Time scale of an early to mid-Paleozoic orogenic cycle of the long-lived Central Asian Orogenic Belt, Inner Mongolia of China: Implications for continental growth   总被引：50，自引：0，他引：50  

Ping Jian  Dunyi Liu  Alfred Krner  Brian F. Windley  Yuruo Shi  Fuqin Zhang  Guanghai Shi  Laicheng Miao  Wei Zhang  Qi Zhang  Liqao Zhang  Jishun Ren 《Lithos》2008,101(3-4):233-259

We present a detailed, new time scale for an orogenic cycle (oceanic accretion–subduction–collision) that provides significant insights into Paleozoic continental growth processes in the southeastern segment of the long-lived Central Asian Orogenic Belt (CAOB). The most prominent tectonic feature in Inner Mongolia is the association of paired orogens. A southern orogen forms a typical arc-trench complex, in which a supra-subduction zone ophiolite records successive phases during its life cycle: birth (ca. 497–477 Ma), when the ocean floor of the ophiolite was formed; (2) youth (ca. 473–470 Ma), characterized by mantle wedge magmatism; (3) shortly after maturity (ca. 461–450 Ma), high-Mg adakite and adakite were produced by slab melting and subsequent interaction of the melt with the mantle wedge; (4) death, caused by subduction of a ridge crest (ca. 451–434 Ma) and by ridge collision with the ophiolite (ca. 428–423 Ma). The evolution of the magmatic arc exhibits three major coherent phases: arc volcanism (ca. 488–444 Ma); adakite plutonism (ca. 448–438 Ma) and collision (ca. 419–415 Ma) of the arc with a passive continental margin. The northern orogen, a product of ridge-trench interaction, evolved progressively from coeval generation of near-trench plutons (ca. 498–461 Ma) and juvenile arc crust (ca. 484–469 Ma), to ridge subduction (ca. 440–434 Ma), microcontinent accretion (ca. 430–420 Ma), and finally to forearc formation. The paired orogens followed a consistent progression from ocean floor subduction/arc formation (ca. 500–438 Ma), ridge subduction (ca. 451–434 Ma) to microcontinent accretion/collision (ca. 430–415 Ma); ridge subduction records the turning point that transformed oceanic lithosphere into continental crust. The recognition of this orogenic cycle followed by Permian–early Triassic terminal collision of the CAOB provides compelling evidence for episodic continental growth.  相似文献   

Sedimentary evolution of a Late Pleistocene temperate red algal reef (Coralligène) on Rhodes,Greece: correlation with global sea‐level fluctuations     

JÜRGEN TITSCHACK  CAMPBELL S. NELSON  TIM BECK  ANDRÉ FREIWALD  ULRICH RADTKE 《Sedimentology》2008,55(6):1747-1776

Autochthonous red algal structures known as coralligène de plateau occur in the modern warm‐temperate Mediterranean Sea at water depths from 20 to 120 m, but fossil counterparts are not so well‐known. This study describes, from an uplifted coastal section at Plimiri on the island of Rhodes, a 450 m long by 10 m thick Late Pleistocene red algal reef (Coralligène Facies), interpreted as being a coralligène de plateau, and its associated deposits. The Coralligène Facies, constructed mainly by Lithophyllum and Titanoderma, sits unconformably upon the Plio‐Pleistocene Rhodes Formation and is overlain by a Maerl Facies (2 m), a Mixed Siliciclastic‐Carbonate Facies (0·2 m) and an Aeolian Sand Facies (2·5 m). The three calcareous facies, of Heterozoan character, are correlated with established members in the Lindos Acropolis Formation in the north of the island, while the aeolian facies is assigned to the new Plimiri Aeolianite Formation. The palaeoenvironmental and genetic‐stratigraphic interpretations of these mixed siliciclastic‐carbonate temperate water deposits involved consideration of certain characteristics associated with siliciclastic shelf and tropical carbonate shelf models, such as vertical grain‐size trends and the stratigraphic position of zooxanthellate coral growths. Integration of these results with electron spin resonance dates of bivalve shells indicates that the Coralligène Facies was deposited during Marine Isotope Stage 6 to 5e transgressive event (ca 135 to 120 ka), in water depths of 20 to 50 m, and the overlying Maerl Facies was deposited during regression from Marine Isotope Stage 5e to 5d (ca 120 to 110 ka), at water depths of 25 to 40 m. The capping Aeolian Sand Facies, involving dual terrestrial subunits, is interpreted as having formed during each of the glacial intervals Marine Isotope Stages 4 (71 to 59 ka) and 2 (24 to 12 ka), with soil formation during the subsequent interglacial periods of Marine Isotope Stages 3 and 1, respectively. Accumulation rates of about 0·7 mm year^?1 are estimated for the Coralligène Facies and minimum accumulation rates of 0·2 mm year^?1 are estimated for the Maerl Facies. The existence of older red algal reefs in the Plimiri region during at least Marine Isotope Stages 7 (245 to 186 ka) and 9 (339 to 303 ka) is inferred from the occurrence of reworked coralligène‐type lithoclasts in the basal part of the section and from the electron spin resonance ages of transported bivalve shells.  相似文献   

