Eastern Domain Research Articles

Exploring a Ring-Closing Metathesis Approach to the Archazolid Macrocycle.

The synthesis of a new "eastern domain" of a proposed dihydroarchazolid analogue is described along with initial results from attempted macrocyclization by RCM. This work has revealed a competing backbiting process that may be preventable by alcohol functionalization and installation of a metathesis relay.

Geological map of the Tellaro River Valley (Hyblean Foreland, southeastern Sicily, Italy)

The Geological map of the Tellaro River Valley, at the 1:25.000 scale, portrays the main stratigraphic and structural features that developed in a 300 km2 wide area of the African foreland in southeastern Sicily (Hyblean Foreland). The NW-SE-oriented Tellaro River Valley marks the transition between the eastern (Siracusa Plateau) and western (Ragusa Plateau) domains of the foreland, where a post-Tortonian structural depression, here designated as Tellaro Basin, originated. The map pictures the geometry and kinematics of the border faults and the structure affecting the basin infilling. The mapped structural pattern denounces a poliphase tectonic evolution of the region, suggesting the occurrence of a major NW-SE-oriented crustal discontinuity that, being active during the different periods of the post-Tortonian evolution of the area, could play a primary role also in the present seismotectonic picture.

Crust‐scale 3D model of the Western Bredasdorp Basin (Southern South Africa): data‐based insights from combined isostatic and 3D gravity modelling

AbstractThe southern South African continental margin documents a complex margin system that has undergone both continental rifting and transform processes in a manner that its present‐day architecture and geodynamic evolution can only be better understood through the application of a multidisciplinary and multi‐scale geo‐modelling procedure. In this study, we focus on the proximal section of the larger Bredasdorp sub‐basin (the westernmost of the five southern South African offshore Mesozoic sub‐basins), which is hereto referred as the Western Bredasdorp Basin. Integration of 1200 km of 2D seismic‐reflection profiles, well‐logs and cores yields a consistent 3D structural model of the Upper Jurassic‐Cenozoic sedimentary megasequence comprising six stratigraphic layers that represent the syn‐rift to post‐rift successions with geometric information and lithology‐depth‐dependent properties (porosities and densities). We subsequently applied a combined approach based on Airy's isostatic concept and 3D gravity modelling to predict the depth to the crust‐mantle boundary (Moho) as well as the density structure of the deep crust. The best‐fit 3D model with the measured gravity field is only achievable by considering a heterogeneous deep crustal domain, consisting of an uppermost less dense prerift meta‐sedimentary layer [ρ = 2600 kg m−3] with a series of structural domains. To reproduce the observed density variations for the Upper Cenomanian–Cenozoic sequence, our model predicts a cumulative eroded thickness of ca. 800–1200 m of Tertiary sediments, which may be related to the Late Miocene margin uplift. Analyses of the key features of the first crust‐scale 3D model of the basin, ranging from thickness distribution pattern, Moho shallowing trend, sub‐crustal thinning to shallow and deep crustal extensional regimes, suggest that basin initiation is typical of a mantle involvement deep‐seated pull‐apart setting that is associated with the development of the Agulhas‐Falkland dextral shear zone, and that the system is not in isostatic equilibrium at present day due to a mass excess in the eastern domain of the basin that may be linked to a compensating rise of the asthenospheric mantle during crustal extension. Further corroborating the strike‐slip setting is the variations of sedimentation rates through time. The estimated syn‐rift sedimentation rates are three to four times higher than the post‐rift sedimentation, thereby indicating that a rather fast and short‐lived subsidence during the syn‐rift phase is succeeded by a significantly poor passive margin development in the post‐rift phase. Moreover, the derived lithospheric stretching factors [β = 1.5–1.75] for the main basin axis do not conform to the weak post‐rift subsidence. This therefore suggests that a differential thinning of the crust and the mantle‐lithosphere typical for strike‐slip basins, rather than the classical uniform stretching model, may be applicable to the Western Bredasdorp Basin.

