Late Cenozoic basaltic rocks in Nang Rong Columnar Jointed Basalts in southern Khorat Plateau are among the greatest columnar basalts in Thailand as famous geoheritage sites. This work aims to characterize and evaluate the post-quarrying area by field investigation, petrography, geochemistry, and geological engineering. A petrographical study determines these basalts as olivine basalts, presenting porphyritic texture with olivine microphenocryst. Geochemical characteristics indicate these basalts were alkaline basalt generated from alkaline sodic magma series within the continental plates. In addition, columnar jointed basalt presents compressive strength and point load strength index higher than platy basalt with a higher percentage of alteration. Local authorities enhance people in the area to develop and promote their georesources through touristic activities. This geoheritage demonstrates high geology and tourism management values; thus, it could be the prototype of the post-quarrying geosite of Thailand.
Lava Durian Sisaket is the first geographically identified (GI) fruit related to the volcano in Thailand and distributed in three districts of Sisaket Province, the southernmost edge of the Khorat Plateau. The parent rocks of orchards are important for the description of soil and rock relation with respect to mineralogical and geochemical characteristics. This work aims to study lithology, mineralogy, and geochemistry of basaltic rocks, parent rocks of in situ soil in these orchards, and delineate the existing basaltic soil models. The several orchards are covered by reddish-brown to brown in situ soils, weathered from mafic volcanic rocks: porphyritic olivine basalt, vesicular olivine basalt, and nephelinite. The microscopic image analysis, XRD, and MiniSEM-EDS are used to classify mineralogy, while XRF and analysis of large and rare elements in ICP-MS/ICP-OES were used to determine parental rocks geochemistry and alteration. The olivine basalts comprise forsterite microphenocrysts associated with bytownite, diopside, augite, pigeonite, and ilmenite groundmass, while nephelinite is composed of nepheline groundmass and bytownite-labradorite, diopside, augite, pigeonite, and ilmenite crystals. In addition, these basalts display high alteration rates, especially olivine highly altered to iddingsite. According to the geochemical data, Sisaket's basalts were identified as alkali basalt and nepheline basanite with high LILEs and LREEs (La, Nd, Pr, Gd, Eu). The kaolinite, smectite, and illite are altered from felsic minerals, while the chlorite and iddingsite are from mafic minerals. The mineralogical analyses classified secondary phyllosilicates related to low-moderate temperature hydrothermal fluid, very high cation exchange capacity (H + , K + , Ca 2+ , Mg 2+ ), and tropical weathering. The alkaline and high alkaline basalts, presenting as parent rocks, are one of the parameters that produced good nitisal soil of Sisaket's agricultural areas.
Khon Kaen Geopark, representing an area of dinosaur fossil diversity, was selected for investigations to reveal the origin and tectonic setting of the Khorat Group. The area occupied by Mesozoic sedimentary rocks of four formal formations of the Khorat Group, namely the Phra Wihan Formation (PWF), Sao Khua Formation (SKF), Phu Phan Formation (PPF), and Khok Kruat Formation (KKF). A field investigation and macroscopic observations suggested that the immature sedimentary rocks of the study area are mainly clast-supported, pebbly sandstone and siltstone with few calcretes. The 50 rock samples that were selected for petrographical and geochemical investigations revealed that the sandstones of the PWF and PPF are quartz arenite and sublitharenite, with some subarkose, whereas those of the SKF are mainly subarkose and sublitharenite. In addition, the KKF dominantly presents sublitharenite with pebbles and calcretes. Mesozoic sandstones contain quartz, feldspars, various types of rock fragments, and accessory minerals (biotite, muscovite, zircon, and tourmaline), with siliceous, ferrous, and calcareous cement. Petrographic (Q–F–L) and geochemical (major and trace element) data suggested that the sources of sediments are mostly quartzose sedimentary rocks and some felsic-intermediate igneous rocks. Chondrite-normalized rare earth element patterns indicated that the origins of the studied sandstones are quartzose sedimentary rocks deposited in a passive continental margin or an upper continental crust. Geochemical traits of the sedimentary successions demonstrated that the provenance of the Khorat Basin prior to reworking by fluvial processes was situated in the passive continental margin or recycled orogen of the paleo-volcanic arc during the Mesozoic period.
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