Статті в журналах: "Rhyolite-melts"

1

Baker, L. L., and Malcolm J. Rutherford. "Sulfur diffusion in rhyolite melts." Contributions to Mineralogy and Petrology 123, no. 4 (May 20, 1996): 335–44. http://dx.doi.org/10.1007/s004100050160.

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2

Bagdassarov, N. S., D. B. Dingwell, and S. L. Webb. "Viscoelasticity of crystal- and bubble-bearing rhyolite melts." Physics of the Earth and Planetary Interiors 83, no. 2 (May 1994): 83–99. http://dx.doi.org/10.1016/0031-9201(94)90066-3.

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3

Neuville, Daniel R., Philippe Courtial, Donald B. Dingwell, and Pascal Richet. "Thermodynamic and rheological properties of rhyolite and andesite melts." Contributions to Mineralogy and Petrology 113, no. 4 (1993): 572–81. http://dx.doi.org/10.1007/bf00698324.

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4

Prokofiev, V. Yu, V. B. Naumov, A. E. Roman’ko, A. L. Balashova, P. Yu Plechov, and N. A. Imamverdiyev. "Low-temperature acidic melts of Bazman volcano (Iran)." Доклады Академии наук 485, no. 5 (May 23, 2019): 614–18. http://dx.doi.org/10.31857/s0869-56524855614-618.

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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.

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5

Gualda, G. A. R., M. S. Ghiorso, R. V. Lemons, and T. L. Carley. "Rhyolite-MELTS: a Modified Calibration of MELTS Optimized for Silica-rich, Fluid-bearing Magmatic Systems." Journal of Petrology 53, no. 5 (January 25, 2012): 875–90. http://dx.doi.org/10.1093/petrology/egr080.

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6

Donaldson, C. H. "Forsterite dissolution in superheated basaltic, andesitic and rhyolitic melts." Mineralogical Magazine 54, no. 374 (March 1990): 67–74. http://dx.doi.org/10.1180/minmag.1990.054.374.06.

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AbstractDissolution rates of small forsterite spheres in superheated melts of basalt, andesite and rhyolite composition have been measured at 1300°C, atmospheric pressure. The rate is constant (83 µm hr−1) in the basalt, regardless of run duration. In the andesite the initial dissolution rate is 200µm hr−1, followed by a decrease to a constant value of 16µmhr−1 in 2–3 hours. Dissolution rate in the rhyolite decreases from an initial value of 1.7 to <0.1 µmhr−1 over 280 hours and never reaches a constant rate. Once the rate of dissolution has become constant, the film of contaminated melt that forms in melt about a crystal does not thicken with time, indicating attainment of a steady-state condition. Steady state is attributed to natural convection arising from the difference in density between the film of contaminated melt surrounding a crystal and that beyond. The density difference is approximately 2% of the density of the rock melt.

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7

Gardner, James E., and Richard A. Ketcham. "Bubble nucleation in rhyolite and dacite melts: temperature dependence of surface tension." Contributions to Mineralogy and Petrology 162, no. 5 (April 10, 2011): 929–43. http://dx.doi.org/10.1007/s00410-011-0632-5.

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8

Gardner, James E., Sahand Hajimirza, James D. Webster, and Helge M. Gonnermann. "The impact of dissolved fluorine on bubble nucleation in hydrous rhyolite melts." Geochimica et Cosmochimica Acta 226 (April 2018): 174–81. http://dx.doi.org/10.1016/j.gca.2018.02.013.

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9

Chamberlain, K. J., J. Barclay, K. J. Preece, R. J. Brown, and J. P. Davidson. "Lower Crustal Heterogeneity and Fractional Crystallization Control Evolution of Small-volume Magma Batches at Ocean Island Volcanoes (Ascension Island, South Atlantic)." Journal of Petrology 60, no. 8 (August 1, 2019): 1489–522. http://dx.doi.org/10.1093/petrology/egz037.

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Abstract Ocean island volcanoes erupt a wide range of magmatic compositions via a diverse range of eruptive styles. Understanding where and how these melts evolve is thus an essential component in the anticipation of future volcanic activity. Here we examine the role of crustal structure and magmatic flux in controlling the location, evolution and ultimately composition of melts at Ascension Island. Located in the South Atlantic, Ascension Island is an ocean island volcano that has produced a continuum of eruptive compositions from basalt to rhyolite in its 1 Myr subaerial eruptive history. Volcanic rocks broadly follow a silica-undersaturated subalkaline evolutionary trend, and new data presented here show a continuous compositional trend from basalt through trachyte to rhyolite. Detailed petrographic observations are combined with in situ geochemical analyses of crystals and glass, and new whole-rock major and trace element data from mafic and felsic pyroclastic and effusive deposits that span the entire range in eruptive ages and compositions found on Ascension Island. These data show that extensive fractional crystallization is the main driver for the production of felsic melts for Ascension Island, a volcano built on thin, young, oceanic crust. Strong spatial variations in the compositions of erupted magmas reveal the role of a heterogeneous lower crust; differing degrees of interaction with a zone of plutonic rocks are responsible for the range in mafic lava compositions, and for the formation of the central and eastern felsic complexes. A central core of nested, small-scale plutonic, or mush-like, bodies inhibits the ascent of mafic magmas, allowing sequential fractional crystallization within the lower crust, and generating felsic magmas in the core of the island. There is no evidence for magma mixing preserved in any of the studied eruptions, suggesting that magma storage regions are transient, and material is not recycled between eruptions.

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10

Macdonald, R., and B. Bagiński. "The central Kenya peralkaline province: a unique assemblage of magmatic systems." Mineralogical Magazine 73, no. 1 (February 2009): 1–16. http://dx.doi.org/10.1180/minmag.2009.073.1.1.

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The review focuses on the evolution of five contiguous peralkaline salic complexes in the south-central Kenya Rift Valley, stressing new developments of general significance to peralkaline magmatism. The complexes have evolved dominantly by combinations of fractional crystallization and magma mixing; volatile-melt interactions, remobilization of plutonic rocks and crystal mushes, and carbonate-silicate liquid immiscibility have been additional petrogenetic processes. Geochemical and experimental studies have shown that pantelleritic magmas can be generated by fractional crystallization of trachyte and high-silica rhyolite. Melts of comenditic composition were also formed by fractionation of trachyte but also locally by partial meltingof syenites. Studies of apparent partition coefficients have provided some of the first data on element distribution between phenocrysts and peralkaline silicic melts. Compositional zonation has been ubiquitous in the complexes, probably a result of the very low viscosity of the magmas.

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11

Wiesmaier, S., D. Morgavi, C. Renggli, D. Perugini, C. P. De Campos, K. U. Hess, W. Ertel-Ingrisch, Y. Lavallée, and D. B. Dingwell. "Magma mixing enhanced by bubble segregation." Solid Earth Discussions 7, no. 2 (April 22, 2015): 1469–515. http://dx.doi.org/10.5194/sed-7-1469-2015.

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Abstract. That rising bubbles may significantly affect magma mixing paths has already been demon strated by analogue experiments. Here, for the first time, bubble-advection experiments are performed employing volcanic melts at magmatic temperatures. Cylinders of basaltic glass were placed below cylinders of rhyolite glass. Upon melting, interstitial air formed bubbles that rose into the rhyolite melt, thereby entraining tails of basaltic liquid. The formation of plume-like filaments of advected basalt within the rhyolite was characterized by microCT and subsequent high-resolution EMP analyses. Melt entrainment by bubble ascent appears to be an efficient mechanism for mingling volcanic melts of highly contrasting compositions and properties. MicroCT imaging reveals bubbles trailing each other and multiple filaments coalescing into bigger ones. Rheological modelling of the filaments yields viscosities of up to 2 orders of magnitude lower than for the surrounding rhyolitic liquid. Such a viscosity contrast implies that bubbles rising successively are likely to follow this pathway of low resistance that previously ascending bubbles have generated. Filaments formed by multiple bubbles would thus experience episodic replenishment with mafic material. Inevitable implications for the concept of bubble advection in magma mixing include thereby both an acceleration of mixing because of decreased viscous resistance for bubbles inside filaments and non-conventional diffusion systematics because of intermittent supply of mafic material (instead of a single pulse) inside a material. Inside the filaments, the mafic material was variably hybridised to andesitic through rhyolitic composition. Compositional profiles alone are ambiguous, however, to determine whether single or multiple bubbles were involved during formation of a filament. Statistical analysis, employing concentration variance as measure of homogenisation, demonstrates that also filaments appearing as single-bubble filaments are likely to have experienced multiple bubbles passages. In cases where bubbles have been essential for magma mixing, standard diffusion analysis may thus be inadequate for constraining timescales. However, data analysis employing concentration variance relaxation permits the distinction of conventional single-pulse filaments from multiple bubble ascent advection in natural samples, demonstrating yet another powerful application of this novel petrological tool.

