Felsic Research Articles

Petrogenesis and Metallogenic Evolution of Leucogranites from the Paleoproterozoic Malanjkhand Granitoids, Central India

Abstract The Birsa and Devgaon leucogranites represent contemporaneous episodes of highly fractionated felsic magmatism associated with the Paleoproterozoic Malanjkhand granitoids in the Bastar craton, Central India. Major element oxides geochemistry reveals that two leucogranites are strictly granite in composition and both show calc-alkaline affinity. Geochemical discrimination diagrams inferred that these leucogranites shows affinity towards I-type magma with metaluminous characters. Geochemical classification inferred that the Birsa leucogranite preferred to be magnesian whereas Devgaon leucogranite designated to be ferroan type. Geothermobarometry estimation suggested that 1.2-4.5 kbar pressure and 750°-830°C temperature conditions at the shallow depth of the continental crust is responsible for the emplacement of leucogranites. Crystallization evolution of feldspar in the leucogranite provided evidences of late stage felsic magmatism in the Malanjkhand pluton. Molybdenum enrichment in the leucogranite possibly due to crystal fractionation under high oxygen fugacity conditions inherited from the magma chamber in the continental crust. Anomalous high concentration of Mo in the Devgaon leucogranite is contributed from episodic hydrothermal system with poor supply of sulphur. Occurrences of molybdenite in the Devgaon leucogranite provides high exploration potential to investigates granite molybdenite system in the Bastar craton.

Partial Melting of Plagioclase-Free Garnet–Two-Mica Metapelite As a Model of the Formation of Ultra-Potassic Felsic Magmas under Conditions of the Continental Crust

Partial Melting of Plagioclase-Free Garnet–Two-Mica Metapelite As a Model of the Formation of Ultra-Potassic Felsic Magmas under Conditions of the Continental Crust

Prediction of multiscale laminae structure and reservoir quality in fine-grained sedimentary rocks: The Permian Lucaogou Formation in Jimusar Sag, Junggar Basin

Fine-grained sedimentary rocks have become a research focus as important reservoirs and source rocks for tight and shale oil and gas. Laminae development determines the accumulation and production of tight and shale oil and gas in fine-grained rocks. However, due to the resolution limit of conventional logs, it is challenging to recognize the features of centimeter-scale laminae. To close this gap, complementary studies, including core observation, thin section, X-ray diffraction (XRD), conventional log analysis, and slabs of image logs, were conducted to unravel the centimeter-scale laminae. The laminae recognition models were built using well logs. The fine-grained rocks can be divided into laminated rocks (lamina thickness of <0.01 m), layered rocks (0.01–0.1 m), and massive rocks (no layer or layer spacing of >0.1 m) according to the laminae scale from core observations. According to the mineral superposition assemblages from thin-section observations, the laminated rocks can be further divided into binary, ternary, and multiple structures. The typical mineral components, slabs, and T 2 spectrum distributions of various lamina types are unraveled. The core can identify the centimeter–millimeter-scale laminae, and the thin section can identify the millimeter–micrometer-scale laminae. Furthermore, they can detect mineral types and their superposition sequence. Conventional logs can identify the meter-scale layers, whereas image logs and related slabs can identify the laminae variations at millimeter–centimeter scales. Therefore, the slab of image logs combined with thin sections can identify laminae assemblage characteristics, including the thickness and vertical assemblage. The identification and classification of lamina structure of various scales on a single well can be predicted using conventional logs, image logs, and slabs combined with thin sections. The layered rocks have better reservoir quality and oil-bearing potential than the massive and laminated rocks. The laminated rocks’ binary lamina is better than the ternary and multiple layers due to the high content of felsic minerals. The abovementioned results build the prediction model for multiscale laminae structure using well logs, helping sweet spots prediction in the Permian Lucaogou Formation in the Jimusar Sag and fine-grained sedimentary rocks worldwide.

Occurrences of Niobium and Tantalum Mineralization in Mongolia

Niobium and tantalum are two rare metals that have similar physical and chemical properties and occur together in nature. They are considered to be strategic and critical materials for the economy and national security of many industrial countries. Both elements are on the 2022 List of Critical Minerals of the USA as well as on the European Union’s List of Critical Raw Materials. They rarely substitute for common elements in rock-forming minerals but are essential components in a range of rare minerals, particularly oxides and subordinately silicates. The economically important minerals are oxides. The columbite-tantalite and pyrochlore-microlite groups are the most common Ta- and Nb-bearing minerals. In Mongolia, primary niobium and tantalum mineralization includes two main types. The first type is mineralization associated with alkaline to peralkaline granites, pegmatites and syenites whereas the second type is related to the lithium-fluorine-rich peraluminous granites and related rocks (pegmatites and ongonites). The host rocks of both types of mineralization are the fractionated felsic rocks, which contain the primary magmatic ore assemblages associated with fractionation of magma rich in rare metals. Both assemblages were subsequently overprinted by the late magmatic to hydrothermal fluids, which remobilized and enriched the original mineralization. The newly formed ore mineral assemblages display complex replacement textures. In the case of peralkaline felsic rocks the processes produced the mineralization of Zr, Nb, heavy REE, Y, U, Th and Ta whereas peraluminous Li-F felsic rocks contain mainly mineralization of Sn, W, Ta, Li, and Nb. Mongolia hosts several promising occurrences of both types of Nb-Ta mineralization. However, they have not yet been sufficiently explored. Currently, the most promising is the occurrence in the Devonian Khalzan Buregtei peralkaline granites in northwestern Mongolia, where Nb-Ta is associated with REE and Zr mineralization. Mesozoic carbonatites of southern Mongolia do not host significant Nb and Ta mineralization.

