Thrust Tectonics Research Articles

The geology and hydrogeology of the Cassino plain (central Apennines, Italy): redefining the regional groundwater balance

Cassino plain is a Quaternary intermontane basin of the central-southern Apennines, Italy. The plain has outstanding groundwater resources (total discharge of 23,000 L/s), thanks to the huge karst basins that surround the area. The area has been involved in many hydrogeological interests since the 1970s due to the economic importance and construction of the Western Campania Aqueduct for the water supply of Naples city and its hinterland. Despite its importance, the area lacks a common accepted hydrogeological conceptual model due to the complex geological setting. Two contrasting conceptual models already exist in the literature, with the first model based on a quantitative hydrogeological approach and the second on fieldwork. Through a literature analysis and further detailed field surveys, a new conceptual model is presented, acknowledging the thrust tectonics of the Apennine chain. The model unveils the most important hydrogeological issues of the area, serving as a useful tool for groundwater management, as well as for considering the changing anthropic and climate scenarios. In particular, the study redefines the hydrostructure extents and the groundwater flowpaths, characterizing the main water resources as Gari and Peccia springs.

Along-strike variations in thin-skinned thrusting style controlled by pre-existing basement structure in the easternmost Jura Mountains (Northern Switzerland)

Abstract A detailed analysis of the Late Miocene Mandach Thrust, a key tectonic structure of the easternmost Jura Mountains (northern Alpine foreland), is presented providing insights into the modes of along-strike structural cover–basement interactions in a classical foreland setting. Our study builds on the construction, restoration and forward modelling of eight closely spaced cross-sections constrained by depth-migrated 2D seismics and geological maps. The results indicate predominantly thin-skinned thrust tectonics without significant inversion of underlying basement structures. However, inherited pre-thrusting normal faults exerted a strong control on the observed thrusting style, changing along-strike from a comparatively simple geometry to a complex, partly overthrust, partly reactivated normal fault. The observed variations relate to changes in the relief of the mechanical basement and the characteristics of pre-thrusting normal faults. The thrust's complexity is further increased by the local activation of secondary detachment horizons and possibly along-strike sedimentary facies changes within the thrust-faulted sedimentary sequence. The variations in thrusting style go along with subtle changes in shortening that may point towards as yet undetected transfer structures. As such, our structural analysis of the Mandach Thrust provides an improved understanding of the fault's kinematics and serves to highlight existing exploration uncertainties.

The three-dimensional electrical structure and metallogenic prospect of the Ning (Nanjing)-Wu (Wuhu) basin and the southern adjacent area in eastern China

The Ning (Nanjing city)-Wu (Wuhu City) volcanic basin, which is famous for its large-scale, high-grade ore deposits, is a typical iron ore district in the middle-lower reaches of the Yangtze River Metallogenic Belt (MLRYMB). The southern part of the basin is primarily covered by Quaternary strata. Few in depth studies have been conducted on this area. Due to the increasing demand for mineral resources and the controversy over regional tectonic models, some fundamental geological issues still need to be addressed. These questions include defining the characteristics of the geological structures and the mineralization prospects. Therefore, a three-dimensional (3D) magnetotelluric survey was conducted in this area to obtain a deep 3D electrical model. It was found that the Yangtze fault (CJF) and the main thrust fault (MTF) in the upper crust have the same deep (middle crust to upper mantle) setting and part of the thrust tectonics of the metallogenic belt. The southern boundary of the Ning-Wu Basin is located on a fault belt (boundary fault, BF) with a northeast-east (or east-west) strike influenced by the MTF in the southern part of the study area. Bounded by the BF and MTF, the southeastern part of the study area exhibits signs of uplift. With the recent discovery of a large porphyry copper deposit to the southeastern part of the study area, which is located in an uplift structure similar to the one south of the Ning-Wu Basin, this local uplift could have potential mineralization prospects based on a previous mineralization theory developed for this belt.

