The Malpica–Lamego Line: a major crustal-scale shear zone in the Variscan belt of Iberia

The Malpica–Lamego Line (MLL) is a deformation zone in the Variscan belt of NW Iberia (NW Spain and N Portugal) that runs parallel to the chain for at least 275 km, bearing I-type granodiorite plutons along most of its length. The MLL affects previous structures by which high pressure and ophiolitic rocks were exhumed and emplaced on the Iberian plate during earlier deformation phases. Correlation and reconstruction of the stratigraphy of these sheets or tectonic units at both sides of the shear zone allows a preliminary estimate of the accumulated vertical and horizontal offsets after the tectonic activity of the fault. The value of the separations, of crustal-scale proportions, reaches a maximum 15 km of vertical offset that decreases gradually to the south. The structural record found in the rocks indicates a strike-slip regime that, in general, does not fit the geometry of the offsets. We suggest that the MLL went through two different stages during the same orogenic cycle: a first dip-slip episode, a reverse faulting event, overprinted by a later strike-slip reactivation.     

Assignment of groundwater level at the wastewater collecting pipe for a landfill groundwater simulation: utilization of the two-dimensional saturated–unsaturated groundwater numerical model

In order to understand the effects of a landfill operation on groundwater flow behavior, a 2D horizontal groundwater simulation model was carried out. The model saved the memory of computer and time consumption, comparing it with the 3D groundwater flow model. However, the greatest difficulty is the assignment of the collecting pipe boundary at the study site. Therefore, a 2D vertical model was applied to calculate the change of the groundwater table above the collecting pipe. This paper focuses on examining the validation of the assignment of the collecting pipe boundary by applying the results of the 2D vertical model. The 2D horizontal model was coupled with the recharge model to solve the partial differential equation of groundwater flow. The finite difference method and iterative successive over relaxation were applied. The drainage volume of leachate collection was summed up in the whole landfill site and compared with the average volume of treated wastewater. The study demonstrated that the results of the 2D vertical model validated and can be applied to the 2D horizontal groundwater flow simulation.     

Macroinvertebrate Production in the Submerged Aquatic Vegetation of the Mobile–Tensaw Delta: Effects of an Exotic Species at the Base of an Estuarine Food Web

This study, conducted in 1997, reports the first estimates of the impacts of the proliferation of an exotic submerged aquatic vegetation (SAV) species (Myriophyllum spicatum) on macroinvertebrate production via comparisons with two co-occurring native SAV species (Heteranthera dubia and Vallisneria americana) in the tide-influenced Mobile–Tensaw Delta (located in the north-central Gulf of Mexico, 30°40′ N, 87°55′ W). Production of macroinvertebrates was greatest on M. spicatum and H. dubia and least on V. americana. The key determinant of these differences was a greater abundance of amphipods (Gammarus mucronatus) found on the leaves of M. spicatum and H. dubia. Macroinvertebrate production on M. spicatum was three times greater (>1 kg m^?2 year^?1) than on either of the native SAV species. No-choice palatability tests showed that these differences could not be attributed to differences in invertebrate grazing on these plants. Instead, it is probable that the high production within the structurally complex M. spicatum and H. dubia was the result of reduced predator foraging efficiency. If true, then the presence of this exotic species probably renders this elevated production inaccessible to most high-order predators.     

Hydrochemical evolution of groundwater in a riparian zone affected by acid mine drainage (AMD), South China: the role of river–groundwater interactions and groundwater residence time

