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The Changbaishan volcanic field is the largest Quaternary volcanic field in China and includes the most dangerous polygenetic volcano, Tianchi volcano. In addition to the Tianchi volcano, the Changbaishan volcanic field contains two other polygenetic volcanoes (Wangtian'e volcano and Namphothe volcano) and at least 150 monogenetic volcanoes. The compositions of these monogenetic volcanoes range from basalt to rhyolite. Basaltic monogenetic volcanoes are the most abundant and spread throughout the volcanic field, whereas intermediate to evolved monogenetic volcanoes are found only within the Touxi subfield. We know very little about these non-basaltic monogenetic volcanoes, especially the magmatic petrogenesis, volcanological origins and structure of the magma plumbing system beneath them. Therefore, in this study, the Xitudingzi volcano within the Touxi subfield is used as an example to study the petrogenesis of silicic magma and explore the structure of the magma system by combining new 40Ar/39Ar dating, whole-rock geochemistry, Sr–Nd isotopes and mineral chemistry. The 40Ar/39Ar chronology results showed that the Xitudingzi volcano erupted at 1.17 Ma; this volcano is younger than the other monogenetic volcanoes in the Touxi subfield. The geochemical results indicated that the eruption products of the Xitudingzi volcano are trachytic and formed from the assimilation fractional crystallization (AFC) process of an alkaline basaltic parental magma. The results from the Rhyolite-MELTS and thermobarometry indicated that the magma plumbing system of the Xitudingzi volcano contained two magma chambers at depths of 8 and 19 km, respectively. The trachytic magma of Xitudingzi was produced by the AFC process from the alkaline basaltic magmas in the deep magma chamber and then transported to the shallow magma chamber. Furthermore, differences in the trace element concentrations between the different units of the Xitudingzi volcano indicated that the shallow pre-eruptive magma chamber was compositionally zoned. Based on the results from our study, the upper crustal magma plumbing system of the Xitutingzi volcano existed independently of the magma plumbing system of the cone-construction stage of the Tianchi volcano, even though the two volcanoes had similar ages of activity, as well as the same chemical composition of eruptive products. Based on these results and other existing studies, a relatively thick crust and the developed faults are likely the key factors for the formation of intermediate to evolved monogenetic volcanos in the Touxi volcanic field. [ABSTRACT FROM AUTHOR]

Tourmaline is a valuable forensic mineral that contains a wide range of elemental components capable of reconstructing its geologic evolution. In this study, we developed detailed petrographic and geochemical research on tourmaline-bearing rocks and tourmalinites found surrounding the ca. 3.30 Ga rhyolite of the Gavião Block, northern São Francisco Craton. Two distinct types of mineral assemblages in the tourmaline-bearing rocks are recognized based on the presence of sulfides, oxide minerals, and carbonaceous matter. Along with these tourmaline-bearing rocks, tourmalinite samples are found. The mineral chemistry of tourmalines from the two types of tourmaline-bearing rocks reveals mainly schorl-dravite as tourmaline from a mineral assemblage containing quartz, tourmaline, pyrite, and hematite, and a diverse composition ranging from schorl-dravite, feruvite-uvite, and schorl-feruvite solid solutions for tourmalines present in the mineral assemblage that contains quartz, pyrite, and carbonaceous matter. The tourmaline composition is essentially foitite-schorl in tourmalinite samples. Most of the metasedimentary rocks studied have felsic and mafic source compositions. The interaction of hydrothermal fluid was crucial for the formation of sulfide and tourmaline minerals. However, distinct tourmaline origins are recognized in tourmaline-rich rocks, pointing out the relevance of sedimentary and metamorphic processes. [ABSTRACT FROM AUTHOR]

Repeated intrusions of mafic magma have long been known to be a driver of long-lived magmatic systems. Although the importance of mafic recharge of silicic magma systems is well-documented in igneous petrology, the origin of this recharge magma is sometimes obscure. By examining the pre-caldera intermediate dome complexes of the Tschicoma Formation and their relationship to a dacitic recharge event into the Tshirege Member of the Bandelier Tuff, we aim to better understand the origin of mafic recharge events into the Bandelier magma chamber of Valles caldera, and the relationship between different stages of volcanic activity within the broader Jemez Mountains volcanic field (JMVF). Based on major, trace element and radiogenic isotopic data, we divide the Tschicoma Formation into three geochemical groups with similar petrologic evolutionary paths. The Cerro Grande, Cerro Rubio and Pajarito Mountain volcanic dome complexes form group A and have assimilated various amounts of a granitoid crustal component with low εNd, εHf and radiogenic Pb. Group B consists of the Sawyer Dome, Rendija Canyon and Caballo Mountain dome complexes, which have principally evolved through different degrees of fractional crystallization of the same parent magma, itself a result of complex interactions of a mafic mantle-derived magma with the crust. The dacite domes and flows around Tschicoma Peak and the newly described Cañada Bonita dacite form group C and are the result of mixing of Rendija Canyon magma with mafic recharge magma which is preserved as distinct mafic enclaves. At a later stage of the JMVF, during the eruption of the Tshirege Member, distinctive hornblende–dacite pumices formed as a result of the influx of more mafic recharge magma into the system, which mobilized a pre-existing dacite intrusion and injected it into the Tshirege rhyolite (Stimac , 1996 ; Boro , et al. 2020). Based on trace element and isotopic compositions, we propose that dacite which was injected into the Tshirege magma chamber was related to the earlier-erupted Tschicoma Formation and itself represents a mixing product of Tshirege rhyolite and a precursor to the Tschicoma dacites. This implies that the Tschicoma magmatic system was long-lived yet dormant during the eruption of the Otowi Member of the Bandelier Tuff, then was reactivated shortly before the Tshirege eruption, temporarily co-existing and interacting with the Bandelier system as it erupted. [ABSTRACT FROM AUTHOR]

We report the whole-rock major and trace element and Sr – Nd – Pb isotopic compositions of volcanic rocks from the Nansatsu area in South Kyushu. We analysed samples from the Oldest stage (middle Miocene), Older stage (late Miocene), and Middle stage (early Pliocene) Nansatsu volcanic rocks, which are andesite to dacite in composition, with an island-arc trace element signature. The compositional variabilities within the Older and the Middle stage rocks are relatively small compared to those in the Oldest stage and Quaternary volcanic rocks. Isotopic characteristics suggested that the Oldest stage volcanic rocks had magma sources similar to regional ilmenite-series granitoids of later ages (Outer Zone granitoids), which incorporated a substantial amount of graphite-bearing accretionary sediments (Shimanto Supergroup). The sources for the Older and Middle stage magmas were similar to those of primary Quaternary basalts in South Kyushu, indicating that Pliocene and Quaternary volcanic rocks in South Kyushu share a common mantle source, despite the change in the nature of volcanic activity from andesite-dominated to more variable volcanism of basalt to rhyolite. [ABSTRACT FROM AUTHOR]

Subduction-related magmatism is a significant contributor to arc building and continental growth. In the active convergent margin of the SW Japan arc, voluminous volcanic rocks and mafic dykes formed through subduction and back-arc rifting during Miocene. In this study, we investigate a suite of felsic volcanic rocks (rhyolite and dacite) and lamprophyres from central Shikoku Island, which occur in the north-central part of the Chichibu belt and Sanbagawa belt in the Outer zone of the SW Japan arc. Whole-rock geochemistry results show that the rhyolite and dacite samples are peraluminous, belong to the high-K calc-alkaline series, show LREE and LILE enrichment, HREE and HFSE depletion that suggest arc volcanic affinity. The lamprophyre samples belong to alkali lamprophyre, show LREE and HFSE enrichments, and display OIB (oceanic island basalt)-like geochemical features. The 206Pb/238U weighted mean ages of the zircons from the rhyolite and dacite samples range from 14.39 ± 0.21 Ma to 13.92 ± 0.30 Ma, whereas the lamprophyre shows 206Pb/238U weighted mean age of 12.21 ± 0.35 Ma. Zircon Lu-Hf isotope data suggest that the rhyolite and dacite were derived from the remelting of the arc crustal rocks and that the lamprophyre was derived from depleted mantle sources and was contaminated by crustal materials. The felsic volcanic rocks (rhyolite and dacite) can be correlated to Miocene (15.5 Ma to 13.5 Ma) magmatism in the Outer Zone of the SW Japan arc. The formation of lamprophyre dykes in the SW Japan arc may be related to the subhorizontal mantle flows beneath the SW Japan arc associated with the opening of the Japan Sea back-arc basin or asthenosphere upwelling through the slab-tear of the Philippine Sea Plate beneath the SW Japan arc. Our study shows that the SW Japan Arc was built by multiple magmatism from diverse sources in an active convergent margin. [ABSTRACT FROM AUTHOR]

This study investigates mineralogy, geochemistry, and the origin of acidic volcanic rocks and stream sediments in the Central Eastern Desert of Egypt, focusing on the southeast G. El-Hadid area. Geological units comprise serpentinites, metasedimentary rocks, metavolcanics, older granites, acidic volcanic rocks, and younger granites. Notably, rhyolites and pyroclastics constitute the acidic volcanics. Early post-volcanic alteration is evident through quartz and fluorite veins, while the presence of common kaolinitization, sericitization, and hematitization indicates late-stage post-volcanic alteration. The mineralogical examination of the acidic volcanics and stream sediments reveals enrichment in thorite, xenotime, monazite, zircon, and fluorite. Pyroclastic composition shows higher concentrations of incompatible trace elements than rhyolite, with enriched large ion lithophile elements (LILE) and relatively depleted high field strength elements (HFSE). Pyroclastic samples notably exhibit higher rare earth element (REE) concentrations (up to 906 ppm) relative to associated rhyolite (up to 95 ppm). The rhyolitic samples are characterized by fairly fractionated patterns ((La/Lu)N = 2.45–3.56) and moderately fractionated HREE contents ((Gd/Lu)N = 0.93–1.06). The pyroclastic samples display relatively weak fractionated patterns ((La/Lu)N = 0.06–2.06) and weak to unfractionated fractionated HREE contents ((Gd/Lu)N = 0.04–0.43). Both the Na/Ta and Y/Nb ratios suggest crustal magma sources for both acidic melts. Stream sediment samples reveal significant REE abundances, and its geochemical maps indicate enrichment in U and Th correlating with anomalies in REEs, Hf, Sn, W, Zr, Y, and Nb. The presence of pyroclastics upstream of Wadi Khor Um Safi suggests potential as a REE resource. The geochemical characteristics resemble a continental-arc setting formed through an active margin. REE abundance patterns in pyroclastic rocks and associated stream sediments exhibit the M-type tetrad effect and strong Europium (Eu) depletion as a result of fluid–melt interaction during late-stage fractional crystallization. Estimated pyroclastic formation temperatures range from 800 to 840 °C, indicating moderate crustal depths. [ABSTRACT FROM AUTHOR]

