Granite Series Research Articles

The Characteristics and Enrichment Process of Dabu Ion-Adsorption Heavy Rare-Earth Element (HREE) Deposits in Jiangxi Province, South China

Ion-adsorption rare-earth deposits supply over 90% of the global market’s heavy rare-earth elements (HREEs). The genesis of these deposits, particularly HREE deposits, has garnered significant attention. To elucidate the metallogenic mechanisms of HREE deposits, a comprehensive study of the weathering profile of granite was conducted in Jiangxi Province, South China. This study focuses on the following two aspects: the petrogeochemistry of HREE-rich granite and the enrichment and fractionation of rare-earth elements (REEs) during the weathering process. The results suggest that the Dabu granites are a typical peraluminous, high-K, calc-alkaline granite series with high silica content (SiO2: 74.5%–76.4%), relatively low phosphorus content (P2O5: <0.05%), and high HREE content (ΣLREE/ΣHREE: 0.16–0.66). Weathering advances the decomposition of minerals and the release of elements. REEs are mainly fixed in the regolith by scavengers, mainly clays, Fe–Mn oxides, and carbonates, and ΣREE can reach 799 ppm in the B horizon. However, HREEs tend to migrate further and preferentially combine with Fe–Mn oxides and carbonates as compared to LREEs, leading to a significant fractionation of REEs in the regolith (ΣLREE/ΣHREE = 0.2–1.1). Additionally, the differential weathering of REE-bearing minerals and the precipitation of secondary REE-bearing minerals are also vital for REE fractionation.

Geochemical and isotopic evidence for early neoproterozoic (ca. 1000 Ma) subduction-related magmatism in the central Borborema Province, Brazil

Early Neoproterozoic (1000-920 Ma) rocks related to the Cariris Velhos event in the central Borborema Province have been linked to either continental rifting or accretionary-collisional orogenesis. The Serra do Jatobá Suite is located in the southwestern part of the Alto Pajeú Terrane along with coeval metasedimentary sequences and Ediacaran granites. This suite is composed of alkali-calcic, meta-to peraluminous granodiorites to monzogranites that share similarities with both ferroan- and magnesian granite series. Chondrite normalized REE (Rare Earth Elements) patterns are moderately fractionated with pronounced negative Eu anomalies. Incompatible element spidergrams show a negative Nb–Ta anomaly, similar to those observed in Cordilleran-type granites. U–Pb zircon data constrain the crystallization ages at around 1000 Ma, whereas calculated εNd(t) values range between −1.74 and −0.94. Obtained TDM model ages range from 1.76 to 1.54 Ga, which corresponds with source ages for the Cariris Velhos magmatic rocks. Our findings suggest that subduction took place in the early Neoproterozoic in the Borborema Province, pointing to an accretionary nature for the Cariris Velhos event.

Influence of magmatic and magmatic-hydrothermal processes on the lithium endowment of micas in the Cornubian Batholith (SW England)

The Cornubian Batholith (SW England) is an archetypal Variscan rare metal granite with potential for Li-mica mineralization. We present a petrographic, trace element and multivariate statistical study of micas from the Cornubian Batholith granite series and related hydrothermally altered units to assess the role of magmatic vs subsolidus processes and of fluxing elements (F and B) on the Li cycle during the evolution of the system. The mica types are as follows: (1) magmatic, which include Fe-biotite, protolithionite I and phengite-muscovite from the most primitive granites, and zinnwaldite I from more fractionated lithologies; (2) subsolidus, which encompass high-temperature autometasomatic Li-micas and low-temperature hydrothermal muscovite-phengite. Autometasomatic species include protolithionite II, zinnwaldite II and lepidolite, which were observed in the most fractionated and hydrothermally altered units, and occur as replacements of magmatic micas. Low-temperature hydrothermal Li-poor micas formed via alteration of magmatic and autometasomatic micas or as replacement of feldspars, and albeit occur in all studied lithologies they are best represented by the granite facies enriched in metasomatic tourmaline. The evolution of micas follows two major trends underlining a coupling and decoupling between the Li(F) and B fluxes. These include as follows: (1) a Li(F)-progressive trend explaining the formation of protolithionite I and zinnwaldite I, which fractionate Li along with Cs, Nb and Sn during the late-magmatic stages of crystallization, and of zinnwaldite II and lepidolite forming from the re-equilibration of primary micas with high-temperature Li-B-W-Tl-Cs-Mn-W-rich autometasomatic fluids; (2) a Li(F)-retrogressive trend explaining the low-temperature hydrothermal muscovitization, which represents the main Li depletion process. Trace element geochemistry and paragenesis of late muscovite-phengite support that muscovitization is a district-scale process that affected the upper parts of the granite cupolas through acidic and B(Fe-Sn)-saturated hydrothermal fluids associated with metasomatic tourmalinization, which were mixed with a low Eh meteoric component.

