Low-grade Metamorphic Rocks Research Articles

Genesis of the Banxi Sb deposit, South China: Constraints from wall-rock geochemistry, fluid inclusion microthermometry, Rb–Sr geochronology, and H–O–S isotopes

The Banxi Sb deposit is located in the world-class central-western Hunan Sb belt in South China, with quartz-vein type Sb-only mineralization hosted by Neoproterozoic epimetamorphic clastic sedimentary rocks. In this contribution, microthermometric, Rb–Sr geochronological and H–O isotopic analyses on fluid inclusions trapped in quartz, S isotopic studies on stibnite, and major-trace elemental measurements on fluid-altered and unaltered wall-rocks are presented to constrain the genesis of the deposit. The fluid inclusions are characterized by low homogenization temperature (170–260 °C) and low salinity 3–7 wt% NaCl equiv., with a low fluid density of 0.72–0.93 g/cm3 and a pH of 5.59. The low δDw (fluid δ2H, –140‰ to –107‰) whereas positive δ18OV-SMOW (15.9–17.2‰) and δ18Ow (fluid δ18O, 5.9–8.4‰) values in quartz indicate that the mineralizing fluid was generated from the low-grade metamorphic basement rocks and received a certain input of meteoric water. The Rb–Sr isotopic compositions of quartz samples yielded an isochron age of 196 ± 4 Ma (1σ, MSWD = 0.70) for quartz-stibnite ores. A highly radiogenic 87Sr/86Sr value (0.72663–0.74002, initial 87Sr/86Sr = 0.72640) indicates that ore-forming materials are derived mainly from basement rocks, and a direct material contribution from local granitic rocks can be ruled out. The δ34SV-CDT values of stibnite range narrowly from 4.81‰ to 6.72‰ and are in the δ34SV-CDT range of the metamorphic rocks, indicating that the sulfur was sourced from the basement rocks by sulfate reduction. Compositional differences between fluid-altered (decolorized) and unaltered wall-rocks are obvious: the migrated SiO2, SO3, LREE, Hf, Nb, Zr, Ta, Th, U, Mo, Sn, W into altered wall-rocks suggests a deep basement metamorphic rocks-derived Si-rich alkaline brine for the fluid-rock interaction; while the leached Fe2O3, MgO, MnO, TiO2, Ba, Cs, Rb, As, Co, V, Ni, Sb, Sc, Cu, Pb and Zn from the altered rocks imply a material contribution of Banxi Group wall-rocks during the Sb mineralization process. Consequently, we conclude that the quartz-stibnite stage of the Banxi Sb deposit was formed during the Late Triassic orogeny in the Xuefeng Mountain region. Heated by granitic magmatism, Sb and S were leached from the basement rocks, forming an initial Si-rich and alkaline ore-bearing fluid. Precipitation of stibnite from the fluid resulted from interacting with wall-rocks and mixing of meteoric water, coupled by releasing of stress, decreasing of temperature and lowering of the pH at higher crustal levels.

Trace elements geochemistry in high-incidence areas of liver-related diseases, northwestern Ethiopia

This paper reports the results of trace elements geochemistry from Tigray national state, northwestern Ethiopia. The area is part of the Arabian-Nubian Shield, where the dominant exposure is low-grade metamorphic rocks and has a long history of liver-related diseases. The increase in the number of liver-related disease patients of the area has been an environmental health issue of national concern. The aim of the study is to determine the level of trace element concentrations and distributions in water and stream sediments of the area and identify the possible sources in relation to human health. Water, stream sediment and rocks samples (20 water, 20 stream sediments, and 6 rock samples) were collected in March 2011 and analyzed for major and trace element contents using ICP-MS, ICP-OES, ion Chromatography, and XRF methods. Bromine, aluminum, fluorine, arsenic, and nitrate values exceed the WHO maximum acceptable concentration (MAC) for drinking purpose. Bromine ranges from 0.11 to 1.48 mg/l show higher values in all samples, and fluorine ranges from 0.21 to 16.49 mg/l show higher values in 20% of the samples. Other trace elements are aluminum—30%, arsenic—10%, and nitrate (NO3)—10%, and they are examples of elements which have above MAC for drinking water. Selenium deficiency may be the other problematic element in the area for which its deficiency is associated with liver damage and heart muscle disorder. The concentration of cobalt and chromium exceeded world geochemical background value in average shale at most sample stations indicated that these stations were in potential risk.

