Marginal Belt Research Articles

Main stages and geodynamic regimes of the Earth’s crust formation in East Antarctica in the Proterozoic and Early Paleozoic

Geological, geochemical, and isotopic data (U-Pb for zircon and Sm-Nd for whole-rock samples) are summarized for Proterozoic and Early Paleozoic geological complexes known from various regions of East Antarctica. The main events of tectonothermal and magmatic activity are outlined and correlated in space and time. The Paleoproterozoic is characterized as a period of rifting in Archean blocks, their partial mobilization, and formation of a new crustal material over a vast area occupied by present-day East Antarctica. In most areas, this material was repeatedly reworked at the subsequent stages of evolution (1800–1700, 1100–1000, 550–500 Ma). Complexes of Mesoproterozoic juvenile rocks (1500, 1400–1200, 1150–1100 Ma) arising in convergent suprasubduction geodynamic settings are established in some areas (basalt-andesite and tonalite-granodiorite associations with characteristic geochemical signatures). The evolution of the Proterozoic regions in East Antarctica may be interpreted as a Wilson cycle with the destruction of the Archean megacontinent 2250 Ma ago and the ultimate closure of the secondary oceanic basins by 1000 Ma ago. The Mesoproterozoic regions make up a marginal volcanic-plutonic belt that combines three provinces of different ages corresponding to consecutive accretion of terranes 1500–1150, 1400–950, and 1150–1050 Ma ago. The Neoproterozoic and Early Paleozoic tectonomagmatic activity developed nonuniformly. In some regions, it is expressed in ductile deformation, granulite-facies metamorphism, and postcollision magmatism; in other regions, a weak thermal effect and anorogenic magmatism are noted. The evolution of metamorphic complexes in the regime of isothermal decompression and the intraplate character of granitoids testify to the collision nature of the Early Paleozoic tectonomagmatic activity.

Vegetation patterns and species—environment relationships in the Gurbantunggut Desert of China

The Gurbantunggut Desert is the largest stable and semi-stable sand desert in China, yet few data exist on vegetation pattern and species-environment relationships for these diverse desert landscapes. The sand dunes of the survey area are mainly of the longitudinal form from north to south, but checkerboard-shaped and honeycomb-shaped forms are also present, with the height of 10–50 m. We measured vegetation and soil data on north-south transects and compared them with vegetation and soil data on east-west transects. Analysis revealed that the varying trend and strength of the species diversity, dominance and cover of the plant communities in the longitudinal and transverse directions across the landscape are significantly different. The results of CCA ordination show that the microhabitats of soil organic matter (OM), soil salts (TS), sorting index (σ), topsoil water-content (SM) and pH relate to the differences in vegetation observed as differences in species assemblage from salt-intolerant ephemerals, micro-subshrubs and subshrubs to salt-tolerant shrubs and micro-arbors. The terrain (alt.) and soil texture (the contents of Mz and ϕ1) affect the spatial differentiation of many species. However, this spatial differentiation is not so marked on transects running longitudinally with the landscape, in the same direction as the dunes. The species of the desert vegetation have formed three assemblages under the action of habitat gradients, relating to three sections running transversely across the landscape, at right angles to the direction of the dune crests. In the mid-east section of the study area the topography is higher, with sand-lands or dune-slopes with coarse particles. Here the dominant vegetation comprises shrubs and subshrubs of Seriphidium santolium and Ephedra distachya, with large numbers of ephemeral and ephemeroid plants of Senecio subdentatus, and Carex physodes in spring and summer. On the soil of the dune-slopes in the mid-west of the study area, with coarse particles and abundant TK, the plant assemblage of Haloxylon persicum, Soranthus meyeri and Agriophyllum squarrosum is developed. The species composition in the east marginal belt of the study area has similar characteristics to the mid-west section. There is no corresponding section in the north-south transects (except for the north and south margins). This is because the habitats of most plants are located in the middle of the microhabitat gradients in the north-south direction in the desert.

