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The small island of Groix in southern Brittany, France, is well known for its excellent outcrops of Variscan blueschists, eclogites and garnetiferous micaschists that define a Late-Devonian suture between Gondwana and Armorica. The kinematics of polyphase deformation in these rocks is reconstructed based on 3D microstructural analysis of inclusion trails in garnet- and pseudomorphed lawsonite porphyroblasts using multiple, differently oriented thin sections of single samples and X-ray tomography. Three sets of inclusion trails striking NE-SW, NNW-SSE and WNW-ESE are interpreted to witness a succession of different crustal shortening directions orthogonal to these trends. The curvature sense of sigmoidal- and spiral-shaped inclusion trails of the youngest set is shown to be consistent with southward thrusting or northward subduction of Gondwana under Armorica, provided that these microstructures developed by overgrowth of actively forming crenulations instead of the previously envisaged 'snowball' mechanism. The latter predicts an opposite thrusting direction which is at odds with the regional tectono-metamorphic zonation in the Ibero-Armorican Arc. Strongly non-cylindrical folds locally found on Ile de Groix are reinterpreted as fold-interference structures instead of having formed by progressive shearing. Six additional samples of lower-grade footwall units of the Groix ophiolite were also studied. The oldest inclusion trails in these rocks have similar trends as the youngest one in Ile de Groix. Our new inclusion-trail data for southern Brittany bear a strong resemblance with those documented previously in the north-western Iberian Massif and suggest about 20° anticlockwise rotation of Iberia during the early Cretaceous opening of the Gulf of Biscay. [ABSTRACT FROM AUTHOR]

The Ylitornio area in northern Finland is a typical example of a poorly outcropping, multiply deformed, complex Precambrian terrain. U-Pb, Sm-Nd and geochemical data from metavolcanic, metasedimentary and plutonic rocks combined with structural data define the lithodemic units and tectonostratigraphy of the area. The Mellajoki, Martimo, Hosiojoki, Kierovaara and Uusivirka suites form the Ylitornio nappe complex. Although main thrust stacking had occurred between 1.921.89 Ga, later reverse faulting probably continued until 1.78 Ga. The Váystájá bimodal volcanic rocks (2.09-2.05 Ga) from the Martimo suite are plume-related EMORB-OIB rocks formed during a continent breakup. The Kaskimaa greywacke of the Martimo suite is inferred to represent sedimentation in a deepening rift basin in the continental margin. The coeval Hosiojoki felsic rocks with A-type affinity and the Kierovaara suite granites (2.00-1.98 Ga) represent dry melting of a dominantly 2.1-2.05 Ga contaminated mafic underplate, and hydrous melting of both the mafic underplate and a refractory lower crust of Archean age, respectively. The older rocks of the Uusivirka suite are early-collisional (1.92-1.91 Ga) and derived from poorly mixed local sources, whereas younger psammite-pelite associations (Ristivuoma) are syn-collisional (1.911.89 Ga) and derive from multiply recycled and thoroughly mixed sources. These rocks were deformed during continued collision with the development of foreland fold- and thrust belt. [ABSTRACT FROM AUTHOR]

