Deformation fabrics of the Cima di Gagnone peridotite massif, Central Alps, Switzerland: evidence of deformation at low temperatures in the presence of water   总被引：1，自引：0，他引：1  

Philip Skemer  Ikuo Katayama  Shun-ichiro Karato 《Contributions to Mineralogy and Petrology》2006,152(1):43-51

We report a new observation of the olivine B-type lattice-preferred orientation (LPO), from the garnet peridotite at Cima di Gagnone, Switzerland. The olivine B-type fabric forms at low temperatures and/or high stress in the presence of water, and is of particular interest because it may be used to explain the trench-parallel shear-wave splitting that is often observed at subduction zones. In conjunction with the olivine B-type fabric, we have found strong orthopyroxene LPO that is identical to those formed under water-free conditions. This suggests that water may not have a significant effect on orthopyroxene fabric. From the olivine microstructure, we determine that a stress of 22 ± 8 MPa was applied during the deformation event that formed the olivine LPO. Using an olivine flow-law, and assuming geological strain-rates, we determine the temperature of deformation to be 800 ± 175°C. This does not preclude an ultra-deep origin for the ultramafic rocks at Cima di Gagnone, but indicates that much of the deformation recorded in the microstructure occurred at modest temperatures.Communicated by T.L. Grove  相似文献   

Experimental determination of partition coefficients of ten rare earth elements and barium between clinopyroxene and liquid in the synthetic silicate system at 20 kilobar pressure     

Akimasa Masuda  Ikuo Kushiro 《Contributions to Mineralogy and Petrology》1970,26(1):42-49

Two experiments were carried out at 20 kb pressure for the measurement of partition coefficients of ten lanthanides and barium between diopside clinopyroxene and liquid in the synthetic system diopside-enstatite-silica-H₂O. Starting materials are glass of two different compositions CaMgSi₂O₆ 56, MgSiO₃ 14, SiO₂ 30 weight % and CaMgSi₂O₆ 80, MgSiO₃ 20 weight %.In the experiment on the former composition, the partition coefficient increases regularly with decrease of ionic radii from La to Dy and decreases also regularly from Dy to Lu. In the experiment on the latter composition, stepwise shift of partition coefficient was observed between Dy and Er.The results suggest that the lanthanide cations occupy the site of 8-fold coordination in the clinopyroxene and that the partition coefficients depend on the ionic radii of lanthanide elements and also on the chemical composition of the starting material or heating process during the run.  相似文献   

An ultimate steady-state pattern of c-axis fabric of quartz in metamorphic tectonites     

Dr. Ikuo Hara 《International Journal of Earth Sciences》1971,60(3):1142-1173

The c-axis fabrics of quartz grains at the hinge zones of the orthorhombic buckle folds of quartz-rich layers which were collected from the Sambagawa crystalline schists of Shikoku, Japan, have been described and discussed. Especially, attempt to correlate the pattern of the quartz fabric with the strain picture has been made. It has been pointed out that the high concentration of quartz axes on two positions which are symmetrically placed on the plane of the longest principal axis and the shortest principal axis of the strain ellipsoid and at an angle of ca. 30 to the latter axis may be regarded as an ultimate steady-state pattern of preferred orientation of quartz axes developed under non-rotational two dimensional strain.

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Zusammenfassung Untersucht wurden die Quarzachsen-Gefüge in den Scheiteln der orthorhombischen Biegefalten der quarzreichen Lagen aus dem Sambagawa-Schiefer von Shikoku, Japan. Besonders wurde es versucht, die Quarzachsen-Orientierung mit dem Verformungsbild zu vergleichen. Zwei Quarzachsen-Maxima in der Ebene von der lÄngsten Hauptachse und der kürzesten Hauptachse des Verformungsellipsoides, die symmetrisch zur kürzesten Hauptachse im Abstand von etwa 30 liegen, wurden als bevorzugte Endlagenorientierung der Quarzachsen angesprochen, die durch die zweidimensionale Verformung ohne Rotation erzeugt wurden.

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Résumé La fabrique c-axiale des grains de quartz dans les charnières de plis, collectionnés dans les schistes cristallins de Sambagawa prés de Shikoku (Japon) sont décrits et interprétés dans cette étude. Il a été essayé spécialement de comparer le type de la fabrique du quartz au type de la déformation. Enfin il a été prouvé que la forte concentration des axes de quartz en deux lieux fixes des diagrammes, qui sont situés symétriquement aux deux axes principaux (long et petit) de l ellipsoide de déformation et qui forment un angle de 30 avec le petit axe, sont les positions définitives et stables de l'orientation préférée des axes de quartz qui à été produite par une déformation bi-dimensionelle sans rotation.

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