Unravelling the fluid flow evolution and precipitation mechanisms recorded in calcite veins in relation to Pangea rifting–Newark Basin,USA

Calcite veins hosted in the Triassic Stockton, Lockatong and Passaic formations of the Newark Basin are investigated to reconstruct the fluid evolution. To constrain the parameters of calcite precipitation, a microthermometry study was carried, which reveals precipitation of calcite from a low to moderate saline H₂O-NaCl fluid (0.4 to 13.2 wt% NaCl equiv.) under low to moderate hydrothermal (137 °C to 232 °C) conditions. This fluid composition is interpreted to reflect mixing between a deep basement-derived heated diluted fluid and relatively low to moderate saline diagenetic formation waters hosted in the different Triassic formations. Carbon and strontium isotope analysis on the vein calcites suggests that these elements are derived from the pre-Triassic basement and the sedimentary cover through fluid-rock interactions. The aforementioned geochemical findings are supported by Rare Earth Elements and Yttrium (REY) systematics and oxygen isotope data.The Late Triassic extensional activity and gravity-driven fluid flow mechanism facilitated the infiltration of meteoric waters to deeper lithostratigraphic units (i.e., Precambrian-Paleozoic basement-Triassic Stockton Formation) where they became heated. In response to the extensional tectonics, the deep-seated hydrothermal basement-derived diluted fluids migrated upward along the tectonic-related fractures and the major faults to upper shallow crustal levels. Here, the heated, diluted meteoric waters were mixed with low, moderately saline, and relatively cooler formation waters, leading to calcite precipitation. The pH increase is suggested to be a contributing factor in the precipitation of calcite.     

Tremolite–calcite veins in the footwall of the Simplon Fault,Antigorio Valley,Lepontine Alps (Italy)

The lowermost units of the nappe pile of the Lepontine Alps crop out in the Antigorio valley in the footwall of the Simplon Fault. The whole orthogneiss section of the Antigorio Unit is exposed on both sides of the valley, sandwiched between the Mesozoic metasedimentary sequences of the Baceno unit below and the Tèggiolo unit above. The petrography and mineral composition of tremolite–calcite veins occurring in dolomite marble in both metasedimentary sequences were investigated. Tremolite–calcite (with lesser talc and minor phlogopite) veins have rhythmic banded texture. Banding is due to cyclic differences in modal abundances and fabric of tremolite and calcite. These veins are very similar to those occurring in dolomite rafts within the Bergell granite and it is inferred that they formed by the same “fracture-reaction-seal” mechanism. Veins formed by reaction of a silica-rich aqueous fluid with the host dolomite marble along fractures. According to thermo-barometric calculations, based on electron microprobe analyses, reaction occurred at temperatures between 450 and 490°C and minimum pressure of 2–3 kbar. Such temperature conditions occurred in this footwall region of the Simplon Fault Zone around 15 Ma, during exhumation and cooling of the nappe pile and a transition to brittle behaviour. Aqueous, silica-rich fluids concentrated along fractures, forming tremolite–calcite veins in the dolomite marbles and quartz veins in the orthogneiss.     

Fluid immiscibility and gold deposition in the Birimian quartz veins of the Angovia deposit (Yaouré, Ivory Coast)

The Paleoproterozoic terranes (Birimian) of West Africa are well known to host numerous economic gold mineralizations. The Angovia gold mineralization is located in a brecciated and mylonitic zone within the Birimian greenstones. The sulfide–gold mineralization is mainly represented by gold associated with pyrite and chalcopyrite. A fluid inclusion study undertaken on mineralized quartz veins revealed the presence of aqueous-carbonic (CO₂–H₂O) fluids, the association of carbonic (CO₂) and early aqueous fluids, followed by later aqueous (H₂O-salt) and finally nitrogen-rich fluids. Entrapment of the initial homogeneous aqueous-carbonic fluids prior to fluid immiscibility depicts the evolution of the P–T conditions during the exhumation of the terranes after the peak of green-schist metamorphism. The CO₂ rich-fluid occurs especially in gold-bearing quartz, and are considered as the main evidence of the ore-forming process in the gold-bearing quartz veins. It is considered as a product of immiscibility of the CO₂–H₂O parent. The volatile fraction of carbonic and aqueous-carbonic fluid inclusions is dominated by CO₂, containing minor amounts of N₂, even smaller amounts of CH₄ and sporadically, H₂S. The aqueous-carbonic fluids have moderate salinity (3–10 wt.% eq. NaCl). Late aqueous and N₂ – (CH₄–CO₂) fluids are considered as later, unrelated to the main ore stage, and were trapped during the cooling of the hydrothermal system from 300 to 200 °C.The immiscibility has been favored by a strong pressure drop, the main trapping P–T conditions being 320–370 °C and 105–135 MPa. The mineralizing process is likely related to the immiscibility event, which was probably favored by the release of the fluid pressure after fracturing along the main shear zones. The ore process is likely to have occurred along the main shear zones or related secondary structures affected by cycling of the fluid pressure and quartz sealing–fracturing processes. The superimposed process can also explain the relative complexity of the quartz textures and fluid inclusion microfractures, and the rather wide range in the density of both parent fluid and CO₂-dominated fluid.     