Geodynamics and nature of the basement of the northern Lhasa Terrane: Insights from Early Cretaceous highly fractionated I-type granites in the Beila and Dongga areas, central Tibetan Plateau

Collisional orogenic belts serve as excellent places for investigating geodynamic process and growth mechanism of the continental crust. As one of the largest collisional orogenic belts worldwide, the Tibetan Plateau is formed by the amalgamation of multiple tectonic terranes. However, the nature and composition of the crustal basement beneath the northern Lhasa Terrane, located in central Tibetan Plateau, is still a matter of debate. Here, we investigated a series of Early Cretaceous granites in the Beila and Dongga areas, northern Lhasa Terrane. Zircon U-Pb dating reveals that the Beila and Dongga granites were emplaced at ca. 118 Ma and 110 Ma, respectively. These granites are characterized by high SiO2 and K2O, low TiO2 and P2O5 contents and low Mg#. They exhibit enrichment in light rare earth elements, significant negative Eu anomalies, and depletion in Ba and Sr. These geochemical features suggest that they belong to highly fractionated I-type granites. Both the Beila and Dongga granites display similar and enriched whole-rock Sr-Nd and zircon Hf isotope compositions, implying a likely common ancient crustal origin. Given the temporal sequences and redox conditions during their formation, it is highly probable that the Beila and Dongga granites formed during the syn-collision stage between the Lhasa and Qiangtang Terranes and the breakoff of the Bangong-Nujiang oceanic slab, respectively. Integrated with coeval magmatism in the central Tibetan Plateau, our new data reveal the presence of a regionally preserved ancient basement beneath the northern Lhasa Terrane, analogous to the equivalent basement beneath the central Lhasa Terrane.

Petrogenesis and Tectonic Implications of the Qulihai Pluton in the Northern Margin of the Yili Block, NW China

Abstract Despite extensive research work that has been done, whether the northern margin of the Yili Block (YB) is still an active continental margin during the early Carboniferous period is still in debate. Herein, we conducted zircon U–Pb geochronology, geochemistry, and zircon Lu–Hf isotope studies on the Qulihai pluton in the northern margin of the YB to constrain the petrogenesis and dynamic process. The Qulihai pluton is a granitoid complex that is composed of quartz diorite, quartz monzonite, and syenogranite. The zircon U–Pb dating results revealed that the pluton was formed and emplaced between 346 and 342 Ma. The three different Qulihai pluton rock types had comparable εHf(t) values, ranging from +3 to +8. The corresponding two-stage model ages of 817–1182 Ma indicated their potential derivation from the Meso-Neoproterozoic juvenile crust. The Qulihai pluton typically features medium-to-high SiO2, K2O, and Al2O3 contents and low MgO and Fe2O3T contents. The quartz diorite and quartz monzonite samples had Mg# values of 43–47, indicating the input of mantle-derived melts in the source area. In contrast, the source region of syenogranite was purely crustal material. The Qulihai pluton is mainly characterized as strong metaluminous moderate-to-high-K cal-alkaline rocks of the I-type granite series, which are enriched in large-ion lithophile elements and depleted in high field strength elements while exhibiting active continental margin island arc magmatism. Our findings, combined with the comprehensive analysis of previous studies, suggest that the Qulihai pluton formation resulted from the subduction of the North Tianshan oceanic crust beneath the YB during the early Carboniferous period, contemporary with the tectonic regime transition from subduction advance to subduction retreat.

