The radiolarian evidence for the accretion of the Fu-saki Formation with the inferred oceanic plate stratigraphy: A case of weakly-metamorphosed accretionary complex in Ishigaki Jima,southern Ryukyu Arc,Japan     

《Journal of Asian Earth Sciences》2013

The island of Ishigaki Jima, located in the western part of the southern Ryukyu Arc, Japan, is underlain by a basement comprising the Tumuru and Fu-saki formations. The former is a pelitic glaucophane schist with a metamorphic age of 220–190 Ma, and the latter is a weakly metamorphosed accretionary complex, composed mainly of chert, mudstone and sandstone with minor amounts of limestone and mafic rocks. The Fu-saki Formation was weakly metamorphosed at ∼140 Ma. Latest Carboniferous–Early Jurassic microfossils have been obtained from the limestones, cherts and siliceous mudstones of this formation, but no fossils have been collected from the phyllitic mudstones. The radiolarian fauna of the phyllitic mudstones described herein indicates a late Pliensbachian–early Toarcian (Early Jurassic) age. This result, when combined with existing data, enables the reconstruction of an oceanic plate stratigraphy, showing a succession of (in ascending order) Upper Carboniferous–Triassic cherts, Sinemurian–lower Pliensbachian siliceous mudstones and upper Pliensbachian–lower Toarcian phyllitic mudstones and sandstones. The radiolarians from the phyllitic mudstones are important in constraining the timing of the accretion of the Fu-saki Formation to the base of the Tumuru Formation.  相似文献   

Late Ordovician to early Silurian calc-alkaline magmatism in the Xiemisitai Mountains,northern West Junggar: a response to the subduction of the Junggar-Balkhash Ocean     

《International Geology Review》2012,54(16):2000-2014

Basement exposed in the Placer de Guadalupe–Plomosas uplift in northern Mexico provides important clues for the geologic evolution of the region. The stratigraphic units form stacked thrust sheets of psammitic and calcareous formations, interlayered with magmatic rock. The eastern calcareous and quartzite formations exhibit structures associated with ductile deformation, whereas the upper stratigraphic units only contain structures formed via younger brittle deformation. Porphyry interlayered in the upper Plomosas Formation has a U-Pb zircon age of 171 ± 1 Ma. This age is consistent with its stratigraphic position, interbedded quartzarenites with a maximum depositional age of ~168 Ma. Granite flakes within the Horquilla Formation are dated at 209 ± 3 Ma, and the La Viñata quartzite exhibits a maximum age of ~193 Ma. The Upper Plomosas Formation correlates well with the arc-related Middle Jurassic Nazas Formation of northeastern Mexico, constituting the first report of a Jurassic continental margin arc outcrop in the ‘Central Mexican Gap zone’. We document Late Norian to Bajocian ages for the stratigraphic units cropping out in the Placer de Guadalupe area. The Jurassic age cluster indicates that the Nazas Arc magmatism in the region occurred during the Late Triassic and ended in the Middle Jurassic times. Permian ages previously assigned to these rocks and the occurrence of a Permo–Triassic deformation event have to be dismissed.  相似文献   

Late Cretaceous calcareous nannofossil and planktonic foraminiferal bioevents of the shallow-marine carbonate platform in the Mitla Pass, west central Sinai, Egypt     

Sherif Farouk  Mahmoud Faris 《Cretaceous Research》2012,33(1):50-65

The first detailed biostratigraphic analyses of the Coniacian-middle Campanian shallow-marine carbonate successions exposed in the Mitla Pass, west central Sinai, Egypt have revealed the stratigraphic distribution of diverse calcareous nannofossil and planktonic foraminiferal species. Thirty-six calcareous nannofossils and thirty-two planktonic foraminifera are identified, indicating a Coniacian to middle Campanian age and four Tethyan planktonic foraminiferal and five calcareous nannofossil zones. A comparison of these bioevents from different palaeolatitudes shows considerable variation in age.Three sequence boundaries coincident with the Turonian/Coniacian, Coniacian/Santonian and Santonian/Campanian stage boundaries are recognized. A fourth sequence boundary is marked by a major upper Campanian to early Ypresian (early Eocene) unconformity. These sequence boundaries are primarily related to regional tectonism associated with the Syrian Arc Fold System and secondarily to eustatic sea-level fluctuations.  相似文献   