Palaeozoic palaeogeography of the East European Craton (Poland) in the framework of global plate tectonics

Global palaeogeographic maps were constructed for eight time intervals in the Palaeozoic. The maps contain information concerning plate tectonics and palaeoenvironment during the Cambrian, Ordovician, Silurian, Devonian and Carboniferous. The East European Craton belonged to the Palaeozoic Baltica Plate, which originated as a result of disintegration of the supercontinent Pannotia during the early Cambrian. Baltica included part of Poland and adjacent areas northeast of a line that extends between Scania and the Black Sea. This plate was located in the Southern Hemisphere and drifted northward during Early Palaeozoic time. The Early Ordovician was the time of maximum dispersion of continents during the Palaeozoic. Avalonia probably started to drift away from Gondwana and moved towards Baltica during Ordovician time. Between Gondwana, Baltica, Avalonia and Laurentia, a large longitudinal oceanic unit, known as the Rheic Ocean, was formed. Avalonia was probably sutured to Baltica by the end of the Ordovician or in the Early Silurian. This process was dominated by the strike-slip suturing of the two continents, rather than a full-scale continent-continent collision. Silurian was a time of Caledonian orogeny, closing of the Early Palaeozoic oceans, collision of Baltica with Avalonia and Laurentia and the assembly of the supercontinent Laurussia. The Variscan orogeny in Poland was caused by the collision of the Bohemian Massif plates and the Protocarpathian terrane with Laurussia. The Protocarpathian terrane acted as an indentor that caused thrust tectonics in the East European Platform, Holy Cross Mountains and the Lublin area.

The Jurassic to Palaeogene strata in the northern boundary fault zone in deep borehole PD-9 at Szczawnica, Pieniny Klippen Belt, West Carpathians, Poland: biostratigraphy and tectonic implications

The Jurassic through Palaeogene stratigraphy and tectonic structure of the PD-9 borehole at Szczawnica, Pieniny Klippen Belt, West Carpathians, Poland, is revised. The borehole was drilled in the strongly tectonized northern boundary fault zone of the Pieniny Klippen Belt, of Miocene age. Age revision is given by dinoflagellate cysts. Late Cretaceous taxa are reported from the Haluszowa Formation. The Bryjarka Member (previously with the rank of formation) yielded rich Early Eocene (Ypresian) assemblages. Similar ones are reported from the Szczawnica Formation. A tectonic thrust sheet of the Jurassic Szlachtowa Formation (Grajcarek Unit) in the Palaeogene of the Magura Nappe is evidenced; it yielded late Toarcian–Aalenian dinoflagellate cyst assemblages. The succession of strata recorded from the PD-9 borehole shows the steep, almost vertical attitude of the Grajcarek Main Dislocation at Szczawnica, separating the structures of the Magura Nappe (to the north) and the Pieniny Klippen Belt to the south.

CONTEXTO ESTRUTURAL DA ÁREA DA FOLHA TOPOGRÁFICA GUAPIARA

A Folha Topográfica de Guapiara 1: 50.000, localiza-se no extremo sul do estado de São Paulo e compreende a porção norte do Terreno Apiaí, de idade meso- a neoproterozoicas, inserido na faixa centro-sul do Cinturão Ribeira da Província Mantiqueira Central. A região caracteriza-se pelas rochas da sequência metavulcanossedimentar do Supergrupo Açungui, definidas pela Formação Água Clara e os grupos Votuverava e Itaiacoca, além de corpos graníticos do Granito Três Córregos e do Granito Capão Bonito, rochas sedimentares do Grupo Itararé, intrusivas básicas associadas ao Magmatismo Serra Geral e sedimentos quaternários. O quadro estrutural é determinado dominantemente pelo arranjo tectônico neoproterozoico. As rochas apresentam uma evolução estrutural do tipo polifásica, evidenciada pela superposição de eventos de principalmente quatro fases deformacionais Dn, Dn+1, Dn+2 e Dn+3. Os dois eventos iniciais são relacionados a uma tectônica de cavalgamento, de direção NE/SW e NW/SE, respectivamente, acompanhado de estruturas geneticamente associadas, tais como falhas de cavalgamentos, dobras e as foliações Sn e Sn+1. Superpondo-se a estas estruturas, ocorrem dois eventos Dn+2 e Dn+3, ligados a fase colisional final e uma tectônica transcorrente/transpressiva. Esse evento é responsável pelo dobramento das estruturas pré-formadas, com plano axial de direção NE/SW e NW/SE, respectivamente.