This investigation reports the first discovery of more than 70 tuff intervals in the Upper Triassic, South Qilian Basin. Petrographic and geochemical analyses were carried out on ten tuff samples and zircon U-Pb dating were on three. Thin section and X-ray diffraction (XRD) results indicate that the tuffs were composed of crystal shards and altered glass shards; crystal shards include plagio-clase and quartz. Most of the tuffs had been transformed into illite/smectite mixed-layers (I/S). In addition, calcite, pyrite, dolomite and siderite were also identified in some of the tuff samples. Analysis of major elements suggests that the tuffs are peraluminous high-K calcalkaline series. Trace elements indicate that the tuffs are enriched in high field strength elements (HFSE), including Th, U, Ta, Zr and Hf. Geochemical characteristics suggest that the tuffs originated from comendite pantellerite and rhyolite from within plate setting. Zircon U-Pb dating (236.0 ± 1.7, 231.4 ± 1.6, and 223.1 ± 3.9 Ma) indicate that the tuffs were erupted in the Late Triassic. Comparative chronology and geochemical analyses suggest that the West Qinling belt and the East Kunlun belt are the potential source regions of these tuffs, and they originated from the within plate magma during a post-collisional period. [ABSTRACT FROM AUTHOR]

Outcrops of late Paleozoic magmatic rocks are common in the Southern Beishan Orogenic Belt (SBOB), Southern Central Asian Orogenic Belt (CAOB), which is a key object for the understanding of regional tectonism and defining the final closure time of the Paleo-Asian Ocean (PAO). We present zircon U-Pb chronology and whole-rock geochemistry data for late Paleozoic granodiorites and bimodal volcanic rocks from the Shuangyingshan-Huaniushan unit in the north Huitongshan-Zhangfangshan ophiolitic belt in the SBOB. The Zhangfangshan granodiorites (LA-ICP-MS, Ca. 288 Ma) are A2-type granite enriched in Rb, Th, Pb and LREEs and depleted in Nb, Ta, Ti, Sr, Ba and HREEs. They have varying MgO and TFe2O3 contents with high Mg# (38.56~48.97) values; the Lu/Yb ratios (0.14~0.15) of these granodiorites are similar to mantle-derived magma. A clear plagioclase zoning structure and acicular apatite occur in mineral assemblages derived from magma mixing between mafic and felsic magmas. The Baishantang bimodal volcanic rocks (272 Ma) consist of rhyolite and basaltic andesite. Baishantang rhyolites are A2-type felsic rock enriched in Rb, Th, Pb and LREEs and depleted in Nb, Ta, Ti, Sr, Ba and HREEs, with negative εNd(t) and εHf(t) (−5.2~−4.8 and −2.2~−1.9, respectively). Rhyolites originated from the partial melting of the crust, influenced by mantle material. Basaltic andesites belong to calc-alkaline series and have an enrichment of Rb, Ba, Th, U, Pb and LREEs, are weakly enriched in Zr-Hf, and are depleted in Nb, Ta, Ti and HREEs. The Nd-Hf isotopes of these basaltic andesites are not coupled with negative εNd(t) (−2.8~−0.4) and positive εHf(t) (1.8~5.5) values. These characteristics indicate that they originated from the partial melting of the mantle mixed with sediment-derived melts. In combination with previous studies, our findings show that the early Permian Zhangfangshan granodiorites and Baishantang bimodal volcanic rocks formed in a post-collision extensional setting, and the Huitongshan-Zhangfangshan ocean had been closed before early Permian. [ABSTRACT FROM AUTHOR]

The current debate on volcanic-plutonic connection is centered on whether eficient liquid-crystal segregation dominates the evolution of a mushy reservoir to produce evolved, crystal-poor rhyolite and cumulate leftover. However, magma recharge may remarkably influence the evolution of a mushy reservoir and obscure the evidence of liquid-crystal segregation. This complexity poses a challenge to exploring the connection of volcanic-plutonic rocks. This study investigates the Qinzhou Bay granitic complex (~250–248 Ma) from South China, which contains crystal-poor (<19 vol%) peraluminous rhyolites and subsequent crystal-rich (28–54 vol%) porphyries. Although the rhyolite and porphyry units have a close spatio-temporal link, they do not share a fractionation trend and similar whole-rock Sr-Nd-O isotopic compositions; thus, a direct connection is not evidenced. We further present textural analyses, mineral and melt inclusion compositions, thermobarometry (the combination of Ti-in-zircon thermometer and Ti-in-quartz thermobarometer), and thermodynamic modeling to examine the alternative interpretations, i.e., the two units may have intrinsically independent origins or the connection of the two units has been obscured. For the rhyolite unit, thermobarometric results reveal a polybaric storage system consisting of middle (>600 ± 80 MPa) and upper (~150 ± 40 and ~60 ± 20 MPa) crustal reservoirs. Variations in quartz Fe content and chlorine-rich, metaluminous melt inclusions suggest that magma hybridization with less-evolved metaluminous magmas occurred at both crustal levels. In particular, the elevated Fe contents in the quartz population that crystallized at the shallowest level (~60 ± 20 MPa) suggest that recharge magmas were directly injected into the shallowest reservoir. Deviation of the whole-rock composition from the liquid evolution trend recorded in melt inclusions suggests a combined efect of magma mixing and crystal-melt segregation processes in upper crustal reservoirs. Thermodynamic modeling and mass balance calculations suggest that the whole-rock composition of the rhyolite could be reproduced by mixing between regionally exposed dacites and segregated melts at crystallinities of 50–60% (using parental magma represented by the least-evolved melt inclusion). For the porphyry unit, thermobarometric results reveal magma storage at middle (more than 450 ± 40 to 550 ± 40 MPa) and upper (110 ± 20 to 140 ± 20 MPa) crustal levels. The small-scale oscillatory zonation of plagioclase, the pervasive resorption of quartz and alkali feldspar, and the presence of peraluminous microgranular enclaves in the porphyries suggest a recharge event of metasediment-sourced magmas, triggering reactivation and convection of the reservoir. Autoclastic and overgrowth textures of quartz, plagioclase, and alkali feldspar phenocrysts and development of columnar jointing suggest that the reactivated porphyritic magmas ascended and emplaced at ultrashallow levels (~30 ± 10 MPa). Because of the similar storage pressures, the porphyries may represent remobilized cumulates of rhyolitic magmas, whereas the texture and geochemistry of the cumulate-liquid pair were modified, a key factor rendering a cryptic connection between the rhyolite and porphyry. Alternatively, the plumbing systems feeding the rhyolite and porphyry units are horizontally independent or vertically discrete, but this circumstance is inconsistent with the same evolution trend of quartz Fe and Al contents of the rhyolite and porphyry. Our study highlights that whole-rock composition may record blended information of complex processes, and caution should be taken when whole-rock composition is used to extract information of a single process. Multi-method constraints are required to evaluate the influence of recharge processes on the modification of liquid-cumulate records, and big data analysis on the basis of geochemistry should be conducted with caution to avoid biased understanding. [ABSTRACT FROM AUTHOR]

At least 28 rhyolitic lava flows, domes, and tuffs erupted within Yellowstone caldera following its formation 631 ka. Understanding the timing of intracaldera eruptions is essential for characterizing natural hazards posed by Yellowstone volcano. We present 40Ar/39Ar eruption ages for the Mallard Lake Member and Central Plateau Member of the Plateau Rhyolite, which comprise products from 22 eruptions spanning ~160 to ~70 ka. These eruptions occurred along two linear vent zones within Yellowstone caldera that appear to be extensions of major extracaldera normal faults. Eruptions took place in five brief clusters with group mean ages of 160.3±1.0 ka (2σ), 149.8±4.0 ka, 111.4±0.9 ka, 104.1±0.8 ka, and 70.8±0.7 ka. All mapped products within each informal group have indistinguishable 40Ar/39Ar eruption ages implying brief eruption durations. Eruption products of each group are spatially clustered, with only one of the two linear vent zones being active during an eruption group. Using the oldest group (160 ka), we apply paleomagnetic and geochemical analyses to investigate the duration of these eruption groups and their pre-eruptive magma reservoir configuration. Paleomagnetic analyses suggest that the nine rhyolite eruptions ~160 ka spanned 400 years or less. Glass and sanidine compositions of each rhyolite are nearly identical, which is consistent with pre-eruptive storage of a large (~130 km3), interconnected melt body within Yellowstone volcano's crystal-rich magma reservoir. These characteristics differ from intracaldera eruptions that vented near the caldera's inner ring fracture system, which tend to be compositionally disparate with less temporal clustering. These insights inform hazard mitigation scenarios. [ABSTRACT FROM AUTHOR]

Widespread tuffs are known from the lower Cambrian succession of the Arrowie Basin, Flinders Ranges, mainly from the lower parts of both the Mernmerna Formation and the Billy Creek Formation. Up to 2.5 m of potassium-rich (K2O 6.32–9.60 wt%) rhyolite tuffs are known from the Mernmerna Formation, with the 'Big Green Tuff' from Bunyeroo Gorge yielding a TIMS age of 515.4 ± 0.2 Ma (i.e. unnamed Cambrian stage 3). The petrography of the Big Green Tuff, with numerous glass shards, suggests an explosive subaqueous pyroclastic deposit or ash-flow tuff. The presence of several layers of identical green tuff indicates that these were produced by a multi-phase volcanic event. There are up to thirty tuff horizons (5–50 cm thick) within the Warragee Member of the Billy Creek Formation. The tuffs within the Billy Creek Formation occur over a wide area, with an east–west extent of 250 km and a north–south extent of up to 80 km. It is suggested that they are in part ash-flow tuffs. A previous TIMS age for the Billy Creek Formation was 511.87 ± 0.14 Ma (i.e. unnamed Cambrian stage 4). The source of the tuffs, both from the Mernmerna Formation and the Billy Creek Formation is unknown. Detailed study of the whole-rock and trace-element geochemistry is required to fully document them. Widespread tuffs have been known for about sixty years from the lower Cambrian Mernmerna and Billy Creek formations in the Flinders Ranges, but only a limited amount of work has been done on them. The potassium-rich rhyolitic tuffs of the Mernmerna Formation occur in several horizons up to 2.5 m thick, thus indicating a substantial volcanic event. Sources of the tuffs from both the Mernmerna and Billy Creek formations are unknown. The widespread distribution of both the Billy Creek Formation tuffs and the rhyolitic tuffs in the Mernmerna Formation and the uppermost Wilkawillina Formation indicates that the volcanic activity within the Arrowie Basin was widespread and at times intense. [ABSTRACT FROM AUTHOR]

