The characteristic differences of tropical cyclones forming over the western North Pacific and the South China Sea

The best track dataset of tropical cyclones in the western North Pacific （WNP） and the South China Sea （SCS） from 1977 to 2005 during the satellite era, the NCEP/NCAR reanalysis dataset and the extended reconstructed sea surface temperature dataset are employed in this study. The main climatological characteristics of tropical cyclone formation over the WNP and the SCS are compared. It is found that there is obviously different for the locations of tropical cyclone origins, achieving the lowest central pressure and termination points between over the WNP and over the SCS. The annual number of tropical cyclones forming over the SCS is obviously less than over the WNP, and there is a significant negative correlation with the correlation coefficient being - 0.36 at the 5% significance level between over the WNP and over the SCS. The mean speed of tropical cyclone moving is 6.5 m/s over the WNP and 4.6 m/s over the SCS. The mean lowest central pressure of tropical cyclones is obviously weaker over the SCS than over the WNP. The tropical cyclone days per year, mean total distance and total displacement of tropical cyclone traveled over the WNP are all obviously longer than those over the SCS. Tropical cyclone may intensify to Saffir - Simpson hurricane scale 5 over the WNP, but no tropical cyclone can intensify to Saffir - Simpson hurricane scale 3 over the SCS. The changing ranges of the radii （R15,R16） of the 15.4 m/s winds them and the 25.7 m/s winds over the WNP are obviously wider than those over the SCS, and the median values of the radii over the WNP are also larger than those over the SCS. For the same intensity of tropical cyclones, both radii have larger medians over the WNP than over the SCS. The correlations of annual mean tropical cyclone size parameters between over the WNP and over the SCS are not significant. At the same time, the asymmetric radii of tropical cyclones over the WNP are different from those over the SCS.

Crustal density structures and isostasy beneath the Western North China craton,Trans-North China Orogen,and surrounding regions

To determine the lateral and vertical variations in crustal structure and their influence on the seismicity of the Western North China Craton,the Trans-North China Orogen,and the surrounding regions,the wavelet multi-scale structures,Moho depth,crustal density structures,and isostatic state are modelled using Bouguer gravity anomaly data,topography,and earthquake focal mechanisms.We obtained homogeneous crustal densities and deviations of<1 km between the crustal thicknesses estimated from the isostatic model and those inverted from the Bouguer gravity anomalies in the Ordos Block,the Inner Mongolia Suture Zone,the Sichuan Basin,and the Jizhong Depression.These results provide new evidence for relatively simple and stable continental crustal structures,and indicate that these regions will remain stable in both the vertical and lateral directions.The Hetao Graben,Yinchuan Graben,Weihe Basin,and Shanxi graben system have heterogeneous crustal densities and are isostatically over-compensated.In contrast,the crust beneath the Yinshan Uplift,Lvliang Uplift,and northern and central Taihang Uplift is thin and under-compensated.The heterogeneous crustal densities and non-isostatic state beneath the Tibetan Plateau and Qinling Central China Orogen indicate that these two blocks are unstable in the vertical and lateral directions.Although Cenozoic deformation of the North China Craton is thought to be driven by lithospheric stresses related to the India-Eurasia collision and Pacific slab retreat in South East Asia,we suggest that gravitational potential energy created by the heterogeneous crustal structure modulates these first-order forces.The results of this study could constrain the causes of seismicity in systems surrounding the Ordos Block.

Effects of South China Sea/western North Pacific summer monsoon on tropospheric biennial oscillation （TBO）

Several theories have been developed to explain tropical biennial oscillation （TBO）, as an air-sea interactive system to impact Asian and global weather and climate, and some models have been established to produce a TBO. A simple 5-box model, with almost all the key processes associated with TBO, can produce a TBO by including airsea interactions in the monsoon regions. Despite that, the South China Sea/western North Pacific summer monsoon （SCS/WNPSM）, a very important monsoon subsystem, is neglected. In this paper, based on the dynamical framework of 5-box model, the term of SCS/WNPSM has been added and a 6-box model has been developed. Comparing the difference of TBO sensibilities with several key parameters, air-sea coupling coefficient α, SST-thermocline feedback coefficient γand wind-evaporation feedback coefficient λ, between the modified model and original model, TBO is more sensible to the parameters in the new model. The results imply that the eastern Pacific and local wind-evaporation play more important roles in the TBO when including SCS /WNPSM.