Genesis of the Selinsing gold deposit, Peninsular Malaysia: Constraints from mineralogy, geochemistry and in situ sulfur isotope compositions of sulfides

As a renowned orogenic lode gold deposit, the Selinsing gold deposit is located in the Central Belt of Peninsular Malaysia. Geologically, the gold deposit is characterized by auriferous quartz veins and fine-grained gold minerals coexisted with sulfides, and the ore body is hosted by low-grade metamorphic sedimentary rocks and volcanic rocks. Furthermore, gold mineralization is closely related to tectonic deformation. Four main stages of vein formation have been identified, namely, (1) quartz-pyrite-arsenopyrite vein, (2) quartz-pyrite-gold vein, (3) quartz-stibnite-pyrite vein, and (4) quartz-chlorite vein. The occurrence of gold includes two types, i.e., visible gold and invisible gold. The former is featured by coarse-grained gold (millimeter-scale, such as auriferous quartz veins) and fine-grained gold (micron-scale, such as native gold, calaverite, and electrum), the latter is contained in pyrite and arsenopyrite in the form of nano-scale native gold particles (Au0) and lattice gold (Au1+). The geothermometer of arsenopyrite and chlorite as well as temperature-sulfur fugacity diagram indicate that the temperature and sulfur fugacity of hydrothermal fluid decrease gradually. Considering that the sulfur fugacity drops gradually and aqueous inclusions coexist with carbonic inclusions, it is inferred that sulfuration reaction in which sulfur is consumed to produce sulfides and fluid immiscibility or phase separation may be responsible for gold precipitation. Tested by LA-MC-ICP-MS, the in-situ sulfur isotope compositions of sulfides formed in different stages are homogenous (about −1 to 1‰) and the calculated H2S-dominated hydrothermal fluid is also consistent (about −2 to 0‰) in sulfur isotope compositions, which reflect the mantle or ultrabasic rock and basic rock or magmatic rocks may be a potential source of sulfur. Combined with possible source and tectonic evolution of Peninsular Malaysia, possible metallogenic processes are proposed to explain genesis of the Selinsing gold deposit and other gold deposits in the Central Belt, i.e., ore-forming fluid was differentiated from oceanic crust and/or fertilized mantle wedge, or ore-forming fluid may be sourced from concealed magmatic rocks that formed by subduction of the Palaeo-Tethys toward the East Malaysia block.

Geological setting of the Chandragiri-Chitlang Range, southwest of Kathmandu Valley, central Nepal

Geological mapping was carried out in the scale of 1:25000 in the Chandragiri-Chitlang Range of central Nepal, SW of the Kathmandu Valley. In the area, lower four formations of the Phulchoki Group (Paleozoic age) from older to younger sequence, i.e. the Tistung Formation, the Sopyang Formation, the Chandragiri Limestone and the Chitlang Formation along with the Alluvial Fan Deposits and the Kathmandu valley sediments were mapped. Low-grade metamorphic rocks like met sandstone, phyllite, argillaceous limestone, ortho-quartzite and slate dominate the study area. The whole succession of the area is calcareous. The succession consists of a biotitezone in the lower part of the Tistung Formation, whereas the overlying younger succession belongs to a chlorite zone. The Chitlang Formation lies at the core of the Mahabharata Synclinorium and other local-scale structures in the area are the Chitlang Syncline, the Kirtipur Anticline and the Chandragiri Thrust (CT). The repetition of the older Sopyang Formation around the southeastern area and the Tistung Formation around northwestern area over the younger Chandragiri Limestone justifies the presence of the Chandragiri Thrust (CT).

Regional sediment sources versus the Indus River system: The Plio-Pleistocene of the Peshawar Basin (NW-Pakistan)

