Palaeomagnetism of the Tudor gabbro, Ontario: evidence for divergence between Grenvillia and interior Laurentia     

David J. Dunlop  Hironobu Hyodo  Todd Knight  Alan G. Steele 《Geophysical Journal International》1985,83(3):699-720

Summary. After thermal and alternating field (AF) cleaning, the characteristic high blocking temperature A component of natural remanent magnetization (NRM) of the Tudor gabbro of southern Ontario has a mean direction D = 326°, I =–46° ( k = 132, α₉₅= 4.8°, N = 8 sites). The corresponding palaeopole, 133°E, 12°N ( dp = 4°, dm = 6°), confirms the palaeopole 137°E, 17°N (α₉₅= 8.4°) reported earlier by Palmer & Carmichael, based on AF cleaning only. The A NRM has unblocking temperatures > 515–525°C which exceed the estimated 500°C peak temperature reached locally during ∼ 1050 Ma Grenvillian regional metamorphism. The A NRM therefore predates metamorphism and is probably a primary thermoremanence (TRM). The age of the Tudor NRM has previously been taken to be about 675 Ma, but recent ⁴⁰Ar/³⁹Ar dating by Baksi has shown that this is the time of post-metamorphic cooling to 200–250°C. Hornblendes record initial cooling of the intrusion to 590±20°C at 1110 Ma and this is the best estimate of the age of the A remanence. Successful Thellier-type palaeointensity determinations on 11 Tudor samples confirm that the A NRM is a TRM and indicate a palaeofield at this time of 18–27 μT, about 50–70 per cent of the present field intensity at 27° magnetic latitude. The anomalous Tudor A palaeopole, which lies well to the west of both 1000–800 Ma Grenvillian palaeopoles and 1100–1050 Ma poles from Interior Laurentia, is interpreted as recording divergence between Grenvillia and Interior Laurentia just before the Grenvillian orogeny, rather than a post-metamorphic extension of the apparent polar wander path as previously assumed.  相似文献   

Sonar acoustic facies and sediment distribution on an area of the deep ocean floor     

Robert B. Kidd  Robert W. Simm  Roger C. Searle 《Marine and Petroleum Geology》1985,2(3):210-221

Long-range sidescan sonar can be used to map sediment distributions over wide expanses of deep ocean floor. Seven acoustic facies that arise from differing sediment or rock types have been mapped over the low-relief Saharan continental rise and Madeira abyssal plain. These have been calibrated with sampling, profiling and camera studies and the facies can be traced confidently on a regional scale using the sidescan data. The mapping of the sediment distribution shows that a complex interplay of turbidity current and debris flow processes can occur at a continental rise/abysaal plain transition over 1000 km from the nearest continental slope.  相似文献   

IMPACTS OF FUTURE SEA LEVEL RISE ON SALT WATER INTRUSION IN THE CHANGJIANG RIVER ESTUARY   总被引：1，自引：0，他引：1  

杨桂山 《中国地理科学(英文版)》1992,2(1):30-41

Sea level rise could increase the salinity of an estuary by altering the balance between fresh water and salt water. The implications of sea level rise for increasing salinity have been examined in the Changjiang (Yangtze) River estuary. By correlative analysis of chlorinity, discharge and tidal level and calculation of two-dimensional chlorinity, distribution of the Changjiang River estuary, the changes of the intensity and lasting hours of salt water intrusion at Wusong Station and the changes of chlorinity distribution in the South Branch of the Changjiang River estuary have been estimated when future sea level rises 50-100 cm. The intensity of salt water intrusion in the future will be far more serious than current trend.  相似文献   

Opening of the Fram Strait gateway: A review of plate tectonic constraints   总被引：1，自引：0，他引：1  

  yvind Engen  Jan Inge Faleide  Toril Karlberg Dyreng 《Tectonophysics》2008,450(1-4):51-69

We have revised the regional crustal structure, oceanic age distribution, and conjugate margin segmentation in and around the Lena Trough, the oceanic part of the Fram Strait between the Norwegian–Greenland Sea and the Eurasia Basin (Arctic Ocean). The Lena Trough started to open after Eurasia–Greenland relative plate motions changed from right-lateral shear to oblique divergence at Chron 13 times (33.3 Ma; earliest Oligocene). A new Bouguer gravity map, supported by existing seismic data and aeromagnetic profiles, has been applied to interpret the continent–ocean transition and the influence of Eocene shear structures on the timing of breakup and initial seafloor spreading. Assuming that the onset of deep-water exchange depended on the formation of a narrow, oceanic corridor, the gateway formed during early Miocene times (20–15 Ma). However, if the initial Lena Trough was blocked by terrigenous sediments or was insufficiently subsided to allow for deep-water circulation, the gateway probably formed with the first well developed magnetic seafloor spreading anomaly around Chron 5 times (9.8 Ma; Late Miocene). Paleoceanographic changes at ODP Site 909 (northern Hovgård Ridge) are consistent with both hypotheses of gateway formation. We cannot rule out that a minor gateway formed across stretched continental crust prior to the onset of seafloor spreading in the Lena Trough. The gravity, seismic and magnetic observations question the prevailing hypotheses on the Yermak Plateau and the Morris Jesup Rise as Eocene oceanic plateaus and the Hovgård Ridge as a microcontinent.  相似文献   

