Zippered Shear Zone Model for Interacting Shear Zones in the Borborema Province, Brazil, as Constrained by U‐Pb Dating

The Borborema Province, northeastern Brazil, exhibit an extensive framework of shear zones in spatial proximity with syn-tectonic magmatism that makes it a perfect place to understand their relationship. In the eastern portion of this province an important dextral shear zone, that divides into two terranes, was originated during an escape tectonics after an oblique collision after a tectonic transport to NW. The recrystallization of quartz and feldspar shows a remarkable increase towards the shear zone, interpreted as a temperature increase during deformation. Thermodynamic modelling coupled with field relationship shows that high strain migmatitic textures such as stromatic structure was formed at ~650 °C and ~0.9 GPa prior to the shear development. Whereas low strain migmatites with schollen texture was formed at ~750 °C and ~0.7 GPa. We propose that the presence of melt during an oblique collision facilitated the emplacement of shear structures due to a thermal anomaly during the emplacement of syn-tectonic plutons.

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AGE CONSTRAINTS ON INTERACTING SHEAR ZONES IN SHEAR ZONE NETWORK: A CASE STUDY FROM THE BORBOREMA PROVINCE, NE BRAZIL

10.1130/abs/2019am-337260 ◽

2019 ◽

Author(s):

Carlos J. Archanjo ◽

◽

Carlos Avila Rodrigues

Keyword(s):

Shear Zone ◽

Shear Zones ◽

Borborema Province ◽

Age Constraints

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Integration of remote sensing and airborne geophysical data applied to geological mapping: a case study of the Vieirópolis region (Paraíba), Rio Grande do Norte Subprovince, Borborema Province

Geologia USP Série Científica ◽

10.11606/issn.2316-9095.v18-140834 ◽

2018 ◽

Vol 18 (3) ◽

pp. 89-103 ◽

Cited By ~ 2

Author(s):

José Ferreira de Araújo Neto ◽

Glenda Lira Santos ◽

Igor Manoel Belo de Albuquerque e Souza ◽

Sandra De Brito Barreto ◽

Lauro Cézar Montefalco de Lira Santos ◽

...

Keyword(s):

Remote Sensing ◽

Shear Zone ◽

Gamma Ray ◽

Rio Grande ◽

Shear Zones ◽

Geological Mapping ◽

Gamma Ray Spectrometry ◽

Borborema Province ◽

Geological Map

The integration of geological data obtained through fieldwork, remote sensing and airborne geophysics has been shown to be efficient in creation of precise geological maps. The Vieirópolis region, sited in the west of the Rio Grande do Norte Subprovince of the Borborema Province, is characteristically made up of rocks intensely deformed by transcurrent shear zones and late brittle structures which control the mineralization of gemmological and industrial minerals. ASTER GDEM and airborne geophysical images (magnetometry and gamma-ray spectrometry) were used in order to enhance the geological knowledge of this region and to facilitate the identification and delimitation of structures and lithologies mapped during stages of fieldwork. Thus, a geological map on a scale of 1:50,000 was achieved, made up of six main lithological units and three new shear zones (Vieirópolis, Lastro and São Pedro), as well as the NE-SW-trending Portalegre Shear Zone. Within the newly mapped structures, the Vieirópolis Shear Zone stands out due to its expressiveness. Aeromagnetometry data suggest that this zone originated on the edge of the Brejo das Freiras Subbasin, part of the Portalegre Shear Zone System. NW-SE, ESE-WNW and E-W lineaments were correlated to lesser extent brittle structures which sometimes transversely cut the regional foliation, allowing pegmatite fluids to rise. The RGB ternary composition map (K, eTh, eU) also corroborates the presence of these structures, besides helping to determine lithological units. In this case study, the integration of direct and indirect data showed to be essential for the understanding and producing of local geological map.

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Decratonization by rifting enables orogenic reworking and transcurrent dispersal of old terranes in NE Brazil

Scientific Reports ◽

10.1038/s41598-021-84703-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Carlos E. Ganade ◽

Roberto F. Weinberg ◽

Fabricio A. Caxito ◽

Leonardo B. L. Lopes ◽

Lucas R. Tesser ◽

...