Sedimentary archives within the Peshawar Basin in northwest Pakistan preserve a record of siliciclastic supply patterns during the Plio-Pleistocene epoch. The basin fill consists of fluvial-floodplain clays overlain by thick lacustrine-glaciofluvial rhythmites with deposits of multiple alluvial fans in the southern parts of the basin and topped by loess deposits in ideal vertical successions. Framework mineralogical composition and bulk sediment geochemical proxies of these sediments indicate detritus derivation from dominantly acidic igneous sources with contribution from medium-grade metamorphic rocks. There appears to be no significant contribution from ultramafic-mafic or very high grade metamorphic sources. In addition, sediments from the southern part of the basin support supply from low-grade metamorphic rocks and carbonate sediments. Overall sedimentation occurred in an active continental margin setting under conditions of insignificant chemical weathering. The uplift of the Attock–Cherat Range during the late Pliocene (2.8 Ma) restricted the Indus River from shedding its detritus into the basin. Therefore, the sediments of the Peshawar Basin do not reflect signatures of the Indus River siliciclastics and thus lack the basic igneous geochemical signal, which is otherwise typical for the Himalayas hinterland. On the contrary, the geochemical signatures of these sediments favour predominant detritus flux from the acidic rocks of the Peshawar Plain Alkaline Igneous Complex (PPAIC) and associated metasediments. Therefore, the Kabul-Swat River and other local tributaries of this smaller river system that originated within the PPAIC and associated mountains are considered the major transporting agents which contributed siliciclastics into the Peshawar Basin during the Plio-Pleistocene. Additionally, in the southern part of the basin the uplifting Attock–Cherat Range appeared to have contributed detritus in the form of alluvial-fluvial fan deposits.

U–Th-total Pb ages of monazite from the Eckergneiss (Harz Mountains, Germany): evidence for Namurian to Westfalian granulite facies metamorphism at the margin of Laurussia

Four samples of garnet-bearing metapsammitic gneisses and one sample of a kinzigitic sillimanite-garnet-cordierite gneiss from the Eckergneiss Complex (Harz Mountains, Germany) were studied in detail for U–Th-total Pb dating with the electron microprobe. Monazite in all samples occurs in the matrix and show similar chemical compositional variation. A single stage monazite growth during the highest stages of metamorphism was deduced and chemical ages of all samples are between 313 ± 4 and 328 ± 6 Ma. These ages are interpreted as the time of granulite facies metamorphism in the Eckergneiss Complex. This metamorphism post-dates the formation of the main foliation, presumably developed under amphibolite facies conditions, as indicated by overprinting static grain growth and partial melt microstructures. It pre-dates the significantly younger intrusion of the Harzburg Gabbronorite and the Brocken Granite that are of post-Variscan age. Our results, in combination with P–T conditions for the peak of granulite facies metamorphism, show that the Eckergneiss Complex must have resided at a depth of at least 15 km during the Namurian to Westfalian. Later exhumation of the Eckergneiss Complex and its tectonic emplacement within the low-grade metamorphic Rhenohercynian rock units of the NW-Harz most likely occurred along the Acker-Bruchberg Thrust Zone, which marks the transition between the allochthonous and autochthonous domains of the Harz Mountains. At Early Permian time, this imbricated sequence was intruded and sealed by the post-Variscan intrusions.

Discussion of: Ortega-Flores et al. (2018) Provenance analysis of Oligocene sandstone from the Cerro Pelón area, southern Gulf of Mexico.https://doi.org/10.1080/00206814.2018.1476922

ABSTRACTWe discuss the 2018 publication that reports petrographic, heavy mineral data, mineral chemistry, and zircon geochronology for Oligocene sandstones in the Cerro Pelón area in southern Mexico Sureste basin. As the title of their paper says, the goal of their study is to establish the source (s) of the voluminous Cenozoic section in this region, reaching several kilometres in thickness and important as a petroleum system. These authors conclude that Oligocene sandstones of La Laja Formation were mostly sourced from eclogite- to greenschist-facies metasedimentary, metaigneous, and ultramafic rocks of the Guatemala suture complex. Minor contributions from the Chiapas Massif Complex, exposed directly to the south ~60 km of the Cerro Pelón area, were also suggested by the authors. They thus conclude that the Palaeogene stratigraphic record in southeastern Mexico was mostly controlled by the development of the Caribbean–North America plate boundary rather than by orogenic processes at the Pacific margin of North America. Presently, we do not agree with the conclusions of Ortega Flores and colleagues who studied the Cerro Pelón section, thus some discussion is required. Serpentinite bearing Nanchital Conglomerate is well exposed in the Cerro Pelón area, and high- to low-grade metamorphic rocks experienced an uplift in the vicinity of the Cerro Pelón area at the time of deposition of the La Laja Formation. We believe the data are better explained by multiple local sources in southern and eastern Oaxaca as well as sources to the south and southwest, which include the Cenozoic coastal batholith, the Grenvillean/Guichicovi basement complexes, the Chiapas Massif, the Mazatlán schist and other units in the Cuicateco Belt, as well as the Mesozoic cover of these areas (Todos Santos Formation, Cretaceous carbonate rocks, and Paleogene strata such as the Soyaló and Bosque Formations).

