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Field photographs of Boualapha Formation and Khammouan Group from central Laos. (A) Outcrop of carbonaceous limestone belonging to the Boualapha Formation north of Boualapha Town. (B) Close-up of (A), (C) Large outcrop of limestone of the Khammouan Group north of Lak Xao Town. (D) Limestone belonging to the Khammouan Group, south of Lak Xao Town, central Laos [see Figure 4 and Thassanapak et al. (2012) for localities]. Lak Xao township is shown as LX in Figure 4.
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The three main regions of Indochina are defined as the Truong Son, Loei-Phetchabun, and Kontum terranes. The aim of this review is to integrate numerous petrological studies with sedimentary, palaeontological, and provenance studies in order to construct a preliminary tectonic model which shows the terranes docked in the earliest Carboniferous (Tru...
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Based on multiple datasets and methods, this study reveals a close relation between the South China Sea summer monsoon (SCSSM) onset and the occurrence frequency of extreme rainfall over Southeast Asia (including the Indochina Peninsula, Hainan Island, and Philippines) in May. Specifically, an early SCSSM onset tends to be accompanied by a higher c...
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... The north-south trending Loei fold belt (or Loei-Phetchabun Terrane) is considered as the western and southwestern part of the Indochina Terrane (Burrett et al., 2021). Tropical Permian limestones belonging to the histories of the terranes, platforms and the basin are still controversial (e.g., Helmcke, 1985;Chutakositkanon et al., 1999;Chonglakmani and Helmcke, 2001;Metcalfe, 2002Metcalfe, , 2011Ueno and Charoentitirat, 2011;Burrett et al., 2014). ...
... These ages are also helpful in resolving the timing of Indosinian Ⅰ, Ⅱ, and Ⅲ events. Furthermore, the Indosinian Orogeny within the Indochina Block is interpreted to have been related not only to collision between the South China and Indochina blocks but also to Paleo-Tethyan subduction beneath the Indochina Block (Barber et al., 2011;Minezaki et al., 2019;Burrett et al., 2021;Morley et al., 2022). In this study, we provide new insights into Indosinian Ⅰ, Ⅱ, and Ⅲ events, based on the depositional process and age of the conglomerates overlying Indosinian Ⅰ, Ⅱ, and Ⅲ ...
... Regional map of Eastern Tibet, western China, and SE Asia, showing key geological units, tectonic terranes and the main Cenozoic strike-slip faults that are the focus of this study. Fault patterns are updated and modified from Morley (2013), geology and terranes are modified from Searle et al. (2017) and Burrett et al. (2021). Zahirovic et al., 2016). ...
... The numerous accreted continental fragments of SE Asia (e.g. Metcalfe, 2013;Hall, 2012;Morley, 2018;Burrett et al., 2021) offer many potential suture zones, and juxtaposed regions of different strength crust (5) for strike-slip faults to follow (Figs. 1, 11 and 12). While some of the sutures are long and linear, many are relatively short, vary in orientation, are highly deformed, and are also intruded by granitic plutons, rendering them mechanically highly heterogenous. ...
Cenozoic strike-slip faults in Indochina were initially interpreted as related to SE expulsion of rigid blocks of continental crust between narrow, high-displacement strike-slip faults away from the Himalayan Orogen. Revision of this view indicates four main stages of development are present. The main ‘rigid’ block of Indochina actually underwent extensive, widespread Paleogene transpressional deformation during stage 1, involving pervasive strike-slip faulting, folding, structural inversion, sub-horizontal mid-lower crustal shearing, and widespread exhumation of several kilometres. This stage is associated with ∼E-W oriented maximum horizontal stress (SHmax) (modern orientation). The three subsequent stages are: 2) 30–27 Ma transition, with retreat of transpressional deformation to the SE Tibetan Plateau, 3) 27–17 Ma onset of major sinistral displacement on ASRRSZ, 4) <17 Ma-present, diachronous reversal of motion on many faults, and cessation of extension in Thailand rifts. SHmax orientations evolved dominantly to between NE-SW and NW-SE orientations. Stage 4 is strongly linked with growth of the Tibetan Plateau, the modern GPS field, stress state, and geophysically-defined orientations of crustal and mantle flow. Five different strike-slip provinces have been identified for the post 30 Ma period, based on variations in structural style and kinematics caused by interacting factors including: 1) distance from the East Himalayan Syntaxis, 2) strength variations within SE Asian lithosphere, 3) pre-existing crustal fabrics 4) proximity to key regions contributing to the stress-state of SE Asia, 5) crustal and/or mantle flow. Whether the strike-slip faults are a product of a top- or bottom- driven system remains uncertain. Probably, the system is a hybrid.
