Journal articles on the topic 'Regional orogenesis'

New 40Ar/39Ar mineral ages from rocks collected west of Penobscot Bay, Maine, indicate this region was regionally deformed, metamorphosed to amphibolite facies conditions, and intruded by plutons in Silurian times rather than in the Devonian as previously assumed. Disturbed hornblende age spectra, along with the presence of some Devonian felsic plutons and extensive retrograde metamorphic textures do suggest, however, that these rocks were subsequently affected by low-grade Devonian thermal events. In sharp contrast, rocks west of the Sennebec Pond thrust fault, a major tectono-stratigraphic boundary in this region, lack a significant Silurian tectono-thermal signature, and instead record the effects of intense Devonian deformation and high-grade regional metamorphism. The data suggest the two regions experienced very different pre-Devonian histories and were most likely juxtaposed by the Sennebec Pond thrust fault in latest Silurian to Early Devonian time. Rocks now exposed east of the Sennebec Pond fault probably occupied much higher structural levels during Devonian orogenesis and were not subjected to the same intense Devonian deformation and metamorphism as those rocks now found to the west of this structure. The Silurian tectonism now recognized in this region bears striking resemblance to events of similar age recorded along the northwest margin of the Avalon composite terrane throughout much of Atlantic Canada. This greatly extends the zone of Silurian orogenesis in the northern Appalachians and requires that previous models of New England middle Paleozoic tectonism be significantly revised.

Abstract. In the paper we discuss the problem of continental collision and related volcanism in the Caucasus and surrounding areas based on analysis of the upper mantle seismic structure in a recently derived model by Koulakov (2011). This model, which includes P- and S-velocity anomalies down to 1000 km depth, was obtained from tomographic inversion of worldwide travel time data from the catalogue of the International Seismological Center. It can be seen that the Caucasus region is squeezed between two continental plates, Arabian to the south and European to the north, which are displayed in the tomographic model as high-velocity bodies down to about 200–250 km depth. On the contrary, a very bright low-velocity anomaly beneath the collision area implies that the lithosphere in this zone is very thin, which is also supported by strong deformations indicating weak properties of the lithosphere. In the contact between stable continental and collision zones we observe a rather complex alternation of seismic anomalies having the shapes of sinking drops. We propose that the convergence process causes crustal thickening and transformation of the lower crust material into the dense eclogite. When achieving a critical mass, the dense eclogitic drops trigger detachment of the mantle lithosphere and its delamination. The observed high-velocity bodies in the upper mantle may indicate the parts of the descending mantle lithosphere which were detached from the edges of the continental lithosphere plates. Very thin or even absent mantle part of the lithosphere leads to the presence of hot asthenosphere just below the crust. The crustal shortening and eclogitization of the lower crustal layer leads to the dominantly felsic composition of the crust which is favorable for the upward heat transport from the mantle. This, and also the factor of frictional heating, may cause to the origin of volcanic centers in the Caucasus and surrounding collisional areas.

Abstract. In the paper, we discuss the problem of continental collision and related volcanism in the Caucasus and surrounding areas based on the analysis of the upper mantle seismic structure in a recently derived model by Koulakov (2011). This model, which includes P and S-velocity anomalies down to 1000 km depth, was obtained from tomographic inversion of worldwide travel time data from the catalogue of the International Seismological Center. It can be seen that the Caucasus region is squeezed between two continental plates, Arabian to the south and European to the north, which are displayed in the tomographic model as high-velocity bodies down to about 200–250 km depth. On the contrary, a very bright low-velocity anomaly beneath the collision area implies that the lithosphere in this zone is very thin, which is also supported by strong horizontal deformations and crustal thickening indicating weak properties of the lithosphere. In the contact between stable continental and collision zones, we observe a rather complex alternation of seismic anomalies having the shapes of sinking drops. We propose that the convergence process causes crustal thickening and transformation of the lower crust material into the dense eclogite. When achieving a critical mass, the dense eclogitic drops trigger detachment of the mantle lithosphere and its delamination. The observed high-velocity bodies in the upper mantle may indicate the parts of the descending mantle lithosphere which were detached from the edges of the continental lithosphere plates. Very thin, or even absent, mantle parts of the lithosphere leads to the presence of hot asthenosphere just below the crust. The crustal shortening and eclogitisation of the lower crustal layer leads to the dominantly felsic composition of the crust which is favourable for the upward heat transport from the mantle. This, and also the factors of frictional heating and the radioactivity of felsic rocks, may be the origin of volcanic centres in the Caucasus and surrounding collisional areas.

Surface and subsurface data from northern Yukon document a northward facies transition from shelf carbonates to basinal graptolitic shales and cherts from Late Cambrian to Early Devonian time. Parts of this north-facing continental margin were deformed during separate orogenic events of Early Devonian and Early Carboniferous ages. The first event, the Romanzof Orogeny, is identified in exposures across northwestern Yukon, in adjacent northeastern Alaska, and locally in the subsurface of the Alaska North Slope. It resulted in tight folds, north-directed thrust faults, and intrusion by Late Devonian posttectonic granitic plutons. Notwithstanding the thrust-fault orientations, southward diminution of deformation intensity combined with facies variations suggest that tectonic transport was generally southward. Evidence for an Early Carboniferous event is preserved in the northern Richardson Mountains and locally in the subsurface of the Mackenzie Delta region. It consists of detached open folds and minor thrust faults. Geological and geophysical data from northern Yukon document the location and orientation of the Early Carboniferous deformation front, and define a regional tectonic transport direction toward the south or southeast. This event is a distal foreland element of the Ellesmerian Orogeny (sensu stricto) of the Canadian Arctic Islands and is distinct from the Romanzof event in age, intensity, and extent. Endicott and Lisburne group strata, deposited on a southwest-facing subsiding shelf, overstep rocks deformed by the Romanzof event even as Ellesmerian deformation encroached from the north.

The Pyrenees is a collisional orogen built by inversion of an immature rift system during convergence of the Iberian and European plates from Late Cretaceous to late Cenozoic. The full mountain belt consists of the pro-foreland southern Pyrenees and the retro-foreland northern Pyrenees, where the inverted lower Cretaceous rift system is mainly preserved. Due to low overall convergence and absence of oceanic subduction, this orogen preserves one of the best geological records of early orogenesis, the transition from early convergence to main collision and the transition from collision to post-convergence. During these transitional periods major changes in orogen behavior reflect evolving lithospheric processes and tectonic drivers. Contributions by the OROGEN project have shed new light on these critical periods, on the evolution of the orogen as a whole, and in particular on the early convergence stage. By integrating results of OROGEN with those of other recent collaborative projects in the Pyrenean domain (e.g., PYRAMID, PYROPE, RGF-Pyrénées), this paper offers a synthesis of current knowledge and debate on the evolution of this immature orogen as recorded in the synorogenic basins and fold and thrust belts of both the upper European and lower Iberian plates. Expanding insight on the role of salt tectonics at local to regional scales is summarised and discussed. Uncertainties involved in data compilation across a whole orogen using different datasets are discussed, for example for deriving shortening values and distribution.

AbstractThis study characterizes the effects of fluid migration into a predominantly shale cover which seals the active geothermal system of Mt. Amiata (Tuscany, Italy). During Alpine orogenesis the shale unit was affected by regional metamorphism at the limit of the diagenesis-anchizone. Subsequently, the phyllosilicate clay minerals of the shales underwent significant alteration at diagenetic temperatures (175±25ºC as determined by the geochemical model) by the pervasive circulation of fluids activated by the geothermal field. The overall mineralogical assemblages indicate that the main transformations consisted mostly of destabilization of illite and formation of kaolinite together with large amounts of I-S mixed layers, with higher smectite content and decreased Reichweite I-S ordering (from R3 to R1) with respect to the original, unaltered phases. Application of computer modelling indicates that the circulation of CO2-rich geothermal fluids into the shale unit was responsible for the observed phyllosilicate clay mineral transformations.

AbstractThe 1.1–0.9 Ga Sveconorwegian orogen in southwestern Scandinavia belongs to the global system of mountain belts established during the assembly of the supercontinent Rodinia. An overall north–south structural trend and five lithotectonic units bounded by crustal-scale shear zones characterize this orogen. In Sweden, the Eastern Segment abuts the orogen's cratonic foreland eastwards and is separated from the Idefjorden terrane westwards by a ductile shear zone, up to 5 km thick, displaying a sinistral transpressive component. These two lithotectonic units differ on the basis of their pre-Sveconorwegian accretionary tectonic evolution, and the timing of Sveconorwegian high-pressure metamorphism, anatexis and polyphase deformation. High-pressure granulites and migmatites formed at c. 1.05–1.02 Ga in the Idefjorden terrane; eclogites, high-pressure granulites and migmatites at c. 0.99–0.95 Ga in the Eastern Segment. Magmatic activity and crustal extension progressed westwards at c. 0.98–0.92 Ga. Prior to or at 0.93–0.91 Ga, greenschist facies shear deformation with top-to-the-foreland movement affected the frontal part of the orogen. Geodynamic uncertainties concern the affinity of the Idefjorden terrane relative to Fennoscandia (Baltica), the character of the Sveconorwegian orogenesis, and the contiguous or non-contiguous nature of the erosional fronts of the late Mesoproterozoic–early Neoproterozoic orogens in Sweden and Canada.

Geza island arc located in the southwest Sanjiang tectonic igneous rock belts, it was a products of Ganzi-Litang oceanic crust diving to Zhongdian Landmasses in late Triassic and a important of newly discovered copper polymetallic belts in the recent years in China. The regional strong tectonic-magmatic activity throughout the island-arc orogenesis from beginning to the end, the rich mineralization developed in the different times and different circumstances. Based on the development stage of island arc orogenic,the distribution of intrusive rocks, rocks composition, geochemical characteristics, Geza island arc granit belt can be divided into three belts. Lithogeochemical characteristics show that the porphyry (porphyrite) and island-arc granite rocks have the same rock series (high-K calc-alkaline) and the same genetic type (I-type granite); these rocks trace elements very similar to granite of island arc, which enriched in Ba, La, Hf, Au,chalcophile elements Cu,Pb, siderophile elements Mo, Ni, and depleted in Rb, Nb, P, Ti.

