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1.
Thermochronological studies of Variscan basement in Iberia yield cooling ages typically younger than ~ 200 Ma. In this paper, we explore the regional implications of this recurrent age maximum by examination of low and high temperature thermochronological datasets from all over Iberia. Based on these results, we show that in general the lack of cooling ages older than 200 Ma is the result of several important regional periods of thermal resetting. Resetting took place in areas of extension and burial during the Mesozoic break-up of Pangea. Evidence for large scale magmatism and mineralisation is found in Iberia during the Mesozoic, since at that time Iberia formed part of the Central Atlantic Magmatic Province and a large mineralization province extending from North Africa to Western Europe. Numerical modelling allows us to assess the conditions under which rocks in the upper crust may have been thermally reset and the mechanisms likely involved. Results show that active rifting combined with shallow magmatism, and to a lesser extent deep sedimentary burial, could have led to an increase of the geothermal gradient up to ~ 73 °C/km and the reset of thermochronometers with closure temperatures up to 200 °C. Yet, we suggest that also hydrothermal activity, associated to extensional basins, played an important role to the increase of temperatures of some basement rocks above 300 °C. 相似文献
2.
F. López Díaz 《International Journal of Earth Sciences》1995,84(1):151-163
The Navalpino Anticline is a major Variscan structure in the Central Iberian Zone of Spain. Three lithological groups are defined in the pre-Ordovician rocks of this anticline. The Rifean or Lower Vendian Extremeño Dome Group is unconformably overlain by the Upper Vendian Ibor-Navalpino Group. This latter group presents two different facies separated by a NW-SE trending synsedimentary fault. The Lower Cambrian Valdelacasa Group unconformably overlies both the Extremeno Dome and the Ibor-Navalpino Groups.Three pre-Variscan episodes of deformation have been defined in the area of the Navalpino Anticline. A major asymmetrical fold with a subvertical east-west-striking limb is the result of the first deformation event of pre-Late Vendian age. The second deformation event is of Cadomian (Late Precambrian) age and is composed of two stages; (i) an early extensional stage including NW - SE trending extensional fault and basin development in the north-eastern block; and (ii) a second compressive stage giving rise to north-south trending upright folds. This second compressive stage possibly inverted the basin. A final pre-Variscan deformation event took place between the Early Cambrian and the Early Ordovician resulting in a 5–10° tilting to the north-east.There are two main phases of Variscan deformation in the area. The first deformation event (Dv1) gave rise to a upright WNW - ESE trending folds on all scales, whereas the second (Dv2) gave rise to a brittle—ductile sinistral strike-slip shear zone tending subparallel to the axial trace of the Dv1 folds. 相似文献
3.
The main meteorological features of catastrophic rainfall events in Catalonia are described. Data come from several sources listed in the text. Surface and upper air synoptic and some subsynoptic conditions under which these events occur are described. Two kinds of events are identified, depending on the amount of forced lift required to release potential instability: Type A events, which take place on the coastal area when the forcing due to littoral and prelittoral hills is enough, and type B events require a large forced lift and occur near the Pyrenees. Local topographical and mesoscale meteorological conditions turn out to have a relevant role in connection with such events. 相似文献
4.
Palynological studies undertaken in the mountainous regions of the northwest of the Iberian Peninsula are few in number and have been concerned largely with the second half of the Holocene. New pollen data from two Galician sierras, the Courel and Queixa Sierras, provide a 10000‐yr record of vegetation and climate change. In the Courel Sierra before 9750 yr BP, Laguna Lucenza (1420 m a.s.l.) reflects a period of open landscape covered by Poaceae and heliophilous plants, which may be correlated with the Younger Dryas. The onset of the Holocene is characterised by the expansion of oak woodland, prior to 9300 yr BP, following a short phase of birch along with the gradual decline of pine. The oak values reach a peak at 8350 ± 80 yr BP. Towards 8800 yr BP Corylus begins to expand, followed by Alnus (7500 yr BP) and Ulmus. During this period, the Fraga pollen assemblage (Queixa Sierra, 1360 m a.s.l.) indicates Betula woodland surrounding the site, masking the regional predominance of oak. After 5000 yr BP there is a gradual decrease in arboreal pollen values in both Sierras. Castanea appears in Laguna Lucenza (Courel Sierra) at 4075 ± 75 yr BP. There is widespread deforestation during the last 4000 yr. During this period the presence of large quantities of microcharcoal particles points to the occurrence of fire. The reduction in forest is associated with the arrival of cultivation at 4000 yr BP at low altitudes in the Queixa Sierra. At higher altitudes the first agricultural activity is dated at later than 2000 yr BP. This coincides with the first record of cereal cultivation at high altitude in the Courel Sierra. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
5.