西天山特克斯北中酸性火成岩地球化学特征及成因意义   总被引：2，自引：2，他引：0  

朱志敏  赵振华  熊小林 《岩石学报》2012,28(7):2145-2157

新疆西天山特克斯县城北部伊特公路沿线和库勒萨依出露大量中酸性火成岩,伊特公路沿线为石英钠长斑岩,库勒萨依为石英闪长斑岩和花岗闪长斑岩。岩石地球化学和同位素组成研究表明,前者为典型的岛(陆)弧带火成岩,而后者具有埃达克岩的成分特征,两者均为古亚洲洋壳在俯冲过程中岩浆活动的产物。早先俯冲的较冷洋壳板片在深处脱水诱发上覆地幔楔熔融,熔体上升并经历壳幔相互作用等过程引发伊特公路一带弧岩浆活动; 由于洋壳持续俯冲,后来新形成的靠近洋脊的年轻板片由于高热在较浅处直接发生部分熔融形成埃达克岩浆,并上侵至库勒萨依一带。库勒萨依斑岩体SIMS锆石 U-Pb年龄为342.5±2.3Ma,属于早石炭世。两组中酸性火成岩的地球化学特征表明,古亚洲洋(南天山洋)在早石炭世还未完全闭合,洋壳向北的持续俯冲过程造成伊犁-中天山板块南缘广泛的岩浆活动,此时西天山陆壳增生方式主要为侧向增生,增生物质主要为洋壳板片(埃达克岩)和洋壳板片流体交代的地幔楔成分。  相似文献   

基于WebGIS的视频星车流量分析与路况查询系统     

夏广申  张正鹏  陈奕帆 《测绘与空间地理信息》2017,40(9)

车流量作为衡量路况信息的重要因素,需要一个低成本且高效的可视化监控系统。本文对视频监控中的车流量信息进行了提取分析,采用背景差分的方法对视频中有关的车辆因子进行提取,包括车流量信息提取、车辆类型提取、车速提取,并将分析得到的数据通过Web GIS发布到网络上支持在线预览,结合GIS和视频监控的特点,解决了传统视频监控系统空间位置感较差的问题。  相似文献   

拉萨地块中北部白垩纪则弄群火山岩:Slainajap洋南向俯冲的产物?   总被引：12，自引：3，他引：9  

康志强  许继峰  董彦辉  王保弟 《岩石学报》2008,24(2)

拉萨地块广泛分布有中生代的岩浆活动,研究它们对于认识特提斯洋的演化和理解整个青藏高原的形成过程有着重要的启示。本文对出露于拉萨地块中北部的则弄群火山岩进行了系统的年代学以及元素地球化学研究。研究的则弄群火山岩主要由玄武安山岩、安山岩和英安岩组成,根据化学成分可将其分为中基性(SiO_2<58%)和中酸性(SiO_2>58%)两个组。中基性岩以低钾和中钾钙碱性岩为主,而中酸性岩则主要位于高钾钙碱性系列;二者微量元素分布特征相似,如均富集Rb、Ba、Th、U等大离子亲石元素(LILE),Nb、Ta、Ti等高场强元素(HFSE)有着明显的负异常,具有明显的弧火山岩成分特征;稀土配分模式均表现为一致的轻稀土富集右倾型,可能反应了其母岩浆的同源性。精确的锆石U-Pb LA-ICPMS定年获得了113.6±1.0Ma年龄,说明研究区则弄群火山岩形成于早白垩世中期。综合前人的研究成果,我们初步认为则弄群火山岩可能为班公湖-怒江缝合带南侧的狮泉河-永珠-纳木错-嘉黎蛇绿岩带所代表的古洋(Slainajap洋)在早白垩世向南俯冲消减的产物。  相似文献   

