Gneiss Research Articles

National-scale distribution of strontium isotope ratios in environmental samples from South Korea and its implications for provenance studies

Successful application and accurate interpretation of strontium (Sr) isotope ratios (87Sr/86Sr) requires underlying information about the large-scale variabilities in their signatures from a variety of environmental samples, which can be correlated with the Sr isotopic signatures of underlying local geology. In this national-scale study, we analyzed 87Sr/86Sr in soil, plants, stream water, and Chinese mystery snail (Cipangopaludina chinensis) shells collected from South Korea to evaluate large-scale spatial variabilities, interpret relationships among isotopic signatures of various sample types, and generate spatial distribution isoscapes reflecting the heterogeneity of isotopic signatures across South Korea. Non-parametric comparisons among environmental samples showed non-significant differences in their isotopic ratios. The 87Sr/86Sr of plant and soil samples were strongly correlated (R2adj = 0.93), suggesting that both reflect national-scale lithological properties. Similarly, the 87Sr/86Sr of shells showed strong correlations with the 87Sr/86Sr of both plant and soil samples (R2adj = 0.90). The 87Sr/86Sr signatures of environmental samples in this study aligned with expected Sr isotopic values and generally reflected local geology. Spatial distribution maps of samples showed similar 87Sr/86Sr spatial patterns, with high radiogenic values from granitic and granitic gneiss rocks systems and low radiogenic values from volcanic and sedimentary rock systems. Stream water samples showed significant correlations with soil and plant isotopic ratios, but with a low coefficient of determination (R2adj = 0.68). The deviations were much larger for samples with 87Sr/86Sr > 0.720. Further study is needed to improve the accuracy of baseline determination and interpretation of stream water isotopic variations.

Geological evolution of the Proterozoic Betul belt (∼2.16–0.95 Ga) of the Central Indian tectonic Zone: Its linkage to the assembly and dispersal of Columbia and Rodinia supercontinents

The Proterozoic Betul Belt is an important supracrustal unit that records the protracted history of crustal accretion and growth in the Central Indian Tectonic Zone (CITZ). Here, we present results from systematic geological mapping, petrological, geochemical (including Sm-Nd isotope) studies, and U-Th-Pb geochronology on rocks from the Betul belt, with the objective of reconstructing its Proterozoic evolution and its link with past supercontinents. The Betul belt comprises ca. 2167 ± 11 Ma granite gneisses, ca. 2051 ± 80 Ma mafic volcanics (pillowed lava), 1715 ± 10 Ma rhyolite, and older granitoids (1671 ± 29 Ma) that have undergone multi-stage deformation and amphibolite-facies regional metamorphism. The bulk rock geochemistry of gneisses, pillow lava, and mafic intrusions are characterized by arc-like signatures, whereas the rhyolite and granites are anorogenic and back-arc related. The whole-rock geochemical and Sr-Nd isotopic compositions of pillow lavas and mafic intrusions suggest the involvement of recycled crustal material in their source, possibly in the form of associated sediments. The Betul granite gneisses were emplaced at 2167 Ma in a collisional setting by melting crustal protoliths having an affinity with the Bundelkhand craton and may constitute the basement for the supracrustal sequence. The supracrustal units, i.e., mafic volcanics and rhyolites, occur as a bimodal suite formed in the arc and back-arc environment with penecontemporaneous sedimentation. Bulk rock geochemistry and age data indicate two phases of A-type granite magmatism at 1674 Ma and 1079 Ma, with post-collisional geochemical traits forming within an anorogenic and back-arc setting, respectively. Younger post-orogenic granites (Navegaon) were emplaced in a back-arc setting at ca 1079–954 Ma, synchronous with a collisional event in the Sausar belt. Spot ages from monazite in Hbl gabbro yield a weighted mean of 1026 ± 97 Ma (MSWD = 0.15), reflecting Grenville-age regional metamorphism in the CITZ. The geological events recorded in the rocks of the Betul belt between ca 2167 Ga and 954 Ma correlate well with events that affected Laurentia, Baltica, Australia, and East Antarctica within the frameworks of the Columbia (ca. 2.1–1.7 Ga) and Rodinia (ca.1.2–0.9 Ga) supercontinents.

