Rural labor migration and farmers’arrangements of rice production systems in Central China:Insight from the intergenerational division of labor

Rice production is crucial for food security in China,and its relationship with rural labor migration has been studied extensively.Labor migration in rural China has taken new forms in recent years.There has been a discernible trend wherein adult children have started migrating to cities while their elderly parents return to villages to re-engage in on-farm work.The phenomenon has notably shaped the intergenerational division of labor(IDL)within households.However,it remains to be seen how farmers adjust their rice production systems in response to the IDL.The age of 60 years for employment injury insurance is the eligibility threshold for off-farm employment and is used to obtain a source of exogenous variation in the IDL.Based on a representative household survey of 1,752 rice farmers in the Hubei Province of Central China,our fuzzy regression discontinuity analysis reveals that farmers in IDL households are more likely to adopt ratoon rice(RR)than single cropping rice(SR)or double cropping rice(DR).The effect of the IDL varies under different levels of operational scales and specialized agricultural service availability.Further analysis suggests that farmers’arrangements are associated with two potential mechanisms of downward intergenerational transfer.Monetary transfer for urban housing purchases increases RR in IDL households,and time transfer for intergenerational childcare significantly promotes SR in IDL households.This study enhances the understanding of the relationship between rural labor migration and rice production in China,providing a reference for adjusting rice production systems to ensure food security.

Sedimentary systems of the Oligocene Huagang Formation in the central anticline zone of the Xihu Depression,East China Sea Shelf Basin

The Xihu Depression is the largest hydrocarbon-bearing depression of the East China Sea Shelf Basin(also referred to as the ECSSB).However,the depositional systems and reservoir distribution of the Oligocene Huagang Formation in the Xihu Depression are still controversial.Under the guidance of sedimentology and stratigraphy,this study documented a marine-terrestrial transitional environment in the restricted bay setting of the Oligocene Huagang Formation through core description,well logging,and seismic data analysis.This study also revealed that the Oligocene Huagang Formation is dominated by tidal delta,estuary,and gravity flow deposits in the central anticline zone of the Xihu Depression.The new understanding of the sedimentary systems and the discovery of the transgressive gap in the eastern Diaoyu Islands uplift explain the origin of fine-grained sediments and the EW-trending sand bodies in the central depression and the sand bodies parallel to shoreline in the west slope belt,which cannot be explained by previous study results,such as southern transgression or fluvial deltas and even lacustrine deposition.Moreover,the tidal channels,tidal sand flats,and gravity flow sand bodies formed by the transgressive tides are high-quality reservoirs.The study will provide a basis for well placement and serve as guidance for the selection of favorable hydrocarbon exploration areas in the Xihu Depression.

Genetic and biological properties of H9N2 avian influenza viruses isolated in central China from2020 to 2022

The H9N2 subtype of avian influenza virus(AIV)is widely prevalent in poultry and wild birds globally,and has become the predominant subtype circulating in poultry in China.The H9N2 AIV can directly or indirectly(by serving as a"donor virus")infect humans,posing a significant threat to public health.Currently,there is a lack of in-depth research on the prevalence of H9N2 viruses in Shanxi Province,central China.In this study,we isolated 14 H9N2 AIVs from October 2020 to April 2022 in Shanxi Province,and genetic analysis revealed that these viruses belonged to 7 different genotypes.Our study on animals revealed that the H9N2 strains we identified displayed high transmission efficiency among chicken populations,and exhibited diverse replication abilities within these birds.These viruses could replicate efficiently in the lungs of mice,with one strain also demonstrating the capacity to reproduce in organs like the brain and kidneys.At the cellular level,the replication ability of different H9N2 strains was evaluated using plaque formation assays and multi-step growth curve assays,revealing significant differences in the replication and proliferation efficiency of the various H9N2 viruses at the cellular level.The antigenicity analysis suggested that these isolates could be classified into 2 separate antigenic clusters.Our research provides crucial data to help understand the prevalence and biological characteristics of H9N2 AIVs in central China.It also highlights the necessity of enhancing the surveillance of H9N2 AIVs.