Ramn Pellitero Jos M. Fernndez‐Fernndez Nstor Campos Enrique Serrano Alfonso Pisabarro 《第四纪科学杂志》2019,34(4-5):342-354
New 10Be dates for glacial landforms in the Fuentes Carrionas area (Cantabrian Mountains, nothern Spain) are presented. Mapped and dated landforms in Fuentes Carrionas made possible a palaeoglacier reconstruction for four glacial stages. Results were compared to other nearby palaeoenvironmental proxies, so a final approximation on the mean annual temperature and annual precipitation that caused the four glacial advance stages is proposed. Glaciers reached their maximum extension at 36 ka, in a cold and dry environment. A second advance stage took place between 18.5 and 19.5 ka, during the Last Glacial Maximum (LGM), when glaciers advanced in a wet environment, with positive rainfall anomalies. A third glacial advance was dated during the Oldest Dryas, in which climate shifted to extremely cold and dry conditions. Finally, a last stage has been identified and proposed to the Younger Dryas, in which precipitation anomalies are negligible. Our results confirm some of the previously made palaeoglacial and palaeoenvironmental inferences for the Iberian Peninsula, as well as provide valuable and accurate anomalies, which are useful for climate modelling. 相似文献
6.
A. Azor F. González Lodeiro D. Martínez Poyatos J. F. Simancas 《International Journal of Earth Sciences》1994,83(2):377-387
On the southern border of the Central Iberian Zone there are two sectors with different styles of deformation. To the south-west, in the Hornachos sector, large-scale recumbent folds associated with ductile shearing can be seen. This shearing is characterized by a direction of movement parallel to the fold axes and can be correlated for 150 km along strike. The K-values of the strain ellipsoid range from 0.8 to 2.0. Stretching in the X direction, parallel to the recumbent fold axes, is more than 100%. To the north-east, in the Oliva sector, first-phase folds are upright and the strain intensity is lower than in the Hornachos sector. Metamorphic, geometric and kinematic considerations lead us to conclude that the shearing in the Hornachos sector is better explained as conjugate to a main shear zone along which the southern border of the Central Iberian Zone is moved onto the Ossa-Morena Zone. This main thrust is at present obliterated by a left-lateral extensional shear zone that affects a high pressure exotic unit located between the Central Iberian and the Ossa-Morena Zones. This high pressure unit constitutes a suture of the Variscan belt in the Iberian Peninsula. 相似文献
7.
The Iberian Peninsula hosts the world-class Hg mining district of Almadén. Besides pre-Hercynian ore bodies, alpine-cycle Hg-bearing veins are also present in the eastern Iberian Ranges (Espadán deposits). We present both the first absolute ages (84±4 and 85±3 Ma) for a post-Hercynian Hg deposit in Spain, obtained from primary muscovites, and a complete compilation of published Mesozoic radiometric absolute ages of the Iberian Peninsula. We deduce that there are three main thermal episodes that affected the Iberian Peninsula, which have been revealed after the comparison among the magmatic, metamorphic and hydrothermal ages. Moreover, the Espadán hydrothermal system was active when both the Cretaceous alkalic magmatism took place in Southern Portugal and in the Pyrenees, and during the opening of the Bay of Biscay. 相似文献
8.