Integrated field structural studies and SHRIMP U–Pb zircon and monazite dating have been undertaken in Renland, west of Scoresby Sund district in the southern part of the East Greenland Caledonides. Southwest Renland is dominated by metasedimentary rocks correlated with the Krummedal supracrustal succession of East Greenland and which on Renland were intruded by augen granites. Krummedal psammite from Renland yielded a spectrum of Mesoproterozoic to Palaeoproterozoic detrital U–Pb zircon dates, the youngest of which indicate deposition of the psammite occurred c. 1000 Ma ago, thus post-dating Grenvillian continent–continent collision in North American Laurentia. These Krummedal metasediments were deformed into regional nappe-scale folds prior to metamorphism, crustal anatexis and genesis of augen granites; an example of the latter has been dated at 915±18 Ma (U–Pb zircon). This demonstrates early Neoproterozoic high-temperature tectono-metamorphism affecting rocks within the southern East Greenland Caledonides, broadly contemporaneous with similar rocks farther north in East Greenland and with Sveconorwegian events on Baltica. Still in southwestern Renland, a later thermal event led to development of uppermost amphibolite to granulite facies metamorphic assemblages, veins and patches of in situ garnetiferous melt-bearing neosome in both metasediments (432±6 Ma, U–Pb zircon) and in the augen granites, and contemporaneous biotite-bearing granite sheets in top-down-to-the-E extensional shear zones (434±5 Ma, U–Pb zircon). Monazites from southwestern Renland record Caledonian thermal events as late as 410−400 Ma. In contrast, southeastern Renland is dominated by quartzofeldspathic migmatites with a strongly Caledonian signature but enclosing relicts of augen granite and retrogressed granulite facies psammitic and pelitic metasediment. There is also a sequence of Caledonian granitoid intrusions. Two samples from a hypersthene monzonite intrusion yielded U–Pb zircon dates of 424±8 Ma and 424±6 Ma. This pluton shows the marginal effects of the regional migmatization and was intruded early in the sequence of granitoid emplacement. An amphibolite facies migmatite, textural evidence from which suggests that it had never hosted granulite facies assemblages, records zircon growth at 423±6 Ma, and closure of monazite by 402±10 Ma. High grade metamorphism, and the protracted sequence of granitoid emplacement and still younger thermal events which together span the period between 430 and 400 Ma may, in part, reflect complicated lithospheric dynamics associated with subduction outboard of the Laurentian margin. Crustal segments carrying the relict evidence of Neoproterozoic and early Caledonian events must then quickly have been thrust northwestwards in foreland-propagating, northwesterly directed thrusts over Cambro-Ordovician platformal sequences on the Laurentian margin. This records the final closure of Iapetus, encroachment of Baltica and continent–continent collision from late Llandovery times (425–430 Ma).

AbstractAbridged English version. – The Variscan Pyrenean belt (fig. 1) has been for long famous for its Late Carboniferous LP-HT metamorphism, characterised by the prograde succession, in medium grade metapelites, of biotite, cordierite, andalusite and sillimanite, together with staurolite and garnet [Guitard et al., 1996]. However, the discovery of two kyanite generations lead Azambre and Guitard [2001] to propose a polymetamorphic evolution, with an early (MI) and a late (MIII) kyanite-bearing Barrovian stage, preceding and following the main LP-HT stage (MII).Geological settingThe Variscan orogeny in the Pyrenees occurred from Namurian to Early Stephanian (c. 325-300 Ma), following the deposition of thick Ediacarian-Ordovician silico-clastites, Silurian to Early Caboniferous carbonates, and pre-orogenic Mid-Carboniferous flyschs.Two main tectonic events are recorded, each one subdivided into regionally correlated sub-events (phases) (table I), allowing a detailed correlation between tectonics, metamorphism and plutonism. The Namurian to Westphalian D1 event (c. 325-310 Ma) resulted in a S-vergent fold and thrust belt (with 100–150 km of N-S shortening) and the development of the main, sub-horizontal, Sr schistosity (D1c phase), coeval with MI. The Westphalian-Early Stephanian D2 event (310-300 Ma) was more complex. First, a syn-convergence extensional phase (N-vergent backfolds and E-W extension) resulted in the E-directed escape of the upper crust (D2a phase). Then, a renewal of the N-S shortening was marked by large upright anticlines (domes) and narrower synclines, with up to 10 km amplitudes (e.g., the Canigou anticline-Villefranche syncline pair) (D2b phase). Both D2a and D2b were coeval with MII and the emplacement of early granitoid sills and laccoliths (e.g., the Ansignan hypersthene-granite in the Agly Massif). Later on, D2 evolved into a transcurrent regime, with belt-parallel dextral transpression (D2c and D2c phases). D2c was coeval with the main stage of granite emplacement under low-grade conditions, allowing the expression of a conspicuous Mγ contact metamorphism (e.g., Mont-Louis pluton). D2d ended the D2 event, with the development of retrograde dextral-reverse mylonites. The late MIII metamorphic event encompassed D2c and D2d (and possibly D2b).The early MI Barrovian metamorphic eventThe MI Barrovian metamorphic event resulted from the crustal thickening associated with the development of the D1 intra-cratonic wedge. It was of low-grade, with a chlorite-muscovite Sr schistosity, in the part of the belt that was subsequently overprinted by the syn-MII transformation of chlorite into biotite. The only remnants of MI medium-grade conditions are found as early kyanite in the deepest domains of the Castillon, St-Barthélémy, Agly and Aston massifs, being there obliterated under high-grade MII conditions, and in the core of the Canigou anticline (Velmanya, point v in fig. 2), where a relict kyanite-staurolite-anorthite paragenesis is known, shielded by MII cordierite. The reconstructed P-T conditions at the thermal peak of MI are 5 kbar (19 km) and 575oC (fig. 2), implying the existence of a (now eroded) major D1 nappe (≥ 7 km thick).The main MII LP-HT metamorphic eventStructural domes and medium– or high-grade MII zones are broadly coincident, high-grade conditions being only encountered in the core of the Albères massif, the southern Aston Dome and the North-Pyrenean massifs (grading there up to the LP granulite facies) (fig. 1).Subdivisions of the MII eventThe prograde MII metamorphism is essentially syn-D2a, with clear syn-kinematic growth of the medium-grade minerals, and the main regional tectono-metamorphic D2a/MII structure is evidently deformed and strongly folded by the D2b phase: the D2b domes are basically post-metamorphic. However, a detailed examination of the blastesis-deformation relationships shows that staurolite is pre- to-synkinematic for D2a, whereas andalusite is strictly synkinematic (and consequently is often observed shielding the staurolite), cordierite being syn-to post-kinematic and syn-D2b in some instances. This allows a subdivision of the MII event into three stages:– MIIs, pre-to-syn-D2a, characterised by the staurolite-andalusite (And1 without cordierite) association, with development of a staurolite zone grading downwards into an andalusite (St → And1) zone. – MIIa, syn-to post-D2a (but always developed prior to D2b), characterised by the cordierite (Cord1)-andalusite (And2) association (without staurolite), with development of a thin cordierite zone grading downwards into an andalusite (Cord1 → And2) zone. – MIIb, post-D2a and syn-D2b, characterised by a large cordierite (Cord2) zone developed at the expense of an-dalusite (And → Cord2), only found in the core of the D2b anticlines (e.g., the Garonne dome).Thus, although MII is basically pre-D2b, and the MIIs and MIIa medium-grade isogrades are folded, it appears that metamorphism was still active in the cores of the ascending D2b domes (MIIb). Moreover, in the core of some domes, prograde sillimanite is also syn-kinematic of the D2b phase, and the sillimanite-muscovite isograde may obliquely overprint the MIIa isogrades, as in the Canigou dome. This is related to the syn-D2b emplacement of granite sheets (e.g., the Canigou granite) and may be interpreted as an aureola of “regional-contact” metamorphism, noted MIIγ, that was evidently coeval with MIIb, and enhanced its effects.P-T-t path of the MII eventThe P-T-t path of the MII event may be described using the petrogenetic grids of Pattison et al. [2002] and Pattison and Vogl [2005] (fig. 3). From MIIs to MIIb, it records a prograde anti-clockwise path, following a post-MI clockwise exhumation path, with ≥ 7 km eroded (fig. 2B). The MIIs pressure was close to 3 kbar (10–11 km) in the St zone and decreased to 2.5 kbar (9 km) at the MIIa stage (And2 isograde), for an estimated temperature of 540oC (based on the triple point of Holdaway [1971], the thermobarometer of Pattison et al. [2002] and independent fluid inclusion data by Kister et al. [2003]). A further pressure decrease, down to 2 kbar (7 km), and a temperature increase (up to 600oC) is registered in the MIIb cordierite zone in the core of active D2b domes. Except for the cores of the domes, MIIa remained the peak temperature event, and during MIIb pressure remained constant (or was re-increasing in the syncline cores) and temperature was constant or decreasing. At the end of the MII event (MIIb-MIIγ), extreme conditions of c. 4 kbar and 700–730oC are recorded in the deepest parts of the belt, where anatexis, succeeding to a sillimanite-K-feldspar zone, is observed, as in the Albères Massif and some North-Pyrenean Massifs.The MII metamorphism as a syn-tectonic plutono-metamorphic eventBased on the observation of the deep crust outcropping in the North Pyrenean massifs, Vielzeuf [in Guitard et al., 1996] concluded that emplacement of mafic melts in the Carboniferous lower crust was responsible for the MII metamorphism. At the beginning of the process, a regional thermal anomaly is superimposed to the middle crust (MIIs-MIIa), directly reflecting the emplacement of mafic sills in the underlying lower crust (fig. 4A). Heat is transferred conductively and, most likely, advected by the aqueous-carbonic fluids issued from the devolatilising lower crust (fluid inclusion data). Heat advection by melts characterised the end of the MII event, with development of more or less local thermal anomalies: still “regional” (MIIbγ) as in the Garonne dome, or directly liked to sheet-like granite intrusions (MIIγ) as at the bottom of the Mont-Louis pluton (fig. 4B) or at the contact of the Canigou granite (fig. 4C).The late MIII Barrovian metamorphic eventThe MIII event is mainly characterised in the eastern massifs (Albères, Cap de Creus), where a retrogressive kyanite (so-called “hysterogenic” kyanite) is overprinting high-grade assemblages. Although poorly expressed, MIII minerals in these massifs define two zones, with an external chloritoid zone and an internal kyanite-staurolite zone. A MIII chloritoid zone (sillimanite → chloritoid) is also observed in the core of the Canigou dome. Under the kyanite-staurolite equilibrium hypothesis, the peak MIII P-T conditions in the eastern massifs are estimated at 5 kbar and 575oC, that would imply a pressure increase of 1 to 1.5 kbar (4–6 km deepening) starting from the end of MII, associated with a severe temperature decrease of 150oC. Such an overpressure cannot be due to the D2d dextral-inverse mylonites. However, a fluid inclusion study [Kister et al., 2003] demonstrated that the rocks of the Villefranche syncline did register a pressure increase at the D2b stage, i.e., experienced effective downwards displacement during the syncline formation, and it may be estimated that, in the core of the syncline, a depth increase of 7–8 km could have been attained. Now, in the Cap de Creus massif, the highest MIII grade is observed in the core of the D2b Birba syncline, analogous to the Villefranche syncline. Thus, D2b deepening in the syncline cores may have contributed to the pressure increase. An additional increase may have been provided by sedimentary accumulation in an overlying (and now eroded) syn-orogenic basin (fig. 5). While such a process may explain the development of MIII associations in the D2b synclines, it remains to explain its appearance in the anticlines (Albères, Canigou). However, in the same fluid inclusion study referred to just above [Kister et al., 2003], it is demonstrated that, post-dating D2c and the late pluton emplacement, the studied area suffered a severe isobaric temperature drop, allowing the appearance of chloritoid in the Canigou core (fig. 5). A similar explanation may hold for the Albères massif, if it is accepted there that late kyanite and staurolite were not in equilibrium: starting from the peak MII conditions (c. 4 kbar and 650o–700oC), a strong isobaric cooling would have allowed the successive appearance of staurolite and kyanite.Discussion and conclusionTimingThe youngest pre-orogenic flyschs are dated (in the Axial Zone) from the Namurian-Westphalian boundary (315±5 Ma), thus setting a minimal age for D1-MI. On the other hand, in the northern Pyrenean Agly massif, the Ansignan hypersthene-granite, which is coeval with MII, is dated at around 315-305 Ma, and the associated norites, likely testifying for the mafic magmatism at the origin of the heat flux responsible for MII, are themselves dated at c. 315 Ma. Finally, the large syn-D2c (post-MII) granite plutons are all dated at 307±3 Ma (i.e., close to the Westphalian-Stephanian boundary). Taken together (with the possibility of a slight diachronism between the North Pyrenean massifs and the Axial Zone, and, within the Axial Zone, between east and west), these data indicate that the MI-MII transition and the whole D2a–c/MII development took place in a very restricted time interval (c. 10 Ma), in Westphalian to Stephanian times.Crustal rheology and orogenic developmentAt the end of the Namurian crustal subduction (D1-MI), the Pyrenean crust, that had been thickened with at least a doubling of the upper crust thickness, had begun to experience uplift and erosion. This exhumation process rapidly changed from retrograde to prograde (MIIs-MIIa) during the D2a (MII) syn-convergence extensional phase.The D2a sub-event was marked by the development of three interrelated processes: (i) isotherm upwelling, regional stratiform MII metamorphism and partial melting in the middle crust, as a result from the intrusion, in the lower crust, of mafic magmas of mantellic derivation; (ii) thinning of the thickened crust; (iii) first arrival of granite plutons in the middle crust. It is thought, according to Vielzeuf [inGuitard et al., 1996], that these processes were initiated by a lithospheric delamination process.At the end of D2a, the crustal rheology had been modified, with a partially melted middle crust that received granitic melts issued from the melting of the lower crust. This highly ductile middle crust was sandwiched between a thick (≥ 10 km) rigid upper crust and a less ductile granulitised hot lower crust (800o–900oC), thus allowing the progressive decoupling of the upper and lower crust from D2a to D2c. The buckling of the upper crust, with formation of the large upright D2b folds, became therefore possible, forcing the injection of deep anatectic melts in the anticline cores (a probable explanation of the MIIbγ thermal culmination), and creating, in the deepened syncline cores, the strong pressure increase that favoured MIII inception.However, the MII isogrades are frozen in their folded position, indicating that cooling of the belt had indeed begun since at least the end of the D2b phase. The cooling was sufficiently rapid to be expressed in the Axial Zone by a sub-isobaric temperature decrease, at the origin of the MIII Barrovian and retrograde event, coeval with the late D2c and D2d phases. In the North Pyrenean Massifs, where the D2d phase was extensive, the retrograde MIII event could not be expressed, due to both decompression and thermal effects of the extension.A summary of this complex evolution is given in figure 6. Finally, the interrelated D2 and MII events appear as the record, in the middle-upper crust, of a very short, but very intense heating event that strongly modified the rheologic behaviour of the crust inherited from the D1 crustal subduction and allowed a transitory decoupling of the upper and lower crust. The isobaric MIII event records an exceptionally rapid return to the “normal” thermal and rheologic structures of the crust.The rapidly changing tectonic and thermal conditions that characterise the Variscan Pyrenees during the D2 event may be understood if the position of the Pyrenees within the southern branch of the West European Variscan belt is considered (fig. 7).