Mineral Composition and Full-Scale Pore Structure of Qianjiadian Sandstone-Type Uranium Deposits: Application for In Situ Leaching Mining

In situ leaching (ISL) is becoming the main mining practice for sandstone-type uranium deposits in China. The key to ISL technology is to aid the leaching solution in contacting the ore bed over a large range, which will induce a series of chemical reactions to extract uranium; thus, it is essential to thoroughly understand the reservoir physical properties of uranium deposits. Taking the Qianjiadian sandstone-type uranium deposits (southern Songliao Basin, China) as an example, the mineral composition and pore structure of samples in different layers were measured using X-ray diffraction (XRD), thin section analysis (TSA), low-temperature N2 adsorption (LTN2A), and mercury intrusion porosimetry (MIP), and their influences on the ISL effect were analyzed. The results show that more than 65% of the minerals in the Qianjiadian uranium deposits are felsic minerals, and the carbonate minerals, clay minerals, and augite are auxiliary minerals. The primary intergranular pores, intergranular-dissolved pores, intragranular-dissolved pores, intercrystalline pores, and microfractures are developed in uranium deposits with various lithologies to different degrees. The macropores ( &gt;1000 nm) and mesopores (100-1000 nm) of medium sandstone, argillaceous sandstone, and siltstone are well developed; in contrast, the proportions of micropores ( &lt;10 nm) and transition pores (10-100 nm) in coarse sandstone, fine sandstone, and sandy mudstone are quite high. The heterogeneity of pores in uranium deposits of different lithologies is strong and influences the mineral composition and its fabric mode. Coarse sandstone, fine sandstone, and sandy mudstone are favorable for ISL mining in Qianjiadian uranium deposits because their permeability is above the required permeability threshold of ISL. The uranium deposits with permeability below the threshold are recommended to adopt the blasting-enhanced permeability method to improve their permeability for achieving large-scale and high-efficiency ISL mining. This study can provide guidance for the selection of favorable ore beds for ISL mining and reservoir stimulation methods in low-permeability sandstone-type uranium deposits.

Baddeleyite U-Pb age and Hf isotopes, and constraints on genesis of the Panzhihua carbonatite in SW China

The Panzhihua district is well-known for its magmatic V-Ti-magnetite deposit, with plenty of carbonatite intrusions and extrusives (total length: over 20 km), making it one of the world’s largest carbonatitic belts. Mantle-derived xenoliths (dunite, lherzolite and olivine lamprophyre) of different sizes are the most direct and important evidence of magmatic carbonatite. The carbonatite consists mainly of calcite, dolomite, olivine, clinopyroxene, orthopyroxene and biotite, almost without felsic minerals. We performed baddeleyite U-Pb dating on the four largest carbonatite intrusions at Panzhihua, which yielded weighted mean 206Pb/238U ages (from NE to SW: Zhujiabaobao, Jianbao, Gongshan and Lanaqing) of 261.8 ± 3.8 Ma (MSWD = 0.084, n = 28), 263.7 ± 2.3 Ma (MSWD = 0.10, n = 27), 260.6 ± 2.3 Ma (MSWD = 0.27, n = 22), and 262.3 ± 1.8 Ma (MSWD = 0.44, n = 34). Samples of three extrusive carbonatites and one carbonatitic breccia yielded weighted average baddeleyite 206Pb/238U ages of 261.7 ± 3.0 Ma (MSWD = 0.095, n = 33), 263.8 ± 2.5 Ma (MSWD = 0.21, n = 30), 263.2 ± 2.9 Ma (MSWD = 0.13, n = 28), and 259.1 ± 3.6 Ma (MSWD = 0.12, n = 28), respectively. The weighted 206Pb/238U ages of baddeleyites for all intrusions and extrusives are 262.1 ± 1.2 Ma (MSWD = 0.26, n = 111) and 262.4 ± 1.5 Ma (MSWD = 0.18, n = 119), respectively. Baddeleyites from different intrusions and extrusives have varying Hf isotope compositions, with the weighted average εHf(t) of −0.8 ± 0.5 (Zhujiabaobao), −3.2 ± 0.8 (Jianbaobao), −5.5 ± 1.5 (Gongshan) and −11.9 ± 0.5 (Lanaqing), which are largely negative and decrease progressively from northeast to southwest. εHf(t) values of the two extrusive carbonatite and one carbonatitic breccia samples from the southwest of Panzhihua are −14.5 ± 0.7, −15.1 ± 0.8 and −7.8 ± 1.3, and one extrusive sample from the Lanjian ore-block has weighted mean εHf(t) of −7.8 ± 1.3. δ13CVPDB and δ18OV-SMOW values of the Panzhihua carbonatite range, respectively, −13.4 to +0.4 ‰ (avg. −3.7 ‰) and +15.4 to +21.8 ‰ (avg. +19.5 ‰), similar to those of most global carbonatites. εHf(t) of baddeleyites in Panzhihua carbonatite are dominantly negative, and analogous to that of the standard Phalaborwa baddeleyite, indicating that carbonatitic magma may have been derived from partial melting of the metasomatized lithospheric mantle or an enriched asthenospheric component during the Permian intracontinental rifting (Emeishan mantle plume-related). The hyperthermal carbonatitic magma has partially or completely assimilated mantle xenoliths in the chamber and during its ascent, implying it was of high temperature greater than the solidus curve of peridotite (≥1100℃). Assimilation of xenoliths and wallrocks may have altered the Hf isotope compositions and yielded the distinctive alternating dark peridotite and white carbonatite layers around each xenolith. As a newly identified rock type, the Panzhihua may be one of the global largest carbonatite belts, which also enrich the rock sequences of Emeishan large igneous province.

