Sagaing Fault Zone Research Articles

Sediment‐hosted disseminated gold mineralization at the Gegalaw deposit in Central Myanmar

AbstractGegalaw is one of the gold deposits situated in the Sagaing Fault zone, which marks the boundary between the Central Myanmar Basin to the west and the Mogok metamorphic belt to the east. The gold mineralization is mainly confined along northeast striking faults between carbonaceous silty limestone of the Kywethe Chaung Formation and carbonaceous and calcareous shale of the Eocene Male Formation. Hydrothermally induced dissolution breccia associated with progressive silica replacement increase near the northeast trending faults. The hydrothermal alteration associated with the mineralization is silicification in addition to illite‐kaolinite argillic alteration, of which illite is dated by the K‐Ar method as 40.26 ± 0.91 Ma. Sulfide minerals contained in the ores are mainly pyrite and arsenopyrite, with minor to trace amounts of marcasite, chalcopyrite, and sphalerite, among which pyrite and arsenopyrite are the hosts of gold. Pyrite and arsenopyrite are divided into diagenetic and hydrothermal stages, based on their mineral textures. Diagenetic stage pyrites are framboidal (Py1A) and coalescent framboidal (Py1B). Those of the hydrothermal stage are zoned pyrite with porous cores (Py2) and compact rims (Py4). In addition, euhedral homogeneous pyrites with or without compact rim are present (Py3). Some pyrites show pseudomorphs of ilmenite (Py3i) and carbonate minerals, possibly ankerite (Py3c). Arsenopyrites are also divided into porous, sooty arsenopyrite (Apy1), and compact arsenopyrite (Apy2) that co‐exists with Py3 and Py4 pyrites. Electron probe microanalysis for sulfides indicates that Py1A and Py1B are deficient in Fe while Py2, Py3 and Py4 are deficient in S compared to stoichiometry of pyrite. Such deficiencies are compensated by metal ions such as Co2+ and Ni2+ for Py1A, As2+ for Py1B, and As1− for Py2, Py3, and Py4. Arsenic equilibrium temperature of Apy2‐Py3 pairs shows a mode range of 250–270°C. Detected gold concentrations (~650 ppm) in arsenian pyrite (Py2, Py3, and Py4) indicate that gold in pyrite are below the solubility, suggesting that gold is present as solid‐solution in pyrite. Sulfur isotopic values of the pyrites in the unaltered host rocks are −18.9‰ and −8.9‰, and those of the pyrites from the hydrothermal altered rocks range from −17.3‰ to −0.5‰. These similar negative δ34S ranges of the pyrites suggest that the source of sulfur is dominated in biogenic reduction origin. Nevertheless, the two relatively heavier sulfur isotopic values (−4.9‰ and −0.5‰) suggest a contribution of an external hydrothermal fluid source. The research results indicate that gold mineralization occurred by infiltration of auriferous reduced hydrothermal fluids into the carbonaceous silty limestone and carbonaceous and calcareous shale through northeast trending secondary faults of the dextrally moving Sagaing Fault system and the fluids reacted with framboidal pyrite as well as iron‐bearing minerals in the host rocks to precipitate gold‐bearing arsenian pyrite. The age of hydrothermal illite suggests a link to the right‐lateral strike‐slip movement of the Sagaing Fault that is related to the collision of the Indian and Asian plates.

