Gneiss Research Articles

Authigenic haematite may exhibit similar rock magnetic properties to detrital haematite: a case study from early triassic red beds in North China

Summary Haematite-bearing red beds are widespread across the Earth and play a pivotal role in palaeomagnetic studies. However, chemical remanent magnetisation (CRM) typically associated with authigenic haematite is not fully understood, which precludes more accurate interpretations of natural remanent magnetisation (NRM) in red beds. Here, we use electron microscopy, rock magnetism, and palaeomagnetism to investigate authigenic haematite in Early Triassic red beds in North China. Our findings reveal that the biotite-hosted haematite grains with grain sizes of several to tens of microns carry a significant portion of the NRM in these sedimentary rocks. We propose that these authigenic haematite particles primarily form during the early stages of diagenesis process. This authigenic haematite's growth is controlled by the crystal structure of the host biotite. Furthermore, this authigenic haematite displays high coercivity (> 100 mT) and high unblocking temperature (> 650 ° C), comparable to that of typical detrital haematite (30–1000 mT, > 650 ° C), which is usually the primary carrier of detrital remanent magnetisation (DRM) in such red beds. This study highlights the significance of combining mineralogical analysis with rock magnetism and palaeomagnetism to differentiate between CRM and DRM and thereby identify the primary NRM component within red beds. We hypothesize that the abundant iron supplied by biotite promotes the growth of authigenic haematite. This study illustrates the need to use caution when studying sedimentary NRM, particularly in rocks from source areas containing acidic igneous and metamorphic rocks (e.g. granite, diorite, and biotite gneiss) that contain a large proportion of iron-bearing minerals, such as the biotite observed in this study.

Uptake of Eu, Th, U, and Pu by granite and biotite gneiss in Korean fresh groundwater under oxidizing and reducing conditions

Abstract The uptake of Eu, Th, U, and Pu by Korean granite and biotite gneiss was investigated in a series of batch experiments. Experiments were conducted under well-defined redox conditions, i.e., oxidizing (air), mildly reducing (Ar-atmosphere and buffered with hydroquinone, pe + pH ≈ 8–9), and strongly reducing (Ar-atmosphere and buffered with Na2S2O4, pe + pH ≈ 0.5–3). Radionuclide concentration, pH and E h were systematically monitored up to t ≤ 113 days after the addition of the radionuclide. The natural content of Eu, Th and U in pristine granite and biotite gneiss materials was quantified by means of alkaline fusion. Eu exhibited moderate sorption on biotite gneiss displaying higher distribution ratios (R d) compared to granite. This observation was possibly explained by the affinity of Ln(III)/An(III) towards biotite mineral absent in the investigated granite material. Strong sorption was observed for Th, U, and Pu in reducing systems where the predominance of the +IV oxidation state is expected. For these three systems, the strength of the uptake follows the order R d(Pu(IV)) > R d(U(IV)) > R d(Th(IV)), consistent with the hydrolysis strength of the corresponding aquo-ions. A significantly weaker sorption was observed for U and Pu under oxidizing conditions, although R d values are manifestly higher for Pu than U. Thermodynamic calculations for the oxidizing conditions predicted the predominance of U(VI) and Pu(V)/Pu(IV), explaining observed differences in retention under oxidizing conditions. These results contribute to a quantitative description and a better understanding of the retention of redox-sensitive radionuclides in crystalline host rocks. Emphasis is placed on the importance of utilizing both redox-stable probes (e.g., Eu, Th) and redox-sensitive actinides (e.g., U, Pu), as well as well-defined redox conditions for accurate predictions of radionuclide retention.

