Resorption process in Astypalaea Linea extensive region (Europa)     

Loïc Mével  Eric Mercier 《Planetary and Space Science》2005,53(7):771-779

Whereas numerous extensive features, where new crust is created, are now well recognized on Europa's surface, those relevant to crust disappearance remain difficult to find. This work presents a reconstruction of the surface prior to Astypalaea Linea's emplacement (one of the features where new crustal material appears). We demonstrate that a scattered disappearance of crust takes place in an extensive region close to Astypalaea Linea. Physical processes invoked for disappearance are discussed: pressure melting may be responsible for the mobilization of surface material and its collapse down through the icy crust.  相似文献   

Deformation and metamorphism in the Fenes Nappe (southern Apuseni Mountains,Romania)Déformation et métamorphisme dans la nappe de Fenes (monts Apuseni méridionaux,Roumanie)     

Alessandro Ellero  Leonardo Leoni  Michele Marroni  Ionel Nicolae  Luca Pandolfi  Franco Sartori 《Comptes Rendus Geoscience》2002,334(5):347-354

The Fenes Nappe belongs to the stack of tectonic units cropping out in the southern Apuseni Mts (Romania). It is characterised by a structural history consisting of two folding phases that developed during the time spanning from Early Aptian to Late Maastrichtian. The D1 phase produced west-northwest-verging, isoclinal to very tight folds, associated to a slaty cleavage. The main metamorphic imprint of the Fenes Nappe is linked to this deformation phase; illite and chlorite ‘crystallinity’ values indicate metamorphic conditions of the late diagenesis, close to the diagenetic zone/anchizone boundary. The subsequent D2 phase produced north-northwest-verging, parallel folds, not associated with synkinematic recrystallisation. These phases are interpreted as developed during a structural path, which includes burial at a depth of 8–10 km, followed by exhumation at shallower structural levels. To cite this article: A. Ellero et al., C. R. Geoscience 334 (2002) 347–354.  相似文献   

Tectonically driven fluid flow and gold mineralisation in active collisional orogenic belts: comparison between New Zealand and western Himalaya     

D. Craw  P. O. Koons  T. Horton  C. P. Chamberlain 《Tectonophysics》2002,348(1-3)

Hydrothermal activity and mesothermal-styled gold mineralisation occurs near the main topographic divide of most active or young collisional mountain belts. The Southern Alps of New Zealand is used in this study as a model for the mineralising processes. The collisional tectonics results in a two-sided wedge-shaped orogen into which rock is transported horizontally. Upper crustal rocks pass through the orogen and leave the orogen by erosion, whereas lower crustal rocks are deformed into the mountain roots. High relief drives meteoric water flow to near the brittle–ductile transition. Lower to upper greenschist facies metamorphic reactions, driven by deformation at the crustal decollement and in the root, release water-rich fluids that rise through the orogen. Intimate chemical interaction between fluid and rock results in dissolution and later precipitation of gold, arsenic and sulphur. Fluid flow and mineralisation in the topographic divide region is facilitated by a network of steeply dipping faults and associated rock damage zones where oblique strike-slip faults intersect the thrust faults that strike subparallel to the main mountain range.The Nanga Parbat massif of the western Himalaya is an example of an active collisional zone which hosts hydrothermal activity but no gold mineralisation. The lack of gold mineralisation is due to the following factors: CO₂-dominated rising metamorphic fluid in dehydrated amphibolite-granulite facies metamorphic rocks does not dissolve gold and arsenic; hot (up to 400 °C) meteoric water confined to fractures in the gneiss limits dissolution of gold and arsenic; low density of hot water/dry steam, and low reduced sulphur content of fluid, restrict solubility of gold and arsenic; absence of fracture networks in the core of the massif and the small volumes of circulating fluid limit metal concentration; and lack of reactive rock compositions limits chemically mediated metal deposition.  相似文献   

Post Late Paleozoic tectonism in the southern Catalan Coastal Ranges (NE Spain), assessed by apatite fission track analysis     

