Geodetic control on recent tectonic movements in the central Mediterranean area

During the Neogene and Quaternary, the western Mediterranean geodynamics was apparently dominated by the nearly eastward migration of the Apenninic arc and the associated opening (spreading) of the back-arc basin (Tyrrhenian Sea). However, during the last 5 My, the collision of the arc with the Apulian platform led to a dramatic change in the tectonic setting of the area. As geological processes require a long period of time to register the displacements of the different blocks, it is indispensable to take into account the present-day motion given by space geodesy data analysis in order to better constrain the geological models.Geodetic motions were derived from Global Positioning System (GPS), Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI) observations collected from different networks. All the geodetic solutions have been computed and combined at the Centre of Space Geodesy (CGS), at Matera, Italy.The geodetic results show a NNE motion of the Adriatic plate with a small component of counter-clockwise rotation, in good agreement with the geological and geophysical observations.In the southern Tyrrhenian area, the lengthening of the Matera–Cagliari baseline should imply that convergence cannot be considered as the driving mechanism for the Apenninic subduction process. The estimated motion of Noto is in quite good agreement with the estimated motion of the African plate.     

The petrology of the Ditrau alkaline complex, Eastern Carpathians

Summary ?The Ditrau complex in eastern Transsylvania, Romania is a large (ca. 18 km diameter) Mesozoic alkaline igneous complex generated in an extensional environment associated with a rifted continental margin. It comprises an eccentric arcuate suite of intrusions in which there was a generalised migration of focus from west to east. Whereas most of the complex consists of salic rocks (syenites, nepheline syenites and alkali granites) a spectrum of intermediate rock types (monzonites, monzodiorites and alkali diorites) grades to alkali gabbros. Isolated masses of ultramafic rocks may represent autoliths derived from early cumulates. The earliest components appear to be the ultramafic, gabbroic and dioritic rocks of the north-west whereas the large area of nepheline syenites in the east of the complex represents the youngest large-scale intrusive event. An interval of dyke intrusion and widespread hydrothermal alteration marked the end of activity. Rocks of contrasted composition commonly show intricate and complex geometric relationships. Those between mafic (especially alkali gabbroic and dioritic) facies and salic (syenite and quartz syenite) facies display pillowy forms suggesting synchronous emplacement of mafic and salic magmas with the former intruded into, and chilled against, the latter. Mixing, mingling and hybridisation in these pillowed associations has been widespread. Olivine is confined to some of the ultramafic rocks. The basic rocks contain diopsidic pyroxene and amphibole ranging from kaersutite through ferroan pargasite to hastingsite although edenitic and actinolitic varieties occur. Titanite is ubiquitous and is a major component in some facies of the basic rocks. The syenites consist of sodic plagioclase, alkali feldspar and hastingsite whereas the nepheline syenites comprise alkali feldspar, nepheline and aegirine-augite with accessory cancrinite, scapolite and sodalite. The complex is deduced to have been generated from primitive basanitic magmas, formed as small-fraction asthenospheric melts, with progressive evolution through to phonolitic residues. Fractional crystallisation is inferred to have involved olivine and spinel in the early stages, followed by the incoming of clinopyroxene and amphibole (with loss of olivine in increasingly hydrous residual melts). A generalised increase in Nb/Ta from basic to nepheline syenite compositions is ascribed to titanite fractionation. The divergence towards silica oversaturated products is attributed to crustal assimilation and concomitant fractional crystallisation of the basic magmas at a relatively early stage in the development of the complex. An overall rise in δ¹⁸O with increasing SiO₂ supports this conclusion. Evidence from the broad metamorphic aureole around the complex, the importance of amphiboles and extensive late-stage alteration of many of the rocks (with formation of e.g. scapolite, sodalite and cancrinite), suggests that the Ditrau magmas were notably volatile-rich. Factors responsible for the upwardly concave (chondrite-normalised) REE patterns exhibited by the salic rocks may include fractionation of minerals (kaersuite, titanite, apatite) preferentially removing MREE, accumulation of HREE-rich phases (zircon) and interaction with late-stage fluids enriched in HREE. The intrusive sequence and the inter-relationships of the basic and salic rocks suggest that stratified magma bodies may have been generated, with salic melts overlying denser basaltic melts. Mixing is inferred to have taken place during subsequent emplacement.