The Xisha Trough, located in the northwest of the South China Sea (SCS) mainly rifted 30 Ma ago, has been a failed rift since the cessation of the seafloor spreading of the NW subbasin. Based on the velocity–depth model along Profile OBH-4 across the Xisha Trough, a seven-layer density–depth model is used to estimate density structure for the profile. The relationship between seismic velocity and radiogenic heat production is used to estimate the vertical distribution of heat sources in the lower crust. The 2-D temperature field is calculated by applying a 2-D numerical solution of the heat conduction equation and the thermal lithosphere thickness is obtained from the basalt dry solidus (BDS). The rheology of the profile is estimated on the basis of frictional failure in the brittle regime and power-law steady-state creep in the ductile regime. Rheological model is constructed for a three-layer model involving a granitic upper crust, a quartz diorite lower crust and an olivine upper mantle. Gravity modeling supports basically the velocity–depth model. The Moho along Profile OBH-4 is of relatively high heat flow ranging from 46 to 60 mW/m2 and the Moho heat flow is higher in the trough than on the flanks. The depth of the “thermal” lithospheric lower boundary is about 54 km in the center, deepens toward two sides, and is about 75 km at the northern slope area and about 70 km at the southern Xisha–Zhongsha Block. Rheological calculation indicates that the two thinnest ductile layers in the crust and the thickest brittle layer in the uppermost mantle lie in the central region, showing that the Xisha Trough has been rheologically strengthened, which are mainly due to later thermal relaxation. In addition, the strengthening in rheology during rifting was not the main factor in hampering the breakup of the Xisha Trough. 相似文献
9.
胶东地区地层岩性多为岩浆岩和变质岩,富水性差异大,整体为缺水区。伴随着社会经济发展,人民对美好生活的需求不断提升,优质、稳定的地下饮用水也成为胶东人民的重要民生问题之一。笔者等通过大比例尺水文地质调查成果总结和已有研究成果分析,结合地下水勘查案例,从水文、地形地貌、含水层岩性和地质构造4个方面,对岩浆岩地区的地下水富集机理进行分析,提出了断裂型、接触带型、岩脉型、洼地风化带型和多期变质作用形成的5种蓄水构造模式,并对各类蓄水构造特征进行了分析,同时总结了风化裂隙水、构造裂隙水和岩溶裂隙水3类岩浆岩、变质岩分布区裂隙水的找水方向,进一步丰富了岩浆岩与变质岩缺水地区蓄水构造模式研究,对该地区地下水资源探寻具有一定的指导作用。 相似文献
10.
Buntsandstein deposits generated in a slowly subsiding basin on the western margin of the Iberian Chain are represented by a stratigraphic succession of fluvial deposits less than 100 m thick (conglomerates, sandstones, and shales). Diagenetic processes in sandstones can be grouped as eodiagenetic, mesodiagenetic, and telodiagenetic. Eodiagenesis can be associated with Muschelkalk, Keuper, and probably early Jurassic times. Mesodiagenesis is probably related to Jurassic times. Diagenetic chemical reactions suggest a maximum burial less than 1.5 km and low temperatures (<120°C). Patterns of porosity reduction by compaction and cementation suggest four diagenetic stages: (1) Loss of primary porosity by early mechanical compaction; (2) early cementation (K-feldspar and dolomite); (3) dissolution of cements; and (4) framework collapse by re-compaction. These stages are manifested by the presence of two types of sandstone. Type I sandstones present high intergranular volume (mean, 30%). Type II sandstones are characterized by high compactional porosity loss and exhibit low values of intergranular volume (mean, 16.9%). Type II sandstones are associated with the dissolution of cement and later re-compaction of type I sandstones. An intermediate telodiagenetic phase is deduced and related to the sharp unconformity between Lower Cretaceous sediments and the underlying sediments. This suggests that a mechanically unstable framework collapsed during the Cretaceous, generating type II sandstones. The analyzed diagenetic paths have a wide applicability on similar marginal areas of rift basins. 相似文献
11.