Repeated seismic slips recorded in ultracataclastic veins along active faults of the Arima–Takatsuki Tectonic Line,southwest Japan

Field investigations, combined with meso- and microstructural analyses, reveal that numerous ultracataclastic veins are widely developed within a fault zone (<150 m wide) as simple veins, complex lenses, and networks, along active faults of the Arima–Takatsuki Tectonic Line, southwest Japan. These veins comprise mainly pseudotachylyte-like vein and weakly consolidated to unconsolidated fault gouge that is black, dark-brown, brown, gray, and brownish-red in color. Meso- and microstructural features show that these pseudotachylyte-like and fault gouge veins and networks formed during multiple stages, as earlier veins are generally cut and overprinted by younger veins, indicating that the vein-forming events occurred repeatedly and that ultracataclastic material was injected into networks of faults and fractures in the fault zone. The pseudotachylyte-like and fault gouge veins are characterized by an ultrafine- to fine-grained matrix and angular to subangular fragments of host granitic rocks of various sizes, ranging from submicron to millimeters. SEM–EDS (Scanning Electronic Microscope-Energy Dispersive X-ray) and powder X-ray diffraction analyses show that all the ultracataclastic veins are characterized by crystalline materials composed mainly of quartz and feldspar, similar to the host granitic rocks.The present results support the existing hypothesis that ultrafine- to fine-grained materials formed by comminution can be fluidized and injected rapidly into fracture networks located far from the source fault plane in a solid–fluid–gas system during seismic slip; therefore, such materials provide a record of paleoseismic faulting events that occurred repeatedly within the seismogenic fault zone.     

UHP metamorphism recorded by kyanite-bearing eclogite in the Seve Nappe Complex of northern Jämtland,Swedish Caledonides

The first evidence for ultrahigh-pressure (UHP) metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides is recorded by kyanite-bearing eclogite, found in a basic dyke within a garnet peridotite body exposed close to the lake Friningen in northern Jämtland (central Sweden). UHP metamorphic conditions of ~ 3 GPa and 800 °C, within the stability field of coesite, are constrained from geothermobarometry and calculated phase equilibria for the peak-pressure assemblage garnet + omphacite + kyanite + phengite. A prograde metamorphic evolution from a lower P–T (1.5–1.7 GPa and 700–750 °C) stage during subduction is inferred from inclusions of pargasitic amphibole, zoisite and kyanite in garnet cores. The post-UHP evolution is constrained from breakdown textures, such as exsolutions of kyanite and silica from the Ca-Eskola clinopyroxene. Near isothermal decompression of eclogite to lower crustal levels (~ 0.8–1.0 GPa ) led to formation of sapphirine, spinel, orthopyroxene and diopside at granulite facies conditions. Published age data suggest a Late Ordovician (460–445 Ma) age of the UHP metamorphism, interpreted to be related to subduction of Baltoscandian continental margin underneath an outboard terrane, possibly outermost Laurentia, during the final stages of closure of the Iapetus Ocean. The UHP rocks were emplaced from the hinterland collision zone during Scandian thrusting of the nappes onto the Baltoscandian foreland basin and platform. The record of P–T conditions and geochonological data from UHP rocks occurring within the allochthonous units of the Scandinavian Caledonides indicate that Ordovician UHP events may have affected much wider parts of the orogen than previously thought, involving deep subduction of the continental crust prior to final Scandian collision between Baltica and Laurentia.     

