East West Convergence Research Articles

The Tectonic Map and Structural Provinces of the Late Neoproterozoic Egyptian Nubian Shield: Implications for Crustal Growth of the Arabian–Nubian Shield (East African Orogen)

The Late Neoproterozoic Egyptian Nubian Shield (ENS) has attracted increasing attention since the establishment of the Egyptian Geological Survey and Mining Authority (EGSMA (1896)), which conducted the first mapping. In the last three decades, rapid improvements in analytical techniques, along with field-oriented studies, have made it possible for the interpretation of the ENS as an integral part of the juvenile Arabian–Nubian Shield (ANS) as a portion of the East African Orogen (EAO). However, a consistent tectonic map of the ENS does not exist. Presentation of such a map is the main objective of the present work where Landsat-based lithological discrimination is combined with the systematic structural investigation and careful reassessment of previously published geological maps. Our interpretation of this map indicates that in accordance with previous work, the basement units of the Eastern Desert (ED) can be divided into three structural domains: Northern, Central, and South-Eastern Desert provinces. The proposed provinces are ascribed to three different plate tectonic far-field boundary conditions. The earliest magmatic, metamorphic, and tectonic history was set off by the approximate north–south convergence of the Gabgaba-Gebeit, Jiddah-Asir terranes, and Eastern Desert-Midyan terranes along the Yanbo-Onib-Sol-Hamid-Gerf-Allaqi-Heiani (YOSHGAH) suture between c. 800 and 620 Ma. The second event between c. 640 and 580 Ma was correlated with the Nabitah Orogeny when the Ad Dawadimi-Ar Rayn terranes in the eastern Arabian Shield accreted to the earlier consolidated arc terranes (Afif and Tathlith terranes). During this period, east–west convergence between northwestern Saudi Arabia and the Central Eastern Desert (CED) in Egypt caused a pronounced strike-slip deformation associated with the displacement along the wider Najd Fault system. The third orogenic phase, which was younger than c. 580 Ma, was controlled by the evolution and retreat of the Cadomian Arc. The northern portions of the ENS and the northern Arabian Shield experienced extension whereas extensive post-orogenic magmatism was related to mantle delamination and associated crustal thinning.

A regional explanation for Laxfordian tectonic evolution and its implications for the Lewisian terrane model

The later Paleoproterozoic (Laxfordian) structural and metamorphic history of the Lewisian Complex can be explained by several major kinematic changes. At c. 1.9 Ga, the neighbouring Archean cratons of Rae, North Atlantic (NAC), Kola and Karelia were isolated from each other and subduction and accretion were active at their margins. At c. 1.85 Ga, during the ‘Early Laxfordian’, the Lewisian, then part of the Nagssugtoqidian orogenic belt, experienced NW–SE-directed tectonic movements attributed to east–west convergence between the Rae Craton and the NAC, probably prompted by collision with Baltica. At c. 1.7 Ga, during the ‘Late Laxfordian’, a major change to north–south convergence produced a combination of NW–SE-trending folds and NW–SE dextral shear zones. The kinematic system changed again after c. 1.6 Ga. The latter two changes may be attributable to the docking of further large cratons as the Nuna supercontinent was assembled. The Lewisian terrane model can be interpreted in terms of the relative movements between two major cratons, Rae and NAC. Sandwiched between them was a third, composed of material partly derived from a juvenile magmatic arc or arcs situated in oceanic crust. The Assynt terrane may be an isolated remnant of the upper-plate NAC, whereas most of the remaining Lewisian outcrop may consist of modified Rae material.

Hungarian health care in the 1930s and 1940s: health care at a crossroads in East Central Europe before World War II