Palaeoenvironmental significance of Late Permian palaeosols in the South‐Eastern Iberian Ranges,Spain     

RAÚL DE LA HORRA  Ma ISABEL BENITO  JOSE LÓPEZ‐GÓMEZ  ALFREDO ARCHE  JOSÉ F. BARRENECHEA  JAVIER LUQUE 《Sedimentology》2008,55(6):1849-1873

The Late Permian (Wuchiapingian) Alcotas Formation in the SE Iberian Ranges consists of one red alluvial succession where abundant soil profiles developed. Detailed petrographical and sedimentological studies in seven sections of the Alcotas Formation allow six different types of palaeosols, with distinctive characteristics and different palaeogeographical distribution, to be distinguished throughout the South‐eastern Iberian Basin. These characteristics are, in turn, related to topographic, climatic and tectonic controls. The vertical distribution of the palaeosols is used to differentiate the formation in three parts from bottom to top showing both drastic and gradual vertical upwards palaeoenvironmental changes in the sections. Reconstruction of palaeoenvironmental conditions based on palaeosols provides evidence for understanding the events that occurred during the Late Permian, some few millions of years before the well‐known Permian‐Triassic global crisis.  相似文献   

Carbonate aeolianites of western Saurashtra,India: experimental decipherment of the depositional mechanisms     

PRABIR DASGUPTA  SUBIKASH BANDYOPADHYAY 《Sedimentology》2008,55(5):1361-1374

Granular carbonate deposits of Late Pleistocene to Early Holocene age, commonly referred to as ‘miliolite limestone’, occur in a linear belt, parallel to the southern coast of Saurashtra, India. In the present study area these carbonate deposits are found in select valleys between ridges and mounds of pyroclastic material present in the Deccan trap plateau. Two different depositional histories have been proposed for these sediments. The presence of marine bioclasts led to the postulation of a marine origin for these deposits. The second school of thought propounded redeposition of the coastal sediments by aeolian processes. Although a few features could not be explained by the proposed aeolian model, critical comparison of these two views favoured the aeolian origin. The mode of occurrence, lithological and structural attributes, and microscopic evidence presented here, also support a possible aeolian origin for these deposits. Experimental observation indicates that these carbonate aeolianites represent backflow deposits, which accumulated because of the flow separation caused by the presence of topographic highs. The conspicuous concave‐up geometry of the deposit conformed to the shape of the separation bulb. In view of the inferred depositional mechanism, the disposition of the deposits and the signature of the palaeoflow direction suggest that the carbonate particles were derived from the north‐western coast of Saurashtra by strong south‐easterly winds. Massive granular carbonates with outsized basement clasts appear to be the product of avalanching of granular material from the higher contours because of oversteepening of the primary deposit.  相似文献   

An Atomic Force Microscopy study of the growth of calcite in the presence of sodium sulfate   总被引：1，自引：0，他引：1  

Aikaterini I. Vavouraki  Christine V. Putnis  Andrew Putnis  Petros G. Koutsoukos   《Chemical Geology》2008,253(3-4):243-251

In situ atomic force microscopy (AFM) has been used to compare the growth of pure calcite and the growth of calcite in the presence of sulfate ions from aqueous solutions at a constant value of supersaturation (S.I. = 0.89) with respect to calcite. The effect of sulfate ions on calcite growth rates is determined and a potential incorporation of sulfate ions is identified in the calcite during growth. Solutions supersaturated with respect to calcite with solution concentration ratio of one and a constant pH of 10.2, were prepared and sulfate was added as Na₂SO₄ aqueous solution. The solution composition was readjusted in order to keep the supersaturation and pH constant. PHREEQC was used to determine relevant solution concentrations. In situ AFM experiments of calcite growth were performed using a fluid cell and flowing solutions passed over a freshly cleaved calcite surface. Growth rates were determined from the closure of the rhombohedral etch pits induced by initial dissolution with pure water. The spreading rate of 2-dimensional nuclei was also measured. At low concentrations of sulfate (≤ 0.5 mM), no effect on the growth rate of the calcite was observed. At higher concentrations (2 to 3 mM) of sulfate, the growth rate increased, possibly because a higher concentration of calcium and carbonate was necessary to maintain the supersaturation constant. At much higher concentrations of additional sulfate (up to 60 mM) the growth rate of the calcite was substantially decreased, despite the fact that a further increase of calcium and carbonate was required. The morphology of 2-dimensional growth nuclei became increasingly elongated with increasing sulfate content. Measurements of step height showed that newly grown steps were approximately 1 Å higher when grown in high sulfate concentrations, compared to steps grown in sulfate-free solutions. At sulfate concentrations above 5 mM the growth mechanism changes from layer growth to surface roughening. These observations suggest that the new growth has incorporated sulfate into the calcite surface.  相似文献   