Tectonics, geochronology, and petrology of the Walker Top Granite, Appalachian Inner Piedmont, North Carolina (USA): Implications for Acadian and Neoacadian orogenesis

Abstract The Walker Top Granite (here formally named) is a peraluminous megacrystic granite that occurs in the Cat Square terrane, Inner Piedmont, part of the southern Appalachian Acadian-Neoacadian deformational and metamorphic core. The granite occurs as disconnected concordant to semi-concordant plutons in migmatitic, sillimanite zone rocks of the Brindle Creek thrust sheet. Locally garnet-bearing, the Walker Top Granite contains blocky alkali feldspar megacrysts 1–10 cm long in a groundmass of muscovite-biotite-quartz-plagioclase-alkali feldspar and accessory to trace zircon, titanite, epidote, sillimanite (xenocrysts), and apatite. It varies from granite to granodiorite and contains several xenoliths of biotite gneiss, amphibolite, quartzite, and in one location encloses charnockite (here formally named Vale Charnockite). New sensitive high-resolution ion microprobe U-Pb zircon magmatic crystallization ages obtained from the plutons of the Walker Top Granite are: 407 ± 1 Ma in the Brushy Mountains; 366 ± 2 Ma in the South Mountains; and 358 ± 5 Ma in the Vale–Cat Square area. An age of 366 ± 3 Ma was obtained from the Vale Charnockite at its type locality. Major-, trace-element, and isotopic chemistry indicates that Walker Top is a high-K, peraluminous granite, plotting as volcanic arc or syn-collisional on tectonic discrimination diagrams and suggests that it represents deep-seated anatectic magma with S- to I-type affinity. The alkali calcic, ferroan Vale Charnockite likely formed by deep crustal melting, and similar geochemical and trace-element compositions suggest a similar tectonic origin as Walker Top Granite. The discontinuous nature of the Walker Top Granite plutons precludes it intruded as a volcanic arc. Instead, the peraluminous nature, common xenoliths of surrounding country rock, and geochemical and isotopic signatures suggest it formed by partial melting of Cat Square and Tugaloo terrane rocks. Following emplacement and crystallization, Walker Top plutons were deformed into elliptical to linear shapes—SW-directed sheath folds—enveloped by partially melted, pelitic and quart-zofeldspathic rocks. Collectively, Walker Top and other plutons helped weaken the crust and facilitate lateral crustal flow in a SW-directed, tectonically driven orogenic channel during the Acadian-Neoacadian event. A comparison with the northern Appalachians recognizes a similar temporal magmatic and deformational history during the Acadian and Neoacadian orogenies, although while the Walker Top Granite intruded the lower plate during eastward subduction beneath the peri-Gondwanan Carolina superterrane, the northern Appalachian plutons intruded the upper plate during subduction of the Avalon superterrane westward beneath Laurentia. We hypothesize that a transform fault, located near the southern end of the New York promontory, accommodated oppositely directed lateral plate motion and different subduction polarity between the Carolina and Avalon superterranes during the Acadian and Neoacadian orogenies.

Sediment Properties and Provenance Study of Heavy Minerals Along Chinnavilai and Erayumanthurai Beach, South West Coast of India

The Chinnavilai and Erayumanthurai beach sediments of the Kanyakumari District consist of medium-grained, moderately well-sorted, unimodal, occasionally bimodal, mesokurtic, leptokurtic and platykurtic. The fine skewed and symmetrical nature of sediments implies the prevalence of high and low energy, entailing a mixed distribution of coarse and fine sediments. The washing and backwashing of waves cause the coarser sediments to retainment and entrapped amidst finer sediments. The heavy minerals distribution reflects that the less content in Erayumanthurai samples, whereas the Manavalakurichi, Enayam, Kurumpanai sediments comprise >60%. The oval shape zircon is devoid of inclusions, whereas, the euhedral zircons comprise subhedral inclusions. Distinct fractures in zircons are caused due to transportation by waves and currents. The garnet and zircon grains are well-rounded, implying the source for these sediments are an admixture of medium to high-grade metamorphic rocks, reworked sediments, charnockite, and granite gneisses. Keywords : Sediment Texture, Provenance, Heavy Minerals, Kanyakumari,South West Coast of India

Zircon geochronology of high-grade metamorphic rocks from outcrops along the Prince Olav Coast, East Antarctica: Implications for multi-thermal events and regional correlations

This paper reports laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) zircon U–Pb ages of a suite of high-grade metamorphic rocks collected from Sinnan Rocks, Akebono Rock, Niban Rock, Gobanme Rock, Tenmondai Rock, Akarui Point, Cape Omega, and Oku-iwa Rock along the Prince Olav Coast, in the Lützow-Holm Complex (LHC), East Antarctica. The dating results indicate that a newly detected ~ 990 Ma metamorphism of garnet–sillimanite–biotite gneiss from Niban Rock. A thermal event at 931.7 ± 9.8 Ma is recorded in zircon from staurolite-bearing garnet–gedrite–biotite–chlorite gneiss in Akebono Rock. The metamorphic zircon grains in other analyzed samples provide Ediacaran to Cambrian ages. Their multi-growth textures and age populations are possibly interpreted to exhibit three metamorphic stages during >600–580 Ma, 580–550 Ma, and 550–500 Ma. Combined with previous reports, the metamorphic rocks in Cape Hinode, Niban-nishi Rock of Niban Rock, and Akebono Rock might have experienced earlier high-temperature metamorphism at ~ 990–930 Ma without younger overprinting. Extensive high-grade metamorphism during ~ 650–500 Ma is recorded from not only the granulite-facies zone in the west of the LHC but also the amphibolite-facies zone in its east. The main metamorphic episode in the LHC is likely to be subdivided into a preceding thermal event (either independent single metamorphic event or prograde stage) at pre-580 Ma, near-peak condition stage during 580–560 Ma, and subsequent retrograde stage after 550 Ma. In regional context this indicates that the assembly at the central Gondwana started with the collision of early and late Neoproterozoic terranes prior to 580 Ma, as a part of the East Africa-Antarctic Orogeny. Subsequent collisions took place among late Neoproterozoic igneous terrane, above terranes collided at pre-580 Ma, and Neoarchean terrane, which were probably driven by the Kuunga Orogeny.

