Intermediate Level Of Structure Research Articles

Thrust tectonics in the Fuegian Andes central belt: A detailed geometric-kinematic analysis and new thermochronological constraints

New structural data from the central belt of the Fuegian Andes (Argentina), allowed us to constrain the geometry of a previously interpreted Cenozoic duplex thrust system that connects forelandwards with the frontal thrust-fold belt. This duplex developed between two main detachment horizons: a basal detachment between Jurassic rocks and pre-Jurassic basement, and a roof detachment between Jurassic rocks and the Lower Cretaceous sedimentary fill of the Rocas Verdes back-arc basin. The duplex constitutes an intermediate structural level within a multiple detachment thrust belt and covers deeper structures that accommodated crustal deformation during the Cenozoic evolution of the Fuegian Andes. New zircon and apatite fission track and (UTh)/He cooling ages from rocks within the duplex were modelled together with previously published data, finding time-temperature trajectories that indicate acceleration in cooling rates during the middle Eocene to earliest Miocene, but with more moderate rates than previously reported. This is interpreted as exhumation associated with rock uplift due to duplex thrusting in the hinterland and shortening transference to the foreland, where known contractional stages are as young as early Miocene, and Oligocene-Miocene increased supply of detritus from the eroded central belt is widely reported.

ФОРМИРОВАНИЕ МАРШРУТА МАГИСТРАЛЬНОЙ ТРЕЩИНЫ РАЗРУШЕНИЯ В МНОГОУРОВНЕВОЙ СТРУКТУРЕ КОНГЛОМЕРАТНЫХ СТРОИТЕЛЬНЫХ КОМПОЗИТОВ

In the publication, conglomerate building composites (concrete) are identified as heterogeneous solids with a hierarchically organized spatial-geometric structure with a characteristic dimension from 10-10 to 10-1 m, with a minimum of 5-6 scale levels and three types of substructure design that differ in scale, genesis and mechanics of properties manifestation. The first type is characteristic of the macro-, meso- and microscale levels and is taken in the form of a two-component “construction” of a spatially continuous matrix and discrete solid and gaseous (macropores) inclusions deterministically and stochastically distributed in it; the second type refers to the submicro-, ultra-micro- and nanoscale levels and is believed to be in the form of a “microscale spatial structure” of new formations of a cementitious substance from consolidated individual crystalline differences; the third type, finally, corresponds to the atomic-molecular structure of new formations of the cementing substance. Characteristics of the distinguished types of substructures are given according to the scale of their components, the peculiarities of formation, the mechanics of manifestation of properties, design criteria and means of synthesis of each substructure. The patterns of formation of the fracture route in substructures of all types and substances of each scale level are analyzed. In this case, the development of the stress-strain state of the conglomerate composite according to the principle of energy dissipation, localization and increase (concentration) of stress is realized in the direction from the macro- to the atomic-molecular level of the structure of the composite, and the destruction itself and, accordingly, the formation of the crack route in time and in space of the composite passes in the direction from the atomic-molecular level to the macrolevel in a cascade through all intermediate structural levels. Within the framework of an integrated mechano-physico-chemical approach, the place of thermofluctuation theory (fracture physics) at the stages of breaking single atomic-molecular bonds and crack mechanics at the stages of development of micro- and macrodamage is shown. The possibilities of using theoretical principles of crack route formation to formulate and solve practical problems of designing and synthesizing optimal structures of conglomerate building composites are discussed.

Structural overprinting and style of deformation at sierra Beauvoir and sierra de Apen: A geometric and kinematic model for the evolution of the internal thrust-fold belt, Fuegian Andes, Argentina

A detailed study of the structural fabrics and overprinting relationships exposed at sierra Beauvoir and sierra de Apen, which include folds, foliations and thrust faults, allowed us to settle a deformation sequence of the internal thrust-fold belt of the Fuegian Andes. Our results, together with previous geochronology results, indicate that ductile structures developed during a Late Cretaceous simple shear deformation that formed asymmetric folds and related foliations under very-low grade metamorphism. This deformation affected rocks not younger than the Campanian, and is here related to the front of the orogenic wedge formed during arc-continent collision associated with the closure of a prior back-arc basin. Thrust systems overprint this ductile deformation, and even though they were considered in previous theoretical models, this is the first time their detailed geometry and time constraints are reported from field data. We identified an older, brittle-ductile thrust system formed during the Danian, with the slight penetrative deformation and very gentle folding of the Maastrichtian-Danian Policarpo Formation representing the frontal part of this thrust wedge. This thrust system formed at intermediate structural levels and was linked with basement-involved thrusting in the hinterland, which caused the shortening accommodated in the internal thrust-fold belt. The Eocene Apen-Malvinera thrust system, formed by brittle faults, was responsible for later exhumation of the Cretaceous rocks deformed by prior brittle-ductile structures. This deformation sequence implies that a significant supply of detritus to the foreland basin, originated from the erosion of the Cretaceous cover of the brittle-ductile structures of sierra Beauvoir, should be not older than the Eocene.

