Late Palaeozoic and Mesozoic tectonic and palaeogeographical evolution of SE Asia
SE Asia comprises a collage of continental terranes derived directly or indirectly from the India–Australian margin of eastern Gondwana. The Late Palaeozoic and Mesozoic evolution of the region involved the rifting and separation of three elongate continental slivers from eastern Gondwana and the successive opening and closure of three ocean basins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys. The Sukhothai Island Arc System, including the Linchang, Sukhothai and Chanthaburi terranes, is identified between the Sibumasu and Indochina–East Malaya terranes in SE Asia and was formed by back-arc spreading in the Permian. The Jinghong, Nan–Uttaradit and Sra Kaeo sutures represent the closed back-arc basin. The Palaeo-Tethys is represented to the west by the Changning–Menglian, Chiang Mai/Inthanon and Bentong–Raub suture zones. The West Sumatra and West Burma blocks rifted and separated from Gondwana, along with Indochina and East Malaya in the Devonian, and together with South China formed a composite terrane 'Cathaysialand' in the Permian. They were translated westwards to their positions outboard of the Sibumasu Terrane by strike-slip tectonics in the Late Permian–Early Triassic at the zone of convergence between the Meso-Tethys and Palaeo-Pacific plates. SW Borneo is tentatively identified as possibly being the missing 'Argoland' that separated from NW Australia in the Jurassic. Palaeogeographical reconstructions for the Late Palaeozoic and Mesozoic illustrating the tectonic and palaeogeographical evolution of SE Asia are presented.
Arcs, ophiolites, basins and continental fragments: the assembly of the SE Asian continental crust
SE Asian continental crust comprises a heterogeneous collage of continental blocks, derived from the India-west Australian margin of eastern Gondwana, and subduction related volcanic arcs assembled by the closure of multiple Tethyan and back-arc ocean basins now represented by suture zones containing ophiolites and accretionary complexes. The continental core, Sundaland, comprises a western Sibumasu block and an eastern Indochina-East Malaya block with an island arc terrane, the Sukhothai Island Arc System, sandwiched between. This island arc formed on the margin of Indochina-East Malaya, and then separated by back-arc spreading in the Permian. The Jinghong, Nan-Uttaradit and Sra Kaeo Sutures represent this closed back-arc basin. The Palaeo Tethys is represented to the west by the Changning-Menglian, Chiang Mai/Inthanon and Bentong-Raub Suture Zones. The Cathaysian West Sumatra and West Burma blocks, rifted and separated from Gondwana, along with Indochina and East Malaya in the Devonian and were accreted to the Sundaland core in the Triassic. South West Borneo and East Java-West Sulawesi are now identified as the missing Banda and "Argoland" blocks which must have separated from NW Australia in the Jurassic by opening of the Ceno-Tethys and accreted to SE Sundaland by subduction of the Meso-Tethys in the Cretaceous. Palaeogeographic reconstructions illustrating long-term subduction and terrane accretion orogenesis in SE Asia and adjacent regions are presented.
Tectonic evolution of Sundaland
Sundaland, the continental core of SE Asia, is a heterogeneous collage of continental blocks and volcanic arcs bounded by narrow suture zones that represent the remnants of ancient ocean basins. All the continental blocks of Sundaland were derived directly or indirectly from the Arabia-India–Australia margin of eastern Gondwana by the opening and closure of three successive ocean basins, the Palaeo-Tethys (Devonian-Triassic) Meso-Tethys (Permian-Cretaceous) and Ceno-Tethys (Jurassic-Cretaceous), and assembled by the closure of these ocean basins. Core Sundaland comprises a western Sibumasu block and an eastern Indochina–East Malaya block with an island arc terrane, the Sukhothai Island Arc, sandwiched between. The Palaeo-Tethys is represented by the Changning–Menglian, Chiang Mai-Chiang Rai, Chanthaburi and Bentong–Raub Suture Zones that form the boundary between Sibumasu and the Sukhothai Arc. The Indochina block was derived from Gondwana in the Devonian when the Palaeo-Tethys opened. The Sukhothai Arc formed on the margin of Indochina in the Carboniferous, and then separated by back-arc spreading in the Permian. The Jinghong, Nan–Uttaradit and Sra Kaeo Sutures represent this closed back-arc basin. The Sibumasu Terrane separated from Gondwana in the late Early Permian when the Meso-Tethys opened and collided with the Sukhothai Arc and Indochina in the Middle-Late Triassic. The Cathaysian West Sumatra block possibly represents a part of the Sukhothai Arc and was emplaced by strike-slip tectonics outboard of Sibumasu in the Triassic. The West Burma Block was already attached to Sundaland before the Late Triassic and is likely a disrupted part of Sibumasu. East Java-West Sulawesi and South West Borneo are tentatively identified as the missing 'Argoland' and 'Banda' blocks which must have separated from NW Australia in the Jurassic and subsequently accreted to SE Sundaland in the Cretaceous.