The evolution of quartz veins during the tectonometamorphic development of the Brusque Metamorphic Complex, Brazil

Microstructural analysis and characterization of quartz veins hosted in rocks from the Brusque Metamorphic Complex in the region of Brusque, State of Santa Catarina, have been performed to establish the relations between fluid regimes, tectonic styles and deformation/recrystallization mechanisms. The analysis was based on observations of structural overprinting, spatial structural relations, the origin of the quartz veins and microtectonics studies. Five types of veins were identified: meter-long veins parallel to the regional foliation (V1-veins); massive, meterwide veins present in thermal aureoles (V2-veins); millimeter-wide, erratic veins, also present in thermal aureoles (V3-veins); tabular, undeformed and NW striking (V4-veins); millimeter-wide erratic veins restricted to brittle reactivation of strike-slip shear zones (V5-veins). The regional foliation, developed under garnet zone metamorphic conditions, was more effective in vein production when compared to the steeply dipping mylonitic foliation corridors developed under chlorite zone conditions. Pressure solution was the main deformation mechanism during the regional foliation development. However, granoblastic and decussate textures in hornfels reveal an influence of grain boundary area reduction mechanism. The granoblastic texture in hornfels would have inhibited fluid circulation during dehydration reactions, increasing fluid pressure and promoting massive (V2-veins) and erratic hydraulic fracture-related (V3) veins. In dextral NEtrending strike-slip shear zones, tabular quartz veins (V4-veins) are parallel to tension gashes. Reactivation of strike-slip shear zones under brittle conditions has produced local brecciated millimeter-wide quartz veins (V5-veins). This study underscores the important role of fluids during orogenic evolution near the brittle-plastic transition of the crust, and demonstrates how combined vein and microtextural analysis can reveal the tectonometamorphic history of lowgrade metamorphic rocks.

Extensional neotectonic regime in West-southwest Konya, Central Anatolia, Turkey

ABSTRACT In the Central Anatolia, the style of neotectonic regime governing the region has been a controversial issue. A tectonic study was carried out in order to contribute to this issue and better understand the neotectonic stress distribution and style of deformation in the west-southwest of the Konya region. From Middle Miocene to Recent time, Konya region was part of the Central Anatolia extensional province. The present-day topography in the west-southwestern part of Konya is characterized by alternating elongate grabens and horsts trending E-W and NW-SE. The grabens were developed upon low-grade metamorphic rocks of Palaeozoic and Mesozoic ages and ophiolite slabs of possibly Late Cretaceous age. The evolutionary history of grabens is episodic as evidenced by two graben infills; older and younger graben infills separated by an angular unconformity. The older infill consists of fluviolacustrine sequence intercalated with calc-alkaline lavas and pyroclastic rocks. This infill is folded; thrust faulted and Middle Miocene-Early Pliocene in age. The younger and undeformed basin fill comprises mainly of Plio-Quaternary conglomerates, sandstone-mudstone alternations of alluvial fan and recent basin floor deposits. Three major tectonic phases were differentiated based on the detailed mapping, morphological features and kinematic analysis. Approximately N-S trending extension began in the Middle Miocene-Early Pliocene in the region with the formation of E-W and NW-SE-trending grabens. Following NE-SW-directed compression which deformed the older basin fill deposits by folding and thrusting, a second period of ENE-WSW-trending extension began in the late Pliocene and continued to the present. The west-southwestern margin of the Konya depression is bounded by the Konya Fault Zone. It is an oblique-slip normal fault with a minor dextral strike-slip component and exhibits well-preserved fault slickensides and slickenlines. Recent seismicity and fault-related morphological features reveal that the Konya Fault Zone is an active neotectonic structure.