Earthquake Activities along the Sagaing Fault Zone, Central Myanmar: Implications for Fault Segmentation

In this study, the three terms related to the seismic activities of the Sagaing Fault Zone (SFZ), central Myanmar, of the possible maximum magnitude, return period, and probability of exceedance (POE) of an earthquake of given magnitude were evaluated and mapped using an improved earthquake catalog (free of duplicate records, foreshocks, aftershocks and recording artifacts) and implementation of a statistical approach. As a result, the SFZ was separated into five segments with different seismicity levels. The highest hazard level was found for the segment between Myitkyina–Northern Mandalay, with a likely generation of an Mw 6.4–7.2 earthquake in the next 50 years. For the Naypyidaw–Bago segment, the hazard levels were in the comparatively medium range with a magnitude 6.0–7.0 Mw earthquake return period of 20–50 and 100–200 years, respectively. The Offshore Andaman Sea segment of the SFZ was defined to have the lower hazard, with only a 10% or lower POE of a 7.0 Mw earthquake within the next 50 years. Therefore, effective mitigation plans should be prepared for this area and in particular for the region nearby to the Myitkyina–Northern Mandalay segment as the highest earthquake-prone area.

Seismic Risk Analysis for Critical Infrastructure: The Case Study of a Medical Center and its Supporting Systems in Yangon, Myanmar

Myanmar has a great strike-slip active fault called the “Sagaing Fault Zone” besides the Sumatra-Andaman Subduction Zone. Major cities (Yangon, Naypyitaw, Bago and Mandalay) are at risk along this fault. Recently, in 2012, Thabeikkyin earthquake with Magnitude of 6.8 caused collapse of many residential housings and ground failures near Mandalay. Therefore more attention should be paid for Yangon which has no large earthquakes since 1930 and is the largest not only in population but also in socio-economic activity. One of the most important concerns after an earthquake is to survive under any disastrous conditions. The medical care is requested not only for emergent injured people after an earthquake, but also for various types of patient and aged people from several weeks to longer periods. So medical center must be always functional before and after earthquake. For this purpose, medical buildings should be structurally resilient and also be functional for medical services by sustainable supply of electric power, water and any other delivery service which can be carried out by urban lifeline systems. This research is to investigate the structural vulnerability of hospital buildings and facilities, to assess the performance of urban lifeline systems and to check the operational capability of medical services in which surgical capability and life safety management method should be discussed. The water supply system is adopted as a typical lifeline system in Yangon in this study. One sample medical center in Yangon is adopted to carry out this analysis. Finally, the performance of medical services after the earthquakes can be assessed in a probabilistic manner.

Precursory seismicity rate changes prior to the large and major earthquakes along the Sagaing fault zone, Central Myanmar

In this study, the seismicity rate changes that can represent an earthquake precursor were investigated along the Sagaing Fault Zone (SFZ), Central Myanmar, using the Z value technique. After statistical improvement of the existing seismicity data (the instrumental earthquake records) by removal of the foreshocks and aftershocks and man-made seismicity changes and standardization of the reported magnitude scales, 3574 earthquake events with a M w ≥ 4.2 reported during 1977–2015 were found to directly represent the seismotectonic activities of the SFZ. To find the characteristic parameters specifically suitable for the SFZ, seven known events of M w ≥ 6.0 earthquakes were recognized and used for retrospective tests. As a result, utilizing the conditions of 25 fixed earthquake events considered (N) and a 2-year time window (T w), a significantly high Z value was found to precede most of the M w ≥ 6.0 earthquakes. Therefore, to evaluate the prospective areas of upcoming earthquakes, these conditions (N = 25 and T w = 2) were applied with the most up-to-date seismicity data of 2010–2015. The results illustrate that the vicinity of Myitkyina and Naypyidaw (Z = 4.2–5.1) cities might be subject to strong or major earthquakes in the future.

Precursory seismic quiescence along the Sagaing fault zone, Central Myanmar–application of the region-time-length algorithm

In this study, the quiescence stage of seismicity prior to seven strong-to-major earthquakes posed along the Sagaing Fault Zone (SFZ), Central of Myanmar were evaluated using the Region-Time-Length (RTL) algorithm. After improving the completeness of the earthquake catalogue, the suitable characteristics of RTL parameters were tested retrospectively with seven strong-to-major earthquakes available in the catalogue. According to the iterative test, the parameters r0 = 150 km and t0 = 3 y were suitable for detecting the precursory seismic quiescence along the SFZ. Consequently, with the implementation of these parameters and the present-day seismicity data of 1960–2015, the quiescence maps obtained indicated that western Myitkyina and the area in the vicinity of the Naypyidaw segments of the SFZ are at risk from future earthquakes. Therefore, effective mitigation plans should be developed.