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12

Larsen, Jessica F., and James E. Gardner. "Experimental constraints on bubble interactions in rhyolite melts: implications for vesicle size distributions." Earth and Planetary Science Letters 180, no. 1-2 (July 2000): 201–14. http://dx.doi.org/10.1016/s0012-821x(00)00166-7.

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13

Gardner, James E., and James D. Webster. "The impact of dissolved CO 2 on bubble nucleation in water-poor rhyolite melts." Chemical Geology 420 (January 2016): 180–85. http://dx.doi.org/10.1016/j.chemgeo.2015.11.017.

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14

González-García, Diego, Harald Behrens, Maurizio Petrelli, Francesco Vetere, Daniele Morgavi, Chao Zhang, and Diego Perugini. "Water-enhanced interdiffusion of major elements between natural shoshonite and high-K rhyolite melts." Chemical Geology 466 (September 2017): 86–101. http://dx.doi.org/10.1016/j.chemgeo.2017.05.023.

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15

Pundir, Shailendra, Vikas Adlakha, Santosh Kumar, and Saurabh Singhal. "Closure of India–Asia collision margin along the Shyok Suture Zone in the eastern Karakoram: new geochemical and zircon U–Pb geochronological observations." Geological Magazine 157, no. 9 (February 24, 2020): 1451–72. http://dx.doi.org/10.1017/s0016756819001547.

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AbstractNew whole-rock geochemical analyses along with laser ablation multi-collector inductively coupled plasma mass spectrometry U–Pb zircon ages of the granite–rhyolite from the Karakoram Batholith, exposed along the Shyok Valley, NW India, have been performed to understand the timing and geochemical evolution of these magmatic bodies and their implications for the geodynamic evolution of the Karakoram Batholith. New geochronological data on granites and rhyolites along with previously published geochronological data indicate that the Karakoram Batholith evolved during Albian time (~110–100 Ma) owing to the subduction of Tethys oceanic lithosphere along the Shyok Suture Zone. This region witnessed a period of no magmatism during ~99–85 Ma. Following this, the Kohistan–Ladakh arc and Karakoram Batholith evolved as a single entity in Late Cretaceous and early Palaeogene times. Late Cretaceous (~85 Ma) rhyolite intrusions within the Karakoram Batholith show calc-alkaline subduction-related signatures with a highly peraluminous nature (molar A/CNK = 1.42–1.81). These intrusions may have resulted from c. ~13.8 % to ~34.5 % assimilation of pre-existing granites accompanied by fractional crystallization during the ascent of the magma. The contamination of mantle wedge-derived melts with crust of the active continental margin of the Karakoram most likely enhanced the high peraluminous nature of the rhyolite magma, as has been constrained by assimilation fractional crystallization modelling. Two granite samples from the contact of the Shyok Metamorphic Complex and Karakoram Batholith indicate that the post-collisional Miocene magmatism was not only confined along the Karakoram Fault zone but also extends ~30 km beyond the Shyok–Muglib strand.

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16

Shahbazi, Hossein, Yasaman Taheri Maghami, Hossein Azizi, Yoshihiro Asahara, Wolfgang Siebel, Mohammad Maanijou, and Ali Rezai. "Zircon U–Pb ages and petrogenesis of late Miocene adakitic rocks from the Sari Gunay gold deposit, NW Iran." Geological Magazine 158, no. 10 (April 26, 2021): 1733–55. http://dx.doi.org/10.1017/s0016756821000297.

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AbstractLate Miocene volcanic rocks host the Sari Gunay epithermal gold deposit in NW Iran. These rocks are located within the Hamedan–Tabriz volcanic belt and occupy the northwestern part of the Sanandaj–Sirjan zone (SaSZ). The volcanic rocks span in composition from latite to dacite and rhyolite. Plagioclase, hornblende, biotite and quartz are the main phenocrysts in a fine-grained and glassy matrix. Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating yielded crystallization ages of 10.10 ± 0.01 Ma and 11.18 ± 0.14 Ma for rhyolite and dacite, respectively. High ratios of Sr/Y (> 20) and La/Yb (> 20), high contents of Sr (≥ 400 ppm), low contents of MgO (≤ 6 wt%), Y ≤ 18 ppm (c. 16.5 ppm), Yb ≤ 1.9 ppm (c. 1.53 ppm) and weak negative Eu anomalies (Eu*/Eu c. 0.81) are compatible with a high-silica adakitic signature of the rocks. Regarding the location of the study area nearly 100 km from the Zagros suture zone, we argue that delamination of lithospheric mantle beneath the SaSZ has played a key role in the development of the adakitic rocks in a post-collision tectonic regime. The adakitic melts are suggested to have formed by partial melting of delaminated continental lithosphere and/or lower crustal amphibolite following the collision of the Arabian and Iranian plates.

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17

Baker, Don R. "Interdiffusion of hydrous dacitic and rhyolitic melts and the efficacy of rhyolite contamination of dacitic enclaves." Contributions to Mineralogy and Petrology 106, no. 4 (February 1991): 462–73. http://dx.doi.org/10.1007/bf00321988.

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18

Kwak, Ho-Young, and Hyup Yang. "Homogeneous nucleation of nano size H2O bubbles and their growth to micro size in rhyolite melts." Geosciences Journal 23, no. 3 (November 27, 2018): 425–38. http://dx.doi.org/10.1007/s12303-018-0059-3.

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19

Pierosan, Ronaldo, Evandro F. Lima, Lauro V. S. Nardi, Cristina P. de Campos, Artur C. Bastos Neto, José M. T. M. Ferron, and Maurício Prado. "Paleoproterozoic (~1.88Ga) felsic volcanism of the Iricoumé Group in the Pitinga Mining District area, Amazonian Craton, Brazil: insights in ancient volcanic processes from field and petrologic data." Anais da Academia Brasileira de Ciências 83, no. 3 (September 2011): 921–37. http://dx.doi.org/10.1590/s0001-37652011000300012.

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The Iricoumé Group correspond to the most expressive Paleoproterozoic volcanism in the Guyana Shield, Amazonian craton. The volcanics are coeval with Mapuera granitoids, and belong to the Uatumã magmatism. They have U-Pb ages around 1880 Ma, and geochemical signatures of α-type magmas. Iricoumé volcanics consist of porphyritic trachyte to rhyolite, associated to crystal-rich ignimbrites and co-ignimbritic fall tuffs and surges. The amount and morphology of phenocrysts can be useful to distinguish lava (flow and dome) from hypabyssal units. The morphology of ignimbrite crystals allows the distinction between effusive units and ignimbrite, when pyroclasts are obliterated. Co-ignimbritic tuffs are massive, and some show stratifications that suggest deposition by current traction flow. Zircon and apatite saturation temperatures vary from 799°C to 980°C, are in agreement with most temperatures of α-type melts and can be interpreted as minimum liquidus temperature. The viscosities estimation for rhyolitic and trachytic compositions yield values close to experimentally determined melts, and show a typical exponential decay with water addition. The emplacement of Iricoumé volcanics and part of Mapuera granitoids was controlled by ring-faults in an intracratonic environment. A genesis related to the caldera complex setting can be assumed for the Iricoumé-Mapuera volcano-plutonic association in the Pitinga Mining District.