Variscan orogeny in Corsica: new structural and geochronological insights, and its place in the Variscan geodynamic framework

In Western Corsica, remnants of pre-batholitic lithological and metamorphic assemblages are preserved as km-scale septa enclosed within Lower Carboniferous to Early Permian plutons. Two groups of septa were recognized: (1) the Argentella and Agriates-Tenda fragments correspond to Neoproterozoic rocks deformed and metamorphosed during the Cadomian–Panafrican orogeny, and (2) the Zicavo, Porto-Vecchio, Solenzara–Fautea, Belgodère, Topiti, and Vignola fragments consist of Variscan metamorphic rocks. The lithological content and the main ductile deformation events for each septum are presented. In the Zicavo, Porto-Vecchio, and Topiti septa, a top-to-the-SW ductile shearing (D1 event) coeval with an amphibolite facies metamorphism is responsible for crustal thickening at ca 360 Ma. This main event was preceded by eclogite and granulite facies metamorphic events preserved as restites within migmatites dated at ca 345–330 Ma. A top-to-the-SE ductile shearing (D2 event) coeval with the crustal melting accommodated the exhumation of the D1 event. In contrast, the Belgodère segment is peculiar as it exhibits a top-to-the-E vergence, although retrogressed high-pressure rocks are also recognized. The pre-Permian fragments are arranged in four NW–SE-striking stripes that define a SW–NE zoning with (1) a Western domain in Topiti, Vignola, Zicavo, Porto-Vecchio, and Solenzara–Fautea; (2) a Neoproterozoic basement with its unconformable Early Paleozoic sedimentary cover in Argentella; (3) an Eastern metamorphic domain in Belgodère; (4) another Neoproterozoic basement with its Upper Paleozoic sedimentary cover in Agriates-Tenda. The Argentella basement is separated from the Western and Eastern domains by two sutures: S1 and S2. The Variscan Corsica represents the Eastern part of the Sardinia–Corsica–Maures segment. The comparison of this segment with other Variscan domains allows us to propose some possible correlations. We argue that the Western domain, Argentella, Belgodère, and Agriates-Tenda domains can be compared with the Southern Variscan belt exposed in French Massif Central–Southern Massif Armoricain, Armorica microblock, Léon block, respectively.

Rates of geodetic deformation across active faults in southern Italy

Abstract Active deformation in southern Italy is accommodated by a distributed number of faults with low–moderate slip rates. Outcropping extensional faults and mostly blind transcurrent faults are mapped within a western (or axial) and an eastern domain, respectively. We use a combination of continuous (2001.00–2011.84) and episodic (1995.68–2010.79) GNSS observations to firstly estimate the geodetic deformation rate on 32 faults. Geodetic results were successively compared with geological displacement estimates. In agreement with seismological and geological information, a net spatial segregation emerges between the extensional axial belt, and the eastern domain where strike–slip faults are geodetically active. Although uncertainties are at times large, average displacement rates show broadly consistent patterns within both domains. A longitudinal gradient in extension rate is observed for the axial fault array, with two sectors of higher magnitude (~ 0.8–1.7 mm/yr for individual faults). This result is consistent with geological observations and supports the notion that extension occurs in discrete patches. Faults of the eastern domain have lower (few 0.1 to ~ 1.2 mm/yr) strike–slip rates and an eastward-decreasing extensional component, but significant geodetic displacement is detected in areas lacking clear evidence of activity. Few faults with 1–2 mm/yr extension rate are locally found in the eastern domain, but, based on their limited length and on inconsistency with seismology and geology, they are considered as due to deep-seated gravitational spreading. For crustal faults, although geodetic slip and moment rates are larger than geological rates, the broad trend of long- to short-term rates is similar, indicating the feasibility of geodetic analysis to contribute estimating fault slip rate and testing tectonic models in the region. Whereas the western domain extension is thought to be controlled by potential energy related to the Tyrrhenian Moho uplift beneath the Apennines, strike–slip in the east is related to shear on inherited faults within the Adriatic crust.

Surface sediment dinoflagellate cysts from the Hudson Bay system and their relation to freshwater and nutrient cycling