Uncovering the mesoscale structure of the credit default swap market to improve portfolio risk modelling

One of the most challenging aspects in the analysis and modelling of financial markets, including Credit Default Swap (CDS) markets, is the presence of an emergent, intermediate level of structure standing in between the microscopic dynamics of individual financial entities and the macroscopic dynamics of the market as a whole. This elusive, mesoscopic level of organisation is often sought for via factor models that ultimately decompose the market according to geographic regions and economic industries. However, at a more general level, the presence of mesoscopic structure might be revealed in an entirely data-driven approach, looking for a modular and possibly hierarchical organisation of the empirical correlation matrix between financial time series. The crucial ingredient in such an approach is the definition of an appropriate null model for the correlation matrix. Recent research showed that community detection techniques developed for networks become intrinsically biased when applied to correlation matrices. For this reason, a method based on Random Matrix Theory has been developed, which identifies the optimal hierarchical decomposition of the system into internally correlated and mutually anti-correlated communities. Building upon this technique, here we resolve the mesoscopic structure of the CDS market and identify groups of issuers that cannot be traced back to standard industry/region taxonomies, thereby being inaccessible to standard factor models. We use this decomposition to introduce a novel default risk model that is shown to outperform more traditional alternatives.

Modularity along organism dispersal gradients challenges a prevailing view of abrupt transitions in animal landscape perception

A common property of landscapes and metacommunities is the occurrence of abrupt shifts in connectivity along gradients of individual dispersal abilities. Animals with short‐range dispersal capability perceive fragmented landscapes, but organisms moving across critical thresholds perceive continuous landscapes. This qualitative shift in landscape perception may determine several attributes of local communities and the dynamics of whole metacommunities. Modularity describes the existence in some communities of relatively high numbers of mutual connections favoring the movement of neighboring individuals (even when each individual is able to reach any patch in the landscape). Local patch linkages and metacommunity connectivity along gradients of dispersal ability have been reported frequently. However, the intermediate level of structure captured by modularity has not been considered. We evaluated landscape connectivity and modularity along gradients of individual dispersal abilities. Random landscapes with different degrees of cell aggregation and occupancy were simulated; we also analyzed ten real ecosystems. An expected, a shift in landscape connectivity was always detected; modularity consistently decreased gradually along dispersal gradients in both simulated networks and empirical landscapes. Neutral metacommunities within simulated landscapes demonstrated that modularity and connectivity may reflect landscape traits in the shaping of metacommunity diversity. Average beta‐diversity was strongly associated with modularity, particularly with low migration rates, while connectivity trends tracked changes in beta‐diversity at intermediate to high migrations rates. Consequently, while some species are able to perceive abrupt transitions in the landscape, many others probably experience a gradual continuum in landscape perception, contrary to predictions from previous analyses. Furthermore, the gradual behavior of modularity indicates that it may represent an exceptional early‐warning tool that measures system distance to tipping points. Our study highlights the multiple perceptions that different species may have of a single landscape and shows, for the first time, a theoretical and empirical relationship between landscape modularity, and metacommunity diversity.

3D hierarchical geometric modeling and multiscale FE analysis as a base for individualized medical diagnosis of bone structure

This paper describes a new alternative for individualized mechanical analysis of bone trabecular structure. This new method closes the gap between the classic homogenization approach that is applied to macro-scale models and the modern micro-finite element method that is applied directly to micro-scale high-resolution models. The method is based on multiresolution geometrical modeling that generates intermediate structural levels. A new method for estimating multiscale material properties has also been developed to facilitate reliable and efficient mechanical analysis. What makes this method unique is that it enables direct and interactive analysis of the model at every intermediate level. Such flexibility is of principal importance in the analysis of trabecular porous structure. The method enables physicians to zoom-in dynamically and focus on the volume of interest (VOI), thus paving the way for a large class of investigations into the mechanical behavior of bone structure. This is one of the very few methods in the field of computational bio-mechanics that applies mechanical analysis adaptively on large-scale high resolution models. The proposed computational multiscale FE method can serve as an infrastructure for a future comprehensive computerized system for diagnosis of bone structures. The aim of such a system is to assist physicians in diagnosis, prognosis, drug treatment simulation and monitoring. Such a system can provide a better understanding of the disease, and hence benefit patients by providing better and more individualized treatment and high quality healthcare. In this paper, we demonstrate the feasibility of our method on a high-resolution model of vertebra L3.