Environmental changes and carbon cycle perturbations at the Triassic–Jurassic boundary in northern Switzerland

The Triassic–Jurassic boundary is characterized by strong perturbations of the global carbon cycle, triggered by massive volcanic eruptions related to the onset of the Central Atlantic Magmatic Province. These perturbations are recorded by negative carbon isotope excursions (CIEs) which have been reported worldwide. In this study, Triassic–Jurassic boundary sections from the southern margin of the Central European Basin (CEB) located in northern Switzerland are analyzed for organic carbon and nitrogen isotopes in combination with particulate organic matter (POM) analyses. We reconstruct the evolution of the depositional environment from Late Triassic to Early Jurassic in northern Switzerland and show that observed negative shifts in δ¹³C of the total organic carbon (δ¹³C_TOC) in the sediment are only subordinately influenced by varying organic matter (OM) composition and primarily reflect global changes in the carbon cycle. Based on palynology and the stratigraphic positions of isotopic shifts, the δ¹³C_TOC record of the studied sections is correlated with the GSSP section at Kuhjoch (Tethyan realm) in Austria and with the St. Audrie’s Bay section (CEB realm) in southwest England. We also show that in contrast to POM analyses the applicability of organic carbon/total nitrogen (OC/TN) atomic ratios and stable isotopes of total nitrogen (δ¹⁵N_TN) for detecting changes in source of OM is limited in marginal depositional environments with frequent changes in lithology and OM contents.     

Stress orientation to 5 km depth in the basement below Basel (Switzerland) from borehole failure analysis

A vertical profile of maximum horizontal principal stress, SHmax, orientation to 5 km depth was obtained beneath the Swiss city of Basel from observations of wellbore failure derived from ultrasonic televiewer images obtained in two 1 km distant near-vertical boreholes: a 2755 m exploration well (OT2) imaged from 2550 m to 2753 m across the granitic basement-sediment interface at 2649 m; and a 5 km deep borehole (BS1) imaged entirely within the granite from 2569 m to 4992 m. Stress-related wellbore failure in the form of breakouts or drilling-induced tension fractures (DITFs) occurs throughout the depth range of the logs with breakouts predominant. Within the granite, DITFs are intermittently present, and breakouts more or less continuously present over all but the uppermost 100 m where they are sparse. The mean SHmax orientations from DITFs is 151 ± 13° whereas breakouts yield 143 ± 14°, the combined value weighted for frequency of occurrence being N144°E ± 14°. No marked depth dependence in mean SHmax orientation averaged over several hundred meters depth intervals is evident. This mean SHmax orientation for the granite is consistent with the results of the inversion of populations of focal mechanism solutions of earthquakes occurring between depths of 10–15 km within regions immediately to the north and south of Basel, and with the T-axis of events occurring within the reservoir (Deichmann and Ernst, this volume). DITFs and breakouts identified in OT2 above and below the sediment-basement interface suggest that a change in SHmax orientation to N115°E ± 12° within the Rotliegendes sandstone occurs near its interface with the basement. The origin of the 20–30° change is uncertain, as is its lateral extent. The logs do not extend higher than 80 m above the interface, and so the data do not define whether a further change in stress orientation occurs at the evaporites. Near-surface measurements taken within 50 km of Basel suggest a mean orientation of N–S, albeit with large variability, as do the orientation of hydrofractures at depths up to 850 m within and above the evaporite layers and an active salt diapir, also within 50 km of Basel. Thus, the available evidence supports the notion that the orientation of SHmax above the evaporites is on average more N–S oriented and thus differs from the NW–SE inferred for the basement from the BS1/OS2 wellbore failure data and the earthquake data. Changes in stress orientation with depth can have significant practical consequences for the development of an EGS reservoir, and serve to emphasise the importance of obtaining estimates from within the target rock mass.     

