The evolution of arc-continent collision between the Palawan microcontinental block and the Cagayan Ridge in the southeastern margin of the South China Sea (SCS) is vital to understand how this collision correlated with seafloor spreading of the SCS. To address the evolution of arc-continent collision, we studied the biostratigraphy and provenance of syn-collisional sediments in the Isugod Basin in central-southern Palawan. Microfossil analysis indicates a Late Miocene age (11.5-5.6 Ma) for the Isugod and Alfonso XIII Formations and rapid subsidence during initiation of the basin which may have been triggered by local extensional collapse of the wedge in response to forearc uplift. Multidisciplinary provenance analysis reveals that the Isugod and Alfonso XIII Formations were derived from the Middle Eocene-lower Oligocene Panas-Pandian Formation on the Palawan wedge and the Late Eocene Central Palawan Ophiolite. These results suggest the emergence of both the orogenic wedge and obducted forearc ophiolite at similar to 11.5 Ma, implying collision onset before similar to 11.5 Ma. The collision initiation in Palawan could be better constrained to similar to 18 Ma, based on the drowning of the Nido carbonate platform in the foreland. Therefore, the gravitational collapse of the Palawan wedge and the subsidence/formation of the Isugod Basin might reflect a significant uplift pulse in the hinterland of the wedge beginning within 13.4-11.5 Ma in the late stage of collision. It indicates that although compression originated from spreading of the SCS had ceased at 16-15 Ma, arc-continent collision in Palawan did not stop and was sustained by compression from the upper plate afterward. The Palawan microcontinental block is a continental fragment separated from the South China margin along with the seafloor spreading of the South China Sea (SCS). It finally collided with the Cagayan Ridge volcanic arc because of southward subduction of the Proto-SCS. Therefore, precisely constraining the evolution of arc-continent collision could help us to understand its association with the ending of the SCS spreading. To constrain the evolution of arc-continent collision, we determined the depositional age and source of syn-collisional sediments in the Isugod Basin in central-southern Palawan. Our results shows that the Isugod Basin sediments were deposited during the Late Miocene (11.5-5.6 Ma) following local gravitational collapse of the Palawan orogenic wedge driven by uplift and oversteepening. Isugod Basin sediments were eroded from both the orogenic wedge and obducted forearc ophiolite that were uplifted and exposed subaerially, indicating collision began before similar to 11.5 Ma. As the onset of collision could be constrained to similar to 18 Ma, we propose a significant uplift pulse in the hinterland of the wedge began at 13.4-11.5 Ma in the late stage of collision. This further indicates that arc-continent collision in Palawan did not stop although compression derived from spreading of the SCS had ceased at 16-15 Ma. Sediments in the Isugod Basin were deposited at 11.5-5.6 Ma following local gravitational collapse of the Palawan wedge driven by uplift The Isugod Basin sediments were supplied by erosion of the Palawan wedge and obducted forearc ophiolite exposed subaerially since similar to 11.5 Ma Onset of Palawan arc-continent collision at similar to 18 Ma followed by a significant uplift pulse in the Palawan wedge beginning within 13.4-11.5 Ma

The young Taiwan orogenic belt is a classic example of a modern arc-continent convergence zone, which displays a longitudinal transition from active collision in the north to oceanic subduction in the south. However, the timing of its initial exposure above the sea level and the early-stage uplift mechanism has been a point of much debate. Here we applied major and trace element, Nd isotope and heavy minerals analysis on the Miocene sedimentary rocks from the Hengchun Peninsula to trace sediment provenance and to further constrain the tectonic-sedimentary evolution of the Taiwan accretionary prism. Results show that the Hengchun mudstones (-11.6-6.5 Ma) are characterized by higher CaO (1.42 wt %) and MgO (2.57 wt %) contents, Cr/Zr (0.52) and Co/Th (1.58) ratios, and less negative epsilon Nd (t) values (-12 to -7) than those from the Chinese passive continental margin sediments. It indicates that the Chinese mainland was not exclusive sediment contributor for the Hengchun sediments. Combined with the high content of Cr-spinel heavy mineral (mean value - 28.2%) in the Hengchun Miocene sandstones, and the presence of mafic lithic grains and N-MORB-type mafic rocks of 26-22 Ma in the Hengchun Peninsula, it is clear that the subducting South China Sea oceanic lithosphere should be also considered for the origin of the Hengchun sediments. The most likely source of these oceanic clasts being transported to the Hengchun Peninsula is the equivalent prism to the north, which had involved oceanic fragments during the subduction process. Consequently, Taiwan accretionary prism should have been already partly exposed prior to -11.6 Ma, considerably earlier than most previous estimates and the onset of arc-continent collision. Underplating of seamounts and/or the thinned Chinese continental margin beneath the overlying Taiwan accretionary prism, together with wedge extrusion tectonics, may have played an important role for this early-stage uplift, which now is also observed in the sandbox experiments, marine observation and analogue modeling. Our study not only better integrates the subduction and then erosion history of the South China Sea oceanic crust with sedimentary records in Taiwan, but also signifies a modern example from Taiwan that highlights the importance of soft exhumation mechanism in worldwide plate convergence zones relative to hard collision.