Ordovician−Early Devonian granitic magmatism as the consequence of intracontinental orogenic activity along the Qinhang belt in South China

The early Paleozoic tectono-magmatic activity within the South China block, which is well illustrated by Ordovician−Devonian granites in the western Qinhang belt, was the response to closure of the Proto-Tethys Ocean and convergence of continental blocks. The spatiotemporal distribution and source characteristics of the granites provide us the opportunity to understand the processes and driving mechanisms of intracontinental orogeny. As an example, the Miaoershan-Yuechengling granite batholith in northern Guangxi, located along the western margin of the Qinhang orogenic belt, is mainly composed of quartz monzonite and monzogranite. All the granitic rocks from Miaoershan-Yuechengling batholith are composed of K-feldspar, quartz, plagioclase, biotite, and hornblende. Geochronologic dating indicates that the Miaoershan-Yuechengling batholith was emplaced during the late Silurian and Early Devonian, respectively. The rocks have high SiO2, with an average value of 73.29 wt%, and total alkalis (Na2O + K2O = 7.21−10.03 wt%), but low Al2O3 (12.96−15.51 wt%), showing characteristics of the high-potassium calc-alkaline series of S-type peraluminous granites (Al2O3/[CaO + Na2O + K2O] = 1.03−1.22). Trace elements in the Miaoershan-Yuechengling granitic rocks are characterized by enrichment of large ion lithophile elements and depletion of high field strength elements. Their rare earth element (REE) trends are characterized by relatively flat distribution patterns with weak light REE enrichment, weak heavy REE fractionation, and negative Eu anomalies. Zircons from the rocks have negative εHf(t) values ranging from −13.24 to −5.1, with crustal model ages (THf2) of 2.2−1.7 Ga. These features indicate that they are S-type granites with parental magmas originating from partial melting of sandy argillaceous sources of Paleoproterozoic lower continental crust. The thermal budget for Ordovician to Early Devonian magmatism is attributed either to crustal thickening in relation to intracontinental orogenic compression or to crustal thinning due to postorogenic tectonic extension during assembly and breakup of Greater Gondwana. This study reveals that the change in mantle convection systems during plate interactions acted as a major driving force for the early orogenic processes, late collapse of the orogenic belt, and massive syncollisional to postorogenic magmatism.

Geochronological and geochemical study of the Late Carboniferous volcanic drilling cores from the Piedmont of the Hala'alate Mountain in West Junggar: Implications for stratigraphic division and tectonic evolution

The West Junggar tectono-magmatic processes are critical for reconstructing the amalgamation history of the Central Asian Orogenic Belt (CAOB). However, the lack of consensus regarding the geochronology, petrogenesis, and tectonic setting of the complex igneous rocks poses a challenge to comprehending the Late Paleozoic tectonic evolution of West Junggar. This study focuses on systematic geochronological and geochemical research of well-preserved drill cores from the Piedmont of the Hala'alate Mountain, including rhyolite, felsic tuff, basalt, and andesite. The ages of these rocks in Late Carboniferous (310–301 Ma) are constrained by zircon UPb dating, excluding them from the Jiamuhe Formation of the Early Permian. The rhyolites and felsic tuffs exhibit apparent affinity to the A-type granite series, characterized by high total alkali and FeOT/MgO values. Plagioclase controls the main residual facies and depleted isotopic compositions (εHf(t) = +10.2 to +13.4; εNd(t) = +7.6 to +8.1), indicating that the magma source originated from the partial melting of juvenile continental materials in an extensional background. The basalts and andesites display high LILEs/LREEs, LILEs/HFSEs ratios, along with low HFSEs, which correspond to arc-affinity geochemical compositions. The high zircon εHf(t) (+7.5 to +14.3) and whole-rock εNd(t) (+7.8 to +7.9) values indicate a depleted pyroxene-rich mantle source modified by metasomatic slab-derived fluids. This implies a large-scale upwelling of mantle materials driven by the overlying lithospheric crustal thinning. Combining the temporal variations of crustal thickness recorded by the Sr/Y and (La/Yb)N ratios in igneous rocks, the tectonic processes of West Junggar during the Carboniferous to Early Permian can be divided into three stages. The first stage involves sustained subduction processes from 350 Ma to 320 Ma, followed by the closure of the oceanic crust and collision orogenesis from 320 Ma to 310 Ma. Finally, and a post-collision extension setting occurred after 310 Ma.