Calculation of a synthetic seismic reflection trace from detailed descriptions of exposed Proterozoic strata in northwestern Canada permits correlation of reflections on regional seismic profiles to surface outcrop. Approximately 5.4 km (composite thickness) of Paleo- and Mesoproterozoic strata are exposed in the Muskwa anticlinorium that is located within the foreland of the Cordillera in northeastern British Columbia. The Tuchodi anticline is the easternmost structure of the Muskwa anticlinorium and has the deepest levels of Proterozoic strata exposed. At this location, prominent seismic reflection layering rises toward the surface and is easily correlated to the deeper formations of the Muskwa assemblage stratigraphy. These layers are followed westward into the middle crust, where they are overlain by dramatically thickened (by about five times) strata, primarily of the Tuchodi Formation. Along the same line of section, the Muskwa assemblage reflections overlie additional subparallel layered reflections at depth whose lithology and origin are unknown. However, coupled with other observations, including regional refraction results that indicate the crustal layers have both low seismic p-wave velocities and low ratios of p- and s-velocities, regional gravity observations that indicate the layers are low density, and correlation to similar layers on other seismic profiles that exhibit characteristic seismic stratigraphic features, the subparallel layers that are present beneath the known Muskwa assemblage are most easily interpreted as layered Proterozoic (meta-) sedimentary rocks. These results provide the basis for interpreting the Muskwa anticlinorium as a crustal-scale structure that formed when a deep basin of Proterozoic strata was inverted and thrust over an ~20 km high footwall ramp during Cordilleran orogenesis.

AbstractThe Polish Sudetes on the NE margin of the Bohemian Massif comprise a complex mosaic of pre-Permian basement units, traditionally included in the Variscides. A hypothesis of significant Caledonian orogenesis in this area originated in the 1920s, was subsequently rejected, and then was recently revived in models which invoked Early Palaeozoic to Early-Mid Devonian subduction and continental collision along a proposed extension of the Tornquist suture zone. We reassess the evidence invoked in support of the Caledonian orogeny, such as supposed regional pre-Upper Devonian unconformity, Ordovician bimodal magmatism and radiometric, palaeontological, palaeomagnetic and structural data, and suggest these are either inconclusive or misinterpreted. On the other hand, the Sudetes record Mid?-Late Devonian blueschist metamorphism followed by an Early Carboniferous regional high temperature event, widespread Late Devonian/Early Carboniferous flysch/molasse sedimentation and abundant granite intrusion in the Carboniferous to Early Permian. We discuss the usage of the term ‘Caledonian’ in a plate tectonic context and suggest it should not be used simply to denote Early to Mid-Palaeozoic tectonic activity. The tectonic evolution of the Sudetes was temporally different from, and resulted from convergence of different crustal domains than that of the British-Scandinavian-Pomeranian Caledonides. The Sudetic Palaeozoic sequences most probably developed on Armorican Neoproterozoic crust and in adjacent oceanic(?) domains and, therefore, the Sudetes form part of the Variscan orogenic belt.

For the first time, on the basis of the data set of the Taimyr geophysical site, the processes that cause vertical oscillatory movements of large blocks of the continental crust and largely determine its deep structure are confidently recorded. In this regard, the conceptual apparatus of plate tectonics is being expanded due to terms that were not originally used for it, previously used within the framework of geosyncline theory. Modern geodynamics combines concepts opposed in the past, thereby forming a conceptually new geosyncline plate tectonics. Under the new paradigm, the oil and gas prospects of an area are determined not so much by its confinement to a geostructure of any age, as by the current stage of the geosyncline cycle, characterized by subsidence, active sedimentation processes and formation of a sedimentary basin or, conversely, orogenesis and dominant erosion of sediments. Thus, one or another scenario will cause a different inflow of hydrocarbons from the generation area, which means that regional tectonic movements largely predetermine the realization of the hydrocarbon potential, making them one of the most important criteria for its assessment.

Pre-Silurian bedrock units played key roles in the early Paleozoic history of the Maine–Quebec Appalachians. These units represent peri-Laurentian material whose collision with the craton deformed the Neoproteozoic passive margin and initiated the Appalachian mountain-building cycle. We present new field, petrological, geochronological, and geochemical data to support the following interpretations related to these units. (1) The Boil Mountain Complex and Jim Pond Formation do not represent part of a coherent ophiolite. (2) Gabbro and tonalite of the Boil Mountain Complex intruded the Chain Lakes massif at ca. 477 Ma. (3) The Skinner pluton, an arc-related granodiorite, intruded the Chain Lakes massif at ca. 472 Ma. (4) The Attean pluton, with a reconfirmed age of ca. 443 Ma, is unrelated to Early Ordovician orogenesis. (5) The most likely timing for the juxtaposition of the Jim Pond Formation and the Boil Mountain Complex was during regional Devonian deformation. These interpretations suggest that the Boundary Mountains were once part of a series of arcs extending at least from central New England through Newfoundland.

