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Flow geometries of high-strain zones and resulting strain patterns (modified from Lin et al., 1998 and Jiang and Williams, 1998). (a) A high-strain zone; and (b) a domain in the zone in the initial (undeformed) state. (c) The domain in the final (deformed) state resulting from triclinic transpression (0 < 4 < 90 ), with both a boundary-parallel simple shear component and a boundary-normal pure shear component. _ g: shear strain rate; _ 3 a , _ 3 b and _ 3 c : the three principal components of the pure shear; 4: the angle between the shear direction and the _ 3 a direction; W: vorticity; VNS: vorticity-normal section (the section parallel to the shear direction and perpendicular to the shear zone boundary). (d) The domain in the final state resulting from simple shear, with monoclinic symmetry. (e) The domain in the final state resulting from a monoclinic transpression (4 ¼ 0 ). Other monoclinic situations (not shown) are 4 ¼ 90 and _ 3 a ¼ _ 3 c . (f)e(h) Equal-area lowerhemisphere projections showing variation and evolution with time of stretching lineations (Ls, subparallel to l 1 ) and poles to S-foliations (tS, subparallel to l 3 ) in an isochoric transpressional shear zone with constant strike length (_ 3 a ¼ 0) (from Lin et al., 1998). (f) Triclinic transpression (4 ¼ 20 ). Numerals 1, 2, 4, 6 and 20 are values of _ g=_ 3 b ratio. (g) Simple shear, with monoclinic symmetry. (h) Monoclinic transpression (4 ¼ 0 ). HSZB: high-strain zone boundary. White arrows indicate the evolution with time (increasing finite strain) for different _ g=_ 3 b 's. The dashed white arrow in (h) indicates ''switch'' of orientation of stretching lineations from horizontal to vertical.
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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, striation...
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... the difficulty of using stretching lineations to infer the shear direction. We then discuss how to distinguish Lc from Ls. Finally, we present a description of a natural high-strain zone and show how differentiating the two types of lineations can lead to recognition of new phenomena as well as kinematic insights into a highstrain zone. Fig. 2c; Jiang and Williams, 1998;Lin et al., 1998). These parameters can vary from one domain to ...
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... the deformation of the domain is simple shear (Fig. 2d). Otherwise it is a general shear (a thinning zone if _ 3 b < 0, and a thickening zone if _ 3 b > 0; Jiang and Williams, 1998). In the general shear case, if 4 ¼ 0 or 90 or _ 3 a ¼ _ 3 c , the flow geometry is reduced to monoclinic symmetry (Fig. 2e); otherwise, it has triclinic symmetry (Fig. 2c). The flow geometry of simple shear also ...
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... the deformation of the domain is simple shear (Fig. 2d). Otherwise it is a general shear (a thinning zone if _ 3 b < 0, and a thickening zone if _ 3 b > 0; Jiang and Williams, 1998). In the general shear case, if 4 ¼ 0 or 90 or _ 3 a ¼ _ 3 c , the flow geometry is reduced to monoclinic symmetry (Fig. 2e); otherwise, it has triclinic symmetry (Fig. 2c). The flow geometry of simple shear also has monoclinic symmetry. It should be noted that simple shear and pure shear are independent components and the cases of 4 ¼ 0 or 90 , or _ 3 a ¼ _ 3 c are probably rare. Therefore, the flow geometry of general shear is expected to be generally ...
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... the deformation of the domain is simple shear (Fig. 2d). Otherwise it is a general shear (a thinning zone if _ 3 b < 0, and a thickening zone if _ 3 b > 0; Jiang and Williams, 1998). In the general shear case, if 4 ¼ 0 or 90 or _ 3 a ¼ _ 3 c , the flow geometry is reduced to monoclinic symmetry (Fig. 2e); otherwise, it has triclinic symmetry (Fig. 2c). The flow geometry of simple shear also has monoclinic symmetry. It should be noted that simple shear and pure shear are independent components and the cases of 4 ¼ 0 or 90 , or _ 3 a ¼ _ 3 c are probably rare. Therefore, the flow geometry of general shear is expected to be generally triclinic, as concluded by Lin et al. (1998) and ...
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... modeling has shown that the symmetry of the S/Ls fabric (strain geometry) in a high-strain zone corresponds to that of the flow geometry, so long as the latter does not change during deformation (i.e. the flow is steady) (Fig. 2feh). In simple shear high-strain zones, Ls and poles to S all plot parallel to the vorticity-normal section (VNS) e the section parallel to the shear direction and perpendicular to the shear zone boundary, which is also the symmetry plane (Fig. 2g). In monoclinic transpressional or transtensional zones, they either plot parallel to the VNS ...