A new transversely isotropic nonlinear creep model for layered phyllite and its application

Phyllite, which is a low-grade metamorphic rock with well-developed foliation planes, is encountered frequently during tunnel construction in western China. Its creep behavior is affected significantly by the foliation planes and has a crucial influence on the long-term safety of tunnel structures. Uniaxial compressive creep testing was conducted to analyze the time-dependent features of phyllite obtained from the Zhegu mountain tunnel on the Wenma expressway, China. A new creep model that connects a Maxwell body, a Kelvin body, and a nonlinear visco-plastic body was proposed to describe both the full creep process (including the transient, steady, and accelerated creep stages) and the transversely isotropic characteristics of phyllite. The creep model was also applied to investigate the long-term safety of a cracked tunnel lining in phyllite bedrock. The results showed that the creep strength and corresponding axial strain of phyllite exhibited maximum and minimum values at θ (the angle between the loading direction and the weak planes) = 90° and 30°, respectively. Good agreement was found between the calculated and experimental creep curves, indicating that the creep model replicates the physical creep process of phyllite well. The safety of the cracked lining was affected mainly by the damage degree of cracks and the creep behavior of the surrounding rock. Uncracked sections, because of their greater stiffness, were more sensitive to creep load than cracked ones. The inclination angle of foliation planes influenced the location of unsafe sections (those with a safety factor less than one), and this effect was weakened as the number of pre-existing cracks increased.

Lithogeochemistry of Pegmatites at Broken Hill: An Exploration Vector to Mineralisation

A sampling program was undertaken to assess pegmatite geochemistry with the view to using the data to vector towards economic mineralisation. The work has shown that pegmatites hosted in high grade metamorphic rocks (granulite and upper amphibolite facies) are either leucogranites, quartz-feldspar-mica pegmatites or feldspar-rich pegmatites. In contrast those that occur within lower grade metamorphic rocks (lower amphibolite to greenschist facies) are feldspar poor and quartz-muscovite rich, locally highly sheared, with tourmaline on their margins and as replacements of surrounding host sediments.Element classification diagrams suggest a geochemical continuum from poorly evolved pegmatites hosted in the highest grade metamorphic rocks to highly evolved pegmatites in the lowest grade metamorphic rocks. Spatially, this trend is broadly from the south and southwest toward the north and northeast and from west to east.Economic element content is similarly divided into two broad groups; Pegmatites within higher grade metamorphic rocks host elevated lead-zinc-silver-manganese.Pegmatites within lower grade metamorphic rocks contain elevated tin, tungsten, lithium, niobium and tantalum. The presence of abundant tourmaline in association with these indicates highly elevated boron.Elevated base metals and silver in the granulite and amphibolite facies rock is attributed to the elevated nature of these elements in the metasedimentary protolith being largely the Broken Hill Group. Our interpretation suggests these are probably not allochthonous but are nearly in-situ bodies resulting from partial melting of the Broken Hill Group. Their chemistry reflects that of the surrounding rock. Analysis of the spatial distribution of pegmatites with elevated lead-zinc-silver-manganese indicates many of these are located close to known base metal and/or silver occurrences of the Broken Hill types (BHTs).In contrast the concentration of tin, tungsten, lithium and other incompatible elements in pegmatites which are allochthonous and intrude rocks of lower metamorphic grade, suggests these elements have accumulated as fractionation has taken place.This study has highlighted three areas of elevated base metal-silver within pegmatites where no known mineralisation is documented either as an occurrence or in historic exploration data. Systematic pegmatite sampling at Broken Hill has the potential to enable vectoring toward buried silver-lead-zinc ores of the Broken Hill type.

The petrogenesis of albitized Early-Permian trachyandesites from Świerki quarry (Lower Silesia, Poland) - constraints on spilitization supported by mineralogical and geochemical data