ABSTRACT The relationship between the Horthy era (1920–44) and the communist era shows continuities from a social historical perspective. The paper contributes to the reinterpretation of these relations by examining Hungarian health care in the 1930s and 1940s with a focus on the relationship between international transfers and path dependency in forging health care reforms. The author argues that the achievements communists regarded as inventions of socialism in health care and the welfare state had already been developed in the 1930s and 1940s. It was only because of the strict wartime budget of the early 1940s that these welfare reforms had not been realized. With the help of internal affairs documents, essays on health care, official statistics records in the National Archives of Hungary and the Semmelweis Library and Archives of Medical History as well as press material, Cora demonstrates that, even if communists depicted the interwar period as ‘fascist and imperialist’, the health care system of the so-called ‘productive social policy’ showed continuities. Moreover, social policy makers of the 1930s and early 1940s, such as Béla Johan, Ferenc Keresztes-Fischer and Béla Kovrig also designed welfare and health care reforms for the post-war period by both developing already existing Hungarian programmes and selectively adapting foreign welfare models (American management principles, the Alsace scheme and the Beveridge Plan). The study investigates Hungarian health care in view of the theory of path dependency and the macrohistorical convergence thesis developed by Tomka (on East–West convergence). It is within this framework that the paper addresses the issue of health care transfers to better understand the development of twentieth-century European health care systems by identifying similarities and differences in their development as well as to speculate on the trajectory of various political solutions to social challenges, including health care.

Seismotectonics of the 2017–2018 Songyuan Earthquake Sequence, Northeastern China: Passive Bookshelf Faulting and Block Rotation in the Songliao Basin

AbstractThe high frequency of earthquake clusters generated by pure strike-slip faulting over the past 3 yr (beginning in 2017 in the Songliao basin, northeastern China) has motivated us to consider why lateral strike slip and not extension determines the seismic activity within the Songliao basin. Precise location and characterization of relocated aftershocks, forward modeling of the coseismic displacement field, and Global Positioning System (GPS) monitoring data are combined to detect the possible seismogenic structures of the Songyuan earthquake sequence. The 2017 ML 5.3 aftershock cluster coincided with the northeast-striking Fuyu–Zhaodong fault (FZF), and the 2018 aftershock swarm followed the linear trend (N42°W) of the Songhuajiang fault (SHF). In addition, the forward modeling results indicate that during the earthquakes, right-lateral and left-lateral strike-slip displacements occurred simultaneously along the FZF and SHF, respectively. These two strike-slip faults joined to accommodate the intervening crustal blocks’ asymmetrical east–west convergence and a single northward extrusion. We also utilize 5 yr of GPS data to construct the regional strain-rate map for the basin. The measurements show that right-lateral transform motion along the immense northeast-striking right-lateral strike-slip faults, for example, the Tanlu fault zone and the FZF, impose a northeast-striking simple shear across the Songliao basin. This simple shear not only caused left-lateral movement on the minor northwest-striking left-lateral strike-slip faults such as the SHF but also rotated them ∼14° clockwise into their present orientations. The results of the proposed bookshelf faulting model in which the predominant northeast-striking parallel faults are initiated are consistent with the observed lineament orientations, focal mechanisms, and earthquake distributions. The sharp shift in the subduction direction of the Pacific plate seems to have had a considerable influence on the intracontinental deformation in China, at least throughout northeastern China.

Scenes of Cold War Diplomacy: Romania and the International Theatre Institute, 1956–1969

The article maps Romania’s involvement with the International Theatre Institute during its first decade of membership. The argument revolves around a number of East–West convergence high points such as the 1959 Helsinki Congress or the 1964 Bucharest Symposium. It analyzes the connections developed by Romanian theatre specialists within the framework provided by iti, the specialized networks they helped create and the domestic impact of these interactions. The article examines the multifaceted Romanian involvement with these projects in national and international context. It begins in 1956, Romania’s first participation at the Dramatic Art Festival in Paris, the forerunner of iti’s Theatre of Nations Festival. It closes the arc of the story with the 1969 international symposium on training young theatre directors. The article shows that soon after joining iti ranks, Romanian theatre artist were propelled into the international limelight and were recognized by their Western peers. It advances the idea that East European theatre practitioners had a role in shaping their respective community of knowledge as much as their Western counterparts did.

