Geoscience

The extrusive rock samples were collected from outcrops at Khun Dan Prakarn Chon Dam site, Nakhon Nayok Province. They are parts of the Pre-Cretaceous Khao Yai Volcanics located at the southern end of the western Loei-Petchabun-Nakhon Nayok Volcanic Subbelt. Petrological study found that the extrusive rock samples can be classified into four groups: felsic pyroclastic rocks, felsic volcanic lava flows, mafic pyroclastic rocks, and mafic-to-intermediate volcanic/hypabyssal rocks. Geochemical characteristics of the extrusive rock samples, however, can be divided into two groups which are mafic-to-intermediate extrusive rocks and felsic extrusive rocks. Although the major and some trace element signatures of these extrusive rocks are identical to those of typical calc-alkalic magmas, the tectonic discrimination diagrams for least-altered rocks showed that they were different in the magmatic suite and erupting episode; and discriminant diagrams can be successfully used to identify the tectonic environments of extrusive rocks and to evaluate the tectonic setting of a region. Incompatible trace element plot on the tectonic discrimination diagrams for the mafic-to-intermediate extrusive rock samples indicated high affinity with a within-plate tectonic setting, while felsic extrusive rock samples had high affinity with continental volcanic arc tectonic setting. In addition, the tectonic setting of these mafic-to-intermediate extrusive rock samples could be correlated to the Khiao Andesite located in the east of studied area. Dykes could be associated with multiple arc magmatism in Loei Fold Belt and resulted in the subduction in the Late Permian.

U/Pb-SHRIMP dating and Pb stepwise leaching (PbSL) experiments on zircons and garnets, respectively have confirmed the lack of Precambrian outcrops within the crystalline basement of Thailand. The obtained data for the high grade metamorphism show Indosinian ages ranging from 225 -200 Ma as previously suggested for the vast majority of outcrops in NW-Thailand ([1] and references therein), as well as a small group of ages in the range of 445 Ma in the Lampang Province. Further, the age of a thermal imprint around 60 Ma was confirmed near Surat Thani, Peninsular Thailand, and only a few indications of older ages for the unknown source areas were detected in detrital components.

Bamnet Narong is located in northeastern Thailand (Chaiyaphum Province). It is the largest salt mine in the country and has been mined for decades. The landscape in this part of Thailand is characterised by a low plateau, which is called the Khorat Plateau. The plateau is divided into two basins by the Phu Phan Range, the Sakhon Nakhon Basin in the north and the Khorat Basin in the south. The analysed potashes and rock salts are deposited in the Maha Sarakham Formation, which represents the salt-bearing strata of the Khorat Basin. The stratigraphic age of this deposit has been debated since the late 1960's. The assigned ages range from Mid-Cretaceous to Late Cretaceous and up to the Eocene. In this study different isotopic dating systems (Rb-Sr, Sr-Sr, K-Ar and K-Ca) were applied. The stratigraphic age for the time of deposition was confirmed to be Mid Cretaceous (Cenomanian). Furthermore, the homogeneity of the carnallites was investigated in order to trace a possible redistribution of rubidium.

We recovered Australasian tektites in place throughout a 40X130 km region in northeast Thailand extending from the Laotian border westward to a line connecting Na Pho Klang in the northeast through Det Udom to Nam Yun in the south. With two exceptions, in sites near the western edge of this region, all fragments are layered (muong-Nong-type) tektites. It appears that large layered tektites are mainly found by rice farmers in fields that were forested until the recent past. The presence of layered tektites in this 40X130 km area implies that impact melt that fell in these areas was hot enough to flow if it was deposited on a sloping surface. The absence of splashform tektites from the region indicates that the layer was still molten when masses having shapes (teardrops, dumbbells, etc.) produced by spinning reached the ground. To account for this and to allow time for the melt to flow a few tens of centimeters requires that the atmosphere remained hot (>2300 K) for a few minutes. Tektites that are in place are almost always associated with a widespread 10-cm to meter-thick layer of laterite. In two cases (one involving layered, one involving splash-form tektites), where accurate stratigraphic control demonstrated that the tektites were still in section, they were sited on top of the laterite layer just below a layer of aeolian sand. sediments. Four fields are known; common names and approxi