Chapter 12 Tectonic and metamorphic evolution of the Mogok Metamorphic and Jade Mines belts and ophiolitic terranes of Burma (Myanmar)

The Mogok Metamorphic Belt is a north–south-aligned belt of mainly high-grade metamorphic rocks and granites that extends the length of Burma (Myanmar) along the western margin of the Sibumasu block from the Andaman Sea to the East Himalayan (Namche Barwa) Syntaxis (Figs 12.1 & 12.2). The Mogok metamorphic rocks host some of the world's finest rubies and sapphires, the former mainly from high-grade phlogopite + corundum marbles and the latter from a heterogeneous suite of syenite and charnockites that intrude the metamorphic rocks (Chhibber 1934 a , b ; Iyer 1953; Searle & Haq 1964; Bender 1983; Mitchell et al. 2007; Searle et al. 2007; Themelis 2008). Gem spinels are also found in forsterite-bearing marbles. Gemstones have been mined in the Mogok region since at least the mid-1800s (O'Connor 1888; Gubelin 1965 a , b ; Keller 1982, 1983; Kane & Kammerling 1992). Together with the adjacent Mergui Slate Belt these rocks lie to the west of the Shan Scarp and the Paung Laung-Mawchi Zone, interpreted by Mitchell et al. (2012) as a possible suture zone. We refer to this entire zone of metamorphic rocks, plus the Slate Belt and pre-collisional granites east of the Sagaing Fault and west of the Paung Laung-Mawchi Zone, as the Mogok–Mandalay–Mergui (MMM) Belt; the metamorphic rocks are referred to solely as the Mogok Metamorphic Belt (MMB). Fig. 12.1. Geological terrane map of the Eastern Himalaya, SE Tibet, Burma (Myanmar), Yunnan and Thailand. Lines of cross-sections in Figures 12.2 and 12.5 are shown. NLB, North Lhasa Block; SLB, South Lhasa Block; ITS, Indus-Tsangpo Suture Zone; GHS, Greater Himalayan sequence; LHS, Lesser Himalayan sequence; SH, Shillong Plateau; IBR, Indo-Burman Ranges; CB, Central (Chindwin) Basin; SFZ, Sagaing Fault Zone; TPFZ, Three Pagodas Fault Zone; MPFZ, Mae Ping Fault Zone; ST, Shan-Thai …

Syn‐kinematic sedimentation at a releasing splay in the northern Minwun Ranges, Sagaing Fault zone, Myanmar: significance for fault timing and displacement

AbstractThe Sagaing Fault zone is the largest active fault in SE Asia, whose current displacement rate of around 1.8 cm year−1 is well‐established from GPS data. Yet determining the timing of initiation and total displacement on the fault zone has proven controversial. The timing problem can potentially be resolved through a newly identified syn‐kinematic sedimentary section directly related to displacement on the Sagaing Fault in the northern Minwun Ranges. The northern part of the western strand of the Sagaing Fault has a releasing splay geometry that sets up a syn‐kinematic oblique‐extensional basin in its hangingwall, here called the North Minwun Basin. A series of thick ridges probably composed of alluvial fan and fluvial sandstones dipping between 20 and 70° to the north, and younging northwards comprise the basin fill over a distance of 40 km. Total stratigraphic thickness (not vertical thickness) is estimated at 25 km. The basin in terms of depositional geometries, large displacements, and large stratigraphic thickness and appearance on satellite images has parallels with the extensional Hornelen basin, Norway and the strike‐slip Ridge Basin, California. Minimum likely displacement on the fault strand is 40 km, and may possibly be in excess of 100 km. The remote and inaccessible basin has yet to be properly dated, likely ages range between Eocene and Miocene. When dated the basin will provide an important constraint on the timing of deformation. The potential for this basin to constrain the timing and displacement along the northern part of the Sagaing Fault has not been previously recognised.