The felsic volcanic rocks in orogenic belts are vital probes to understand the tectonic evolution and continental crust growth. Here, we present a comprehensive study on the zircon U–Pb geochronology, whole-rock geochemistry, and zircon Lu-Hf isotopes of Early felsic volcanic rocks from the Hongshuichuan Formation, East Kunlun Orogen, Northern Tibet, aiming to explore their petrogenesis and implications for the Paleo-Tethyan orogeny and crustal evolution. The studied felsic volcanics comprise rhyolite porphyry and rhyolite, exhibiting coeval zircon U–Pb ages of ca. 247–251 Ma. Rhyolite porphyries show metaluminous to peraluminous nature (A/CNK = 0.88–1.24) with high SiO2 contents (72.1–78.9 wt%) and moderate Mg# values (22–40), and they display enrichment of LREE with (La/Yb)N ratios of 6.02–17.9 and depletion of high field strength elements. In comparison, the rhyolites are strongly peraluminous (A/CNK = 1.09–1.74) with high SiO2 contents (71.7–74.3 wt%) and high Mg# values (43–52) and are also enriched in LREE ((La/Yb)N of 6.65–18.4) and depleted in HFSE (e.g., Nb, Ta, Ti). Combining with their different zircon Lu-Hf isotopes, i.e., enriched isotopes for the rhyolite porphyries (εHf(t) = −7.3 to −3.8) and depleted Hf isotopes for the rhyolites (ɛHf = −0.6 to +3.0), we interpret that the studied rhyolite porphyries and rhyolites were derived by partial melting of Mesoproterozoic metagreywacke sources followed by plagioclase-dominated fractional crystallization, but the latter shows the significant contribution of crust–mantle magma mixing. The mixed mantle-derived magma comes from an enriched lithospheric mantle source that had been metasomatized by subduction-related fluids. Combining with other geological evidence, we propose that the studied Early Triassic felsic volcanic rocks were formed in a subduction arc setting, and the reworking of ancient continental crust with crust–mantle magma mixing is the major mechanism of crustal evolution in the East Kunlun Paleo-Tethyan orogenic belt. [ABSTRACT FROM AUTHOR]

Late Paleozoic (Variscan) magmatism is widespread in Central Europe. One of the critical areas that contributes to the understanding of the complex volcanotectonic processes at the Pennsylvanian to Cisuralian transition is the Chemnitz- Flöha Volcanic Zone (CFVZ). The latter is part of the type region of the Saxo-Thuringian Zone of the European Variscides. For the Altenhain Rhyolite, which is part of the CFVZ we present a complete dataset concerning its whole-rock geochemistry. The potassium-rich Altenhain Rhyolite originated from a highly differentiated, calc-alkaline, peraluminous, A-type granitic melt with an intra-plate signature. There are strong geochemical similarities to the Flöha Ignimbrite and the Zeisigwald Tuff pyroclastics, both belonging to the CFVZ. The occurrence of a rare mineral from the arsenogoyazite/arsenoflorencite-(Ce) solid solution series is recognised. [ABSTRACT FROM AUTHOR]

Exposed at the Lake City caldera (Colorado, USA) is the ca. 23 Ma reversely stratified (rhyolite to trachyte) Sunshine Peak Tuff and post-collapse syenite and monzonite resurgent intrusions. Existing models for this system suggest that the rhyolites are related to the trachyte and resurgent syenite through fractional crystallization, separation, and remobilization (crystal mush model), and that multiple magma batches were involved in the system (Hon, 1987; Kennedy et al., 2016; Lubbers et al., 2020). We use U-Pb zircon CA-ID-TIMS-TEA and zircon trace-element modeling to further probe age and geochemical relationships between the extrusive and intrusive units. Zircon ages and compositions from the erupted units and the syenite overlap, suggesting these magmas were related and may have mixed prior to eruption. Results from the monzonite suggest it was a contemporaneous but distinct magma batch that mixed with parts of the larger system. Trends in zircon geochemistry are decoupled from time, reflecting a complex history of accessory mineral saturation and mixing of magma batches, and a distinct high-Hf population of zircon grains hints at the existence of an additional, independent batch of rhyolitic magma in the system. The new ages we present shorten the lifetime of the Lake City magmatic system from 80 to 300 k.y. (Bove et al., 2001) to 60 to 220 k.y. and suggest the high-silica rhyolite magma crystallized over a minimum of ~160 k.y. This latter timescale likely reflects a protracted history that includes differentiation of a parent melt prior to extraction of eruptible high-silica rhyolite magma. [ABSTRACT FROM AUTHOR]

Demingding is a promising porphyry Mo-dominated deposit recently discovered in the eastern Gangdese metallogenic belt in Tibet, China. We present zircon U-Pb-Lu-Hf isotopic studies, as well as geochemical data of the late monzogranites and the prior rhyolites from the Demingding porphyry deposit to uncover their origin and geodynamic mechanism. Zircon U–Pb dating yielded precise crystallization ages of 17.3 ± 0.6 Ma (MSWD = 2.5) and 186.5 ± 3.0 Ma (MSWD = 2.0) for monzogranite and rhyolite, respectively. The monzogranite is characterized by high-K calc-alkaline, adakitic affinities, and positive zircon εHf(t) values (+0.9∼+5.6, avg.+3.1) with TDM2 (0.73–1.04 Ga), while the rhyolite has εHf(t) values of (+2.1∼+7.3, avg.+5.2) and TDM2 of (0.76–1.09 Ga) similar to the monzogranite. Our results suggest that the Demingding porphyry Mo (Cu) deposit is related to magma generated from the Neo-Tethyan oceanic subduction. The subsequent monzogranite porphyry was likely formed by the remelting of previously subduction-modified arc lithosphere, triggered by continental collision crustal thickening in Miocene. The lower positive εHf(t) values of monzogranites suggest minor inputs from the Mo-rich ancient crust, suggesting that Mo favors the silicate melt. Such magmatic events and special metallogenesis typify intracontinental processes and porphyry copper deposits, which are normally confined to oceanic subduction and Cu-dominated style, thereby making the continental setting and Mo-dominated style of Demingding exceptional and possibly unique. [ABSTRACT FROM AUTHOR]

Dike swarms and structural lineaments were investigated in the Hada Alsham area, west-central Arabian Shield of Saudi Arabia, using remote sensing, field observations, and geochemical analysis techniques. SPOT-7 digital satellite data were employed in the analysis of these structural lineaments and dike swarms. The extracted orientations of the structural lineaments and dike swarms confirm that they are approximately identical, trending mainly in the NNW–WNW, NE–ENE, and E–W directions. Based on field observations and cross-cutting relationships, these dike swarms can be geochronologically arranged (from oldest to youngest) as mafic NNW- to WNW-trending dikes, mafic NE- to ENE-trending dikes, felsic NE-trending dikes, and local mafic E–W dikes. Major and trace elements geochemistry indicates that the studied dike swarms are basalt, basaltic andesite, and rhyolite in composition. Trace and REE diagrams, as well as their immobile elemental ratios of the studied dike swarms suggesting their formation in a typical intraoceanic island arc setting. In addition, the felsic NE dikes may represent extensive fractionation of the mafic magma from which the mafic NE dikes were formed because their incompatible elements signatures are almost similar. All dike swarms were likely emplaced between 620 and 576 Ma, and during the post-collisional extension and relaxation, following the amalgamation of terranes (island arcs) during the collision between the East and West Gondwana. [ABSTRACT FROM AUTHOR]

The Rupnica geosite, a key locality of the UNESCO-protected Papuk Geopark in northern Croatia, is well-known for an excellent exposure of columnar jointing in volcanic rock. This rock is defined as an albite rhyolite that comprises almost pure albite phenocrysts within a fine-grained matrix composed of microphenocrysts of albite, quartz and devitrified volcanic glass. Primary accessory minerals are clinopyroxene, apatite, zircon and magnetite. Haematite, apatite and anatase were found as inclusions in zircon. The albite rhyolite is characterized by a highly siliceous, peraluminous, oxidized (ferroan), dry, alkali-calcic to alkalic composition, with low CaO, MgO, and MnO contents and high FeOT/(FeOT+MgO) ratios. Normalized trace element contents display positive anomalies of K, Pb, and Zr as well as negative anomalies of Nb, P, Ti, Ba and Eu, together with an enrichment of light rare-earth elements (REE) relative to heavy REE. Zircon from the rhyolite of Rupnica is characterized by ratios of Th/U=1.13 and Zr/Hf=55 and contents of HfO2=1.04 wt. % typical for an early-stage igneous zircon crystallized from a dry high-temperature magma in a deep magma chamber. Apatite REE patterns show enrichment of light REE over heavy REE and a pronounced Eu anomaly, typical for apatite from granitoids formed in an oxidizing environment. The magma is of A-type and was generated at high temperatures at 800-900 °C by partial melting of lower- to mid-crustal rocks. The age of the albite rhyolite of Rupnica is Late Cretaceous at 80.8±1.8 (2σ) Ma, according to U-Pb dating of zircon, coeval with geochemically similar igneous rocks of Mt. Požeška Gora and Mt. Kozara within the Sava Zone. [ABSTRACT FROM AUTHOR]

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The volcanic rocks of the Colíder and Roosevelt formations are extensively exposed in the south-central portion of the Amazonian Craton where effusive and pyroclastic rocks have been mapped. Both units, topped by chemical sediments and oceanic facies as rhyolite and andesite lavas, rhyodacite, and porphyritic dacite, with frequent intercalations of pyroclastic and epiclastic deposits. Whole-rock geochemistry for 55 samples of rhyolitic to andesitic composition suggests the involvement of fertile mantle-derived components with E-MORB to OIB compositions. The analyzed rocks display calc-alkaline to shoshonitic affinity consistent with generation related to an active continental margin. The whole-rock Sm-Nd isotope data from selected felsic volcanic rocks of the Colíder and Roosevelt formations yield negative initial εNd values between –3 and –9, indicating the predominantly crustal nature of the parental magmas with early Archean to late Paleoproterozoic (ca. 2.5–2.0 Ga) depleted mantle model ages. [ABSTRACT FROM AUTHOR]

The Dong'an Au deposit is a large-sized epithermal Au deposit discovered in the Lesser Xing'an Range, Northeastern China. Intermediate-acid volcanic rocks (e.g., trachyandesite, andesite, dacite, rhyolite, and rhyolitic tuff) of the Lower Cretaceous Fuminghe Formation are the important surrounding rocks for Au mineralization in the Dong'an Au deposit. However, the relationship between the intermediate volcanic rocks and the acidic volcanic rocks is unclear. The authors present new geochemical, zircon U-Pb and Hf isotope data for the trachyandesites in the Dong'an Au deposit. The whole-rock geochemical data indicate that the trachyandesite samples are high-K calc-alkaline. They are enriched in LILEs (e.g., K, Rb, and Ba), LREEs, and incompatible elements (e.g., Th and U), but are depleted in HFSEs (e.g., Nb, Ta, P, and Ti), showing characteristics of volcanic arc magmas. They have low Mg# values (32.77–48.12), Cr, Ni, and Co contents. Zircons U-Pb dating of the trachyandesites from sample DA-N1 and DA-N2 yield weighted average ages of 108.0 ± 1.1 Ma (MSWD = 0.91) and 104.7 ± 4.3 Ma (MSWD = 17). In situ zircon Hf isotope analyses of the trachyandesites from sample DA-N1 and DA-N2 yield εHf(t) values of −3.2 – 1.2 and −2.3 – 2.6, and two-stage model age (TDM2) of 1372-1090 Ma and 1321-1009 Ma, respectively. These suggest the trachyandesite were derived from partial melting of the juvenile lower crust with involvement of the ancient crustal materials. Combined with previous geological and petrogeochemical characteristics of the Lower Cretaceous Fuminghe Formation volcanic rocks in the Dong'an Au deposit, the Fuminghe Formation volcanic rocks are believed to be comagmatic, and fractional crystallization played an important role in the differentiation of these volcanic rocks. They were likely formed during the retreat of the subducted Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

