南海南北陆缘中生代地层—构造特征及碰撞造山

为进一步深入了解南海地区中生代构造演化过程.本文对南海南北陆缘的中生代地层进行了分析对比,在此基础上挑选了南北陆缘处的两条地震测线07ns-6和97301进行了详细的解释分析.通过地震剖面的解释发现,南海北部和南部(礼乐地块)地震剖面中的中生代地层均显示有褶皱—冲断构造发育.据此推断,研究区在中生代先后经历了洋—陆俯冲活动、陆 陆碰撞造山运动及中生代晚期开始的造山带的塌陷.提出南海地区中生代晚期的“古双峰笔架碰撞造山带”概念.     

Metallogenic systems related to Mesozoic and Cenozoic granitoids in South China

CenteredbytheNanlingRange,SouthChinaisanimportantareaofmineralresourcesproduction,especiallyfornonferrous,precious,andraremetals.Manydepositsoflargeandsuper-largesizesarelocatedinthisarea,includingtheworldlargestantimonydeposit(Xikuangshan),severalworld-c…     

Remelting of subducted continental lithosphere: Petrogenesis of Mesozoic magmatic rocks in the Dabie-Sulu orogenic belt

The Dabie-Sulu orogenic belt was formed by the Triassic continental collision between the South China Block and the North China Block. There is a large area of Mesozoic magmatic rocks along this orogenic belt, with emplacement ages mainly at Late Triassic, Late Jurassic and Early Cretaceous. The Late Triassic alkaline rocks and the Late Jurassic granitoids only crop out in the eastern part of the Sulu orogen, whereas the Early Cretaceous magmatic rocks occur as massive granitoids, sporadic intermedi- ate-ma...     

利用S波接收函数研究华南块体的岩石圈结构

本文基于跨越华夏块体至四川盆地西部的130个线性流动地震台站及其附近90个固定台网台站的观测资料,采用S波接收函数波动方程叠后偏移方法,开展了华南大陆岩石圈结构研究.成像结果显示,研究区岩石圈结构复杂,不同构造单元之间差异显著,构造边界带附近小尺度变化强烈.150 km以上的厚岩石圈主要位于四川盆地,不足100 km的薄岩石圈主要分布于川东褶皱带和华夏块体.雪峰山下方岩石圈厚度显著增加,且以雪峰山为界岩石圈结构和性质存在着显著的东西差异.结合其它地球物理观测得到的地壳-上地幔结构信息,我们提出：（1）四川盆地还保留着厚而冷的克拉通岩石圈根,且岩石圈地幔具有结构分层特征;（2）雪峰山可能是扬子克拉通与华夏块体在西南部的边界;（3）雪峰山以东区域可能经历了岩石圈的减薄和改造,且华南岩石圈的减薄与华北相似,都主体发生在东部地区,造成现今南北重力梯度带两侧强烈的结构差异.研究结果为认识华南大陆的构造演化及其深部动力学提供了地震学约束.

     

四川江油-北川地区下石炭统灰岩的古地磁研究

对采于四川北部江油 北川地区 (31.4°N ,10 4 .3°E)下石炭统 39个采点的 334块灰岩标本进行了较为系统的古地磁学研究 ,结果表明 ,标本中剩磁方向具有明显的双分量特征 ,低温 (10 0～ 30 0℃ )分量在地理坐标系下与现代地磁场方向基本一致 ,且不能通过褶皱检验 ,应是现代地磁场的重磁化 ,中温 (30 0～ 4 80℃ )反极性分量在地层坐标系中具有高负倾角的特征 ,其形成可能与早侏罗世岩层的褶皱弯曲有关 .     

U-Pb dating of early Mesozoic granodioritic intrusions in southeastern Hunan Province, South China and its petrogenetic implications

The NE-trended Mesozoic granodioritic intrusions are spatially and temporally associated with the copper multi-metal mineralization in southeastern Hunan Province, South China. U-Pb dating result of single-grained zircons of four samples respectively from Shuikoushan, Baoshan, western Tongshanling and eastern Tongshanling intrusions reveals that their crystallization age spans a range from 172 Ma to 181 Ma, which also represents the oldest age of the regional copper multi-metal mineralization. Some of the zircon grains give an upper intercept age of about 1753 Ma and ²⁰⁷Pb/²⁰⁶Pb apparent age of (1752 ± 4) Ma, implying the involvement of the pre-Cambrian metamorphic (possible Middle Proterozoic) basement in their genesis. The presence of such a kind of zircon grains in these granodiorites indicates either that the parental magmas were assimilated by basement rocks during magma ascent or that lower/middle crustal rocks were one of the important components during the melting process.     