Deep‐water foreland basin deposits of the Cerro Toro Formation, Magallanes basin, Chile: architectural elements of a sinuous basin axial channel belt

AbstractCoarse‐grained deep‐water strata of the Cerro Toro Formation in the Cordillera Manuel Señoret, southern Chile, represent the deposits of a major channel belt (4 to 8 km wide by >100 km long) that occupied the foredeep of the Magallanes basin during the Late Cretaceous. Channel belt deposits comprise a ca 400 m thick conglomeratic interval (informally named the ‘Lago Sofia Member’) encased in bathyal fine‐grained units. Facies of the Lago Sofia Member include sandy matrix conglomerate (that show evidence of traction‐dominated deposition and sedimentation from turbulent gravity flows), muddy matrix conglomerate (graded units interpreted as coarse‐grained slurry‐flow deposits) and massive sandstone beds (high‐density turbidity current deposits). Interbedded sandstone and mudstone intervals are present locally, interpreted as inner levée deposits. The channel belt was characterized by a low sinuousity planform architecture, as inferred from outcrop mapping and extensive palaeocurrent measurements. Laterally adjacent to the Lago Sofia Member are interbedded mudstone and sandstone facies derived from gravity flows that spilled over the channel belt margin. A levée interpretation for these fine‐grained units is based on several observations, which include: (i) palaeocurrent measurements that indicate flows diverged (50° to 100°) once they spilled over the confining channel margin; (ii) sandstone beds progressively thin, away from the channel belt margin; (iii) evidence that the eroded channel base was not very well indurated, including a stepped margin and injection of coarse‐grained channel material into surrounding fine‐grained units; and (iv) the presence of sedimentary features common to levées, including slumped units inferring depositional slopes dipping away from the channel margin, lenticular sandstone beds thinning distally from the channel margin, soft sediment deformation and climbing ripples. The tectonic setting and foredeep architecture influenced deposition in the axial channel belt. A significant downstream constriction of the channel belt is reflected by a transition from more tabular units to an internal architecture dominated by lenticular beds associated with a substantially increased degree of scour. Differential propagation of the fold‐thrust belt from the west is speculated to have had a major control on basin, and subsequently channel, width. The confining influence of the basin slopes that paralleled the channel belt, as well as the likelihood that numerous conduits fed into the basin along the length of the active fold‐thrust belt to the west, suggest that proximal–distal relationships observed from large channels in passive margin settings are not necessarily applicable to axial channels in elongate basins.

Reservoir-forming conditions of platform margin belt in southern slope of Tazhong, Tarim Basin

Abstract Based on the new seismic and logging data, this paper identifies the location and shape of the platform margin belt in Tazhong, Tarim Basin and studies its structural characteristics and reservoir-forming conditions using isochronous sequence framework, structural analysis, sedimentary evolution, and other methods. The platform margin belt is a large composite slope break belt formed from the end of the early Ordovician to the early of the Late Ordovician. Its east section is a complicated faulted slope break resulted from erosion before Late Ordovician, and its west is a carbonate sedimentary slope break in which the platform margin reef flat complex was developed in the Lianglitage Formation of the Upper Ordovician. The belt can be divided into six parts with different structural and sedimentary characteristics. The first and second parts are the superimposed segments of the on-lap trigonal zone and the erosional trigonal zone, in which karst and lithologic reservoirs were well-developed. Platform margin reef flats were well-developed in the fifth part. These three zones are the main exploration targets.

Terminal stages of the evolution of sheet and mountain glaciations in Khibiny

The purpose of this work is to reconstruct terminal stages of the evolution of sheet and mountain glaciations in the Khibiny mountainous massif. We investigated a vast area of nepheline syenites of the Khibiny pluton in the southern Khibiny Massif. This area is characterized by an abundance of glacial cirques and the existence of mountain glaciations [1, 2]. We revealed here typical structures of the marginal belt of the Scandinavian glacier as dump and push moraine ridges [3] (Fig. 1). The northern part of the area includes deposits of mountain glaciers with a specific composition of clastic material. Judging from the petrographic composition of the pebble fraction and the mineral composition of sand and silt, the clastic material is almost entirely represented by products of destruction of nepheline syenites of the Khibiny intrusive massif. Mountain glaciers and their meltwaters include the following structures: (i) end moraines damming valleys of the Poachvumjok and Vudjavrjok rivers; (ii) ridges resembling De Geer moraines; (iii) glaciofluvial deltas formed by meltwater running southward and located in valleys of the Poachvumjok and Vudjavrjok rivers behind end moraines; (iv) periglacial lake terraces developed at an altitude of about 500 m in the Poachvumjok river valley; and (v) a small sandur with an even surface complicated by “pocks” of the Malyi Vudjavr and Kupal’noe lakes obviously indicating the filling of lake depressions with dead ice during the sandur formation. The southern part of the study area includes sheet glaciation deposits that are developed represented by dump and push moraine ridges, as well as a thin cover