Abstract Surface sediment samples from the Hudson Bay system were analysed in order to examine the role of key regulators of arctic marine productivity — light and nutrients as affected by freshwater stratification and sea-ice cover — on the spatial distribution and production of dinoflagellate cysts. Total cyst fluxes vary from 0.2 × 10 6 to 30.6 × 10 6 cysts m − 2 a − 1 , with the highest values observed in eastern Hudson Bay. A total of 24 cyst taxa, representing 11 genera of five orders, were identified and distribution maps of the most common taxa have been produced. This is the first record of Echinidinium aculeatum , Echinidinium karaense , cf. Echinidinium delicatum , Islandinium brevispinosum , Selenopemphix quanta , cysts of Protoperidinium americanum , cysts of cf. Biecheleria sp. and Polarella glacialis in the Hudson Bay system. Dinoflagellate cyst assemblages show distinct spatial patterns revealing three compositional domains: eastern Hudson Bay, western-central Hudson Bay and Hudson Strait. The eastern domain is characterised by a dominance of autotrophic cysts of Pentapharsodinium dalei whereas the western-central domain is characterised by autotrophic Operculodinium centrocarpum with some contribution by heterotrophic Polykrikos sp. var. arctic morphotype and Polykrikos spp. Sites from Hudson Strait are distinguished by an overwhelming prevalence of heterotrophic Protoperidiniaceae cysts, mainly Islandinium minutum , and have the highest values of sedimentary biogenic silica, used as a proxy for diatom productivity. Sediment geochemical tracers are used as proxies for freshwater inputs (lignin and its biomarkers) and nitrate availability (nitrogen isotopes), and sea-ice concentrations derived from passive microwave data as a proxy for light availability. Sea-ice regulated length of the dark season has a negligible influence on the proportion and production of heterotrophic (dark-adapted) versus autotrophic (light-dependent) dinoflagellate cysts, perhaps due to the location of our study area on the southern fringe of the Arctic. Instead, cyst populations in Hudson Bay are primarily regulated by vertical stratification and nitrate availability, while in Hudson Strait the pivotal mechanism constitutes food availability.

Salt tectonics and Pliocene stratigraphic framework at MC-118, Gulf of Mexico: An integrated approach with application to deep-water confined structures in salt basins

Integrated tectono-stratigraphic interpretation at MC-118 using 3D seismic, well logs and biostratigraphy reveals an area dominated by allochthonous salt and its related structures. OCS-Block MC-118 is located 130 km southeast of New Orleans on the Gulf of Mexico middle slope in ∼2600 ft of water.The area is divided into three domains based on their structural styles: (1) a western domain consisting of a basinward-dipping normal fault family and associated strata; (2) a central domain composed of a landward-plunging diapiric salt tongue canopy and associated salt welds, two flanking NE–SW trending salt-withdrawal mini-basins, and a crestal fault family; and (3) an eastern domain comprised of basinward/landward-dipping normal and listric normal fault families with their associated rollovers. These structural domains are genetically-and-kinematically related to the salt structure and extend beyond MC-118 boundaries. The salt structure is postulated to have evolved mostly passive, with punctuated active episodes, and by lateral spreading. This is part of a larger regional structure, eastern Gulf of Mexico, which involves some amalgamation between small-scale salt canopies and salt diapirs although collectively they appear mostly disconnected.A Pliocene (3.13–4.95 Ma) third-order genetic stratigraphic sequence, the focus of this study, is as much as ∼3600 ft thick within the mini-basins and contains: muddy mass transport complexes; sandy slope fans; muddy turbidites and condensed sections; and transitional facies flanking the salt structure that collectively have ponded and wedged external geometries. Mass transport complexes and muddy turbidites and condensed sections make most of the studied genetic sequence in a mud-dominated deltaic setting eastern Gulf of Mexico.Facies kinematic indicators and a matching number of genetic sequences accounted on the sea level chart support a eustatically driven mini-basin sedimentation. Nonetheless salt still plays a role in sedimentation (secondary/minor) by slumping generated during passive/active salt diapiric evolution.

Influence of deep Louann structure on the evolution of the northern Gulf of Mexico

Three aspects of basement structure and rift-related salt distribution have especially influenced the evolution of the deep-water northern Gulf of Mexico: (1) creation of a basement high (Toledo Bend flexure), separating a chain of interior basins from the central Louann salt basin, (2) segmentation of the central Louann salt basin by the Brazos transfer fault into eastern and central domains, and (3) salt provinces formed during basin opening. The Toledo Bend flexure was reactivated as a hinge during the Cenozoic uplift of the North American craton. This uplift triggered gravity gliding, forming fold belts in the seaward parts of the continental margin. The geometry of the Toledo Bend flexure influenced the position of these fold belts. The Brazos transfer fault separates the west sector of the study area from the central and east sectors. Most of the salt in the deep-water northern Gulf of Mexico lay in the central sector, which sourced most of the Sigsbee salt canopy. The western sector was narrower and was subdivided by the East Breaks basement high. Splitting the Callovian salt basin in two as the gulf opened created a southward-thinning wedge of salt at the seaward end of the northern Gulf of Mexico. We divide this wedge into a series of provinces on the basis of the geometry of the base of the deep salt. Original salt thickness influenced diapir location, the geometry of the Sigsbee canopy, the geometry and style of later compressional fold belts, and petroleum systems.

