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1.
Barbara Carrapa Sharon Bywater‐Reyes Peter G. DeCelles Estelle Mortimer George E. Gehrels 《Basin Research》2012,24(3):249-268
Important aspects of the Andean foreland basin in Argentina remain poorly constrained, such as the effect of deformation on deposition, in which foreland basin depozones Cenozoic sedimentary units were deposited, how sediment sources and drainages evolved in response to tectonics, and the thickness of sediment accumulation. Zircon U‐Pb geochronological data from Eocene–Pliocene sedimentary strata in the Eastern Cordillera of northwestern Argentina (Pucará–Angastaco and La Viña areas) provide an Eocene (ca. 38 Ma) maximum depositional age for the Quebrada de los Colorados Formation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system affected by inherited palaeotopography. The Quebrada de los Colorados Formation represents deposition in the distal to proximal foredeep depozone. Development of an angular unconformity at ca. 14 Ma and the coarse‐grained, proximal character of the overlying Angastaco Formation (lower to upper Miocene) suggest deposition in a wedge‐top depozone. Axial drainage during deposition of the Palo Pintado Formation (upper Miocene) suggests a fluvial‐lacustrine intramontane setting. By ca. 4 Ma, during deposition of the San Felipe Formation, the Angastaco area had become structurally isolated by the uplift of the Sierra de los Colorados Range to the east. Overall, the Eastern Cordillera sedimentary record is consistent with a continuous foreland basin system that migrated through the region from late Eocene through middle Miocene time. By middle Miocene time, the region lay within the topographically complex wedge‐top depozone, influenced by thick‐skinned deformation and re‐activation of Cretaceous rift structures. The association of the Eocene Quebrada del los Colorados Formation with a foredeep depozone implies that more distal foreland deposits should be represented by pre‐Eocene strata (Santa Barbara Subgroup) within the region. 相似文献
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A.G. Green B. Milkereit L. Mayrand C. Spencer R. Kurtz R. M. Clowes 《Geophysical Journal International》1987,89(1):85-90
Summary. Multichannel seismic reflection sections recorded across Vancouver Island have revealed two extensive zones of deep seismic reflections that dip gently to the northeast, and a number of moderate northeasterly dipping reflections that can be traced to the surface where major faults are exposed. Based on an integrated interpretation of these data with information from gravity, heat flow, seismicity, seismic refraction, magnetotelluric and geological studies it is concluded that the lower zone of gently dipping reflections is due to underplated oceanic sediments and igneous rocks associated with the current subduction of the Juan de Fuca plate, and that the upper zone represents a similar sequence of accreted rocks associated with an earlier episode of subduction. The high density/high velocity material between the two reflection zones is either an underplated slab of oceanic lithosphere or an imbricated package of mafic rocks. Reprocessing of data from two of the seismic lines has produced a remarkable image of the terrane bounding Leech River fault, with its dip undulating from >60° near the surface to 20° at 3 km depth and ∼38° at 6 km depth. 相似文献
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J. Urrutia Fucugauchi 《Geophysical Journal International》1980,61(2):243-251
