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Tuff‐bearing upper Cambrian to lowermost Ordovician strata on Ko Tarutao island, Satun province, southernmost peninsular Thailand, contain a rich trilobite fauna relevant to global biostratigraphy, peri‐Gondwanan palaeogeography and shifting evolutionary mode. This area of Sibumasu, a lower Palaeozoic marginal Gondwanan terrane, is shown to have been closely associated with Australia, North China (Sino‐Korea) and other continental fragments from the supercontinent's northern equatorial sector, including South China at that time. Shared faunas also suggest a Kazakhstani and Laurentian association. Collections from eight sections yielded 10 newly discovered species and one new genus from ancient shoreface and inner shelf siliciclastic deposits. With the new taxa and revision of taxa known previously, we refine the age of the upper two formations of the Tarutao Group to the middle of Cambrian Stage 10, and lower–middle Tremadocian. Two biozones are erected for Sibumasu: the Eosaukia buravasi Zone, encompassing all Cambrian sections from Ko Tarutao, and the Asaphellus charoenmiti Zone, encompassing the Tremadocian fauna discussed herein. The new genus is Tarutaoia and new species are Tsinania sirindhornae, Pseudokoldinioidia maneekuti, Pagodia? uhleini, Asaphellus charoenmiti, Tarutaoia techawani, Jiia talowaois, Caznaia imsamuti, Anderssonella undulata, Lophosaukia nuchanongi and Corbinia perforata. Other taxa reported for the first time from Tarutao are Mansuyia? sp., Parakoldinioidia callosa Qian, Pseudagnostus sp., Homagnostus sp., Haniwa mucronata Shergold, Haniwa sosanensis? Kobayashi, Lichengia simplex Shergold, Pacootasaukia sp., Wuhuia? sp., Plethopeltella sp., Apatokephalus sp., Akoldinioidia sp. 1 and Koldinioidia sp. [ABSTRACT FROM AUTHOR]

The Mae Ping shear zone (MPSZ), a major shear zone trending NW-SE in Thailand, is responsible for the left-lateral displacement of the N-S Triassic-Jurassic granitoid and gneiss belt. This displacement is postulated to have contributed to Cenozoic extrusion tectonics. Within the Lan Sang National Park, the MPSZ exposes several intensely deformed lithologies, collectively known as the Lan Sang gneisses. These gneisses have attracted considerable attention for their potential to substantiate the extrusion model. However, the timing of the emplacement of the orthogneiss protolith is still debated. Moreover, the origin and distribution of the Eocene syn-shearing granodiorite within this shear zone are not well understood. To shed light on the magmatic history of the MPSZ, this study utilized zircon U-Pb geochronology to systematically investigate the Lan Sang gneisses. Our findings demonstrate that these gneisses can be categorized into paragneiss and orthogneiss groups. Paragneiss samples feature zircons displaying rounded detrital cores ranging from 3,078 to 450 Ma, with metamorphic rim overgrowth of ca. 200 Ma (most Th/U

We present a regional thermal structure as well as a new crustal thickness model beneath the Peninsular Malaysia and the surrounding regions. Curie point depth estimates for the entire area range between ∼ 17 – 46 km with a mean of 29 km. The estimated crustal thickness for the study area varies from ∼ 28 – 35 km with an average of ∼ 31 km. Uplifted Curie depths (20 – 25 km) and deeper Moho depths (30 – 34 km) are observed over most parts of Peninsular Malaysia continent. In contrast, the NW Peninsular Malaysia continent and the southern Thailand are characterized by deeper Curie depths between 30 and 40 km. These regions with deeper Curie depths are coincident with the oldest dated rocks on the Sibumasu terrane. The observation of larger Curie depths in NW Peninsular Malaysia implies that the region is presently thermally stable than the remaining parts of the Peninsular. Consistent with deeper crustal thickness (30 – 35 km), the west Sumatra block yields the deepest Curie point depth that ranges between 30 and 46 km. The west Sumatra block and the NW Peninsular Malaysia have low Bouguer anomalies and comparable crustal thickness indicating similarity in regional features. This suggests that these regions are linked by a common ancient continental core. A comparison between the Curie depths and crustal thickness shows that the upper mantle beneath the Island of Sumatra, Singapore, Malay basin, NW Peninsular Malaysia continent, and southern Thailand are significantly magnetized.

[Display omitted] • Cassiterite U–Pb data indicate that the Haobadi Sn deposit occurred at late Cretaceous. • Zircon U–Pb data indicate granites outcropped at Haobadi was formed at the late Triassic. • Late Cretaceous Lvyintang pluton in the southeastern of Haobadi would be associated with Sn mineralization. The Late Cretaceous marks a significant period for tin mineralization in the Sibumasu block. Although the Baoshan block has been considered as the northern extension of the Sibumasu block, the genetic connection of tin mineralization remains unclear due to a lack of robust age data. To address this issue, we present cassiterite and zircon U–Pb geochronological data in the Haobadi tin deposit in the northern Baoshan block. This deposit is hosted by the Triassic sedimentary rocks intruded by the Triassic Lailitoushan pluton with zircon U–Pb ages ranging from 219.1±1.3 Ma to 215.7±1.4 Ma. Cassiterite U–Pb data indicate that tin mineralization occurred at 75.5±2.7 Ma. Notably, zircons from the Lvyintang pluton yield zircon U–Pb ages of 75.6±0.6 Ma and 77.4±0.5 Ma for the biotite granite and two-mica granite, respectively. Zircon trace element compositions indicate that the two-mica granite is more evolved and has lower magmatic oxygen fugacity than the biotite granite. These data indicate that Haobadi tin mineralization is not linked to the Triassic Lailitoushan pluton but associated with the Late Cretaceous granite such as the Lvyintang two-mica granite. The Late Cretaceous tin mineralization observed in the Baoshan block is attributed to the eastward subduction of the New-Tethys Ocean. Given the paramount importance of the Late Cretaceous episode in tin mineralization within the Baoshan block, more attention in future ore exploration should be paid. [ABSTRACT FROM AUTHOR]

Abstract New geochronological and geochemical data document a new and widely distributed succession of igneous and sedimentary rocks within the Sibumasu that extend from SW Yunnan through SE Asia as far as Sumatra. Our data revealed the presence of an Ordovician‐Silurian (mainly ∼490–430 Ma) igneous zone. The early Paleozoic granites in the zone display similar elemental and Sr–Nd–Pb–Hf isotopic compositions. They were derived from a common mixed source of ancient crustal materials with a juvenile component and formed in a subduction‐related setting. Detrital‐zircon U‐Pb apparent ages from the previously defined Precambrian Lancang and Ximeng units in the SW Yunnan portion of the Sibumasu are in the range of 3,306–428 Ma and 3,316–512 Ma, with the youngest age‐peaks of 505 Ma and 447 Ma, respectively, indicating the lower Paleozoic (Cambrian‐Silurian) sedimentary sequences. The Tarutao Unit and its equivalents in the SE Asia portion of the Sibumasu yield the U‐Pb apparent ages of 3,177–510 Ma, suggesting the maximum deposited time being Cambrian‐Ordovician. All these detrital zircon U‐Pb ages define two main peaks of ∼554–528 Ma and 964–905 Ma with εHf(t) values similar to those in the Qiangtang, Tethyan Himalaya, and eastern Indochina. The lower Paleozoic detritus in the Sibumasu were likely derived from the India‐Antarctica region of East Gondwana. We propose that the late Cambrian‐Silurian units formed in an outward‐propagating accretionary orogen in response to the consumption of the Prototethyan Ocean in SW Yunnan and SE Asia. Sibumasu might represent a part of the easterly migrating accretionary orogen along the northern margin of East Gondwana in the late Cambrian‐late Silurian.

