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We present balanced and restored cross-sections across the Western Cuba fold and thrust belt, based on MCS profiles, field data and balancing techniques. The cross-section intersects the Los Palacios Basin, the Sierra del Rosario antiformal stack, the Bahía Honda unit, the frontal imbricated thrust sheets, the foredeep basin and a buried, geometrically inferred duplex. The minimum calculated shortening is 130 km. Syntectonic deposits and a forward kinematic model provide a good constraint for the Cenozoic tectonic evolution of the orogen, from the emplacement of the Bahía Honda unit to the final infill of the foredeep. [ABSTRACT FROM AUTHOR]

We analyse broad-band SS waveform data recorded by several networks in Europe with sources mainly in the west Pacific to study the underside reflections of teleseismic SS waves in the lithosphere and the upper mantle beneath eastern Asia and the NW Pacific ocean. SS bounce points sample a corridor from the Aleutian, Kamchatka and Japan subduction zones through the North China Craton and Central Asian Orogenic Belt to the Tibetan plateau. The corridor passes through different tectonic units such as subduction zones, an old continental shield, a fold belt and a high plateau. We investigate the seismic structure of the lithosphere and the mantle transition zone beneath the different geotectonic units along the profile and infer the correlation of geodynamic processes at different depths. We explore the short period frequency content in the SS waveform data and use moveout correction and common midpoint stack to acquire profiles with high lateral and depth resolution from the crust to the mantle transition zone. Clear SS precursors of the 410 and 660 km discontinuities show the effects of the interaction between the subducted oceanic lithosphere and the mantle transition zone beneath the NW Pacific subduction zones. A low-velocity layer has also been detected beneath the 410 km discontinuity and can be traced along the entire profile. Due to the improved resolution acquired by the method presented here we have been able to study the shallower structures such as the Moho and the lithosphere–asthenosphere boundary by SS precursors. The continental Moho can be clearly seen along this corridor. The depth variation agrees well with earlier receiver function results. We also see negative reflectors along the profile at varying depths, which can be interpreted as the lithosphere–asthenosphere boundary. [ABSTRACT FROM AUTHOR]

Terra Nova, 22, 315–323, 2010 End-member cases for the fate of the crust at convergent lithospheric plate boundaries accommodated by subduction are considered combining (i) plate kinematics (slab retreat vs. slab advance) and (ii) mechanical coupling/decoupling within the subducting slab. Slab advance is accommodated by thickening of the overriding lithospheric mantle, whereas slab retreat is associated with thinning. Crust–mantle mechanical coupling results in continental subduction, whereas decoupling leads to continental accretion. The thermal and topographic evolutions of the associated orogenic belts are functions of the crust–mantle thickness ratio resulting from the combined effects of crust–mantle coupling/decoupling and slab advance/retreat. Crustal accretion associated with slab advance results in crustal thickening and contributes to an increase in radioactive heat production and buoyancy, which is impeded by concomitant thickening of the conductive and dense lithospheric mantle. In contrast, crustal accretion combined with slab retreat results in thickening simultaneous with thinning of the lithospheric mantle. This peculiar situation is the most favourable for generating a high-temperature and buoyant orogenic belt. [ABSTRACT FROM AUTHOR]

Abstract: The Neoproterozoic Sergipano Belt formed by the collision of the Pernambuco-Alagoas Block in the north with the São Francisco Craton in the south, but the timing, duration and mechanics of this amalgamation are poorly understood. The belt is divided into the Canindé, Poço Redondo-Marancó, Macururé, Vaza Barris, and Estância lithostratigraphic domains; the first three are composed of plutonic, volcanic and sedimentary rocks and the last three of sedimentary rocks. Our new field, structural, and geochemical data, and Sm–Nd, Ar–Ar and U–Pb geochronology provide robust constraints for the following evolution. A Mesoproterozoic (∼980–960Ma) continental arc (Poço Redondo tonalitic gneisses) developed on the margin of the Palaeoproterozoic Pernambuco-Alagoas Block. Extension of this continental block gave rise to (i) A-type crustal granites and associated sedimentary rocks on the stretched, rifted margin of the Poço Redondo-Marancó Domain, (ii) the Canindé rift sequence between the Pernambuco-Alagoas Block and the Poço Redondo/Marancó domain, (iii) a passive margin on the southern boundary of the Pernambuco-Alagoas Block on which sediments were deposited after 900Ma, (iv) and a second passive margin on the São Francisco Craton. In the Canindé Domain, rifting continued until ca. 640Ma and led to emplacement of a bimodal association of A-type granite (715 Ma) and continental mafic volcanic rocks, a continental-type layered gabbroic complex (ca. 700Ma), magma-mingled gabbro/quartz–monzodiorite (688Ma), and rapakivi granites (684Ma and 641Ma). Deformed pillow basalts and interleaved marble lenses are likely ocean floor relicts in the Canindé Domain. Closure of the Canindé oceanic basin began at ca. 630Ma with the intrusion of arc-type granitic plutons. Convergence of the Pernambuco-Alagoas Block and the São Francisco Craton led to deformation on the passive margins and granite emplacement in the Macururé (628–625Ma, and 590–570Ma), Canindé (ca. 621Ma) and Poço Redondo-Marancó (ca. 625Ma) domains. A small oceanic basin was most likely subducted beneath the Poço Redondo-Marancó Domain to account for the presence of 602Ma arc-type volcanic rocks. Shortly after, exhumation of the Pernambuco-Alagoas Block and Canindé, Poço Redondo-Marancó and Macururé domains in the north led to deposition of uppermost clastic sediments in the Estância and Vaza Barris domains in the south, possibly in a foreland basin, and to final thrusting of the continental margin sedimentary rocks onto the São Francisco Craton. Our results indicate that the construction of western Gondwana involved a ca. 300 million years long history of plate breakup and collision. [Copyright &y& Elsevier]

Mobile belts are long-lived deformation zones composed of an ensemble of crustal fragments, distributed over hundreds of kilometres inside continental convergent margins. The Mediterranean represents a remarkable example of this tectonic setting: the region hosts a diffuse boundary between the Nubia and Eurasia plates comprised of a mosaic of microplates that move and deform independently from the overall plate convergence. Surface expressions of Mediterranean tectonics include deep, subsiding backarc basins, intraplate plateaux and uplifting orogenic belts. Although the kinematics of the area are now fairly well defined, the dynamical origins of many of these active features are controversial and usually attributed to crustal and lithospheric interactions. However, the effects of mantle convection, well established for continental interiors, should be particularly relevant in a mobile belt, and modelling may constrain important parameters such as slab coherence and lithospheric strength. Here we compute global mantle flow on the basis of recent, high-resolution seismic tomography to investigate the role of buoyancy-driven and plate-motion-induced mantle circulation for the Mediterranean. We show that mantle flow provides an explanation for much of the observed dynamic topography and microplate motion in the region. More generally, vigorous small-scale convection in the uppermost mantle may also underpin other complex mobile belts such as the North American Cordillera or the Himalayan–Tibetan collision zone. [ABSTRACT FROM AUTHOR]

