Search

Although Peninsular Malaysia abundant Permo-Triassic Malayan granitic plutons and volcanics (292–198 Ma) generate an enormous volume of detrital zircons that masks other detrital sources in fluvial sediments, there are suggestions that Peninsular Malaysia could recycle detrital zircons from Indochina (through Jurassic-Cretaceous strata) to other parts of Sundaland by paleoriver after the Indochina-Sundaland sediment link diminishes in the Cenozoic. As there is insufficient data to prove this, we compiled our new detrital zircon U-Pb isotopic data from modern river sands in Peninsular Malaysia with all available data to create a dataset that revealed five detrital zircon age pattern zones: (1) Northeast Coastal Zone (~73 Ma and ~223 Ma), (2) Mid-East Coastal Zone (~236 Ma and ~280 Ma), (3) Southeast Coastal Zone (~170 Ma, ~243 Ma, ~291 Ma, 400–416 Ma and 1545–1852 Ma), (4) Central Zone (~220 Ma) and (5) Mid-West Coastal Zone (~227 Ma and 1105–1173 Ma). All detrital age pattern zones show a clear detrital contribution from Malayan granitoids and volcanics. However, the Southeast Coastal Zone also shows significant contributions from Jurassic-Cretaceous strata in the northwest, e.g. Bertangga and Gerek sandstones, making them comparable with sources from Indochina and Lower Cretaceous strata in Singapore. We suggest a defunct drainage during Paleogene which transports the eroded sediments from the Jurassic-Cretaceous strata in the northwest to the sink in the southeast coast of Peninsular Malaysia recycled “Indochina signature” detrital zircons. If the sink connects with the Sundaland paleoriver system, it might contribute to the “Indochina signature” detrital provenance in West Borneo.

Taiping Island, also known as Itu Aba, is the largest natural terrestrial landmass in the South China Sea and is centrally located. Using bathymetry and marine multi-channel seismic data, we explored the seismic stratigraphic features of the offshore and isolated carbonate platform north of Taiping Island. The western flank of the carbonate platform is characterized by an intercalation between high-amplitude and low-amplitude reflections, showing the landward and seaward migration of the platform foreslope deposits. In addition, there are two offshore carbonate build-ups that are underlain by normal faults. Six sequence boundaries and five depositional sequences caused by eustatic sea level cycles are identified and correlated with the eustatic sea level change chart. Although the evolution of the seismic sequences is partly controlled by local tectonics, the overall stacking pattern of the sedimentary strata in our study area reveals five third-order cycles and one second-order cycle, which is in accordance with the eustatic sea level chart. Additionally, the formations of the Western Taiping Seamount Group and the Zhenghe-Daoming Trough are preliminarily analyzed based on seismic data.

The late Permian Doba (257 ± 1 Ma) gabbro was discovered at the base of an exploration well through the Cretaceous Doba Basin of Southern Chad. The gabbro is at least 250 m thick, has cumulus mineral textures and consists of plagioclase, clinopyroxene, orthopyroxene, Fe–Ti oxide, apatite and quartz. The composition of the silicate minerals (i.e. plagioclase, pyroxenes) from the lowest part of the intrusion tend to be more primitive (i.e. An59, Wo40-44En33-47Fs12-25) than the upper part (i.e. An41, Wo39-43En30-44Fs14-29) suggesting the magmatic system differentiated internally by crystal fractionation and crystal redistribution. Based on the chemistry of the pyroxenes, the parental magma was compositionally similar to a Ti-rich, within-plate continental tholeiite that had a bulk Mg# of ∼44. The relative oxidation state of the magma was initially moderately reducing (i.e. ΔFMQ-0.3) and then became more reducing after a period of fractionation (i.e. ΔFMQ-1.2). The estimated initial magma temperature was at least 1100 °C. The within-plate composition suggests there was rifting-related magmatism near the boundary of the Saharan Metacraton that could be related to edge-driven mantle convection.