The evolution of central environmental protection inspection policy attention in China: An investigation based on inspection reports

The central environmental protection inspection (CEPI) system in China is a significant institutional innova‐tion in national environmental governance. The CEPI applies a joint supervision strategy to address salient en‐vironmental issues and strictly enforce the environmental responsibilities of local governments. This study col‐lects and organizes CEPI inspection reports covering three stages that encompass the first round, the “look back”, and the second round, applying text analysis to obtain sample data and conduct statistical quantifica‐tion of word frequency in inspection reports and identify notable changes. The study explores the allocation of CEPI attention between policy objectives and the intensity of policy instruments. We determine that in con‐junction with public opinion feedback, the CEPI conducts targeted inspections and focuses more on pollutant governance, which has high severity and can be addressed quickly. The CEPI fills the gap of normalized gover‐nance with a campaign-style governance approach. Regarding the intensity of policy measures, the CEPI pri‐marily uses economic incentive policy instruments, supplemented by command-and-control and public guid‐ance approaches, advancing the sustainability of regulatory effectiveness through economic, social, and politi‐cal activities. This study extends knowledge in the field of CEPI policy priorities and implementation, expand‐ing the literature related to outcomes of environmental policy in developing countries.

Causes of the Extreme Hot Midsummer in Central and South China during 2017:Role of the Western Tropical Pacific Warming

This study investigates why an extreme hot midsummer occurred in Central and South China(CSC) during 2017. It is shown that the western North Pacific subtropical high(WNPSH) was abnormally intensified and westward-extending,resulting in anomalous high pressure and consequent extreme heat over CSC. The abnormal WNPSH was favored by the warming of the western tropical Pacific(WTP), which was unrelated to ENSO and manifested its own individual effect.The WTP warming enhanced the convection in-situ and led to anomalous high pressure over CSC via a local meridional circulation. The influence of the WTP was confirmed by CAM4 model experiments. A comparison between the 2017 midsummer and 2010 midsummer(with a stronger WNPSH but weaker extreme heat) indicated that the influence of the WNPSH on extreme heat can be modulated by the associated precipitation in the northwestern flank.The role of the WTP was verified by regression analyses on the interannual variation of the WTP sea surface temperature anomaly(SSTA). On the other hand, the WTP has undergone prominent warming during the past few decades, resulting from decadal to long-term changes and favoring extreme warm conditions. Through a mechanism similar to the interannual variation, the decadal to long-term changes have reinforced the influence of WTP warming on the temperature over CSC,contributing to the more frequent hot midsummers recently. It is estimated that more than 50% of the temperature anomaly over CSC in the 2017 midsummer was due to the WTP warming, and 40% was related to the decadal to long-term changes of the WTP SSTA.

SIMPLE ECOSYSTEM MODEL OF THE CENTRAL PART OF THE EAST CHINA SEA IN SPRING

This paper’s simple ecological model to simulate the ecosystem variation and the vertical carbon flux in the central part of the East China Sea in spring, inter-reated the phytoplankton, zooplankton,autotrophic and heterotrophic bacterioplankton, nitrate, and dissolved organic carbon (DOC) in a run lasting 90 days. Except for DOC, because of poor observation precision,the major seasonal features of the vertical distribution for these components can be simulated by this model. The results show that spring bloom is just a short period of 1-2 weeks and that deposit carbon flux at the bottom interface is about 200 mg /m2 ·d in the first 20 days and then reaches its maximum of 1500mg/m2·d about 2 months later after the spring bloom.

Petrology, Metamorphic Process and Genesis of The Dabie--Sulu Eclogite Belt, Eastern--Central China