New geochronological and geochemical data document a new and widely distributed succession of igneous and sedimentary rocks within the Sibumasu that extend from SW Yunnan through SE Asia as far as Sumatra. Our data revealed the presence of an Ordovician‐Silurian (mainly ∼490–430 Ma) igneous zone. The early Paleozoic granites in the zone display similar elemental and Sr–Nd–Pb–Hf isotopic compositions. They were derived from a common mixed source of ancient crustal materials with a juvenile component and formed in a subduction‐related setting. Detrital‐zircon U‐Pb apparent ages from the previously defined Precambrian Lancang and Ximeng units in the SW Yunnan portion of the Sibumasu are in the range of 3,306–428 Ma and 3,316–512 Ma, with the youngest age‐peaks of 505 Ma and 447 Ma, respectively, indicating the lower Paleozoic (Cambrian‐Silurian) sedimentary sequences. The Tarutao Unit and its equivalents in the SE Asia portion of the Sibumasu yield the U‐Pb apparent ages of 3,177–510 Ma, suggesting the maximum deposited time being Cambrian‐Ordovician. All these detrital zircon U‐Pb ages define two main peaks of ∼554–528 Ma and 964–905 Ma with εHf(t) values similar to those in the Qiangtang, Tethyan Himalaya, and eastern Indochina. The lower Paleozoic detritus in the Sibumasu were likely derived from the India‐Antarctica region of East Gondwana. We propose that the late Cambrian‐Silurian units formed in an outward‐propagating accretionary orogen in response to the consumption of the Prototethyan Ocean in SW Yunnan and SE Asia. Sibumasu might represent a part of the easterly migrating accretionary orogen along the northern margin of East Gondwana in the late Cambrian‐late Silurian. Key Points: An Ordovician‐Silurian (∼490–450 Ma) igneous zone extends from SW Yunnan through SE Asia to SumatraThe Ordovician‐Silurian sedimentary sequences are extensively identified in SW Yunnan and SE AsiaAn outward‐propagating Ordovician‐Silurian orogenesis developed, which resulting from the Prototethyan consumption [ABSTRACT FROM AUTHOR]

The Baoshan region of Yunnan Province, SW China, is one of the best locations to study Wenlock to Pridoli conodonts in China. Detailed analysis of conodont collections from the Silurian strata (the "Lichaiba" and Niushiping formations) of the Laojianshan section in the Baoshan region resulted in revised dating of the section. In stratigraphically ascending order, the Pterospathodus amorphognathoides amorphognathoides Zonal Group, the Pterospathodus pennatus procerus Superbiozone (probably only the Lower Pterospathodus pennatus procerus Biozone), the Ozarkodina sagitta sagitta Biozone, the Kockelella ortus absidata Biozone, the Kockelella crassa Biozone, the Polygnathoides siluricus Biozone and the "Ozarkodina" eosteinhornensis s.l. Interval Biozone are recognised. The conodont faunas recovered indicate that the "Lichaiba Formation" corresponds to the upper Telychian–upper Wenlock, and the Niushiping Formation to the Ludlow–Pridoli. Part of the Ireviken Event, that is, from Datum 3 to Datum 4 can be recognised from the studied section. The late Telychian conodont fauna from the Laojianshan section is characteristic of distal, open‐shelf depositional environments. [ABSTRACT FROM AUTHOR]

A 'top-to-the-east' ultramylonite zone is identified in north-eastern Kuala Lumpur and named here as the 'Ukay Perdana Shear Zone (UPSZ). The UPSZ is at least 250-300 m thick, east-verging, and superimposed on the later stages of assembly of the c. 200 Ma S-type 'Western Belt' granite plutons generated by crustal thickening and assigned to the Main Range Granite Province. Younger bodies of S-type granitic rocks cut the shear zone. These intensely deformed quartzofeldspathic rocks contain distinctive relict porphyroclasts of perthitic K-feldspar (microcline), oligoclase and quartz, entrained within the ultramylonitic fabric. Migrating sub-grain boundaries in quartz indicate deformation occurred under moderate to high temperature conditions during ductile deformation (c. 500-600°C); undulose extinction suggests down-temperature evolution of the deformation history. This deformation event implies that the final stages of collisional interaction between Sibumasu and the Sukhothai Arc would have involved now east-directed (080°N, then generally northward) over-thrusting of the leading edge of Sibumasu onto the Sukhothai Arc/Indochina-East Malaya margin after 198 ±2 Ma. Kenny Hill Formation strata in Kuala Lumpur preserve widespread evidence of a dominant phase of E- or ENE-verging, upward-facing fabrics and folds; that deformation is judged to be a hanging wall response to deformation in the UPSZ. This early-Mesozoic structural framework is significant during assembly of the Peninsular Malaysia region of Sundaland; evidence form Kuala Lumpur is combined with new published Singapore data. Dextral strike-slip tectonics is superimposed on this collisional framework in the later Mesozoic and Cenozoic; subsurface development across Peninsular Malaysia, and in Kuala Lumpur and Singapore in particular, should account for deformation structures linked with this expanded record of Mesozoic tectonics. [ABSTRACT FROM AUTHOR]

Continental rift-related magmatism provides important clues to continental rifting and breakup, but the petrogenesis and geodynamic processes remain debatable. Here we report a detailed study on zircon and apatite U Pb dating, whole-rock geochemistry, and Sr-Nd-Hf isotopes for the hornblende gabbros in northern Thailand. Zircon and apatite U Pb age data reveal emplacement of the hornblende gabbros at ca. 290 Ma. The hornblende gabbros are alkaline in composition and characterized by slight negative Nb-Ta-Zr-Hf and marked negative Ti anomalies. They have enriched Sr-Nd-Hf isotopic values [whole-rock (87Sr/86Sr) i = 0.705970–0.706756; ε Nd (t) = +0.1 to +0.7; zircon ε Hf (t) = +0.2 to +9.2]. Their geochemical affinities to within-plate basalts suggest a continental rifting setting. These combined features reveal that the hornblende gabbros in northern Thailand originated from a subcontinental lithospheric mantle previously modified by subducted sediments. Our results combined with published data indicate that the continental rift-related magmatism in the Sibumasu Block took place over a long period of ca. 309–282 Ma. We suggest that the slab pull force of the Paleo-Tethys oceanic lithosphere is a likely mechanism for the Late Carboniferous-Early Permian magmatic event in the passive margin of the Sibumasu Block. [Display omitted] • Early Permian hornblende gabbros occur in the Sibumasu Block, northern Thailand. • The gabbros derived from lithospheric mantle modified by subducted sediments. • The gabbros formed in a continental rifting setting. • Slab-pull force of the Paleo-Tethys Ocean induced continental rifting. [ABSTRACT FROM AUTHOR]