The late Archean Opatica granitoid-gneiss belt is situated within the northern Abitibi Subprovince, along the northern margin of the Abitibi greenstone belt. Approximately 200 km of structural section was mapped along three traverses within the previously unstudied Opatica belt. The earliest preserved structures are penetrative foliations and stretching and mineral lineations recording regional ductile shearing (D1). Late-D1 deformation was concentrated into kilometre-scale ductile fault zones, typically with L > S tectonite fabrics. Two families of lineations are associated with D1, indicating shearing both parallel and transverse to the east-northeast trend of the belt. Lineations trending east-northeast or northwest–southeast tend to be dominant within domains separated by major fault zones. In light of the abundant evidence for early north–south compression documented throughout southern Superior Province, including the Abitibi greenstone belt, D1 is interpreted in terms of mid-crustal thrusting, probably resulting in considerable crustal thickening. Movement-sense indicators suggest that thrusting was dominantly southward vergent. D2 deformation resulted in the development of vertical, regional-scale dextral and sinistral transcurrent fault zones and open to tight upright horizontal folds of D1 fabrics. In the context of late Archean orogenesis in southern Superior Province, the tectonic histories of the Abitibi and Opatica belts should not be considered separately. The Opatica belt may correlate with the present-day mid-crustal levels of the Abitibi greenstone belt, and to crystalline complexes within the Abitibi belt. It is suggested that the Abitibi Subprovince should be viewed, at the regional scale, as a dominantly southward-vergent orogenic belt. This work demonstrates that structural study of granitoid-gneiss belts adjacent to greenstone belts can shed considerable light on the regional structure and structural evolution of late Archean terranes.

A regional metamorphic gradient from upper greenschist to granulite facies is identified south of the Grenville front in the Double Mer – Lake Melville area of eastern Labrador. Mineral assemblages in politic–granitic gneiss, amphibole-bearing quartzo-feldspathic gneiss, and coronitic metagabbro allow three major metamorphic domains to be established. These are collectively divisible into 11 subdomains. Geothermobarometry applied to the higher grade domains suggests that each is characterized by specific P–T conditions, which achieved 1000–1100 MPa and 700–800 °C in the deepest level rocks.The problem of reconciling geochronological data (which record a major orogenic event at 1650 Ma) with the occurrence of high-grade mineral assemblages in 1426 Ma metagabbro (which suggests a pervasive Grenvillian event) is discussed in terms of three models. The preferred model envisages crustal stabilization at 1650–1600 Ma to give high-grade mineral assemblages seen in the host rocks and with which mineral assemblages in coronitic metagabbro equilibrated after their emplacement at 1426 Ma. During Grenvillian orogenesis (1080–920 Ma) the present structural configuration was achieved by thrust stacking. This imparted a sporadic metamorphic and structural overprint and Grenvillian ages in selected accessory minerals.

New U-Pb age data from the southwestern Slave Province demonstrate that units of the Indin Lake supracrustal belt form an imbricated structural stack. The oldest rocks of the belt are undated mafic volcanic flows of the Hewitt Lake group that are crosscut by a 2670 Ma felsic sill, itself coeval with mafic through felsic volcanic rocks of the 2668-2671 Ma Leta Arm group. The youngest rocks of the belt are 2647-2629 Ma turbidites and felsic volcanic rocks of the unconformably overlying Chalco Lake group. Tonalite orthogneiss of the adjacent Cotterill gneiss complex is 2680 Ma, suggesting that it does not represent in situ basement to the supracrustal belt. Intercalation of the older Hewitt Lake and Leta Arm groups with the younger Chalco Lake group is interpreted to result from D1 imbrication and folding between 2629 and 2609 Ma, the age of a crosscutting tonalite intrusion. Subsequent D2 folding and regional low-pressure metamorphism occurred between 2609 Ma and ca. 2590 Ma. D3 normal faulting between the belt and Cotterill gneisses, ca. 2590 Ma, is interpreted to overlap with retrograde amphibolite-facies metamorphism and decompression of the gneiss complex. Comparisons between the tectonic history of the Indin Lake area and the central Slave Province show that turbidite deposition was regionally diachronous and overlapped with regional deformation elsewhere, supporting existing models favouring some form of accretionary orogenesis. The imbricated and intercalated 2670-2629 Ma supracrustal sequence may characterize a distinct crustal block in the southwestern Slave Province.

The provenance of Devonian Old Red Sandstone (ORS) continental successions in the northern Scottish Caledonides is poorly known: were they derived locally or from more distal sources? The integration of U–Pb and Hf isotope analyses in detrital zircon crystals reduces potential ambiguities arising from non-unique age populations and yields information on the crustal evolution of the source terranes. Samples of basal ORS successions yield zircon U–Pb age groupings of c. 1800–1500 and c. 1200–900 Ma, with minor Neoarchean, Tonian, Ediacaran and Ordovician contributions. SW Baltica provides the best match for detrital zircon ages and Hf isotopic signatures and much of the >900 Ma zircon population was probably recycled from Neoproterozoic successions. εHf(t) values in c. 1800–1000 Ma grains reflect the assembly of Nuna, the development of a long-lived retreating subduction system along its margin and Grenville collisional orogenesis. These basal ORS successions were probably deposited within the same regional fluvial system as coeval sedimentary rocks in the Midland Valley, draining an area of positive relief in SW Baltica where continental convergence continued through the Early Devonian.Supplementary material: Isotopic data, statistical comparison of selected samples and TIMA heavy mineral data are available at https://doi.org/10.6084/m9.figshare.c.5301780

Eoalpine (Cretaceous) very low- to low-grade metamorphism recorded on the illite-muscovite-rich fraction of metasediments from South Tisia (eastern Mt Papuk, Croatia)Eoalpine very low- to low-grade metamorphism related to Cretaceous orogenesis has been investigated in the Slavonian Mts, Croatia. Samples belonging to the Psunj metamorphic complex (PMC), the Radlovac metamorphic complex (RMC) and Permian-Triassic and Triassic sedimentary sequences (PTSS) were studied. The Kübler and Árkai indices of all the analysed samples indicate high-anchizonal to epizonal metamorphism. The degree of Eoalpine metamorphism tends to be constant in all samples implying that the different complexes passed through and recorded the same event. Measurements of illite-white K-micab0-parameter of the RMC samples imply transitional low- to medium-pressure character of the metamorphism. These data together with K-Ar ages (~100-80 Ma) measured on illite-white K-mica rich < 2 μm grain-size fractions point to Late Cretaceous very low- to low-grade regional metamorphism presumably related to the main nappe-forming compressional events in the Pannonian Basin and the Carpathians. The P-T-t (pressure-temperature-time) evolution of the studied area is in good agreement with similar scenarios in the surrounding areas of Tisia, but also in Eastern Alps, Carpathians and Pannonian Basin (ALCAPA).

To date the formation of ruby deposits and link it to the regional metamorphism associated with Tertiary Himalayan orogenesis, 40Ar–39Ar stepwise heating experiments were performed on single grains of phlogopite syngenetic with ruby, and zircon inclusions in ruby and spinel were dated with the U–Pb method by ion-probe. The Ar–Ar ages of phlogopites associated with ruby are Oligocene (24.7 ± 0.3 Ma) at Jegdalek in Afghanistan; Miocene at Mogok in Myanmar (18.7 ± 0.2 to 17.1 ± 0.2 Ma), at Hunza in Pakistan (10.8 ± 0.3 to 5.4 ± 0.3 Ma), and Chumar in Nepal (5.6 ± 0.4 Ma); and Pliocene (4.6 ± 0.1 Ma) at Ruyil in Nepal. In Vietnam, a zircon included in a ruby from the Quy Chau deposit yielded a 238U–206Pb age of 53.8 ± 4.6 Ma, whereas in the Red River shear zone, ruby formed at around 40–36 Ma during ductile deformation under peak metamorphic conditions. The ages obtained in this study are in agreement with those previously published for the ruby-bearing metamorphic belts and document extensional tectonics that were active from Afghanistan to Vietnam between the Oligocene and the Pliocene. Ruby-bearing marbles define a high-quality gem belt linked to the high-temperature metamorphism of the Himalayan fold belt that developed during the Tertiary collision of the Indian plate with Asia.

The Upper Eocene – Miocene Cypress Hills Formation of the Cypress Hills plateau, in southwestern Saskatchewan and southeastern Alberta, is interpreted as a braidplain deposit. The regional paleoslope dipped to the northeast, and the east–west distribution of outcrop exposes facies representing lateral variation across the slope of the braidplain. Overall, the average clast size of the deposits decreases from west to east, with western area sediments dominated by boulder-sized gravels deposited on longitudinal bars. The eastern outcrop area contains deposits of braided channels cut into and interbedded with finer interchannel material including lacustrine marlstones, silcretes, and debris-flow deposits, the latter commonly containing abundant fossils.The gravels of the Cypress Hills Formation are multicyclic; they were originally derived from the western ranges of the Rocky Mountains during Laramide orogenesis and later shed farther into the basin during rebound due to unloading of the Laramide thrusts by erosion. Most recent transport resulted from uplift by intrusive activity of the Sweetgrass Hills, the Bearpaw Mountains, and the Highwood Mountains in northern Montana. Transport from the uplifted source areas was largely restricted to valley-confined rivers with the braidplains beginning beyond the valley termini. The lateral extent of the gravel braidplain was limited by the position of valleys and resulted in the observed variation in facies. Climate, as indicated by the sedimentology, faunal assemblages, silcretes, and palynology, was semi-arid with seasonal rainfall.

The geological and structural evolution assessment of the Basement Complex rocks in Iwaraja area, southwestern Nigeria showed that the basement rocks comprise quartzites and quartz-schists of the Effon Psammite Formation, quartz-mica schists, biotite schists, migmatitic gneisses, granitic gneisses, late and post-tectonic granitic rocks including pegmatites, which have been subjected to two phases of deformation. The first phase is mainly a fabric forming deformation that also led to the development of moderately plunging mineral lineation. No minor fold of this phase was recognized. The second deformation phase gave rise to the development of Iwaraja (ductile) shear zone. Mylonitic foliation is sub-vertical and steeply dipping and while the mineral lineation is sub-horizontal and shallowly plunging. Within granitic gneiss mylonites, the shear zone is characterised by early and late open to tight folds of pegmatite dykes. Adjacent the shear zone, ptygmatic folds of quartzo-feldspathic veins in gneisses and crenulated cleavages that overprinted earlier schistosity surfaces in the quartz-mica schist also characterised this deformation phase. Extensional fractures in the various lithologies generally show bimodal orientations mainly in the WNW-ESE and NW-SE directions, which are nearly perpendicular to the regional metamorphic foliations. These deformation conditions depict structural features that are associated with internal zones of orogenic belts. Within the study area, the structures document late-Precambrian deformation during the closing stages of Pan-African orogenesis.