A long connection (750–380 Ma) between South China and Australia: paleomagnetic constraints

A new paleomagnetic study has been carried out on sediments of middle Cambrian age in the North Sichuan Basin (Yangtze Block). Detailed stepwise thermal demagnetizations allowed us to isolate three components. Site-mean direction derived from higher temperature components is D/I=146.9°/–17.1° (₉₅=8.3°) yielding a pole position at 51.3°S, 166.0°E. The fold and reversal tests suggest that remanence was acquired during early stage of sedimentation. Combined with the high-qualities early Sinian (748 Ma) and middle Silurian poles obtained recently from the Yangtze block, the deriving polar track demonstrates a similar loop to that of Australia. After rotating these poles from South China to fit that of Australia, the South China Block is placed against northwestern Australia. This reconstruction favors the correlations of the Jiangnan Grenville-age orogenic belt with the Rudall belt of western Australia, and subsequently the late Proterozoic Jiangnan and Officer/Adelaide rift systems. The paleobiogeographic evidence also indicates that this configuration might maintain by the middle Devonian.     

综合地球物理方法对南海西北部-印支半岛地区中生界分布的研究

南海西北部是我国海洋油气的重要基地.为了研究该区前新生代尤其是中生代油气资源潜力,本文以岩石物性的差异为基础,建立地质界面与物性界面的联系,利用综合地球物理方法来分析目标物性界面的分布特征.在地震资料控制浅层沉积结构的约束下,根据重力资料,通过小波分析位场剥离等方法得到剩余场,由Parker界面反演法反演计算了研究区的重力基底,结合新生代沉积分布得出中生界分布特征并给出了中生代残留盆地的可能分布范围,为分析研究区中生代油气资源潜力提供参考.     

华南已知地点信息的地震活动特征

“已知地点信息”指根据华南地区历史地震活动分布特征,将华南地震活动区划分为老震区、水库区和小震活动区。本文分析了华南地区以上3种区域1980年以来22次已知地点信息的M_L≥5.0地震事件前的地震活动现象,总结探讨了各区中强地震前的异常特征:水库区表现为震中的地震平静—增强,老震区和小震活动区则为区域的地震增强—活跃—平静。综合以上分析研究,提出了华南已知地点信息的地震预测对策。     

蛇绿岩研究现状及华南蛇绿岩问题

蛇绿岩概念自上世纪70年代提出以来,就成为确定古板块边界的重要证据,具有重要大地构造学意义,一直是地质学家研究的热点之一。近年来,随着地球化学技术的发展以及深海钻探计划和大洋钻探计划的实施,世界各地蛇绿岩研究不断深入,取得了很大的发展,同时也提出了很多新的问题。本文主要论述了蛇绿岩研究的最新动态,并对华南蛇绿岩的研究进展进行了分析梳理,对存在的一些问题作了初步讨论。     

华南地区地幔过渡带结构及其动力学意义

华南地区同时受特提斯构造域和太平洋构造域影响, 是研究板块相互作用的最佳场所之一.为研究华南地区深部动力学过程, 本文基于国家固定台网30°N以南的宽频带台站数据, 利用接收函数方法开展了华南地区地幔过渡带结构研究, 并结合已有地质、地球物理资料, 讨论了华南地区深部构造单元划分及其浅部构造响应.研究结果表明: (1)扬子克拉通下方地幔过渡带结构接近全球平均水平, 相对稳定; (2)海南岛地区地幔过渡带厚度偏薄, 且410-km和660-km界面分别显著下沉和上升, 可能与海南地幔柱密切相关; (3)太平洋构造域和特提斯构造域深部构造边界显著, 青藏高原东南缘主要受特提斯构造域影响, 其地幔过渡带中可能残留有拆沉的岩石圈板片; (4)雪峰山以东地区的地幔过渡带主要受太平洋构造域影响, 但南北也存在局部差异, 南部华夏地块下方可能不存在滞留板片, 太平洋板块的俯冲、后撤与东南沿海地区地壳减薄和大规模出露的中-新生代岩浆岩密切相关.