The Middle to Late Ordovician sedimentary records are of great interest because they potentially contain critical signatures about triggers of the Great Ordovician Biodiversification Event and the Late Ordovician Mass Extinction. A long climate cooling has been proposed by some scholars, which may have initiated in Middle Ordovician and eventually culminated in the Late Ordovician (Hirnantian) glaciation; however, the origin, frequency, magnitude and duration of this cooling-glaciation event are still in debate. A sedimentary and multi-stratigraphic study of the Middle to Late Ordovician transition records may help reveal the evolutionary history of this great climate change. Here we document and correlate the sedimentary facies, conodont biostratigraphy and carbon isotope chemostratigraphy of latest Darriwilian through early Katian limestone successions in the Kanchanaburi area of western Thailand and in South China. This correlation reveals two remarkably cross-regional transgression events and their following sea-level highstand periods. The first transgression happened in the latest Darriwilian, leading to the deposition of the Tha Manao Formation of restricted carbonate facies at the Nautiloid Site Geopark in Thailand, Sibumasu Terrane, and the Miaopo and chert-rich Hulo formations of black shale facies in South China. The second transgression was initiated in the earliest Katian, forming the extensively distributed open-marine carbonates of the Pa Kae and Pagoda formations in platform settings, and the debrite-rich, deep-water carbonate of the Yenwashan Formation in slope settings. We also document coupled changes in depositional facies and carbon isotopic compositions, showing that the rising limb of the Guttenberg Isotopic Carbon Excursion (GICE) co-occurred with the second transgression period. The South China and Thailand Sibumasu records are comparable to those of many North American successions, indicating a presumably global sea-level rise in the early Katian, which may have been caused by the waning of the potential Darriwilian–Sandbian icecaps. • Correlation of facies and carbon isotope variations of Middle to Upper Ordovician. • First identification of GICE in Thailand, Sibumasu Terrane. • Two transgression events are recognized during late Darriwilian to early Katian. • Waning of icecaps may lead to the earlist Katian transgression and trigger GICE. [ABSTRACT FROM AUTHOR]

Abstract: Sibumasu is inferred to have developed as a united terrane in East Gondwana, with West Sumatra linked to Cathaysia. New detrital zircon U‐Pb and Hf isotopic data from Sumatra, complemented by literature data, challenge the above views. The scarcity of early Neoproterozoic zircons in West Sumatra argues against a direct connection between West Sumatra and Cathaysia. Detrital zircons from East Sumatra exhibit age profiles similar to those of Lhasa, West Burma, and Western Australia, with detritus most probably sourced from Western Australia. By contrast, Sibusima (Sibumasu excluding East Sumatra) shows detrital zircon age patterns resembling those of the South Qiangtang and the Tethyan and High Himalaya terranes, whose detrital materials are most likely derived from northern India. Our observations require disaggregation of Sibumasu and a new configuration of northern East Gondwana in the early Paleozoic, with East Sumatra and West Burma occupying a position outboard the Lhasa terrane along the NW Australian margin and Sibusima situated on the northern Greater Indian margin. [ABSTRACT FROM AUTHOR]

The Ordovician and Silurian of the Baoshan and Mangshi regions in western Yunnan Province, SW China, have long been regarded as being continuous and representative of the Sibumasu terrane. However, our recent biostratigraphical investigations of three Katian to Llandovery sections of predominantly clastic facies reveal a significant, largely correlative disconformity within the Upper Ordovician. These sections include the Laojianshan and Feida Storehouse sections in Baoshan, and the Shaodihe section in Mangshi. In the Baoshan region, the disconformity lies at the base of the overlying Jenhochiao Formation and spans a time interval from earliest late Katian (Dicellograptus complexus Biozone) to early Hirnantian (lower Metabolograptus extraordinarius Biozone), as constrained by the trilobites and brachiopods from the underlying strata and the graptolites from the overlying strata. In the Mangshi region, the disconformity lies at the base of the overlying Wanyaoshu Formation, spanning nearly the entire late Katian (Dicellograptus complexus Biozone to lower Paraorthograptus pacificus Biozone), as constrained by graptolites, trilobites and brachiopods from underlying and overlying beds. A considerably diverse, typical Hirnantia fauna occurs in the Wanyaoshu Formation, which is correlated with the same fauna from the Kuanyinchiao Formation in the Yangtze region, South China, and its equivalents elsewhere. A weathering crust of 10–20 cm in thickness occurs ubiquitously in both regions, in association with the disconformity. This stratigraphical gap within the Upper Ordovician in western Yunnan is probably resulted from the abrupt sea‐level drop induced by Late Ordovician Glaciations, or alternatively and less likely result from a regional tectonic uplift in northern Sibumasu terrane. [ABSTRACT FROM AUTHOR]

The South-East Asian Tin Belt is one of the most tin-productive regions in the world. It comprises three north-south oriented granite provinces, of which the arc-related Eastern granite province and the collision-related Main Range granite province run across Thailand, Singapore, and Indonesia. These tin-producing granite provinces with different mineral assemblages are separated by Paleo-Tethyan sutures exposed in Thailand and Malaysia. The Eastern Province is usually characterised by granites with biotite ± hornblende. Main Range granites are sometimes characterised by the presence of biotite ± muscovite. However, the physical boundary between the two types of granite is not well-defined on the Indonesian Tin Islands, because the Paleo-Tethyan suture is not exposed on land there. Both hornblende-bearing (previously interpreted as I-type) and hornblende-barren (previously interpreted as S-type) granites are apparently randomly distributed on the Indonesian Tin Islands. Granites exposed on Bangka, the largest and southernmost Tin Island, no matter whether they are hornblende-bearing or hornblende-barren, are geochemically similar to Malaysian Main Range granites. The average ɛ Nd (t) value obtained from the granites from Bangka (average ɛ Nd (t) = −8.2) falls within the range of the Main Range Province (−9.6 to −5.4). These granites have SIMS zircon U-Pb ages of ca. 225 Ma and ca. 220 Ma, respectively that are both within the period of Main Range magmatism (∼226–201 Ma) in the Peninsular Malaysia. We suggest that the granites exposed on Bangka represent the continuation of the Main Range Province, and that the Paleo-Tethyan suture lies to the east of the island. [ABSTRACT FROM AUTHOR]

