraphic Assemblage 6: post-mountainous
Mesozoic (MZ) is Suoi Bang, Nam Po, Nam Ma, Yen Chau formations.
2.2.8. Tectono-stratigraphic Assemblage 7: intraplate intrusive,
early Cenozoic is Ye Yen Sun, Pu Sam Cap complex; intraplate rift, late
Cenozoic is effusive basalt and Mio-Pliocene sediments.
2.2.9. Loose modern formations
2.3. Characteristics of deformation phases
2.3.1. Criteria of recognition and classification of deformation
phases

- Deformation characteristics and deformation products
- Deformation state: ductile, ductile-brittle, brittle
- Superimposed and penetrated relationship, Pumperly law
- Tectonic stress field
- Effected tectono-stratigraphy assemblages
- Deformation age
2.3.2. Characteristics of deformation phases of the Lai Chau -
Dien Bien fault
2.3.2.1. First deformation phase (B.1)

initially those two samples were in a unified magmatic block of Dien
Bien complex, but later were moved by the Lai Chau - Dien Bien fault
by right strike-slip mechanism.
- The surface layers of T
3
n-r sb Suoi Bang formation which is
corresponding to 220-210 million years had been cut by foliation
surfaces of the zone shear show that the relative age of the fault zone
rocks is younger than Suoi Bang formation.
Therefore, the formation of the Lai Chau - Dien Bien fault zone
was completely in the intraplate Indochina block after a powerful strike
of Southeast Asia in the Permian-Triassic. This fault zone does not play
a role of boundary between Indochina and Sibumasu blocks.
2.3.2.2. The second deformation phase (B.2)
The second deformation phase also was a ductile deformation.
Product of this phase is also shear zone with sub-longitudinal direction
developed over the first deformation phase. Similarly, the second
deformation phase also formed the foliation surfaces in most rocks of the
Nam Po formation (J
1-2
np) to the older rocks distributed along the shear
zone. In some places it is also observed veins of bright color granite
applite which cut through foliation surfaces of the first deformation
phase (B.1) and was simultaneously deformed. This shear zone has right
strike-slip mechanism (Figure 2.1 and Table 2.1.)
Age of the deformation phase (B.2):
Samples were taken from bright color granite applite have mostly
felsite composition. Field relations: this is a vein of applite granite,
which was simultaneously deformed along foliation surfaces of the first
deformation phase in Lai Chau formation and which simultaneously

observed the interference of folds of the first and the third deformation
phases. The third deformation phase affected all tectono-strategraphic
assemblages in the region, but did not effect on tectono-strategraphic
assemblages of the late Cenozoic intraplate rift (Figure 2.1; Table 2.1).
Age of the third deformation phase (B.3):
Samples were taken from bright color granite have mostly felsite
composition. Field relations: this is a vein of granite before deformation,
which intruded into foliation surfaces (B.1) and (B.2) in Lai Chau
formation and crystallized, and then deformed into folds in the Lai Chau
- Dien Bien fault zone.
Results: Analysis by LA-ICPMS method for the two samples VN-
M2 and VN-M6 in Muong Muon and Huoi Leng areas gave the age of
crystallization (35.05 ± 0.46 million years) and (33.7 ± 0.79 million
years).
Interpretation: VN-M2 sample had 9 zircon grains and VN-M6 had
3 zircon grains numbering A192, A202 and A203 are located on
discordant straight line at lower crossing with concordant line gave value
(35.05 ± 0.46) million years and (33.7 ± 0.79) million years. The
intersection under sample VN-M6, VN-M2 is a vein of granite which
crystallized before the deformation, so the age of crystallization should
also give the maximum age of the Lai Chau - Dien Bien fault zone in the
third deformation phase. Along with deformation phase, the folds have
axial faces perpendicular on the Red river zone. The student proposes
that this tectonic phase took place in a short time since (33-28) million
years.
2.3.2.4. The fourth deformation phase (B.4)
This is a brittle deformation development phase superimposed on
the structures of older deformation phases. The products of this
deformation phase is characterized by a system of gentle slopping to
horizontal scratches developed on steep to vertical slipping surfaces with