     

南海共轭大陆边缘构造属性的综合地球物理研究

利用南海最新的重磁资料,在岩石物性分析和全海域分带变倾角化极磁异常反演磁性基底分布的基础上,选择6条典型剖面拟合反演其密度与磁性结构,在此基础上进行了深部结构的对比分析.反演中尽可能以海底地震仪探测数据(OBS)、多道地震等结果作为约束,其中FF'剖面层速度分析是利用“南海大陆边缘动力学及油气资源潜力”973项目200...     

Late Mesozoic crust-mantle interaction and lower crust components in South China: A geochemical study of mafic granulite xenoliths from Cenozoic basalts

Mafic granulite xenoliths have been discovered in many volcanoes (especially alkali basalt and kimberlite) all over the world. They formed generally in lower crust, and recorded lots of in- formation on the lithosphere formation and crust-mantle interacti…     

华南及南海北部地区瑞利面波层析成像

基于华南及周边地区106个宽频带地震台站多年记录的MS≥5.0中浅源地震事件, 开展瑞利面波层析成像和速度结构特征研究, 获得了华南大陆及南海北部地区10~100 s瑞利波群速度分布图像和典型剖面下方地壳上地幔速度结构, 为理解该地区构造演化和深部过程提供约束.考虑到实际地震射线的覆盖情况以及华南地区主要构造的主体展布特征, 本文同时采用传统的规则网格剖分和平行主要构造走向的非规则网格剖分方法, 分别进行分格频散反演, 开展了不同参数化方案对反演结果影响的对比分析研究.基于瑞利面波层析成像结果, 进行了典型剖面横波速度结构反演, 重建了华南地区由内陆至南海海域主要构造单元的壳幔横波速度结构.研究结果表明, 扬子和华夏块体地壳上地幔结构特征差异显著, 扬子块体地壳和岩石圈厚度均大于华夏地块, 且扬子块体上地幔顶部速度较华夏块体低, 岩石圈厚度在雪峰山造山带下方发生过渡和转换;南海北部陆缘和南海海盆上地幔速度较高且形态相对完整, 表现为非火山型大陆边缘和已停止扩张海盆的壳幔结构特征.     

根据深反射地震资料识别南海北部洋陆过渡带

洋陆过渡带是被动大陆边缘的重要特征,对于理解大陆岩石圈破裂,随后的海底扩张及被动大陆边缘的形成与演化至关重要.前人通过重磁、地震等地球物理资料对南海北部洋陆过渡带进行过一些研究,但不同学者利用不同资料所确定的洋陆过渡带位置存在较大差异.本文基于高品质深反射地震剖面对南海北部洋陆过渡带进行重新解释,根据莫霍面快速抬升、地壳急剧减薄特征确定洋陆过渡带的分布范围.结果表明,南海北部洋陆过渡带位于大陆边缘减薄陆壳与正常洋壳之间,是受岩浆活动改造了的厚度急剧减薄的地壳,洋陆过渡带地壳深部发生岩浆侵入.减薄陆壳莫霍面平均埋深为21.9 km,地壳平均厚度约20.2 km;正常洋壳莫霍面平均埋深为12.0 km,地壳平均厚度为8.1 km,洋陆过渡带莫霍面埋深和地壳厚度急剧变化,其宽度大致介于46~99 km之间.南海北部磁异常条带和自由空间重力异常分布,验证了本文确定的洋陆过渡带范围的合理性.综合分析认为,南海北部洋陆过渡带的特征介于典型火山型与非火山型之间.

     

华南大陆东部地壳物质组成的地震学研究

中生代晚期华南大陆东部发生了大规模的火成岩活动,对地壳物质组成属性有显著影响,地壳中SiO2的平均含量是判别其属性的重要参数.基于华南大陆东部布设的宽频带地震台阵和固定台站数据,利用噪声成像获取高分辨率的面波频散,联合利用接收函数反演地壳的S波速度结构.由地壳的平均波速比和速度信息,通过与岩石物理实验数据对比,估测了华...     