The “Panghkawkwo graptolite bed” is shown to comprise several graptolitic horizons extending through the Aeronian (middle Llandovery) and into the lower Telychian (upper Llandovery). Graptolite assemblages are diverse indicating an outer shelf (or deeper) depositional environment. They are similar to those of Bohemia and Saudi Arabia (peri-Gondwanan Europe and core Gondwana respectively), but include also taxa ( Agetograptus and species of Metaclimacograptus ) not known from these regions, but which characterize lower latitude Llandovery graptolite assemblages. The evidence for the Silurian location of the Sibuma(su) Terrane is discussed. The presence of Monograptus belophorus and Cyrtograptus rigidus in the lower Sheinwoodian (Wenlock) of western Yunnan suggests a non-equatorial palaeolatitude. The Panghkawkwo graptolites suggest a location for Sibuma(su) between Gondwana and South China. [ABSTRACT FROM AUTHOR]

The orogenic petrological processes associated with the amalgamation of Rodinia (ca. 1 Ga) and Gondwana (ca. 550 Ma) reflect distinct tectonic dynamics that might have contributed to the contrasting geochemical and biological evolution following the orogenies. In this study, we explore these differences using the time sequence analysis of geochemical proxies in the detrital zircons sourced from the margin of East Gondwana. The zircon Eu anomalies are stronger during the formation of Gondwana than Rodinia, indicating a thicker Gondwana crust than Rodinia; the hinterland of Rodinia (∼35 km) is significantly thinner than its core Grenville Province (55–60 km). The Ce to U and Ti ratio, U/Yb, and ε Hf (t) proxies suggest that the Rodinia assembly was dominated by non-arc intraplate magmatism, consistent with widespread high-temperature magmatism and protracted granulite-facies metamorphism. The thin crust and accordingly, low-elevation terrain, possibly overriding an anomalously hot mantle, limited continental weathering flux, and primary productivity in the Mesoproterozoic oceans. By contrast, the orogenies leading to the assembly of Gondwana may have proceeded in a modern-style plate tectonic manner, resulting in rapid uplift at the Gondwana margin, where voluminous clastic sediments were subsequently recycled and contributed to the post-orogenic magmatism from ca. 500 Ma. This massive crustal reworking is reflected by negative ε Hf (t) values of zircons that contrast ε Hf (t) ∼ 0 in the Mesoproterozoic. The emergence of extensive mountains accelerated erosion and delivered key nutrients that might have fueled the rapid diversification of life forms in the late Precambrian and early Paleozoic. • Zircons record Rodinian within-plate and Gondwanan arc-dominant magmatism. • Gondwanan magmas were more evolved and reflected active plate tectonics. • Distinct tectonic regimes result in a thicker Gondwana margin than that of Rodinia. [ABSTRACT FROM AUTHOR]

The micro-continental blocks in SE Asia are thought to be derived from the East Gondwana which has a basement as old as Hadean–Mesoarchean. However, such old crustal materials have not been found anywhere in SE Asia. In this paper, we report the occurrence of the Hadean–Mesoarchean crustal materials in the northern Sibumasu block, SW China. Our finding is based on inherited zircon U–Pb ages and Hf isotope model ages of co-magmatic zircon crystals from early-Paleozoic S-type granitoids in the northernmost Sibumasu. LA-ICP-MS zircon U–Pb isotopic analysis reveals that some S-type granitoids in this region formed between 468 Ma and 447 Ma. These rocks are strongly peraluminous, with high A/CNK ratios > 1.2 and normative corundum content >2 wt%, and have low CaO/Na 2 O ratios <0.3, which indicates that they formed by anatexis of metapelitic crustal rocks. The ca. 470–450 Ma S-type granitoids contain inherited zircon crystals as old as Mesoarchean (∼3.1 Ga). The ɛ Hf ( t ) values of zircon crystallized from the magmas of these rocks vary from −49 to +16, with major peaks approximately at −46, −35 and −27. The corresponding model ages for the formation of the source crust are ∼4.39 Ga, ∼3.62 Ga and ∼3.12 Ga. This, together with the discovery of ∼3.1 Ga inherited zircon in the granitoids, indicates that the northern Sibumasu block has Hadean–Mesoarchean crustal materials. A Gondwana-wide comparison of crustal formation time data reveals that these Hadean–Mesoarchean crustal materials show similar age distribution with the crusts of the Pilbara and Yilgarn Cratons, Western Australia. Their derivation analysis provides a new line of evidence for the majority view that the Sibumasu block was attached to NW Australia before its breakup from Gondwana. [ABSTRACT FROM AUTHOR]

The east flank of the Sibumasu block was a passive continental margin, and in NW Thailand is marked by the absence of the autochthonous Middle Permian–Triassic platform carbonates which are widespread across the rest of Sibumasu further west. Instead, the carbonates are represented by hemipelagic cherts, mudstones and sandstones including turbidites. During the northward drift of Sibumasu, following its Early Permian rifting from Gondwana, an accretionary complex was present where Palaeotethyan pelagic rocks as old as Devonian were subducted beneath the Sukhothai volcanic arc. At the time of Sibumasu’s collision with the Sukhothai arc, beginning in the Middle Triassic, the accretionary complex was thrust westwards across the east flank of Sibumasu. It is suggested that in the Late Triassic the thrust pile which had been the accretionary complex underwent erosion and was the source of terrigenous clastic rocks deposited further west in a foredeep basin. The boundary of Sibumasu’s east flank with the Permo-Triassic carbonate platform further west is the arcuate Mae Ping-Nam Teng Fault system. Notwithstanding later Cenozoic strike-slip displacement, those faults (as well as the Mae Yuam Fault) are interpreted to have had an earlier history of westward-directed Indosinian thrusting. Northwards in Myanmar and Yunnan the Sibumasu Permo-Triassic carbonate shelf continues as the Shan Plateau and Baoshan Block. The east flank is represented by the Changning–Menglian Belt, and the Palaeotethys ‘cryptic suture’ in Thailand possibly joins with the Lancangjiang Suture. [ABSTRACT FROM AUTHOR]