Terra Nova, 22, 155–165, 2010 Sequence stratigraphy in the hinterland, kinematic analysis of thin-skinned thrusting in the foreland and thermochronological tracking of exhumation in the orogenic core are combined to quantify the mechanics of an orogen with low topographic build-up. The Carpathian system demonstrates that collisional deformation can couple and thicken the lower orogenic plate along reverse faults that dip more steeply than the subduction zone, defining a ‘foreland-coupling’ type of collision. Near the surface, this is expressed by wide antiforms in the upper plate and the thin-skinned orogenic wedge. A sequence stratigraphic analysis of the back-arc Transylvanian Basin demonstrates that the sedimentary architecture records orogenic uplift pulses with both short and long wavelengths. These correspond to the activation of individual thrust sheets in the thin-skinned wedge and to lower-plate coupling events respectively. [ABSTRACT FROM AUTHOR]

Numerical models offer powerful insights into tectonic processes, especially when their validity can be tested against geological and geophysical observations from natural orogenic belts. Here we explain some of the criteria for success in integrating orogenic models with data, using examples from the Grenville Orogen. Model designs must be simplified by comparison with nature to illuminate the first-order processes that control orogenic evolution, which limits the extent to which model results can reproduce geological observations. For the western Grenville Orogen, observed variations in geological properties are represented by lower crustal blocks with strength decreasing from the exterior to the interior of the model. GO-series models with this design reproduce the first-order crustal architecture of the Georgian Bay and Montréal – Val d’Or Lithoprobe transects. Both constant-convergence and stop-convergence models produce similar geometries, but only stop-convergence models produce normal-sense shear zones like those observed. EGO-series models, incorporating an initial weak zone bounded by stronger lower crustal blocks, predict exhumation of high-pressure rocks as observed in the eastern Grenville Orogen, although other aspects of these model results are not as successful. The single most important test of a geodynamic model is its ability to integrate diverse and independent observations in a self-consistent manner. Other criteria include consistency with crustal-scale geometry and structural and metamorphic histories. By these criteria, the present models account reasonably well for the syn- and post-convergent evolution of the western Grenville Orogen, but further work is required to produce a fully satisfactory model for the eastern end of the system. Plusieurs modèles numériques offrent des aperçus révélateurs de processus tectoniques, surtout lorsqu’ils peuvent être validés par rapport à des observations géologiques et géophysiques de ceintures orogéniques naturelles. Dans cet article, nous expliquons quelques critères pour réussir l’intégration de modèles orogéniques avec les données, en utilisant des exemples de l’orogène de Grenville. Les conceptions des modèles doivent être simplifiées par rapport à la nature afin de souligner les processus de premier ordre qui contrôlent l’évolution de l’orogène, ce qui limite l’étendue selon laquelle les résultats des modèles peuvent reproduire les observations géologiques. En ce qui concerne la partie ouest de l’orogène de Grenville, les variations observées dans les propriétés géologiques sont représentées par des blocs de la croûte inférieure dont la puissance décroît de l’extérieur vers l’intérieur du modèle. Les modèles de séries de l’orogène de Grenville conçus de cette manière reproduisent l’architecture de premier ordre de la croûte des transects Lithoprobe de la baie Georgienne et de Montréal – Val-d’Or. Les modèles de convergence constante et de convergence par à-coups produisent des géométries similaires, mais seuls les modèles par à-coups produisent des zones de cisaillement distensif comme celles observées. Les modèles des séries de l’orogène de Grenville oriental, incorporant une zone initiale faible limitée par des blocs plus forts de la croûte, exhument les roches de haute pression tel qu’observé dans l’orogène de Grenville oriental, bien que d’autres aspects des résultats de ces modèles ne soient pas aussi réussis. La vérification la plus importante d’un modèle géodynamique est sa capacité d’intégrer des observations diverses et indépendantes d’une manière autoconsistante. D’autres critères comprennent la conformité avec la géométrie à l’échelle de la croûte et les historiques de structure et de métamorphisme. Selon ces critères, les modèles actuels tiennent raisonnablement compte de l’évolution syn- et post-convergente de l’orogène de Grenville occidental mais il faudrait plus de travaux pour établir un modèle pleinement satisfaisant pour l’extrémité est du système. [ABSTRACT FROM AUTHOR]

Earth's continental crust today is both created and destroyed by plate tectonic processes, a balance that is encapsulated by the traditional Chinese concept of yin-yang, whereby dualities act in concert as well as in opposition. Yin-yang conceptualizations of crustal growth and destruction are mostly related to plate tectonics; both occur mostly at subduction zones, by arc magmatic creation and by subduction removal. Crust is also created and destroyed by processes unrelated to plate tectonics, including losses by lower crust foundering and additions at hotspots. At present, creation and destruction of continental crust is either in balance (∼3.2 km3/year, or 3.2 AU) or more crust is being destroyed than created; the uncertainty comes from unknown deep losses of continental crust at collision zones and due to lower crustal foundering. The yin-yang creation-destruction balance changes over a supercontinent cycle, with crustal growth being greatest during supercontinent break-up due to high magmatic flux at new arcs and crustal destruction being greatest during supercontinent amalgamation due to subduction of continental material and increased sediment flux due to orogenic uplift. These conclusions challenge the widely held view that continental crust volume has increased over time due to plate tectonic activity; it is just as likely that this volume has decreased. [ABSTRACT FROM AUTHOR]

Abstract: In the last years, the deep crustal structure of the North-Western part of the Iberian Peninsula has been explored using teleseismic receiver function (RF) analysis of P to S conversions at main crustal interfaces. This area has been previously investigated by seismic reflection and refraction experiments and therefore provides an excellent opportunity to compare the results of both approaches. The region shows the imprint of two orogenic events, the Variscan and Alpine ones that exhibit different, reverse intensities from west to east. In a first stage, a N–S transect across the Cantabrian Mountains was instrumented to study the area affected by the Alpine compressional tectonics. Later on, the limit between the undisturbed Variscan units and the reworked Alpine zones was explored by N–S and E–W transects. Finally, an array was deployed in the NW edge of Iberia, over the Variscan hinterland zone. The receiver functions are calculated by inverse filtering deconvolution of the L component from the Q component, and the resulting RF are processed using a simple form of migration to obtain images in depth of the lithosphere that can be compared to the 2-D velocity–depth models from active seismic experiments. The deep crustal structure constrained by both techniques is remarkably consistent, and provides further evidence on the crustal doubling and wedging between the Iberian and European crusts throughout the northern part of the Iberian Peninsula affected by the Alpine tectonics. The undisturbed Variscan domains, characterized by a clear subhorizontal Moho and few intracrustal convertors, show up at the southern edge of the N–S transects (southward of the Alpine deformation front) and over the Variscan hinterland in the E–W transect. The crust resulting from Alpine reworking presents a complex structure, with short and frequently dipping convertors, which in some cases seem to image preserved Variscan structures. [Copyright &y& Elsevier]

