Paleogeographic and paleotectonic response to magmatic processes: a case history from the Archean sequence in the Chibougamau area,Quebec     

Erich Dimroth  Michel Rochelau  Wulf Mueller  Paul Archer  Harold Brisson  Gabriel Fortin  Marc Jutras  Christian Lefebvre  Mathieu Piché  Pierre Pilote  Pierre Simoneau 《International Journal of Earth Sciences》1985,74(1):11-32

The Chibougamau area, Québec, is characteristic of the internal zone of the Archean Abitibi Orogenic Belt. The paleogeographic, paleotectonic and magmatic history of the Archean sequence in the Chibougamau area is subdivided into three stages.In the first stage a submarine volcanic chain formed mainly by the effusion of submarine lava flows composed of primitive, potash-poor, tholeiitic basalt. The volcanic chain gradually grew to sea level. In the second stage, volcanic islands emerged and grew. Mainly pyroclastic eruptions of strongly differentiated, calc-alkaline andesite and dacite concentrated on the volcanic islands, whereas effusion of basalt continued at first in the surrounding basin. A felsic volcaniclastic apron was deposited around the volcanic islands. In the third stage, the volcanic islands were uplifted and were eroded to the level of their subvolcanic plutons. The debris derived from this volcanic-plutonic terrain was deposited in downfaulted marine and continental basins. The contemporaneous volcanism was shoshonitic.The first paleogeographic stage is interpreted as the growth of an immature island arc. During the second stage, the island arc became mature and its crust was thickened by accretion of plutonic material. The third stage is a period of back-arc extension.

---

Zusammenfassung Das Gebiet von Chibougamau, Québec, ist characteristisch für die interne Zone des Archaischen Abitibi Orogens. Man kann seine paleogeographische, paleotectonische und magmatische Geschichte in drei Phasen gliedern.Eine submarine Vulkankette formte sich in der ersten Phase, hauptsächlich durch Effusion von submarinen Lavaergüssen aus primitivem, kaliarmen, tholeiitischem Basalt. Die Vulkankette wuchs langsam bis zum Meeresspiegel. Vulkanische Inseln bildeten sich und wuchsen während der zweiten paleogeographischen Phase. Vorwiegend pyroklastische Eruptionen von stark differenzierten, kalk-alkalischem Andesit und Dazit konzentrierten sich mehr und mehr auf den Inselvulkanen, während die Effusion von Basalt zunächst in den Becken noch stattfand. Ein Mantel aus felsitischen vulkanoklastischen Gesteinen wurde um die Inselvulkane abgelagert. Die dritte Phase begann mit einer Hebung der Inselvulkane und mit ihrer Erosion bis zum Niveau ihrer subvulkanischen Plutone. Der Detritus dieses vulkanisch-plutonischen Geländes wurde in marinen und kontinentalen Verwerfungsbecken abgelagert. Der gleichalte Vulkanismus ist shoshonitisch.Wir deuten die erste paleogeographische Phase als Wachstumsphase eines primitven Inselbogens. Während der zweiten Phase reifte der Inselbogen und seine Kruste verdickte sich durch Akkretion plutonischen Materials. Die dritte Phase ist eine Periode der Dehnung im Hinterland eines Inselbogens.

---

Résumé La région de Chibougamau, Québec, est caractéristique de la zone interne de la ceinture orogénique archéenne de l'Abitibi. Son évolution paléogéographique, paléotectonique et magmatique se subdivise en trois phases.Lors de la première phase paléogéographique, une chaîne sous-marine de volcans se formait, essentiellement par l'émission de coulées de lave composée de basalte primitif, hypopotassique, tholéiitique. Graduellement cette chaîne volcanique s'élevait jusqu'au niveau de la mer. A la phase suivante, des îles volcaniques émergeaient et croissaient. Des éruptions essentiellement pyroclastiques d'andésites et de dacites calco-alcalines et fortement différenciées se concentraient sur les îles tandis que l'effusion de laves basaltiques continuaient dans le bassin. Un manteau de roches volcaniclastiques felsiques se déposait autour des îles volcaniques. Lors de la troisième phase, les îles volcaniques furent soulevées et furent érodées jusqu'au niveau des masses plutoniques sub-volcaniques. Le débris de ce terrain volcano-plutonique fut déposé dans des bassins de faille marins et continentaux. Des shoshonites dominaient le volcanisme contemporain.Nous interprétons la première phase paléogéographique comme une phase de croissance d'un arc insulaire immature. Lors de la deuxième phase, 1'arc insulaire devenait mature et sa croûte s'epaissît par accrétion de matériel plutoni-que. Enfin, la troisième phase est une période d'extension en arrière d'un arc insulaire.

