NNW-SSE Direction Research Articles

Chronology of fracture sealing under a meteoric fluid environment: Microtectonic and isotopic evidence of major Cainozoic events in the eastern Paris Basin (France)

A detailed reappraisal of the sequence of tectonic stages that has affected the eastern part of the Paris Basin from the late Jurassic to the end of Cainozoic is presented in order to improve knowledge of the relationships between tectonics and fluid/mass palaeo-transfers in that basin. This goal was performed in two steps: i) establishing a relative tectonic chronology on the basis of numerous observations and detailed analysis of geometrical relationships between striated planes, vertical and bedding stylolites, and tension gashes, and ii) discussing the geochemical signatures ( δ 18O and δ 13C) of calcite from fracture infillings well positioned within the relative tectonic chronology. The resulting tectonic sequence agrees with the main events described by previous papers, but the present work details the Pyrenean s.l. (Eocene–Oligocene) and Alpine (Miocene–Pliocene) convergence stages and explains the mechanisms of the Oligocene–Miocene transition between the two previous events. The different tectonic stages are as follows: i) late Jurassic to early Cretaceous extension starting with a WNW–ESE direction but changing to E–W; ii) the Pyrenean convergence (Eocene), changing from NNE–SSW to NE–SW and finally ENE–WSW compression; iii) Oligocene transition from Pyrenean to Alpine convergence, marked by a drastic evolution of main stress which swaps from a horizontal position to a vertical one and radial extension marked by a strong reactivation of bedding stylolitisation; iv) the Alpine convergence (late Miocene to present-day), changing from WNW–ESE to NNW–SSE direction of shortening. δ 18O- and δ 13C-values of calcite from tension gashes associated to each tectonic stage spread from 18‰ to 27‰ (SMOW) and from 0.8‰ to 3‰ (PDB), respectively. According to the maximum thermal history of this part of the basin ( T MAX = 40 °C or 60 °C according to the available published estimates), the calculated δ 18O-values of fluids (− 7‰ to − 4‰) involved in mass transfer processes are interpreted as meteoric. The lowest δ 18O-values (18–20‰) are located around the main regional faults and associated with δ 13C-values that are rather different from those of host rocks. In contrast, calcites from non-faulted area present a higher δ 18O- (> 20‰) and δ 13C-values close to those of host rocks. These data are explainable in terms of differences in the fluid/rock ratios prevailing during carbonate redistribution, the highest ratios being associated to discontinuities (faults, sometimes with hydraulic breccias) that were active during the Tertiary tectonic events. Outside the fault zones, the isotopic compositions of calcite from tension gashes are similar, at the regional scale, to those of calcite from geodes or cements analysed in previous studies on localized areas. As a result, we emphasize the fact that a significant part of the carbonate redistribution in the Middle to Upper Jurassic limestones from the eastern Paris Basin occurred during the Tertiary s.l., enlightening the influence of distant orogenic systems (extensive or compressive) in the matter redistribution within sedimentary basins, at variance of models inferring a porosity cementation predominantly during burial.

Recent and active tectonics of the external zone of the Northern Apennines (Italy)

We present a comprehensive study of the recent and active tectonics of the external part of the Northern Apennines (Italy) by using morphotectonic, geological–structural, and stratigraphic analysis, compared with the current seismicity of the region. This analysis suggests that the external part of the Northern Apennines is characterised by presence of three major systems of Quaternary compressive structures corresponding to (1) the Apenninic watershed, (2) the Apennines–Po Plain margin (pede-Apenninic thrust front), and (3) the Emilia, Ferrara, and Adriatic Fold systems buried below the Po Plain. Geological data and interpreted seismic sections indicate a roughly N–S Quaternary deformation direction, with rates <2.5 mm/year. The shortening decreased since the Pliocene, when our data indicate compression in a NNW–SSE direction and rates up to 7 mm/year. The trend and kinematics of the structures affecting the Apennines–Po Plain margin and the Po Plain subsoil fit well the pattern of the current seismicity of the area, as well as recent GPS and geodetic levelling data, pointing to a current activity of these thrust systems controlled by an overall compressive stress field. Close to the Apenninic watershed, earthquake focal mechanisms indicate that shallow extension is associated to deep compression. The extensional events may be related to a secondary extensional stress field developing on the hangingwall of the thrust system affecting the Apenninic watershed; alternatively, this thrust system may have been recently deactivated and overprinted by active normal faulting. Deeper compressive events are related to the activity of both a major basement thrust that connects at surface with the pede-Apenninic thrust front and a major Moho structure.