Late Quaternary vegetation reconstruction from the Eastern Arc Mountains, Tanzania     

C.T. Mumbi  R. Marchant  H. Hooghiemstra 《Quaternary Research》2008,69(2):326-341

Pollen, spore, macrofossil and stable isotope (C and N) analyses from a 266-cm sediment core collected from a swamp on the Eastern Arc Mountains, Tanzania, are used to reconstruct vegetation and environmental history. An estimated time scale based on five ¹⁴C ages records approximately 38,000 yr. This palaeorecord is the first from this biodiversity hotspot and importantly extends through the last glacial maximum (LGM). The altitudinal transition from montane to upper montane forest shifted from 1700-1800 m (38,000 ¹⁴C yr BP) to 1800-1900 m (35,000-29,000 ¹⁴C yr BP). From 29,000 to 10,000 ¹⁴C yr BP, it shifted from 1850-1950 m across the LGM to 1750-1800 m (during 10,000-3500 ¹⁴C yr BP), and to present-day elevations at 2000 m during the last 3500 ¹⁴C yr BP. The relative ecosystem stability across the LGM may be explained by the Indian Ocean's influence in maintaining continuous moist forest cover during a period of East African regional climate aridity. During the late Holocene, presence of abundant coprophilous fungi and algal blooms demonstrates increasing human impact. Neurospora spores indicate frequent fires, coinciding with clear signals of decline in Podocarpus and Psychotria trees that possibly represent selective logging.  相似文献   

一种计算机辅助设计数据与GIS数据转换方法     

耿继军  刘荣  吴聪聪  李亚威 《测绘科学》2016,41(8):134-137

针对GIS数据与计算机辅助设计(CAD)数据之间的差异性,以及现有转换方法存在的问题,该文提出了一种计算机辅助设计数据处理方法——采用空间数据操作引擎(FME)和Arc Map联合使用的方法。该方法能够较好地解决计算机辅助设计数据向GIS数据转换的难题,实现了对计算机辅助设计数据的批量转换和处理。以某市的地形图为数据源进行实例论证,实验结果显示运用该文所提方法能够更好地处理计算机辅助设计数据,为计算机辅助设计地形图的转换提供了可行的方案;特别是对转换出来的数据进行了拓扑重建、附属性值以及多边形数据分类处理,能够更好地保持数据的精度和完整性,更有利于数据的入库。  相似文献   