An integrated approach for evaluating groundwater resources of the weathered granite gneiss aquifer of the Usri watershed, Jharkhand, India

An integrated approach for evaluating groundwater resources of the weathered granite gneiss aquifer of the Usri watershed, Jharkhand, India

Geology and landforms of Two Peoples Bay Nature Reserve, Western Australia

Context Underlying geology strongly influences landforms, soil composition, and hydrogeology in Two Peoples Bay Nature Reserve, Western Australia, which was mapped by P. E. Playford in 1982. Aims To review the mapping of the Reserve, with the aim to better understand the geological history and landforms of the area. Methods In 2024, I. M. Tyler and K. A. Evans reviewed P. E. Playford’s mapping in the field, viewed aerial photography and geophysical imagery, and reviewed research published since 1984. Key results The oldest rocks are 1290 Ma granitic gneiss and an 1180 Ma granite intrusion. Amalgamation of the Meso- to Neoproterozoic Rodinian Supercontinent put the Albany−Fraser Orogen at the heart of east Gondwana for ~1.0 billion years. At 165 Ma, that plate configuration began to break up, and from 83 Ma, the Eucla Basin opened. Cenozoic landforms and surficial deposits record northward plate movement and collision with south-east Asia at around 23 Ma, causing tectonic uplift, sea-level change, and climate change. The middle to upper Eocene Plantagenet Group was deposited in a shallow marine embayment with Maardjitup Gurlin/Mount Gardner, forming an island. The uplifted Eocene sea floor was lateritized in the Miocene and is presently covered by Holocene eolian sand dunes, peaty swamps and lakes. Maardjitup Gurlin/Mount Gardner was connected to the mainland by Pleistocene eolianite deposits. Conclusions The influence of plate tectonics on the geological evolution of an area is profound, from the origin and composition of the oldest rocks to the present landscape and the youngest surficial deposits. Implications Understanding the geological history of an area is essential to understanding landscape evolution and the natural history of the flora and fauna that inhabit it.

2.08 Ga andesitic gneisses in the southwestern Yangtze Block: Unveiling new insights into its geological evolution

The early geological history of the Yangtze Block has been difficult to unravel due to limited exposure of Archean to Paleoproterozoic rocks. Through detailed geological investigations and mapping in the southwestern (SW) Yangtze Block, this study identified Paleoproterozoic andesitic and granitic gneisses, as well as associated sedimentary rocks, within the Xinanchang (XAC) Complex. Zircon U-Pb dating yields a concordant age of 2078 ± 11 Ma for the andesitic gneiss, and a weighted mean 207Pb/206Pb age of 1835 ± 12 Ma for the granitic gneiss. The zircon grains from these gneisses exhibit oscillatory zoning and Th/U ratios of 0.40–0.94, corroborating their magmatic origins. Additionally, U-Pb age spectra of concordant zircon grains from the XAC strata range from 1.80 to 2.69 Ga. Together with the intrusive relationship between the 1.84 Ga granitic gneiss and the strata, this implies a depositional age of ca. 1.84 Ga for the XAC strata. The andesitic gneiss exhibits enrichment in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), but shows depletion in Nb, Ta, and Ti. These geochemical signatures are consistent with those of contemporaneous andesitic magmatic rocks in the northern Yangtze Block, suggesting that they were derived from subduction-related sources. In contrast, the granitic gneiss in the XAC Complex shows A-type granite affinities, similar to contemporaneous granitoids widely found across the Yangtze Block. This indicates that these granitoids were formed in a post-orogenic extensional tectonic setting. The northern and SW Yangtze blocks both show records of a transition from subduction to post-orogenic extensional environments between 2.10 Ga and 1.85 Ga, suggesting that the proto-Yangtze Block likely aggregated before 2.10 Ga.

The Petrochemistry and Origin of Precambrian Gneisses around Madaka and Kwana-Bala Area, North Central Nigeria

This paper discusses the petrochemistry and origin of gneisses within basement complex of Nigeria around Madaka and Kwana-Bala area. The lithological units of rocks from Madaka and Kwana-Bala area comprises of gneisses (migmatitic, banded, granitic), kyanite-sillimanite schist, semi-pelitic schist, amphibolites, talcose rock, quartzite, phyllite, granodiorite, fine-medium-grained granites and porphyritic granite. Seven samples of gneisses were analyzed for major element oxides using (ICM-MS). The gneisses are often variable in colour which depending on the nature and proportion of the feldspar and the ferromagnesian minerals. The variation in textures of these rocks from study area is due to varying size and amount of the K-feldspar porphyroblasts couple with varying degree of foliation. In thin section, the characteristics granoblastic textures were observed in migmatitic and granitic gneisses. The mineral compositions of the gneisses rocks are variable, the common minerals assemblage includes: migmatitic gneiss quartz + plagioclase +microcline +biotite + chlorite +garnet, banded gneiss: quartz + plagioclase+ muscovite +biotite+sphene +chlorite+ garnet and granitic gneiss contain quartz +plagioclase+microcline + muscovite+ biotite + chlorite +garnet + opaque minerals. The gneisses of the study area are product of reworked rocks during the Pan-African with a positive DF values, this suggests igneous sources for the protoliths of these rocks in the study area. The chemistry of the gneissic rock also show a variable proportion of Na2O and K2O with alkali-calcic affinity, which suggests, a closed system behaviour during metamorphism on one hand, and possibly a co-magmatic origin of the igneous protolith on the other hand.

