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31.
Qiang Wang Derek A. Wyman Jifeng Xu Yusheng Wan Chaofeng Li Feng Zi Ziqi Jiang Huaning Qiu Zhuyin Chu Zhenhua Zhao Yanhui Dong 《Contributions to Mineralogy and Petrology》2008,155(4):473-490
New chronological, geochemical, and isotopic data are reported for Triassic (219–236 Ma) adakite-magnesian andesite-Nb-enriched
basaltic rock associations from the Tuotuohe area, central Qiangtang terrane. The adakites and magnesian andesites are characterized
by high Sr/Y (25–45), La/Yb (14–42) and Na2O/K2O (12–49) ratios, high Al2O3 (15.34–18.28 wt%) and moderate to high Sr concentrations (220–498 ppm) and εND (t) (+0.86 to +1.21) values. Low enrichments of Th, Rb relative to Nb, and subequal normalized Nb and La contents, and enrichments
of light rare earth elements combine to distinguish a group of Nb-enriched basaltic rocks (NEBs). They have positive εND (t) (+2.57 to +5.16) values. Positive correlations between Th, La and Nb and an absence of negative Nb anomalies on mantle
normalized plots indicate the NEBs are products of a mantle source metasomatized by a slab melt rather than by hydrous fluids.
A continuous compositional variation between adakites and magnesian andesites confirms slab melt interaction with mantle peridotite.
The spatial association of the NEBs with adakites and magnesian andesites define an “adakitic metasomatic volcanic series”
recognized in many demonstrably subduction-related environments (e.g., Mindanao arc, Philippines; Kamchatka arc, Russia; and
southern Baja California arc, Mexico). The age of the Touhuohe suite, and its correlation with Triassic NEB to the north indicates
that volcanism derived from subduction-modified mantle was abundant prior to 220 Ma in the central Qiangtang terrane. 相似文献
32.
The character of convergence along the Arabian–Iranian plate boundary changes radically eastward from the Zagros ranges to
the Makran region. This appears to be due to collision of continental crust in the west, in contrast to subduction of oceanic
crust in the east. The Makran subduction zone with a length of about 900 km display progressively older and highly deformed
sedimentary units northward from the coast, together with an increase in elevation of the ranges. North of the Makran ranges
are large subsiding basins, flanked to the north by active volcanoes. Based on 2D seismic reflection data obtained in this
study, the main structural provinces and elements in the Gulf of Oman include: (i) the structural elements on the northeastern
part of the Arabian Plate and, (ii) the Offshore Makran Accretionary Complex. Based on detailed analysis of these data on
the northeastern part of the Arabian Plate five structural provinces and elements—the Musendam High, the Musendam Peneplain,
the Musendam Slope, the Dibba Zone, and the Abyssal Plain have been identified. Further, the Offshore Makran Accretionary
Complex shown is to consist Accretionary Prism and the For-Arc Basin, while the Accretionary Prism has been subdivided into
the Accretionary Wedge and the Accreted/Colored Mélange. Lastly, it is important to note that the Makran subduction zone lacks
the trench. The identification of these structural elements should help in better understanding the seismicity of the Makran
region in general and the subduction zone in particular. The 1945 magnitude 8.1 tsunamigenic earthquake of the Makran and
some other historical events are illustrative of the coastal region’s vulnerability to future tsunami in the area, and such
data should be of value to the developing Indian Ocean Tsunami Warning System. 相似文献
33.
甘新交界红柳河蛇绿岩形成和侵位年龄的准确限定及大地构造意义 总被引:18,自引:10,他引:8
采用锆石SHRIMP U-Pb同位素定年方法,获得新甘交界红柳河蛇绿岩中的堆晶辉长岩年龄为516.2±7.1Ma,代表了红柳河蛇绿岩的形成年龄;侵入到红柳河蛇绿岩中未变形变质的黑云母花岗岩的年龄为404.8±5.2Ma,限定了红柳河蛇绿岩侵位的上限。作为南天山洋壳的残骸,红柳河蛇绿岩新的可靠年龄数据表明,南天山洋在早寒武世已经开始形成,并于早泥盆世埃姆斯阶之前在红柳河地区已经闭合。上述洋盆演化过程对进一步研究东天山的大地构造演化具有重要的意义。 相似文献
34.