The Karakoram Metamorphic Complex (KMC) marks the southern margin of the Karakorum plate and mainly consists of metasedimentary rock sequences. These metasediments are mainly pelitic with carbonate layers, cut across by granitic sheets. The complex is bounded by the Indus Suture Zone in the south and Karakoram Axial batholiths in the north. This study focuses on detailed microstructural analyses of the metapelitic rocks of the KMC exposed along the Karakorum Highway of the Hunza region. Foliation Intersection Axis (FIA) method of Bell et al., (1995) and matrix foliation overprinting relationship were used to deduce the tectonic history of the KMC. FIA technique measures the axis of curvature of curved inclusion trails preserved in porphyroblasts (garnet and staurolite), whereas, the foliation overprinting relationship further establishes the latest phases of deformation in the given area. A total of 16 samples were collected, however, 11 samples preserved sufficient quality of inclusion trails to work further on FIA technique. Two dominant trends (sets) were measured by 'asymmetry switch' of inclusion trail geometry. The older E-W trending FIA (set 1) formed as a result of bulk N-S shortening, whereas, the younger FIA set (set 2) trending NE-SW direction formed as a result of bulk NW- SE shortening. At least two phases of deformation were observed in matrix from the Hunza Karakorum (1) an early phase of intense deformation resulting in the formation of continuous generally E-W and WNW-ESE striking foliation (Fig. 1a,b,c; stage 6 of Bell and Rubenach, 1983 classification) formed in response of N-S shortening, and (2) the latter phase is responsible for the formation of upright to isoclinal folding with an axial planer NE-SW foliation falls in stage 2 to 3 of Bell and Rubenach (1983) scheme (Fig. 1d). The first event represents the south verging tectonics and crustal thickening followed by younger NW-SE shortening event. The geometry of an early FIA set (E-W) preserve an overall clockwise asymmetry, whereas the younger FIA set (NE-SW) preserves counter-clockwise asymmetry, while looking towards west. The data set obtained from this study is significant because it has close similarity to the FIA data obtained from the Nepal Himalaya (Fig. 2; Sapkota and Bell, 2012). [ABSTRACT FROM AUTHOR]

The formation of antitaxial calcite veins in sandstone and their kinematic evolution have received less attention, partly because of their complex growth with respect to wall rock. The modes of deformation in which these antitaxial veins nucleate and deform are still not well understood. For this purpose we have investigated complex network of antitaxial veins and associated shear bands in a hand specimen sample. Since, veins and shear bands accommodate volume gain and loss, respectively; therefore, systematic study of strain partitioning and kinematic track is developed, consistent with the deformation history of the rock under study. Three sets of antitaxial veins and one set of shear band have been recognized. Set 1 consists of veins that are truncated against younger veins and shear bands (Fig.1). Set 2 consists of all those veins that are oriented at low- to high- angle with respect to set 1 veins. These veins cut across set 1 veins or vice versa. This suggests that both set 2 and set 1 form synchronously. Internal geometry of both set 1 and 2 veins form calcite fibers that are asymmetric and interpreted to have developed by repeated growth of fibers, at least in two stages, in two directions (Fig. 1). Set 2 veins have shear sense opposite to that of set 1 veins. The fibers are smoothly curved from median to the margins and this geometrical relationship suggests that the change in the rotation of the kinematic axes was gradual. Power law relationship on length vs frequency of veins suggests that both set 1 and 2 veins propagated sequentially. Shear bands cut set 1 and 2 veins and are categorized under set 3. These bands are evenly spaced, consist of pulverized/opaque material, parallel to each other and accommodated shearing. Veins belonging to set 4 are relatively thick and cross cut set 1, 2 and 3. The spatial distribution of set 4 veins is low as compared to set 1 and 2 veins. Micro-textural study shows that these veins are filled with blocky crystals of quartz or calcite and are different than set 1 and set 2 veins. At the margins of set 4 veins, asymmetric remnants of calcite fibers are preserved with distinct shear sense. This firmly suggests that set 4 veins initially formed as 'antitaxial 'veins with asymmetric fibers, however as the deformation progressed, new material in the form of either quartz or calcite intruded. Detailed fabric analysis of calcite fibers indicates that both set 1 and 2 veins dilated perpendicular to the wall rock and then subsequently sheared in opposite direction. Since, set 1 and 2 veins have an angle ranging between 60° and 120° , therefore, we propose that the stretching direction switched gradually with a maximum angle of 120°. The margins of the veins show asymmetry and distinct shear sense, this further suggests that once formed, both sets 1 and 2 were subjected to shearing. These two sets were then subject to shearing followed by the formation of set 4 antitaxial veins. [ABSTRACT FROM AUTHOR]

This article describes a study which adopted numerical approach to simulate nucleation and growth of conjugate Riedel deformation bands in sandstone. Researchers used finite difference code to simulate the structural evolution of deformation bands in sandstone and adopted Mohr-Coulomb material model with variable boundary conditions. They learned that the formation of Riedel geometry is not dependent on lateral shear, rather their growth is controlled by conjugate sets lying at an acute angle.