Multi‐scale analysis of a migrating submarine channel system in a tectonically‐confined basin: The Miocene Gorgoglione Flysch Formation, southern Italy

AbstractThe Miocene Gorgoglione Flysch Formation records the stratigraphic product of protracted sediment transfer and deposition through a long‐lived submarine channel system developed in a narrow and elongate thrust‐top basin of the Southern Apennines (Italy). Channel‐fill deposits are exposed in an outcrop belt approximately 500 m thick and 15 km long, oriented oblique to the palaeoflow, which was roughly south‐eastward. These exceptional exposures of channel‐fill strata allow the stacking architectures and the evolution of the channel system to be analyzed at multiple scales, enabling the effects of syn‐sedimentary thrust tectonics and basin confinement on the depositional system development to be deciphered. Two end‐member types of elementary channel architecture have been identified: high‐aspect‐ratio, weakly‐confined channels, and low‐aspect‐ratio, incisional channels. Their systematic stacking results in a complex pattern of seismic‐scale depositional architectures that determines the stratigraphic framework of the deep‐water system. From the base of the succession, two prominent channel complex sets have been recognized, namely CS1 and CS2, consisting of amalgamated incisional channel elements and weakly‐confined channel elements. These channelized units are overlain by isolated incisional channels, erosional into mud‐prone slope deposits. The juxtaposition of different channel architectures is interpreted to have been governed by regional thrust‐tectonics, in combination with a high subsidence rate that promoted significant aggradation. In this scenario, the alternating ‘in sequence’ and ‘out of sequence’ tectonic pulses of the basin‐bounding thrusts controlled the activation of coarse‐clastic inputs in the basin and the resulting stacking architectures of channelized units. The tectonically‐driven confinement of the depositional system limited the lateral offset in channel stacking, preventing large‐scale avulsions. This study represents an excellent opportunity to analyze the stratigraphic evolution of a submarine channel system in tectonically‐active settings from an outcrop perspective. It should find wide applicability in analogous depositional systems, whose stratigraphic architecture has been influenced by tectonically‐controlled lateral confinement and associated lateral tilting.

The Zhayao tectonic window of the Jurassic Yuantai thrust system in Liaodong Peninsula, NE China: Geometry, kinematics and tectonic implications

Liaodong Peninsula on the northeastern North China Block that witnessed the spectacular Late Mesozoic tectonics is a key area to probe the transition from compression to extension. Borehole data clearly reveals that the Cambrian limestone overlay the Jurassic limestone, which identified the Yuantai thrust system in Liaodong Peninsula. Zircon grains from a granodiorite dike that intruded the thrust system yielded U-Pb age of 128.3 ± 1.3 Ma, further constraining the timing of the thrusting between Late Jurassic to early Early Cretaceous. A detailed field study of three-dimensional fault-zone exposures in the Zhayao tectonic window are conducted to decipher the thrust tectonics before the extension in Liaodong Peninsula. The key observations are: (1) meter-scale asymmetric folds in deformed mid-Cambrian rocks; (2) decameter-scale recumbent folds and secondary imbricate thrusts in deformed Middle Jurassic rocks; and (3) non-foliated breccia, fault gouge, and brittle porphyroclasts adjacent to fault planes. The combined brittle–ductile style of deformation indicates that the fault zone operated under near-surface conditions. In addition, we infer that the folds were formed first at the propagating fault tip and subsequently dismembered by normal faults. We interpret the Zhayao thrust, which is located around the margin of the tectonic window, as the frontal thrust of the Yuantai thrust system. Furthermore, by applying the theory of fault-related folds, we deduce that the Zhayao frontal thrust is a secondary duplex. Based on our field observations and borehole data, we propose an imbricate thrust model for the fold-and-thrust belt of the southern Liaodong Peninsula. The structural data indicate that the transport direction of the Yuantai thrust system was top-to-the-southeast, suggesting that the thrust system was resulted due to northwest-ward subduction of the paleo-Pacific plate during the Mesozoic.

Study of fault plane solutions and stress drop using local broadband network data: The 2011 Sikkim Himalaya earthquake Mw 6.9 and its aftershocks

Fault plane solutions of the September 18, 2011 Sikkim Himalaya earthquake Mw 6.9 and its four aftershocks (Mw>4.0) are studied by waveform inversion using the local broadband network data. The solutions show pure strike-slip mechanisms; one aftershock show thrust faulting with strike-slip component. Strike-slip mechanisms indicate predominant transverse tectonics in Sikkim, in the eastern Himalaya region, unlike predominant thrust tectonics in the western Himalaya. The 2011 main shock occurred at a much deeper depth (~47 km) compared to the shallower (<20 km) thrust events in the western Himalaya. Further, analysis of ground acceleration spectra reveals low stress drop (14-38 bars) in agreement with the relatively long source duration and small co-seismic slip of the main shock as well as the aftershocks. We interpret the low stress drop in terms of lower energy release due to reactivation of the Tista fault in opposite sense to that of the Himalayan thrust tectonics. The low stress drop also indicates a pre-existing brittle zone or fault zone at deeper depth or mantle depth.