Geochronology of igneous rocks and formation of the Late Paleozoic south Mongolian active margin of the Siberian continent

The succession of magmatic events associated with development of the Early Carboniferous-Early Permian marginal continental magmatic belt of southern Mongolia is studied. In the belt structure there are defined the successive rock complexes: the older one represented by differentiated basalt-andesite-rhyodacite series and younger bimodal complex of basalt-comendite-trachyrhyolite composition. The granodiorite-plagiogranite and banatite (diorite-monzonite-granodiorite) plutonic massifs are associated with the former, while peralkaline granite massifs are characteristic of the latter. First systematic geochronological study of igneous rock associations is performed to establish time succession and structural position of both complexes. Geochronological results and geological relations between rocks of the bimodal and differentiated complexes showed first that rocks of the differentiated complex originated 350 to 330 Ma ago at the initial stage of development of the marginal continental belt. This is evident from geochronological dates obtained for the Adzh-Bogd and Edrengiyn-Nuruu massifs and for volcanic associations of the complex. The dates are consistent with paleontological data. The bimodal association was formed later, 320 to 290 Ma ago. The time span separating formation of two igneous complexes ranges from several to 20–30 m.y. in different areas of the marginal belt. The bimodal magmatism was interrelated with rifting responsible for development of the Gobi-Tien Shan rift zone in the belt axial part and the Main Mongolian lineament along the belt northern boundary. Loci of bimodal rift magmatism likely migrated with time: the respective magmatic activity first initiated on the west of the rift system and then advanced gradually eastward with development of rift structures. Normal granitoids untypical but occurring nevertheless among the products of rift magmatism in addition to peralkaline massifs are assumed to have been formed, when the basic magmatism associated with rifting stimulated crustal anatexis and generation of crustal granitoid magmas under specific conditions of rifting within the active continental margin.

The formation of triangle zones in already deformed belts: the case study of an external area of the northern Apennines (Italy)

This study reconstructs the sequence of deformation that affected a sector of the northern Apennines accretionary wedge (external Ligurian Units located in the Parma and Piacenza provinces). This external sector of the belt underwent several superposed events due to oceanic accretion and subsequent continental collision, at shallow structural levels. To this purpose, microstructural analysis was applied to the calcite veins. Twinned calcite crystals represent stress-strain markers and make it possible to estimate (1) pressure-temperature conditions, (2) amount and pressure of circulating fluids and (3) paleostress determinations. This methodology permitted to reconstruct the peculiar kinematics and tentatively interpreting this frontal zone of the belt as a tectonic wedge (triangle zone). The Ligurian wedge in the studied area differs from classical triangle zones, which typically form at foreland margins of thrust belts, in that its para-autocthon was already deformed when passively uplifted by the wedging event.

A study on the geochemical characteristics of Upper Permian continental marginal arc volcanic rocks in the northern segment of South Lancangjiang Belt

Geochemical characteristics of the Upper Permian (P2) continental marginal arc volcanic rocks are described, which have been found recently around the areas of Xiaodingxi and Zangli on the eastern side of the Yunxian-Lincang granite, in terms of rock assemblage, petrochemistry, REE, trace elements, Pb isotopes, geotectonic environment and so on. The volcanic rock assemblage is dominated by basalt-andesite-dacite, with minor trachyte andecite-trachyte; the volcanic rock series is predominated by the calc-alkaline series, with minor tholleiite series and alkaline series rocks ; the volcanic rocks are characterized by high A12O3 and low TiO2, with K2O contents showing extremely strong polarity; the REE distribution patterns are characterized by LREE enrichment and right-inclined type; trace elements and large cation elements are highly enriched, Ti and Cr are depleted, and P and Nb are partially depleted; the Pb composition is of the Gondwana type; the petrochemical points mostly fall within the field of island-arc volcanic rocks, in consistency with the projection of data points of continental marginal volcanic rocks in the southern segment of the South Lancangjiang Belt and the North Lancangjiang Belt. This continental marginal arc volcanic rock belt, together with the ocean-ridge and ocean-island volcanic rocks and ophiolites in the Changning-Menglian Belt, constitute the ocean-ridge volcanic rock, ophiolite-arc rock-magmatic rock belts which are distributed in pairs, indicating that the Lancangjiang oceanic crust subducted eastwards. This result is of great importance in constraining the evolution of the paleo-Tethys in the Lancangjiang Belt.