Petrogenesis of Eagle Lake Granite and Its Associated Cu–Mo–Au Mineralization, Southwestern New Brunswick, Canada

The NE-trending multiphase Late Devonian Eagle Lake granite (ELG) in southwestern New Brunswick is mineralized, consisting of hypabyssal porphyritic stocks and dikes that intruded Silurian metabasic volcanic rocks; however, its various phases, ages, and associations with notable stockwork Cu–Mo–Au mineralization and alteration have yet to have been studied. The ELG suite is predominantly composed of phenocrysts and a microcrystalline groundmass of quartz, K-feldspar, and plagioclase, with minor biotite and accessory minerals. In situ LA ICP-MS U–Pb zircon dating of this pluton yielded 360 ± 5 Ma (Late Devonian), so this pluton is considered part of the Late Devonian granitic series in southwestern New Brunswick. The isotopic analysis of two granitic samples yielded an initial 143Nd/144Nd of 0.512164 and 0.512184, initial 87Sr/86Sr of 0.70168 and 0. 70675, and initial 176Hf/177Hf of 0.282619 and 0.282631. The εNd (360 Ma) is −0.37 to +0.03, whereas the εHf (360 Ma) values are +2.1 and +2.5. Pb isotopic analysis yielded a 206Pb/204Pb of 18.49 and 18.72, 207Pb/204Pb of 15.62 and 15.63, and 208Pb/204Pb of 38.26 and 38.37, indicative of a relatively radiogenic source contaminating a primitive mantle melt. Potassic alteration and pyrite-quartz stockwork Cu–Mo–Au veining is evident in some parts of these porphyries. Petrographic and geochemical evidence indicates that this composite pluton is a low-T, I-type granite with zircon saturation temperatures between 720° and 825 °C, with emplacement depths of 10.3 to 4.4 km. ELG was emplaced along a major structural trend manifested by contemporaneous faults and shear zones, i.e., the Belleisle Fault Zone in southern New Brunswick.

Magnetovariational Sounding in South Vietnam according to the Dalat Observatory Data

Abstract —This paper describes a three-dimensional inversion of magnetovariational tippers calculated for the Dalat observatory in South Vietnam on the basis of the geomagnetic variation records obtained from the INTERMAGNET network. The frequency dependences of the tippers are inverted using the ModEM software, which makes it possible to construct a geoelectric model of the Dalat zone in a 300 × 300 × 150-km spatial region (x, y, and z axes, respectively) with its center located at the observatory. The resulting model of the geoelectric section contains both surface and deep conductive blocks located at the top and bottom of the Earth’s crust and in the upper mantle. The central part of the upper local conducting block with a resistivity of 0.5–1.0 Ohm⋅m is located near the observatory at a depth of 12–14 km. A more massive conductive block is located to the east of the observatory in the coastal region. Its central part with a resistivity of 0.3 Ohm⋅m is located at a depth of 24–28 km and extends under the continent along the coast for about 80 km. The roots of this block are visible to depths of ~100 km in the South China Sea shelf region. It is assumed that the high electrical conductivity of these blocks is provided by melting in the presence of aqueous fluids and granite series rocks, which are widely distributed in the Dalat zone. The crystallization depths of the samples of these granites estimated from the geothermobarometry data are close to the depth intervals of conductive blocks in the model section, which was also observed in the interpretation of magnetotelluric soundings in Southern Tibet, where granitoid rocks are widespread.

