Structural Setting, Paleomagnetism, and Magnetic Fabric of Miocene Plutons in a Transpressional Sinistral Shear Zone, Tonalá, Chiapas, Mexico: Evidence of Shortening During Magma Emplacement

Tectonics ◽  
2021 ◽  
Vol 40 (2) ◽  
Author(s):  
Roberto S. Molina Garza ◽  
John W. Geissman ◽  
Tomás Peña Alonso ◽  
Jorge Aranda Gómez ◽  
Timothy Wawrzyniec
Keyword(s):  
Shear Zone ◽  
Magnetic Fabric ◽  
Structural Setting ◽  
Magma Emplacement

Magnetic fabric and structural setting of Plio-Pleistocene clayey units in an extensional regime: the Tyrrhenian margin of central Italy

1994 ◽  
Vol 16 (9) ◽  
pp. 1243-1257 ◽  
Author(s):  
Leonardo Sagnotti ◽  
Claudio Faccenna ◽  
Renato Funiciello ◽  
Massimo Mattei
Keyword(s):  
Central Italy ◽  
Magnetic Fabric ◽  
Structural Setting

scholarly journals Localization effect on AMS fabric revealed by microstructural evidence across small-scale shear zone in marble

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
V. K. Kusbach ◽  
M. Machek ◽  
Z. Roxerová ◽  
M. Racek ◽  
P. F. Silva
Keyword(s):  
Shear Zone ◽  
Magnetic Fabric ◽  
Small Scale ◽  
Angular Deviation ◽  
Localized Deformation ◽  
Fine Grained ◽  
Localization Of Deformation ◽  
Strain Relationship ◽  
Rock Microstructure ◽  
Scale Shear

AbstractAnisotropy of magnetic susceptibility (AMS) is regularly applied as a tool to infer structural analysis of deformation and flow in rocks, particularly, with low anisotropy. AMS integrates the magnetic signature of crystallographic and shape preferred orientation of all mineral grains present in the rock microstructure. Those preferred orientations result from multiple processes affecting the rock during its evolution, therefore the desirable AMS-strain relationship is not straightforward. Here we show that due to localization of deformation, AMS is indirectly dependent on the magnitude and character of deformation. In order to decipher the AMS-strain relationship, AMS studies should be accompanied by microstructural analyses combined with numerical modelling of magnetic fabric. A small-scale shear zone produced by single deformation event was studied. The resultant AMS fabric is “inverse” due to the presence of Fe-dolomite and controlled by calcite and dolomite crystallographic preferred orientations. The localized deformation resulted in the angular deviation between macroscopic and magnetic fabric in the shear zone, systematically increasing with increasing strain. This is a result of the presence of microstructural subfabrics of coarse porphyroclasts and fine-grained recrystallized matrix produced by localization.The localization of deformation is a multiscale and widespread process that should be considered whenever interpreting AMS in deformed rocks and regions.

Palaeomagnetic and anisotropy of magnetic susceptibility data bearing on the emplacement of the Western Granite, Isle of Rum, NW Scotland

2008 ◽  
Vol 146 (3) ◽  
pp. 419-436 ◽  
Author(s):  
M. S. PETRONIS ◽  
B. O'DRISCOLL ◽  
V. R. TROLL ◽  
C. H. EMELEUS ◽  
J. W. GEISSMAN
Keyword(s):  
Magnetic Susceptibility ◽  
Country Rock ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Magnetic Fabric ◽  
Contact Aureole ◽  
Data Set ◽  
The North ◽  
Early Paleocene ◽  
Magma Emplacement

AbstractThe Western Granite is the largest of several granitic bodies around the margin of the Rum Central Igneous Complex. We report palaeomagnetic and anisotropy of magnetic susceptibility (AMS) data that bear on the emplacement and deformation of the Western Granite. The collection includes samples from 27 sites throughout the Western Granite, five sites in adjacent feldspathic peridotite, and two sites in intermediate to mafic hybrid contact aureole rocks. Palaeomagnetic data from 22 of the 27 sites in the granite provide an in situ group mean D = 213.2°, I = −69.5°, α95 = 5.5° that is discordant to an early Paleocene reverse polarity expected field (about 184°, −66°, α95 = 4.3°). The discrepancy is eliminated by removing an inferred 15° of northwest-side-down tilting about a best fit horizontal tilt axis trending 040°. Data from the younger peridotite and hybrid rocks of the Rum Layered Suite provide an in situ group mean of D = 182.6°, I = −64.8°, α95 = 4.0°, which is statistically indistinguishable from an early Paleocene expected field, and imply no post-emplacement tilting of these rocks since remanence acquisition. The inferred tilt recorded in the Western Granite, which did not affect the younger Layered Suite, suggests that emplacement of the ultrabasic rocks resulted in roof uplift and associated tilt of the Western Granite to make space for mafic magma emplacement. Magnetic fabric magnitude and susceptibility parameters yield two subtle groupings in the Western Granite AMS data set. Group 1 data, defined by rocks from exposures to the east and south, have comparatively high bulk susceptibilities (Kmean, 29.51 × 10−3 in SI system), stronger anisotropies (Pj, 1.031) and oblate susceptibility ellipsoids. Group 2 data, from rocks in the west part of the pluton, have lower values of Kmean (15.89 × 10−3 SI) and Pj (1.014), and triaxial susceptibility ellipsoids. Magnetic lineations argue for emplacement of the granite as a tabular sheet from the south–southeast toward the north and west. Moderate to steeply outward-dipping magnetic foliations, together with deflection of the country rock bedding in the north, are consistent with doming accompanying magma emplacement.

The magnetic fabric of metasediments in a detachment shear zone: the example of Tinos Island (Greece)

2000 ◽  
Vol 321 (2) ◽  
pp. 219-236 ◽  
Author(s):  
C. Aubourg ◽  
R. Hebert ◽  
L. Jolivet ◽  
G. Cartayrade
Keyword(s):  
Shear Zone ◽  
Magnetic Fabric
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