Topology-energy relationships and lowest energy configurations for pentagonal dodecahedral (H2O)20X clusters, X=empty, H2O, NH3, H3O+: The importance of O-topology

For (H(2)O)(20)X water clusters consisting of X enclosed by the 5(12) dodecahedral cage, X = empty, H(2)O, NH(3), and H(3)O(+), databases are made consisting of 55-82 isomers optimized via B3LYP/6-311++G(**). Correlations are explored between ground state electronic energy (Ee) or electronic energy plus zero point energy (Ee+ZPE) and the clusters' topology, defined as the set of directed H-bonds. Linear regression is done to identify topological features that correlate with cluster energy. For each X, variables are found that account for 99% of the variance in Ee and predict it with a rms error under 0.2 kcal/mol. The method of analysis emphasizes the importance of an intermediate level of structure, the "O-topology," consisting of O-types and a list of O pairs that are bonded but omitting H-bond directions, as a device to organize the databases and reduce the number of structures one needs to consider. Relevant variables include three parameters, which count the number of H-bonds having particular donor and acceptor types; absolute value(M)(2), where M is the cluster's vector dipole moment; and the projection of M onto the symmetry axis of X. Scatter diagrams for Ee or Ee+ZPE versus absolute value(M) show that clusters fall naturally into "families" defined by the values of certain discrete parameters, the "major parameters," for each X. Combining "family" analysis and O-topologies, a small group of clusters is identified for each X that are candidates to be the global minimum, and the minimum is determined. For X = H(3)O(+), one cluster with central hydronium lies just 2.08 kcal/mol above the lowest isomer with surface hydronium. Implications of the methodology for dodecahedral (H(2)O)(20)(NH(4)(+)) and (H(2)O)(20)(NH(4)(+))(OH(-)) are discussed, and new lower energy isomers are found. For MP2/TZVP, the lowest-energy (H(2)O)(20)(NH(4)(+)) isomer features a trifurcated H-bond. The results suggest a much more efficient and comprehensive way of seeking low-energy water cluster geometries that may have wide applicability.

Calculation of mesoscopic strain characteristics for the study of the behavior of porous ceramics under uniaxial compression

The paper studies the deformation behavior of zirconia ceramic specimens with different porous structure under uniaxial static compression. In specimens with large pores the latter refer to an active intermediate structural level of deformation. Its involvement into the resistance to plastic deformation governs a considerable strain increase (by 3 times) at fracture when ultimate strengths in both specimen types are comparable. The stage of deformation processes at the mesolevel is determined by the construction and analysis of the dependence of external stress on shear strain intensity logarithm. The obtained data make it possible to offer a scheme of structural deformation levels for studied materials, which is based on the analysis of the stage character of the σ-γ dependence.

Pressure-Temperature-time Evolution of Metamorphic Rocks from Naxos (Cyclades, Greece): Constraints from Thermobarometry and Rb/Sr dating

The Pressure-Temperature-time paths of metapelites sampled on an east-west transect across the structural dome of Naxos (Greece) have been reconstructed on the basis of new geothermobarometric data and Rb/Sr dating, as well as previously published data. One sample from an intermediate structural level records pressure and temperature conditions of 10 kbar, 500°C, corresponding to its exhumation in a highpressure/low-temperature (HP/LT) setting. The corresponding Rb/Sr exhumation age is 29.3±1.3(2s) Ma. Toward the center of the dome, metamorphic assemblages record an increase in peak-temperature and corresponding pressure (from 500 to 700°C, and from 5 to 8 kbar), in a medium-pressure/medium-temperature (MP/MT) metamorphic field gradient. Whole-rock, muscovite and biotite on two samples from deep structural levels define ages of 5.2 and 7.0 Ma, whereas garnets fall outside the isochrons and retain earlier less radiogenic signatures. Rb/Sr data on these two samples demonstrate open system behaviour coeval with, or subsequent to MP/MT metamorphism. The interpretation of the Pressure-Temperature-time paths indicates a time span of 15-20 Ma for dome formation. It also suggests that the HP/LT to MP/MT transition is due to i) heating of deeper parts of the dome through magma injection or ii) either homogeneous (75 %) or localized thinning during dome formation.