Aerial photographic maps and landsat image interpretations suggest the major fault segments of the Three Pagoda Fault (TPF) Zone and Sri Swat Fault (SSF) Zone are oriented parallel or sub-parallel in the same NW-SE directions. The Kwae Noi River is running along the TPF in the south whereas the Kwae Yai River is running along the SSF in the north. The southeastern continuation of both faults is obscured by thick Cenozoic sediments. Hence, surface lineaments cannot be traced with confidence. However, based on some interpretations of the airborne magnetic survey data, the trace of such faults are designated to run through the western part of Bangkok and the northern end of the Gulf of Thailand. Paleo-earthquakes and the presence of hot springs along the fault zones indicate that they are tectonically active. The changes of both physical and chemical properties of the water from Hin Dart Hot Spring and those of the surface water from a shallow well at Ban Khao Lao during the Great Suma...

Hot spring systems in Thailand are in general of two types, either directly connected to a granitic basement or indirectly communicated through an intermediate sedimentary rock layer. They are commonly found along some fault systems, such as the Three Pagodas fault zone of western Thailand. The changing characteristics of many hot springs during the 26 December 2004 Sumatra Earthquake include both temperature and chemical compositions indicate the value to study them in connection with the regional tectonics. However, in this paper the focus is on investigation of hot spring sites for development of tourist/local industry as it has been done in many locations in Thailand. The results of geophysical and geotechnical investigations, jointly conducted by the AIT and Mahidol University research teams, in Kanchanaburi province of western Thailand are presented.

Moderately-preserved radiolarians have been identified from black chert interbedded with layers of mediumto coarse-grained sandstone and variegated siliceous shale outcropped at a quarry near Ka Bang, Songkhla Province, southern peninsular Thailand. The following radiolarians (13 species belonging to seven genera) were identified and systematically investigated: namely Albaillella sp., Ceratoikiscum sp., Stigmosphaerostylus variospina, Stigmosphaerostylus cfr. vulgaris, Stigmosphaerostylus cfr. delvolei, Stigmosphaerostylus sp., Stigmosphaerostylus? sp. A, Stigmosphae-rostylus? sp. B, Stigmosphaerostylus? sp. C, Trilonche? sp., Spongentactnia exilispina, Pylentonema antiqia, and Archocyrtium sp. These radiolarians indicate the Tournaisian–Visean, Mississippian (early Carboniferous) in age. The present authors have already reported a Tournaisian radiolarian fauna which is slightly older than the present fauna from black bedded chert in the Saba YoiKabang area. This is an additional r...

Tha Chang sand pits, Nakhon Ratchasima Province and many other sand pits in the area adjacent to the Mun River are characterized by their fluviatile environment in association with mass wasting deposits, along the paleo-river channel and the flood plain of the Mun River. Sediments of these deposits are characterized by clasts of various rock types especially the resistant ones with frequent big tree trunks, logs and wood fragments in different sizes and various stages of transformation from moldering stage to lignification and petrification. Widespread pyritization of the lower horizon suggests strongly reducing environment during burial. The Tha Chang deposits have been received much attention from geoscientists especially paleontologist communities, as they contain fragments of some distinct vertebrate species such as Stegadon sp., hominoid primate, rhinoceros Aceratherium and others. Based on the associated mammal fauna and hominoid fossils, the late Miocene ( 9 - 6 Ma) was given...