3D gravity interpretation of the pre-Tertiary basement in the intramontane depressions of the Western Carpathians: a case study from the Turiec Basin

Abstract New results related to the thickness and density of the sedimentary fill of the Turiec Basin allowed us to construct the first original stripped gravity map for this typical intramontane Neogene depression of the Western Carpathians. The stripped gravity map of the Turiec Basin represents the Bouguer gravity anomalies corrected for the gravity effect of the density contrast of its Quaternary-Tertiary sedimentary basin fill. It means that the map reflects the gravity effects of the density inhomogeneities which are located beneath the sedimentary basin fill. This map is therefore suitable for the interpretation of the structure and composition of the pre-Tertiary basement. Based on the new data analysis, two different density models of the sedimentary fill were constructed. The 3D density modelling was used to calculate the gravity effect of the density models. The stripped gravity maps were produced by subtracting the density model gravity effects from Bouguer anomalies. The regional trend was also removed from the stripped gravity maps. The residual stripped gravity maps were consequently used for geological interpretation of the pre-Tertiary basement of the Turiec Basin. The pre-Tertiary basement of the Turiec Basin can be divided into northern and southern parts due to its gravity characteristics. Furthermore the northern part can be split into two domains: western and eastern. The crystalline basement of the western domain is probably formed by the Hercynian crystalline basement of the Tatric Unit. In the eastern domain the basement could consist mostly of the Mesozoic complexes of the Fatric Unit. The southern part of the pre-Tertiary basement of the Turiec Basin is built predominantly by Mesozoic complexes of the Hronic Unit. It is suggested that the Hronic Unit also forms the bedrock of the volcano-sedimentary complex of the Kremnické vrchy Mts. The resultant stripped gravity maps and the map of total horizontal gravity gradients have also proven to be very useful for the interpretation of faults or fault systems in the study area. Various faults, particularly of NNE-SSW and NW-SE directions were discovered. The analysis of the faults indicates clearly that the contact of the Turiec Basin with the Malá Fatra Mts and the Veľká Fatra Mts is tectonic.

Present vertical movements in Central and Northern Italy from GPS data: Possible role of natural and anthropogenic causes

Insights into the present vertical kinematic pattern in Central and Northern Italy are gained by the analysis of GPS data acquired by a network of 262 permanent stations, working over various time intervals since 2001. Uplift is observed in the Alps (up to 5mm/yr) and Apennines (1–2mm/yr), whereas subsidence is recognized in the southern Venetian Plain (2–4mm/yr) and the eastern Po Valley, where the highest rates are observed (up to 9mm/yr between Reggio Emilia and Rimini). On the other hand, the western part of the Po Valley presents very low vertical rates. The boundary between subsiding and not subsiding Po Valley nearly corresponds to the Giudicarie tectonic discontinuity. It is argued that the different kinematic patterns of the eastern and western Padanian sectors may also be related to the underthrusting of the eastern domain beneath the western one. Some considerations are then reported on how the various causes of vertical movements (tectonic and sedimentological processes) may contribute to the observed kinematics.

Spatial distribution of cephalopod paralarvae in San José Gulf (Northern Patagonia, Argentina): The role of tidal circulation in larval dispersal

The spatial distribution of cephalopod paralarvae was studied in waters of San José Gulf (SJG), a shallow basin connected to a larger gulf (San Matías, SMG) through a narrow mouth located on its northwestern margin. The gulf is characterized by a remarkable tidal circulation pattern providing contrasting hydrodynamic conditions between the western and eastern domains. Zooplankton net tows (n=104) and depth-temperature profiling (n=70) were conducted on a monthly basis at fixed stations forming a regular grid from October (mid spring) 2011 to March (late summer) 2012. Temperature-depth profiles showed that while the western domain seawater column remains well mixed by tidal currents during the whole period, stratification develops from November to March on the eastern domain. Positive zooplankton net tows were sporadic for early-life stages of Semirossia tenera (n=1) and Robsonella fontaniana (n=3), and more frequent for those of Doryteuthis sanpaulensis (n=9) and Illex argentinus (n=9). The latter were found almost exclusively in the western domain whereas those from D. sanpaulensis were mainly sampled in the eastern domain. Low abundance of I. argentinus paralarvae in the eastern domain suggests that buoyant egg masses of this squid are not released in SJG; instead they, or the hatching paralarvae emerging from them, could be sequentially advected from and expelled to SMG by tidal currents. On the other hand, the spatial distribution of D. sanpaulensis paralarvae suggests that those hatching on the shallow marginal bottoms of the eastern domain are retained in this region while those hatching at the western domain are flushed out to SMG by tidal currents.