Evidence for early Pennsylvanian subduction initiation in the Mongol–Okhotsk Ocean from the Adaatsag ophiolite (Mongolia)

The Late Paleozoic–Mesozoic Mongol–Okhotsk Ocean was the latest ocean basin witnessing the final amalgamation of East Asia. However, the kinematic evolution and geodynamics of Mongol–Okhotsk's subduction initiation remain enigmatic mainly due to the lack of appropriate studies of its ophiolitic records. Here, we report for the first time a subduction initiation record from the Adaatsag ophiolite in the central Mongolia. This ophiolite presents a magmatic sequence akin to that in the Izu–Bonin–Mariana forearc, considered archetypical of subduction initiation. The gabbroic and basaltic rocks of the ophiolite display geochemical signatures similar to the forearc basalts. Zircon UPb geochronology of the gabbro shows a mean age of 319 ± 2 Ma, which we interpret as crystallization age. The high-Mg diorite intruding the gabbros of the ophiolite displays a transitional affinity between sanukite and boninite. Zircon UPb geochronology of the high-Mg diorite shows a mean age of 317 ± 2 Ma. Together with the neighbor Khuhu Davaa suprasubduction zone ophiolite (∼321 Ma), we interpret that the subduction of the southwestern Mongol–Okhotsk Ocean initiated during the Early Pennsylvanian (∼320 Ma). The structurally underlying gneissic granite (∼534 Ma) indicates the Adaatsag ophiolite was emplaced southward onto the Ereendavaa cratonic terrane, and the overlying molassic sequences (youngest detrital zircon peak age of ∼252 Ma) constrain this emplacement occurred before ∼252 Ma. The older (499–870 Ma) inherited zircons of the ophiolites and negative Hf isotope data of the high-Mg diorite indicate that a continental fragment existed in the newly formed intra-oceanic arc, which probably facilitated the Early Pennsylvanian subduction initiation in the Mongol–Okhotsk Ocean.

Discovery of a >1,000 km Cambrian Eclogite‐Bearing High‐Pressure Metamorphic Belt in the Central Asian Orogenic Belt: Implications for the Final Closure of the Pan‐Rodinian Ocean

AbstractThe immense Central Asian Orogenic Belt (CAOB) records the transition from the Pan‐Rodinian Mirovoi Ocean to the Paleo‐Asian Ocean, but the final closure of the Mirovoi Ocean remains unexplored. Here we document two new eclogite occurrences, located between CAOB microcontinents and the Ediacaran–Cambrian island arc in Mongolia. Pseudosection modeling and geothermobarometry constrain peak conditions of ∼560°C and ∼2.2 GPa for the Urgamal eclogite and ∼715°C and ∼2.0 GPa for the Tsengel eclogite. Zircon U‐Pb dating results suggest the Urgamal eclogite‐facies metamorphism occurred at ∼522 Ma, and the granite gneiss enclosing the eclogite yielded ∼811 Ma crystallization age and ∼519 Ma metamorphic age. Detrital zircon age spectra of the paragneisses associated with the eclogite suggest a probable provenance from the adjacent Zavkhan microcontinent and the Neoproterozoic arc superimposed on the microcontinent. The Tsengel eclogite has a protolith age of ∼853 Ma and an eclogite‐facies metamorphic age of ∼522 Ma, and the associated migmatite gneiss record a ∼520 Ma migmatization event. The rock associations and geochemical affinities indicate that their protoliths represent mafic rocks formed in a continental rift setting and the Early Neoproterozoic subduction–accretion complex, respectively. Their similar tectonic position and metamorphic age suggest that these rocks are part of a single >1,000 km long Cambrian high‐pressure metamorphic belt. The rocks record closure of the Mirovoi Ocean within the CAOB and constrain this crucial event to ∼520 Ma along the western margin of the microcontinents in Mongolia.

