Arcuate Structure Research Articles

Gravity anomalies and crustal signature of volcano-tectonic structures of Pico Island (Azores)

Pico Island is the youngest (< 300 ka) island of the Azores archipelago, dominated on its western sector by the stratovolcano of Pico Mountain, which rises about 3.5 km above the surrounding ocean floor. The other two major morpho-tectonic units of the island include the shield volcano of Topo, and the “Achada Plateau,” a 29 km long volcanic ridge, with a WNW–ESE trend. A gravimetric study on Pico Island, coupled with geological and volcanological data, was aimed towards a better understanding of its deep volcano-tectonic structures. From a total of 407 stations, a regional model of density contrasts was developed in order to reproduce the crustal structure of the island. In addition a local high-resolution model of the sub-surface structure of the westernmost part of the island is presented. Both models were obtained by means of an inversion global adjustment, on fixed density contrasts in order to determine the three-dimensional geometry of the sources of the anomalous gravity field. The most prominent anomalous gravity structure found in Pico Island is a body with positive density contrast located on the SE slopes of Topo volcano. This anomaly extends to depth of approximately 8 km (mean depth of 4.5 km) and has a volume of 310 km 3. This anomaly maybe best interpreted by the presence of a major intrusive system beneath Topo volcano and can be also correlated to gravitational collapses at the shield volcano. A second body of positive density contrast which appears to extend to 4–5 km depth is located near the town of Madalena. This anomaly may be correlated to a high-density anomaly recently detected in the NE sector of Faial Island. Smaller sized high-density bodies at shallow depths of around 1.3 km are located beneath Pico Mountain volcano and all together define a semi-circular arc with an average diameter of 8 km. We propose that this arcuate structure might outline a ring fracture associated with the collapse of the central sector of Pico Mountain volcano early in its growth. Low-density bodies are located on the NW flanks of Pico Mountain, along a linear ENE trending structure. These bodies extend to depths of 4 km and have a total volume of 69 km 3. They are interpreted as being associated with an “old” extensional fracture zone. Previous studies suggested the existence of a shallow and large magma reservoir (with volumes up to 1000 km 3) beneath Pico Mountain volcano. In this study we have not found any evidence of the existence of such huge magma body. On the contrary, we propose that those discrete low-density bodies correspond to complex intersections of different sets of tectonic lineaments, along which magma tends to intrude, as shallow (2–5 km) and small (10–20 km 3) magma pockets.

The Multitude of Molecular Hydrogen Knots in the Helix Nebula

We present HST/NICMOS imaging of the H_2 2.12 \mu m emission in 5 fields in the Helix Nebula ranging in radial distance from 250-450 from the central star. The images reveal arcuate structures with their apexes pointing towards the central star. Comparison of these images with comparable resolution ground based images reveals that the molecular gas is more highly clumped than the ionized gas line tracers. From our images, we determine an average number density of knots in the molecular gas ranging from 162 knots/arcmin^2 in the denser regions to 18 knots/arcmin^2 in the lower density outer regions. Using this new number density, we estimate that the total number of knots in the Helix to be ~23,000 which is a factor of 6.5 larger than previous estimates. The total neutral gas mass in the Helix is 0.35 M_\odot assuming a mass of \~1.5x10^{-5} M_\odot for the individual knots. The H_2 intensity, 5-9x10^{-5} erg s^{-1} cm^{-2} sr^{-1}, remains relatively constant with projected distance from the central star suggesting a heating mechanism for the molecular gas that is distributed almost uniformly in the knots throughout the nebula. The temperature and H_2 2.12 \mu m intensity of the knots can be approximately explained by photodissociation regions (PDRs) in the individual knots; however, theoretical PDR models of PN under-predict the intensities of some knots by a factor of 10.