The Palawan microcontinental block is thought to have separated from the South China margin due to seafloor spreading and opening of the South China Sea. However, it is uncertain when and from which section the Palawan microcontinental block rifted from the South China margin and little is known about sediment routing across the rifted margin before continental breakup. To address these aspects, we studied the biostratigraphy and provenance of syn‐rift sedimentary rocks collected from the Panas‐Pandian Formation in central‐southern Palawan. Micropaleontological evidence indicates a Middle Eocene‐earliest Oligocene (47.7–32.9 Ma) age for the Panas‐Pandian Formation. Based on this and the oldest age of the post‐rift Nido Limestone (∼32 Ma), the breakup unconformity on the Palawan microcontinent block is dated around 33–32 Ma. This timing of breakup unconformity is close to that of the Pearl River Mouth Basin (∼30 Ma) and IODP Site U1435 (∼34 Ma), suggesting a conjugate relationship between the Palawan microcontinental block and the Pearl River Mouth Basin. Trace fossils and benthic foraminifera from the Panas‐Pandian Formation indicate a middle bathyal to abyssal environment on the continental slope of the South China margin. Multidisciplinary provenance analysis reveals that the Panas‐Pandian Formation was derived from both local Mesozoic basement uplifts and the interior Cathaysia Block. It indicates that a paleo‐Pearl River has been established at least since the Middle Eocene (47.7–41.9 Ma) and could deliver sediments from the interior Cathaysia Block to the continental slope, across the wide rifted margin with a low topographic gradient.

The eastern Himalayan syntaxis, where the Yarlung Tsangpo sharply bends, is one of the areas experiencing most rapid exhumation on Earth. The rapid exhumation is often regarded as the result of capture of the Yarlung Tsangpo by the Brahmaputra River. However, both the timing of integration of the Yarlung Tsangpo-Brahmaputra River and initiation of the rapid syntaxial exhumation are debated. As the ultimate sedimentary trap of the Yarlung Tsangpo-Brahmaputra River, the Nicobar Fan is a window to look into the drainage evolution and exhumation history of the eastern Himalaya. International Ocean Discovery Program Expedition 362 drilled the Nicobar Fan for the first time, recovering fan sediments dating back to the Early Miocene (similar to 19 Ma). We apply trace elements and Sr-Nd isotopes to investigate the provenance of the sediments in the Nicobar Fan with the aim of constraining the timing of integration of the Yarlung Tsangpo-Brahmaputra River and initiation of the rapid syntaxial exhumation. The geochemical and Sr-Nd isotope compositions indicate an eastern Himalayan source dominated by the Greater Himalaya, with significant Gangdese arc contribution and primarily carried by the Brahmaputra River. Flux of Gangdese arc material appears to have been continuous from the base of the Nicobar Fan, suggesting that the Yarlung Tsangpo-Brahmaputra River has been established at least since similar to 19 Ma. Synchronously with the sharp rise in sedimentation rate, the abrupt change of geochemical and isotope compositions at similar to 9.2 Ma indicates an increase in erosion of the Greater Himalaya as the result of initiation of rapid exhumation in the broad syntaxial region. The proportion of Greater Himalayan material increased again at 3.5-1.7 Ma, consistent with a younger pulse of rapid exhumation focused in the core of the syntaxis since similar to 3.5 Ma. Our results show that initiation of the rapid syntaxial exhumation postdated integration of the Yarlung Tsangpo-Brahmaputra River by at least similar to 10 m.y. Therefore, tectonic uplift rather than river capture could be responsible for the initiation of the rapid syntaxial exhumation. (C) 2020 Elsevier B.V. All rights reserved.

