Solid-state Deformation Research Articles

S-type granite generation and emplacement during a regional switch from extensional to contractional deformation (Central Iberian Zone, Iberian autochthonous domain, Variscan Orogeny)

Zircon grains extracted from S-type granites of the Meda-Escalhao-Penedono Massif (Central Iberian Zone, Variscan Orogen) constrain the timing of emplacement and provide information about potential magma sources. Simple and composite zircon grains from three samples of S-type granite were analyzed by LA-ICP-MS. New U–Pb data indicate that granites crystallized in the Bashkirian (318.7 ± 4.8 Ma) overlapping the proposed age range of ca. 321–317 Ma of the nearby S-type granitic rocks of the Carrazeda de Anciaes, Lamego and Ucanha-Vilar massifs. The timing of emplacement of such S-type granites seems to coincide with the waning stages of activity of a D2 extensional shear zone (i.e. Pinhel shear zone) developed in metamorphic conditions that reached partial melting and anatexis (ca. 321–317 Ma). Dykes of two-mica granites (resembling diatexite migmatite) are concordant and discordant to the compositional layering and S2 (main) foliation of the high-grade metamorphic rocks of the Pinhel shear zone. Much of the planar fabric in these dykes was formed during magmatic crystallization and subsequent solid-state deformation. Field relationships suggest contemporaneity between the ca. 319–317 Ma old magmatism of the study area and the switch from late D2 extensional deformation to early D3 contractional deformation. Inherited zircon cores are well preserved in these late D2-early D3 S-type granite plutons. U–Pb ages of inherited zircon cores range from ca. 2576 to ca. 421 Ma. The spectra of inherited cores overlap closely the range of detrital and magmatic zircon grains displayed by the Ediacaran to Silurian metasedimentary and metaigneous rocks of the Iberian autochthonous and parautochthonous domains. This is evidence of a genetic relationship between S-type granites and the host metamorphic rocks. There is no substantial evidence for the addition of mantle-derived material in the genesis of these late D2–early D3 S-type granitic rocks. The eNd arrays of heterogeneous crustal anatectic melts may be just inherited from the source, probably reflecting mixing of a range of crustal materials with different ages and primary isotopic signatures. The generation of the Bashkirian S-type granites has been dominated by continental crust recycling, rather than the addition of new material from mantle sources.

Geochronological, geochemical and petrographic constraints on the Paleoproterozoic Tocantinzinho gold deposit (Tapajos Gold Province, Amazonian Craton - Brazil): Implications for timing, regional evolution and deformation style of its host rocks

The Tapajós Domain in the Amazonian Craton comprises hundreds of gold occurrences mainly hosted by Paleoproterozoic granitic rocks, whose geotectonic evolution and deformation style are poorly understood. The Tocantinzinho granite hosts a large amount of gold, forming the largest gold deposit known in the Tapajós Domain. The Tocantinzinho area is formed by plutonic rocks cut by subvolcanic rocks shallowly emplaced and constrained by NW-SE strike-slip faults, probably in a transtensive site. The magmatism started with the emplacement of huge granodiorite that presently formed the basement country rocks (2007–1997Ma), it was followed by the Tocantinzinho granite magmatism (1989–1979 Ma), and the coeval to late andesite emplacement. Petrological and textural evidence suggest the complex and synchronous occurrence of tectonics and few magmatic events expressed by the emplacement of successive granite, aplite, pegmatite, andesite, and dacite. The magmatic event finished with the cooling of this set of rocks below c. 320 °C, at c. 1950 Ma. The cooling rates vary from c. 3.6–14.7°C/Ma, with an average of 7.5°C/Ma, indicating no important vertical exhumations. The elongated geometry of the Tocantinzinho granite and related rocks, features of solid-state deformation within granites and syntectonic deformation of some andesite dikes imply the existence of wrench type tectonic control. The I-type signature of these rocks, their high-K calc-alkaline and metaluminous to peraluminous affinities combined with the tectonic style indicate a post-collisional tectonic setting. Based on geochemical and structural constrains, the rocks from the Tocantinzinho area are interpreted as a part of the Creporizão Suite and probably represent the first expressions of this syn-to late-tectonic magmatism in the region. A continuous and progressive process of magmatic emplacement controlled by tectonics will be proposed and discussed in conclusion.