The tectonic frame of the Variscan–Alleghanian orogen in Southern Europe and Northern Africa

By confronting different geological and geophysical data, we attempt to reconstruct the Variscan–Alleghanian orogenic belt, with especial emphasis on the links between Iberia, northwest Africa, and northeast America. The northern Iberia transect corresponds to the rifted margin of Gondwana, inverted during the Variscan orogeny and overthrust in its westernmost sector by a pile of allochthonous units, some of them with oceanic affinity and witnessing an orogenic suture. The southern Iberia section reveals two sutures at both boundaries of a terrane closely tied to Gondwana, namely the Ossa–Morena Zone. The southern boundary of this zone (i.e., the contact with the South Portuguese Zone) is enhanced by amphibolites with oceanic affinity and probably represents the suture of the Rheic Ocean. The Moroccan Variscides can be divided into: (i) a western external zone, namely the Coastal Block and the Central Massif; (ii) an internal zone, namely the Eastern Meseta; (iii) an eastern external zone represented in the Anti Atlas region; and (iv) the African cratonic foreland. Since neither ophiolites nor eclogites crop out along this transect of the orogen, we consider it to be an incomplete transect, lacking the main suture zone (Rheic Ocean). Stratigraphic and faunal affinities between the Moroccan Meseta, on the one hand, and the Central Iberian, Western Asturian–Leonese, and Cantabrian zones of Iberia, on the other hand, suggest that they may well have been part of a common pre-orogenic domain at the margin of Gondwana. On the contrary, there are no counterparts in Morocco for the Ossa–Morena Zone. Thus, the northern Iberia palaeogeographic zones would prolong in the Moroccan Meseta through an eastward arcuate structure, while the suture of the Rheic Ocean would do so offshore Morocco. In our reconstruction, an Avalonian spur (Grand Banks indentor), which included the Caledonian Sehoul block in northern Morocco and the crust of the South Portuguese Zone in SW Iberia, played an important role on the kinematic evolution of the orogen as well as on the final configuration of the suture of the Rheic Ocean. This suture would mould around the Avalonian spur, being laterally translated to southeastern Nova Scotia–Newfoundland.

Seismic anisotropy and velocity structure beneath the southern half of the Iberian Peninsula

Travel times of 11,612 Pn arrivals collected from 7675 earthquakes are inverted to image the uppermost mantle velocity and anisotropy structure beneath the southern half of the Iberian Peninsula and surrounding regions. Pn phases are routinely identified and picked for epicentral distances from 200 to 1200 km. The method used in this study allows simultaneous imaging of variations of Pn velocity and anisotropy. The results show an average uppermost mantle velocity beneath the study area of 8.0 km/s. The peninsular area covered by the Iberian massif is characterized by high Pn velocity, as expected in tectonically stable regions, indicating areas of the Hercynian belt that have not recently been reactivated. The margins of the Iberian Peninsula have undergone a great number of recent tectonic events and are characterized by a pronouncedly low Pn velocity, as is common in areas greatly affected by recent tectonic and magmatic activity. Our model indicates that the Betic crustal root might be underlined by a negative anomaly beneath the southeastern Iberian Peninsula. In the Atlantic Ocean, we find a sharp variation in the uppermost mantle velocities that coincides with the structural complexity of the European and African plate boundary in the Gulf of Cadiz. Our results show a very pronounced low-velocity anomaly offshore from Cape San Vicente whereas high velocities are distributed along the coast in the Gulf of Cadiz. In the Alboran Sea and northern Morocco, the direction of the fastest Pn velocity found is almost parallel to the Africa–Eurasia plate convergence vector (northwest–southeast) whereas to the north, this direction is almost parallel to the main trend of the Betic Cordillera, i.e. east–west in its central part and north–south in the curvature of the Arc of Gibraltar. This suggests that a significant portion of the uppermost mantle has been involved in the orogenic deformation that produced the arcuate structure of the Betic Cordillera. However, we assume that the Neogene extension had no major influence on a lithospheric scale in the Alboran Sea. Our results also show a quite complex pattern of anisotropy in the southwest Iberian lithospheric mantle since the relationship between the direction of fastest Pn velocity and major Hercynian tectonic trends cannot be directly established.

