Geometry and kinematics of the Roisan-Cignana Shear Zone, and the orogenic evolution of the Dent Blanche Tectonic System (Western Alps)

A previous study of the Dabie area has been supposed that a strong extensional event happened between the Yangtze and North China blocks. The entire extensional system is divided into the Northern Dabie metamorphic complex belt and the south extensional tectonic System according to geological and geochemical characteristics in our study. The Xiaotian-Mozitan shear zone in the north boundary of the north system is a thrust detachment, showing upper block sliding to the NNE, with a displacement of more than 56 km. However, in the south system, the shearing direction along the Shuihou-Wuhe and Taihu-Mamiao shear zones is tending towards SSE, whereas that along the Susong-Qingshuihe shear zone tending towards SW, with a displacement of about 12 km. Flinn index results of both the north and south extensional systems indicate that there is a shear mechanism transition from pure to simple, implying that the extensional event in the south tectonic system could be related to a magma intrusion in the Northern Dabie metamorphic complex belt. Two 40Ar-39Ar ages of mylonite rocks in the above mentioned shear zones yielded, separately, ~190 Ma and ~124 Ma, referring to a cooling age of ultrahigh-pressure rocks and an extensional era later.

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The influence of dikes on auriferous shear zone development within granitoid intrusions: the Bourlamaque pluton, Val-d'Or district, Abitibi greenstone belt

Canadian Journal of Earth Sciences ◽

10.1139/e93-170 ◽

1993 ◽

Vol 30 (9) ◽

pp. 1924-1933 ◽

Cited By ~ 9

Author(s):

Abdelhay Belkabir ◽

François Robert ◽

L. Vu ◽

C. Hubert

Keyword(s):

Shear Zone ◽

Shear Zones ◽

Slip Direction ◽

Principal Stresses ◽

Quartz Veins ◽

Profound Influence ◽

Complex Shear ◽

Zone Development ◽

Granitoid Intrusions ◽

Geometry And Kinematics

Shear-zone-related gold–quartz veins in granitoid intrusions are commonly intimately associated with mafic dikes, which may have a profound influence on the localization, orientation, and kinematics of auriferous shear zones. The Bourlamaque pluton of the Val-d'Or district contains several economic auriferous shear zones, most of which follow and overprint diorite dikes. Mineralization in all deposits consists of quartz–tourmaline–pyrite veins in reverse- oblique orientation with a significant range of strike, dip, and slip direction. The geometry and kinematics of shear zone and vein array within the pluton is more complex than the simple conjugate pattern predicted for a deforming homogeneous intrusion. The stress tensor determined from the auriferous shear zones within the pluton indicates the same northerly-directed compression recorded by similar shear zones outside the pluton. This indicates that the complex shear zone and vein pattern within the pluton reflects the influence of diorite dikes, which acted as weak layers that were activated during subsequent deformation, showing the importance of layer anisotropy in auriferous shear zone development.The plunges of orebodies bear simple geometric relationships to the slip direction along a host shear zone: these are generally perpendicular to, or in some cases parallel to, the slip direction. Knowledge of the slip directions along activated dikes would therefore allow prediction of the possible plunge(s) of orebodies at early stages of exploration programs. Slip direction along an activated layer is controlled by the orientation of the layer with respect to the stress field and by the relative magnitudes of the three principal stresses. Using techniques developed for analysis of fault slip data, both parameters can be determined, provided there is a sufficient database, and slip direction can be predicted for activated layers of any orientations.

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Kinematic and geochronological constraints on shear deformation in the Ferriere-Mollières shear zone (Argentera-Mercantour Massif, Western Alps): implications for the evolution of the Southern European Variscan Belt

International Journal of Earth Sciences ◽

10.1007/s00531-018-1593-y ◽

2018 ◽

Vol 107 (6) ◽

pp. 2163-2189 ◽

Cited By ~ 13

Author(s):

Matteo Simonetti ◽

Rodolfo Carosi ◽

Chiara Montomoli ◽

Antonio Langone ◽

Enrico D’Addario ◽

...

Keyword(s):

Shear Deformation ◽

Shear Zone ◽

Western Alps ◽

Variscan Belt ◽

Geochronological Constraints

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Crystallographic and Seismic Anisotropies of Calcite at Different Depths: A Study Using Quantitative Texture Analysis by Neutron Diffraction

Minerals ◽

10.3390/min10010026 ◽

2019 ◽

Vol 10 (1) ◽

pp. 26 ◽

Cited By ~ 2

Author(s):

Michele Zucali ◽

Daniel Chateigner ◽

and Bachir Ouladdiaf

Keyword(s):