Detection and documentation of petro-structural features such as alignment features of minerals/grains, and extraction of such spatial property data are two fundamental steps for structural geology. Such tasks were mostly carried out manually. However, manual analysis is laborious and potentially biased. These drawbacks are less obvious when the foliation is well developed and the amount of platy mineral is higher. For samples with weakly developed foliation and low platy mineral content, automatic method is required for subjective interpretation. A semi-automatic computerized method of 3D foliation orientation reconstruction via two-dimensional petrographic-shape fabric analysis from serial oriented digital microphotograph has been developed and demonstrated in this study. The foliation is reconstructed by fitting a best fitting plane to the maximum modal peaks of micro textural parameters (SPO) for different mineral groups of platy and granular minerals from each thin section on a stereonet for four coarse grained biotite gneiss samples collected along the Jialie fault, SE Tibet, China. Regardless of platy or granular mineral aggregates, the reconstructed foliations showed similar orientation within 10° angular variation to the field measurement. The 10° angular variation can be maintained if the foliations are reconstructed by consecutive thin section groupings ≦ 50° angular intervals and a horizontal thin section. The angular spread increased to 30° for thin section groupings with > 50° to 100° angular intervals with a horizontal thin section. Major advantages of the computerized photometric methods demonstrated by this study are: the reduction of human prejudice and obtaining quantified and repeatable data sets.

The PoSen complex, located closely adjacent to the southwestern margin of the Red River shear zone represents the uplifted basement of north Vietnam and may record the motion of the shear zone. However, its thermochronological history has not been fully examined yet. Here we applied U–Pb and 40 Ar/ 39 Ar dating methods to reveal its thermochronological history. U–Pb analysis of composite zircon grains by TIMS yielded an average age of 760 ± 25 Ma, clustering on the concordia line. Twelve SHRIMP U–Pb analyses also yielded a consistent result of 751 ± 7 Ma. Along with the geochemical features, the U–Pb dating results suggest the PoSen complex was a late Proterozoic magmatic complex, which could correspond to the Chengjiang orogeny, a widespread thermal event in southwest China. Results of 40 Ar/ 39 Ar dating of micas and K-feldspars were in the range of 36–30 Ma, revealing a rapid cooling and exhumation history of the PoSen complex during the late Paleogene. The time span of cooling and exhumation of the PoSen complex is slightly older than the main cooling phases of the Ailao Shan–Red River (ASRR) metamorphic massifs (28–17 Ma), but is synchronous with the early igneous activity stage in the eastern Indo-Asian collision zone of southeast China and north Vietnam. Owing to the ongoing debate about the initiation and offset of the ASRR shear zone, the tectonic force for the late Paleogene cooling of the PoSen complex is still inconclusive. The rapid exhumation of the PoSen complex could be in response to either the detachment of the Neo-Tethyan slab or a transpressional phase of continental subduction along the ASRR shear system in the eastern Indo-Asian collision zone.