A new triradial species from the Neoproterozoic formations of the Chenachene region, north-east of the Taoudeni basin (south-western Algeria)

Precambrian life remains enigmatic, the traces of life of this period discovered throughout the world, have been interpreted differently; the observations made in the Chenachene region will deepen the knowledge and enrich the debate on these fascinating organisms.The Chenachene area represents the north-eastern margin of the Taoudeni Basin, where the Reguibat Shield outcrops with Pleoproterozoic metamorphic, metasedimentary and granitic series, constituting the Eburnian basement of the Eglab, surmounted in major discontinuity by a Meso-Neoproterozoic and Paleozoic sedimentary cover little or no deformed. A trace fossil was collected in a coredrill from the Chenachene region, in the Cheikhia-Bir Amrane Group, with an absolute age obtained by Rb/Sr ranging from 775 to 650 Ma corresponding to the Cryogenian.The diagnosis of the collected specimen allows us to recognize similarities with the genus Rugoconites described by Glaessner and Wade in 1966 from Flinders Ranges, South Australia, with notable differences from the two species already described (R. enigmaticus and R. tenuirugosus), which allows us to present it as a new species: Rugoconites reguibatensis.The exceptional state of preservation of Rugoconites reguibatensis has permitted to characterize it and reconstitute it, presenting great morphological similarities with present-day jellyfish, this revive, once again, the debate on the Precambrian life and the disappearance of this fauna at the end of the Proterozoic.

Magnetic susceptibility, mineral chemistry, and geothermobarometry of granitoids from Lohit Plutonic Complex, Arunachal Trans‐Himalaya, Northeast India: Implications on emplacement and crystallization conditions of oxidized calc alkaline magmatic arc system

AbstractThe Lohit Plutonic Complex (LPC) of Arunachal Trans‐Himalaya represents the northeast extension of Trans‐Himalayan magmatic arc system located in the north of Indus Tsangpo Suture Zone (ITSZ). Field relation, magnetic susceptibility (MS), and phase petrology on the granitoids of LPC was conducted in order to assess the granite series (magnetite, oxidized vs. ilmenite, reduced types), and physico‐chemical conditions of the LPC granitoid magmas. The studied granitoids are well‐exposed in the Dibang and Lohit valleys, and their MS values indicate a bi‐modal patterns corresponding to ilmenite (reduced) series (71%) and magnetite (oxidized) series (29%) granites. The variation of MS in the LPC granitoids is related to the alteration of ferromagnetic minerals, and later tectonic and deformational processes that acted upon them. The amphiboles from the LPC granitoids are calcic (CaB >1.5, Si = 6.30–7.06 apfu) and exhibit tschermak substitutions typical to their evolution in a calc alkaline, metaluminous (I‐type) felsic magmas. Al‐in‐hornblende rims estimate the emplacement of quartz diorite and granodiorite magmas at shallow (~5 km) and mid (~16 km) crustal depths. Geothermometric results point to a regime of magmatic crystallization (940–837°C for quartz diorite; 882–829°C for granodiorite) sufficiently above the solidus of respective melts. Biotites from LPC granitoids are primary to re‐equilibrated, and transitional between magnesio‐ and ferri‐biotites. Quartz diorite and granodiorite biotites evolved under oxidizing magmas (log ƒO2−14 to log ƒO2−13) in a temperature range of ~750–950°C, typical to their formation in a calc alkaline magma of subduction zone environment. However, the biotites from leucogranite appear to have evolved under a mildly reducing magma environment, most likely attained in a collisional setting. The obtained results suggest that the oxidized nature of calc alkaline, subduction‐related magmatic arc rocks of the LPC is largely modified and reduced by post‐magmatic, and later tectonothermal and deformational events that operated during Himalayan and Trans‐Himalayan orogenesis.

Restoring the river, restoring relations: on Anishinaabe artist Michael Belmore’s stone series, Replenishment

In his work and creative practice, Anishinaabe artist Michael Belmore shows that materials have language and rock tells a story. Belmore’s land-based installation on Manitoulin Island, a three-part granite series titled, Replenishment, tells a story about place that is activated by relationship and reciprocity between people and with the Earth. It reinscribes Indigenous presence on the land, rewrites settler-colonial narratives about place, and broadens the scope and intent of ecological restoration. Drawing on my interactions with the artist and his work during the 2017 Manitoulin Island Summer Historical Institute, a field school on Anishinaabe history, I explore the circulation of knowledge and agency in an Anishinaabe world and consider relationship as essential to decolonizing geography’s engagement with Indigenous peoples and territories. Through rock as mnemonic device, Belmore demonstrates the restorative power of subtle and not so subtle acts of interconnection and relationship.

