Chongpan Chonglakmani

Zircon U-Pb geochronological evidence for the evolution of the Nan-Uttaradit suture in northern Thailand

The Nan-Uttaradit suture is marked by a narrow N-S trending and discontinuous ophiolite belt in northern Thailand. This suture zone is a mélange composed of gabbro, tholeiitic metabasalt, andesite and radiolarian chert. Samples of gabbro and meta-basalt in the Nan-Uttaradit suture yield zircon U-Pb ages of 311±10 and 316±3 Ma, respectively, interpreted as the crystallization ages of the rocks, suggesting the Nan-Uttaradit Ocean existed in the Late Carboniferous. Our results indicate that the Nan-Uttaradit Ocean co-existed with the Ailaoshan-Jinshajiang Ocean to the north and was probably an along-strike extension of the latter.

Geochemical and geochronological constrains on the Chiang Khong volcanic rocks (northwestern Thailand) and its tectonic implications

Volcanic rocks in northwestern Thailand exposed dominantly in the Chiang Khong area, are commonly considered to be genetically linked to the tectonic evolution of the Paleo-Tethyan Ocean. The volcanic rocks consist mainly of andesitic to rhyolitic rocks and are traditionally mapped as Permian-Triassic sequences. Our zircon U-Pb geochronological results show that two andesitic samples (TL-1-B and TL-31-B), are representative of the Doi Yao volcanic zone, and give a mean weighted age of 241.2±4.6 Ma and 241.7±2.9 Ma, respectively. The rhyolitic sample (TL-32-B1) from the Doi Khun Ta Khuan volcanic zone erupted at 238.3±3.8 Ma. Such ages indicate that Chiang Khong volcanic rocks erputed during the early Middle Triassic period. Seven samples from the Doi Yao and Doi Khun Ta Khuan zones exhibit an affinity to arc volcanics. Three rhyolitic samples from the Chiang Khong area have a geochemical affinity to both arc and syn-collisional volcanic rocks. The Chiang Khong arc volcanic rocks can be geochemically compared with those in the Lampang area in northern Thailand, also consistent with those in Jinghong area of southwestern Yunnan. This indicates that the Chiang Rai arc-volcanic zone might northwardly link to the Lancangjiang volcanic zone in southwestern China.

Geodynamic Evolution of Loei and Phetchabun Regions — Does the Discovery of Detrital Chromian Spinels from the Nam Duk Formation (Permian, North-Central Thailand) Provide New Constraint?

Abstract The discovery of the chromian spinel detritus in sandstones from the Permian Nam Duk Formation (Phetchabun region) confirms that the siliciclastic part of this formation is related to the erosion of a mountain belt caused by compressional deformation. The question discussed is whether this detritus is derived from an older orogen exposed today in the region of Loei east of the Nam Duk Basin, or it is from a mountain belt which evolved during Permian times in the west (Nan-Uttaradit region). In the first case the Nam Duk Formation would represent the passive continental margin sequence of the “Indochina craton”, and in the second case it would be part of the sedimentary wedge associated with the compressional deformation and subsequent uplift to the erosional level during Middle to Upper Permian of a rising mountain belt further in the west. In this contribution, arguments in favour of the second scenario are discussed. The region close to the Nan-Uttaradit suture zone shows evidence of compressional deformation and subsequent uplift to an erosional level in the Permian when the chromian spinel detritus was deposited in the Nam Duk Formation.

An integrative approach for regional landslide susceptibility assessment using weight of evidence method: a case study of Yom River Basin, Phrae Province, Northern Thailand

A landslide susceptibility assessment was conducted for the Yom River catchment, North Thailand, using a weight of evidence approach. In total, 1630 landslide events were detected using remote sensing techniques. An integrated workflow based on robust statistical threshold criteria was applied to reveal the landslide-controlling factors that can be utilised on a regional scale. Initially, approximately 15 different factors were considered within this study. After a sensitivity and plausibility analysis, a final susceptibility map was generated based on the three most essential factors, which fulfilled the statistical requirements of independence, prediction power and plausibility. The final map was subdivided into five susceptibility zones using quantitative classification. The map provides a suitable and reliable starting point for further detailed mass movement analysis in the Yom River Basin and can be used to support strategic spatial planning measures on a regional scale.

Petrochemistry and tectonic setting of the Middle Triassic arc-like volcanic rocks in the Sayabouli area, NW Laos

The volcanic rocks from the Sayabouli area in northwestern Laos have been poorly studied. These volcanic rocks are traditionally mapped as the Permian–Early Triassic sequences on the geological map. One basaltic-andesite from the Sayabouli area yields a zircon U-Pb age of 237.7±1.7 Ma, suggesting a Middle Triassic origin. All basalt and basaltic-andesite samples from the Sayabouli area show depletions in HFSEs (e.g., Nb, Ta, Ti) and have high LILE/HFSE ratios, and exhibit the geochemical affinity to the continental arc volcanic rocks and are geochemically similar to the continental arc volcanic rocks from the Phetchabun belt in northeastern Thailand, suggesting a Late Permian–Middle Triassic continental margin in the Sayabouli area of northwestern Laos and Phetchabun area of northeastern Thailand. Our data indicate that the Phetchabun arc volcanic belt through the western Loei sub-belt can be linked to the Sayabouli area in northwestern Laos.

