Major Rock Research Articles

Spatially selective myosin regulatory light chain regulation is absent in dedifferentiated vascular smooth muscle cells but is partially induced by fibronectin and Klf4.

The phosphorylation state of myosin regulatory light chain (MRLC) is central to the regulation of contractility that impacts cellular homeostasis and fate decisions. Rho-kinase (ROCK) and myosin light chain kinase (MLCK) are major kinases for MRLC documented to selectively regulate MRLC in a subcellular position-specific manner; specifically, MLCK in some nonmuscle cell types works in the cell periphery to promote migration, while ROCK does so at the central region to sustain contractility. However, it remains unclear whether or not the spatially selective regulation of the MRLC kinases is universally present in other cell types, including dedifferentiated vascular smooth muscle cells (SMCs). Here, we demonstrate the absence of the spatial regulation in dedifferentiated SMCs using both cell lines and primary cells. Thus, our work is distinct from previous reports on cells with migratory potential. We also observed that the spatial regulation is partly induced upon fibronectin stimulation and Krüppel-like factor 4 overexpression. To find clues to the mechanism, we reveal how the phosphorylation state of MRLC is determined within dedifferentiated A7r5 SMCs under the enzymatic competition among three major regulators ROCK, MLCK, and MRLC phosphatase (MLCP). We show that ROCK, but not MLCK, predominantly regulates the MRLC phosphorylation in a manner distinct from previous in vitro-based and in silico-based reports. In this ROCK-dominating cellular system, the contractility at physiological conditions was regulated at the level of MRLC diphosphorylation, because its monophosphorylation is already saturated. Thus, the present study provides insights into the molecular basis underlying the absence of spatial MRLC regulation in dedifferentiated SMCs.

Geology and Petrography of Basement Rocks around Tsauni, Northwestern Nigeria

This work studied the geology and petrography of basement rocks around Tsauni and its environs with the main aim of establishing the different rock types present macroscopically and microscopically. The study area is part of sheet 54 Gusau NW, Northwestern Nigeria defined by latitude 12˚12'00”N and 12˚9'00”N and longitude 6˚43'30”E and 6˚40'30”E. To achieve the aim, geological mapping was conducted in which fresh rock samples were collected and structures were studied and measured. The samples were subjected to petrographic analyses and their microscopic features were observed under the microscope. On the field, one major rock is encountered, granites (fine-medium grained and medium-coarse grained granites) while two minor rocks;quartz and xenoliths are mapped with the former being younger and the latter older than the granites. All the analyzed rocks are seen to contain quartz (40%), orthoclase feldspar (40-50%) and biotite (10-20%). They are therefore said to be granites of the Older Granites of northwestern Nigeria believed to be of late Cambrian to lower Paleozoic in age. Strike-slip faults and joints were found as the structures associated with the rocks. Economically, these rocks can be best used in engineering constructions. There exist meandering rivers in the area enriching the inhabitants with surface water and presence of hand dug wells pinpointing the availability of groundwater. However, geophysical survey is recommended to back this up.

Assessment of Rock Mass Quality and Support Estimation along Headrace Tunnel of a Small Hydropower in District Mansehra, Khyber Pakhtunkhwa, Pakistan

The main purpose of this study is to classify the rock mass quality by using rock mass quality (Q) and Rock Mass Rating (RMR) systems along headrace tunnel of small hydropower in Mansehra District, Khyber Pakhtunkhwa. Geological field work was carried out to determine the orientation, spacing, aperture, roughness and alteration of discontinuities of rock mass. The quality of rock mass along the tunnel route is classified as good to very poor quality by Q system, while very good to very poor by RMR classification system. The relatively good rock conditions are acquired via RMR values that are attributed to ground water conditions, joint spacing, RQD and favorable orientation of discontinuities with respect to the tunnel drive. The petrographic studies revealed that study area is mainly comprised of five major geological rock units namely quartz mica schist (QMS), garnet mica schist (GMS), garnet bearing quartz mica schist (G-QMS), calcareous schist (CS), marble (M). The collected samples of quartz mica schist, marble and garnet bearing quartz mica schist are fine to medium grained, compact and are cross cut by few discontinuities having greater spacing. Therefore, these rocks have greater average RQD, Q values, RMR ratings as compared to garnet mica schist and calcareous schist.