Antimoniferous vein-type mineralization of the Berga Antiform, Eastern-Thuringia, Germany: A fluid inclusion study

The antimoniferous vein-mineralization in the Schleiz and Greiz area, eastern Thuringia, are bound to NE-SW striking Variscan fault zones along the margins of the Berga Antiform. The Sb-Pb-Zn ores form massive sulfide-sulfosalt-quartz ± carbonate veins, breccias or stockworks within Ordovician and Silurian metasedimentary units, Devonian metabasalts and metagranitoids. Mineralogical investigations from several Sb mines and hard rock quarries near Schleiz and Greiz, Germany, show that the Sb-Pb-Zn-sulfides are texturally in close association with quartz and carbonates. Stibnite is the major Sb-bearing mineral. Minerals of the Sb-Pb-Zn-sulfide assemblage replace an earlier Zn-Fe-As-sulfide-quartz assemblage (quartz I), named the ore-stage I mineralization. Stibnite and quartz II overgrow these early sulfides accounting for the ore-stage II. Lead-dominated Sb-sulfides (e.g., zinkenite, plagionite, semseyite) represent the ore-stage III phase followed by sphalerite II, galena and quartz III accounting for ore-stage IV. Fluid inclusion studies on ore and gangue minerals of the different ore stages give insights into the composition and temperature of the mineralizing fluid(s). Primary fluid inclusion assemblages in ore-stage II stibnite and co-genetic quartz II show variable vapor fractions within fluid inclusion assemblages. Heterogeneous trapping of CO2 at constant salinities of fluid inclusions of the same assemblage indicates the influx of a buoyant pure CO2 fluid into an aqueous fluid phase. The presented data demonstrates the first example of CO2-influx into an aqueous fluid identified by fluid inclusion analyses. During this ore-stage II a H2O-CO2-NaCl fluid, with eq. w(NaCl) of 1 to 2.7% at 220–226 °C prevails. In contrast, fluid inclusions in ore-stage III minerals (boulangerite) contain a homogeneously trapped H2O-NaCl-CaCl2 fluid, with eq. w(NaCl) up to 8.1% at temperatures ≥146 °C. Ore-stage IV minerals (sphalerite II, quartz III) contain a homogeneously trapped H2O-NaCl-CaCl2 fluid with eq. w(NaCl) of >20% and homogenization into the liquid phase at around 120 °C. Fluid inclusion data suggest P-T-conditions at the onset of mineralization at around 220 °C at 0.70 to 0.75 kbar (fluid pressure). The mechanisms of Sb-ore precipitation were induced by the influx of CO2, fluid cooling (quartz II – stibnite – boulangerite) and late stage mixing with a high salinity fluid resulting in the precipitation of sphalerite II, galena and quartz III. The unique opportunity to analyze fluid inclusions in many different, subsequently precipitating ore and gangue minerals enables the reconstruction of the temporal evolution of the Sb-veins. The distinct change of the ore-forming processes from the influx of CO2 into an aqueous fluid and cooling (ore-stage I, II) to mixing (ore-stage III, IV) as the dominant precipitation mechanisms are also accompanied by a drastic change in the mineralogy from Sb-sulfides to Pb-Zn-sulfides.Late-orogenic granitic intrusions served as a potential heat, metal and sulfur source. Variscan wrench and thrust tectonics and associated metamorphism account for the ore-stage I mineralization. Hydrothermal Sb-Pb-Zn assemblages (ore-stages II, III and IV) precipitated during the latest part of the Variscan orogeny most likely around the Carboniferous/Permian boundary. Although, fluid composition and formation temperatures of the Greiz and Schleiz mineralization are on the first view quite similar to those of other Variscan Sb mineralization, the observation of CO2-influx and fluid mixing with a high-salinity fluid is unique for European Sb-occurrences.