Ophiolites from the Mianlüe Suture in the Southern Qinling and Their Relationship with the Eastern Paleotethys Evolution

Abstract The Mianlüe suture extends from Derni‐Nanping‐Pipasi‐Kangxian to the Lüeyang‐Mianxian area, then traverses the Bashan arcuate structure eastward to the Huashan region, and finally to the Qingshuihe area of the southern Dabie Mountains. From east to west, with a length of over 1500 km, the ophiolitic melangé associations are distributed discontinuously along the suture. The rock assemblages include ophiolite, island‐arc and oceanic island rock series, indicating that there existed a suture zone and a vanished paleo‐ocean basin. The Mianlüe paleo‐ocean basin experienced its main expansion and formation process during the Carboniferous‐Permian and closed totally in the Triassic. It belongs to the northern branch of the eastern paleotethys, separated from the northern margin of the Yangtze block under the paleotethys mantle dynamic system.

Stress field variations in the Swiss Alps and the northern Alpine foreland derived from inversion of fault plane solutions

This study is devoted to a systematic analysis of the state of stress of the central European Alps and northern Alpine foreland in Switzerland based on focal mechanisms of 138 earthquakes with magnitudes between 1 and 5. The most robust feature of the results is that the azimuth of the minimum compressive stress, S3, is generally well constrained for all data subsets and always lies in the NE quadrant. However, within this quadrant, the orientation of S3 changes systematically both along the structural strike of the Alpine chain and across it. The variation in stress along the mountain belt from NE to SW involves a progressive, counterclockwise rotation of S3 and is most clear in the foreland, where it amounts to 45°–50°. This pattern of rotation is compatible with the disturbance to the stress field expected from the indentation of the Adriatic Block into the central European Plate, possibly together with buoyancy forces arising from the strongly arcuate structure of the Moho to the immediate west of our study area. Across the Alps, the variation in azimuth of S3 is defined by a progressive, counterclockwise rotation of about 45° from the foreland in the north across the Helvetic domain to the Penninic nappes in the south and is accompanied by a change from a slight predominance of strike‐slip mechanisms in the foreland to a strong predominance of normal faulting in the high parts of the Alps. The observed rotation can be explained by the perturbation of the large‐scale regional stress by a local uniaxial deviatoric tension with a magnitude similar to that of the regional differential stress and with an orientation perpendicular to the strike of the Alpine belt. The tensile nature and orientation of this stress is consistent with the “spreading” stress expected from lateral density changes due to a crustal root beneath the Alps.

Lithostratigraphy and tectonic evolution of contrasting greenstone successions in the central Yilgarn Craton, Western Australia

Abstract Lithostratigraphy of the Late Archaean Marda–Diemals greenstone belt in the Southern Cross Terrane, central Yilgarn Craton defines a temporal change from mafic volcanism to felsic-intermediate volcanism to clastic sedimentation. A ca. 3.0 Ga lower greenstone succession is characterised by mafic volcanic rocks and banded iron-formation (BIF). It is subdivided into three lithostratigraphic associations and unconformably overlain by the ca. 2.73 Ga upper greenstone succession of calc-alkaline volcanic (Marda Complex) and clastic sedimentary rocks (Diemals Formation). D 1 north–south, low-angle thrusting was restricted to the lower greenstone succession and preceded deposition of the upper greenstone succession. D 2 east–west, orogenic compression ca. 2730–2680 Ma occurred in two stages; an earlier folding phase and a late phase that resulted in deposition and deformation of the Diemals Formation. Progressive and inhomogeneous east–west shortening ca. 2680–2655 Ma (D 3 ) produced regional-scale shear zones and arcuate structures. The lithostratigraphy and tectonic history of the Marda–Diemals greenstone belt are broadly similar to the northern Murchison Terrane in the western Yilgarn Craton, but has older greenstones and deformation events than the southern Eastern Goldfields Terrane of the eastern Yilgarn Craton. This indicates that the Eastern Goldfields Terrane may have accreted to an older Murchison–Southern Cross granite–greenstone nucleus.