Subducting an old subduction zone sideways provides insights into what controls plate coupling

The Hikurangi Plateau has had two episodes of subduction beneath New Zealand – firstly at ca. 100 Ma during north–south convergence with Gondwana, and currently during east–west convergence between the Pacific and Australian plates. As a result of this ninety-degree change in convergence direction, an old subduction zone is now being subducted sideways, and the tectonic history of the subducted plate varies dramatically along the strike of the Hikurangi Margin. Here we identify the location of the underplated Hikurangi Plateau along the shallow part of the Hikurangi Margin, using results from both relocated seismicity and seismic tomography. Next we decipher the tectonic history of the plateau along strike, particularly in terms of the hydration state of the plateau, and the nature of any sedimentary rock units capping the plateau. We then use this information to understand plate coupling at two scales: on the large scale, the southward transition from typical subduction in the North Island to continental collision in the South Island; and at a smaller scale, the strong lateral change from a high deficit in slip rate at the plate interface in the southern North Island to a low deficit in slip rate in the northeastern North Island. We find that the southward transition from subduction to continental collision is controlled by the plateau being more dehydrated to the south, as a result of being more deeply subducted at the Gondwana margin. The southward transition from localized slip at the plate interface to distributed upper plate deformation with no active plate interface occurs in Cook Strait and is relatively sharp. The high deficit in slip rate at the plate interface in the southern North Island is likely due to a relatively smooth plate interface from sedimentary rocks capping the Hikurangi Plateau, an impermeable terrane in the overlying plate, and the hydrated plateau acting in concert to produce an interseismically sealed plate interface. Further northeast where the slip rate deficit at the plate interface is low, the plate interface has a rough topography (including seamounts), there is no impermeable terrane in the overlying plate, and fluid from the dehydrating plateau migrates across the plate interface.

Mechanism of a torrential rainstorm that occurred to the west of a Mei-yu frontal low

Heavy rainfall usually occurs to the southeast of a Mei-yu frontal low. The rainstorms appeared to the west of Mei-yu frontal lows are difficult to forecast because their formation mechanisms are not well understood. An extreme rainfall event occurred to the west of a Mei-yu frontal low in Anqing City, Anhui Province, China, on 13 July 2010, which was not well predicted. Based on observation data, NCEP/NCAR reanalysis data and high-resolution numerical simulation output, the mechanisms of this severe rainstorm are analyzed in this paper. The results indicate that the eastward moving meso-α-scale low was a key synoptic system that resulted in the formation of the mesoscale convective system causing the rainstorm. As the low moved eastward and strengthened, the increasing northerly flow and the southerly warm/moist flow formed an eastwest elongated convergence line (frontal zone) at the west part of the low. While the low moved to the coastal region, its intensity was enhanced and its moving speed was reduced. As a result, the convergence line and the frontal zone remained quasi-stationary near Anqing. Furthermore, Anqing is located in a valley between the Dabie and Wannan Mountains; the northerly winds flowed around Dabie Mountains and entered the valley, leading to an intense local convergence and frontogenesis near Anqing. Under the unstable environments with sufficient water vapor, the local intense frontogenesis along with intense convergence triggered and maintained the quasi-stationary mesoscale convective system that resulted in the record-breaking rainfall in Anqing.

Complex, 3D strain patterns in a synkinematic tonalite batholith from the Araçuaí Neoproterozoic orogen (Eastern Brazil): Evidence from combined magnetic and isotopic chronology studies

This work combines structural and geochronological data to improve our understanding of the mechanical behaviour of continental crust involving large amount of magma or partially melted material in an abnormally hot collisional belt. We performed a magnetic and geochronological (U/Pb) study on a huge tonalitic batholith from the Neoproterozoic Araçuaí belt of East Brazil to determine the strain distribution through space and time. Anisotropy of magnetic susceptibility, combined with rock magnetism investigations, supports that the magnetic fabric is a good proxy of the structural fabric. Field measurements together with the magnetic fabrics highlight the presence in the batholith of four domains characterized by contrasted magmatic flow patterns. The western part is characterized by a gently dipping, orogen-parallel (∼NS) magmatic foliation that bears down-dip lineations, in agreement with westward thrusting onto the São Francisco craton. Eastward, the magmatic foliation progressively turns sub-vertical with a lineation that flips from sub-horizontal to sub-vertical over short distances. This latter domain involves an elongated corridor in which the magmatic foliation is sub-horizontal and bears an orogen-parallel lineation. Finally the fourth, narrow domain displays sub-horizontal lineations on a sub-vertical magmatic foliation oblique (∼N150°E) to the trend of the belt.U/Pb dating of zircons from the various domains revealed homogeneity in age for all samples. This, together with the lack of solid-state deformation suggests that: 1) the whole batholith emplaced during a magmatic event at ∼580 Ma, 2) the deformation occurred before complete solidification, and 3) the various fabrics are roughly contemporaneous.The complex structural pattern mapped in the studied tonalitic batholith suggests a 3D deformation of a slowly cooling, large magmatic body and its country rock. We suggest that the development of the observed 3D flow field was promoted by the low viscosity of the middle crust that turned gravitational force as an active tectonic force combining with the East-West convergence between the São Francisco and Congo cratons.