Cretaceous partial melting, deformation, and exhumation of the Potters Pond migmatite domain, west-central Idaho

The Potters Pond migmatite domain (PPMD) is a heterogeneous zone of migmatites located ∼10 km southwest of Cascade, Idaho, within the western Idaho shear zone (WISZ). The PPMD is the only known exposure of migmatites within the WISZ over its ∼300 km length, occurring where the shear zone orientation changes from 024° south to 005° north of the migmatite domain. Structural mapping within the PPMD has identified multiple generations of migmatite with varied structural fabrics. Leucosome layers were sampled from distinct migmatite localities and morphologies (e.g., metatexite and diatexite) to determine the timing and duration of partial melting in the PPMD. U-Pb age determinations of zircon by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) document two periods of protracted migmatite crystallization during the Early and Late Cretaceous. Early Cretaceous (ca. 145–128 Ma) migmatite crystallization ages are coeval with the collision and suturing of oceanic terranes of the Blue Mountains province with North America and the formation of the Salmon River suture zone (SRSZ). Migmatite crystallization ages from ca. 104–90 Ma are associated with Late Cretaceous dextral transpression in the WISZ. Field observations and geochronology of crosscutting leucosome relationships are interpreted to record deep crustal deformation and anatexis associated with formation of the SRSZ, subsequently overprinted by solid-state deformation and renewed anatexis during the evolution of the WISZ. These data are the first direct evidence of the synmetamorphic fabric related to the SRSZ east of the initial Sr 0.706 isopleth and indicate that the WISZ is a temporally distinct overprinting structure.

Emplacement and deformation of the A-type Madeira granite (Amazonian Craton, Brazil)

The Madeira granite is one of the Paleoproterozoic (1.82Ga) A-type granite intrusions in the Amazonian Craton. It is elongated in the NE–SW direction and is composed of four facies. Classical structural techniques and the anisotropy of magnetic susceptibility (AMS) method were applied to the study of its internal fabric. Magnetic susceptibility measurements, thermomagnetic curves, remanent coercivity spectra, optical microscopy and SEM (scanning electron microscopy) analyses were carried out on the earlier and later facies of the Madeira granite: the rapakivi granite (RG) and the albite granite (AG) respectively. The last one is subdivided into the border albite granite (BAG) and the core albite granite (CAG) subfacies. AMS fabric pattern is controlled by pure magnetite in all facies, despite significant amounts of hematite in the BAG subfacies. Microstructural observations show that in almost all sites, magnetic fabric correlates to magmatic state fabrics that are defined by a weak NE–SW orientation of mafic and felsic silicates. However, strain mechanisms in both subfacies of AG also exhibit evidence for solid-state deformation at high to moderate temperatures. Pegmatite dyke, strike slip fault (SFA–B–C), hydrothermal vein, normal fault (F1–2) and joint (J) structures were observed and their orientation and kinematics is consistent with the magmatic and solid-state structures. Dykes, SFA–C and F1, are usually orientated along the N70°E/40°N plane, which is nearly parallel to the strike of AMS and magmatic foliations. In contrast, veins, SFB, F2 and some J are oriented perpendicular to the N70°E trend. Kinematic analysis in these structures shows evidence for a dextral sense of movement in the system in the brittle regime. The coherent structural pattern for the three facies of Madeira granite suggests that the different facies form a nested pluton. The coherence in orientation and kinematics from magmatic to high-temperature solid-state, and into the brittle regime indicates the continuity in the stress regime from the last magmatic stages until the complete cooling of the pluton, likely along a NE–SW dextral corridor related to the regional deformation in the Uatumã–Anauá Domain of the Amazonian Craton.