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20

Pulvirenti, Fabio, Francesca Silverii, and Maurizio Battaglia. "A New Analysis of Caldera Unrest through the Integration of Geophysical Data and FEM Modeling: The Long Valley Caldera Case Study." Remote Sensing 13, no. 20 (October 11, 2021): 4054. http://dx.doi.org/10.3390/rs13204054.

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The Long Valley Caldera, located at the eastern edge of the Sierra Nevada range in California, has been in a state of unrest since the late 1970s. Seismic, gravity and geodetic data strongly suggest that the source of unrest is an intrusion beneath the caldera resurgent dome. However, it is not clear yet if the main contribution to the deformation comes from pulses of ascending high-pressure hydrothermal fluids or low viscosity magmatic melts. To characterize the nature of the intrusion, we developed a 3D finite element model which includes topography and crust heterogeneities. We first performed joint numerical inversions of uplift and Electronic Distance Measurement baseline length change data, collected during the period 1985–1999, to infer the deformation-source size, position, and overpressure. Successively, we used this information to refine the source overpressure estimation, compute the gravity potential and infer the intrusion density from the inversion of deformation and gravity data collected in 1982–1998. The deformation source is located beneath the resurgent dome, at a depth of 7.5 ± 0.5 km and a volume change of 0.21 ± 0.04 km3. We assumed a rhyolite compressibility of 0.026 ± 0.0011 GPa−1 (volume fraction of water between 0% and 30%) and estimated a reservoir compressibility of 0.147 ± 0.037 GPa−1. We obtained a density of 1856 ± 72 kg/m3. This density is consistent with a rhyolite melt, with 20% to 30% of dissolved hydrothermal fluids.

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21

Guo, Haihao, Ying Xia, Ruixia Bai, Xingchao Zhang, and Fang Huang. "Experiments on Cu-isotope fractionation between chlorine-bearing fluid and silicate magma: implications for fluid exsolution and porphyry Cu deposits." National Science Review 7, no. 8 (January 2, 2020): 1319–30. http://dx.doi.org/10.1093/nsr/nwz221.

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Abstract Hydrothermal fluid is essential for transporting metals in the crust and mantle. To explore the potential of Cu isotopes as a tracer of hydrothermal-fluid activity, Cu-isotope fractionation factors between Cl-bearing aqueous fluids and silicate magmas (andesite, dacite, rhyolite dacite, rhyolite and haplogranite) were experimentally calibrated. Fluids containing 1.75–14 wt.% Cl were mixed together with rock powders in Au95Cu5 alloy capsules, which were equilibrated in cold-seal pressure vessels for 5–13 days at 800–850°C and 2 kbar. The elemental and Cu-isotopic compositions of the recovered aqueous fluid and solid phases were analyzed by (LA-) ICP–MS and multi-collector inductively coupled plasma mass spectrometry, respectively. Our experimental results show that the fluid phases are consistently enriched in heavy Cu isotope (65Cu) relative to the coexisting silicates. The Cu-isotope fractionation factor (Δ65CuFLUID-MELT) ranges from 0.08 ± 0.01‰ to 0.69 ± 0.02‰. The experimental results show that the Cu-isotopic fractionation factors between aqueous fluids and silicates strongly depend on the Cu speciation in the fluids (e.g. CuCl(H2O), CuCl2– and CuCl32−) and silicate melts (CuO1/2), suggesting that the exsolved fluids may have higher δ65Cu than the residual magmas. Our results suggest the elevated δ65Cu values in Cu-enriched rocks could be produced by addition of aqueous fluids exsolved from magmas. Together with previous studies on Cu isotopes in the brine and vapor phases of porphyry deposits, our results are helpful for better understanding Cu-mineralization processes.

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22

Urabe, Tetsuro. "The effect of pressure on the partitioning ratios of lead and zinc between vapor and rhyolite melts." Economic Geology 82, no. 4 (July 1, 1987): 1049–52. http://dx.doi.org/10.2113/gsecongeo.82.4.1049.

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23

Chevychelov, V. Yu, A. A. Korneeva, A. A. Virus, and Yu B. Shapovalov. "The effect of CO2 on the solubility of aqueous chloride fluid in dacite, phonolite, and rhyolite melts." Doklady Earth Sciences 473, no. 2 (April 2017): 454–56. http://dx.doi.org/10.1134/s1028334x17040092.

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24

Malfait, Wim J., Rene Verel, Paola Ardia, and Carmen Sanchez-Valle. "Aluminum coordination in rhyolite and andesite glasses and melts: Effect of temperature, pressure, composition and water content." Geochimica et Cosmochimica Acta 77 (January 2012): 11–26. http://dx.doi.org/10.1016/j.gca.2011.11.011.

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25

Morris, George A., and Robert A. Creaser. "Crustal recycling during subduction at the Eocene Cordilleran margin of North America: a petrogenetic study from the southwestern Yukon." Canadian Journal of Earth Sciences 40, no. 12 (December 1, 2003): 1805–21. http://dx.doi.org/10.1139/e03-063.

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The early Eocene (57.355.4 Ma) Bennett Lake and Mount Skukum Volcanic Complexes lie on the Coast Plutonic Complex and Intermontane Belt boundary of the Canadian Cordillera at the British Columbia Yukon border, some 200 km east of the current and Eocene continental margin. Both complexes contain rock types from basaltic andesite to rhyolite in a series of lava and pyroclastic flows. The location relative to the continental margin, the rock types, and the presence of an enhanced LILE/HFSE (large-ion lithophile / high field strength element) signatures in all samples imply that contemporaneous subduction was the controlling factor in the formation of these complexes. The majority of samples, however, return unusually low compatible element concentrations for given rock types. We interpret this data to show that partial melting of the crust was the major source of erupted magmas. One formation of andesites at Mount Skukum and one late dyke at Bennett Lake do show higher concentrations of compatible trace elements, suggesting the presence of primitive magmas in the crust at the time of eruption, which contaminated and were erupted with the crustal melts. SrNd isotopic data at both complexes are consistently primitive regardless of rock type and compatible element content, requiring a primitive crustal source for these magmas. We propose that the complexes were formed as a result of early Eocene subduction of the Kula Plate beneath the Canadian Cordillera. Intrusion of hot primitive melts caused partial melting of young crust to produce the majority of lavas observed. Contamination of these melts by primitive magmas is observed at both Mount Skukum and Bennett Lake.

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26

MacDonald, R., B. Baginíski, H. E. Belkin, P. Dzieržanowski, and L. Jeżak. "REE partitioning between apatite and melt in a peralkaline volcanic suite, Kenya Rift Valley." Mineralogical Magazine 72, no. 6 (December 2008): 1147–61. http://dx.doi.org/10.1180/minmag.2008.072.6.1147.

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AbstractElectron microprobe analyses are presented for fluorapatite phenocrysts from a benmoreite-peralkaline rhyolite volcanic suite from the Kenya Rift Valley. The rocks have previously been well characterized petrographically and their crystallization conditions are reasonably well known. The REE contents in the M site increase towards the rhyolites, with a maximum britholite component of ~35 mol.%. Chondrite-normalized REE patterns are rather flat between La and Sm and then decrease towards Yb. Sodium and Fe occupy up to 1% and 4%, respectively, of the M site. The major coupled substitution is REE3+ + Si4+ ↔ Ca2+ + P5+. The substitution REE3+ + Na+ ↔ 2Ca2+has been of minor importance. The relatively large Fe contents were perhaps facilitated by the low fO2 conditions of crystallization. Zoning is ubiquitous and resulted from both fractional crystallization and magma mixing. Apatites in some rhyolites are relatively Y-depleted, perhaps reflecting crystallization from melts which had precipitated zircon. Mineral/glass (melt) ratios for two rhyolites are unusually high, with maxima at Sm (762, 1123).

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27

Costa, Simone, Matteo Masotta, Anna Gioncada, and Marco Pistolesi. "A Crystal Mush Perspective Explains Magma Variability at La Fossa Volcano (Vulcano, Italy)." Minerals 11, no. 10 (October 5, 2021): 1094. http://dx.doi.org/10.3390/min11101094.