The Qinling-Dabie-Sulu high-pressure and ultra-high pressure metamorphic belt wasformed by subduction and collision between the North China and Yangtze plates. The study ofthe eclogite belt is very important in understanding the evolution of the Qinling Dabie orogen. Inthe present paper the geology, petrology, minerology and chronology of the eclogites in the Dabieand Sulu areas are described. The principal conclusions of this work are as follows: (1) Based up-on the field occurrence and the P-T conditions of the eclogites, two types of eclogite can be dis-tinguished: Type 1—the low-temperature and high-pressure eclogite in the mid-late Proterozoicmetamorphic series, and Type 2—the ultra-high pressure eclogite in the late Archaean to earlyProterozoic metamorphic complex. In the Dabie area, the ultra-high-pressure eclogite,high-pressure eclogite and epidote-blueschist units are nearly parallel to each other and stretchintermittently from north to south. (2) The P-T conditions of the high-pressure eclogites and ul-tra-high pressure eclogites have been estimated. The former are formed at 450-550℃ and1.4-1.6 GPa; while the latter at 650-870℃ and >2.7-2.9 GPa in the Dabie area and at820-1000℃ and >2.8-3.1 GPa in the Sulu area. The metamorphic temperatures of the eclogitesincrease progressively from west to east. (3) The ultra-high pressure eclogites were subjected to 5stages of metamorphism: pre-eclogite epidote amphibolite facies, peak coesite eclogite facies,post-eclogite amphibolite facies, epidote-blueschist facies or epidote amphibolite facies andgreenschist facies. The general features of the PTt path of the ultra-high pressure eclogite are:clockwise pattern, progressive metamorphism being a process of slow increasing temperature andrapid increasing pressure, and the retrogressive section with nearly isothermal decompression atthe early stage, isobaric cooling at the middle stage and nearly isothermal decompression at thelate stage. (4) At least two stages of high-pressure metamorphism occurred in the orogenic belt:the high-pressure eclogite and ultra-high pressure eclogite were formed by the subduction of theoceanic crust northward beneath the North China plate or the Dabie block during theCaledonian; while the epidote-blueschist belt came into being by subdution and collision be-tween the two continental plates during the Indosinian. (5) Due to the continuous sequentialsubduction of the cold plate, the ultra high-presssure metamorphic rocks were uplifted to thecrust by the underplating processes. They can be preserved just because of the 'frozen effect' re-sulting from the continuous subduction of the cold plate. (6) The carbonates, such as magnesite,breunnerite, aragonite and dolomite, and the H_2O-bearing minerals, such as phengite, epidoteand zoisite, were stable during the high-pressure and/or ultra-high pressure metamorphism.

Geology and hydrocarbon accumulations in the deepwater of the northwestern South China Sea——with focus on natural gas

The deepwater of the northwestern South China Sea is located in the central to southern parts of the Qiongdongnan Basin （QDN Basin）, which is a key site for hydrocarbon exploration in recent years. In this study, the authors did a comprehensive analysis of gravity-magnetic data, extensive 3D seismic survey, cores and cuttings, paleontology and geochemical indexes, proposed the mechanism of natural gas origin, identified different oil and gas systems, and established the model of hydrocarbon accumulations in the deep-water region. Our basin tectonic simulation indicates that the evolution of QDN Basin was controlled by multiple-phased tectonic movements, such as Indochina-Eurasian Plate collision, Tibetan Uplift, Red River faulting and the expansion of the South China Sea which is characterized by Paleogene rifting, Neogene depression, and Eocene intensive faulting and lacustrine deposits. The drilling results show that this region is dominated by marine- terrestrial transitional and neritic-bathyal facies from the early Oligocene. The Yacheng Formation of the early Oligocene is rich in organic matter and a main gas-source rock. According to the geological-geochemical data from the latest drilling wells, Lingshui, Baodao, Changchang Sags have good hydrocarbon-generating potentials, where two plays from the Paleogene and Neogene reservoirs were developed. Those reservoirs occur in central canyon structural-lithologic trap zone, Changchang marginal trap zone and southern fault terrace of Baodao Sag. Among them, the central canyon trap zone has a great potential for exploration because the various reservoir- forming elements are well developed, i.e., good coal-measure source rocks, sufficient reservoirs from the Neogene turbidity sandstone and submarine fan, faults connecting source rock and reservoirs, effective vertical migration, late stage aggregation and favorable structural-lithological composite trapping. These study results provide an important scientific basis for hydrocarbon exploration in this region, evidenced by the recent discovery of the significant commercial LS-A gas field in the central canyon of the Lingshui Sag.