Associations between the Western North Pacific Monsoon and the South China Sea Monsoon

Based on the interannual variability of convection over the tropical western North Pacific (WNP), a region of 130°—160°E, 10°—20°N, a composite analysis is performed on the fields of surface temperature, outgoing longwave radiation and 850 hPa zonal wind. The composite results show that the weaker (stronger) WNP convection is related to the El Nino (La Nina)—pattern sea surface temperature (SST) anomalies in the preceding winter and in spring. A comparison with previous results indicates that a similar spatial and temporal distribution of SST anomalies is also associated with the onsets of both the WNP and South China Sea (SCS) monsoons. The composite results also show that the weaker (stronger) convection over the WNP corresponds to the easterly (westerly) anomalies that extend westward from the WNP into the Bay of Bengal. A numerical experiment by an atmospheric general circulation model shows a similar result. In addition, during weaker (stronger) convection summer, the convection over the WNP and lower-level zonal winds over the SCS exhibit a small (large) extent of seasonal evolution.

Response of the western North Pacific subtropical ocean to the slow-moving super typhoon Nanmadol

Based on in-situ observation,satellite and reanalysis data,responses of the western North Pacific subtropical ocean(WNPSO)to the slow-moving category 5 super typhoon Nanmadol in 2011 are analyzed.The dynamical response is dominated by near-inertial currents and Ekman currents with maximum amplitude of 0.39m/s and 0.15m/s,respectively.The near-inertial currents concentrated around 100m below the sea surface and had an e-folding timescale of 4 days.The near-inertial energy propagated both upward and downward,and the vertical phase speed and wavelength were estimated to be 5m/h and 175m,respectively.The frequency of the near-inertial currents was blue-shifted near the surface and redshifted in ocean interior which may relate to wave propagation and/or background vorticity.The resultant surface cooling reaches-4.35℃ and happens when translation speed of Nanmadol is smaller than 3.0m/s.When Nanmadol reaches super typhoon intensity,the cooling is less than 3.0℃ suggesting that the typhoon translation speed plays important roles as well as typhoon intensity in surface cooling.Upwelling induced by the slow-moving typhoon wind leads to typhoon track confined cooling area and the right-hand bias of cooling is slight.The mixed layer cooling and thermocline warming are induced by wind-generated upwelling and vertical entrainment.Vertical entrainment also led to mixed layer salinity increase and thermocline salinity decrease,however,mixed layer salinity decrease occurs at certain stations as well.Our results suggest that typhoon translation speed is a vital factor responsible for the oceanic thermohaline and dynamical responses,and the small Mach number(slow typhoon translation speed)facilitate development of Ekman current and upwelling.

Variations in High-frequency Oscillations of Tropical Cyclones over the Western North Pacific

Variations in the high-frequency oscillations of tropical cyclones （TCs） over the western North Pacific （WNP） are studied in numerical model simulations. Power spectrum analysis of maximum wind speeds at 10 m （MWS10） from an ensemble of 15 simulated TCs shows that oscillations are significant for all TCs. The magnitudes of oscillations in MWS10 are similar in the WNP and South China Sea （SCS）; however, the mean of the averaged significant periods in the SCS （1.93 h） is shorter than that in the open water of the WNP （2.83 h）. The shorter period in the SCS is examined through an ensemble of simulations, and a case simulation as well as a sensitivity experiment in which the continent is replaced by ocean for Typhoon Hagupit （2008）. The analysis of the convergence efficiency within the boundary layer suggests that the shorter periods in the SCS are possibly due to the stronger terrain effect, which intensifies convergence through greater friction. The enhanced convergence strengthens the disturbance of the gradient and thermal wind balances, and then contributes to the shorter oscillation periods in the SCS.