Petrogenesis of metamorphosed Paleoproterozoic, arc-related tonalites, granodiorites and coeval basic to intermediate rocks from southernmost Brazil, based on elemental and isotope geochemistry

In southern Brazil, three associations of metamorphosed tonalites and granodiorites that are compositionally similar to tonalite–trondhjemite–granodiorite (TTG) or adakitic associations have been identified in the Arroio dos Ratos Complex (ARC) Paleoproterozoic magmatism. The metatonalites of Association 1 (A1; 2148±33Ma) have a well-developed fabric, compatible with strong solid-state deformation. The metatonalites and metagranodiorites of Association 2 (A2; 2150±28Ma) are intrusive in A1 and have a similar composition, but are less deformed, and their primary structures are partly preserved. Both associations display contemporaneity relations with basic to intermediate magmas. Association 3 (A3; 2077±13Ma) is represented by tonalitic to granodioritic gneisses, without any associated basic to intermediate magmatism, and its main characteristic is the banding that resulted from strong solid-state deformation. Partial melting features are locally present in A3. The geochemical compositions of the three associations are similar and indicate sources related to a continental magmatic arc environment. The 87Sr/86Sr(i) ratios (between 0.701 and 0.703), positive ƐNd(t) values (+1.45 to +5.19), and TDM ages close to the crystallization ages indicate juvenile sources for the A1 and A2 associations. The A3 rocks have a 87Sr/86Sr(i) ratio of 0.715, an ƐNd(t) value of +0.47 and a TDM age that is close to the crystallization age, indicating a source composition different from those of the other associations. The Pb isotope ratios of A1 and A2 are similar and compatible with the evolution of mantle and orogen (208Pb/204Pb=37.3–37.6; 207Pb/204Pb=15.62–15.65; 206Pb/204Pb=18.0–18.2). The Pb isotope ratios of A3 differ from A1 and A2, indicating a more Th-poor source (208Pb/204Pb=37.1; 207Pb/204Pb=15.64; 206Pb/204Pb=18.5). The geochemistry of associations A1 and A2 suggests a juvenile source with contamination by crustal material. However, the Sr–Nd–Pb isotope signature of this contaminant is similar to that of the source material that originated these associations. This may be the crust generated in the magmatic arc, which is compatible with the geochronological results. The dataset points to the occurrence of self-cannibalism processes in the generation of the ARC rocks. The similar chemical composition and ƐNd(t) values of A3 relative to A1 and A2 indicate that the A3 source is similar to the one that generated the tonalitic and granodioritic rocks of A1 and A2. However, the slightly lower 208Pb/204Pb, and higher 206Pb/204Pb and 87Sr/86Sr(i) ratios indicate that the A3 association has also the addition of a distinct crustal source. The A3 association high values of the parameter 87Sr/86Sr(i) and its Pb isotope signature indicate a source with high Rb and U, and low Th contents. Such features, and moreover the depletion of HREE combined with TDM values near the igneous age, suggest that the source for A3 may be juvenile arc sediments. The greater degree of crustal contribution, the lack of associated basic to intermediate rocks, and the younger age possibly mark the more mature or late stages of the arc. The major and trace elements, as well as the isotope data obtained in this study suggest that melting of a metasomatized mantle wedge can be the process that generated the ARC basic to intermediate rocks (A1 and A2). The generation of tonalitic and granodioritic rocks with adakitic characteristics (i.e., the depletion of heavy rare earth elements in tonalitic and granodioritic rocks of A1, A2 and A3) may have arisen from the melting of a garnet-rich source or from fractional crystallization of ARC basic to intermediate magmas, which in time increased crustal assimilation under high-pressure conditions. The crustal garnet-rich source could be the basic rocks newly placed at the base of the crust, derived from partial melting of metasomatized mantle. The remobilization of this material by partial melting may have generated tonalitic and granodioritic liquids depleted in heavy REE due to the presence of garnet in the residue. The three associations display microstructures that indicate two episodes of recrystallization, one of a higher temperature and one of a lower temperature. The age of the high-temperature structure remains under discussion and may be attributed to a Paleoproterozoic metamorphic event. The low-temperature event is compatible with the temperature conditions observed in adjacent areas, in the host rocks of the Neoproterozoic post-collisional granitoids that have been emplaced along the Southern Brazilian Shear Belt (SBSB). Zircon crystals with Paleoproterozoic igneous cores exhibit a metamorphic overgrowth at 635±6Ma, compatible with the crystallization ages of the SBSB granitoids.