Permo-Triassic high-pressure(HP) mafic granulites, together with the Bibong retrogressed eclogite,preserved along the central western Korean Peninsula provide important insights into the Late Permian to Triassic collisional orogeny in northeast Asia. The metamorphic pressureetemperatureetime(P-T-t)paths of these rocks, however, remain poorly constrained and even overestimated, owing to outdated geothermobarometers and inaccurate isopleth techniques. Here we evaluate the metamorphic Pe T conditions of Triassic HP mafic granulites including those in Baekdong, Sinri and Daepan and the Bibong Triassic retrogressed eclogite in the Hongseong area, and the Permo-Triassic Samgot mafic granulite in the Imjingang Belt of the central western Korean Peninsula through the application of modern phase equilibria techniques. The Baekdong and Samgot mafic granulites and the Bibong retrogressed eclogite yield a range of 12.0 -16.0 kbar and 800 -900℃, representing HP granulite facies conditions. The Sinri and Daepan granulites from the Hongseong area show relatively lower grade metamorphic conditions between HP granulite and normal granulite facies, and are characterized by sub-isothermal decompression during exhumation. The similarities in the metamorphic ages and the post-collisional igneous activity from the central western Korean Peninsula indicate that the Triassic ages represent the retrograde stage of the metamorphic Pe T paths. In contrast, the Late Permian metamorphic ages, which are older than protolith ages of the post-collisional igneous rocks, correspond to the possible prograde stage of metamorphism. The P-T-t paths presented in this paper, together with the metamorphic ages and post-orogenic igneous events reported from these areas suggest trace of the subduction, accretion and exhumation history, and indicate a tectonic linkage among the northeast Asian continents during the Paleo-Tethyan Ocean closure. 相似文献
12.
Antonio Azor Francisco González Lodeiro J. Fernando Simancas Fernando Bea 《International Journal of Earth Sciences》1995,84(2):375-383
One of the main tectonic boundaries of the Variscan Belt in the Iberian Peninsula is the Ossa-Morena/Central Iberian contact. This contact is marked by a highly deformed unit (Central Unit) which recorded an initial high-pressure/high-temperature metamorphic evolution. Rb-Sr whole-rock isotopic data from three gneissic bodies cropping out in the Central Unit yield two Late Proterozoic ages (690 ± 134 and 632 ± 103 Ma) and an early Palaeozoic age (495 ± 13 Ma), which we interpret as protolith ages. The two Late Proterozoic orthogneisses show initial 87Sr/86Sr ratios typical of mantle-derived materials or those with significant mantle participation (87Sr/86Sr > 0.709). These new radiometric data, together with ages previously published and the structural evolution of the Central Unit, lead to the conclusions that: (1) there are magmatic protoliths of Late Proterozoic and Early Palaeozoic ages; (2) the metamorphic evolution of this area, including the high-pressure event, belongs to the Variscan orogenic cycle; (3) the deformations observed affect the rocks of the entire Central Unit, accordingly they are post-Ordovician, i.e. Variscan; and (4) consequently, the Ossa-Morena/Central Iberian contact is interpreted here as a Variscan suture. 相似文献
13.
In the Central Iberian Zone (CIZ) of the Iberian Massif large volumes of granitoids were emplaced during the post-collisional stage of the Hercynian orogeny (syn- to post-D3, the last ductile deformation phase). Twelve granitic units and a quartz monzodiorite were selected for a U–Pb zircon and monazite geochronological study. They represent successive stages of the D3 event. The Ucanha-Vilar, Lamego, Sameiro and Refoios do Lima plutons are coeval (313±2 Ma, 319±4 Ma, 316±2 Ma and 314±2 Ma, respectively) and belong to the earliest stage. Later on the Braga massif was emplaced, its different units yielding the same age: 309±3 Ma for the Braga granite, 309±1 Ma for the Gonça granite and 311±5 Ma for a related quartz monzodiorite. The Braga massif is subcontemporaneous with the Agrela and Celeirós plutons (307±3.5 Ma and 306±2 Ma, respectively), in agreement with field data. The Briteiros granite is younger (300±1 Ma), followed by the emplacement of the Peneda–Gerês massif (Gerês, Paufito, Illa and Carris granites). The Gerês granite, emplaced at 296±2 Ma, seems to represent a first magmatic pulse immediately followed by the intrusion of the Paufito granite at 290±2.5 Ma. For the Carris granite a minimum emplacement age of 280±5 Ma was obtained. Based on these results the following chronology is proposed: (1) syn-D3 biotite granitoids, 313–319 Ma; (2) late-D3 biotite-dominant granitoids, 306–311 Ma; (3) late- to post-D3 granitoids, ca. 300 Ma; (4) post-D3 granitoids, 290–296 Ma. These chronological data indicate that successive granitic intrusions were emplaced in the CIZ during a short time span of about 30 Ma that corresponds to the latest stages of the Hercynian orogeny. A rapid and drastic change occurred at about 300 Ma, between a compressive ductile tectonic regime (D3, ca. 300–320 Ma) associated to calc-alkaline, monzonitic and aluminopotassic plutonism and a fragile phase of deformation (D4) which controlled the emplacement of the subalkaline ferro-potassic plutonism at 290–296 Ma. 相似文献
14.
