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711.
William L. Bandy Franois Michaud Jrme Dyment Carlos A. Mortera-Gutirrez Jacques Bourgois Thierry Calmus Marc Sosson Jose Ortega-Ramirez Jean-Yves Royer Bernard Pontoise Bertrand Sichler 《Tectonophysics》2008,454(1-4):70-85
To better understand the recent motion of the Pacific plate relative to the Rivera plate and to better define the limitations of the existing Rivera–Pacific plate motion models for accurately predicting this motion, total-field magnetic data, multibeam bathymetric data and sidescan sonar images were collected during the BART and FAMEX campaigns of the N/O L'Atalante conducted in April and May 2002 in the area surrounding the Moctezuma Spreading Segment of the East Pacific Rise, located offshore of Manzanillo, Mexico, at 106°16′W, between 17.8°N and 18.5°N. Among the main results are: (1) the principle transform displacement zone of the Rivera Transform is narrow and well defined east of 107o15′W and these azimuths should be used preferentially when deriving new plate motion models, and (2) spreading rates along the Moctezuma Spreading Segment should not be used in plate motion studies as either seafloor spreading has been accommodated at more than one location since the initiation of seafloor spreading in the area of the Moctezuma Spreading Segment, or this spreading center is not a Rivera–Pacific plate boundary as has been previously assumed. Comparison of observed transform azimuths with those predicted by the best-fit poles of six previous models of Rivera–Pacific relative motion indicate that, in the study area, a significant systematic bias is present in the predictions of Rivera–Pacific motion. Although the exact source of this bias remains unclear, this bias indicates the need to derive a new Rivera–Pacific relative plate motion model. 相似文献
712.
Elena Ortu Odile Peyron Amandine Bordon Jacques Louis de Beaulieu Consolata Siniscalco Rosanna Caramiello 《Quaternary International》2008,190(1):71
The high topographic complexity of the Alpine region is the origin of important climate differences that characterise the different areas of the Alps. These differences might have had a strong influence on vegetation and on migrations of human populations in the past. Based on an improved database containing about 3000 modern pollen samples, the standard “Modern Analogue Technique” has been applied to five pollen sequences from the subalpine belt of the South-western Italian Alps (Laghi dell’Orgials, 2240 m, Lago delle Fate, 2130 m, Torbiera del Biecai, 1920 m, Rifugio Mondovì, 1760 m, Pian Marchisio, 1624 m) to provide quantitative climate estimates for the Lateglacial and Holocene periods. Consistent climate trends are reconstructed for the different sequences. Sites recorded in detail the climate variations when they were located at the limit of two ecotones. Sites above the tree line recorded lower temperature values and less important variations. Climate was cold and dry during the Oldest and Younger Dryas and close to present-day values during the Bølling/Allerød interstadial. At the beginning of the Holocene, climate changed to warmer and moister conditions; a high number of climate fluctuations are recorded at several sites. A climate optimum is recorded in the Atlantic period, which caused a development of fir above its present-day altitudinal distribution. Climatic differences recorded at the various sites are discussed taking into account the limits of the method. 相似文献
713.
新疆北部古生代大陆增生构造 总被引:35,自引:2,他引:35
古生代亚洲中部是一幅两陆夹一洋、洋中多地体的构造图案,大地构造框架与现代西南太平洋格局十分相似。中亚造山带是晚古生代复杂地体的拼贴带。新疆北部古生代存在4类成因的8个地体构造。它们以裂解陆块地层块体、海山和火山弧的形式散布在中蒙大洋中,诸地体间是一系列的小洋盆。晚古生代,这些地体开始彼此拼贴并导致强烈推覆作用。石炭纪末-二叠纪初,中蒙大洋闭合,散布其中的诸地体分别增生到塔里木大陆北缘和西伯利亚大陆南缘。北天山-准噶尔地区6条蛇绿岩带记录了诸地体间碰撞事件。 相似文献
714.
The island of St. Paul in the Indian Ocean is located on the axis of the southeastern branch of the Indian Ocean Rise, as is the similar volcano of Amsterdam, 80 km to the north. Both volcanoes and possibly part of the local ridge are formed of a high-alumina plagioclase tholeiite making this a distinctive volcanic province. Lavas with Al2O2 contents of 12 to 22% are directly related by plagioclase fractionation. Residual rocks are a distinctive low silica, low alumina, potassic andesite with andesine and even olligoclase feldspar. Parallel lines of evolution exist in the sea floor plagioclase tholeiites, which differ only in slightly lower tenor of Sr and potassium group elements, and in the Steens Mountain tholeiites of Oregon, which differ in their significantly higher Sr and K group elements 相似文献
715.
The Bolcana ore deposit (Metaliferi Mountains, western Romania) is a porphyry ore deposit with associated epithermal veins. On the basis of different parageneses, four alteration types were distinguished: potassic, phyllic, argillic and propylitic. The mineralogical and geochemical data and estimated crystallisation temperatures of alteration minerals indicate an evolution of the system from an early period of porphyry type mineralisation (Cu+Au) to a late period of low-sulphidation epithermal mineralisation (Au+base metal). To cite this article: V. Milu et al., C. R. Geoscience 335 (2003). 相似文献
716.
717.
