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Qiuli Li - One of the best experts on this subject based on the ideXlab platform.
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late triassic extensional tectonics in the northern north china craton insights from a multidisciplinary study of the wangtufang pluton
Journal of Asian Earth Sciences, 2020Co-Authors: Michel Faure, Yan Chen, Lingtong Meng, Jipei Zeng, Yin Wang, Qiuli LiAbstract:Abstract To better understand Late Triassic tectonic setting in the northern North China Craton (NCC), the emplacement mechanism of the Wangtufang pluton, which recorded the synmagmatic regional tectonic signature, has been investigated. Zircon U-Pb ages, and Hf isotopic data, and whole-rock geochemical analyses suggest that the Late Triassic Wangtufang pluton composed of syenogranite and diorite is derived from partial melting of lower crust with some depleted mantle components. Both the syenogranite and diorite appear isotropic. Anisotropy of magnetic susceptibility and gravity studies have been carried out to characterize internal fabrics and shape of the pluton. The diorite forms just thin remnants above the syenogranite. The syenogranite with a series of NW-SE trending dykes intruded into the diorite and its country rocks. In the syenogranite, the gently dipping magnetic foliations strike nearly parallel to the pluton border. The shallow plunging magnetic Lineations mainly strike NE–SW. Combining NE-SW trending elongated subsurface shape with central root, unflat bottom, and moderate- to high- inward dipping sidewalls, the syenogranite could be considered as a lopolith-like intrusion. The syenogranite was likely emplaced by inflation of magma pulses from its central conduit and built up by floor depression. Emplacement of the syenogranite was in an extensional setting, considering: (1) the NE–SW striking magnetic Lineation, (2) the NE–SW trending elongated subsurface pluton shape, and (3) the orthogonal NW–SE striking syenogranitic dykes considered as tension gashes during the NE–SW trending extension. The Wangtufang pluton provides reliable arguments to the Late Triassic intracontinental extensional setting already suggested in the northern NCC.
Paul F. Williams - One of the best experts on this subject based on the ideXlab platform.
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Importance of differentiating ductile slickenside striations from stretching Lineations and variation of shear direction across a high-strain zone
Journal of Structural Geology, 2007Co-Authors: Shoufa Lin, Dazhi Jiang, Paul F. WilliamsAbstract:Shear direction is an important parameter in the kinematic interpretation of high-strain zones. Recent developments in the study of high-strain zones show that there is no simple relationship between the orientation of stretching Lineations and the shear direction and it is difficult to use the former to determine the latter. In contrast, striations on C-surfaces, a product of ductile deformation, form parallel to the shear direction. It is therefore important for the kinematic interpretation of high-strain zones to differentiate such striations from stretching Lineations. Ductile striations are much more common in natural high-strain zones than reported in the literature. We discuss how to differentiate the two types of Lineations and describe a natural high-strain zone example from the Superior craton of Canada. The striation data show that the shear direction of the high-strain zone varies from subhorizontal to moderately plunging across the strike of the zone. We conclude that well-developed ridgein-groove type striations are a reliable indicator of the shear direction. We also discuss situations where the orientation of stretching Lineations can potentially be used as an indicator of shear direction. 2007 Elsevier Ltd. All rights reserved.
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origin of a vertical Lineation in conjugate transcurrent shear zones at broken hill australia
Tectonophysics, 2001Co-Authors: Paul F. Williams, R H VernonAbstract:Abstract Shear-zones at Little Broken Hill are interpreted as conjugate transcurrent structures. They developed before dolerite dyke emplacement in response to N–S horizontal shortening. They were reactivated as conjugate transcurrent structures after dyke emplacement in response to horizontal E–W shortening. Shear-zone deformation was accompanied by retrograde metamorphic conditions for at least the later part of the history. Displacement on the shear-zones was accommodated by coeval deformation within the shear-zone-bound blocks. This deformation involved shear on the pre shear-zone S1 foliation and resulted in incomplete retrogression of earlier peak metamorphic mineral assemblages. It also resulted in a vertical extension and a component of dip slip on the shear-zones. A near-vertical stretching-Lineation occurs parallel to the intersection of the shear-zones and is interpreted as a localised response to an overall vertical extension. Localisation of the Lineation is explained in terms of grain-scale partitioning of deformation mechanisms. In the country rock, vertical extension was achieved by shear on S1 with very little intragranular deformation. Consequently this deformation failed to produce a Lineation. In the shear-zones, where all fabric elements were tending to vertical, the only deformation mechanism available for vertical extension was intragranular deformation, which resulted in a shape fabric, viz the stretching-Lineation. Shear within the zones had both horizontal and vertical components parallel to the shear-zone foliation. Because the shear was achievable by slip on the foliation and did not involve intragranular mechanisms, it did not modify the Lineation. Late shear-zone movement resulted in local crenulation of the shear-zone foliation about the early-formed stretching-Lineation. The result was vertical plunging folds and a more pronounced “stretching” Lineation. It is concluded that stretching-Lineations in shear-zones should not be considered indicators of movement direction or of instantaneous or finite strain axes.