Tectonic framework and Phanerozoic evolution of Sundaland
Sundaland comprises a heterogeneous collage of continental blocks derived from the India–Australian margin of eastern Gondwana and assembled by the closure of multiple Tethyan and back-arc ocean basins now represented by suture zones. The continental core of Sundaland comprises a western Sibumasu block and an eastern Indochina–East Malaya block with an island arc terrane, the Sukhothai Island Arc System, comprising the Linchang, Sukhothai and Chanthaburi blocks sandwiched between. This island arc formed on the margin of Indochina–East Malaya, and then separated by back-arc spreading in the Permian. The Jinghong, Nan–Uttaradit and Sra Kaeo Sutures represent this closed back-arc basin. The Palaeo-Tethys is represented to the west by the Changning–Menglian, Chiang Mai/Inthanon and Bentong–Raub Suture Zones. The West Sumatra block, and possibly the West Burma block, rifted and separated from Gondwana, along with Indochina and East Malaya in the Devonian and were accreted to the Sundaland core in the Triassic. West Burma is now considered to be probably Cathaysian in nature and similar to West Sumatra, from which it was separated by opening of the Andaman Sea basin. South West Borneo and/or East Java-West Sulawesi are now tentatively identified as the missing "Argoland" which must have separated from NW Australia in the Jurassic and these were accreted to SE Sundaland in the Cretaceous. Revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of Sundaland and adjacent regions are presented.
Tectonic evolution of the Malay Peninsula
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.
ASIA | South-East
South-east Asia is a giant 'jigsaw puzzle' of allochthonous continental lithospheric blocks and fragments (terranes) and that are bounded by suture zones (remnants of Palaeo-Tethys, Meso-Tethys and Ceno-Tethys oceans and back-arc basins). 400 million years of geological evolution have resulted in major collisional orogenic belts, magmatic belts and volcanic arcs. Tectonic evolution in the region has produced significant oil and gas reserves and mineral deposits, and underpins major biogeographic divides (e.g. Wallace's Line), biodiversity and diversity hotspots in the region.
Changhsingian (Late Permian) conodonts from Son La, northwest Vietnam and their stratigraphic and tectonic implications
Late Permian conodonts are for the first time reported from Vietnam. Pa, Sa, Sb, Sc and M elements of the Changhsingian conodont species 'Hindeodus julfensis' (Sweet) are reported from a 40 cm thick limestone in the middle part of the Yenduyet Formation near Son La, NW Vietnam. The occurrence of 'H. julfensis' indicates a Changhsingian age that is consistent with an interpreted early Changhsingian age for a brachiopod fauna slightly higher in the sampled section. The Son La section is located in the Song Da Rift Zone and overlies basaltic volcanics considered equivalent to the Emeishan large igneous province basalts that are plume related. The Permian-Triassic boundary in Vietnam is yet to be precisely located biostratigraphically but proxy chemostratigraphic data indicate its likely position in sections at Nhi Tao and Lung Cam, N. Vietnam and correlation with the Global Stratotype Section and Point at Meishan, South China. The recovered conodonts have a Conodont Colour Alteration Index of 5 and have been heated to c. 600°C but they do not show any evidence of textural alteration due to regional metamorphism such as micro-folding or stretching that would indicate any direct effects of the compressional Indosinian Orogeny.
The Chanthaburi terrane of southeastern Thailand: Stratigraphic confirmation as a disrupted segment of the Sukhothai Arc
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).