Summary. In palaeomagnetic studies of volcanic rocks it is often considered that, if the direction of NRM does not change much and the intensity de-creases gradually and smoothly during ac cleaning, then the remanent magnetization is stable and chiefly composed of TRM. This argument is extended as a consistency check to detect unwanted effects during laboratory heating. A simple procedure which employs orientated samples and a short heating (15 min) for TRM acquisition in the laboratory has been used for determining the ancient geomagnetic field intensity using seven volcanic rocks of Late Cenozoic age from central Mexico. The main reliability tests are based on the stability of direction, the close correspondence of the entire coercitivity spectra of both NRM and TRM to ac demagnetization, the low scatter of TRM directions, close correspondence of the TRM directions and the direction of the laboratory magnetic field, proportionality of TRM intensities to applied field, susceptibility comparison before and after heating, and the within-unit consistency of palaeointensity determinations. 相似文献
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A palaeomagnetic study has been carried out on late Palaeozoic rocks exposed in the Sierras Australes thrust and fold belt of Buenos Aires province (Argentina), in the early Permian red sandstones and clay siltstones of the Tunas Formation. The sections sampled are exposed in the eastern parts of the belt, in Sierra de las Tunas (north) and Sierra de Pillahuincó (south). More than 300 specimens were collected from 25 sites, in three localities with different structural attitudes. Demagnetization at high temperatures isolated a characteristic remanence at 20 sites. All the localities have a reverse characteristic remanence, suggesting that the magnetization was acquired during the Kiaman interval. Stepwise tectonic tilt correction suggests that the Tunas Formation in these localities acquired its magnetization during folding in early Permian times. Palaeomagnetic poles were computed for each locality based on partial tilt-corrected remanence directions. Taking into account the fact that these localities are close to one another and that the rocks are all of reverse polarity, a group syntectonic palaeomagnetic pole called Tunas was calculated: longitude: 13.9°E, latitude: 63.0°S; A 95 = 5.4°, K = 39.7, N = 19. This pole is consistent with previously calculated poles from South America assigned to the early Permian. In age it corresponds to the early Permian San Rafaelic tectonic phase of the Sierras Australes. Independent geological evidence indicates that the Tunas Formation underwent syndepositional deformation. We conclude that the Tunas Formation was deposited, deformed and remagnetized, all during the early Permian. 相似文献
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Rocks from the Massif de la Serre in the French Jura (latitude: 47.3°N longitude: 5.6°E) belonging to an ignimbritic assemblage dominated by vitrophyric rhyolites, and whose age of formation is probably Permian (Autunian to Saxonian) have been studied by applying thermal and alternating field demagnetization. the characteristic magnetization has a mean direction derived from 89 samples of D= 170°, I = - 16°, k = 26.2°, α95 = 3° and a corresponding north palaeopole at 41°N, 172°E, A 95 = 5°. the pole, which is very close to the Permian European poles, can thus be considered as a new contribution. Some samples are found to carry a unique normal polarity magnetization, others carry both normal and reverse polarities. It therefore seems that, similar to Permian series in the USSR, these west European rocks have registered a normal event in the Kiaman interval. From a structural point of view, we may conclude that during the Alpine tectonic phases the Massif de la Serre has not been subjected to substantial rotation. 相似文献