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The eruptive products of the last 1000 years at La Fossa volcano on the island of Vulcano (Italy) are characterized by abrupt changes of chemical composition that span from latite to rhyolite. The wide variety of textural features of these products has given rise to several petrological models dealing with the mingling/mixing processes involving mafic-intermediate and rhyolitic magmas. In this paper, we use published whole-rock data for the erupted products of La Fossa and combine them in geochemical and thermodynamic modelling in order to provide new constrains for the interpretations of the dynamics of the active magmatic system. The obtained results allow us to picture a polybaric plumbing system characterized by multiple magma reservoirs and related crystal mushes, formed from time to time during the differentiation of shoshonitic magmas, to produce latites, trachytes and rhyolites. The residing crystal mushes are periodically perturbated by new, fresh magma injections that, on one hand, induce the partial melting of the mush and, on the other hand, favor the extraction of highly differentiated interstitial melts. The subsequent mixing and mingling of mush-derived melts ultimately determine the formation of magmas erupted at La Fossa, whose textural and chemical features are otherwise not explained by simple assimilation and fractional crystallization models. In such a system, the compositional variability of the erupted products reflects the complexity of the physical and chemical interactions among recharging magmas and the crystal mushes.

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28

Tian, Li, Deyou Sun, Jun Gou, Shan Jiang, Zhao Feng, Duo Zhang, and Yujie Hao. "Petrogenesis of the Newly Discovered Early Cretaceous Peralkaline Granitic Dikes in Baerzhe Area of Jarud Banner, Inner Mongolia: Implications for Deciphering Magma Evolution." Minerals 12, no. 12 (November 29, 2022): 1532. http://dx.doi.org/10.3390/min12121532.

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The super-large Baerzhe Be–Nb–Zr–REE deposit in NE China is hosted in the Early Cretaceous peralkaline granites. In this work, the newly discovered granitic dikes developed around the Baerzhe deposit were studied for the first time, focusing on their genesis and genetic relationships with the Baerzhe peralkaline granites. Zircon U-Pb dating of these granitic rocks (including the granite porphyry, rhyolite and miarolitic granite) yielded Early Cretaceous ages of 125–121 Ma. Their mineral assemblages and geochemical features suggest that they share similar features with the peralkaline A-type granites. Their geochemical data and zircon Hf isotopic compositions (εHf(t) = +3.4 to +10.5) indicate that the peralkaline granitic rocks were formed by the partial melting of dehydrated charnockite with extensive plagioclase crystal fractionation, which resulted in a peralkaline affinity. There are two types of distinct zircons in the studied samples: the type I zircon with a bright rim and dark core, which may represent a cumulate mineral phase captured together with aggregates during eruption, and the type II zircon with a higher evolution degree crystallized in the residual melts. Combined with the simulation results using whole-rock trace elements, we proposed that the peralkaline granitic dikes represent more evolved interstitial melts than the Baerzhe granitic magma. In the Early Cretaceous extensional tectonic settings, mantle-derived magma upwelled, which induced the melting of the lower crust and prolonged the evolutionary process of the magma crystal mush.

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Myšľan, Pavol, Peter Ružička, Tomáš Mikuš, and Miroslav Hain. "3D distribúcia minerálnych inklúzií v granátoch z lokalít Lesné - Potičky a Beňatinská voda (Slovenská republika)." Bulletin Mineralogie Petrologie 28, no. 2 (2020): 246–60. http://dx.doi.org/10.46861/bmp.28.246.

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Visualization of garnets and their mineral inclusions was performed by X-ray microtomography by reconstructing 3D image from 1800 measured 2D X-ray projections. Visualization procedure of 3D distribution of mineral inclusions was based on the different absorption of X-ray radiation between the host garnet and mineral inclusions. 3D visualization provided a realistic picture of a distribution of the 126 identified mineral inclusions in garnet from rhyolite and rhyodacite Beňatinská voda and 21 inclusions in garnet from Lesné - Potičky (Slovak Republic). Composition of garnet from locality Lesné - Potičky is Alm71.0-73.7Prp8.3-9.0Grs14.7-16.6 and from locality Beňatinská voda is Alm72.1-73.2 Prp5.5-5.9Grs18.3-19.4. Mineral inclusions in garnets from locality Lesné - Potičky are represented by fluorapatite, zircon, ilmenite, annite and magmatic melts preserved in the form of glass inclusions trapped in apatite inclusions. Mineral inclusions in garnets from locality Beňatinská voda are represented by fluorapatite, zircon and plagioclase An78.53-57.12. Chemical composition of zircons and fluorapatites are similar from both localities. Based on the chemical composition, the high-pressure origin of garnets associated with I-type magmas was confirmed.

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Brandt, S., R. Klemd, K. M. Haase, M. L. Fassbender, and T. Vennemann. "Formation of the Vergenoeg F–Fe–REE Deposit (South Africa) by Accumulation from a Ferroan Silicic Magma." Journal of Petrology 60, no. 12 (December 1, 2019): 2339–68. http://dx.doi.org/10.1093/petrology/egaa010.

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Abstract Situated in the centre of the Paleoproterozoic Bushveld Large Igneous Province (LIP) of South Africa the Vergenoeg F–Fe–REE deposit is one of the largest, but at the same time most unusual, fluorite deposits on Earth. In situ major and trace element analyses of fayalite, magnetite, ilmenite, fluorapatite, fluorite and allanite from fayalite-rich rocks are combined with oxygen isotope data for fayalite, magnetite and ilmenite to unravel the complex evolution of the deposit. Textural and compositional characterization of the fayalite-rich rocks supports a magmatic formation as cumulates and an intense late hydrothermal overprint. Fayalite accumulated together with minor Ti-rich magnetite, ilmenite, fluorapatite and allanite from a highly evolved, H2O-poor felsic melt at low oxygen fugacity. Chondrite-normalized rare earth element (REE) patterns of fayalite and the recalculated parental melts, using fayalite–rhyolite partition coefficients, exhibit positive trends with strong enrichment of the heavy REE (HREE) relative to the light REE (LREE). Apart from the LREE depletion the patterns are similar to those of highly fractionated high-silica REE rhyolites that often occur in siliceous LIPs. We attribute the LREE depletion to crystallization of accessory allanite, the main host of the LREE in the cumulates. Chondrite-normalized REE patterns of the parental melt prior to fayalite accumulation, recalculated using allanite–rhyolite partition coefficients, resemble the composition of the rhyolites of the Rooiberg Group and therefore document a petrogenetic link to the Bushveld LIP. High δ18O values of fayalite (up to ≈7·4 ‰) are consistent with its crystallization in a rhyolitic melt that has formed by extensive fractionation from basic melts of the Rustenburg Layer Suite, the mafic member of the Bushveld LIP. Primary fluorite crystallized together with rare quartz, and a second generation of fayalite, magnetite and ilmenite from rare intercumulus melt in interstices between cumulate fayalite. Textural and mineral compositional data, as well as the generally negative δ18O values of magnetite (–2·9 to 0 ‰), are in agreement with the main magnetite–fluorite ore formation in Vergenoeg being related to a hydrothermal overprint, which was responsible for further F and Fe enrichments of the rocks. Fluorine-rich fluids, released from the crystallizing granites of the felsic member of the Bushveld LIP (Lebowa Granite Suite), caused the extensive alteration of fayalite to bowlingite and its replacement by Ti-poor magnetite and quartz. The hydrothermal overprint was associated with the widespread formation of secondary fluorite and minor fluorapatite. Our new petrogenetic model for the Vergenoeg deposit, as constrained from the primary fayalite cumulates, implies that the formation of the Vergenoeg deposit was directly linked to the evolution of the Bushveld LIP.

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31

Webb, Sharon L., and Donald B. Dingwell. "Non-Newtonian rheology of igneous melts at high stresses and strain rates: Experimental results for rhyolite, andesite, basalt, and nephelinite." Journal of Geophysical Research 95, B10 (1990): 15695. http://dx.doi.org/10.1029/jb095ib10p15695.