Analysis on Variations of the Temperature and Precipitation in North Slope Area of the Western Tianshan in Recent 50 Years

[Objective] The research aimed to analyze variation characteristics of the temperature and precipitation in north slope area of the Western Tianshan in recent 50 years.[Method] According to temperature and rainfall data from 1961 to 2010 at three meteorological stations in north slope area of the Western Tianshan,climate change in the zone in recent 50 years was analyzed by using linear trend analysis method and 5-year sliding average method.[Result] The temperature in north slope area of the Western Tianshan showed significant warming trend.The annual average temperature significantly increased at 0.3 ℃/10 a in recent 50 years.But rise rates of the temperature in different seasons were different:autumn> winter> spring> summer.The annual rainfall in north slope area of the Western Tianshan in recent 50 years overall presented relative increase trend.Seen from annual rainfall,it significantly increased at 16.9 mm/10 a.Seen from seasonal rainfall,except in autumn,rainfalls in other three seasons in the past 50 years all showed significant increase trends,with amplitude of 3.2-11.2 mm/10 a.The largest increase amplitude was in summer.After a small precipitation peak in the 1980s,autumn rainfall slightly declined in the past 20 years.[Conclusion] The climate in north slope area of the Western Tianshan become warm and wet.

Impacts of Two Types of Northward Jumps of the East Asian Upper-tropospheric Jet Stream in Midsummer on Rainfall in Eastern China

The East Asian upper-tropospheric jet stream （EAJS） typically jumps north of 45~N in midsummer. These annual northward jumps are mostly classified into two dominant types： the first type corresponds to the enhanced westerly to the north of the EAJS＇s axis （type A）, while the second type is related to the weakened westerly within the EAJS＇s axis （type B）. In this study, the impacts of these two types of northward jumps on rainfall in eastern China are investigated. Our results show that rainfall significantly increases in northern Northeast China and decreases in the Yellow River-Huaihe River valleys, as well as in North China, during the type A jump. As a result of the type B jump, rainfall is enhanced in North China and suppressed in the Yangtze River valley. The changes in rainfall in eastern China during these two types of northward jumps are mainly caused by the northward shifts of the ascending air flow that is directly related to the EAJS. Concurrent with the type A （B） jump, the EAJS-related ascending branch moves from the Yangtze-Huai River valley to northern Northeast （North） China when the EAJS＇s axis jumps from 40~N to 55~N （50~N）. Meanwhile, the type A jump also strengthens the Northeast Asian low in the lower troposphere, leading to more moisture transport to northern Northeast China. The type B jump, however, induces a northwestward extension of the lower-tropospheric western North Pacific subtropical high and more moisture transport to North China.

鲁西地区中生代高镁闪长岩角闪石成分变化特征及其对矽卡岩型铁矿成矿作用的启示

矽卡岩型铁矿床是我国最重要的铁矿床类型之一,在华北克拉通东部广泛发育,时空上与中生代高镁闪长岩体紧密伴生,研究其物质来源和成岩成矿过程具有重要的意义。本文对鲁西地区与金岭铁矿床具有成因联系的中生代高镁闪长岩中的角闪石进行了详细的成分研究,限定高镁闪长岩的岩浆演化过程及其物理化学条件变化,探讨高镁闪长岩的岩石成因机制及其与矽卡岩型铁矿床成矿作用之间的联系。金岭高镁闪长岩的角闪石斑晶边部与基质角闪石具有一致的主量元素成分,记录了相似的T-P-fO_(2)-H_(2)O条件,显著不同于角闪石斑晶核部。角闪石斑晶核部的平衡岩浆来源于地幔部分熔融,而角闪石斑晶边部与基质角闪石的平衡岩浆中则存在地壳组分的贡献。高镁闪长岩-矽卡岩型铁矿床体系为极其复杂的成岩成矿系统,起源于高氧逸度和高水含量的地幔源区,并经历了包括结晶分异、同化混染、岩浆混合以及流体出溶、迁移和淋滤在内的诸多复杂岩浆热液演化过程。这些源区特征和岩浆-热液过程记录了不同深度岩石圈对华北克拉通破坏的构造响应。