Abstract: The deformation history of sedimentary units incorporated in the North Cuban fold and thrust belt in the Paleocene to middle–late Eocene was associated with major shortening between the Caribbean and North American plates. This led to the formation of an intensely deformed tectonic pile comprising from top to bottom of a volcanic arc nappe, a deformed mafic–ultramafic complex with Mesozoic ophiolite components and a serpentinitic mélange with blocks of sedimentary (the Placetas belt) and metamorphic rocks; and the structurally lower unit composed of folded and thrusted sediments of the southern promontory of the Bahamas platform. In this paper we study the deformation history of sedimentary units incorporated in the North Cuban fold and thrust belt associated with this shortening history. We find that the occurrences of the Placetas sedimentary rocks within the foliated serpentinite mélange show varying styles and intensity of deformation, and varying number of deformation phases. They form isolated blocks within the serpentinite mélange and do not represent a coherent nappe underlying the allochtonous mafic–ultramafic complex. The deformation of the Remedios belt, part of the Bahamas platform, underwent a single phase of folding and thrusting, with shortening perpendicular to the plate contact. This folding occurred in the middle to late Eocene and marks the arrest of subduction and arc–continent collision. We find no evidence for a component of strike-slip during collision. The volcanic arc is thrusted upon the mafic–ultramafic complex, and the original forearc ophiolite appears to be shortened. This shortening may attest to a period of subduction erosion. Thrusting of the volcanic arc led to deposition of the Paleocene-lower Eocene Taguasco olistostrome which may date this event. We show that careful analysis of the complexly deformed Cuban fold and thrust belt may allow identification of subduction erosion and subduction accretion episodes. Expanding the analysis carried out in this paper to the scale of the northern Caribbean fold and thrust belt may provide a new and independent geological tool to constrain the geodynamic processes associated with subduction and arc–continent collision along the northern Caribbean margin. [Copyright &y& Elsevier]

Abstract: The sub-Himalayan thrust belt is an active thrust wedge which progresses southward over the north-dipping Indian plate. The north–south compression resulted in severe deformation of sedimentary rocks in this belt. Distinct thrust geometries and topography have evolved under the interaction between tectonic and erosional environments. To better understand the relationship between tectonics and topography, A Digital Elevation Model (DEM) derived from Shuttle Radar Topography Mission (SRTM) data was used to extract the geomorphic and drainage features. Based on comprehensive analyses of topographic relief, drainage density, and drainage patterns, nine topographic units were identified. The thrust wedge was divided into three physiographic assemblages with apparent lateral variations. These units match up with the interpreted main structures from the Landsat Enhanced Thematic Mapper Plus (ETM+) images and published geological maps. The relationship between geomorphometric features and tectonics indicates that structural activities primarily control the topography in the sub-Himalayan thrust belt. Topographic features are indicative of tectonics in the young tectonic regions with low elevation. [Copyright &y& Elsevier]

Abstract: There are very close relationships between orogenic belts and their peripheral sedimentary basins: they are spatially interdependent in structure, mutually compensatory in material, interactive in tectonics, simultaneous in tectonic evolution. The relationships indicate a unified formation mechanism for the continental orogenic belts and the sedimentary basins, which can be presented as follows: lower crustal ductile lateral flow from the basin to the orogen, driven by thermal energy related to upwelling mantle plume in the intracontinental crust and by vertical diaper movement of dehydration and magma of the subduction plate on the active continental margin, results in the circulative movement of crust materials between basins and orogens. The coupling between the Qinghai–Tibet Plateau and its peripheral basins is a typical basin-orogen coupling occurring in the intraplate tectonic setting. The formation of the Qinghai–Tibet Plateau is not a result of collision between the India plate and the Eurasia plate, but rather the result of intraplate basin-orogen formation process driven by lower crustal flow. The tectonic evolution of intraplate basin-orogen system in the Qinghai–Tibet Plateau can be divided into two stages: (1) intraplate orogen-basin formation stage. During this stage, the spatial and temporal evolution of the intraplate orogens and basins in the Qinghai–Tibet Plateau is indicated by the successive geographic movement of the locations of the new basin-orogen systems from the northern and eastern, to the central, and finally to the southern Qinghai–Tibet Plateau, corresponding geochronologically to periods from 180–120 Ma, to 65–30 Ma, and finally to 23–7 Ma. This stage was manifested by extensive intraplate faulting, folding, block movement, magmatism and metallogeny. (2) isostatic mountain building and basin margin subsidence stage. In this stage, there were rapid uplift and strong erosion of the entire Qinghai–Tibet Plateau and rapid subsidence and molasse formation in the depressions on the margins of the peripheral basins resulted from gravity isostasy since 3.6 Ma. The stage is characterized by pulsative uplift and subsidence, crust-scale vertical movement, integral rapid uplifting of the Plateau, local subsiding of basin margin, and tremendous change in topography and environment, with pulses at 3.6 Ma B.P., 2.5 Ma B.P., 1.8–1.2 Ma B.P., 0.8 Ma B.P., 0.15 Ma B.P., etc. The intracontinental basin-orogen systems also underwent tectonic transformation from extension to compression, and the active movement respectively changed from the basin to the orogen. Non-Anderson low-angle detachment, wavy thrust faults, and abnormal conjugate strike-slip faults are formed due to lower crustal flow and intraplate basin-orogeny coupling. [Copyright &y& Elsevier]

Abstract: An investigation of the anisotropy of magnetic susceptibility (AMS) in 39 sites has been carried out in the northwestern Sichuan Basin which is adjacent to the northeastern Tibetan plateau, discussing the deformation pattern of the basin and the orogenic process of the corresponding orogens. Stepwise demagnetization of three orthogonal isothermal remanent magnetization suggests that hematite is the main magnetic carrier mineral. Combined with the low value of magnetic susceptibility, it is considered that the AMS is some combination of hematite and paramagnetic matrix minerals. Different types of magnetic fabrics from sedimentary to pencil structure magnetic fabric and sharps of susceptibility ellipsoids from oblate to prolate were observed. The existence of sedimentary magnetic fabric and the accordance of magnetic lineation and bedding strike indicate the magnetic fabrics along the front of Longmen Shan belt were the result of tectonic deformation. Thermochronology researches in the orogens and our apatite fission track analysis in the northwestern Sichuan Basin suggest that magnetic fabric mainly reflects the Cenozoic deformation. The magnetic lineation which is consistent with the fault and fold strikes in the Longmen Shan was induced by Mesozoic and Cenozoic deformation, and the latter is the primary one. Besides the typical weak deformation magnetic fabrics, atypical magnetic fabrics characterized by a magnetic lineation that is oblique to the bedding strike are shown in 53% sites along the front of Micang Shan. It is proposed that such a type of atypical magnetic fabric is the result of two competing sub-fabrics in the weakly deformed tectonic superposition region. [Copyright &y& Elsevier]