Reply to comment by P. Olivier on “Preorogenic exhumation of the North Pyrenean Agly Massif (Eastern Pyrenees, France)”

We make this reply to Philippe Oliver's comments on the deformation of the Mesozoic cover of the northern Agly massif.

Structural geometries and magnitude of shortening in the eastern Kura fold‐thrust belt, Azerbaijan: Implications for the development of the Greater Caucasus Mountains

AbstractThe Greater Caucasus are the northernmost extent of the Arabia‐Eurasia collision and are thought to represent the main locus of shortening within the central portion of the collision zone between 40° and 48°E. Recent work suggests that in detail, since the Plio‐Pleistocene, much of the shortening in the eastern portion of the Caucasus system has been focused within the Kura fold‐thrust belt along the southeastern margin of the Greater Caucasus. Here we present new field mapping and stratigraphic investigations of the eastern termination of the Kura fold‐thrust belt in Azerbaijan to better constrain the structural geometries, magnitude of shortening, and initiation age for this portion of the fold‐thrust belt. Our work suggests that this area of the fold‐thrust belt exhibits significant along‐strike variations in structural style and evolution and can effectively be divided into two distinct domains at ~48°E. The western domain is characterized by a subcritical median surface slope and isolated folds and thrusts propagating out of sequence, whereas the eastern domain is dominated by a single duplex structure and a history of in‐sequence development in a critically tapered wedge. We hypothesize that these variations result from changes in relative rates of syn‐tectonic sedimentation, erosion, and convergence velocity along strike. We find that within the western domain, the fold‐thrust belt has accommodated ~12 km of total shortening. An unconformity within the western domain brackets the initiation age of this portion of the fold‐thrust belt to between 1.8 and 0.88 Ma yielding permissible average shortening rates of between 6.7 and 13.6 mm/yr. Comparison of these average shortening rates to the geodetically measured shortening rate of 8 mm/yr indicates that since initiation, the fold‐thrust belt has accommodated 83–100% of convergence between the Greater and Lesser Caucasus at this longitude.

Proterozoic orogens in southern Peninsular India: Contiguities and complexities

The Precambrian terranes of southern Peninsular India have been central to discussions on the history of formation and breakup of supercontinents. Of particular interest are the Proterozoic high grade metamorphic orogens at the southern and eastern margins of the Indian shield, skirting the 3.4Ga Dharwar craton which not only preserve important records of lower crustal processes and lithospheric geodynamics, but also carry imprints of the tectonic framework related to the assembly of the major Neoproterozoic supercontinents – Rodinia and Gondwana. These Proterozoic orogens are described as Southern Granulite Terrane (SGT) in the southern tip and the Eastern Ghats Mobile Belt (EGMB) in the eastern domains of the peninsula. The contiguity of these orogens is broken for a distance of ∼400km and disappears in the Bay of Bengal. These orogens expose windows of middle to lower crust with well-preserved rock records displaying multiple tectonothermal events and multiphase exhumation paths.Recent studies in these orogens have led to the recognition of discrete crustal blocks or terranes separated by major shear zone systems, some of which represent collisional sutures. The SGT and EGMB carry several important features such as fold-thrust tectonics, regional granulite facies metamorphism of up to ultrahigh-temperature conditions in some cases, multiple P–T paths, development of lithospheric shear zones, emplacement of ophiolites, presence of alkaline and anorthositic complexes, development of crustal-scale “flower structures”, transpressional strains, and reactivation tectonics. A heterogeneous distribution of different metamorphic and magmatic assemblages with distinct spatial and temporal strain variations in shaping the fabric elements in different blocks is identified. Both EGMB and SGT share a common transpressional deformation history during the latest Neoproterozoic characterized by the steepening of the initial low angle crustal scale structures leading to a subvertical grain conducive to reactivation tectonics. Our synthesis of the spatial distribution, geometry, kinematics and the transpressional strain of the shear zone systems provides insights into the tectono-metamorphic history of the Proterozoic orogens of southern India and their contiguity and complexities. Recent understanding of subduction, accretion and collisional history along these zones together with a long lived transpressional tectonic regime imply that these orogens witnessed identical tectonic regimes at different times in Earth history, although the major and common structural architecture was built during the final assembly of the Gondwana supercontinent.