Trachyandesites from Świerki quarry (Lower Silesia, Poland), related to the post-collisional extension-related magmatic activity developed within the Intra-Sudetic Basin during Early-Permian times, are well-known for the occurrence of mineral associations typical of spilites (low-grade metamorphic rocks affected by Na-metasomatism). This paper deals with the reconstruction of the evolution of these rocks and puts constraints on the spilitization mechanism and its role in redistributing main and trace elements based on cathodoluminescence microscopy and spectroscopy combined with electron microprobe analysis. Our study reveals that the trachyandesites were strongly affected by low-temperature albitization, which occurred during the post-magmatic stage of the rock formation. The replacement of primary green luminescent andesine-labradorite (An39-50Ab47-58Or2–3) by weakly-luminescent to dark-brown luminescent secondary albite (Ab∼99 mol.%) was related to the CO2-induced, crystallographically-controlled, interface-coupled dissolution-reprecipitation mechanism, triggered by hydraulic fracturing of fluids and/or contractional cooling forces. The replacive albite forms isolated and homogenous patches along polysynthetic twinning planes of andesine-labradorite and/or within intergranular fractures. It is closely associated with such minerals as calcite, chlorite and kaolinite, and exhibits enhanced microporosity. Moreover, the low-temperature alteration was accompanied by physicochemical fluctuations (alkaline-acidic) during rock formation as revealed by two generations of fluoroapatite: (1) violet-pink (REE3+-activated) overprinted by (2) yellowish (Mn2+-activated) luminescent domains. We also report that primary (green luminescent) plagioclases (andesine-labradorite) are rimmed by bright-blue luminescent Ab-rich (An2-7Ab34-61Or32–64) alkali-feldspars followed by dull-blue luminescent Or-rich alkali-feldspars (An2Ab38-44Or54–60). The bright-blue luminescent crystals contain higher amounts of BaO (∼0.59 wt.%) and TiO2 (∼0.08 wt.%) than the dull-blue luminescent domains (∼0.12 and 0.03 wt.%, respectively). Hence, the difference in CL intensity in blue wavelengths are ascribed to the presence of both Al-O−-Al centres, related to a coupled KSi-BaAl substitution, and Al-O-Ti bridges. Not only the geochemical affinities of the rocks are peculiar to those reported for within-plate basalts, but also reveal similarities with arc-related geotectonic environments. Trachyandesites sourced from enriched subcontinental lithospheric mantle source owing to the strong LREE and LILE enrichment relative to Nb and Ta, while the presence of positive ZrHf anomalies coupled with low Nb/U ratios points to the involvement of crustal material during magma evolution. The spilitization has predominately resulted in the increase of Cs and decrease of Sr concentration among strongly-altered samples, while its influence on REE distribution was insignificant.

Geology and Mineral Resources of Phalamdada-Dhuwakot Section of West-Central Nepal, Lesser Himalaya

Geological mapping was carried out along the Phalamdanda-Dhuwakot section of west-central Nepal in the Lesser Himalaya. The aim of geological mapping was to prospect the metallic mineral resources in the area especially to assess the geological control of mineralization as prognostic mapping and study the genesis of mineralization. The area has developed low-grade metamorphic rocks of the Nawakot Group. Geological rock units like the Kuncha Formation, Fagfog Quartzite, Dandagaon Phyllite, Nourpul Formation and Dhading Dolomite are mapped in the area. Jal Bhanjyang Thrust carries the more older rocks of the Nourpul Formation over the Dhading Dolomite. The area is highly deformed as indicated by presence of folds. Outliers of Fagfog Quartzite and Dhading Dolomite are developed at the core part of the syncline. Phalamdada iron and Anbu Khaireni as well as Dharapani copper are the major metallic deposits reported in the area. Both deposits are considered as the syngenetic in nature. Bulletin of Department of Geology, vol. 20-21, 2018, pp:59-64

Provenance and palaeogeographic evolution of Lower Miocene sediments in the eastern North Alpine Foreland Basin

Detrital heavy mineral analysis and sediment chemistry of Lower Miocene sediments of the Lower Austrian Northern Alpine Foreland Basin generally indicate provenance from metapelitic source rocks. The sediments of the Traisen Formation (Ottnangian) were primarily derived from Alpine sources such as the Austroalpine crystalline units of the Eastern Alps and reworked and eroded siliciclastics strata on top of the Northern Calcareous Alps and, in addition, low-grade metamorphic rocks of the Bohemian Massif. Ottnangian and Karpatian sediments in the subground of the northern Lower Austrian Molasse basin were mainly fed from the same southern sources, from low-grade metamorphic rocks of the Bohemian Massif and via resedimentation of Lower Miocene and Palaeogene of the Waschberg–Ždanice Unit and the Vienna Basin. A large-scale input of material from the Rhenodanubian Flysch Zone and of higher-grade metamorphic units and granites of the Bohemian Massif in the Lower Miocene Molasse basin can be ruled out. A compilation of well sections and heavy mineral data point to the existence of a partly emerged, N–S oriented ridge during the Egerian.