AbstractOpening of the South China Sea and upwelling of the Hainan Plume are among the most challenging issues related to the tectonic evolution of East Asia. However, when and how the Hainan Plume affected the opening of the South China Sea remains unclear. Here we investigate the geochemical and isotopic features of the ~25 Ma mid‐ocean ridge basalt (MORB) in the Kenting Mélange, southern Taiwan, ~16 Ma MORB drilled by the IODP Expedition 349, and ~9 Ma ocean island basalt‐type dredged seamount basalt. The ~25 Ma MORBs reveal a less metasomatic depleted MORB mantle‐like source. In contrast, the Miocene samples record progressive mantle enrichment and possibly signal the contribution of the Hainan Plume. We speculate that MORBs of the South China Sea which could have recorded plume‐ridge source mixing perhaps appear since ~23.8 Ma. On the contrary, the Paleocene‐Eocene ocean island basalt‐type intraplate volcanism of the South China continental margin is correlated to decompression melting of a passively upwelling fertile asthenosphere due to continental rifting.

The continental margin of Southeast Asia evolved from a dominantly Andean‐type active margin during Mesozoic to a Western Pacific‐type since Late Cretaceous. With the spreading of the South China Sea, the Palawan‐Mindoro Block drifted from mainland Asia and the Cenozoic strata provide an excellent window to gain insights into the tectonic evolution of the margin of Southeast Asia. Here we present U‐Pb age and Hf isotopic data on detrital zircon grains from Cenozoic sedimentary rocks in the Palawan‐Mindoro Block, Philippines, to evaluate the provenance and tectonic evolution of the South China Sea. Zircon grains in Eocene‐Miocene sedimentary rocks from the Palawan‐Mindoro Block show a wide range in age from 60 to 2700 Ma, with four major age groups of 80–120 Ma, 160–180 Ma, 1600–2100 Ma, and 2200–2700 Ma. The εHf(t) of the zircon grains of the samples from Mindoro Island range from −39 to +13.7, and similar Hf isotopic composition is recorded in Paleogene and Neogene strata. Zircon U‐Pb ages and Hf isotopic data of the Eocene samples from the Palawan‐Mindoro Block show a similar pattern with those from Taiwan, which suggests that the Palawan‐Mindoro Block was attached to the margin of South China during Late Cretaceous‐Eocene times. The difference of zircon U‐Pb age composition in the Miocene samples between the Palawan‐Mindoro Block and Taiwan reflects southward drifting of the Palawan‐Mindoro Block and seafloor spreading of the South China Sea at that time.