... Of particular interest is the evolution of the Indochina terrane as it was affected by multiple collisional and accretionary events related to the subduction of the Paleotethys Ocean (Sone and Metcalfe, 2008;Hutchinson, 2014;Metcalfe, 2017;Faure et al., 2018;Wang et al., 2018;Tran et al., 2020;Waight et al., 2021). During the Early Triassic, the Indochina terrane collided and accreted to the South China Block whereas during the Late Triassic it was affected by collision and accretion of the Sukhothai and Sibumasu terranes (Lepvrier et al., 2008;Burrett et al., 2021;Jiang et al., 2021). Furthermore, the Paleo-Pacific plate subducted beneath the Indochina terrane beginning in the Early Cretaceous and was responsible for the generation of widespread Cordilleran Batholiths throughout the Dalat-Kratie Fold Belt of southern Vietnam and eastern Cambodia (Nguyen et al., 2004a;Nguyen et al., 2004b;Shellnutt et al., 2013;Cheng et al., 2019;Hennig-Breitfeld et al., 2021;Nong et al., 2021;Nong et al., 2022). ...
... The Indochina Block is bounded to the northeast by the Ailaoshan-Song Ma suture and to the west by the Sukhothai-Chanthaburi arc and the Paleo-Tethys suture. The block is generally divided into several tectonic zones: the Truong Son Fold Belt (Laos and western Vietnam) and Kontum massif (central Vietnam) along its eastern margin, the Loei Fold Belt (western Cambodia, Thailand and eastern Myanmar) along the western margin and the Dalat-Kratie Fold Belt (eastern Cambodia and southern Vietnam) in the south (Hutchinson, 2014;Metcalfe, 2017;Burrett et al., 2021). ...
... Subsequent deformation and metamorphic overprinting on the Truong Son and Kontum rocks suggests that the accretion of the Indochina Block to the Eurasia margin occurred during the Early Triassic (260-240 Ma; Carter et al., 2001;Lepvrier et al., 2004;Roger et al., 2007). The Loei Fold Belt is composed of a succession of carbonates and metamorphosed tuffaceous rocks, intruded or overlain by Silurian to Late Cenozoic igneous rock (Wang et al., 2018;Burrett et al., 2021;Shi et al., 2021). ...
Mesozoic granitic plutons are found throughout the Indochina terrane of eastern Cambodia and southern Vietnam. The granitic rocks range in age from Early Triassic (240 Ma) to Late Cretaceous (80 Ma) and record distinct tectonomagmatic periods associated with subduction of the Paleotethys and Paleo-Pacific oceans. Samples collected from the Snoul pluton, eastern Cambodia are composed of silicic and intermediate dioritic rocks, and basalt. The quartz diorites and diorites are magnesian, metaluminous, calcic to calc-alkalic, and similar to volcanic-arc granitoids whereas the basaltic rocks are compositionally similar to within-plate basalt. Zircon U-Pb geochronology and Lu-Hf isotopes and whole rock Sr-Nd isotopes show that the silicic rocks are Albian and isotopically juvenile (107.5 ± 0.3 Ma, 109.1 ± 0.4 Ma; εHf(t) = +7.0–+17.0; ⁸⁷Sr/⁸⁶Sri = 0.704313–0.707681; εNd(t) = +3.1–+4.9). Fractional crystallization modeling using a dioritic composition as the parental magma demonstrates that it is possible to generate the quartz diorite compositions under oxidizing (ΔFMQ +1) and hydrous (H2O = 2 wt%) conditions suggesting that they are consanguineous. The isotopically juvenile nature of the dioritic rocks and their compositional similarity (SiO2 ≥ 56 wt%, Al2O3 ≥ 15 wt%, Sr ≥ 400 ppm, Y ≤ 18 ppm, Yb ≤ 1.9 ppm) to adakitic rocks indicates that the parental magmas of the Snoul pluton were likely derived by partial melting of juvenile mafic basement rocks of the Indochina terrane. Moreover, Early Cretaceous plutonic rocks of Cambodia are isotopically distinct from plutonic rocks of similar age and tectonic setting from Vietnam suggesting that there could be a lithotectonic domain boundary within the Southern Indochina terrane. In contrast, the basaltic rocks likely record a temporally distinct period of magmatism associated with Late Cenozoic tensional plate stress.