Partial melting of subducted continental crust during the exhumation: Insights from Palaeozoic granitic rocks in South Altyn, western China

The early Palaeozoic continental subduction–collisional belt in South Altyn (SA) western China distributes a large amount of (ultra)-high-pressure ((U)HP) metamorphic and granitic rocks associated with subduction, collision, and exhumation. In this study, four granitic rocks were collected from Bashenwake located in eastern SA. The ages of the garnet-bearing alkali-feldspar granite (GAFG), garnet-bearing granitic gneiss (GGG), alkali-feldspar granite (AFG), and syenogranite (SG) are 458.0 ± 4.1, 483.0 ± 4.1, 450.0 ± 2.4, and 482.0 ± 4.9 Ma, respectively. Whole-rock major and trace elements and Sr–Nd–Pb isotope, and zircon Hf isotope compositions for all samples exhibit characteristics of a continental crustal source. Based on partial melting modeling, the source temperature of the GGG, GAFG, AFG and SG was concluded as 750–780 °C, 730–760 °C, 730–770 °C and ca. 800 °C, respectively. The source pressure was estimated as ca. 0.8 GPa for the GGG, GAFG and AFG, and ca.1.2 GPa for SG. Combined with studies on (U)HP metamorphic rocks in SA, this study reveals that GGG is formed by metamorphism while SG is formed from partial melting of upper crustal rocks heated by upwelling mantle during the initial stage of exhumation (ca. 480 Ma) of subducted continental crust in SA. During further stage of exhumation of the subducted continental crust at ca. 450 Ma, the GAFG and AFG were formed from partial melting of GGG as a result of decreased pressure and further mantle upwelling. Consequently, the exhumation age of subducted continental crust in eastern SA is ca. 30 Myr earlier than that in western SA. Thus, the geochronology and petrogenesis of four granitic samples in this study exhibit one of very few evidence for partial melting of subducted continental crust during the exhumation and also provide magmatism exhibits evidence for the differential exhumation model of eastern SA in Palaeozoic.

Assessment of Chemical Properties of Soils Derived from Basement Complex Rocks of the Jos Plateau

Information on the chemical characteristics of soils is required in the sustainable the management of soil fertility and productivity. The objective of this study was to determine chemical characteristics of basement complex derived soils of the Jos Plateau. Soil study followed the approach in the Soil Survey manual and began by identification of three geologic units: granite gneiss, biotite granite and migmatite. Furthermore, eighteen soil profile pits were dug in each geologic units and eighty-four samples were taken from genetic horizons. Standard laboratory procedures were used to analyze soil samples for pH, organic matter, nitrogen and phosphorus. Results showed that organic matter contents in the soils were generally low and seemed to influence the distribution of nitrogen in the soils. Consequently, contents of total nitrogen were low. Mean contents of pH in the A horizon were 5.15, 4.64 and 5.58 respectively for soils derived from granite gneiss, biotite granite and migmatite. Low pH levels are linked to the basic cations draining out of the profile and the acidic character of the basement complex rocks from which the soils were formed. Soil reaction in most cases indicated that soils had a net negative charge. Available P contents in the magmatic soils was significantly higher than those of other geologic units. Effects of granite gneiss, biotite granite and migmatite parent materials on variation in soil chemical properties were more noticeable for soil reaction and available P contents.

Evaluation of Physical Characteristics of Soils Derived from Basement Complex Rocks of the Jos Plateau

The physical characteristics of soils to a large extent influences soil productivity. The objective of this study therefore is to evaluate the physical characteristics of soils derived from basement complex rocks of the Jos Plateau. According to the methodology outlined in the Soil Survey manual, the stratification of the study region into three geologic units—granite gneiss, biotite granite, and migmatite—was the first step in the soil research process. Additionally, soil samples were collected from genetic strata and soil profile pits were dug in each of these geologic units. Following standard procedure soils were analyzed for color, particles size distribution, structure, and bulk density. Results indicated that physical soil characteristics over the geologic units studied were in most cases similar. However significant differences were observed in particle size distribution in the A-horizons. Clay content in the A horizon of these soils generally ranged from a minimum of 8% to a maximum of 28%. Clay content in the A-horizons of the magmatic soils were significantly higher (P<0.05) than soils over granite gneiss but statistically similar (P>0.05) to those of biotite granite. Particle size distribution data indicate that the soils have undergone intensive weathering. Soil structures were on the average moderately developed in the soils studied with angular and sub-angular blocky structures. Although there was evidence of soil compaction to suggest plant root development could be affected or inhibited in these soils. .

나주읍성 동점문 성벽부재에 대한 암석학적 연구 및 산지 추정

This study is based on the mentorship course in CNU Science Education Institute For the Gifted. The Naju Eupseong Dongjeommun Gate, which was built in the Goryeo Dynasty, was restored in 2002, but a heterogeneous stone material that showed a significant difference from the original stone of the fortress wall, was used as the restoration stone. This study aims to clarify the difference between raw stones and restored stones by the investigation of the petrological features of the stone materials for the Naju Eupseong Dongjeommun Gate, and to estimate the provenances of the raw stones through the geologic survey. In addition, replacement stones that can be used for when the Naju Eupseong Dongdaemun Gate is renovated are presented. As a result of measured magnetic susceptibility and visual observation, the stone materials of the Naju Eupseong Dongjeommun Gate consist of granodiorite, and granite gneiss. Compared to the original stone, the restored stone is judged to be a granite, which shows a clear difference in the petrographical features such as the results of visual observation and the magnetic susceptibility. As a result of the geologic survey around Naju Eupseong Walled Town, the area of Geumseongsan Mountain in Naju is presumed to be the source of the original stones. Granite diorite is considered appropriate as a substitute stone if the restoration of Naju Eupseong Dongjeommun Gate is carried out.

