Статті в журналах: "Ti-in-zircon thermometry"

1

Fu, Bin, F. Zeb Page, Aaron J. Cavosie, John Fournelle, Noriko T. Kita, Jade Star Lackey, Simon A. Wilde, and John W. Valley. "Ti-in-zircon thermometry: applications and limitations." Contributions to Mineralogy and Petrology 156, no. 2 (February 12, 2008): 197–215. http://dx.doi.org/10.1007/s00410-008-0281-5.

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2

Bloch, E. M., M. C. Jollands, P. Tollan, F. Plane, A. S. Bouvier, R. Hervig, A. J. Berry, et al. "Diffusion anisotropy of Ti in zircon and implications for Ti-in-zircon thermometry." Earth and Planetary Science Letters 578 (January 2022): 117317. http://dx.doi.org/10.1016/j.epsl.2021.117317.

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3

Szymanowski, Dawid, Manuela A. Fehr, Marcel Guillong, Matthew A. Coble, Jörn-Frederik Wotzlaw, Lutz Nasdala, Ben S. Ellis, Olivier Bachmann, and Maria Schönbächler. "Isotope-dilution anchoring of zircon reference materials for accurate Ti-in-zircon thermometry." Chemical Geology 481 (March 2018): 146–54. http://dx.doi.org/10.1016/j.chemgeo.2018.02.001.

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4

Lin, Meng, Guibin Zhang, Shuguang Song, Huijuan Li, and Lijuan Zhang. "The validity of Ti-in-zircon thermometry in low temperature eclogites." Geological Society, London, Special Publications 474, no. 1 (September 14, 2018): 69–87. http://dx.doi.org/10.1144/sp474.13.

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5

Moecher, D. P., S. M. McDowell, S. D. Samson, and C. F. Miller. "Ti-in-zircon thermometry and crystallization modeling support hot Grenville granite hypothesis." Geology 42, no. 3 (March 2014): 267–70. http://dx.doi.org/10.1130/g35156.1.

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6

Hiess, Joe, Allen P. Nutman, Vickie C. Bennett, and Peter Holden. "Ti-in-zircon thermometry applied to contrasting Archean metamorphic and igneous systems." Chemical Geology 247, no. 3-4 (January 2008): 323–38. http://dx.doi.org/10.1016/j.chemgeo.2007.10.012.

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7

Reguir, Ekaterina, Anton Chakhmouradian, Barrett Elliott, Ankar Sheng, and Panseok Yang. "Zircon Macrocrysts from the Drybones Bay Kimberlite Pipe (Northwest Territories, Canada): A High-Resolution Trace Element and Geochronological Study." Minerals 8, no. 11 (October 25, 2018): 481. http://dx.doi.org/10.3390/min8110481.

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Анотація:

Zircon macrocrysts in (sub)volcanic silica-undersaturated rocks are an important source of information about mantle processes and their relative timing with respect to magmatism. The present work describes variations in trace element (Sc, Ti, Y, Nb, lanthanides, Hf, Ta, Pb, Th, and U) and isotopic (U-Pb) composition of zircon from the Drybones Bay kimberlite, Northwest Territories, Canada. These data were acquired at a spatial resolution of ≤100 µm and correlated to the internal characteristics of macrocrysts (imaged using cathodoluminescence, CL). Six types of zircon were distinguished on the basis of its luminescence characteristics, with the majority of grains exhibiting more than one type of CL response. The oscillatory-zoned core and growth sectors of Drybones Bay zircon show consistent variations in rare-earth elements (REE), Hf, Th, and U. Their chondrite-normalized REE patterns are typical of macrocrystic zircon and exhibit extreme enrichment in heavy lanthanides and a positive Ce anomaly. Their Ti content decreases slightly from the core into growth sectors, but the Ti-in-zircon thermometry gives overlapping average crystallization temperatures (820 ± 26 °C to 781 ± 19 °C, respectively). There is no trace element or CL evidence for Pb loss or other forms of chemical re-equilibration. All distinct zircon types are concordant and give a U-Pb age of 445.6 ± 0.8 Ma. We interpret the examined macrocrysts as products of interaction between a shallow (<100 km) mantle source and transient kimberlitic melt.

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8

Chen, Xiao-Dong, Bin Li, Chong-Bo Sun, and Hong-Bing Zhou. "Protracted Storage for Calc-Alkaline Andesitic Magma in Magma Chambers: Perspective from the Nageng Andesite, East Kunlun Orogen, NW China." Minerals 11, no. 2 (February 13, 2021): 198. http://dx.doi.org/10.3390/min11020198.

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Анотація:

Calc-alkaline andesitic rocks are a major product of subduction-related magmatism at convergent margins. Where these melts are originated, how long they are stored in the magma chambers, and how they evolved is still a matter of debate. In this study, we present new data of whole-rock elemental and Sr-Nd-Pb isotope compositions, and zircon U-Pb-Th isotopes and trace element contents of Nageng (basaltic-)andesites in the East Kunlun Orogen (NW China). The similar age and whole-rock elemental and Sr-Nd-Pb isotope contents suggest that the Nageng andesite and basaltic andesite are co-magmatic. Their low initial 87Sr/86Sr (0.7084–0.7086) but negative εNd(t) values (−10.61 to −9.49) are consistent with a magma source from the juvenile mafic lower crust, possibly related to the mantle wedge with recycled sediment input. The U-Pb age gap between the zircon core (ca. 248 Ma) and rim (ca. 240 Ma) reveals a protracted magma storage (~8 Myr) prior to the volcanic eruption. When compared to the zircon rims, the zircon cores have higher Ti content and Zr/Hf and Nb/Ta ratios, but lower Hf content and light/heavy rare earth element ratios, which suggests that the parental magma was hotter and less evolved than the basaltic andesite. The plagioclase accumulation likely resulted in Al2O3-enrichment and Fe-depletion, forming the calc-alkaline signature of the Nageng (basaltic-)andesites. The magma temperature, as indicated by the zircon saturation and Ti-in-zircon thermometry, remained low (725–828 °C), and allowed for the magma chamber to survive over ~8 Myr. The decreasing εHf(t) values from zircon core (avg. 0.21, range: −1.28 to 1.32) to rim (avg. −3.68, range: −7.30 to −1.13), together with the presence of some very old xenocrystic zircons (268–856 Ma), suggest that the magma chamber had undergone extensive crustal contamination.

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9

Timms, Nick E., Peter D. Kinny, Steven M. Reddy, Katy Evans, Chris Clark, and Dave Healy. "Relationship among titanium, rare earth elements, U–Pb ages and deformation microstructures in zircon: Implications for Ti-in-zircon thermometry." Chemical Geology 280, no. 1-2 (January 2011): 33–46. http://dx.doi.org/10.1016/j.chemgeo.2010.10.005.

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10

Ngoniri, Alexis Hamdja, Habib Dadjo Djomo, Timoleon Ngnotue, Patrick Ayonta Kenne, Ghislain Ngassam Mbianya, Sylvestre Ganno, and Jean Paul Nzenti. "Zircon Trace Element Geochemistry and Ti-in-Zircon Thermometry of the Ngazi-Tina Pan-African Post-Collisional Granitoids, Adamawa Cameroon." International Journal of Geosciences 12, no. 04 (2021): 307–28. http://dx.doi.org/10.4236/ijg.2021.124017.