Southward extrusion of eclogite-bearing mafic–ultramafic bodies in the Sanbagawa belt, central Shikoku, Japan

Several mafic rock masses, which have experienced eclogite facies metamorphism, are distributed in flat-lying non-eclogitic schists in an intermediate structural level (thermal core) of the Sanbagawa belt. The largest, Iratsu mass, and an associated peridotite, the Higashi-Akaishi mass, extend E–W for about 8 km, and N–S for about 3 km, and are surrounded by pelitic, basic and quartz schists. The Iratsu mass consists of metabasites of gabbroic and basaltic origin, with intercalations of ultramafic rocks, felsic gneiss, quartz schist and metacarbonate. The Iratsu mass can be divided into two layers along a WNW-trending metacarbonate layer. The Higashi-Akaishi mass consists of peridotite with intercalations of garnet clinopyroxenite. It is situated beneath the western half of the Iratsu mass, and their mutual boundary dips gently or steeply to the N or NE. These masses underwent eclogite, and subsequent epidote-amphibolite facies metamorphism as has been reported elsewhere. The Iratsu–Higashi-Akaishi masses and the surrounding rocks underwent ductile deformation under epidote-amphibolite facies (or lower P– T) metamorphic conditions. Their foliation generally trends WNW and dips moderately to the NNE, and the mineral lineation mostly plunges to the N and NE. In non-eclogitic schists surrounding the Iratsu–Higashi-Akaishi masses, the foliation generally trends WNW and dips gently or steeply to the N or S and the mineral lineation mostly plunges to the NW, N and NE. Kinematic analysis of deformation structures in outcrops and oriented samples has been performed to determine shear senses. Consistent top-to-the-north, normal fault displacements are observed in peridotite layers of the Higashi-Akaishi mass and eclogite-bearing epidote amphibolite layers of the Iratsu mass. Top-to-the-northeast or top-to-the-northwest displacements also occur in non-eclogitic pelitic–quartz schists on the northern side of the Iratsu mass. In the structural bottom of the Iratsu–Higashi-Akaishi masses and to the south, reverse fault (top-to-the-south) movements are recognized in serpentinized peridotite and non-eclogitic schists. These observations provide the following constraints on the kinematics of the rock masses: (1) northward normal displacement of Iratsu relative to Higashi-Akaishi, (2) northward normal displacement of non-eclogitic schists on the north of the Iratsu mass and (3) southward thrusting of the Iratsu–Higashi-Akaishi masses upon non-eclogitic schists in the south. The exhumation process of the Iratsu–Higashi-Akaishi masses can be explained by their southward extrusion.

Collision‐Orogen Provenance (Western Alps): Detrital Signatures and Unroofing Trends

The Alps are perhaps the best studied thrust belt formed during continent‐continent convergence (collision orogen). Shallow, intermediate, and deep structural levels can be distinguished within the Alpine thrust stack, each shedding sediments with distinct petrographic and mineralogical signatures. In modern first‐cycle sands carried by Alpine rivers, bulk composition, rank of metamorphic lithic grains (metamorphic index [MI]), and dense mineral assemblages all faithfully mirror the tectono‐metamorphic history of exposed basement and cover units. The shallow structural level, widely preserved in the Ligurian Alps, consists of remnant ocean turbidites, shedding sedimentary to very low rank metasedimentary detritus ($$\mathrm{MI}\,< 180$$). The few dense minerals include recycled ultrastables and garnet. The intermediate structural level, widely exposed in the Western Alps from the Simplon Fault to the Sestri‐Voltaggio Zone, consists of high‐pressure nappes retrogressed to greenschist facies. Detritus includes medium‐rank metasedimentary lithic grains from cover units, quartz and feldspars from continental basements, or metabasite and foliated serpentine‐schist lithic grains from subducted ophiolites. Dense minerals are epidote dominated and include high‐pressure minerals (e.g., carpholite, Mg‐chloritoid, glaucophane); Austroalpine and Penninic massifs supply abundant garnet. The deep structural level, unroofed in the Lepontine Dome, consists of amphibolite facies granitoid gneisses shedding very high rank quartzofeldspathic detritus ($$\mathrm{MI}\,> 380$$). Dense minerals are hornblende dominated. The hornblende/epidote ratio increases, and the color of hornblende grains (hornblende‐color index [HCI]) changes from dominantly blue green to green and green brown, from the periphery ($$\mathrm{HCI}\,< 10$$) to the core (HCI 25–50) of the Lepontine Dome. Before reaching foreland basins on both sides of doubly vergent collision orogens, detritus from axial nappes mixes with detritus from basement and cover units uplifted in external thrust belts, and further modifications occur as a result of recycling of accreted molasse and alluvial plain deposits. This case study, which emphasizes both the complexities involved in provenance studies of foreland basin fills and their potential, provides detailed petrographic and mineralogical data on modern orogenic sands. Such actualistic information is the key for reconstructing paleotectonic and erosional evolution of orogenic source areas from detrital modes of ancient clastic wedges.