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Hollows in the Sierra de Aracena, part of western sector of Sierra Morena region (Huelva, Spain), are geoecologically unusual macroforms. They are underlain by deeply weathered bedrock but have eutrophic soils with distinctive vegetation. Paleosols with very dark colours, a predominance of smectites and large amounts of total and free iron occur on the floors on the hollows. An evolutionary model is proposed for the hollows, involving differential weathering during the Mesozoic on plutonic and amphibolitic rocks, alpine tectonic activity followed by Quaternary erosion and exhumation leading to formation of erosional terraces. 相似文献
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《The Journal of geography》2012,111(3):116-119
Abstract Geography And Man's Environment. By Arthur N. Strahler and Alan H. Strahler. New York: John Wiley &; Sons, 1977. Pp. xi + 525. Order Upon the Land: The U.S. Rectangular Land Survey and the Upper Mississippi Country. By Hildegard Binder Johnson. The Andrew H. Clark Series in the Historical Geography of North America. New York: Oxford University Press, 1976. Pp. 268, $9.00 and $5.00. The Earth in Profile: A Physical Geography. By David Greenland and Harm J. de Blij. New York: Canfield Press, Harper &; Row, 1977. Pp. xi + 468. Global Perspectives on Ecology. Edited by Thomas C. Emmel. Palo Alto, Calif.: Mayfield Publishing Company, 1977. Pp. viii + 522, $6.95. Space and Place: The Perspective of Experience. By Yi-Fu Tuan. Minneapolis: University of Minnesota Press, 1977. Pp. vi + 235, $12.95. African Survey. By Alan C. G. Best and Harm J. de Blij. New York: John Wiley &; Sons, 1977. Pp. xi + 626, $17.95. 相似文献
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M. J. Pasqualetti 《The Professional geographer》1983,35(4):427-436
Impacts of nuclear power plants are generally considered on a local scale only. A schema that considers local and interstate convergence and divergence is found useful in identifying the widespread nature of the impacts, especially those associated with a local decision to build a nuclear facility. Of the four possible subdivisions within this schema, three apply to the Palo Verde power plant near Phoenix, AZ. 相似文献
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《The Professional geographer》2013,65(4):427-436
Impacts of nuclear power plants are generally considered on a local scale only. A schema that considers local and interstate convergence and divergence is found useful in identifying the widespread nature of the impacts, especially those associated with a local decision to build a nuclear facility. Of the four possible subdivisions within this schema, three apply to the Palo Verde power plant near Phoenix, AZ. 相似文献
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利文斯顿岛火山岩是南极南设得兰岩浆弧的一部分。对岩石的Ｓｒ、Ｎｄ、Ｐｂ同位素组成以及８７Ｓｒ／８６Ｓｒ与１／Ｓｒ、Ｒｂ、Ｋ和ＳｉＯ２关系的研究表明,利文斯顿岛火山岩具有不同的源区特征。百耳斯半岛和史莱夫角的火山岩、西多斯角的粗玄岩和第三纪的英云闪长岩显示出同成因的特点,和依诺特角第四纪橄榄玄武岩一样,它们均具有原生地幔的同位素组分,源区岩浆可能直接来自上地幔。汉那角和中利文斯顿岛火山岩岩浆则受到地壳成分的混染。不相容元素对Ｌａ／Ｓｍ－Ｌａ和Ｃｅ／Ｙｂ－Ｃｅ的研究进一步显示出,上述不同产地的岩石分别为不同源岩浆不同程度部分熔融的产物。结合岩相学和岩石化学特征的研究,提出百耳斯半岛和史莱夫角的火山岩以及西多斯角的粗玄岩是上地幔发生部分熔融所生成的玄武岩岩浆从深部岩浆囊沿构造薄弱带直接喷出形成的。古生代基底岩系的存在对中利文斯顿岛和汉那角火山岩的成因过程有重要的影响,即来自深部岩浆囊的原始岩浆在上地壳中的浅部岩浆囊受到了壳源物质混染。更新世－现代火山岩的源区岩浆直接自上地幔部分熔融生成,火山作用与晚新生代时该区的拉张构造有关。 相似文献
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José E. Mendía 《Geophysical Journal International》1978,54(3):539-546
Summary. Stable components of magnetization have been isolated in 15 lava flows (mean K-Ar age 123 ± 4 Myr) from the alkaline sequence outcropping at El Salto-Almafuerte, Province of Cordoba, Argentina. Magnetic and geologic stratigraphy, as well as K-Ar ages indicate that this sequence was probably extruded in the Lower Cretaceous during the first volcanic cycle of the Sierra de los Cóndores Group (Vulcanitas Cerro Colorado Formation).