2024年春季中国东部降水季节内异常特征及成因分析

2024年春季(3—5月)我国平均降水量为163 mm,为1961年以来历史同期第六多,4—5月东部地区旱涝灾害并重,华南和江南大部降水较常年同期偏多,尤其是华南大部降水偏多5成以上,多次暴雨过程造成部分地区发生洪涝;而黄淮、江淮北部降水显著偏少,春季后期干旱迅速发展。春季“华南涝、黄淮旱”的形成与东亚大气环流关键系统异常及其季节内阶段性变化密切相关。4月异常偏强、偏南的西北太平洋副热带高压和低层850 hPa偏强的西北太平洋反气旋为华南和江南提供了有利的水汽输送条件,导致南方地区发生多次强降水过程;而黄淮干旱主要受4—5月持续偏强的朝鲜半岛-日本海高压(小笠原高压)和偏南的西北太平洋副热带高压共同影响。此外,春季El Ni o衰减和热带印度洋海温异常偏暖有助于激发异常偏强的西北太平洋反气旋,是我国南方强降水发生的重要海洋外强迫背景。

基于分子标记的白蜡树属椒叶梣组系统发育及谱系地理格局形成

木犀科白蜡树属椒叶梣组(Fraxinus sect. Sciadanthus)由自然分布于中国中部的对节白蜡(Fraxinus hupehensis S.Z.Qu,C.B.Shang&P.L.Su)、喜马拉雅西部的椒叶梣(Fraxinusxanthoxyloides(G.Don)DC.)和非洲北部的Fraxinus dimorpha 3个物种组成,呈现出特殊的间断分布模式,目前该组的起源和演化过程尚不清楚。利用ITS、psbA-trnH、rpl32-trnL和matK 4个标记对白蜡树属42个物种间的系统发育关系进行分析,结果表明:(1)利用ITS序列构建的贝叶斯系统树支持Wallander的分类方法,即属内再分成6个组,对节白蜡、椒叶梣和F. dimorpha都属于椒叶梣组,且该组与欧梣组(sect. Fraxinus)的亲缘关系最近,形成姐妹组;(2)椒叶梣可能是F. dimorpha与欧亚种的杂交后代;(3)BEAST分化时间图显示,白蜡树属最早起源于42.05 Ma,椒叶梣组最早分化于21.86 Ma,对节白蜡最早分化于11.87 Ma。青藏高原的快速隆起可能是导致椒叶组物种间断分布的重要原因,对节白蜡和椒叶梣可能是其影响下的孑遗植物。

“23·7”华北极端暴雨精细特征和天气学成因分析

2023年7月29日至8月1日,华北京津冀地区遭受极端特大暴雨袭击,导致区域性洪涝灾害,造成重大经济损失和人员伤亡。为探明此次“23·7”华北极端降水过程的基本特征和形成原因,基于地面自动气象站分钟级降水资料、风廓线雷达和雨滴谱仪观测资料及ERA5再分析数据,揭示了“23·7”华北极端暴雨的精细特征和天气学成因。结果表明:(1)此次降水过程持续时间长、累计雨量极大,特大暴雨落区、突破降水量历史极值的国家级观测站站点密集分布在京津冀太行山近山地区,降水呈现显著极端性、区域性差异和阶段性变化。河北和北京太行山东侧迎风坡地区出现持续性、强度相对稳定的强降水过程,雨滴谱分布偏向于高雨滴数密度、小雨滴直径的海洋型对流降水;京津冀平原地区过程雨量明显小于山区,但中尺度对流雨带活跃,降水阵性、对流性特征明显。(2)在“杜苏芮”台风残涡、西太平洋副热带高压、大陆高压等天气系统协同作用下,中层位势高度场出现罕见的“北高南低”+“西低东高”的稳定天气形势。北上台风“杜苏芮”残涡在高压坝以及太行山、燕山地形影响下移动缓慢,残涡中心北侧的地形障碍流与低空东南风之间形成稳定倒槽,京津冀地区出现持续性低层辐合,同时配合来自南海季风和东部洋面台风“卡努”的双路水汽输送,导致京津冀地区出现长历时、区域性极端暴雨过程。(3)在阶段性降水发展过程中,与台风残涡相关的倒槽、暖切变线、低空急流等精细结构调控了中尺度对流系统的组织和发展特征,7月31日早晨至上午京津冀地区出现超过22 m/s的超低空东南风急流,配合对流和地形抬升等因素影响,降水强度明显增强,北京西部山前出现超100 mm/h的极端雨强。此次极端降水事件中的地形影响、中小尺度特征以及极端暴雨可预报性等问题尚待更深入研究。