Insights into the Weathering Crust Reservoirs of Granitoids: A Case Study from Qinghai Oilfield of Qaidam Basin, Northwest China

With proven reserves of 9.836 × 1010 m3, the largest known natural gas reservoir among terrigenous basement rocks has been discovered within the granitoids of the northern Qaidam Basin. Due to their high heterogeneity, the genesis of basement reservoirs remains unknown. Herein, the structure of the weathering crust in granitoids and their potential controlling factors on the reservoir development mechanism are discussed using a multidisciplinary approach based on data from cores, thin sections, scanning electron microscopy (SEM), conventional and imaging logs, and physical property and major elements analyses. Moreover, the classification standard of the weathering crust structure is established. The dissolution belt holding diverse reservoir spaces accounts for more than 50% of the total porosity, while the disintegration belt is the main context for the development of cleavage fractures and crack fractures. The original pores exist mainly among the crystal grains of quartz and mica, while the secondary pores and fractures were generated by the alteration of aluminosilicate minerals as well as biotite or hornblende. The quality of these reservoirs is controlled by their mineral composition, tectonic uplift, faulting, and paleogeomorphology. The femic granitoid is the main reservoir-forming lithology in the case of dissolution, while the felsic granitoid is more likely to develop cracks. The formation of the disintegration belt is significantly linked to the presence of faulting. These belts were mostly induced by tectonic deformation along the Altyn fault belt from the late Oligocene to the early Miocene. The diversity in paleogeomorphology influences the extent of the weathering. The exhumation in the Altyn terrane from the late Jurassic to the Cenozoic corresponds to the weathering and hypergene leaching period of the weathering crust within granitoids. Three types of reservoirs are present in the rocks: fractured-porous (Type Ⅰ); porous (Type Ⅱ); and fractured (Type Ⅲ). The fractured-porous and fractured reservoirs were developed mainly in the granitic gneiss and granite, while the porous reservoir was formed in granitic diorite and granitic gneiss. The reservoirs that developed in the weathering crust of granitoids are dominated by Type Ⅰ and Type Ⅱ. The highest quality reservoir, which is the fractured-porous type, developed mainly in the dissolution belt of the weathering crust, and has a porosity ranging from 1.56% to 8.48% and a permeability ranging from 0.03 mD to 14.48 mD. The mechanisms of the development of weathering crust reservoirs provide further information for the hydrocarbon exploration of basement rocks worldwide.

Geochronological constraints for a two-stage history of the Sveconorwegian rare-element pegmatite province formation

Most pegmatites of southern Norway seem to be derived from anatectic melting of metamorphic rocks during the Sveconorwegian orogeny rather than to be highly evolved residual melts derived from granites. We test this hypothesis by providing new age data for thirteen pegmatites and one granite. Based on these new age data, we distinguish two age groups of Sveconorwegian pegmatites (>1,000 m3 in size); Group 1: 1100–1030 Ma and Group 2: 930–890 Ma. All pegmatites except those from the Østfold area crystallized significantly earlier or later than adjacent granites. The Tørdal granite, yielding an age of 946 ± 4 Ma, is about 40 Ma older than the adjacent pegmatites. Field evidence and the age difference between pegmatites and granites supports an anatectic origin for these pegmatites. Sources of these pegmatite melts are biotite- and biotite-amphibole gneisses and amphibolites. Group 1 pegmatites formed in transpressional regimes after peak metamorphism, whereas Group 2 pegmatites formed in an extensional regime and the required heat for partial melting was provided by mafic magma underplating.Differences in the rheological behavior of amphibolite and granitic gneiss during extensional tectonics are the major reason why Group 2 pegmatites occur preferentially in large amphibolite bodies. Under mid-crustal conditions, amphibolite reacts brittle to semi-brittle forming open structures in an extensional tectonic regime where partial melts drained into. Granitic gneisses react in a ductile manner and do not have the ability to drain partial melt.Pegmatite formation in the Grenville Province, i.e., the Laurentian part of the Grenville–Sveconorwegian orogenic belt, formed between ca. 1090 and 980 Ma peaking at 1010 to 980 Ma. Thus, the Grenville peak postdates the Sveconorwegian Group 1 peak by about 30 Ma. These pegmatites formed in similar orogenic settings, implying that similar tectono-metamorphic developments along the Grenville–Sveconorwegian orogenic belt were diachronous.We conclude that local anatexis is the major pegmatite-melt forming process in the Sveconorwegian as well as Grenville orogen. Local anatexis also may be important in other pegmatite provinces.