Thermobaric structure and metamorphic evolution of the Iratsu eclogite body in the Sanbagawa belt, central Shikoku, Japan

The Iratsu body is the largest eclogitic body in the Sanbagawa belt, central Shikoku, composed of schists with pumpellyite–actinolite, through blueschist/greenschist transition and epidote-amphibolite, up to eclogite-facies grades. The Iratsu body and the underlying Higashi-Akaishi peridotite body are situated in the intermediate structural level of the Sanbagawa belt which occurs as a subhorizontal thin slab. In the Iratsu body, eclogites and eclogitic metagabbros (garnet-clinopyroxenites) contain garnet+omphacite+epidote+quartz+rutile±phengite±glaucophane±paragonite±barroisite±kyanite, and garnet+sodic augite+rutile±epidote±zoisite±quartz, respectively, as mineral assemblages at the peak P– T conditions. Textural relations between these minerals and secondary minerals indicate that the eclogites were retrograded by hydration under eclogite through epidote-amphibolite to greenschist-facies conditions. Geothermobarometry for the peak metamorphism of the eclogites yielded conditions of 1.4–2.5 GPa and 500–800 °C in the Iratsu body; the estimated P– T conditions gradually change across the body. Eclogites with higher P– T estimates are predominant in the southern part of the body, and the eclogites near a contact with the Higashi-Akaishi body show the highest P– T conditions. Integration of these results with previously published P– T estimates for various rock types suggests a sandwiched thermobaric structure. The highest P– T area is situated in an intermediate structural level, i.e., in the upper part of the Higashi-Akaishi body near the boundary with the Iratsu body, and the metamorphic conditions systematically decrease towards the upper and lower levels not only within the Iratsu body but also in the surrounding lower grade schists. Our thermobaric structure implies that the Iratsu and Higashi-Akaishi composite mass is not a tectonic block but is the integral part of the Sanbagawa belt, which has been formed together with the surrounding schists under a specific thermal gradient at depths in the subduction zone. The Sanbagawa metamorphic facies series, newly proposed, draws a convex curve towards the lower P and higher T side in a P– T diagram, and is similar to a steady-state P– T path in a subduction zone, calculated by numerical models.

Contact Metamorphism of the Daulet Suite by Solid-State Emplacement of the Kokchetav UHP-HP Metamorphic Slab

The andalusite-sillimanite-type low-pressure Daulet Suite underlies the Kokchetav ultrahigh-pressure—high-pressure (UHP-HP) massif of northern Kazakhstan. The Daulet Suite is composed of pelitic-psammitic gneisses or schists and quartz schist with minor amounts of metacarbonate and metabasite. About 300 thin sections were examined from the Daulet metapelites; rocks were divided into two mineral zones. Zone A is characterized by andalusite + cordierite + biotite, and zone B by sillimanite + cordierite + biotite with excess K-feldspar, quartz, and plagioclase in both zones. K-feldspar appears with andalusite at lower temperatures than the first formation of sillimanite. Pressure-temperature conditions of the Daulet metamorphism range from 580 to 680°C at a nearly constant pressure of ~2 kbar. Comparison of compositions of solid-solution minerals with a buffered assemblage indicates that the metamorphic grade increases towards the boundary with the overlying UHP-HP unit. Detailed mapping revealed that the primary structure of both the Kokchetav UHP-HP massif and its surrounding units is subhorizontal; the UHP-HP unit has been thrust over the Daulet Suite with a top-to-the-north movement. The thermal structure of the Daulet Suite is subhorizontal and metamorphic grade increases upwards—i.e., toward the boundary with the UHP-HP unit—whereas the thermobaric maximum of the UHP-HP unit occurs at an intermediate structural level. The upward increase in metamorphic grade within the Daulet Suite implies contact metamorphism by the tectonic juxtaposition of the "hot" Kokchetav UHP-HP unit at shallow crustal levels.

U–Pb geochronology of detrital zircons in metasedimentary rocks from southern Baffin Island: implications for the Paleoproterozoic tectonic evolution of Northeastern Laurentia