The glacial geomorphology of Kola Peninsula and adjacent areas in the Murmansk Region, Russia

Please click here to download the map associated with this article. A map of the glacial geomorphology of Kola Peninsula and adjacent areas in the Murmansk region, northwestern Russia, is presented. The primary data source for identification and classification of landforms has been Landsat 7 Enhanced Thematic Mapper Plus (ETM+) satellite images, and aerial photograph interpretation and field work in selected areas. The map, at the scale 1:900,000, consists of over 20,000 landforms pertaining to the Quaternary glacial activity, considerably improving existing knowledge of this area. The landform types that have been mapped are glacial lineations, ribbed moraine, end moraines, end moraine complexes, hummocky moraine, eskers, glaciouvial accumulations, lateral meltwater channels, large meltwater channels, very large meltwater channels, and relict shorelines. The distribution of landforms shows large variations. The central part of the peninsula lacks signs of glacial activity, apart from abundant lateral meltwater channels. In the rest of the area glacial lineations (drumlins, utes, crag-and-tails) are the dominant landform type. The largest glacial landform system in the area is an ice marginal system running parallel to the southern and eastern coast of Kola Peninsula. This ice marginal system, the Keiva moraine complex, has in part been overrun and drumlinised by ice ow from the southwest. This indicates that this ice marginal belt was deposited before the last major ice expansion. The map presented will be used as the main source of data for a new reconstruction of glacial events in the eastern part of the Fennoscandian ice sheet area.

A new concept on tectonic correlation between Korea, China and Japan: Histories from the late Proterozoic to Cretaceous

The Dabie–Sulu collision belt in China extends to the Hongseong–Odesan belt in Korea while the Okcheon metamorphic belt in Korea is considered as an extension of the Nanhua rift within the South China block. The Hongseong–Odesan belt divides Korea's Gyeonggi massif into northern and southern portions. The southern Gyeonggi massif and the Yeongnam massif are correlated with China's Yangtze and Cathaysia blocks, respectively, while the northern Gyeonggi massif is part of the southern margin of the North China block. The southern and northern Gyeonggi massifs rifted from the Rodinia supercontinent during the Neoproterozoic, to form the borders of the South China and North China blocks, respectively. Subduction commenced along the southern and eastern borders of the North China block in the Ordovician and continued until a Triassic collision between the North China and South China blocks. While subduction was occurring on the margin of the North China block, high-P/T metamorphic belts and accretionary complexes developed along the inner zone of southwest Japan from the Ordovician to the Permian. During the subduction, the Hida belt in Japan grew as a continental margin or continental arc. Collision between the North and South China blocks began in Korea during the Permian (290–260 Ma), and propagated westwards until the Late Triassic (230–210 Ma) creating the sinistral TanLu fault in China and the dextral fault in the Hida and Hida marginal belt in Japan. Phanerozoic subduction and collision along the southern and western borders of the North China block led to formation of the Qinling–Dabie–Sulu–Hongseong–Hida–Yanji belt.