Detailed analysis of the sequence stratigraphy in 30 cores from the Late Quaternary deposits of the Changhua Coastal Plain provides a 25 ka record of the depositional history of a region situated in the frontal arc-continent collision belt of Taiwan. Twenty-five lithofacies and nine facies associations are recognized. An alluvial plain was the dominant feature during a pronounced sea-level fall at 25–20 ka ago. Between 20 and 10 ka, alluvial fans were deposited along the western front of the Pakua Tableland during movement along the Changhua Fault, and a local sag basin was produced. No other deposits in the seaward area are recognized between 20 and 16 ka, or in the landward area between 20 and 10 ka. Between 16 and 6 ka, the Changhua Coastal Plain experienced rising sea level and retrogradational deposition. From 16 to 10 ka, estuarine deposits (lower transgressive systems tract) were deposited, and the base of these deposits defines the Last Glacial Maximum (LGM) unconformity (sequence boundary), now preserved in four regions to the east of the plain. From 10 to 6 ka, shelf, shoreface, and lagoonal deposits (upper transgressive systems tract) were laid either on top of the estuarine deposits or directly on the LGM unconformity surface. By about 7–6 ka, sea level had reached its peak (maximum flooding surface), and shelf and marginal marine sediments covered most of the study area. After 6 ka, the highstand was dominated by progradation of offshore-transition, shoreface, lagoonal, tidal channel, tidal flat and alluvial plain deposits. One-thousand-year-old fluvial deposits in incised channels are preserved in the central part of the Changhua Coastal Plain. Since then, fluvial channels shifted southward to the present-day Chuoshuei River. The depositional patterns in this tectonically active area during the last interglacial period reflect the complex interplay between high-frequency sea-level fluctuations, tectonics (subsidence and uplift), and autocyclic processes. In the seaward area, however, fluctuations in sea level were clearly the dominant factor in controlling the nature of depositional facies.

Rising as “the roof of the world” the Tibetan plateau is now underlain with the thickest continental crust on Earth. How and when was this crust formed, which would have exerted pivotal controls to the formation of the plateau, has long been an issue of hot debates. This paper reports zircon U–Pb ages and Hf isotope data for postcollisional (~ 30–9 Ma) adakites in the southern Lhasa terrane, southern Tibet. A comparative analysis of whole-rock rare earth element geochemistry and zircon Hf isotopes between the adakites and associated Gangdese igneous rocks suggests that the Tibetan crust underwent a major phase of tectonic thickening between ca. 45 and 30 Ma in the region. The lower part of the thickened crust consisted prevailingly of mafic lithologies, which we argue to have resulted from intense basaltic underplating and subsequent remelting that took place during the Late Cretaceous and Eocene time related to the Neotethyan subduction processes including breakoff of the subducted slab at ca. 50 Ma in the early stage of the India–Asia collision. These processes were responsible for not only the juvenile crust formation but also for the creation of a thermally softened lithosphere in the southern Lhasa terrane. The indentation of India, consequently, caused distributed lithospheric thickening with formation of an orogenic root beneath southern Tibet. Root foundering during the Oligocene gave rise to the adakitic magmatism, regional topographic uplift, and onset of northward underthrusting of the Indian plate that has since played a key role in forming the entire Tibetan plateau.

Formation of the Linzizong volcanic successions in the Lhasa terrane, southern Tibet has long been related to northward subduction of the Neotethyan oceanic slab under Asia. Here we report new 40Ar/39Ar age results for the volcanic rocks recovered from a large area (29°N to 32°N and 85°E to 93°E) that, together with literature data, delineate two discrete stages of volcanism. These are a widespread Cretaceous stage and an intense, but spatially confined, Paleogene stage. The latter, occurring only in the southern part of the Lhasa terrane, resulted in the Linzizong volcanic successions. Our data, furthermore, suggest southward migration and intensification of the volcanism in the Lhasa terrane with magmatic “flare-ups” at ca. 50 Ma. While the volcanic successions consist dominantly of calc–alkaline rocks typical of arc lava geochemistry, those formed during the flare-up period show significant compositional variations from low-K tholeiitic through calc–alkaline to shoshonitic magma suites. These observations enable us to interpret the volcanic southward migration and following flare-ups as the consequences of rollback and breakoff of the subducted Neotethyan slab that occurred ahead and in the early stage, respectively, of the India–Asia collision. Our interpretation that involves a major Eocene tectonomagmatic activity, and concomitant topographic uplift, in southern Tibet is consistent with Himalayan metamorphic constraints, regional sedimentary records and seismic tomography.