Platinum-group element (PGE) geochemistry of arc-related magmas can be used to constrain the timing of sulfide saturation, which plays a critical role in the chalcophile element fertility of evolving magmatic systems. In this study, we provide new major and trace elements, PGE, Re and Au data for the shoshonitic suite (from basalt to rhyolite) of the active volcanic system of Vulcano (Aeolian Islands, Italy), an excellent study case for investigating mineralizing processes in arc volcanoes. The most primitive magma erupted at Vulcano is characterized by fractionation of Ir-group PGE (Ir, Os, Ru) relative to the Pd-group PGE (Pd, Pt, Rh), which is attributed to the magma being saturated with a Pt-rich alloy and possibly spinel and Os–Ir alloy. A negative Au anomaly, shown by Vulcano magmas, suggests that the Au was lost to an early exsolved S– (and moderately Cl–) rich fluid phase that, upon migration to higher levels of the feeding system, could have enhanced the mineralizing potential of the magmatic system. The Pd content of Vulcano primitive magmas is high (~ 8 ppb) and comparable to values found in other arc-related mineralized systems. The early Pd depletion, relative to Au and Cu, during evolution towards more evolved magmas, suggests that the magmatic system reached sulfide saturation at about 4 wt.% MgO. Chalcophile element fractionation modeling shows that the immiscible sulfide mass proportion was initially very low (~ 0.0015%), and gradually increased to about 0.1% at about 2 wt.% MgO, causing a late depletion of the less compatible chalcophile elements, including Cu. A significant chalcophile metal depletion in the silicate melt occurred once sulfide saturation was achieved, well before hydrosaline fluid exsolution at < 0.5 wt.% MgO. As a consequence, when the evolving melt reached volatile saturation at the rhyolite stage, it did not contain enough Cu and Au to form a mineralized system. [ABSTRACT FROM AUTHOR]

The Huayra Huasi Volcanic Complex of Miocene age (11.88 ± 0.15 Ma U–Pb zircon) was emplaced in the Northern Puna plateau of Argentina, spatially associated with ignimbrites erupted from Altiplano–Puna Volcanic Complex calderas. The complex comprises biotite-bearing dacites and low-SiO2 rhyolites in the northern area and high-SiO2 rhyolites in the south, all with peraluminous compositions (A/CNK > 1.0–1.22). The units have broadly similar initial Sr and Nd isotopic ratios (87Sr/86Sr ∼ 0.71013–0.71225 and εNd ∼ −5.4 to −7.0) and are composed of plagioclase, quartz, sanidine and biotite as the main phenocryst phases. All units host macroscopic microgranular enclaves and xenoliths of sillimanite–biotite schists, sillimanite- and sillimanite–garnet gneisses, as well as fibrous alumina-rich microxenoliths, the latter being especially abundant in the southern rhyolites. Petrographic, mineral and whole-rock geochemistry, geothermometric and isotopic data indicate that all units of the complex originated by contamination of andesite magmas through assimilation of upper crustal lithologies in early stages of magma evolution. The fibrous alumina-rich microxenoliths are composed almost entirely of refractory minerals (sill + Kfsp ± Pl ± Bt) and interpreted as peritectic or restitic products of partial melting of assimilated metasedimentary rocks similar to the unmodified metamorphic xenoliths in the complex. Geochemical modeling indicates that, after early-stage contamination, each magmatic unit evolved separately. Whereas the northern dacites and low-SiO2 rhyolites underwent assimilation and fractional crystallization throughout their history, the southern rhyolites mainly evolved via fractional crystallization of felsic phases alone. This study shows that the peraluminous nature of felsic magmas do not necessarily originate by partial melting of crustal material but can be acquired by metaluminous magmas during later evolution. The processes shown here of assimilation and fractional crystallization and pure fractional crystallization has relevance for other igneous bodies of similar compositions in the Puna backarc and worldwide. [ABSTRACT FROM AUTHOR]

To assess the eruption and emplacement of volumetrically diverse rhyolite lavas, we measured microlite number densities and orientations from samples collected from nine lavas in Yellowstone Caldera and two from Mono Craters, USA. Microlite populations are composed of Fe-Ti oxides ± alkali feldspar ± clinopyroxene. Number densities range from 108.11 ± 0.03 to 109.45 ± 0.15 cm−3 and do not correlate with distance from the vent across individual flows and are remarkably similar between large- and small-volume lavas. Together, those observations suggest that number densities are unmodified during emplacement and that ascent rates in the conduit are similar between small domes and large lava flows. Microtextures produced by continuous decompression experiments best replicate natural textures at decompression rates of 1–2 MPa hr−1. Acicular microlites have a preferred orientation in all natural samples. Because the standard deviation of microlite orientation does not become better aligned with distance travelled, we conclude that microlites exit the conduit aligned and that strain during subaerial flow was insufficient to further align microlites. The orientations of microlite trend and plunge in near-vent samples indicate that pure shear was the dominant style of deformation in the conduit. We speculate that collapsing permeable foam(s) provides a mechanism to concurrently allow microlite formation and alignment in response to the combination of degassing and flattening by pure shear.

Perlites in the Central Slovakia Volcanic Field are associated with with rhyolite dykes, cryptodomes, extrusive domes, coulées and volcanoclastic rocks of the Jastrabá Fm. (12.3-11.4 Ma). From numerous occurrences only the Lehôtka pod Brehmi (LPB) and Jastrabá (JST) represent deposits of economic interest. The LPB deposit exploits a pile of extruded hyaloclastite breccia composed of grey porous and dark dense fragments. The JST deposit exploits glassy rhyolite breccia composed of grey porous fragments associated with an extrusive dome/coulée. The perlites at both deposits are peraluminous, calc-alkaline of the high-K type, poor in phenocrysts (around 5 %) of plagioclase, biotite and minor amphibole (LPB) or sanidine/anorthoclase (JST). Glass at both deposits is silica rich (75.4-79.5 wt. % dry) with Al2O3, K2O and Na2O as other major constituents. It is inhomogeneous showing domains enriched in Na2O or K2O. Glass water content (3.0-6.0 wt. %) shows a weak positive correlation with its silica content and a negative correlation with its Na2O content. Perlites show porosities of 5-16 % (dark dense), 16-30 % (grey porous) and 30-44 % (pale grey pumiceous). Narrow stretched pores represent remnants after outgassing of ascending magma while open undeformed pores grew at a low pressure before quenching. The transformation of volcanic glass into perlite took place owing to the hydration by heated fluids of meteoric origin. The hydration was supported by a significant porosity with interconnected pores and by sustained elevated temperature. Perlites at both deposits show a low content of tightly-bound water and a low Na/K ratio. These properties are responsible for their relatively low degree of expansion. On the other hand, due to the same reason, the perlites have a good mechanical stability. [ABSTRACT FROM AUTHOR]

The intrabasinal felsic pyroclastics and rhyolite in the lower part of Semri Group of Vindhyan Supergroup are intruded by 3–11 m thick mafic plugs. These mafic bodies intrude Kajrahat Limestone of Semri Group. Earlier studies pertaining to these dykes are restricted to petrography; however, geochemical data on these rocks are lacking. Ca‐plagioclase, augite, and enstatite‐bearing dolerites show sub‐alkaline nature with basaltic andesitic (52–56% SiO2) composition. They exhibit moderate incompatible trace elemental enrichment, characterized by enriched LREE and depleted HREE [(La/Yb)N = 3.5–5.7] contents akin to those reported from the intraplate continental rift‐related basalts. Moreover, high Ba, Th, U together with the low Nb, Ta, and Ti values suggests crustal contamination. Chondrite‐normalized REE patterns and trace element ratios when compared to continental rift basalts show similarity with them. Th/Ta and La/Yb discriminant diagram represents mixed sources and characterizes the occurrence in the sub‐continental lithosphere. High La/Nb, La/Ta ratios, and positive Eu anomaly indicate that the basalt was derived from a depleted mantle source but mixed with crustal components. It is further supported by the ratios of Yb/Ta, Nb/Ta, and Zr/Hf indicating crustal contamination. In this article, we report the petrological and geochemical characteristics for the bimodal volcanics in order to understand their magma source and implications on tectonic setting in the lower part of Vindhyan Basin. [ABSTRACT FROM AUTHOR]

The Manzhouli–Xin Barag right banner are located in the southwest of the Ergun Massif (NE China), the tectonic evolution of these areas are still controversial. In this study, a series of rocks comprising rhyolites (LA–ICP–MS U–Pb zircon ages of 206 ± 2 Ma and 195 ± 2 Ma), granodiorites (196 ± 1 Ma and 190 ± 1 Ma), and monzogranites (206 ± 5 Ma and 196 ± 1 Ma) are newly identified. Whole-rock major and trace element analyses show that these felsic rocks and granites belong to the metaluminous to peraluminous, high-K calc-alkaline series, and can be classified as I-type granites. The zircon in-situ Lu–Hf isotope analyses on rhyolite, granodiorite, and monzogranite, yielded the εHf(t) values that are ranging from of 9.7–12.1, and two-stage model age are in the range of 0.5 Ga to 0.6 Ga, εHf(t) values of 4.4–7.5, 0.8–1.0 Ga, εHf(t) values of 6.0–10.5, 0.6–0.9 Ga, respectively. The whole-rock Sr–Nd isotope analyses on rhyolite, granodiorite, and monzogranite, yielded lower initial 87Sr/86Sr ratios (ISr) of 0.703374–0.703586, 0.704503–0.704577, 0.704936–0.704379, with medium εNd(t) values of 4.32–4.38, 1.54–2.96, − 0.68 to 2.73, respectively, suggesting that they are derived from the partial melting of a juvenile depleted lower crust. They all show enrichment in the large ion lithophile elements (e.g., Rb, Ba, and K) and depletion in the high field strength elements (e.g., Nb, Ta, and Ti), indicating that they are generated in an Andean-type arc setting and are metasomatized by subduction-slab released fluids or melts with minor crustal contamination. Mainly three magmatic phases: ca. 283–225 Ma, ca. 225–166 Ma, and ca. 166 Ma–114 Ma are identified in the Ergun Massif, and above Late Triassic to Early Jurassic magmatic rocks are related to the second phase, which attribute to the Mongol–Okhotsk ocean southward subduction and lateral crustal growth. [ABSTRACT FROM AUTHOR]