Structure and evolution of the Bohemian Arc

Abstract Tectonic zones and palaeogeographic units (terranes) in the German segment of the Variscides correlate with equivalents in the Sudetes at the NE margin of the Bohemian Massif. This correlation defines an arcuate structure with an opening angle of about 90°. The structure is truncated to the SE by a crustal scale. NE-trending fault zone with dextral transpression, the Moldanubian Thrust (MT). The arc cannot have been formed by northeastward indentation of the Bohemian Massif, since there is no evidence of a fault zone on the NW flank of the notional indenter, and little evidence for northeastward tectonic transport. Kinematic and age constraints on the main fault zones instead suggest that the structural array was formed by a complex sequence of events. Northwestward displacement along the margin of the East European Platform (EEP) with clockwise rotation was followed by large southwestward movements along the Moldanubian Thrust, and renewed northwestward displacement along the SW margin of the East European Platform.

Discovery of Linear “Building Blocks” of Water Masers Shaping Linear/Arcuate Microstructures in Cepheus A

We report three epochs of VLBA water maser observations toward the radio jet Cepheus A HW2. The VLBA data show that some of the masers detected previously with the VLA unfold into unexpected and remarkable linear/arcuate microstructures, revealing, in particular three filaments (R1, R2, R3) with length sizes 3-25 mas (2-18 AU) and unresolved in the perpendicular direction (0.1 AU), an arcuate structure (R4-A) of 20 mas size (15 AU), and a curved chain of masers (R5; which we have previously reported) of 100 mas size (72 AU). Some of these structures unfold into even smaller linear building blocks (down to scales of 0.4 AU) shaping the larger structures. The flattened appearance of these small pieces argues strongly for a shock nature. Both the morphology and the observed proper motions found in these water maser structures have allowed us to identify at least three different centers of star formation activity in a region of 300 mas (200 AU) projected radius, unknown previously, and that could constitute a triple star system. We suggest that R1, R2, and R3, which are located close to the HW2 radio jet but offset by 200 mas with respect to its axis, could originate at the shocked walls of an inner cavity excavated by the HW2 wind in the circumstellar molecular gas. The presence of a wide-angle wind associated with the central HW2 object is implied. We also propose that the arcuate structure R4-A corresponds to a bow-shock structure produced by the wind of an undetected protostar (which we predict to be located toward the southeast of R4-A, 200 mas south from HW2). Finally, the third energy source of this small region could be that one exciting the arc R5, which, as we have previously reported, is expanding and related to an unidentified protostar located 600 mas south of HW2. The flux density of the water masers of the R5 arc excited by this unknown protostar (~500 Jy) represents an important fraction (~50%) of the total flux density of the maser emission in the entire Cepheus A star-forming region, suggesting that the exciting object could be a high-mass star. Furthermore, we find that the center of the circle, which fit the R5 arc structure for each epoch, is moving with a velocity of ~6 km s-1. This could be caused by proper motions of the associated protostar because of relative orbital motions within the triple star system formed by HW2 and the energy sources of the R4-A and R5 structures.