新疆塔里木北缘色日牙克依拉克一带泥盆纪花岗质侵入体的确定及其地质意义   总被引：15，自引：7，他引：8  

朱志新  李锦轶  董连慧  王克卓  刘国忠  李亚萍  刘振涛 《岩石学报》2008,24(5)

位于新疆南天山色日牙克依拉克一带发育较多的中酸性侵入岩,前人均划为石炭纪侵入岩,作者对其中花岗闪长岩锆石进行SHRIMP定年,获得侵入岩形成年龄387±8Ma,另有一组捕获锆石的年龄为418.4±6.5Ma,通过对这些侵入岩的岩石学研究,结果显示该区泥盆纪侵入岩均具较典型活动陆缘侵入岩的特征.结合区域岩浆活动资料及前人成果,初步确定在塔里木北缘木札尔特、色日牙克依拉克、虎拉山南缘野云沟至库尔勒一带在古生代为一活动陆缘.  相似文献   

Tidal and Subtidal Flow along a Cross-Shelf Transect on the East China Sea     

Arnoldo Valle-Levinson  Takeshi Matsuno 《Journal of Oceanography》2003,59(5):573-584

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试论东海陆架盆地的基底构造演化和盆地形成机制   总被引：4，自引：0，他引：4  

李培廉  朱平 《海洋地质与第四纪地质》1992,(3)

本文主要根据东海陆架盆地和周边的地质、地球物理资料,分析盆地的基底岩性特征、结构特征。认为东海陆架盆地的基底除元古界片麻岩外,还分布有一定范围的中生界及古生界。基底构造特征是纵向上多层次,横向上不均一,南北有别,东西分带。构造演化上经历了张、合、压、扭等复杂过程。  相似文献   

河口环流和盐水入侵Ⅱ--径流量和海平面上升的影响   总被引：1，自引：0，他引：1  

胡松  朱建荣  傅得健  吴辉 《中国海洋大学学报(自然科学版)》2003,33(3):337-342

本文利用本序列上篇论文建立的理想河口数值模式,研究径流量和海平面上升对河口环流和盐水入侵的影响.在径流量增大的情况下,口门内表层向海的流速增大,底层向陆的密度流减弱,滞流点下移.口门外侧向口门的密度流增大,上升流趋于增强.口门内盐水入侵减弱,口外盐度减小、冲淡水扩展范围增大.在口门上游北岸底层盐度下降明显,口门处南岸表层盐度下降明显.径流量变化对盐水入侵影响十分巨大.在海平面上升的情况下,拦门沙区域向陆的密度流增强,滞流点上移,表层向海的流动增大.口门内盐水入侵增强,口外盐度增大,冲淡水扩展范围减小.海平面上升对盐水入侵影响十分明显,北岸底层盐度增大尤为特出.  相似文献   

Forearc structures and tectonics in the southern Peru—northern Chile Continental Margin     

Chang Li 《Marine Geophysical Researches》1995,17(1):97-113

SeaMARC II side-scan images, bathymetry, and single-channel seismic reflection data along the southern Peru—northern Chile forearc area between 16° and 23° S reveal a complex region of morpho-structural, submarine drainage and depression patterns. In the subducting plate area, the NW—SE trending primary normal fault system represented by trench-paralleled scarps was incipiently formed as the Nazca Plate was bent in the outer edge and further intensified as the plate approached the trench. The NE—SW trending secondary normal fault system that consists of discontinuous and smaller faults, usually intersect the primary trench-paralleled fault system. Similar to the Nazca Plate, the overriding continental plate also shows two major NW—SE and NE—SW trending fault systems represented by fault scarps or narrow elongated depressions.The submarine drainage systems represented by a series of canyon and channel courses appear to be partly controlled by the faults and exhibit a pattern similar to the onshore drainage which flows into the central region of the coastal area. Two large depressions occurring along the middle—upper slope areas of the continental margin are recognized as collapse and slump that perhaps are a major result of increased slope gradient. The subsidence of the forearc area in the southern Peru—northern Chile Continental Margin is indicated by: a) drainage systems flowing into the central region, b) the slope collapse and slumps heading to the central region, c) the deepening of the trench and inclining of the lower slope terrace to the central region, and d) submerging of the upper-slope ridge and the Peru—Chile Coast Range off the Arica Bight area.The subsidence of the forearc area in the southern Perunorthern Chile margin is probably attributed to a subduction erosion which causes wearing away and removal of the rock and sedimentary masses of the overriding plate as the Nazca Plate subducts under the South American Plate.  相似文献   

珠江口外陆架表层沉积物的地球化学分区     

周蒂  陈绍谋  陈汉宗 《热带海洋学报》1991,(3)

根据249个表层沉积物样品的Ca,Al,N,P,Mg,Fe,Mn,Ti和有机碳的测定数据,利用稳健RQ型主分量分析及Q型聚类分析方法,对珠江口外陆架表层沉积物进行了地球化学分类,并将该陆架区划分成陆源细碎屑沉积区、经叠加改造的残留泥砂质沉积区、生物碎屑沉积区以及高能环境下的石英砂质沉积区。结果表明了稳健统计方法相对于传统统计方法的优越性,以及采用稳健主分量的Q载荷进行聚类分析相对于用原始变量进行聚类分析的优越性。  相似文献