Geology, Petrology and Petrographic Analysis of Ruwan Tabo Area, Northwestern Nigeria

The study area overlies the Nigerian basement complex that is made up of Liberian to Pan African rock units, falling within latitudes 110 17’ 00” N and 110 21’20.27” N and longitudes 080 18’ 43.33” E and 080 21’ 33.33” E, in the northern part of thecountry, covering an area of 40km2, mapped at a scale of 1:25,000. The area was mapped using compass clinometer and GPS,rock samples were collected using hammer and chisel and then taken to the laboratory for thin sectioning. Structures weremeasured and recorded. Petrologically, the rock units mapped in the area are gneiss, covering about 50% of the total area,coarse-grained granite which covers about 40% of the total area of study, while the remaining 10% constitutes the minor rocks.Gneisses and granites from the major rock types in the area, while migmatite, pegmatites and laterites form the minor components of the rock units in the area. Pertographically, the gneiss consists of biotite (10%), plagioclase (25%), quartz (20%), orthoclase (7%), microcline (30%) and muscovite (11%), while the coarse-grained granite consists of biotite (10%), plagioclase (15%), quartz (15%), orthoclase (8%) and microcline (45%) as essential minerals. Structurally, faults, foliations, joints, and veins are the main structures observed in the study area and are mostly attributed to the effects of Pan-African Orogeny which resulted in the N-S trending pattern of the structures in the associated lithologies.

Satellite-Derived Regional Apparent Thermal Inertia and Gravity for Mapping Different Rock Types in Parts of Banswara, Rajasthan

In this study, utility of satellite derived Apparent Thermal Inertia (ATI) and residual gravity data have been analyzed for delineating the major rock types of Aravalli Supergroup. Density is a common contributing factor responsible for ATI and gravity variations of rock types. In addition to density, thermal inertia is also controlled by specific heat and thermal conductivity. In the present study, MODIS (Moderate resolution imaging spectrometer) day and consecutive night time land surface temperature (LST), albedo data have been processed to derive ATI image for the study area. On the other hand, Bouguer gravity generated from EIGEN6C4 gravity model data is processed to derive the residual gravity over the study area. It has been observed that ATI values of different rock types are influenced by the variations in weathering pattern and forest cover developed over the rock in addition to the thermophysical parameters of rocks. Forest cover and agricultural activity are responsible for shifting the ATI values to higher side for any rocks due to evapotranspiration; which is responsible for reducing day and night land surface temperature difference. ATI pixels( collected from large rock pavements) of different rocks can however, be used to discriminate them from each other. Conjugate analysis of residual gravity and ATI has been proved useful to discriminate different rock types of spatially well distributed rock exposures. It is found that ATI and gravity values are well correlated for the spatially large surface exposures of rocks. In regional scale, low frequency changes of ATI broadly matches with the changes observed on the corresponding spatial profiles of residual gravity with some localized variations. This is due to the fact that shallow surface gravity anomaly is cumulative effect of vertical and horizontal variations of density in contrast to ATI which is more sensitive to near surface density, conductivity and specific heat variations of rocks. Moreover, high frequency variations imprinted on regional ATI spatial profiles are due to the cumulative effect of complex thermophysical properties of surface elements (weathering residuum, surface moisture variations) density variation and intrinsic thermophysical properties of rocks measured at regional scale. High frequency changes of ATI do not correspond well with residual gravity variation.

Mineral-controlled nm-μm-scale pore structure of saline lacustrine shale in Qianjiang Depression, Jianghan Basin, China

Abstract The pore structure of the saline lacustrine shales in the Eq3 unit of the Qianjiang Formation was characterized for pore space of μm-nm scales through a combined study of mercury injection capillary pressure (MICP) and small/ultra-small angle neutron scattering (SANS and USANS). X-ray diffraction (XRD) and total organic carbon (TOC) content tests, as well as field emission-scanning electron microscopy (FE-SEM) imaging, are also employed to obtain the mineralogical composition, organic richness, as well as the general pore types and sizes of the selected Qianjiang shale samples. In these samples, three major rock types are identified: (1) silica-rich carbonate mudstone; (2) carbonate/siliceous mudstone; and (3) salt. The porosity, as well as pore size and pore-throat size distributions, generated from both SANS/USANS and MICP techniques indicate a porous rock matrix and well-connected pore networks in the two mudstone rock types. Meanwhile, an averaged TOC of around 3.5 wt% for Eq3 unit exhibits a good quality for oil generation potential. This study primarily provides new insights into the pore structure of the Qianjiang shales across a wide measurable range for both pore and pore-throat sizes, and correlates the pore structure and mineral compositions at different scales.