Petrography and Geochemistry for Proposal of Geodynamic Model For The Irbiben Granite in Tagragra d’Akka inlier, (western Anti-Atlas, Morocco)

This study aims to contribute to improve the knowledge on the setting of the Irbiben granites, located south of the gold deposit of this locality (Tagragra d'Akka buttonhole, Anti-Atlas, Morocco). The petrographic characterization showed leucocratic porphyry rocks, with a mineralogy dominated by quartz and phenocrysts of plagioclase, alkali feldspars of sometimes centimetric size as well as very small sulphides of metallic luster. Two generations of quartz have been identified: a QIquartz with undulating extinction phenocrysts testifying to an episode of deformation orchestrated in this inlier, and a QII quartz with more rounded and limpid minerals indicating an intense silicification. Plagioclase and alkali feldspars are deeply altered to sericite and epidote. Geochemical characterization classifies these rocks as calc-alkaline series granites, rich in potassium, with a peraluminous character indicating their crustal origin. Their arc geochemical signature, Ba enrichment, and negative Nb, Ti, and P anomalies are characteristic of a subduction zone. This subduction could be associated with an episode of convergence between an oceanic lithosphere located in the north and the West African craton in the south, as shown by the proposed geodynamic model.

Constraint on the temperature of A-type magma from contact metamorphic aureole, Biesituobie batholith, West Junggar in NW China, Central Asian Orogenic Belt

The Biesituobie A-type batholith in West Junggar in NW China of the Central Asian Orogenic Belt contains metapelite xenoliths derived from the contact metamorphic aureole. These xenoliths could be divided into two types: biotite-muscovite-andalusite hornfels and cordierite-alkaline feldspar-sillimanite-corundum gneiss, indicating prograde metamorphism. The phase equilibrium modeling on the cordierite-alkaline feldspar-sillimanite-corundum gneiss sample yielded a peak condition of P = 3.0−4.0 kbar, T = 760−800 °C. Similarly, the Na-in-cordierite geothermometer yielded a peak condition of T = 771−780 °C. The temperature of the peak metamorphism could be considered as a lower limit of the temperature of the Biesituobie A-type batholith. On the contrary, the Ti-in-zircon geothermometer applied to the Biesituobie A-type batholith zircons yields a mean temperature of 672 ± 22 °C. It suggested that the application of Ti-in-zircon geothermometer on A-type magma may involve a >100 °C underestimation. Zircon U-Pb dating indicates that the age of the contact metamorphism is between 263 and 286 Ma, consistent with the age of the pluton at 274 Ma. The result of 760−800 °C calculated from the contact metamorphic aureole of the Biesituobie batholith put a lower limit on considering the temperature condition of the A-type granite series from a metamorphic constraint.

Early Triassic Monzonite–Granite Series in Eastern Kazakhstan as a Reflection of Siberian Large Igneous Province Activity

We provide the results of studying the internal structure and composition of the rocks of the Semeitau and Delbegetei massifs located in Eastern Kazakhstan. It was previously believed that these massifs have different ages and were formed in different geodynamic settings. The U-Pb zircon age from the monzonites and quartz monzonites was determined to be 249 ± 2 Ma, which showed the same Early Triassic age of the massifs. Both massifs are composed of rocks of the same monzonite–granite series of rocks with a significant proportion of high-silica rocks (leucocratic granites). Intermediate rocks are formed due to the differentiation of subalkaline mafic magmas, and the felsic rocks (rhyolites and granites) are the result of partial melting of crustal substrates. The massif formation model assumes the intrusion of mafic magmas into the crust, their differentiation and mixing with crustal melts, and then the intrusion of various rocks into the upper crustal levels. Analysis of the geological position, age and composition of the rocks allows us to conclude that the Semeitau and Delbegetei massifs were formed in an intraplate geodynamic setting. The activity of the mantle plume is the most probable reason for their formation. The Semeitau and Delbegetei massifs can be included in the southern part of the range of the Early Triassic Siberian Large Igneous Province.

Granite series assessment, nature and crystallization condition of Paleoproterozoic granite gneisses from Askot and Chiplakot klippe, Kumaun Lesser Himalaya, India

Granite series assessment, nature and crystallization condition of Paleoproterozoic granite gneisses from Askot and Chiplakot klippe, Kumaun Lesser Himalaya, India

Geophysical Analysis of Thermo-physical Properties of Rocks in Ikogosi field for Geothermal Energy Prospect.

