Controls on structural styles along the deformation front of the Subandean zone of southern Bolivia     

《Journal of Structural Geology》2015

The Subandean zone of southern Bolivia is a typical thin-skinned fold and thrust belt with remarkable regularity in the geometry of the structures. However, when the structural geometry and evolution are analyzed in detail, it is verified that there are many deviations from such regularity. In this paper, special emphasis has been placed on analyzing those processes that could explain the along strike variations in structural styles of the deformation front.Particularly, the role that played the upper detachment level in the development of the different structural styles observed along the deformation front is analyzed herein. This analysis is focused on the development of overpressures, which may have been essential for the activation of the detachment level in the Devonian shales of the Los Monos Formation. To do this, we made a series of 1D petroleum system models at different locations along the deformation front. This analysis allowed to model primary gas generation and secondary cracking — processes that are related to overpressure occurrence, and therefore, to the efficiency of the upper detachment level. The models suggest a close relationship between thermal evolution of the foreland basin and generation of gas, with different structural styles observed at the deformation front. Thus, it was possible to divide the deformation front of the southern Subandean zone into two distinct segments. In the northern segment, where models suggest that gas generation and overpressures of the Los Monos Formation would be well developed, the existence of composite roof duplexes is verified. On the other hand, where the models suggest that generation of gas in the Los Monos Formation would be limited, the upper detachment level is not involved in the deformation, and the existence of fault bend fold structures is verified.  相似文献   

Consolidation behavior of soft deposits considering the variation of prefabricated vertical drain discharge capacity     

《Computers and Geotechnics》2014

This paper is primarily focused on why and how to consider the varied discharge capacity during simulations of consolidation via prefabricated vertical drains (PVDs) for soft soil deposits. First, the existing studies regarding discharge capacity are summarized and discussed. These studies conclude that the discharge capacity of PVDs at sites vary with the confining pressure and consolidation time. Next, a series of analytical solutions that consider the variation of discharge capacity with ground depth, consolidation time or both simultaneously are presented and compared. Applications of these solutions and of the newly introduced parameters are described. Then, a well-documented case history on ground treatment with PVDs is analyzed, in which the parameters related to the time-dependent discharge capacity were obtained from laboratory tests. A comparison between a classical solution and the newly presented method indicates that consideration of the varied discharge capacity in the consolidation theory can better predict the consolidation process of PVD-improved ground.  相似文献   

Earthquake hazard of dams along the Mekong mainstream     

Santi Pailoplee 《Natural Hazards》2014,74(3):1813-1827

In this study, the earthquake hazard was evaluated for all of 19 of the proposed or built dams along the Mekong River. All values representing a potential indication of hazardous earthquakes, such as the closest earthquake and seismogenic faults and including the seismic parameters required for a seismic safety evaluation, were clarified. The results will be useful in reviewing the safety of existing dams and for the design of suitable earthquake resistant specifications for any currently or future planned dam construction in this area. Seismotectonically, 14 of the 19 proposed Mekong River dams are located within an earthquake source zone. Most of faults are potentially still active, according to both seismicity and paleoseismological evidence. In addition, the maximum credible earthquakes were estimated to be in the range of 7–8 Mw for the closest fault zone of each dam. Previous isoseismal maps indicated a risk of shaking intensities of around scale III–IV (Modified Mercalli Intensity Scale) for the dams. According to the preliminary ranging of the International Commission on Large Dams, 9 of these 19 dams are classified as in an extreme hazard class and so need careful observation and monitoring of hazardous earthquakes. An effective mitigation plan should also be prepared for each operating dam.  相似文献   

Carbonate platform growth and demise offshore Central Vietnam: Effects of Early Miocene transgression and subsequent onshore uplift     

《Journal of Asian Earth Sciences》2013

Miocene carbonate platforms cover a large part of the Central Vietnamese South China Sea margin. Early carbonate deposition took place on two regional platforms separated by a narrow depression developed along the trace of the East Vietnam Boundary Fault Zone. West of the East Vietnam Boundary Fault Zone, the Tuy Hoa Carbonate Platform fringes the continental margin between Da Nang and Nha Trang. Here, platform growth initiated during the Early Miocene and continued until Middle Miocene time when regional uplift led to subaerial exposure, termination of platform growth and karstification. East of the fault zone, the Triton Carbonate Platform was also initiated during the Early Miocene. Carbonate growth thrived during Early and part of Middle Miocene time and a thick, clean Lower and Middle Miocene carbonate succession cover the Triton Horst and the Qui Nhon Ridge. During the Middle Miocene, partial drowning resulted in the split-up of the Triton Carbonate Platform. Repeated partial drowning events throughout the Middle and Late Miocene resulted in westwards retreat of platform growth and eventual platform drowning and termination of carbonate deposition. Modern carbonate growth continues on isolated platforms hosting the Paracel Islands farther seawards. The onset of widespread carbonate deposition largely reflects the Early Miocene transgression of the area linked with early post-rift subsidence and the opening of the South China Sea. The mid-Neogene shift in carbonate deposition is interpreted as a consequence of regional uplift and denudation of central and south Indochina starting during Middle Miocene time when the Tuy Hoa Carbonate Platform became subaerially exposed. Stressed carbonate growth conditions on the Triton Carbonate Platform probably resulted from increased inorganic nutrient input derived from the uplifted mainland, possibly enhanced by deteriorated climatic conditions and rapid sea-level fluctuations promoting platform drowning.  相似文献   