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... the flow geometry, so long as the latter does not change during deformation (i.e. the flow is steady) (Fig. 2feh). In simple shear high-strain zones, Ls and poles to S all plot parallel to the vorticity-normal section (VNS) e the section parallel to the shear direction and perpendicular to the shear zone boundary, which is also the symmetry plane (Fig. 2g). In monoclinic transpressional or transtensional zones, they either plot parallel to the VNS or parallel to the vorticity vector, and the VNS is still the symmetry plane (Fig. 2h). In triclinic high-strain zones, Ls varies continuously between the VNS and the vorticity vector and there is no symmetry plane, as illustrated in Fig. 2f by ...
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... to the vorticity-normal section (VNS) e the section parallel to the shear direction and perpendicular to the shear zone boundary, which is also the symmetry plane (Fig. 2g). In monoclinic transpressional or transtensional zones, they either plot parallel to the VNS or parallel to the vorticity vector, and the VNS is still the symmetry plane (Fig. 2h). In triclinic high-strain zones, Ls varies continuously between the VNS and the vorticity vector and there is no symmetry plane, as illustrated in Fig. 2f by means of a transpressional example where _ 3 b ¼ À_ 3 c , _ 3 a ¼ 0, and 4 ¼ 20 . It should be noted that apparent monoclinic strain geometry can potentially occur in domains ...
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... plane (Fig. 2g). In monoclinic transpressional or transtensional zones, they either plot parallel to the VNS or parallel to the vorticity vector, and the VNS is still the symmetry plane (Fig. 2h). In triclinic high-strain zones, Ls varies continuously between the VNS and the vorticity vector and there is no symmetry plane, as illustrated in Fig. 2f by means of a transpressional example where _ 3 b ¼ À_ 3 c , _ 3 a ¼ 0, and 4 ¼ 20 . It should be noted that apparent monoclinic strain geometry can potentially occur in domains within a high-strain zone with a triclinic flow geometry where the _ g=_ 3 b ratio is high and the finite strain is below a certain value (see Lin et al., ...
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... value (see Lin et al., 1998). On the other hand, perfectly monoclinic transpression (or transtension) without even infinitesimal perturbations is rare in nature, if it occurs at all, and the ''lineation switch'' (from horizontal to vertical when the strain increases to a critical value), theoretically predicted for transcurrent transpression ( Fig. 2h; Fossen and Tikoff, 1993;Tikoff and Greene, 1997), is unlikely to be common in natural high-strain zones (Jiang, 2005). Jiang (2005) demonstrated that even an infinitesimally small deviation from the perfect condition of monoclinic symmetry would lead the l 1 -axis (the ''lineation'') to rotate progressively, rather than ''switching'' ...
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... al. (2006), simple shear tends to be localized and pure shear tends to be widely distributed (see also Tikoff and Teyssier, 1994;Jones and Tanner, 1995). The result is that the simple shear/pure shear ratio generally varies across a highstrain zone, a phenomenon referred to as deformation path partitioning by Lin et al. (1999). As is evident from Fig. 2feh (in particular Fig. 2f), such variation can lead to significant variation in the orientation of Ls. This is further discussed below. (2) Variation in strain: Strain in high-strain zones is generally heterogeneous, and it is well known that the orientation of Ls can vary with strain. This is most evident in triclinic high-strain zones ...
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... tends to be localized and pure shear tends to be widely distributed (see also Tikoff and Teyssier, 1994;Jones and Tanner, 1995). The result is that the simple shear/pure shear ratio generally varies across a highstrain zone, a phenomenon referred to as deformation path partitioning by Lin et al. (1999). As is evident from Fig. 2feh (in particular Fig. 2f), such variation can lead to significant variation in the orientation of Ls. This is further discussed below. (2) Variation in strain: Strain in high-strain zones is generally heterogeneous, and it is well known that the orientation of Ls can vary with strain. This is most evident in triclinic high-strain zones (e.g. Fig. 2f), but also ...
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... 2feh (in particular Fig. 2f), such variation can lead to significant variation in the orientation of Ls. This is further discussed below. (2) Variation in strain: Strain in high-strain zones is generally heterogeneous, and it is well known that the orientation of Ls can vary with strain. This is most evident in triclinic high-strain zones (e.g. Fig. 2f), but also occurs in monoclinic transpressional and transtensional shear zones (e.g. Fig. 2h), and even in zones of simple shear (e.g. Lin and Williams, 1992b). (3) Variation in angle 4: Lineation orientation varies with the 4 value which is evident from figures 8e11 of Jiang and Williams (1998) and figure 9 of Lin et al. (1998). The ...