Tectonothermal analysis of a major unit of the Cantabrian Zone: the Ponga unit (Variscan belt, NW Spain)

The paleothermometric evolution of the Ponga unit at the core of the Cantabrian Zone, the arcuate foreland fold and thrust belt of the Variscan orogen in NW Spain, is analyzed using the conodont Color Alteration Index and the Kubler Index of illite. The results indicate that the distribution of the thermal maturity patterns is independent of the stratigraphy and the structure of the unit. These include the occurrence of dominant diagenetic values and very low-to-low-grade metamorphism in the southern area. The main thermal event is interpreted to be related to hydrothermal fluids ascending through late-Variscan extensional faults. The anomalous high heat flow in the southern sector of the Ponga unit is part of a previously identified large band in the Cantabrian Zone, where the common occurrence of low-grade metamorphic rocks, hydrothermal dolostones, and ore mineralizations is related to an extensional orogenic episode that started near the Carboniferous–Permian boundary, soon after the closure of the Asturian arc.

Geothermal play fairway analysis at a populated rifting basin area of Taiwan

Taiwan is located in the active mountain belts on the west side of the Pacific Rim with promising potentials for geothermal resources. The triangular shaped Yilan Plain, our study area chosen for a geothermal development pilot project, resides at the southwestern end of the Okinawa Trough behind the Ryukyu Arc-Trench where the Philippine Sea Plate is subducting beneath the Eurasian Plate with low-grade metamorphic rocks exposed in the surrounding mountain ranges.Play Fairway Analysis (PFA) is adapted to demonstrate important aspects, predicting geothermal potential through quantitative and statistical methods in a given type by overlapping each element layer into a composite favorability map with properly calculated weights accounting for uncertainty levels. Highlighted exploratory sweet spots on a regional scale can be identified with the easy-to-read map for decision-making stakeholders.Three components are selected for this analysis: they include (1) heat sources: with temperatures of hot springs, geothermal gradients, and silica geothermometry, (2) permeable fracture networks: with fault lines, drainage network, micro-earthquake activities, and dilation rate distribution, and (3) human activities: with population density, sediment thickness, and hazardous risk. Expert opinion on factor weighting for two geological components and Analytic Hierarchy Process (AHP) for the socioeconomic component are utilized to determine weightings representing the assigned confidence and uncertainty levels. ArcGIS software is used as the platform for data processing and map demonstration.The final map displayed the combined geothermal favorability from the two geological aspects blocked out with the riskier zones from the socioeconomic aspect. It indicates two potential prospects with one in the southwestern hillside where the Chingshui power plant resided and another in the southeastern portion of the Yilan Plain, which could interfere with certain human activities.

The Žermanice sill: new insights into the mineralogy, petrology, age, and origin of the teschenite association rocks in the Western Carpathians, Czech Republic

The Žermanice locality represents the best-exposed example of the meta-basaltoid/meta-gabbroic rock type of the teschenite association. It forms a subhorizontal volcanic body (sill) 27–30 m thick. The subvolcanic rock is inhomogeneous and slightly differentiated. The predominant rock type is a basaltoid (diabase-dolerite), medium-grained, speckled, mesocratic rock exhibiting an evident subophitic texture. Miarolitic cavities are abundant in some places. The major rock constituents are albite, microcline, chlorite, and pyroxene, as well as analcime and plagioclase in places. The accessory magmatic phases are biotite, ilmenite, fluorapatite, sulphides, Ti-rich magnetite, Nb-rich baddeleyite, and chevkinite–(Ce) or perrierite–(Ce). A large extent of alteration is evident from the presence of chloritization, albitization of plagioclases, and zeolitization (analcimization). Geochemical analyses reveal an affinity for metaluminous igneous rocks. The best fit is with the within-plate basalts or the within-plate volcanic zones. The classification of this rock is problematic because of the mixed intrusive and extrusive features; the choice is between meta-alkali basalt and metadolerite (meta-microgabbro). 207Pb common lead-corrected U–Pb apatite dating yields a weighted mean age of 120.4 ± 9.6 Ma, which corresponds to the middle Aptian. The igneous body is at most ca. 10 Ma younger than the surrounding late Hauterivian sediments and might have been emplaced into unconsolidated or partly consolidated sediments. According to our research, it is evident that at least some teschenite association rocks are in fact low-grade metamorphic rocks.