Middle Pleistocene to Holocene fluvial terrace development and uplift-driven valley incision in the SE Carpathians, Romania

Abstract This study reveals that in the SE Carpathians terrace development and fluvial incision during the Middle Pleistocene–Holocene are predominantly controlled by tectonic uplift as shown by terrace distributions and uplift amounts and rates. The work focuses on a transect from the internal nappes and Brasov intramontane basin (western domain) to the external nappes and Focsani foredeep basin (eastern domain). New infrared stimulated luminescence ages were obtained and minimum terrace formation ages were determined to derive fluvial incision rates, and thereby, to constrain tectonic uplift. In the eastern domain, non-uniform terrace distributions in adjacent sub-parallel more active Punta and less active Susiţa rivers and an eastward migrated fluvial incision from the orogen to the foredeep basin indicate tectonic uplift as dominant control on terrace development. Strath-terraces in the western and eastern domains indicate repeated events of vertical fluvial incision and lateral erosion during the early Middle Pleistocene and late Middle Pleistocene–Holocene, respectively. These events imply successive recurrent disturbances of equilibrium conditions due to pulses of increased tectonic uplift. Fill-terraces in the western domain show that initial aggradation periods were followed by uplift-driven vertical incision during the late Middle–Late Pleistocene. As fill-terraces show a wide-spread development, climatic change and complex response cannot be excluded as contributing factors. Synchronous to terrace development, loess deposition periods during the late Middle–Late Pleistocene and Latest Pleistocene and intercalated episodes of palaeosol formation during the Late Pleistocene imply comparable climatic conditions across the SE Carpathians. Dominant strath-terraces of the eastern domain indicate stronger fluvial incision (~ 240 m) since the late Middle Pleistocene, whereas older strath- and younger dominant fill-terraces of the western domain designate a lower amount (~ 90 m) since the early Middle Pleistocene. Middle Pleistocene–Holocene fluvial incision rates document higher tectonic uplift in the external nappes and lower towards the western intramontane and eastern foredeep basins.

EARLY LADINIAN RADIOLARIAN FAUNA FROM THE MONTE SAN GIORGIO (SOUTHERN ALPS, SWITZERLAND): SYSTEMATICS, BIOSTRATIGRAPHY AND PALEO(BIO)GEOGRAPHIC IMPLICATIONS

A well-preserved radiolarian fauna was recovered from the lower part of the San Giorgio Dolomite (Monte San Giorgio, UNESCO WHL, Switzerland), belonging to the Eoprotrachyceras curionii Ammonoid Zone (earliest Ladinian). The depositional environment, consisting of an intraplatform basin with restricted circulation, seemingly resulted in an unusual radiolarian assemblage displaying neglegible percentages and very low diversity of Nassellaria. Seventy-three species have been identified and seven new species have been described: Eptingium danieli n. sp., Eptingium neriae n. sp., Parentactinosphaera eoladinica n. sp., Sepsagon ticinensis n. sp., Sepsagon ? valporinae n. sp., Novamuria wirzi n. sp. and Pessagnollum hexaspinosum n. sp. The taxonomic status of the recovered species has been reassessed and four new genera have been introduced: Bernoulliella gen. n., Eohexastylus gen. n., Ticinosphaera gen. n. and Lahmosphaera gen. n. The new radiolarian assemblages, the first so far described from the Monte San Giorgio, supplement further information to the taxa occurring in the uppermost Ladinocampe multiperforata Radiolarian Zone, as yet poorly defined, also confirming the absence of major changes in the radiolarian fauna across the Anisian/Ladinian boundary. The widespread co-occurrence of taxa doubtlessly testifies to the existence, in early Ladinian times, of open-marine connections between the basin of the Monte San Giorgio and the pelagic “Buchenstein” basins of the central and eastern South-Alpine domain and farther afield across the Tethys.