We conducted a comprehensive 40Ar/39Ar geochronological study of the Jiali and Gaoligong shear zones to obtain a better understanding of crustal deformation and tectonic evolution around the Eastern Himalayan Syntaxis (EHS). The new age data reveal that the main phase of deformation in the Jiali and Gaoligong shear zones occurred from 22 to 11 Ma and from 18 to 13 Ma, respectively. Structural data collected during this study indicate that the Jiali shear zone underwent a change in shear sense from sinistral to dextral during its movement history. Based on a comparison with the deformation histories of other major shear zones in the region, we argue that the initial sinistral motion recorded by the Jiali shear zone was coincident with that of the Ailao Shan–Red River shear zone, which marked the northern boundary of the southeastward extrusion of the Indochina block during the Early Miocene. From the Middle Miocene (∼18 Ma), the Jiali shear zone changed to dextral displacement, becoming linked with the dextral Gaoligong shear zone that developed as a consequence of continued northward indentation of the Indian continent into Asia. Since this time, the Jiali and Gaoligong shear zones have been united, defining the southwestern boundary of the EHS during clockwise rotation of the eastward-extruding Tibetan block, as revealed by recent GPS data. The temporal change in regional deformation pattern from southeastward block extrusion to clockwise rotation of crustal fragments may have played an important role in the development of the eastern Himalayan drainage system around the EHS.

Left-lateral motion along the Ailao Shan‐Red River (ASRR) Shear Zone has been widely advocated to be the result of the collision between the Indian and Eurasian plates and to account for sea-floor spreading in the South China Sea. Our new 40 Ar/ 39 Ar data on the south-easternmost outcrop of the Day Nui Con Voi metamorphic massif, northern Vietnam, suggest that the exhumation of metamorphic massif by shearing along the ASRR zone began 027 Ma and lasted until 022 Ma. A perfect correlation between location and cooling path for the samples along the shear zone suggests that the transtensional deformation may have propagated northwestward at a rate of 0 6c m y ˇ1 . Such a good correlation also indicates that the onset of the leftlateral movement of the shear zone may have occurred later than 027.5 Ma. This conclusion is consistent with our previous interpretation that collision-induced southeastward extrusion of Indochina along the ASRR Shear Zone postdates the opening of the South China Sea, and that extrusion tectonics in SE China may not be responsible for the opening of the South China Sea. # 2000 Elsevier Science Ltd. All rights reserved.

Recent interpretation of seismic sections and free-air gravity anomalies in offshore northern Taiwan reveals that the southern Taiwan–Sinzi Folded Zone began to form in late Middle Miocene, though it was mainly constructed in the Late Pliocene with strong reverse faulting and folding. Two westward progradational sequences were deposited in the shelf basin with sediments supplied from the southern Taiwan–Sinzi Folded Zone and the southern Ryukyu Arc. These two structures are displaced by several northwest-striking dextral strike–slip faults that were active in the early Quaternary when the clockwise-rotated southern Ryukyu Arc and the folded southern Taiwan–Sinzi Folded Zone were broken. It is believed that recent extension in the southern Okinawa Trough started in the early Quaternary because uplift on the southern Taiwan–Sinzi Folded Zone continued to latest Pliocene–early Quaternary. Paleogene–Miocene sediments of the East China Sea Shelf in the western part of the southern Okinawa Trough Basin are interpreted to indicate that the East China Sea Shelf Basin extended to the east of the southern Taiwan–Sinzi Folded Zone.