Abstract: The Armorican Massif (western France) provides an excellent record of the Palaeozoic history of the Variscan belt. Following the Late Neoproterozoic Cadomian orogeny, the Cambro-Ordovician rifting was associated with oceanic spreading. The Central- and North-Amorican domains (which together constitute the core of the Armorica microplate) are bounded by two composite suture zones. To the north, the Léon domain (correlated with the “Normannian High” and the “Mid-German Crystalline Rise” in the Saxo-Thuringian Zone) records the development of a nappe stack along the northern suture zone, and was backthrusted over the central-Armorican domain during the Carboniferous. To the south, an intermediate block (“Upper Allochthon”) records a complex, polyorogenic history, with an early high-temperature event followed by the first generation of eclogites (Essarts). This intermediate block overthrusts to the north the Armorica microplate (Saint-Georges-sur-Loire), to the south: (i) relics of an oceanic domain; and (ii) the Gondwana palaeomargin. The collision occurred during a Late Devonian event, associated with a second generation of eclogites (Cellier). [Copyright &y& Elsevier]

The Llano uplift of central Texas, United States, exposes the core of a Mesoproterozoic orogenic belt that formed along the southern margin of Laurentia during Grenville time. A new collisional model is proposed that reconciles differences in structural stacking, apparent tectonic transport, and deformation conditions between the eastern and western portions of the uplift and explains uplift and exhumation of high-pressure eclogitic rocks, emplacement of ophiolitic rocks, and subsequent late-stage to postcollisional plutonism. Our model proposes that subduction with southward polarity resulted in collision of an exotic arc with Laurentia, emplacement of ophiolitic rocks, and telescoping of the intervening basinal sediments, followed by overriding of the arc and margin of Laurentia by a southern continent with transport toward Laurentia. The model further proposes that convergence led to subduction of the Laurentian margin, resulting in high-pressure metamorphism, but buoyancy forces due to subduction of continental crust under the southern continent resulted in uplift and retrotransport away from Laurentia, in a manner similar to that proposed for the Alpine orogeny. Slab breakoff resulted in upwelling of the asthenosphere, leading to intrusion of juvenile granitic plutons. Subduction along strike caused continued contraction that waned with time. The eastern uplift records continent-arc-continent collision, whereas the western uplift records continent-continent collision; the two regions also expose different crustal levels in the orogen. The striking similarity with Phanerozoic orogens, including emplacement of ophio lites and formation of high-pressure rocks, implies that plate tectonic processes including subduction were active prior to the Neoproterozoic. [ABSTRACT FROM AUTHOR]

The subduction phase in the development of the Variscan Orogen in SW Europe was followed by an extended period of ‘intracontinental’ tectonics. The progressive temperature rise in the hinterland during plate convergence was accompanied by widespread partial melting in the lower crust and the nucleation of kilometric buckle folds and crustal-scale shear zones in the stronger upper crust. Thermal mechanical weakening in the core of the orogen was contemporaneous with shortening and thickening in the foreland fold-and-thrust belt. We evaluate lithospheric strength profiles in the hinterland and foreland based on the metamorphic and structural record for three tectonic stages. We find that lower crustal strength varied in space as well as in time during orogenesis. Strength contrasts between the foreland and the hot hinterland during convergence may have led to the additional indentation of the foreland into the hinterland of the Ibero-Armorican Arc. [ABSTRACT FROM AUTHOR]

The extensional Pannonian Basin was formed in a few million years during Miocene time synchronously with contraction in the surrounding Alpine and Carpathian orogens. This system is characteristic of a class of extensional basins that form in the midst of active orogenic (mountainforming) belts. The mechanism that causes this type of geological event is enigmatic but usually has been associated with subduction. We examine a new hypothesis for intra-orogenic extensional basin formation in which gravitational spreading of previously thickened crust triggers gravitational instability of the mantle lithosphere. A basin is formed by lithospheric extension as shortening and lithospheric downwelling occur in the surrounding mountain belts. This mechanism provides a mechanically self-consistent explanation for all of the main structural features of the Pannonian-Carpathian system and presents a plausible alternative to the popular view that subduction and slab rollback have driven the development of this basin. [ABSTRACT FROM AUTHOR]

The ∼2800-km-long Snowbird tectonic zone is one of the most controversial tectonic features of the Canadian shield. Metamorphic and in situ geochronologic data reported here reveal that a 1.9 Ga medium- to high-pressure belt extends along most of this tectonic zone. In contrast to recent interpretations, a collisional origin is indicated by the length of this metamorphic belt, tectonic thickening documented in parts of it, geological contrasts across it, and subduction-type microdiamonds within it. This collisional event marks a pre—1.865 Ga phase of the Hudsonian orogeny involving microcontinent accretion that was fundamental to the growth of Laurentia. [ABSTRACT FROM AUTHOR]

The northern Cordilleran fold-and-thrust belt in Canada and Alaska is at the boundary between the broad continental margin mobile belt and the stable North American craton. The fold-and-thrust belt is marked by several significant changes in geometry: cratonward extensions in the central Yukon Territory and northeastern Alaska are separated by marginward re-entrants. These geometric features of the Cordilleran mobile belt are controlled by relations between lithospheric strength and compressional tectonic forces developed along the continental margin. Regional magnetic anomalies indicate deep thermal and compositional characteristics that contribute to variations in crustal strength. Our detailed analysis of one such anomaly, the North Slope deep magnetic high, helps to explain the geometry of the fold-and-thrust front in northern Alaska. This large magnetic anomaly is inferred to reflect voluminous mafic magmatism in an old (Devonian?) extensional domain. The presence of massive amounts of mafic material in the lower crust implies geochemical depletion of the underlying upper mantle, which serves to strengthen the lithosphere against thermal erosion by upper mantle convection. We infer that deep-source magnetic highs are an important indicator of strong lower crust and upper mantle. This stronger lithosphere forms buttresses that play an important role in the structural development of the northern Cordilleran fold-and-thrust belt. [ABSTRACT FROM AUTHOR]

Understanding uplift and exhumation in orogenesis requires integrating the effects of both climatic and tectonic forcing. Punctuated thrust activity is widely documented from field studies in a range of mountain belts. The potential for climatic forcing of thrust activity has been a subject of recent debate. Here we use a modeling approach to analyze the behavior of individual thrust units in the context of asymmetric doubly vergent thrust wedges. The model predicts that rates of surface uplift, frontal accretion, and exhumation should be punctuated on a time scale linked to thrust sheet geometry and convergence rates. This time scale ranges from 0.1 to 5 m.y. for various settings, and should be calculated before external forcings such as climate are invoked. [ABSTRACT FROM AUTHOR]