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Zusammenfassung ?Petrologie des Alkali-Komplexes von Ditrau in den Ost-Karpaten Der Ditrau-Komplex im ?stlichen Transsylvanien, Rum?nien, ist ein gro?er (ca. 18 km Durchmesser) mesozoischer Alkali-Komplex, der in einem extensionalen Umfeld im Zusammenhang mit dem Aufbrechen eines Kontinentalrandes entstanden ist. Es liegt eine bogenf?rmige, exzentrische Gruppe von Intrusionen vor, innerhalb derer der Fokus von West nach Ost gewandert ist. W?hrend der Gro?teil des Komplexes aus salischen Gesteinen (Syeniten, Nephelin-Syeniten und Alkali Graniten) besteht, liegen auch intermedi?re Gesteine (Monzonite, Monzodiorite und Alkali Diorite) vor, die in Alkaligabbros übergehen. Isolierte Massen von ultramafischen Gesteinen k?nnten Autolithe, die aus frühen Kumulaten abstammen, darstellen. Die ?ltesten Komponenten scheinen die ultramafischen, gabbroischen und dioritischen Gesteine des Nordwestens zu sein, w?hrend das gro?e Gebiet von Nephelin-Syeniten im Osten des Komplexes das jüngste Intrusionsstadium darstellt. Ein Intervall mit Gang-Intrusion und verbreiteter hydrothermaler Umwandlung markiert das Ende dieser Aktivit?t. Gesteine von gegens?tzlicher Zusammensetzung zeigen h?ufig komplizierte geometrische Beziehungen. Diejenigen zwischen mafischen (besondern alkaligabbroischen und dioritischen) Typen und salischen (Syeniten und Quarz-Syeniten) zeigen polsterartige Formen, die auf m?glicherweise gleichzeitige Platznahme von mafischen und salischen Magmen hinweisen; dabei dürften die ersteren die letzteren intrudiert haben. Mischung, Mingling und Hybridisation ist in diesen polsterf?rmigen Assoziationen weit verbreitet. Olivin ist auf einige der ultramafischen Gesteine beschr?nkt. Die basischen Gesteine enthalten diopsidischen Pyroxen und Amphibole, die von Kaersutit über “ferroan” Pargasit zu Hastingsit übergehen, obwohl auch edenitische und aktinolitische Variet?ten vorkommen. Titanit ist weit verbreitet und eine Hauptkomponente in einigen Typen der basischen Gesteine. Die Syenite bestehen aus sodischem Plagioklas, Alkali-Feldspat und Hastingsit, w?hrend Nephelin-Syenite, Alkali-Feldspat, Nephelin und Aeginin-Augit mit akzessorischem Cancrinit, Skapolith und Sodalit umfassen. Der Ditrau-Komplex dürfte aus primitiven basanitischen Magmen entstanden sein, die sich als “small-fraction” asthenosph?rischer Schmelzen bildeten, mit progressiver Evolution bis hin zu phonolitischen Residuen. Fraktionierte Kristallisation dürfte Olivin und Spinell in den Frühstadien betroffen haben, gefolgt vom Auftreten des Klinopyroxen und Amphibol (wobei Olivin in den zunehmend wasserreichen Restschmelzen verlorengeht). Eine allgemeine Zunahme in Nb/Ta von basischen zu nephelinsyenitischen Zusammensetzungen wird auf Titanit-Fraktionierung zurückgeführt. Die Entwicklung in Richtung Silika-übers?ttigter Produkte geht auf krustale Assimilation und fraktionelle Kristallisation des basischen Magmas in einem relativ frühen Stadium der Entwicklung des Komplexes zurück. Ein allgemeiner Anstieg in δ¹⁸O mit zunehmendem SiO₂ unterstützt diese Schlu?folgerung. Daten aus der breiten metamorphen Aureole des Komplexes, die Bedeutung der Amphibole und extensive Alteration im Sp?tstadium der Entwicklung vieler Gesteine (mit Bildung von Skapolith, Soldalit und Cancrinit) weist darauf hin, dass die Ditrau-Magmen sehr reich an volatilen Phasen waren. Die nach oben zu konkaven (Chondrit-normalisierten) SEE-Verteilungsmuster in den salischen Gesteinen dürften auf Mineralfraktionierung (Kaersuit, Titanit, Apatit) die vorzugsweise MSEE entfernt hat, Ansammlung von HSEE-reichen Phasen (Zirkon) und Wechselwirkungen mit sp?ten Fluiden, die an HSEE angereichert waren, zurückgehen. Die intrusive Abfolge und die Wechselbeziehungen zwischen den basischen und salischen Gesteinen legt nahe, dass geschichtete Magmenk?rper entstanden sind, wobei salische Schmelzen die dichteren basaltischen Schmelzen überlagert haben. W?hrend der darauf folgenden Platznahme dürfte Magmamixing stattgefunden haben.