Extensive crystal fractionation of high-silica magmas revealed by K isotopes.

Fractional crystallization plays a critical role in generating the differentiated continental crust on Earth. However, whether efficient crystal-melt separation can occur in viscous felsic magmas remains a long-standing debate because of the difficulty in discriminating between differentiated melts and complementary cumulates. Here, we found large (~1 per mil) potassium isotopic variation in 54 strongly peraluminous high-silica (silicon dioxide >70 weight %) leucogranites from the Himalayan orogen, with potassium isotopes correlated with trace elemental proxies (e.g., strontium, rubidium/strontium, and europium anomaly) for plagioclase crystallization. Quantitative modeling requires up to ~60 to 90% fractional crystallization to account for the progressively light potassium isotopic composition of the fractionated leucogranites, while plagioclase accumulation results in enrichment of heavy potassium isotopes in cumulate leucogranites. Our findings strongly support fractional crystallization of high-silica magmas and highlight the great potential of potassium isotopes in studying felsic magma differentiation.

Significance of a late neoproterozoic – Early Cambrian southern Baltica active margin in late-stage Rodinian and early Gondwanan reconstructions

New whole-rock geochemical data indicate changing provenance of sedimentary rocks deposited on the southern margin of Baltica in the late Neoproterozoic to early Paleozoic. The oldest part of the sequence is characterized by highly weathered detritus sourced from a mafic igneous source, inferred to be the nearby Volyn Large Igneous Province (L.I.P.), in an intracontinental rift (aulacogen) setting. Neoproterozoic–Cambrian boundary sequences are weakly weathered and sourced from intermediate to felsic rocks in an active margin setting whereas the youngest parts of the sequence exhibit significant quartz accumulation consistent with deposition of recycled material in a passive margin setting. These data support published U-Pb and Lu-Hf zircon data from the same sedimentary sequence where the Neoproterozoic-Cambrian boundary strata are characterized by anomalously high Ediacaran–Cambrian zircon contribution with juvenile isotopic composition. Taken together, these data indicate a cryptic late Neoproterozoic–early Cambrian active margin along the periphery of southern Baltica. Based on a correlation of similarly aged foreland basin and accretionary complexes, and links to paleomagnetically constrained plate reconstructions it is hypothesized that this detritus was sourced from the Avalonian micro-continent and a Cambrian arc terrane that is today preserved in high-grade metamorphic complexes of the European Variscides. These findings have potentially profound implications for our understanding of the supercontinent cycle that links the Rodinia to Pangea supercontinents, in particular the role played by Baltica-derived terranes in Paleozoic collisional orogeny.

Origin of the Songpan-Garze Terrane on the northeastern Tibetan Plateau, eastern segment of the Tethyan tectonic domain: A Middle Permian−Early Triassic intracontinental rifting system

The initiation of a continental rift or the birth of an oceanic basin, and their long-term evolution, are challenges in the understanding of the evolution of regional and global tectonics. Rifts develop within the interior or margins of plates, essentially as extensional structures, and they have been studied widely since the discovery of plate tectonics. The eastern segment of the Paleo-Tethys traversed central Asia, its structural features, timing, geological setting, and geodynamic mechanisms are poorly understood. The Songpan-Garze Terrane (SGT) on the northeastern Tibetan Plateau has been regarded as either a remnant of the Paleo-Tethys Ocean or a continental rift basin. Different interpretations of the SGT lead to various tectonic reconstructions between Gondwana and Laurasia. Here, sedimentology, geochemistry, and geochronology have been applied to the southern and northern parts of the SGT to reconstruct the initiation of a Permian rift system. In this area, for the first time, field investigation reveals that the SGT is characterized by a continuous succession of Permian−Lower Triassic terrestrial-neritic deposits and ocean island basalt (OIB)-type basalts, and that it developed as an intracontinental rift basin in the Yangtze Block. Zircons from gabbros with OIB-type geochemical signatures intruded in the southern SGT yield U-Pb ages of 263−254 Ma, constraining the timing of the initial rifting. Proterozoic felsic rocks collected from the southern SGT yield U-Pb ages of 761−865 Ma, and they are petrologically and geochemically comparable to Neoproterozoic basement rocks along the western margin of the Yangtze Block. The Middle−Late Permian volcano-sedimentary sequences of the SGT and their geochemistry and geochronology are comparable to rift sequences in the Panxi region of the western Yangtze Block. Thus, it has been proposed that the SGT originated as an intracontinental rift within the Yangtze Block during the Middle Permian−Early Triassic, and that it continued to deepen as a rift basin through the Middle−Late Triassic.