Influence of the Asian-Pacific Oscillation on Spring Precipitation over Central Eastern China

The linkage between the Asian-Pacific oscillation （APO） and the precipitation over central eastern China in spring is preliminarily addressed by use of the observed data. Results show that they correlate very well, with the positive （negative） phase of APO tending to increase （decrease） the precipitation over central eastern China. Such a relationship can be explained by the atmospheric circulation changes over Asia and the North Pacific in association with the anomalous APO. A positive phase of APO, characterized by a positive anomaly over Asia and a negative anomaly over the North Pacific in the upper-tropospheric temperature, corresponds to decreased low-level geopotential height （H） and increased high-level H over Asia, and these effects are concurrent with increased low-level H and decreased high-level H over the North Pacific. Meanwhile, an anticyclonic circulation anomaly in the upper troposphere and a cyclonic circulation anomaly in the lower troposphere are introduced in East Asia, and the low-level southerly wind is strengthened over central eastern China. These changes provide advantageous conditions for enhanced precipitation over central eastern China. The situation is reversed in the negative phase of APO, leading to reduced precipitation in this region.

Stability of Spatial Structure of Urban Agglomeration in China Based on Central Place Theory

This paper brings forward the concept of stability of the spatial structure of urban agglomeration(UA)based on Central Place Theory by introducing centrality index and fractal theory.Before assessment,K=4 is selected as parameter to calculate centrality index and fractal dimension(K represents the quantitive relationship between city and the counties in Central Place Theory),and then found the number of nodes,the type of spatial structure,the spatial allocation of nodes with different hierarchy affecting the stability of spatial structure.According to spatial contact direction and the level of stability,UAs in China are classified into five types.Finally,it is posed as a further question that how to use hierarchical relation K=6 and K=7 in central place system to coordinate with the assessment of stability of soatial structure is brought forward.

Combined Impacts of Warm Central Equatorial Pacific Sea Surface Temperatures and Anthropogenic Warming on the 2019 Severe Drought in East China

A severe drought occurred in East China(EC)from August to October 2019 against a background of long-term significant warming and caused widespread impacts on agriculture and society,emphasizing the urgent need to understand the mechanism responsible for this drought and its linkage to global warming.Our results show that the warm central equatorial Pacific(CEP)sea surface temperature(SST)and anthropogenic warming were possibly responsible for this drought event.The warm CEP SST anomaly resulted in an anomalous cyclone over the western North Pacific,where enhanced northerly winds in the northwestern sector led to decreased water vapor transport from the South China Sea and enhanced descending air motion,preventing local convection and favoring a precipitation deficiency over EC.Model simulations in the Community Earth System Model Large Ensemble Project confirmed the physical connection between the warm CEP SST anomaly and the drought in EC.The extremely warm CEP SST from August to October 2019,which was largely the result of natural internal variability,played a crucial role in the simultaneous severe drought in EC.The model simulations showed that anthropogenic warming has greatly increased the frequency of extreme droughts in EC.They indicated an approximate twofold increase in extremely low rainfall events,high temperature events,and concurrently dry and hot events analogous to the event in 2019.Therefore,the persistent severe drought over EC in 2019 can be attributed to the combined impacts of warm CEP SST and anthropogenic warming.

Isotopic Ages of the Carbonatitic Volcanic Rocks in the Kunyang Rift Zone in Central Yunnan,China

The Mesoproterozoic Kunyang rift, which is located on the western margin of the Yangtze platform and the southern section of the Kangdian axis, is a rare massive Precambrian iron-copper polymetallic mineralization zone in China. The Mesoproterozoic Wulu (Wuding-Lufeng) basin in the middle of the rift is an elliptic basin controlled by a ring fracture system. Moreover, volcanic activities in the basin display zonation of an outer ring, a middle ring and an inner ring with carbonatitic volcanic rocks and sub-volcanic dykes discovered in the outer and middle rings. The Sm-Nd isochron ages have been determined for the outer-ring carbonatitic lavas (1685 Ma) and basaltic porphyrite of the radiating dyke swarm (1645 Ma) and the Rb-Sr isochron ages for the out-ring carbonatitic lavas (893 Ma) and the middle-ring dykes (1048 Ma). In combination of the U-Pb concordant ages of zircon (1743 Ma) in trachy-andesite of the corresponding period and stratum (1569 Ma) of the Etouchang Formation, as well as the Rb-Sr isochron age (1024 Ma) and K-Ar age (1186 Ma) of the dykes in the middle ring, the age of carbonarites in the basin is preliminarily determined. It is ensured that all of these carbonatites were formed in the Mesoprotero/oic period, whereby two stages could be identified as follows: in the first stage, carbonatitic volcanic groups, such as lavas, pyroclastic rocks and volcaniclastic sedimentary rocks, were formed in the outer ring; in the second stage, carbonatitic breccias and dykes appeared in the middle ring. The metamorphic age of the carbonatitic lavas in the outer ring was determined to be concurrent with the end of the first stage of the Neoproterozoic period, corresponding to the Jinning movement in central Yunnan.