The geological and structural evolution assessment of the Basement Complex rocks in Iwaraja area, southwestern Nigeria showed that the basement rocks comprise quartzites and quartz-schists of the Effon Psammite Formation, quartz-mica schists, biotite schists, migmatitic gneisses, granitic gneisses, late and post-tectonic granitic rocks including pegmatites, which have been subjected to two phases of deformation. The first phase is mainly a fabric forming deformation that also led to the development of moderately plunging mineral lineation. No minor fold of this phase was recognized. The second deformation phase gave rise to the development of Iwaraja (ductile) shear zone. Mylonitic foliation is sub-vertical and steeply dipping and while the mineral lineation is sub-horizontal and shallowly plunging. Within granitic gneiss mylonites, the shear zone is characterised by early and late open to tight folds of pegmatite dykes. Adjacent the shear zone, ptygmatic folds of quartzo-feldspathic veins in gneisses and crenulated cleavages that overprinted earlier schistosity surfaces in the quartz-mica schist also characterised this deformation phase. Extensional fractures in the various lithologies generally show bimodal orientations mainly in the WNW-ESE and NW-SE directions, which are nearly perpendicular to the regional metamorphic foliations. These deformation conditions depict structural features that are associated with internal zones of orogenic belts. Within the study area, the structures document late-Precambrian deformation during the closing stages of Pan-African orogenesis.

The Verkhoyansk-Kolyma orogenic region is the main element of the morphostructure of the Western part of the Verkhoyano-Chukotka mountain country. The territory of the orogenic region covers the Verkhoyansk system of mountain ranges in the West, the system of Chersky and Momsky ridges in the North-East and Suntar-Khayata ridge in the South. The results of spectral-statistical analysis of the Verkhoyansk-Kolyma orogenic region relief digital models in the various radiuses averaging and separation of the gravitational field at different frequency components, corresponding to different depth levels of the lithosphere, is made to identify the spatial changes in geomorphological and geophysical parameters of the orogenic region, and also conditions of its mountain facilities formation. It is shown that the mountain systems correspond to linear gravitational minima, and the Verkhoyano-Kolyma positive regional anomaly of the low-frequency component of the relief-Verkhoyansk regional gravitational minimum with an amplitude of up to 100 mGal and a diameter of 1100–1200 km. The morphostructure of the Verkhoyansk-Kolyma orogenic region is characterized by a straight relief, which allows the deep structure of mountain structures and their formation to be considered within the framework of their corresponding folded structures. On the example of the Verkhoyansky meganticlinory deep structure, the model of the Verkhoyansky ridge formation is substantiated. Orogenesis of the Verkhoyansk-Kolyma orogenic region is considered on the basis of the proposed model of the deep structure, namely as a result of granitization of the crystalline basement and lower sedimentary layer under the influence of mantle fluids actinolite at depths of 45–120 km. Rheomorphic processes of the crystalline basement resulted in the formation granite-gneiss domes and the rise of mountain ranges.

Stromatolites are abundant and widely distributed within two narrow stratigraphic intervals in Middle (Darriwilian) and Upper (lower Turinian) Ordovician strata of the Laurentian foreland interior in the Ottawa Embayment, eastern Ontario. These lithostratigraphic markers coincide with rapid, tectonically driven flooding of the foreland interior and may identify an opportunistic microbial response to nutrient loading with shallow (peritidal, subtidal) marine reworking of terrestrial or nutrient-rich coastal systems. The remaining (Chatfieldian–Edenian) foreland-platform succession represents deeper-water deposition in response to elevated subsidence rates along the Laurentian margin. Stromatolites are absent in this higher-energy setting, but microbial calcite is preserved as coccoid-like microencrustations on skeletal debris. Stromatolites of Darriwilian age are dolomitic, occur in the Carillon Formation, and are part of a regional (200+ km) onlap of peritidal sediment during onset of Taconic orogenesis. Stratiform to large (2 m diameter) low-relief domal stromatolites contain rhythmic laminations of inclusion-rich and -poor dolomicrospar grouped by Fe-oxide-stained erosional surfaces. Domal forms also contain thrombolitic microstructure. Patterns of lamination and stable (C, O) isotopes suggest a balance between abiotic and microbial carbonate production, likely influenced by water depth and temperature. Stromatolites of Turinian age are calcitic and form a regional (80+ km) thin (<8 m) subtidal biostromal unit in the lowermost Pamelia Formation. Their occurrence defines an abrupt vertical transition from initial intrabasinal transgressive subtidal phosphatic siliciclastics and carbonates to an interbasinal stratigraphy of peritidal lime mudstone. Arrhythmic laminations of microbial peloid packstone, with possible eukaryote alga moulds, and locally evaporitic spongiostromate microstructure identify salinity and energy as primary depositional controls. The stromatolite–?eukaryotic association is similar to some modern subtidal microstructures and is part of the reef-community diversification in the Ordovician.

The eastern Cascades foldbelt is one of three structural domains lying within the complex collision zone between the Insular and Intermontane composite terranes in northern Washington and southern British Columbia. The foldbelt resides between the high-grade metamorphic backbone of the Cascade orogen on the west and rocks of the composite Intermontane terrane to the east. It encompasses the stratigraphically coherent, basalt-floored Jura–Cretaceous Methow basin as well as more chaotically disposed Permian–Jurassic oceanic rocks of the Hozameen terrane. Methow basin rocks are thought to have been sutured above the oceanic rocks prior to the middle Cretaceous contractional episode described in this report.Based on the analysis presented herein, between ca. 100 and 88 Ma the rocks in the foldbelt underwent shortening in an east-northeast – west-southwest direction by 50 km or more, largely by displacement on the east-vergent Jack Mountain – Chuwanten thrust system. The early stages of contraction occurred by the process of tectonic wedging, whereby rocks of the Hozameen terrane and western Methow basin translated eastward by delaminating eastern Methow basin strata along west-vergent thrusts. In later stages of shortening, the tectonic wedge became inactive and was carried piggyback atop the east-vergent Cascade Crest and Chuwanten faults.Presently available geochronologic data indicate overlap in the time periods during which eastern and western Cascades foldbelts were deforming and the Cascade metamorphic core was undergoing amphibolite-facies regional metamorphism. Therefore, contraction of rocks in the eastern foldbelt was an important product of the middle Cretaceous orogeny in the Cascades and must be considered in any regional tectonic model for orogenesis. The eastern foldbelt clearly accommodated substantially less shortening than the western foldbelt and is herein proposed to be a backthrust system in the rear of the predominantly west-vergent Cascade orogen.

AbstractU–Pb ages and Hf isotope compositions of zircons from the Chencai complex in Zhejiang Province have been determined to provide constraints on mechanisms of migmatization and tectonic evolution related to the early Palaeozoic orogeny in the Cathaysia Block, South China. Zircons from leucosome samples of migmatites are characterized by nebulous overgrowths enclosing inherited cores or occur as newly formed grains with weak zoning. Five samples gave weighted mean ages ranging from 438±3 Ma to 432±4 Ma, which are interpreted as recording the time of anatexis of a regional tectono-thermal event. TheirεHf(t) values range from −21.4 to −4.8 (with peak at −11), with correspondingTDM2ages of 1.73–2.77 Ga (with peak atc.1.9–2.3 Ga), suggesting that the protoliths formed by reworking of ancient crust evolved from Late Palaeoproterozoic – early Archaean crust–mantle differentiation. The migmatization was spatially and temporally associated with reported 460–435 Ma metamorphism with a clockwise pressure–temperature (P–T) path and was most likely controlled by crustal thickening driven by the early Palaeozoic orogenesis. TheTDM2ages of the Chencai complex are consistent with those of the Wuyi–Yunkai structural belt in the Cathaysia Block, but distinct from those (with peak at 2.7–3.0 Ga) of the Badu complex which lacks early Palaeozoic tectono-thermal records. The data support the suggestion that a postulated geological entity, instead of the east domain (the Badu complex being its main part) of the Cathaysia Block, was probably involved in the early Palaeozoic orogeny.

Dulaankhan granitic pluton, which is situated in northern Mongolia, the southern portion of the Mongolian-Transbaikalian belt (MTB), is petrographically composed of fine to medium-grained peralkaline granite and is intruded by a small body of quartz syenite. Geochemical data show the Dulaankhan granite and the intruding quartz syenite are both slightly peraluminous and high-K calc-alkaline, and are enriched in LREEs relative to the HREEs, with negative Eu anomaly, and in large ion lithophile elements (LILEs; such as K, Cs and Rb) with respect to high field strength elements (HFSEs; e.g., Nb, Ta and Ti). In terms of relations of Nb, Zr and Y to Ga/Al, however, the Dulaankhan granite and quartz syenite show geochemical features of A-type granites and can be classified into the A2-sub type granite, implying that the pluton formed in an post-collision extensional environment. LA-ICPMS zircon U-Pb dating results suggest that the Dulaankhan granite crystallized at 198±1 Ma, whereas the intruding quartz syenite at 180±1 Ma, consistent with our field observation that the quartz syenite intrudes the granite, attesting that the two granitic bodies were emplaced at different times although both of them formed during the Early Jurassic period. According to these new data, as well as regional ones, we propose that the Dulaankhan granitic pluton was likely generated in the post-collision setting related to the orogenesis of the Mongol-Okhotsk belt that seems to occur prior to Early Jurassic in the northern Mongolian segment.