The palaeomagnetic pole-position for El Salto-Almafuerte lava flows, computed from the mean of 15 virtual geomagnetic poles and denoted SAK7 , is: 25° E, 72° S ( k = 35, α95 = 6.5°); it is fairly close to other Lower Cretaceous palaeomagnetic poles for South America. The elongated distribution of Cretaceous palaeomagnetic poles suggest recurrent drift for South America in early Cretaceous time.
The palaeomagnetic and radiometric data for the igneous rocks from El Salto-Almafuerte support the magnetic reversal time-scale for the early Cretaceous suggested by oceanic magnetic lineations. 相似文献
The palaeomagnetic pole-position for El Salto-Almafuerte lava flows, computed from the mean of 15 virtual geomagnetic poles and denoted SAK
The palaeomagnetic and radiometric data for the igneous rocks from El Salto-Almafuerte support the magnetic reversal time-scale for the early Cretaceous suggested by oceanic magnetic lineations. 相似文献
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乔治王岛北海岸的第三纪火山岩包括菲尔德斯半岛组（ＦＰＧ）熔岩、Ａｄｍｉｒａｌｔｙ湾组（ＡＢＧ）岩颈和Ｗｅｇｇｅｒ峰组（ＷＰＧ）侵入岩。大多数中基性熔岩为斑状结构，斜长石和普通辉石是岩石中最主要的斑晶相。安山岩中尚含有少量斜方辉石，英安岩质熔岩则为细晶质结构。岩颈相岩石的物质组成与熔岩相似，但斑晶含量往往较少。岩石化学成分表明，所有岩石均富铝，为亚碱性火山岩，属于钙碱性岩石系列。岩石富集大离子亲石元素，轻稀土元素略为富集，稀土元素总含量落在钙碱性岩石的含量范围之内并基本随硅含量的增加而增加。岩石具有很低的８７Ｓｒ／８６Ｓｒ比值（０．７０３４左右）和较高的１４３Ｎｄ／１４４Ｎｄ比值（０．５１２７８－０．５１２８８），εＮｄ平均值在＋６左右。８７Ｓｒ／８６Ｓｒ比值与Ｓｉ、Ｋ、Ｒｂ、１／Ｓｒ等元素呈水平线性关系。在Ｃｅ／Ｙｂ－Ｃｅ和Ｔｈ／Ｔａ－Ｔｈ图解上所有岩石的投影点分布趋势相同，趋势线的斜率＞０。上述特征表明，乔治王岛北海岸第三纪火山岩均由上地幔物质直接生成而未受壳源物质的混染。推测在古太平洋板块向南极板块下俯冲的过程中，上地幔发生的不同程度部分熔融所生成的玄武岩岩浆从深部岩浆囊沿构造薄弱带穿过地壳直接喷出形成 相似文献
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西南极纳尔逊岛Stansbury半岛基本被玄武质、玄武安山质熔岩以及火山角砾岩和含植物化石的火山-碎屑沉积岩所覆盖。地层接触关系和火山岩岩石组合显示,该半岛的熔岩和火山角砾岩主要形成于第一阶段的火山活动,可与菲尔德斯半岛的碧玉山段以及玛瑙滩段地层对比;含化石的火山-碎屑沉积岩和角砾熔岩、火山角砾岩分别相当于长城站地区的化石山段和岩块山段的岩层,它们是晚期火山作用的产物。stansbury半岛和菲尔德斯半岛发育有基本相同的火山岩地层,并且都在化石山段地层中发现了植物化石,这表明两个半岛上的火山岩可能是早第三纪区域火山作用的共同产物。 半岛所出露的断裂大致平行菲尔德斯海峡并且控制了次火山岩的分布。 岩石学特征说明,Stansbury半岛的熔岩和次火山岩主要为玄武质和玄武安山质,岩石中的斑晶矿物包括偏基性的斜长石、单斜辉石。岩石化学成分中,随着SiO_2含量增高,Al_2O_3、CaO、MgO和铁含量下降,碱质则升高。和菲尔德斯半岛的火山岩一样,这个半岛的火山岩也基本沿着钙碱趋势演化。微量元素和稀土元素的丰度以及配分模式证明,这套岩石具有同源岩浆的亲缘关系并且可能经历了分离结晶作用过程。 相似文献
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Unraveling the Peruvian Phase of the Central Andes: stratigraphy,sedimentology and geochronology of the Salar de Atacama Basin (22°30–23°S), northern Chile 
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下载免费PDF全文 The Salar de Atacama Basin holds important information regarding the tectonic activity, sedimentary environments and their variations in northern Chile during Cretaceous times. About 4000 m of high‐resolution stratigraphic columns of the Tonel, Purilactis and Barros Arana Formations reveal braided fluvial and alluvial facies, typical of arid to semi‐arid environments, interrupted by scarce intervals with evaporitic, aeolian and lacustrine sedimentation, displaying an overall coarsening‐upward trend. Clast‐count and point‐count data evidence the progressive erosion from Mesozoic volcanic rocks to Palaeozoic basement granitoids and deposits located around the Cordillera de Domeyko area, which is indicative of an unroofing process. The palaeocurrent data show that the source area was located to the west. The U/Pb detrital zircon geochronological data give maximum depositional ages of 149 Ma for the base of the Tonel Formation (Agua Salada Member), and 107 Ma for its middle member (La Escalera Member); 79 Ma for the lower Purilactis Formation (Limón Verde Member), and 73 Ma for the Barros Arana Formation. The sources of these zircons were located mainly to the west, and