History of crustal growth and recycling at the Pacific convergent margin of South America at latitudes 29°–36° S revealed by a U–Pb and Lu–Hf isotope study of detrital zircon from late Paleozoic accretionary systems     

A.P. Willner  A. Gerdes  H.-J. Massonne 《Chemical Geology》2008,253(3-4):114-129

Detrital zircon provides a powerful archive of continental growth and recycling processes. We have tested this by a combined laser ablation ICP-MS U–Pb and Lu–Hf analysis of homogeneous growth domains in detrital zircon from late Paleozoic coastal accretionary systems in central Chile and the collisional Guarguaráz Complex in W Argentina. Because detritus from a large part of W Gondwana is present here, the data delineate the crustal evolution of southern South America at its Paleopacific margin, consistent with known data in the source regions.Zircon in the Guarguaráz Complex mainly displays an U–Pb age cluster at 0.93–1.46 Ga, similar to zircon in sediments of the adjacent allochthonous Cuyania Terrane. By contrast, zircon from the coastal accretionary systems shows a mixed provenance: Age clusters at 363–722 Ma are typical for zircon grown during the Braziliano, Pampean, Famatinian and post-Famatinian orogenic episodes east of Cuyania. An age spectrum at 1.00–1.39 Ga is interpreted as a mixture of zircon from Cuyania and several sources further east. Minor age clusters between 1.46 and 3.20 Ga suggest recycling of material from cratons within W Gondwana.The youngest age cluster (294–346 Ma) in the coastal accretionary prisms reflects a so far unknown local magmatic event, also represented by rhyolite and leucogranite pebbles. It sets time marks for the accretion history: Maximum depositional ages of most accreted metasediments are Middle to Upper Carboniferous. A change of the accretion mode occurred before 308 Ma, when also a concomitant retrowedge basin formed.Initial Hf-isotope compositions reveal at least three juvenile crust-forming periods in southern South America characterised by three major periods of juvenile magma production at 2.7–3.4 Ga, 1.9–2.3 Ga and 0.8–1.5 Ga. The ¹⁷⁶Hf/¹⁷⁷Hf of Mesoproterozoic zircon from the coastal accretionary systems is consistent with extensive crustal recycling and addition of some juvenile, mantle-derived magma, while that of zircon from the Guarguaráz Complex has a largely juvenile crustal signature. Zircon with Pampean, Famatinian and Braziliano ages (< 660 Ma) originated from recycled crust of variable age, which is, however, mainly Mesoproterozoic. By contrast, the Carboniferous magmatic event shows less variable and more radiogenic ¹⁷⁶Hf/¹⁷⁷Hf, pointing to a mean early Neoproterozoic crustal residence. This zircon is unlikely to have crystallized from melts of metasediments of the accretionary systems, but probably derived from a more juvenile crust in their backstop system.  相似文献   

Quick-look assessments to identify optimal CO2 EOR storage sites   总被引：1，自引：0，他引：1  

Vanessa Núñez-López  Mark H. Holtz  Derek J. Wood  William A. Ambrose  Susan D. Hovorka 《Environmental Geology》2008,54(8):1695-1706

A newly developed, multistage quick-look methodology allows for the efficient screening of an unmanageably large number of reservoirs to generate a workable set of sites that closely match the requirements for optimal CO₂ enhanced oil recovery (EOR) storage. The objective of the study is to quickly identify miscible CO₂ EOR candidates in areas that contain thousands of reservoirs and to estimate additional oil recovery and sequestration capacities of selected top options through dimensionless modeling and reservoir characterization. Quick-look assessments indicate that the CO₂ EOR resource potential along the US Gulf Coast is 4.7 billion barrels, and CO₂ sequestration capacity is 2.6 billion metric tons. In the first stage, oil reservoirs are screened and ranked in terms of technical and practical feasibility for miscible CO₂ EOR. The second stage provides quick estimates of CO₂ EOR potential and sequestration capacities. In the third stage, a dimensionless group model is applied to a selected set of sites to improve the estimates of oil recovery and storage potential using appropriate inputs for rock and fluid properties, disregarding reservoir architecture and sweep design. The fourth stage validates and refines the results by simulating flow in a model that describes the internal architecture and fluid distribution in the reservoir. The stated approach both saves time and allows more resources to be applied to the best candidate sites.  相似文献   