Velocity field and tectonic strain in Southern Spain and surrounding areas derived from GPS episodic measurements

Abstract The goal of this paper is to study the velocity field and deformation parameters in Southern Spain and surrounding areas (Ibero-Maghrebian region) using GPS episodic measurements. Results are compared to those previously published as well as deformation parameters derived from seismic data. For this purpose, a geodetic GPS network of 12 stations was observed during eight field campaigns from 1998 to 2005 by the San Fernando Naval Observatory (ROA), Spain. Relative GPS velocities in the Gulf of Cadiz with respect to the stable part of Eurasia are ∼4.1 mm/yr in a NW–SE to NNW–SSE direction. In the Betics, Alboran Sea and North of Morocco, velocities are ∼4.4 mm/yr in a NW–SE direction, and they are ∼2.3 mm/yr in a N–S direction in the eastern part of the Iberian Peninsula. These results are in agreement with the anticlockwise rotation of the African plate. GPS strain tensors are determined from the velocity model, to obtain a more realistic crustal deformation model. The Gulf of Cadiz is subjected to uniform horizontal compression in a NNW–SSE direction, with a rotation to N–S in the Alboran Sea and Northern Morocco. An extensional regime in a NW–SE direction, which rotates to W–E, is present in the Internal Betics area. In the Betic, Alboran Sea and North of Morocco regions we compare seismic deformation rates from shallow earthquakes with the determined GPS deformation rates. The comparison indicates a seismic coupling of 27%, while the remaining 73% might be generated in aseismic processes. Deformations measured in the Ibero-Maghrebian region with GPS could be interpreted in terms of either elastic loading or ductile deformation.

日露共同地震観測による２００７年８月２日に発生したサハリン南西沖の地震（ＭＪＭＡ６．４）の余震活動

On August 2, 2007, an MJMA 6.4 moderate earthquake occurred off the southwest coast of Sakhalin Island, far eastern Russia. In the city of Nevelsk, situated just in the aftershock region, two people were killed and more than 240 buildings were damaged (we call this event as the 2007 Nevelsk earthquake). We have operated a temporal seismological network in southern Sakhalin consisted in ten stations with short-period sensors and 16-bit recorders since 2003. This dense network well recorded this earthquake and the following aftershock sequence. Initial aftershock hypocenters were calculated using a 1-D P-wave velocity structure that was estimated from 746 P-wave arrival times, including data from the aftershocks. To obtain a more precise aftershock distribution, we applied a double-difference hypocenter determination method. The well-determined aftershock hypocenters shows the following features; (1) in the northern and central parts of aftershock region, epicenters were distributed in the sea along the coast with NE-SW direction, (2) while in the southern part of aftershock region trend of epicenters changed toward land with NNW-SSE direction. This southern most part intersects the city of Nevelsk where severe damage occurred. On August 17, 2006, the 2006 Gomozavodskoe earthquake (MJMA 5.9) occurred near the southeastward aftershock region of the 2007 Nevelsk earthquake. The 2006 earthquake sequence was occurred deeper area as compared to the 2007 event. We examine the change in Coulomb failure function produced by the 2006 event and conclude that the 2006 event has less influence on occurrence of the 2007 event.

Application of the resistivity/gravity joint inversion technique for Nubian sandstone aquifer assessment on the area located at the central part of Sinai, Egypt

Eleven deep vertical electrical soundings of AB/2 spacing ranging from 5 to 3000 m were carried out to investigate the upper part of the Nubian groundwater aquifer at the central part of Sinai, Egypt. These soundings have been jointly inverted using the SA algorithm with 160 gravity stations measured in the study area, assuming that density and resistivity contrast are represented by coincident interfaces. One hundred and sixty magnetic stations were executed at the same locations as gravity measurements to estimate the depth of basement rocks. The results of the joint interpretation indicated that the depth of the groundwater aquifer ranges from 500 to 800 m with resistivity values ranging from 6 to 562 Ω m, suggesting that the fresh water is of good quality towards the northern part of the area. The top of the basement, which is mainly defined by gravity and magnetic data, lies at a depth ranging from 830 to 2788 m. The results also show that the aquifer configuration is controlled by different regional faults in the NNW–SSE direction.