Interpretation of Archaeogeological and Lithological Characters for Stones Used in Korean Ancient Tombs around the Songpa of Seoul

This study concerns the lithologic characteristics of the stone used as the main construction materials of ancient Korean tombs, and aims to understand how they were supplied. Specifically, we investigated the main ancient tombs in the Songpa district, south of the Hangang River in Seoul, composing the connected stone-mound tombs in the Seokchon-dong tomb complex, Bangi-dong tomb No. 3, and 13 horizontal stone-chamber tombs in the Gamil-dong tomb complex. There are major differences among the tombs reflected in the types of rock used as construction materials in these sites. Tombs at Seokchon-dong and Bangi-dong were built mainly using biotite gneiss, whereas those at Gamil-dong are composed of amphibole schist. By comparing the characteristics of the rocks collected from the provenance sites, we concluded that the quartzite used at the Gamil-dong tombs was from Cheonma Mountain, the gneiss at the Bangi-dong sites was from Daemo Mountain, and the amphibole schist and diabase at the Gamil-dong sites were from Cheonma Mountain. On the other hand, gravel-shaped stone materials are found in the tombs of Seokchon-dong and Bangi-dong, but not in Gamil-dong tombs. Therefore, it can be seen that between Seokchon-dong, Bangi-dong, and Gamil-dong tombs, there is a difference not only in the main constituent rock types, but also in the shape of the stone materials. These gravel-shaped stones are assumed to have been transported via the Hangang River drainage system and supplied to Seokchon-dong and Bangi-dong tombs. Therefore, we consider that the constructors of the tombs in the ancient Songpa district locally sourced materials of different rock types.

Latest Cambrian stage of evolution of Precambrian continental crust in the Aktyuz high-pressure Complex (Chu-Kendyktas terrane; North Tien Shan): New evidence from the SW part of the Central Asian Orogenic Belt

Metamorphic crustal formations of the Aktyuz block (SE part of the Chu-Kendyktas terrane; SW segment of the Central Asian Orogenic Belt) include garnet-bearing orthogneisses and gneissic granites of the Aktyuz Complex, garnet-bearing ortho- and paragneisses of the Kemin Complex and paragneisses with schists of the Kokdzhon Complex. The gneisses of the Aktyuz and Kemin Complexes associated with intensively altered eclogites, are referred to the retrogressed felsic granulites, which likely experienced high-pressure re-equilibration and dehydration melting under eclogite facies conditions. The eclogite-bearing garnet-mica gneisses of the Aktyuz Complex contain zircons with magmatic cores, overgrown by the rims with the low Th/U ratios of 0.005–0.05. The obtained age clusters of ca. 844 Ma and ca. 490 Ma likely characterize two stages of the rocks’ evolution in the late Neoproterozoic (emplacement of the gneisses’ protoliths) and in the latest Cambrian (high-pressure metamorphism of the gneisses’ protoliths). The garnet-epidote gneissic granites of the Aktyuz Complex and garnet-bearing chloritized orthogneisses of the Kemin Complex yielded late Neoproterozoic (Tonian) protoliths’ crystallization ages of 820–805 Ma, but these rocks do not show any evidence of the later re-equilibration and apparently avoided high-pressure metamorphism. Thus, the protoliths of the late Neoproterozoic orthogneisses represented by anorogenic granitoids, comprised Precambrian basement of the Aktyuz block in the Chu-Kendyktas terrane, and some part of the felsic rocks was involved into Early Palaeozoic subduction processes. Detrital zircons from the metasedimentary formations of the Kokdzhon and Kemin Complexes of the Aktyuz block display the main age peaks at 600, 800, 1000 Ma and weaker peaks at ∼1.5 and 2.5 Ga. The protoliths of the rocks were terrigenous lithologies, which are believed to have been formed after eroded felsic complexes of mostly Ediacaran, late Neoproterozoic, Mesoproterozoic and Palaeoproterozoic-to-Neoarchean ages, and accumulated during the Cambrian. The rocks likely made up sedimentary cover of the Chu-Kendyktas terrane and constituted the sand-siltstone-shale series. The presence of varisized rims of 495–471 Ma in the detrital zircons of the metasedimentary formations of the Kokdzhon and Kemin Complexes is consistent with the near-peak-to-retrograde stages of the latest Cambrian-Middle Ordovician metamorphic evolution of the rocks. The age estimates obtained for the crustal complexes of the Aktyuz block correlate well with those of the similar complexes known from the adjacent Issyk-Kul (North Tien Shan) terrane (Makbal Complex) and Zheltau terrane (Southern Kazakhstan; Koyandy Complex) in the SW part of the Central Asian Orogenic Belt.