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Received October 20, 1998;/revised version accepted July 16, 1999     

Late Holocene tectonic movements at Akhziv,Mediterranean coastline of northern Israel

The recent discovery of a post-Roman-aged marine calcarenite terrace, at an altitude of 7 to 8 m at the ancient harbor of Akhziv, supports the hypothesis of oscillatory tectonic movements along the coastline of Israel during the late Holocene. The marine to estuarine origin of this terrace is indicated by the presence within it of a biocoenosic, sea-marginal to estuarine, assemblage of well-preserved molluscs consisting of taxa tolerating brackish-water, together with a few fresh-water specimens. The transgressive marine sediments onlap and overlie a 2700-yr-old middle Iron Age (Phoenician) tomb, which was built on a dark clay layer, containing a middle Bronze HB (3750 yr B.P.) settlement. In post-Roman times the coastal zone at this site, both east and west of the present coastline, was first subjected to tectonic subsidence of a few meters, and was then tectonically uplifted to its present altitude.     

New results on the properties of recent crustal movements in the Bohemian Massif and its boundary with the West Carpathians

Preliminary analysis of the new results of repeated levellings within the territory of the Bohemian Massif and its border with the Carpathians is made, and the correlation between horizontal gradients of vertical movements and main fault zones discussed. The results indicated the continuance of the main movement's tendencies, determined by the foregoing measurements. Also discussed are the vertical and horizontal crustal movements between the Bohemian Massif and the Carpathians. The active zones are connected with the main fault systems, and the horizontal movements indicated the spreading tendencies between both geological structures. These results are in accord with the tendencies of horizontal movements in the Soviet Carpathians.     

Biodegradation and migrational fractionation of oils from the Eastern Carpathians, Poland

Nineteen oil samples from Silesian Unit of the eastern Carpathian Overthrust have been characterised geochemically in order to determine the causes of compositional differences among them and elucidating the processes responsible for their differences. Some of analysed crude oils have undergone post-emplacement alteration in the reservoir such as biodegradation and evaporative fractionation. This explains much of the chemical and physical properties variability across individual fields from one tectonic unit. Geochemical correlation based on biomarker distributions showed a close relationship between all oils (included biodegraded oils). However, data based on the whole oil GC analysis of selected oils suggest that the process of evaporative fractionation may change the composition of lower molecular weight hydrocarbons of the oils in this region. This paper outlines the probable mechanisms for oil mixing in the region and describes how this can lead to observable lateral differences in the composition of oils.     

Monitoring tectonic movements in the Simitli Graben, SW Bulgaria

Long-term in situ monitoring of slow tectonic movements has been applied to a seismoactive region of SW Bulgaria, within the epicentral zone of one of the strongest earthquakes in Europe (4 April 1904, M=7.8). The region has been found the most seismoactive in Bulgaria being of interest to many scientists. Three spatial extensometers were installed here in carefully selected sites to reflect fault movements on fissures. The extensometer TM-71 used here, enables three-dimensional detecting of even very slow movements with the accuracy of 0.01 mm and high stability over time. After 17 years of measuring, the rates of tectonic movements were established at all three monitoring points. Movements recorded at point B6 located in the seismoactive Kroupnik fault zone are of a relatively high rate. Locally, they show left-lateral strike–slips at rates of ca. 2.7 mm year⁻¹, as well as thrusting with a mean rate of 1.9 mm year⁻¹. Monitoring point K7 located in a fissure of the same zone on a steep slope affected by recent earthquakes has shown an uplift tendency of the block W of the Strouma Fault, with a result of gradual slope subsidence occurring from time to time. Monitoring point K5 located in a fissure of Strouma Fault zone became increasingly active during the last 2 years after 8 years of relative quiescence. Before that, only low left-lateral movements could be observed. Long-term fissure monitoring has shown quite a number of details interpretable to the dynamics of a broad region. Permanent shear displacements were found to develop after earthquakes. It was established that only a certain distinct part of local earthquakes provide such a displacement reaction at the monitoring points showing particular seismic connections.     