Revisiting the Second EOF Mode of Interannual Variation in Summer Rainfall over East China

The second EOF（EOF2） mode of interannual variation in summer rainfall over East China is characterized by inverse rainfall changes between South China（SC） and the Yellow River-Huaihe River valleys（YH）.However,understanding of the EOF2 mode is still limited.In this study,the authors identify that the EOF2 mode physically depicts the latitudinal variation of the climatological summer-mean rainy belt along the Yangtze River valley（YRRB）,based on a 160-station rainfall dataset in China for the period 1951-2011.The latitudinal variation of the YRRB is mostly attributed to two different rainfall patterns：one reflects the seesaw（SS） rainfall changes between the YH and SC（SS pattern）,and the other features rainfall anomalies concentrated in SC only（SC pattern）.Corresponding to a southward shift of the YRRB,the SS pattern,with above-normal rainfall in SC and below-normal rainfall in the YH,is related to a cyclonic anomaly centered over the SC-East China Sea region,with a northerly anomaly blowing from the YH to SC;while the SC pattern,with above-normal rainfall in SC,is related to an anticyclonic anomaly over the western North Pacific（WNP）,corresponding to an enhanced southwest monsoon over SC.The cyclonic anomaly,related to the SS pattern,is induced by a near-barotropic eastward propagating wave train along the Asian upper-tropospheric westerly jet,originating from the mid-high latitudes of the North Atlantic.The anticyclonic anomaly,for the SC pattern,is related to suppressed rainfall in the WNP.

The ENSO’s Effect on Eastern China Rainfall in the Following Early Summer

ENSO＇s effect on the rainfall in eastern China in the following early summer is investigated by using station precipitation data and the ERA-40 reanalysis data from 1958 to 2002. In June, after the E1 Nifio peak, the precipitation is significantly enhanced in the Yangtze River valley while suppressed in the Huaihe River-Yellow River valleys. This relationship between ENSO and the rainfall in eastern China is established possibly through two teleconnections： One is related to the western North Pacific （WNP） anticyclonic anomaly in the lower troposphere leading to enhanced precipitation in the Yangtze River valley, and the other is related to the southward displacement of the Asian jet stream （AJS） in the upper troposphere resulting in suppressed precipitation in the Huaihe River-Yellow River valleys. This southward displacement of the AJS is one part of ENSO＇s effect on the zonal flow in the whole Northern Hemisphere. After the E1 Nifio peak, the ENSO-related warming in the tropical troposphere persists into the following early summer, increasing the meridional temperature gradient and through the thermal wind balance, leads to the enhancement of westerly flow in the subtropics south of the westerly jet stream and results in a southward displacement of the westerly jet stream.