New understandings of the June 24th 2017 Xinmo Landslide, Maoxian, Sichuan, China

On June 24, 2017 (21:39 UTC, June 23rd), a catastrophic landslide occurred at Xinmo village of Mao County, Sichuan Province, China. Soon after the event, some research teams carried out field investigations in order to both support the emergency operations and to understand the failure mechanism and possible evolutionary scenarios. Based on further in-depth interpretation of high-resolution remote-sensing images and detailed field surveys, it is newly found that there are at least six old rockfall deposits in the source area that prove the historic activity of the landslide scarp. Seismic data of the event and morphological evidences along the slope indicate that the landslide was preceded by a significant rockfall. Mechanical calculations show that the surface force due to pore water was far less than the impact force due to the rockfall. It means that the subsequent major rock avalanche was more likely due to the impact of the rockfall on the rock slope below, which broke the rock bridges and caused drop of shear resistance along the fractures. According to these new understandings, a different triggering mechanism for the landslide is proposed.

The ca. 2785–2805 Ma High Temperature Ilivertalik Intrusive Complex of Southern West Greenland

Ferroan granitoid intrusions are rare in the Archaean rock record, but have played a large role in the evolution of the Proterozoic crust, particular in relation to anorthosite-mangerite-charnockite-granite suites. Here we discuss the petrogenesis of the ca. 2785–2805 Ma ferroan Ilivertalik Intrusive Complex, which has many geochemical similarities to Proterozoic iron rich granitoids. We present major and trace element whole rock chemistry and combined in-situ zircon U-Pb, Hf and O isotope data. The intrusive complex divides into: (i) minor tabular units of mainly diorite-tonalite compositions, which are typically situated along contacts to the host basement and (ii) interior larger, bodies of mainly granite-granodiorite composition. Geochemically these two unites display continuous to semi-continuous trends in Haker-diagrams. Whole rock REE enrichment display increases from Yb to La, from 10–25 to 80–100 times chondrite, respectively. The diorite-tonalite samples are generally more enriched in REE compared to the granite-granodiorite samples. The complex has hafnium isotope compositions from around +1.5 to −2.5 epsilon units and δ18O compositions in the range of 6.3 to 6.6‰. The complex is interpreted to be derived from partial melting in a crustal source region during anomalously high crustal temperatures.

Interaction Between Moderate Earthquakes and Volcanic Eruptions: Analyses of Global Data Catalog

AbstractThe interaction between earthquakes and volcanic eruptions is investigated by analyzing a modern seismic data catalog of centroid moment tensor solutions and eruption records summarized by the Smithsonian Institution. To determine the average features of the interactions, the numbers of earthquakes that occurred before and after the initiation of each eruption with a volcanic explosivity index of larger than or equal to 2 are analyzed. The results show that moderate earthquakes, which have moment magnitudes of 5 to 6 (Mw 5–6), are activated within a horizontal distance of 50 km from volcanoes for about 0.3 years after the initiation of an eruption. About 13% of volcanic eruptions are accompanied by moderate earthquakes. The occurrence possibility of earthquakes every 0.1 years for 0.3 years after an eruption is about 5 times larger than normal. No significant dependence on the tectonic settings and major rock types is recognized.

Extension Strain and Rock Strength Limits for Deep Tunnels, Cliffs, Mountain Walls and the Highest Mountains

Brittle rock can fail in tension even when all principal stresses are compressive. The culprit is Poisson’s ratio, but marked stress anisotropy due to a neighbouring free surface, and due to a raised principal tangential stress is also necessary. Extension strain-induced failure causes fracture initiation in tension. Propagation in unstable shear may occur if the tunnels or mine openings are deep enough, and if they are located in hard, brittle, sparsely jointed rock. Both in laboratory uniaxial compression test samples with strength σc and in deep tunnels, extension fracturing and acoustic emission begin when the principal applied or induced stress reaches the magnitude of tensile strength divided by Poisson’s ratio σt/ν. The traditionally expected fracture initiation when the principal or maximum tangential stress σ1 or σθ = 0.4 ± 0.1 × σc can actually be explained with arithmetic. Using related logic, cliffs and the near-vertical mountain walls frequented by rock climbers, may have erosional or glacial origin, but extension strain limits their height, including vertical walls of sheeting joints and long continuous fractures. Shear failure seems to be reserved for occasional major rock avalanches. Equations with soil mechanics origin involving Coulomb parameters c and φ and density that may apply to vertical cuts in soil, give greatly exaggerated heights for rock cliffs and mountain walls since rock is brittle and favours failure in tension. Tensile strength, Poisson’s ratio and density are suggested for estimating the maximum heights of rock cliffs and mountain walls, not compression strength and density. However, overall mountain heights are limited by critical state maximum shear strength, or by the slightly lower brittle–ductile transition strength.