Fluid–rock interactions related to metamorphic reducing fluid flow in meta-sediments: example of the Pic-de-Port-Vieux thrust (Pyrenees,Spain)

In orogens, shortening is mainly accommodated by thrusts, which constitute preferential zones for fluid–rock interactions. Fluid flow, mass transfer, and mineralogical reactions taking place along thrusts have been intensely investigated, especially in sedimentary basins for petroleum and uranium research. This study combines petrological investigations, mineralogical quantifications, and geochemical characterizations with a wide range of analytical tools with the aim of defining the fluid properties (nature, origin, temperature, and redox) and fluid–host rock interactions (mass transfers, recrystallization mechanisms, and newly formed synkinematic mineralization) in the Pic-de-Port-Vieux thrust fault zone (Pyrenees, Spain). We demonstrate that two geochemically contrasted rocks have been transformed by fluid flow under low-grade metamorphism conditions during thrusting. The hanging-wall Triassic red pelite was locally bleached, while the footwall Cretaceous dolomitic limestone was mylonitized. The results suggest that thrusting was accompanied by a dynamic calcite recrystallization in the dolomitic limestone as well as by leaching of iron via destabilization of iron oxides and phyllosilicate crystallization in the pelite. Geochemical and physical changes highlighted in this study have strong implications on the understanding of the thrust behavior (tectonic and hydraulic), and improve our knowledge of fluid–rock interactions in open fluid systems in the crust.     

Nd isotope systematics of the Vendian–Early Cambrian sedimentary ores in the northern segment of the Paleoasian Ocean

Isotope–geochemical studies of Mn, P, and Ba ores were performed in order to establish the influence of submarine hydrotherms on the formation of Early Cambrian sedimentary rocks of the southern environs of the Siberian Platform. Based on study of the geochemical and isotope (ε_Nd) characteristics of the shallow-water Mn and Ba ores and phosphorites of southern environs of the Siberian Platform with similar ages, two types of sedimentary basins of the different geodynamic origins were distinguished: intraplate oceanic and those of the active continental margin, for which the sources of ore materials differ by the proportions of the mantle and contaminated crustal matter.     

Fluid–rock interaction during subsolidus microtextural development of alkali granite as exemplified by the Saertielieke pluton,Ulungur of the northern Xinjiang,China

Three lithological Groups I (medium-grained, with magmatogenic arfvedsonite), II (medium-grained, with secondary arfvedsonite) and III (fine-grained, with magmatogenic arfvedsonite) are identified in the Saertielieke alkali granite pluton, Ulungur of the northern Xinjiang, China. A weak negative correlation between the δ¹⁸O values of alkali feldspar and quartz separates from each group, and the distinctly lower δ¹⁸O values of alkali feldspar separates from Groups I and II than those from Group III are interpreted in terms of superimposed closed-system and open-system isotope exchange. A small amount of locally exsolved magmatic fluid is involved in the development of the perthitic texture in alkali feldspar at ∼400 °C that results in a volume increase and, hence, causes quartz deformation. The microtextural changes promote the closed-system oxygen isotope exchange between quartz and alkali feldspar that causes a dispersion in the quartz δ¹⁸O values. However, the distinctly lower δ¹⁸O values of alkali feldspar and secondary arfvedsonite coupled with their microtextural characteristics indicate that meteoric-derived water plays an important role in the further development of alkali feldspar exsolution texture at T<400 °C and directly causes secondary arfvedsonite formation. The estimated relative exchange rates k_Quartz/k_Feldspar/k_Arfvedsonite of ∼10/100/1 for Groups I and III, and ∼10/100/100 for Group II suggest that alkali feldspar, quartz, and secondary arfvedsonite have exchanged with meteoric-derived water mainly via dissolution–reprecipitation, whereas magmatogenic arfvedsonite has exchanged via diffusion.     

Cold subduction zone in northern Calabria (Italy) revealed by lawsonite–clinopyroxene blueschists

Lawsonite blueschists are important markers of cold subduction zones, subjected to intense fluid circulation. This is because lawsonite preservation in exhumed blueschists and eclogites is typically linked to cold exhumation paths, accompanied by hydration. In the Catena Costiera (Calabria, southern Italy), lawsonite–clinopyroxene blueschists of the Diamante–Terranova Unit, affected by ductile shearing and retrogression, are exposed. Blueschists contain zoned clinopyroxene crystals, showing core–rim compositional variation from diopside to omphacite and hosting primary inclusions of lawsonite and titanite. Thermodynamic modelling of phase equilibria in the NCKFMASHTO system revealed peak metamorphic conditions of 2.0–2.1 GPa and 475–490°C for the Alpine subduction in Calabria. The subsequent post-peak metamorphic evolution mainly proceeded along a decompression and cooling path up to ~1.1 GPa and ~380°C. The final exhumation stages are recorded in the sheared blueschists where a mylonitic to ultramylonitic foliation developed at ~0.7 GPa and 290–315°C. Therefore, the P–T evolution of the Diamante–Terranova blueschists mostly occurred in the stability field of lawsonite, sustained by H₂O-saturated conditions during the exhumation path. The results of this study indicate that the blueschists underwent peak metamorphic conditions higher than previously thought, reaching a maximum depth of ~70 km under a very cold geothermal gradient (~6.6°C/km), during the Eocene subduction of the Ligurian Tethys oceanic crust in Calabria.     