THE GEO-DISASTER MITIGATION MEASURES IN MYANMAR

Myanmar has frequent geological disasters including earthquakes, tsunamis, landslides, and subsidences in karst area. Myanmar indeed is an earthquake-prone area as it lies in one of the two main earthquake belts of the world, known as the Alpide Belt that extends from the Mediterranean through Turkey, Iran, Afghanistan the Himalayas and Myanmar to finally Indonesia. Therefore, Myanmar is vulnerable to hazards from moderate and large magnitude earthquakes, including tsunami hazards along its long coastal areas.
 
 The seismotectonics of the region indicate that earthquakes in Myanmar mostly originates along an active subduction zone (Andaman Megathrust Zone) in the West and along a large active transform fault zone (Sagaing Fault Zone) in the middle part of the country. Local historic records and legends also confirmed the fact that intermittent jerks along these major active faults have caused the majority of earthquakes in Myanmar. These seismotectonic processes are still going on. Along these fault zones stand many large urban cities where thick populations live in. Liquefaction is a very considerable factor according to the past events in the water saturated area near the fault zones.
 
 Geomorphologically, Myanmar has two mountainous provinces: namely, the Western Ranges and the Eastern Highland. These provinces have inherently unstable nature among the areas of the country. The steep slopes, unstable geologic conditions and heavy rains combine together to make the mountainous regions one of the most hazard-prone areas in Myanmar. Landslides frequently happens in these regions, disturbing the connection roads and infrastructures rather than rural houses. Moreover, there has been an increase in human settlement in hazard-prone areas as a result of rapid population growth, as well as improvement in accessibility by road and the onset of other infrastructure development. Consequently, natural and man-made disasters are on the increase and each event affects people more than before. Even in central low land between the two mountainous ranges, landslide features occur along the bank of Ayeyarwady River and its tributaries.
 
 There were also records of moderate tsunami generated by two large magnitude earthquakes, which originated in the Andaman-Nicobar Islands. Of course, the tsunami generated by the giant 2004 Sumatra Earthquake also caused moderate causalities in some parts of the Myanmar coast. Thus, it is evident that Myanmar is vulnerable to disaster from moderate and large tsunamis along its long coastal line.
 
 To mitigate loss of lives and damages of properties, the Natural Disaster Mitigation Committee of Myanmar has been formed since 2004. Moreover, Seismic Hazard Zonation Map of Myanmar has already been prepared with the collaboration of engineering geologists, geoscientists and engineers since 2006. During the year of 2006 to 2008, the Myanmar Geosciences Society (MGS) in collaboration with MEC has prepared the preliminary deterministic seismic zonation maps for four seismically hazardous cities.
 
 Although modern seismological instruments and technical improvement are very essential, earthquake resistant design code shall be enhanced by the cooperative works among the scientists and engineers from various organizations. Landslide potential map and tsunami inundation map are going to be established this year. Moreover, to increase the awareness of the geo-disaster, education and knowledge have been given to those who live in hazardous-prone areas by the collaboration of DMH, RRD, MES, MGS, ADPC and Universities in Yangon. Besides, landslide mitigation technology applied in Myanmar and construction of tsunami shelter in coastal areas are also discussed in this paper.
 