A new and unified approach to improved scalability and volumetric fracture intensity quantification for GSI and rockmass strength and deformability estimation

Several investigators have attempted to quantify the Geological Strength Index (GSI) chart, with the latest modification of the chart (2013) utilizing RQD as a measure of blockiness. This approach has limitations where discontinuity spacing is wide (typically greater than 0.3 m) and RQD alone cannot adequately characterize the degree of blockiness, since it remains static at 100%. This paper introduces a new approach to quantifying widely spaced jointed rockmasses that is not dependent on RQD alone. At the core of the approach is a bias free volumetric fracture count (VFC) parameter (fractures/m3), that is integrated into the newly defined GSI chart as an aid to alleviate scalability and bias concerns related to the use of RQD in the quantification process. While the new GSI chart builds on the work of many, it is unique in the sense that not only is it fully quantifiable for a full range of block sizes, including block sizes much larger that possible with RQD alone, but it provides a unique approach linking the VFC parameter with P32, a parameter frequently used in DFN modelling. The correlation of VFC with P32 in particular, is possible because the VFC parameter has no constraints of a limited number and/or assumed orthogonality of discontinuity sets or rectilinear block shapes or the need for block shape correction factors. The new chart also includes correlated scales on both the vertical and horizontal axis using both the RMR and the Q-systems, providing a unified approach that is both scalable and easily quantifiable and allows for the use of all three major rock mass classification systems along with P32 within one chart, something not attempted before. Data from a dam foundation rockmass in the Lesotho Highlands are introduced and are used to validate the quantification process for the overall GSI ratings for the foundation rock mass. These ratings have been used to estimate strength and deformability parameters for the foundation rock mass using the Hoek-Brown empirical failure criteria equations and then they were compared to the large-scale in-situ test results to validate the use of the V-GSI chart and system as a new tool for use in rock engineering.

Upper mantle xenoliths as sources of geophysical information: the Perşani Mts. area as a case study

The aim is to give an overview on how geochemical and petrological data, obtained from upper mantle xenoliths, could be utilized to provide information on the geophysical properties of the upper mantle at their origin. First we demonstrate how a tentative lithospheric column may be constructed based on the equilibrium temperature of upper mantle xenoliths and the area specific depth-temperature curves. Then it is described how the speed of seismic waves at the given pressure and temperature conditions could be calculated from the modal composition and geochemistry of major rock forming minerals of upper mantle xenoliths (e.g. olivine and orthopyroxene). It is also discussed how the lattice preferred orientation of minerals in upper mantle xenoliths provides information on the seismic anisotropy of the upper mantle, and how this information could be used to calculate the orientation and thickness of the anisotropic layer in the upper mantle if one anisotropic layer is assumed. Structural hydroxyl (or most commonly referred to as ‘water’) incorporated in nominally anhydrous minerals plays a critical role in determining the electrical conductivity and rheology of the upper mantle. Finally, it is presented how electrical conductivity and effective viscosity of the upper mantle could be approximated based on the structural hydroxyl content in olivine, the most abundant mineral constituent of the upper mantle. Our study area, the Persani Mountains is situated in the Carpathian Bend area (Romania) which is geologically one of the most active areas in Europe. Abundant upper mantle xenoliths from the Persani Mountains (Eastern Carpathians) will serve as examples how meaningful geophysical information can be obtained for the upper mantle. Furthermore, it is shown how these pieces of information may be utilized in interpreting geophysical and geodynamic challenges of this area.