The Geochemical Complexity of Kimberlite Rocks and their Olivine Populations: a Reply to the Comment on Cordieret al.(2015) by Andrea Giuliani & Stephen F. Foley

We thank sincerely Giuliani & Foley for their discussion of the textures and compositions of olivine in kimberlites. We do not agree with many of their interpretations and therefore welcome the chance to respond, particularly because it provides an opportunity to explain once again the characteristics of olivine in kimberlites that we think are most important—features that have commonly been misinterpreted or overlooked in many other papers. In publications such as those by Kamenetsky et al. (2008), Brett et al. (2009) or Pilbeam et al. (2013), the emphasis has been on mineral compositions and internal zonation whereas in our paper (Cordier et al., 2015) and in an earlier study (Arndt et al., 2010), we emphasized the internal structures and fabrics of olivine grains. In the earlier paper, we described structures produced by solid-state deformation and showed that these could only have formed in the lithosphere. In our 2015 paper, we focused on grain boundary migration zones. These features, which typically develop during fluid-assisted recrystallization, may be unfamiliar to igneous petrologists but are well known to metamorphic and structural geologists. Like the internal deformation features, they form slowly or under high-stress conditions and could only have been produced within the lithosphere. We emphasize that these deformation or recrystallization features formed within rock of dunitic composition: the orthopyroxene, clinopyroxene and garnet–spinel that make up a large proportion of most mantle xenoliths were absent when these textures originated. In our opinion, these observations indicate clearly that orthopyroxene was eliminated before entrainment of xenoliths into the ascending kimberlite magma. If this interpretation is correct (and we have not heard or read any arguments to negate it), it calls into question the commonly accepted model that proposes loss of orthopyroxene within ascending kimberlite magma.

Thermoplastic elastomers reinforced with poly(tetrafluoroethylene) nanofibers

The effect of poly(tetrafluoroethylene) (PTFE) nanofibers content on the rheological and mechanical properties of thermoplastic elastomer/low density polyethylene (TPE/LDPE) blends was investigated. The PTFE nanofibers were generated in situ during compounding of crystalline PTFE grains with molten matrix based on TPE/LDPE blends. The studies revealed that PTFE nanofibers produced by solid-state deformation of PTFE crystals formed an entangled network which significantly improved both rheological and mechanical properties of TPE/LDPE blends. The maximum strain hardening coefficient was found to depend on the concentration of the PTFE nanofibers. The material based on TPE/LDPE blend containing 5wt% of PTFE nanofibers (75/20/5) exhibited strain hardening coefficient about three times higher as compared to conventional TPE/LDPE blend (60/40). Also, the mechanical properties of the blends depended on the content of PTFE nanofibers. Higher the content of PTFE nanofibers the stiffer TPE/LDPE blend. At 8wt% of PTFE nanofibers (60/32/8) the modulus of elasticity was two times higher in comparison to 60/40 blend.

Friction crush welding of aluminium, copper and steel sheetmetals with flanged edges

The implementation of friction crush welding (FCW) offers a versatile application in the welding of sheet metals. Three materials (EN AW 5754H22, DC01 and Cu-DHP) were analysed by applying the method with flanged edges. The additional material required to form the weld is provided by the flanged edges of the parent sheet metal. The joint is formed by the relative motion between a rotating disc, which is applied with a crushing force, and two sheet metal parts. The fundamental process variables and the requirements of the welding preparation are shown. Bond strengths, as a percentage of the yield strength of the parent material, of around 95% (DC01) 90% (EN AW 5754H22) and 62% (Cu-DHP) are achieved. Microstructural investigations reveal that a dynamic solid-state deformation and recrystallization of the additional flanged material results in a fine grain microstructure in the weld region. Reduced metallurgical changes along with minimized distortion and residual stresses in the parent material indicate low heat input. By creating a fine grain microstructure in the welding line, the friction crush welding method reveals great potential, especially for welding steel.