surfaces, different shapes of structure, subsidence holes, Quaternary
trenches.
The left strike-slip mechanism J the normal left strike-slip
mechanism of the Lai Chau - Dien Bien fault zone in this phase is clearly
expressed via slip surfaces-cleavages, structure shape “pull apart” in
Chan Nua and is rather clear in the orientation samples taken from Mio-
Pliocene formation in River crossing where the above-mentioned fault
cut through. The normal part of the fault zone is relatively expressed
through slip surfaces containing cleavages and the formation of series of
subsidized holes and Quaternary trenches along the fault zone (Figure
2.1; Table 2.1).
The deformation phase age:
The age of the fifth deformation phase is determined to be 5.3
million years based on that it cut through tectonic structures of the
previous deformation phases (especially through Mio-Pliocene
formations), Chan Nua Quaternary tectonic structure, Quaternary
formation valleys along the fault, effusive basalt olivine around Dien
Bien basin.
CHAPTER 3. SEGMENTARY CHARACTERISTICS OF THE LAI
CHAU - DIEN BIEN FAULT ZONE IN THE MODERN PERIOD
The Lai Chau - Dien Bien fault zone has sub-longitudinal direction
which is gently changing to northerneast-southernwest in the south-west
region. This is north-west part of the Lai Chau - Luong Pha Bang - Phet
Cha Bun fault zone and has a length in Vietnam territory of about
150km.
To have scientific basis for dividing the fault into segments it needs
to determine the special features of the fault zone and their changes
along its development line.
3.1. General characteristics
3.1. 1. Geomorphological characteristics

rock with the absolute age of 4.4 to 5.8 million years distributed in the
valley of Dien Bien Phu and Co Chay mountain pass; Mio-Pliocene
sediment rocks in the area River crossing in the north of old Lai Chau
town. Besides, there are also the distribution of Quaternary formations in
the valley along the zone (Pa Tan, Chan Nua, Lai Chau, Na Pheo,
Muong Muon, Huoi Chan, Muong Pon, Dien Bien).
3.1.3. Structural characteristics
On the map of modern architecture, the Lai Chau - Dien Bien fault
zone includes the main fault zone developed along the central and
secondary faults developed on both the East and West wings which had
formed 7-8km wide zone. From Huoi Chan the fault divided into 2
branches: a main branch and a tributary. Along the main fault there are
some "pull apart" valleys (Chan Nua) and rift type (Pa Tan, Lai Chau,
Na Pheo, Muong Muon, Huoi Chan, Muong Pon, Dien Bien Phu)
developed.
The west strip is the tributary short faults between 10 - 20km long,
while the east strip is of 15 - 20km to 50 - 60km long. The combination
of faults in the Lai Chau - Dien Bien fault zone had created a relatively
clear "feather" architecture, especially the southern part of the zone.
3.1.4. Characteristics of dynamic zone
According to the study of geomorphology, geology and tectonic
physics, the dynamic Lai Chau - Dien Bien fault zone is narrowed in the
middle, expanded at both ends. The average width of 7 - 8 km, the
narrowest is 6km in the south of Lai Chau town, the widest is about
25km in the area of Dien Bien Phu (partly in Laos).
3.1.5. Characteristics of fault surface
At the outcrop in Nam Sao, Chieng Chan, old Lai Chau, old Muong
Lay, Cong Troi mountain pass, Hang Lia, Pu Ca and especially Pa Tan
villages it is clearly observed the slipping surface of the Lai Chau - Dien
Bien fault, which is represented by position of the system of the main

system of rivers and streams across the fault in areas in Lai Chau black
stone company such as Chan Nua, Lai Chau, Na Pheo, Nam Muc; by
structure of epicenter of earthquake on the 19th of February 2001 in Thin
Toc village; by tectonic stress field of the modern and last tectonic stages
by repeated GPS measurements of Lai Chau in three measurement
cycles.
- The normal dip-slip component is determined by the difference in
elevations and the preservation of the terraces and flood plains between
east and west wings in Nam Sao and Lai Chau area; normal dip-slip
movement of strata is marked at the river crossing, north of Cong Troi
mountainous pass; slipping surface of the fault contains normal
scratches; by the tectonic facets dipping into west in Chan Nua and
Muong Pon on different architectural shapes; by the formation of a series
of Quaternary depressions such as Pa Tan, Chan Nua, Lai Chau, Na
Pheo, Muong Muon, Huoi Chan, Muong Pon, Dien Bien; by the
meandering rivers in the subsiding zones in Pa Tan, Lai Chau; by the
streams in the east wing are much shorter and steeper than in the west
wing in Lai Chau due to large amplitude upward movement to 300-500m
in the east wing; by the Mio-Pliocene sediments in the river crossing and
basalt eruption at Dien Bien valley, Co Chay mountainous pass; by the
modern tectonic field.
3.1.7. Amplitude and velocity movement
The left-lateral strike-slip rate of the Lai Chau - Dien Bien fault
zone in Quaternary is determined by the meandering of Nam Na river in
Chan Nua and Da river in river crossing area in north of old Lai Chau
town (magnitude 1200 - 2000m) to be from 0.55 to 0.66 mm/year. In Na
Pheo area the maximum amplitude of about 3000m that is about 1.66
mm/year. In Nam Ty area, the rivers and streams have not only been
impacted by the left-lateral strike-slip mechanism, but also the whole
area had been impacted as reflected by a greater left-lateral strike-slip.