Investigations were undertaken in the riparian zone near Shangba village, an AMD area, in southern China to determine the effects that river–groundwater interactions and groundwater residence time have had on environmental quality and geochemical evolution of groundwater. Based on the Darcy’s law and ionic mass balances as well as the method of isotopic tracer, the results showed that there were active interactions between AMD-contaminated river water and groundwater in the riparian zone in the study area. River water was found to be the main source of groundwater recharge in the northwestern part of the study area, whereas groundwater was found to be discharging into the river in the southeastern part of the study area throughout the year. End-member mixing analysis quantified that the contributions of river water to groundwater decreased gradually from 35.9% to negligible levels along the flow path. The calculated mixing concentrations of major ions indicated that water–rock reactions were the most important influence on groundwater quality. The wide range of Ca²⁺?+?Mg²⁺ and HCO₃^? ratios and the change of groundwater type from Ca²⁺–SO₄^2? type to a chemical composition dominated by Ca²⁺–HCO₃^? type indicated a change of the major water–rock reaction process from the influence of H₂SO₄ (AMD) to that of CO₂ (soil respiration) along a groundwater flow path. Furthermore, the kinetics interpretation of SO₄^2? and HCO₃^? concentrations suggested that the overlapping time of their kinetics triggered the hydrochemical evolution and the change of major weathering agent. This process might take approximately 8 years and this kinetic time will be continued when a steady source of contamination enter the aquifer.     

Modeling CO2–brine–rock interactions in the Knox Group: Implications of a deep carbon storage field test in western Kentucky

The Cambrian–Ordovician Knox Group, a thick sequence of dolostone and minor dolomitic sandstone, is a prospective CO₂ sequestration target in the southern Illinois Basin, USA. Thorough evaluation of the Knox Group is critical because the main sequestration target elsewhere in the Illinois Basin, the Cambrian Mount Simon Sandstone, is thin or absent throughout most of Kentucky. A 2477-m-deep carbon storage test well in Hancock County, Kentucky, was drilled, and 626 metric tons of CO₂ was injected into the Knox saline reservoirs. To understand the long-term fate of CO₂ injected into the Knox reservoirs, geochemical reactions between CO₂, brine and rock-forming minerals were modeled using TOUGHREACT. The modeling benefited from a robust data set collected from the test well, including core porosity and permeability, petrographic and X-ray powder diffraction mineralogy, brine chemistry, temperature and pressure measurements. Kinetic batch models and 2-D radial reactive transport models were used to evaluate the migration of the injected CO₂, changes in brine chemistry, and mineral dissolution and precipitation. Results from the kinetic models suggest that sections of the Knox dominated by dolomite have very limited mineral-trapping capacity for CO₂, whereas thin sections of dolomitic sandstone with aluminosilicate minerals such as K-feldspar facilitate mineral trapping. The 2-D model for the CO₂ injection test suggests that, because of the presence of thick permeable intervals in the Knox and the small volume of injected CO₂ in the test, the radius of influence is less than 11 m from the well. The hypothetical long-term injection model indicates, on the other hand, that commercial-scale injection would influence a much larger area and part of the injected CO₂ remains in the supercritical/gas phase for a long time. Because of the buoyancy effect, most supercritical/gas-phase CO₂ migrates upward and stays in the top of the reservoirs dominated by dolomite with small mineral-trapping capacity.     

Geochemical processes in the saltwater–freshwater transition zone: comparing results of a sand tank experiment with field data

Geochemical processes, occurring in a stable transition zone between saltwater and freshwater, were simulated in a 2D, multi-layer flow chamber experiment. Mixing, calcite dissolution, and oxidative degradation of organic matter were identified as the main controlling factors. The results of the chamber experiment were compared to field data and verified by thermodynamic modeling. Similarity in most ion distributions suggests the general applicability of the experimental method. Differences in the redox conditions between field and experiment were reflected by the oxidants involved in the mineralization of organic carbon; while field data show evidence of sulfate reduction, the presence of oxygen in the laboratory experiment resulted in the reoxidation of sulfides.     

Kinematics and significance of a poly-deformed crustal-scale shear zone in central to south-eastern Madagascar: the Itremo–Ikalamavony thrust

International Journal of Earth Sciences - Across the crystalline basement of Madagascar, late Archaean rocks of the Antananarivo Block are tectonically overlain by Proterozoic, predominantly...     