The Powderhouse formation of the Paleoproterozoic Snow Lake arc assemblage comprises the stratigraphic footwall to six volcanogenic massive sulfide (VMS) deposits at Snow Lake, Manitoba, Canada. It is interpreted to be a product of voluminous pyroclastic eruptions and concomitant subsidence followed by a period of relative volcanic quiescence that was dominated by suspension sedimentation, the reworking of previously deposited pyroclastic units by debris flows and bottom currents, and localized emplacement of rhyolite domes. The rhyolite domes are spatially associated with the Chisel, Chisel North, Lost, Ghost, Photo, and Lalor deposits. The Chisel, Lalor, and Lost members compose the Powderhouse formation and are subdivided into 13 lithologically distinct lithofacies, which allows, for the first time, correlation of stratigraphy between the South Chisel basin and Lalor areas, critical in predicting the location of largely stratiform VMS deposits. The Chisel and Lalor members contain lithofacies and bedforms that are characteristic of emplacement by subaqueous pyroclastic mass flows and concomitant subsidence. The Chisel member also contains coarse volcaniclastic breccias emplaced by mass debris flows derived from movement along fault scarps following early pyroclastic eruptions, and during continued subsidence. The Lost member consists of lithofacies deposited by mass flows generated from faults scraps during continued subsidence, but also contains lithofacies reworked by bottom currents, those deposited by suspension sedimentation, and, locally, coherent rhyolite. The Lost member represents a time stratigraphic interval, the "ore interval", that marks contemporaneous rhyolite dome emplacement, VMS formation, and a hiatus in explosive volcanism. [ABSTRACT FROM AUTHOR]

The newly discovered Dongyang low‐sulphidation epithermal Au deposit is located in central‐eastern Fujian Province, coastal SE China. Ore bodies occur in Late Jurassic rhyolite porphyry, rhyolite, and dacitic crystal tuff lava. In this study, rhyolite and dacitic crystal tuff lava are dated to 151.9 ± 0.4 Ma and 158.3 ± 0.4 Ma, respectively, and belong to the second member of the Nanyuan Formation. They are high in K2O (6.91–3.81 wt%) and Na2O/K2O (0.55–0.02), strongly peraluminous (A/CNK = 2.11–1.67) and high‐K calc‐alkaline or shoshonitic. They contain low ∑REEs (248–125 ppm), are enriched in Rb, K, Au, and depleted in Ba, Sr, P, Zr, Hf, and have slightly negative Eu anomalies (δEu = 0.94–0.56), suggesting that they are weakly fractionated felsic volcanic rocks. The zircon εHf(t) values (−11.2 to −5.4; two‐stage model ages = 2,650–2,128 Ma) suggest that they were mainly derived from Palaeoproterozoic crust. Lead isotope compositions also imply a dominantly lower crustal source. Detailed geological characteristics and elemental and isotopic data suggest that the oxidizing and weakly fractionated nature of the Dongyang high‐K felsic magma may have played a key role in Au mineralization. Integrating new and published data on the tectonic evolution, we suggest that the Late Jurassic Au mineralization and its causative magmatism actually extended to the SE China coastal area. The Dongyang rhyolite and dacitic crystal tuff lava may have been generated from partial melting of the crust caused by underplating of mantle‐derived magmas in an extensional environment. Regional extension may have been related to the NW‐directed roll‐back of the Palaeo‐Pacific Plate beneath the South China Block. [ABSTRACT FROM AUTHOR]

We present a detailed review of the petrological and geochemical aspects of rhyolite and associated silicic volcanic rocks (up to 20 ​vol% of all rocks) reported to date from twelve well known Phanerozoic continental mafic Large Igneous Provinces (LIPs). These typically spread over ≤104 ​km2 (rarely 105 ​km2 for Paraná-Etendeka) area and comprise ≤104 ​km3 of extrusive silicic rocks, erupted either during or after the main basaltic eruption within <5 Myr, with some eruption(s) continuing for ≤30 Myr. These rhyolites and associated silicic volcanic rocks (60−81 ​wt.% of SiO 2) are mostly metaluminous to peraluminous and are formed via (i) fractional crystallization of parental mafic magma with negligible crustal contamination, and (ii) melting of continental crust or assimilation and fractional crystallization (AFC) of mafic magma with significant crustal contribution. Rhyolites formed by extensive fractional crystallization are characterized by the presence of clinopyroxene phenocrysts, exhibit steep negative slopes in bivariate major oxides plots and weak to no Nb-Ta anomaly; these typically have temperature >900 ​°C. Rhyolites formed by significant crustal contribution are characterized by strong negative Nb-Ta anomalies, absence of clinopyroxene phenocrysts, and are likely to have a magma temperature <900 ​°C. Geochemical signatures suggest rhyolite melt generation in the plagioclase stability field with a minor fraction originating from lower crustal depths. A large part of the compositional variability in rhyolites, particularly the Sr-Nd-Pb-O isotope ratios, suggests a significant role of continental crust (upper crustal melting or AFC) in the evolution of these silicic rocks in the continental mafic LIPs. Image 1 • Composition of rhyolites of 12 Phanerozoic continental mafic LIPs are presented. • Rhyolites formed in plagioclase stability field with significant crustal contribution. • High-T rhyolites (>900 ​°C) formed by fractional crystallization of mafic magma. • Low-T rhyolites (<900 ​°C) formed via pure crustal melting or AFC of mafic magma. [ABSTRACT FROM AUTHOR]

The correlation of late Palaeozoic eruption centres situated at the northwestern margin of the Erzgebirge (Saxothuringian Zone, Germany) with the regional post-Variscan magmatism has as yet remained unresolved. Our study focuses on the petrography, geochemistry, and the formation age of the Obermühlbach volcano as one of these eruption centres. The outcropping and drilled, potassium-rich, volcanic rocks originate from a highly differentiated, calc-alkaline, peraluminous A-type granitic melt with intra-plate signature. The Obermühlbach tuff bear strong geochemical similarity to the Lower Permian Zeisigwald tuff in the near-by Chemnitz Basin. LA-ICP-MS U-Pb zircon dating of the Obermühlbach tuff and rhyolite clasts contained therein has yielded ages of 302.8 ± 3.8 Ma and 314.6 ± 2.4 Ma, respectively. Zircon saturation models suggest a temperature range of 750-800 °C for zircon crystallisation in the subvolcanic Obermühlbach rhyolites, and of ~840 °C in rhyolite clasts intercalated within the Obermühlbach tuff. The Obermühlbach tuff itself records zircon saturation temperatures in both aforementioned temperature ranges, based on different samples. The rhyolite clasts and the volcanic/sub-volcanic rocks of the Flöha Basin are similar in petrography and geochemistry. The new evidence allows a better understanding of the evolution of the Obermühlbach volcano and discloses its correlation with the regional Permo-Carboniferous magmatism. [ABSTRACT FROM AUTHOR]

The Alamdar rhyolite has been cropped out at the highest top of Mishow Mountain Ranges (i.e. Alamdar top), east of Tasouj. Considering that the rhyolite has been intruded the Kahar Formation, its Precambrian age is more probable. The constituent minerals are quartz, K-feldspar and rare plagioclase characterizing by crystalline to hyalo-crystalline, microlitic porphyric, perthitic, hyalo porphyric and flow textures. Magmatic series of the rocks are high K calc-alkaline and shoshonite. In the view of Al-index, they are peraluminous. The investigated rocks have been classified as A-type (A2 subgroup) granitoids. REE diagrams show high enrichment of LREE relative to HREE and MREE. Spider diagrams have positive anamolies of K, Nd, Rb and negative anomalies of Ta, Nb, and Ti indicating their likely crustal source generation. On the basis of discrimination diagrams they are formed related to Post-COLG tectonic setting. Extensional regimes following to continental collision between Northern lands with Gondwanian terrains during Ediacaran has been caused decompression melting of continental crust and the Alamdar rhyolite has been originated at the Mishow collisional zone.

Copyright of Geology & Resources is the property of Geology & Resources Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Jemez Mountains volcanic field (JMVF) is the site of the two voluminous, caldera-forming members of the Bandelier Tuff, erupted at 1·60 and 1·25 Ma, following a long and continuous pre-caldera volcanic history (∼10 Myr) in this region. Previous investigations utilizing whole-rock geochemistry identified complex magmatic processes in the two major pulses of pre-caldera magmatism including assimilation–fractional crystallization (AFC) and magma mixing. Here we extend the petrological investigation of the pre-caldera volcanic rocks into the micro-realm and use mineral chemistry and textural information to refine magma evolution models. The results show an increasing diversity of mineral populations as the volcanic field evolved. A range of plagioclase textures (e.g. sieved cores and rims) indicate disequilibrium conditions in almost all pre-caldera magmas ranging from andesite to rhyolite, reflecting plagioclase dissolution and regrowth. Coarsely sieved or dissolved plagioclase cores are explained by resorption via water-undersaturated decompression during upward migration from a deep melting, assimilation, storage and homogenization (MASH) zone. Plagioclase crystals with sieved rims are almost ubiquitous in dacite-dominated magmatism (La Grulla Plateau andesite and dacite erupted at ∼8–7 Ma, as well as Tschicoma Formation andesite, dacite and rhyolite at ∼5–2 Ma), reflecting heating induced by magma mixing. These plagioclase crystals often have An-poor cores that are chemically distinct from their An-rich rims. The existence of different plagioclase populations is consistent with two distinct amphibole groups that co-crystallized with plagioclase: a low-Al, low-temperature, high- f O2 group, and a high-Al, high-temperature, low- f O2 group. Calculation of melt Sr, Ba, La, and Ce concentrations from plagioclase core and rim compositions suggests that these chemical variations are largely produced by magma mixing. Multiple mafic endmembers were identified that may be connected by AFC processes in the MASH zone in the middle to lower crust. The silicic component in an early andesite-dominated magmatic system (Paliza Canyon andesite, dacite and rhyolite, 10–7 Ma) is represented by contemporaneous early rhyolite (Canovas Canyon Rhyolite). A silicic mush zone in the shallow crust is inferred as both the silicic endmember involved in the dacite-dominant magmatic systems and source of the late low-temperature rhyolite (Bearhead Rhyolite, 7–6 Ma). Recharging of the silicic mush by mafic melts can explain observed diversity in both mineral disequilibrium textures and compositions in the dacitic magmas. Overall, the pre-caldera JMVF magmatic system evolved towards cooler and more oxidized conditions with time, indicating gradual thermal maturation of local crust, building up to a transcrustal magmatic system, which culminated in 'super-scale' silicic volcanism. Such conditioning of crust with heat and mass by early magmatism might be common in other long-lived volcanic fields. [ABSTRACT FROM AUTHOR]