Example of Neogene tectonic indentation in the Eastern Betic Cordilleras: the Arc of Aguilas (Southeastern Spain)

Abstract

Neogene deformations have deeply disturbed the initial architecture of the pile of nappes within the Eastern Betic zone. The Arc of Aguilas, displaying a southeast-facing concavity, is a spectacular example of such a post-nappe structuration. Miocene deposits involved in the torsion of the Arc provide a chronology of the deformation. The Arc of Aguilas is one element within a system of rigid-plastic indentation including the following units, from the inner (SE) to the outer (NW) zones : — A rigid block, little deformed, located in the present day abyssal plain, play the part of the indenter.

— A structural pad corresponding to the Aguilas Arc itself. It was severely folded during Miocene times.

— A large peripheral zone mainly subjected to faulting during the Neogene (essentially strike-slip faults). These faults control the evolution of different types of sedimentary basins during the Late Neogene (Tortonian to Pliocene).

Two large shear zones: N020 sinistral (Palomares and Terreros faults), N100 dextral (Las Moreras faults) guided the deformation of the Aguilas Arc within a compressive stressfield of which major tensor axis oscillated between NW-SE and N-S.     

Late Quaternary vegetation reconstruction from the Eastern Arc Mountains, Tanzania

Pollen, spore, macrofossil and stable isotope (C and N) analyses from a 266-cm sediment core collected from a swamp on the Eastern Arc Mountains, Tanzania, are used to reconstruct vegetation and environmental history. An estimated time scale based on five ¹⁴C ages records approximately 38,000 yr. This palaeorecord is the first from this biodiversity hotspot and importantly extends through the last glacial maximum (LGM). The altitudinal transition from montane to upper montane forest shifted from 1700-1800 m (38,000 ¹⁴C yr BP) to 1800-1900 m (35,000-29,000 ¹⁴C yr BP). From 29,000 to 10,000 ¹⁴C yr BP, it shifted from 1850-1950 m across the LGM to 1750-1800 m (during 10,000-3500 ¹⁴C yr BP), and to present-day elevations at 2000 m during the last 3500 ¹⁴C yr BP. The relative ecosystem stability across the LGM may be explained by the Indian Ocean's influence in maintaining continuous moist forest cover during a period of East African regional climate aridity. During the late Holocene, presence of abundant coprophilous fungi and algal blooms demonstrates increasing human impact. Neurospora spores indicate frequent fires, coinciding with clear signals of decline in Podocarpus and Psychotria trees that possibly represent selective logging.     

Calcite from the Quaternary spring waters at Tylicz, Krynica, Polish Carpathians

At Tylicz, near Krynica Spa (Polish Carpathians), spelean deposits fill fissures and caverns in Eocene flysch rocks. They occur as: (1) clastic cave sediments transformed into hard crusts due to cementation by finely crystalline low-Mg calcite, (2) drusy calcite that covers crust surfaces and fills voids in the crust and (3) colloform calcite. Two varieties of drusy calcite are distinguished: acicular and columnar. The acicular calcite is built up of crystallites forming spherulitic fans or cones. In places it is syntaxially covered with colloform calcite. The drusy calcite is low-Mg ferroan calcite with non-ferroan subzones, whereas the colloform calcite is a low-Mg non-ferroan variety. The columnar calcite crystals form fan-like bundles. Cross-sections cut perpendicular to the c-axes of columnar crystals are equilateral triangular in shape, although some have slightly curved edges. The columnar crystals have steep rhombic terminations and most have curved triangular faces, i.e. gothic-arch calcite. Saddle crystals have also been observed. The columnar crystals are composed of radially orientated crystallites whose long dimension is parallel to the c-axis. The curved crystal faces of such polycrystals are interpreted as a result of differential growth rates of the crystallites. The spelean calcites precipitated from CO₂-saturated water. The high rate of CaCO₃ precipitation is thought to be responsible for the formation of radial structures. Finely crystalline calcite formed within pore spaces of clastic sediments close to the water-air interface, drusy calcite crystallized beneath the water-air interface, and colloform calcite precipitated from thin films of water.     