Geomorphic development of the escarpment of the Eritrean margin, southern Red Sea from combined apatite fission-track and (U–Th)/He thermochronometry

Apatite (U–Th)/He and fission-track thermochronometers are combined to constrain models of denudation and escarpment development of the high elevation Eritrean margin along the southern Red Sea. (U–Th)/He ages have been determined for apatites from two coast-perpendicular transects that were previously used for apatite fission-track analysis [E. Abbate, M.L. Balestrieri, G. Bigazzi, Morphostructural development of the Eritrean rift flank (southern Red Sea) inferred from apatite fission track analysis, J. Geophys. Res., 107, B11, doi: 10.1029/2001JB001009, (2002)]. In central Eritrea near Asmara, He ages increase from c. 7 Ma at the coast to 152 Ma on the plateau along a transect. Further south, He ages from the margin border to the base of the escarpment span a narrower range (7 to 12 Ma). One sample from the top of a marginal high (2950 m) yields older ages (22–43 Ma). Forward modeling suggests that the He age distribution across the margin should allow scarp retreat and downwearing mechanisms to be distinguished in the case of a margin formed in the last twenty million years. The distribution of He ages suggests that the escarpment evolved by downwearing and that post-break up erosion of the escarpment was facilitated by in situ excavation rather than parallel retreat. This implies the existence of an inland drainage divide located seaward of the present day escarpment rim. We envisage that the inland divide formed during or immediately after continent break up, and that the eastern marginal belt represents a remnant of the apex structure. The short distance between the eastern marginal belt and the rim (c. 10 km) represents the total retreat of the escarpment. Comparison of the measured He ages from the coastal plain with those predicted from forward modelling indicates that the main phase of post-break up erosion started at about 15 Ma, closer to the initiation of seafloor spreading in the Red Sea than was thought previously.

Recovery of carbonate platform production in the Lombardy Basin during the Anisian: paleoecological significance and constrain on paleogeographic evolution

In the Central Lombardy Basin (Southern Alps) Anisian carbonate platform marginal facies yielding the first documented occurrence of coral colonies in this area of the Western Tethys has been recognized. These marginal facies identify the east-west transition between two sectors with a different Anisian evolution. West of the recognized marginal facies the Anisian succession is characterised by subtidal bioturbated limestones passing upward to peritidal dolostones, whereas toward the east a thicker succession of subtidal facies persist until the end of the Anisian. The margin belt develops at the passage between a more subsiding eastern portion and a less subsiding one toward the west. The different facies and thickness of the Anisian succession east and west of the marginal facies is indicative of syndepositional tectonics. The transition from subtidal to peritidal facies in the western sector is ascribed to a sea-level fall that favoured the onsetting of peritidal facies on the less subsiding block and of marginal facies on its border. The occurrence of a N-S trending syndepositional Anisian fault system could also explain the scarce progradational evolution of the margin facies, prevented both by the paleobathymetric setting and by the scarce productivity of the Anisian marginal communities. The presence, in the Anisian marginal facies, of crinoids and corals (together with the occurrence of one of the oldest specimen of coralline red algae) outlines the return to normal marine conditions and documents the recovery of the carbonate platform marginal faunal association after the Permo-Triassic crisis in the Western Southern Alps.

On the English expression of the Hida Gaien belt

The Hida belt, one of the Paleozoic-Mesozoic geologic units in central Japan, has been expressed in various ways in English, such as Hida Gaien belt, Hida marginal belt, Circum-Hida terrane, Circum-Hida tectonic zone, etc. When the special issue of this journal entitled Recent progress and future perspective of research on the Hida was edited for publication, as invited editors we recommended the authors to use the expression of Hida belt in order to avoid misunderstanding of the geologic characteristics of this belt by foreign researchers. This note summarizes the discussion between the authors during the process of deciding which is the best expression.

Intrusion‐Related Gold Deposits of North China Craton, People's Republic of China