南海-西北太平洋季风槽及其与热带气旋的关系:不同再分析资料对比

利用1981—2020年中国气象局(CMA)热带气旋最佳路径数据集、CMA大气再分析资料(CMA-RA)、欧洲中期天气预报中心再分析资料(ERA5)及NCEP/NCAR再分析资料(NCEP-I),对比CMA-RA与ERA5、NCEP-I对南海-西北太平洋季风槽及其与南海热带气旋活动关系的表现能力,探讨CMA-RA的适用性。结果表明:不同资料均表征出南海和西北太平洋西段槽区低层气旋式涡旋明显、东段均匀的特征,CMA-RA和ERA5对低层涡度场描述的差异较小。两两资料间得到的季风槽强度的相关性较高,且为CMA-RA>ERA5>NCEP-I,对南海槽区的描述差异最大;对东伸点的刻画具有较高一致性,CMA-RA较ERA5和NCEP-I偏西;但对南北位置的刻画一致性较差,其中CMA-RA与ERA5的差异较小。所有资料均刻画出季风槽区中、低层强辐合、高层强辐散的结构,沿105°~160°E平均的涡度垂直剖面差异以CMA-RA与ERA5最小、CMA-RA与NCEP-I最大。CMA-RA季风槽与热带气旋频数关系最密切,ERA5次之,ERA5季风槽强度与热带气旋强度关系最密切,ERA5和CMA-RA季风槽东伸点与热带气旋强度关系较NCEP-I密切。总体来看,CMA-RA对季风槽及其与南海热带气旋活动关系的刻画具有与ERA5和NCEP-I相当的表现能力,且与ERA5的一致性高。

热带气旋影响吕宋海峡输运的研究进展与展望

吕宋海峡是连接南海与西太平洋的唯一深水通道,也是调节南海环流及其热力特征的关键海洋通道。在大尺度西边界流、中尺度涡、热带气旋等众多因子的共同影响下,吕宋海峡输运表现出显著的多时间尺度变率特征,其中热带气旋是影响该海域强烈且频繁的天气过程之一,解析吕宋海峡输运与热带气旋之间的动力联系也是近年来南海海洋研究的热点之一。本文主要从吕宋海峡附近热带气旋活动特征及其对黑潮、吕宋海峡附近环流结构、吕宋海峡输运的影响等方面回顾最新的研究进展。最后,本文认为接下来应当在热带气旋调制吕宋海峡输运的机制,以及对吕宋海峡输运年际变化的贡献等方面加强研究。

春季厄尔尼诺快速衰减对华北夏季降水的影响

利用再分析的陆地降水、环流和辐射数据,以及表征大气波动的指数,对比了1951—2020年期间El Nino春季快速衰减年和缓慢衰减年的东亚环流和华北夏季降水异常情况,并从大气波动强度的角度探讨了为何El Nino在一些年份的春季会发生快速衰减。结果表明,相较于其他不发生El Nino衰减的年份,El Nino春季快速衰减年华北7、8月的降水量显著偏多,尤其是8月;而El Nino缓慢衰减年夏季,华北降水相较其他年份偏多不明显。El Nino春季快速衰减年6—8月850 hPa上菲律宾到南海存在异常反气旋,其强度强于El Nino缓慢衰减年;El Nino春季快速衰减年8月500 hPa西太平洋副热带高压(西太副高)显著偏北,而缓慢衰减年西太副高偏北的特征不明显,而是以偏西为主;200 hPa副热带西风急流在El Nino春季快速衰减年8月显著偏北,而在El Nino缓慢衰减年中反而略偏南;El Nino春季快速衰减年6—8月沃克环流显著偏强,相比之下El Nino缓慢衰减年沃克环流偏强的特征要弱很多。上述环流异常特征为El Nino春季快速衰减年华北7—8月降水异常偏多提供了有利条件。通过近地面风场合成分析发现,春季El Nino快速衰减月前后,赤道中西太平洋异常东风爆发非常明显,而El Nino缓慢衰减年的异常东风信号较弱。春季El Nino快速衰减前印度洋对流活动非常强盛,并向海洋性大陆传播,这种对流可能通过不断激发大气波动,继而引发近地面东风爆发,最终导致El Nino出现快速衰减。

Perceived resource support for chronic illnesses among diabetics in north-western China