Coastal vulnerability assessment of the future sea level rise in Udupi coastal zone of Karnataka state, west coast of India

Udupi coast in Karnataka state, along the west coast of India, selected as a study area, is well known for sandy beaches, aquaculture ponds, lush greenery, temples and major and minor industries. It lies between 13°00′00″–13°45′00″ north latitudes and 74°47′30″–74°30′00″ east longitudes, the length of the coastline is 95 km, and is oriented along the NNW–SSE direction. It is vulnerable to accelerated sea level rise (SLR) due to its low topography and its high ecological and touristy value. The present study has been carried out with a view to calculate the coastal vulnerability index (CVI) to know the high and low vulnerable areas and area of inundation due to future SLR, and land loss due to coastal erosion. Both conventional and remotely sensed data were used and analysed through the modelling technique and by using ERDAS Imagine and geographical information system software. The rate of erosion was 0.6018 km 2/yr during 2000–2006 and around 46 km of the total 95 km stretch is under critical erosion. Out of the 95 km stretch coastline, 59% is at very high risk, 7% high, 4% moderate and 30% in the low vulnerable category, due to SLR. Results of the inundation analysis indicate that 42.19 km 2 and 372.08 km 2 of the land area will be submerged by flooding at 1 m and 10 m inundation levels. The most severely affected sectors are expected to be the residential and recreational areas, agricultural land, and the natural ecosystem. As this coast is planned for future coastal developmental activities, measures such as building regulation, urban growth planning, development of an integrated coastal zone management, strict enforcement of the Coastal Regulation Zone (CRZ) Act 1991, monitoring of impacts and further research in this regard are recommended for the study area.

Assessing image processing techniques for geological mapping: a case study in Eljufra, Libya

Various image processing techniques were experimented with in this study to evaluate their efficiency for geological mapping in the Eljufra area of northwest Libya. Remote sensing data including multi-spectral optical Landsat Enhanced Thematic Mapper (ETM+), Synthetic Aperture Radar (ERS-2 SAR) and Digital Elevation Models (DEMs) extracted from the Shuttle Radar Topography Mission (SRTM) data were used to trace different lithological units as well as extracting geological lineaments in the study area. The study area is located in an arid environment mostly devoid of any vegetation. Most lithological and structural units are distinguishable based on their topographic form and spectral properties. Fusion of ETM+ and ERS-2 images was experimented with to further identify lithological units. Shaded relief techniques were implemented to enhance terrain perspective views and to extract geological lineaments. The results discriminated different rock units and modified formation boundaries and revealed new geological lineaments. Nine rock units were identified and plotted in the new geological map defined by the new boundaries. The dominant lineaments tend to run in the NNW-SSE and NNE-SSW directions. Analysis and interpretation of the lineaments provided information about the tectonic evolution of the study area.

옥천습곡대 서남부지역에 분포하는 쥬라기 화강암류의 석영내 아문 미세균열 및 유체포유물을 이용한 고응력장

옥천습곡대의 서남부지역에서 분포하는 쥬라기 화강암류의 석영내에 존재하는 아문 미세균열과 유체표유물을 분석하여 이 지역에 작용한 고응력장을 해석하였다. 연구지역에서 나타나는 아문 미세균열의 방향성은 전체적으로 <TEX>$N30^{\circ}W$</TEX>의 방향이 가장 우세하며 <TEX>$N70^{\circ}W$</TEX>의 방향도 나타난다. 연구지역의 아문 미세균열 생성온도는 <TEX>$380-550^{\circ}C$</TEX> 범위를 보이며, 이들 아문 미세균열은 약 166-200Ma의 기간 동안 형성되었을 것으로 추정된다. 아문 미세균열의 방향성을 통한 고응력장의 작용 방향과 유체포유물에 의한 아문 미세균열의 형성시기를 비교하여 볼 때, 연구지역 내에서 발달하는 화강암질암체는 NNW-SSE와 WNW-ESE 방향의 최대수평주응력인 고응력장이 쥬라기 초기에서 쥬라기 중기 기간 동안 작용하였을 것으로 사료된다. Paleostress was interpreted by analyzing the healed microcracks and the secondary fluid inclusions in quartz of the Jurassic granites distributed in the southwestern Ogcheon Folded Belt, South Korea. The most dominant direction of healed microcracks in the study area was oriented <TEX>$N30^{\circ}W$</TEX>, and <TEX>$N70^{\circ}W$</TEX> direction was also recognized. The formation temperatures of fluid inclusions were ranged <TEX>$380-550^{\circ}C$</TEX> and the age of healed microcrack formations might have been approximately 166-200 Ma. Comparing the paleostress orientation obtained from the direction of healed microcracks to the formation age of healed microcracks estimated from the secondary fluid inclusions, it is considered that granitic rock body in study area was subject to a maximum horizontal principal stress along the NNW-SSE and WNW-ESE directions in the early Jurassic to middle Jurassic.