Transition Zone from Precambrian Low-grade to High-grade Metamorphic Rocks and the Cauvery Suture Zone in Southern India: Traditional Concepts and Recent Researches

ABSTRACT The contact zone (transition zone) between the low-grade tonalitic and granitic gneisses of the Archaean Dharwar craton and the Neoarchean high-grade granulite facies metamorphic rocks of the Southern Granulite Terrane (SGT) and the existence of Cauvery Suture Zone have been topics of discussion since long. Traditionally, it was strongly believed that there has been gradual transition from low- grade granitic gneisses to high- grade charnockitic rocks from north to south and the concept of transformation finds place even today in some of the latest publications. The existence of Cauvery Suture Zone/shear zone is also being questioned by a few workers. However, accumulation of large volumes of geological, geochemical, geochronological and geophysical data in the form of innumerable publications in the last 2–3 decades has transformed the traditional concepts and several new concepts and innovative ideas have emerged. Recent multidisciplinary studies clearly demarcated the tectonic contact in the place of gradual transition zone and established the existence of Cauvery suture zone and their linkage with the evolution of SGT in terms of fold-thrust tectonics related to convergent tectonic processes.

Tensile Fracture Initiation and Propagation of Granite and Gneiss at Wedge Splitting Tests: Part 2—Fracturing Studies Based on Digital Image Correlation and Thin Section Analysis

AbstractThe crack development in quasi-brittle granite and brittle gneiss under mode I loading condition was monitored using digital image correlation (DIC) technique during wedge splitting tests. The cracking behavior was studied on granite specimens that were split in one material direction, perpendicular to the rift plane, and gneiss specimens that were split in three different material directions, parallel and perpendicular to the foliation (along and across a lineation). The granite specimens had a saw cut 5 mm-wide notch and a blunt round notch in form of a 32 mm borehole. The gneiss specimens had a saw cut notch. The results from the DIC measurements revealed a meandering and branching crack path for the granite, whereas a smoother crack path for the gneiss with almost no branching. This behavior was confirmed by microscopy images from thin sections taken from specimens after testing. The thin sections showed that the fractures were prone to propagate across grains in the more coarse-grained granite than in the fine-grained gneiss, where the fractures propagated almost entirely along grain boundaries. The crack initiation occurred mainly in the corner of the saw cut notches and centrally in the round notch. However, the initiation locations in the granite were affected by the medium- to coarse-grained microstructure with grains preventing initiation and propagation which yielded displaced positions out from the ideal ones with respect to the highest stress in some cases. The crack opening displacement was determined along the crack path from the DIC measurements at 12 stages on each specimen of the advancing crack during the splitting progress. The critical crack opening displacement and length of the fracture process zone were assessed and the crack front position yielding the crack length along the tests was determined. The results showed a critical crack length when the deformations in the ligament (also called plastic hinge) affected the cracking process. The average crack velocity in gneiss during the test was more than twice as high as in the granite. This is attributed to a combined effect of the higher brittleness in the gneiss and the effect of a too large elastic energy in the specimen and test setup in relation to the dissipated fracture energy which made the initial crack propagation in the gneiss specimens nearly unstable. The strain energy release rate was calculated along the crack propagation and showed a lower value when the crack lengths were less than 40–60 mm. The calculation of the strain energy release rate was made on crack length measurements from DIC results. The results from the investigation were discussed in relation to the few other similar results found in the literature. The findings give an insight and understanding of the cracking process via both qualitative and quantitative results. Several used methods were novel or not used together in a single study as in this one.