内蒙古中部苏尼特左旗地区早古生代火成岩年代学、地球化学、锆石Hf同位素特征及其构造意义   总被引：3，自引：2，他引：1  

唐建洲  张志诚  陈彦  姬泽佳  杨金福 《岩石学报》2018,34(10):2973-2994

内蒙古中部苏尼特左旗南东地区出露的早古生代花岗岩类岩石和玄武-安山岩序列,对于限定苏尼特左旗岛弧演化以及兴蒙造山带在该地区的构造演化具有重要意义。花岗岩类岩石主要由花岗闪长岩和花岗岩组成,LA-ICP-MS锆石UPb测年结果显示其形成于晚奥陶世-早志留世(441～449Ma)。花岗岩类岩石表现出高硅(Si O2=69. 60%～77. 36%)、铝(Al_2O_3=12. 70%～15. 40%),低镁(MgO=0. 19%～0. 81%)、铁(Fe2O3=0. 94%～3. 49%)的特征。此外,花岗岩类岩石εHf(t)值介于-0. 81～+5. 64之间,且二阶段模式年龄介于1119～1478Ma之间,这表明其主要来源于新生地壳的部分熔融。玄武-安山岩SiO2含量介于49. 13%～57. 82%之间,并具有较高的镁(MgO=3. 31%～6. 57%)、铁(Fe2O3=6. 54%～9. 63%)含量,且Zr/Hf比值(35. 4～37. 6)与原始地幔相应值接近,再结合该火山岩高铝(Al2O3=16. 77%～18. 34%)、高钠(Na2O=3. 46%～5. 05%)、高Th/Ce比值(0. 12～0. 25)以及Sr正异常等特征,表明其来源于俯冲交代的地幔楔的部分熔融。本次研究的所有火成岩样品均属于钙碱性系列,并表现出富集大离子亲石元素(Rb、Th、K等)和轻稀土元素,亏损高场强元素(Nb、Ta、Ti、P等)的特征。此外,其Rb/Zr比值(0. 07～1. 0)以及Nb(4. 24×10-6～15. 17×10-6)含量与正常大陆弧接近,结合前人已报道的年代学以及地球化学资料,表明苏尼特左旗东南地区早古生代火成岩与古亚洲洋向北的俯冲演化有关。  相似文献   

Identification of Magma Mixing: A Case Study of the Daocheng Batholith in the Yidun Arc     

Ruigang Zhang  Xue Gao  Liqiang Yang 《地球科学进展》2018,33(10):1058-1074

The Daocheng batholiths, located in the east of the Yidun arc, consist of granite, granodiorite and K-feldspar granite. Abundant massive mafic microgranular enclaves (MMEs) mainly developed within the granodiorite and K-feldspar granite, and they have clear contacts with the hosted granites. The MMEs are characterized by the quartz eye structure, quenched apatite, and plagioclases phenocrysts with obvious oscillatory zones. Petrographical studies on MMEs and host granites, zoned plagioclase and whole-rock geochemical analysis were carried out to identify the presence of magma mixing. Combined with the previous studies on the whole-rock Sr-Nd-Hf isotopic signatures, the petrogenesis of Daocheng batholith was discussed. The zoned plagioclases from MMEs have An contents varying between 29 and 44, while those from the host granites have An contents of 21~50. The compositional variations and corrosion structure of plagioclase are probably related to magma mixing. Geochemically, the MMEs have relatively low SiO₂ contents (56.34~60.91wt%), high Al₂O₃ contents of 16.06~17.98wt%, and are enriched in magnesium and iron, belonging to metalumnious series (A/CNK=0.82~0.98). The Daocheng batholith belongs to high-K calc-alkaline series, which have high alkaline contents (Na₂O+K₂O=6.25~7.79wt%) and low CaO contents (1.40~3.22wt%). Furthermore, both the MMEs and hosted granites are enriched in LILEs (K, Rb and Pb) and LREEs and depleted in HFSEs (Nb, Ta, Zr, Hf, P and Ti), showing affinities of typical arc magmas. Compared with the host granites, the MMEs are characterized by lower (La/Yb)_N ratios of 1.99 to 2.46, and much more obvious Eu depletions (Eu/Eu^*=0.30~0.50). The host granites have Rb/Sr ratios ranging from 1.0 to 1.9, and they are consistent with the crust-derived materials (Rb/Sr>0.5). Their Zr/Hf ratios range from 27.5 to 36.9, which are close to the transitional Zr/Hf ratios between mantle-and crust-derived materials. This indicates that the formation of Daocheng batholith is genetically related to the mixing between mantle-and crust-derived materials. In addition, the relatively low silica contents and high Mg# values, and the linear patterns of MgO, Al₂O₃ and Fe₂O₃ with SiO₂ contents from the MMEs and host granites, show that the formation of MMEs is genetically related to magma mixing. Overall, the parent magmas of Daocheng granites are derived from the partial melting of Late Triassic arc lower crust, with the input of minor mantle-derived materials. The MMEs are generated by the mixing of the mafic magma with felsic magma.  相似文献