In this study, we focused on the origin and tectonic significance of millipede inclusion trail microstructures preserved within garnet porphyroblasts of typical Barrovian-type schist from the Swat region of the Himalayas in Pakistan. Two possible kinematic models were assessed envisaging bulk coaxial shortening and progressive simple shear. Three D microstructural analysis of three samples hosting the millipedes reveals a poly-phase deformation history that produced three sub-orthogonal foliations (called Sx, Sy, Sz). Successive inclusion of Sx and Sy in garnet porphyroblasts produced two sets of millipedes with distinctive subvertical and subhorizontal orientations, respectively. This kinematic reconstruction is supported further with a numerical simulation using finite difference code of millipede formation in a spherical porphyroblast subjected to a superposition of two orthogonal shortening directions. Measurements of inclusion-trail curvature axes or FIA (Foliation Intersection/Inflexion Axes in porphyroblasts) in 61 additional samples from the study area, which contain straight, sigmoidal or spiral inclusion trails, reflect two principle orogenic episodes. During the first episode, FIAs developed with WNW-ESE (set 1) and E-W (set 2) trends associated with thrusting and collision tectonics. A younger FIA (set 3) with NNE-SSW trend developed as a result of subsequent bulk E-W crustal shortening and associated regional-scale folding. Sigmoidal or straight inclusion trails defining this FIA set can be correlated with the millipede microstructures based on their similar trends and timing relative to matrix fabrics. These results are consistent with the meso- and macro-scale structures in the region and significant in terms of establishing relative timing of formation of different structures in the region. Well developed preferred vertical and horizontal orientations of both sigmoidal and millipede inclusion trails imply that their development involved limited or no relative rotations between porphyroblasts. Sigmoidal trails formed in zones where bulk shearing caused progressively reoriented matrix foliations around stable garnets, while millipedes formed simultaneously in local coaxial-strain pods. [ABSTRACT FROM AUTHOR]

Fractal is a mathematical set that has a fractal dimension that usually exceeds its topological dimension and may fall between integers. They represent the idea of detailed self-similar repetition at same scale or they may nearly be the same at different scales. Fractals are geometrical objects with the fractal dimension (D). Their fractal geometry deals with the objects and spaces. They occupy space (x,y,z) of any dimension greater than or equal to the dimension of the objects. In this study, hydrothermally altered zones of porphyry copper deposits of Reko-Dik, Chagai Belt, are taken into account to see whether alternation patterns follow any fractal law. Rowan et al. (2006) carried out detailed spectral analyses of different alteration zones nicely exposed around the Reko-Dik. We have used the same images as base map in our calculations for spatial analysis. A refined box-counting method is used, where the number of boxes (Nr) containing the alteration versus the box size (r) repeatedly tested. To start with, the scaling properties of box size (r) were taken at 0.5 km interval, following 0.5 km addition in each analysis ending at 5 km. The spatial distributions of hydrothermally altered zones show following fractal dimension values: (D) for argillic (D = 1.0±0.05), phyllic (muscovite + jarosite) (D = 1.2±0.04), phyllic (muscovite) (D= 0.8±0.05), propylitic (D = 1.2±0.04), and siliceous (D = 0.8±0.07). Further work is in progress to refine the D values using improved box-counting method (Roy et al., 2007). [ABSTRACT FROM AUTHOR]