New geochronological constraints on the geological evolution of Espinhaço basin within the São Francisco Craton—Brazil

The São Francisco Craton, in the central-eastern region of Brazil, is a cratonic fragment stabilized after the Rhyacian tectono-metamorphic event (2.25–2.05 Ga). Volcanic and sedimentary rocks of the Espinhaço (Paleo- to Mesoproterozoic) and São Francisco (Neoproterozoic) basins crop out on this craton. In the northern sector of the craton, the Espinhaço basin crops out in two domains: the Northern Espinhaço Range and the Chapada Diamantina, that are separated by the Paramirim Corridor, a Brasiliano/Pan African (650–500 Ma) deformation zone, which crosses the craton in NNW–SSE direction. The stratigraphic framework of the Northern Espinhaço is characterized by eight synthems that comprise units bound by unconformities, or stratigraphic discontinuities with regional extent over the Espinhaço basin. These synthems are: Algodão, São Simão, Sapiranga, Pajeú and Bom Retiro (lower interval), São Marcos and Sítio Novo (intermediate interval) and Santo Onofre (upper interval). For each interval the sedimentary processes, the depositional systems, the filling style of the basin and the tectonic settings were evaluated, based mainly on the facies association characteristics and their lateral/vertical changes. Zircon U–Pb SHRIMP and basin analysis studies carried out along the eastern border of the Northern Espinhaço Range provide a few new or improved anchors upon which the tectonic evolution of the Espinhaco basin can be pinned. We identified Statherian rifting in the São Simão Synthem, by dating volcanic rocks at 1.73 Ga. This is followed by a previously unknown, minor intracratonic rift phase within the São Francisco Craton, dated at circa 1.57 Ga through a volcanic unit within the Pajeú Synthem. The entire lower interval is cut by mafic intrusive dykes of which we dated one at 850 Ma, which we correlate with a Tonian rifting phase affecting the eastern part of the São Francisco craton, and related to the break-up of the Rodinia Supercontinent. Our data show that the development of the Northern Espinhaço Range spans a large time interval, and comprises a discontinuous series of tectonic events that gave rise to the formation of the various synthems and are punctuated by the extrusion of minor volcanic units and emplacement of dykes within the eastern part of the São Francisco Craton.

Hallazgo de sedimentitas sinorogénicas neógenas en los alrededores de Chos Malal, Cuenca Neuquina, Argentina

Finding of Neogene synorogenic sedimentites around Chos Malal, Neuquén Basin, Argentina. The Chos Malal Formation nov. is proposed to group a 140,50 m thick neogene succession of epiclastic sedimentites including sandstones, silstones and mudstones with tuffaceous input, which were previously ascribed to the Early Cretaceous Rayoso Formation. They were accumulated during the formation of a syncline elongated in a NNW-SSE direction, being deposited in angular unconformity on the Rincon Member of the Rayoso Formation, and covered in the same way by the Middle Miocene-Early Pliocene Rincón Bayo Formation. According to its stratigraphic position and correlations with near geographically situated units, they are ascribed to the Middle Miocene.

Structure and isostatic compensation of the Comorin Ridge, north central Indian Ocean

SUMMARY Bathymetry, gravity and magnetic data (about 9200 lkm) of the Comorin Ridge, north central Indian Ocean were investigated using the transfer function and forward model techniques to understand the mode of isostatic compensation and origin of the ridge. The ridge extends for about 500 km in NNW–SSE direction and associates with low-amplitude gravity anomalies ranging from 25 to 30 mGal compared to the ridge relief, suggesting that the anomalies are compensated at deeper depths. From Admittance analysis an Airy model or local compensation with an elastic plate thickness (T e) of about 3 km and crust thickness (t) of 15–20 km are suggested for the southern part of the Comorin Ridge (south of 5 ◦ N), whereas for the northern part a flexural plate model with an elastic thickness of about 15 km is obtained. Admittance analysis together with the results from gravity forward modelling reveal that the south part was emplaced on relatively weak oceanic crust with both surface and subsurface loading, while the north part was emplaced on the continental crust. Based on present studies and published plate kinematic models we interpret that the Comorin Ridge was evolved at about 90 Ma during the rift stage of Madagascar from the southwest of India. We have also demarcated the continent–ocean boundary (COB) west of Sri Lanka and southern tip of India, which runs across the strike of the ridge, placing the northern part of the ridge on continent and southern part on oceanic crust. On the southern part of the ridge eastern flank is steep-faulted up to 0.6 km and is controlled by the 79 ◦ E FZ and then by COB.