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32

Romanko, Alexander, Vsevolod Prokof’ev, Nazim Imamverdiyev, Vladimir Naumov, Pavel Plechov, Anna Balashova, Bahman Rashidi, Mehrdad Hedari, Ilya Vikentev, and Alexander Savichev. "The First Discovery of Low-temperature Rhyolite Melts in Cenozoic Long-lived Bazman Volcano, East Iran; Some Problems and Discussion." International Journal of Sustainable and Green Energy 8, no. 4 (2019): 81. http://dx.doi.org/10.11648/j.ijrse.20190804.12.

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33

Kularatne, Kanchana, and Andreas Audétat. "Rutile solubility in hydrous rhyolite melts at 750–900°C and 2kbar, with application to titanium-in-quartz (TitaniQ) thermobarometry." Geochimica et Cosmochimica Acta 125 (January 2014): 196–209. http://dx.doi.org/10.1016/j.gca.2013.10.020.

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34

Manikyamba, C., R. Kerrich, Tarun C. Khanna, and D. V. Subba Rao. "Geochemistry of adakites and rhyolites from the Neoarchaean Gadwal greenstone belt, eastern Dharwar craton, India: implications for sources and geodynamic setting." Canadian Journal of Earth Sciences 44, no. 11 (November 1, 2007): 1517–35. http://dx.doi.org/10.1139/e07-034.

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Adakite and rhyolite volcanic flows with different petrographic and geochemical characteristics have been identified from the Neoarchaean Gadwal greenstone terrane of the eastern Dharwar craton, India. These are part of the bimodal basalt–felsic association that dominates the belt, which includes previously documented boninites and Nb-enriched basalts. Adakites plot in the MgO–SiO2 field of Cenozoic adakites, distinct from high-Mg andesites, and have low Yb (1.2 ppm) and fractionated rare-earth elements (REE) (La/Ybn = 16) of Cenozoic counterparts. They also possess the Cr/Ni (1.3–4.0), Nb/Ta (8.6–12.8), and Zr/Sm (33–58) ratios distinctive of adakites from recent oceanic arcs. Zero to positive Eu anomalies contrast with negative Eu present in older Dharwar cratonic crust, such that crustal contamination is unlikely, endorsing an intraoceanic setting. Cenozoic oceanic adakites may form by slab melting, then hybridizing to variable degree with wedge peridotite, and Gadwal adakites are also interpreted to be slab melts. Rhyolites have greater SiO2, highly incompatible elements (Th, La, Zr), and higher Yb (2.41 ppm) contents than adakites, with fractionated REE and pronounced negative Eu anomalies; they are comparable to FI type rhyolites of other Archean greenstone belts, likely melts of thick mafic crust at ~40 km with residual garnet, in an extensional setting. Consequently, the switch from arc basalts and boninites to adakites, Nb-enriched basalt, and rhyolites in the Gadwal terrane signifies a transition from slab dehydration-wedge melting to slab melting-wedge hybridization, possibly triggered by ridge subduction or flattening of the slab, as well as crustal melting. These new observations endorse the emergence of complex arc magmatism in Neoarchean terranes.

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35

Imamverdiyev, N. A., and M. Y. Hasanguliyeva. "Geochemical aspects of the formation of Neogene volcanism in the central part of the Lesser Caucasus." Scientific Petroleum, no. 1 (June 30, 2021): 8–15. http://dx.doi.org/10.53404/sci.petro.20210100001.

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The article considers the formation of Neogene volcanism in the central part of the Lesser Caucasus on the basis of geochemical features. It was found that in the andesite-dasite-rhyolite association rocks, where volcanism is expressed, light lanthanides predominate over weight, and therefore the La/Sm, La/Yb ratios are high. In medium rocks (quartz latites, andesites) the Eu/Eu* ratio is close to unity (Eu/Eu* = 0.94-1.05), in more acidic rocks the weak Eu-minimum (Eu/Eu* = 0.58-0 ,63) and indicates the fractionation of plagioclase in the formation of acidic rocks. Enrichment melts and fluids with a relatively high melting point caused the increase of Ba/Y, Rb/Y, Th/Yb, Nb/Y, Nb/Yb ratios in the association rocks and their enrichment with Ba, Sr, rare earth elements. It was concluded that the source of the enriched mantle played a key role in the formation of andesite-dasite-riolite association rocks of the central part of the Lesser Caucasus. Keywords: Central part of the Lesser Caucasus, Neogene volcanism, distribution of rare earth and rare elements, source of enriched mantle.

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36

Rzaeva, S. J. "The use of biologically active agents in the methods of intensification of oil production." Scientific Petroleum, no. 1 (June 30, 2021): 31–36. http://dx.doi.org/10.53404/sci.petro.20210100004.

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The article considers the formation of Neogene volcanism in the central part of the Lesser Caucasus on the basis of geochemical features. It was found that in the andesite-dasite-rhyolite association rocks, where volcanism is expressed, light lanthanides predominate over weight, and therefore the La/Sm, La/Yb ratios are high. In medium rocks (quartz latites, andesites) the Eu/Eu* ratio is close to unity (Eu/Eu* = 0.94-1.05), in more acidic rocks the weak Eu-minimum (Eu/Eu* = 0.58-0 ,63) and indicates the fractionation of plagioclase in the formation of acidic rocks. Enrichment melts and fluids with a relatively high melting point caused the increase of Ba/Y, Rb/Y, Th/Yb, Nb/Y, Nb/Yb ratios in the association rocks and their enrichment with Ba, Sr, rare earth elements. It was concluded that the source of the enriched mantle played a key role in the formation of andesite-dasite-riolite association rocks of the central part of the Lesser Caucasus. Keywords: Central part of the Lesser Caucasus, Neogene volcanism, distribution of rare earth and rare elements, source of enriched mantle.

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37

Sosa-Ceballos, Giovanni, Mario Emmanuel Boijseauneau-López, Juan Daniel Pérez-Orozco, Gerardo Cifuentes-Nava, Xavier Bolós, Mathieu Perton, and David Simón-Velázquez. "Silicic magmas in the Michoacán-Guanajuato Volcanic Field: an overview about plumbing systems, crustal storage and genesis processes." Revista Mexicana de Ciencias Geológicas 38, no. 3 (November 24, 2021): 210–25. http://dx.doi.org/10.22201/cgeo.20072902e.2021.3.1668.

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The origin of silicic rocks in the Michoacán-Guanajuato volcanic field (MGVF) has been understudied since the volcanic field attracted the attention of researchers. Using geochemical, petrological and structural data from the literature, here we propose a model for the origin of silicic magmas. We found that all volcanic rocks known to date in the MGVF can be divided in 40 % andesite, 33 % basaltic andesite, 15 % basalt, 2 % trachybasalt to trachyandesite, and 10 % dacite-rhyolite. The structural systems that deformed the crust in the MGVF are NNW-SSE-oriented normal faults of the Taxco-San Miguel de Allende fault system, developed during the Oligocene, and the Morelia-Acambay fault system consisting of ENE-SSW to E-W sinistral strike-slip faults developed during the Oligocene-Miocene. In addition to bibliographic data, we present a gravimetric-magnetometric model to investigate the characteristics of the local basement where magmas acquire their final silicic composition, and a seismic tomography model to investigate the deep plumbing system that contribute to form the silicic rocks emplaced on the surface. The only report of assimilation experiments we found in the MGVF literature suggest that plagioclase and pyroxene are more easily digested than quartz by hotter magmas. The digestion of these mineral phases has a direct consequence on the generation of dacites and rhyolites. We propose that regardless of the genesis of andesitic melts, such intermediate magmas arrive to the upper-crust and are forced to evolve within local compression zones where they melt the local granitic basement and form crystal mushes. The compositional variability of silicic rocks in the MGVF is a consequence of the variable mixing between the intermediate magmas and the granitic partial melts.