Global geological occurrence and character of the carcinogenic zeolite mineral, erionite: A review.

As with the six regulated asbestos minerals (chrysotile, amosite, crocidolite, anthophyllite, tremolite, and actinolite), the zeolite mineral, erionite, can exhibit a fibrous morphology. When fibrous erionite is aerosolized and inhaled, it has been linked to cases of lung cancers, such as malignant mesothelioma. Importantly, fibrous erionite appears to be more carcinogenic than the six regulated asbestos minerals. The first health issues regarding erionite exposure were reported in Cappadocia (Turkey), and more recently, occupational exposure issues have emerged in the United States. Erionite is now classified as a Group 1 carcinogen. Thus, identifying the geological occurrence of erionite is a prudent step in determining possible exposure pathways, but a global review of the geological occurrence of erionite is currently lacking. Here, we provide a review of the >100 global locations where erionite has been reported, including: 1) geological setting of host rocks; 2) paragenetic sequence of erionite formation, including associated zeolite minerals; 3) fiber morphological properties and erionite mineral series (i.e., Ca, K, Na); and 4) a brief overview of the techniques that have been used to identify and characterize erionite. Accordingly, erionite has been found to commonly occur within two major rock types: felsic and mafic. Within felsic rocks (in particular, tuffaceous layers within lacustrine paleoenvironments), erionite is disseminated through the layer as a cementing matrix. In contrast, within mafic (i.e., basaltic) rocks, erionite is typically found within vesicles. Nevertheless, aside from detailed studies in Italy and the United States, there is a paucity of specific information on erionite geological provenance or fiber morphology. The latter issue is a significant drawback given its impact on erionite toxicity. Future erionite studies should aim to provide more detailed information, including variables such as rock type and lithological properties, quantitative geochemistry, and fiber morphology.

A linked evolution for granite-greenstone terranes of the Pilbara Craton from Nd and Hf isotopes, with implications for Archean continental growth

Granite-greenstone terranes, such as in the Pilbara Craton (Western Australia), record the growth and stabilisation of Archean (>2.5 Ga) continental crust. Yet, uncertainty surrounds the formation of the silica-rich portions of these terranes, important for preservation of continental lithosphere, specifically whether this involved reprocessing of older continental nuclei over hundreds of millions of years, or rapid differentiation of juvenile mantle additions, as preserved in the greenstone belt volcanic sequences. In part, the uncertainty reflects difficulties with establishing the isotope evolution of the early Archean mantle, critical for ascertaining the time gap between the extraction of new crust and granitic emplacement in Archean cratons. To investigate the formation of silica-rich Archean crust, we report Hf and Nd isotope data for 46 mafic–ultramafic samples and zircon Hf isotope data for 83 felsic igneous rocks from the Pilbara Craton, selected to be representative of the major magmatic episodes from 3.56 to 2.72 Ga. The strikingly similar secular isotope trends defined by mafic and felsic rocks reveal a linkage between mantle and crustal processes throughout the history of the craton. From 3.56 Ga to 3.12 Ga, craton evolution was dominated by the transformation of juvenile mantle derived inputs into felsic igneous rocks on short timescales, thus recording sustained continental growth over 400 million years. Incorporation of older crust by felsic magmas was minor during this interval. Evolution toward sub-chondritic Nd and Hf after collision of the East and West Pilbara terranes at 3.1 Ga signals greater involvement of pre-existing crust in magma generation, possibly by recycling of crustal material into mantle source regions or by enhanced reworking of older, thickened cratonic lithosphere. Mafic–ultramafic rocks provide no evidence for anomalous or strongly depleted mantle domains in the Paleoarchean. Rather, the flat zircon εHf–time array indicates extraction of continental materials from mildly super-chondritic mantle from ca. 3.6 to 3.12 Ga and attests to a distinctive style of crust production that operated in the Archean. This study highlights the importance of comparing the mantle and crustal isotope records in order to reconstruct the crustal growth rates in ancient terranes.