Zircon dating and mineralogy of the Mokong Pan-African magmatic epidote-bearing granite (North Cameroon)

We present the mineralogy and age of the magmatic epidote-bearing granite composing most of the Mokong pluton, in the Central Africa orogenic belt (North Cameroon). This pluton intrudes Neoproterozoic (~830 to 700 Ma) low- to high-grade schists and gneisses (Poli-Maroua group), and is crosscut or interleaved with bodies of biotite granite of various sizes. The pluton is weakly deformed in its interior, but solid-state deformation increases toward its margins marked by narrow mylonitic bands trending NNE–SSW. The magmatic epidote granitic rocks are classified as quartz monzodiorite, granodiorite, monzogranite, and syenogranite. They are medium- to coarse-grained and composed of K-feldspar + plagioclase + biotite + amphibole + epidote + magnetite + titanite + zircon + apatite. In these granites, the pistacite component [atomic Fe+3/(Fe3+ + Al)] in epidote ranges from 16 to 29 %. High oxygen fugacity (log ƒO2 − 14 to −11) and the preservation of epidote suggest that the magma was oxidized. Al-in hornblende barometry and hornblende–plagioclase thermometry indicate hornblende crystallization between 0.53 and 0.78 GPa at a temperature ranging from 633 to 779 °C. Zircon saturation thermometry gives temperature estimates ranging from 504 to 916 °C, the latter being obtained on samples containing inherited zircons. U/Pb geochronology by LA-ICP-MS on zircon grains characterized by magmatic zoning yields a concordia age of 668 ± 11 Ma (2σ). The Mokong granite is the only known occurrence magmatic epidote in Cameroon, and is an important milestone for the comparison of the Central Africa orogenic belt with the Brasiliano Fold Belt, where such granites are much more abundant.

Formation of polypropylene nanofibers by solid state deformation during blending with molten polyethylene

Formation of polypropylene nanofibers by solid state deformation during blending with molten polyethylene

Aluminoxane co-catalysts for the activation of a bis phenoxyimine titanium (IV) catalyst in the synthesis of disentangled ultra-high molecular weight polyethylene

New activation systems for the bis[N-(3-tert-butylsalicylidene)pentafluoroanilinato] Ti (IV) dichloride catalyst (FI) for the synthesis of ultra-high molecular weight polyethylene (UHMWPE) with reduced entanglement density are explored. Together with the well-studied FI catalyst-methylaluminoxane (MAO) catalytic system, different aluminoxanes, namely polymethylaluminoxane-improved performance (PMAO), modified methylaluminoxane type 12 (MMAO12) and type 3A (MMAO3A) have been used. The catalyst activity increases with the addition of a co-catalyst modifier (2,6-di-tert-butyl-4-methylphenol, BHT). For an example when using MMAO3A as co-catalyst in combination with BHT the catalyst activity increases by tenfold. The synthesized UHMWPEs have been characterized via rheology, differential scanning calorimetry and uniaxial solid-state deformation to evaluate the influence that the different co-catalysts have on the catalyst activation and the entangled state of the polymer. Entanglement density increases when PMAO is used as a co-catalyst influencing the rheological response of the polymer melt and melting kinetics of nascent powder. Mechanical properties increase when MMAO12 is used in place of MMAO3A as co-catalyst. However, the earlier reported mechanical properties of UHMWPE synthesized using the FI/MAO are found to be better than those obtained using the co-catalysts investigated in this study.

Effect of flow forming on mechanical properties of high density polyethylene pipes

Flow forming is a single rotary-contact-point cold-forming process, in which the thickness of a tubular pre-form is reduced while its length increases without any change in internal diameter. Although metal flow forming has been studied by many researchers and industries, there does not appear to be any published study on the flow forming of polyethylene pipes. The main purpose of this study was to find out the applicability of flow forming on polyethylene pipes and the effects of process parameters on mechanical properties of polyethylene flow formed parts. The experiments were carried out using HDPE80 tubular pre-forms. Thickness reduction ratio, feed rate and rotation speed of mandrel were considered as variables. An L9 orthogonal array of Taguchi method was applied to carry out the experiments. Tensile and impact tests were performed to examine the failure behavior of specimens. Scanning electron microscopy (SEM) was implemented to find out the relation between mechanical properties and microstructure of the material. Stress at break, yield Stress, percentage of elongation at break and impact endurance were measured as indicators of mechanical properties. It was found that mechanical properties of HDPE increase significantly during flow forming. The solid state deformation makes material more oriented and anisotropic that leads to an enhancement in mechanical properties of HDPE. Through SEM it was found that the material experiences a transformation from an isotropic spherulite structure into an anisotropic lamellar-fibrous structure at large deformation.

