Detrital chromian spinels from the Sa Kaeo-Chanthaburi accretionary complex, eastern Thailand : tectonic evolution of the western margin of Indochina

The geological evidence regarding the origin and tectonic setting of eastern Thailand now still be limited. In this study, I studied a melange terrane in the Sa Kaeo-Chanthaburi area, and discriminated tectono-stratigraphic units there. To establish the tectonic evolution , the geochemistry of chromian spinels is applied to determine the composition and provenance of their ultramafic-mafic rocks. Two kinds of rock assemblages are generally recognized in the Sa Kaeo-Chanthaburi area. They are a various kind of melanges, and turbidite deposits. These rock assemblages are called here as the Sa Kaeo-Chanthaburi accretionary complex. It comprises five new rock units from north to south, Khao Prik, Khao Hleam, Ban Nong Bon and Soi Dao units, and Pong Nam Ron Formation. The covering sediments, Pong Nam Ron sandstones belong to the dissected arc. In this Sa Kaeo-Chanthaburi accretionary complex, numerous detrital chromian spinels are discovered as the accessory mineral in turbiditic sandstones of the Pong Nam Ron Formation, sandstone blocks in melanges, and volcaniclastic rocks. The petrographical characteristics under the microscope indicate volcanic origins. Geochemistry the detrial chromian spinels from sandstone beds of the Pong Nam Ron Formation and sandstone blocks in melange have wider Cr content. On the other hand, detrital spinels from volcaniclastic rock have high Cr content, and vary widely in TiO2 content. The Fe3+ is consistently low in both clastic and volcaniclastic rocks. Based upon provenance discrimination fields on the Fe3+/(Cr+Al+Fe3+)-TiO2 diagram proposed by Arai (1992), plots of detrial chromian spinels in sandstones of the Pong Nam Ron Formation and sandstone blocks in melanges seem to correspond to island-arc region, whereas plots of detrital chromian spinels in volcaniclastic rock can be related with spinels from intraplate basalt and island arc basalt. ･･･Thesis (Ph. D. in Science)--University of Tsukuba, (A), no. 3398, 2004.3.25Includes bibliographical referencesTitlepage, Contents -- Abstract -- List of Figures, List of Table -- CHAPTER 1 INTRODUCTION -- CHAPTER 2 GEOLOGY OF SA KAEO-CHANTHABURI ACCRETIONARY COMPLEX -- CHAPTER 3 PETROGRAPHY OF SANDSTONES -- CHAPTER 4 DETRITAL CHROMIAN SPINELS -- CHAPTER 5 TECTONIC SETTING OF SA KAEO-CHANTHABURI ACCRETIONARY COMPLEX-DICUSSIONS -- CHAPTER 6 CONCLUSIONS -- ACKNOWLEDGEMENTS -- REFERENCES -- APPENDICES -- PLATES 1-28 AND EXPLANATION OF PLATE

Earthquake Activities in the Thailand-Laos-Myanmar Border Region: A Statistical Approach

A large number of earthquakes have been recorded by instrument in the past along the Thailand-Laos-Myanmar border region. However, the locations of most of these earthquakes do not coincide with the location of morphological features which indicate seismogenic faults. Thus, a statistical evaluation of the earthquake record is focused upon in this earthquake hazard study. The spatial distributions of the a- and b-values from the frequency-magnitude distribution relationship were investigated from the complete earthquake catalogue

Stalagmites from western Thailand: preliminary investigations and challenges for palaeoenvironmental research

Locating suitable caves and stalagmites for palaeoenvironmental and palaeoclimatic studies can be challenging. Isotopic geochemical analyses, albeit comm performed for palaeoclimatic reconstruction, are also time consuming and costly. Therefore, petrographic and non‐destructive morphological studies on speleothems are desirable to facilitate sample selection for further analysis. In this study, 20 caves were surveyed in Ban Rai district, Uthai Thani province in western Thailand. After external physical observations in the field, three stalagmite samples were collected from Tham Nam Cave to test their potential for palaeoclimatic research. Firstly, the stalagmites were scanned by X‐ray computed tomography (CT scanning) and subsequently the CT images were compared with petrographic inspections. Columnar fabrics show the highest density, whereas closed and open dendritic fabrics have medium and the lowest densities, respectively. Layers near the top and bottom of the three stalagmites were dated by U‐Th mass spectrometric techniques. All three samples were deposited between c. 87 and c. 105 ka ago; therefore, they are probably the oldest stalagmites that have been reported so far from mainland Southeast Asia. However, their physical features indicate that all the samples have suffered from postdepositional dissolution, and are unlikely to be suitable for palaeoclimatic research. The internal dissolution feature of stalagmites, however, cannot be identified by visual inspection of uncut samples. We hereby argue that CT images are useful to characterize stalagmite petrography, in particular fabric, porosity and density. Such features can be used to select the ideal plane of a stalagmite for sectioning, to maximize the chances of robust climatic reconstruction