Coseismic Contortion and Coupled Nocturnal Ionospheric Perturbations During 2016 Kaikoura, Mw 7.8 New Zealand Earthquake

AbstractThe oblique‐thrust Kaikoura earthquake of Mw 7.8 that struck New Zealand on 13 November 2016 at 11:02:56 UTC (local time at 00:02:56 a.m. on 14 November 2016) was one of the most geometrically and tectonically complex earthquakes recorded onshore in modern seismology. The event ruptured in the region of multisegmented faults and propagated unilaterally northeastward for more than 170 km from the epicenter. The GPS derived coseismic surface displacements reveal a larger widespread horizontal and vertical coseismic surface offsets of ~6 m and ~2 m, respectively, with two distinct tectonic thrust zones. We study the characteristics of coseismic ionospheric perturbations based on tectonic and nontectonic forcing mechanisms and demonstrate that these perturbations are linked to two distinct surface thrust zones with rotating horizontal reinforcement trending the rupture, rather than merely to the displacements oriented along the rupture propagation direction.

Low-temperature metamorphism in the Capiru Formation, Morro Grande Synform, Southern Ribeira Belt

ABSTRACT: The Capiru Formation consists of a low-grade meta-sedimentary succession of slates, phyllites, quartzites and marbles, disposed in blocks delimited by thrust and strike-slip faults in the Curitiba Terrane, Southern Ribeira Belt, Southern Brazil. The metamorphic and deformation records are heterogeneous, with deformed zones tectonically interbedded by domains with preserved sedimentary features. The present work aims to understand the development of mineral paragenesis based on geochemical and petrographic analysis. We selected samples of metasandstones, slates, phyllites and rhythmic phyllites, with different metamorphic and deformation records to be analysed. We selected samples with different metamorphic records to be analysed. The petrographic characterization of foliations was made through field studies supported by microtectonic analysis. The mineralogical and chemical compositions were determined by X-ray diffractometry and X-ray fluorescence, respectively. The results show a preserved sedimentary bedding (S0), defined by sedimentary structures with top-and-bottom indicators. The S1 foliation is related to a thrust tectonics, and it is characterized by a continuous slaty cleavage. The S1 slaty cleavage is crenulated and cut by a millimetric S2 cleavage. The mineral assemblage is composed by quartz, sericite, magnetite/goethite and carbonaceous material. The metamorphism was developed under low-temperature conditions (between 250-350oC) and low pressure gradients (2.5-4.5 kbar). The geotectonic environment is considered as a thrust-and-fold-belt system, with structures developed in superior crust levels.

3D seismic investigation of the structural and stratigraphic characteristics of the Pagasa Wedge, Southwest Palawan Basin, Philippines, and their tectonic implications

The Pagasa Wedge is a poorly imaged deepwater orogenic wedge that has been variously interpreted as representing an accretionary prism, a former accretionary prism modified by thrusting onto a thinned continental margin, and a gravity-driven fold-thrust belt. This study, using 2D and 3D seismic data, together with well information indicates that at least the external part of the wedge is dominantly composed of mass transport complexes, capped by syn-kinematic sediments that have thrusts and normal faults superimposed upon them. Drilling shows that despite stratigraphic repetition of Eocene Middle Miocene units, there is stratigraphic omission of Oligocene and Early Miocene units. This absence suggests that mass transport processes have introduced the Eocene section into the wedge rather than tectonic thrusting. The accretionary prism stage (Oligocene) of the Central Palawan Ophiolite history appears to be marked by predominantly north-vergent deformation. The Deep Regional Unconformity (∼17 Ma) likely indicates the approximate time when obduction ceased in Palawan. The Pagasa Wedge is a late-stage product of the convergence history that was active in its final phase sometime above the top of the Nido Limestone (∼16 Ma) and the base of the Tabon Limestone in the Aboabo-A1X well (∼9 Ma). The top of the wedge is traditionally associated with the Middle Miocene Unconformity (MMU), However the presence of multiple unconformities, diachronous formation tops, local tectonic unconformities and regional diachronous events (e.g. migrating forebulges) all suggest simply giving a single age (or assigning a single unconformity, such as the MMU as defining the top of the Pagasa Wedge is inappropriate. The overall NE-SW trend of the wedge, and the dominant NW transport of structures within the wedge diverge from the more northerly transport direction determined from outcrops in Palawan, and also from the Nido Limestone in the SW part of the Pagasa Wedge. Possibly this NW transport direction is more related to gravity-driven structures responding to uplift of NE-SW Dangerous Grounds margin during the Middle Miocene (related to slab breakoff?) than it is to thrusting rooted in a plate boundary. The final modification of the wedge occurred when the effects of compression deformation on the wedge had largely ended, but gravity processes (in particular mass transport and normal faulting) still operated.