The Pisco (Peru) Earthquake of 15 August 2007

The seismic activity in Peru has its origin in the convergence process between the Nazca and South American plates. Such convergence takes place at an average speed on the order of 7–8 cm/year (DeMets et al. 1980; Norabuena et al. 1999). This process is responsible for the offshore earthquakes with depths smaller than 60 km that take place off the coast of Peru (Dorbath et al. 1990; Tavera and Buforn 2001), which are all associated with seismogenic contact. Moderate to large earthquakes occur on average at a rate of more than 60 per year and usually affect the towns near their epicenters. Earthquakes of larger magnitude ( Mw > 7.0) have produced significant damage over broad areas, such as the event that occurred in southern Peru on 23 June 2001 ( Mw = 8.2), which affected an area of 370 × 70 km2 between the towns of Atico (Arequipa) and Ilo (Moquegua) (Tavera et al. 2006). The earthquake that is the subject of this article occurred on 15 August 2007 with a magnitude of Mw 7.9 and was named “the Pisco earthquake” because its epicenter was located 60 km west of Pisco city. The earthquake produced significant damage in Pisco city (approximately 80% of all structures) and minor damage in nearby towns, and it was assigned an approximate intensity of VII–VIII on the Modified Mercalli Intensity (MMI) scale in Pisco city. The epicenter of the Pisco earthquake and its aftershocks were located between the rupture areas of the 1974 Lima earthquake (Mw 7.5) and the 1996 Nazca earthquake (Mw 7.7). The earthquake also produced a tsunami, which originated south of the epicenter in the Paracas Peninsula. Focal mechanisms for these earthquakes generally correspond to reverse motion with nodal planes oriented in a NNW-SSE direction and near horizontal plane …

Geophysical investigation of Al Jaww Plain, eastern Abu Dhabi: Implications for structure and evolution of the frontal fold belts of the Oman Mountains

ABSTRACT The area to the southeast of the city of Al Ain, Abu Dhabi, United Arab Emirates, is part of an arcuate sedimentary basin whose trend gradually changes from NNW near Al Ain to NNE at Ras Al Khaimah. The basin is bounded to the east by the generally N-trending Oman Mountains and on the west by an arcuate, overall west-verging fold-thrust front that involves Mesozoic carbonates. The fold-thrust front is part of the overall compressional system of Late Cretaceous age (with Late Tertiary reactivation) associated with obduction and emplacement of the Semail Ophiolite, Haybi, Hawasina and Sumeini sheets onto the continental margin of the Arabian Plate. Near Al Ain, the fold-thrust front is expressed as the remarkable, NNW-trending Jabal Hafit that rises one kilometer above the gravel-filled Al Jaww Plain. Gravity and magnetic investigations were carried-out in the Al Jaww Plain, an area of approximately 550 square km. The interpretation of these new data, including measurements of physical properties of rock samples from the area, were integrated with a new interpretation of an industry seismic reflection profile to provide constraints on the modelling of the subsurface structure and evolution of the sedimentary basin beneath Al Jaww Plain. We recognised four major tectono-stratigraphic units in the seismic profiles: autochthonous shelf carbonates, the Hawasina allochthon, Upper Cretaceous foreland basin sediments (primarily Fiqa Formation), and Tertiary neo-authochthonous units. Along-strike variations in the residual Bouguer gravity field were interpreted as being due to either variations in the thickness, or even total absence, of the Hawasina sheet. Comparison of two E-W gravity profiles, one in the southern part of our study area and the other to the north, suggest that the Hawasina sheet underlies little of the southern area but almost all of the northern area. Magnetic anomalies are weak (&amp;lt; 50 nT) over most of the area but peak (&amp;gt; 300 nT) in the easternmost part of the southern profile, where the high-susceptibility rocks of the Semail Ophiolite are exposed. Thus, we interpret that no continuation of the ophiolite extends westward from this outcrop into the subsurface of the study area. The structural geometries described here have resulted from two major tectonic events. The first, a Late Cretaceous phase, emplaced the obduction-related allochthonous thrust sheets of the Oman Mountains westward onto the Mesozoic carbonate platform. This phase primarily affected the eastern part of the study area and contributed to both the high magnetic (&amp;gt; 300 nT) and residual Bouguer gravity (&amp;gt; 14.0 mGal) anomalies. The second event, a Tertiary deformation phase, affected most parts of the area and produced a series of asymmetrical anticlines and synclines trending in a NNW-SSE direction. This phase contributed to the low residual gravity anomaly (&amp;lt; -9.0 mGal) in the center of the study area. We modelled that area as containing a sequence of post-Eocene carbonate sediments with a minimum thickness of 2.0 km. The Tertiary folding and thrusting formed as a result of a regional compressive deformation, whose principal compressive stress axes were sub-parallel to those of the Late Cretaceous compressional stress regime. The younger event reactivated high-angle reverse faults within the Mesozoic platform succession. Precise timing of the Tertiary deformation is debatable; it is most likely that the rejuvenation of the E-W to ENE-WSW Cretaceous stress regime took place in the Late Eocene-Miocene but gradually shifted to become N-S to NE-SW. This shift could be due to the collision of the Arabian and Eurasian plates and the opening of the Red Sea which started during Late Eocene and continues until the present-day.