Geochemical and Petrological Studies on the Early Carboniferous Sidingheishan Mafic-Ultramafic Iintrusion in the Southern Margin of the Central Asian Orogenic Belt,NW China

The Sidingheishan mafic-ultramafic intrusion is located in the eastern part of the Northern Tianshan Mountain, along the southern margin of the Central Asian Orogenic Belt in northern Xinjiang autonomous region of China. The Sidingheishan intrusion is mainly composed of wehrlite, olivine websterite, olivine gabbro, gabbro and hornblende gabbro. At least two pulses of magma were involved in the formation of the intrusion. The first pulse of magma produced an olivine-free unit and the second pulse produced an olivine-bearing unit. The magmas intruded the Devonian granites and granodiorites.An age of 351.4±5.8 Ma(Early Carboniferous) for the Sidingheishan intrusion has been determined by U-Pb SHRIMP analysis of zircon grains separated from the olivine gabbro unit. A U-Pb age of 359.2±6.4 Ma from the gabbro unit has been obtained by LA-ICP-MS. Olivine of the Sidingheishan intrusion reaches 82.52 mole% Fo and 1414 ppm Ni. On the basis of olivine-liquid equilibria, it has been calculated that the MgO and FeO included in the parental magma of a wehrlite sample were approximately10.43 wt% and 13.14 wt%, respectively. The Sidingheishan intrusive rocks are characterized by moderate enrichments in Th and Sm, slight enrichments in light REE, and depletions in Nb, Ta, Zr and Hf. The εNd(t) values in the rock units vary from +6.70 to +9.64, and initial87Sr/86Sr ratios range between 0.7035 and0.7042. Initial206Pb/204Pb,207Pb/204Pb and208Pb/204Pb values fall in the ranges of 17.23-17.91,15.45-15.54 and 37.54-38.09 respectively. These characteristics are collectively similar to the Heishan intrusion and the Early Carboniferous subduction related volcanic rocks in the Santanghu Basin, North Tianshan and Beishan area. The low(La/Gd)PMvalues between 0.26 and 1.77 indicate that the magma of the Sidingheishan intrusion was most likely derived from a depleted spinel-peridotite mantle.(Th/Nb)PMratios from 0.59 to 20.25 indicate contamination of the parental magma in the upper crust.Crystallization modeling methods suggest that the parental magma of the Sidingheishan intrusion was generated by flush melting of the asthenosphere and subsequently there was about 10 vol%contamination from a granitic melt. This was followed by about 5 vol% assimilation of upper crustal rocks. Thus, the high-Mg basaltic parental magma of Sidingheishan intrusion is interpreted to have formed from partial melting of the asthenosphere during the break-off of a subducted slab.

ECHAM5-Simulated Impacts of Two Types of El Nio on the Winter Precipitation Anomalies in South China

The authors used an atmospheric general circulation model （AGCM） of European Centre Hamburg Model （ECHAM5.4） and investigated the possible impacts of eastern Pacific （EP） and central Pacific （CP） El Ni（n）o on the winter precipitation anomalies in South China.A composite analysis suggested much more rainfall during the mature phase of EP El Ni（n）o than in the case of CP El Ni（n）o,and their corresponding observed wet centers to be located in the southeast coast and the region to the south of the Yangtze River,respectively.Results obtained on the basis of model-sensitive run imply that the modelsimulated rainfall anomalies agree well with the observation,and the magnitude of simulated rainfall anomalies were found to be reduced when the amplitude of sea surface temperature anomaly （SSTA） forcing of EP and CP El Ni（n）o was cut down.These results imply that the rainfall anomaly in South China is very sensitive not only to the type of El Ni（n）o but also to its intensity.