---

Chibougamau, Quebec, Abitibi. , . , . . , , . . , . - , , . . . . , , . , — . — . .

  相似文献   

Determining past atmospheric HCl mixing ratios from ice core analyses     

Florent Dominé  Emmanuel Thibert  Eric Silvente  Michel Legrand  Jean-Luc Jaffrezo 《Journal of Atmospheric Chemistry》1995,21(2):165-186

Laboratory and field measurements have been performed in order to improve our understanding of the HCl air-snow transfer function. The solubility and diffusion of HCl in laboratory grown single crystals of ice have been measured as a function of HCl partial pressure,P _HCl, between –8 and –25 °C. Measurements ofP _HCl and of the mole fraction of HCl in snow,X'_HCl, have been measured at Summit, Greenland. Comparison of the field and laboratory measurements show that theX'_HCl values are well below equilibrium values. The major processes involved in the formation of snow crystals and in their evolution after deposition are discussed in order to attempt to understand theX'_HCl values and their variations. The discussion is focussed on a few well identified snow layers. It is concluded that sublimation and recrystallization of snow probably play a major role in the evolution ofX'_HCl, but that our understanding of the HCl transfer function is very incomplete. Laboratory and field measurements are suggested to improve this situation.  相似文献   

Long-period Love wave overtone data in North America and the Pacific Ocean: new evidence for upper mantle anisotropy     

Jean-Jacques Lévêque  Michel Cara 《Physics of the Earth and Planetary Interiors》1983,33(3):164-179

Two Tonga-trench earthquakes recorded in North America on WWSSN long-period instruments have been processed by making use of spatial analysis techniques to retrieve the phase velocities of Love wave modes. Dispersion data up to the third overtone at periods longer than 30 s have been obtained for two broad areas: the Pacific Ocean and North America. It is found that the observed Love wave phase velocities are not in agreement with the values predicted from the previously published models inferred from Rayleigh wave data. Phase velocity discrepancies as large as 3–4% in the Pacific Ocean and 2% in North America are observed up to the second overtone. Preliminary direct computations, which have been performed in the framework of transversely isotropic models with the axis of symmetry oriented vertically, suggest that the cause for this departure from isotropy probably extends to depths > 200 km.  相似文献   

Harmonisation et définition des unités lithostratigraphiques brian?onnaises dans les nappes penniques du Valais     

Mario Sartori  Yves Gouffon  Michel Marthaler 《Eclogae Geologicae Helvetiae》2006,99(3):363-407

  相似文献   

Potential Flank-Collapse of Soufrière Volcano, Guadeloupe, Lesser Antilles? Numerical Simulation and Hazards     

Anne Le Friant  Georges Boudon  Jean-Christophe Komorowski  Philippe Heinrich  Michel P. Semet 《Natural Hazards》2006,39(3):381-393

The past history of recurrent flank collapses of la Soufrière volcano of Guadeloupe, its structure, its well-developed hydrothermal system and the current activity constitute factors that could promote a future flank collapse, particularly in the case of a significant increase of activity, with or without shallow magmatic input. To address the hazards associated with such a collapse, we model the emplacement of the debris avalanche generated by a flank-collapse event in 1,250 BC (3,100 years B.P.). We use a finite-difference grain-flow model solving mass and momentum conservation equations that are depth-averaged over the slide thickness, and a Coulomb-type friction law with a variable basal (minimum) friction angle. Using the parameter values determined from this simulation, we then simulate the debris avalanche which could be generated by a potential collapse of the present lava dome. We then discuss the region which could be affected by such a future collapse, and additional associated hazards of concern.  相似文献   