Interne Migration, regionale Arbeitsmarktdynamik und Implikationen für Ost-West-Disparitäten: Ergebnisse auf Basis einer Panel VAR Analyse

This paper analyses the causal linkages between regional labour market variables and internal migration flows among German states between 1991–2006. We adopt a Panel VAR approach to identify the feedback effects among the variables and analyse the dynamic properties of the system through impulse-response functions. We also use the model to track the evolution of the particular East-West migration since re-unification aiming to shed more light on the East German ‘empirical puzzle’, characterized by lower migration responses than expected from the regional labour market position relative to the West. Indeed we get evidence for such a puzzle throughout the mid-1990s, which is likely to be caused by huge West-East income transfers, a fast exogenously driven wage convergence and the possibility of East-West commuting. However, we also observe an inversion of this relationship for later periods: That is, along with a second wave of East-West movements around 2001 net flows out of East Germany were much higher than expected after controlling for its weak labour market and macroeconomic performance. Since this second wave is also accompanied by a gradual fading out of economic distortions and a downward adjustment of expectations about the speed of East-West convergence in standard of livings, this supports the view of ‘repressed’ migration flows for that period.

Viscoelastic-cycle model of interseismic deformation in the northwestern United States

SUMMARY We apply a viscoelastic cycle model to a compilation of GPS velocity fields in order to address the kinematics of deformation in the northwestern United States. A viscoelastic cycle model accounts for time-dependent deformation following large crustal earthquakes and is an alternative to block models for explaining the interseismic crustal velocity field. Building on the approach taken in Pollitz et al., we construct a deformation model for the entire western United States—based on combined fault slip and distributed deformation—and focus on the implications for the Mendocino triple junction (MTJ), Cascadia megathrust, and western Washington. We find significant partitioning between strike-slip and dip-slip motion near the MTJ as the tectonic environment shifts from northwest-directed shear along the San Andreas fault system to east–west convergence along the Juan de Fuca Plate. By better accounting for the budget of aseismic and seismic slip along the Cascadia subduction interface in conjunction with an assumed rheology, we revise a previous model of slip for the M∼ 9 1700 Cascadia earthquake. In western Washington, we infer slip rates on a number of strike-slip and dip-slip faults that accommodate northward convergence of the Oregon Coast block and northwestward convergence of the Juan de Fuca Plate. Lateral variations in first order mechanical properties (e.g. mantle viscosity, vertically averaged rigidity) explain, to a large extent, crustal strain that cannot be rationalized with cyclic deformation on a laterally homogeneous viscoelastic structure. Our analysis also shows that present crustal deformation measurements, particularly with the addition of the Plate Boundary Observatory, can constrain such lateral variations.

Economic ‘Clusters’ in East Germany: Evidence on the Location and Characteristics of Spatially Concentrated Industries

This article presents the results of an empirical study on spatially concentrated industries (SCI) with ‘cluster’ qualities in the eastern part of Germany which have emerged so far in the process of transformation. The findings reveal that SCI in East Germany which show ‘cluster’ qualities, i.e. SCI being supported by network activities and by innovative competences, are relatively rare, and they are strongly concentrated in agglomerated spaces. As the regional policy scheme which up to now has followed the ‘watering can principle’ has brought, so far, only poor results in terms of East–West convergence, a renewed policy with a special focus on agglomerated spaces (with more favourable conditions for economic growth) and with a stronger orientation on support for networking and innovative competences will probably be more effective in stimulating economic growth in East Germany.