Neutron Diffraction ◽

Texture Analysis ◽

Shear Zone ◽

Shear Zones ◽

Orientation Distribution ◽

Western Alps ◽

S Wave ◽

Wide Variability ◽

Fold Belts ◽

Different Depths

Eight samples of limestones and marbles were studied by neutron diffraction to collect quantitative texture (i.e., crystallographic preferred orientations or CPO) of calcite deforming at different depths in the crust. We studied the different Texture patterns developed in shear zones at different depth and their influence on seismic anisotropies. Samples were collected in the French and Italian Alps, Apennines, and Paleozoic Sardinian basement. They are characterized by isotropic to highly anisotropic (e.g., mylonite shear zone) fabrics. Mylonite limestones occur as shear zone horizons within the Cenozoic Southern Domain in Alpine thrust-and-fold belts (Italy), the Briançonnais domain of the Western Alps (Italy-France border), the Sardinian Paleozoic back-thrusts, or in the Austroalpine intermediate units. The analyzed marbles were collected in the Carrara Marble, in the Austroalpine Units in the Central (Mortirolo) and Western Alps (Valpelline). The temperature and depth of development of fabrics vary from <100 ∘ C, to 800 ∘ C and depth from <10 km to about 30 km, corresponding from upper to lower crust conditions. Quantitative Texture Analysis shows different types of patterns for calcite: random to strongly textured. Textured types may be further separated in orthorhombic and monoclinic (Types A and B), based on the angle defined with the mesoscopic fabrics. Seismic anisotropies were calculated by homogenizing the single-crystal elastic tensor, using the Orientation Distribution Function calculated by Quantitative Texture Analysis. The resulting P- and S-wave anisotropies show a wide variability due to the textural types, temperature and pressure conditions, and dip of the shear planes.

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Suture zones and importance of strike-slip faulting for Variscan geodynamic reconstructions of the External Crystalline Massifs of the western Alps

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.180.6.483 ◽

2009 ◽

Vol 180 (6) ◽

pp. 483-500 ◽

Cited By ~ 28

Author(s):

Stéphane Guillot ◽

Silvia di Paola ◽

René-Pierre Ménot ◽

Patrick Ledru ◽

Maria Iole Spalla ◽

...

Keyword(s):

Shear Zone ◽

Bohemian Massif ◽

Western Alps ◽

Alkaline Magmatism ◽

Calc Alkaline ◽

Geodynamic Evolution ◽

Central European ◽

Back Arc ◽

Eastern Domain ◽

Geodynamic Reconstructions

Abstract This paper reviews the geodynamic evolution of the Belledonne, Grandes Rousses and Oisans massifs in the western Alps from Early Ordovician to Permian times. Three domains are distinguished. The eastern domain, which includes the NE Belledonne massif and the inner Oisans massif, records the subduction of the Central-European ocean along a NW dipping subduction zone. The western domain is marked by Cambro-Ordovician back-arc rifting (Chamrousse ophiolite) initiating the opening of the Rheic ocean. It was followed by Mid-Devonian obduction of the back-arc Chamrousse ophiolite, towards the NW in relation with the SE dipping subduction of the Saxo-Thuringian ocean. The central domain, including the SW part of the Belledonne massif, the Grandes Rousses massif and the outer Oisans massif, records the Devonian to Carboniferous orogenic activity that produced calc-alkaline magmatism, Mg-K granite intrusions and syn-collisional sedimentation related to Visean nappe stacking that we relate to the closure of the Saxo-Thuringian ocean. Based on tectonostratigraphic correlations we propose that these domains initially correspond to the northeastward extension of the Bohemian massif. During the late Carboniferous, the External Crystalline Massifs including Sardinia and Corsica were stretched towards the SW along the > 600 km long dextral External Crystalline Massifs shear zone. Offset of the Saxo-Thuringian and eo-Variscan suture zones from the Bohemian massif to the ECM suggests a possible dextral displacement of about 300 km along the ECM shear zone.

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P-T-testimation of deformation in low-grade quartz-feldspar-bearing rocks using thermodynamic modelling and40Ar/39Ar dating techniques: example of the Plan-de-Phasy shear zone unit (Briançonnais Zone, Western Alps)

Terra Nova ◽

10.1111/ter.12079 ◽

2013 ◽

Vol 26 (2) ◽

pp. 130-138 ◽

Cited By ~ 33

Author(s):

Pierre Lanari ◽

Yann Rolland ◽

Stéphane Schwartz ◽

Olivier Vidal ◽

Stéphane Guillot ◽

...

Keyword(s):

Shear Zone ◽

Western Alps ◽

Thermodynamic Modelling ◽

Low Grade

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Geometry and kinematics of Wager shear zone interpreted from structural fabrics and magnetic data

Canadian Journal of Earth Sciences ◽

10.1139/e90-055 ◽

1990 ◽

Vol 27 (4) ◽

pp. 590-604 ◽

Cited By ~ 5

Author(s):

J. R. Henderson ◽

J. Broome

Keyword(s):

Shear Zone ◽

Magnetic Data ◽

Hudson Bay ◽

Shear Direction ◽

The North ◽

Stable Orientation ◽

Axis Parallel ◽

Dextral Shear ◽

The Right ◽

Geometry And Kinematics

The Wager shear zone (WSZ) is characterized by progressive bending of northeast–southwest-trending aeromagnetic anomalies to the right as they merge with east–west-trending anomalies characterizing the shear zone. This feature indicates dextral net shear. Mapping of abundant and diverse asymmetrical structural fabric elements within the shear zone where it is well exposed along the south coast of Wager Bay, northwestern Hudson Bay, consistently confirmed dextral shear sense.Pervasive, dextral shear-zone mylonites were deformed by folds with hinges parallel to the shear direction (a folds), as well as by discrete, conjugate sinistral and dextral mylonitic shears. To form a folds in mylonites it is necessary for the mylonitic fabric to rotate out of a stable orientation in the plane of shear and flattening and also to rotate about an axis parallel to the shear direction, for which we have no general explanation.We conclude with the speculation that the WSZ is a strike-slip fault related to terminal collision of the Archean plate of Ungava with the Archean plate to the north marked by the 1.8 Ga Sugluk suture.

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