Aerial photographic maps and landsat image interpretations suggest the major fault segments of the Three Pagoda Fault (TPF) Zone and Sri Swat Fault (SSF) Zone are oriented parallel or sub-parallel in the same NW-SE directions. The Kwae Noi River is running along the TPF in the south whereas the Kwae Yai River is running along the SSF in the north. The southeastern continuation of both faults is obscured by thick Cenozoic sediments. Hence, surface lineaments cannot be traced with confidence. However, based on some interpretations of the airborne magnetic survey data, the trace of such faults are designated to run through the western part of Bangkok and the northern end of the Gulf of Thailand. Paleo-earthquakes and the presence of hot springs along the fault zones indicate that they are tectonically active. The changes of both physical and chemical properties of the water from Hin Dart Hot Spring and those of the surface water from a shallow well at Ban Khao Lao during the Great Sumatra-Andaman Earthquake on 26 th of December 2004 clearly indicated that the southeastern continuation of the TPF is at least as far south as Pak Tho District, Ratburi. Our new evidence of the alignment of the high heat flow in the upper part of the Gulf of Thailand verified that the TPF also extend into the Gulf via Samut Songkhram Province. Studies of the seismic data from two survey lines along the Western part of the upper Gulf of Thailand acquired by Britoil Plc. in 1986, namely Line A which is approximately 60 km long, starting from Bang Khen passing through Bang Khae and ending in Samut Songkhram and Line B is approximately 30 km long starting from Samut Sakon ending in Samut Song Khram suggest that all the faults or fractures along these seismic profiles are covered by sediments of approximately 230 m thick which explain that the fault underneath these seismic lines is quite old and may not be active. The absent of sign or trace of the TPF Path to the west suggested that there is no segment of such fault along these seismic lines.

Simple veins arc the most abundant type of hydrothermal ore deposit, constituting 52% of all known primary tin-tungsten deposits. Complex infilling-dominated deposits of the sheeted-vein or stockwork type are less abundant (10% of primary deposits). Other types arc replacement-dominated deposits (24%). tin-tantalum mineralized pegmatites (12%) and breccia deposits (1%). Placer tin deposits derived from the primary tin mineralization in the pre-Miocene basement are the major source of tin. The oldest terrestrial sediments deposited on the extensively pcneplaned basement have a Miocene-Pliocene to Lower Pleistocene age. These sediments, which arc up to 60 m thick, host the most important placers. They are overlain by younger alluvial strata or marine sediments, which are up to 25 m thick and usually do not contain minable tin mineralization. Fluvial allochthonous bottom placers are of major economic importance. Fluvial residual bottom placers, fluvial above-bottom placers and alluvial-fan placers are also significant. Eluvial, colluvial and littoral placers arc of minor importance.

Hot spring systems in Thailand are in general of two types, either directly connected to a granitic basement or indirectly communicated through an intermediate sedimentary rock layer. They are commonly found along some fault systems, such as the Three Pagodas fault zone of western Thailand. The changing characteristics of many hot springs during the 26 December 2004 Sumatra Earthquake include both temperature and chemical compositions indicate the value to study them in connection with the regional tectonics. However, in this paper the focus is on investigation of hot spring sites for development of tourist/local industry as it has been done in many locations in Thailand. The results of geophysical and geotechnical investigations, jointly conducted by the AIT and Mahidol University research teams, in Kanchanaburi province of western Thailand are presented.

To assess the subsurface conditions beneath a 4-floor public building, where sinkhole collapses had already occurred, twenty-three 2D cross-borehole resistivity tomographies were conducted beneath the building foundations in January and February 2004. The aim of these geophysical investigations was to build a model of the complex subsurface geometry in order to estimate and minimize costs of remediation works. In cross-borehole resistivity tomography standard electrode configurations do not exist yet. Thus, preliminary field tests were performed to determine a suitable combination of arrays and to estimate the stability of these measurements on the site. A combination of cross-borehole arrays and single-hole arrays was then selected. The measures were conducted on each panel using this combination of arrays. Over 2500 apparent resistivities were measured on each panel. The inversion problem was solved within the Res2DInv® software. On tomographies weathered zones were clearly identified as low resistivity zones (< 50 Ωm). The strong contrast in resistivities compared to solid limestone (ρ > 200Ω m) led to establish a 3D model of the ground conditions. This model showed large variations in buried rockhead depths from 6 to more than 24 m. Four zones of different ranges of depth-to-bedrock were identified inside, which three vertically elongated weathered zones were also delineated. Based on these results, a remediation plan which consisted in underpinning the foundations with about 250 micropiles was designed. The feedback of the remedial works showed that tomographies gave a very accurate overview of the buried rockhead depths (with a precision of about 1 m).