15.
Effect of brittle fracture on the rheological structure of the lithosphere and its application in the Ordos 总被引:2,自引:0,他引:2
An empirical formula for the fracture strength of the principal rock type in the lithosphere is obtained based on the experimental data from previous studies, in which the effects of the confining pressure, size of the rock sample, temperature, strain rate and the pore pressure are taken into account, the empirical formulae for the effects of them are also presented. By comparing the frictional strength to the fracture strength calculated using the new empirical formula, it is shown that frictional sliding is dominant in the upper crust but brittle fracture is dominant in the lower part of the crust and the lithosphere beneath the crust. Therefore the fracture mechanism must be taken into account in the study of the rheological structure of the lithosphere. The empirical formula for the fracture strength is applied to study the rheological structure of the lithosphere in the Ordos block. Brittle regime in the rheological structure can be divided into two sub-regions, in one of which brittle fracture and in the other frictional sliding are dominant, respectively, unlike previous conventional studies in which frictional sliding is assumed to be the only factor; the magnitude of the rheological strength of the lithosphere calculated by the empirical formula is also lower than that obtained in previous conventional studies. 相似文献
16.
Daniel Pastor-Galán Ícaro Fróis Dias da Silva Thomas Groenewegen Wout Krijgsman 《International Geology Review》2019,61(2):240-255
The amalgamation of Pangea during the Carboniferous produced a winding mountain belt: the Variscan orogen of West Europe. In the Iberian Peninsula, this tortuous geometry is dominated by two major structures: the Cantabrian Orocline, to the north, and the Central Iberian curve (CIC) to the south. Here, we perform a detailed structural analysis of an area within the core of the CIC. This core was intensively deformed resulting in a corrugated superimposed folding pattern. We have identified three different phases of deformation that can be linked to regional Variscan deformation phases. The main collisional event produced upright to moderately inclined cylindrical folds with an associated axial planar cleavage. These folds were subsequently folded during extensional collapse, in which a second fold system with subhorizontal axes and an intense subhorizontal cleavage formed. Finally, during the formation of the Cantabrian Orocline, a third folding event refolded the two previous fold systems. This later phase formed upright open folds with fold axis trending 100° to 130°, a crenulation cleavage and brittle–ductile transcurrent conjugated shearing. Our results show that the first and last deformation phases are close to coaxial, which does not allow the CIC to be formed as a product of vertical axis rotations, i.e. an orocline. The origin of the curvature in Central Iberia, if a single process, had to be coeval or previous to the first deformation phase. 相似文献
17.
We re-processed the seismic reflection survey data of the Kakkonda geothermal field. The pre-stack migration delineates a strong and continuous reflector between 1800- and 2800-m depth, below which formations are not reflective. Earthquake data exhibit seismicity in the upper crust. The lower boundary of seismogenic layer is interpreted as the brittle–ductile transition. The thermal structure is thought to be the major factor controlling its depth. We compared the strong reflector with the thermal and rheological structure from drillholes. The depth of the reflector corresponds to the top of the highly–very highly fractured zone observed from formation microscanner imagery (FMI) logging in the Miocene formations. The density of fracture in the Kakkonda granite is very low, suggesting that granite corresponds to the nonreflective zone. The temperature–depth profile of well WD-1a shows that the temperature at the highly–very highly fractured zone is about 350 °C. This corresponds to a hydrothermal convection zone filled with two-phase geothermal fluid. The cut-off depth of seismicity that indicates the brittle–ductile transition lies at the isotherm of 300–350 °C near the reflector. We conclude that the strong seismic reflector is a strong contrast in acoustic impedance at the top of the fractured layer. The fractured layer could be a decoupling plane caused by different tectonic behaviors between the upper brittle and the lower ductile layers or a dehydration front by thermal diffusion. The similarity between the strong reflector and K-horizon, the strong reflector, found in southern Tuscany, Italy suggests that the P-wave reflector at the top of highly fractured zone at the brittle–ductile transition be common in areas with magmatic activity. 相似文献
18.