Carboniferous conodonts are reported for the first time from Myanmar (Burma). Conodont faunas representative of the Scaliognathus anchoralis and Gnathodus typicus – Protognathodus cordiformis conodont zones date the sampled Taungnyo Group south of Loi Kaw, Kayah State as late Tournaisian confirming a Mississippian (Lower Carboniferous) age for the sampled part of this stratigraphic unit. The dated strata are stratigraphically just below the Tournaisian–Visean (T-V) boundary. Tournaisian strata are thus for the first time unequivocally demonstrated in the Shan Plateau region of Myanmar. Similar conodont faunas from the T-V boundary interval in SE Asia indicate a complete stratigraphic sequence at this level in shallow-marine sequences on intra-Tethyan Cathaysian tectonic blocks (South China) and in deep-marine Palaeo-Tethyan sediments (cherts of the Inthanon suture zone, Thailand). However, in shallow-marine sequences on the Sibumasu Block, located on the NE margin of Gondwana in the Carboniferous, they demonstrate a non-sequence or unconformity at this level, also seen elsewhere in Gondwana. Biogeographic links between upper Tournaisian and early Visean conodonts on the Sibumasu Terrane and Laurentia and Eastern Australian Gondwana support a NW Australian Gondwana margin position for Sibumasu in the Late Palaeozoic. [ABSTRACT FROM AUTHOR]

Abstract: The fine clastic and siliceous sedimentary successions distributed in the Hat Yai area, southeastern peninsular Thailand were examined using radiolarian biostratigraphy, lithology, and stratigraphy. The studied succession was essentially divided into two kinds of fine-grained sedimentary rock units: the lower shale unit and the upper chert unit. The lower shale unit and the upper chert unit yielded late Middle to early Late Permian and Early to Middle Triassic radiolarians, respectively. We clarified that the sedimentary rocks distributed in the study area are not entirely Carboniferous, but contain some sediments from the Permian and Triassic. This age determination suggests that the clastic–chert succession distributed in the study area should be distinguished from the Carboniferous Yaha Formation and correlated with the Permian to Triassic Semanggol Formation. Lithological change with increasing siliceous composition was observed in the uppermost part of the lower shale unit, and the geological age based on the radiolarians indicates a nearly conformable stratigraphic relationship for the lower shale unit and the upper chert unit. The stratigraphy and lithology of the Permian to Triassic succession in the study area, together with geological correlation around southernmost Thailand and northern Malaysia, suggest that the Triassic chert should be interpreted as continental slope sediments overlying Permian clastic and/or calcareous facies, rather than typical pelagic deep-water sediments formed on an abyssal plain. The depositional environment of the chert in this area was likely restricted to the vicinity of a continental slope. Considering with the wide distribution of Triassic platform carbonates over southeastern peninsular Thailand, the continental margin of the Sibumasu along the Paleo-Tethys was represented by a stable passive margin during the Middle–early Late Triassic time. On the basis of the sedimentary setting and stratigraphy in the Permian and Triassic, it is suggested that the closure of the Paleo-Tethys between the Sibumasu and Indochina continental blocks took place at least after the Middle Triassic in southeastern peninsular Thailand. [Copyright &y& Elsevier]

Highlights: [•] The Mid-Palaeozoic stratigraphy of Peninsular Malaysia is revised. [•] A new ammonoid species, Praedaraelites tuntungensis, is described. [•] Possible Mississippian (Viséan) glacial marine conditions on Sibumasu interpreted. [•] The Mid-Palaeozoic Unconformity marks initiation of rifting on Sibumasu. [ABSTRACT FROM AUTHOR]

Highlights: [•] Provide the petrogenesis of the mafic dyke from the Eastern Belt of Peninsular Malaysia. [•] First report on Ar–Ar ages of the mafic dyke from Peninsular Malaysia. [•] Discussion on the tectonic setting of the mafic dyke magma from the Eastern Belt of Peninsular Malaysia. [•] Why do the dykes only occur in the Eastern Belt rather than the Western Belt of Peninsular Malaysia? [Copyright &y& Elsevier]

Abstract: The Malay Peninsula is characterised by three north–south belts, the Western, Central, and Eastern belts based on distinct differences in stratigraphy, structure, magmatism, geophysical signatures and geological evolution. The Western Belt forms part of the Sibumasu Terrane, derived from the NW Australian Gondwana margin in the late Early Permian. The Central and Eastern Belts represent the Sukhothai Arc constructed in the Late Carboniferous–Early Permian on the margin of the Indochina Block (derived from the Gondwana margin in the Early Devonian). This arc was then separated from Indochina by back-arc spreading in the Permian. The Bentong-Raub suture zone forms the boundary between the Sibumasu Terrane (Western Belt) and Sukhothai Arc (Central and Eastern Belts) and preserves remnants of the Devonian–Permian main Palaeo-Tethys ocean basin destroyed by subduction beneath the Indochina Block/Sukhothai Arc, which produced the Permian–Triassic andesitic volcanism and I-Type granitoids observed in the Central and Eastern Belts of the Malay Peninsula. The collision between Sibumasu and the Sukhothai Arc began in Early Triassic times and was completed by the Late Triassic. Triassic cherts, turbidites and conglomerates of the Semanggol “Formation” were deposited in a fore-deep basin constructed on the leading edge of Sibumasu and the uplifted accretionary complex. Collisional crustal thickening, coupled with slab break off and rising hot asthenosphere produced the Main Range Late Triassic-earliest Jurassic S-Type granitoids that intrude the Western Belt and Bentong-Raub suture zone. The Sukhothai back-arc basin opened in the Early Permian and collapsed and closed in the Middle–Late Triassic. Marine sedimentation ceased in the Late Triassic in the Malay Peninsula due to tectonic and isostatic uplift, and Jurassic–Cretaceous continental red beds form a cover sequence. A significant Late Cretaceous tectono-thermal event affected the Peninsula with major faulting, granitoid intrusion and re-setting of palaeomagnetic signatures. [Copyright &y& Elsevier]

Abstract: The Semanggol Formation of NW Peninsular Malaysia is a Middle Permian–Late Triassic sequence of predominantly radiolarian chert, sandstone and mudstone (including turbidites), and conglomerate. The belt of country occupied by this unit extends into Thailand where various names including Na Thawi formation have been applied to its correlatives. Fossil evidence, particularly radiolarian, has established its age but also revealed that it is tectonically complex, with numerous out-of-sequence slices interpreted here to be caused by thrusting. The model proposed here involves, initially, in the Middle Permian, accumulation in the oceanward part of an accretionary complex as Palaeotethys began subducting beneath Indochina/East Malaya. This regime, it is proposed, continued until about the end of the Middle Triassic when Sibumasu collided with Indochina/East Malaya bringing an end to subduction. But as crustal shortening continued into the Late Triassic a foredeep basin formed in front of the now-inactive subduction zone and accretionary complex, and the youngest part of the Semanggol Formation was deposited. During this final stage the whole package of rocks comprising those in the accretionary complex and those deposited in the foredeep basin underwent lateral compression resulting in a thrust complex. The Semanggol Formation and its Thailand correlatives occupy part of a N–S belt of imbricately-thrust, deeper-water, sediments which include slope-deposited Carboniferous and Lower Permian beds. That belt is interpreted as a series of thrust slices juxtaposing rocks of different ages, referred to here as the Songkhla–Semanggol terrane. Its western boundary is a N–S line of inferred thrusting which coincides with a major westward facies change to platform carbonates of Middle Permian to Late Triassic age, called here the Rattaphum–Kodiang tectonic line. [Copyright &y& Elsevier]