Abstract: Modern orogenic belts may be rifted and reworked during later tectonic cycles. In ancient collision zones, such as the Eastern Ghats Belt (EGB), India, identification of such processes is complicated by the multiply folded nature of the exposed deep crustal section. Along the northern EGB margin, (M1) granulite facies metamorphism (∼7–8kbar, >760°C) at ∼960–930Ma outlasted D1 fabric formation, and D2 isoclinal folding and shearing. N-S trending mafic dykes and N-S trending, west-dipping shear zones accompanied D3 extension. Syn-D3 cooling and decompression caused garnet breakdown in mafic granulites. Granite and pegmatite emplacement at c. 850Ma accompanied uplift on E-W trending, subvertical D4 shear planes. Top-to-the-south thrusting on WNW-ESE trending, north-dipping D5 shears resulted in regional-scale fabric reorientation. During M2 amphibolite facies metamorphism (∼5.5kbar, 630°C) at c. 700Ma following D5, garnet reformed in mafic granulites, and stabilized within syn-D3 mafic dykes and syn-D4 granites. Thus, the terrane margin experienced heating, loading and uplift during a first tectonic cycle, followed by renewed burial during a later orogeny. Since the mesoscopic-scale folds correspond to shears that interfere in low strain zones, the structural pattern represents heterogeneous, rather than homogeneous strain accommodation during mid-crustal deformation. [Copyright &y& Elsevier]

By selecting a limited number of variables (westward vs. eastward subduction polarity; oceanic vs. continental origin of downgoing and overriding plates), we identify eight end-member scenarios of plate convergence and orogeny. These are characterized by five different types of composite orogenic prisms uplifted above subduction zones to become sources of terrigenous sediments (Indo-Burman-type subduction complexes, Apennine-type thin-skinned orogens, Oman-type obduction orogens, Andean-type cordilleras, and Alpine-type collision orogens). Each type of composite orogen is envisaged here as the tectonic assembly of subparallel geological domains consisting of genetically associated rock complexes. Five types of such elongated orogenic domains are identified as the primary building blocks of composite orogens: magmatic arcs, obducted or accreted ophiolites, neometamorphic axial belts, accreted paleomargin remnants, and accreted orogenic clastic wedges. Detailed provenance studies on modern convergent-margin settings from the Mediterranean Sea to the Indian Ocean show that erosion of each single orogenic domain produces peculiar detrital modes, heavy-mineral assemblages, and unroofing trends that can be predicted and modeled. Five corresponding primary types of sediment provenances (magmatic arc, ophiolite, axial belt, continental block, and clastic wedge provenances) are thus identified, which reproduce, redefine, or integrate provenance types and variants originally recognized by W. R. Dickinson and C. A. Suczek in 1979. These five primary provenances may be variously recombined in order to describe the full complexities of mixed detrital signatures produced by erosion of different types of composite orogenic prisms. Our provenance model represents a flexible and valuable conceptual tool to predict the evolutionary trends of detrital modes and heavy-mineral assemblages produced by uplift and progressive erosional unroofing of various types of orogenic belts and to interpret petrofacies from arc-related, foreland-basin, foredeep, and remnant-ocean clastic wedges. [ABSTRACT FROM AUTHOR]

In eastern China, the Dabie Shan–Su–Lu orogenic belt has been separated by the Tan–Lu sinistral strike–slip fault. Mylonites are exposed along the strike–slip fault system in the southern segment, and along the eastern margin of the Dabie Shan orogenic belt. The country rocks of the mylonites are retrograde UHP eclogites, gneissic granites, muscovite granites and gneisses. The ductile strike–slip shear zone trends 30–40°N (NE30–40°-trending) and exhibits stretching lineations and nearly vertical, SE-dipping foliations. Most of the zircon grains separated from mylonites have a weighted average radiometric age of 233 ± 6–225 ± 6 Myr. These data constrain the onset of the Tan–Lu sinistral strike–slip movement and imply that the Tan–Lu sinistral strike–slip motion developed after retrograde UHP metamorphism. The related phengite within the eclogite rocks on the western side of the Tan–Lu fault, with 40Ar/39Ar plateau ages of c. 182–190 Myr, is also deformed and aligned parallel to the almost NE trending stretching lineations. Non-metamorphosed granites exhibit sinistral strike–slip shearing and indicate that the Tan–Lu fault initially developed after 182–190 Myr. Muscovite collected from the mylonite yields 40Ar/39Ar plateau ages of 162 ± 1–156 ± 2 Myr. The zircon SHRIMP age data, the muscovite 40Ar/39Ar plateau ages, together with structural and petrological field information support the interpretation that the Tan–Lu strike–slip fault was not related to the Yangtze–north China plates collision, but corresponded to the formation of a NE-trending tectonic framework in eastern China starting c. 165–160 Ma. [ABSTRACT FROM AUTHOR]

The uplift and evolution of a noncollisional orogen developed along a subduction zone, such as the Andean system, is a direct consequence of the interrelation between plate tectonic stresses and erosion. Tectonic stresses are related to the convergence velocity and thermal state, among other causes. In this paper, a new model designed to investigate the evolution of the topography and the upper crustal deformation of noncollisional orogens in a subduction zone produced by the oceanic crust being subducted is presented. The mechanical behavior of the crust was modeled by means of finite elements methods to solve Stokes equations for a strain-rate-dependent viscoplastic rheology. The model takes into account erosion effects using interface-tracking methods to assign fictitious properties to nonmaterial elements. [ABSTRACT FROM AUTHOR]

The historical superstructure-infrastructure concept (S-I) expressed contrasts in structural style and metamorphic grade between shallow and deep orogenic levels. Two-dimensional thermalmechanical models provide a quantitative explanation in terms of progressive crustal shortening and thickening (phase 1), thermal relaxation and rheological weakening (phase 2), and ductile flow at depth (phase 3). Results predict an upper-crustal superstructure, dominated by early steep structures, separated across a subhorizontal high-strain zone from a ductile infrastructure with late gently dipping structures; this is consistent with observations from the western Superior Province. These models can account for contrasts in structural style, metamorphic grade, seismic reflectivity, and age between upperand lower-crustal levels. In contrast to conventional thrust-tectonics models, the revived S-I model shows how young structures can form beneath older ones during progressive convergence, thereby encouraging reassessment of standard seismic reflection interpretations. [ABSTRACT FROM AUTHOR]

We estimate strain rates of three parameters that describe the buildup of a tectonic wedge (Jura front, France). The uplift rate on frontal ramps decreases with the slip on the ramps and the coeval increase of vertical loads. The migration rate of the tip of the sole thrust appears to be episodic and faster than the translation rate of the backstop. The long-term tilting rate appears to be constant, whereas the short-term rate is slightly slower. We propose a model of wedge growth that proceeds without underthrusting. In a prefractured medium, the wedge would activate the frontal ramp with a weaker frictional resistance than the forward décollement. An instantaneous forward jump of the deformation front would occur when the resistance on the ramp equals the resistance of the frontal décollement. This model differs from those proposed for accretionary zones, and relates to the backstop of a single tapered orogenic belt. [ABSTRACT FROM AUTHOR]