Sediment dispersal system in the Taiwan–South China Sea collision zone along a convergent margin: A comparison with the Papua New Guinea collision zone of the western Solomon Sea

Through a large-scale examination of the morpho-sedimentary features on sea floors in the Taiwan–Luzon convergent margin, we determined the main sediment dispersal system which stretches from 23°N to 20°N and displays as an aligned linear sediment pathway, consisting of the Penghu Canyon, the deep-sea Penghu Channel and northern Manila Trench. The seafloor of South China Sea north of 21°N are underlain by a triangle-shaped collision marine basin, resulting from oblique collision between the Luzon Arc and Chinese margin, and are mainly occupied by two juxtaposed slopes, the South China Sea and Kaoping Slopes, and a southward tilting basin axis located along the Penghu Canyon. Two major tributary canyons of the Formosa and Kaoping and small channels and gullies on both slopes join into the axial Penghu Canyon and form a dendritic canyon drainage system in this collision marine basin. The canyon drainage system is characteristic of lateral sediment supply from flank slopes and axial sediment transport down-canyon following the tilting basin axis. The significance of the collision marine basin in term of source to sink is that sediments derived from nearby orogen and continental margins are transported to and accumulated in the collision basin, serving as a temporary sediment sink and major marine transport route along the basin axis. The comparison of the Taiwan–South China Sea collision zone with the Papua New Guinea collision zone of the western Solomon Sea reveals remarkable similarities in tectonic settings and sedimentary processes that have resulted in similar sediment dispersal systems consisting of (1) a canyon drainage network mainly in the collision basin and (2) a longitudinal sediment transport system comprising a linear connection of submarine canyon, deep-sea channel and oceanic trench beyond the collision marine basin.     

Iblean diatremes 2: shallow marine volcanism in the Central Mediterranean at the onset of the Messinian Salinity Crisis (Iblean Mountains, SE-Sicily)—a multidisciplinary approach

A multidisciplinary analysis of intraplate volcanic complexes interbedded with shallow and deeper marine sediments of a Late Miocene carbonate platform (Iblean Plateau, Sicily) has allowed a detailed paleo-environmental reconstruction. Our approach includes sedimentology, physical volcanology, stratigraphy, geochemistry/mineralogy, paleontology and ⁴⁰Ar/³⁹Ar dating. Four volcanic complexes are distinguished from each other. Two comprise an eastern shallow water platform (diatreme field and Carlentini complex) and two a western deeper water environment representing a seamount belt on the carbonate ramp (Valle Guffari seamount and Mineo complex). The late Miocene volcanism was not time-equivalent: episodic eruptions took place from the Late Tortonian (ca. 9.38 Ma at Mt. Carrubba) to Early Messinian (ca. 6.46 Ma at Valle Guffari). Explosive volcanism of the diatreme field may be related geodynamically to the period of periodic sea-level oscillations at the onset of the Messinian Salinity Crisis. Marine diatomites preserved in the crater areas of two diatremes are the only remnants of Early Messinian diatomites in the eastern Iblean Mountains.     

Evidence of Sr mobility in and around the albite–lepidolite–topaz granite of Beauvoir (France): an in-situ ion and electron probe study of secondary Sr-rich phosphates

The Beauvoir albite–lepidolite–topaz granite is a small, highly evolved intrusion, rich in Li, Rb, F, but also paradoxically rich (or enriched) in Sr (up to 755 ppm) and Ca, a provocative chemical contradiction. Goyazite, an Sr-rich phosphate, is ubiquitous as small secondary grains growing exclusively in albite. Ion microprobe spot analyses reveal variable, higher than whole-rock ⁸⁷Sr/⁸⁶Sr ratios at the crystal scale. These data suggest exchanges between the granite and the surrounding micaschists. A two-stage scenario is proposed: (1) Sr, mainly common, was introduced from the micaschists into the Sr-poor granite at the vanishing time of crystallization, redistributed into zones of preferential permeability and stored in recrystallized P-rich albite, (2) the low-temperature destabilization of albite and lepidolite (host for radiogenic Sr produced by in-situ radioactive ⁸⁷Rb decay), during the Oligocene extensive period, provoked the consequent mixture of both Sr in variable proportions, resulting in the precipitation of goyazite. These results highlight the strong disturbance affecting the Rb–Sr granite system which can be visualized in secondary minerals, such as these low-temperature, micron-size Sr-rich phosphates.Editorial responsibility: J. Touret     