Abstract: New palaeogeographical reconstructions are presented for eleven time intervals through the Palaeozoic of the eastern Asia region from the Middle Cambrian at 510Ma to the end of the Permian at 250Ma. They centre on the continental blocks of North China, South China, and Annamia (Indochina) and their relationships with northeastern Gondwana (which was united to form part of Pangea from the Late Carboniferous onwards). Also shown is the continent of Tarim during the Lower Palaeozoic, as well as the Hutag Uul–Songliao and Khanka–Jiamasu–Bureya terranes, both of which straddle the Russian, Mongolian and Chinese borders today, from Silurian times onwards. We conclude that Annamia and South China were united as a single continent throughout the Lower Palaeozoic and Early Devonian and were translocated by major strike-slip faulting along the northeastern Gondwana margin during that period from off Afghanistan to outboard of the Sibumasu and Australian sectors of the superterrane. They left the Gondwana marginal area together during the Lower Devonian opening of the Palaeotethys Ocean, but very shortly afterwards they themselves divided into the two separate continental blocks that we recognise today, not to reunite until the Triassic. The various Cambrian to Permian rocks found in Japan largely represent active volcanic arcs which originally lay to the southeast of South China, although the Carboniferous was more quiescent there. The Neotethys Ocean opened during the Permian, dividing Sibumasu and the Tibetan terranes from Gondwana, and the Palaeotethys Ocean started to close progressively in the Upper Palaeozoic as most of the East Asian continents and smaller terranes moved towards Siberia. The positions of the various continents and terranes have been deduced from a mixture of palaeomagnetic and faunal data, the positions of Large Igneous Provinces and kimberlites, and the need to provide kinematic continuity between maps of successive ages. However, many uncertainties remain. [Copyright &y& Elsevier]

Abstract: A Permo-Triassic volcanic arc system, the Sukhothai Arc, is recognised between the Indochina and Sibumasu continental blocks. The Chanthaburi terrane is here interpreted as a fault-detached, highly disrupted southern segment of the Sukhothai Arc, occupying part of southeastern Thailand and extending into Cambodia. The Klaeng tectonic line is defined as the boundary between the Chanthaburi terrane and Sibumasu block. The stratigraphy of the Chanthaburi terrane is compared with that of the Sukhothai terrane in Northern Thailand. The Late Palaeozoic–Mesozoic sequences of these two volcanic arc terranes in the Sukhothai Zone share important similarities, but show marked contrasts to those of the Sibumasu and Indochina blocks, where the Late Permian–Triassic is largely absent due to the Indosinian I unconformity (western Indochina) or is dominantly carbonates with little terrigenous clastic input (Sibumasu). There is no clear evidence of pre-Carboniferous sedimentary rocks for either the Sukhothai or Chanthaburi terranes. Late Permian lyttoniid brachiopod shale near Klaeng in the Chanthaburi terrane was revisited. The brachiopod, previously reported as Leptodus, is re-identified to Oldhamina, the genus previously known, elsewhere in Southeast Asia, only in the Huai Tak Formation of the Sukhothai terrane. Oldhamina in Thailand is confined to the Sukhothai Arc. The marine stratigraphy of the Sukhothai Arc is represented by a Permian–Triassic lithological succession of mixed carbonates and siliciclastics, with common volcanic material. The Late Permian and Triassic litho- and biostratigraphy of the Chanthaburi terrane are comparable with the upper Ngao and Lampang groups of the Sukhothai terrane; in particular, they share similar successions from Oldhamina brachiopod bearing shale to Palaeofusulina–Colaniella foraminifer bearing limestone in the latest Permian. Marine depositional conditions were terminated on the Sukhothai Arc by end-Triassic times, later than on the Indochina block (Late Permian) but earlier than on the Sibumasu block (Jurassic/Cretaceous). [Copyright &y& Elsevier]

Abstract: Six N–S tectono-stratigraphic belts can be recognized in Southeast Thailand, each with a distinct stratigraphy and igneous history. The westernmost Belt (I) is thought to be part of the Sibumasu Block, and the easternmost (V) to include part of the Indochina Block. Between those, Belt III comprises acid volcanic rocks, volcaniclastics, and Carboniferous to Triassic sedimentary rocks with distinctive faunas, interpreted to be a volcanic arc; Belt IV comprises Triassic rocks of back-arc basin origin; Belt V is interpreted as a Permian accretionary complex on the western flank of Indochina; and VI is an unconformable cover of Jurassic–Cretaceous red-beds correlating with the Khorat Group. A history of the Triassic Indosinian Orogeny is proposed, leading to the cratonization of Southeast Thailand by the end-Triassic. The apparent absence in Southeast Thailand of rocks from the Devonian–Triassic Palaeotethys ocean (the Inthanon Zone of Northern Thailand) is suggested to have resulted from a phase of post-Indosinian, oblique to longitudinal, sinistral, strike-slip faulting. That phase is thought to have included displacement on the Mae Yuam Fault which bounds the Inthanon Zone in Northern Thailand. Then followed a phase of transverse, sinistral, strike-slip faulting which offset the tectono-stratigraphic belts and faults of the earlier phase. [Copyright &y& Elsevier]

Abstract: It is widely accepted that Sibumasu rifted from Gondwana in the Late Palaeozoic. But the rifts themselves have not previously been documented in Southeast Asia. This paper identifies the pre-Middle Permian Kaeng Krachan Group of Upper Peninsular Thailand as the infill of one such rift, which is given the name Phuket Terrane. Indirect evidence suggests the rift-infill is several kilometres thick and glacially-influenced diamictites are conspicuous in the succession. There are significant similarities with the >3km thick pre-Middle Permian rift-infill of the Carnarvon Basin of Western Australia. East of the Khlong Marui Fault belt the succession is thinner and diamictites are a minor component. A tectono-stratigraphic model is proposed involving Gondwana glaciers dropping their load at the (present) western margin of the Phuket Terrane from where it was re-sedimented in the rapidly subsiding marine rift basin. It is suggested that the Khlong Marui Fault formed part of the eastern boundary of the rift system. The Three Pagodas Fault belt similarly juxtaposes different pre-Middle Permian successions. Rifting ceased in the Early Permian and a passive margin formed as the Mesotethys ocean widened, the upper part of the Kaeng Krachan Group and the overlying Ratburi Limestone representing the post-rift sequence. [Copyright &y& Elsevier]