东天山觉罗塔格红云滩花岗岩年代学、地球化学及其构造意义

东天山觉罗塔格地区广泛发育的晚古生代岩浆岩及相关的矿产一直是东天山大地构造研究的焦点。觉罗塔格南缘红云滩花岗质岩体的岩石、矿物组合显示典型的钙碱性火山弧花岗岩特征。岩石地球化学研究表明,该花岗质岩石富集大离子亲石元素而亏损高场强元素,是洋壳俯冲所导致的下地壳物质部分熔融、岩浆分离结晶和上地壳同化混染作用的产物。LAM-ICP/MS锆石定年结果表明,红云滩花岗岩侵位于早-中石炭世(328．5±9．3Ma)。结合觉罗塔格地区由南至北,晚古生代矿产分布由火山沉积-热液改造型铁矿向斑岩型铜钼矿过渡的特征、火山-沉积岩分布和该区晚古生代的大地构造演化历史,作者推测:早古生代觉罗塔格洋向塔里木板块俯冲并形成中天山岛弧之后,该洋盆并未完全消亡,并于晚古生代时极性反转,向北俯冲于准-吐-哈地块之下。红云滩花岗岩正是形成于晚古生代觉罗塔格俯冲洋壳之上的火山弧环境。觉罗塔格地区晚古生代的岩浆岩,火山-沉积岩和矿产分布均不同程度受控于这一大地构造背景。     

Tectonic vs. gravitational morphostructures in the central Eastern Alps (Italy): Constraints on the recent evolution of the mountain range

Deep-seated gravitational slope deformations (DSGSDs) influence landscape development in tectonically active mountain ranges. Nevertheless, the relationships among tectonics, DSGSDs, and topography are poorly known. In this paper, the distribution of DSGSDs and their relationships with tectonic structures and active processes, surface processes, and topography were investigated at different scales. Over 100 DSGSDs were mapped in a 5000 km² sector of the central Eastern Alps between the Valtellina, Engadine and Venosta valleys. Detailed lineament mapping was carried out by photo-interpretation in a smaller area (about 750 km²) including the upper Valtellina and Val Venosta. Fault populations were also analysed in the field and their mechanisms unravelled, allowing to identify different structural stages, the youngest being consistent with the regional pattern of the ongoing crustal deformation. Finally, four DSGSD examples have been investigated in detail by geological and 2D geomechanical modelling.DSGSDs affect more than 10% of the study area, and mainly cluster in areas where anisotropic fractured rock mass and high local relief occur. Their onset and development is subjected to a strong passive control by mesoscopic and major tectonic features, including regional nappe boundaries as well as NW–SE, N–S and NE–SW trending recent brittle structures. The kinematic consistency between these structures and the pattern of seismicity suggests that active tectonics may force DSGSDs, although field evidence and numerical models indicate slope debuttressing related to deglaciation as a primary triggering mechanism.     

斯洛伐克西喀尔巴阡山脉Gemerská Poloma滑石-菱镁矿矿床中镁的交代作用

Gemerská Poloma矿床是个重要的滑石矿床(储量20万吨),位于西喀尔巴阡山脉Germeric地区。部分滑石化的镁质碳酸盐体赋存在早古生代火山沉积杂岩体中(黑色片岩,变质泥岩),在Variscan变质作用(M1)过程中受到了绿泥石-黑云母带区域变质相的改造。这种原岩是石灰岩的矿体由白色-灰白或者灰色-黑色的菱镁矿与白云石1组成,被次生的白云石2和滑石脉切割。本次研究考察了两次变质事件(M1和M2)的几个连续的矿物组合,最早的组合包括铁白云石,镁菱铁矿与菱铁矿,(并与黑电气石,铁绿泥石,磷灰石,与伊利石-白云母伴生),它们以微小残留物形式产出在菱镁矿和白云石1中,其形成可能早于M1变质作用高峰期。M1变质事件的高峰期以富铁金云母,镁绿泥石1,镁电气石(黑电气石的边缘)和石英的组合为代表。在M1退变质作用过程中,发生了镁交代作用,开始是白云石1结晶,接下来形成菱镁矿,最后是以铁菱镁矿沿裂隙的形成而终。根据碳酸盐地质测温原理,M1变质事件的高峰期温度为460~490℃,变质矿物组合特征也支持这一测温结果。滑石,白云石2,与镁绿泥石2沿着镁碳酸盐岩石裂隙的发育,主要受到M2变质事件的影响,这个变质事件与较年青的Alpine造山事件有关。 菱镁矿流体包裹体的研究表明,成矿流体具有复杂的组成,可能以MgCl2组分为主,主要来     