... The scarcity of Devonian magmatic rocks in South China but abundant coeval zircons in the southeastern South China basins raises a question on the potential sediment provenance (e.g., Hara et al., 2010;Li et al., 2012;Nie et al., 2016;H.R. Zhang et al., 2016;Hu et al., 2015Hu et al., , 2017Wang et al., 2017;Duan et al., 2018;X.C. Zhang et al., 2019;Liu et al., 2020;Burrett et al., 2021). For example, Li et al. (2012) surmised that the ~370 Ma zircon grains in the Late Permian strata of the Yongding Basin were sourced from local crustal uplifts due to the "Huinan Movement", but no coeval igneous rocks have been identified in SE China. ...
... In addition, it is well known that the North Qiangtang and Simao-Indochina blocks were dispersed northward from Gondwana in the Devonian due to the opening the Paleo-Tethys, and the southern Hainan and the East Malaya were thought to be part of the Indochina block and the continuation of the Sukhothai arc (on the margin of Indochina Block), respectively Cai and Zhang, 2009;Metcalfe, 2013Metcalfe, , 2017Faure et al., 2016Faure et al., , 2017He et al., 2020). Thus, these above-mentioned blocks were all located on the northern margin of the Paleo-Tethys, suggesting that the Paleo-Tethys may have subducted northward beneath the North Qiangtang, Simao-Indochina, southern Hainan, and generated volcanism on the overlying plate in the Late Devonian ( Fig. 9b; Nie et al., 2016;Metcalfe, 2017;Liu et al., 2020;Burrett et al., 2021). This conclusion can be further supported by the sedimentary records that numerous 400-350 Ma detrital zircons/monazites (peak age at ~370 Ma) are widespread in the Permian-Early Triassic sedimentary rocks (Fig. 7h), and in the modern river sediments in the Simao-Indochina Block (Yokoyama et al., 2010;Bodet and Schärer, 2000;Wang et al., 2014;Xing et al., 2016;Arboit et al., 2016;Li et al., 2021). ...