A new model for the Hercynian Orogen of Gondwanan France and Iberia: discussion

The study by Shelley and BossieAre (2000) is an important contribution to the discussion concerning the Ibero±Armorican arc (IAA) generation model. This model comes as one of a sequence of previous ideas already published in several papers (Bard, 1971; Matte and Ribeiro, 1975; Lefort and Ribeiro, 1980; Ribeiro et al., 1980; Burg et al., 1981; Brun and Burg, 1982; Julivert, 1987; Ribeiro et al., 1990; Dias and Ribeiro, 1995; Ribeiro et al., 1995; Silva, 1997). A common feature of the interpretations in these papers is the great importance attributed to two major transcurrent faults: the dextral Porto±Tomar shear zone (PTSZ) and the sinistral Tomar±Badajoz±Cordoba shear zone (BCSZ), to explain the extension of the Iberian structures into the Armorican Massif in the form of trace the arcuate shape of the IAA. The large-scale migration, rotation and accretion of microplates controlled by oblique interactions have been a matter of controversy since researchers applied different kinematic models to reconstruct such global tectonic movements. For example, Badham (1982) interpreted the Hercynides as the result of dextral interaction between Europe and Africa and considered the arcuate geometry of the IAA as a secondary structure. In contrast, Matte (1986) compared the present example of the Himalayas with the structures of the IAA in terms of an indentation of crustal fragments, and proposed the progressive development of the symmetrical outward lateral escape of blocks in France and Iberia. In this model, the indentor migration caused opposing strike-slip movements on either side represented by the major transcurrent faults of the Armorican Massif and the Iberian Massif. This geometry and kinematics were considered to be syngenetic with the formation of the arcuate structure of the IAA. However, the main geologic lines linking these western European Hercynian massifs through major shear zones are still questionable (e.g. Lefort, 1989). In this comment we believe that the regional approach regarding the transcurrent faults of Hercynian Iberia (BCSZ and PTSZ) cannot be considered to be well established. In the following text we will comment on signi®cant omissions concerning available work of the last decade and also focus our discussion on ®eld data and the structural interpretation of Hercynian Iberia (Portugal and Spain).

The aeromagnetic map of the French Cadomian belt

In order to obtain an image of the subsurface of the Armorican Massif, two detailed aeromagnetic surveys were combined to obtain an aeromagnetic map at 350m altitude with an interpolated grid of 250m×250m. The map shows good correlation between the magnetic anomalies and known geological structures and also distinguishes between long- and short-wavelength anomalies. The long-wavelength anomalies are associated with the overall subsurface arcuate structure of the Cadomian belt. The short-wavelength anomalies are commonly associated with the Lanvollon acid volcanic rocks and syntectonic diorites, with one set of short-wavelength anomalies in the east of the Saint-Malo region being associated with dykes that are exposed onshore and continue offshore.

Geometry and kinematics of large arcuate structures formed by impingement of rigid granitoids into greenstone belts during progressive shortening

Regional-scale arcuate structures in the central part of the Archean Yilgarn craton, Western Australia, were generated by impingement of competent granitoid blocks into less competent greenstone belts during progressive east-west shortening. Sinistral shear zones developed along northwest-trending margins of the granitoid blocks, whereas dextral shear zones developed along northeast-trending margins. In apex regions, these northeast- and northwest-trending shear zones are linked by north-trending contractional zones along which shortening was accommodated by the formation of folds and reverse faults in the greenstone belts and a coaxial flattening fabric in granitoid rocks. Lateral escape of the greenstone belts is indicated by the progressive rotation of early macroscopic folds into parallelism with the strike-slip shear zones during granitoid impingement. This recently recognized deformation style may have important tectonic implications for other Archean granite-greenstone terranes and where rock heterogeneity and competency differences are significant.

Evolution of Mg/Fe Ratios in Late Variscan Plutonic Rocks from the External Crystalline Massifs of the Alps (France, Italy, Switzerland)