in from Cong Troi mountainous pass to Thin Toc village show that the
south part is more active than the north.
Modern rather active activity of the Lai Chau - Dien Bien fault is
also expressed quite clearly by geothermal anomalies in the survey
routes: Lai Chau; Na Pheo, Ban Linh, Nam Ty.
In recent years many mud flows occurred in the east wing, in the
area of old Lai Chau town to old Muong Lay. Mud flows have destroyed
many houses, land and human lives, which forced Muong Lay town to
be relocated to Na Pheo.
Many earthquakes having magnitude 5.0÷5.5 level on Richter scale,
mainly concentrated in three important epicenter positions: Chan Nua,
Huoi Leng, Thin Toc and Dien Bien Phu city with a higher frequency.
3.2. Segmentary characteristics of the Lai Chau - Dien Bien
fault zone
Based on the results of detailed studies of geological,
geomorphological features along the length of the Lai Chau - Dien Bien
fault zone and based on six criteria: 1 - horizontal deviation across the
fault; 2 - the shape slip direction change; 3 - characteristics of
development of branches; 4 - morphology of the fault (slipping surface,
slipping mechanism rate for the period N
2
- Q); 5 - level of expression of
earthquakes; 6 - characteristics of different endogenic and exogenous
processes, such as cracking, landslides, hot water - mineral water, gas
geochemical anomalies, etc., it allows the author divide the Lai Chau -
Dien Bien fault zone on the territory of Vietnam into three segments with
the different features and activity extent, including:
3.2.1. The first segment: Ma Lu Thang - Chan Nua
This segment begins from Ma Lu Thang border gate in Vietnam-
China border through Pa Tan and finishes at the Chan Nua "pull apart"

can evaluate the left-lateral strike-slip rate of this segment from 0.66 to
1.11mm/year (Table 3.2; 3.3).
3.2.3. The third segment: Huoi Leng-Thin Toc (Laos)
This segment has a length of about 70km starting from Huoi Leng
through Na Pheo, Muong Muon and to Huoi Chan and with sub-
longitudinal direction. From Huoi Chan the Lai Chau - Dien Bien fault
developed into branches, main branch turning to north east - south west
running through the Nam Ty, then to Thin Toc (Laos). Tributaries from
Huoi Chan through Muong Pon, Co Chay mountainous pass and the
Dien Bien valley with sub-longitudinal direction.
The width of the branch destruction zone is about 800 - 1000m as a
result of geological survey and the route magnetic field 7. In the field, in
Ban Nam Ty it is observed foliation zone and then crushed into small
pieces and silts which overlap developed over 1-2km width with steep
sloping to the west northwest, where the structures are navigated by the
fault direction from Huoi Chan to Nam Ty.
Huoi Chan - Dien Bien Phu secondary fault destruction zone has
width 200 - 350 detected by the VLF anomalies, with a length of about
40km. Tectonic fracture study results show that of the fault slip surface
slopes into west with a quite steep angle (70 - 80
o
) and had formed
Quaternary trench-form valleys with sub-longitudinal direction.
The regional structure of Na Pheo area is characterized by
combinations of trench-form rift type and normal left-lateral strike-slip
of continuous alternate type. Nam Muc bridge area has a similar picture,
but was transformed by system of small northeast - southwest faults. The
modern movement with some tendency of the streams flowing into the
Nam Muon with a total amplitude of up to 2500 - 3000 meters, the left-
lateral strike-slip rate has a value of 1.38 to 1.66 mm/year (Table 3.2,