Potassium isotope fractionation during granitic magmatic differentiation: Mineral-pair perspectives

To constrain the behavior of K isotopes during granitic magmatic differentiation, we present high-precision K isotope data for bulk granitoids and their K-bearing minerals from Dabie and Himalayan orogens in China. Plagioclase displays extremely large K isotopic variation, with δ41K ranging from −0.56 to 1.91‰. Other minerals also have heterogeneous K isotopic compositions, with δ41K varying from −0.56 to −0.24‰ in hornblende, from −0.72 to −0.39‰ in biotite, from −0.79 to −0.47‰ in K-feldspar, and from −0.74 to −0.61‰ in muscovite. The general trend of 41K enrichment follows the order of plagioclase ≫ hornblende > biotite ≈ K-feldspar ≥ muscovite, which can be attributed to the difference in KO bond strengths. Both δ41K of plagioclase and K isotope fractionation factors between plagioclase and other minerals are negatively correlated with K concentration in plagioclase, suggesting a compositional control on isotope fractionations. Inter-mineral K isotope fractionations among other minerals are roughly temperature-dependent. Potassium isotopic compositions of whole rocks display measurable variations (δ41K = –0.69 to −0.28‰), which are correlated with proxies for plagioclase fractionation (e.g., Sr and Rb/Sr). The correlation indicates that fractional crystallization may account for the whole-rock K isotopic variations observed in high-silica igneous rocks, which is supported by modeling of fractional crystallization using the apparent isotope fractionation factors determined in this work. Our study demonstrates the existence of large K isotope fractionation during granitic magmatism, making K isotopes a potential tool for studying differentiation of felsic magmas.

Geological framework of the concealed East Tennant area constrained by SHRIMP U–Pb zircon geochronology: Implications for Paleoproterozoic stratigraphic correlations in northern Australia

The fundamental geological framework of the concealed Paleoproterozoic East Tennant area of northern Australia is very poorly understood, despite its relatively thin veneer of Phanerozoic cover and its position along-strike from significant Au–Cu–Bi mineralisation of the Tennant Creek mining district within the outcropping Warramunga Province. We present 18 new U–Pb dates, obtained via Sensitive High Resolution Ion Micro Probe (SHRIMP), constraining the geological evolution of predominantly Paleoproterozoic metasedimentary and igneous rocks intersected by 10 stratigraphic holes drilled in the East Tennant area. The oldest rocks identified in the East Tennant area are two metasedimentary units with maximum depositional ages of ca. 1970 Ma and ca. 1895 Ma respectively, plus ca. 1870 Ma metagranitic gneiss. These units, which are unknown in the nearby Murphy Province and outcropping Warramunga Province, underlie widespread metasedimentary rocks of the Alroy Formation, which yield maximum depositional ages of 1873–1864 Ma. While parts of this unit appear to be correlative with the ca. 1860 Ma Warramunga Formation of the Warramunga Province, our data suggest that the bulk of the Alroy Formation in the East Tennant area is slightly older, reflecting widespread sedimentation at ca. 1870 Ma. Throughout the East Tennant area, the Alroy Formation was intruded by voluminous 1854–1845 Ma granites, contemporaneous with similar felsic magmatism in the outcropping Warramunga Province (Tennant Creek Supersuite) and Murphy Province (Nicholson Granite Complex). In contrast with the outcropping Warramunga Province, supracrustal rocks equivalent to the 1845–1810 Ma Ooradidgee Group are rare in the East Tennant area. Detrital zircon data from younger sedimentary successions corroborate seismic evidence that at least some of the thick sedimentary sequences intersected along the southern margin of the recently defined Brunette Downs rift corridor are possible age equivalents of the ca. 1670–1600 Ma Isa Superbasin. Our new results strengthen ca. 1870–1860 Ma stratigraphic and ca. 1850 Ma tectono-magmatic affinities between the East Tennant area, the Murphy Province, and the mineralised Warramunga Province around Tennant Creek, with important implications for mineral prospectivity of the East Tennant area.

Relationship between the Texture and Composition of Titanomagnetite in Hannuoba Alkaline Basalt: A New Geospeedometer

The nucleation and growth of crystals in igneous rocks is usually thought to occur under thermodynamic equilibrium conditions. However, recent studies on igneous textures and mineral compositions have shown that these processes probably occur under thermodynamic disequilibrium conditions. Titanomagnetite with variable crystal sizes can be observed in Hannuoba alkaline basalt, indicating disequilibrium crystallization processes (different cooling rates). The ratio of the maximum particle size to the area abundance of titanomagnetite, as determined by an analysis of previous studies on the texture of minerals, was negatively correlated with the apparent cooling rate. We analyzed the chemical composition and crystal size distribution of titanomagnetite in ten Hannuoba alkaline basalt samples to determine the connection between the apparent cooling rate and titanomagnetite composition. In Hannuoba samples, the cooling rate was found to affect cationic substitution in the titanomagnetite solid solution, and an increase in cooling rate led to a decrease in Ti4+ and an increase in Fe3+. The partition coefficient of Ti between titanomagnetite and the melt (DTi) is negatively correlated with the apparent cooling rate. These findings are consistent with those in experimental petrology and help us propose a better, more general geospeedometer. The cooling rate also impacted Mg2+ and Al3+, but they were more impacted by the melt composition and crystallinity of the coexisting melt. Therefore, a new geospeedometer was calibrated by considering the titanomagnetite composition, melt composition and the content of the clinopyroxene.The cooling rates of the Hannuoba basalt samples measured using the new geospeedometer calibrated in this study range from 0.7 to 7.0 (±0.5) °C/min. It cannot accurately predict the cooling rate from titanomagnetite in intermediate rock, felsic rock or Fe-rich basaltic melts. The new titanomagnetite geospeedometer can better measure the cooling rate of alkaline basalt and may help identify the effects of kinetically controlled crystallization on isotope fractionation, evaluate mineral thermobarometers and better recognize thermal remanence magnetization and ancient magnetic fields.