The Kisseynew domain within the central Trans-Hudson orogen constitutes a high-temperature (T) and low- to medium–pressure (P) metasedimentary belt characterized by uniform peak metamorphic conditions of 750 ± 50 °C and 5–6 kbar (1 kbar = 100 MPa). To investigate the thermal evolution of the Kisseynew domain 1-dimensional thermal modelling was conducted for a range of thermal parameters, including the effects of exhumation and incorporating current information about the crustal architecture. The results show that tectonic thickening of the sedimentary pile to ~40 km, consistent with present-day thickness estimates and erosional levels, is capable of producing enough crustal heating to melt the base of the sedimentary pile, advect heat to shallower crustal levels, and produce the observed P–T conditions. Deep-seated mantle heat sources, though not excluded, are not required. [ABSTRACT FROM AUTHOR]

A three-dimensional model of the regional crustal architecture of the western Trans-Hudson Orogen, based on the interpretation of 590 km of deep-sounding seismic reflection data and a comparable length of existing seismic reflection information, is presented. The seismic images identify the regional geometry of the basal detachment zone (Pelican thrust) that separates juvenile allochthonous terranes from the underlying Archean microcontinent (Sask craton). The Sask Craton is inferred to have a minimum spatial extent of over 100 000 km2 with an associated crustal root that extends for 200 km along strike. During terminal collision, complete convergence of the Rae–Hearne and Superior continental blocks was precluded by the presence of the Sask Craton, resulting in the preservation of anomalous amounts of oceanic and associated sedimentary juvenile material. Along regional tectonic strike, consistency of crustal structure across the Rae–Hearne margin – Reindeer zone boundary is established. Several phases of tectonic development, including multistage subduction and continent–continent collision, are inferred for the western margin of the orogen. A bright, shallow (2–3.5 s two-way traveltime) band of reflectivity (Wollaston Lake reflector) imaged over ~150 000 km2 area is inferred to be a large post-orogenic mafic intrusion. A highly reflective, well-defined and structurally disturbed Moho discontinuity is mapped throughout the western Trans-Hudson Orogen. The present-day crustal architecture of the western Trans-Hudson Orogen is described in terms of the tectonic evolution within the region. [ABSTRACT FROM AUTHOR]

The Wudalianchi volcanic field developed during the Pleistocene–Holocene but is dormant at present. Its latest eruption occurred in 1719–1721 AD. The volcanic rocks are high-potassium alkaline basalts derived from the upper mantle (c. 100–120 km depth) as indicated by geochemical data. The field is located in an old tectonic transition zone surrounded by four regional normal faults. The volcanic craters are aligned along NE–NNE-striking fractures and faults, although a NNW-striking sub-surface fracture zone probably controlled the eruptions beginning at 1.33±0.08 Ma. Beneath the volcanic field, the Moho interface lies at a depth of 33.5–35 km. Eruptions evolved from fissure type to central type eruptions. The field is characterized by an intraplate tectonic setting in a non-orogenic compressional regime which resulted from the subduction of the West Pacific plate beneath the eastern Asian continental margin starting 3–2 Ma ago. [Copyright &y& Elsevier]

Tectonic evolution of the orogenic belt in the region located between Kerman and Neyriz is explored within the context of two NE-dipping Neotethyan subduction zones. The northern subduction zone was responsible for formation of the Mesozoic Sanandaj-Sirjan magmatic arc and the Late Cretaceous Shahr Babak-Baft ensimatic back-arc extensional basin. The southern subduction zone was responsible for formation of the reverse primitive Neyriz island-arc, the Central Iranian volcanic belt, and its line of porphyry copper deposits, as well as the Rafsanjan back-arc extensional basin (proto-Rafsanjan depression). Due to the collision of the Neyriz island arc with the Sanandaj-Sirjan active continental margin, the Shahr Babak-Baft back-arc basin was tectonically inverted into the Shahr Babak-Baft ophiolite belt. Finally, the continental collision between the Arabian and the Central Iranian plates took place during the Neogene. This led to the tectonic inversion of the Rafsanjan ensialic basin into the Rafsanjan retro arc basin (the present Rafsanjan depression), and emplacement of the syncollision to late- or post-orogenic granitoid rocks (felsic mass) in the Rafsanjan region. [Copyright &y& Elsevier]

The Lachlan Orogen, like many other orogenic belts, has undergone paradigm shifts from geosynclinal to plate-tectonic theory of evolution over the past 40 years. Initial plate-tectonic interpretations were based on lithologic associations and recognition of key plate-tectonic elements such as andesites and palaeo-subduction complexes. Understanding and knowledge of modern plate settings led to the application of actualistic models and the development of palaeogeographical reconstructions, commonly using a non-palinspastic base. Igneous petrology and geochemistry led to characterisation of granite types into ‘I’ and ‘S’, the delineation of granite basement terranes, and to non-mobilistic tectonic scenarios involving plumes as a heat source to drive crustal melting and lithospheric deformation, More recently, measurements of isotopic tracers (Nd, Sr, Pb) and U-Pb SHRIMP age determinations on inherited zircons from granitoids and detrital zircons from sedimentary successions led to the development of multiple component mixing models to explain granite geochemistry. These have focused tectonic arguments for magma genesis again more on plate Interactions. The recognition of fault zones in the turbidites, their polydeformed character and their thin-skinned nature, as well as belts of distinct tectonic vergence has led to a major reassessment of tectonic development, Other geochemical studies on Cambrian metavolcanic belts showed that the basement was partly backarc basin- and forearc basin-type oceanic crust. The application of 40Ar-39Ar geochronology and thermochronology on slates, schist and granitoids has better constrained the timing of deformation and plutonism, and illite crystallinity and bo mica spacing studies on slates have better defined the background metamorphic conditions in the low-grade parts. The Lachlan deformation pattern involves three thrust systems that constitute the western Lachlan Orogen, central Lachlan Orogen and eastern Lachlan Orogen. The faults in the western Lachlan Orogen show a generalised east-younging (450–395 Ma), which probably relates to imbrication and rock uplift of the sediment wedge, because detailed analyses show that the décollement system is as old in the east as it is in the west. Overall, deformation in the eastern Lachlan Orogen is younger (400–380 Ma), apart from the Narooma Accretionary Complex (ca 445 Ma), Preservation of extensional basins and evidence far basin inversion are largely restricted to the central and eastern parts of the Lachlan Orogen. The presence of dismembered ophiolite slivers along some major fault zones, as well as the recognition of relict blueschist metamorphism and serpentinite-matrix melanges requires an oceanic setting involving oceanic underthrusting (subductian) for the western Lachlan Orogen and central Lachlan Orogen for parts of their history inhibited by deep weathering and a general tack of exposure, the recent application of geophysical techniques including gravity, aeromagnetic imaging and deep crustal seismic reflection profiling has led to greater recognition of structural elements through the sub-crop, a better delineation of their lateral continuity, and a better understanding of the crustal-scale architecture of the orogen. The Lachlan Orogen clearly represents a class of orogen, distinct from the Alps, Canadian Rockies and Appalachians, and is an excellent example of a Palaeozoic accretionary orogen. [ABSTRACT FROM AUTHOR]

Reports the zircon ion microprobe (SHRIMP) dating results for Songshugou garnet pyroxenite and Fushui gabbro. Suggestion that the Fushui gabbro-diorite complex body possesses characters of Alaska-type island-arc mafic-ultramafic plutonic complex which is an important component of the island-arc magmatic belt; Kinds of rocks that constructed the Early Paleozoic tectonic pattern of plate subduction and collision; Implications for the understanding of the tectonic evolution of the Qinling Orogenic Belt.