Abstract. Intrusion‐related gold deposits are widely distributed within the North China craton or along its marginal fold belts. Presently, about 200 individual intrusion‐related gold deposits (prospects) have been discovered, among which Yuerya, Anjia‐yingzi, Linglong, Jiaojia, Chenjiazhangzi, Qiyugou, Jinjiazhuang, Dongping, Hougou, Huangtuliang, Guilaizhuang, Wulashan and Donghuofang are the most important ones. In general, the intrusion‐related gold deposits can be classified into three major groups according to their host rocks: (1) hosted by or related to felsic intrusions, including (la) calc‐alkaline granitoid intrusions and (lb) cryptoexplosion breccia pipes; (2) related to ultramafic intrusions, and (3) hosted by or related to alkaline intrusions. The first group contains the Yuerya, Anjiayingzi, Linglong, Jiaojia, Chenjiazhangzi and Qiyugou gold deposits. Gold mineralization at these deposits occurs within Mesozoic Yanshanian calc‐alkaline granitoid intrusions or cryptoexplosion breccia pipes as gold‐bearing quartz veins and replacement bodies. Pyrite, galena, sphalerite, chalcopyrite, native gold and electrum are major metallic minerals. The Jinjiazhuang deposit belongs to the second group, and occurs within Hercynian diopsidite and peridotite as quartz veins and replacement bodies. Pyrite, marcasite, arsenopyrite, native gold and electrum are identified. The third group includes the Dongping, Hougou, Huangtuliang, Guilaizhuang, Wulashan and Donghuofang deposits. Gold mineralization at these deposits occurs predominantly within the Hercynian alkaline intrusive complexes as K‐feldspar‐quartz veins and replacement bodies. Major metal minerals are pyrite, galena, chalcopyrite, tellurides, native gold and electrum.All these pyrite separates from Hercynian and Yanshanian intrusions or cryptoexplosion pipes associated with the gold deposits show a broad range in δ34S value, which is overall higher than those Precambrian rocks and their hosted gold deposits. For the alkaline intrusion‐related gold deposits, the δ34S values of the sulfides (pyrite, galena and chalcopyrite) from the deposits increase systematically from orebodies to the alkaline intrusions. All of these intrusion‐related gold deposits show relatively radiogenic lead isotopic compositions compared to mantle or lower crust curves. Most lead isotope data of sulfides from the gold ores plot in between the fields of the intrusions and Precambrian metamorphic rocks. Data are interpreted as indicative of a mixing of sulfur and lead from magma with those from Precambrian metamorphic rocks.Isotopic age data, geological and geochemical evidences suggest that the ore‐forming materials for the intrusion‐related gold deposits were generated during the emplacement of the Hercynian or Yanshanian intrusion. The calc‐alkaline or alkaline magma may provide heat, volatiles and metals for the intrusion‐related gold deposits. Evolved meteoric water, which circulated the wall rocks, was also progressively involved in the magmatic hydrothermal system, and may have dominated the ore fluids during late stage of ore‐forming processes. Therefore, the ore fluid may have resulted from the mixing of calc‐alkaline or alkaline magmatic fluids and evolved meteoric water. All these intrusion‐related gold deposits are believed to be products of Hercynian or Yanshanian calc‐alkaline and alkaline igneous processes along deep‐seated fault zones within the North China craton or along its marginal belts.

Jurassic Dextral and Cretaceous Sinistral Movements Along the Hida Marginal Belt

The Hida marginal belt (HMB), which consists of various kinds of fault-bound blocks, is located between the continental massif of the Hida belt and the Mesozoic accretionary complex of the Mino belt in Central Japan. Detailed field investigation reveals that the HMB had grown through the two different movements, i.e., Jurassic dextral and Cretaceous sinistral movements. The Jurassic dextral ductile shear zones run in the southern marginal part of the Hida belt and the northern part of the HMB, whereas the Cretaceous sinistral cataclastic shear zones occur in the southern part of the HMB and the northern marginal part of the Mino belt. Geologic map and field evidence seem to suggest that the Jurassic dextral movement form the fault-bound blocks of the HMB to form the basic structure of the Hida marginal belt, i.e., formation of the ‘proto-HMB.’ Following the dextral movement, the sinistral one restructured the ‘proto-HMB’ to complete the present feature of the Hida marginal belt. The Cretaceous sinistral movement might result in the sinistral collision between the proto-HMB and the Mino belt.

Late-stage alteration and tin–tungsten mineralization in the Khuntan Batholith, northern Thailand