Fault induced rock bursts and micro-tremors – Experiences from the Gotthard Base Tunnel

During the construction of the Faido Multifunction Station of the Gotthard Base Tunnel, a previously unknown and unanticipated major tectonical fault has been encountered. Upon completion of the advance through the fault, systematic and major rock burst events occurred in the competent Gneiss rock mass adjacent to the fault.The Swiss Earthquake Service (Schweizer Erdbebendienst – SED) observed an increase of microtremors in the vicinity of the tunnelling site, in a region where usually very low seismic activity is present. As a consequence, the seismic monitoring grid has been enhanced in the project area, allowing reliable pin-pointing of the microtremor hypocenters and examination on the interaction with the tunnel advance and the observed rock burst events.Due to the vast amount of scientific work with regard to rock burst causes, classification, prediction and mitigation, this publication deliberately abstains from trying to add yet another set of relationships and/or classification schemes. Instead, a case study is presented, with the peculiarity that excellent seismic monitoring and very well documented rock mass conditions are seamlessly available, allowing direct correlation and insight into the interaction between seismicity and strike-slip rock bursts. In addition, the results of a dynamic analysis performed in UDEC, with excitation wave data and rock mass parameters calibrated on the field measurements, are presented. They allow greater understanding of the events caused by seismicity-induced rock burst phenomena.The experiences with prediction and mitigation of rock burst are shown, leading to conclusions with regard to efficient and safe tunnelling in rock-burst prone rock masses.

Petrography and Geochemistry of Rocks of Northern Part of Wonaka Schist Belt, Northwestern Nigeria

Systematic mapping and sampling of rocks of northern part of Wonaka schist belt on a scale of 1:50,000 shows that the belt is composed of gneiss, granite gneiss, muscovite-biotite schist, banded iron formation, amphibolite, granite, granodiorite and diorite as major rock types, other rocks are aplite, and pegmatite. Petrographic and geochemical data shows that the there are two types of gneisses in the area: the orthogneiss and the paragneiss. Plots of TiO2 vs SiO2 shows that the granite gneiss is paragneiss while the gneiss is an orthogneiss. The granites and the granodiorite are I – Type and the amphibolite is volcaniclastic. The banded iron formation (BIF) is shown to be hematite facies type from a plot of MnO vs FeO(T). It can therefore be said that the orthogneiss represents the original basement rock possibly dating back to the early phase of the Eburnean orogeny. At later stages of the Eburnean, sedimentary deposition and subsequent metamorphism of the sediments might have led to the formation of the paragneiss and the metasediments with the associated BIF as indicated by the REE distribution pattern. The NNE – SSW and the N – S structural trends on the rocks might have been developed by the over printing effects of the Pan- African orogenyKeywords: orthogneiss, schist belt, paragneiss, banded iron formation, metasediments

Magnetotelluric evidence on the southward extension of the Eastern Ghats mobile belt from Ongole, India

There has been a longstanding and scientifically contentious issue, concerning whether or not the Eastern Ghats mobile belt (EGMB) extends southward beyond Ongole in the state of Andhra Pradesh, in south India. Various geological and geophysical investigations carried out in different campaigns could not conclusively address this important issue. Some argued that the EGMB that originates near Mahanadi in the northeast of India and extends along the eastern continental boundary, is abruptly cut near Ongole in the south, swerves eastward towards the Bay of Bengal and joins the erstwhile east Antarctica boundary. Others opined differently and debated about its southward extension beyond Ongole. In the present study, we provide a conclusive evidence for the first time on this perplexing issue, by determining the deep earth electrical resistivity structure of the EGMB region through broad-band magnetotelluric (MT) investigations carried out along two different profiles laid out one near the Ongole region (profile AA′ of 35 km length) and the other near the Nellore region (profile BB′ of 52 km length). The latter is located at a distance of about 125 km south of the former. The lengths of both these profiles are sufficiently far from the influences of the electrical nature of the subsurface of the adjoining geological terrains namely, the east Dharwar craton, the Cuddappah basin and the southern granulite terrain. This enables to determine the electrical nature of the EGMB alone and examine whether or not it extends south of Ongole. Two-dimensional inversion of MT data of both the profiles revealed a very thin top conductive layer of about 1–10 Ω-m with an average thickness of about 500 m, representing the alluvium. This layer is underlain by very high resistive subsurface with resistivity of about 107 Ω-m extending up to about 30 km and probably further beyond (not shown in the present study). Since the major rock types in the study area, namely, Khondalites, Calc-granulites, Charnockites and Granitic gneisses of Archaean age, have large overlapping resistivities, MT data could not explicitly discern the nature of the multilayered crust beneath the EGMB. As a result, the subsurface beneath both the regions shows up as a very thick single layer of very high resistivity. The high grade rocks of the Ongole domain and supracrustals of Nellore Schist Belt (NSB), which lies south of Ongole domain, have undergone synchronous tectonic activity at ca.1.6 By. This is evident by the Kanigiri and Kandra ophiolites within NSB that signify the Proterozoic subduction of the EGMB. This geological evidence together with the similar nature of the high electrical resistivity of the subsurface observed at Ongole and Nellore regions confirm the southward extension of the EGMB beyond Ongole.