Late Variscan plutonic bodies are widespread in the External Raumer et al., 1993; Menot et al., 1994). From south to Crystalline Massifs of the Alps (Argentera, Pelvoux, Belledonne, north, they are the Argentera, Pelvoux, Belledonne, Grandes Rousses, Mont Blanc, Aiguilles Rouges, Aar, Gotthard). Grandes Rousses, Mont Blanc and Aiguilles Rouges They can be classified on the basis of their Mg/(Fe+ Mg) ratio massifs (Western Alps), and the Aar and Gotthard massifs and mafic mineral content (expressed by the B = Fe + Mg + (Central Alps) (Fig. 1). They appear as dome-like strucTi parameter). Together with available ages of emplacement, this tures of crystalline basement surrounded by a mostly classification highlights the existence of two plutonic suites, one Mesozoic sedimentary cover. As a whole, they define an early, Visean (~330–340 Ma), and highly magnesian, the other arcuate structure, possibly inherited from the Variscan later, mainly Stephanian (~295–305 Ma), and more ferriferous. orogeny (Bogdanoff et al., 1991). This evolution from a magnesian plutonism to a more ferriferous During the Variscan orogeny, the ECM were part of one, which also occurs in other Variscan massifs (e.g. Corsica), the Helvetic–Moldanubian terrane of the internal zone might be accounted for by a combination of factors related to the of the Variscides (von Raumer & Neubauer, 1993). nature of the source of the magmas, the physical and chemical Precambrian metamorphic units and Precambrian to conditions of melting, and the Late Variscan geodynamic setting. Palaeozoic sediments, interlayered with volcanic and As a basis for these considerations a comprehensive review is ultramafic rocks, display in most areas a polymetamorphic presented of all the External Crystalline Massifs and their history and underwent a highly complex pre-Variscan Late Variscan intrusions. and Variscan evolution. Although they share a number of similarities, the ECM each have also specific characteristics (von Raumer et al., 1993). In addition to orthogneisses deriving from Early Palaeozoic plutonic (and volcanic?) protoliths (Bussy & von

Lithospheric boundaries and plate motions in the Cyprus area

Accurate location of earthquakes recorded by seismographs and reliable fault plane solutions of strong recent earthquakes are used to define the plate boundaries and the pattern of plate motion in Cyprus and surrounding area. Spatial distribution of shallow ( h<60 km) and intermediate depth (60 km ≤ h ≤130 km) earthquakes define a continuous boundary between the Eurasian and the African lithospheric plates in this area. This boundary is formed of two arcuate structures, the eastern and western, which have their concave side to the north and are connected by a NNE striking transform dextral fault, the Paphos Transform Fault (PTF), just west of Cyprus. The eastern structure consists of the Cyprean arc and its continuation to the Gulf of Adana, which then joins the Eastern Anatolian Fault. The western one is an arc-like structure which strikes in a northwest direction following the Florence rise and joins the Rhodes thrust fault. The African plate is slowly subducted under the Eurasian plate from south to north but in the Cyprean arc the Cyprean microplate overrides also the Levantine lithosphere in a SW direction. Some interesting tectonic similarities between the Cyprean and the Hellenic arcs are pointed out.

Oroclinal bending in the Caledonides of western Ireland: a mid-Palaeozoic feature controlled by a pre-existing structural grain

The Caledonides of the west of Ireland mark a segment of the Caledonian–Appalachian orogen where the structural grain swings from the NE–SW trend that typifies the Caledonides of northern Britain to an E–W orientation. The origin of this arcuate structure has previously been proposed to be either primary, reflecting the original geometry of promontories and embayments in the Laurentian margin in this sector of the orogen, or secondary, as evidenced by palaeomagnetically determined clockwise rotations in Silurian rocks in the region. We report the results of a palaeomagnetic investigation of the Early to middle Ordovician Mweelrea Ignimbrites (Llanvirn), from an accreted Taconic arc (the South Mayo Trough) in that part of the western Irish Caledonides that has an E–W trend. After removal of a low-temperature component of magnetisation, (L), interpreted to represent a viscous component of the earth's present field, a high-temperature component of magnetisation, (H), was isolated at fifteen sites in four ignimbrite flows. H passes a palaeomagnetic fold test yielding a tilt-corrected mean remanence direction D=132.6°, I=29.1°, α 95=17.9° which corresponds to a palaeopole at 36.4°E, 9.9°S. The pole is in reasonable agreement with established Early to middle Ordovician reference poles for Laurentia and indicates that no significant rotation occurred between the E–W South Mayo Trough and the Laurentian margin after accretion, and therefore that the curvature of this segment of the orogen is likely to be primary. This contrasts with other results from Silurian sequences to the south, which record significant post-Silurian clockwise rotations. Examination of all reliable palaeomagnetic data from the region indicates that the clockwise rotations are restricted to the rocks south of the South Mayo Trough. We propose that the rotations in the south are linked with the superposition of the pre-existing structural grain on the younger rock units during Late Silurian and Early Devonian sinistral transpression.

