Magmatic evolution of Li–F, rare-metal granites: a case study of melt inclusions in the Khangilay complex, Eastern Transbaikalia (Russia)     

E. V. Badanina  I. V. Veksler  R. Thomas  L. F. Syritso  R. B. Trumbull 《Chemical Geology》2004,210(1-4):113-133

We report compositions of homogenized quartz-hosted melt inclusions from a layered sequence of Li-, F-rich granites in the Khangilay complex that document the range of melt evolution from barren biotite granites to Ta-rich, lepidolite–amazonite–albite granites. The melt inclusions are crystalline at room temperature and were homogenized in a rapid-quench hydrothermal apparatus at 200 MPa before analysis. Homogenization runs determined solidus temperatures near 550 °C and full homogenization between 650 and 750 °C. The compositions of inclusions, determined by electron microprobe and Raman spectroscopy (for H₂O), show regular overall trends of increasing differentiation from the least-evolved Khangilay units to apical units in the Orlovka intrusion. Total volatile contents in the most-evolved melts reach over 11 wt.% (H₂O: 8.6 wt.%, F: 1.6 wt.%, B₂O₃: 1.5 wt.%). Concentrations of Rb range from about 1000 to 3600 ppm but other trace elements could not be measured reliably by electron microprobe. The resulting trends of melt evolution are similar to those described by the whole-rock samples, despite petrographic evidence for albite- and mica-rich segregations previously taken as evidence for post-magmatic metasomatism.

Melt variation trends in most samples are consistent with fractional crystallization as the main process of magma evolution and residual melt compositions plot at the granite minimum in the normative Qz–Ab–Or system. However, melts trapped in the highly evolved pegmatitic samples from Orlovka deviate from the minimum melt composition and show compositional variations in Al, Na and K that requires a different explanation. We suggest that unmixing of the late-stage residual melt into an aluminosilicate melt and a salt-rich dense aqueous fluid (hydrosaline melt) occurred. Experimental data show the effectiveness of this process to separate K (aluminosilicate melt) from Na (hydrosaline melt) and high mobility of the latter due to its low viscosity and relatively low density may explain local zones of albitization in the upper parts of the granite.  相似文献   

The magmatic–hydrothermal transition—evidence from quartz phenocryst textures and endoskarn abundance in Cu–Zn skarns at the Empire Mine, Idaho, USA     

Zhaoshan Chang  L.D. Meinert 《Chemical Geology》2004,210(1-4):149-171

Information about the magmatic to hydrothermal transition is preserved in late-stage features of quartz phenocrysts and endoskarn alteration in some Cu–Zn skarn deposits such as the Empire Mine in Idaho. Important features include: (1) quartz phenocrysts with strong resorption textures such as vermicular zones of igneous groundmass cutting primary quartz cathodoluminescence banding, (2) anomalous amounts of endoskarn (more than 50% of mineralized rock), (3) high F activities as evidenced by fluorite as an accessory mineral in igneous rocks, in alteration assemblages, and in fluid inclusions and by high F in hydroxyl sites in igneous biotite and amphibole, and (4) direct association of Zn, which normally is deposited distally at low temperature, with Cu in proximal locations and in endoskarn. These features are explained by the following model: (1) F lowers the solidus temperature of the magma, thus changing the timing, temperature, and duration of hydrothermal fluid exsolution. (2) Upon magmatic vapor saturation the F-rich hydrothermal fluids form bubbles that adhere to quartz phenocrysts and chemically corrode/tunnel into the quartz forming vermicular resorption textures. (3) F-rich hydrothermal fluids also promote the formation of endoskarn; silicic rocks are attacked by F-rich fluids in the same sense that carbonate wall rocks are dissolved by weakly to moderately acidic hydrothermal fluids. (4) Low fluid exsolution temperature facilitated by high F activity promotes high Zn/Cu ratios in proximal locations due to the solubility of Zn relative to Cu at lower temperatures. This model may be applicable at other localities such as the world-class Cu–Zn skarn Antamina mine, as well as some tin and rapakivi granites.  相似文献   

Nouvelle interprétation structurale de la « faille Nord- Pyrénéenne » en vallée d'Aspe (Pyrénées-Atlantiques). Remise en question d'un plutonisme ophitique danien dans le secteur de Bedous     

Joseph Canérot  Claude Majesté-Menjoulas  Yves Ternet 《Comptes Rendus Geoscience》2004,336(2):135-142