Emplacement and geochemical evolution of highly evolved syenites investigated by a combined structural and geochemical field study: The lujavrites of the Ilímaussaq complex, SW Greenland

Structural mapping and the combined study of magmatic to solid-state deformation textures and mineral compositions in highly evolved nepheline syenites (lujavrites) of the alkaline to peralkaline Ilímaussaq complex (South Greenland) reveal detailed insight into the emplacement and geochemical evolution of the melts they crystallized from.Based on magmatic to solid-state flow textures such as foliations and lineations, we propose that the investigated rock sequence forms a sill-like structure with a steep feeder zone that flattens out over a short distance and intrudes into less evolved overlying units as sub-horizontal sheets by roof uplift. Systematic compositional variation of early-magmatic eudialyte-group minerals (EGM) in the investigated rock sequence monitors the geochemical evolution of the lujavrite-forming melt(s). The chlorine contents of EGM decrease successively upwards within the rock sequence, which probably indicates a successive increase of water activity during differentiation, consistent with a change from sodic pyroxene (aegirine) to sodic amphibole (arfvedsonite) in the mineral assemblage. Both REE contents and Fe/Mn ratios of EGM are promising differentiation indicators, which increase and decrease, respectively, upwards within the sequence due to fractional crystallization. This closed-system evolution is interrupted by a shift towards less evolved melt compositions in one lujavrite unit, for which we assume magma recharge.Our study demonstrates the strength of a combined structural and petrological approach to understand the petrogenesis of an igneous body in more detail and highlights their close connection.

Tectonic rotations and internal structure of Eocene plutons in Chuquicamata, northern Chile

A paleomagnetic and AMS study on Eocene plutonic complexes in the Calama area, northern Chile, reveals high-temperature, high-coercivity magnetizations of dominantly thermoremanent origin and magnetic fabrics controlled by magnetite. The paleomagnetic results indicate that ~43Ma plutons underwent clockwise tectonic rotation, whereas adjacent ~39Ma plutons did not undergo discernible rotation. This points to a middle Eocene age for the younger tectonic rotations associated with the Central Andean Rotation Pattern in the Chuquicamata–Calama area.The petrofabric in these rocks formed under conditions ranging from purely magmatic (i.e. before full crystallization) to low-temperature solid-state deformation. AMS and paleomagnetism suggest that the plutonic bodies were formed by progressive amalgamation of subvertical magma sheets spanning multiple magnetic polarity chrons. The parallelism between magmatic and tectonic foliations suggests that regional tectonic stress controlled ascent, emplacement and rock deformation during cooling. In this context, we suggest that magma ascent and emplacement in the upper crust likely exploited Mesozoic structures which were locally reactivated in the Eocene.

An integrated approach to the late stages of Neoproterozoic post-collisional magmatism from Southern Brazil: Structural geology, geochemistry and geochronology of the Corre-mar Granite