The Khuntan Batholith is part of the Triassic–Jurassic eastern marginal belt of the Northern Thailand Granite Province. Most of the batholith consists of coarse-grained, porphyritic to megacrystic biotite–muscovite granite (Huai Mae San unit). However, the southeastern part, called the Muang Yao unit, consists of coarse- to medium-grained muscovite and muscovite–tourmaline granite and is associated with Sn–W mineralization. The Huai Mae San granite has S-type petrological features typical of batholiths in the eastern marginal belt, which formed in a syn-collisional setting. The more silicic Muang Yao granite differs chemically from felsic S-type granite, for example in extreme Rb–Y–Nb enrichment and Ba–Sr–Zr depletion, probably as a result of late-stage fluid alteration. Vein-hosted deposits of cassiterite, scheelite, and wolframite associated with minor sulfides occur in both the Muang Yao granite and adjacent metamorphic rocks. Fluid-inclusion studies indicate that both aqueous and aqueous-carbonic fluids of low salinity (0–8 wt% equiv. NaCl) were involved in vein formation, and were subject to pressure fluctuation between essentially lithostatic and hydrostatic conditions. Dilution of magmatic hydrous fluid by influx of meteoric water may explain the anomalously low salinity. Oxygen isotope data support a primary magmatic origin for the fluid, and indicate temperatures of ca. 400 °C for ore deposition. The three vein-type Sn–W deposits of this study represent a spectrum from an endogranite vein system to proximal-intermediate vein systems of magmatic-hydrothermal origin.

Hierarchic three‐dimensional structure and slip partitioning in the western Dead Sea pull‐apart

Rifted basins are bounded by marginal belts with fault networks and flexures. We analyze the internal structure of such a belt, the western margins of the Dead Sea basin. This basin is 150 km long, 15–20 km wide with more than 10 km of sediment fill; and it is currently subsiding due to slip of the Dead Sea pull‐apart. The western margin of the Dead Sea basin is an elongated N‐S belt with an intricate three‐dimensional (3‐D) pattern of zigzag faults, flexures and joints. The dominant structures are four sets of oblique‐normal faults, arranged in orthorhombic symmetry. The faults are steep with prevalent strike directions of NNW and NNE. Large flexures developed along and above these faults, forming tilted blocks and localized asymmetric folds. Two sets of subvertical joints that dominate the area trend NNE and NNW, subparallel to the strikes of the dominant fault sets. The parallel relations between these structures at all scales suggest that they formed during a single tectonic phase. Three‐dimensional fault modeling reveals a 3‐D strain field with a large vertical shortening, a minor horizontal shortening in N‐S direction (belt‐parallel) and a large horizontal E‐W extension (basinward). The calculated stress fields associated with the zigzag fault segments are compatible with the observed fault‐parallel flexures. Further, the calculations predict the formation of local tensile belts above the faults, and these tensile belts could explain the penecontemporaneous development of the two joint sets. Architecture similar to the western margins of the Dead Sea basin is likely to develop on rifted margins wherever 3‐D deformation is required by the rifting kinematics.

Deep tectonic processes and super-accumulation of metals

Super-accumulation of metals means exceptional large ore deposits with very large ore reserves, which have been called so far by different names as superlarge ore deposits, supergiant ore deposits, gigantic ore deposits, world-class ore deposits, and so on. As they are identical, we propose a unified term of exceptional large ore deposits. From the viewpoint of ore-forming process, the exceptionally large ore deposits are characterized by an explosive anomaly of mineralization. The explosive anomaly usually includes plenty of metal supply, exceptional metallotect convergence and stable physico-chemical conditions needed for super accumulation of metals. This is especially dependent on ore-forming elements, deposit types, metallogenic geochronology, and geological settings. The minimum reserve criteria of exceptional large ore deposits have been proposed for 17 ore-forming commodities, and the exceptional large ore deposits have been selected from the class of world deposits. Their macroscopic distribution generally shows concentration in two gigantic active belts, four stable massifs and on a transitional zone between those two tectonic units. The specific localities could be defined by exceptional metallotect convergence. New attempts have been made to assess the intensity of an explosive anomaly and prove the super-accumulation of metals. These attempts included studies as: (1) ore-forming geochronology by a multidiscipline methods, (2) analysis of thermal events of certain deposit types, (3) analysis of relative abundance of ore reserve and ore-forming period of the deposit. Regarding the genesis of an explosive anomaly, we hereby propose that global thermal event in certain eons and eras in geologic history created them. The global thermal events are tentatively distinguished as an 'excess-oxygen atmospheric event' in the Archean, a 'lack-on-oxygen atmospheric event' in the Proterozoic-Paleozoic, and a major 'tectono-magmatic thermal event' in the Mesozoic-Cenozoic. One example of banded iron formation (BIF), related to an 'excess-oxygen atmospheric event' has been explained. Based on the tectonic settings, geophysical data and metallogenic features mentioned above, we summarize below the deep tectonic processes and super-accumulation of metals as occurred in the Nanling metallogenic province: (1) Continental orogeny is generally divided into 3 types: the marginal continental, intercontinental and intracontinental. The orogenic belt of the Nanling metallogenic province consisted of the Southeastern Coast folded system belonging to the continental marginal orogenic belt in the Mesozoic, and the collision suture belt between the Yangtze and Cathaysian plates and their forelands as the intercontinental orogenic belt in Late Proterozoic to Devonian. After that, a large-scale intracontinental orogenic belt was formed by subduction of the oceanic crust and delamination caused by crust thickening in the Mesozoic, almost completely superimposed on the above two orogenic belts. (2) Eight metallogenic zones and three minerogenic series have been distinguished in the Nanling metallogenic province, based on the tectonic settings and the concept of minerogenic series. One of the mineralization zones is related to continental margin orogeny; another one to intracontinental orogeny; and one is situated in the transitional belt between the two orogenic belts.