A geochronological investigation of metasedimentary rocks from southern Baffin Island using the Geological Survey of Canada SHRIMP II (sensitive high-resolution ion microprobe) has characterized the ages of detrital zircon populations to determine their provenance, bracket timing of deposition, and distinguish potentially distinct sequences of rocks. Four lithologically and structurally distinct metasedimentary packages have been identified; each appears to have been derived from a different source region. In the structurally lowest package, all analysed zircons are Archean, and &gt; 90% have ages between 2.83 and 2.63 Ga; these rocks are interpreted as the northernmost exposures of the Paleoproterozoic Povungnituk Group of the Cape Smith Belt, northern Quebec, with detritus derived from the Superior craton. Occupying the intermediate structural levels, the most abundant supracrustal rocks on southern Baffin Island are siliciclastic and carbonate units of the Lake Harbour Group, and the Tasiuyak paragneiss. Five samples show a dominantly Paleoproterozoic signature (2.2–1.9 Ga), with only rare Archean zircons; the provenance of this detritus is uncertain. In the distinct package of feldspathic quartzite and pelite that stratigraphically overlies the Lake Harbour Group, all of the analysed detrital grains are Archean, ~80% are &gt; 2.83 Ga, with a small proportion of the grains in excess of 3.0 Ga; all of this material is thought to be derived from the Archean craton exposed on the Hall Peninsula east of the study area. Finally, at the highest structural level, a sample associated with the Hall Peninsula orthogneisses contains zircons with prominent modes at 2.92, 2.82, and 2.77 Ga, consistent with derivation from the surrounding orthogneisses.

Upper and lower plate juxtaposition, deformation and metamorphism during crustal convergence, Trans-Hudson Orogen (Quebec–Baffin segment), Canada

The lower plate of the Quebec–Baffin segment of Paleoproterozoic Trans-Hudson Orogen comprises parautochthonous Archean crystalline basement of the Superior Province (3.22–2.74 Ga) and imbricated Paleoproterozoic rift-margin strata (2.04–1.92 Ga). The collisional upper plate contains (1) allochthonous ophiolitic units (2.00 Ga), (2) a continental arc terrane (Narsajuaq arc; 1.86–1.82 Ga), (3) shelf sequence strata (ca. <1.93 Ga and >1.86 Ga) and basement orthogneisses (ca. 1.95 Ga), (4) foreland basin deposits (<1.93 Ga and >1.86 Ga), and (5) a batholith which intrudes the shelf and foreland basin rocks (Cumberland batholith; 1.86–1.85 Ga). Lower and upper plate assemblages were juxtaposed during a 1.82–1.79 Ga accretion–collision event, and deformed into regional-scale folds during two post-collisional folding episodes (ca. 1.76–1.74 Ga). As a result of the structural relief generated by the post-collisional folding and subsequent exhumation, all orogenic elements can be directly examined along a 400 km, across-strike transect. In the external zone (northern Quebec), lower plate rift-margin units were internally imbricated (Cape Smith Belt) and translated southward across the Superior Province basement. Paleoproterozoic amphibolite facies mineral growth is syn to post-thrusting. Tectonic imbrication has resulted in a structural inversion of the accreted (i.e. upper plate) ophiolite stratigraphy. North of the Cape Smith Belt, mid-crustal plutonic units of the Narsajuaq arc form an upper plate crystalline wedge whose sole thrust is localized near the thrust belt's basal décollement. Within Narsajuaq arc, syn-magmatic granulite facies assemblages are retrogressed to amphibolite facies assemblages in proximity to major accretion–collision faults. In the internal zone (southern Baffin Island), a tripartite orogen-scale tectonostratigraphy is exposed on the flanks of the post-collisional fold structures. At the lowest structural level, lower plate Superior Province orthogneisses are imbricated with Paleoproterozoic rift-margin units, and mineral growth is syn-thrusting. At intermediate structural level, upper plate orthogneisses are correlated with the Narsajuaq arc in northern Quebec. At the highest structural level, a north-facing shelf sequence is structurally overlain by an assemblage of clastic rocks interpreted as a foreland basin sequence. Dominantly-monzogranite plutons of the Cumberland batholith are restricted to the upper structural level and indicate pre-emplacement imbrication of tectonostratigraphic units. Within both upper and lower plates, granulite facies assemblages are retrogressed to upper amphibolite assemblages in proximity to 1.82–1.79 Ga accretion–collision structures. Exposures of Superior Province basement across the orogen document a progressive increase in the extent of reworking during accretion of upper plate units, from a narrow shear zone in the external zone to km-scale imbrication and more pervasive shear deformation in the internal zone. A minimum of 160 km of basement underthrusting is constrained by the structural overlap of upper plate allochthons on lower plate units. Basement involvement during post-collision shortening is manifest as thick-skinned folding, indicating coupling across the collisional basal décollement.