Cation sorption on the muscovite (0 0 1) surface in chloride solutions using high-resolution X-ray reflectivity     

Michel L. Schlegel  Kathryn. L. Nagy  Paul Fenter  Neil C. Sturchio 《Geochimica et cosmochimica acta》2006,70(14):3549-3565

The structure and mechanism of cation sorption at the (0 0 1) muscovite-water interface were investigated in 0.01 and 0.5 m KCl, CsCl, and CaCl₂ and 0.01 m BaCl₂ solutions at slightly acidic pH by high-resolution X-ray reflectivity. Structural relaxations of atom positions in the 2M₁ muscovite were small (?0.07 Å) and occurred over a distance of 30 to 40 Å perpendicular to the interface. Cations in all solutions were sorbed dominantly in the first and second solution layers adjacent to the mineral surface. The derived heights of the first solution layer in KCl and CsCl solutions, 1.67(6)-1.77(7) and 2.15(9)-2.16(2) Å, respectively, differ in magnitude by the approximate difference in crystallographic radii between K and Cs, and correspond closely to the interlayer cation positions in bulk K- and Cs-mica structures. The first solution layer heights in CaCl₂ and BaCl₂ solutions, 2.46(5)-2.56(11) and 2.02(5) Å, respectively, differ in a sense opposite to that expected based on crystallographic or hydrated radii of the divalent cations. The derived ion heights in all solutions imply that there is no intercalated water layer between the first solution layer and the muscovite surface. Molecular compositions were assigned to the first two solution layers in the electron density profiles using models that constrain the number density of sorbed cations, water molecules, and anions by considering the permanent negative charge of the muscovite and average solution density. The models result in partial charge balance (at least 50%) by cations sorbed in the first two layers in the 0.01 m solutions and approximately full charge balance in the 0.5 m solutions. Damped oscillations of model water density away from the first two solution layers agree with previous X-ray reflectivity results on the muscovite (0 0 1) surface in pure water.  相似文献   

Trace element geochemistry of the 1991 Mt. Pinatubo silicic melts, Philippines: Implications for ore-forming potential of adakitic magmatism     

Anastassia Yu. Borisova  Michel Pichavant  Michael Wiedenbeck  Frédéric Candaudap 《Geochimica et cosmochimica acta》2006,70(14):3702-3716

The dacite pumice erupted from Mt. Pinatubo on June 15, 1991 (whole-rock, rhyolitic groundmass glasses and homogenized melt inclusions) has been analyzed using inductively coupled plasma-mass spectrometry (ICP-MS), nanosecond and femtosecond laser ablation ICP-MS and secondary ion mass spectrometry (SIMS) to evaluate its ore-forming potential. Data suggest that adakite magmas are metal-rich and concentrate ore metals during magmatic differentiation. Sulfides segregate in limited amounts under the hydrous, oxidizing conditions typical of adakitic magmas resulting in incompatible behavior for Au (6-22 ppb), Cu (26-77 ppm), and Pb, Mo, As, and Sb in melts of dacitic to rhyolitic compositions. Metal transfer from this adakite magma to the coexisting aqueous phase was favored by the peraluminous composition of the rhyolitic melt and high aqueous chloride concentrations. Mass balance calculations suggest that the pre-eruptive aqueous phase could have extracted a minimum of 100 t Au and 5 × 10⁵ t Cu from the Mt. Pinatubo magma. Our data suggest that intrusives having adakitic signatures are genetically associated with Au-Cu and Cu-Mo mineralization, auriferous porphyry copper deposits, and epithermal gold veins. High H₂O, Cl, Sr/Y, Pb/Ce, Mo/Ce, As/Ce and Sb/Ce in Mt. Pinatubo melts reflect the contribution of deep fluids derived from subducted sediments and altered MORBs in the dacite genesis. The slab-derived fluids carrying mobile elements are likely responsible for the enrichment of adakite magmas in gold, associated metals and H₂O, and may explain the exceptional ore-forming potential of adakite magmatism.  相似文献   