J. Juez-Larr  P. A. M. Andriessen 《Tectonophysics》2002,349(1-4)

We report the first apatite fission-track thermochronologic data for 17 samples from the southern Catalan Coastal Ranges of NE Spain. Thermal histories of Carboniferous metasediments, Late Hercynian intrusions and Lower-Triassic Buntsandstein sediments from three tectonic blocks, Miramar, Prades and Priorat, are derived and interpreted within the geodynamic framework and tectonic evolution of the region. The apatite fission-track ages range from 198±24 to 38±5 Ma and mean fission-track lengths are all <13.3 μm. Samples throughout the study area underwent total track annealing during the Late Hercynian magmatic episode, followed by fast cooling prior to the deposition of Lower Triassic sediments. The Lower Triassic sediments and basement rocks underwent a temperature increase during a first Mesozoic rift phase in Middle Triassic–Early Jurassic times resulting in the complete or near complete annealing of the fission-tracks. During a second Mesozoic rifting stage, in Late Jurassic to Early Cretaceous time, differential tectonic block activity is observed in the three studied tectonic blocks. Subsequently, during Late Cretaceous a long-period of thermal stability, detected in all samples, is related to the post-rift episode. The onset of fast cooling registered in the apatite fission track system during Paleogene times is related to the Pyrenean orogeny. Compressional forces associated with the ongoing southern migration of the convergence forces at the Iberian plate boundaries caused unroofing of about 2–3 km of material of the Prades and northwestern flank of the Priorat block. Extensional collapse in Late Oligocene–Miocene related to the Western Mediterranean rifting triggered the denudation of about 2 km of material from the southeastern flank of the Miramar, Prades and Priorat blocks.  相似文献   

TECTONICS OF THE DABIE OROGENIC BELT, CENTRAL CHINA     

GUO Fu-sheng XIA Fei PENG Hua-ming DU Yang-song 《大地构造与成矿学(英文版)》2002,(2):52-62

Tectonically the Dabie orogenic belt consists mainly of the Dabieshan Yanshanian uplifted zone and the Beihuaiyang Variscan-Indosinian folding zone. In the north boundary adjoining the North China Block, there are an Early Palaeozoic ophiolitic mixtite belt and the Hefei Mesozoic-Cenozoic faulted basin which overlaps on the suture belt. In the south of Dabie orogen, there is a secondary tectonic unit called Foreland thrust-faulted structural zone which was mainly formed by the intracontinental subductions during Mesozoic era. The study shows that the Dabie Block is a part of mid-late Proterozoic palaeo-island arc at the north margin of Yangtze Block. During Caledonian period, as a submerged uplift at the northen continental margin of Yangtze Block, the Dabie Block collided with the early Palaeozoic palaeo-island arc at the south margin of North China Block, resulting in the convergence of the North and South China Blocks and the disappearance of oceanic crust. Since then,large-scale intracontinental subductions were followed. Dabie Orogenic Belt is the product of overlapping of Yangtze Block, Dabie Block and North China Block under the mechanism of intracontinental subduction. Indosinian period is the period of chief deformation and high pressure dynamic metamorphism for Dabie Block, and Yanshan period is the main orogenic period in which the remelting of crust caused by basement shearing resulted in large scale thermometamorphism. The present tectonic framework of the orogen was finally formed by the rapid uplifting of the Dabieshan mountains and gliding southwards, which result in the developing of thrust belt on south side and the extensional tectonic movement on north side.  相似文献   

Fission-track dating of the western border of the Bohemian massif: thermochronology and tectonic implications     

E. Hejl  D. Coyle  Nand Lal  P. Van den Haute  G. A. Wagner 《International Journal of Earth Sciences》1997,86(1):210-219

 Since 1985, apatite fission-track analysis was applied to more than 70 samples from surface outcrops and shallow boreholes at the western margin of the Bohemian massif. Apatite ages were determined by the grain-population method. Additional information from the frequency distributions of fully confined spontaneous tracks was used for modelling of t–T paths in the low-temperature range (<120 °C). Seven zircon samples were dated by the external detector method. Zircon ages between 283 and 215 Ma indicate unroofing during the Permian molasse stage and the Triassic. Tectonic quiescence and slow subsidence prevailed from the Jurassic until the middle Cretaceous. In the basement area south of Weiden, a Mesozoic partial annealing zone (for apatite fission tracks) is now exposed at the surface. Farther north, the basement was affected by stronger Cretaceous and Palaeogene erosion, which yielded cooling ages between 110 and 49 Ma. This second period of post-Variscan denudation was correlated to reverse faulting along the Franconian Line. Received: 30 June 1996 / Accepted: 24 October 1996  相似文献   

全球地震面波相速度变化及其大地构造学意义   总被引：6，自引：4，他引：6       下载免费PDF全文

张禹慎  马石庄 《地球物理学报》1997,40(2):181-192

从1980年到1992年间震级M≥6．0天然地震的全球数字地震台网记录，搜集约30000个长周期地震图波形数据，建立了周期为85-250s的全球Love波和Rayleish波相速度变化模型．全部地震图均通过时间域和频率域的质量控制，震相为短大圆弧和长大圆弧基频振型G1，R1，G2和R2．利用将区域高分辨率反演结果嵌入全球模型框架的混合反演参量化方法，以及地形、地貌和地壳厚度模型，得到校正前、后的两种反演结果．与已有全球相速度模型比较，长波分量的幅度和空间图像符合较好．短周期相速度异常反映了地表板块构造，与大陆地盾、大洋中脊和构造活动区相关；板块构造相关性随面波周期增大而逐渐消失；部分海洋热点与100-200s周期的低速异常相联系．  相似文献   