U-Pb isotope geochronology and geochemistry of granites from Hainan Island (northern South China Sea margin): Constraints on late Paleozoic-Mesozoic tectonic evolution
Hainan Island is a key component of the South China Sea region and provides insights on regional geological evolution since the Paleozoic. Ten newLA-ICPMS zircon U-Pb ages from granites of Hainan Island include Late Permian (254±3Ma; 252±3 Ma), Middle-Late Triassic (243±2Ma; 242±3Ma; 240±2Ma; 228±2 Ma) and late Early to early Late Cretaceous (105±1Ma; 101±1Ma; 96±2Ma; 95±3 Ma) ages. All samples in the present study, including late Permian, Middle-Late Triassic, and late Early to early Late Cretaceous granitic rocks show geochemical characteristics similar to those of calc-alkaline to high-K calc-alkaline I-type granites. Major and trace element geochemical variations show that during petrogenesis, these granites experienced fractional crystallization of minerals (e.g., Ti oxides and apatite). Compared to the late Permian and Middle-Late Triassic granitic rocks, middle to late Cretaceous granites generally have lower initial ⁸⁷Sr/⁸⁶Sr ratios of 0.70594 to 0.70886, lower TDM2 ages of 1314 to 1382 Ma, and higher εNd(t) of -4.94 to -5.96, implying that the magmatic source for Cretaceous granites received more significant contribution from juvenile material relative to that for Permo-Triassic granites. These new data, combined with data from literature for Hainan Island and the South China Sea (SCS) region underpin a conceptual model for late Paleozoic to Mesozoic tectonic evolution for Hainan Island and the general SCS region as follows, (a) Late Permian (272-252 Ma), the initiation and development of continental arc related to the subduction of Palaeo-Tethys ocean; (b) Triassic (249-228 Ma), continued arc magmatism, the gradual cessation of Palaeo-Tethys subduction and subsequent development of an extensional setting; (c) Early Jurassic to early Cretaceous (190-130Ma), the development of an Andean-type continental arc, and regional tectonic regime switch to the westward subduction of the Palaeo-Pacific plate; (d) Middle to late Cretaceous (128-70Ma), the continuation of the Andean-type arc, the development of an extensional setting due to slab rollback, and the cessation (~70 Ma) of Palaeo-Pacific plate subduction.
Gondwana dispersion and Asian accretion: Tectonic and palaeogeographic evolution of eastern Tethys
Present-day Asia comprises a heterogeneous collage of continental blocks, derived from the Indian-west Australian margin of eastern Gondwana, and subduction related volcanic arcs assembled by the closure of multiple Tethyan and back-arc ocean basins now represented by suture zones containing ophiolites, accretionary complexes and remnants of ocean island arcs. The Phanerozoic evolution of the region is the result of more than 400 million years of continental dispersion from Gondwana and plate tectonic convergence, collision and accretion. This involved successive dispersion of continental blocks, the northwards translation of these, and their amalgamation and accretion to form present-day Asia. Separation and northwards migration of the various continental terranes/blocks from Gondwana occurred in three phases linked with the successive opening and closure of three intervening Tethyan oceans, the Palaeo-Tethys (Devonian-Triassic), Meso-Tethys (late Early Permian-Late Cretaceous) and Ceno-Tethys (Late Triassic-Late Cretaceous). The first group of continental blocks dispersed from Gondwana in the Devonian, opening the Palaeo-Tethys behind them, and included the North China, Tarim, South China and Indochina blocks (including West Sumatra and West Burma). Remnants of the main Palaeo-Tethys ocean are now preserved within the Longmu Co-Shuanghu, Changning-Menglian, Chiang Mai/Inthanon and Bentong-Raub Suture Zones. During northwards subduction of the Palaeo-Tethys, the Sukhothai Arc was constructed on the margin of South China-Indochina and separated from those terranes by a short-lived back-arc basin now represented by the Jinghong, Nan-Uttaradit and Sra Kaeo Sutures. Concurrently, a second continental sliver or collage of blocks (Cimmerian continent) rifted and separated from northern Gondwana and the Meso-Tethys opened in the late Early Permian between these separating blocks and Gondwana. The eastern Cimmerian continent, including the South Qiangtang block and Sibumasu Terrane (including the Baoshan and Tengchong blocks of Yunnan) collided with the Sukhothai Arc and South China/Indochina in the Triassic, closing the Palaeo-Tethys. A third collage of continental blocks, including the Lhasa block, South West Borneo and East Java-West Sulawesi (now identified as the missing "Banda" and "Argoland" blocks) separated from NW Australia in the Late Triassic-Late Jurassic by opening of the Ceno-Tethys and accreted to SE Sundaland by subduction of the Meso-Tethys in the Cretaceous.