Petrography, geochemistry and U-Pb detrital zircon dating of the clastic Phu Khat Formation in the Nakhon Thai region, Thailand: Implications for provenance and geotectonic setting

The purpose of this paper is to determine the provenance and tectonic setting of the Phu Khat Formation and get a better understanding of the tectonic evolution of the Nakhon Thai region using the petrography and whole-rock geochemistry integrated with the U-Pb detrital zircon dating. The sandstone of the Late Cretaceous to Early Tertiary Phu Khat Formation is chiefly characterized by unsorted texture and highly unstable volcanic lithic fragments. The formation overlies unconformably on a high textural and mineral maturity of clastic sandstone of the Late Cretaceous Khao Ya Puk Formation. Geochemically, the tectonic setting discrimination (K2O/Na2O-SiO2, Al2O3/SiO2-Fe2O3+MgO, and Th-Sc-Zr/10) and the petrography indicate that the Phu Khat Formation was accumulated in a passive margin tectonic setting which is the same as the Khao Ya Puk Formation but with a different depositional environment. The plots of geochemical provenance discrimination (La/Th-Hf, Th/Sc-Zr/Sc, Eu anomaly Eu/Eu* 0.42 to 0.74) and the petrography reveal that the provenance of the Khao Ya Puk Formation is mainly recycled sedimentary rocks while the Phu Khat Formation consists primarily of recycled sedimentary rocks associated with minor felsic volcanic rocks from the old continental island arc of the uplifted either western or eastern continental terranes or both. However, the U-Pb detrital zircon dating indicates a unique provenance of the Phu Khat Formation from the terrane west of the Nakhon Thai region where the volcanic continental arc is active predominantly in the Middle to Late Triassic. The results indicate that while the Phu Khat Formation was accumulated in Nakhon Thai region, the western terrane was uplifted by reactivation of the preexisting structure probably since the Maastrichtian time to be the source area of sediments. Meanwhile, the eastern terrane (mainly Loei-Phetchabun fold belt) had not been uplifted probably until, the accumulation of the Phu Khat Formation terminated. Subsequently, the whole region began to uplift forming a high mountainous area since the Ypresian time when the Greater India collided with the Eurasia.

Middle Permian Productidine Brachiopods from Central Thailand (the Indochina Terrane) with Paleobiogeographic Implications

Abstract Three productidine brachiopods of Haydenella, Paraplicatifera, and Compressoproductus are recovered from the Tak Fa Formation (Wordian, Middle Permian) of the upper Saraburi Limestone Group exposed at Khao Wong of central Thailand (the western margin of the Indochina Terrane). The latter two genera are new to the Permian of Thailand, and the new species Paraplicatifera thaica is proposed herewith. Some taxonomic and nomenclatural problems in relation to the three genera are discussed. The assemblage suggests endemism for a Middle Permian marine faunule of the Indochina Terrane.

Paleoproductivity and paleoredox condition of the Huai Hin Lat Formation in northeastern Thailand

The petroleum exploration has been conducted in the Khorat Plateau since 1962 and two gas fields have been discovered and commercially produced. The lacustrine facies of the Huai Hin Lat Formation is believed to be one of the main source rocks of the gas. Therefore, investigation and analysis of the Huai Hin Lat shale for understanding the paleoenvironment and petroleum source rock are carried out in this study. Petrographical study and geochemical analysis of shale samples were performed to explain the paleoproductivity and past redox condition. The palynofacies assemblage comprises abundant AOM, acritarchs, phytoclasts, and very small amount of spores and pollen. Geochemical analysis was used to determine the total organic carbon (TOC) and the concentration of major, trace, and rare earth elements. The paleoproductivity proxies are composed of palynofacies, TOC, excess SiO2, Ba/Al, and P/Al. They reflect a high paleoproductivity except the middle of the lower part (bed 3) and the lower bed 13 of the upper part. Bed 3 shows the highest peak of TOC and the lower bed 13 exhibits a relatively lower TOC, which can be explained by the excellent and the poorer preservation condition, respectively. The paleoredox proxies consist of U/Th, V/Cr, NiCo, (Cu+Mo)/Zn, Ni/V, and Ce anomaly. They are used to establish the depositional environments, to characterize the organic matter content, and to assess the source rock potential. They reflect many high peaks and predominantly high values of paleoredox proxies except the middle part and the lower bed (lower bed 13) of the upper part. They indicate that the section was mainly under anoxic or reducing condition, which is supported by the high Ce/Ce* (>0.8) and V/Cr (>2.0) values. The middle of the lower part (bed 3) shows lower productivity but it contains the highest peak of TOC, which is conformed to be the excellent preservation of organic matters in the strong reducing condition. The middle part, which shows high productivity, contains relatively lower TOC as it possesses a less reducing condition compared to the more reducing intervals. The lower bed 13 of the upper part shows a less reducing condition and a lower TOC, which conforms to a lower productivity. The organic matters of the Huai Hin Lat Formation consist mainly of AOM and acritarchs and possess good to excellent TOC (2%–7%). They belong mainly to type I and type II kerogens with some mixture of type III as indicated by the presence of phytoclasts, spores, and pollen. The organic matters of the Huai Hin Lat Formation, based on the kerogen type and the thermal history, have already generated significant amount of oil and some gas to the Sap Phlu Basin.