Mobility of rare earth elements in the system soils–plants–groundwaters: a case study of an arid area (Oman)

Groundwater samples from six wells and various species of plants from soils developed on ophiolites were collected from an arid area (AlKhod area, Oman) and analyzed for trace elements including rare earth elements (REEs). The distribution patterns of REEs in plants indicated an enrichment in middle REEs (MREEs?=?Sm to Dy) and heavy REEs (HREEs?=?Ho to Lu), when they are normalized to the REE composition of the Post Archean Australian Shale (PAAS), with a significant negative anomaly in Ce and a positive anomaly in Eu. Compared to Oman ophiolites, the REEs in different species of plants are depleted in Ce and enriched in MREEs and slightly enriched in light REE (LREE?=?from La to Nd). Relative to PAAS, the distribution of REEs in groundwaters revealed similar patterns to the REE distribution in plants. The distribution patterns of REEs in plants relative to those in waters are nearly flat. These patterns suggest that the transfer of REEs from soil solutions to the groundwaters in Oman occurs without any significant fractionation.     

Water–Rock Interactions: An Investigation of the Relationships Between Mineralogy and Groundwater Composition and Flow in a Subtropical Basalt Aquifer

A holistic study of the composition of the basalt groundwaters of the Atherton Tablelands region in Queensland, Australia was undertaken to elucidate possible mechanisms for the evolution of these very low salinity, silica- and bicarbonate-rich groundwaters. It is proposed that aluminosilicate mineral weathering is the major contributing process to the overall composition of the basalt groundwaters. The groundwaters approach equilibrium with respect to the primary minerals with increasing pH and are mostly in equilibrium with the major secondary minerals (kaolinite and smectite), and other secondary phases such as goethite, hematite, and gibbsite, which are common accessory minerals in the Atherton basalts. The mineralogy of the basalt rocks, which has been examined using X-ray diffraction and whole rock geochemistry methods, supports the proposed model for the hydrogeochemical evolution of these groundwaters: precipitation + CO₂ (atmospheric + soil) + pyroxene + feldspars + olivine yields H₄SiO₄, HCO₃ ⁻, Mg²⁺, Na⁺, Ca²⁺ + kaolinite and smectite clays + amorphous or crystalline silica + accessory minerals (hematite, goethite, gibbsite, carbonates, zeolites, and pyrite). The variations in the mineralogical content of these basalts also provide insights into the controls on groundwater storage and movement in this aquifer system. The fresh and weathered vesicular basalts are considered to be important in terms of zones of groundwater occurrence, while the fractures in the massive basalt are important pathways for groundwater movement.     

Fault-related rocks: deciphering the structural–metamorphic evolution of an accretionary wedge in a collisional belt,NE Sicily