Geometry and kinematic evolution of a long‐living foreland structure inferred from field data and cross section balancing, the Sainte‐Victoire System, Provence, France

The Sainte‐Victoire System (SVS) is a key area to understand how the shortening is accommodated in outer foreland of the Pyrenean‐Provence orogen between Late Cretaceous and Eocene. Structural data, growth strata and fault slip analysis, and four balanced cross sections are used to decipher the along‐strike geometry, deformational characteristics and kinematics of the SVS. The SVS is divided into two structural domains separated by a regional relay zone: the eastern domain is governed by a N‐vergent thin‐skinned tectonic style above Triassic series and the western domain, by a mixed S‐vergent thick‐ and thin‐skinned tectonic style with tectonic inversion of Late Paleozoic‐Triassic half grabens. Growth strata indicate that the eastern SVS grew during Danian as a result of shortening transfer from the southern Arc Basin. In contrast, the western SVS is an independent structure which has recorded the early stage (∼83 Ma) of shortening and focused continuous deformation during ∼40 Myr. The shallow N‐S shortening is ∼5 km (∼25%) and ∼8 km (∼34%) in the western and eastern SVS, respectively. At a regional scale, the tectonic inversion of the SVS and the Arc Basin recorded a deep shortening of the order of 15–18 km (∼34%). Although the shortening magnitude of the SVS remains small, other structures similar to the SVS were synchronously active across foreland basin, suggesting a significant amount of cumulated shortening. This outer foreland shortening may account for a non‐negligible amount of deformation at the Pyrenean‐Provence orogen scale.

Magnetic susceptibilities of rocks of the Antarctic Peninsula: Implications for the redox state of the batholith and the extent of metamorphic zones

A combination of 1555 magnetic susceptibility measurements from the Antarctic Peninsula between 65°S to 72°S (for which the raw data are made available), and petrological, structural and metamorphic data, has been used to improve understanding of: (1) magma sources for the Antarctic Peninsula batholith; (2) genetic relationships between granitoids and metamorphic rocks, and; (3) to provide a semi-quantitative measure of the extent and grade of metamorphic zones. The redox state of Jurassic plutonic rocks indicates that these had continental magma sources in the tectonostratigraphic terranes of the Central and Eastern domains. Triassic and Cretaceous plutons, on the other hand, had subduction-related sources in the Central Domain of the western Antarctic Peninsula and continental sources in the Gondwana-margin Eastern Domain. Circum-Pacific comparisons of magnetite–ilmenite belt geometries identify the Antarctic Peninsula belt as a natural continuation of comparable South American belts. Susceptibility trends are generally retained by orthogneisses, suggesting that they formed by deformation of plutonic rocks mostly at or below upper amphibolite-facies conditions. Metasedimentary rocks are weakly magnetic across the peninsula, and are spatially associated with continentally derived or crustally contaminated plutons (ilmenite-series). Orthogneisses and metabasites from strongly magnetic plutonic environments show areas of very low magnetic susceptibilities that may be linked to fluid-enhanced, tectonometamorphism-induced reduction of magnetic susceptibility. The distribution of reduced magnetic susceptibility areas follows the surface traces of major shear and fault zones in Palmer Land. Our results are consistent with tectonic interpretations of oblique compression and uplift of an arc block on the Pacific margin of Gondwana during the Palmer Land Event.

Active extension in Taiwan's precollision zone: A new model of plate bending in continental crust

Recent multichannel seismic reflection data acquired offshore southwest Taiwan identify active extension along a deep-seated normal fault in the precollision setting of the Taiwan arc-continent collision. While ubiquitous minor flexural faulting may be observed in the Taiwan foreland, these new data image a listric, rift basin–bounding normal fault that penetrates deep into the crust and forms a significant fault scarp with ∼850 m of relief near the continental shelf break southwest of the Taiwan collision zone. These observations, along with new geodynamic models of collision between a subduction zone and a young passive margin, indicate that the recent extension may be the expression of plate bending in continental crust as thin transitional crust subducts at the Manila Trench. A similar extensional episode prior to the onset of arc-continent collision ca. 6.7 Ma has been identified in rift basins of the southern Chinese margin near Taiwan, further suggesting that collision may be preceded by bending-related extension of the continental shelf. The Lishan fault, a major structural and morphologic boundary in the Taiwan orogen, may have been a similar rift basin–bounding fault before being reactivated during the Taiwan arc-continent collision. In this scenario, the Lishan fault divides Taiwan into a western domain representing collision of the thick crust of the continental shelf and an eastern domain representing subduction and collision of thin transitional crust along the continental slope with the Manila Trench.