The thermal and physical properties of rock units from Ikogosi Warm Spring (IKGWS) in the Southwestern part of Nigeria were examined in order to characterize and explore its geothermal prospect and to provide an insight into the different thermal properties of rocks of the study area. A total of 40 rock samples made up of granite, quartzite and gneiss series were collected from the outcrops of the study area and analyzed for Thermal conductivity (TC), Radiogenic heat production (RHP), Heat flow (HF), Porosity, Density and surface spring temperature measurements. The RHP values for all samples varied from 1.8 to 3.5μWm-3 with an average value of 2.5μWm-3 and standard deviation (SD) of 0.4 while the heat flow values varied from 14 to 27mWm-2 with an average of 19mWm-2 and SD of 3.4. The TC values varied from 2.95 to 4.11 with a mean of 3.49mWK-1 with a SD of 0.4 while the porosity values varied from 0.21-1.15 % with a mean of 0.62% with SD of 0.39. The density values varied from 2.68 to 2.85gcm-3 with a mean of 2.76gcm-3 and SD of 0.067. The surface temperature of the spring varied from 32 to 45°C with a mean of 38.9°C. From these results the average RHP and HF values estimated from all samples was below the 4μWm-3 and 100mWm-2 recommended value of heat to be considered for economic importance. Thus, the IKGWS geothermal field cannot be explored for power generation but for other geothermal activities and may be classified as a low enthalpy geothermal system (

Petrographic evidences of open-system magmatic processes in the felsic rocks of the northern part of the Ditrău Alkaline Massif (Eastern Carpathians, Romania)

Abstract Over the almost 190 years-long research of the Ditrău Alkaline Massif (Eastern Carpathians, Romania), felsic rocks have been regarded as homogeneous, uniform units of the igneous complex. Nevertheless, our detailed textural study revealed that the felsic suite (diorite–alkaline feldspar syenite and nepheline-bearing syenite–granite series) cropping out north of the Jolotca Creek valley is more heterogenous at micro-scale than previously thought. This heterogeneity partly derives from abundant mafic mineral-rich clusters; nevertheless, felsic minerals also exhibit various, remarkable textural features. Outcrop to micro-scale traits of felsic crystal settling, mafic mineral aggregates and flow fabrics along with metamorphic country rock xenoliths suggest that the studied rocks crystallized under dynamic magmatic conditions. Cumulate formation, shear flow, convection currents as well as various open-system magmatic processes (e.g., magma recharge, magma mixing and mingling, crystal or mush transfer and recycling, country rock assimilation) played a significant role in the petrogenesis of the examined felsic suite. Based on field observations as well as on the microtextural relationship of the minerals, two major groups of felsic rocks were distinguished: (1) felsic rocks (lacking or containing sparse mafic minerals) spatially associated with mafic rocks and (2) felsic rocks (with mafic minerals and clots) spatially unassociated with mafic rocks. Rocks of the former group are dominated by plagioclase, accompanied by minor alkaline feldspar, biotite and accessory titanite. Distinct structural and textural features suggest the physical accumulation of the rock-forming phases. Such textural properties can also be observed in some rocks of the second group. Isolated mafic minerals are rather scarce in the latter; nevertheless, different types of aggregates made up of either identical or various mafic phases are more common. Clustered minerals are either intact or show different stages of alteration. A detailed petrographic study of the above-mentioned peculiarities has been implemented in order to define their potential origin(s) and petrogenetic significance.