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11

Page, F. Zeb, Bin Fu, Noriko T. Kita, John Fournelle, Michael J. Spicuzza, Daniel J. Schulze, Fanus Viljoen, Miguel A. S. Basei, and John W. Valley. "Zircons from kimberlite: New insights from oxygen isotopes, trace elements, and Ti in zircon thermometry." Geochimica et Cosmochimica Acta 71, no. 15 (August 2007): 3887–903. http://dx.doi.org/10.1016/j.gca.2007.04.031.

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12

Hayden, Leslie A., and E. Bruce Watson. "Rutile saturation in hydrous siliceous melts and its bearing on Ti-thermometry of quartz and zircon." Earth and Planetary Science Letters 258, no. 3-4 (June 2007): 561–68. http://dx.doi.org/10.1016/j.epsl.2007.04.020.

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13

Crow, Carolyn A., Kevin D. McKeegan, and Desmond E. Moser. "Coordinated U–Pb geochronology, trace element, Ti-in-zircon thermometry and microstructural analysis of Apollo zircons." Geochimica et Cosmochimica Acta 202 (April 2017): 264–84. http://dx.doi.org/10.1016/j.gca.2016.12.019.

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14

Sepahi, Ali A., Hamed Vahidpour, David R. Lentz, Chris RM McFarlane, Mohammad Maanijou, Sedigheh Salami, Mirmohammad Miri, Mehrak Mansouri, and Razieh Mohammadi. "Rare sapphire-bearing syenitoid pegmatites and associated granitoids of the Hamedan region, Sanandaj–Sirjan zone, Iran: analysis of petrology, lithogeochemistry and zircon geochronology / trace element geochemistry." Geological Magazine 157, no. 9 (February 24, 2020): 1499–525. http://dx.doi.org/10.1017/s0016756820000023.

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Анотація:

AbstractPegmatites and associated granitoids are integral parts of the Alvand plutonic complex in the Sanandaj–Sirjan zone, Iran. Whole rock major- and trace-element lithogeochemistry together with zircon U–Pb geochronology and zircon geochemistry are examined to evaluate the petrogenesis of sapphire-bearing pegmatites and other peraluminous pegmatites in the region. Pegmatites vary in their chemical compositions from mostly peraluminous, high-K calc-alkaline to shoshonitic signatures. A rare variety of extremely peraluminous sapphire-bearing syenitoid pegmatite (Al2O3 > 30 wt %; A/CNK > 2) exists. This silica-undersaturated pegmatite and its sapphire crystals have a primary igneous origin. U–Pb zircon geochronology of three separate samples from this pegmatite indicates the following ages: 168 ± 1 Ma, 166 ± 1 Ma and 164 ± 1 Ma. The zircon grains have notable amounts of Hf (up to 17 200 ppm), U (up to 13 580 ppm), Th (up to 5148 ppm), Y (up to 4764 ppm) and ∑REE (up to 2534 ppm). There is a positive correlation between Hf and Th, Nb and Ta, U and Th, and Y and HREE and a negative correlation between Hf and Y values in the zircons. These zircons exhibit pronounced positive Ce anomalies (Ce/Ce* = 1.15–68.06) and negative Eu anomalies (Eu/Eu* = 0.001–0.56), indicative of the relatively oxidized conditions of the parent magma. Ti-in-zircon thermometry reveals temperatures from as low as ~683 °C up to ~828 °C (average = 755° ± 73 °C). Zircon and monazite saturation equilibria are also consistent with these temperatures. Zircon grains are magmatic (average La < 1.5, (Sm/La)N > 100 and Th/U > 0.7), with chemical characteristics similar to zircons from continental crust.

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15

Liu, Jingbo, Lingmin Zhang, Nanfei Cheng, Yijie Gao, and Liewen Xie. "Thermal structure of the Dabie eclogite-bearing terrane revealed from the results of Ti-in-zircon thermometry." Geological Society, London, Special Publications 474, no. 1 (March 12, 2018): 309–30. http://dx.doi.org/10.1144/sp474.1.

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16

Sepidbar, Fatemeh, Hassan Mirnejad, and Changqian Ma. "Mineral chemistry and Ti in zircon thermometry: Insights into magmatic evolution of the Sangan igneous rocks, NE Iran." Geochemistry 78, no. 2 (May 2018): 205–14. http://dx.doi.org/10.1016/j.chemer.2018.02.001.

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17

Lei, Hengcong, Haijin Xu, and Penglei Liu. "Decoupling between Ti‐in‐zircon and Zr‐in‐rutile thermometry during ultrahigh temperature metamorphism of the Dabie Orogen, China." Geological Journal 55, no. 9 (March 25, 2020): 6442–49. http://dx.doi.org/10.1002/gj.3819.

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18

Barnes, Calvin G., Kevin Werts, Vali Memeti, and Katie Ardill. "Most Granitoid Rocks are Cumulates: Deductions from Hornblende Compositions and Zircon Saturation." Journal of Petrology 60, no. 11 (November 1, 2019): 2227–40. http://dx.doi.org/10.1093/petrology/egaa008.

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Abstract Cumulate processes in granitic magma systems are thought by some to be negligible and by others to be common and widespread. Because most granitic rocks lack obvious evidence of accumulation, such as modal layering, other means of identifying cumulate rocks and estimating proportions of melt lost must be developed. The approach presented here utilizes major and trace element compositions of hornblende to estimate melt compositions necessary for zircon saturation. It then compares these estimates with bulk-rock compositions to estimate proportions of extracted melt. Data from three arc-related magmatic systems were used (English Peak pluton, Wooley Creek batholith, and Tuolumne Intrusive Complex). In all three systems, magmatic hornblende displays core-to-rim decreases in Zr, Hf, and Zr/Hf. This zoning indicates that zircon must have fractionated during crystallization of hornblende, at temperatures greater than 800 °C. This T estimate is in agreement with Ti-in-zircon thermometry, which yields a maximum T estimate of 855 °C. On the basis of this evidence, concentrations of Zr in melts from which hornblende and zircon crystallized were calculated by (1) applying saturation equations to bulk-rock compositions, (2) applying saturation equations to calculated melt compositions, and (3) using hornblende/melt partition coefficients for Zr. The results indicate that melt was lost during crystallization of the granitic magmas, conservatively at least as much as 40 %. These results are in agreement with published estimates of melt loss from other plutonic systems and suggest that bulk-rock compositions of many granitic rocks reflect crystal accumulation and are therefore inappropriate for use in thermodynamic calculations and in direct comparison of potentially consanguineous volcanic and plutonic suites.

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19

Wu, Hailin, Wenbin Zhu, and Rongfeng Ge. "Late Paleoproterozoic granulite-facies metamorphism in the North Altyn Tagh area, southeastern Tarim craton: Pressure-temperature paths, zircon U-Pb ages, and tectonic implications." GSA Bulletin 131, no. 9-10 (March 29, 2019): 1591–606. http://dx.doi.org/10.1130/b35085.1.

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Abstract Granulite occupies the root of orogenic belts, and understanding its formation and evolution may provide critical information on orogenic processes. Previous studies have mainly focused on garnet-bearing high-pressure and medium-pressure granulites, whereas the metamorphic evolution and pressure-temperature (P-T) paths of garnet-absent, low-pressure granulites are more difficult to constrain. Here, we present zircon U-Pb ages and mineral chemistry for a suite of newly discovered two-pyroxene granulites in the North Altyn Tagh area, southeastern Tarim craton, northwestern China. Conventional geothermobarometry and phase equilibrium modeling revealed that these rocks experienced a peak granulite-facies metamorphism at T = 790–890 °C and P = 8–11 kbar. The mineral compositions and retrograde symplectites record a clockwise cooling and exhumation path, possibly involving near-isothermal decompression followed by near-isobaric cooling. Zircon U-Pb dating yielded a ca. 1.97 Ga metamorphic age, which likely represents the initial cooling age, based on Ti-in-zircon thermometry. Combined with regional geological records, we interpret that these granulites originated from the basement rocks of a late Paleoproterozoic magmatic arc that was subsequently involved in a collisional orogen in the southern Tarim craton, presumably related to the assembly of the Columbia/Nuna supercontinent. The clockwise P-T paths of the granulites record crustal thickening and burial followed by crustal thinning and exhumation in the upper plate of the collisional orogen. Our data indicate that the initial exhumation of this orogen probably occurred no later than ca. 1.97 Ga, which is supported by widespread 1.93–1.85 Ga postorogenic magmatism in this area.