The South China Sea oceanic lithosphere has been subducting eastward beneath the Huatung Basin/Philippine Sea Plate since the Early Miocene (similar to 18 Ma). The subduction is followed by the oblique collision between the Luzon arc and the subducting Eurasian plate from 6.5 Ma. The North Luzon Trough forearc strata and the Luzon arc are then obducted northwestward as the Coastal Range, eastern Taiwan, in the last 1 Ma. The collision propagates southward and is presently active in the region offshore SE Taiwan. Integrating seismic surveys offshore and a detailed forearc stratigraphy study onshore the Coastal Range, this paper overviews the characteristics of forearc deformation, dynamic sequence stratigraphy, temporal-spatial variations of forearc sedimentation and stratigraphic correlation onshore and offshore forearc sequences in response to the oblique convergent tectonics north of 20 degrees N. Combining onshore and offshore forearc geology together allows us to reconstruct a structural evolution of the North Luzon Trough forearc basin from subduction through collision to obduction, and to discuss the mechanism and processes responsible for developments of the modern-forming forearc Lichi Melange during the active Taiwan orogeny. Seismic surveys offshore show that forearc deformation in the subduction zone is primarily caused by increase of rear prism slope and west-vergent thrusting of forearc strata along the prism top since the early forearc sedimentation. East-vergent backthrusting occurs during the late forearc sedimentation and propagates arcward when the volcanic arc collides with the accretionary prism in the collision zone. Bivergent thrusting leads to a development of the forearc Huatung Ridge popup as a bathymetric high which further controls the sedimentation of the younger forearc sequence in the collision zone. In response to the syn-sedimentation deformation, forearc depocenter shifts progressively eastward. Forearc stratigraphy thus changes from two syn-sequences bounded by an unconformity in the subduction zone to three mega-sequences juxtaposed from west to east unconformably in the collision zone. As a consequence, the forearc deformation and stratigraphy in the oblique collision zone off SE Taiwan show a characteristic temporal-spatial pattern that the lowest mega-sequence with the most intensive deformation occurs restrictedly in the west, whiles the middle and the upper mega-sequences with mild deformation crop out in the center and the eastern part of the forearc basin, respectively. Detailed biostratigraphy study using planktonic foraminifera and calcareous nannoplanktons indicates that the forearc strata onshore the Coastal Range are also composed of three sequences (lower unit S-1: 6.5-5.8 Ma; middle unit S-2: 5.8-3.0 Ma; and upper unit S-3: < 3.0-1 Ma). They were previously mapped as lithostratigraphy units of the Lichi Melange (6.5-3.0 Ma) in the west and the coherent flysch sequences of the Fanshuliao Formation (5.8-3.0 Ma) and the Paliwan Formation (< 3.0-1 Ma) the east. However, the young coherent forearc sequences in the east thrust westward ubiquitously over the old and highly deformed Lichi Melange in the west along the listric east-dipping Tuluanshan fault during the obduction. Detailed biostratigraphy study reveals that the lower sequence unit S-1 exposes restrictedly in the Lichi Melange west of the Tuluanshan fault, whereas the middle sequence unit S-2 are either mapped as part of the Lichi Melange or the coherent Fanshuliao Formation in both sides of the Tuluanshan fault, respectively. The upper sequence unit S-3 exposes exclusively east of middle sequence unit S-2 in the eastern Coastal Range. Stratigraphy and sedimentology study also reveals a temporal-spatial sedimentation variation of the upper sequence unit S-3 owing to deformation of the sequence units S-1 and S-2 together as a Pliocene Forearc Ridge at similar to 3 Ma, a scenario analog to development of the modern Huatung Ridge at similar to 1 Ma in active collision zone offshore. Temporal-spatial pattern of forearc sequences onshore the Coastal Range suggests that these three sequence units are juxtaposed from west to east and are bounded by two unconformities analog to what occur today in the collision zone offshore SE Taiwan. The characteristic deformation and an eastward-youngling trend of strata distribution onshore the Coastal Range all indicate Syn-sedimentation deformation during the oblique collision in 6.5-1 Ma. Furthermore, along the N-S orogenic strike, events of the forearc sedimentation and bivergent thrusting occur earlier onshore the obduction zone in the north than the modem collision zone offshore in the south. Across the orogenic strike forearc strata get older and deformation gets intensive from east to west onshore the Coastal Range, a scenario analog to what observed in the oblique convergent region offshore SE Taiwan. A structure reconstruction reveals that the North Luzon Trough forearc strata have experienced multiple stages of thrust deformation from subduction through collision to obduction. These deformations account for the mechanism and processes to develop the modem-forming highly sheared SSZ-bearing forearc Lichi Melange tectonically in the western Coastal Range during the last 1 Ma.

Plate-boundary fault rupture during the 2004 Sumatra-Andaman subduction earthquake extended closer to the trench than expected, increasing earthquake and tsunami size. International Ocean Discovery Program Expedition 362 sampled incoming sediments offshore northern Sumatra, revealing recent release of fresh water within the deep sediments. Thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial-induced temperature increases in the past 9 million years. Complete dehydration of silicates is expected before plate subduction, contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction. Shallow slip offshore Sumatra appears driven by diagenetic strengthening of deeply buried fault-forming sediments, contrasting with weakening proposed for the shallow Tohoku-Oki 2011 rupture, but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records.

A holistic view of the Bengal–Nicobar Fan system requires sampling the full sedimentary section of the Nicobar Fan, which was achieved for the first time by International Ocean Discovery Program (IODP) Expedition 362 west of North Sumatra. We identified a distinct rise in sediment accumulation rate (SAR) beginning ∼9.5 Ma and reaching 250–350 m/Myr in the 9.5–2 Ma interval, which equal or far exceed rates on the Bengal Fan at similar latitudes. This marked rise in SAR and a constant Himalayan-derived provenance necessitates a major restructuring of sediment routing in the Bengal–Nicobar submarine fan. This coincides with the inversion of the Eastern Himalayan Shillong Plateau and encroachment of the west-propagating Indo–Burmese wedge, which reduced continental accommodation space and increased sediment supply directly to the fan. Our results challenge a commonly held view that changes in sediment flux seen in the Bengal–Nicobar submarine fan were caused by discrete tectonic or climatic events acting on the Himalayan–Tibetan Plateau. Instead, an interplay of tectonic and climatic processes caused the fan system to develop by punctuated changes rather than gradual progradation.