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38

Swallow, Elliot J., Colin J. N. Wilson, Bruce L. A. Charlier, and John A. Gamble. "The Huckleberry Ridge Tuff, Yellowstone: evacuation of multiple magmatic systems in a complex episodic eruption." Journal of Petrology 60, no. 7 (June 28, 2019): 1371–426. http://dx.doi.org/10.1093/petrology/egz034.

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Abstract The 2·08 Ma, ∼2500 km3 Huckleberry Ridge Tuff (HRT) eruption, Yellowstone, generated two fall deposits and three ignimbrite members (A, B, C), accompanying a ∼95 x 65 km caldera collapse. Field data imply that the pre-A fall deposits took weeks to be erupted, then breaks of weeks to months occurred between members A and B, and years to decades between B and C. We present compositional and isotopic data from single silicic clasts (pumice or fiamme) in the three ignimbrite members, plus new data from co-eruptive mafic components to reconstruct the nature and evacuation history of the HRT crustal magmatic complex. Geochemical data, building on field characteristics, are used to group nine silicic clast types into seven compositional suites (A1-A3; B1; C1-C3) within their respective members A, B and C. Isotopic data are then added to define four magmatic systems that were tapped simultaneously and/or sequentially during the eruption. Systems 1 and 2 fed the initial fall deposits and then vented throughout member A, accompanied by trace amounts of mafic magma. In member A, volumetrically dominant system 1 is represented by a rhyolite suite (A1: 73·0–77·7 wt % SiO2, 450–1680 ppm Ba) plus a distinct low-silica rhyolite suite (A2: 69·2–71·6 wt % SiO2, >2500 ppm Ba). System 2 yielded only a low-Ba, high-silica rhyolite suite (A3: 76·7–77·4 wt % SiO2, ≤250 ppm Ba). Glass compositions in pumices from systems 1 and 2 show clustering, indicative of the same multiple melt-dominant bodies identified in the initial fall deposits and earliest ignimbrite. Member B samples define suite B1 (70·7–77·4 wt % SiO2, 540–3040 ppm Ba) derived from magmatic system 1 (but not 2) that had undergone mixing and reorganisation during the A: B time break, accompanying mafic magma inputs. Mafic scoriae erupted in upper member B cover similar compositions to the member A clasts, but extend over a much broader compositional range. Member C clast compositions reflect major changes during the B: C time break, including rejuvenation of magmatic system 2 (last seen in member A) as suite C3 (75·3–77·2 wt % SiO2, 100–410 ppm Ba), plus the appearance of two new suites with strong crustal signatures. Suite C2 is another rhyolite (74·7–77·6 wt % SiO2, with Ba decreasing with silica from 2840 to 470 ppm) that defines magmatic system 3. Suite C2 also shows clustered glass compositions, suggesting that multiple melt-dominant bodies were a repetitive feature of the HRT magmatic complex. Suite C1, in contrast, is dacite to rhyolite (65·6–75·0 wt % SiO2, with Ba increasing with silica from 750 to 1710 ppm) that defines magmatic system 4. Compositions from magmatic systems 1 and 2 dominantly reflect fractional crystallization, but include partial melting of cumulates related to earlier intrusions of the same mafic magmas as those syn-eruptively vented. Country rock assimilation was limited to minor amounts of a more radiogenic (with respect to Sr) evolved contaminant. In contrast, systems 3 and 4 show similar strongly crustal isotopic compositions (despite their differences in elemental composition) consistent with assimilation of Archean rocks via partial melts derived from cumulates associated with contrasting mafic lineages. System 3 links to the same HRT mafic compositions co-erupted in members A and B. In contrast, system 4 links to olivine tholeiite compositions erupted in the Yellowstone area before, sparsely during, and following the HRT itself. All four magmatic systems were housed beneath the HRT caldera area. Systems 1 and 2 were hosted in Archean crust that had been modified by Cretaceous/Eocene magmatism, whereas systems 3 and 4 were hosted within crust that retained Archean isotopic characteristics. The extreme compositional diversity in the HRT highlights the spatial and temporal complexities that can be associated with large-volume silicic magmatism.

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39

Leat, Philip T., and Teal R. Riley. "Chapter 3.1b Antarctic Peninsula and South Shetland Islands: petrology." Geological Society, London, Memoirs 55, no. 1 (2021): 213–26. http://dx.doi.org/10.1144/m55-2018-68.

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AbstractThe Antarctic Peninsula contains a record of continental-margin volcanism extending from Jurassic to Recent times. Subduction of the Pacific oceanic lithosphere beneath the continental margin developed after Late Jurassic volcanism in Alexander Island that was related to extension of the continental margin. Mesozoic ocean-floor basalts emplaced within the Alexander Island accretionary complex have compositions derived from Pacific mantle. The Antarctic Peninsula volcanic arc was active from about Early Cretaceous times until the Early Miocene. It was affected by hydrothermal alteration, and by regional and contact metamorphism generally of zeolite to prehnite–pumpellyite facies. Distinct geochemical groups recognized within the volcanic rocks suggest varied magma generation processes related to changes in subduction dynamics. The four groups are: calc-alkaline, high-Mg andesitic, adakitic and high-Zr, the last two being described in this arc for the first time. The dominant calc-alkaline group ranges from primitive mafic magmas to rhyolite, and from low- to high-K in composition, and was generated from a mantle wedge with variable depletion. The high-Mg and adakitic rocks indicate periods of melting of the subducting slab and variable equilibration of the melts with mantle. The high-Zr group is interpreted as peralkaline and may have been related to extension of the arc.

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40

Wendi, Abimnui Norine, Njilah Isaac Konfor, Yongue Fouateu Rose, Mosere Felicia Nanje, and Nfor Bruno Ndicho. "Geology, Palaeodeposition and the Involvement of Rhyolite Melts in the Petrogenesis of the Tabenken Coal Seam in the North West Region of Cameroon." Journal of Geoscience and Environment Protection 10, no. 04 (2022): 111–26. http://dx.doi.org/10.4236/gep.2022.104008.

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41

González-García, Diego, Francesco Vetere, Harald Behrens, Maurizio Petrelli, Daniele Morgavi, and Diego Perugini. "Interdiffusion of major elements at 1 atmosphere between natural shoshonitic and rhyolitic melts." American Mineralogist 104, no. 10 (October 1, 2019): 1444–54. http://dx.doi.org/10.2138/am-2019-6997.

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Abstract The diffusive mass exchange of eight major elements (Si, Ti, Al, Fe, Mg, Ca, Na, and K) between natural, nominally dry shoshonitic and rhyolitic melts was studied at atmospheric pressure and temperatures between 1230 and 1413 °C using the diffusion couple method. For six elements, effective binary diffusion coefficients were calculated by means of a concentration-dependent method to obtain an internally consistent data set. Among these components, the range in diffusivities is restricted, pointing to a coupling of their diffusive fluxes. We find that the calculated diffusivities fit well into the Arrhenius relation, with activation energies (Ea) ranging from 258 to 399 kJ/mol in rhyolitic (70 wt% SiO2) melt and from 294 to 426 kJ/mol in the latitic melt (58 wt% SiO2). Ti shows the lowest Ea, while Si, Fe, Mg, Ca, and K have a similar value. A strong linear correlation is observed between logD0 and Ea, confirming the validity of the compensation law for this system. Uphill diffusion is observed in Al in the form of a concentration minimum in the rhyolitic side of the couple, (at ca. 69 wt% SiO2), and in Na indicated by a maximum in the shoshonitic side (ca. 59 wt% SiO2). Fe shows weak signs of uphill diffusion, possibly due to the contribution of ferric iron. The data presented here extend the database of previously published diffusivities in the shoshonite-rhyolite system (González-García et al. 2017) toward the water-free end and allows us to better constrain the water-dependence of major element diffusion at very low water concentrations. Combining both data sets, we find that logD is proportional to the square root of water concentration for a range between 0 and 2 wt% H2O. These results are of particular interest in the study of mass transfer phenomena in alkaline volcanic systems.

