Đặc điểm phát triển kiến tạo đới đứt gãy lai châu điện biên bản tóm tắt tiếng anh

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: 1. Dr. Tran Van Thang Institute of Geological Sciences - Vietnam Academy of Science and Technology 2. Assoc. Prof. Dr. Tran Thanh Hai Hanoi University of Mining and Geology Examiner 1: Prof. Dr.Sc. Dang Van Bat Hanoi University of Mining and Geology Examiner 2: Assoc. Prof. Dr. Sc. Phan Van Quynh Hanoi University of Science - Vietnam National University Hanoi Examiner 3: Dr. Pham Van Hung Institute of Geological Sciences - Vietnam Academy of Science and Technology This thesis is going to be defended at the council of doctorate thesis examiners of Institute of Geological Sciences - Vietnam Academy of Science and Technology on………date………month………year 2011 This thesis can be found at Hanoi National Library or Library of Institute of Geological Sciences - VIETNAM ACADEMY of SCIENCE and TECHNOLOGY INTRODUCTION Study urgency The Lai Chau - Dien Bien fault is a large scale fault which plays an important role in structural formation and geotectonic development of 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. - Restoring of processes of the regional tectonic development related to the development stages of the Lai Chau - Dien Bien fault zone. - Study of the conditions of formation and development of some geological hazards associated with the modern activity of the Lai Chau - Dien Bien fault zone. Scientific and practical importance of the study - Clarification of the history of formation and development in stages and deformation phases, restoration of the tectonic and geodynamic regime for each stage. - Contribution to confirmation of the role of intraplate tectonics in in study of regional geological structure and geodynamics. - Provision of scientific basis for determining the causes and mechanism and for zonation of hazard risk: earthquake, landslides, mudflows, etc. - Provision of scientific basis for planning development and exploitation and sustainable utilization of territory and proposing solutions to prevent and mitigate natural disasters for socio-economic development and enhancing national security, etc. Thesis data and documents: the following are three main data sources: Study results and data of projects and studies in which the student has participated since 1999: - Report “Survey for Lai Chau hydropower plant: Investment preparation stage (2000), Feasibility and technical design (2004), Technical design (2008); “Supplementary geological survey for Dien Bien Phu town” (2002); Survey for Nam Na hydropower plant 2 (2009). - Independent governmental studies; KC 08.10; ĐTĐL.2009T/09; Studies of Vietnam academy of science and technology. Published archive documents: - Data and documents of geological and mineral mapping of 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 New discovered study points 1. The Lai Chau - Dien Bien fault zone was formed in the early- middle Jurassic (198-158 million years) in the first phase of deformation and intraplate nature. In the history of development since the formation of the fault zone until now it has gone through five phases of deformation. 2. For the first time it had been discovered the Mio-Pliocene sediments and their deformation in the Lai Chau - Dien Bien fault zone, which gave proof about sinistral slipping activity phase in the Pliocene- Quaternary period. 3. For the first time the tectono-petrography assemblage 7a, a light colored granite complex with 33-35 million years old intruded into foliation surfaces of 198 to 158 million years in Lai Chau formation, was discovered. 4. It had been established a young deformation phase of thrust type under the third deformation phase aged 33 to 28 million years developed along the Lai Chau - Dien Bien fault zone in the Cenozoic. 5. For the first time the segmentary characteristics of the Lai Chau - Dien Bien fault zone had been clarified with three development stages in Vietnam territory. Defensive points of view: Point of view 1. The Lai Chau - Dien Bien fault zone was formed in early-middle Jurassic and belongs to deformation phase 1 and went through five phases of deformation with different deformation mechanisms: the first phase is characterized by the plasticity which is a shear zone, right-lateral strike-slip with the age of deformation of about 198-158 million years; the second phase is also characterized by plastic deformation mechanism and also is a shear zone, right-lateral strike-slip occurred in about 135-80 million years ago; the third phase was plastic to brittle-plastic deformation mechanism and is characterized by reverse 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 Acknowledgement The thesis was completed at Division of Tectonics, Institute of Geological Sciences under the supervision of Dr. Tran Van Thang and Dr. Associate professor Tran Thanh Hai. The author would like to express his deep gratitude for the guidance of scientists inside and outside the Institute of Geological Sciences, of the family and friends, leadership board of Institute of Geological Sciences who dedicated study guidance through the whole study, research and thesis writing. CHAPTER 1. OVERVIEW OF THE PAST STUDIES AND STUDY METHODS 1.1. Overview of the past studies The Lai Chau - Dien Bien fault zone plays an important role in the northwest Vietnam geotectonic map. Furthermore, in recent years many disasters: earthquakes, landslides, mud-flows, etc. closely related to modern activities of the fault zone cause serious human life and property consequences to the people in the region. Therefore, the Lai Chau - Dien Bien fault zone had been interested in the early past years and especially in the present time has more promoted research including the following issues: Studies of development scale and history are of Dovjikov A.E (1960 - 1964); Tran Van Tri (1977, 2009); Van Duc Chuong (1979- 2002); Tran Thanh Hai (2002, 2004, 2006). Studies of active period are of Wemmer K. et al. (1999); Charusiri (2006); Te-Hsien Lin (2009). Studies of slipping and movement mechanism and rate of different development stages and the role of the Lai Chau - Dien Bien fault in the regional tectonics are of Nguyen Trong Yem et al. (1996); Tran Van Thang (2001- 2003); Zuchiewicz W. et al. (2004); Nguyen Van Hung (2001); Van Duc Tung (2006-2009). 