The India-Eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt. Changes in the rate and angle of convergence between the India and Eurasia plates reflect different stages of tectonic development in Southeast Asia. For example, extrusion of the Indochina block induced the consumption of the pre-existing proto-South China Sea along northeastern Kalimantan and led to the eventual opening of the South China Sea along the South China margin. Subsequent motions of the Sino-Burma-Thailand, Malay Peninsula, Sumatra, and Kalimantan blocks have produced a succession of basins stretching from north Sumatra to central Thailand and on to the Natuna area. We present reconstructions of the Southeast Asia region at 60 Ma, 50 Ma, 40 Ma, 30 Ma, 20 Ma, 15 Ma, 10 Ma, and 5 Ma. It is clear, from the reconstructions, that the impact between Greater India and Southeast Asia took place in the northwestern part of Southeast Asia. The duration for the impact was probably from the Middle Eocene to Early Miocene. This timing is in good agreement with the dating of the main Red River Fault motion (Wu et al., 1989; Scharer et al., 1990). Since the impact between Greater India and Southeast Asia was basically west of the Burma block, there is no reason to assume that the Sumatra, Malay Peninsula, and Kalimantan should extrude to the southeast first along the left-laterally displaced Mae Ping and Three Pagodas fault zones as suggested by Peltzer and Tapponnier (1988). If the opening of the central Thailand basins, the Gulf of Thailand, and the Malay Basin are taken into consideration, a dextral megashear zone is required to compensate the relative motion between Indochina and the Malay Peninsula. This dextral megashear zone might even extend into western Kalimantan and serve as a boundary between the Indochina block and Kalimantan.

We have attempted to quantify the relative motion history between southernmost South America (SSA) and the Antarctic Peninsula (AP) by calculating and comparing SSA-Africa, AP-Africa and SSA-AP synthetic flow lines for 84–0 Ma. The flow lines were created using published poles of rotation and plate reconstruction software. The results indicate that since 84 Ma, SSA and AP have moved approximately westward relative to a fixed Africa; however, SSA's rate of westerly motion in that reference frame has been significantly more rapid than AP's rate. Approximately 1320 km of east-west, left-lateral strike-slip displacement and 490 km of north-south, divergent displacement have occurred between the southern tip of SSA and the northern tip of AP since 84 Ma. Increased rates of SSA-AP interplate separation and a change in the angle of plate divergence at approximately 55–40 Ma marked the onset of accelerated continental separation that eventually led to seafloor spreading in the western Scotia Sea at 30 Ma and the development of the Scotia Arc. Increased separation rates between SSA and AP at 55–40 Ma may be related to a global Eocene plate reorganization event. The northeast-southwest oriented western Scotia Sea spreading centers appear to have accommodated all of the SSA-AP interplate motion between 30 and 9 Ma. We suggest that prior to 30 Ma and the opening of Drake Passage, components of interplate strike-slip and divergent motion were accommodated by intracontinental deformation that included strike-slip faulting, counterclockwise tectonic rotation, and continental extension in the southernmost Andes. The results indicate that the opening of the Scotia Sea was caused by plate-scale motions as SSA and AP drifted away from Africa at different velocities along different, nonparallel trajectories. Subduction retreat along the South Scotia Ridge and South Sandwich arc and back arc spreading in the Scotia Sea contributed to the width of separation between SSA and AP across Drake Passage. The results place limits on how SSA-AP relative motion has been temporally and spatially partitioned in the Scotia Arc region.