U–Pb ages of detrital zircons within the Inthanon Zone of the Paleo-Tethyan subduction zone,northern Thailand: New constraints on accretionary age and arc activity     

《Journal of Asian Earth Sciences》2013

U–Pb dating of detrital zircons was performed on mélange-hosted lithic and basaltic sandstones from the Inthanon Zone in northern Thailand to determine the timing of accretion and arc activity associated with Paleo-Tethys subduction. The detrital zircons have peak ages at 3400–3200, 2600–2400, 1000–700, 600–400, and 300–250 Ma, similar to the peaks ages of detrital zircons associated with other circum-Paleo-Tethys subduction zones. We identified two types of sandstone in the study area based on the youngest detrital zircon ages: Type 1 sandstones have Late Carboniferous youngest zircon U–Pb ages of 308 ± 14 and 300 ± 16 Ma, older than associated radiolarian chert blocks within the same outcrop. In contrast, Type 2 sandstones have youngest zircon U–Pb ages of 238 ± 10 and 236 ± 15 Ma, suggesting a Middle Triassic maximum depositional age. The youngest detrital zircons in Type 1 sandstones were derived from a Late Carboniferous–Early Permian ‘missing’ arc, suggesting that the Sukhothai Arc was active during sedimentation. The data presented within this study provide information on the development of the Sukhothai Arc, and further suggest that subduction of the Paleo-Tethyan oceanic plate beneath the Indochina Block had already commenced by the Late Carboniferous. Significant Middle Triassic arc magmatism, following the Late Carboniferous–Early Permian arc activity, is inferred from the presence of conspicuous detrital zircon U–Pb age peaks in Type 2 sandstones and the igneous rock record of the Sukhothai Arc. In contrast, only minimal arc activity occurred during the Middle Permian–earliest Triassic. Type 1 sandstones were deposited between the Late Permian and the earliest Triassic, after the deposition of associated Middle–Late Permian cherts that occur in the same mélanges and during a hiatus in Sukhothai Arc magmatism. In contrast, Type 2 sandstones were deposited during the Middle Triassic, coincident with the timing of maximum magmatism in the Sukhothai Arc, as evidenced by the presence of abundant Middle Triassic detrital zircons. These two types of sandstone were probably derived from discrete accretionary units in an original accretionary prism that was located along the western margin of the Sukhothai Arc.  相似文献   

Deformation history and U–Pb zircon geochronology of the high grade metamorphic rocks within the Klaeng fault zone,eastern Thailand     

《Journal of Asian Earth Sciences》2013

In eastern Thailand the Klaeng fault zone includes a high-grade metamorphic rock assemblage, named Nong Yai Gneiss, which extends about 30 km in a NW–SE direction along the fault zone. The rocks of this brittle-fault strand consist of amphibolite to granulite grade gneissic rocks. Structural analysis indicates that the rocks in this area experienced three distinct episodes of deformation (D₁–D₃). The first (D₁) formed large-scale NW–SE-trending isoclinal folds (F₁) that were reworked by small-scale tight to open folds (F₂) during the second deformation (D₂). D₁ and D₂ resulted from NE–SW shortening during the Triassic Indosinian orogeny before being cross-cut by leucogranites. D₁ and D₂ fabrics were then reworked by D₃ sinistral shearing, including shear planes (S₃) and mineral stretching lineations (L₃). LA–MC–ICP–MS U–Pb zircon dating suggested that the leucogranite intrusion and the magmatic crystallization took place at 78.6 ± 0.7 Ma followed by a second crystallization at 67 ± 1 to 72.1 ± 0.6 Ma. Both crystallizations occurred in the Late Cretaceous and, it is suggested, were tectonically influenced by SE Asian region effects of the West Burma and Shan-Thai/Sibumasu collision or development of an Andean-type margin. The sinistral ductile movement of D₃ was coeval with the peak metamorphism that occurred in the Eocene during the early phases of the India–Asia collision.  相似文献   

Probabilities of earthquake occurrences in Mainland Southeast Asia     

Santi Pailoplee  Montri Choowong 《Arabian Journal of Geosciences》2013,6(12):4993-5006

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.  相似文献   

泰国东南部Rayong省Klaeng地区的中-晚泥盆世放射虫     

Yoshihito KAMATA  Miyako KATO  Katsumi UENO  Akira MIYAHIGASHI  Thasinee CHAROENTITIRAT  Apsorn SARDSUD 《地球学报》2012,33(S1):33-35