As a major boundary between the Simao-Indochina and South China blocks, the Jinshajiang–Ailaoshan–Song Ma suture zone preserves the remnants of a back-arc basin or a branch of the Paleo-Tethys Ocean. However, whether this suture zone extends eastward to the Hainan Island is still controversial. Here, we use detrital zircon U–Pb geochronology to explore the source-to-sink characteristics of the Lower Carboniferous-Lower Permian strata in Hainan Island and mainland southeast China (SE China). The results, combined with published data for the Devonian-Triassic sandstones from Hainan and SE China, show that the Devonian-Lower Permian samples display similar detrital zircon age populations at ∼430 Ma, ∼930–980 Ma, ∼1600–1800 Ma and ∼2400 Ma. However, the Upper Permian-Triassic sandstones have a predominant zircon population at ∼370 Ma, indicating a dramatic change in the detritus provenance for Hainan-SE China since the early Late Permian. The presence of similar 400-350 Ma detrital zircons peaked at ∼370 Ma with ɛHf(t) values from −12 to +3 in the sedimentary rocks from both Hainan-SE China and Simao-Indochina blocks indicates that these two terranes should have a similar detritus source with abundant Late Devonian magmatic rock exposure during the Late Permian-Triassic. These Late Devonian magmatic rocks were most likely formed by the north-dipping Paleotethyan subduction. This conclusion is consistent with the recent discovery of Upper Devonian arc-related tuffs, volcaniclastics, tuffaceous chert and rhyolite in the North Qiangtang, Simao-Indochina and East Malaya terranes, and possibly also in the southern Hainan. These Upper Devonian rocks could have acted as detritus source for the basins in SE China-Hainan, as well as the Youjiang Basin in SW China, after the collision between the Indochina and South China blocks. Combined with the transition from a carbonate platform to clastic facies in the early Late Permian in SE China, the Indochina-South China collision on Hainan Island may have occurred at ∼266-260 Ma, earlier than that (∼250-230 Ma) along the Jinshajiang–Ailaoshan–Song Ma suture zone. Such a temporal–spatial source-to-sink relationship between the Late Devonian arc and basins on the southern margin of South China suggests that SE China-Hainan should be located within the Paleo-Tethys rather than the Paleo-Pacific tectonic domain during the Early Carboniferous-early Late Permian.
... The Indochina Terrane is a major tectonic unit of mainland Southeast Asia and is made up of several tectonic domains, volcanic arcs, and suture zones (Charusiri et al., 2002;Metcalfe, 2002;Lepvrier et al., 2004;Burrett et al., 2021). The Tam Ky-Phuoc Son and Poko suture zones mark the tectonic collision between the main part of the Indochina Terrane and the Kontum Massif in central Vietnam and southeastern Laos, respectively (Figure 1; Lepvrier et al., 2004Lepvrier et al., , 2008Tran et al., 2014). ...
The Vangtat deposit is the major gold deposit in a new orogenic gold belt dis- covered and developed in southeastern Laos in the past two decades. Our study of the Vangtat orogenic gold deposit shows that it formed within a convergent margin along the western segment of the Poko suture zone, which marks the collision between the Indochina Terrane and the Kontum Massif. Shear structure and greenschist facies metamorphic rocks are the main hosts for gold mineralization in the Vangtat deposit. High-grade gold-bearing quartz-sulfide veins and wall rock hydrothermal alteration are genetically related, and alteration minerals consist of quartz, carbonate, graphite, white mica, chlorite, and pyrite. The study of fluid inclusions and wall rock alteration assemblages indicate that the Vangtat gold deposit was formed by an aqueous-carbonic, low salinity, reduced, weakly alkaline to near-neutral pH fluid, mainly composed of H2O, NaCl, CO2, CH4, N2, H2S, H2, O2, Si, and K. Gold was predominantly carried as a sulfide complex. The precipitation of gold is related to wall rock sulfidation and the further reduction with the carbon-bearing host rock. The correlation between trapping temperature obtained from arsenopyrite geothermometry (360–395�C) and homogenization temperature obtained from primary fluid inclusion microthermometry (240–250�C), indicates a pressure and depth range for the Vangtat deposit of 380–420 MPa and 11–13 km, respectively. Gold appears as inclusions mainly in pyrite, and auriferous pyrite is homogeneous in textural, chemical, and sulfur isotopic composition. Auriferous pyrite δ34S values range from +4 to +6‰, which is compatible with the δ34S composition of igneous rocks. Together with cobalt/nickel ratios from the Vangtat auriferous pyrite, which are significantly greater than one (avg. 6.3), we suggest that mafic-ultramafic rocks in the geologic basement of the Vangtat deposit are the plausible source of hydrothermal gold and sulfur. The formation of this orogenic gold deposit is associated with metamorphic dehydration and devolatilization that transported gold to the site of deposition.