Petrology and geochemistry of the Suhum Basin granitoid complex, Ghana: Implications for crustal growth during the Rhyacian orogeny of the West African Craton

The Suhum Basin granitoid complex is an important granitoid complex of the Birimian terrane of Ghana for unravelling the crustal growth and evolution of the West African Craton (WAC) during the Rhyacian Eburnean orogeny. Almost the entire Suhum Basin is occupied by an extensive granitoid complex, which contains useful information for constraining debatable plate tectonic issues, especially during the Archean-Paleoproterozoic transition period. We present petrography, whole-rock geochemistry, and mineral chemistry data of biotite, amphibole, and plagioclase to constrain the temperature-pressure conditions of emplacement, petrogenesis, tectonic setting, the evolution of the granitoids complex of the Suhum Basin, and its implications for the crustal growth and evolution of the WAC. Four lithological types; granite gneiss, migmatites, leucogranites, and mafic enclaves, characterise the granitoid complex of the Suhum Basin. Biotites from the granitoid complex have an annite-siderophyllite composition, and that, coupled with their calc-alkaline and I-type signatures, indicates crystallisation of the granitoid complex of the Suhum Basin under oxidised conditions. The medium-to high-K character of the rocks, together with the calc-alkaline nature, may be a reflection of the generation of magma in regions where the mantle wedge might have interacted with enriched fluids from the underlying plate during dehydration. The enrichment of LILE and LREE relative to HREE and HFSE and the negative Eu, Nb-Ta, and Ti anomalies of the granitoids complex may indicate derivation from enriched magma sources with varying degrees of fractionation in an arc environment. Amphibole-plagioclase thermobarometry indicates that the granitoid complex formed at P-T conditions of 600–712 °C and 5.2–7.2 kbar, signifying a deeper depth (19–27 km) of emplacement. The overall geochemical data suggest that the rocks formed during a single orogenic event related to a volcanic arc environment where subduction zone components played a role in the generation of their parental magmas. This finding is therefore consistent with the onset of “modern-style” subduction-related processes during the Archean-Paleoproterozoic transitional period.

Top-to-south shear at the base of the eastern Tethyan Himalayan Sequence during the Eocene-Oligocene Himalayan orogeny

The early mountain building processes in the Himalayan orogen are still not clear because of extensive deformation and metamorphism since the Miocene. A large gently dipping ductile shear zone, referred as the Tethyan Himalayan Décollement (THD), is defined here as the sole décollement of the south-verging Tethyan fold-and-thrust belt in the Lhozag-Cuona area of the eastern Himalayan orogen. The ∼4 km-thick THD is characterized by a top-to-south shear sense, moderate T/P Barrovian to high T/P Buchan type metamorphism and Eocene-Miocene partial melting. Zircon U-Pb dating of metasedimentary rocks and granitic gneisses from the THD yields protolith ages of the Late Cambrian to Early Ordovician. Based on structural analysis, zircon U-Pb ages, monazite U-Pb ages and mica 40Ar/39Ar thermochronology, the THD was the boundary shear zone at the top of the Greater Himalayan Crystalline Complex (GHC) and accommodated the persistent north-south shortening in the Tethyan Himalayan Sequence (THS) from ∼50 Ma to 20–17 Ma. From ∼20–17 Ma, the top-to-north South Tibetan Detachment System (STDS) was predominantly activated to juxtapose the unmetamorphosed or low-grade THS over the GHC. This tectonic transition can be attributed to the roof collapse in the eastern Himalaya (younger than that of the central-western Himalaya), which triggered rapid exhumation of the GHC and the northern Tethyan Himalayan gneiss domes. Hence, the THD was the predecessor of the STDS and a prolonged pathway for leucogranitic melts from the Eocene to early Miocene. The transition from the THD-controlled crustal thickening in the Eocene and Oligocene to the STDS-controlled extrusion in the Miocene shed insights on a new synthesis of the tectonic wedging model for the Himalayan evolution.