High-strain zones from mesoto macro-scale at different structural levels, Central Norwegian Caledonides

High-strain shear zones of diverse character, metamorphic grade and scale occur in different tectonic settings in the Caledonides of Central Norway. Three specific examples are described. Strain products range from high-PT granulite to amphibolite-facies, thrust-related, Scandian mylonites at deep structural levels, to ultracataclasites and mylonites generated in the ductile to ductile-brittle transition regimes along the multiply reactivated, orogen-oblique Møre-Trøndelag Fault Complex. In another example, geochemical data from a transformation of granite to mylonite at an intermediate structural level indicate that the high-strain change-over probably occurred as an open, volume-gain system involving silicification. In the case of the Møre-Trøndelag Fault Complex, a sinistral strike-slip regime during Devonian time was coeval with regionally extensive top-to-the-SW shear in the country rocks outside the fault zone. Later components of movement along the multiphase fault zone, from latest Palaeozoic to Cenozoic time, were mainly of brittle, dip-slip to dextral strike- or oblique-slip character.

Sequence of Thrusting Within A Thick‐Skinned Tectonic Wedge: Evidence From40Ar/39Ar and Rb‐Sr Ages From the Austroalpine Nappe Complex of the Eastern Alps

The sequence of thrusting within a regional‐scale Alpine thick‐skinned tectonic wedge has been constrained by Rb‐Sr and 40Ar/39Ar dating of whole‐rock, constituent white mica and biotite from structural units of the Austroalpine Nappe Complex, Eastern Alps (Austria). Preservation of Variscan and pre‐Variscan isotopic signatures in pre‐Alpine basement units indicates a non‐penetrative metamorphic Alpine overprint. Alpine nappe assembly and accompanying ductile deformation occurred during maintenance of lower greenschist‐facies metamorphic conditions (c. 300°–450°C). Analyses from greenschist‐facies metamorphic mylonites and penetratively ductile deformed cover sequences display decreasing 40Ar/39Ar plateau ages structurally downward. Thrusting and accompanied ductile deformation commenced at c. 100–90 Ma in the uppermost structural levels. Footwall fault propagation effected internal deformation and out‐of‐sequence thrusting within intermediate structural levels at c. 95–80 Ma. This was contemporaneous with regional exhumation and cooling of deeper crustal basement units at c. 88–82 Ma and was associated with extension and strike‐slip faulting, leading to the formation of synorogenic sedimentary basins. Additional foot‐wall thrust propagation was associated with ductile deformation within lowermost structural units at c. 80–70 Ma. The structural and new geochronologic results presented herein suggest that (1) the Austroalpine Nappe Complex represents a forward propagating thrust complex that formed as a result of footwall propagation of a master fault and associated piggyback transport of hangingwall structural units; (2) most parts of the Austroalpine block occupied a lower‐plate tectonic setting during Cretaceous tectonics subsequent to subduction of the Meliata‐Hallstatt ocean; and (3) the Austroalpine Nappe Complex had already been formed when subduction of Penninic oceanic domains was active.

On the internal perceptual structure of phonological features: The [voice] distinction

Apart from phonological features and their individual phonetic correlates, an intermediate level of structure apparently exists in which subsets of phonetic properties form perceptually coherent units, referred to here as ‘‘integrated perceptual properties.’’ The mapping between each successive level of structure is arguably many‐to‐one, elevating both redundancy and distinctiveness at the level of phonological features. For the distinctive feature [voice], a main integrated perceptual property corresponding to the [+voice] value is the presence of low‐frequency energy during or near the consonant, which may be further analyzed into at least three phonetically distinct subproperties: voicing during the consonant constriction, a low F1 near the constriction, and a low F0 in the same region. Two predictions follow if these three subproperties contribute to a single integrated perceptual property. One is that the effects on [voice] judgments of varying either a low F1 or F0 should pattern in similar ways for a given utterance position and stress pattern; this prediction was confirmed. The second prediction is that two stimuli in which separate subproperties of the low‐frequency property are positively correlated (i.e., they are either both present or both absent) will be more distinguishable than two stimuli in which the subproperties are negatively correlated; though not yet confirmed for the pairing of F1 with F0, this prediction was confirmed for pairings of F1 or F0 with constriction voicing.

Meteoric water‐rock interaction in the lower plate of the Whipple Mountain metamorphic core complex, California