 Keywords: Earthquake, tsunamis, active fault, landslide, liquefaction

MAPPING ASPERITIES ALONG THE SAGAING FAULT ZONE, MYANMAR USING b-VALUE ANOMALIES

In this study, the b-values of frequency-magnitude earthquake distributions were mapped spatially along the sagaing fault zone (SFZ), central Myanmar. Three sub-datasets of the complete earthquake catalogue were tested in order to ensure the applied assumption. Using the present-day dataset (1980–2010), two areas of low b-values, which are prospective potential earthquake sources, were identified at the Naypyidaw-Mandalay and southwestern part of Myitkyina in the central and northern part of the SFZ, respectively. To assess the possible earthquake magnitudes, the b-values were mapped in the cross-section dimension along the SFZ. The obtained areas of low b-values, referred to as the fault asperity regions, conformed to those illustrated in the surface map. The asperity's sizes, examined from specific low b-values of ≤ 0.65 and ≤ 0.060 were quantitatively estimated and empirically converted to the potential earthquake magnitudes. This analysis revealed three prospective areas surrounding the Myitkyina regions capable of generating earthquakes in the future with a possible magnitude of 8.6 Richter. The contribution of effective mitigation plans are, therefore, urgently needed for Myanmar and the adjacent area.

SEISMIC HAZARD ANALYSIS FOR MYANMAR

In this study, the seismic hazards of Myanmar are analyzed based on both deterministic and probabilistic scenarios. The area of the Sumatra–Andaman Subduction Zone is newly defined and the lines of faults proposed previously are grouped into nine earthquake sources that might affect the Myanmar region. The earthquake parameters required for the seismic hazard analysis (SHA) were determined from seismicity data including paleoseismological information. Using previously determined suitable attenuation models, SHA maps were developed. For the deterministic SHA, the earthquake hazard in Myanmar varies between 0.1 g in the Eastern part up to 0.45 g along the Western part (Arakan Yoma Thrust Range). Moreover, probabilistic SHA revealed that for a 2% probability of exceedance in 50 and 100 years, the levels of ground shaking along the remote area of the Arakan Yoma Thrust Range are 0.35 and 0.45 g, respectively. Meanwhile, the main cities of Myanmar located nearby the Sagaing Fault Zone, such as Mandalay, Yangon, and Naypyidaw, may be subjected to peak horizontal ground acceleration levels of around 0.25 g.

State of Tectonic Stress in Northeast India and Adjoining South Asia Region: An Appraisal

An attempt is made to map the spatial variation of the tectonic stress pattern in northeast India and its adjoining south Asia region using stress tensor inversion of some 516 fault‐plane solutions. The Bhutan Himalaya and the Arunachal Himalaya are mapped with north–south to north‐northwest–south‐southeast compression. The eastern Himalaya syntaxis zone, on the other hand, shows a clockwise rotation; a north‐northeast compression is dominant. To the south, in the intraplate part of the region, the Shillong plateau, Assam valley, Bengal basin (Bangladesh), and Tripura fold belt exhibit north‐northwest to north‐northeast compression. Orthogonal horizontal extension is dominant in southern Tibet, Bhutan, and partly in the syntaxis zone, and the same is also observed in the Shillong plateau and Assam valley area of the intraplate region. The Indo–Burma ranges and the Sagaing fault in the Myanmar region show a northeast–southwest compression; an orthogonal horizontal northwest–southeast extension is also observed in the Sagaing fault zone. A depth variation of the tectonic stress is observed below the Indo–Burma ranges; it changes from north–south to northeast–southwest in the southern part, and from northeast–southwest to north‐northeast–south‐southwest in the northern part in the deeper seismogenic zone. The stress inversion results of clusters of events in individual zones, though mostly conformable with the average observations, indicate a variation in the Shillong plateau due to heterogeneity and tectonic complexity.