Keyword(s):

Shear Zones ◽

Boundary Region ◽

The North ◽

Pan African ◽

Juvenile Material ◽

Oceanic Basin ◽

Borborema Province ◽

Isotopic Model ◽

Late Neoproterozoic

AbstractDispersion and deformation of cratonic fragments within orogens require weakening of the craton margins in a process of decratonization. The orogenic Borborema Province, in NE Brazil, is one of several Brasiliano/Pan-African late Neoproterozoic orogens that led to the amalgamation of Gondwana. A common feature of these orogens is that a period of extension and opening of narrow oceans preceded inversion and collision. For the case of the Borborema Province, the São Francisco Craton was pulled away from its other half, the Benino-Nigerian Shield, during an intermittent extension event between 1.0–0.92 and 0.9–0.82 Ga. This was followed by inversion of an embryonic and confined oceanic basin at ca. 0.60 Ga and transpressional orogeny from ca. 0.59 Ga onwards. Here we investigate the boundary region between the north São Francisco Craton and the Borborema Province and demonstrate how cratonic blocks became physically involved in the orogeny. We combine these results with a wide compilation of U–Pb and Nd-isotopic model ages to show that the Borborema Province consists of up to 65% of strongly sheared ancient rocks affiliated with the São Francisco/Benino-Nigerian Craton, separated by major transcurrent shear zones, with only ≈ 15% addition of juvenile material during the Neoproterozoic orogeny. This evolution is repeated across a number of Brasiliano/Pan-African orogens, with significant local variations, and indicate that extension weakened cratonic regions in a process of decratonization that prepared them for involvement in the orogenies, that led to the amalgamation of Gondwana.

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Correction and accuracy improvement of non-parallel shear zone model

MATEC Web of Conferences ◽

10.1051/matecconf/201820702002 ◽

2018 ◽

Vol 207 ◽

pp. 02002

Author(s):

Yaoke Wang ◽

Meng Kou ◽

Wei Ding ◽

Huan Ma ◽

Liangshan Xiong

Keyword(s):

Experimental Data ◽

Cutting Force ◽

Shear Zone ◽

Coordinate Transformation ◽

Chip Thickness ◽

Zone Model ◽

Aisi 1045 Steel ◽

Aisi 1045 ◽

Experimental Values ◽

1045 Steel

When applying the non-parallel shear zone model to predict the cutting process parameters of carbon steel workpiece, it is found that there is a big error between the prediction results and the experimental values. And also, the former approach to obtain the relevant cutting parameters of the non-parallel shear zone model by applying coordinate transformation to the parallel shear zone model has a theoretical error – it erroneously regards the determinant (|J|) of the Jacobian matrix (J) in the coordinate transformation as a constant. The shape of the shear zone obtained when |J| is not constant is drew and it is found that the two boundaries of the shear zone are two slightly curved surfaces rather than two inclined planes. Also, the error between predicted values and experimental values of cutting force and cutting thrust is slightly smaller than that of constant |J|. A corrected model where |J| is a variable is proposed. Since the specific values of inclination of the shear zone (α, β), the thickness coefficient of the shear zone (as) and the constants related to the material (f0, p) are not given in the former work, a method to obtain the above-mentioned five constants by solving multivariable constrained optimization problem based on experimental data was also proposed; based on the obtained experimental data of AISI 1045 steel workpiece cutting force, cutting thrust, chip thickness, the results of five above-mentioned model constants are obtained. It is found that, compared with prediction from uncorrected model, the cutting force and cutting thrust of AISI 1045 steel predicted by the corrected model with the obtained constants has a better agreement with the experimental values obtained by Ivester.

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The Dabie Extensional Tectonic System: Structural Framework

Journal of Geological Research ◽

10.1155/2012/369513 ◽

2012 ◽

Vol 2012 ◽

pp. 1-8 ◽

Cited By ~ 1

Author(s):

Quanlin Hou ◽

Hongyuan Zhang ◽

Qing Liu ◽

Jun Li ◽

Yudong Wu

Keyword(s):