Multiple magmatic-hydrothermal processes recorded by titanite from the Early Cretaceous Liangwan pluton, Tongbai Orogen

Titanite is a common accessory mineral in igneous rocks and hydrothermal deposits. Micro-texture and in situ chemical analyses on titanite are expected to reveal complex magmatic-hydrothermal processes. The Liangwan granitic pluton in the Tongbai Orogen is dominated by monzogranite with abundant mafic microgranular enclaves (MMEs). In this paper, an integrated study of LA-ICP-MS U Pb ages, textural, trace elemental and Nd isotopic compositions of titanites were carried out for the Liangwan pluton to decipher multiple magmatic-hydrothermal processes. U Pb dating results of zircon and titanite show that the Liangwan monzogranite and MMEs have similar crystallization ages of ca. 130 Ma. Combined with petrography and titanite geochemistry studies, MMEs are considered as magma mingling origin. According to the occurrence, texture, and chemical characteristics of titanite, four main types (Ttn-1 to Ttn-4) and several sub-types of titanite are identified in the Liangwan pluton. Among these types, Ttn-1, Ttn-2 g, and Ttn-4 g are from the monzogranites, while Ttn-2 m, Ttn-3, and Ttn-4 m mainly form in the MMEs. Ttn-1 grains are euhedral and show core-mantle texture. Their cores are characterized by high REEs, Nb, Ta, Th and Y contents, Th/U, Lu/Hf, and Y/Zr ratios, and low La/Ce, Nb/Ta rations, and relatively lower εNd (t) (−13.3 to −14.6) values, indicating that they are of magmatic origin and crystallized from the host monzogranites. However, Ttn-1's mantles and Ttn-3 grains show a reverse geochemical feature to those of Ttn-1's cores. Their relative higher εNd (t) (−12.1 to −13.9) values, suggest that they crystallized from a mafic magma. Both Ttn-2 g and Ttn-2 m contain abundant magnetite and ilmenite inclusions. They display geochemical characteristics between Ttn-1's cores and Ttn-3 but are closer to their host rocks, respectively. These features suggest that they are the product of the dissolution-reprecipitation of Ttn-1 in different magmas. Ttn-4 with few fluid inclusions, mostly existing as interstitial phases, is characterized by low REE, Y, HFSE, Th/U, LREEs( N )/HREEs( N ), and high Nb/Ta, indicating that they are hydrothermal origin that were derived from the residual melt. Textural and geochemical features of various types of titanites indicate that repeated recharges of mafic magmas happened at the syn - to late- fractional crystallization of felsic magmas. Nd isotopic data on titanite recorded various degrees of isotopic re-equilibration between the two end-member magmas during different pulses of mafic magma. Our study demonstrates that titanite is a reliable indicator to reveal complicated magmatic-hydrothermal processes. • Monzogranite and MMEs of the Liangwan pluton were both formed at ∼130 Ma. • MMEs in the Liangwan pluton were formed by magma mingling. • Titanite is a reliable indicator to reveal complicated magmatic-hydrothermal processes • Early Cretaceous granite could provide hydrothermal fluids for regional Au—Ag mineralization.

In Situ Trace Elements in Quartz and K-Feldspar from Felsic Igneous Rocks: A Titanium-in-K-Feldspar Geothermometer for Natural Magmatic Systems

Abstract Scanning electron microscope, cathodoluminescence (CL) imaging and laser ablation–inductively coupled plasma–mass spectrometry analyses were conducted on coexisting pairs of quartz and K-feldspar from 14 samples of various types of felsic igneous rocks. Difference of the concentration of trace elements in quartz and K-feldspar among plutonic, pegmatitic and volcanic rocks is closely related to the rock-forming process and P–T condition. In general, a decreasing Ti concentration and increasing Al, Li, and Ge concentrations from plutonic to pegmatitic quartz suggest a higher degree of magmatic fractionation and lower crystallization temperature. Sensitive elements to magma differentiation in K-feldspar such as Ba, Sr, and LREE show a decreasing trend from various granitic rocks to pegmatite, while Rb, Cs, Li, Ge, and P exhibit increasing trends. The K-feldspar from various types of felsic igneous rocks typically shows similar CL textures but relatively higher luminescence intensity compared with coexisting quartz. Both quartz and K-feldspar phenocrysts in the volcanic rhyolite have a bright rim and a dark core in CL images, corresponding to bimodal Ti concentrations. Among all samples, Ti concentrations in both quartz and coexisting K-feldspar positively correlate with their CL intensities, suggesting the activation of Ti-impurity in these minerals leads to increased CL intensity. Meanwhile, there is a good positive correlation between Ti concentrations in quartz and those in K-feldspar with an R2 value of 0.86. It is considered that Ti concentrations in the both minerals are mainly temperature dependent at relatively constant pressure on basis of a fair aTiO2 restriction. Here, for the first time, we calculated a titanium-in-K-feldspar (TitaniKfs) thermometer in the form of log (XTi, kfs/aTiO2) = −(3430 ± 268)/T(K) + (5.081 ± 0.298) for natural felsic magma systems. The Ti contents of K-feldspar (in ppm by weight) increase exponentially with reciprocal T at temperatures ranging from 500°C to 800°C, at 200–300 MPa. An application of this thermometer to granitic rocks from Xinjiang and Inner Mongolia in China fits well with other geothermometers. In addition, the present TitaniKfs thermometer is expected to be particularly useful in determining the temperature condition of K-feldspar-bearing extraterrestrial materials such as lunar rocks.