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transpression or transtension zones of triclinic symmetry natural example and theoretical modelling
Geological Society London Special Publications, 1998Co-Authors: Shoufa Lin, Dazhi Jiang, Paul F. WilliamsAbstract:We describe a natural shear zone with triclinic symmetry, present a general model for triclinic shear zones based on natural examples, and investigate the kinematics and strain geometry within such zones. In the Roper Lake shear zone in the Canadian Appalachians, the orientation of a stretching Lineation is oriented approximately down-dip near the shear zone boundary and becomes gradually shallower towards the centre. The structures in the central portion of the shear zone exhibit approximately monoclinic symmetry where the poles to both the S- and C-surfaces, the stretching Lineation on the S-surfaces and the striations on the C-surfaces all plot in a great circle girdle. However, the Lineations from the marginal portion do not plot in the same girdle, and the bulk symmetry of the shear zone is triclinic. Theoretical modelling shows that the observed strain geometry can be interpreted by an oblique transpression with a larger ratio of simple shear to pure shear in the centre of the shear zone than in the margin. The latter suggests a higher degree of localization of the zone boundary-parallel movement component relative to the boundary-normal compression component. We emphasize that since the imposed boundary displacements for most natural shear zones lie between dip slip and strike slip, their movement pictures are generally triclinic; monoclinic shear zones are special end members. Structural data that exhibit monoclinic symmetry do not necessarily mean that they resulted from a monoclinic movement picture; the present modelling demonstrates that a triclinic movement picture with a high ratio of boundary-parallel movement to boundary-normal movement can result in apparent monoclinic structural geometry. The results of the modelling also show that the simple statement made for simple shear zones that stretching Lineations will align with, and therefore indicate, the shear direction cannot be extrapolated to three dimensional transpressional(-transtensional) shear zones.
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The geometrical relationship between the stretching Lineation and the movement direction of shear zones
Journal of Structural Geology, 1993Co-Authors: Paul F. WilliamsAbstract:Abstract The geometrical relationship between foliations and Lineations in shear zones is considered quantitatively, assuming that the internal structures of shear zones have monoclinic symmetry. The common practice of directly correlating the pitch (or plunge) of the stretching Lineation with the obliquity of the shear direction is challenged. It is the orthogonal projection of the stretching Lineation on the shear zone boundary that is parallel to the shear direction. A shear zone is parallel to a plane containing both the pole to the symmetry plane and the strike of the shear zone, and the shear direction is parallel to the intersection of the symmetry plane and the shear zone boundary. The symmetry plane is determined by the stretching Lineation and the poles to the S -foliation. The implications of this study for the interpretation of shear zones are discussed with reference to an actual example.
Michel Faure - One of the best experts on this subject based on the ideXlab platform.
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late triassic extensional tectonics in the northern north china craton insights from a multidisciplinary study of the wangtufang pluton
Journal of Asian Earth Sciences, 2020Co-Authors: Michel Faure, Yan Chen, Lingtong Meng, Jipei Zeng, Yin Wang, Qiuli LiAbstract:Abstract To better understand Late Triassic tectonic setting in the northern North China Craton (NCC), the emplacement mechanism of the Wangtufang pluton, which recorded the synmagmatic regional tectonic signature, has been investigated. Zircon U-Pb ages, and Hf isotopic data, and whole-rock geochemical analyses suggest that the Late Triassic Wangtufang pluton composed of syenogranite and diorite is derived from partial melting of lower crust with some depleted mantle components. Both the syenogranite and diorite appear isotropic. Anisotropy of magnetic susceptibility and gravity studies have been carried out to characterize internal fabrics and shape of the pluton. The diorite forms just thin remnants above the syenogranite. The syenogranite with a series of NW-SE trending dykes intruded into the diorite and its country rocks. In the syenogranite, the gently dipping magnetic foliations strike nearly parallel to the pluton border. The shallow plunging magnetic Lineations mainly strike NE–SW. Combining NE-SW trending elongated subsurface shape with central root, unflat bottom, and moderate- to high- inward dipping sidewalls, the syenogranite could be considered as a lopolith-like intrusion. The syenogranite was likely emplaced by inflation of magma pulses from its central conduit and built up by floor depression. Emplacement of the syenogranite was in an extensional setting, considering: (1) the NE–SW striking magnetic Lineation, (2) the NE–SW trending elongated subsurface pluton shape, and (3) the orthogonal NW–SE striking syenogranitic dykes considered as tension gashes during the NE–SW trending extension. The Wangtufang pluton provides reliable arguments to the Late Triassic intracontinental extensional setting already suggested in the northern NCC.