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... of Ls. This is further discussed below. (2) Variation in strain: Strain in high-strain zones is generally heterogeneous, and it is well known that the orientation of Ls can vary with strain. This is most evident in triclinic high-strain zones (e.g. Fig. 2f), but also occurs in monoclinic transpressional and transtensional shear zones (e.g. Fig. 2h), and even in zones of simple shear (e.g. Lin and Williams, 1992b). (3) Variation in angle 4: Lineation orientation varies with the 4 value which is evident from figures 8e11 of Jiang and Williams (1998) and figure 9 of Lin et al. (1998). The variation in 4 can be due to variation in shear direction and/or variation in orientation of _ ...
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... In the case of a transpressional zone of _ 3 b ¼ À_ 3 c and _ 3 a ¼ 0, the rotation due to boundary stretching is given by tan(4 f ) ¼ exp(_ 3 c t) tan(4 i ), where 4 i and 4 f are the angles between the striation and the _ 3 a direction before and after rotation, respectively, _ 3 c is the strain rate, and t is time. 4 i is equal to 4 in Fig. 2c. It is evident that rotation of striations only occurs in triclinic high-strain zones (4 i s 0 or 90 ) and is related to the pure shear component only. If rotation does occur and the striations are continuously being rotated away from the shear direction as they are being formed, no well-developed ridge-in-groove type striations are ...
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... When focusing on Archean gneiss domes, these are different from the structural patterns of the post-Archean linear orogenic belts related to subduction and collision (François et al., 2014). Archean tectonics is dominated by two models: horizontal tectonism and vertical tectonism (Hippertt & Davis, 2000;Lin, 2005;Lin et al., 2007;Lin & Beakhouse, 2013;Moyen et al., 2006;Parmenter et al., 2006;Van Kranendonk, 2011;Van Kranendonk et al., 2004). The horizontal tectonism is a plate tectonic-like process characterized by large-scale horizontal displacement and collision of different plates and their interactions (Calvert & Ludden, 1999). ...
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... At places dip direction changed to NNE-N-NNW (Fig. 6a) due to progressive shearing. Perfectly down dip (D 3 ) stretching lineations/ductile slickenlines (e.g., Lin et al., 2007) were developed on gently dipping (D 3 ) mylonitic foliation (Fig. 7a). Steeply plunging (D 3 ) stretching lineations (70-80 pitch) were present on the D 3 subvertical mylonitic foliation (Figs. ...
Structural mapping, strain analysis, and a variety of geochronological studies were carried out to determine the tectonothermal evolution of the Salem-Attur shear zone in the Southern Granulite terrane of South India. The Salem-Namakkal blocks containing the shear zone consisted of quartzofeldspathic gneiss, charnockite and mafic
granulite, and had undergone multiple phases of magmatism spanning over a period of 3.2–0.5 Ga. The rocks were deformed by four phases of deformation D1–D4. The D1 deformation was characterized by isoclinal and recumbent NE-SW trending F1 fold with a pervasive subhorizontal axial planar granulitic fabric, S1, and associated quartzofeldspathic leucosomes. Granulite metamorphism was dated at ca. 2.5–2.3 Ga. The F1 fold and S1 fabric were coaxially refolded by tight to isoclinal, upright to steeply inclined NE-SW trending F2 folds during D2 deformation. The D2 deformation was associated with F2 axial planar shear zones, crenulations and leucosomes, S2 fabric. Large-scale D2 shear zones characterized by high-temperature ductile shear fabric with a vertical flow
host syntectonic syenite pluton which was dated at ca. 2.5–2.4 Ga. A P-T condition of 7 kb/600 °C was inferred for the D2 deformation. The D3 deformation was characterized by NW-SE to E-W trending F3 folds and the Salem-Attur shear zone. The shear zone was a greenschist to amphibolite facies shear zone being characterized by mylonitic foliation and dominantly down-dip stretching lineation defined by quartz, biotite and hornblende minerals and dated at ca. 2.0 Ga. It indicated N-NNE vergence of thrusting with the mean kinematic vorticity number, Wm, as 0.7 suggesting general simple shear strain with 50% pure shear component. The D4 deformation was manifested as NNE-SSW striking strike-slip faults and NW-SE striking extensional normal faults. Pseudotachylite veins having an age of 1.9 Ga injected during strike-slip faulting and granite-pegmatite veins showing age of 0.8–0.5 Ga intruded during normal faulting. The Salem-Namakkal blocks thus recorded a longlived shearing history. We suggest that the Salem-Attur shear zone and other shear zones such as Palghat-Cauvery, Moyar, Bhavani, Karur-Kambam-Painavu-Trichur and Achankovil shear zones, were Paleoproterozoic intraterrane shear zones which were overprinted by Meso-Neoproterozoic-Cambrian ductile and brittle deformations.