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42

Edgar, A. D., L. A. Pizzolato, and J. Sheen. "Fluorine in igneous rocks and minerals with emphasis on ultrapotassic mafic and ultramafic magmas and their mantle source regions." Mineralogical Magazine 60, no. 399 (April 1996): 243–57. http://dx.doi.org/10.1180/minmag.1996.060.399.01.

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AbstractIn reviewing the distribution of fluorine in igneous rocks it is clear that F abundance is related to alkalinity and to some extent to volatile contents. Two important F-bearing series are recognized: (1) the alkali basalt—ultrapotassic rocks in which F increases with increasing K2O and decreasing SiO2 contents; and (2) the alkali basalt—phonolite—rhyolite series with F showing positive correlation with both total alkalis and SiO2. Detailed studies of series (1) show that F abundance in ultrapotassic magmas (lamproite, kamafugite, lamprophyre) occurs in descending order in the sequence phlogopite>apatite>amphibole>glass. Fluorine contents in the same minerals from fresh and altered mantle xenoliths may be several orders of magnitude less than those in the host kamafugite. For many lamproites, F contents correlate with higher mg# suggesting that F is highest in the more primitive magmas.Experiments at mantle conditions (20 kbar, 900–1400°C) on simplified F-bearing mineral systems containing phlogopite, apatite, K-richterite, and melt show that F is generally a compatible element. Additionally, low F abundance in minerals from mantle xenoliths suggests that F may not be available in mantle source regions and hence is unlikely to partition into the melt phase on partial melting. Melting experiments on the compositions of F-free and F-bearing model phlogopite harzburgite indicate that even small variations in F content produce melts similar in composition to those of lamproite.

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43

Pamukcu, Ayla S., Tamara L. Carley, Guilherme A. R. Gualda, Calvin F. Miller, and Charles A. Ferguson. "The Evolution of the Peach Spring Giant Magma Body: Evidence from Accessory Mineral Textures and Compositions, Bulk Pumice and Glass Geochemistry, and Rhyolite-MELTS Modeling." Journal of Petrology 54, no. 6 (February 26, 2013): 1109–48. http://dx.doi.org/10.1093/petrology/egt007.

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44

Miyagi, Isoji, Hisayoshi Yurimoto, and Eiichi Takahashi. "Water solubility in albite-orthoclase join and JR-1 rhyolite melts at 1000.DEG.C. and 500 to 2000 bars, determined by micro-analysis with SIMS." GEOCHEMICAL JOURNAL 31, no. 1 (1997): 57–61. http://dx.doi.org/10.2343/geochemj.31.57.

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45

Coyle, Marylou, and D. F. Strong. "Geology of the Springdale Group: a newly recognized Silurian epicontinental-type caldera in Newfoundland." Canadian Journal of Earth Sciences 24, no. 6 (June 1, 1987): 1135–48. http://dx.doi.org/10.1139/e87-110.

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Volcanic–sedimentary facies and structural relationships of the Silurian Springdale Group in west-central Newfoundland are indicative of a large collapse caldera with an area of more than 2000 km2. Basaltic flows, andesite flows and pyroclastic rocks, silicic ash-flow tuffs, high-silica rhyolite domes, and volcanically derived debris flows and breccias, fluviatile red sandstones, and conglomerates make up the group. It is bounded on the east and west by up-faulted basement rocks, which include gneisses, amphibolites, and pillow lavas, and in the northwest it unconformably overlies Lower Orodovician submarine volcanics. These margins are intruded by cogenetic and younger granitoid rocks. The volcanic rocks form a calc-alkaline series, although gaps in silica content at 52–56, 67–68, and 73–74% separate them into four groups: basalts, andesites–dacites, rhyolites, and high-silica rhyolites.The high-silica rhyolites are chemically comparable to melts thought to form the upper parts of large, layered silicic magma chambers of epicontinental regions. Such an environment is also suggested by the large area of the Springdale caldera and the fact that it is one of a number of calderas that make up a large Silurian volcanic field in western Newfoundland. An epicontinental tectonothermal environment for central Newfoundland in Silurian–Devonian times is readily explained by the fact that this magmatic activity followed a period of destruction and closure of the early Paleozoic Iapetus Ocean, with trapped heat and basaltic magma causing large-scale melting of thickened and subducted continental crust in an overall transpressional tectonic regime.

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AWDANKIEWICZ, MAREK, RYSZARD KRYZA, and NORBERT SZCZEPARA. "Timing of post-collisional volcanism in the eastern part of the Variscan Belt: constraints from SHRIMP zircon dating of Permian rhyolites in the North-Sudetic Basin (SW Poland)." Geological Magazine 151, no. 4 (September 12, 2013): 611–28. http://dx.doi.org/10.1017/s0016756813000678.

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AbstractThe final stages of the Variscan orogeny in Central Europe were associated with voluminous granitic plutonism and widespread volcanism. Four samples representative of the main rhyolitic volcanic units from the Stephanian–Permian continental succession of the North-Sudetic Basin, in the eastern part of the Variscan Belt, were dated using the SIMS (SHRIMP) zircon method. Three samples show overlapping206Pb–238U mean ages of 294 ± 3, 293 ± 2 and 292 ± 2 Ma, and constrain the age of the rhyolitic volcanism in the North-Sudetic Basin at 294–292 Ma. This age corresponds to the Early Permian – Sakmarian Stage and is consistent with the stratigraphic position of the lava units. The fourth sample dated at 288 ± 4 Ma reflects a minor, younger stage of (sub)volcanic activity in the Artinskian. The silicic activity was shortly followed by mafic volcanism. The rhyolite samples contained very few inherited zircons, possibly owing to limited contribution of crustal sources to the silicic magma, or owing to processes involved in anatectic melting and magma differentiation (e.g. resorption of old zircon by Zr-undersaturated melts). The SHRIMP results and the stratigraphic evidence suggest that the bimodal volcanism terminated the early, short-lived (10–15 Ma) and vigorous stage of basin evolution. The Permian volcanism in the North-Sudetic Basin may be correlated with relatively late phases of the regional climax of Late Palaeozoic volcanism in Central Europe, constrained by 41 published SHRIMP zircon age determinations at 299–291 Ma. The Permian volcanism and coeval plutonism in the NE part of the Bohemian Massif can be linked to late Variscan, post-collisional extension.

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47

de Silva, S. L., J. Roberge, L. Bardelli, W. Báez, A. Ortiz, J. G. Viramonte, J. M. Arnosio, and R. Becchio. "Magmatic evolution and architecture of an arc-related, rhyolitic caldera complex: The late Pleistocene to Holocene Cerro Blanco volcanic complex, southern Puna, Argentina." Geosphere 18, no. 2 (January 25, 2022): 394–423. http://dx.doi.org/10.1130/ges02294.1.