Massimo Mattei - One of the best experts on this subject based on the ideXlab platform.
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the origin of tectonic Lineation in extensional basins combined neutron texture and magnetic analyses on undeformed clays
Earth and Planetary Science Letters, 2005Co-Authors: Francesca Cifelli, Massimo Mattei, Martin Chadima, Ann M Hirt, Anke HansenAbstract:Abstract In extensional sedimentary basins fine-grained sediments that appear undeformed at the outcrop scale can carry a magnetic fabric consistent with the regional deformation pattern. The origin of the magnetic Lineation, which is often found in extensional basins, is not yet well understood. In clays from extensional basins in southern Italy, the magnetic Lineation is tectonically controlled and oriented perpendicular to the main normal faults. A combined analysis of magnetic and mineral fabrics was made to gain insight into the processes that lead to a Lineation in extensional settings. Low-field, high-field and low-temperature susceptibility measurements were used to distinguish the ferrimagnetic and paramagnetic contributions to the magnetic susceptibility and its anisotropy. The magnetic anisotropy of the sediments is predominantly carried by paramagnetic phyllosilicates. Neutron texture analysis was used to evaluate the spatial distribution of chlorite basal planes. Results demonstrate that the orientation of the magnetic Lineation is related to the spatial distribution of chlorite, lying parallel to the common axis of differently oriented basal planes. A quantitative correlation between the magnetic and rock fabric was made comparing the low- and high-field magnetic anisotropy (AMS, HFA) to the theoretical anisotropy calculated from the chlorite-preferred orientation. A good linear correlation is found between the degree of theoretical anisotropy and the AMS and HFA. Results show that the integrated approach of magnetic and mineral fabric investigations represents a valid alternative tool for detecting grain scale and regional deformation patterns in weakly deformed extensional basins, where macroscopic evidence of deformation is often not visible.
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extensional tectonics in the amantea basin calabria italy a comparison between structural and magnetic anisotropy data
Tectonophysics, 1999Co-Authors: Massimo Mattei, Fabio Speranza, Alessio Argentieri, Federico Rossetti, Leonardo Sagnotti, R FunicielloAbstract:Abstract We report on structural and anisotropy of magnetic susceptibility (AMS) results from the Upper Miocene sediments of the Amantea basin, located on the Tyrrhenian coast of the Calabrian Arc (Southern Italy). The stratigraphic succession of the basin is organized in three depositional sequences, separated by two major angular unconformities. Detailed geological mapping and structural analysis demonstrate that the stratigraphic evolution of the Amantea basin is strongly controlled by a synsedimentary extensional tectonic regime. Several NNE-SSW-trending normal fault arrays with large scatter in inclination values have been interpreted as due to a domino faulting mechanism, consistent with a WNW-ESE stretching direction. AMS data have been obtained for 13 sites, both in the not constrained in age first depositional sequence (3 sites), and in the upper Tortonian-lower Messinian clays from the second depositional sequence (10 sites). All the sites show a strong magnetic foliation parallel to the bedding planes, and a well defined magnetic Lineation subparallel to the local bedding dip directions. The magnetic Lineations cluster around a WNW-ESE trend and are parallel to the stretching directions inferred by fault-slip analysis and basin architecture. These new data then confirm the possibility to use the magnetic Lineation to map the strain trajectory in weakly deformed extensional sedimentary basins. Paleomagnetic data (from previous studies) show that the whole Calabrian block underwent a 15°–20° clockwise rotation probably in the Pleistocene, postdating the extensional tectonic events which controlled the Amantea basin geometry. Therefore we suggest for the Amantea basin an original E-W-oriented stretching direction, which may be considered as the older extensional direction characterizing the Late Miocene evolution of the southern Tyrrhenian Sea domain.