Selection of Optimum Enhancement Technique for the Discrimination of Alkali Granites and Syenites around Suryamalai Batholith of Central Tamil Nadu, India

Image processing techniques such as Band Ratio, Principal Component Analysis, Supervised, Unsupervised classification and Reclassification techniques are generally used as an enhancement technique for alteration zone demarcation and lithological discrimination in geosciences environment. In the present study, Landsat OLI satellite imagery has been utilized to produce various combinations of image enhancement to discriminate alkali syenite and alkali granite of Proterozoic age. These techniques were also used to differentiate three phases of granites reported in Suryamalai Batholith which is very difficult to map by conventional method due to its rugged topographic nature. 12 types of enhancement techniques were applied to differentiate rock alkali syenite from granite, however only few methods such as Kaufmanns ratio, ratio of 5/7, 3/1 and 3/5 and supervised classification were found to be suitable for the discrimination of those rocky types. Band ratio 5/7, 3/1 and 3/5, Crosta analysis and thermal reclassification techniques significantly brought to light the difference between the metamorphic rocks such as fissile hornblende biotite gneiss and hornblende biotite gneiss of Archaean age. Similarly, phase I and phase III granites were perfectly discriminated from all the image enhancement techniques. It is differentiated mainly based on its grain size and mineral variation between these two rock types. Study revealed that standard digital image processing technique can be effectively used for lithological mapping.

Lithological and Structural Mapping of Basement Rock Units in the Ikara North-Central Basement Complex, Nigeria

Study’s Excerpt The lithological and structural composition of the Ikara North-Central Basement Complex in Nigeria is investigated. Detailed field and petrographic analyses were carried out to identify the rock types of the area. The geological map of the area is updated. Full Abstract The lithological and structural architecture to unravel the compositions and tectonic evolution of the Nigerian Basement Complex has not been fully documented by geoscientists. As such, this research aimed to investigate the lithological and structural characteristics of the Ikara North-Central Basement Complex. Detailed petrographic and field analysis reveals the prevalence of gneiss and granite lithologies characterized by significant structural features such as fractures, folds, and foliations. These findings offer new understandings of the tectonic evolution of the region. The study area mapped is the Ikara Sheet 103 Federal Survey Topographic Sheet to a scale of 1:100,000. The major lithological units underlying the study area are gneisses and granites. However, these major rock types have varieties, namely migmatitic gneiss, granite gneiss, migmatitic (augen) gneiss, porphyroblastic gneiss, medium to coarse-grained granites, and porphyritic granites. These rock types were intruded by quartzites, pegmatitic dykes, quartz, and aplite veins. Rock samples were observed and studied based on their mineralogical composition, color, and texture. The results of the petrographic analysis showed that the rocks are mainly composed of quartz, plagioclase feldspars, alkali feldspars, mica (biotite and muscovite), hornblende, garnet, and accessory minerals like zircon and magnetite. Geological structures were also observed during the field study, namely fractures (joints and fractures), foliations, lineations, veins, dykes, and various landforms. Photomicrographs from thin section analyses revealed micro-structures like myrmekites, micro-folds, and micro-fractures were also observed. Mineralization such as amethyst and cassiterite were hosted by quartz veins and pegmatites in porphyritic granites, respectively. A litho-structural map was produced, exhibiting the lithological units and regional structures cross-cutting the area of research.

Monazite Beats Zircon Regarding Dating of Young Metamorphic Events—An Example From Polycyclic Granitic Gneiss of the Pohorje Mountains, Slovenia

ABSTRACTThe result of dating U–(Th)–Pb bearing minerals in metamorphic rocks frequently suffers from the interpretative relation of their growth to a specific metamorphic event. This problem occurs in the southern Pohorje Mountains. Therefore, granitic gneiss from this area was studied. Rims of zircon in these rocks gave U–Pb ages around 90 Ma interpreted as an indicator of Late Cretaceous metamorphism. However, in situ dating of monazite with LA–ICP–MS yielded Early Miocene U–Th–Pb ages consistent with contact metamorphism by magmas forming the Pohorje pluton. This is supported by geothermobarometry using compositions of garnet and muscovite in granitic gneiss. This method led to pressure–temperature conditions of 6.5 kbar and 625°C, in line with intrusion depths estimated for the southeastern part of the Pohorje pluton. Consequently, zircon was not suitable for dating the latest metamorphic event but monazite was. Furthermore, monazite dating suggests two main intrusion pulses of magmas differing by 2–3 Ma.