The impact of wildfire on an Early Carboniferous coastal environment, North Mayo, Ireland

At Creevagh Head, near Ballycastle, North Mayo, Ireland, a 28-m sequence of Lower Carboniferous (Holkerian-Arundian) carbonates and clastics is exposed in low sea-cliffs. These rocks have been described in terms of five facies and were deposited in a coastal marine setting. Horizontally laminated heterolithic siltstones were formed in a tidal flat environment (Facies 1). Lithologically similar deposits infilling a broad (150 m wide), shallow (2 m deep) erosional surface represent the sediments of a major estuarine channel (Facies 2). Units of inclined heterolithic stratification (IHS), 2–4 m thick, displaying arcuate structures in plan, record the migration of meandering estuarine creeks which dissected the tidal flat (Facies 3). Beds of carbonate mudstone bearing abundant Volvocacean green algae and organic rich siltstones probably formed in oligohaline coastal lagoons (Facies 4). Finally, bioclastic sandstones with in situ corals formed in stenohaline waters at the mouth of tidally dominated estuaries (Facies 5). Vast quantities of charcoal present in one of the IHS units (the Charcoal Unit) are interpreted as the product of a single, catastrophic wildfire at this time. The fire appears to have destroyed vegetation cover on the hinterland destabilising local sedimentary, hydrological and biochemical systems. Comparison of the Charcoal Unit with IHS units immediately underlying it, suggest that run-off and sediment discharge were increased greatly downstream following the fire, replacing tide-dominated sedimentation with a river-dominated regime. Abundant fish skeletal remains in the Charcoal Unit indicate that this event coincided with massive mortalities amongst marine fish populations. This ecological catastrophe may have been linked to increased turbidity and nutrient flushing into the estuary, causing eutrophication and short-lived anoxia.

The Epi-continental arc of Southeast China and relevant earthquakes

Epi-continental arc system is a series of arcuate structures along coastlines of the mainland and behind the island arc system on the margin of the Northwest peri-Pacific region. Epi-continental arc is similar to the island arc in geometery and kinematics, but it was characterised by an arcuate fracture zone and compensated front-sag, basic volcanic activity, shallow earthquake belt and the latest active tectonics. The eastern China continent is dominated by the coastal epi-continental arc of Southeast China. Its front arc is situated along the coastline of Zhejiang, Fujian and eastern Guangdong provinces which is convex to SE. The left NW-trending flank extended along the NW-trending coast line of northern Jiangsu and traversed Shangdong Peninsula to northern Hebei and Shanxi provinces; and the right E-W trending flank along the western Guangdong, southern Guangxi, northern Hainan coastlines extended to northern Hanoi. This arc controlls activities of the most modern intense earthquakes in eastern China continents. The compressing thrust-type earthquakes occurred along the front arc, especially the “collison belt”, and the strike-slip-type earthquakes along the both flanks sinistral and dextral strike-slip faults respectively. Earthquakes of epi-continental arc type is characterised by segmentation in space and periodicity in time.

Isolation and characterization of endothelial cells from different organs of fetal pigs.