The Taiwan orogenic belt,located in the juncture of the Eurasian plate and the Philippine Sea plate,is one of the youngest active orogenic belts in the world within a unique geological environment.The Coastal Mountains,which is located in the east of the Island,are composed of a residual fore-arc basin and a volcanic island,and the former of which is evolved from the fore-arc basin of the north Luzon Trough after two-stages of strong extrusion of shearing structure.This paper adopts FLAC6.0 to simulate the thrust structural inversion of the Taiwan fore-arc basin.It is found out through analysis of simulation results that the reversal of thrust structure in the Taiwan fore-arc basin is developed from east to west gradually,and evolves from local tectonic inversion in the beginning to overall thrust structure westward finally.In addition,stratum thickness and slope angle of basement plays certain control roles in the formation and evolution of folding.

The Lichi Mélange in the Coastal Range, eastern Taiwan, is considered as sheared forearc sequences. However, the age of these sequences is still uncertain, and their significance for the arc‐continent collision has been overlooked. Based on field surveys and micropaleontological analysis, four independent biostratigraphic units ranging from <8.5 to 3.0 Ma are discerned in the Lichi Mélange. These units are obviously older than the remnant forearc sequences in the east (3.4–1.2 Ma), supporting the interpretation that the Lichi Mélange arose from the shearing of the lower forearc basin sequences. The stratigraphy also suggests that the older forearc strata (<8.5–3.4 Ma) were deformed and uplifted as a bathymetric high similar to the Huatung Ridge in the western North Luzon Trough by arcward back thrusting before 3.4 Ma, while sedimentation continued in the remnant forearc basin in the east during 3.4–1.2 Ma. The older forearc strata possess vitrinite reflectance values even lower than those of the remnant forearc sequences, which also supports that they were uplifted by back thrusting and therefore did not experience significant burial. Neodymium isotope analysis shows that the <8.5–6.4 Ma forearc sediments were sourced from both the volcanic arc and the accretionary prism, indicating the emergence of the accretionary prism within <8.5–6.4 Ma. It might have resulted from the underplating of thinned continental crust and provides a good time constraint for the onset of arc‐continent collision. The post 6.4 Ma forearc sediments were mainly derived from the accretionary prism, reflecting its constant uplift and large‐scale exposure.

The uplift of Tibet Plateau and the marginal sea spreading have had important influence on the tectonic, landform and drainage system in East Asia, although the marginal sea spreading in shaping the topography and drainage reorganization in East Asia has been still controversial. Here we present U-Pb age and Hf isotopic composition of detrital zircon grains from Cenozoic sedimentary rocks in Taiwan to understand how the provenance and river systems evolved. Our data show that the U-Pb age spectra of detrital zircon grains in Paleogene sandstones are dominated by Yanshanian (180–67Ma) zircon grains and with subordinate or nil Proterozoic and Archean zircon grains. These results are in contrast to those in Miocene rocks that are dominated by the Indosinian (257–205Ma) zircon grains together with Yanshanian, Proterozoic and Archean population. The initial Hf isotope ratios [εHf(t)] of the zircon grains also display systematic change in Paleogene and Neogene strata. Our data demonstrate that the Hsuehshan Range and Western Foothills in Taiwan have the same sedimentary sources. The source region of Paleogene strata was mainly located at the coast in southeast China and migrated inland over time. The source might have reached the Lower Yangtze region during early Miocene. Although the mechanism of transport of sediments from the Lower Yangtze region to Taiwan is unclear, we speculate that the Minjiang River might have been larger in Early Miocene than the present and might have delivered inland material along the boundary of Yangtze and Cathaysia Blocks to Taiwan. These were then captured by the Yangtze River systems at some time after Late Miocene. This change corresponds to the time of the drainage reorganization in East Tibet, such as Yangtze River, and the regional subsidence resulting from the opening of marginal sea. The combined effects of Tibet uplift and opening of marginal sea might have shaped the topography and river system reorganization in East Tibet. The evolution of topography and drainage systems in southeast China seems to be mainly controlled by the opening of marginal sea.