The Neoproterozoic post-collisional stage in south Brazil is marked by intense granitic magmatism controlled by transcurrent shear zones related to the Southern Brazilian Shear Belt (SBSB). The SBSB has controlled the ascent and emplacement of magmas from crust and mantle. In such scenario, the Corre-mar Granite (CMG), represents a small intrusion emplaced in a low-strain zone located between two important segments of the SBSB: the Major Gercino and Itajaí-Perimbó shear zones. The CMG has a diagnostic subvertical S–C foliation pair present in all intrusions, regardless of their size. It was emplaced within a conjugate system where sinistral NNE shearing and NW–SE extension were both active, generating space along the NE direction. Solid-state deformation associated to the NNE shearing is attested to by microstructures as feldspar recrystallization and asymmetric recrystallization tails. The opening is attributed to the regional dextral transcurrent dynamics of the Major Gercino and Itajaí-Perimbó shear zones and magma emplacement was essentially conditioned by the NW extension component. Zircon U–Pb LA-MC-ICP-MS crystallization age of CMG at 615±4Ma, very close to other regional granites, as the 611Ma Serra dos Macacos (SMG) and 620Ma Rio Pequeno Granite (RPG) points these three granitic bodies as synchronous. The strong deformation features present in the CMG, as opposed to the other Neoproterozoic granites, demonstrate that space, rather than time, must be called upon to explain the difference in structural patterns identified in the CMG. Geochemical and Sr–Nd isotopic signatures, as the slightly peraluminous character, high K contents, high LREE/HREE ratios, moderate Rb, Nb, Zr, and REE contents to regular SiO2, together with low 87Sr/86Sri and the strongly negative ɛNdt values indicate that the CMG is derived from old crustal sources, possibly related to the Paleoproterozoic Camboriú Complex quartz-feldspathic orthogneisses. The coincidence of CMG Archean to Paleoproterozoic inheritance ages with the age of a migmatization event identified in the Camboriú Complex, and moreover the coincidence of the crystallization age intervals of the granites (∼615–611Ma) with the last migmatization event at 640–610Ma reinforces the genetic link between them. The Paleoproterozoic TDM ages, the geochemical and isotopic signatures, the zircon U–Pb crystallization and inheritance age, and the resemblance of the CMG and the SMG suggest that they represent comagmatic and contemporaneous granitic pulses, with a possible genetic link with the Neoproterozoic migmatization event in the Camboriú Complex.

Intrusive and deformation history of the Ševětín Pluton, Moldanubian Batholith: record of polyphase tectonic evolution of the Blanice Graben, Bohemian Massif

The Sevětin Pluton, located c. 15 km NNE of Ceske Budějovice, is a small, isolated, petrologically and structurally complex intrusive body that is genetically related to the youngest intrusions of the Moldanubian Batholith. As documented in this study, its overall shape, internal magmatic fabric as well as brittle structures (dikes, veins, joints, faults) are, however, related to the formation and polyphase tectonic evolution of the Blanice Graben, an about 200 km long and 5–15 km wide NNE–SSW-trending, deep-seated fault zone that cuts across the Moldanubian Unit. In total, one pre-intrusive and three synto post-intrusive tectonic phases have been distinguished. The oblique, NW–SE oriented compression controlled both the intrusion of the Sevětin biotite–muscovite granite and the early stage of its brittle deformation. Sigmoidal pattern of magnetic foliations in this pluton documents its mostly solid-state deformation during oblique sinistral movements on the main faults of the Blanice Graben. The subsequent strike-slip phase was characterized by E–W oriented subhorizontal extension and can be correlated with the intrusion of c. 270 Ma old microgranodiorite dikes. The last extensional phase was associated with the formation of subeconomic Pb–Zn–(Ag?) quartz–calcite veins at c. 265 Ma.

General view of severe plastic deformation in solid state

A general approach to the description of the basic laws of structural and phase solid state transformations occurring upon severe plastic deformation (SPD) is proposed within the concept of the appearance of additional channels for the dissipation of mechanical energy supplied to the solid state. It is shown that the active involvement of cyclic processes of low-temperature dynamic recrystallization and of the ≪crystal⇔amorphous state≫ phase transformations in combination with additional thermal effects under the conditions of insufficient efficiency of dislocation and disclination accommodation processes can consistently explain almost all the main experimental results obtained to date for SPD.

Pegmatite mylonites: origin and significance

Abstract Pegmatites generally behave as resistant objects compared to their host rocks during solid-state deformation. They usually show folding or boudinage within their host rocks, features observed from low-grade to high-grade deformations, up to upper-amphibolite metamorphic conditions. Here we describe mylonitic pegmatite veins emplaced within S-C fabric-bearing two-mica granites. Pegmatites consist mainly of feldspar and quartz ribbons, with remnants of coarse-grained Kfs phenocrysts. Quartz ribbons are made of large grains elongated in the shearing direction, with evidence of dynamic recrystallization involving grain boundary migration. Ribbons show very strong lattice-preferred orientations of c-axes at low angles to the stretching lineation. From these, we propose that quartz ribbons are formed by oriented growth during syn-shearing crystallization of the pegmatite. Subsequent syn-shearing solid-state deformation involved grain size reduction accompanied by prism <a> slip. The occurrence of pegmatite mylonites within granitoid intrusions should be considered as a univocal argument for synkinematic emplacement.