The purpose of this study was to isolate endothelial cells from different organs of porcine fetuses and to examine the binding of endothelial markers including lectins. Endothelial cells were isolated from the aorta, cerebral cortex, myocardium, ovary and testis. Binding of the antibodies to von Willebrand factor (vWF) and angiotensin converting enzyme (ACE), the presence of Weibel Palade bodies (WPB), uptake of acetylated low density lipoprotein (acLDL), and labelling with the lectins Bandeiraea simplicifolia agglutinin I (BS I), Peanut agglutinin (PNA), Dolichos biflorus agglutinin (DBA) and Ulex europaeus agglutinin I (UEA I) were examined. Cell preparations displayed cobblestone-like morphology with the exception of testicular endothelium, which formed arcuate structures. Endothelium isolated from the brain labelled more strongly than any other cell line with the lectin PNA, but it did not express ACE. In contrast to other cell preparations, myocardial endothelium showed very low binding of anti-vWF. Ovarian endothelium was able to perform in vitro angiogenesis. Moreover, these endothelial cells possessed the largest number of WPB. Testicular endothelium displayed highest binding of vWF. Endothelium isolated from the aorta, in contrast to all other endothelial cells, did not take up acLDL. These results demonstrate that organ- and tissue-specific heterogeneity is already expressed in fetal endothelium.

Simulation of Particle Paths and Deformation of Ice Structures Along a Flow-Line on Storglaciären, Sweden

Paths, travel times and deformation of particles are simulated with a flow model in order to study two questions regarding the ice flow in Storglaciaren. This model suggest that blue-ice structures observed on the ice surface did not originate as crevasses. The two applications of the model are: 1. To investigate advection and deformation of extensional crevasses in the upper accumulation area, too see whether they are the source of extensive arcuate blue-ice structures found at a lower altitude on the glacier surface. 2. To determine whether traces from crevasses originated in different areas would mix into each other during the transportation through the glacier.The simulations of the particle paths and their deformation shows that: 1. Crevasses visible today in the accumulation area will emerge upglacier from the zone where the arcuate structures are found. Consequently, the model does not support explanation of the blue-ice arcs as closed or frozen water-filled crevasses. 2. Traces of crevasse...

Does climate control the morphological fabric of freshwater carbonates? A comparative study of Holocene barrage tufas from Spain and Britain

Calcium carbonate production in most freshwater tufa systems is controlled by a combination of physico-chemical precipitation, and biomediation associated with procaryote-microphyte biofilms. Inorganic precipitation is dominant under turbulent flow regimes, whereas biomediation necessitates sluggish flow or static water. We show here that temperature is also likely to affect tufa formation rates and architecture, leading to the development of a clearly definable range of fabrics. Two contrasting models are proposed: Warm semi-arid tufas: well seen in the Ruidera Pools National Park, Albacete Province, Central Spain, where tufa barrages consist of vertical, narrow rimmed arcuate structures. Frequently these are bounded both upstream and downstream by deep lakes. Laterally accreting mammilate stromatolites dominate the upper two thirds of lake margin subaqueous overhangs, whereas conical growth-forms dominate shady basal parts of subaqueous overhangs. Dense reed stands grow in thin peats on top of the vertical lake margin walls. Resistivity survey and percussion augering show up to 20 m of earlier lake fill which is banded into dark and pale beds. The upper 10 m accumulated in 4600 years. There is little or no preservation of organic material within these deposits. Cool temperate tufas: typified by slowly accumulating barrage tufas at Caerwys (N. Wales) and Alport (N. Derbyshire, UK). Transverse barriers across valleys are dominated by arcuate buttress developments built up of downstream-facing tabular carbonate sheets. Pools upstream of the barriers are shallow, dominated by clotted lime mud and organic sapropels in their depocentres, and stromatolite-dominated (laminar to low domes, or oncoidal) facies in broad marginal zones. Marginal stands of semi-aquatic vegetation are rooted in thick peats but frequently are also encrusted around their exposed stems by oncoidal carbonate. Fabric preservation is good for the carbonate material, however, marginal peats rapidly oxidise and stem encrustations collapse to produce cylindrical oncoid beds. Depocentre sapropels are always preserved and contain important pollen records otherwise rare in carbonate regions. Carbonates in both models accumulate relatively rapidly. They have a moderate preservation potential within Late Cenozoic terrestrial successions. The distinctly different characteristics of their preserved fabrics should allow recognition of two contrasting “climatic” models for fluvial barrage tufas in ancient deposits.