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Shardakova, G. Yu, S. V. Pribavkin, A. A. Krasnobaev, N. S. Borodina, and M. V. Chervyakovskaya. "ZIRCONS FROM ROCKS OF THE MURZINKA-ADUI METAMORPHIC COMPLEX: GEOCHEMISTRY, THERMOMETRY, POLYCHRONISM, AND GENETIC CONSEQUENCES." Geodynamics & Tectonophysics 12, no. 2 (June 23, 2021): 332–49. http://dx.doi.org/10.5800/gt-2021-12-2-0527.

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Transformation of the oceanic crust into the continental one in orogenic belts is an important problem in petrological studies. In the paleocontinental sector of the Urals, a key object for tracing the stages of metamorphism and investigating the origin of anatectic granites is the Murzinka-Adui metamorphic complex. We have analyzed trace elements in zircons and established their genesis, sources, crystallization conditions, and stages of metamorphic events and granite generation in this complex. Zircons compositions were determined by the LA-ICP-MS method. Temperatures were calculated from Ti contents in the zircons. We distinguish three geochemical types of zircons, which differ in the ratios of light and heavy REE, U, Th, Ti, Y and show different values of Ce- and Eu-anomalies and Zr/Hf ratios, which are indicative of different crystallization conditions, as follows. Type I: minimal total LREE content; clear negative Eu- and Ce- anomalies; features of magmatic genesis; crystallization temperatures from 629 to 782 °C. Type II: higher contents of Ti, La, and LREE; low Ce-anomaly; assumed crystallization from highly fluidized melts or solutions. Type III: low positive Eu-anomaly; high REE content; low Th/U-ratio; zircons are assumed to originate from a specific fluidized melt with a high Eu-concentration. Ancient relict zircons (2300–330 Ma) in gneisses and granites show features of magma genesis and belong to types I and II. Such grains were possibly inherited from granitoid sources with different SiO2 contents and different degrees of metamorphism. Based on the geological and petrogeochemical features and zircon geochemistry of the Murzinka-Adui complex, there are grounds to conclude that the material composing this complex was generated from the sialic crust. The main stages of metamorphism and/or granite generation, which are traceable from the changes in types and compositions of the zircons, are dated at 1639, 380–370, 330, and 276–246 Ma. Thus, transformation of the oceanic crust into the continental one was a long-term and complicated process, and, as a result, the thickness of the sialic crust is increased in the study area.

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21

Jollands, Michael C., Elias Bloch, and Othmar Müntener. "New Ti-in-quartz diffusivities reconcile natural Ti zoning with time scales and temperatures of upper crustal magma reservoirs." Geology 48, no. 7 (April 13, 2020): 654–57. http://dx.doi.org/10.1130/g47238.1.

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Abstract Titanium-in-quartz thermometry and diffusion chronometry are routinely applied to felsic magmatic systems. These techniques can be used to determine for how long, and at what temperatures, shallow crustal magmatic systems remain partially molten, both of which are fundamental for assessing volcanic hazards. We have conducted new Ti-in-quartz diffusion experiments at 1 bar, in air, between 900 and 1490 °C, and analyzed the products by secondary ion mass spectrometry (SIMS) depth profiling. The results show that Ti diffusivity is two to three orders of magnitude lower than previously determined {log10D = –8.3 ± 0.4 m2 s–1 – [311 ± 12 kJ mol–1/(2.303RT)]}, where R is the universal gas constant (kJK–1 mol–1) and T is the temperature in Kelvin. Application of these new diffusivities brings time scales determined by Ti-in-quartz diffusion chronometry, using quartz primarily from ignimbrites, into agreement with those determined from zircon U-Pb ages from the Bishop Tuff system (California, USA). This indicates that quartz crystallized early and recorded all, or much of, the thermal history of this magmatic system. These new data also show that sharp Ti zoning profiles can be maintained in quartz within slowly cooled rocks without necessitating that the quartz crystallization temperature is significantly lower than the experimentally determined H2O-saturated granite solidus, or that such samples underwent ultrafast cooling, as has recently been proposed for the granitoids from the Tuolumne Intrusive Suite (California, USA). Finally, our data also indicate that, at least regarding the Bishop Tuff, temperatures must have remained at near-solidus conditions for the entire pre-eruptive evolution of the system, thus relaxing interpretations of “cold storage” for this magmatic system.

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22

Ayonta Kenne, Patrick, Evine Laure Tanko Njiosseu, Sylvestre Ganno, Timoleon Ngnotue, Donald Hermann Fossi, Alexis Hamdja Ngoniri, Philomene Nga Essomba, and Jean Paul Nzenti. "Zircon trace element geochemistry and Ti‐in‐zircon thermometry of the Linté Pan‐African granitoids, Central Cameroon: Constraints on the genesis of host magma and tectonic implications." Geological Journal 56, no. 9 (July 15, 2021): 4830–48. http://dx.doi.org/10.1002/gj.4208.

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23

Win, Maw Maw, M. Enami, T. Kato, and Ye Kyaw Thu. "A mechanism for Nb incorporation in rutile and application of Zr-in-rutile thermometry: A case study from granulite facies paragneisses of the Mogok metamorphic belt, Myanmar." Mineralogical Magazine 81, no. 6 (December 2017): 1503–21. http://dx.doi.org/10.1180/minmag.2017.081.014.

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AbstractRutile grains occur extensively in host phases of biotite and quartz-feldspar aggregate in high-temperature paragneisses of the Mogok metamorphic belt of Myanmar. They occur as an isolated phase and sometimes show intergrowth texture with ilmenite. Most rutile grains contain up to 3.7 wt.% Nb2O5, which shows positive correlations with Fe and trivalent elements. Niobium substitutes for Ti by a coupled substitution with the trivalent cations (M3+) of Nb5+M3+Ti4+-2. Fine-grained rutile grains included in ilmenite are distinctly poor in Nb (<0.1 wt.% as Nb2O5) and contain Fe of 1.7–3.2 wt.% as Fe2O3, suggesting vacancybearing substitution of Fe3+4 Ti4+-3□–1, where □ indicates a vacancy. The rutile grains in the felsic phases contain high Zr contents of up to 4200 ppm, suggesting equilibrium temperatures over 800°C using the Ti-in-rutile geothermometer. These high-temperature conditions are consistent with those estimated by conventional methods reported in the literature and suggest widespread occurrences of the upperamphibolite and granulite facies metamorphic rocks in the middle segment of the Mogok metamorphic belt. In contrast, the Zr contents of rutile grains in biotite are usually <1000 ppm, implying equilibrium temperatures lower than 750°C. Most of the rutile grains poorer in Zr might have been included in biotite and were isolated from the zircon-bearing system during an early stage of prograde metamorphism. Some other rutile grains poorer in Zr might have been an exsolved phase from Ti-rich biotite during retrograde metamorphism, which was furthered by the infiltration of metamorphic fluid under lower-amphibolite facies conditions.