A high level of social support can improve long-term diabetes self-management. Support from a single source has been evaluated. This study aims to analyze support from multiple and multilevel sources for diabetic patients by using the Chronic Illness Resources Survey （CIRS）. Factors influencing the utilization of the CIRS were also evaluated. A total of 297 patients with diabetes were investigated using the CIRS and Perceived Diabetes Self-management Scale in Shihezi City, China. Descriptive statistics were used to explain demographic variables and scores of the scales. Factors affecting the utilization of chronic illness resources were determined through univariate analysis and then examined by multivariate logistic regression analysis. Of the 297 diabetic patients surveyed, 67% failed to reach the standard （more than 3 points） of utilizing chronic illness resources. Moreover, utilization of chronic illness resources was positively moderately correlated with self-management of diabetes （r = 0.75, P 〈 0.05）. According to the multivariate logistic regression analysis, age （OR, 3.42; 95%CI, 1.19-9.84） and monthly income （OR, 5.27; 95%CI, 1.86-14.90） were significantly positively associated with the CIRS score. Individuals with high school （OR, 2.61; 95%CI, 1.13-6.05） and college （OR, 3.02; 95%CI, 1.13-8.04） degrees obtained higher scores in the survey than those with elementary school education. Results indicated that utilization of resources and support for chronic illness self-management, particularly personal adjustment and organization, were not ideal among diabetics in the communities of north-western China. Improved utilization of chronic illness resources was conducive for proper diabetes self-management. Furthermore, the level of utilization of chronic illness resources increased with age, literacy level, and monthly income.

山东汞丹山地区新太古代变基性岩地球化学特征及其构造意义

为探讨华北克拉通鲁西地区前板块构造与板块构造体制转换时间问题,利用LA-ICP-MS锆石U-Pb测年和全岩主微量元素特征对山东沂水地区汞丹山一带的新太古代变基性岩进行了年代学和地球化学分析。汞丹山变基性岩为斜长角闪岩,具有较强的面理化特征,主要由角闪石和斜长石组成,其原岩(玄武岩/安山岩)的结晶年龄为2626±28 Ma,可划分为拉斑系列和钙碱性系列,拉斑系列的岩浆源区可能为亏损地幔,且形成过程中有俯冲流体/熔体的参与,而钙碱性系列与太古宙硅质高镁玄武岩具有相似的地球化学特征,是俯冲板片流体或含水熔体交代的地幔楔在相对较浅的条件下发生较高程度部分熔融的产物。汞丹山变基性岩以及华北克拉通已识别出的一系列新太古代晚期玄武质-安山质岩浆岩均存在明显的Nb、Ta、P、Ti亏损,与岛弧玄武岩的特征一致,表明华北克拉通在新太古代晚期经历了大规模的俯冲作用。

The genesis of Archean supracrustal rocks in the western Shandong Province of North China Craton: Constraints on regional crustal evolution

Archean greenstone belts are supracrustal sequences, the lower part of which is usually composed of voluminous ultramafic-mafic volcanics. Intermediate and acid volcanic rocks increase in abundance towards the upper domains. Greenstone belts constitute ~30% of the total volume of Archean cratons, and preserve significant information on the surface environment and magmatism in the early earth, which are useful in unraveling the nature of crustal formation and evolution. The western Shandong Province(WSP) is located at the eastern part of the North China Craton(NCC), where greenstone sequences formed at ~2.7 and ~2.5 Ga were well preserved. The early Neoarchean supracrustal rocks include komatiite-basalt sequence, some meta-sediments of the lower part of the Taishan Group and the Mengjiatun Formation. The volcanism had been correlated to mantle plume, which resulted in vertical crustal accretion. The late Neoarchean supracrustal rocks were composed of metamorphosed felsic volcano-sedimentary sequences and BIFs of the upper part of the Taishan Group and the Jining Group. The geochemical features of the meta-volcanics show calc-alkaline affinities, similar to modern arc-related magmatism, suggesting that the continental crust in the western Shandong Province witnessed horizontal plate movements at ~2.5 Ga. The metasediments and leucosomes in the Qixingtai area display regional upper amphibolite facies metamorphism and anatexis at 2.53–2.50 Ga, coeval with formation of large volumes of crustally-derived granites. These tectono-thermal events suggest that a unified continental crust was formed in the western Shandong Province at the end of Neoarchean.