青藏高原北缘阿尔金走滑边界的侧向扩展——甘肃北山晚新生代走滑构造与地壳稳定性分析     

郭召杰  ;张志诚  ;张臣  ;刘畅  ;张宇  ;王驹  ;陈伟明 《中国区域地质》2008,(10):1678-1686

对北山地区遥感影像和野外地质特征的分析表明,自阿尔金断裂带向NW方向依次出露三危山-双塔断裂、大泉断裂和红柳河断裂。这些断裂近于平行,且同为左行走滑断裂,具有相似的展布特征,空间走向均为NE40-50°,断裂系末端均发育“树枝状”分支断层．在断层夹块之间形成“多米诺”构造,构成了北山地区主要的构造样式。断层谷地沉积物分析和断层泥ESR年代学测试结果表明,三危山-双塔断裂形成于上新世（N2k）,大泉断裂形成于早更新世（1．2-1．5Ma）．而北山地区分支断层和次级断层的活动在400ka之后。对北山地区断裂构造几何学和年代学的研究表明．阿尔金断裂系晚新生代以来向NW方向的侧向扩展．是阿尔金走滑边界重要的生长方式。北山地区特殊的走滑构造组合样式．使该地区的构造变形难于在某条断层上聚集能量,而分散在若干条次级断层上的位移量又微乎其微,该地区成为“最稳定的活动区”。  相似文献   

温度对不同大小墨西哥湾扇贝生长的影响   总被引：2，自引：0，他引：2  

刘志刚  王辉  栗志民  郑云龙 《热带海洋学报》2007,26(5):47-52

在8—32℃实验室控温范围内以2℃为梯度,以壳高及体重增长作为观察指标,研究3个规格墨西哥湾扇贝Argopecten irradians concentricus的适宜、较适宜及最适宜生长温度。研究结果表明,小苗(壳高6.2mm,体重48.3mg)、中苗(壳高18.1mm,体重1191.1mg)、大苗(壳高30.7mm,体重5809.9mg)在8—32℃水温下均能生长,但在水温8及32℃,3种规格增长率均较低;适宜生长温度分别为小苗11.2—31.1℃、中苗9.8—31.8℃、大苗9.8—32.4℃;较适宜生长温度分别为小苗18.1—29.4℃、中苗18.5—29.4℃、大苗16.9—30.4℃;3种苗随规格增大,适温范围扩大(p<0.01);最适生长温度3种苗均为24—28.0℃,其范围向高温端漂移;在水温为8℃时,3种苗存活率均达到97.0%以上,水温在32℃时则小苗为47.0%、中苗为67.5%、大苗为76.0%,表现出3种苗对低温有更强的忍耐力,大苗对高温有更强的适应性。  相似文献   

珠江口东岸池养鲻鱼的年龄与生长     

李加儿  区又君  王仕宏  丁彦文  郑建民 《热带海洋学报》1996,(4)

研究池养条件下鲻鱼ＭｕｇｉｌｃｅｐｈａｌｕｓＬｉｎｎａｅｕｓ的年龄和生长特性，结果表明，鳞片新年轮主要在１０—１月出现；鳞长与体长关系式为：Ｒ—０．００９０７Ｌ（０．７７６４）；Ｉ—Ｖ龄鱼体长和体重相对生长率和生长指标随着年龄增长而逐渐下降；体长与体重关系式为：Ｗ＝１．２７１６×１０（－５）Ｌ（３．０６９５），体长与全长关系式为：ＬＴ＝１０．３７１１＋１．１８０６ＬＢ，当年鱼体长和体重生长与月龄的关系分别为：ＬＢ＝８．６６６９＋２５．５７６９ｔ，Ｗ＝０．１１７０ｔ（３．５５３０），ｖｏｎＢｅｒｔａｌｌａｎｆｆｙ生长参数Ｌ∞＝６１３．２５ｍｍ，Ｋ＝０．３４１２，ｔ０＝－０．８２５，体重生长拐点值为２．４６ａ。  相似文献