Fault plane solutions in Sichuan-Yunnan rhombic block and their dynamic implications

Harvard Centroid Moment Tensor (CMT) solutions for earthquakes from 1977 to 2004 showed that the stress fields are obviously different in northwestern Sichuan sub-block (NWSSB), western parts of Central Yunnan sub-block (CYSB) and eastern part of CYSB. The characteristics of the mean stress fields in these three regions are obtained by fitting to CMT solutions. The stress state in NWSSB is characterized by its sub-horizontal tensile principal axis of stress (T axis) in roughly N-S direction and west dipping compressive principal axis of stress (P axis); the one in western part of CYSB is characterized by its ENE dipping T axis and sub-horizontal medium principal axis of stress (B axis) in roughly N-S direction; the one in eastern part of CYSB is characterized by its sub-horizontal P axis in roughly NNW-SSE direction and sub-horizontal T axis in roughly WSW-ENE direction. Finite element method simulation clearly shows that the Indian Plate imposes great extrusion on Sichuan-Yunnan rhombic block (SYRB) near Assam massif. The value of the simulated compressive principal stress decreases with the distance from Assam massif. The simulated directions of the T axes in SYRB form annular distribution encircling Assam. For a homogeneous elastic medium with free boundary conditions on the top and bottom surfaces as well as the displacement boundary conditions derived from the GPS observations on the lateral boundaries, the computation results are consistent with the Harvard CMT solutions in NWSSB and western part of CYSB, while inconsistent with the Harvard CMT solutions in eastern part of CYSB. The inconsistency in eastern part of CYSB can be reduced when it includes inhomogeneous elastic media. The stress states in NWSSB and western part of CYSB revealed by the Harvard CMT solutions are not local, which are mainly controlled by the boundary force on the whole region. On the other hand, the stress state in eastern part of CYSB given by the Harvard CMT solutions is local, which may be affected by local topography, material inhomogeneity, and the drag force underneath.

Evolution of paleostress fields and brittle deformation of the Tornquist Zone in Scania (Sweden) during Permo-Mesozoic and Cenozoic times

The NW-SE oriented Sorgenfrei–Tornquist Zone (STZ) has been thoroughly studied during the last 25 years, especially by means of well data and seismic profiles. We present the results of a first brittle tectonic analysis based on about 850 dykes, veins and minor fault-slip data measured in the field in Scania, including paleostress reconstruction. We discuss the relationships between normal and strike-slip faulting in Scania since the Permian extension to the Late Cretaceous–Tertiary structural inversions. Our paleostress determinations reveal six successive or coeval main stress states in the evolution of Scania since the Permian. Two stress states correspond to normal faulting with NE-SW and NW-SE extensions, one stress state is mainly of reverse type with NE-SW compression, and three stress states are strike-slip in type with NNW-SSE, WNW-ESE and NNE-SSW directions of compression. The NE-SW extension partly corresponds to the Late Carboniferous–Permian important extensional period, dated by dykes and fault mineralisations. However extension existed along a similar direction during the Mesozoic. It has been locally observed until within the Danian. A perpendicular NW-SE extension reveals the occurrence of stress permutations. The NNW-SSE strike-slip episode is also expected to belong to the Late Carboniferous–Permian episode and is interpreted in terms of right-lateral wrench faulting along STZ-oriented faults. The inversion process has been characterised by reverse and strike-slip faulting related to the NE-SW compressional stress state. This study highlights the importance of extensional tectonics in northwest Europe since the end of the Palaeozoic until the end of the Cretaceous. The importance and role of wrench faulting in the tectonic evolution of the Sorgenfrei–Tornquist Zone are discussed.