Shear Zone ◽

Shear Zones ◽

Ultrahigh Pressure ◽

Metamorphic Complex ◽

The South ◽

Magma Intrusion ◽

The North ◽

Extensional Tectonic ◽

Mechanism Transition ◽

Tectonic System

A previous study of the Dabie area has been supposed that a strong extensional event happened between the Yangtze and North China blocks. The entire extensional system is divided into the Northern Dabie metamorphic complex belt and the south extensional tectonic System according to geological and geochemical characteristics in our study. The Xiaotian-Mozitan shear zone in the north boundary of the north system is a thrust detachment, showing upper block sliding to the NNE, with a displacement of more than 56 km. However, in the south system, the shearing direction along the Shuihou-Wuhe and Taihu-Mamiao shear zones is tending towards SSE, whereas that along the Susong-Qingshuihe shear zone tending towards SW, with a displacement of about 12 km. Flinn index results of both the north and south extensional systems indicate that there is a shear mechanism transition from pure to simple, implying that the extensional event in the south tectonic system could be related to a magma intrusion in the Northern Dabie metamorphic complex belt. Two 40Ar-39Ar ages of mylonite rocks in the above mentioned shear zones yielded, separately, ~190 Ma and ~124 Ma, referring to a cooling age of ultrahigh-pressure rocks and an extensional era later.

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Effect of kinematics of orogenic wedge on kinematic evolutionary paths and deformation profiles of major shear zones: An example from the eastern Himalaya

10.5194/egusphere-egu21-3824 ◽

2021 ◽

Author(s):

Pritam Ghosh ◽

Kathakali Bhattacharyya

Keyword(s):

Shear Zone ◽

Strain Softening ◽

Leading Edge ◽

Shear Zones ◽

Deformation History ◽

Progressive Deformation ◽

Trailing Edge ◽

Orogenic Wedge ◽

Transport Direction ◽

Evolutionary Paths

We examine how the deformation profile and kinematic evolutionary paths of two major shear zones with prolonged deformation history and large translations differ with varying structural positions along its transport direction in an orogenic wedge. We conduct this analysis on multiple exposures of the internal thrusts from the Sikkim Himalayan fold thrust belt, the Pelling-Munsiari thrust (PT), the roof thrust of the Lesser Himalayan duplex (LHD), and the overlying Main Central thrust (MCT). These two thrusts are regionally folded due to growth of the LHD and are exposed at different structural positions. The hinterlandmost exposures of the MCT and PT zones lie in the trailing parts of the duplex, while the foreland-most exposures of the same studied shear zones lie in the leading part of the duplex, and thus have recorded a greater connectivity with the duplex. The thicknesses of the shear zones progressively decrease toward the leading edge indicating variation in deformation conditions. Thickness-displacement plot reveals strain-softening from all the five studied MCT and the PT mylonite zones. However, the strain-softening mechanisms varied along its transport direction with the hinterland exposures recording dominantly dislocation-creep, while dissolution-creep and reaction-softening are dominant in the forelandmost exposures. Based on overburden estimation, the loss of overburden on the MCT and the PT zones is more in the leading edge (~26km and ~15km, respectively) than in the trailing edge (~10km and ~17km, respectively), during progressive deformation. Based on recalibrated recrystallized quartz grain thermometer (Law, 2014), the estimated deformation temperatures in the trailing edge are higher (~450-650&#176;C) than in the leading edge (350-550&#176;C) of the shear zones. This variation in the deformation conditions is also reflected in the shallow-crustal deformation structures with higher fracture intensity and lower spacing in the leading edge exposures of the shear zones as compared to the trailing edge exposures.The proportion of mylonitic domains and micaceous minerals within the exposed shear zones increase and grain-size of the constituent minerals decreases progressively along the transport direction. This is also consistent with progressive increase in mean Rs-values toward leading edge exposures of the same shear zones. Additionally, the &#945;-value (stretch ratio) gradually increases toward the foreland-most exposures along with increasing angular shear strain. Vorticity estimates from multiple incremental strain markers indicate that the MCT and PT zones generally record a decelerating strain path. Therefore, the results from this study are counterintuitive to the general observation of a direct relationship between higher Rs-value and higher pure-shear component. We explain this observation in the context of the larger kinematics of the orogen, where the leading edge exposures have passed through the duplex structure, recording the greatest connectivity and most complete deformation history, resulting in the weakest shear zone that is also reflected in the deformation profiles and strain attributes. This study demonstrates that the same shear zone records varying deformation profile, strain and kinematic evolutionary paths due to varying deformation conditions and varying connectivity to the underlying footwall structures during progressive deformation of an orogenic wedge.