Petrogenesis of supracrustal rocks from the Maxianshan and Xinglongshan Groups in the eastern Central Qilian block: Constraints on the construction of Rodinia

Controversy has long surrounded the reconstruction of the East Asian blocks in the Rodinia supercontinent, which was a coherent large landmass during 900–750 Ma and is now dispersed over all current major continents. The Central Qilian block is a Precambrian microcontinent in the early Paleozoic Qilian orogenic belt, which marks the junction of the North China, South China and Tarim cratons. In this paper, we present a systematic study of the petrology, whole-rock geochemistry, and geochronology of supracrustal rocks from the Maxianshan Group and the Xinglongshan Group in the easternmost part of the block. The metasedimentary rocks from both groups overlie a gneissic granite, which has a zircon U-Pb age of 970 ± 6 Ma with εHf(t) values of −3.5 to + 2.5 and is an I-type granite formed in a back-arc setting. Paragneisses from the Maxianshan Group and micaschists from the lower formation of the Xinglongshan Group have detrital zircon U-Pb ages of 2465–876 Ma that peak at ca. 950 Ma. They show strongly decreasing zircon εHf(t) values of + 0.8 to −11.3 and ages from 1174 Ma to 876 Ma. Their protoliths constituted a sedimentary sequence with a long history of deposition during 1174–911 Ma in a continental arc-related basin. Metabasaltic tuffs from the middle formation of the Xinglongshan Group are tholeiitic with a zircon U-Pb age of 958 ± 9 Ma and indicate a back-arc setting. Metasandstones from the upper formation of the Xinglongshan Group have detrital zircon ages of 2668–732 Ma that peak at 810 Ma and 984 Ma and indicate a passive margin setting. Combining our results with existing data, we propose that the Maxianshan Group and the Xinglongshan Group make up an early Neoproterozoic trench-arc-basin system at a continental margin of Rodinia. Oceanic crust subduction underneath the continent at 1174–896 Ma with formation of a mature continental arc, and continuous subduction from 824 to 735 Ma with opening of the Proto-Tethys Ocean as a back-arc basin are suggested for the formation of the Central Qilian block.

Tectonic reevaluation of West Cameroon domain: Insights from high-resolution gravity models and advanced edge detection methods

The West Cameroon region, characterized by a diverse geomorphology of highlands and plains resulting from tectonic processes across different geological ages, has been extensively explored for natural resources. Recognizing the significance of its tectonic and magmatic features associated with seismic and volcanic activity, this study focuses on geodynamic investigations of the Cameroon Volcanic Line (CVL). Despite previous efforts, detailed structural geophysical studies of the West Cameroon domain have proven inconclusive, prompting a comprehensive structural reinterpretation. Utilizing the high-resolution SGG-UGM-2 satellite gravity model and innovative processing techniques, including the horizontal gradient of a modified tilt (HGSTDR), the balanced horizontal gradient (BHG), the tilt of the horizontal gradient (TAHG), the improvised horizontal gradient tilt angle (impTAHG), and the Tilt Depth method, our research aims to enhance the interpretational quality of tectonic lineaments. By separating regional and residual anomalies in the Bouguer gravity map and applying a combination of filters to delineate geological units, the BHG filter emerges as a robust tool that highlights subsurface edges without generating false features. This approach unveils previously undetected NNW-SSE-oriented lineaments, confirming the presence of deep fractures and faults in Bafoussam, Nkongsamba, and along the Benue Trough, corroborated by newly discovered NNW-SSW trending lineaments. The study suggests that the region’s topography is overcompensated by deep mountain roots and compressive tectonism. Digitizing the BHG filter produces a structural map, revealing predominant NE trends in identified geological margins, including NNE-SSW, N-S, NW-SE, E-W, and NE-SW directions. Geological contacts between granite and high-grade gneiss are indicated by NNW-SSE and NNE-SSW trending lineaments along the Benue Trough. These results contribute significantly to the understanding of the tectonic setting of the West Cameroon Domain.