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Dutta, Upama, Ayan Kumar Sarkar, Sadhana M. Chatterjee, Anirban Manna, Alip Roy, and Subhrajyoti Das. "Petrological implications of element redistribution during metamorphism: insights from meta-granite of the South Delhi Fold Belt, Rajasthan, India." Geological Magazine 159, no. 5 (February 23, 2022): 735–60. http://dx.doi.org/10.1017/s0016756821001345.

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AbstractMeta-granites of the South Delhi Fold Belt, northwestern India, contain spectacular reaction textures formed during the metamorphic replacement of primary minerals. Textural relationships imply that amphibole was replaced sequentially in two stages. Epidote + titanite + quartz symplectite formed syn-tectonically on amphibole grain boundaries/fractures, followed by post-deformational growth of euhedral garnet overprinting amphibole grains. Besides occurring as symplectite grown during deformation, titanite in this rock also developed as a post-tectonic corona around magnetite. Parent magnetite contains exsolutions of ilmenite and/or ultrafine lamellae of Ti-rich oxide (Ti-oxd). Textures involving coronal titanite suggest their formation through a magnetite + ilmenite(/Ti-oxd) + plagioclase → titanite reaction. Compositional attributes and the calculation of the gain versus loss of components during the reaction suggest that the Mn2+ for garnet (XSpss = 0.23–0.29) that grew replacing amphibole was supplied by ilmenite (Mn2+ is 0.118–0.128 apfu) as it disintegrated to form coronal titanite. The redistribution of components between the metamorphic reaction sites connects the texturally unrelated domains and suggests that these zones were in chemical equilibrium during metamorphism. We estimated the P–T conditions of metamorphism for these post-tectonic assemblages as ∼650–700 °C from pseudosection modelling and conventional thermometry. Zircon data from this study suggest that the granitic rock crystallized at 988.8 ± 8.8 Ma. We propose that the metamorphic phases replaced the primary minerals during the mid Neoproterozoic tectonic activity reported from this terrane. The syn-tectonic symplectitic assemblage formed as the temperature increased during prograde metamorphism, and the post-tectonic minerals developed at peak conditions following the cessation of deformation.

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Kotková, J., and S. L. Harley. "Anatexis during High-pressure Crustal Metamorphism: Evidence from Garnet–Whole-rock REE Relationships and Zircon–Rutile Ti–Zr Thermometry in Leucogranulites from the Bohemian Massif." Journal of Petrology 51, no. 10 (August 26, 2010): 1967–2001. http://dx.doi.org/10.1093/petrology/egq045.

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26

Liu, Xuan, Kuifeng Yang, Brian Rusk, Zhengjie Qiu, Fangfang Hu, and Jacques Pironon. "Copper Sulfide Remobilization and Mineralization during Paleoproterozoic Retrograde Metamorphism in the Tongkuangyu Copper Deposit, North China Craton." Minerals 9, no. 7 (July 18, 2019): 443. http://dx.doi.org/10.3390/min9070443.

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Анотація:

The Tongkuangyu copper deposit, North China Craton, is hosted in a volcano-sedimentary sequence (ca. 2.2 Ga) that metamorphosed to the lower amphibolite facies at ca. 1.9 Ga. Petrographic observations revealed various metamorphic fabrics (mineral alignment and foliations) and several generations of biotite, chlorite, and pyrite. Sulfide Pb-Pb dating indicates that copper mineralization occurred at 1960+46/−58 Ma, younger than the zircon U-Pb age of the host metatuff (2180 Ma to 2190 Ma), but close to the timing of regional metamorphism (ca. 1.9 Ga). Electron probe analyses show that the biotites belong to the magnesium-rich variety, and were formed at 470 to 500 ° C based on Ti-in-biotite thermometry. Chlorites belong to ripidolite and pycnochlorite, and were formed at ca. 350 ° C based on the Al geothermometer. Pyrites in porphyry, metatuffs, and quartz veins have contrasting Ni and Co concentrations, pointing to a local remobilization. Hydrogen and oxygen isotopic analyses suggest that biotite and chlorite were formed by metamorphic waters whereas quartz records much lower δ D f l u i d values, reflecting the influence of meteoric water. Fluid inclusions in pyrite and chalcopyrite in metatuff and quartz vein contain extremely radiogenic 4 He and 40 Ar, indicating a crustal origin for the fluids. Sulfides show a magmatic sulfur isotopic signature, likely indicating the presence of preexisting volcanism-related sulfides. We proposed that the early layered copper sulfides formed during metamorphic retrogression at ca. 1.9 Ga and the late vein-type sulfides were derived from the remobilization of the earlier sulfides by infiltration of external fluids such as residual seawater and metamorphic fluids at shallow level.

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27

Uher, Pavel, Igor Broska, Ewa Krzemińska, Martin Ondrejka, Tomáš Mikuš, and Tomáš Vaculovič. "Titanite composition and SHRIMP U–Pb dating as indicators of post-magmatic tectono-thermal activity: Variscan I-type tonalites to granodiorites, the Western Carpathians." Geologica Carpathica 70, no. 6 (December 1, 2019): 449–70. http://dx.doi.org/10.2478/geoca-2019-0026.

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Abstract Titanite belongs to the common accessory minerals in Variscan (~360–350 Ma) metaluminous to slightly peraluminous tonalites to granodiorites of I-type affinity in the Tatric and Veporic Units, the Western Carpathians, Slovakia. It forms brown tabular prismatic-dipyramidal crystals (~0.5 to 10 mm in size) in association with quartz, plagioclase, and biotite. Titanite crystals commonly shows oscillatory, sector and convolute irregular zonal textures, reflecting mainly variations in Ca and Ti versus Al (1–2 wt. % Al2O3, 0.04–0.08 Al apfu), Fe (0.6–1.6 wt. % Fe2O3, 0.02–0.04 Fe apfu), REE (La to Lu + Y; ≤4.8 wt. % REE2O3, ≤ 0.06 REE apfu), and Nb (up to 0.5 wt. % Nb2O5, ≤0.01 Nb apfu). Fluorine content is up to 0.5 wt. % (0.06 F apfu). The compositional variations indicate the following principal substitutions in titanite: REE3+ + Fe3+ = Ca2+ + Ti4+, 2REE3+ + Fe2+ = 2Ca2+ + Ti4+, and (Al, Fe)3+ + (OH, F)− = Ti4+ + O2−. The U–Pb SHRIMP dating of titanite reveal their Variscan ages in an interval of 351.0 ± 6.5 to 337.9 ± 6.1 Ma (Tournaisian to Visean); titanite U–Pb ages are thus ~5 to 19 Ma younger than the primary magmatic zircon of the host rocks. The Zr-in-titanite thermometry indicates a relatively high temperature range of titanite precipitation (~650–750 °C), calculated for assumed pressures of 0.2 to 0.4 GPa and a(TiO2) = 0.6–1.0. Consequently, the textural, geochronological and compositional data indicate relatively high-temperature, most probably early post-magmatic (subsolidus) precipitation of titanite. Such titanite origin could be connected with a subsequent Variscan tectono-thermal event (~340 ± 10 Ma), probably related with younger small granite intrusions and/or increased fluid activity. Moreover, some titanite crystals show partial alteration and formation of secondary titanite (depleted in Fe and REE) + allanite-(Ce) veinlets (Sihla tonalite, Veporic Unit), which probably reflects younger Alpine (Cretaceous) tectono-thermal overprint of the Variscan basement of the Western Carpathians.