Apatite fission track thermochronology (AFTT) has been applied to the Precambrian basement rocks of southern Finland in an attempt to detect within the long-term thermal history, thermal manifestations in the cratonic interior of tectonic events at the craton margin. The likely subtle magnitude of these manifestations means that AFTT is a useful technique for such a study due to its low temperature sensitivity. A total of 10 samples have been analysed, generating AFTT ages, length statistics and thermal models. Ages range from 313 ± 22 to 848 ± 60 Ma and mean track lengths range from 11.0 ± 1.6 to 13.3 ± 1.8 μm. The data suggests the presence of thermal overprinting of an earlier cooling event. Thermal modelling produces similar results for all samples and typically contains the following major events: (1) two phases of Late-Proterozoic cooling, (2) Late-Silurian re-heating, (3) Cenozoic cooling. The first phase of Late-Proterozoic cooling is interpreted to be due to aulacogen inversion as a result of stress propagation from the collisional tectonics of the Sveconorwegian orogeny. The second phase is discussed in relation to passive margin formation and possible asthenospheric diaper induced relief and exhumation. The Late-Silurian re-heating coincides in time with a proposed Caledonian foreland basin. The Cenozoic cooling is interpreted to represent the latest exposure resulting from North Atlantic Margin formation induced uplift and associated denudation. [Copyright &y& Elsevier]

Explains that this issue contains a selection of papers presented in "Geodynamics of the Western Part of the Eurasia-Africa Plate Boundary (Azores-Tunisia)" workshop on May 31 to June 2, 2001 in Cadiz, Spain. Model for the orogenic evolution of the central part of the region; Subduction-subduction-transform fault triple junction in the Betic-Rif orogenic belt; Tectonic deformations in the frontal part of the Rif cordillera and the Sais basin.

—The Rif belt forms with the Betic Cordilleras an asymmetric arcuate mountain belt (Gibraltar Arc) around the Alboran Sea, at the western tip of the Alpine orogen. The Gibraltar Arc consists of an exotic terrane (Alboran Terrane) thrust over the African and Iberian margins. The Alboran Terrane itself includes stacked nappes which originate from an easterly, Alboran-Kabylias-Peloritani-Calabria (Alkapeca) continental domain, and displays Variscan low-grade and high-grade schists (Ghomarides-Malaguides and Sebtides-Alpujarrides, respectively), shallow water Mesozoic sediments (mainly in the Dorsale Calcaire passive margin units), and infracontinental peridotite slices (Beni Bousera, Ronda). During the Late Cretaceous?-Eocene, the Alboran Terrane was likely located south of a SE-dipping Alpine-Betic subduction (cf. Nevado-Filabride HP-LT metamorphism of central-eastern Betics). An incipient collision against Iberia triggered back-thrust tectonics south of the deformed terrane during the Late Eocene-Oligocene, and the onset of the NW-dipping Apenninic-Maghrebian subduction. The early, HP-LT phase of the Sebtide-Alpujarride metamorphism could be hypothetically referred to the Alpine-Betic subduction, or alternatively to the Apenninic-Maghrebian subduction, depending on the interpretation of the geochronologic data set. Both subduction zones merged during the Early Miocene west of the Alboran Terrane and formed a triple junction with the Azores-Gibraltar transform fault. A westward roll back of the N-trending subduction segment was responsible for the Neogene rifting of the internal Alboran Terrane, and for its coeval, oblique docking onto the African and Iberian margins. Seismic evidence of active E-dipping subduction, and opposite paleomagnetic rotations in the Rif and Betic limbs of the Gibraltar Arc support this structurally-based scenario. [ABSTRACT FROM AUTHOR]

—Extreme cooling rates (∼500 °C/m.y.) during the late stage, 22–18 Ma, orogenic evolution of the Alpine Betic-Rif belt are suggested to result from rapid exhumation caused by tectonic extrusion and concomitant extensional tectonics. The extrusional/extensional tectonic setting is controlled by the SW-NE trending break-off scar left in the lithosphere of the Alborán Sea and SE Spain after detachment of a lithospheric slab. The extruded material represents the collisional crustal nappe pile (together with fragments of underlying mantle, such as the Ronda peridotites) and the cause of the extrusion is the thermal softening within the crustal section during and after collision. The extrusion/extension took place under the influence of a NW-SE directed compressive regime, perpendicular to the collisional belt. At the same time the sub-lithospheric mantle still showed the E-W compressive regime of the collisional stage. The Alpine tectono-metamorphic evolution of the Betic-Rif belt in the W Mediterranean thus comprises two main stages: (1) continental collision with formation of primary nappes and high-pressure metamorphic parageneses, (2) tectonic extrusion with vertically directed tectonics (high pressure, very rapid decompression) and extensional tectonics with roughly horizontal, lateral transport and final emplacement of the extruded mélange in the form of a stack of detachment sheets (low pressure, very rapid cooling). This model for the Betic-Rif may offer important constraints to all rapidly exhumed convergent terranes. [ABSTRACT FROM AUTHOR]