Probabilities of earthquake occurrences in Mainland Southeast Asia

The frequency–magnitude distributions of earthquakes are used in this study to estimate the earthquake hazard parameters for individual earthquake source zones within the Mainland Southeast Asia. For this purpose, 13 earthquake source zones are newly defined based on the most recent geological, tectonic, and seismicity data. A homogeneous and complete seismicity database covering the period from 1964 to 2010 is prepared for this region and then used for the estimation of the constants, a and b, of the frequency–magnitude distributions. These constants are then applied to evaluate the most probable largest magnitude, the mean return period, and the probability of earthquake of different magnitudes in different time spans. The results clearly show that zones A, B, and E have the high probability for the earthquake occurrence comparing with the other seismic zones. All seismic source zones have 100 % probability that the earthquake with magnitude ≤6.0 generates in the next 25 years. For the Sagaing Fault Zone (zones C), the next Mw 7.2–7.5 earthquake may generate in this zone within the next two decades and should be aware of the prospective Mw 8.0 earthquake. Meanwhile, in Sumatra-Andaman Interplate (zone A), an earthquake with a magnitude of Mw 9.0 can possibly occur in every 50 years. Since an earthquake of magnitude Mw 9.0 was recorded in this region in 2004, there is a possibility of another Mw 9.0 earthquake within the next 50 years.

Exhumation of the Diancang Shan metamorphic complex along the Ailao Shan-Red River belt, southwestern Yunnan, China: Evidence from 40Ar/ 39Ar thermochronology

Exhumation of the high-grade metamorphic rocks from deep to shallow crustal levels in the Diancang Shan (DCS) massif is evident by the temporal transition from shearing and mylonitization at the amphibolite facies in the lower to middle crust, through retrograde ductile–brittle faulting at greenschist facies in the middle crust and brittle faulting near the surface. New 40Ar/ 39Ar ages of amphibole, muscovite, biotite and K-feldspar, mostly from mylonitic rocks, help constrain the thermal evolution of the massif during its exhumation. The thermochronologic studies have shown at least three stages of exhumation and cooling from late Oligocene to Pliocene, e.g., 28–13 Ma, 13–4 Ma and 4–0 Ma, respectively. The initiation of the unroofing history of the DCS massif resulted from ductile left-lateral shearing along the Ailao Shan-Red River shear zone (ASRR) since the late Oligocene. Diachronous onset and subsequent parallel cooling and exhumation characterize the early thermal history of the massif. The first stage of exhumation might have stopped due to the cessation of the left-lateral shearing at ca. 21 Ma, although cooling continued until 13 Ma ago to relatively low-temperature conditions. The second and third stages of cooling started from 13 Ma and lasted until the recent active faulting. The diversity of cooling rates during the second stage from 13 to 4 Ma suggests differences in exhumation rates at various localities. Ductile to brittle shearing along the eastern flank retrograde normal shear zone is the best explanation for the exhumation during this stage. The inhomogeneous cooling and exhumation of the lower plate of the normal fault zone possibly resulted from the tilting of the lower plate or differential exhumation of slabs in the lower plate. During the third stage, cooling and exhumation of the DCS massif since 4 Ma ago is recognized when higher temperature cooling paths are extended and plotted at a lower temperature of about 16 °C, the present day average surface temperature. Therefore, the diachronous cooling and exhumation continuously spanned to the surface. The tectonic exhumation of the DCS massif constitutes a part of the tectono-thermal evolution and diachronous exhumation of the metamorphic complexes in the fan-shaped area bounded broadly in SE Asia by the Red River fault zone and Sagaing fault zone since 36 Ma. Extrusion-induced strike-slip shearing and rotation-associated normal faulting, played important roles in the diachronous cooling and exhumation of the DCS massif and other metamorphic complexes in SE Asia.