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Comment on “Miocene to Quaternary tectonostratigraphic evolution of the middle section of the Burdur-Fethiye Shear Zone, south-western Turkey: Implications for the wide inter-plate shear zones. Tectonophysics 690, 336–354”

Tectonophysics ◽

10.1016/j.tecto.2017.05.027 ◽

2018 ◽

Vol 722 ◽

pp. 595-600 ◽

Cited By ~ 2

Author(s):

M. Cihat Alçiçek ◽

Lars W. van den Hoek Ostende ◽

Gerçek Saraç ◽

Alexey S. Tesakov ◽

Alison M. Murray ◽

...

Keyword(s):

Shear Zone ◽

Shear Zones ◽

Middle Section ◽

Western Turkey

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Lithospheric and sublithospheric deformation under the Borborema Province of northeastern Brazil from receiver function harmonic stripping

Solid Earth ◽

10.5194/se-10-893-2019 ◽

2019 ◽

Vol 10 (3) ◽

pp. 893-905 ◽

Cited By ~ 3

Author(s):

Gaelle Lamarque ◽

Jordi Julià

Keyword(s):

Lithospheric Mantle ◽

Seismic Anisotropy ◽

Receiver Function ◽

Seismic Station ◽

Atlantic Coast ◽

Shear Zones ◽

Receiver Functions ◽

Azimuthal Anisotropy ◽

Northeastern Brazil ◽

Borborema Province

Abstract. The depth-dependent anisotropic structure of the lithosphere under the Borborema Province in northeast Brazil has been investigated via harmonic stripping of receiver functions developed at 39 stations in the region. This method retrieves the first (k=1) and second (k=2) degree harmonics of a receiver function dataset, which characterize seismic anisotropy beneath a seismic station. Anisotropic fabrics are in turn directly related to the deformation of the lithosphere from past and current tectonic processes. Our results reveal the presence of anisotropy within the crust and the lithospheric mantle throughout the entire province. Most stations in the continental interior report consistent anisotropic orientations in the crust and lithospheric mantle, suggesting a dominant northeast–southwest pervasive deformation along lithospheric-scale shear zones developed during the Brasiliano–Pan-African orogeny. Several stations aligned along a northeast–southwest trend located above the (now aborted) Mesozoic Cariri–Potiguar rift display large uncertainties for the fast-axis direction. This non-azimuthal anisotropy may be related to a complex anisotropic fabric resulting from a combination of deformation along the ancient collision between Precambrian blocks, Mesozoic extension and thermomechanical erosion dragging by sublithospheric flow. Finally, several stations along the Atlantic coast reveal depth-dependent anisotropic orientations roughly (sub)perpendicular to the margin. These results suggest a more recent overprint, probably related to the presence of frozen anisotropy in the lithosphere due to stretching and rifting during the opening of the South Atlantic.

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The internal structure and composition of a plate boundary-scale serpentinite shear zone: The Livingstone Fault, New Zealand

10.5194/se-2019-62 ◽

2019 ◽

Author(s):

Matthew S. Tarling ◽

Steven A. F. Smith ◽

James M. Scott ◽

Jeremy S. Rooney ◽

Cecilia Viti ◽

...

Keyword(s):

New Zealand ◽

Internal Structure ◽

Shear Zone ◽

Plate Boundary ◽

Shear Zones ◽

East Side ◽

Local Dispersion ◽

Fine Grained ◽

Shear Sense ◽

Tectonic Settings

Abstract. Deciphering the internal structural and composition of large serpentinite-dominated shear zones will lead to an improved understanding of the rheology of the lithosphere in a range of tectonic settings. The Livingstone Fault in New Zealand is a > 1000 km long terrane-bounding structure that separates the basal portions (peridotite; serpentinised peridotite; metagabbros) of the Dun Mountain Ophiolite Belt from quartzofeldspathic schists of the Caples or Aspiring Terranes. Field and microstructural observations from eleven localities along a strike length of c. 140 km show that the Livingstone Fault is a steeply-dipping, serpentinite-dominated shear zone tens to several hundreds of metres wide. The bulk shear zone has a pervasive scaly fabric that wraps around fractured and faulted pods of massive serpentinite, rodingite and partially metasomatised quartzofeldspathic schist up to a few tens of metres long. S-C fabrics and lineations in the shear zone consistently indicate a steep Caples-side-up (i.e. east-side-up) shear sense, with significant local dispersion in kinematics where the shear zone fabrics wrap around pods. The scaly fabric is dominated (> 98 vol %) by fine-grained (&ll; 10 μm) fibrous chrysotile and lizardite/polygonal serpentine, but infrequent (

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