Significant progress of continental petroleum geological theory in basins of Central and Western China

China's continental oil and gas geological theory occupies an important academic position in the world's academic circle of petroleum geology. China's oil and gas resources are dominated by continental resources. Chinese geologists have successfully explored and developed complex continental oil and gas, and developed a continental oil and gas geological theory system. This paper summarizes the development history and theoretical achievements of continental oil and gas geological theory since the 1940 s and proposes that the development of this theory should be divided into three stages(i.e., proposal, formation and development). The China's continental oil and gas geological theory has formed a basically perfect theoretical system consisting of five parts, i.e., continental basin structure theory, continental basin sediments and reservoirs theory, continental oil generation theory, continental oil and gas accumulation theory, and continental sandstone oil and gas field development geology. As an advanced geological theory, it has a universal significance globally. This paper focuses on the major discoveries of oil and gas exploration and development and the production growth in the basins of the Central and Western China in the past 30 years as well as the major advances in the continental oil and gas geological theory, including the continental basin tectonics of Central and Western China under the compression background, special reservoir geology such as various types of lake basin sedimentary systems and deep conglomerate, new fields of continental hydrocarbon generation such as coal-generated hydrocarbons, continental oil and gas enrichment regularity such as foreland thrust belts and lithologic-stratigraphic reservoirs, continental unconventional oil and gas geology and continental low-permeability oil and gas development geology. These major advances have greatly developed and enriched the continental oil and gas geological theory and become an important part of it.

Seasonal and annual variations of marine sinking particulate flux during 1993 ~ 1996 in the central South China Sea

A total of 67 samples from the upper and lower sediment traps in the central South China Sea were analyzed, which were collected during 1993 ~ 1996. It is indicated that the distribution of stable isotope values, surface primary productivity, fluxes of total particulate matter, carbonate, biogenic opal, organic carbon, planktonic foraminiferal species and their total amount exhibit obviously seasonal and annual fluctuations. High values of the fluxes occurred in the prevailing periods of the northeastern and southwestern monsoons, and the low values occurred during the periods between the two monsoons. The fluxes of some planktonic foraminiferal species （ Globigerinoides sacculifer , G. ruber , Globigerinita glutinata, Neogloboquadrina dutertrei ） and their percentages also exhibit two prominent peaks during the prevailing periods of the northeastern and southwestern monsoons respectively, while those of Globigerina bulloides, Globorotalia menardii and Pulleniatina obliquiloculata only exhibit one peak in the prevailing periods of the northeastern monsoon. In addition, fluxes and percentages of Globigerinoides sacculifer and Globorotalia menardii as well as the fluxes of carbonate and total amount of planktonic foraminifera decrease gradually from 1993 to 1996, and those of Globigerina bulloides, Globigerinita glutinata and biogenic opal increase gradually from 1993 to 1996. The fluxes of carbonate and organic carbon in the upper trap are higher than those in the lower one. The study indicates that the seasonal and annual variations of the sediment fluxes and planktonic foraminiferal species are mainly controlled by the changes of surface primary productivity and hydrological conditions related to the East Asian monsoon. The lower carbonate and organic carbon fluxes in the lower trap are related to the dissolution.

Multi-Method Chronometric Constraints on the Thermal Evolution of the Central Tianshan,NW China

The Tianshan orogenic belt is a major part of the southern Central Asian Orogenic Belt（CAOB）,extending from west to east for over 2500 km through Uzbekistan,Tajikistan,Kyrgyzstan and Kazakhstan to Xinjiang in NW China,and contains the record of multi-phase tectonothermal evolution.Till now.

Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt in NE China

The eastern Central Asian Orogenic Belt(CAOB)in NE China is a key area for investigating continental growth.However,the complexity of its Paleozoic geological history has meant that the tectonic development of this belt is not fully understood.NE China is composed of the Erguna and Jiamusi blocks in the northern and eastern parts and the Xing’an and Songliao-Xilinhot accretionary terranes in the central and southern parts.The Erguna and Jiamusi blocks have Precambrian basements with Siberia and Gondwana affinities,respectively.In contrast,the Xing’an and Songliao-Xilinhot accretionary terranes were formed via subduction and collision processes.These blocks and terranes were separated by the Xinlin-Xiguitu,Heilongjiang,Nenjiang,and Solonker oceans from north to south,and these oceans closed during the Cambrian(ca.500 Ma),Late Silurian(ca.420 Ma),early Late Carboniferous(ca.320 Ma),and Late Permian to Middle Triassic(260-240 Ma),respectively,forming the Xinlin-Xiguitu,Mudanjiang-Yilan,Hegenshan-Heihe,Solonker-Linxi,and Changchun-Yanji suture zones.Two oceanic tectonic cycles took place in the eastern Paleo-Asian Ocean(PAO),namely,the Early Paleozoic cycle involving the Xinlin-Xiguitu and Heilongjiang oceans and the late Paleozoic cycle involving the Nenjiang-Solonker oceans.The Paleozoic tectonic pattern of the eastern CAOB generally shows structural features that trend east-west.The timing of accretion and collision events of the eastern CAOB during the Paleozoic youngs progressively from north to south.The branch ocean basins of the eastern PAO closed from west to east in a scissor-like manner.A bi-directional subduction regime dominated during the narrowing and closure process of the eastern PAO,which led to“soft collision”of tectonic units on each side,forming huge accretionary orogenic belts in central Asia.

Discovery of the Dagele Eclogite in East Kunlun,Western China and Its Zircon SHRIMP U-Pb Ages:New Constrains on the Central Kunlun Suture Zone

Objective Eclogites are important indicators of ancient plate boundaries or paleosuture zones. Despite their great geological significance, very few investigations have been carried out in the Kunlun region. The Central East Kunlun fault zone was believed to be an Early Paleozoic suture zone, but there has been no reliable evidence for this, though studies on ophiolite, granite, and basic granulite indicate that the Early Paleozoic orogeny occurred in the East Kunlun. This work focused on the Dagele eclogites in Central East Kunlun to provide new constraints for the Central East Kunlun suture zone.

A Comparison about Metamorphism among the Oldest-Rock Units from Orogenic Belts of Dabie,Eastern Qinling and Eastern Kunlun of Central Mountain Ranges,China

The Dabie orogen, Eastern Qinling orogen and Eastern Kunlun orogen are the major components of the Central Mountain Ranges of China and each has distinctively metamorphic processes in their oldest rock units. The Dabie orogen oldest rock units had experienced an intermediate-higher pressure, upper amphibolite to lower granulite facies metamorphism in the Indosinian intracontinental subduction collision event. The clockwise pt path, synchronous attainment of t max and p max and a segment of high slope retrograde path suggest a tectono driven rapid exhumation of the oldest rock units to upper middle crustal level following the end of the subduction collision process. The oldest rock units, also called Qinling Group, of Eastern Qinling Mountains suffered intensively collisional metamorphism at an immature plate tectonic framework during Jinningian movement about 1 000 Ma ago. The clockwise pt path with reach of t max following several hundreds of MPa decreasing from p max suggests that the denudation of the deeply burial rock units was due essentially to isostatic relaxation. During the Caledonian stage, the highly metamorphosed oldest rock units suffered from a high t thermal event in arc environment and superimposed by contact metamorphism. After thermal peaks, the rock units were exhumed in a short distance and cooled down isobarically. No regional metamorphism higher than upper greenschist facies condition since 300 Ma has been traced within exposed rocks in the eastern portion of Northern Qinling orogen. The oldest rock units in the Eastern Kunlun orogen were metamorphosed to upper amphibolite facies to lower granulite facies rocks early or during the Luliang movement (some 1 800 Ma ago). The high grade metamorphic rock units had a long resident time at the deep crustal level, and were exhumed to middle upper crustal level during the Caledonian to Hercynian tectonometamorphic events. Shallow erosion of the orogenic belt led to good preservation of the low pressure metamorphic belt.