A new airborne magnetic survey of the southeastern Antarctic Peninsula and adjacent Weddell Sea embayment (WSE) region suggests a continuity of geological structure between the eastern Antarctic Peninsula and the attenuated continental crust of the Filchner Block. This has implications for the reconstructed position of the Ellsworth–Whitmore Mountains block in Gondwana, which is currently uncertain. Palaeomagnetic data indicate that it has migrated from a Palaeozoic position between South Africa and Coats Land to its current position as a microplate embedded in central West Antarctica. The most obvious route for migration is between the Antarctic Peninsula and the Weddell Sea embayment. Evidence that geological structures are continuous across the boundary places constraints on the timing and pathway of migration. Magnetic textures suggest the presence of shallow features extending from the Beaumont Glacier Zone (BGZ) in the west for at least 200 km into the Weddell Sea embayment. These data suggest that the Eastern Domain of the Antarctic Peninsula and the stretched continental crust of the Filchner Block share a common recent, probably post-Early Jurassic, history. However, examination of deep anomalies indicates differences in the magnetic characteristics of the two blocks. The boundary may mark either the edge of extended continental crust, or a discontinuity between two, once separated, blocks. This discontinuity, or pre-Late Jurassic Antarctic Peninsula terrane boundaries to the west, may have allowed the passage of the Ellsworth–Whitmore Mountains block to its present location. 相似文献
19.
东南亚中南半岛成矿带初步划分与区域成矿特征 总被引:2,自引:0,他引:2
东南亚中南半岛成矿带是特提斯(地中海-喜马拉雅-东南亚)洲际成矿域的重要组成部分,富含丰富的矿产资源。基于该区的地质矿产图,结合前人的研究,分别以古地缝合带和深断裂为界,将其划分为5个一级成矿省,19个二级成矿带。研究表明:①在古老陆核结晶基底区形成沉积变质型铁、铜和稀土金属矿床;②在板(断)块的结合带形成典型的与基性—超基性岩浆活动有关的铬铁和铜镍硫化物矿床;③在板内沉积凹陷区形成盐类矿床;④在造山带的各个演化阶段形成与花岗质岩浆活动有关的斑岩铜金矿床、热液型铅锌矿床、热液脉状金矿床与热液脉状钨锡矿床。研究成果不仅为从整体上认识该区的成矿规律提供了基本框架,而且为在中国西南“三江”成矿带寻找与毗邻国家类似的矿床提供了新的启示。 相似文献
20.
东南亚中南半岛成矿带是特提斯(地中海-喜马拉雅-东南亚)洲际成矿域的重要组成部分,富含丰富的矿产资源。基于该区的地质矿产图,结合前人的研究,分别以古地缝合带和深断裂为界,将其划分为5个一级成矿省,19个二级成矿带。研究表明:①在古老陆核结晶基底区形成沉积变质型铁、铜和稀土金属矿床;②在板(断)块的结合带形成典型的与基性—超基性岩浆活动有关的铬铁和铜镍硫化物矿床;③在板内沉积凹陷区形成盐类矿床;④在造山带的各个演化阶段形成与花岗质岩浆活动有关的斑岩铜金矿床、热液型铅锌矿床、热液脉状金矿床与热液脉状钨锡矿床。研究成果不仅为从整体上认识该区的成矿规律提供了基本框架,而且为在中国西南“三江”成矿带寻找与毗邻国家类似的矿床提供了新的启示。 相似文献