The role of gas flushing on magma reservoir crystallization and its consequences for the growth of planetary crust

Many crustal magmatic reservoirs are fundamentally powered by basalt injection at their base. Asides from transfer of silicate liquid and crystals and accompanying heat, basaltic magma also provides large amounts of fluids to the overlying magma. This work explores how water activity and temperature, hence degree of crystallisation , of magmatic reservoirs are affected by such a mechanism at various levels in the crust. By using recent experimental phase equilibria , thermodynamic relationships between gas and silicate melts , and heat balance, it is shown that, depending on the level of magma storage, diffusive exchange during bubble uprise and stalling may produce either crystallisation or melting of magmas. Long term fluxing of felsic to intermediate magma bodies stored in upper crust by mafic volatiles will generally lead to their near isothermal solidification. Conversely, for bodies stagnating in the mid to deep crust, such a process almost inevitably enhances melting, driving or maintaining magmas beyond the threshold of mobility needed for upward material transfer, unless the percolating fluid is very CO 2 -rich. Compilation of basaltic melt inclusion data gathered in arc, hot-spot and ridge settings, shows that the two last categories coexist with CO 2 -rich fluids at high pressures (XH 2 O fluid < 0.1), which will almost always enhance crystallisation. In contrast arc basalts record a wide and continuous range of fluid compositions, from dry to almost H 2 O-saturated conditions, which may either favour (low pressure) or inhibit (high pressure) the crystallisation of felsic reservoirs which they underplate. Crustal growth may thus be in part limited by the difficulty of crystallising deep-seated magma bodies, in particular in arc settings. This pressure controlled effect is related to the contrasted solubilities of H 2 O and CO 2 in silicate melts, and to the much stronger non-ideal behaviour of CO 2 relative to H 2 O as pressure increases. Asides from tectonic and density inversion processes, a thick crust may fundamentally reflect the fact that basalt underplating in the lower crust has proceeded at a rate sufficiently slow so as to prevent remelting of earlier intrusions (or melting of lower crust lithologies) or that the outcoming fluid was CO 2 -rich, or both. Application to other terrestrial planets is hindered by the paucity of data regarding crust thickness and composition, and it can be only conjectured that the thin crust of large planets (Earth, Venus) reflects in part the operation of subduction process during their evolution, while the comparatively thicker crust inferred for smaller bodies (e.g. Mars, the Moon, Vesta) primarily reflects processes related to a primordial crust. • Long term fluxing of felsic magma bodies in upper crust by mafic volatiles generally leads to their solidification. • Conversely, in the deep crust, such a process almost inevitably enhances melting, unless the mafic fluid is very CO2-rich. • Crustal growth may thus be limited by the difficulty of crystallising deep-seated magma bodies, in particular in arc settings. • A relatively thin crust on large planets may reflect the operation of subduction

Permian ridge subduction-related magmatism in the Eastern Tianshan: Implications for the evolution of the southern Altaids

Permian large-scale transcurrent tectonics and syn -kinematic ultramafic–felsic magmatism are prominent features in the Eastern Tianshan of the southern Altaids. However, the genetic relationship between coeval Ni Cu mineralized mafic-ultramafic intrusions and felsic intrusions, and the geodynamics of the region remains equivocal. To assess these topics and improve our understanding of this geologically complex and economically significant region, zircon Hf isotope and bulk-rock geochemical data from Permian granitoids along the Kanggur–Huangshan Shear Zone (KHSZ) in the Eastern Tianshan are determined and interpreted in the context of previous geochronological–geochemical data. The Kungurian Longdong (ca. 278 Ma) and Hongshi (ca. 273 Ma) granitoids are high-K, calc-alkaline, metaluminous to weakly peraluminous I-type granitoids, whereas the Capitanian Shuangchagoubei (ca. 262 Ma) granitoids are calc-alkaline, peraluminous, adakitic I-type granitoids. All of the granitoid samples are enriched in light rare earth elements and large ion lithophile elements (e.g., Rb, U, and K), and depleted in high field strength elements (e.g., Nb, Ta, and Ti), similar to arc magmas, indicating that subduction-related magmatism was still active in the late Permian. Taking into account the regional geology, and the presence of Permian high-temperature metamorphism, adakites, I-type granites, Alaskan-type Ni Cu sulfide and orogenic Au mineralization, and EW-trending N-MORB type gabbro and mélange along the KHSZ, we suggest that subduction of a spreading center during the Permian generated a slab window, allowing the upwelling of asthenospheric mantle. This permitted the generation and migration of mantle-derived magmas to shallower crustal levels along translithospheric faults (e.g., Kanggur and Yamansu faults), forming the mafic–ultramafic intrusions and associated Ni Cu sulfide deposits. The continuous migration of magma provided the necessary heat to induce partial melting of juvenile crust, generating the Permian high-K to calc-alkaline I-type granitoids. Ridge subduction-induced juvenile crustal reworking likely played a central role in the formation of the granitoids during the late Paleozoic accretionary orogenesis of the southern Altaids. • Subduction-related magmatism was active in the Eastern Tianshan in the late Permian. • Crustal growth and reworking processes must have occurred simultaneously in the Eastern Tianshan during the Permian. • Ridge subduction-induced juvenile crustal reworking likely played an important role in the formation of the granitoids in the southern Altaids.