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Abstract Through the lens of bulk-rock and matrix glass geochemistry, we investigated the magmatic evolution and pre-eruptive architecture of the siliceous magma complex beneath the Cerro Blanco volcanic complex, a Crater Lake–type caldera complex in the southern Puna Plateau of the Central Andes of Argentina. The Cerro Blanco volcanic complex has been the site of two caldera-forming eruptions with volcanic explosivity index (VEI) 6+ that emplaced the ca. 54 ka Campo Piedra Pomez ignimbrite and the ca. 4.2 ka Cerro Blanco ignimbrite. As such, it is the most productive recent explosive volcano in the Central Andes. The most recent eruptions (younger than 4.2 ka) are dominantly postcaldera effusions of crystal-rich domes and associated small explosive pulses. Previous work has demonstrated that andesitic recharge of and mixing with rhyolitic magma occurred at the base of the magma complex, at ~10 km depth. New isotopic data (Sr, Nd, Pb, and O) confirm that the Cerro Blanco volcanic complex rhyolite suite is part of a regional southern Puna, arc-related ignimbrite group. The suite defines a tight group of consanguineous siliceous magmas that serves as a model for the evolution of arc-related, caldera-forming silicic magma systems in the region and elsewhere. These data indicate that the rhyolites originated through limited assimilation of and mixing with upper-crustal lithologies by regional basaltic andesite parent materials, followed by extensive fractional crystallization. Least squares models of major elements in tandem with Rayleigh fractionation models for trace elements reveal that the internal variations among the rhyolites through time can be derived by extensive fractionation of a quartz–two feldspar (granitic minimum) assemblage with limited assimilation. The rare earth element character of local volumes of melt in some samples of the Campo Piedra Pomez ignimbrite basal fallout requires significant fractionation of amphibole. The distinctive major- and trace-element characteristics of bulk rock and matrix of the Campo Piedra Pomez and Cerro Blanco tephras provide useful geochemical fingerprints to facilitate regional tephrochronology. Available data indicate that rhyolites from other neighborhood centers, such as Cueros de Purulla, share bulk chemical characteristics with the Campo Piedra Pomez ignimbrite rhyolites, but they appear to be isotopically distinct. Pre-eruptive storage and final equilibration of the rhyolitic melts were estimated from matrix glass compositions projected onto the haplogranitic system (quartz-albite-orthoclase-H2O) and using rhyolite-MELTS models. These revealed equilibration pressures between 360 and 60 MPa (~10–2 km depth) with lowest pressures in the Holocene eruptions. Model temperatures for the suite ranged from 695 to 790 °C. Integrated together, our results reveal that the Cerro Blanco volcanic complex is a steady-state (low-magmatic-flux), arc-related complex, standing in contrast to the flare-up (high-magmatic-flux) supervolcanoes that dominate the Neogene volcanic stratigraphy. The silicic magmas of the Cerro Blanco volcanic complex were derived more directly from mafic and intermediate precursors through extensive fractional crystallization, albeit with some mixing and assimilation of local basement. Geochemical models and pressure-temperature estimates indicate that significant volumes of remnant cumulates of felsic and intermediate composition should dominate the polybaric magma complex beneath the Cerro Blanco volcanic complex, which gradually shallowed through time. Evolution to the most silicic compositions and final equilibration of some of the postcaldera domes occurred during ascent and decompression at depths less than 2 km. Our work connotes an incrementally accumulated (over at least 54 k.y.), upper-crustal pluton beneath the Cerro Blanco volcanic complex between 2 and 10 km depth. The composition of this pluton is predicted to be dominantly granitic, with deeper parts being granodioritic to tonalitic. The progressive solidification and eventual contraction of the magma complex may account for the decades of deflation that has characterized Cerro Blanco. The presently active geothermal anomaly and hydrothermal springs indicate the Cerro Blanco volcanic complex remains potentially active.

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48

Mills, Andrea, and Hamish Sandeman. "Lithostratigraphy and lithogeochemistry of Ediacaran alkaline basaltic rocks of the Musgravetown Group, Bonavista Peninsula, northeastern Newfoundland, Canada: an extensional volcanogenic basin in the type-Avalon terrane." Atlantic Geology 57 (August 5, 2021): 207–34. http://dx.doi.org/10.4138/atlgeol.2021.010.

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Volcanic rocks of the Ediacaran Musgravetown Group on Bonavista Peninsula, Avalon terrane, Newfoundland, include basal ca. 600 Ma calc-alkaline basalt succeeded by continental tholeiite and alkaline rhyolite of the ca. 592 Ma Plate Cove volcanic belt (Bull Arm Formation), indicating a change from subduction-related to extensionrelated tectonic regimes during that interval. Alkalic basalts on northeastern (Dam Pond area) and southwestern (British Harbour area) Bonavista Peninsula occur below and above, respectively, the ca. 580 Ma glacial Trinity facies. Dam Pond basalt occurs in a structural dome intercalated with and flanked by fine-grained, siliciclastic deposits (Big Head Formation) overlain by Trinity facies. The British Harbour basalt occurs above the Trinity facies, in an upward- coarsening sandstone sequence (Rocky Harbour Formation) overlain by red beds of the Crown Hill Formation (uppermost Musgravetown Group). The Rocky Harbour and Big Head formations are likely stratigraphically interfingered proximal and distal deposits, respectively, derived from erosion of the Bull Arm Formation and older Avalonian assemblages.The Big Head basalts have lower SiO2, Zr, FeOT, P2O5, TiO2 and higher Mg#, Cr, V, Co and Ni contents, and are therefore more primitive than the more FeOT-, TiO2-, and P2O5-rich British Harbour basalts. Large-ionlithophile and rare-earth-element concentrations and ratios indicate that both suites originated from low degree partial melts of deep, weakly garnet-bearing, undepleted asthenospheric peridotite sources, with magma conduits likely focused along regional extensional faults. The protracted and episodic extension-related volcanic activity is consistent with a geodynamic setting that evolved from a mature arc into extensional basins with slowly waning magmatism, possibly involving slab rollback and delamination followed by magmatic underplating. The duration and variation of both volcanism and sedimentation indicate that the Musgravetown Group should be elevated to a Supergroup in order to facilitate future correlation of its constituent parts with other Avalonian basins.

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49

Cucciniello, Ciro, Ashwini Kumar Choudhary, Kanchan Pande, and Hetu Sheth. "Mineralogy, geochemistry and 40Ar–39Ar geochronology of the Barda and Alech complexes, Saurashtra, northwestern Deccan Traps: early silicic magmas derived by flood basalt fractionation." Geological Magazine 156, no. 10 (January 22, 2019): 1668–90. http://dx.doi.org/10.1017/s0016756818000924.

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AbstractMost 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.

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50

Wiesmaier, S., D. Morgavi, C. J. Renggli, D. Perugini, C. P. De Campos, K. U. Hess, W. Ertel-Ingrisch, Y. Lavallée, and D. B. Dingwell. "Magma mixing enhanced by bubble segregation." Solid Earth 6, no. 3 (August 21, 2015): 1007–23. http://dx.doi.org/10.5194/se-6-1007-2015.

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Abstract. In order to explore the materials' complexity induced by bubbles rising through mixing magmas, bubble-advection experiments have been performed, employing natural silicate melts at magmatic temperatures. A cylinder of basaltic glass was placed below a cylinder of rhyolitic glass. Upon melting, bubbles formed from interstitial air. During the course of the experimental runs, those bubbles rose via buoyancy forces into the rhyolitic melt, thereby entraining tails of basaltic liquid. In the experimental run products, these plume-like filaments of advected basalt within rhyolite were clearly visible and were characterised by microCT and high-resolution EMP analyses. The entrained filaments of mafic material have been hybridised. Their post-experimental compositions range from the originally basaltic composition through andesitic to rhyolitic composition. Rheological modelling of the compositions of these hybridised filaments yield viscosities up to 2 orders of magnitude lower than that of the host rhyolitic liquid. Importantly, such lowered viscosities inside the filaments implies that rising bubbles can ascend more efficiently through pre-existing filaments that have been generated by earlier ascending bubbles. MicroCT imaging of the run products provides textural confirmation of the phenomenon of bubbles trailing one another through filaments. This phenomenon enhances the relevance of bubble advection in magma mixing scenarios, implying as it does so, an acceleration of bubble ascent due to the decreased viscous resistance facing bubbles inside filaments and yielding enhanced mass flux of mafic melt into felsic melt via entrainment. In magma mixing events involving melts of high volatile content, bubbles may be an essential catalyst for magma mixing. Moreover, the reduced viscosity contrast within filaments implies repeated replenishment of filaments with fresh end-member melt. As a result, complex compositional gradients and therefore diffusion systematics can be expected at the filament–host melt interface, due to the repetitive nature of the process. However, previously magmatic filaments were tacitly assumed to be of single-pulse origin. Consequently, the potential for multi-pulse filaments has to be considered in outcrop analyses. As compositional profiles alone may remain ambiguous for constraining the origin of filaments, and as 3-D visual evidence demonstrates that filaments may have experienced multiple bubbles passages even when featuring standard diffusion gradients, therefore, the calculation of diffusive timescales may be inadequate for constraining timescales in cases where bubbles have played an essential role in magma mixing. Data analysis employing concentration variance relaxation in natural samples can distinguish conventional single-pulse filaments from advection via multiple bubble ascent advection in natural samples, raising the prospect of yet another powerful application of this novel petrological tool.

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