Risk mitigation measures against falling rock at Jelicni vrh

AbstractJelični Vrh is a steep cliff located above the main road Ljubljana –Idrija on the important connection between the Slovenian Central and Primorska regions. The falling rock is constantly endangering the traffic on the road. Additionally, there is an overhang block of rock at the top of the cliff that distinguishes this location in terms of high geotechnical hazard. The risk assessment for the management of the geotechnical hazard assessed two scenarios, one for constantly falling rock and the second for the major rock fall event, which can be caused by the fall of the overhang blocks. The block of the overhang rock was assessed for the stability conditions and for the wider consequences of the passible fall. Several different solutions for the management of the geotechnical hazard, which were proposed, are described in the paper. The combination of the energy absorbing nets and the 105 m long reinforced concrete gallery were accepted as an optimum solution.

Newspaper reporting of the April 2007 eruption of Piton de la Fournaise part 1: useful information or tabloid sensationalism?

During March, April and May 2007 the local newspaper for the island of La Réunion, “Le Journal de L’Ile de La Réunion” (JIR), published 427 articles relating to natural hazards, with hazard-related articles occupying a total paper area of 21.94 m2 and appearing in all but four of the 90 editions of the newspaper. This high level of coverage was due to the passage of two cyclones in March, the largest historical eruption of Piton de la Fournaise in April, and a major rock fall event in May. The high level of coverage may also be due to the fact that JIR is a tabloid that follows tabloid news values. Cyclones, volcanic eruptions and rock falls fit the news values of a tabloid well, especially when the stories involve the power elite, feature stories of human interest, include surprise elements and rescues, and are of high impact, especially to the local population. Disasters also provide spectacular imagery and the opportunity for eye-catching headlines, which is another element of the tabloid format. These key parameters thus all flag stories about natural hazards and, in particular, volcanic eruptions as being newsworthy for a tabloid.Of the page space devoted to natural hazards, 9.24 m2 (42%) were set aside to reporting of volcanic activity, specifically the April 2007 eruption of Piton de la Fournaise. We completed a content analysis of these reports to understand the quality of information disseminated to the readership and to extract data regarding the impact of the eruption on local communities. We found the information to be of extremely high quality, with lava reporting being the most important issue covered by page area, mostly due to its photogenic nature. If we consider text-dominated reports, and exclude photo-montages, then the order of importance in terms of space set aside to reporting of a particular theme becomes: (i) general eruption details; (ii) summit collapse; (iii) lava flows; (iv) evacuation; (v) gas; (vi) ocean-entry; (v) air fall; (vi) vegetation fires (lit by lava contact); and (vii) volcano-seismicity. As the eruption and the nature of the hazard evolved (from lava flow through air-fall and gas, to summit collapse and ocean-entry) so too did the focus of the reporting. Once the eruption had finished, emphasis shifted from the hardships of the impacted community to sightseeing and tourism. We found that the quality of the reporting resulted from the use of journalists who were specialized in their reporting areas and who therefore knew the background and the correct sources to seek out for information. This shows that a well-informed journalist can be (i) a means to disseminate information and educate an impacted population, and (ii) a source of information for the volcanologist regarding societal impacts of, and population responses to, natural hazards.

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.

The Ediacaran volcanosedimentary succession of Gabal Abu Had, North Eastern Desert, Egypt: geological study, facies analyses, and depositional setting

