Journal of Southeast Asian earth sciences最新文献

The Archaean continental crust in China originated from dispersed nuclei under the influence of whirl tectonics 2.5 Ga ago. From the beginning of the early Proterozoic, the crustal evolution process was controlled by the plate tectonics. A tectonic regime of coexisting mobile belts of different characteristics and rigid blocks emerged. The diversity of tectonic setting and structures marked the beginning of a new epoch of crustal evolution. The north China protoplatform, the Tarim protoplatform and the Yangtze protoplatform are considered to have separated from each other by least at the end of Archaean, based on the early Proterozoic accretion zones developed between them. Cathaysia gradually moved closer to the Yangtze protoplatform in the early Proterozoic. The nearly north-south primary structural trend of the early Proterozoic formations in the northern margin of the modern north China platform indicates that the north China protoplatform had been connected with the Siberian craton during and before early Proterozoic times.

Since 1982, numerous indicators of catastrophic eventshave been observed at the main stratigraphic boundaries in China during the Phanerozoic, i.e. Precambrian-Cambrian, Permian-Triassic, Cretaceous-Tertiary as well as Ordovician-Silurian and Devonian-Carboniferous boundaries. These markers are boundary clay layer, microspherules, high Ir anomaly, mass extinction of organisms and impact of meteorite. We support the hypothesis of the extraterrestrial origin of catastrophic events and suggest that the events at different stratigraphic boundaries might be different in features and processes.

This paper aims to give answers to the questions of timing, tectonic style and geodynamic interpretation of south China geologic development. In the middle Jiangnan segment, Yangzi plate and Cathaysia got clearly welded during a Late Proterozoic orogeny of collisional type, marked by HP/LT metamorphism, ophiolite melange obduction, thrusting of greenschist nappes, emplacement of collisional S-type granites. This collision, which built the initial Jiangnan belt, began around 950 ± 40 Ma and was completed at about 770–800 Ma ago. Kinematic study indicates that the Cathaysia plate was underthrust beneath the Yangzi plate. A likely earlier collisional event occurred around 1500 Ma, but is poorly preserved in the studied area. The proposed geodynamic model implies two successive suturings of oceanic domains during the Middle-Late Proterozoic: one about 1500 Ma and one about 950 Ma. A strong remobilization occurred during the Early Paleozoic ‘Caledonian’ orogeny, which induced transpressive ductile deformation. Thin-skinned folding and thrusting took place during the Mesozoic; this intracontinental shortening could be due to collision between the China-Indochina and west Philippines blocks. South China is a composite block, comprising the relics of at least three, maybe four sutures from Jiangnan to the coast.

New discoveries of Silurian and Devonian vertebrates in China and their palaeogeographical significance are reviewed. The Middle Paleozoic fish assemblages of the Tarim basin are similar to those of South China. Fossil vertebrate evidence shows the appearance of the Chinese platform in Middle Paleozoic and its close relation with East Gondwana at least in Early Devonian.

The aim of this study is to discuss the tectonic position of Baoshan in Yunnan Province, China, during the Late Paleozoic by comparison of the sedimentary facies, fauna and palaeomagnetic data from the Baoshan region with those from the Yangtze region and southern Tibet. The sedimentary facies change suggests that in the Late Palaeozoic the Baoshan region underwent a similar geological history to southern Tibet, but different from that of the Yangtze region. The rugose corals and brachiopods as well as vertebrates of Baoshan are different from those of the Yangtze region during the Late Palaeozoic. An evident segregation seems to exist between them. The Late Paleozoic fauna of Baoshan shows certain similarities to southern Tibet. The Devonian and Late Carboniferous faunas, especially, are very similar to those in southern Tibet. This indicates that there was no evident segregation between them in the Late Palaeozoic. The palaeomagnetic data reveal that in the Late Palaeozoic the Yangtze region was close to the equator, while the Baoshan region and southern Tibet were situated in the middle latitudes.

On the basis of the palaeontological, sedimentological and palaeomagnetic data, it is inferred that Baoshan and southern Tibet were situated in the same continental margin, and both regions were far from the Yangtze region during the Late Paleozoic. The Baoshan region may be considered as a massif within the Gondwana tectonic domain which includes southern Tibet, while the Yangtze region was located in another tectonic domain—the South Asian domain, with a wide ocean, the Tethys between them.