Distinct wind convergence patterns in the Mexico City basin due to the interaction of the gap winds with the synoptic flow

Abstract. Mexico City lies in a high altitude basin where air quality and pollutant fate is strongly influenced by local winds. The combination of high terrain with weak synoptic forcing leads to weak and variable winds with complex circulation patterns. A gap wind entering the basin in the afternoon leads to very different wind convergence lines over the city depending on the meteorological conditions. Surface and upper-air meteorological observations are analysed during the MCMA-2003 field campaign to establish the meteorological conditions and obtain an index of the strength and timing of the gap wind. A mesoscale meteorological model (MM5) is used in combination with high-resolution satellite data for the land surface parameters and soil moisture maps derived from diurnal ground temperature range. A simple method to map the lines of wind convergence both in the basin and on the regional scale is used to show the different convergence patterns according to episode types. The gap wind is found to occur on most days of the campaign and is the result of a temperature gradient across the southern basin rim which is very similar from day to day. Momentum mixing from winds aloft into the surface layer is much more variable and can determine both the strength of the flow and the pattern of the convergence zones. Northerly flows aloft lead to a weak jet with an east-west convergence line that progresses northwards in the late afternoon and early evening. Westerlies aloft lead to both stronger gap flows due to channelling and winds over the southern and western basin rim. This results in a north-south convergence line through the middle of the basin starting in the early afternoon. Improved understanding of basin meteorology will lead to better air quality forecasts for the city and better understanding of the chemical regimes in the urban atmosphere.

Miocene sedimentation and subsidence during continent–continent collision, Bengal basin, Bangladesh

The Bengal basin, a complex foreland basin south of the eastern Himalayas, exhibits dramatic variability in Neogene sediment thickness that reflects a complicated depositional and tectonic history. This basin originally formed as a trailing margin SE of the Indian continental crust, complicated by convergence with Asia to the north and oblique convergence with Burma to the east. Newly compiled isopach data and previously reported seismic data show evidence of thickening of basin fill toward the south, opposite of the pattern typically seen in foreland basins. This is presumably due to sedimentary loading of voluminous deltaic sediments near the continent–ocean boundary and basinward downfaulting analogous to that in the Gulf of Mexico. Isopach data show that there is considerable vertical relief along the base of the Miocene stratigraphic sequence, probably due to down-to-the-basin faulting caused by focused deltaic sedimentation and associated crustal flexure. In contrast, when viewed in east–west profile, basin shape is more typical of a foreland basin, with strata thickening eastward toward the Indo–Burman ranges, which reflects east–west convergence with Southeast Asia. Comparison of the lateral and vertical extent of the Bhuban and Boka Bil Formations with the Bouguer anomaly map of Bangladesh suggests that considerable subsidence of the Sylhet trough (in the northeastern part of the Bengal basin), which has the lowest gravity value of the region, had not taken place by the end of the Miocene. This post-Miocene subsidence is attributed to tectonic loading from southward thrusting of the Shillong Plateau along the Dauki fault. Relatively uniform Miocene isopachs across the Sylhet trough confirm that this began in the Pliocene, consistent with results of recent research on sediment provenance. In the northwest, in the region south of the Siwalik foreland basin, continental crust has not as yet been loaded, allowing relatively little accommodation space for sediment accumulation. The Miocene here is very thin. Deltaic progradation across most of Bangladesh during the Miocene followed earlier, more proximal progradation across Assam, immediately northeast of the Bengal basin, and has been followed by continued progradation into the southern Bangladesh coastal and offshore region.

NOVAS OCORRÊNCIAS DE URÂNIO NA REGIÃO DE LAGOA REAL, A PARTIR DA SUPERPOSIÇÃO DE DADOS GEOFÍSICOS, GEOLÓGICOS E DE SENSORIAMENTO REMOTO

The origin and control of Uranium occurrences and deposits at the Uraniferous District of Lagoa Real, State of Bahia (Brazil), has been largely studied over the last decades. Currently, the deposit controls are bounded to albitites in the Granite-Gneissic Complex at the center-south area of Lagoa Real. Data from the Sao Timoteo Airborne Geophysical Project have been analyzed and superimposed to geological, geophysical and remote sensing data in order to identify new occurrences of Uranium for prospection. Reappraisal of the gammaspectrometric data (K, U e Th) shows that distinctive litotypes indicate some radiometric anomalies in the northeast area. The magnetometric data suggest the existence of depth-rooted magnetic blocks separated by shear zones recognized by the Landsat-5TM’s image. The combination of these products with the geological information shows a structural evolution not previously described in literature. The kinematics of the shear zones with NS, NE-SW and NE-SW directions was established based on bodies´ displacement and magnetic features. The ductile-ruptile, ruptileductile and ruptile structures are compatible with the geological framework of the Sao Francisco Craton during the Brazilian Cicle: East-West convergence with West mass transport. The continuing deformation produced dextral and sinistral shear zones that resulted in the inflection of the pre-existent foliation. The well-known Uranium deposits are located in the N-S shear zones; the new occurrences, located in the northeastern area, are associated with the NW-SE shear zones and they introduce new targets for prospection.