In the past two decades, the U.S. Geological Survey and the National Park Service have studied hydrothermal activity across the Yellowstone Plateau Volcanic Field (YPVF) to improve the understanding of the magmatic‐hydrothermal system and to provide a baseline for detecting future anomalous activity. In 2017 and 2018 we sampled water and gas over a large area in the southwest YPVF and used Landsat 8 thermal infrared data to estimate radiative heat flow. Most of the thermal activity in this region is in close proximity to the Yellowstone Caldera boundary. Springs and fumaroles discharge from a variety of lithologies, including some of the youngest rhyolites in the YPVF. Gas compositions and helium isotope ratios of most samples resemble those in other parts of the YPVF. The waters have meteoric origins, and tritium was detected in several samples. Thermal waters from some areas have compositions that plot along a line connecting thermal and nonthermal water endmember compositions. The thermal water endmember equilibrated at 160°C–170°C, lower than waters in Yellowstone's geyser basins. Heat discharged by springs and fumaroles originates from within the Yellowstone Caldera and is transported laterally by advection, mainly along the base of rhyolite flows that cover the inferred caldera boundaries. Plain Language Summary: The Yellowstone Plateau Volcanic Field has had three cataclysmic volcanic eruptions over the past ~2.1 million years. The youngest of these eruptions at 0.631 Ma resulted in the formation of the Yellowstone Caldera and was followed by several smaller eruptive episodes of large volume rhyolite flows up to ~70,000 years ago. The diversity of Yellowstone's hydrothermal system is unparalleled with more than 10,000 thermal features that have diverse chemical compositions. To improve the understanding of Yellowstone's magmatic‐hydrothermal system and to provide a baseline for detecting future anomalous activity, we sampled water and gas in southwest Yellowstone and analyzed satellite‐derived thermal infrared images. Most of the hot springs and fumaroles in the study area are near the Yellowstone Caldera boundary. The area is characterized by different rock types including some of the youngest rhyolites in Yellowstone. Whereas gas compositions mostly resemble those in other parts of Yellowstone, the chemical compositions of waters differ from those within the Yellowstone Caldera. The heat and gas discharged by springs and fumaroles originate from within the Yellowstone Caldera and are transported laterally, mainly along the base of rhyolite flows that cover the inferred Yellowstone Caldera boundary. Key Points: Hot springs and fumaroles discharge from a variety of lithologies in proximity to the Yellowstone Caldera boundaryThe thermal water endmember equilibrates with rhyolite at temperatures lower than in Yellowstone's geyser basinsHeat and gases discharged by springs and fumaroles originate in the Yellowstone Caldera and are transported laterally by advection [ABSTRACT FROM AUTHOR]

Crystalline domains in rhyolitic domes and coulees are commonly characterized by spherulites and lithophysae. Spherulites typically range from microscopic to a few centimeters in diameter. Larger spherulites, termed "megaspherulites," are rare but have been reported in the USA and Mexico. The uncommon nature of such structures supports the need for a study to explore the factors and special conditions that allow them to reach such a large size. In the Southern Puna of Argentina, El Viejo Coulee includes megaspherulites up to 4 m in diameter. We present observations from field work, petrography, scanning electron microscopy, bulk geochemistry, and Fourier transform infrared spectroscopy. The megaspherulites occur in obsidian lenses that differ in phenocryst content and composition from the foliated coherent facies that forms the rest of the coulee. The obsidian lacks vesicles and microlites and is unaltered. The megaspherulites comprise growth cones consisting of micropoikilitic texture where quartz encloses potassium feldspar. The growth cones are separated by interconal areas composed of lithophysae. We propose that the megaspherulites were formed above the glass transition temperature (Tg) and are the product of primary crystallization of rhyolitic melt. The exceptionally large size of the megaspherulites implies high diffusion rates which are favored by temperatures above Tg during crystallization. The large size also suggests scarcity of nucleation sites, which is consistent with the megaspherulites being hosted by unaltered microlite- and vesicle-free glass. The position of the obsidian lens at the base of the coulee may have played a critical role in maintaining the temperature above the Tg long enough to allow the crystallization of the megaspherulites. These conditions also favored crystallization in the most advanced stage where micropoikilitic texture replaced the fans of crystal fibers typical of spherulites. Crystallization of anhydrous quartz and feldspar in the growth cones led to the concentration of volatiles in the melt in the interconal areas, resulting in volatile exsolution and formation of vesicles that became nucleation sites for lithophysae. The study advances our understanding of some of the special processes that are involved in the cooling and solidification of rhyolitic magmas. Fundamentally, we find that the position of the obsidian at the base of the coulee was critically important because this position favored maintenance of the temperature above the Tg which, in turn, favored high diffusion rates. Also, the scarcity of nucleation sites in the obsidian melt allowed only a small number of spherulites to nucleate; those that nucleated therefore grew very large. The meter-scale megaspherulites may have taken ~ 55 years to create. [ABSTRACT FROM AUTHOR]

The 60 × 20-km Samosir resurgent dome within the 74-ka Toba Caldera features several clusters of rhyolitic lava domes. Because the previously known Tuk-Tuk and Samosir Fault lava domes occur near the base of a major resurgent dome fault, they appear associated with resurgent uplift, and dating them could provide constraints on the timing of resurgence. Towards that goal, we mapped and sampled the Tuk-Tuk and Samosir Fault lava domes, discovered two additional lava dome clusters in the uplifted interior of Samosir Island, then determined modal mineralogy, major and trace element geochemistry, and 40Ar/39Ar sanidine ages on several samples from each cluster. These quartz-bearing rhyolite lava domes have SiO2 contents ranging from ~ 70-76 wt%, crystallinities of 28-54%, and 40Ar/39Ar ages (~ 74-76 ka) that overlap with those of the Youngest Toba Tuff (YTT), ~ 74-75 ka. Our field observations and the remarkable similarity in mineralogy, geochemistry, and ages among the dome clusters and YTT support the interpretation that these domes represent remnant YTT magma that erupted shortly after the climactic YTT eruption. Later, during resurgence, these pre-resurgent lava domes were uplifted to their present locations, some near current lake level, others up to 440 m above lake level. [ABSTRACT FROM AUTHOR]

The rhyolite of Bodie Hills (California) is characterized compositionally and the geochronology of selected phases is studied. Sanidine (BHs) from the rhyolite is well suited as a 40Ar/39Ar reference material with high K/Ca and radiogenic yield. Intercalibration with GA1550 biotite from the Dromedary igneous complex (New South Wales, Australia) yields an age of 9.7946 ± 0.0031 Ma for BHs relative to an age of 98.79 ± 0.54 Ma for GA1550 and a calibration factor (R BHs/GA1550) of 0.096719 ± 0.000032. BHs is also intercalibrated with sanidines of the Taylor Creek Rhyolite (TCs; R TCs/BHs of 2.90874 ± 0.00067), Fish Canyon Tuff (FCs; R FCs/BHs of 2.88339 ± 0.00088), and rhyolite of Alder Creek (ACs; R ACs/BHs of 0.12028 ± 0.00024). These calibration factors yield ages of 28.344 ± 0.011 Ma, 28.099 ± 0.013 Ma, and 1.1809 ± 0.0024 Ma for TCs, FCs, and ACs, respectively, relative to GA1550. Full propagation of errors increases these uncertainties and that of BHs to ±0.9% of their ages. Calibration of BHs using the astronomically tuned age of FCs determined by Kuiper et al. (2008) yields an age of 9.8295 ± 0.0036 Ma. Stepwise heating of BHs reveals the same small, progressive increase in age across the age spectrum reported for FCs, ACs, and other potassium feldspars (e.g., Foland and Xu, 1990; Phillips et al., 2017). This increase is consistent with mass fractionation of argon during step heating and favors use of single-step fusion ages of all sanidines for monitor and calibration purposes. Zircons from the rhyolite of Bodie Hills are strongly zoned in U and Th, and U/Pb geochronologic analyses suggest multiple generations of zircon growth. The youngest ages indicate a crystallization age of 9.97 ± 0.08 Ma (2σ); arguably similar to the 40Ar/39Ar results when residence time is considered, but previous episodes of zircon growth began at least 400 ka prior to eruption. Precise (U - Th)/He thermochronology of these zircons is difficult because crystal-to-crystal variations in the magnitude and complexity of their U + Th zoning complicates accurate alpha ejection calculations. Replicate conventional (single-crystal) (U - Th)/He ages are more widely dispersed than predicted by analytical uncertainties, but laser ablation (U - Th)/He ages are more reproducible, with an inverse variance-weighted mean of 9.71 ± 0.58 Ma. • Characterization of the Bodie Hills sanidine standard with 40Ar/39Ar, U/Pb, and (UTh)/He geochronology and geochemistry. • Intercalibration of a high K/Ca, highly radiogenic 9.8-Ma sanidine standard with widely used 40Ar/39Ar mineral standards. • Further documentation of mass fractionation of Ar isotopes during stepwise heating argues against its use for standards. • SHRIMP U - Pb analyses of Bodie Hills zircons show at least 400 ka of pre-emplacement history similar to Fish Canyon Tuff. [ABSTRACT FROM AUTHOR]

Most continental flood basalt (CFB) provinces of the world contain silicic (granitic and rhyolitic) rocks, which are of significant petrogenetic interest. These rocks can form by advanced fractional crystallization of basaltic magmas, crustal assimilation with fractional crystallization, partial melting of hydrothermally altered basaltic lava flows or intrusions, anatexis of old basement crust, or hybridization between basaltic and crustal melts. In the Deccan Traps CFB province of India, the Barda and Alech Hills, dominated by granophyre and rhyolite, respectively, form the largest silicic complexes. We present petrographic, mineral chemical, and whole-rock geochemical (major and trace element and Sr–Nd isotopic) data on rocks of both complexes, along with 40Ar–39Ar ages of 69.5–68.5 Ma on three Barda granophyres. Whereas silicic magmatism in the Deccan Traps typically postdates flood basalt eruptions, the Barda granophyre intrusions (and the Deccan basalt flows they intrude) significantly pre-date (by 3–4 My) the intense 66–65 Ma flood basalt phase forming the bulk of the province. A tholeiitic dyke cutting the Barda granophyres contains quartzite xenoliths, the first being reported from Saurashtra and probably representing Precambrian basement crust. However, geochemical–isotopic data show little involvement of ancient basement crust in the genesis of the Barda–Alech silicic rocks. We conclude that these rocks formed by advanced (70–75 %), nearly-closed system fractional crystallization of basaltic magmas in crustal magma chambers. The sheer size of each complex (tens of kilometres in diameter) indicates a very large mafic magma chamber, and a wide, pronounced, circular-shaped gravity high and magnetic anomaly mapped over these complexes is arguably the geophysical signature of this solidified magma chamber. The Barda and Alech complexes are important for understanding CFB-associated silicic magmatism, and anorogenic, intraplate silicic magmatism in general. [ABSTRACT FROM AUTHOR]