The paper aims to assess the Holocene natural vegetation on the Loess Plateau before human reclamation, a contentious point in paleo-environmental studies. Coordinated analyses on the soils, phytolith assemblage, organic carbon isotope composition and pollen data from selected sites suggest that the Holocene vegetation on the Loess Plateau was dominated by steppe. During the mid-Holocene, corresponding to the climatic optimum, the southernmost part of the Plateau (Weinan and Xian) was covered by an open meadow steppe with the presence of some coniferous species, while the middle part of the plateau (Luochuan) was covered by steppe. Our results do not support the notion that dense forest cover had developed on the Loess Plateau during the Holocene.

Mesozoic tectonism in Korea is characterized by polycyclic and reiterated intracratonic deformations, which include (a) strike-slip movement of ductile or brittle-ductile shearings, (b) compressive phase of folding, thrusting and transpression of strike-slip movement and (c) extensional phase of basin formation by normal or domino fault system and transtension of strike-slip movement. It occurred during three events; Songnim, Daebo and Bulgugsa orogeneis. Late Permian to Early Triassic Songnim orogeny can be divided into two stages. In the early stage, ductile shearing has affected the southwestern part of the Ogcheon Belt and northwest-trending folds developed in the Paleozoic sedimentary sequences. During the late stage, folding and thrust movement have affected the Paleozoic rocks and produced northwest-trending folds and thrusts which moved toward the southeast. When the Songmin orogeny was diminished, post-tectonic granites were emplaced and the Daedong basins were formed by extensional tectonic fields. The Daebo orogeny follows the deposition of the Later Triassic to Early Jurassic Daedong Group, which inclues northeast-trending folds and thrusts. This phase was continued on the Songnim phase, in which folds and thrust faults had similar trends and transport directions. The Songnim phase was then associated with high angle thrust faults. During the late stage, brittle-ductile strike-slip faults predominated, and produced pull-apart basins along the contact boundary of the Ogcheon belt. S-type granites were emplaced with the northeast trend. From the Late Cretaceous to Early Tertiary periods, the Bulgugsa orogeny produced east-west trending folds and thrusts. Thrust movements prevailed ini the northeastern part of the Ogcheon belt, whereas other areas were affected by east-west trending folds. Sedimentary rocks in the pull-apart basins were affected by transpression and produced en-echelon arrays of folds and flower structures. Mesozoic tectonism in Korea can be correlated to Indosinian, Yanshanian, and Sichuanian tectonisms in China.

Professor Huang Jiqing (T. K. Huang) put forward the concept of polycyclic tectonic movement which was developed into the polycyclicity theory that is influential all over the world. This paper outlines the basics of this theory.

The present author tries to distinguish between two kinds of polycyclic tectonic movements: in situ superimposition and recurrence in other places according to whether or not they recur at the same place. Further study on the latter led to the concept of tectonic migration. Tectonic migration is the vivid representation of the recurrence of polycyclic movements, an in-depth development of the polycyclicity theory.

Applying the plate tectonics theory to the practical geology of China, Huang set up the accordion movement model of plate movement, which has enriched plate tectonics theory and polycyclicity theory. Based on this pioneer's research, the present author has proposed the concept of open-and-close tectonics, interrelating the polycyclicity theory, accordion movement, tectonic migration and plate tectonics, and attempts to find a new way in the study of geotectonics.

From the polycyclicity theory through the tectonic migration theory to open-and-close tectonics, one can trace the trajectory of the polycyclicity theory and see its development, with the open-and-close tectonics (OC tectonics) being a milestone in the development of the polycyclicity theory.

After going through intense detachment and plate collision, the Late Proterozoic plate sutures and Paleozoic aulacogens evolved into a series of overthrusts which were thrusted onto the craton, forming the Indosinian Longmen mountains. Continental marginal slope which had dipped westward for a long time was changed into the Sichuan foreland basin. Superimposed orogenic movements and related migration of sedimentary basins controlled the generation, migration, accumulation and disappearance of hydrocarbons. Subsequently, rock overtightening and the formation of the Himalayas led to the unique hydrocarbon characters at the foreland of the Longmen mountains.

The Chinese continent is a composite continent made up of many blocks of various sizes. It features soft-collision and polycyclic suturing between the blocks and the resulting composite orogeny. The continent has distinctive polycyclic evolution by stages and multilevel mosaic and flyover-type structures. Since the Paleozoic, the tectonic development of China has been controlled by the three global dynamic systems: The Paleo-Asian, Tethyan and Pacific systems. The geodynamic processes were marked by Gondwana dispersion, blocks drifting northward, fold belts migrating southward and Asian accretion.