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28

Bolhar, R., A. Hofmann, C. M. Allen, and R. Maas. "A LA-ICPMS zircon record of magmatic crystallization and compositional alteration in meta-igneous rocks of the eastern Kaapvaal Craton." South African Journal of Geology 124, no. 3 (September 1, 2021): 761–82. http://dx.doi.org/10.25131/sajg.124.0042.

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Abstract Archaean zircons from the Kaapvaal Craton, South Africa, were analyzed by Laser Ablation (LA)-ICP-MS to obtain a coupled record of U-Th-Pb isotope ratios and selected trace elements with the aim to develop insights into physico-chemical conditions during igneous zircon crystallization and subsequent compositional alteration. Four rock samples previously dated by SIMS U-Pb using zircon were selected: 3.56 Ga Ngwane Gneiss, 3.55 Ga Theespruit felsic metavolcanic, 3.50 Ga Steynsdorp Gneiss and 2.98 Ga Nhlangano Gneiss. LA-ICP-MS U-Pb zircon ages agree with published SIMS U-Pb ages within analytical uncertainty. Assessment of the magmatic crystallization histories was based on near-concordant grains, and discordant grains were used to examine post-igneous element mobilization and alteration. Time-resolved laser drilling experiments allowed distinction of concordant and discordant zircon domains, but also revealed systematic changes in REE + Ti geochemistry, U + Th content, discordance and metamictization. Th/U and Zr/Hf, coupled with REE patterns, effectively distinguish compositional zircon types that reflect variable degrees of igneous differentiation and melt compositions. Eu/Eu* values indicate significant feldspar fractionation in some magmas. Averaged crystallization temperatures of magmatic zircons, as derived from the Ti-in-zircon thermometer, define a narrow range of 650 to 750°C for (near-)concordant grains, consistent with general constraints on temperatures at zircon saturation for felsic magmas, and testifying to a closed-system behavior of Ti (and other trace elements). Systematic deviations from primary igneous trace element signatures are strongly correlated with radiation damage. Specifically, Th/U and, to some extent, Zr/Hf decrease, and Ti increases with increasing U (+Th) content and isotopic disturbance (discordance).

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29

Ferry, J. M., and E. B. Watson. "New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers." Contributions to Mineralogy and Petrology 154, no. 4 (May 8, 2007): 429–37. http://dx.doi.org/10.1007/s00410-007-0201-0.

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30

Filina, Maria I., Elena S. Sorokina, Roman Botcharnikov, Stefanos Karampelas, Mikhail A. Rassomakhin, Natalia N. Kononkova, Anatoly G. Nikolaev, Jasper Berndt, and Wolfgang Hofmeister. "Corundum Anorthosites-Kyshtymites from the South Urals, Russia: A Combined Mineralogical, Geochemical, and U-Pb Zircon Geochronological Study." Minerals 9, no. 4 (April 16, 2019): 234. http://dx.doi.org/10.3390/min9040234.

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Kyshtymites are the unique corundum-blue sapphire-bearing variety of anorthosites of debatable geological origin found in the Ilmenogorsky-Vishnevogorsky complex (IVC) in the South Urals, Russia. Their mineral association includes corundum-sapphire, plagioclase (An61–93), muscovite, clinochlore, and clinozoisite. Zircon, churchite-(Y), monazite-(Ce), and apatite group minerals are found as accessory phases. Besides, churchite-(Y) and zircon are also identified as syngenetic solid inclusions within the sapphires. In situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb zircon geochronology showed the ages at about 290–330 Ma linked to the Hercynian orogeny in IVC. These ages are close to those of the syenitic and carbonatitic magmas of the IVC, pointing to their syngenetic origin, which is in agreement with the trace element geochemistry of the zircons demonstrating clear magmatic signature. However, the trace element composition of sapphires shows mostly metamorphic signature with metasomatic overprints in contrast to the geochemistry of zircons. The reason for this discrepancy can be the fact that the discrimination diagrams for sapphires are not as universal as assumed. Hence, they cannot provide an unambiguous determination of sapphire origin. If it is true and zircons can be used as traces of anorthosite genesis, then it can be suggested that kyshtymites are formed in a magmatic process at 440–420 Ma ago, most probably as plagioclase cumulates in a magma chamber. This cumulate rock was affected by a second magmatic event at 290–330 Ma as recorded in zircon and sapphire zoning. On the other hand, Ti-in-zircon thermometer indicates that processes operated at relatively lower temperature (<900 °C), which is not enough to re-melt the anorthosites. Hence, zircons in kyshtymites can be magmatic but inherited from another rock, which was re-worked during metamorphism. The most probable candidate for the anorthosite protolith is carbonatites assuming that metamorphic fluids could likely leave Al- and Si-rich residue, but removed Ca and CO2. Further, Si is consumed by the silicification of ultramafic host rocks. However, kyshtymites do not show clear evidence of pronounced metasomatic zonation and evidence for large volume changes due to metamorphic alteration of carbonatites. Thus, the obtained data still do not allow for univocal reconstruction of the kyshtymite origin and further investigations are required.

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31

Ewing, Tanya A., Jörg Hermann, and Daniela Rubatto. "The robustness of the Zr-in-rutile and Ti-in-zircon thermometers during high-temperature metamorphism (Ivrea-Verbano Zone, northern Italy)." Contributions to Mineralogy and Petrology 165, no. 4 (November 28, 2012): 757–79. http://dx.doi.org/10.1007/s00410-012-0834-5.

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32

Vetrov, Evgeny V., Evgeny A. Pikhutin, and Natalia I. Vetrova. "Geochemical Constraints on Petrogenesis and Tectonics of the Middle Devonian Granitic and Coeval Mafic Magmatism from the Tannuola Terrane (Northern Central Asian Orogenic Belt)." Minerals 12, no. 10 (October 12, 2022): 1282. http://dx.doi.org/10.3390/min12101282.

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Анотація:

The Tannuola terrane, located in the northern Central Asian Orogenic Belt, comprises magmatic rocks, attributed to island-arc and collisional settings during the Early Cambrian to the Late Ordovician. However, zircon U-Pb age, geochemical, and Sr-Nd isotopic constraints demonstrate that there was a short episode of peralkaline A-type granite magmatism in the northeast border area of the Tannuola terrane. The obtained zircon U-Pb age of 387.7 ± 3.3 Ma indicates emplacement of the peralkaline A-type granitic rocks in the Middle Devonian (Eifelian–Givetian period boundary). Petrologically, these rocks are mainly composed of riebeckite granites and aplites, which are approximately synchronous with augite-rich dolerites. The granitic rocks are ferroan and calc-alkalic to alkali-calcic in composition. They are characterized by a high content of SiO2, total alkali, Zr, and total REE. Significant depletion of Ba, Sr, P, Ti, and Eu indicates fractionation of plagioclase and/or K-feldspar. The values of εNd(t) in riebeckite granites range from +5.61 to +6.55, and the calculated two-stage model age ranges between 610 and 520 Ma. Coeval dolerites on the chondrite-normalized REE pattern, (Th/Yb)pm–(Nb/Yb)pm, and Th/Yb–Nb/Yb diagrams show compositional affinity between E-MORB and OIB. They are rich in incompatible elements with high HFSE/LREE ratios (Nb/La > 1), indicating that the primary magma originated from the lithospheric mantle metasomatized by asthenosphere-derived melt. Based on these geochemical characteristics, it can be reasonably inferred that the peralkaline A-type granitic rocks, and the coeval mafic rocks, are anorogenic and were emplaced in an extensional tectonic environment despite slightly higher Y/Nb values, which might be caused by a crustal contamination effect. The geochemistry of mafic rocks suggests that the magma originated from the enriched mantle sources. The results of a zircon-saturation thermometer show high initial magma temperatures between 923 and 1184 °C, with an average of 1030 °C, indicating this rock association might be related to a mantle plume beneath the northern Central Asian Orogenic Belt.

