Early Permian radiolarians from the extension of the Sa Kaeo Suture in Cambodia – tectonic implications

Abstract

A reconnaissance survey of part of western Cambodia has found quarries in and near the town of Pailin containing chert, basalt, volcaniclastic rocks, gabbro and serpentinite. Abandoned quarries contain chert and basalt clasts in a volcaniclastic matrix and may constitute a mélange. A new, recently active, quarry contains these rock units in close and coherent contact but they lack the serpentinitic matrix of the Thung Kabin Mélange of eastern Thailand. The rock units are in close contact and may best be described collectively as a dismembered ophiolite. The mélange-ophiolite association constitutes a 3 km wide, 20 km long E-W belt separating a northern 200 km 2 block of the mainly amphibolitic Pailin Crystalline Complex from a southern area of Triassic submarine fan siliciclastic rocks. The cherts yield the first documented radiolarian fauna from Cambodia and include a moderately well-preserved Asselian-Sakmarian age fauna consisting of Pseudoalbaillella sakmarensis, Pseudoalbaillella scalprata morphotype scalprata, Pseudoalbaillella sp. cf. P. simplex, Pseudoalbaillella u-forma morphotype II, Pseudoalbaillella sp. cf. P. elegans, Pseudoalbaillella sp. cf. P. lomentaria, Albaillella sp., Pseudoalbaillella spp., Trilonche? sp., Latentifistularia gen. et sp. indet. and Entactinaria gen. et sp. indet. The Pailin ophiolitic rocks, mélange and volcanic rocks occur within a generally E-W-trending belt, which suggests that the Sa Kaeo Suture does not extend southeastwards paralleling the Thai-Cambodian border, nor extend under the Cardamom Mountains but, rather, extends eastwards into Cambodia and possibly then turns southwards along the strike of the Pursat-Kampot Fold Belt.

Revisiting the tectonic evolution of the Triassic Palaeo-Tethys convergence zone in northern Thailand inferred from detrital zircon U–Pb ages

“…13). This chert and tuff/greenschist probably correspond to the cover sediments overlying the ophiolite sequence, as well as to Permian pelagic chert reported from the Nan Back-arc Basin (Hada et al 1999;Yang et al 2009) and Sa Kaeo Back-arc Basin (Hada et al 1999;Saesaengseerung et al 2009;Udchachon et al 2018). In addition, Middle Triassic radiolarians have been reported from chert of the Lab Lae Formation (Thassanapak et al 2011(Thassanapak et al , 2017 and Khao Phueng Formation (Vimuktanandana et al 2008b).…”

“…A 266 Ma granite has been recorded in eastern Myanmar along the Sukhothai Arc (Gardiner et al 2016). Andesitic volcaniclastic rocks underlying middle Permian limestone are considered as evidence of Permian igneous activity in NW Cambodia (Udchachon et al 2018). Permian zircons have been found in felsic igneous rocks in western Cambodia and are related to magmatism in the Sa Kaeo Back-arc Basin (Hara et al 2020).…”

The Truong Son, Loei-Phetchabun, and Kontum Terranes in Indochina: Provenance, Rifting, and Collisions

“…These sediments interdigitate with a "late" Carboniferous volcanic arc in the Phetchabun Province area (Salam et al, 2014) and all are overlain by widespread Visean to Permian platform carbonates (Ueno and Charoentitirat, 2011;Udchachon et al, 2015). Arc magmatism is again established in the Phetchabun Province area and along the southern margin of the Khorat Plateau in Thailand and Cambodia in the Permian to Late Triassic (Salam et al, 2014;Udchachon et al, 2018;Cheng et al, 2019) (Figures 1-5).…”

“…Their extent shown in Figure 1 is, however, plausible based on seismic and other geophysical data (Figure 3). The extension of the Loei Suture eastwards through Cambodia is based on Cheng et al (2019), Khin et al (2014), and Udchachon et al (2018). The extension of the Sra Kaeo-Pailin Suture through Cambodia is based on Udchachon et al (2018).…”

“…The extension of the Loei Suture eastwards through Cambodia is based on Cheng et al (2019), Khin et al (2014), and Udchachon et al (2018). The extension of the Sra Kaeo-Pailin Suture through Cambodia is based on Udchachon et al (2018). Note that much of Cambodia is terra incognita geologically and the area in southern Cambodia colored yellow is not assigned to a terrane.…”