The Kenting Mélange on the Hengchun Peninsula, Taiwan, formed through tectonic shearing of subduction complex lithologies, probably within the plate boundary subduction channel between the Eurasian and Philippine Sea plates, with further deformation and exhumation in the Pliocene–Pleistocene during arc–continent collision. Field relations reveal a structural gradation from normal stratified turbidite sequence (Mutan Formation) through broken formation to highly sheared Kenting Mélange containing allochthonous polygenic blocks. This gradation is consistent with an increase of average vitrinite reflection values from ~0.72% in the Mutan Formation through ~0.93% in the broken formation to ~0.99% in the mélange, suggesting temperatures of at least 140°C during formation of the Kenting Mélange. Zircons from gabbro in the Kenting Mélange are dated as 25.46±0.18Ma, which together with geochemical data constrains the source to South China Sea oceanic lithosphere. In combination with the field relationships, vitrinite reflectance values, microfossil stratigraphy, and offshore geophysical data from S and SE Taiwan, we propose that the Kenting Mélange initially formed at the subduction plate boundary from off-scraped trench deposits. Minor Plio–Pleistocene microfossils (<5%) occur within the mélange in proximity to slope basin of equivalent age and were likely sheared into the mélange during out-of-sequence thrusting associated with active arc–continent collision, which in the Hengchun Peninsula commenced after 6.5Ma.

南海南、北共轭大陆边缘盆地的对比研究是深入了解南海扩张过程及古地理格局的重要途径.由于历史原因,目前对南海南缘盆地构造-沉积演化研究还非常薄弱,极大地限制了对南海扩张及海陆变迁等基础地质问题的整体认识.综合南海及其周缘盆地沉积地层和沉积环境的研究进展,对南海扩张过程和古地理格局演化进行了分析.南海南、北缘盆地破裂不整合面存在着明显的穿时性,从NE向SW逐渐变年轻,对应南海海底扩张从NE向SW渐进式打开.台湾新生代地层破裂不整合面位于33～39 Ma之间,暗示南海洋壳开始形成的时间可能在33～39 Ma之间,有部分较老的洋壳可能已经向东俯冲消减掉.南海经历了从早期“北陆南海”逐渐演变为现今“北海南陆”的过程,南海北缘早期存在一个向东开口的海湾,可能为古南海的一部分.伴随南海的扩张,海侵范围由东向西逐渐扩展,从一个狭窄的海湾形成今日的形貌.南海北缘盆地物源在～25 Ma左右发生明显的改变,早期主要为华南沿海的近源剥蚀沉积.在～25 Ma后,来自扬子地块的沉积物逐渐增多.南海南缘盆地物源在～25 Ma前与南海北缘盆地具有相似的物质来源,～25 Ma后南海洋盆阻挡扬子地块的物源向南输送,南海南缘仍以陆块内部中生代花岗岩及火山岩为主要物质来源.

有孔虫壳体的氧同位素值(δ18O)是由其生长时海水δ18O和温度决定的,在海水δ18O已知的情况下,可以由壳体的δ18O值估算海水温度.本文以南海北部沿岸地区9个站位的柱状沉积物中浮游有孔虫Globigerinoides ruber为研究对象,测试了其壳体的δ18O值.分别以相应站点夏季与冬季表层海水的实测δ18O值代入温度公式,估算了对应的夏季与冬季的海水温度值.然后把计算结果与World Ocean Atlas(WOA)数据库相应站点的海水温度数据作比较.结果表明,计算出的夏季海水温度与WOA的夏季温度有较大差别,而计算出的冬季海水温度则与WOA的冬季海水温度基本相当.这说明δ18Oruber记录的是该区域冬季表层海水的温度,此区域内G.ruber这一属种的生产力和沉积通量在东亚冬季风盛行期间出现了最高值.

