Petrogenesis of Late Triassic Post-Collisional Volcanic Rocks from Loei Zone in Southeastern Thailand and Its Paleotethyan Tectonic Implications
Yan Qiutong
Qian Xin
Zhang Feifei
Mongkol Udchachon
Wang Yiwen
Abstract：Thailand is located in the core region of the East Paleotethyan Domain,preserves numerous tectonic-magmatic belts related to the subduction-collision-closure evolution of the Paleotethyan Ocean.However,the study on the Early-Middle Mesozoic volcanic rocks in the Loei zone remains unclear and the related petrogenesis and tectonic setting have not been constrained.Therefore,this study carries out detailed petrographic,zircon U-Pb geochronology,geochemistry and Sr-Nd-Hf isotopic studies on the Late Triassic volcanic rocks along the Loei zone in southeastern Thailand.Our study along with regional comparisins comprehensively analyze the Late Triassic magmatism and geodynamics process in the East Paleotethyan Domain.The study samples include basalts,rhyolites and dacites,with Late Triassic zircon U-Pb ages of 204-200 Ma.The basalts exhibit characteristics of Nb-enriched basalts,with(87Sr/86Sr)i=0.703 98-0.704 00,εNd(t)=+5.0-+5.3,εHf(t)=+0.3-+15.5.The felsic volcanic samples exhibit A-type characteristics and share similar isotopic compositions with the basalt samples,with(87Sr/86Sr)i=0.702 71-0.704 72,εNd(t)=+4.0-+4.2,εHf(t)=+6.8-+16.0.Geochemical characteristics indicate that these basalts originated from a depleted OIB-like asthenospheric mantle source,while the felsic volcanic rocks possibly originated from the low level partial melting of these newly underplated mafic rocks.Regional comparisons indicate that these Late Triassic volcanic rocks were formed in a post-collisional extensional setting,representing the latest magmatism after the collision and closure of the East Paleotethyan Ocean.Comparison of chronological data shows that the Loei zone and the Chiang Khong-Lampang-Tak zones share similar Triassic age-spectra pattern,confirming that the Loei zone also recorded the collisional and post-collisional magmatism related to the Eastern Paleotethyan evolution during the Middle-Late Triassic.
Keywords：southeastern ThailandLoei zoneLate Triassicpost-collisional magmatismEast Paleotethyan Oceanpetrologytectonic
Publication Date：2025-06-30
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：19( 2144-2162 )