In the Aspe Valley (western Pyrenees), the Europe/Iberia boundary corresponds to a complex fracturing zone, called the ‘Bielle–Accous Wrench-Faulting Corridor’, which represents the classical ‘North-Pyrenean Fault’. Located between the High Primary Range and the North-Pyrenean Zone, the BAWC shows different south-verging sheets mainly composed of Triassic materials. The Bedous ophite, associated with Muschelkalk and Keuper sediments, is also Triassic in age and involved in the same Pyrenean thrusting structures. So, contrary to a recent interpretation, this magmatic rock cannot be related to a supposed Danian plutonism inducing metamorphic processes in the surrounding Mesozoic formations. To cite this article: J. Canérot et al., C. R. Geoscience 336 (2004).  相似文献   

A study of microearthquake seismicity and focal mechanisms within the Sea of Marmara (NW Turkey) using ocean bottom seismometers (OBSs)   总被引：1，自引：0，他引：1  

Toshinori Sato  Junzo Kasahara  Tuncay Taymaz  Masakazu Ito  Aya Kamimura  Tadaaki Hayakawa  Onur Tan 《Tectonophysics》2004,391(1-4):303

We have carried out seismological observations within the Sea of Marmara (NW Turkey) in order to investigate the seismicity induced after Gölcük–İzmit (Kocaeli) earthquake (M_w 7.4) of August 17, 1999, using ocean bottom seismometers (OBSs). High-resolution hypocenters and focal mechanisms of microearthquakes have been investigated during this Marmara Sea OBS project involving deployment of 10 OBSs within the Çınarcık (eastern Marmara Sea) and Central-Tekirdağ (western Marmara Sea) basins during April–July 2000. Little was known about microearthquake activity and their source mechanisms in the Marmara Sea. We have detected numerous microearthquakes within the main basins of the Sea of Marmara along the imaged strands of the North Anatolian Fault (NAF). We obtained more than 350 well-constrained hypocenters and nine composite focal mechanisms during 70 days of observation. Microseismicity mainly occurred along the Main Marmara Fault (MMF) in the Marmara Sea. There are a few events along the Southern Shelf. Seismic activity along the Main Marmara Fault is quite high, and focal depth distribution was shallower than 20 km along the western part of this fault, and shallower than 15 km along its eastern part. From high-resolution relative relocation studies of some of the microearthquake clusters, we suggest that the western Main Marmara Fault is subvertical and the eastern Main Marmara Fault dips to south at 45°. Composite focal mechanisms show a strike-slip regime on the western Main Marmara Fault and complex faulting (strike-slip and normal faulting) on the eastern Main Marmara Fault.  相似文献   

Imaging the Dead Sea Transform with scattered seismic waves   总被引：2，自引：0，他引：2  

N. Maercklin  C. Haberland  T. Ryberg  M. Weber  Y. Bartov  the DESERT Group 《Geophysical Journal International》2004,158(1):179-186

  相似文献   

Structural and geotechnical impacts of surface rupture on highway structures during recent earthquakes in Turkey   总被引：4，自引：0，他引：4  

A. Pamuk  E. Kalkan  H.I. Ling 《Soil Dynamics and Earthquake Engineering》2005,25(7-10):581-589

The most significant damage on highway bridges during the recent earthquakes in Turkey (Kocaeli and Duzce earthquakes) and Taiwan (Chi–Chi earthquake) was the result of fault ruptures traversing transportation infrastructure. This phenomenon and its consequences accentuate the need to examine surface rupture hazards and to identify those areas at risk. This understanding can help to develop remedial measures for both structural and geotechnical engineering. For that purpose, damage to highway bridges during the recent events was reviewed. The total collapse of the highway overpass in Arifiye, during the Kocaeli earthquake, was investigated. The major problems under consideration (in Arifiye) were: (i) dislodging of the bridge spans, and consequently, the total separation of the reinforced concrete girders from the piers; and (ii) the stability of a mechanically stabilized earth wall (MSEW) system under extreme loading conditions. The results of the structural and geotechnical investigations presented herein can be taken in consideration to improve transportation infrastructure against surface rupture hazards.  相似文献   