Sierra de Reyes 3D seismic survey (onshore Argentina): depth imaging complex geology by applying multi-focusing, Kirchhoff, Beam and RTM workflows

Seismic acquisition and processing for imaging the subsurface is an important workflow in the petroleum industry. Complex geological settings such as tectonic thrust belts are a major challenge. The Sierra de Reyes 3D (SR3D) seismic survey in western Argentina is an example of where rough terrain land acquisition is combined with complex structural geology. These two problems have to be solved concurrently during the depth imaging steps. The SR3D land seismic project (270 km2) is located in the SE part of the Ranquil Norte concession (Neuquen Basin, Figure 1). The area lies in the Southern Central Andes, in the external Malargue fold and thrust belt (FTB). The FTB is characterized by the coexistence of thick and thin skin thrusting. This compressive regime has produced the structural traps of several main oil and gas fields of the northern Neuquen Basin. The further exploration of this hydrocarbon play has driven the development of the SR3D project (Figure 2).

Crustal shortening and thickening in Neoarchean granite-greenstone belts: A case study from the link between the ∼2.7 Ga Elu and Hope Bay belts, northeast Slave craton, Canada

The Elu Link between the ∼2.7 Ga Hope Bay and Elu belts in the northeast Bathurst Block of the Slave craton comprises supracrustal and intrusive rocks variably deformed by three tectono-metamorphic events (D1–D3). The geometry of D1 structures formed during prograde metamorphism is uncertain, because of subsequent overprint. D2 occurred in two stages predating (D2a) and postdating (D2b) peak metamorphism. D1 and D2a were thrusting events inferred from peak metamorphic pressures of ∼6.7 kbar (670 MPa) retained by a garnet orthogneiss. The latter is diagnostic of thrust tectonism in Archean granite-greenstone belts with no characteristic thrust faults. Unlike D2a, D2b was a vertical general flattening event prevailing during the formation of magmatic domes and interdomal folds that form the main strain patterns of the belts. This was followed by the formation of buckled F3 folds associated with D3 vertical constriction. The switch from thrust to vertical tectonics during peak metamorphism and subsequent deformation resulted in intense recrystallization that explains the poor preservation and scarcity of early-formed shears, including thrust zones. A tectonic process, combining D1+D2a thrust stacking, sagduction, and vertical stretching during D2b and D3, is suggested to explain crustal thickening in the Elu Link and terrains of similar ages.

Two-stage terrane assembly in Western Gondwana: Insights from structural geology and geophysical data of central Borborema Province, NE Brazil

Combined geophysical and structural data from the Transversal Subprovince of the Borborema Province (NE Brazil) highlight the internal structure of, and interrelationships between, the constituent terranes. Radiometric and magnetic maps show distinctive signatures for the Archean-Paleoproterozoic Alto Moxotó and Meso-to Neoproterozoic Alto Pajeú and Pernambuco-Alagoas terranes. Mapped radiometric and first and second order magnetic lineaments, associated with Euler deconvolution, enable correlation between geophysical data and major structures. In addition to early related deformation of the Alto Moxotó Terrane, combined analysis of late transposition foliations, lineations and kinematic criteria reveal a complex structural evolution marked by two distinct assembly stages. The first phase is characterized by thrust tectonics with top-to-the-south vergence, resulting in the juxtaposition of the allochtonous Alto Pajeú Terrane with the structurally underlying Alto Moxotó Terrane. The terrane boundary is delineated by the Serra de Jabitacá Shear Zone, which is associated with low dipping collisional granitic sheets and ca. 1.0 Ga mafic-ultramafic rocks interpreted as obtudcted ophiolite remnants. Later strike-slip movements strongly folded and obliterated thrust-related markers, and the continental scale E-W Pernambuco Lineament is interpreted as the result of lateral assembly between the composite Alto Pajeú-Alto Moxotó terranes and the Pernambuco-Alagoas Terrane during the metamorphic peak of the Brasiliano orogeny. Evolution of the Borborema Province reflects accretionary processes during the assembly of Western Gondwana.