EARTHQUAKE AND TSUNAMI HAZARD IN MYANMAR

Myanmar, lying in a major seismic belt, is indeed earthquake-prone and is vulnerable to hazards from moderate and large magnitude earthquakes, including tsunami hazards along its long coastal areas. The seismotectonics of the region indicates that earthquakes in Myanmar mostly have originated along an active subduction zone (Andaman Megathrust Zone) in the west and along a large transform fault zone (Sagaing Fault Zone) in the middle part of the country. In the past, at least two large magnitude earthquakes along that subduction zones were tsunamigenic. Of course, the tsunami generated by the giant 2004 Sumatra Earthquake also caused moderate damage in some parts of the Myanmar Coast. Thus, it is evident that Myanmar is vulnerable to hazards from moderate and large magnitude earthquakes, including tsunami hazards along its long coastline.The active fault studies (from paleoseismological survey through tectonic geodesy), upgrade and newly installation of seismic station networks, public awareness and curriculum development, building code development and technical training program are priority requirements in the country. Recently, researchers on tectonic geology recognize some active segments of the Sagaing, Kyaukkyan and Kabaw faults, as well as marine and fluvial terraces which seemed to be associated with subduction of India and Burma (Myanmar) plates along the Bengal tectonic boundary. Their study should be extended by providing some instrumentation schemes like global positioning system (GPS) network. Myanmar Earthquake Committee (MEC) has developed a seismic zone map of Myanmar in deterministic approach in 2006, for the sake of providing general information to the user for various purposes, and for public information. Technical development is needed for the completeness of the next generation of seismic zone map of Myanmar which is to be incorporated in Building Code, which in turn requires researches and findings on tectonics of Myanmar.

Rotation of Crustal Blocks as an Explanation of Oligo-Miocene Extension in Southeastern Tibet—Evidenced by the Diancangshan and Nearby Metamorphic Core Complexes

The Diancangshan (DCS) metamorphic core complex (mcc) along the Red River Fault Zone (RRFZ) is an incomplete mcc composed of two units with distinct characteristics, i. e. a lower plate of amphibolite grade tectonites intruded by synkinematic monzogranite, and a greenschist grade detachment fault zone. Lower plate rocks possess high temperature (high- T) structures and L or L>>S mylonites with left-lateral strike-slip shear sense. The detachment fault zone is a low temperature (low- T) shear zone with top to the E to SE extensional shearing and has typical S-L mylonites with both shearing and flattening strains. Low- T tectonites also include several mylonitized porphyritic monzogranite intrusions in the lower plate. The mcc is juxtaposed by non-metamorphosed Mesozoic sedimentary rocks to the west, and cut by Quaternary faults in the east, presenting a Pleistocene to Holocene sedimentary basin along Er Hai Lake. Through structural analysis of the DCS mcc, together with the geochronological and paleomagnetic analysis of mcc's in contiguous areas, we would argue that the occurrence of mcc's in a fan-shaped area between the Red River fault zone and Sagaing fault zone in SE Asia is related to regional extension during Oligo-Miocene period. The extension is attributed to the differential rotation in the Indochina block, caused by the clockwise rotation and rollback of the obliquely subducting Indian plate since about 33 Ma.

Relationships between Cenozoic strike-slip faulting and basin opening in northern Thailand

Abstract Northern Thailand is located in a structurally complex area between three major tectonic regimes, a region of extensional tectonics to the south and two major strike-slip zones, the Sagaing fault zone to the west and the Red River fault zone to the northeast. Cenozoic tectonics in northern Thailand resulted from the collision between the Indian plate and Eurasia. The continued indentation of the Indian plate into Eurasia caused polyphase extrusion of Sundaland and the movement of major strike-slip faults. The movement of these faults accompanying the regional east-west extension during Late Oligocene to Early Miocene initiated the formation of the Tertiary basins. Thirty-six major faults and forty-two intra-cratonic depositional basins in northern Thailand have been recognized and delineated using Landsat TM images. More than 70% of these basins are related to strike-slip tectonics. Five basin types have been recognized on the basis of geometric and kinematic considerations. These are fault-tip basins, pull-apart basins, fault-wedge basins, fault zone basins, and extensional basins. The opening and development of these basins was influenced by the movement of NW-trending dextral faults and NE-trending sinistral faults associated with north-south shortening and east-west extension.