been recorded along the Lai Chau - Dien Bien fault zone with the result
K-Ar isotopic age and U-Pb isotopes (91-113 million years).
4.2. Cenozoic and modern period
During the whole Cenozoic tectonic movement, the study area is
controlled directly by the interaction between the major plates: the
Pacific plate in the east, the India - Australian plate in the south and west
and Europe - Asia plate in the north. Because of the three mentioned
plates that made the study area experience with periods of tectonic
activity under the influence of the stress fields with the compression
direction changing in accordance with this relation.
- The first stage in the development of reverse tectonic stress field
of east-west compression force on the area to create the folds with nearly
horizontal axes developed along the Lai Chau - Dien Bien fault in the
range of 33 to 28 million years. This resource originated from the
simultaneous impact of the Pacific plate attracting from the east and the
collision of the Indian continent from the west.
- The second stage developed in normal tectonic stress field due to
the overwhelming northeast - southwest compression force on the region
corresponding to left-lateral strike-slip phase of the Red river fault zone,
making the Lai Chau - Dien Bien fault zone have right-lateral strike-slip
about 28 to 5.3 million years. This force source was due to the
simultaneous impact of the Pacific plate attracting from the northeast and
the collision of Indo-Australia plate in southwest.
- The third phase had normal tectonic stress field with the main
compression of north-south direction, due to the simultaneous impact of
the Indo - Australian plate with Europe - Asia continent through
attracting south Indonesia strip and partially direct effect of the collision
of Indian and European - Asian continents at the northwest of the area
which made the Lai Chau - Dien Bien fault zone experience the left-
lateral slip about 5.3 to 0 million years.

but mainly in area of old Muong Lay town then in Cong Troi area.
Landslides in Muong Lay town and Cong Troi areas often happen,
repeat from time to time, large landslide on the slope s of more than 25
0

in products of tectonic destruction. Almost every year landslides are
recorded with high density.
Along Huoi Lo stream many large landslides are observed in
tectonic destruction zone with hundreds of meters wide, short and steep
streams, high topographic differentiation, the east wing is currently
rising to create steep slopes which are favorable conditions for landslide
occurrence. Huoi Phan stream also has similar picture.
5.1.3. Mudflows
Mudflows happen along the length of national road 12, but mostly
in the old Muong Lay town.
From 1990 until now there were four earthquakes (1990, 1991,
1994 and 1996) which has caused enormous losses of life and property,
and the psychological fear among the population in the area. Mudflow on
the 27th of June 1990 devastated Lai Chau town, caused many people
deaths, hundreds of buildings and houses were washed away. Mudflow
on the 23rd July 1994 in Huoi Lo destroyed 18 houses, 11 people dead,
20 wounded. Mudflow in Muong Lay on the 17th of August 1996 has
broken most of the irrigation system and bridges in Muong Lay town,
caused many people dead and wounded.
5.2. Relationship between the Lai Chau - Dien Bien fault zone
activity and typical geohazards: earthquake, landslide, mudflow
5.2.1. Relationship between the Lai Chau - Dien Bien fault zone
activity and earthquake
The first segment has normal left-lateral strike-slip mechanism with
small slip amplitude and rate along with the absence of mineral and hot

were located within destruction zone width from 1000 - 2000m width,
where rocks have been destroyed into loose small pieces and particles,
limestone and metamorphic rocks were broken and distributed in
disorder. With the large normal component due to strong tectonic rise
and tectonic fault running closely to east slope it had created huge energy
level to create conditions favorable for landslide development. The most
powerful area is Muong Lay with very large intensity and frequency and
scale. Huoi Leng area was formed in the normal slip-compressive
mechanism had created reverse structure of "horse tail" made the terrain
in this area unusually high, so large and very large landslides often
occurred in the this area.
Segment 3 has direction changing from the sub-longitude to the
northeast - southwest. Landslides occur most powerfully in the Cong
Troi and Na Pheo area. Besides, landslides also occur scattered in some
places in the intersection of the Lai Chau - Dien Bien fault zone and
minor northeast - southwest faults. In Cong Troi area landslides usually
occur because of Huoi Leng node. This segment had large left-lateral
strike-slip and small normal slip so the terrain differences are not large,
destruction zone has width of 800 - 1000m, magnitude and rate are far
greater than the first two segments which can create large landslides, but
it is separated by small faults so the activity much decreases and weaker
than segment 2.
5.2.3. Relationship between the Lai Chau - Dien Bien fault zone
activity and mudflow
Mudflows occur scattered and not concentrated, and it is extremely
serious in old Muong Lay area. This area is located on the second
segment, where landslide phenomena occur frequently and continuously
and a source of great material for mudflows is available. Due to strong
tectonic destruction, topography is much differentiated, the east wing
much raised with large slope from 30 to 45