A unique Paleoproterozoic HP–UHT metamorphic event recorded by the Bengbu mafic granulites in the southwestern Jiao–Liao–Ji Belt,North China Craton

The Wuhe Complex in the Bengbu area of the Jiao–Liao–Ji Belt, southeast North China Craton, contains garnet-bearing mafic granulites that have undergone high-pressure (HP) and ultrahigh-temperature (UHT) metamorphism. These granulites also experienced partial melting and occur as lenses within marbles. Petrographic observations and quantitative phase equilibria modeling reveal clockwise P–T paths, involving an inferred HP stage followed by decompressional, medium-pressure, granulite-facies metamorphism and subsequent cooling. The HP assemblage of garnet + clinopyroxene + plagioclase + K-feldspar ± amphibole ± quartz ± rutile indicates P–T conditions of 840–980 °C and 12–17 kbar. This was followed by post-peak, near-isothermal decompression with the development of orthopyroxene + clinopyroxene + plagioclase + K-feldspar + garnet + amphibole + ilmenite at 850–960 °C and 7–10 kbar, resulting in the development of orthopyroxene rims on resorbed garnet. Pyroxene and ternary feldspar thermometry yielded high temperatures of ~1150 °C and 1055–1087 °C at 10 kbar, respectively, which constrain the minimum crystallization temperatures of the igneous protoliths. The host and lamellae of the pyroxene and ternary feldspar are relict magmatic minerals/textures that survived metamorphism due to the silica-undersaturated bulk-rock conditions. Zr-in-rutile thermometry yielded temperatures of ~935 °C and 800 °C, with the former being consistent with the predicted peak metamorphic temperatures. Small amounts of melts (up to 5%) were generated during decompression of the Bengbu mafic granulites. The generated partial melts were mainly (quartz) monzonite at 900–920 °C, and the silica contents of the melts were controlled by the quartz stability field in P–T pseudosections. The partial melts were enriched in Na and strongly depleted in Fe–Mg at the peak pressure of ~14 kbar and 920 °C, and later evolved to Fe–Mg-rich and high-K compositions during decompression. The melt compositions in the studied rocks are similar when the pressures reached ~9 kbar. The modal proportion of amphibole increased as the melt H₂O content decreased at lower pressures, indicating that the limited H₂O remaining in the host rocks was consumed to produce amphibole. U–Pb geochronology of zircon containing inclusions of clinopyroxene, plagioclase, and apatite constrains the timing of metamorphism to 1930–1840 Ma, as is the case for HP granulites from Shandong, Liaoning, and southern Jilin in the central and northeastern Jiao–Liao–Ji Belt. The Wuhe HP–UHT mafic granulites were ultimately sourced from upwelling asthenosphere-derived magma at ~2.1 Ga, which intruded and crystallized at shallower depths. The igneous protoliths were then buried to middle–lower crustal levels and experienced HP–UHT granulite-facies metamorphism and partial melting at 1.95–1.90 Ga related to continental subduction and overthickening. The HP–UHT mafic granulites were rapidly exhumed at ~1.85 Ga and generated small volumes of (quartz) monzonite during decompression. The newly discovered Paleoproterozoic HP–UHT mafic granulites associated with partial melting suggest that the continent materials were deeply subducted to the lower crustal levels and that additional heating was not involved. The finding of the HP–UHT granulites, together with the widespread distributions of the granulite-facies metamorphic rocks and the determination of the clockwise P–T–t paths, reveal that the Paleoproterozoic Jiao–Liao–Ji orogenic belt extends at least 1000 km, starting from southern Jilin, passing through the southeastern Liaoning and Jiaobei terranes, and elongating to the Bengbu area in Anhui.     