The Chevreuil intrusive suite (1.17-1.16 Ga) represents a chronological field marker of regional extent that intruded the Central Metasedimentary Belt in the western Grenville Province of Quebec after peak metamorphism. Style and site of magma emplacement, and extent of deformation of Chevreuil plutons and dykes permit unravelling of the early Grenvillian evolution of the belt with respect to cratonal North America. The suite comprises a series of vertically layered gabbro stocks and monzonite-diorite-gabbro sheet intrusions, and a swarm of microdiorite dykes that cut across gneisses. The dykes display systematic variations in extent of deformation across the belt. We targeted U-Pb geochronology on gneisses within the identified strain windows; they preserve the record of a ca. 1.20 Ga high pressure-temperature (P-T) metamorphic event. The sheet intrusions define magmatic corridors all along, and concordant with, the western, northern, and eastern tectonic boundaries of the belt. The concordant and elongate shape of these bodies results from emplacement, not deformation. Chevreuil magmas thus sealed the belt boundaries largely in their current positions, with the implication that docking of Elzevirian and pre-Elzevirian terranes with cratonal North America predates 1.17 Ga. We interpret the 1.20 Ga metamorphism as evidence for the initiation of Grenvillian continent-continent collision during the culmination of the Elzevirian orogeny at ca. 1.22 Ga. Emplacement-related fabrics indicate that the Chevreuil suite and the coeval Morin anorthosite suite intruded during renewed orogenesis. This orogenic pulse (Shawinigan) is not accretionary, but represents a strongly partitioned, compressive, intraplate reactivation event.

Mountain building in the western part of the Archean Superior Province culminated with the formation of regional strike-slip faults. This paper reports on the kinematics and timing of several major faults at the juncture between the Uchi, English River, Winnipeg River, and western Wabigoon subprovinces. Sinistral-oblique mylonitization along the northeast-striking Miniss River fault occurred at 2681 [Formula: see text] Ma. This involved ~40 km of sinistral offset and a scissor-like motion whereby vertical displacement increased southwestward toward a restraining bend near Sioux Lookout. To the north, the Miniss River fault is intersected by the east-striking, dextral strike-slip Sydney Lake – Lake St. Joseph fault; the latter merges along strike with the Pashkokogan fault. Restoration of respective displacements indicates that the faults formed sequentially, not simultaneously in response to tectonic indentation. Dextral strike-slip motion along the Sydney Lake – Lake St. Joseph (– Pashkokogan) fault was instigated at ≤2670 Ma and drove greenschist-grade, dextral reactivation of the southwest segment of the Miniss River fault. U–Pb geochronology suggests that the latter coincides with an older terrane-boundary fault that juxtaposed ca. 2735 Ma juvenile, western Wabigoon arc complexes against ca. 3.05 Ga granitoid rocks of the Winnipeg River terrane. The Sydney Lake – Lake St. Joseph (– Pashkokogan) fault similarly demarcates a fundamental boundary between Uchian volcanoplutonic rocks and the English River accretionary prism. Strike-slip faults in this region therefore initiated at terrane boundaries and in some cases evolved so as to transect and displace these boundaries to accommodate further shortening during final stages of Archean orogenesis.

The Makkovik Province is a segment of a Paleoproterozoic accretionary belt (the Makkovik–Ketilidian orogen) that developed on the southern margin of Laurentia at 1.9–1.7 Ga. In contrast to coeval Laurentian orogenic belts that mainly resulted from collision of Archean plates, Makkovikian–Ketilidian orogenesis was dominated by active-margin processes including continental margin arc plutonism and juvenile terrane accretion, both of which were accompanied by regional transpression. In the Makkovik Province, earliest deformation and amphibolite-facies metamorphism of Paleoproterozoic rift–drift assemblages (Post Hill and Moran Lake groups) and the Archean foreland (Nain Province) occurred at 1.9 Ga in response to accretion of a Paleoproterozoic island arc. Following this collision, cratonward-dipping subduction was established, resulting in the formation of the 1895–1870 Ma Island Harbour Bay Plutonic Suite, a calc-alkaline magmatic arc built on reworked Archean crust. Crust formation continued between ca. 1860 and 1850 Ma with deposition of the Aillik Group on a largely juvenile basement in a rifted-arc or back-arc setting. Sometime before 1802 Ma this depositional basin was tectonically inverted, with resultant northwestward thrusting of the Aillik Group over reworked Archean crust. This phase of deformation may have been driven by accretion of a second island arc potentially represented by the Cape Harrison Metamorphic Suite. Regional transpression and amphibolite-facies metamorphism at ca. 1815–1780 Ma were accompanied by widespread granitoid plutonism. These events were mainly concentrated in the juvenile domains and are thought to reflect processes in a broad continental back-arc setting. A final orogenic pulse, marked by regional greenschist-facies transpression and emplacement of A-type granitoid plutons, occurred between 1740 and 1700 Ma, with deformation and plutonism potentially linked to crust–mantle detachment and incursion of mafic magmas at the base of the crust, respectively. The record of crustal development suggests that the coeval themes of spatially and temporally linked structural and plutonic activity, oceanward migration of this activity over time, and a trend toward increasingly more localized deformation occurred throughout the orogenic history of the Makkovik Province. These characteristics are thought to broadly reflect oceanward crustal growth of the orogen over time. In the correlative Ketilidian mobile belt of southern Greenland, these themes were also operative but appear to have been less pronounced, most likely due to minimal or a complete absence of accretion of island-arc material.

The research aimed to reconstruct the geological structures and tectonics of the Bayah complex area. The structures found that grouped into regional structural patterns used to determine the ages and the events that responsible to its formation. The methods used in this research include field and studio method. Field method carried out to map the outcrops and record geological structures data using geological compass, GPS, tape measurement, and geological hammer, while studio method performed to process and analyze data using software such as Win Tensor, Dips, MapInfo Professional 10.5 and CorelDraw X4. The geological structure of the Bayah has varying patterns and ages. The fracture patterns show N-S and E-W direction which is belong to Sundanese and Java Pattern formed in range of the Early Eocene to Pliocene. While the faults that have direction of SW-NE and E-W are classified into Meratus and Java Pattern. However, metamorphic rock foliations show NW-SE and N-S direction that belonging to the Pre-Tertiary Sumatra Pattern. The three faults of this research are estimated to be formed by the effect of orogenesis that occurring in different events and ages. JSA-014 fault is predicted to form due to orogeny I or orogeny II in the Early Oligocene - Middle Miocene, this fault classified as the 2nd order right lateral wrench fault. JSA-034 fault is formed by orogeny I in Early Oligocene - Middle Miocene, this fault is also classified as the 2nd order right lateral wrench fault. While JSA-080 fault has relatively young age that formed due to orogeny III in the Middle Miocene - Pliocene and belonging to the 3rd order left lateral wrench fault.

Comparison of litho-, bio-, and chemostratigraphy in two cores from the northeastern margin of the Michigan Basin (Manitoulin Island) and from within the Ottawa Embayment (eastern Ontario) identifies interbasinal differences of Late Ordovician platform foundering linked to Taconic orogenesis. Graptolite biostratigraphy defines an east-to-west younging (late Edenian to early Maysvillian) of platform burial. A regional unconformity likely caps the platform succession. In both basins, an increased supply of mafic material appears during the final stages of platform collapse, with the accumulation of organic-rich (<8%), petroliferous shales (Collingwood Member — Michigan Basin; Eastview Member — Ottawa Embayment). Both units preserve evidence for deposition coincident with increased dysoxic to possible anoxic bottom-water conditions, but the Collingwood Member accumulated under a relatively stable paleoceanographic environment. Rhythmic interbedding with platform limestone in eastern Ontario, combined with evidence for fluctuating paleoproductivity, suggests the depositional environment of the Eastview Member was more sensitive to higher order controls affiliated with tectonic, oceanographic, and (or) sea level variation. Such interbasinal differences likely reflect a greater rate of subsidence in the Manitoulin region transforming platform sedimentation to a distal ramp facies. In eastern Ontario, a lesser rate of subsidence maintained a shallower water, but open margin, setting. Burial of the Upper Ordovician platform, as preserved in eastern Ontario, occurred during peak dysoxic conditions, with deposition of a hemipelagic facies (Billings Formation) that marks the peak supply of clay-size mafic-derived sediment. Bottom-water ventilation occurred only with appearance of abundant Taconic-derived distal turbidites. An equivalent hemipelagic facies appears to be absent from the Manitoulin region. However, equivalent resedimented deposits are represented by the Blue Mountain Formation.

The Chuduoqu Pb-Zn-Cu deposit is located in the Tuotuohe area in the northern part of the Sanjiang Metallogenic Belt, central Tibet. The Pb-Zn-Cu ore bodies in this deposit are hosted mainly by Middle Jurassic Xiali Formation limestone and sandstone, and are structurally controlled by a series of NWW trending faults. In this paper, we present the results of fluid inclusions and isotope (C, H, O, S, and Pb) investigations of the Chuduoqu deposit. Four stages of hydrothermal ore mineralization are identified: quartz–specularite (stage I), quartz–barite–chalcopyrite (stage II), quartz–polymetallic sulfide (stage III), and quartz–carbonate (stage IV). Two types of fluid inclusions are identified in the Chuduoqu Pb-Zn-Cu deposit: liquid-rich and vapor-rich. The homogenization temperatures of fluid inclusions for stages I–IV are 318–370 °C, 250–308 °C, 230–294 °C, and 144–233 °C, respectively. Fluid salinities range from 2.07 wt. % to 11.81 wt. % NaCl equivalent. The microthermometric data indicate that the fluid mixing and cooling are two important mechanisms for ore precipitation. The H and O isotopic compositions of quartz indicate a primarily magmatic origin for the ore-forming fluids, with the proportion of meteoric water increasing over time. The C and O isotopic compositions of carbonate samples indicate that a large amount of magmatic water was still involved in the final stage of mineralization. The S and Pb isotopic compositions of sulfides, demonstrate that the ore minerals have a magmatic source. On a regional basis, the most likely source of the metallogenic material was regional potassium-enriched magmatic hydrothermal fluid. Specifically for the Chuduoqu Pb-Zn-Cu deposit, the magmatic activity of a syenite porphyry was the likely heat source, and this porphyry also provided the main metallogenic material for the deposit. Mineralization took place between 40 and 24 Ma. The Chuduoqu deposit is a mesothermal hydrothermal vein deposit and was formed in an extensional environment related to the late stage of intracontinental orogenesis resulting from India–Asia collision. The determination of the deposit type and genesis of Chuduoqu is important because it will inform and guide further exploration for hydrothermal-type Pb and Zn deposits in the Tuotuohe area and in the wider Sanjiang Metallogenic Belt.