Tectonic subdivision of mainland Thailand has been discussed by means of Paleozoic and Mesozoic stratigraphy, micropaleontology represented by fo-raminiferal and radiolarian biostratigraphy and paleo-biogeography, tectonic settings of granitoids, and ul-tramafic rocks that are distinctive of suture lines. Re-cently, Ueno (2002) and Ueno and Charoentitilat (2011) proposed a new tectonic scheme of mainland Thailand and divided it into three geotectonic units: the Sibu-masu Block, Sukhothai Zone, and Indochina Block from west to east, which are separated by the Mae Yuan Fault, the Chiang Rai Tectonic Line, and the Nan–Uttaradit Suture, respectively. In Northern Thai-land, moreover, the peculiar Inthanon Zone is recog-nized in the eastern part of the Sibumasu Block, where Paleo-Tethyan oceanic rocks are widely distributed as tectonic slices. These geotectonic subdivisions in Northern Thailand are relatively clear. However, the tectonic subdivisions of Central and Southeast Thai-land have not been well documented and are still con-troversial because there is short of information about basement rocks in those areas. In this circumstance, we have examined Paleozoic to Mesozoic stratigraphy, lithology, and radiolarian ages of siliceous rocks dis-tributed in Southeast Thailand to clarify the geotec-tonic belongings of this area and the southern exten-sions of geotectonic units consisting of Northern Thailand. In the course of this research, we could ob-tain Middle to Late Devonian radiolarians from well-bedded siliceous rocks distributed in southwest of Klaeng, Rayong Province. In this study, we report lithology and age of the radiolaria-bearing rocks and discuss their stratigraphy and geological correlation nearby the Klaeng region.  相似文献   

Monotonic and Cyclic Behavior of Chiang Mai Sand Under Simple Shear Mode     

Soksan Thay  Suched Likitlersuang  Thirapong Pipatpongsa 《Geotechnical and Geological Engineering》2013,31(1):67-82

Record of damages and casualties caused by earthquakes in Thailand reveals that Chiang Mai, the second largest province of Thailand, has faced the great threat among other provinces. Triaxial tests, standard penetration tests, and multichannel analysis of surface wave have been recently performed to understand the dynamic response of Chiang Mai ground. However, the cyclic simple shear test, which could convincingly represent the real seismic ground shaking under repeated horizontal shear force, has not been conducted yet. Therefore, this paper aims to characterize the behaviors of Chiang Mai sand under monotonic and cyclic loadings using a direct simple shear apparatus. Sand specimens taken from the Ping River were prepared by dry deposition technique. The mobilized friction angle at the critical state measured by the direct simple shear test is equal to 37.3° which is 9 % less than that measured by direct shear box test. This paper also provides the appropriate dynamic properties of Chiang Mai sand with the shear strain level <2 % for any practical purpose. Test results showed that the normalized shear modulus agrees well with other investigators while the damping ratio is noticeably smaller than the lower-bound range for sand reported in the past studies.  相似文献   

Prehistorical frequency of high‐energy marine inundation events driven by typhoons in the Bay of Bangkok (Thailand), interpreted from coastal carbonate boulders          下载免费PDF全文

James P. Terry  Kieran Dunne  Kruawun Jankaew 《地球表面变化过程与地形》2016,41(4):553-562

Rapidly rising populations of low‐lying megacities in Asia mean that understanding the potential risk of coastal flooding by storm surge is of paramount concern. The city of Bangkok and the wider Chao Phraya River delta at the head of the Gulf of Thailand is a region topographically vulnerable to coastal flooding, but without the record of a high‐energy marine inundation (HEMI) event in historical time owing to the atypical path that a typhoon must take to be able to produce such an event. This work builds upon previous findings that identified coastal depositional evidence for HEMI events in the form of coastal carbonate boulders (CCBs) located on Ko Larn Island in the eastern Bay of Bangkok. The HEMI events were most likely driven by typhoons and the CCBs are therefore interpreted as typhoon deposits. Through uranium/thorium dating, it is revealed that from ad 1400 to ad 1600 the Bay of Bangkok possibly experienced a phase of relatively heightened storm impact. During this period, the frequency of typhoon‐driven HEMI events was approximately four events in 200 years. Waves generated onshore minimum flow velocities (MFVs) in excess of 5 m/s. Such exceptional MFVs are unlikely to be produced during the annual northeast monsoon, but are consistent with typhoon‐impacted coastlines elsewhere in the tropical Asia–Pacific region where similar CCB evidence exists. Since ad 1600, the Bay of Bangkok has enjoyed a relatively quiescent phase, recording less frequent HEMI events and of lower magnitude. However, the re‐occurrence of a typhoon‐driven HEMI event on the scale of the prehistorical events that emplaced carbonate boulders at elevation on Ko Larn Island would threaten low‐lying coasts in the Bay of Bangkok, including the Chao Phraya delta, with potentially damaging inundation. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献