Image processing of 2D resistivity data for imaging faults   总被引：6，自引：0，他引：6  

F. Nguyen  S. Garambois  D. Jongmans  E. Pirard  M.H. Loke   《Journal of Applied Geophysics》2005,57(4):260-277

A methodology to locate automatically limits or boundaries between different geological bodies in 2D electrical tomography is proposed, using a crest line extraction process in gradient images. This method is applied on several synthetic models and on field data set acquired on three experimental sites during the European project PALEOSIS where trenches were dug. The results presented in this work are valid for electrical tomographies data collected with a Wenner-alpha array and computed with an l₁ norm (blocky inversion) as optimization method. For the synthetic cases, three geometric contexts are modelled: a vertical and a dipping fault juxtaposing two different geological formations and a step-like structure. A superficial layer can cover each geological structure. In these three situations, the method locates the synthetic faults and layer boundaries, and determines fault displacement but with several limitations. The estimated fault positions correlate exactly with the synthetic ones if a conductive (or no superficial) layer overlies the studied structure. When a resistive layer with a thickness of 6 m covers the model, faults are positioned with a maximum error of 1 m. Moreover, when a resistive and/or a thick top layer is present, the resolution significantly decreases for the fault displacement estimation (error up to 150%). The tests with the synthetic models for surveys using the Wenner-alpha array indicate that the proposed methodology is best suited to vertical and horizontal contacts. Application of the methodology to real data sets shows that a lateral resistivity contrast of 1:5–1:10 leads to exact faults location. A fault contact with a resistivity contrast of 1:0.75 and overlaid by a resistive layer with a thickness of 1 m gives an error location ranging from 1 to 3 m. Moreover, no result is obtained for a contact with very low contrasts (1:0.85) overlaid by a resistive soil. The method shows poor results when vertical gradients are greater than horizontal ones. This kind of image processing technique should be systematically used for improving the objectiveness of tomography interpretation when looking for limits between geological objects.  相似文献   

Microcrack networks in granite affected by a fault zone: Visualization by confocal laser scanning microscopy     

Celia T. Onishi  Ichiko Shimizu   《Journal of Structural Geology》2005,27(12):170

Microcracks in the Cretaceous Ryoke-type granite in Japan were investigated by using deep drilling core samples collected in the Mizunami Underground Research Project of the Japan Nuclear Cycle Development Institute (JNC). The granite body suffered brittle deformation associated with Tertiary thrust movement. Based on core-scale and microscopic deformation features, the drill core from a depth of 300 to 700 m is divided into four domains, i.e. (A) undeformed granite, (B) granite intruded by cataclastic seams, (C) fractured granite in the fault damage zone, and (D) foliated cataclasite at the fault center. To characterize microcrack geometries in each domain, we employed the impregnation method using a low-viscous acrylic resin doped with fluorescent agents and captured the microcrack images by confocal laser scanning microscopy (CLSM). The CLSM image in the fault damage zone revealed anisotropic development of microcrack networks related to the fault movement. Both CLSM observation and porosity measurements reveal a drastic increase of micro-pores in the foliated cataclasite, possibly caused by fragmentation, and granulation and crack sealing in the fault zone.  相似文献   

Les laves du mont Bangou : une première manifestation volcanique éocène, à affinité transitionnelle,de la Ligne du Cameroun     

Jacob Fosso  Jean-Jacques Ménard  Jacques-Marie Bardintzeff  Pierre Wandji  Félix M. Tchoua  Hervé Bellon 《Comptes Rendus Geoscience》2005,337(3):315-325

Mount Bangou, an Eocene volcano (⁴⁰K–⁴⁰Ar ages between 44.7 and 43.1 ± 1 Ma) is the oldest dated volcano of the Cameroon Line. In this region, two magmatic series, evolving by fractional crystallization, show transitional affinities that are exceptionally known in this sector. Mineral compositions of basaltic rocks (scarce modal olivine and occurrence of normative hypersthene) as well as geochemical characteristics (low Ba, La, Ta contents and high Y/Nb ratios) are in agreement with this trend. The succession of magmas evolving in time from transitional to more typical alkaline compositions is evidenced in a continental setting. To cite this article: J. Fosso et al., C. R. Geoscience 337 (2005).  相似文献   

Representing and communicating deep uncertainty in climate-change assessments   总被引：1，自引：0，他引：1  

Milind Kandlikar  James Risbey  Suraje Dessai 《Comptes Rendus Geoscience》2005,337(4):443-455

IPCC reports provide a synthesis of the state of the science in order to inform the international policy process. This task is made difficult by the presence of deep uncertainty in the climate problem that results from long time scales and complexity. This paper focuses on how deep uncertainty can be effectively communicated. We argue that existing schemes do an inadequate job of communicating deep uncertainty and propose a simple approach that distinguishes between various levels of subjective understanding in a systematic manner. We illustrate our approach with two examples. To cite this article: M. Kandlikar et al., C. R. Geoscience 337 (2005).  相似文献