River channel evolution and tsunami impacts recorded in local sedimentary archives – the ‘Fiume Morto’ at Ostia Antica (Tiber River,Italy)

Ostia, the ancient port of Rome at the mouth of the river Tiber (Italy), flourished until the 2nd Century ad , although massive siltation had already caused the abandonment of its lagoonal harbour in the 1st Century bc . In search of an alternative harbour site, geomorphological and geoarchaeological research was carried out in the ‘Fiume Morto’, an abandoned Tiber meander to the immediate north of the town. To reconstruct its complex development and evaluate the suitability of the river channel as a fluvial harbour, a transect perpendicular to the former river channel's flow axis was systematically explored by a new methodological approach combining electrical resistivity tomography, direct push-electrical conductivity sensing and vibracores. Together with microfossil, mineralogical and geochemical analyses of sediment samples and 50 radiocarbon dates, in-depth stratigraphic data support a detailed reconstruction of different Tiber channel generations. Results reveal a meander development closely related to distinct ‘cut and fill’ dynamics. Inactive river channels were repeatedly filled with lagoonal sediments, abruptly followed by phases of intense incision. Yet, the overall Fiume Morto channel structure remained stable and almost in situ over centuries, showing nearly no lateral changes since the southward shift of the Tiber River mouth in the first millennium bc . In the 1st Century bc , channel conditions favoured navigation and transportation of goods with large ships. Open-water conditions, suitable for anchoring and landing activities, dominate from the 1st Century ad until 1557 ad , when the Fiume Morto meander was finally cut off and silted up within a short time. Within the fluvial deposits, sediments most likely related to tsunami inundations are preserved. These events occurred sometime before the 2nd Century bc , in the early 1st Century ad and in the 17th Century ad or later. Results are consistent with traces of tsunami influence found in Ostia's western lagoonal harbour.     

Tectonically-driven underfilled–overfilled cycles,the middle Cretaceous in the northern Cordilleran foreland basin

It is shown that the middle Cretaceous succession in the northern Cordilleran foreland basin consists of several-million-year tectonically-driven cycles comprising two components: strata deposited in an underfilled basin with a prominent forebulge zone and strata deposited in an overfilled basin lacking evidence of a forebulge. The episodic thrusting of the Cordilleran orogenic wedge and its rich sediment supply to the basin are two main controlling factors for the formation of these cycles. A qualitative model of several-million-year tectonically-driven underfilled–overfilled cycle for migration and stratigraphic fill in this basin is proposed. During the early underfilled period (orogenic loading period), due to orogenic loading of emplaced thrust sheets, flexural subsidence is created in the region proximal to the mountain belt and a prominent forebulge is developed. During the late underfilled period (early orogenic unloading period), as the cratonward migration of the subsidence center of sediment loading in the foredeep zone, forebulge zones and backbulge zones migrate cratonwards, forming a diachronic erosion surface in the central basin. During the overfilled period (late orogenic unloading period), a prominent erosion forms in the proximal basin and a peripheral sag develops above the forebulge area of the previous underfilled period. This model may provide a pattern to subdivide sedimentary successions in the Cordilleran foreland basin. Using this model, alternative interpretations are suggested for some important, but controversial stratigraphic phenomena in the Cretaceous Cordilleran foreland basin: traditionally defined eustatic highstands, wide sedimentation area of the basin, erosion surfaces and widespread subtle topographic uplifts in the central basin, high-frequency coarsening-up cycles, extensively distributed erosive-based sandstones and conglomerates enclosed in marine mudstones.     