Sedimentary records of the late Early Cretaceous compressional setting in the South China block: A case study of the Xingning Basin,Guangdong Province

Recently, some scholars have proposed that the South China Block (SCB) was controlled by a compressive tectonic regime in the middle–late Early Cretaceous, challenging the belief that the SCB was under an extensional setting during the Cretaceous. The Early Cretaceous tectonic setting constraint in the SCB can offer vital insight to clarify the Mesozoic subduction history of the Paleo-Pacific. Therefore, to determine the SCB tectonic regime during the Early Cretaceous, this study investigated sedimentary rocks from the Lower Cretaceous Heshui Formation in the Xingning Basin, a foreland basin located in the southeastern SCB. Provenance analysis was performed using sandstone modal analysis, sandstone geochemical characteristics, and detrital zircon geochronology. Based on the results, we discussed basin sediment sources and the SCB tectonic regime during the Early Cretaceous. The results showed that the maximum Heshui Formation depositional age was 103 Ma ± 1.6 Ma in the Early Cretaceous Albian. Detrital framework modes and geochemical characteristics of sandstone indicated that Heshui Formation's source rocks were granites and sedimentary rocks. The detrital zircon U–Pb ages could be classified into two major and four subordinate age populations. The Wuyi Terrane to the north and southeast coastal regions to the east were the primary potential Heshui Formation source areas. However, the lower and upper sandstones are different in the peak ages, ~437 and ~146 to 104 Ma, respectively, indicating that the major source area shifted from the Wuyi Terrane to the southeastern coastal regions during the late Early Cretaceous. The sandstone modal analysis results indicated that the source area comprised mainly collisional–orogenic material. The SCB was under a compressive tectonic regime during the late Early Cretaceous and this compression action continued until at least 103 Ma ± 1.6 Ma.     

Paleomagnetic results of Paleozoic and Mesozoic rocks from Xingshan-Zigui section in Hubei Province, South China

The paleomagnetic reconnaissance study of the Paleozoic and Mesozoic sedimentary rocks from the Yangtze Block (YZB) was made to conduct the Apparent Polar Wander Path (APWP) of the YZB during the Phanerozoic. A total of 825 samples from 84 sites were collected from a continuous section along the Xiangxi River valley in Xingshan and Zigui counties in Hubei Province, northern margin of the YZB. Stepwise thermal/alternating demagnetization isolated well defined characteristic magnetization (ChRM) at a higher temperature in most of the samples, and relatively thermal stability and high coercivity were revealed from these samples. All the ChRMs can pass the fold and/or reversal tests, suggesting that they are probably primary. Therefore, new pole positions are presented for the YZB. Project supported by the National Natural Science Foundation of China (Grant No. 49334050).     

穿越东沙隆起和潮汕坳陷的OBS广角地震剖面

为了探明南海中北部陆缘深部地壳结构,使用2D射线追踪正演和反演方法,拟合了一条南海中北部陆缘的OBS广角地震剖面(OBS2006-3).该剖面穿越东沙隆起和潮汕坳陷,长319 km,NNW-SSE走向,共投放海底地震仪14台.速度结构模型表明:潮汕坳陷存在巨厚的中生代沉积,最大厚度达到8 km,速度从顶部的4.4 km/s向下增加到底部的5.3 km/s.莫霍面埋藏深度由陆向海方向减小,其埋深从东沙隆起下方的24~25 km减小到南部隆起带的17 km.东沙隆起下方的上地壳中存在一向上突起的高速异常,速度达到6.9 km/s,可能与地幔物质上涌和岩浆活动有关.在整个剖面的下地壳底部存在厚3~12 km,速度为7.1~7.4 km/s的高速层.根据各个时期岩浆活动特征,推测下地壳高速层是由海底扩张停止之后的岩浆底侵作用形成的.     

Pollen record of the last 280 ka from deep sea sediments of the northern South China Sea

Environmental history of the northern continental shelf of the South China Sea during the last 280 ka BP, e.g. Marine Isotope Stages 1–8 (MIS 1–8) was reconstructed based on pollen record from the top 225m of ODP 1144 Site. During the interglacial periods, pollen assemblages are predominated by pine similar to those of the present day indicating that the environment of the interglacial periods was more or less close to that of today. Nevertheless, those from glacial periods are characterized by a large amount of herbaceous pollen, e.g.Artemisia, Gramineae, Cyperaceae, etc. inferring that grassland covered the merged continental shelf when the sea level lowered and the continental shelf was exposed. The exposed areas of the shelf were insignificant before MIS 5, but enlarged since MIS 4 and reached its maximum during MIS 2 according to ratios of pollen percentages between pine and herbs. The history of different exposure of the shelf can be compared with transgression records of the coastal areas of China and might result from neotectonic movement of Chinese continent. Some changes also took place in the components of grassland growing on the shelf during glaciations. Gramineae is the main element at MIS 8. ThenArtemisia increased upwards the profile and at last became the main component at the Last Glacial Maximum (MIS 2). Such changes in vegetation might be in response to cooler and drier climate.