Geomorphic evidence for active tectonic deformation in the coastal part of Eastern Black Sea,Eastern Pontides,Turkey

The Eastern Pontides (EP), which is the under transpressional deformation zone, is an active mountain belt that has been rising rapidly since the Cenozoic era because of the Arabian-Eurasian convergence. Morphometric studies have been performed to investigate the tectonic activity of this region and better understand the characteristics of the faults geomorphologically; the faults control the mountain fronts in the drainage basin of the EP. The results show the Hypsometric Curve (HC)-Hypsometric Integral (0.37-HI-0.67), Basin-Shaped Analysis (1.2-B_s-7), Valley-Floor-Width to Height-Ratio (0.4-V_f-1.2) and Asymmetry Factor (35-AF-81) applied to 46 drainage basins together with 9 tectonically controlled geomorphic indices (1.2-S_mf-1.5) and a Stream Length Gradient (30-S_L-120) indicate that the EP is tectonically active, and when the areas are evaluated according to S_mf and V_f analyses, the tectonic level is relatively high. According to our conceptual model for the uplifting of the EP, with respect to field studies and morphometric analysis, (i) the EP is the active deformation zone and has a “push-up” geometry in conjunction with the North Anatolian Fault; (ii) the EP is progressively uplifting at a rate of more than 0.5 mm/yr in along with the thrust faults of the Black Sea Fault (BSF) and Borjomi-Kazbegi Fault (BKF).     

Shallow and deep aquifer hydrochemistry and chemical variability of water quality at Shariatpur district, Bangladesh

Water quality and hydrochemistry of Shariatpur district were evaluated in terms of hydrochemical composition and some important physico-chemical parameters. The groundwater of the study area is good for drinking, domestic as well as for irrigation purposes. Among the major ions, shallow tube well waters give higher concentration of Ca²⁺ which ranges from 24 to 260 mg/L. The deep tubewell waters show higher concentration of Na⁺ which varies from 74 to 582 mg/L during dry season. Among the trace elements most of the shallow aquifer samples show higher concentration of Fe²⁺, Mn²⁺ and As. Concentration of Fe²⁺ varies from 0.655 to 18.8 mg/L, and Mn²⁺ from trace to 0.868 mg/L during dry period. Hydrochemical analyses reveal significant seasonal variation in water quality of shallow aquifer. Both the shallow aquifer and the surface water of the study area are predominantly of Ca–Mg–HCO₃ type, while the deep aquifer water is mainly of Na–K–Cl–SO₄ type with slight inclination to Ca–Mg–HCO₃ type. The study area is suitable for groundwater development if comprehensive and holistic approaches towards water resource management are taken into consideration.     

