Application of enhanced satellite-borne images to the relationships between fractures and mineralization in the nam Mae moei-nam Mae Ping area,northern Thailand

The study area is located in the Chiang Mai, Tak, and Mae Hong Son provinces of northern Thailand. Digitally enhanced Landsat TM5 and SPOT images and data on economic minerals deposits were used in the investigation. High-pass filtering and principal component analyses were determined to be the most appropriate enhancement methods.Space-borne image interpretation indicates two major faults: the north-trending Mae Hong Son and the northwest-trending Mae Ping. Both large-scale faults are inferred to be closely related to substantial, nearly parallel folds and thrusts. The four main sets of lineaments observed (north-south, northeast-southwest, northwest-southeast, and east-west) are considered to have an essential role in the occurrences of various mineral deposits. Mineral exploration has emphasized areas where several sets of lineaments cross-cut each other, since the possibility of finding concealed ore bodies or potential target areas is considered quite high. Some sets of lineaments probably control post-Triassic granitoid emplacements both directly and indirectly. Three major granitoid series are recognized in the study area: the Mae Lama (ca. 70 Ma), the Tae Song Yang (ca. 45 Ma), and the Mae Sariang (205–210 Ma) Granites. These peraluminous, S-type granites are closely related to tin, tungsten, and fluorite deposits. Fluorite, barite, manganese, and antimony deposits may be related to the northtrending lineaments. Stibnite deposits may be related to the northeast-trending lineaments. The tin/tungsten deposits are likely related to the east- and northwest-trending lineaments. Ovoid-shaped lineaments, found only at a few locations, are interpreted to indicate the granitoid emplacement and are thought to be important in the generation of concealed mineral deposits. We conclude that the existence of such lineaments is related to the post-Triassic abutment and collision of the Shan-Thai, Indochina, and Western Burma microcontinental blocks.     

Flow conditions of the 2004 Indian Ocean tsunami in Thailand,inferred from capping bedforms and sedimentary structures

The 2004 Indian Ocean tsunami deposited a sheet of sand with surficial bedforms at the Andaman coast of Thailand. Here we show the recognition of bedforms and the key internal sedimentary structures as criteria of the tsunami supercritical flow condition. The presence of well‐preserved capping bedforms implied a dominant tsunami inflow. Sets of internal sedimentary structures including parallel lamination, seaward and landward inclined‐laminations, and downstream dipping laminae indicated antidune structures that were generated by a supercritical flow current in a depositional stage during the inflow. A set of seaward dipping cross‐laminations containing sand with mud drape on the surface of one depositional layer are a unique indication of an outflow structure. A majority of deposits show normal grading, but in some areas, localized reverse grading was also observed. The recognition of these capping bedforms and determination of the internal sedimentary structures provides new key criteria to help derive a better understanding of tsunami flow conditions.     

Occurrence of calcrete in the Phu Kradung Formation of the Mesozoic Khorat Group, NE Thailand

The Phu Kradung Formation of the Mesozoic Khorat Group is deposited by meandering river system. Floodplain deposits in the Nong Bua Lamphu section, northeastern Thailand contain paleosols with abundant calcretes. Calcretes occur within about 60 horizons in the studied section. Occurrences of calcretes are related with traces of life, such as roots and burrows. Microstructures of calcretes are mixture of biogenic and non-biogenic origin. It is suggested that the calcrete formation in the Phu Kradung Formation was affected by abundant biological activity.     

Classification of the Sibumasu and Paleo-Tethys tectonic division in Thailand using chert lithofacies

Two types of chert are defined in Thailand based on lithology, faunal content, and stratigraphy. 'Pelagic chert' consists of densely packed radiolarian tests in a microcrystalline quartz matrix with no terrigenous material and is found as blocks embedded within sheared matrix. 'Hemipelagic chert' also has a microcrystalline quartz matrix, and contains not only scattered radiolarian tests, but also calcareous organisms such as foraminifers. The pelagic cherts range in age from Devonian to Middle Triassic, whereas hemipelagic chert is only from the Early to the Late Triassic. Lithological and stratigraphic characteristics indicate that the pelagic chert originated in the Paleo-Tethys, whereas the hemipelagic chert accumulated on the eastern margin of the Sibumasu Block. The hemipelagic and pelagic chert are exposed in two north-trending belt-like zones. The western zone includes the hemipelagic chert, as well as glaciomarine and other Paleozoic to Mesozoic successions, overlying a Precambrian basement that consists exclusively of Sibumasu elements. The eastern zone contains pelagic chert and limestone and should be correlated to the Inthanon Zone. The Inthanon Zone is characterized by the presence not only of Paleo-Tethyan sedimentary rocks, but also of Sibumasu Block elements that structurally underlie the Paleo-Tethyan rocks. The boundary between the Sibumasu and Paleo-Tethys zones is a north-trending, low-angle thrust that resulted from the collision of the Sibumasu and Indochina blocks.