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33

Liu, Yi-Can, Liang-Peng Deng, Xiao-Feng Gu, C. Groppo, and F. Rolfo. "Application of Ti-in-zircon and Zr-in-rutile thermometers to constrain high-temperature metamorphism in eclogites from the Dabie orogen, central China." Gondwana Research 27, no. 1 (January 2015): 410–23. http://dx.doi.org/10.1016/j.gr.2013.10.011.

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34

Qiao, Hengzhong, Changqing Yin, Qiuli Li, Xiaolan He, Jiahui Qian, and Wenjing Li. "Application of the revised Ti-in-zircon thermometer and SIMS zircon U-Pb dating of high-pressure pelitic granulites from the Qianlishan-Helanshan Complex of the Khondalite Belt, North China Craton." Precambrian Research 276 (May 2016): 1–13. http://dx.doi.org/10.1016/j.precamres.2016.01.020.

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35

Xu, Haijin, Kai Ye, and Junfeng Zhang. "Temperature of prograde metamorphism, decompressional partial melting and subsequent melt fractional crystallization in the Weihai migmatitic gneisses, Sulu UHP terrane: Constraints from Ti-in-zircon thermometer." Journal of Earth Science 23, no. 6 (December 2012): 813–27. http://dx.doi.org/10.1007/s12583-012-0303-0.

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36

Clark, Chris, Alan S. Collins, M. Santosh, Richard Taylor, and Benjamin P. Wade. "The P-T-t architecture of a Gondwanan suture: REE, U–Pb and Ti-in-zircon thermometric constraints from the Palghat Cauvery shear system, South India." Precambrian Research 174, no. 1-2 (October 2009): 129–44. http://dx.doi.org/10.1016/j.precamres.2009.07.003.

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37

Volante, S., W. J. Collins, E. Blereau, A. Pourteau, C. Spencer, N. J. Evans, V. Barrote, A. R. Nordsvan, Z. X. Li, and J. Li. "Reassessing zircon-monazite thermometry with thermodynamic modelling: insights from the Georgetown igneous complex, NE Australia." Contributions to Mineralogy and Petrology 175, no. 12 (November 5, 2020). http://dx.doi.org/10.1007/s00410-020-01752-7.

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AbstractAccessory mineral thermometry and thermodynamic modelling are fundamental tools for constraining petrogenetic models of granite magmatism. U–Pb geochronology on zircon and monazite from S-type granites emplaced within a semi-continuous, whole-crust section in the Georgetown Inlier (GTI), NE Australia, indicates synchronous crystallisation at 1550 Ma. Zircon saturation temperature (Tzr) and titanium-in-zircon thermometry (T(Ti–zr)) estimate magma temperatures of ~ 795 ± 41 °C (Tzr) and ~ 845 ± 46 °C (T(Ti-zr)) in the deep crust, ~ 735 ± 30 °C (Tzr) and ~ 785 ± 30 °C (T(Ti-zr)) in the middle crust, and ~ 796 ± 45 °C (Tzr) and ~ 850 ± 40 °C (T(Ti-zr)) in the upper crust. The differing averages reflect ambient temperature conditions (Tzr) within the magma chamber, whereas the higher T(Ti-zr) values represent peak conditions of hotter melt injections. Assuming thermal equilibrium through the crust and adiabatic ascent, shallower magmas contained 4 wt% H2O, whereas deeper melts contained 7 wt% H2O. Using these H2O contents, monazite saturation temperature (Tmz) estimates agree with Tzr values. Thermodynamic modelling indicates that plagioclase, garnet and biotite were restitic phases, and that compositional variation in the GTI suites resulted from entrainment of these minerals in silicic (74–76 wt% SiO2) melts. At inferred emplacement P–T conditions of 5 kbar and 730 °C, additional H2O is required to produce sufficient melt with compositions similar to the GTI granites. Drier and hotter magmas required additional heat to raise adiabatically to upper-crustal levels. S-type granites are low-T mushes of melt and residual phases that stall and equilibrate in the middle crust, suggesting that discussions on the unreliability of zircon-based thermometers should be modulated.

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38

Dardier, Ahmed M., Osama K. Dessouky, and Mohammed Z. El-Bialy. "TZT: a windows program for calculating zircon crystallization temperature based on Ti-in-zircon thermometry." Earth Science Informatics, March 5, 2021. http://dx.doi.org/10.1007/s12145-021-00596-4.

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39

Schiller, David, and Fritz Finger. "Application of Ti-in-zircon thermometry to granite studies: problems and possible solutions." Contributions to Mineralogy and Petrology 174, no. 6 (May 27, 2019). http://dx.doi.org/10.1007/s00410-019-1585-3.

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40

Loucks, Robert R., Marco L. Fiorentini, and Gonzalo J. Henríquez. "New Magmatic Oxybarometer Using Trace Elements in Zircon." Journal of Petrology 61, no. 3 (February 20, 2020). http://dx.doi.org/10.1093/petrology/egaa034.

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Abstract We derive a novel method for determining the oxidation state of a magma as zircon crystallized, with a standard error of ±0·6 log unit ƒO2, using ratios of Ce, U, and Ti in zircon, without explicit determination of the ionic charge of any of them, and without independent determination of crystallization temperature or pressure or parental melt composition. It yields results in good agreement with oxybarometry on Fe–Ti oxide phenocrysts and hornblende phenocrysts quenched in eruptive I- and A-type dacites and rhyolites, but our zircon oxybarometer is also applicable to slowly cooled plutonic rocks and applicable to detrital and xenocrystic zircons. Zircon/melt partition coefficients of Ce and U vary oppositely with ƒO2 variation in the silicate melt. The Ce/U ratio in zircon also varies with the Ce/U element ratio in the silicate melt. During mafic-to-felsic magmatic differentiation, Ce and U are incorporated mainly in calcium-dominated lattice sites of clinopyroxene, hornblende, apatite, and occasionally titanite and/or allanite, all of which have a similar degree of preference for Ce over U. We employ the U/Ti ratio in zircon and in silicate melt as a magmatic differentiation index. Convergent- and divergent-plate-margin differentiation series consistently follow the relation log (Ce/U) ≈ –0·5 log (U/Ti) + C' in silicate melts of basaltic to rhyolitic composition. That correlation permits thermodynamic derivation of the oxybarometry relation among those elements in zircon: log fO2(sample)−log fO2(FMQ)≈42n+1log[Ce/(Ui×Ti)z]+C, wherein Ui denotes age-corrected initial U content, FMQ represents the reference buffer fayalite + magnetite + quartz, superscript z denotes zircon, and n varies with the average valence of uranium in the zircon’s parental silicate melt. We empirically calibrate this relation, using 1042 analysed zircons in 85 natural populations having independently constrained log ƒO2 in the range FMQ – 4·9 to FMQ + 2·9, to obtain the equation log fO2(sample)−log fO2(FMQ)=3·998(±0·124) log[Ce/(Ui×Ti)z]+2·284(±0·101) with a correlation coefficient R = 0·963 and standard error of 0·6 log unit ƒO2 in calc-alkalic, tholeiitic, adakitic, and shoshonitic, metaluminous to mildly peraluminous and mildly peralkaline melts in the composition range from kimberlite to rhyolite. Thermodynamic assessment and empirical tests indicate that our formulation is insensitive to varying crystallization temperature and pressure at lithospheric conditions. We present a revised equation for Ti-in-zircon thermometry that accounts appropriately for pressure as well as reduced activity of TiO2 and SiO2 in rutile- and quartz-undersaturated melts. It can be used to retrieve absolute values of ƒO2 from values of ΔFMQ obtained from a zircon analysis.