The Alpine chain exposed in the Western Mediterranean area represents a front several kilometres in width, dismembered by more recent tectonics and by opening of the Tyrrhenian Basin. In most exposures of this mountain belt, relics of older metamorphic rocks occur. The deformational sequence of events may be revealed by the recognition of metamorphic records associated with different structures. Within a tract of the Alpine front cropping out in the Peloritani Mountains (NE Sicily), we distinguished two metamorphic complexes characterized by different tectonometamorphic histories. Their present tectonic juxtaposition is a cataclastic thrust linked to the recent Africa-verging Sicilian–Maghrebian fold-and-thrust belt. The Lower Complex is characterized by Hercynian metamorphism (P > 0.2 GPa and T ≈ 350°C) exclusively. It essentially consists of very low-grade metapelites and metavolcanic rocks overlain by an unmetamorphosed sedimentary cover. The Upper Complex, comprising different tectonic slices, consists of medium- to high-grade Hercynian metamorphic rocks (P?=?0.3–0.8 GPa and T up to 650°C) with Alpine metamorphic overprint (T > 250°C) affecting also the Mesozoic–Cenozoic cover. Lithotypes, structures, and inferred P–T conditions of investigated rocks suggest the existence of an Alpine accretionary wedge during the Cretaceous deformational collision. Within the Upper Complex, a polyphase Palaeogene mylonitic horizon involving rocks belonging to different tectonic slices fully preserves the tectonometamorphic evolution. For this reason, we focused our attention on these sheared rocks in order to reconstruct the entire tectonic history of this geologically complex area. Our new basic model allows the complex structure of the nappe-pile edifice of the Peloritani Mountains to be simplified, casting new light on the tectonic evolution of this key sector of the southern Calabrian-Peloritani Orogen.     

Congruent melting of calcium carbonate in a static experiment at 3500 K and 10–22 GPa: Its role in the genesis of ultradeep diamonds

Resulting from static experiments performed to study the phase state of CaCO₃, it was found that its melting is congruent at 20–22 GPa and 3500 K. The obtained experiment data show that the field of congruent melting of calcium carbonate is rather broad (form 2300 to 3500–3800 K at 20–22 GPa). However, the potential presence of a high-temperature phase boundary at which CaCO₃ is decomposed into CaO and CO₂ is not ruled out. The existence of a wide area of congruent melting of calcium carbonate (a common primary inclusion in diamonds of the transition zone and lower mantle of the Earth) allow one to consider deep-seated melts as potential parental media for ultradeep diamonds.     

Morphology and impurity elements of zircon in the oceanic lithosphere at the Mid-Atlantic ridge axial zone (6°–13° N): Evidence of specifics of magmatic crystallization and postmagmatic transformations

The paper presents newly obtained original data on the morphology, internal structure (as seen in cathodoluminescence images, CL), and composition of more than 400 zircon grains separated from gabbroids and plagiogranites (OPG) sampled at the axial zone of the Mid-Atlantic Ridge (MAR). The zircons were analyzed for REE by LA-ICP-MS and for Hf, U, Th, Y, and P by EPMA. Magmatic zircon in the gabbroids crystallized from differentiating magmatic melt in a number of episodes, as follows from systematic rimward increase in the Hf concentration, and also often from the simultaneous increase in the (U + Th) and (Y + P) concentrations. These tendencies are also discernible (although much less clearly) in zircons from the OPG. Zircon in the OPG is depleted in REE compared to the least modified zircons in the gabbro, which suggests that the OPG were derived via partial melting of gabbro in the presence of seawater-derived concentrated aqueous salt fluid. Another reason for the REE depletion might be simultaneous crystallization of zircon and apatite. The CL-dark sectors, which are found in practically all of the magmatic zircon grains, have Y/P (a.p.f.u.) ? 1 which most likely resulted from OH accommodation in the zircon structure, a fact suggesting that the OPG parental melt contained water. High-temperature hydrothermal processes induced partial to complete recrystallization of zircon (via dissolution-reprecepitation), a process that was associated with ductile and brittle deformations of the zircon-hosting rocks. The morphology of the hydrothermal zircons varies depending on pH and silica activity in the fluid from weakly corroded subhedral crystals with typical vermicular microtopography of the crystal faces to completely modified grains of colloform structure. Geochemically, the earlier hydrothermal transformations of the zircons resulted in their enrichment in La and other LREE, except only Ce, whose concentration, conversely, decreases compared to that of the unmodified magmatic zircons. The hydrothermal zircon displays a reduced Ce anomaly and its most altered domains typically host minute inclusions of xenotime, U and Th oxides and silicates, and occasionally also baddeleyite, which suggests that the hydrothermal fluid was reduced and highly alkaline. These features were acquired by the seawater-derived fluid when it circulated within the axial MAR zone area due to phase separation in the H₂O–NaCl system and particularly as a result of fluid interaction with the abyssal peridotites of oceanic core complexes. Our data demonstrate that zircon is a sensitive indicator of tectonic and physicochemical processes in the oceanic crust.     