Investigating slow-moving landslides in the Zhouqu region of China using InSAR time series

In the Zhouqu region (Gansu, China), landslide distribution and activity exploits geological weaknesses in the fault-controlled belt of low-grade metamorphic rocks of the Bailong valley and severely impacts lives and livelihoods in this region. Landslides reactivated by the Wenchuan 2008 earthquake and debris flows triggered by rainfall, such as the 2010 Zhouqu debris flow, have caused more than 1700 casualties and estimated economic losses of some US$0.4 billion. Earthflows presently cover some 79% of the total landslide area and have exerted a strong influence on landscape dynamics and evolution in this region. In this study, we use multi-temporal Advanced Land Observing Satellite and Phased Array type L-band Synthetic Aperture Radar (ALOS PALSAR) data and time series interferometric synthetic aperture radar to investigate slow-moving landslides in a mountainous region with steep topography for the period December 2007–August 2010 using the Small Baseline Subsets (SBAS) technique. This enabled the identification of 11 active earthflows, 19 active landslides with deformation rates exceeding 100 mm/year and 20 new instabilities added into the pre-existing landslide inventory map. The activity of these earthflows and landslides exhibits seasonal variations and accelerated deformation following the Wenchuan earthquake. Time series analysis of the Suoertou earthflow reveals that seasonal velocity changes are characterized by comparatively rapid acceleration and gradual deceleration with distinct kinematic zones with different mean velocities, although velocity changes appear to occur synchronously along the landslide body over seasonal timescales. The observations suggest that the post-seismic effects (acceleration period) on landslide deformation last some 6–7 months.

Geology, slow-moving landslides, and damages to buildings in the Verbicaro area (north-western Calabria region, southern Italy)

ABSTRACTThis paper presents a mass movement inventory map at 1:5000 scale of the Verbicaro area (about 13 km2) located in the Calabria region (southern Italy). The Main Map results from the visual interpretation of aerial photographs, multi-temporal geomorphological field surveys, and field investigations of damage suffered by buildings. Some 53% of the study area is affected by a total of 252 landslides, comprising different types, state of activity, and size. The mapped landslides, mainly complex type, involve low-grade metamorphic rocks; among these, 15% are active and slow-move on pre-existing sliding surfaces. Moreover, out of 492 surveyed buildings, 347 are located on landslide-affected areas and experienced damages covering a broad range of severity levels. The Main Map can represent a useful tool for authorities in charge of land-use planning and urban management and can be used to pursue landslide risk analyses.

Lithostratigraphy and Inorganic Geochemical Studies of Cretaceous-Tertiary Lithofacies from Nigerian Three Inland Basin

Studies from selected samples from Chad (Kanadi-1, Albarka-1 and Tuma-1), Sokoto (Dange-1) and Dahomey Basins (Seme-1), were subjected to detailed lithostratigraphic description and inorganic geochemical studies with the aim of determining the provenance, tectonic setting, depositional environment and geochemical characterization. This involves detailed lithologic description, Inductively Coupled Plasma Emission Spectrometry (ICP-ES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) through lithium metaborate fusion method. The lithologies of the study wells from Chad, Sokoto and Dahomey Basins comprise of mudstone, dark shale, brownish sandstone and light brownish shale; mudstone and dark brownish shale and clay, dark brownish shale, siltstone respectively. The geochemical result showed an abundance of SiO2 with an average of 75.05%, Al2O3 average of 12.51% (sandstone), values of 18.10% to 10.12% and 5.51% to 16.17% (shale). The abundance of Fe2O3 range from 2.12% to 8.56% while the other major elements have very low concentration. The high SiO2 content indicated a quartz rich adjoining source rock while low values of ratio K2O/Al2 O3 and Na2O/Al2O3, coupled with high average values (<70%) of Plagioclase Index of Alteration (PIA), Chemical Index of Alteration (CIA) and Chemical Index of Weathering (CIW) indicated intense weathering condition and humid climate at the source area. The sediments classification includes greywacke, arkose, litharenite and quartz arenite. A-K-F plot indicated transitional marine environment. Discrimination function plots revealed felsic igneous, quartzose sedimentary and intermediate igneous provenances. The plot of La-Th-Sc showed deposits of passive margin setting. Chondrite normalized REE plot showed an enrichment of light REE with strong negative Eu anomaly which is an indication of a felsic source. Conclusively, study areas consist of marine deposits with plutonic igneous rock as the main source rock couple with low grade metamorphic and quartzose recycled rocks deposited in transitional marine environment under intense weathering in a tropical, humid climatic condition.