Rheological transition during large strain deformation of melting and crystallizing metapelites

AbstractTorsion experiments ( =3 × 10−4 s−1) were performed to investigate the large strain (γmax = 15) rheology on quartz‐muscovite aggregate as analogue to pelitic rocks undergoing melting and crystallization during deformation at 300 MPa confining pressure and 750°C temperature. Microstructures reveal four distinct but gradational stages of crystal‐melt interactions during deformation—(a) solid state deformation, (b) initiation and domination of partial melting, (c) simultaneous partial melting and crystallization, and (d) domination of crystallization. The microstructural stages are linked to the rheology of the deforming samples. Partial melting starts at relatively low finite shear strains (γ = 1–3) showing approximately 60% strain softening. At γ = 4–10 the partially molten bulk material shows a steady state flow at low stress. Further crystallization of new crystals at the expense of melt between γ = 10 and 15 causes weak strain hardening until the material fails by developing brittle fractures. The stress exponent (n), calculated at γ = 1, 5, and 10, increases from ∼ 3 to ∼ 43, indicating a transition from power to power law breakdown or exponential flow of the bulk system. Hydrostatic experiments for equivalent times and conditions of the torsion experiments were also conducted to evaluate the reaction kinetics and microstructures under static conditions. The new experimental data establish that partially molten rock does not flow according to a constant strain rate‐dependent power law (steady state) rheology. The rheological transition from strain rate sensitive to strain rate insensitive flow is interpreted as a function of melt‐crystal ratio, their mutual interactions, and the evolution of microstructures in the partially molten rock.

Relationships between deformation and magmatism in the Pan-African Kandi Shear Zone: Microstructural and AMS studies of Ediacaran granitoid intrusions in central Bénin (West Africa)

Relationships between the metamorphic basement, granitic intrusions and the Kandi Shear Zone (KSZ) in central Bénin have been investigated using petrological and structural approaches, in order to better understand the space and time parameters of the Pan-African shear deformation and the Ediacaran magmatism. In central Bénin, metamorphic rocks from the KSZ display a steep to vertical N–S trending foliation, a sub-horizontal mineral lineation together with kinematic indicators in agreement with a dextral transcurrent mega-shear zone. Four granitic intrusions (Dassa, Tré, Gobada and Tchetti) show many petrological similarities. They are biotite±amphibole – ilmenite±magnetite monzogranites with ferrous and metaluminous I-type features derived from high-K calk-alkaline magma. A fifth intrusion (Fita) is an alkali-feldspar, biotite, magnetite and ilmenite bearing granite crystallized from an alkaline magma. Moreover, high K2O, Zr, Y, Nb and low CaO, MgO and Al2O3 contents together with high (FeOt/MgO) and low LIL/HFS elements ratios suggesting an A-type granite affinity.Microstructural and AMS investigations presented in this paper show (i) solid-state deformation evidence for Dassa pluton and (ii) a magmatic deformation for the Tré, Tchetti, Gobada and Fita granitoids. Foliation in Dassa is parallel to the mesoscopic planar mylonitic foliation of the metamorphic basement. In the Tré, Tchetti, Gobada and Fita granitoids, magmatic textures and magnetic fabrics are coherent with the KSZ activity. These data suggest (i) a syn-kinematic nature for most of the intrusions (Tré, Gobada, Tchetti and Fita), except Dassa which correspond to an earlier event (ii) the succession of high-K calk-alkaline (Dassa, Tré, Gobada, Tchetti) evolves toward alkaline magmas (Fita) during the KSZ strike-slip tectonics. These observations highlight the changing nature of magma composition, magmatic processes and the different sources during KSZ activity in the Bénin Nigerian Shield. These new results suggest that the previous geodynamic interpretations, which assume a post-tectonic emplacement for the Gobada intrusion or an active continental margin setting for most of the late Pan-African (Ediacaran) granites intruded in central Bénin, has to be re-examined.