Les « Porphyroı̈des » de Bretagne méridionale : une unité de HP–BT dans la chaı̂ne hercynienneEvidence for HP–LT Hercynian metamorphism within the ‘Porphyroı̈des’ of South Brittany (France)     

Florence Le Hébel  Olivier Vidal  Jean-Robert Kienast  Denis Gapais 《Comptes Rendus Geoscience》2002,334(3):205-211

The so-called ‘Porphyro??des’ Unit of South Brittany is located below units marked by an early HP–LT event (blueschists from the Île de Groix) and above units marked by Upper Carboniferous HT metamorphism. P–T estimates in the Porphyro??des (at Belle-Île-en-Mer), using the phengite–chlorite thermobarometer, indicate pressures around 8 kbar and temperatures of 350–400 °C. These new estimates suggest that the early tectonic history of the ‘Porphyro??des’ should be linked to that of the overlying Blueschists, and imply a much larger areal extension of the HP–LT domain in this part of the Hercynian Belt. To cite this article: F. Le Hébel et al., C. R. Geoscience 334 (2002) 205–211.  相似文献   

地质学的若干问题   总被引：19，自引：0，他引：19  

刘宝  李廷栋 《地球科学进展》2001,16(5):607-616

对地质学几个领域近几十年的发展做了扼要的总结,指出了一些有突破性的进展,并提出了这些学科今后若干年可能的发展展望,论文涉及的学科包括矿物学、花岗岩、铁镁－超铁镁岩、变质岩、沉积学、多重地层分类与地质年代学、构造这以及板块构造学与大陆动力学。对于各学科并非全面的论述,而是指出其有重大意义的突破性进展,在矿物学方面强调了由于新技术的运用而大大地促进了矿物学的进展,矿物材料学和环境矿物学都是今后着重发展的方向。总结了当前对花岗岩的基本认识,指出应开展“岩浆系统”与“火山系统”的深层次研究;对于铁镁－超铁镁岩今后要加强壳幔物质的相互作用与深部过程的研究;总结了变质岩研究的三个阶段,今后要在重点地质区坚持长期深入系统的研究,特别是前寒武纪麻粒岩区和造山带。沉积学最近有较大发展,有三方面的意义;在构造地质学方面指出在大陆造山带伸展构造、韧性剪切等研究热点以及从定性到定量的研究趋势;板块构造学是地球科学有史以来最伟大的成就,90年代是大陆构造研究的大发展时期。  相似文献   

Analysis of central western Europe deformation using GPS and seismic data   总被引：1，自引：0，他引：1  

Magdala Tesauro  Christine Hollenstein  Ramon Egli  Alain Geiger  Hans-Gert Kahle 《Journal of Geodynamics》2006,42(4-5):194-209

The kinematic field of central western Europe is characterized by relatively small movements (around 1–2 mm/year) and diffuse seismicity with earthquakes occurring mostly in the shallow crust (within 15 km), prevalently concentrated along the Alps and the European Cenozoic Rift System (ECRIS). In order to study and constrain the current crustal kinematic field we reconstructed the velocity and the strain field using permanent GPS stations, belonging to different networks (AGNES, EUREF, REGAL, RGP). The 2D strain rate tensor has been calculated using the method of least-squares collocation. Our results show that the area of maximum compression is located along the Alpine chain, where maximum values of 7 ± 2 nstrain/year are found, while maximum extension is measured between the Armorican Massif and the Massif Central, where values of 4 ± 2 nstrain/year are reached.The earthquakes with M > 3.0, have been used to estimate the seismic strain rates, while the style of the seismic deformation was reconstructed from the fault plane solutions (FPS) available from the literature. Relatively high values of seismic strain rates (around 10 nstrain/year) are measured along the Alpine Chain and the ECRIS. Results obtained by geodetic and seismic data are quite in agreement and reflect the different tectonic evolution of the geological features characterizing the area of study. The orientation of the compressional geodetic and seismic strain axes are NW-SE in most of the area of study, on account of the action of plate boundary forces. A rotation of the same axes to N-S direction along the eastern Alps, possibly related to the Adria convergence, is found.  相似文献