... Vertical versus horizontal tectonics are two contrasting tectonic models for Archean deformation including crustal growth. Vertical tectonics is dominated by mantle plumes, mantle overturn and typified by the occurrence of dome and keel structures in many Archean granite-greenstone terrains (McGregor, 1951;Anhaeusser et al., 1969;Mareschal and West, 1980;Dixon and Summers, 1983;Collins, 1989Davis, 2000;Zhao et al., 2001;Van Kranendonk et al., 2004;Lin, 2005;Moyen et al., 2006;Parmenter et al., 2006;Lin et al., 2007;Zhao, 2009;Van Kranendonk, 2011;Lin and Beakhouse, 2013). Horizontal tectonics, an uniformitarian process, is similar to the modern style plate tectonics and characterized by some geological indicators such as subduction, collision, arc magmatism (Kröner, 1981;de Wit, 1998;Kusky and Polat, 1999;Calvert and Ludden, 1999;Zhai et al., 2003;Zhao et al., 2001). ...
... Currently, the mainstream opinion is that global tectonic regimes have changed progressively in the Archean: the Archean tectonics or crustal growth are dominated by vertical tectonism (mantle plume model), with small scale or limited horizontal tectonism similar to modern style plate tectonics (also be called ''proto-plate tectonics " ) existed (Lin, 2007;Van Kranendonk et al., 2007;Zhai, 2012;Li et al., 2015d,e). Recent advances in the structural evolution of the greenstone belts in the northwestern Superior Craton of the Canadian shield also show that the regional horizontal tectonism might synchronously present with vertical tectonism in the Archean, and the Neoarchean might represent a transition period from earlier periods dominated by vertical tectonism to later ones dominated by horizontal tectonism (Lin, 2005;Parmenter et al., 2006;Lin et al., 2007;Lin and Beakhouse, 2013). Thus, it can be seen that more studies of the early crustal growth and tectonic evolution are requisite for further understanding geodynamic regimes in the early Precambrian. ...
... The big density contrast between the underlying less dense granitic rocks and the denser iron-rich Anshan Group might offer a gravitationally favourable environment for downward adjoining rock flow (Hippertt and Davis, 2000). We suggest that the Baijiafen ductile shear zone was formed by the downward rock flow due to the BIF-type iron ore sagduction and synchronous Archean granite dome emplacement (Collins, 1989;Hippertt and Davis, 2000;Van Kranendonk et al., 2004;Lin, 2005;Moyen et al., 2006;Parmenter et al., 2006;Lin et al., 2007;Van Kranendonk, 2011;Lin and Beakhouse, 2013). These kinematic features of the shear zones well reflect the vertical tectonism in the Anshan greenstone belt. ...
The North China Craton is one of the major Archean to Paleoproterozoic cratons in the world and oldest craton in China, which preserves a large amount of ancient basement and abundant structures showing the early earth tectonics. The controversy over the Archean tectonic regimes has lasted several decades centering around horizontal and vertical tectonics, the two classical tectonic models for Archean times. Thus, more studies of the early crustal growth and tectonic evolution are requisite for better understanding geodynamic regimes in the early Precambrian. This study provides an example for revealing of Archean tectonics. The NWN-trending, ENE-dipping Baijiafen ductile shear zone is located in the eastern Anshan of the northeastern North China Craton and mainly comprises two types of gneisses, including the Chentaigou porphyritic granitic gneiss and the Baijiafen trondhjemitic gneiss. In this study, we have carried out a detailed study on the macrostructure, microstructure and fabric characteristics of the two main types of deformed gneisses within the shear zone. The ribbon structures formed by intensely elongated quartz grains are widespread in these gneisses. Well-developed mineral stretching lineations and asymmetric fabrics indicate an ESE-directed downward shearing. The quartz c-axis fabric patterns obtained by electron backscatter diffraction technique imply low to middle temperature non-coaxial deformation with active rhomb slip and basal slip. Deformation behaviors of minerals and quartz crystallographic preferred orientations demonstrate that the rocks underwent mylonitization at a temperature of 400–500 °C under greenschist facies metamorphic conditions. Dislocation creep is the main rock deformation mechanism within the shear zone. Finite strain measurement results suggest that the strain types of the shear zone are generally related to elongate-plane deformation, and the tectonites change from L-S- to LS-type across the shear zone. The strain intensity increases obviously towards east, and the Baijiafen gneiss unit is located within the high-strain zone. Kinematic vorticity values of gneisses indicate that the deformed rocks were produced by steady-state simple-shear dominated general shear. Based on abundant structural evidence and previous studies, we infer that the deformation of the Baijiafen ductile shear zone may have resulted from the downward adjoining rock flow during the sagduction of the banded iron formations and synchronous Archean granite dome emplacement, supporting a vertical tectonic regime in Archean times.