Paleo-Mesoarchean crustal growth and reworking in the western Dharwar Craton, southwestern India: Evidence from trondhjemitic gneiss and granitic gneiss

Paleo-Mesoarchean felsic orthogneisses are widely exposed in the southern part of the western Dharwar Craton (WDC), southern India shield. The felsic orthogneisses studied in this paper from the WDC can be divided into two groups based on their geological, geochronological, and geochemical data: the 3.4–3.3 Ga trondhjemitic gneiss (including trondhjemitic veins) and the ∼3.1–3.0 Ga granitic gneiss. The 3.4–3.3 Ga trondhjemitic gneiss is characterized by high contents of SiO2 (70.4–73.1 wt%), Na2O (5.49–5.91 wt%) and Sr (647–740 ppm), high ratios of Na2O/K2O (4.7–7.7) and Sr/Y (53–106), but relatively lower Mg# values (32–39), and Cr (9.5–28.7 ppm) and Ni (1.34–5.33 ppm) concentrations, as well as insignificant Eu anomalies, fractionated REE patterns and mostly positive zircon εHf(t) values (+0.8-+5.9). These data indicate that the trondhjemitic gneiss was derived from partial melting of juvenile mafic crust in a relatively moderate-shallow depth, with residual mineral assemblage of garnet, amphibole and clinopyroxene, implying crustal growth event at 3.4–3.3 Ga. By contrast, the ∼3.1–3.0 Ga granitic gneiss is characterized by relatively lower contents of Na2O (3.82–4.63 wt%) and Sr (96.9–291 ppm), low ratios of Na2O/K2O (1.4–1.7) and Sr/Y (3.02–8.65), as well as significantly negative Eu anomalies and negative to positive zircon εHf(t) values (-5.6-+4.5). Therefore, the granitic gneiss was probably derived from partial melting of pre-existing crustal rocks, suggesting a prominent crustal reworking event at ∼3.1–3.0 Ga. This study emphasizes that the western Dharwar Craton is dominated by Paleoarchean (3.4–3.2 Ga) crustal growth event and a strong crustal reworking event in early Mesoarchean (∼3.1–3.0 Ga), though the Mesoarchean crustal growth event is discernible, evidenced by regional ∼3.0 Ga TTG rocks. The early Mesoarchean (∼3.1–3.0 Ga) crustal reworking event, represented by series of potassium-rich granites, is also reported in other Archean cratons, and thus it may have global significances.

Late Permian-Middle Triassic intermediate-acid intrusive rocks in the Eastern Kunlun Orogenic Belt, NW China: Petrogenesis and implications for geodynamic evolution

ABSTRACT Large areas of intermediate-acid intrusive rocks are widely exposed in the Eastern Kunlun Orogenic Belt (EKOB), which is an ideal place to study crustal reworking and growth and the tectonic setting and evolution of the Paleo-Tethys Ocean. Petrographic research shows that intermediate-acid intrusive rocks are mainly composed of diorite, diorite porphyry, granodiorite, and monzogranite, and their zircon U-Pb ages are 260.8 ± 1.5 Ma, 250.7 ± 1.8 Ma, 242.6 ± 0.7 Ma, 239.8 ± 1.2 Ma, 235.2 ± 0.9 Ma, and 230.2 ± 1.0 Ma. They are generally divided into granite, quartz monzonite and monzodiorite series in the QAP diagram. The granite series (HRGLG and LMR monzogranites and BLGX granodiorite) has high SiO2 contents and calc-alkaline features; it has low P2O5 and Zr+Nb+Ce+Y (75–267 ppm) contents, showing affinities to I-type granite, which reflects reworking of Mesoproterozoic lower crust. The quartz monzonite series (KEQK and DDKD diorites) has medium SiO2 and lower MgO contents (1.63–2.59 wt.%) than mantle-derived magmas and has crustal Nb/U and Ce/Pb ratios but mantle-like Nb/Ta ratios. Their geochemistry with binary properties related to both crust and mantle indicate that they probably originated from an AFC process involving mantle-derived melts and provide an important growth model of the continental crust in the EKOB. The monzodiorite series (BLGX diorite porphyry) has medium SiO2 and high MgO contents and Mg# values (59–61) and contains high-Mg diorites. They are enriched in LILEs and depleted in HFSEs; furthermore, strikingly high enrichments in Rb/Y ratios and Ba contents but a narrow range of Nb/Y ratios suggest that they originated from partial melting of hydrous mantle peridotites affected by fluids from the subducted slab. In conclusion, we suggest that the 261–235 Ma intermediate-acid intrusions represent the sustained subduction of the Paleo-Tethys Ocean slab and that the 230 Ma BLGX diorite porphyry records the breakoff of the Paleo-Tethys Ocean slab.