Experimental Study on Proportion Optimization of Rock-like Materials Based on Genetic Algorithm Inversion.

It is very important to clarify the optimization method of the rock-like material ratio for accurately characterizing mechanical properties similar to the original rock. In order to explore the optimal ratio of rock-like materials in gneissic granite, the water-paste ratio, iron powder content and coarse sand content were selected as the influencing factors of the ratio. An orthogonal test design and sensitivity analysis of variance were used to obtain the significant influencing factors of the ratio factors on seven macroscopic mechanical parameters, including compressive strength σc, tensile strength σt, shear strength τf, elastic modulus E, Poisson's ratio ν, internal friction angle φ and cohesion c. A multivariate linear regression equation was constructed to obtain the quantitative relationship between the significant ratio factors and the macroscopic mechanical parameters. Finally, a rock-like material ratio optimization program based on genetic algorithm inversion was written. The results show that the water-paste ratio had extremely significant effects on σc, σt, τf, E, ν and c. The iron powder content had a highly significant effect on σc, σt, τf and c, and it had a significant effect on ν and φ. Coarse sand content had a significant effect on σc, E and c. The multiple linear regression model has good reliability after testing, which can provide theoretical support for predicting the macroscopic mechanical parameters of rock-like materials to a certain extent. After testing, the ratio optimization program works well. When the water-paste ratio is 0.5325, the iron powder content is 3.975% and the coarse sand content is 15.967%, it is the optimal ratio of rock-like materials.

Zircon U-Pb Age and Hf-O Isotope Evidence of the Taihua Complex on the Southern Margin of the North China Craton: Implications for Its Magmatic Process During the Early Paleoproterozoic

The Xiaoqinling is the largest terrane of the Taihua Complex and records Paleoproterozoic silicic magmatism, which is one of the most potential areas for understanding secular changes in tectonic processes during the Tectono-Magmatic Lull (TML). In this study, we use zircon U–Pb dating, Lu–Hf and O isotopic analysis to constrain the age, provenance, and magmatic processes of the protoliths for the Paleoproterozoic granitic gneiss, tonalitic gneisses, and migmatitized tonalitic gneiss from the Xiaoqinling area. The isotopic composition of zircon provides a key proxy for querying the crustal record. Integration of our new U–Pb and Hf–O isotope data with available published data from other regions of the North China Craton (NCC), allows us to better assess the secular changes of the North China Craton during the magmatic lull at ∼2.3 Ga. This study shows that the protolith of the tonalitic gneisses in the study area have crust-like Hf–O isotopic compositions with slightly negative to positive εHf(t) (−3.0− +2.1) and low to moderately elevated δ18O values (2.71–7.87‰), indicating a mixed origin of continental crust assimilated by mantle-derived magmas.

An assessment of the environmental radiation risk from the petrologic units of north-eastern Nigeria; an insight from aero-radiometric data interpretation

Information regarding the radiation risk posed by radioactive emissions from the petrologic units in North eastern Nigeria is extremely limited. Consequently, there has been little research conducted on the environmental impact of radiation exposure from different petrologic units in this region. Hence, the 13 petrologic components of the area that comprises of the migmatites-gneiss (MG), banded gneiss (BG), biotite-hornblende granites (OGe), porphyritic biotite-hornblende granites (OGp), charnockytes (Ch), ignimbrites (JYG), basalts (bb), Keri-Keri Formation (KK), Gombe Sandstones (GS), Pindiga Formation (PS), Yolde Formation (YL), Bima Sandstones (BS), and alluvium (AL) deposits were assessed using aero-radiometric data (equivalent uranium, equivalent thorium, and percentage potassium radio-elements) acquired by Nigerian geological survey agency (NGSA) in 2009. The objective of this study is to compute the amount of radiation across the various rock units of the study area, and examine their radiation risk parameters. The results of this study showed variable levels of radiation across the various rock units examined. The average total activity concentration values recorded ranges from 261.67 ± 447.12 Bq/Kg across KK rock unit to 1482.02 ± 447.12 Bq/Kg across OGp/OGe rock types of the study area. Moreover, the average radium equivalent (Rn eq), absorbed dose rates (D) estimated ranges from 113.83±461.33 Bq/Kg to 305.19 ± 58.51 Bq/Kg, and 51.88 ± 29.65 nGyh−1 to 144.94 ± 29.65 nGyh−1 along KK Formation, OGp, and same KK Formation, and OGp respectively. The average environmental radiation hazard parameters of the annual effective dose rate (AEDE), activity utilization index (AUI), respiratory dysfunction parameters (RH in, RH out), annual gonad dose equivalent (AGDE), and excess life cancer risk (ELCR) measured across all rock units were found to be within or above their respective acceptable limits of 1 mSv/y, 300 μSv/y, and 0.29 × 10−3. Additionally, based on the conspicuously higher hazardous radiation (D, Rn eq, AEDE AGDE, RH in, RH out, and ELCR) emissions estimated from the OGp, OGe, MG, BG, and Ch petrologic units, the inhabitants of these localities should therefore limit themselves from excessive exposure to these rocks. Therefore, periodic monitoring of these areas is recommended.