ABSTRACTOxygen isotope ratios, whole rock major and trace element compositions, and petrological characteristics of 52 samples from nine distinct igneous lithologies in the lower plate of the Whipple Mountain metamorphic core complex of south‐eastern California indicate that both mylonitic and non‐mylonitic lithologies underwent exchange with surface‐derived meteoric waters. Broadly granodioritic lithologies are characterized by whole rock δ18O values that range from 10.6 to 2.6‰. Isotopic compositions of quartz and feldspar mineral separates indicate that quartz has largely retained original igneous compositions but that feldspar has undergone variable and often large 18O‐depletions (up to 6.5‰).Over 4 km of structural relief is exposed in lower plate gneisses below the Whipple detachment fault including non‐mylonitic lithologies at shallow structural levels above the mylonite front, and mylonitic gneisses at intermediate to deep levels below the mylonite front. Coupled δ18Oqtz ‐ δ18OFsp systematics of non‐mylonitic and mylonitic andesite to rhyolite dykes from shallow and intermediate structural levels of the lower plate document two episodes of hydrothermal alteration: a high‐temperature (&gt;c.600d̀C) episode involving a metamorphic or magmatic fluid with δ18O values ∼ 7‰ and a low‐temperature (c.350d̀C) episode involving low‐δ18O meteoric fluids. All the dykes that document exchange with meteoric fluids are non‐mylonitic. Coupled δ18OFsp systematics of non‐mylonitic and mylonitic granodioritic gneisses from above and below the mylonite front also document low‐temperature (c. 350d̀ C) exchange with meteoric fluids. The data indicate that infiltration of meteoric fluids occurred as lower plate lithologies were juxtaposed against the base of the faulted upper plate. High‐angle normal faults in the upper plate served as the conduits for the downward circulation of surface‐derived fluids. Meteoric fluids were able to penetrate across the detachment fault into the lower plate.Uplift rates coupled with independent cooling rates indicate that surface‐derived fluids penetrated to a depth of c.4km and possibly as deep as c.8km. Penetration of surface‐derived fluid into the ductile deformation regime is not required to explain the low δ18O values observed in lower plate lithologies of the Whipple Mountain metamorphic core complex.

Early stages of foreland basin evolution in the Lesser Himalaya, N India

Abstract In this paper we report preliminary results of an integrated sedimentological and structural study of the Late Cretaceous-Early Tertiary facies exposed in the Lesser Himalaya. The Precambrian-Palaeozoic basement of the Indian plate was initially transgressed in Late Cretaceous times (after c. 100 Ma), with the deposition of shallow shelf carbonates, (50 m thick Singtali Formation). These are depositionally overlain by green ferruginous mudstones and thin limestones of the 150 m thick Palaeocene-Eocene ( c. 65–40 Ma) Subathu Formation. During Late Eocene-Oligocene times ( c. 40–30 Ma), clastic sediment input increased and red lenticular sandstones, thinner planar-bedded sandstones, mudstones and caliche of the 350 m thick Dagshai Formation were deposited. A semi-arid, meandering fluvial/floodplain setting is envisaged, with thick channelised and overbank sands. Palaeocurrent evidence indicates a general SE progradation. Our detailed field mapping shows that where the entire Subathu and Dagshai Formations are intercalated, this is the result of post-depositional tectonics, rather than primary intertonguing as described in some previous reports. The relative abundance of sandstones greatly increased in upper Dagshai times, continuing into the Early-Mid-Miocene ( c. 30–10 Ma) when the 250 m thick Kasauli Formation was laid down. This formation is characterized by lenticular and planar-bedded grey sandstones, rich in plant material including occasional logs (but without caliche) interbedded with minor grey mudstones. A rapidly prograding, braided fluvial environment is proposed, with the petrography (e.g. presence of garnets) suggesting erosion and derivation from deeper levels of the Himalayan mountain belt to the north. The climate had by then changed from semi-arid to humid, possibly in response to the onset of the monsoon, initiated when the mountain belt had reached sufficient height to interfere with the jet-stream. During Late Miocene-Quaternary times (younger than c. 15 Ma), the Tertiary foreland basin was deformed and incorporated into three structural levels of a southward migrating thrust stack. At the lowest level, thick successions of the Tertiary Subathu, Dagshai and Kasauli Formations are structurally underlain by fluvial sediments (Siwalik Gp.) and overlain by the Krol Precambrian-Palaeozoic sedimentary nappe. At the intermediate structural level, Early Tertiary sediments unconformably overlie the stratigraphy within this nappe and comprise, often thin (&lt;50 m), successions of mainly Subathu and Dagshai Formation sediments. The highest structural level sediments form small imbricates, highly dismembered units and melange (including evaporites) beneath the major metamorphic Jutogh Nappe. We interpret the Late Cretaceous-Palaeocene Singtali Formation as pre-collisional transgressive sediments related either to flexural downwarping of the Indian plate due to the obduction of the Spontang ophiolite onto the north Indian plate margin, or to extensional tectonics related to the detachment and drift of India from Gondwana and Neo-Tethyan subduction beneath Asia. This would have been coupled with the Late Cretaceous global eustatic sea-level high stand. The marine Subathu Formation is interpreted as having been deposited between initial and terminal India-Eurasia continental collision, with the overlying fluvial/floodplain Late Eocene-Oligocene Dagshai and Miocene Kasauli Formations as southward prograding foreland basin successions related to progressive stages of India-Eurasia continental collision.