Integrated petrographic, isotopic, fluid inclusion microthermometry, and geochemical analyses of Paleozoic carbonate successions from multiple boreholes within the Huron Domain, southern Ontario were conducted to characterize the diagenetic history and fluid composition, on a regional scale, and evaluate the nature and origin of dolomitized beds. Multiple generations of non-stochiometric dolomite have been observed. These dolomites occur as both replacement (D1 and D2) and cement (saddle dolomite; SD) and formed either at near-surface to shallow burial zone (D1) or intermediate burial (D2 and SD). Petrographic and geochemical data of dolomite types and calcite cement suggest that these carbonates have experienced multiple fluid events that affected dolomite formation and other diagenetic processes. Cambrian and Ordovician strata have two possibly isolated diagenetic fluid systems; an earlier fluid system that is characterized by a pronounced negative shift in oxygen and carbon isotopic composition, more radiogenic Sr ratios, warm and saline signatures, higher average ∑REE compared to warm water marine brachiopods, negative La anomaly, and positive Ce anomaly; and a later Ordovician system, characterized by less negative shifts in oxygen and carbon isotopes, comparable Th, hypersaline, a less radiogenic, less negative La anomaly, and primarily positive Ce anomaly but also higher average ∑REE compared to warm water marine brachiopods. Ordovician, Silurian, and Devonian Sr isotopic ratios, however, show seawater composition of their respective age as the primary source of diagenetic fluids with minor rock/water interactions. In contrast, the isotopic data of the overlying Silurian and Devonian carbonates show overlaps between δ13C and δ18O values. However, δ18O values show evidence of dolomite recrystallization. D2 shows wide Th values and medium to high salinity values. Higher Th and salinity are observed in SD in the Silurian carbonates, which suggest the involvement of localized fluxes of hydrothermal fluids during its formation during Paleozoic orogenesis. Geochemical proxies suggest that in both age groups the diagenetic fluids were originally of coeval seawater composition, subsequently modified via water-rock interaction possibly related to brines, which were modified by the dissolution of Silurian evaporites from the Salina series. The integration of the obtained data in the present study demonstrates the linkage between fluid flux history, fluid compartmentalization, and related diagenesis during the regional tectonic evolution of the Michigan Basin.

Abstract Seismicity in the southeastern United States is relatively poorly characterized and thus not well understood. Structures and heterogeneities from multiple stages of Appalachian orogenesis, continental rifting, and magmatism as well as rivers and reservoirs may be influencing seismic activity in the region, but previous constraints are limited. The addition of seismic stations from the U.S. Transportable Array and the Southeastern Suture of the Appalachian Margin Experiment Array in 2012–2014 provide an opportunity to characterize seismicity in the central Georgia–South Carolina region. We develop a seismic catalog of &gt;1000 events from March 2012 to May 2014 within or near the instrument array boundaries 30.1°–35.2°N, 80.9°– 85.7°W. Many of the events detected were industrial blasts, so multiple strategies were tested to discriminate between earthquakes and blasts based on event locations, timing, and spectral amplitude of the P and S arrivals. Based on this analysis, ∼10% of the events in the catalog were classified as earthquakes. Most earthquakes southeast of the eastern Tennessee seismic zone are located in the Carolina terrane, particularly where the Carolina terrane intersects major rivers or reservoirs. One prominent region of seismicity along the Savannah River near Thurmond Lake corresponds with an ∼4.5 m rise in water levels in 2013. A temporal cluster of earthquakes in April 2013 was followed by increased levels of ambient seismicity preceding the nearby Mw 4.1 earthquake in 2014. Focal mechanisms based on first-motion polarities indicate strike-slip to oblique-thrust motion on structures trending approximately north–south or east–west, and a maximum horizontal stress orientation consistent with the regional trend of ∼N60°E, implying that seismicity may reactivate more optimally oriented structures in the Carolina terrane that are oblique to the trend of the Appalachians. Seismicity in central Georgia appears to be controlled by a complex interaction between preexisting crustal structure and hydrologic variability.

Orogenesis is increasingly interpreted in terms of strain focusing, localization and partitioning processes. Such heterogeneous deformation is considered a consequence of the tectonic framework, with pre-existing structural and stratigraphic variability providing inherent zones of crustal weakness. Detailed structural investigation of Neoproterozoic Dalradian metasediments in the Glencolumbkille region, northwest Ireland, enables patterns of reworking and strain localization to be assessed in terms of four overprinting ductile deformation episodes. A well-defined and intricate Dalradian stratigraphy provides readily distinguishable markers which not only focus deformation along marked rheological boundaries, but also aid in the definition and identification of resultant geometries. Overall structural and stratigraphic relationships show that whilst D1 was not associated with major structures, D2 is related to north–northeast directed folding and ductile thrusting resulting in a major phase of crustal thickening and almandine-amphibolite facies metamorphism. Structures generated during D2 deformation subsequently became the locus of intense D3 strain and were reactivated in an oblique sense associated with south or southwest directed translations. Local overprinting relationships clearly demonstrate S2 fabrics being transposed by S3 resulting in a composite foliation over large areas. Similarly, the L2 mineral lineation is abruptly transposed by L3 over relatively small distances indicating high D3 strain gradients and the susceptibility of lineations to reworking. The final stage of ductile deformation (D4) which was increasingly localized and focused into earlier (D2−D3) high strain zones, is marked by a pronounced phase of sinistral transpression associated with clockwise cleavage and minor fold transection of northwest verging upright folds. Sinistral shear is strongly partitioned in to the steep limbs of mesoscopic F4 folds. The detailed investigation of structures generated within such multiply deformed and reworked zones provides evidence of both the kinematic and tectonic evolution of regional deformation systems.

Abstract Rutile grains often occur in different types of gold deposits, and their U-Pb ages have been widely used to determine the formation time of gold mineralization. However, the origin of rutile grains in the gold deposits remains controversial. In this paper, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of U-Pb ages and trace elements on rutile grains were applied to investigate the metamorphic and hydrothermal processes of the Baiyun gold deposit (70 t Au, avg grade: 3 g/t) in the Liaodong Peninsula in the northeastern part of the North China craton. Rutile grains in the hydrothermal altered gold schist from the Baiyun deposit yielded two group ages of 1924 ± 18 and 237.0 ± 1.8 Ma, respectively. Combined with our systematic U-Pb zircon geochronological results of the ore-hosting schists and post-ore dikes, we suggest these rutile ages record a Paleoproterozoic metamorphic event and a Triassic hydrothermal gold mineralization event, respectively. The metamorphic and hydrothermal rutile grains have no obvious textural differences, but they show distinct trace element contents of Zr, W, Nb, and Ta. Combined with previous published data, we propose that high W (&gt;1,000 ppm) and low Zr (&lt;200 ppm) contents in rutile can be used to distinguish hydrothermal rutile from metamorphic and magmatic rutile. The newly identified ca. 237 Ma hydrothermal event is much older than the ca. 227 to 210 Ma Triassic magmatic rocks in the region, which precludes a temporal and genetic link between the Baiyun gold mineralization and the regional Mesozoic magmatism. Rather, the ca. 237 Ma gold mineralization may be associated with the Triassic orogenic metamorphism, and Baiyun is an orogenic gold deposit. The Triassic gold deposits in the northern margin of the North China craton formed by orogenesis between the Siberian craton and the North China craton. After a hiatus, the large-scale gold deposits formed during the Early Cretaceous in the North China craton due to a westward subduction of the paleo-Pacific plate beneath the craton since the Early Jurassic. Our study highlights that rutile in gold deposits may be inherited from the host rocks and/or formed by hydrothermal fluids. Distinguishing between these two different rutile generations requires a combination of in situ age dating and trace element geochemistry in petrogenetic context.

Shpat mountainous ridge represents a morphological unit with extremely prominent natural borders and rich natural resources. This abstract presents the natural potentials of Shpat mountainous ridge and a synthesized analysis of key aspects of tourism, mineral and water resources, forests and pastures management, etc. Shpat unit, is integral part of Bukanik ultrabasic massive, where are explorated cooper resources. The geological content of this mountain, contribues the mesozoic ultrabasic and flysch, calcareous rocks and quaternary deposition are also present. The morphologic and morphogenetic complex of the relief was created during the tectogenic period, especially during the tecto-orogenesis, where as consequence diverse magmatic, terrigenous and carbonates rocks were created. Structural relief landforms, are structural benches, flat surfaces formed in the aclinal structure, structural surfaces, denudational surfaces and concave fragment of front of the cuestas. The karstic surface forms were developed on limestones of different age and character. There is a conspicuously small number of dolines on the surface of the hardly dissolvable crystalline limestone, and the debris covering the surface is high enough for agriculture. The water infiltrating on the plateau surfaces in the karst springs. The knowledge of present morphodynamics implies features concerning the positive and restrictive role of each factor, which, by association, defines the potential of some gropus of processes and state of morphologic hazards in certain area. Such analyses multiplied in the last couple of years, when the occurrence of some mass wastings determined many geomorphologic risk situations allover Shpat mountainous ridge. The climate by regional and local differences of the weathering elements favorable to the development of morphological processes. In periglacial environments solifluction frequently occurs in association with permafrost or seasonally frozen ground, and under these circumstances it is more specifically described as gelifluction. Snow provides both and as ground insulation. The erosional potential of nivation is controlled primarily snow thickness or absence underlying permafrost. Cryoplanation terraces (also known as altiplanation terraces) are level or gently sloping surfaces found in the periglacial zone which are cut into bedrock on hill summits or upper peaks. The natural potentials of Shpat mountainous ridge have been analyzed as key elements of this area for sustainable development. The effects of the use of the natural resources and their influence on the economic structure have been analyzed defining the directions of the development on perspective of the rural area. The current developments at the agricultural rural area have produced changes to the physical-geographical elements, accelerating the pace of slope processes, where the predominant part of the settlements is established on the terrace levels, causing environmental degradation.

