TY - JOUR
T1 - Contrast in stress-strain history during exhumation between high- and ultrahigh-pressure metamorphic units in the Western Alps
T2 - Microboudinage analysis of piemontite in metacherts
AU - Omori, Yasutomo
AU - Barresi, Antonello
AU - Kimura, Nozomi
AU - Okamoto, Atsushi
AU - Masuda, Toshiaki
N1 - Funding Information:
We thank R. Compagnoni and T. Hirajima for constructive suggestions and H. Mori for the preparation of thin sections. We also thank R.J. Twiss, T. Takeshita, L. Menegon and two anonymous reviewers for helpful comments that improved the manuscript and for encouragement. This study was supported financially by the Japanese Society for the Promotion of Science (16340152 to TM).
Publisher Copyright:
© 2016.
PY - 2016/8/1
Y1 - 2016/8/1
N2 - Our analyses of microboudinage structures of piemontite grains embedded within six samples of metachert, one collected from an ultrahigh-pressure (UHP) metamorphic unit at Lago di Cignana in Italy of the Western Alps, and the other five from surrounding high-pressure (HP) metamorphic units in Italy and France, have revealed that the structures are all symmetrical in type, and were presumably produced in coaxial strain fields. Stress-strain analyses of the microboudinaged grains revealed significant contrasts in the stress and strain histories of the UHP and HP metamorphic units, with the differential stress recorded by the UHP sample being unequivocally lower than that recorded by the five HP samples. In addition, our analyses showed that the UHP sample underwent stress-relaxation during microboudinage, whereas the five HP samples did not. On the basis of these observations and analyses we discuss the mechanical decoupling of the UHP and HP units that led to different histories in differential stress between the units during exhumation of the Western Alps.
AB - Our analyses of microboudinage structures of piemontite grains embedded within six samples of metachert, one collected from an ultrahigh-pressure (UHP) metamorphic unit at Lago di Cignana in Italy of the Western Alps, and the other five from surrounding high-pressure (HP) metamorphic units in Italy and France, have revealed that the structures are all symmetrical in type, and were presumably produced in coaxial strain fields. Stress-strain analyses of the microboudinaged grains revealed significant contrasts in the stress and strain histories of the UHP and HP metamorphic units, with the differential stress recorded by the UHP sample being unequivocally lower than that recorded by the five HP samples. In addition, our analyses showed that the UHP sample underwent stress-relaxation during microboudinage, whereas the five HP samples did not. On the basis of these observations and analyses we discuss the mechanical decoupling of the UHP and HP units that led to different histories in differential stress between the units during exhumation of the Western Alps.
KW - High-and ultrahigh-pressure metamorphism
KW - Microboudinage
KW - Piemonte zone
KW - Piemontite
KW - Stress and strain
KW - Western Alps
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U2 - 10.1016/j.jsg.2016.06.004
DO - 10.1016/j.jsg.2016.06.004
M3 - Article
AN - SCOPUS:84975453413
VL - 89
SP - 168
EP - 180
JO - Journal of Structural Geology
JF - Journal of Structural Geology
SN - 0191-8141
ER -