Formation of the double rift system in the Thaumasia Highlands, Mars

The Thaumasia Highland Rifts are two complex graben structures in the Thaumasia Highland belt, located in the southern Thaumasia region, Mars. The rifts are arranged 90–130 km apart in a nearly subparallel setting and represent a very unusual style of crustal deformation. We have investigated the mechanism responsible for this peculiar style of rifting and found strain localization by volcanic weak zones to be a major factor for fault‐pattern formation, indicating widespread prerift and synrift volcanic activity in the region. This result is consistent with the high heat flow during rift emplacement as estimated from rift flank uplift. Our results indicate that the onset of volcanism predates the rift formation process and that magmatism and the associated lithospheric weak zones control the rift locations. The simulations performed here are in good agreement with the observations for extension in the NW–SE to NNW–SSE direction, and we favor a formation scenario involving passive rifting in a magmatectonically active environment.

Geomorphological, paleontological and 87Sr/ 86Sr isotope analyses of early Pleistocene paleoshorelines to define the uplift of Central Apennines (Italy)

The eastern border of the Middle Valley of the Tiber River is characterized by several Plio-Pleistocene paleoshorelines, which extend for about 100 km along the western margin of the Central Apennines (Italy). We studied these paleoshorelines by the means of geological and paleontological analyses and new 87Sr/ 86Sr isotope analyses. The youngest and uppermost paleoshorelines have been detected and mapped through detailed geologic and stratigraphic surveys, which led to the recognition of nearshore deposits, cliff breccias, alignments of Lithophaga borings, fossil abrasion notches and wave-cut platforms. The altitude of these paleoshorelines decreases almost regularly in the NNW–SSE direction from 480 to 220 m a.s.l. Measurements of the 87Sr/ 86Sr isotope ratio have been conducted on corals and mollusks collected from sediments outcropping close to the paleoshorelines. The isotopic dating results indicate numerical values that range between 0.70907 and 0.70910 all over the 100-km outcrop. These results, together with biostratigraphic data, constrain the age of the youngest paleoshorelines to 1.65–1.50 Ma. These paleoshorelines are thus considered almost isochronous, giving an estimated uplift rate of 0.34–0.17 ± 0.03 mm/a moving from NNW to SSE. Shape, length and continuity of the 100-km-long observed movements indicate that the studied paleoshorelines are an important marker of the Quaternary uplift of the Central Apennines.

首都圏直下とその付近でのフィリピン海プレートスラブの形態

We present a new view of the morphology of slab (s) subducted just beneath the Tokyo Metropolitan Area in Japan. Previously, several different models of the surface geometry of the subducted Philippine sea plate slab (PH slab) have been published mainly using seismicity data (e.g., Nakamura and Shimazaki, 1981; Maki, 1984; Kasahara, 1985; Ishida, 1992; Noguchi, 1998; Hori, 2006).In this study, first we discriminate a previously unknown seismic slab (called slab SG, or seismic slab SG) above the downgoing Pacific plate slab (PC slab), second identify the possible internal structure of slab SG, and third demonstrate tectonic evolution models. It is clear that the currently known surface contours of PH slab indicate the shallowest part of slab SG as well.Most previous studies assumed a PH slab with a constant thickness, and paid little attention to the tectonic characteristics of the vertical extent and/or the bottom geometry of slab SG with variable thickness. The bottom extent of the seismic slab SG beneath the Metropolitan area reaches 36.5N at least. The horizontal extent of seismic slab SG covers most of the lowland Kanto Plain. The bottom depth of slab SG is approximately 120 km near 36.5N and 139.0E, being the same as the surface depth of the PC slab there. Below the Sagami Trough axis near 34.5N and 140.0E, the lowest portion of slab SG is located at a depth of 80 to 90 km. The western bottom end zone of slab SG generally strikes in the NNW-SSE direction, being approximately parallel to the volcanic front.We suggest four basic morphology models of slab SG as follows. (1) Slab SG consists of both the PH slab at a shallower depth and a deeper underlain slab (slab SL). (2) A bookshelf-like configuration of northwardly inclined multi-slabs on the PC slab due to the intermittent southward shift of accumulation sites of short slab tips with episodic subduction at just south of the previously active paleo-Sagami Trough (s). We emphasize that the above evolutional bookshelf model is, to some extent, similar to the sediment layer accretion process near the deep trench system, but the dynamic situation is not the same. (3) A structure combining models (1) and (2). (4) Slab SG is merely the eastern part, having been cooled by the downgoing PC slab, of 65-70 km thick lithosphere of the Izu Outer Block (JOB) without any other slab components.To clarify the structure of the SG slab in more detail, we should incorporate high-gain seismic data from the on-line operating dense seismic observation network deployed at both marine and land areas covering the metropolitan area. In addition, we must study the effects of 3D mantle wedge circulation with dehydration process due to the subduction of both PC and PH slabs from different directions, as well as the space-time evolution history of accretion tectonics at the northern end zone of the Philippine sea plate.