Highlights • Rhyolites with crystallization ages of 906 ± 7 Ma and 908 ± 4 Ma were indentified in the Tongbai orogen. • The studied rhyolites are high-temperature, ferroan, A-type magmatism and the magmatic zircons therein have consistent low-δ18O values. • The low-δ18O A-type magmas indicates a back-arc rift of a Grenvillian accretionary orogen in the northern part of the Yangtze Block at ca. 900 Ma. Abstract An integrated study of zircon U–Pb geochronology and O–Hf isotope compositions, and whole-rock geochemistry was carried out for Dashimen rhyolites from the Tongbai orogen in the northern Yangtze Block. Zircon grains from two rhyolite samples show oscillatory zoning and moderate U (498–1612 and 216–668 ppm) and Th (319–1144 and 161–452 ppm) contents with relatively high Th/U ratios (0.57–0.75 and 0.50–1.31), indicating their magmatic origin. Zircon U–Pb dating yielded consistent U–Pb ages of 906 ± 7 Ma (2σ; MSWD = 0.48) and 908 ± 4 Ma (2σ; MSWD = 0.68), representing the formation ages of the Dashimen rhyolites. The Dashimen rhyolites have relatively high SiO 2 (74.85–76.56 wt%), K 2 O (5.40–6.56 wt%) and Fe 2 O 3 T (1.61–2.33 wt%), and moderate Al 2 O 3 (11.48–12.32 wt%) and Na 2 O (1.76–2.47 wt%), but low MgO (0.15–0.24 wt%) and CaO (0.08–0.10 wt%) contents. They show strong enrichments of almost all incompatible elements, except for the notable depletions in Ba, Sr, Eu, and P. The volcanic rocks have high zircon saturation temperatures of 846 to 876 °C with an average of 862 °C. These features suggest that the Dashimen rhyolites are high-temperature, ferroan, A-type magmatism. The zircons from the two studied samples show δ18O values of 3.6 to 5.0‰ and 3.9 to 4.5‰ with weighted averages of 4.30 ± 0.18‰ and 4.23 ± 0.10‰, respectively. These δ18O values are obviously lower than those of the normal mantle zircons and thus suggest the zircons crystallized from low-δ18O magmas. The rhyolites have negative whole-rock ε Nd (t) (−2.11–−0.28) and subtly positive zircon ε Hf (t) (0.01–3.35) values, with corresponding two stage depleted mantle model ages of 1.73–1.58 Ga and 1.69–1.66 Ga, respectively. The low-δ18O magmas were therefore suggested to be generated by re-melting of meteoric-hydrothermally altered continental crustal rocks. The finding of the high-temperature, ferroan, and low-δ18O A-type Dashimen rhyolites indicates that there existed a back-arc rift of a Grenvillian accretionary orogen in the northern part of the Yangtze Block. [ABSTRACT FROM AUTHOR]

The inclusions of a silicate melt were investigated in quartz insets of the extrusive rhyolite collected at Bazman Cenozoic volcano (Iran) and associated with the process of recent subduction. Low temperatures of the silicate melt along with high concentrations of water in the melt are ascertained. The microelemental composition of the melt showed a similarity to acidic melts of island–arc formations. [ABSTRACT FROM AUTHOR]

Extensive silicic lava (flood rhyolite) constitutes part of the mid –Tertiary Paisano Volcano shield. This lava, borderline peralkaline quartz trachyte/rhyolite, forms part of a sequence of peralkaline rhyolite – quartz trachyte – trachyte produced as eruptions tapped deeper portions of underlying plutons. Flood rhyolite lava extended as far as 20 km from dikes of the eruptive center of the volcano, creating flows as thick as 100 m. Flood rhyolite was nearly aphyric to sparsely porphyritic, relatively hot (~911 °C) and erupted over a topographically subdued region, forming two lobes that extended north-northeast and southeast from a highland of previously-erupted rhyolite domes. Flood rhyolite extrusion followed eruption of a local ignimbrite, which filled valleys, flattening topography. Successive silicic flows off-lapped each other away from the volcano. Flood rhyolite eruption was followed by a second eruptive sequence that contained coarsely-porphyritic mafic trachyte lava. Silicic lava was most-likely generated by filter pressing from mush zones of mafic plutons. Glomeroporphyritic trachytes of the volcano are mixed rocks, silicic lava incompletely segregated from entrained fragments of mafic plutons. Continued evolution of quartz trachyte/low-silica rhyolite to peralkaline rhyolite was dominated by fractionation of alkali feldspar. • Extensive silicic lava of Paisano Volcano flowed up to 20 km from dike vents, aided by rapid eruption from volcanic highlands. • An ignimbrite erupted prior to silicic lava helped extend lava flow by filling valleys. • Trachyte magma was generated by filter pressing from "mush" of mafic plutons. • Quartz trachyte/rhyolite magma evolved from trachyte by fractionation dominated by alkali feldspar. • Glomeroporphyritic trachyte contains clots of plagioclase-cpx-FeTi oxides that represent entrained fragments of cogenetic mafic plutons. [ABSTRACT FROM AUTHOR]

The West Junggar of the western Central Asian Orogenic Belt is one of the typical regions in the term of ocean subduction, contraction and continental growth in the Late Paleozoic. However, it is still controversial on the exact time of ocean‐continent transition so far. This study investigates rhyolites with columnar joint in the West Junggar for the first time. Based on zircon U‐Pb dating, we determined that the ages of the newly‐discovered rhyolites are between 303.6 and 294.5 Ma, belonging to Late Carboniferous–Early Permian, which is the oldest rhyolite with columnar joint preserved in the world at present. Geochemical results show that the characteristics of the major element compositions include a high content of SiO2 (75.78–79.20 wt%) and a moderate content of Al2O3 (12.21–13.19 wt%). The total alkali content (K2O + Na2O) is 6.14–8.05 wt%, among which K2O is 2.09–4.72 wt% and the rate of K2O/Na2O is 0.38–3.05. Over‐based minerals such as Ne, Lc, and Ac do not appear. The contents of TiO2 (0.09–0.24 wt%), CaO (0.15–0.99 wt%) and MgO (0.06–0.18 wt%) are low. A/CNK=0.91–1.68, A/NK=1.06–1.76, and as such, these are associated with the quasi‐aluminum‐weak peraluminous high potassium calc‐alkaline and some calc‐alkaline magma series. These rhyolites show a significant negative Eu anomaly with relative enrichment of LREE and LILE (Rb, Ba, Th, U, K) and depletion of Sr, HREE and HFSE (Nb, Ta, Ti, P). These rhyolites also have the characteristics of an A2‐type granite, similar to the Miaoergou batholith, which indicates they both were affected by post‐orogenic extension. Combining petrological, zircon U‐Pb dating and geochemical characteristics of the rhyolites, we conclude that the specific time of ocean‐continent transition of the West Junggar is the Late Carboniferous–Early Permian. [ABSTRACT FROM AUTHOR]

Highlights • 2.61 Ga intraplate magmatism occurred in the East Sarmatia. • Silicic melt for the rhyolites and granites formed from metapelite-TTG mixture. • Sarmatia, Pilbara, and Kaapvaal Cratons were a single supercontinent Vaalbara. Abstract A 2.61 Ga intraplate magmatism took place locally within the Kursk Domain of the Eastern Sarmatia forming a volcanic-plutonic association of rhyolites and granites. The zircon Lu-Hf and Sm-Nd whole rocks isotope data indicate the crustal source heterogeneity of these Neoarchaean intraplate granitoids. Their protoliths were dominated by Palaeoarchaean metapelites and Mesoarchaean TTG associations. The Neoarchaean rhyolites of the Kursk Domain are characterized by the high crystallization temperatures of c. 900 °C according to the data of mineral geothermobarometry and geochemistry of zircons (TiQ and TiZr). The magmatic chambers were located at a depth of no more than 7 km. The silicic melt, parental for these 2.61 Ga old rhyolites and granites could be formed as a result of 20% dehydration melting of the metapelite-TTG mixture in equilibrium with the Ilm-Bt-Opx-Pl restite at a pressure of no more than 4 kbar. The Atamansky Complex granites crystallized at deeper levels and contain an admixture of Opx-Pl restite or cumulus component. This caused their geochemical differences from rhyolites when these phases were removed during the melts migration to higher levels of the crust. The Atamansky granites are considered as intermediate chambers where differentiation of the initial silicic magmas took place with the formation of the residual rhyolitic melts. The heat source could be a mafic plume magmatism, known in the Eastern Sarmatia. There, in intraplate settings, hot deep plume generated mafic magmas intruded into the crust forming shallow interim chambers; the latter initiated melting of the felsic host-rocks (predominantly metapelites and TTG) in the upper parts of the crust producing the silicic volcanic-plutonic association. The simultaneous 2.61 Ga old granitoid intraplate magmatism in the Eastern Sarmatia and Dharwar Craton, caused by the mafic heat source, adds one more argument in favor of an assumption that the Sarmatia, Pilbara, Kaapvaal and, possibly, Dharwar Cratons composed a single supercontinent Vaalbara in the Neoarchaean. The Dharwar Craton, perhaps, was at the periphery of the Vaalbara supercontinent next to the Eastern Sarmatia. [ABSTRACT FROM AUTHOR]

Abstract The Sergipano Fold Belt is a Neoproterozoic orogen exposed in the southern Borborema Province (Northeast Brazil), which is interpreted as the result of the oblique convergence process between the São Francisco-Congo block and smaller crustal fragments. The Nicolau-Campo Grande Complex is the metavolcanic-sedimentary portion of the Jirau do Ponciano Dome, an important basement inlier within this collisional belt. Whole-rock-geochemical major and trace-element data of major and trace elements from the metavolcanic rocks of the Nicolau-Campo Grande Complex indicate basaltic-andesite, andesitic, rhyodacitic, and rhyolitic compositions. Rare earth element and trace elements show the typical signature of magmatic arc rocks with negative Nb, Ta, P, and Ti anomalies. New U-Pb zircon data from amphibolite and hornblende-biotite paragneiss samples from the complex confirm the existence of a Paleoproterozoic zircon population of a Paleoproterozoic age of approximately ca. 2054 Ma with Archean inheritance ranging in age between 2779 and 3324 Ma. A maximum sedimentation age of 2028 Ma is constrained by the youngest zircon grain in the hornblende-biotite paragneiss. Zircon U-Pb data from the metarhyolite and rhyodacites indicate Paleoproterozoic ages of ca. 2061 and 2074 Ma, respectively, interpreted as their crystallization age. Nd isotopic data in the metarhyolite and rhyodacites indicate Nd T DM ages between 2.54 and 3.07 Ga and 87Sr/86Sr (2061Ma) values from 0.71396 to 0.72351. Based on these data, we suggest that the probable source area of the metavolcanic-sedimentary complex is a Paleoproterozoic magmatic arc that was exhumed and covered by the paleobasins of the Macururé Domain in the northeast portion of the Sergipano Fold Belt. Highlights • Isotope geochemistry is used to understand the source of supracrustal rocks of the Jirau do Ponciano Dome, Borborema Province. • Volcanic magmatism occurred at around c. 2.0 Ga, coeval to detrital zircon major population (ca. 2054 Ma), with inheritance of Archean crust. • Studied rocks are derived from an exhumed Paleoproterozoic magmatic arc covered by paleobasins that comprises this portion of the Western Gondwana. [ABSTRACT FROM AUTHOR]