Bo Wang Liangshu Shu Michel Faure Bor-ming Jahn Dominique Cluzel Jacques Charvet Sun-lin Chung Sébastien Meffre 《Tectonophysics》2011,497(1-4):85-104
In the southern Chinese Tianshan, the southernmost part of the Central Asian Orogenic Belt (CAOB), widespread ophiolitic mélanges form distinct tectonic units that are crucial for understanding the formation of the CAOB. However, the timing of tectonic events and the subduction polarity are still in controversy. In order to better understand these geological problems, a comprehensive study was conducted on the Heiyingshan ophiolitic mélange in the SW Chinese Tianshan. Detailed structural analysis reveals that the ophiolitic mélange is tectonically underlain by sheared and weakly metamorphosed pre-Middle Devonian rocks, and unconformably overlain by non-metamorphic and undeformed lower Carboniferous (Serpukhovian) to Permian strata. The igneous assemblage of the mélange comprises OIB-like alkali basalt and andesite, N-MORB-like tholeiitic basalt, sheeted diabase dikes, cumulate gabbro and peridotite. Mafic rocks display supra-subduction signatures, and some bear evidence of contamination with the continental crust, suggesting a continental marginal (back-arc) basin setting. Zircons of a gabbro were dated at 392 ± 5 Ma by the U–Pb LA-ICP-MS method. Famennian–Visean radiolarian microfossils were found in the siliceous matrix of the ophiolitic mélange. Mylonitic phyllite which displays northward-directed kinematic evidence yielded muscovite 40Ar/39Ar plateau ages of 359 ± 2 Ma and 356 ± 2 Ma.These new data, combined with previously published results, suggest that the mafic protoliths originally formed in a back-arc basin in the Chinese southern Tianshan during the late Silurian to Middle Devonian and were subsequently incorporated into the ophiolitic mélange and thrust northward during the Late Devonian to early Carboniferous. Opening of the back-arc basin was probably induced by south-dipping subduction of the Paleo-Tianshan Ocean in the early Paleozoic, and the Central Tianshan block was rifted away from the Tarim block. Closure of the back-arc basin in the early Carboniferous formed the South Tianshan Suture Zone and re-amalgamated the two blocks. 相似文献
718.
François Prognon Isabelle Cojan Pascal Kindler Michel Demange 《Quaternary Research》2011,75(1):256-266
The alternation of carbonate deposits and paleosols compose the emerged part of the Bermuda archipelago. The pedological units present a complex and diversified mineralogy. Former studies demonstrated that the paleosols are not primarily a product of the unique dissolution of the surrounding carbonates, but contain a massive input of allochthonous non-carbonate detrital material. Researchers during more than the past three decades have attributed this flux of insoluble residues (IR) to Saharan dusts. We carried out systematic field and mineralogical analyses on the Quaternary paleosols from the Bermuda archipelago. Their mineralogical assemblage predominantly includes carbonates, clay minerals (kaolinite, chlorite and chlorite/vermiculite), phosphates, and aluminium and iron oxides/hydroxides. This assemblage is strikingly close to the mineralogy of the weathered volcanic substrate of Bermuda, but noticeably different from the mineralogy of Saharan dust. Moreover, we found volcanic lithoclasts in numerous paleosol profiles all over the archipelago and in all the recorded time intervals. We thus consider the volcanic seamount underlying Bermuda as the main source of non-carbonate minerals detected in the paleosols. This hypothesis further resolves the anomalous maturity of Bermudan paleosols compared to their southern counterparts in the Bahamas and Barbados. 相似文献
719.
Lucien Leclaire Yannis Bassias Micheline Denis-Clocchiatti Hugh Davies Isabelle Gautier Bernard Gensous Pierre-Jean Giannesini Philippe Patriat Jacques Segoufin Michel Tesson Jacques Wannesson 《Geo-Marine Letters》1987,7(4):169-176
Geological samples from the southern Kerguelen Plateau include Lower Cretaceous basalt and lava breccia, probable Lower Cretaceous conglomerate and shelf limestone, Upper Cretaceous chert with dolomite, Upper Cretaceous-Eocene ooze, and Tertiary conglomerate. Neogene sediments are only a few hundred m thick, and include foraminiferal and diatomaceous ooze, and ice-rafted debris. In conjunction with seismic reflection profiles, the samples indicate Early Cretaceous near-shore volcanism, followed by erosion, sedimentation, and subsidence through Cretaceous; arching of the plateau at the end of Cretaceous; subsidence through Paleogene; widespread emergence in mid-Tertiary; and slow subsidence through Neogene. 相似文献
720.
Koen de Jong Bo Wang Michel Faure Liangshu Shu Dominique Cluzel Jacques Charvet Gilles Ruffet Yan Chen 《International Journal of Earth Sciences》2009,98(6):1239-1258
Laser-probe dating of mylonite whole-rock samples from the North Tianshan—Main Tianshan fault zone that cross-cuts the North
Tianshan domain’s southern margin yielded 40Ar/39Ar spectra with 255–285 Ma ages. Biotite from an undeformed, Early Carboniferous granite, which cuts the steep mylonitic foliation
in the Proterozoic basement of the Yili arcs’s southern margin, gave a 263.4 ± 0.6 Ma plateau age (1σ). Pre-Carboniferous
metasediments overlying this basement yielded plateau ages (1σ) of 253.3 ± 0.3 (muscovite) and 252.3 ± 0.3 (biotite) Ma. The
Permian ages of mylonites date movement on these ductile, dextral strike-slip shear zones, whereas the mica ages are interpreted
by recrystallisation as a result of fluid flow around such transcurrent faults. We propose that the Tianshan’s Permian syn-tectonic
bimodal magmatism was created in a non-plume-related Yellowstone-like extensional–transtensional tectonic regime. Gold mineralisation,
tracing aqueous flow in the crust, peaked in Permian time and continued locally into the Triassic. The picture is emerging
that a convective fluid system partly driven by magmatic heat, existed in a strongly fractured and weakened crust with an
elevated heat flow, leading to regional-scale isotope resetting. We suggest that surprisingly young isotopic ages in the literature
for early orogenic (ultra)high-pressure metamorphism are similarly due to fluid-mediated recrystallisation. 相似文献