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41

Guevara, Victor E., Scott A. MacLennan, Besim Dragovic, Mark J. Caddick, Blair Schoene, Andrew R. C. Kylander-Clark, and Chris G. Couëslan. "Polyphase Zircon Growth during Slow Cooling from Ultrahigh Temperature: an Example from the Archean Pikwitonei Granulite Domain." Journal of Petrology 61, no. 1 (January 2020). http://dx.doi.org/10.1093/petrology/egaa021.

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Abstract Quantifying the timescales of Archean ultrahigh temperature (UHT) metamorphism is essential for constraining the style of plate tectonics on the early Earth. However, such timescales can be difficult to quantify, due to the antiquity of Archean rocks and the extreme thermal conditions of UHT metamorphism. We constrain the timescales of Archean UHT metamorphic processes recorded by a single rock sample from the Pikwitonei granulite domain (northwestern Superior Province), through the integration of two U–Pb zircon petrochronologic techniques. In this study we combine: (1) high-spatial resolution laser ablation split-stream inductively coupled mass spectrometry (LASS) on in situ zircon (in thin section) and hand-picked zircon; and (2) high-precision isotope dilution thermal ionization mass spectrometry (ID-TIMS) analyses on microsampled fragments from the same hand-picked zircon analysed by LASS. Phase equilibria modelling and Zr-in-rutile thermometry suggest the rock followed a P–T path characterized by decompression at > 960 °C, followed by near-isobaric cooling at ∼0·8 GPa. In situ LASS zircon analyses could be interpreted to record zircon growth at broadly ∼2665 Ma, though the large uncertainties on isotopic dates make potentially distinct growth episodes difficult to distinguish. ID-TIMS U–Pb dates of zircon fragments reveal a polyphase zircon growth history over a 24 Ma duration, from 2673 to 2649 Ma. Zircon trace element compositions, textures, and microstructural relationships, as well as evaluation of zircon-garnet equilibrium, suggest zircon grew during melt crystallization, after UHT decompression and garnet resorption. Variable Ti concentrations within zircon domains indicate: (1) zircon crystallized through the temperature interval of ∼875 °C to ∼730 °C, potentially in isolated rock domains with variable zircon saturation temperature; and/or (2) zircon crystallized over a narrower temperature interval in isolated rock domains with variable aTiO2 and/or aSiO2. Collectively, the data suggest the west-central Pikwitonei granulite domain reached peak UHT conditions prior to 2673 Ma, after which suprasolidus conditions in the lower crust persisted for at least 24 Ma. Such an interpretation would be impossible if based on either the LASS or ID-TIMS zircon data alone, which highlights the utility of applying both techniques in tandem to constrain metamorphic timescales in ancient UHT terranes.

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42

Hofmann, Amy E., Michael B. Baker, and John M. Eiler. "Sub-micron-scale trace-element distributions in natural zircons of known provenance: implications for Ti-in-zircon thermometry." Contributions to Mineralogy and Petrology 168, no. 3 (September 2014). http://dx.doi.org/10.1007/s00410-014-1057-8.

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43

Groulier, Pierre-Arthur, François Turlin, Anne-Sylvie André-Mayer, Daniel Ohnenstetter, Alexandre Crépon, Philippe Boulvais, Marc Poujol, et al. "Silicate-Carbonate Liquid Immiscibility: Insights from the Crevier Alkaline Intrusion (Quebec)." Journal of Petrology 61, no. 3 (February 19, 2020). http://dx.doi.org/10.1093/petrology/egaa033.

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Abstract This contribution explores the petrogenetic relationships between silicate and carbonatitic rocks in the Crevier Alkaline Intrusion (CAI, Québec, Canada). The CAI is located in the Proterozoic Grenville Province and is composed of a suite of undersaturated peralkaline rocks from ijolite to nepheline syenite and carbonatites. Petrogenetic relationships between different undersaturated alkaline igneous rocks, carbonate-bearing and carbonate-free nepheline syenite and carbonatites observed in the CAI suggest that (1) carbonate-bearing and carbonate-free silicate rocks are comagmatic with carbonatite, and that (2) both silicate and carbonatitic liquids are fractionated from an ijolitic parental magma that has undergone liquid immiscibility. One of the observed facies is characterized by spectacular ocelli of carbonate-bearing nepheline syenite in a matrix of carbonatite. The younger nepheline syenite facies can be divided into two groups based on the presence or absence of magmatic carbonates. Both groups are characterized by the presence of pyrochlore-group minerals that carry the Nb–Ta mineralization. We specifically use accessory minerals such as zircon, pyrochlore and apatite to constrain the temporal and physicochemical parameters of the immiscibility process. By coupling (1) mineral textures, (2) trace elements, (3) Ti-in-zircon thermometry, and (4) oxygen isotope compositions, we have traced the crystallization of zircon before, during and after the immiscibility process. The results allowed us to constrain the minimum temperature of this process at ∼815–865°C. In addition, two magmatic populations of pyrochlore are identified through their petrographic and geochemical characteristics within the younger nepheline syenite facies. Pyrochlore from the earlier ocelli facies of carbonate-bearing nepheline syenite follow a Nb–Ta differentiation trend, whereas pyrochlore from the younger carbonate-free nepheline syenite follow a more classical Nb–Ti trend. Following the complete immiscibility between the silicate and carbonatitic liquids, the fractionation between Nb and Ta stopped while a new generation of Nb-rich pyrochlore grew, displaying a more classical Nb–Ti fractionation trend and a higher Nb/Ta ratio in the nepheline syenite.

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44

Finger, Fritz, David Schiller, Martin Lindner, Christoph Hauzenberger, Kryštof Verner, and Jiří Žák. "Ultrahigh-temperature granites and a curious thermal eye in the post-collisional South Bohemian batholith of the Variscan orogenic belt (Europe)." Geology, February 11, 2022. http://dx.doi.org/10.1130/g49645.1.

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Comprehensive zircon thermometry that takes into account zircon saturation temperatures, Ti-in-zircon measurements, and zircon morphologies and microstructures can provide key information on the thermal evolution of a granite batholith. The Variscan South Bohemian batholith (Germany, Austria, and Czech Republic) comprises a series of granitoid units that intruded between ca. 330 and ca. 300 Ma. We categorize the granitic rocks according to their emplacement temperature into very low temperature (T) (VLT; <750 °C), low T (LT; 750–800 °C), medium T (MT; 800–850 °C), high T (HT; 850–900 °C), and ultrahigh T (UHT; >900 °C). The first stage of batholith formation (ca. 330–325 Ma) is characterized by LT to MT melting of mainly metasedimentary sources driven by their isothermal exhumation. In turn, ca. 322 Ma HT and UHT granites in the southern half of the batholith reveal an ephemeral thermal anomaly in the subbatholithic crust, which is presumably linked to a hidden mafic intrusion. The HT and UHT granites are weakly peraluminous, high-K, I-type rocks. Although sharing some features with A-type granites such as high Zr and rare earth element contents, they differ from classical A-type granites in being magnesian, not enriched in Ga over Al, and having high Ba and Sr contents. A ring structure of ca. 317 Ma MT and/or LT plutons is observed around the HT and/or UHT granite complex and interpreted as an aftermath of the hotspot event. This study is an example of how deep-crustal hotspots, presumably caused by mantle magmatism, can significantly enhance the effects of decompressional crustal melting in a post-collisional setting.