斯洛伐克西喀尔巴阡山脉Gemerská Poloma滑石-菱镁矿矿床中镁的交代作用

Gemerska Poloma矿床是个重要的滑石矿床(储量20万吨),位于西喀尔巴阡山脉Germeric地区.部分滑石化的镁质碳酸盐体赋存在早古生代火山沉积杂岩体中(黑色片岩,变质泥岩),在Variscan变质作用(M1)过程中受到了绿泥石-黑云母带区域变质相的改造.这种原岩是石灰岩的矿体由白色-灰白或者灰色-黑色的菱镁矿与白云石1组成,被次生的白云石2和滑石脉切割.本次研究考察了两次变质事件(M1和M2)的几个连续的矿物组合,最早的组合包括铁白云石,镁菱铁矿与菱铁矿,(并与黑电气石,铁绿泥石,磷灰石,与伊利石-白云母伴生),它们以微小残留物形式产出在菱镁矿和白云石1中,其形成可能早于M1变质作用高峰期.M1变质事件的高峰期以富铁金云母,镁绿泥石1,镁电气石(黑电气石的边缘)和石英的组合为代表.在M1退变质作用过程中,发生了镁交代作用,开始是白云石1结晶,接下来形成菱镁矿,最后是以铁菱镁矿沿裂隙的形成而终.根据碳酸盐地质测温原理,M1变质事件的高峰期温度为460～490°C,变质矿物组合特征也支持这一测温结果.滑石,白云石2,与镁绿泥石2沿着镁碳酸盐岩石裂隙的发育,主要受到M2变质事件的影响,这个变质事件与较年青的Alpine造山事件有关.菱镁矿流体包裹体的研究表明,成矿流体具有复杂的组成,可能以MgCl2组分为主,主要来源于蒸发卤水的演化.原生流体包裹体的盐度～35(wt%MgCl2),均一温度变化范围是216～235℃.石英中流体包裹体也显示了以MgCl2组分为主的相似流体组成,但均一温度比较高,为248～313℃.如果假定石英与M1变质事件同期,那么由流体包裹体计算出的M1变质峰期压力范围是250～350MPa(9～13km),因此地温梯度是35～40℃/km.假定这个梯度在镁交代成矿过程中保持不变,那么相关流体在180～280MPa(7～11km)的压力下的温度为300～350℃.流体包裹体的淋滤分析表明,流体中Cl/Br与Na/Br都很高,说明流体具有蒸发特征.而在Gemeric地区只有在晚二叠纪到早三叠纪这段时间才有如此大量的卤水形成.因此,二叠纪的伸展构造运动与形成菱镁矿的热液系统的形成有关.     

帕米尔弧东段逆冲推覆构造特征

帕米尔弧形构造带是青藏高原碰撞挤压表现最明显的地区之一。通过构造剖面和地震剖面解释,认为帕米尔弧东段逆冲推覆构造具有分带性特点,自南西向北东方向可以划分为逆冲推覆构造的根带、中带、锋带与锋前带,相应地发育叠瓦状逆冲断层、冲断褶皱、断层相关褶皱、单斜构造等不同的构造组合。对逆冲推覆锋带中苏盖特和阿克陶生长背斜、生长地层及形成时序分别进行了研究,确定了帕米尔弧形逆冲推覆构造以前展式（背驮式）向前陆方向扩展,逆冲推覆始于上新世,并一直持续到早更新世。弧形构造东西两段逆冲推覆运动方式和地层缩短量有很大差异：西段为与挤压方向垂直的逆冲,而东段为斜冲兼顺时针走滑;西段地层缩短量大于东段。     

Prehistoric and recent mass movements of the World Cultural Heritage Site Hallstatt, Austria

Hallstatt Village, located in the Austrian Alps, is designated by the United Nations Educational, Scientific and Cultural Organization as part of the World Cultural Heritage Site Hallstatt–Dachstein. This region is recognized for its salt deposits that have been exploited since the Neolithic period. In former times, these salt deposits were very rare and precious. Due to unfortunate bedding conditions, mass movements have been frequent in the past and continue to affect the site today. These active and inactive mass movements were mapped geotechnically to a scale of 1:5,000 and the mineralogical and mechanical properties of the main instable soft rocks were investigated. Rock spreads, rock slides, rock falls, rock topples, earth flows and earth and debris slides are the primary types of mass movements recorded. They are most frequently observed in areas affected by mining, though they may also occur in areas where no anthropogenic influence is recognized. Evidence exists in the archaeological record that indicates prehistoric mining activities were also seriously affected by the impact of mass movements.     

History of metalliferous sedimentation at deep sea drilling site 319 in the South Eastern Pacific

Marked variations in the chemical and mineralogical composition of sediments at Site 319 have occurred during the 15 M.y. history of sedimentation at this site. The change in composition through time parallels the variability observed in surface sediments from various parts of the Nazca Plate and can be related to variations in the proportion of hydrothermal, hydrogenous, detrital and biogenous phases reaching this site at different times. Metal accumulation rates at Site 319 reach a maximum near the basement for most elements, suggesting a strong hydrothermal contribution during the early history of this site. The hydrothermal contribution decreased rapidly as Site 319 moved away from the spreading center, although a subtle increase in this source is detectable about the time spreading began on the East Pacific Rise. The most recent sedimentation exhibits a strong detritalhydrogenous influence. Post-depositional diagenesis of amorphous phases has converted them to ironrich smectite and well-crystallized goethite without significantly altering the bulk composition of the sediment.     