Two types of chert are defined in Thailand based on lithology, faunal content, and stratigraphy. ‘Pelagic chert’ consists of densely packed radiolarian tests in a microcrystalline quartz matrix with no terrigenous material and is found as blocks embedded within sheared matrix. ‘Hemipelagic chert’ also has a microcrystalline quartz matrix, and contains not only scattered radiolarian tests, but also calcareous organisms such as foraminifers. The pelagic cherts range in age from Devonian to Middle Triassic, whereas hemipelagic chert is only from the Early to the Late Triassic. Lithological and stratigraphic characteristics indicate that the pelagic chert originated in the Paleo-Tethys, whereas the hemipelagic chert accumulated on the eastern margin of the Sibumasu Block. The hemipelagic and pelagic chert are exposed in two north-trending belt-like zones. The western zone includes the hemipelagic chert, as well as glaciomarine and other Paleozoic to Mesozoic successions, overlying a Precambrian basement that consists exclusively of Sibumasu elements. The eastern zone contains pelagic chert and limestone and should be correlated to the Inthanon Zone. The Inthanon Zone is characterized by the presence not only of Paleo-Tethyan sedimentary rocks, but also of Sibumasu Block elements that structurally underlie the Paleo-Tethyan rocks. The boundary between the Sibumasu and Paleo-Tethys zones is a north-trending, low-angle thrust that resulted from the collision of the Sibumasu and Indochina blocks. [ABSTRACT FROM AUTHOR]

It is now generally accepted that Southeast Asia is composed of continental blocks which separated from Gondwana with the formation of oceanic crust during the Paleozoic, and were accreted to Asia in the Late Paleozoic or Early Mesozoic, with the subduction of the intervening oceanic crust. From east to west the Malay peninsula and Sumatra are composed of three continental blocks: East Malaya with a Cathaysian Permian flora and fauna; Sibumasu, including the western part of the Malay peninsula and East Sumatra, with Late Carboniferous–Early Permian ‘pebbly mudstones’ interpreted as glaciogenic diamictites; and West Sumatra, again with Cathaysian fauna and flora. A further unit, the Woyla nappe, is interpreted as an intraoceanic arc thrust over the West Sumatra block in the mid Cretaceous. There are varied opinions concerning the age of collision of Sibumasu with East Malaya and the destruction of Paleotethys. In Thailand, radiolarites have been used as evidence that Paleotethys survived until after the Middle Triassic. In the Malay peninsula, structural evidence and the ages of granitic intrusions are used to support a Middle Permian to Early Triassic age for the destruction of Paleotethys. It is suggested that the West Sumatra block was derived from Cathaysia and emplaced against the western margin of Sibumasu by dextral transcurrent faulting along a zone of high deformation, the Medial Sumatra Tectonic Zone. These structural units can be traced northwards in Southeast Asia. The East Malaya block is considered to be part of the Indochina block, Sibumasu can be traced through Thailand into southern China, the Medial Sumatra Tectonic Zone is correlated with the Mogok Belt of Myanmar, the West Burma block is the extension of the West Sumatra block, from which it was separated by the formation of the Andaman Sea in the Miocene, and the Woyla nappe is correlated with the Mawgyi nappe of Myanmar. [ABSTRACT FROM AUTHOR]

[Display omitted] • Permo-Carboniferous basalts in Baoshan block were derived from fertile SCLM. • SCLM fertilization induced mechanical anisotropies that promoted continental rupture. • Magmatic sulfide deposit formed via rifting-induced melting of previously-modified SCLM. The petrogenesis of the rift-related Late Carboniferous–Early Permian mafic igneous rocks (basaltic lavas, dolerite dykes and mafic–ultramafic intrusive rocks) from the Sibumasu block in the eastern end of Cimmeria was still ambiguous. This petrogenesis is related to understand the drive for the formation of Neo-Tethys which was developed along the margin of Cimmeria, and to the generation of magmatic sulfide deposit via partial melting of previously subduction-modified mantle induced by rifting of continental margin. Most of the mafic rock samples belong to the subalkaline series, with lithologies varying from basalt to basaltic andesite. Magmatic zircons from the doleritic dykes yield weighted mean 206Pb/238U ages of 308.7 ± 2.5 Ma. The ε Hf (t) values of zircon are ranging from 3.2 to 11.8, which are much lower than those of the coeval depleted mantle (ε Hf (t) ≈ 16 at 305 Ma). The igneous series share similar features, such as elevated light rare earth elements, negative Nb-Ta anomalies and enriched Sr-Nd-Hf isotopes. Based on geochemical analyses of the mafic igneous series in the northern part of Sibumasu, we suggest that the primary melts of the mafic igneous rocks were derived from a fertile subcontinental lithospheric mantle (SCLM) which was previously modified by oceanic subduction, and these rocks were intruded and erupted in a passive plate margin during plate extension. The subsequent melting-induced softening of SCLM triggered the evolution of continental margin from the rift to the open of Neo-Tethys Ocean. The proposed model emphasizes that the melt generated from previously-modified SCLM in a continental rift setting is beneficial for the generation of magmatic sulfide deposit. [ABSTRACT FROM AUTHOR]

Abstract: Fossils from the Cambrian to Devonian rocks of southern Thailand, the Langkawi Islands, mainland Kedah, Perlis, north Perak and central West Peninsular Malaysia are listed and reviewed, and their stratigraphy and correlation reassessed. The hitherto anomalous record of the trilobite Dalmanitina from Malaysia is reviewed and found to be of latest Ordovician (Hirnantian) age, rather than Lower Silurian age as previously reported, and is considered a probable synonym of the widespread Mucronaspis mucronata. A new stratigraphical nomenclature is erected for part of the Langkawi, mainland Kedah and Perlis area successions, in which the term Setul Limestone (which stretched from the Ordovician to the Devonian) is abandoned and replaced by the Middle Ordovician Kaki Bukit Limestone, the late Ordovician and early Silurian Tanjong Dendang Formation, the Silurian Mempelam Limestone, and the early Devonian Timah Tasoh Formation, all underlying the paraconformity with the late Devonian Langgun Red Beds. There was a single depositional basin in the generally shallow-water and cratonic areas of southern Thailand, Langkawi, and mainland Kedah and Perlis, in contrast to the deeper-water basin of north Perak. Only Silurian rocks are dated with certainty within another basin in central West Malaysia, near Kuala Lumpur, which were also cratonic and shallow-water, although to the east in west Pahang there are basal Devonian deeper-water sediments with graptolites. The area is reviewed in its position within the Sibumasu Terrane, which, in the Palaeozoic, also included central and northern Thailand, Burma (Myanmar) and southwest China (part of Yunnan Province). [Copyright &y& Elsevier]