Petrogenesis and tectonic implications of the Late Triassic intrusions in the North China Craton: Case study on the Huata complex in the western Yanshan

This paper presents geochemical and age data for Late Triassic lamprophyre, syenite, and granite in the Huata area of the western Yanshan belt of the North China Craton, to provide constraints on the origin and tectonic settings of these Late Triassic igneous rocks. The zircons from the Huata lamprophyres and syenites yielded a mean U Pb age of 203 and 206 Ma, respectively. The lamprophyres are enriched in incompatible elements, with (La/Yb) N = 30.57–33.89, (Gd/Yb) N = 3.54–3.64, and Sr-Nd-Hf isotopic signatures ( 87 Sr/ 86 Sr (initial) = 0.7053–0.7061, εNd(t) = −11.11 to −10.50, εHf(t) = −9.33 to −7.70), consistent with them originating from the low-degree melting of previously metasomatized lithospheric mantle in the garnet-stable area. The syenites display similar incompatible elements to the lamprophyres, but have relatively low (La/Yb) N = 14.26–17.23 and (Gd/Yb) N = 1.81–2.15 ratios. Their Sr-Nd-Hf isotopic compositions ( 87 Sr/ 86 Sr (initial) = 0.7045–0.7050, εNd(t) = −12.10 to −11.35 and εHf(t) = −8.64 to −6.81) were also similar to the lamprophyres, and they are considered to have been generated from the low-degree melting of lithospheric mantle in the garnet-spinel transition zone. The granites have major and trace element patterns and Sr Nd isotopes quite different from the syenites, but are similar to the crust-derived felsic rocks, being enriched in large ion lithosphere elements and depleted in high field strength elements. They are enriched in Nd isotope (εNd(t) = −16.63 to −15.18), and are inferred to have been generated by lower crust anataxis. The presence of igneous rocks in the Huata district indicates that the northern margin of the NCC had already entered a non-orogenic regime by the late Late-Triassic. • Lamprophyres and syenites derive from a metasomatized mantle. • Granites originate from the modified lower continental crust. • The tectonic regime transformed from post-collisional to intraplate at 206 Ma.

New insights into the petrogenesis of rhyolites and evolution of volcanic‐hosted massive sulphide mineralization from shallow borehole core, Betul Belt, Central India

Shallow borehole drilling has been conducted at the Sarni area of Betul Belt, Central India to understand the subsurface geology and nature of mineralization. The predominant lithounits are ferruginous quartzites, felsic volcanic rocks, and with minor intrusions of amphibolites. The encountered felsic volcanic rocks are rhyolites varying from pink (rich in K‐feldspar) to grey (rich in Na‐feldspar and amphiboles). The rhyolitic rocks have undergone intense hydrothermal alteration. The alteration zones are defined by the presence of biotite‐chlorite‐garnet‐gahnite; biotite‐sericite‐chlorite‐anthophyllite and anthophyllite‐actinolite‐tremolite‐carbonate mineral assemblages. Sulphide pits, highly leached zones with occasional bluish tinges, limonitic patches are present in the felsic volcanic rocks, followed by semi‐massive to disseminated sulphide mineralization indicative of Kuroku‐ type Zn–Cu–Pb volcanic‐hosted Massive Sulphide (VHMS) mineralization. Scanning electron microscope and energy‐dispersive x‐ray spectroscopy studies documented sphalerite, pyrite, chalcophyrite, arsenopyrite, pyrrhotite, and minor Au–Ag phases. The Sarni rhyolites exhibit chalcopyrite disease in sphalerite, replacement, and overgrowth ore‐textures. The high HFSE, low Zr/Y ratio, pronounced negative Eu anomalies characterize the felsic volcanic rocks as FIIIb type with high zircon saturation temperatures of 856–931°C. These rhyolites are formed at a back‐arc rift setting in an ensialic island‐arc tectonic regime. The synvolcanic structures facilitated the magma ascent to the surface. The hydrothermal circulation due to adequate heat flow in the back‐arc rift environment, in an episodic multicyclic process provided sufficient time for accumulation of sulphides from the seafloor, which was later deposited to form a VHMS mineralization. We also report tungsten (W) mineralization in the quartz veins of these felsic volcanic rocks. It is suggested that the felsic magma has interacted with metasedimentary sequences and assimilated W‐ore bearing fluids, and during remobilization in the later stages of tectonic activity enabled the deposition of tungsten in these quartz veins.