The Linzizong volcanic successions that crop out in the Lhasa terrane, southern Tibet have been conventionally regarded as the products of northward subduction of the Neotethyan oceanic slab beneath South Asia. This study reports geochemical data of 100+ volcanic rocks from the Lhasa terrane to better constrain the temporal–spatial distribution and petrogenesis of the Linzizong volcanism. The Linzizong volcanic successions consist dominantly of calc-alkaline rocks that erupted from ca. 69 to 43 Ma and show typical arc-lava geochemical features marked with LILE enrichment and HFSE depletion in the spidergram. Their Sr and Nd isotope ratios [ e Nd ( T ) = +3.3 to −2.4; I Sr = 0.7048–0.7072] are generally similar to those of the associated Gangdese I-type granitoids. The Linzizong volcanism is characterized by a flare-up period (ca. 50 Ma) that shows significant geochemical variations, manifested by the coexistence of five types of volcanic rocks: (1) the main suite of calc-alkaline rocks [SiO 2 = 45–80 wt.%; La = 12–45 ppm; e Nd ( T ) = +3.8 to −4.9; I Sr = 0.7037–0.7105] that could be interpreted by partial melting of the mantle wedge followed by assimilation and fractional crystallization (AFC) processes with >10% crustal contamination and/or magma mixing; (2) the low-K, low-REE suite (SiO 2 = 48–61 wt.%; K 2 O = 0.5–1.1 wt.%; La = 7–10 ppm) that has the highest Nd isotope ratios [ e Nd ( T ) = +5.9 to 3.5], suggesting a juvenile mantle origin possibly related to decompression melting of the asthenosphere; (3) the shoshonitic suite [SiO 2 = 53–71 wt.%; K 2 O = 3.8–6.7 wt.%; e Nd ( T ) = −2.8 to −6.1] from small-degree melting of the metasomatized lithospheric mantle; (4) the high-REE suite [SiO 2 = 61–75 wt.%; La = 36–87 ppm; e Nd ( T ) = −2.6 to −3.2] originating from remelting of a newly underplated basaltic lower crust; and (5) the evolved suite of rhyolitic flows and ignimbrites (SiO 2 > 65 wt.%) that have the lowest e Nd ( T ) values of −14 to −18, representing remelting products of the basement or continental crust of the Lhasa terrane. Such geochemical heterogeneities are attributed to breakoff of the subducted Neotethyan slab under southern Tibet that occurred in the early stage of the India–Asia collision.

Reconstructions of the South China Sea region at 60 Ma, 40 Ma, 30 Ma, 20 Ma, 10 Ma and 5 Ma are presented. We have attempted to place the South China Sea Basin in a regional tectonic framework. The tectonic evolution of the major blocks surrounding the South China Sea were analyzed, as well as the relative motions of the Indian and Australian plates. We have tried to correct the tectonic models available in this region. A 3-D graphics terminal was used to derive rotation poles for the different tectonic blocks and our model was then tested to determine its self-consistency. When the model conflicted with previous interpretations the input data were evaluated for alternative explanations. At least two, and possibly three, stages of extension can be recognized in this region. The earliest one, active in the Late Cretaceous to Eocene, involved NW-SE extension. The second one, active from the Late Eocene to Early Miocene involved north-south extension. The third stage of extension, which probably trended NW-SE, can be dated as post-Oligocene. The first extensional event produced the NE-SW trending proto-South China Sea and a series of sedimentary basins along the South China margin. Following the southeastward extrusion of Indochina, the proto-South China Sea was mostly consumed at the Palawan Trough. Renewed north-south extension in the South China continental margin started the present-day South China Sea spreading in the Oligocene. The southeastward extrusion of Indochina, blocked by Sundaland, resulted in the NW-SE trending opening of the South China Sea Basin in the Early Miocene. Collision of the North Palawan microcontinental block with the West Philippines block stopped the opening of the South China Sea at the end of Early Miocene. Spreading activity switched to the Sulu Sea Basin in the Middle Miocene but collision between the Sulu Ridge and the West Philippines at Mindanao halted the opening of the Sulu Sea at the end of the Middle Miocene. In the Late Miocene, Greater India continued its northward path and seems to have ripped open the Andaman Sea. In the Pliocene, subduction along the northern Manila Trench placed the North Luzon Arc on a collision path with the East Asia continental margin at Taiwan. Our reconstructions, along with detailed geological and geophysical information, may be used as a predictive tool for basin evolution models and block interactions in this region. The development of the South China Sea Basin, the Gulf of Thailand, the Malay Basin and the central Thailand basins are the result of collision-induced extensional forces. The Sulu, Celebes and Sumatra basins were formed as a consequence of prolonged subduction. The opening of the Pearl River Mouth, West Natuna, South China Sea, Sulu, and possibly Celebes, basins were terminated by various plate collisions. During the course of plate reorganizations major boundary faults have changed their slip senses during different stages of evolution.