The Chaqupacha Mississippi Valley-type Pb–Zn deposit,central Tibet: Ore formation in a fold and thrust belt of the India–Asia continental collision zone

The newly discovered Chaqupacha Mississippi Valley-type (MVT) Pb–Zn deposit in central Tibet has been found to be helpful for understanding MVT ore formation relative to tectonic evolution of a foreland fold and thrust belt. The deposit lies in the Tuotuohe area of the western Fenghuo Shan-Nangqian fold and thrust belt of the India–Asia continental collision zone. It contains NNW-striking and folded Late Permian strata including an upper clastic unit and an underlying limestone unit. The strata overlie late Oligocene clastic rocks through a south-dipping reverse fault that is associated with regional northward thrusting during the Paleogene. The Late Permian and late Oligocene strata are unconformably overlain by flat-lying early Miocene marl and mudstone of the Wudaoliang Formation. Lead and zinc ores are mainly hosted by pre-ore dissolution and collapse breccias in the Late Permian limestone. The style of mineralization is epigenetic, as shown by replacement of the pre-ore dissolution breccia matrix and open-space-fill by galena, sphalerite, calcite, and minor barite and pyrite. δ³⁴S values of the main sulfide galena range from − 27.5‰ to + 12.6‰. These features, together with the lack of magmatic activity during the mineralization, suggest that Chaqupacha is an MVT deposit. Subordinate mineralization is also present in the early Miocene Wudaoliang Formation marl and the paleokarst breccia which contains matrix compositionally equivalent to strata of the Wudaoliang Formation. The mineralization shares similar mineral associations and textures with the pre-ore dissolution breccia-hosted mineralization. Thus, the Pb and Zn mineralization in the entire deposit probably resulted from the same mineralizing event, which is younger than the youngest ore-hosting rocks (i.e., the early Miocene Wudaoliang Formation). Considering that thrusting in the Tuotuohe area had ceased prior to deposition of the Wudaoliang Formation host rocks, the mineralization at Chaqupacha post-dated the regional deformation. The Chaqupacha deposit thus provides a good example of MVT mineralization in a foreland fold and thrust belt that post-dates regional thrusting.     

Thermodynamics of arsenates,selenites and sulfates in the oxidation zone of sulfide ores: XII. Mineral equilibria in the Cd–Se–H<Subscript>2</Subscript>O system at 25°C

Understanding the mechanisms of cadmium and selenium behavior under near-surface conditions is very important for solving certain environmental problems. The principal aim of this study is physicochemical analysis of the formation conditions of synthetic cadmium selenite CdSeO₃ · H₂O and experimental investigation of its thermal stability and dehydration and dissociation mechanisms. The synthesis was performed by boiling-dry aqueous solutions of cadmium nitrate and sodium selenite. The obtained samples were identified with electron microprobe and powder X-ray diffraction. Complex thermal analysis (thermogravimetry and differential scanning calorimetry) have shown that CdSeO₃ · H₂O is dehydrated at 177–241°C in two stages, apparently corresponding to the formation of CdSeO₃ · 2/3H₂O. The Eh–pH diagrams were calculated using the Geochemist’s Workbench (GWB 9.0) software package. The Eh–pH diagrams have been calculated for the Cd–Se–Н₂О and Cd–Se–CO₂–H₂O systems for the average content of these elements in underground waters. The formation of cadmium selenite, CdSeO₃ · H₂O in the oxidation medium is quite possible. The existence of CdSeO₃ is possible at high temperature.