Abstract Widespread remagnetization has been identified in fold belts and forelands inboard of mountain ranges and has usually been interpreted as resulting from fluid migration related to orogenesis in these mountain ranges. The geochemical properties of these fluids should be compatible with the formation or the transformation of ferrimagnetic minerals, thus allowing acquisition of remanent magnetization during fluid migration. Carbonate hosted lead-zinc (+ or -barite and fluorite) mineralization of the Mississippi Valley-type (MVT) are also generally considered to have formed during the migration of enormous volumes of fluids and are commonly located in foreland fold belts or their forelands. This suggests a similar origin for widespread carbonate remagnetization and MVT mineralization. The paleomagnetic dating of MVT deposits has been successfully applied in MVT districts, mainly of North America. Thus, it was used for the MVT deposits hosted by Mesozoic carbonate rocks of the Cevennes region of southern France. In view of the structurally complexity in the region, and because the results presented here are intended to provide an initial reference direction on which further results can be based, only sites belonging to the most stable parts of this border are considered here. Most samples were collected from three surface sites in the area of the Largentiee mine and from independently oriented cores of the two deep boreholes (Balazuc and Morte-Merie) from the Geologie Profonde de la France program. Several samples were also collected from three sites around the area of the Saint Felix-de-Pallieres mine. All these samples come from different stratigraphic levels: Carboniferous, Permian, Triassic, Liassic and Middle Jurassic.

This research aimed to reveal the petrogenesis of granitic rocks of Bayah Complex starting from magma differentiation to exposing event, this research also intended to determine the tectonic environment. The methods carried out in this research include field observation, petrographic analysis using polarized light microscopy, and geochemical analysis using X-Ray Fluorescence (XRF) and Inductively Coupled Mass Spectrometry (ICP-MS). Petrographic analysis shows that Bayah granitic rocks are composed of quartz, plagioclase, and K-feldspar while the rest are amphibole, biotite, sericite, chlorite, epidote, and opaque. Based on its major oxide concentrations, Bayah granitic rocks classified as granite and diorite-quartz which have high-K calc-alkaline magma. 4 samples of granitic rocks showed the A/N+K+C > 1 molar ratios belonging to the peraluminous S-type granite index while the remaining 1 sample showed a molar ratio of A/N+ K+C < 1 and A/N+K > 1 which classified as metaluminous I-type granite. Accordingly, Bayah granitic rocks are S-type granite which crystallized from sediment-derived magma, the sediments itself estimated sourced from continental especially Malay Peninsula, Indonesian Tin Island, and Schwaner Mountains. During differentiation, the magma undergone crustal contamination reflected by the increase in both SiO2 0.51 wt% and Al2O3 1.95 wt%, and decrease in Fe2O3 + MgO 0.61 wt% from the pure composition of sediment-derived magma. Furthermore, the occurrence of crustal contamination also recognized from high concentrations of Rb and Ba which indicate the interaction of magma with the materials of continental crust. Regard to the exposing event, Bayah granitic rocks approximated to be exposed due to regional tectonic activity which caused Orogenesa I in the Early Oligocene to the Late Oligocene. Moreover, based on the plot of trace elements especially Rb, Y, Nb, Ta, and Yb on Harker and tectonic discriminant diagrams, Bayah granitic rocks are formed on volcanic-arc active continental margins in accordance with regional tectonic setting.

Sands are widespread in the upper part of the geological section and are an important study subject in engineering geology. They lie at the base of surface facility, serve as a reservoir of underground objects and actively used as a building material. One of the important scientific and practical tasks facing geological engineers is the study of the regularities of sands distribution by area and geological section. It is especially relevant for the vast territory of our country, but there is currently no generalizing regional engineering-geological summary on sandy soils of all Russia. The article presents a schematic map of the distribution of sands of the Quaternary of various genesis, which fully covers the territory of the country and is compiled taking into account the latest results of geological plotting and mapping. The regularities of the distribution of sandy soils on the territory of Russia as a whole and within separate regions are described: young and ancient platforms of the European part (Timan-Pechora, Scythian and East-European); the ancient Siberian platform; young West-Siberian, Yano-Kolyma and Zeya-Bureya plates; orogenes of the European part, Siberia and the Far East; Baikal rift zone, as well as on the shelves of numerous seas washing the shores of Russia. The distribution of sands on the area and the section is discussed, their association with different genetic complexes of Quaternary deposits and certain elements of the relief. The Quaternary age sands that are developed within the engineering-geological zone of joint distribution of permafrost and thawed rocks and zone of practically continuous distribution of permafrost are described in the cryolithozone, which covers more than half of the country’s territory.

The second part of the article studies the tectonic conditions and natural mechanisms of tectonic inversion of the Dnieper-Donets Basin and the Western Donets Graben. Method. The research uses the original method of reconstruction of fields of tectonic stresses and deformations. It also makes tectonophysical analysis of geostructures was used. The analytical base of the research consisted of the latest materials of geo-mapping, numerical modeling of deformations of the southern edge of the Eastern European platform and comparison of model and reconstructed stress fields. Results. In the geodynamic environment of the interference of the intraplate submeridional collision compression with the regional strike-slip stress field, the inversion deformations of the rift-like geostructure took place in the uplift-thrust and strike-slip modes. This led to significant horizontal movements of geomass of sedimentary rocks, deformation folding with the formation of three inversion floors - Late Hercynian (Saal-Pfalz), Early Alpine (Laramian) and Late Alpine (Attic). They formed structural ensembles of scaly tectonic covers of transverse displacement of geomass a from axial to onboard zones, folded covers of longitudinal approach from the Donbas Foldbelt and long linear anti- and synforms, the axes of which are oriented orthogonally to the direction of geomass advancement. Together they form the body of the Segment of Tectonic Wedging of geomass, which is distinguished as part of the Cover-Folded System of Tectonic Thrusting of regional scale. A feature of the tectonic framework of the Segment is the curvature of the planes of the main thrusts, which limit it, and smaller plumage thrusts, which control the folded covers of the thrust. It is associated with a change in the extension of the thrusts from the north-west in the territory of the Western Donets Graben to the western direction in the extreme south-east of the Basin. This causes the corresponding bending of the axes of the fracture anti- and synforms. Structural patterns of folding with a tendency to adapt the axes of folds to the extension of thrusts indicate significant horizontal displacements of geomas of the sedimentary stratum, which in conditions of limited geological space cause secondary deformations of linear folded forms. Due to the displacement of geomas from the zones of maximum compression in the axial part of the Graben to the zones of geodynamic shadow - in the direction of the Oryl depression and Graben boards, the West Donets Cover-Folded Tectonic Region was formed within the transition zone. Scientific novelty. The study completed an original kinematic model of tectonic inversion of the Western Donets Graben was completed. The mechanism of inversion, due to which the riftogenic structure is completely destroyed by folded deformations of platform orogeneses, is caused by the pressure of the "tectonic stamp" of the Donbas Foldbelt. Under its influence, a segment of tectonic wedge was formed in the Graben, which was diagnosed with oroclin of transverse extension of the sliding type. The body of the Oroclin is formed by echeloned, rock-articulated ensembles of anticlinal uplift -folds, synclines and scaly plates-covers of pushing. A geodynamic injection band was formed in the foreland of the Tectonic Orocline extension, where folded zones of geomas displacement were formed, which consist of coulisse articulated uplift-anticlines. At the top of the Orocline, at the ends of dynamically conjugate main thrusts, an advanced tectonic compression fan is formed. In the rear of the Oroclin – hinterland are tectonic sutures – the roots of the folding covers of the approach. Practical significance. Development of a structural-kinematic model of tectonic inversion of the Western Donets Graben will allow to improve the geodynamic model of tectonic inversion of the Dnieper-Donets paleorift, on the basis of which regional schemes of tectonic and oil-gas-geological zoning will be adjusted.

In central Nepal, the Siwalik front represents the southernmost and younger thrust zone of the Himalayas. Here the detrital Mio-Pleistocene Siwalik Formations overthrust the Gangetic Quaternary. The morphostructural organization depends on lateral variations of the tectonic environment. Two main types are characterized. Escarped fronts (400 to 600 m. of relative altitude) coincide with steeply dipping structures, strong morphology resulting from a thrust ramp; immediately to the south the Terai alluvium are folded in relation with a blind thrust. The smoothed fronts (100 to 300 m) correspond to a flat lying thrust. This regional example allows to propose a geodynamic evolutionary model for a foreland thrust front. During the flat thrust motion, thickening and erosion are balanced (smoothed front). In the following time, the southward propagation of the deformation with addition of new units, results in the formation of a frontal ramp which induces a steepening of the structures. The rate of uplift is not compensated by erosion (escarped front).

The initiation and evolution of compressional intracontinental orogens are favored by rheologically weak lithosphere underneath; however, how this weakened lithosphere responds to the regional stress regime remains vigorously debated. The Tien Shan mountains in central Asia provide the best example to illustrate the deep deformational responses to intracontinental orogenesis. We present new constraints on the nature of seismic anisotropy in the crust and upper mantle of the central Tien Shan through shear-wave splitting analyses. Our results reveal a sharp change in the orientations of crustal anisotropic fabrics on two sides of the mountains. The convergence-parallel fast orientations in the northern segment are closely related to the lower-crustal simple-shear deformation caused by the underthrusting of the Kazakh Shield, whereas the depth-independent orogen-parallel fast orientations in the southern segment suggest vertically coherent pure-shear thickening of the Tien Shan lithosphere in response to the northward indentation of the Tarim Basin. The thickened lithosphere has partly foundered into the deep mantle, contributing to the accelerated shortening deformation in the late Cenozoic. Our observations demonstrate the complex tectonic processes in the Tien Shan and suggest that the rheological properties of bounding blocks can play a significant role in shaping the lithospheric structures of intracontinental orogens.

Abstract The Himalaya are among the youngest and highest mountains in the world, but the exact timing of their uplift and origins of their biodiversity are still in debate. The Himalayan region is a relatively small area but with exceptional diversity and endemism. One common hypothesis to explain the rich montane diversity is uplift-driven diversification–that orogeny creates conditions favoring rapid in situ speciation of resident lineages. We test this hypothesis in the Himalayan region using amphibians and reptiles, two environmental sensitive vertebrate groups. In addition, analysis of diversification of the herpetofauna provides an independent source of information to test competing geological hypotheses of Himalayan orogenesis. We conclude that the origins of the Himalayan herpetofauna date to the early Paleocene, but that diversification of most groups was concentrated in the Miocene. There was an increase in both rates and modes of diversification during the early to middle Miocene, together with regional interchange (dispersal) between the Himalaya and adjacent regions. Our analyses support a recently proposed stepwise geological model of Himalayan uplift beginning in the Paleocene, with a subsequent rapid increase of uplifting during the Miocene, finally give rise to the intensification of the modern South Asia Monsoon.