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 geomorphological factors; 5 - Method of analysis of strutural partten; 6- Remote sensing analysis. In addition, the results of group of study methods such as group of gas geochemical methods; group of geophysical methods; repeated accurate geodetic measurements have been used. CHAPTER 2. CHARACTERISTICS OF TECTONICAL STRUCTURE OF THE LAI CHAU - DIEN BIEN FAULT ZONE 2.1. General characteristics The study area, which includes the Lai Chau - Dien Bien fault, is in the west of north-west Vietnam, and belongs to the north edge of Indochina geological block, and is separated with South China geological block by Ailaoshan suture zone in the north, and with Sibumasu geological block by Jinghong - Nan - Sra Kaeo in the west. 2.2. Tectono-stratigraphy Assemblage 2.2.1. Criteria of division of Tectono-stratigraphy Assemblage According to defened of Hutchison (1992 2.2.2.Tectono-stratigraphy Assemblage 1: Passive continental edge Neoproterozoi (NP) is Nam Co formation. 2.2.3. Tectono-stratigraphy Assemblage 2: Passive continental edge, late to early-middle Paleozoic (PZ 1-2 ), is Ben Khe, Bo Hieng, Nam Cuoi, Tay Trang, Nam Pia and Ban Pap formations. 2.2.4. Tectono-stratigraphy Assemblage 3: Active continental edge, middle Paleozoic (PZ 2 ) is Huoi Tong complex. 2.2.5. Tectono-stratigraphy Assemblage 4: Shallow marine- intermediate continental edge, late Paleozoic (PZ 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) The first deformation phase occurred in the plastic deformation state, which marked the appearance of the Lai Chau - Dien Bien fault zone. The products of this deformation phase is sub-longitudinal shear zone, along with foliation surfaces which are parasite-axis cleavages which coincide with the axis of accompanied small folds. The geodynamic signs were recorded such as boudinage structure, ductile lineation, the axes of sandstone of micro folds, the structure of mylonite and ultramylonite, mineral-orientation tremolite, right slipping porphyroblast, quartz-fish and S-C' structure which express right strike- slip mechanism (Figure 2.1 and Table 2.1). Along with the axial cleavages in this deformation phase are folds from open-shape to narrow with close-to-vertical shaft axis with sub- longitudinal direction. Axes of the folds are gentle and range from 5-15 0 with dipping both to the north and south. The first deformation phase developed in most formations, except the formations of intraplate Cenozoic tectono-stratigraphic assemblages. Deformation phase age (B.1): - This deformation phase marked the beginning of the Lai Chau - Dien Bien fault zone appearance. The 40 Ar/ 39 Ar method used for determining quartz-fish and mylonite (simultaneous deformation) which reflects right strike-slip mechanism inside the shear zone had identified the absolute age of this phase as 198-158 million years. U-Pb isotopic age of zircon in Dien Bien granite complex in the northeastern of Dien Bien city and Muong Tung is 230 million years old. It is probably that 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 [...]... which concentrated in the Lai Chau - Dien Bien fault zone in the sub-longitudinal direction The movement and slipping mechanism must also be observed under the petrographic orientation composition samples In the area of Nam Sao and Nam Cay villages, Ban Pap complex limestone overlies onto Lai Chau complex in the third overthrust deformation phase and then destroyed and cut by the Lai Chau - Dien Bien fault... surface of Lai Chau complex in deformation phase (B.3) which was cut by the Lai Chau - Dien Bien fault with leaving some tectonic remaining structures in the west wing The student proposes that the fourth deformation phase has age of about (28-5.3) million years 2.3.2.5 The fifth deformation phase (B.5) This is the youngest brittle deformation phase had been discovered, which left a clear sign in the Lai. .. 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... 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... 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... shown on the geophysical sections: gravity line in old Muong Lay, Nam Cay - Lai Chau, Lai Ha Muong Mun, Na Pheo-Si Pha Phin, Nam Ty-Deo Co Chay; geomagnetic field in Pa Tan, Chan Nua, Cong Troi, Na Pheo, Muong Muon, Huoi Chan, Ban Linh, Ban Thin Toc areas; the VLF field in Dien Bien city and adjacent areas The Dien Bien - Lai Chau fault zone is met in all the sections with slipping surface steeply... systematical shift of 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... 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... 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... characterized by brittle deformation 3 The Lai Chau - Dien Bien fault zone is a deep fault zone, with width of destruction zone reached 800 - 2000m and the impact zone of 5 - 10 km, with a length of about 150 km on the territory of Vietnam Slipping surface of the main Lai Chau - Dien Bien fault zone dips to west and west-northwest with steep slope angle 4 Modern active of the Lai Chau - Dien Bien fault zone has . 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. 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. development stages of the Lai Chau - Dien Bien fault zone. - Study of the conditions of formation and development of some geological hazards associated with the modern activity of the Lai Chau - Dien