Paleogene-Neogene sediments of Bel’kov Island (New Siberian Islands): Characteristics of sedimentary cover in the eastern Laptev shelf

This work is aimed at characterizing the 40-m-thick Paleogene-Neogene sedimentary sequence of Bel’kov Island, which was accumulated in the marginal part of a fluvial plain. On the basis of the plant megafossils and spore-pollen data, the studied sediments were formed in the Late Eocene-Early Miocene with a probable sedimentation gap at the Eocene-Oligocene boundary. It was substantiated that the Paleogene-Neogene sediments were developed as a continuous cover over the entire area of Bel’kov Island. Later, they were eroded away from the island, but presumably preserved on the Bel’kov Horst and Zarya Strait. This suggests that the pre-Quaternary seismic complex, which continuously covers the Bel’kov Horst, also has Late Eocene-Early Miocene age. Selective dating of nonrounded detrital zircons from Lower Miocene conglomerates allowed us to substantiate the transportation of sediments from the Verkhoyansk-Kolyma Fold System along the Bel’kov-Svyatoi Nos Graben. The crystalline basement similar to the Ust’-Lena inlier was likely exposed on the East Laptev Horst and served as the source of metamorphic detritus, including zircons dated within 1850–2000 Ma.     

Formation of kyanite–quartz veins of the Alpe Sponda,Central Alps,Switzerland: implications for Al transport during regional metamorphism

In this study, we have investigated the formation of quartz–kyanite veins of the Alpe Sponda, Central Alps, Switzerland. We have integrated field observations, fluid inclusion and stable isotope data and combined this with numerical geochemical modeling to constrain the chemical processes of aluminum transport and deposition. The estimated P–T conditions of the quartz–kyanite veins, based on conventional geothermometry (garnet–biotite, white mica solvus and quartz–kyanite oxygen isotope thermometry) and fluid inclusion data, are 550 ± 30°C at 5.0 ± 0.5 kbar. Geochemical modeling involved construction of aqueous species predominance diagrams, calculation of kyanite and quartz solubility, and reaction–path simulations. The results of the modeling demonstrate that (1) for the given chemical composition of the vein-forming fluids mixed Al–Si aqueous species are dominant in transporting Al, and that (2) fluid cooling along a small temperature gradient coupled with a pH decrease is able to explain the precipitation of the quartz–kyanite assemblages in the proportions that are observed in the Alpe Sponda veins. We conclude that sufficient amounts of Al can be transported in typical medium- to high-grade regional metamorphic fluids and that immobile behavior of Al is not very likely in advection–dominanted fluid–rock systems in the upper and middle crust.     

Urban land use/land cover changes in the Tema metropolitan area (1990–2010)

Land use and land cover changes are local and place specific, occurring incrementally in ways that often escape our attention. This study sought to detect changes in land cover in the Tema Metropolis of Ghana from 1990 to 2010. Multispectral Landsat Thematic Mapper data sets of 1990, 2000 and 2007 were acquired, pre-processed and enhanced. Unsupervised classification of the images was performed and six land cover classes (water, wetlands, closed vegetation, open vegetation, cropped lands, and built-up) were derived. The post-classification change detection technique was performed to derive the changes in land cover and their corresponding change matrices. Between 1990 and 2010, built-up areas expanded steadily to become the most prevalent land cover type in the metropolis, reducing vegetation cover dramatically. High population growth with its attendant rise in the demand for housing, and increasing commercial activities, were found to have influenced land cover changes over the period.     

Cephalopod associations and palaeoecology of the Cretaceous (Barremian–Cenomanian) succession of the Alpstein,northeastern Switzerland

The Alpstein (cantons of Appenzell Ausserrhoden, Appenzell Innerrhoden and St. Gallen, northeastern Switzerland) has been of great interest for geologists over the last decades because of its excellent outcrops. However, there was no comprehensive overview over its Cretaceous fossil content. Here, we describe the cephalopod associations, which are moderately to highly diverse in some strata of the Alpstein. Furthermore, we document the regional palaeoecological changes that occurred during the radiation of heteromorph ammonites (ancyloceratids, scaphitids, turrilitids). To examine the palaeoecological changes, we quantitatively determined the macrofossil content of 11 associations of Barremian to early Cenomanian age. Here, we document 6 species (3 genera) of nautilids and 77 species (45 genera) of ammonoids (29 of the species are recorded from Switzerland for the first time). Our palaeoecological analyses revealed the disappearance of nektoplanktonic forms after the late Barremian to the middle early Aptian in the course of the development of a shallow carbonate platform. The upper lower Aptian to middle Albian strata were eroded due to successive emersion phases and condensation processes. In the late Albian, the number of nektoplanktonic species surged again with some benthos, followed by the Cenomanian fauna, which is dominated by nektoplanktonic elements including ammonites, belemnites and nautilids with only very little benthos. These results correlate well with the regional sea level fluctuations.