Integrated 3D density modelling and segmentation of the Dead Sea Transform

A 3D interpretation of the newly compiled Bouguer anomaly in the area of the “Dead Sea Rift” is presented. A high-resolution 3D model constrained with the seismic results reveals the crustal thickness and density distribution beneath the Arava/Araba Valley (AV), the region between the Dead Sea and the Gulf of Aqaba/Elat. The Bouguer anomalies along the axial portion of the AV, as deduced from the modelling results, are mainly caused by deep-seated sedimentary basins (D > 10 km). An inferred zone of intrusion coincides with the maximum gravity anomaly on the eastern flank of the AV. The intrusion is displaced at different sectors along the NNW–SSE direction. The zone of maximum crustal thinning (depth 30 km) is attained in the western sector at the Mediterranean. The southeastern plateau, on the other hand, shows by far the largest crustal thickness of the region (38–42 km). Linked to the left lateral movement of approx. 105 km at the boundary between the African and Arabian plate, and constrained with recent seismic data, a small asymmetric topography of the Moho beneath the Dead Sea Transform (DST) was modelled. The thickness and density of the crust suggest that the AV is underlain by continental crust. The deep basins, the relatively large intrusion and the asymmetric topography of the Moho lead to the conclusion that a small-scale asthenospheric upwelling could be responsible for the thinning of the crust and subsequent creation of the Dead Sea basin during the left lateral movement. A clear segmentation along the strike of the DST was obtained by curvature analysis: the northern part in the neighbourhood of the Dead Sea is characterised by high curvature of the residual gravity field. Flexural rigidity calculations result in very low values of effective elastic lithospheric thickness (te < 5 km). This points to decoupling of crust in the Dead Sea area. In the central, AV the curvature is less pronounced and te increases to approximately 10 km. Curvature is high again in the southernmost part near the Aqaba region. Solutions of Euler deconvolution were visualised together with modelled density bodies and fit very well into the density model structures.

Structural curiosity of the northern Istria

In northern Istria certain structural particularities exist that till now were not explained, and some of them not even known. They are all associated with underthrusting of the Adriatic microplate (Istra) under the Dinarides. The Rokava fault of cross-dinaric direction was discovered that exerts an important influence on hydrographic pattern in this part of Istria. The cross-dinaric sinistral strike-slip faults above Glinščica stream (Rosandra) are of local importance only, since at Kastelec and Črni Kal the dextral strikeslip faults of NNW-SSE direction occur as their conjugated equivalents. This particular feature has been named the Gročana (Grozzana) structure. The reason for such a structure is the echelon folding (complete folding) in the Istrian hinterland (the Kras-Notranjsko folded structure). In the Tinjan area a wedge shaped block occurs between two thrust faults that are turned up and quite steep owing to secondary folding. The wedge is open northwestward, and the flysch beds within it are folded in the cross-dinaric direction. They represent an indication of lateral squeezing in a limited area, since in the close-by roadcut of the Ankaran-Trieste motorway no trace of these folds remains (the Tinjan structure). In the Izola and Strunjan area a complex overthrust structure is present that rapidly wedges out toward central Istria. Indirect data suggest that it extends northwestward below the Bay of Trieste. The elements of this structure are the Izola thrust fault with Izola anticline in the thrust block, and folds at Strunjan that were formed in the belt between the reverse overthrusts in the Strunjan bay and Izola thrust fault area (the Strunjan structure).