Petrography and Geochemical Studies of Basement Rocks around Zango-Daji and Its Environs, North Central Nigeria

The geology of the Zango-Daji area was investigated petrographically and geochemically to determine the study area’s rock types and mineralization potential. The study area is underlain by rocks of the basement complex characterized by hilly and undulating rocks, which include granitic gneiss, migmatite gneiss, biotite hornblende granite gneiss, and pegmatites. Observation from the field shows that the study area is dominantly underlain by granitic gneiss. The granitic gneiss is dark grey, medium-coarse-grained, and characterized by weak foliation defined by the alignment of a streak of light and dark coloured minerals. They are widespread in the area constituting about 70% of rock types found in the study area. The average modal percentage of minerals in the rocks from petrographic studies shows that granitic gneiss had quartz 45%, plagioclase 10%, microcline 20%, hornblende 2%, biotite 10%, muscovite 5%, kyanite 8% and other minerals 5%. Also, the pegmatite of the study area has no evidence of mineralization; it contains minerals like quartz, feldspars (microcline and orthoclase), and micas (mostly muscovite). Geochemical analysis of the granitic gneiss of the study area shows that silica is by far the most abundant with a value of 53.5%, Na2 O value of 32.5%, Al2 O3, and k2 O of 6.1% and 4.0%, respectively. CaO value of 2.630% accounts for plagioclase feldspar in the granitic gneiss. The QAP diagram was used to determine the petrogenesis of the granitic gneiss. The plot shows the parent rock was a monzogranite with a low percentage of plagioclase in a thin section with a high percentage of quartz and alkali feldspar. The pegmatites of the study area are barren, as confirmed by the XRD result.

Structurally controlled mineralization in parts of Aravalli craton, India: Constraints from gravity and magnetic data

Aravalli craton of central Rajasthan comprises Mangalwar Complex and Sandmata Complex with Archean to Proterozoic basement, well known for the mineralization. Recent geological studies have also revealed that the Aravalli mountains of the Banded Gneiss Complex are composed of Paleoproterozoic granulite and amphibolite-facies. Extensive geophysical surveys comprising gravity and magnetic were conducted to assess the occurrence of potential mineral sources in the uplifted crustal blocks of the Aravalli Fold belt. The calculated Bouguer gravity anomalies trending in a NE-SW direction and three broad gravity highs (∼7–10 mGal) were observed. These gravity highs may be due to the uplifting of the basement or the presence of high-density contrast material near the subsurface. A gradient in the gravity contours at the northwestern part of the study area is due to the fault/structural contact trending along the NE-SW direction. The 2D inversion technique is used to model the gravity data perpendicular to fault/contact. The horizontal gradient reflects the distribution of structures and intrusive bodies, which will give new insight for further future mineral exploration. The spectral analysis depicts the three depth interfaces, ∼7, ∼3.1, and ∼1.1 km, representing the basement and shallow depth interfaces. Further, the subsurface ore bodies geometry was obtained through 2D modelling of gravity data incorporating the constraints from the rock sample's physical property (density). We established that the structure and lithology of the host rocks were responsible for controlling mineralization by integrating the geochemical findings with geophysical measurements. In addition, the Archean to the Proterozoic basement of the study area is undulating at a depth of ∼3–5 km.

Multiple Palaeozoic–Mesozoic orogenic events in the SE Yangtze Block, China: evidence from the petrogenesis and deformation of gneissic granites from the Nanwenhe metamorphic dome and regional correlation analysis

ABSTRACT The Nanwenhe metamorphic dome contains a rare Silurian granitic pluton that developed in the SE Yangtze Block during early Palaeozoic orogenesis, and this pluton comprises the Nanwenhe gneissic granites. The petrogenetic and structural deformation histories of the gneissic granites recorded the multi-stage interaction of the SE Yangtze Block with other blocks during the Palaeozoic and Mesozoic, including the Cathaysia, Indochina, and Paleo-Pacific blocks. Zircon U–Pb and Hf isotopes and geochemical data indicate that the Early Palaeozoic granites (433–420 Ma) are S-type granitic rocks, and they were derived from the partial melting of ancient continental crust with no contribution from mantle material. And the large variations and positive values of εHf(t) (−12.25 to +10.69) of the gneissic granites are ascribed to a heterogeneous source and disequilibrium melting. Here we compare early Palaeozoic granitoids in the SE Yangtze Block (foreland belt) with those in the orogenic core, and suggest that the SE Yangtze Block underwent limited syn-collisional crustal thickening and metamorphism, and following which post-collisional granitoids were formed through partial melting of continental crust. Structural analysis of the Nanwenhe gneissic granites allows two stages of deformation to be identified: northward detachment (D1) and northwestward thrusting (D2). 40Ar–39Ar isotope dating of muscovites from the gneissic granites yields a well-defined plateau age of 229.61 Ma, which is interpreted as the timing of Late Triassic structural overprinting associated with the formation of the Nanwenhe metamorphic dome. Integration of our new results with previous research findings from the dome and South China allows us to conclude that the detachment deformation (D1) represents Late Triassic post-collisional extension, and D2 represented Jurassic intracontinental orogeny associated with subduction of the Paleo-Pacific Block.