The Mesoproterozoic Karagwe-Ankole Belt (formerly the NE Kibara Belt): The result of prolonged extensional intracratonic basin development punctuated by two short-lived far-field compressional events

The Mesoproterozoic Kibara Belt (also Kibaran Belt or Kibarides in some references) of Central Africa was often portrayed as a continuous, c. 1500km long orogenic belt, trending NE to NNE from Katanga, Democratic Republic of Congo (DRC) in the south, up into SW Uganda in the north. Recently however, the Karagwe-Ankole Belt (KAB; formerly the NE Kibara Belt) has been redefined as the part north of a NW oriented Palaeoproterozoic basement high of the Ubende-Rusizi Belts, while the Kibara Belt (KIB) is now limited to the part south of this rise.We present a lithostratigraphy for the KAB that takes into account two rheologically contrasting structural domains (Western and Eastern Domain); each of them being characterised by independent sedimentary sub basin(s) and depositional conditions: the ED with Archaean basement versus the WD with Palaeoproterozoic basement. We document new volcanic and detrital U–Pb SHRIMP zircon data which provide new constraints on the timing of deposition and on the detrital provenance of the sedimentary sequences in the KAB. We discuss the evolution of the KAB in a wider regional context, comparing it to other Mesoproterozoic units and with reference to the general geodynamic history of this part of the African continent in Proterozoic times.The lithostratigraphic successions of the KAB are only valid respectively in the ED (Kagera Supergroup) or in the WD (Akanyaru Supergroup), with no correlations between them. Deposition of the Kagera Supergroup in the ED is bracketed between 1.78Ga and 1.37Ga and the deposits have to be considered an Eburnean-age “molasse”. Detrital components comprise material only of Archaean and Palaeoproterozoic age, consistent with derivation from nearby source regions. In the WD, deposition of the two lowermost groups of the Akanyaru Supergroup is bracketed between 1.42Ga and 1.37Ga. The large contribution of detrital Palaeoproterozoic components in the WD strengthens the view that this domain is underlain by Palaeoproterozoic basement and supports the concept that part of the Akanyaru Supergroup sediments consists of reworked Eburnean-aged molasse. In the WD of the Kivu-Maniema area (DRC), later sedimentation periods are documented at respectively 1222Ma and 710Ma. The KAB documents a long-lived period of intracratonic intermittent depositional activity (with periods of interruption of deposition, erosion and magmatism) showing a recurrent subsidence trend controlled by structural activity moving with time from E to W.On a regional scale, we postulate that since 1.8Ga, following the amalgamation of Archaean and Palaeoproterozoic landmasses into a single coherent ‘proto-Congo Craton’, various long-lived shallow-water intracratonic basins (aulacogenes) developed. These basins underwent a comparable Mesoproterozoic geodynamic evolution, as shown not only in the sequences of the KAB and of the relatively close Kibara (KIB), Bangweulu Block and Northern Irumide Belts, but even in more distant sequences located in SW Angola and E Brazil.The long-lived aulacogene history of the KAB within the proto-Congo Craton is interrupted only twice by short-lived compressional deformation reflecting far-field effects of global orogenic events, external to the proto-Congo Craton. The first event at 1.0Ga is related to Rodinia amalgamation. The second event at 550Ma results from Gondwana amalgamation and develops a N–S Pan African overprint in the KAB which has previously been underestimated or even overlooked. Three mineralisation provinces occurring in the KAB, respectively the Bushveld-type, the tin-coltan-wolfram and the gold province, can be ascribed successively to the 1375Ma Kibaran magmatic event, the 1.0Ga Rodinia and the 550Ma Gondwana amalgamation events.Our results give additional weight to the recent redefinition of the KAB and the KIB, forming two distinct Belts respectively north and south of the Palaeoproterozoic basement high of the Ubende-Rusizi Belts, the more that within this basement rise local Mesoproterozoic strike-slip basins, with their own unique lithostratigraphic and geodynamic characteristics (e.g. Itiaso Group) are documented, which differ from those of the KAB or the KIB.