O-19 北部フォッサマグナ北西縁-西頸城山地から直江津沖海域-の断層関連褶曲とスラストテクトニクス(3. 堆積盆テクトニクス(液晶有),口頭発表,一般講演)

O-19 北部フォッサマグナ北西縁-西頸城山地から直江津沖海域-の断層関連褶曲とスラストテクトニクス(3. 堆積盆テクトニクス(液晶有),口頭発表,一般講演)

A complex thrust sequence in western Himalaya: The active Medlicott Wadia Thrust

The recent activity of the Medlicott-Wadia Thrust (MWT) is investigated by geomorphic and tectonic studies in the Riasi zone, south of the Pir Panjal range (India, Jammu-Kasmir state of western Himalaya). In the Riasi area, the MWT forms a splay of five faults that dip northward. The recent activity of the splay is quantified using a set of deformed Quaternary alluvial units. The central branch of the thrust splay moved Precambrian limestones above Quaternary sediments and is sealed by 36 ± 3 ka (youngest OSL age) deposits. The other branches offset the top of a 15 ± 1 ka (youngest OSL age) alluvial fan by 180 to 120 m; the two southernmost branches form 17–34 m high non-cylindrical scarps and the two northernmost branches also offset the fan by ∼8 m and ∼54 m, respectively. A balanced cross-section parallel to the N210°E thrust motion suggests that the sequence of activity is complex: an in-sequence propagation is found for the three southern Tea, Scorpion and Rain faults and an out-of-sequence reactivation for the northern Pillar fault. Furthermore, several thrusts simultaneously activated for intervals of a few thousand years, whereas others are episodically inactive. Nearly 10 mm/yr of India-Eurasia convergence is regularly absorbed by the MWT, a value greater than the one estimated for the western segment of the MWT affected by the 2005 Kashmir earthquake, where the thrust tectonics interacts with the complex kinematics of the syntax. This work indicates that the MWT is very active and might be related to thick-skinned tectonics in the western Himalaya.

Experimental tectonic modelling of East (Iranian) Azerbaijan, inferred from stress pattern

Iranian (East) Azerbaijan plateau, in northwestern Iran, is characterized by relatively thrust tectonics. The area is shaped like a lozenge and is bordered by major strike-slip faults. This region includes three fold and thrust belts, the Arasbaran, Ghoshe Dagh and Bozkosh mountain ranges. The stress inversion analysis results help reconstruction of the stress pattern field. In order to clarify the relationships between the stress state and tectonics, a detailed construction of experimental model was carried out on the boundaries and central part of the Iranian Azerbaijan plateau. In this model structures are compressed in four sides of the E-Azerbaijan lozenge, while from the North and Southern parts of the lozenge structures are squeezed.

Geology of the Magura Nappe in the Osielec area with emphasis on an Eocene olistostrome with metabasite olistoliths (Outer Carpathians, Poland)

The Magura Nappe in the Polish sector of the Outer Carpathians consists of four tectonic subunits characterized by differing development of facies. From the south to the north, they include the Siary, Raca, Bystrica and Krynica subunits. The sedimentary succession in the Raca Subunit in the vicinity of the village of Osielec is composed of Campanian–Palaeogene flysch deposited in the Magura Basin. In this succession, the Middle Eocene Pasierbiec Sandstone Fm consists of thick-bedded sandstones and conglomerates with occasional intercalations of thin-bedded shale-sandstone flysch. Within the Pasierbiec Sandstone Fm at Osielec there is an olistostrome, rich in pebbles and cobbles of exotic rocks. In addition, large blocks of Neoproterozoic metabasites and boulders of Palaeogene organogenic limestones were found. The discovery of metabasites raised the possibility that the rocks in question could be evidence of supposed oceanic crust in the basement of the Magura sedimentary basin, because of the suggestion that they represent the Alpine orogenic cycle. This concept was abandoned when investigations of the absolute age of the metabasites gave a date of ca. 600 Ma. In the Osielec area, there are two tectonic thrust sheets in the Raca Subunit, namely the Osielczyk Thrust Sheet in the north and the Bystra Thrust Sheet in the south; they are folded and cut by a transverse system of strike-slip and oblique faults. The Osielczyk Thrust Sheet was overthrust northwards on to the Siary Subunit.