A statistical procedure for the analysis of seismotectonically induced hydrochemical signals: A case study from the Eastern Carpathians, Romania

Changes in the stress field of an aquifer system induced by seismotectonic activity may change the mixing ratio of groundwaters with different compositions in a well, leading to hydrochemical signals which in principle could be related to discrete earthquake events. Due to the complexity of the interactions and the multitude of involved factors the identification of such relationships is a difficult task. In this study we present an empiric statistical approach suitable to analyse if there is an interdependency between changes in the chemical composition of monitoring wells and the regional seismotectonic activity of a considered area. To allow a rigorous comparison with hydrochemistry the regional earthquake time series was aggregated into an univariate time series. This was realized by expressing each earthquake in form of a parameter “e”, taking into consideration both energetic (magnitude of a seismic event) and spatial parameters (position of epi/hypocentrum relative to the monitoring site). The earthquake and the hydrochemical time-series were synchronised aggregating the e-parameters into “earthquake activity” functions E, which takes into account the time of sampling relative to the earthquakes which occurred in the considered area. For the definition of the aggregation functions a variety of different “e” parameters were considered. The set of earthquake functions E was grouped by means of factor analysis to select a limited number of significant and representative earthquake functions E to be used further on in the relation analysis with the multivariate hydrochemical data set. From the hydrochemical data a restricted number of hydrochemical factors were extracted. Factor scores allow to represent and analyse the variation of the hydrochemical factors as a function of time. Finally, regression analysis was used to detect those hydrochemical factors which significantly correlate with the aggregated earthquake functions.This methodological approach was tested with a hydrochemical data set collected from a deep well monitored for two years in the seismically active Vrancea region, Romania. Three of the hydrochemical factors were found to correlate significantly with the considered earthquake activities. A screening with different time combinations revealed that correlations are strongest when the cumulative seismicity over several weeks was considered. The case study also showed that the character of the interdependency depends sometimes on the geometrical distribution of the earthquake foci. By using aggregated earthquake information it was possible to detect interrelationships which couldn't have been identified by analysing only relations between single geochemical signals and single earthquake events. Further on, the approach allows to determine the influence of different seismotectonic patterns on the hydrochemical composition of the sampled well. The method is suitable to be used as a decision instrument in assessing if a monitoring site is suitable or not to be included in a monitoring net within a complex earthquake prediction strategy.     

Structural and tectonic interpretation of geophysical data along the Eastern Continental Margin of India with special reference to the deep water petroliferous basins

The study area encompasses the Eastern Continental Margin of India (ECMI) and the adjoining deep water areas of Bay of Bengal. The region has evolved through multiple phases of tectonic activity and fed by abundant supply of sediments brought by prominent river systems of the Indian shield. Detailed analysis of total field magnetic and satellite-derived gravity data along with multi channel seismic reflection sections is carried out to decipher major tectonic features, basement structure, and the results have been interpreted in terms of basin configuration and play types for different deep water basins along the ECMI. Interpretation of various image enhanced gravity and magnetic anomaly maps suggest that in general, the ENE–WSW trending faults dominate the structural configuration at the margin. These maps also exhibit a clear density transition from the region of attenuated continental crust/proto oceanic crust to oceanic crust based on which the Continent Ocean Boundary (COB) has been demarcated along the margin. Basement depths estimated from magnetic data indicate that the values range from 1 to 12 km below sea level and deepen towards the Bengal Fan in the north and reveal horst–graben features related to rifting. A comparison of basement depths derived from seismic data indicates that in general, the basement trends and depths are comparable in Cauvery and Krishna–Godavari basins, whereas, in the Mahanadi basin, basement structure over the 85°E ridge is clearly revealed in seismic data. Further, eight multichannel seismic sections across different basins of the margin presented here reveal fault pattern, rift geometries and depositional trends related to canyon fills and channel–levee systems and provide a basic framework for future petroleum in this under explored frontier.