台湾东部海岸山脉弧前盆地层序由西侧的利吉混杂岩和东侧的残留弧前浊积层序组成,记录了北吕宋火山岛弧与欧亚大陆边缘碰撞的构造演化.在海岸山脉中段,利吉混杂岩不仅分布于乐合弧前盆地西侧,也出露于残留弧前层序中央.本文通过野外地质调查及微体化石研究,论述乐合弧前盆地内各地层单元的时空展布特征及其构造控制机制.综合浮游有孔虫与钙质超微化石研究结果,利吉混杂岩泥质基质可限定在早上新世4.3～3.4 Ma内,而残留弧前浊积层序沉积在晚上新世3.4～3.0 Ma,说明利吉混杂岩不是与残留弧前浊积层序同时异相的滑塌堆积,出露于盆地中心的利吉混杂岩也不是沉积于向斜轴部的最年轻地层.在乐合弧前盆地,年老的利吉混杂岩总体上分布于年轻的残留弧前层序西侧,该地层展布特征类似于台湾东南海域北吕宋海槽内受向东背冲构造控制的花东海脊-残留弧前盆地.这说明乐合弧前盆地早期沉积层序在不晚于3.4 Ma时同样受到背冲构造的控制,被变形抬升为花东海脊地形高区.而位于东侧的残留弧前盆地在3.4～3.0 Ma间继续沉积正常浊积层序.乐合弧前盆地的地层展布特征不仅记录了初期弧陆碰撞阶段的向东背冲构造,也记录了成熟期弧陆碰撞阶段的向西逆冲构造.在成熟期弧陆碰撞阶段,花东海脊被进一步向西剪切为利吉混杂岩,残留弧前层序及火山岛弧向西逆掩于利吉混杂岩之上,形成海岸山脉.由于河流的侵蚀作用使得部分利吉混杂岩以构造窗的方式出露于盆地中心.

The Miocene accretionary prism in the Hengchun Peninsula,southern Taiwan,consists of three formations.The Mutan and Loshui Formations are deposited in a middle—lower deep-water fan and the Lilungshan Formation deposited in a shallow-water environment.U-Pb age data show that the age patterns of zircon grains of the Lilungshan and Mutan Formations are similar with those of the Minjiang estuary sands,while the age pattern of the Loshui Formation is identical to the Jiulongjiang estuary sands by absence of 400~600Ma zircon grains and less 700~1 000 Ma and 1 600~2 000 Ma zircon grains.During the Late Miocene,the global sea-level fell significantly due to a dramatic expansion of the Antarctic ice sheet.The coast line of the China continent shifted eastward and a large part of the present East China Sea-Taiwan Strait was exposed.Consequently,large rivers like the Minjiang River in SE China could transport debris flow deposits southeastward to the upper slope of the Chinese continental margin.These turbidite sequences were then deformed as the accretionary prism in the Hengchun Peninsula,while the South China Sea subducted in the Late Miocene time.

菲律宾出露有20余套规模各异的俯冲带上板块(SSZ)型蛇绿岩,它们的时代以晚中生代为主,仅少数为新生代.大多数菲律宾蛇绿岩出露相对完整,包括由二辉橄榄岩、方辉橄榄岩、纯橄岩等组成的变质地幔岩,和堆晶辉石岩、辉长辉绿岩等深成岩,以及枕状玄武岩、熔岩等喷出岩,甚至燧石岩等上覆沉积物,部分发育席状岩墙群和与蛇绿岩相关的构造混杂岩及变质基底.其中喷出岩在地球化学特征上整体表现出类似MORB和IAT的REE配分模式,具LILE富集和HFSE(如Nb、Ta相对La、Th)弱到中等程度亏损的特征.通过对菲律宾蛇绿岩的形成年代、岩石组合、地球化学特征及构造环境的分析,并与东南亚地区其他同时代蛇绿岩和周缘边缘海进行对比,将菲律宾蛇绿岩分为两部分.(1)菲律宾活动带蛇绿岩,该蛇绿岩带自西向东出露晚中生代弧前、新生代弧前扩张盆地和晚中生代岛弧、弧后盆地的残留,推测晚中生代蛇绿岩来自中特提斯洋向古太平洋板块俯冲所形成的沟-弧-盆体系,是菲律宾新生代岛弧岩浆活动的基底,而夹于晚中生代蛇绿岩之间的始新世蛇绿岩来自老的岛弧基底之上由于新特提斯洋俯冲形成的弧前扩张盆地.(2)菲律宾陆块蛇绿岩,其中巴拉望微陆块晚中生代蛇绿岩来源于古南海,而构造叠置于它们之上的新生代蛇绿岩则来源于古南海俯冲对应形成的边缘海,如苏禄海和南海;三宝颜微陆块或可能是古南海的南部被动大陆边缘,其蛇绿岩可能是古南海的残片,抑或三宝颜微陆块可能是婆罗洲南部东爪哇-西苏拉威西地体的延续,故该蛇绿岩又可能是新特提斯洋的残片.