Post-amalgamation basins of the NE Arabian shield and implications for Neoproterozoic III tectonism in the northern East African orogen

Abstract The development and structure of Neoproterozoic III volcanosedimentary basins in the northeastern part of the Arabian shield record periods of uplift, erosion, extension, subsidence, compression, and strike-slip faulting that postdated the completion of terrane amalgamation in the northern East African orogen (EAO) and predated the initiation of a passive margin on the northern flank of the Gondwana supercontinent. The oldest basins, dating from 650 Ma, include as much as 8000 m sandstone, conglomerate, bimodal volcanic rocks, and limestone, and were deposited in a large area (approximately 72,000 km 2 ) of locally fault-controlled subsidence (Murdama basin) and in narrow grabens (Bani Ghayy basins). The regional unconformity at the base of the basins bevels the newly amalgamated terranes and exposes greenschist-, and locally amphibolite-, and granulite-grade metamorphic rocks, indicating possibly >10 km uplift and erosion in parts of the region prior to deposition. The basins were closed and inverted by folding at about 650 Ma and unconformably overlain by rocks of the Jurdhawiyah group and Hibshi formation, which were deposited between 640 and 620 Ma in fault-controlled basins following a further phase of uplift and erosion. The Jurdhawiyah and Hibshi basins closed and inverted during subsequent north–south shortening and north- and south-vergent reverse faulting. A final phase of Neoproterozoic III basin formation resulted in deposition of the Jibalah group (580–570 Ma) in small, isolated, pull-apart basins caused by strike- and dip-slip movements on faults of the Najd fault system. The Murdama and Bani Ghayy basins contain shallow-marine clastic and carbonate deposits indicating that seaways penetrated the core of the EAO soon after terrane amalgamation, which implies that much of the region was at a low elevation soon after terrane amalgamation and orogeny. This limits the extent to which gravity-driven extensional collapse may have been a factor in the Neoproterozoic III tectonic evolution of the region, unlike other parts of the EAO where orogenic extensional collapse was significant. The Jurdhawiyah, Hibshi, and Jibalah basins were probably isolated fault-controlled lakes. The northerly trend of Murdama and Bani Ghayy folds implies bulk east–west shortening, which is consistent with the model of east–west Gondwana convergence conventionally applied to the EAO. East–west convergence conceivably accounts, additionally, for the creation of the Jurdhawiyah and Hibshi basins as a result of concomitant northward extension or tectonic escape. It would also account for the simultaneous creation of the Murdama and Bani Ghayy basins, themselves, linking the two as foreland basins at subsided and extended parts of a newly amalgamated crust in the center of the study area that was downflexed by the overthrusting of an ophiolite complex and other terranes from the east.

Finite strain pattern in Andriamena unit (north-central Madagascar): evidence for late Neoproterozoic–Cambrian thrusting during continental convergence

This paper deals with the late Neoproterozoic–Cambrian tectonic evolution of a part of north-central Madagascar, which is characterized by the occurrence of a mafic-ultramafic sequence (the Andriamena unit) overlying a gneissic-granitic basement. The finite strain pattern has been determined by carrying out a SPOT satellite image analysis, structural mapping of specific areas and kinematic analyses of shear zones. Structural investigations reveal the presence of two superposed finite strain patterns, D1 and D2. The D1 event is related to the emplacement of the Andriamena unit on the top of the gneissic-granitic basement. The western contact between these units is a major mylonitic zone characterized by a non-coaxial strain regime consistent with a top-to-east displacement. We suggest that the Andriamena unit originated as a lower crustal fragment of a middle Neoproterozoic continental magmatic arc related to the closure of the Mozambique Ocean. This fragment was thrusted onto the gneissic-granitic basement after 630 Ma, i.e. the age of emplacement of characteristic stratoid granites found only in the lower unit. The D2 event is related to east-west horizontal shortening mainly accommodated by F2 upright folds. In-situ electron microprobe dating of monazites from the Andriamena unit constrains the age of the D1 and D2 events between 530 and 500 Ma under amphibolite to granulite-facies conditions (5–7 kbar, 650–700 °C). The eastward thrust emplacement of the Andriamena unit (D1) followed by the horizontal shortening (D2) are ascribed to the same Cambrian tectonic regime (i.e. east-west convergence). Such D1–D2 bulk strain pattern has been recognized throughout Madagascar and at various structural levels of the crust: in the lower crust in Southern Madagascar and in the uppermost crustal level in the SQC unit (central Madagascar). The D1–D2 event is interpreted to result from the continental convergence of the Australia–Antarctica block and the Madagascar, India, Sri Lanka block during the final amalgamation of Gondwana.