Pre-Himalayan crustal growth in the Indian plate: Implications from U-Pb dating, geochemical and Sr-Nd isotopic systematics

This study presents detailed petrography, bulk rock geochemistry, U-Pb dating, and Sr-Nd isotopes of pre-Himalayan granite gneisses and granites exposed in the Neelum Valley, NW Pakistan. To understand pre-Himalayan crustal growth history in the Indian plate, basement granitoids provide useful constraints. Two granites (the Jura and Neelum granites) and two granitic gneisses (the Nauseri and Jura gneisses) were investigated with the goal of their petrogenesis and constraining their geotectonic settings. Petrographically both granites and gneisses contain plagioclase, K-feldspar, quartz with S-type granite paragenesis of muscovite, garnet and tourmaline. Geochemically granites and gneisses are characterized by strongly peraluminous (A/NK > 1.1) character with a distinct mafic metapelitic sources. Notable negative Ta, Nb, and Ti compared to La and K, and a pronounced positive Pb anomalies in the studied rocks indicate convergence related source with a similar rare earth element pattern of upper continental crust. Two U-Pb zircon age populations, ca. 2429 ± 17 Ma and 1844 ± 11 Ma were obtained from the Nauseri gneiss whereas Jura gneiss yielded 865 ± 5.6 Ma. In contrast, Neelum and Jura granites yielded ages of 736 ± 11 Ma and 459.1 ± 3.5 Ma, respectively. Sr-Nd isotopic composition ((87Sr/86Sr)i = 0.7099 to 0.7303; εNd(t) = -8.1 to −3.6) together with the major and trace element geochemistry indicate that parental magmas of granites and gneisses were derived from the partial melting of upper continental crust during syn-collision tectonic settings. The Sr-Nd isotopes coupled with two-stage model ages further suggest incorporation of Archean and Paleoproterozoic reworked continental material that contained some mafic metapelitic component as well. Tectonically the parental magma of gneisses and granites could be linked with the global-scale orogenic events that operated during the assembly and rifting of the supercontinents of Columbia to Pangaea. Protoliths of Nauseri gneiss was possibly formed during the assemblage of Columbia supercontinent (1.8 Ga). Later, the Pan-African Orogeny provided additional pulse of magmatism that resulted Jura gneiss and Neelum granite. Moreover, the Bhimphedian orogeny in the Indian plate during Ordovician times generated the Jura granite of ca. 460 Ma.

Mapping Groundwater Potential Zones Using Remote Sensing and GIS Techniques in Sainj River Sub-Watershed, Kullu, Himachal Pradesh

Ensuring availability of drinking and irrigation water for population living in mountainous environment has been an important challenge for researchers, spatial planners and policy makers. The identification and mapping of groundwater potential zones in such type of regions may prove a better input to meet this challenge. The present study is an attempt to find out the groundwater potential zones using state-of-the-art technologies of Remote Sensing (RS) and Geographic Information System (GIS) selecting a case study area of Sainj river sub-watershed (area 81 km 2 ) in Kullu of Himachal Pradesh, India. Landsat-8 (OLI) satellite data (October 2016, spatial resolution (30 m resolution) Survey of India (SOI) Toposheet (Scale 1:50,000) and GIS software ArcGIS version 10.5 were used to prepare various thematic layers such as Geology, Soil, Geomorphology, Land Use Land Cover (LULC), Slope, Lineament, and Drainage Density. The watershed delineation and contour lines (100 m interval) generation were performed using Digital Elevation Model (DEM). The LULC map was prepared through supervised classification using Support Vector Machine (SVM) method in ENVI 5.0 software. Spatial analyst tool of ArcGIS 10.5 was used to identify groundwater potential zones using weighted overlay method. The study indicates that the spatial variations in groundwater occurrence are largely controlled by geological structures, landforms and slope in the study area. The study also reveals the importance and usefulness of RS and GIS techniques for proper groundwater resource appraisal and mapping groundwater potential zones. The five groundwater potential zones were identified and mapped in the study area viz. very poor (1.1 km2, 1.36%), poor (7.3 km 2 ,9.03%), moderate to good (67.2 km 2 ,83.17%), good (4 km2,4.95%) and very good (1.2 km2,1.49%). The weathered / fractured quartzite, limestone, slate, schist, and phyllite, among other minerals, characterize the zone with very good groundwater potential. While, the granite, car-biotite, met basalt, and granite gneiss are commonly found in the zone, which has a moderate to good (medium) groundwater potential. Low groundwater zone locations are generally underlain by granitoid, gneisses, and migmatite.