comprised from the Coastal Cordillera to the Precordillera. The ages and pulses record the tectonic activity during the Peruvian Phase, which can be split into two large events; an early phase, around 107 Ma, showing uplift of the Coastal Cordillera area, and a late phase around 79 Ma indicating an eastward jump of the deformation front to the Cordillera de Domeyko area. The lack of internal deformation and the thicknesses measured suggest that deposition of the units occurred in the foredeep zone of an eastward‐verging basin. This sedimentation would have ended with the K‐T phase, recognized in most of northern Chile. 相似文献
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出露在利文斯顿岛中部的白垩纪火山岩为玄武岩－玄武安山岩－安山岩－英安岩组合，基本属于钙碱性系列，但具有低钾拉斑玄武岩的某些特点。岩石富集Ｒｂ、Ｔｈ、Ｂａ，轻度亏损Ｚｒ、Ｔｉ、Ｈｆ、Ｎｂ，较强亏损Ｃｒ和Ｎｉ，而且随着岩浆从基性向酸性成分的演化，富集（或亏损）程度加大。岩石的轻稀土元素中度富集，岩石的（Ｃｅ／Ｙｂ）ＣＮ比值较低。白垩纪火山岩形成在一个造山环境，是南设得兰岩浆弧的一部分。然而，在利文斯顿岛不同地区出露的岩石其化学性质有所区别，因此认为它们可能源于不同的岩浆体系。在晚古生代至早中生代，利文斯顿岛中部处于一个独特的浊积扇的构造环境。主要产在利文斯顿岛中部和汉那角的鲍勒斯山组火山岩与其它地点的中生代火山岩相比，无论岩相学特征还是岩石化学性质均有所不同。因此认为它们的产生同时受到太平洋板块的俯冲作用和该地构造位置所控制。史莱夫角的橄榄玄武岩成分中碱高硅低，并且通常表现出高铝的特点，这些性质与百耳斯半岛的玄武岩极为相似。区域上火山活动不断发展，活动中心逐渐向北东迁移，导致粗玄岩岩颈和岩席生成，最后是英云闪长岩的侵入。更新世至现代的依诺特角组橄榄玄武岩以化学成分中的低硅高碱含量区别于中生代火山岩。岩石的高Ｍ值 相似文献
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１ＩｎｔｒｏｄｕｃｔｉｏｎＡｓｔｈｅｅａｒｌｉｅｓｔｃｏｌｏｎｉｚｅｒｓｏｆｔｅｒｅｓｔｒｉａｌｈａｂｉｔａｔｓｏｎｔｈｅｅａｒｔｈ,ｔｈｅｏｃｕｒｅｎｃｅｏｆｌｉｃｈｅｎｓｍａｙｂｅｄａｔｅｄｆｒｏｍｔｈｅＥａｒｌｙＤｅｖｏｎｉａｎ（Ｔａｙｌｏｒｅ... 相似文献
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Michel Prévot 《Geophysical Journal International》1981,66(1):169-192
Summary. The magnetic viscosity of 334 Upper Tertiary and pre-Bruhnes Quaternary volcanic rocks from the Massif Central (France) and the Steens Mountain (Oregon), and of 40 basaltic cores from DSDP leg 37 has been investigated. Thellier's viscosity index follows a log normal distribution with mean values equal to 6 and 3.5 per cent for subaerial and submarine rocks respectively. For subaerial rocks, the average intensity of the viscous remanent magnetization (VRM) acquired in the Earth's field since the beginning of the Bruhnes polarity epoch ( t = 0.7 Myr) is estimated to be equal to one-quarter of the average intensity of the primary remanence. Alternating field demagnetization of VRMs acquired in low fields for acquisition times t ranging from 2 day to 32 month indicates the resistance to alternating fields is quite different from sample to sample and increases linearly with log t.
Néel's diagnostic parameter of domain structure of the grains involved in magnetic viscosity shows that hard VRM is carried by single-domain grains and soft VRM carried by multidomain particles. Single domain particles carrying hard VRM in subaerial volcanic rocks are almost equant magnetite intergrowths with size near the superparamagnetism threshold, resulting from high temperature oxidation of titanomagnetite. Soft VRM is carried by low Curie point homogeneous titanomagnetite. Unlike his single domain theory, Néel's multidomain theory of magnetic viscosity does not account quantitatively for the resistance of VRM to alternating fields. 相似文献
Néel's diagnostic parameter of domain structure of the grains involved in magnetic viscosity shows that hard VRM is carried by single-domain grains and soft VRM carried by multidomain particles. Single domain particles carrying hard VRM in subaerial volcanic rocks are almost equant magnetite intergrowths with size near the superparamagnetism threshold, resulting from high temperature oxidation of titanomagnetite. Soft VRM is carried by low Curie point homogeneous titanomagnetite. Unlike his single domain theory, Néel's multidomain theory of magnetic viscosity does not account quantitatively for the resistance of VRM to alternating fields. 相似文献