The Changning Menglian belt is an important area of research on the evolution of the Paleo Tethys ocean structure, the belt can be solved such as the Changning Menglian belt position; sequence stratigraphy; sedimentary environment; nature and its tectonic evolution history and tectonic domain and Gut Tis relationship; therefore, the research on Chang Ning Menglian zone have a great significance to solve many problems of the Sanjiang fold belt in Tethys and Himalaya tectonic area. 'Hot spring' is located in the west margin of the southern Changning Menglian belt, studying Yunnan Fengqing hot spring group 'geological and petrology characteristics roundly and in depth, concluding the metamorphism and deformation characteristics, clarifying the metamorphism effect and its stages, understanding the association its combination with the Changning Menglian belt between, therefore it has the great significance to solve the geological evolution history in the Sanjiang area, especially the paleo Tethyan tectonic belt, as well as Gondwana and Eurasia boundaries and other major problem. Through collect and read the literature data, measurement of field section, geological investigation, research and Study on rock sheet indoor, rock composition test, electron probe testing system, summarize the geological characteristics and petrological characteristics of 'hot springs group ', and through the discussion of the geochemical characteristics of rocks, explore its rock assemblages, characteristics of original rock and analysis of metamorphism and deformation stages, to provide basic data for regional geological evolution. The study shows that the main lithology is biotite quartz schist, mica schist and epimetamorphic sandstone interspersed with a small amount of phyllonite, granulite, silicalite, carbonaceous slate and phyllitic cataclasite that contains some pressure breccia. The metamorphic mineral paragenetic assemblage of the representative rock is: M1 biotite (Bi) + plagioclase (Pl) + quartz (Q), and M2 muscovite (Mus) + quartz (Q). The protolith is felsic rock and sedimentary rock that belongs to argiloid. On the basis of comparison, the stratigraphic sequence of the protolith is consistent with the type section of Wenquan formation. Along with the subduction(Hercynian) - subduction (Indosinian) - orogenic (Yanshan Himalayan period) process of Changning Menglian belt, hot springs group experienced two stages of metamorphism and three stages of deformation, metamorphic temperature at 400-500 °, the pressure is foucs on 0.3-0.62Gpa, and shown the retrograde metamorphism of the low greenschist facies. Geological age of hot springs formation is early Devonian (survey team of Yunnan District three units, 1980), sedimentary environment is mainly shallow and semi deep sea, observed Bouma sequence in rock slice, therefore, the depositional environment may be fan or basin of sea, the sedimentary formations are mainly clastic rock - siliceous rock formation, the upper coal-contained formation. With the Changning Meng Lian ocean expansion, ocean island begin to develop, material deposition continuing, appearing volcano material, the protolith may contain volcano matter through studying the thin section. To the Late Permian, Crust of Changning Menglian ocean begin to subduct to the east of the Yangtze block, ocean basin began to close, but it still has formation here at this time, mainly shallow carbonate formation, with proceeding of subduction, in the low temperature groove (7Km deep), due to changes in temperature and pressurer, appearing metamorphism (M1) and deformation (D1) for the first time, the shear effect produced by deformation lead to some cleavage, occurring regional foliation S1, major metamorphic minerals formed in metamorphism is long flake biotite. The main metamorphic mineral assemblages are biotite (Bi) + feldspar (Pl) + quartz (Q). Subsequently, crustal uplift, depositional break, because the Changning Meng Lianyang has closed during the Indosinian period, Baoshan - Zhenkang block in the west and the Yangtze block in the east knocked each other. In the Indosinian, under the action of faults, the hot spring formation clipping and retracing, back to a position about 1-2Km depth, the position is still belongs to the low temperature groove, and occurring axial cleavage in the core of the fold, namely S2. That is, the emergence of the second metamorphism (M2) and deformation (D2). The deformation is affected by the strong pressure, so the rock have dewatered, so the second metamorphic deformation process is affected by temperature (T), pressure (Ps) and fluid (C). The main metamorphic minerals in the second generation of metamorphism is Muscovite, while there have some of biotite formed in same period, find that the first phase of biotite parallel growth of rock slice, namely S1 parallel S2, and we can see incomplete metamorphism biotite, so the the Muscovite is formed by the first stage of metamorphism and metamorphic biotite. The main mineral of the second stage metamorphism is Muscovite (Mus) + quartz (Q) Then, the crust continues to rise, the sedimentary break continues. In the Jurassic Cretaceous start orogeny, namely Yanshan period intracontinental orogeny, occurred third deformation (D3), under extrusion shearing, S3 emergencing, after Yanshan intracontinental orogenic period, in Himalayan period there have large-scale nappe structure and differential uplift and faulting. So the third deformation (D3) strengthened, with weak metamorphism, sericite emergencing. [ABSTRACT FROM AUTHOR]

The Harz mountains are one of the most impressive examples of a widespread pulse of Late Cretaceous, intraplate shortening and basement uplift which is found across the Central Western European region and is nowadays considered to be causally linked to the early stages of Iberia-Europe convergence associated with the uplift of the Pyrenees. The geometry and kinematics of the Harz uplift can be relatively well constrained by simple structural balancing and suggest a 45 degree dipping basement ramp with 7 km of northeast directed shortening and uplift. The timing of this event is also well constrained thanks to the so-called "Subhercynian Basin" on the northern margin of the Harz, which is filled by their erosive product. Late Cretaceous (Santonian-Campanian) sediments overlie Mesozoic strata in a 20 km wide basin extending 90 km laterally along the entire length of the Harz mountains. At its depocentre it reaches 2500 m thickness. Some interaction between a regional basal detachment rooted in Zechstein evaporites, underlying the Subhercynian basin and the main Harz Boundary Fault (HBF) have led to folding of the infill and the development of a number of angular unconformities. However, the broad geometry of the basin is clearly wedge shaped, and thickest near the HBF. One major question regarding this basin, as well as numerous others along the wider Late Cretaceous deformation front, is how to generate such a short wavelength, high amplitude subsidence pattern in an intraplate setting. Subsidence in compressional settings has generally been associated with foreland basins which require a load to elastically flex and depress the lithosphere. Usually, these are considered to operate at the orogenic and plate tectonic scale with high magnitude loads from major fold thrust belts with 100's kms shortening, and large wavelength (>100 km) basins. The Subhercynian Basin does not fit within this paradigm, and it is easy to show that for a "normal" lithospheric flexure model, the Harz load is insufficient to generate the required subsidence. The same would apply across the rest of the Late Cretaceous inversion front. We propose a modification of the lithospheric flexure condition which we call a "broken plate" model, where we introduce a weakness due to a narrow zone of reduced elastic thickness in the middle of a flexed plate and apply a load across it. Under these conditions, it is easy to produce the short wavelength, high amplitude basins required to explain many Late Cretaceous depocentres in the intraplate setting of the Central Western European paltform. We suggest that weaknesses correspond to basement rooted thrust faults, which reduce the effective elastic thickness of the lithosphere across a narrow zone. Our model thus combines the effects of isostatic subsidence of quasi-distinct crustal blocks and their elastic flexureand is able to match the geometry of the Subhercynian basin very closely. [ABSTRACT FROM AUTHOR]

A correlation chart showing the evolution of the Manitoba–Saskatchewan segment of the Paleoproterozoic Trans-Hudson Orogen (THO) has been constructed based on available geochronological and isotopic data. Geological, petrological, geochemical, and structural data have also been incorporated into the correlation chart to provide finer detail and to allow comparison of specific tectonic events. The chart also emphasizes that the bounding Archean cratons (Superior, Hearne, Sask) have been significantly affected by Paleoproterozoic events, and it is hoped that this chart will also facilitate comparison with other Paleoproterozoic orogens in North America and beyond. [ABSTRACT FROM AUTHOR]