Structure of the Nagavali Shear Zone, Eastern Ghats Mobile Belt, India: Correlation in the East Gondwana Reconstruction

Interpretation of satellite data in combination with regional field traverses, delineating the major structural features such as the Nagavali and Vamsadhara Shear Zones and associated fold patterns, provides a synoptic picture of the regional tectonic framework of the central part of the Eastern Ghats Mobile Belt. The complex geology of the study area can broadly be grouped into three distinct deformational events. D 1 fabrics represented by near flat-lying gneissic foliations, paralleling the lithological banding are best preserved in low strain domains and are related to Middle to late Archaean thrusting (3000-2600 Ma). The second deformational event D 2 is characterized by the development of shear zones and associated mylonitic fabrics and magmatism probably during 1450-850 Ma. The Pan-African thermal (500-550 Ma) overprint is restricted to shear zones in the form of reworking. Regionally, the central part of the Eastern Ghats Mobile Belt can be divided into five distinct structural domains based on structural geometry of folds, foliations and lineations. A three-dimensional block diagram of the Nagavali and Vamsadhara Shear Zones involving fold-thrust tectonics associated with westward thrusting is presented here. A correlation of Pan-African Shear Zones in adjacent continents wrapping around the Archaean Dharwar Craton in the reconstruction of Rodinia and East Gondwana supercontinent suggests an east-west convergence.

Dynamic causes for the opening of the Baikal Rift Zone: a numerical modelling approach

Previous dynamic models of the Baikal Rift Zone (BRZ) are mostly two-dimensional on vertical plane. In this study, a numerical model of neotectonics in the region on map view was constructed using the adapted PLATES program. The present work is an attempt to test different mechanisms for opening Baikal Rift by comparing the modelled and observed stress and strain rate fields. The following rifting scenarios were tested: (1) pure northwest–southeast extension, (2) pure northeast–southwest compression, (3) oblique rift opening and (4) combined northwest–southeast extension and northeast–southwest compression. The models are calibrated using geologically and GPS-derived strain rates and stress-tensor determinations from fault-slip data and earthquake focal mechanisms. The most successful model requires a combination of NE–SW compression and orthogonal extension. The model results indicate that the present extensional regime in BRZ can be explained by combining the India plate indentation northward into Eurasia, east–west convergence between the North America and Eurasia plates and southeastward extrusion of the Amur plate in northeastern Asia. Predicted fault-slip rates for the best-fit model are consistent with the observed Holocene fault-slip rates in the Lake Baikal region. The generally accepted rotation of the Amur and Mongolia microplates are used as independent constraints for the choice of the best-fit model. These data correlate well with the predicted direction of rotation in our best model.

Dioxin in Vietnam: Fighting a Legacy of War

Singapore was the site of an East-West convergence over the week of 27 November-1 December 2000. At the behest of their respective governments, scientists from the United States and Vietnam came together for what promises to be the first of many meetings. Their mission: to explore the possibility of launching a joint research program to study the human and environmental health effects resulting from spraying Agent Orange and other herbicides during the Vietnam War.

Dioxin in Vietnam: fighting a legacy of war.

Singapore was the site of an East-West convergence over the week of 27 November-1 December 2000. At the behest of their respective governments, scientists from the United States and Vietnam came together for what promises to be the first of many meetings. Their mission: to explore the possibility of launching a joint research program to study the human and environmental health effects resulting from spraying Agent Orange and other herbicides during the Vietnam War.