Abstract: A new stratigraphic nomenclature is proposed for the approximately 600m thick, mainly clastic transitional sequence between the underlying Mempelam Limestone and overlying Kubang Pasu/Singa Formation in northwest Peninsular Malaysia. This sequence represents shallow marine deposits of the continental margin of the Sibumasu Terrane during the Middle Palaeozoic (Devonian–Carboniferous). It is separated into several formations. The Timah Tasoh Formation is an approximately 76m sequence consisting of 40m of laminated tentaculitid shales at the base, containing Monograptus yukonensis Jackson and Lenz and Nowakia (Turkestanella) acuaria Alberti, giving an Early Devonian (Pragian–Emsian) age, and about 36m of rhythmically interbedded, light coloured argillo-arenites. The Chepor Formation is about 90m thick and consists mainly of thick red mudstone interbedded with sandstone beds, of Middle to Late Devonian age. A new limestone unit is recognized and named the Sanai Limestone, which contains conodonts of Famennian age. The Binjal Formation consists of red and white mudstone interbedded with sandstone beds showing Bouma sequences. The Telaga Jatoh Formation is 9m thick and consists mainly of radiolarian chert. The Wang Kelian Formation is composed of thick red mudstone beds interbedded with silty sandstone, and contain fossils indicative of an Early Carboniferous (Visean) age. The succession was deposited on the outer shelf, with depositional environments vertically fluctuating from prodelta to basinal marine. The Devonian–Carboniferous boundary is exposed at Hutan Aji and Kampung Guar Jentik, and indicates a major regressive event during the latest Devonian. [Copyright &y& Elsevier]

A comparative analysis of paleolatitudes and latitudinal displacements was undertaken for the South China, Simao, Baoshan, Shan–Thai, Indochina, Qiangtang, Lhasa and Himalayan blocks by using available paleomagnetic data to determine the collisional and amalgamation history of the main blocks in the Three Rivers region, western Yunnan. The results show that (1) the Simao Block is a South China-derived block; (2) the Baoshan and Shan–Thai blocks were subjected to rapid northward drift during the period from Late Carboniferous to Late Permian; (3) the Baoshan Block collided with the Simao Block in the Late Permian and continued to drift rapidly northwards, together with the South China and Shan–Thai blocks, until the Late Triassic; (4) the Paleo-Tethys separating the Baoshan and Simao blocks was possibly opened in the Early Silurian; (5) the Meso-Tethys ranged in age from Early Permian time to Early Cretaceous time, and reached its greatest width of about 42° latitude in the Late Triassic. [Copyright &y& Elsevier]

Thailand comprises two continental blocks: Sibumasu and Indochina. The clastic rocks of the Triassic Mae Sariang Group are distributed in the Mae Hong Son–Mae Sariang area, north-west Thailand, which corresponds to the central part of Sibumasu. The clastic rocks yield abundant detrital chromian spinels, indicating a source of ultramafic/mafic rocks. The chemistry of the detrital chromian spinels suggests that they were derived from three different rock types: ocean-floor peridotite, chromitite and intraplate basalt, and that ophiolitic rocks were exposed in the area, where there are no outcrops of them at present. Exposition of an ophiolitic complex denotes a suture zone or other tectonic boundary. The discovery of chromian spinels suggests that the Gondwana–Tethys divide is located along the Mae Yuam Fault zone. Both paleontological and tectonic aspects support this conclusion. [ABSTRACT FROM AUTHOR]

• Inherited zircon core of granite suggests that granitic magma was derived from Neo-Proterozoic to Paleozoic materials. • First magmatic crystallization derived from anatexis melting during the Middle Triassic. • Second magmatic crytallization was related to cooling during the Late Triassic. • Sibumasu and Indochina collision caused two-step magmatic evolution of the granites in Sibumasu terrane. The widespread granitic rocks of the Sibumasu terrane were emplaced during the collision of the Sibumasu and Indochina in the Triassic. Previous studies have suggested that each granite had a simple, single-step magmatic evolution. In situ LA-MC-ICP-MS U-Pb zircon dating of granites and gneiss from Thailand revealed the evolution of these rocks: Inherited zircon core ages (515 ± 130 Ma) from a granite of the Chonburi pluton in the Central-Granitoid Belt are coeval with an orthogneiss protolith age (513.6 ± 9.2 Ma) from Hua Hin area. Similar Cambrian ages were also reported from the Khao Tao area in southern Thailand. Moreover, there are a series of inherited zircon core ages from Neo-Proterozoic (1017 ± 43 and 984 ± 56 Ma), Ordovician (449 ± 26 Ma), Devonian (385 ± 15 Ma), Carboniferous (316 ± 12 Ma) to Permian (276 ± 31 and 266 ± 12 Ma). Taken together, these Neo-Proterozoic to Permian protolith ages are interpreted to represent the basement of the Sibumasu terrane in Thailand. Two magmatic zircon growth events can be distinguished at approximately (a) 241.8 ± 8.2 to 235 ± 12 Ma and (b) 230.6 ± 3.4 to 213.4 ± 3.0 Ma. We concluded that the Sibumasu and Indochina collision during the Triassic caused a two-step magmatic evolution of the granites of the Sibumasu terrane. The first magmatic crystallization during the Middle Triassic corresponded to the Sibumasu and Indochina collision, and the second magmatic crystallization during the Late Triassic was related to the late-collisional stage. [ABSTRACT FROM AUTHOR]

• Chaung Magyi Group (CMG) is of Neoproterozoic age, to possibly Cambrian age. • Detrital zircon age spectrum for the CMG is similar to the Cambrian of NW Thailand. • CMG formed in long lived Neoproterozoic-Early Palaeozoic convergent margin. The unfossiliferous Chaung Magyi Group of the Northern Shan Plateau of Myanmar, comprises metasedimentary rocks, in particular greywacke, slates, phyllites and schists, of inferred Proterozoic age that unconformably underlie the late Cambrian Pangyun Formation. To address the problem of the youngest stratigraphic extent of the group, four samples of the Chaung Magyi Group from the Yeywa Dome, East of Kyaukse, Mandalay Division, were collected for U-Pb dating of detrital zircons. Based on the youngest detrital zircons present in sandstone samples from the western Yeywa Dome area, at least the upper part of the Chaung Magyi Group is of latest Proterozoic age and possibly extends to the late Cambrian (~500 Ma). Comparison of detrital zircon age-frequency histogram distributions show only slight differences in distributions of detrital zircons in the Cambrian of NW Thailand and the Chaung Magyi Group samples (Sibumasu Terrane), with a concentration of ages between 1300 Ma and 820 Ma, with two major peaks at 1086 Ma and 1022 Ma. A younger Cryogenian age peak at 647 Ma is also observed. A spread of older concordant ages ranges from 3093 Ma to 1406 Ma. The minimum depositional age for the Chaung Magyi Group of the west of the Bawdwin Mine (982 Ma) based on ages of cross-cutting dykes (reported in Mitchell, 2018), and the maximum depositional age for Yeywa Dome (~600–500 Ma) based on detrital zircons suggest the age difference (~>400 my) is too great for the Chaung Magyi Group to be considered a single group, the dyke ages require re-investigation. [ABSTRACT FROM AUTHOR]