... The core of the Indochina plate is a relatively stable Precambrian crustal block that underlies most of south-central Vietnam, Cambodia, southern Laos, and the Khorat Plateau of eastern Thailand (Sone and Metcalfe, 2008;Burrett et al., 2014). It is flanked to the NE and west by terranes that were accreted to the core during a complex series of Paleozoic to Triassic collisional and rifting events (Burrett et al., 2021). The northeastern margin is defined by the Song Ma suture where the South China plate was welded to Indochina in the Early to Middle Triassic (Zhang et al., 2013;Faure et al., 2014Faure et al., , 2016Faure et al., , 2018. ...
The Ban Don Group (BDG) of south-central Vietnam and NE Cambodia significantly constrains the Jurassic tectonic history of the SE Indochina plate margin. The Early to Middle Jurassic BDG comprises internally conformable marine shales and sandstones with a high volcaniclastic content, bounded below and above by major unconformities, deposited in a NW-SE trending basin. A contractional fold belt developed in the basin during the latest Middle to Late Jurassic. Folds are upright, planar, doubly plunging, and lack systematic vergence. Thrust faults are seldom observed. The Ban Don Fold Belt (BDFB) is 350 km long and 240 km wide. It forms an arcuate salient towards the foreland to the NW with nearly a 90° change in fold trend orientation and an estimated average shortening of 37%. The change in fold orientation follows sedimentary facies boundaries, which parallel the depositional basin margins. The NW-trending BDG basin axis forms a line of symmetry for the facies boundaries and fold trends. An analog for the upright fold-dominated, low-taper wedge of the BDFB is the Parry Islands Fold Belt (salt detachment). However, the absence of salt in the BDFB suggests a very weak detachment was facilitated by high fluid pressures in the basal shales. Deposition and deformation of the BDG plus recently published regional data indicate the well documented Late Jurassic and Cretaceous Andean-type margin of Southeast Asia also existed during the Early and Middle Jurassic. The BDG reflects back-arc deposition with subsequent deformation driven by changes in subduction angle and/or subduction obliquity during the Jurassic. Alternatively, the arcuate geometry of the BDFB is also compatible with the collision of a small indenter.
High‐grade metamorphic rocks are widely exposed along the SE–NW‐ to E–W‐trending shear zones in the Truong Son Belt, Central Vietnam, but few petrological studies have been conducted in this area. Herein, we report the occurrence of mylonitized granulites that crop out along the Dai Loc shear zone in the southernmost Truong Son Belt. Detailed petrographic analysis, geochemistry and P–T–t estimates of the evolution of two granulite samples are presented to elucidate the formation processes of these high‐grade metamorphic rocks. The results indicate that the rocks underwent two distinct metamorphic cycles. The first cycle (M1) is characterized by coarse‐grained granulite mineral assemblages, defining a tight clockwise P–T path with near‐isobaric heating to a near ultrahigh‐temperature peak at low pressure, followed by cooling. The prograde mineral assemblage (M1a) is indicated by inclusions of cordierite + sillimanite + biotite + quartz + spinel ± plagioclase in coarse‐grained garnet, orthopyroxene and cordierite. The mineral assemblage of garnet + orthopyroxene + cordierite + plagioclase + K‐feldspar + ilmenite + melt ± biotite (M1b) defines the peak P–T conditions of 5.3–6.3 kbar and 850–920°C. Post‐peak cooling (M1c) is marked by the formation of quartz + biotite symplectites around garnet and orthopyroxene. The second cycle involved medium‐pressure amphibolite facies metamorphism (M2), characterized by domainal development of fine‐grained kyanite‐bearing mineral associations. Petrographic observations indicate that these fine‐grained associations were formed during mylonitization. Zircon U–Pb dating reveals that the timing of granulite facies metamorphism appears to be coeval with the intrusion of a post‐collisional granitoid at 430–410 Ma. Granulite facies metamorphism and crustal melting were probably driven by asthenospheric mantle upwelling triggered by slab breakoff during the Early Palaeozoic. Considering previous structural and geochronological studies, the second metamorphic event likely occurred during the Triassic Indosinian orogeny.