蛇绿岩中的辉绿岩岩墙是洋脊扩张的产物.其形成年龄代表了扩张事件的时间,也代表了蛇绿岩的形成时代?对雅鲁藏布江缝合带西段拉昂错蛇绿岩中的辉绿岩岩墙进行锆石SHRIMPU—Pb定年,得出加权平均年龄为120.2Ma±2.3Ma,代表辉绿岩的结晶年龄。结合已有的关于雅鲁藏布江蛇绿岩的形成年龄(西段休古嘎布122.3Ma±2.4Ma,中段大竹卡126.0Ma±1.5Ma、吉定123.0Ma+_1.8Ma,东段罗布莎162.9Ma±2.8Ma)的报道,表明拉昂错地区特提斯洋海底扩张的时代与体古嘎布地区一致.雅鲁藏布江西段与中段地区洋盆的形成时代一致,但晚于东段的发育时代。这意味着整个东提斯洋盆的发育时代存在东早西晚的特点。 相似文献
35.
在分析综合辽宁省海岸带调查和沿海经济贝类污染监测资料基础上,根据辽宁海岸带水质,沉积物和生物污染现状及发展趋势。针对所存在的问题,讨论了辽宁省海洋污染特别是赤潮对海洋资源的破坏,并在组织机构,地方立法,海岸带环境保护规划,污染源控制与整体环境改进,监测方案等方面提出了建设海上辽宁、加强辽宁省海洋环境保护与海岸可持续开发利用的建议。 相似文献
36.
37.
象山港、三门湾软相潮间带底栖动物数量的水平分布与港湾的屏蔽性程度有一定的关系,生物量是三门湾(180.95g/m2)高于象山港(94.47g/m2),生物密度是象山港(816个/m2)高于三门湾(347个/m2)。决定所面生物数量变化的主要底栖动物种类数随着港湾屏蔽性程度的提高而相应地减少。生物数量的垂直分布主要受潮汐作用的影响,以中潮区为最高。生物量以6月份最大,密度是4月份最大。 相似文献
38.
Gu Jialong Shen Xianrong
Professor Hohai University Nanjing
Engineer The Investigation Design Institute Bureau of Communications of Zhejiang Province Hangzhou 《中国海洋工程》1991,(2)
In accordance with the similarity between breaking waves and hydraulic jumps, the expressions for estimating wave decay and wave energy dissipation in the surf zone are derived based on the fundamental equations of fluid mechanics. Using the numerical solution of cnoidal wave theory, the various kinematic properties of waves in the surf zone, including the relative wave crest height, wave energy, and radiation stress are discussed. The values calculated with the method proposed in this paper are in good agreement with the experimental data gained by other researchers. The present expressions can be used in the studies of sediment transport on gently sloping beaches, especially on muddy beaches. 相似文献
39.
In this paper, we analyse the ability of the nonlinear shallow-water (NSW) equations to predict wave distortion and energy dissipation of periodic broken waves in the inner surf zone. This analysis is based on the weak-solution theory for conservative equations. We derive a new one-way model, which applies to the transformation of non-reflective periodic broken waves on gently sloping beaches. This model can be useful to develop breaking-wave parameterizations (in particular broken-wave celerity expression) in both time-averaged wave models and time-dependent Boussinesq-type models. We also derive a new wave set-up equation which provides a simple and explicit relation between wave set-up and energy dissipation. Finally, we compare numerical simulations of both, the NSW model and the simplified one-way model, with spilling wave breaking experiments and we find a good agreement. 相似文献
40.
C. Riedel A. Tryggvason B. Brandsdottír T. Dahm R. Stéfansson M. Hensch R. Böðvarsson K. S. Vogfjord S. Jakobsdottír T. Eken R. Herber J. Holmjarn M. Schnese M. Thölen B. Hofmann B. Sigurdsson S. Winter 《Marine Geophysical Researches》2006,27(4):267-281
Between June 2004 and September 2004 a temporary seismic network was installed on the northern insular shelf of Iceland and onshore in north Iceland. The seismic setup aimed at resolving the subsurface structure and, thus, the geodynamical transition from Icelandic crust to typical oceanic crust along Kolbeinsey Ridge. The experiment recorded about 1,000 earthquakes. The region encloses the Tjörnes Fracture Zone containing the Husavik–Flatey strike-slip fault and the extensional seismic Grimsey Lineament. Most of the seismicity occurs in swarms offshore. Preliminary results reveal typical mid-ocean crust north of Grimsey and a heterogeneous structure with major velocity anomalies along the seismic lineaments and north–south trending subsurface features. Complementary bathymetric mapping highlight numerous extrusion features along the Grimsey Lineament and Kolbeinsey Ridge. The seismic dataset promises to deliver new insights into the tectonic framework for earthquakes in an extensional transform zone along the global mid-ocean ridge system. 相似文献