A geospatial approach to delineate lineaments on the granite gneissic terrain of Mpwapwa district, Dodoma, central Tanzania

The study sought to utilise Geographic Information Systems (GIS), Remote Sensing, and a blend of manual and automatic techniques to delineate and analyse the spatial distribution and orientation of lineaments within the terrain of Mpwapwa District. The study employed various techniques, including the Optimum Index Factor (OIF), Band Combination, Principal Component Analysis (PCA), and Directional Filtering on the Landsat 8 imagery, and Hill Shading technique was used on Shuttle Radar Topography Mission Digital Elevation Model (SRTM DEM). These techniques were employed in the processing steps for both manual and automatic lineament extraction, utilizing various software tools. Lineament control and validation were executed using digitized geological maps, topographical maps, and Google Earth images.The results revealed lineaments with a total length of 2060.6 km, non-uniformly distributed and predominantly present in hard rock lithologies, such as migmatitic granite, migmatitic biotite gneiss, biotite gneiss, granitoid gneiss, and porphyroblastic gneiss. The findings further indicate that NE-SW and NW-SE are the dominant lineament trends. Additionally, the study revealed that areas with medium, high, and very high lineament density and intersection are primarily located in the southwest and northeast parts of the Mpwapwa District. Meanwhile, regions with low lineament density are spread through the entire district.In this study, GIS and remote sensing emerged as valuable tools for identifying and mapping lineaments within a challenging hydrogeological setting. Findings from this study will serve as a foundational framework for subsequent geological and hydrogeological investigations in the area of study.

Geochemistry and geochronology of 1.7-1.8 Ga peraluminous A-type granites and granite-gneiss from the Mahakoshal Basin, Central Indian Tectonic Zone (CITZ): implications for an accretionary orogen for the evolution of CITZ

ABSTRACT Here, we report petrography, whole-rock geochemistry, and zircon U-Pb geochronology to understand the origin, source, geodynamic setting, and evolution of A-type granite and granite gneiss as well as establish their emplacement age from Mahakoshal Basin. Mineralogically, Sidhi granite gneiss and Madanmahal granite of the Mahakoshal Basin dominantly consist of quartz, K-feldspar, and plagioclase. Geochemically, Sidhi granite gneiss and Madanmahal granite are ferroan in nature. The studied rocks are akin to peraluminous A-type granites and have average zircon saturation temperatures of 955°C and 977°C, respectively. The studied rock types are derived from partial melting of pre-existing crust indicated by (Y/Nb)N >0.18, (Th/Nb)N >2, (Ce/Pb)N <1, and (La/Nb)N >2 accompanied by the Eu, Ba, Sr, Ti, and Nb negative anomalies. The zircon U-Pb geochronology yielded emplacement ages of 1723 ± 16 Ma for the Sidhi granite gneiss and 1801 ± 64 Ma for the Madanmahal granite. Based on similar geochemical characteristics such as rare earth element patterns, Eu anomalies, and Ce/Pb, La/Nb, and Th/Nb ratios, we propose that the Sidhi granite gneiss and Madanmahal granite are derived from the same source i.e. Bundelkhand gneisses and granites, and formed in a post-orogenic rift environment of the accretionary orogen setting.