Abstract The new data coupled with those previously published highlight that, in the last 2 Ma, the Tromen Volcanic System (TVS) erupted transitional, alkali and rhyolitic lavas which built the Tilhué, Chapúa-Maipo-El Puente, Coyocho-Wayle and El Tromen volcanic groups. Four partial melting events have been identified: first at 2.10 ± 0.13 Ma, second at 1.44 ± 0.08 Ma, third at 1.04 ± 0.06 Ma and the last at 0.488 ± 0.007 Ma. Partial melting rates of the TVS sources are about 7% and constant, where first events affected simultaneously a shallower spinel-bearing mantle and a lower continental crust, and later ones a deeper garnet-bearing mantle. The melting of shallower, spinel-bearing, mantle released melts with low and middle-Ni, while the melting of deeper, garnet-bearing mantle, released relatively high-Ni melts. The lower continental crust affected by the first partial melting event could have been of sedimentary origin, thus producing the peraluminous Tilhué evolved lavas. Highlights • New K-Ar ages constrain the timing of the Tromen Volcanic System (TVS). • The TVS was built from about 2.10 ± 0.13 to 0.007 ± 0.002 Ma. • The TVS magmas result from at least four partial melting events at 2.10, 1.44, 1.04 and 0.488 Ma. • The first partial melting affected a shallower spinel-bearing mantle and a lower continental crust. • Subsequent partial melting events affected a deeper and deeper garnet-bearing mantle. [ABSTRACT FROM AUTHOR]

The Mono Craters are an overlapping chain of at least 28 domes and coulees located south of Mono Lake, east central California, and represent the most recent eruptions of high‐silica rhyolite magma in the Mono Lake‐Long Valley volcanic region. Regionally widespread tephra fall deposits from the Mono Craters serve as important chronostratigraphic markers for correlations of late Quaternary terrestrial archives in the western United States. A well‐resolved eruption chronology for the Mono Craters is thus not only critical for volcanic hazard considerations but also for paleoclimatic and paleomagnetic studies. Here we constrain the timing of early Mono Craters volcanism using ion microprobe 238U‐230Th dating of unpolished crystal faces of autocrystic zircon and allanite microphenocrysts, which samples the final stage of crystallization prior to eruption. The stratigraphically oldest domes (biotite‐bearing rhyolites) yield 238U‐230Th isochron dates between ca. 42 and ca. 19 ka and are unambiguously linked to dated tephras in the Wilson Creek formation of ancestral Mono Lake via coupled 238U‐230Th geochronology and titanomagnetite geochemistry. The second oldest set of domes (orthopyroxene‐bearing rhyolites) have overlapping 238U‐230Th isochron dates that are within uncertainty of published K/Ar and 40Ar/39Ar dates for the fayalite‐bearing rhyolite domes, suggesting a period of intense effusive activity for the Mono Craters near the Pleistocene‐Holocene boundary. Our new and previously published 238U‐230Th dates for tephras in the Wilson Creek formation provide robust geochronologic constraints for the controversial geomagnetic excursion recorded in the Wilson Creek formation. Key Points: U‐Th isochron dating of zircon and allanite crystal faces extend the chronology of Mono Craters effusive volcanism well into the late PleistoceneCombined U‐Th geochronology and titanomagnetite chemistry links dated tephras in the Wilson Creek formation to proximal dome equivalents in the Mono CratersAge and stratigraphic position of the Laschamp geomagnetic excursion in the Wilson Creek formation is confirmed [ABSTRACT FROM AUTHOR]

We report field observation, age, chemical (major and trace elements), and isotope (Sr‐Nd‐Pb) data for felsic volcanic rocks from Central Afar and adjacent western margin. Investigated volcanic rocks are dominantly rhyolites with minor trachytes, and they are geochemically similar. Their ages range from ~30 Ma (prerift stage), ~20 Ma (early synrift), ~8–4 Ma (main thinning event) to ~2.5–0.1 Ma (late synrift/continental breakup), representing the entire volcanic‐tectonic events that occurred episodically. Major element variations are consistent with fractionation of gabbroic cumulates. Trace element and isotope data preclude an origin by crustal anatexis; the rhyolites are rather genetically linked to the associated basalts and variously contaminated by the crust during differentiation of magmas. Chemical and isotopic data of the rhyolites support an origin by open system differentiation at deep crustal levels (hot wall rock and high r = rate of assimilation/rate of crystallization) and shallow crustal levels (cold wall rock and low r) with a change in the composition of the assimilated material from lower crustal to upper crustal type. Assimilation appears to decrease in recent times with Quaternary rhyolites, emplaced nearby the active magmatic segments in Afar, which exhibit the isotopic compositions closest to original mantle signature. This is compatible with a crust below the active magmatic segments resulting from important addition of juvenile basic magmas. Such results and interpretations provide actual constrains to suggest that the present‐day stage is probably very close to continental breakup, which will be achieved once the continental crust will be entirely replaced by new magmatic crust. Key Points: The origin of rhyolite over the last 30 Ma has been addressedAn attempt was made to understand the evolution of crustal contamination through timeThe relations between rhyolite genesis and rifting have been constrained [ABSTRACT FROM AUTHOR]

Abstract Precise timing and constraints for magma source(s) are critical to understand the post-subduction tectonomagmatic evolution of the world's largest Cenozoic Silicic Large Igneous Province in western Mexico. We provide in-situ zircon U–Pb ages and Hf isotope compositions of rhyolitic ignimbrites exposed in the Palmarejo and Guazapares at the northwestern extremity of Sierra Madre Occidental. Four rhyolite ignimbrite samples from Palmarejo yielded zircon weighted mean U–Pb ages between 23 and 24 Ma. However, five individual analyses from one sample yielded the oldest age of 25.09 ± 0.41 Ma (MSWD = 1.7, n = 5). A rhyolitic tuff from the Guazapares district yielded older individual dates varying from 25.7 to 28.6 Ma with a main population yielding a weighted mean age of 27.31 ± 0.36 Ma. Zircon U–Pb ages suggest that the ignimbrite flare-up in southwestern Chihuahua remained restricted to the Early Middle Oligocene to Early Miocene. We suggest that the zircon U–Pb dates >24 Ma (particularly from Guazapares) are the antecrystic zircons included from the underlying older ignimbrites. The zircon U–Pb dates of 25–28 Ma are related to the culmination of syn -extensional first ignimbrite flare-up and bimodal volcanism started as early as 35 Ma. The first ignimbrite flare-up is possibly resulted from the detachment of the leading edge of the Farallon slab around 35–28 Ma. The younger age of 24–23 Ma from Palmarejo can be correlated to the second episode of ignimbrite flare-up erupted during the pervasive regional extension, normal faulting and onset of formation of metamorphic core complexes. This second flare-up is resulted by the subsequent events of break off/rollback of the Farallon plate. The positive Hf isotope composition (εHf (t) = +1.0 to +5.8) and concomitant mafic volcanism suggest partial melting of subcontinental lithospheric mantle and the overlying Laramide crust by upwelling of decompressing asthenosphere during post-Laramide regional extension. This interpretation is consistent with the successive detachments, fragmental removal and/or rollback of the leading edges of the Farallon slab beneath the western continental margin of North America. We did not find any xenocrystic zircon inheritance neither from the Laramide plutonic basement/roots of the Jurassic Guerrero terrane nor from the Proterozoic North American crust. However, zircon inheritance of Laramide age has been reported from the Guazapares district. Partial melting of Laramide basement was possibly facilitated by the heat advection and ponding of subcontinental lithospheric mantle-related magmas in the crust during the Cenozoic regional extension. Highlights • Zircon U–Pb ages and Hf isotope compositions of ignimbrites from southwestern Chihuahua, Mexico. • Rhyolite ignimbrite eruption has been restricted between 28 and 23 Ma. • Partial melting of lithospheric mantle and Laramide crust by upwelling asthenospheric magmas. • Cenozoic ignimbrites and Late Cretaceous -Tertiary granodiorites share similar magma sources. [ABSTRACT FROM AUTHOR]

In the southwestern Okinawa Trough, a cluster of approximate 70 submarine volcanoes is located at the cross back‐arc volcanic trail (CBVT), with the eruptive products dominated by rhyolites. New whole‐rock major and trace element and Sr–Nd–Pb–O isotopic data and previously available geochemistry data of volcanic rocks from this region are presented to determine the petrogenesis of these rhyolites. The rhyolites have high SiO2 (>70.01 wt.%), K2O + Na2O (6.71–7.16 wt.%) contents and differentiation index (DI) values (DI > 93), and are metaluminous to weakly peraluminous (A/CNK = 0.99–1.11) and medium‐K calc‐alkaline in composition. The relatively low 104*Ga/Al (2.06–2.17) and FeO*/MgO ratios (4.50–6.62), as well as Zr (91–174 ppm) and Zr + Ce + Nb + Y (175–271) contents suggest that the rhyolites, which contain hornblende, are generally similar to those of typical highly fractionated I‐type granitoids. The rhyolites show arc‐related features such as enrichment in LILEs (Rb, Ba, K), Th, U, Pb, and LREEs ((La/Yb)N = 6.21–6.74) and strong depletion in HFSEs (Nb, Ta, P, Ti) with both nearly identical and more enriched isotopic compositions, including εNd (from −3.2 to −3.5), 87Sr/86Sr ratios (0.705552 to 0.705713), δ18O values (+8.1‰ to +8.6‰), and Pb isotopic compositions (206Pb/204Pb = 18.568–18.589, 207Pb/204Pb = 15.641–15.656, and 208Pb/204Pb = 38.848–38.904). Based on these characteristics, we propose that subduction‐related basalt magma and crust‐derived magma mixed and homogenized within a shallow magma chamber with a homogeneous "base‐level" isotopic signature of >0·7055 (87Sr/86Sr) and > −3 (εNd). This magma would have then experienced the extensive fractional crystallization of minerals, including plagioclase, hornblende, apatite, sphene, and Fe–Ti oxides, to form the CBVT rhyolites. Our geochemical interpretation of the existence of a long‐lived, convecting magma chamber beneath the CBVT is also consistent with seismic tomography results. [ABSTRACT FROM AUTHOR]