Mechanisms and duration of non-tectonically assisted magma emplacement in the upper crust: The Black Mesa pluton, Henry Mountains, Utah     

Michel de Saint-Blanquat  Guillaume Habert  Eric Horsman  Sven S. Morgan  Basil Tikoff  Patrick Launeau  Grard Gleizes 《Tectonophysics》2006,428(1-4):1-31

A new study of Black Mesa pluton (Henry Mountains, Colorado Plateau, Utah, USA) indicates that it is a classic example of a small upper-crustal pluton assembled over a few years by incremental amalgamation of discrete magma pulses. The results of our petrostructural study of the pluton interior allow us to constrain the geometry, kinematics and timing of the processes. The symmetric internal fabric is interpreted as an evidence for a feeding by below and not laterally. The observed rotation of the lineation, from WNW–ESE on the very top to NNE–SSW below, lead us to propose that the fabric at the base of the pluton is a record of magma infilling process, and the fabric at the very top is a record of the strain due to the relative movement between magma and wallrocks. A consequence is that except at the contact between pluton and wallrocks (top and margins), the stretching direction, recorded by the lineation, is not parallel to the flow direction of the magma i.e. displacement. The Black Mesa pluton is a sheeted laccolith on its western edge and a bysmalith on its eastern edge. This E–W asymmetry in pluton geometry/construction and the symmetrical internal fabric indicates that the apparently different west and east growth histories could have occurred simultaneously. Our field data indicate pluton growth through an asymmetric vertical stacking of sill-like horizontal magma sheets.One-dimensional thermal models of the pluton provide maximum limits on the duration of its growth. We have constrained the number, the thickness, and the frequency of magma pulses with our structural observations, including: (1) the emplacement of the pluton by under-accretion of successive magma pulses, (2) the absence of solid-state deformation textures at internal contacts, and (3) the apparent absence of significant recrystallization in the wallrocks. Our results suggest that the emplacement of the Black Mesa pluton was an extremely rapid event, with a maximum duration on the order of 100 years, which requires a minimum vertical displacement rate of the wallrocks immediately above the pluton greater than 2 m/yr. Finally, our data show that the rates of plutonic and volcanic processes could be similar, a significant result for interpretation of magma transfer in arc systems.  相似文献   

Les paléoenvironnements éocènes à crinoïdes pédonculés des marnes de Miretrain (Angoumé, SW France) : interprétations paléobathymétriques     

Michel Roux  Bruno Cahuzac  Károly Sztrákos 《Comptes Rendus Geoscience》2006,338(4):262-271

A well-diversified fauna of stalked crinoids was found in the Eocene series exposed in the quarry of Miretrain at Angoumé (Landes, southwestern Aquitaine, northern edge of the Tercis diapir structure). The most frequent taxa belong to the genera Isselicrinus and Conocrinus. Adaptive stalk characters related to depth in the pentacrinid genus Isselicrinus allow us to document the bathymetric zonation of stalked crinoids during the Eocene. Both stalked crinoids, benthic foraminifera and additional organisms give convergent information on palaeodepths throughout the progradation of sedimentary bathyal slope between the two major tectonic events providing Pyrenean foreland shortening. The depth changes from more than 700 m (maybe about 1000 m) at the base of the series (Middle Lutetian) to about 50 m at the top (Late Bartonian). To cite this article: M. Roux et al., C. R. Geoscience 338 (2006).  相似文献   

Gully erosion in mountain areas: processes,measurement, modelling and regionalization     

John Wainwright  Nicolle Mathys  Michel Esteves 《地球表面变化过程与地形》2006,31(2):133-134

  相似文献