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magnetic fabric of weakly deformed clay rich sediments in the italian peninsula relationship with compressional and extensional tectonics
Tectonophysics, 1997Co-Authors: Massimo Mattei, Leonardo Sagnotti, Claudio Faccenna, R FunicielloAbstract:Abstract We present the results of anisotropy of magnetic susceptibility (AMS) analyses carried out in weakly deformed Neogene and Quaternary clay-rich sediments from different compressional and extensional settings of the Italian peninsula, discussing the relationships between the magnetic fabrics and the tectonic settings. A well defined magnetic Lineation of tectonic origin was found in several structures. The studied cases indicate that the AMS analysis of fine-grained sediments constitutes a powerful method to better constrain the tectonic evolution of sedimentary basins, where strain markers are not available. In the extensional basins the magnetic Lineation coincides almost always with the stretching direction, obtained from mesostructral analysis of faults and joints, and it is generally aligned with the bedding dip. This geometric relationship is different in the compressional basins, where the magnetic Lineation is almost parallel to the bedding strike. In both the extensional and compressional environments the magnetic Lineation was acquired during the early stages of deformation, when the bedding was still sub-horizontal and it was not modified by the subsequent tectonic phases.
R Funiciello - One of the best experts on this subject based on the ideXlab platform.
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extensional tectonics in the amantea basin calabria italy a comparison between structural and magnetic anisotropy data
Tectonophysics, 1999Co-Authors: Massimo Mattei, Fabio Speranza, Alessio Argentieri, Federico Rossetti, Leonardo Sagnotti, R FunicielloAbstract:Abstract We report on structural and anisotropy of magnetic susceptibility (AMS) results from the Upper Miocene sediments of the Amantea basin, located on the Tyrrhenian coast of the Calabrian Arc (Southern Italy). The stratigraphic succession of the basin is organized in three depositional sequences, separated by two major angular unconformities. Detailed geological mapping and structural analysis demonstrate that the stratigraphic evolution of the Amantea basin is strongly controlled by a synsedimentary extensional tectonic regime. Several NNE-SSW-trending normal fault arrays with large scatter in inclination values have been interpreted as due to a domino faulting mechanism, consistent with a WNW-ESE stretching direction. AMS data have been obtained for 13 sites, both in the not constrained in age first depositional sequence (3 sites), and in the upper Tortonian-lower Messinian clays from the second depositional sequence (10 sites). All the sites show a strong magnetic foliation parallel to the bedding planes, and a well defined magnetic Lineation subparallel to the local bedding dip directions. The magnetic Lineations cluster around a WNW-ESE trend and are parallel to the stretching directions inferred by fault-slip analysis and basin architecture. These new data then confirm the possibility to use the magnetic Lineation to map the strain trajectory in weakly deformed extensional sedimentary basins. Paleomagnetic data (from previous studies) show that the whole Calabrian block underwent a 15°–20° clockwise rotation probably in the Pleistocene, postdating the extensional tectonic events which controlled the Amantea basin geometry. Therefore we suggest for the Amantea basin an original E-W-oriented stretching direction, which may be considered as the older extensional direction characterizing the Late Miocene evolution of the southern Tyrrhenian Sea domain.
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magnetic fabric of weakly deformed clay rich sediments in the italian peninsula relationship with compressional and extensional tectonics
Tectonophysics, 1997Co-Authors: Massimo Mattei, Leonardo Sagnotti, Claudio Faccenna, R FunicielloAbstract:Abstract We present the results of anisotropy of magnetic susceptibility (AMS) analyses carried out in weakly deformed Neogene and Quaternary clay-rich sediments from different compressional and extensional settings of the Italian peninsula, discussing the relationships between the magnetic fabrics and the tectonic settings. A well defined magnetic Lineation of tectonic origin was found in several structures. The studied cases indicate that the AMS analysis of fine-grained sediments constitutes a powerful method to better constrain the tectonic evolution of sedimentary basins, where strain markers are not available. In the extensional basins the magnetic Lineation coincides almost always with the stretching direction, obtained from mesostructral analysis of faults and joints, and it is generally aligned with the bedding dip. This geometric relationship is different in the compressional basins, where the magnetic Lineation is almost parallel to the bedding strike. In both the extensional and compressional environments the magnetic Lineation was acquired during the early stages of deformation, when the bedding was still sub-horizontal and it was not modified by the subsequent tectonic phases.