Gabal Abu Had is an exposure of a volcanosedimentary succession in the North Eastern Desert Basement Complex. This succession includes intercalation of two major rock units, which are Dokhan Volcanics and Hammamat Group with different styles of formation, deposition environments, and genesis. Gabal Abu Had succession (GHS) is a northward dipping, c. 700-m-thick volcanosedimentary succession that rests on metavolcanic and old granitoid rocks with erosion unconformity. The lower part of GHS is dominated by volcaniclastic mass flow deposits and andesitic lava with interbedded gravely sandstone, whereas the upper sequence is composed of pyroclastic flow deposits including welded to no welded ignimbrite intercalated with gravely sandstone and massive clast-support conglomerate toward the top. Facies analysis study of GHS presented eight lithofacies types, which grouped into five lithofacies associations. The GHS basin started with effusive eruption of silica-poor volcanic center, which produced andesitic lava. A part of lava underwent hyaloclastic fragmentation due to the presence of fluvial water in places producing the volcaniclastic mass flow deposits. Later, an explosive silica-rich volcanic center affected the GHS basin and created the pyroclastic plain deposits (ignimbrite and bedded tuff). The fluvial braided river is still in action since the first eruption, producing gravely sandstone, which is intercalated with the volcanic sequence. The upper GHS is characterized by thick, massive, and clast-supported conglomerate (well rounded clasts up to 100 cm) of alluvial fan facies. Several silica-rich and silica-poor subvolcanic intrusions were emplaced in the GHS. The GHS development displays a cycle from low- to high-energy sedimentation under humid climatic conditions, in addition to extension and down faulting of basin shoulders. In comparison with Gabal El Urf, located to the north of GHS and was studied by El-Gameel (2010), the GHS is a lava-rich succession rather than Gabal El Urf succession which is mainly pyroclastic rich.

Late Carboniferous to Early Permian magmatic pulses in the Uliastai continental margin linked to slab rollback: Implications for evolution of the Central Asian Orogenic Belt

The Paleo Asian Ocean underwent a protracted closure history during Late Paleozoic. Here we investigate the magmatic evolution during this process based on a detailed study in the Baiyinwula region along the Uliastai continental margin. The major rock types in this area are Late Carboniferous-Early Permian volcanic sequences and coeval intrusions. We identified four stages of magmatic evolution based on the diverse assemblages and their precise isotopic ages. The first stage is represented by andesites with a zircon 206Pb/238U age of ca. 326±12Ma. These rocks are metaluminous to weakly peraluminous, high-K calc-alkaline, and possess high Na2O/K2O ratios in the range of 1.23 to 2.45. They also display enrichment of large ion lithophile elements (LILE) and depletion of high field strength elements (HFSE), with markedly positive zircon εHf (t) varying from 8.1 to 15.6.The geochemical features of these andesites are similar to those of typical arc volcanic rocks. The second stage includes granodiorites emplaced at 318.6+1.8Ma. The rocks are high-K calc-alkaline with A/CNK values ranging from 0.95 to 1.06, and show enrichment in LILE and depletion in HFSE. They show geochemical affinities to adakites, with high Sr and low Y and Yb contents, indicating magma derivation from thickened lower crust. Zircon grains from these rocks display positive initial εHf (t) values ranging from 11.1 to 14.6 with corresponding two-stage Hf model ages (TDM2) of 394–622Ma. The third stage consists of syenogranite together with a volcanic suite ranging in composition from rhyolite todacite, which formed during 303.4±1.2 to 285.1±2.2Ma. They possess elevated silica and alkali contents, high FeOt/MgO and Ga/Al ratios, low Al2O3, MgO and CaO contents, and high Rb, Y, Nb, Ce, Zr, Y, and Ga contents, strong negative Ba, Sr and Eu anomalies, showing I- to A-type granitic affinities. Zircons in these rocks show elevated Hf isotopic compositions (εHf (t)=9.9 to 14.6) with TDM2 varying from 324 to 673Ma. The fourth magmatic pulse is represented by K-feldspar granite with zircon U-Pb ages from 283.2±1.9Ma to 280.0±1.4Ma, and typical alkalic A-type granite geochemistry. These rocks possess positive εHf (t) values in the range of 9.7 to15.2, and a restricted range of Hf model age from 327 to 684Ma. The magmatic rocks from the four stages show comparable εHf (t) and T2DM, suggesting that the magmas were derived from the same evolving mantle-derived source. We propose a tectonic model linking the evolution of the magmatism with the closure of the Paleo Asian Ocean that involved the following stages. The andesites were formed during the initial oceanic subduction stage with magma sourced from the metasomatized lithospheric mantle. Stage 2 adakite-like rocks were derived from subduction-induced thickened crust. Subsequent slab rollback resulted in asthenospheric upwelling and melting of residual juvenile crust to generate the I- and A- type syenogranite, rhyolite and dacite suite, finally followed by the A-type K-feldspar granite.