Geophysical records of dispersed weathering products on the Frasnian carbonate platform and early Famennian ramps in Moravia, Czech Republic: proxies for eustasy and palaeoclimate

An exceptionally high sea level in Frasnian times (early Late Devonian) changed many peneplained, cratonised and tectonically undisturbed continental margins of tropical belts into carbonate platforms which became covered by thick banks of limestone. The stages marked by very pure carbonates developed during partial sea-level highstands since, when the flooding reached its maximum, the shoreline was distant and conditions for reef growth were good. An increased extension of emerged, flat, coastal areas was coupled with an opposite situation, when oscillating sea level fell to its momentary minimum and the accommodation space available for accumulation of carbonate material was low. Subaerially exposed surfaces were subject to weathering and the products were dispersed by aeolian or aquatic means to form layers when these weathering materials were trapped in carbonates. This overall scenario relating to the trapping of weathering products in pure carbonates was tested at geographically isolated platform with a stable and only slowly subsiding basement (Eastern Moravia, Czech Republic). The amounts of weathering products dispersed in limestone were documented using the combined methods of γ-ray logging, γ-ray spectrometry and magnetic susceptibility measuring, i.e. according to their radioactivity (K, Th and U) and magnetism (Fe). Six third-order Frasnian eustatic cycles have been inferred from the data, with an estimated period of 1 Ma. The Late Frasnian and especially the Frasnian/Famennian (F/F) transition brought the total destruction or at least a strong overlay on this hypothetical background setting. The record of strong sea-level fluctuations in the F/F interval is shown in strong oscillations and offsets related to pronounced hiatuses and flooding surfaces. Such rapid sea-level fluctuation is typical for glacioeustatic control, although the present estimates of the maximum amplitudes are larger than realisable by glaciation events and may be explained in combination with tectonoeustatic models. Comparison of sections between the centre and periphery of the platform substantiates the concept that oscillating Late Frasnian shorelines were rapidly prograding. Very low sea-level stages of early Famennian times changed the depositionary systems from extensive platforms to narrow carbonate ramps which were positioned out and down on the extinct reef bank slopes. The central parts of the Eastern Moravian and also other Frasnian platforms in the world were not normally covered by F/F sediments, the transgressive onlaps above any crystalline highs were not observed and therefore the drowned Frasnian reefs on their periphery, although emphasised by many geologists, may reflect sliding or tectonic subsidence on the margins of platform blocks rather than eustatic rise of sea level.

Thermochronologic constraints on the Late Cenozoic exhumation along the Alpine and West Carpathian margins of the Pannonian basin

The uplifted and partly re-exhumed basement of the Neogene Pannonian basin was investigated by the ap- atite fission track thermochronometer along the marginal belt to the Eastern Alps and the Western Carpathians. In some zones the reset Late Miocene apatite FT ages and the high organic maturation of the Neogene sediments give evidences on the high magnitude of the post-Middle Miocene sediment removal. Thermal modeling of the fission track data allows to quantify this removal and to conclude that its magnitude in the investigated sites was in the range of 1-1.5 km. In this pa- per we review the thermochronologic data and integrate them with the seismic, structural and sedimentological evidences on the Late Miocene-Pliocene erosional phases.