Hydrocarbon traps in the Potwar Plateau are generally structurally controlled; however, local stratigraphic traps are also reported. The structural traps are the product of the Tertiary Himalayan orogeny. This firmly suggests that the structural traps in the Potwar should be analyzed under the framework of fold-and thrust-belt system. For the last about two decades, the Potwar Plateau received much attention in terms of petroleum exploration. In this regard, a number of petroleum national and multinational companies are seriously been involved to understand the structural complexities of the area. However, very limited data is published highlighting the trap configurations and their 2D and 3D geometries. In this study, a key area known as Talagang, located in the centre of the Potwar Plateau, is selected to decipher the 2D structural geometries of the structural traps. For this purpose, surface geological maps and 2D (after permission from DGPC) subsurface geophysical seismic sections along and across the strike of the beds are integrated. The surface structural cross-section shows gentle-dipping pair of anticline (Jhatla) and syncline (Khichh) with open interlimb angle, therefore, the same, at least part of, is well manifested in the N-S trending seismic sections. However, the E-W trending strike-seismic section shows prominent anticlinal structure. The geometry of this fold is not picked in the N-S dip-seismic section, therefore, it can be inferred that this fold can best be viewed in the E-W strike section. From here, it is interpreted that the axis of this fold is ca. N-S, means that this fold is formed by E-W crustal subsurface shortening. Surface expression of E-W shortening is manifested in the form of many folded structures exposed in the eastern part of the Potwar and in the western Trans-Indus Ranges, where N-S trending Surghar-Shinghar Anticline and the Makarwal Anticline are excellent surface examples of N-S trending folds. Thus, it can be further interpreted that the N-S trending structures overprint over the E-W as shown here. This can also suggests the formation of domal (type-1 of Ramsay and Huber fold interference classification, 1987) structures, may be responsible for the trap of hydrocarbons. [ABSTRACT FROM AUTHOR]

Multiply deformed and metamorphosed rocks commonly preserve a record of lengthy periods of deformation and associated several phases of porphyroblast growth. This is evident from several sets of foliations and lineations reported from a number of orogenic terrains around the globe. However, when it comes to the interpretation of foliations and associated lineations, controversies arise in terms of their tectonic control and kinematic models. To resolve the tectonic origin of foliations and lineations, sophisticated structural techniques have been devised and their refinements over the years allow the users to track the tectonic history of a given orogenic terrain as accurately as possible. The purpose of this research is to reconstruct 'original' geometrical orientation of foliations and lineations that are preserved in porphyroblasts in the form of inclusion trails from the multiply deformed and metamorphosed sequences of the Kaghan-Naran valley, north Pakistan. No such studies have been carried out to date in the proposed region. Yet, the metamorphic rocks of the Kagahn-Naran valley are crucial in many ways not only to decode the sequential two-phase exhumation tectonics of this important region within the Himalaya, but also to understand the synchronous collision-extension history of this world-class orogenic system. Inclusion trail geometries in porphyroblasts can help us to thoroughly investigate fine-scale processes involved in crustal-scale mechanics, where synorogenic two-phase collision and exhumation have been proposed. Two conflicting hypothesis have been postulated for the asymmetric inclusion trail geometries: porphyroblast rotation and non-rotation. Porphyroblast non-rotation assumes that porphyroblast preserve successive sets of foliations with respect to fixed geographic coordinates during progressive deformation in case not obliterated internally. Hence, multiple deformation phases can be deduced and correlated from sample to sample and from one region to other. Rotation model postulates that during simple shear, porphyroblasts synchronously grow and trap single foliation during progressive shearing. In this study, not only the two models are tested but the inclusion trail geometries preserved in porphyroblasts are also measured and an attempt is made to reconstruct the deformation and associated metamorphic sequences of the Kaghan-Naran valley. Two main FIA sets are obtained through 'asymmetry switch' method. The first FIA is E-W trending mostly obtained from garnet porphyroblasts, and corresponding to the N-S bulk shortening of the Indian Plate with Kohistan-Island Arc. The second FIA set is N-S trending and obtained from both garnet and staurolite porphyroblasts and formed as a result of E-W bulk shortening. The two distinct shortening directions match well with the FIA data obtained from the Swat area. [ABSTRACT FROM AUTHOR]