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45

Wu, Hongjie, Yongsheng He, Shuguang Li, Chuanwei Zhu, and Zhenhui Hou. "Partial Melts of Intermediate–Felsic Sources in a Wedged Thickened Crust: Insights from Granites in the Sulu Orogen." Journal of Petrology 61, no. 5 (May 2020). http://dx.doi.org/10.1093/petrology/egaa053.

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Abstract High-pressure (>15 kbar) melts of intermediate–felsic materials have been well studied by experiments, whereas their existence in nature, especially in orogenic belts, is rarely examined. With the aim of identifying and characterizing high-pressure partial melts of intermediate–felsic continental crusts, this study presents comprehensive geochemical and geochronological data for 47 Jurassic granites (166∼157 Ma) from the Sulu orogen. These Sulu Jurassic granites (SJG) consist of quartz, K-feldspar and plagioclase with minor mineral assemblages of biotite ± muscovite ± garnet ± epidote ± allanite. Their low mafic mineral abundance, high SiO2 and Al2O3, and low FeOt + MgO contents show leucogranite-like affinities. They have low Mg#, low Rb/Sr, and mildly peraluminous features, collectively suggesting an intermediate–felsic orthogneissic source. Whole-rock Zr saturation thermometry and Ti-in-zircon thermometry together suggest initial magma temperatures between 695 ± 32 °C and 751 ± 27 °C (1 standard deviation), indicating derivation from water-present melting. The SJG notably feature high Sr contents (average 792 ppm), high Sr/CaO ratios (average 476) as well as inter-correlated low REE concentrations (average ΣREE 87 ppm), low Th concentrations (average 5·1 ppm) and positive Eu anomalies (Eu/Eu* up to 2·94). These characteristics are best explained by partial melting of intermediate–felsic sources under high pressure (>15 kbar), leaving residuum where feldspar is sparse or absent and allanite is present. Inherited zircon age spectra and Sr–Nd–Pb isotopic compositions suggest that their source components could be mainly the Triassic orthogneisses whose protoliths are from the northern margin of the South China Block, probably in a wedge structure where the exhumed felsic slabs were wedged into the crust of the North China Block in the middle–late Jurassic and formed a stacked thickened crust. The wedge structure was most probably driven by synchronous large-scale strike-slip of the Tanlu fault, as a far-field effect of the oblique subduction of the paleo-Pacific plate. The characteristic chemical features observed in this study may be applied to identifying partial melts with similar petrogenesis elsewhere.

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46

Couzinié, Simon, Pierre Bouilhol, Oscar Laurent, Thomas Grocolas, and Jean-Marc Montel. "Cambro–Ordovician ferrosilicic magmatism along the northern Gondwana margin: constraints from the Cézarenque–Joyeuse gneiss complex (French Massif Central)." BSGF - Earth Sciences Bulletin, June 28, 2022. http://dx.doi.org/10.1051/bsgf/2022010.

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It is well-acknowledged that the northern margin of the Gondwana supercontinent was affected by a major magmatic event at late Cambrian (Furongian) to early Ordovician (Tremadocian) times. However, an accurate assessment of its extent, origin, and significance is partly hampered by the incomplete characterization of the numerous gneiss massifs exposed in the inner part of the Variscan belt, as some of them possibly represent dismembered and deformed Furongian–Tremadocian igneous bodies. In this study, we document the case of the “Cézarenque–Joyeuse” gneisses in the Cévennes parautochton domain of the French Massif Central. The gneisses form decametre- to kilometre-thick concordant massifs interlayered within a pluri-kilometric sequence of mica- and quartz schists. They encompass two main petrological types: augen gneisses and albite gneisses, both typified by their blue and engulfed quartz grains with the augen facies differing by the presence of centimetre-sized pseudomorphs after K-feldspar and the local preservation of igneous textures. Whole-rock geochemistry highlights that many gneisses have magmatic ferrosilicic (acidic with anomalously high FeOt and low CaO) compositions while others are akin to grauwackes. Collectively, it is inferred that the bulk of the Cézarenque–Joyeuse gneisses represent former rhyodacite lava flows or ignimbrites and associated epiclastic tuffs. Volumetrically subordinate, finer-grained, and strongly silicic leucogneisses are interpreted as microgranite dykes originally intrusive within the volcanic edifices. LA–ICP–MS U–Pb dating of magmatic zircon grains extracted from an augen gneiss and a leucogneiss brackets the crystallization age of the silicic magmas between 486.1±5.5 Ma and 483.0±5.5 Ma which unambiguously ties the Cézarenque–Joyeuse gneisses to the Furongian–Tremadocian volcanic belt of SW Europe. Inherited zircon date distributions, Ti-in-zircon and zircon saturation thermometry demonstrate that they formed by melting at 750–820 °C of Ediacaran sediments. Zircon Eu/Eu* and Ce/Ce* systematics indicate that the melts were strongly reduced (fO2 probably close to the values expected for the iron–wustite buffer), possibly because they interacted during ascent with Lower Cambrian black shales. This would have enhanced Fe solubility in the melt phase and may explain the peculiar ferrosilicic signature displayed by many Furongian–Tremadocian igneous rocks in the northern Gondwana realm. We infer that crustal melting resulted from a combination of mantle-derived magma underplating in an extensional environment and anomalously elevated radiogenic heat production within the Ediacaran sedimentary sequences.

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47

Pitcher, Bradley W., Guilherme A. R. Gualda, and Takeshi Hasegawa. "Repetitive duality of rhyolite compositions, timescales, and storage and extraction conditions for pleistocene caldera-forming eruptions, Hokkaido, Japan." Journal of Petrology, December 18, 2020. http://dx.doi.org/10.1093/petrology/egaa106.

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Abstract During the Early Pleistocene, numerous caldera-forming eruptions occurred in the southernmost Kurile arc (central Hokkaido, Japan), building an extensive pyroclastic plateau with an area >1600 km2. The arc remains active today, and proximity to populations and infrastructure makes understanding these magmatic systems a critical endeavor. We investigate three major caldera-forming ignimbrite eruptions: Biei (ca. 2.0 Ma), Tokachi (ca. 1.2 Ma), and Tokachi-Mitsumata (ca. 1.0 Ma), with an emphasis on constraining the pressures of magma extraction and storage and the timescales of crystallization. Although all pumice glass compositions from the three eruptions are high-silica rhyolites (77-78 wt. % SiO2), hierarchical clustering analysis of major and trace element glass data indicates that the Tokachi and Tokachi-Mistumata ignimbrites each have two distinct pumice populations (Type-1F and Type-2F). We find that these two distinct pumice types record pre-eruptive temperatures, extraction pressures, and crystallization timescales that are strikingly similar between the two eruptions. Using the rhyolite-MELTS geobarometer, we estimate that although all magma types from all three eruptions had storage pressures of 50-150 MPa (∼2-6 km), Type-1F magma was extracted from a deeper mush reservoir (200-450 MPa) compared to Type-2F (100-200 MPa). Pre-eruptive temperatures, constrained by plagioclase-liquid equilibration thermometry and rhyolite-MELTS, suggest that Type-1F magma in both eruptions was hotter (800-820 °C) compared to Type-2F (780-800 °C), but that both reached thermal equilibrium upon eruption (760-780 °C). Since zircon is only observed as inclusions and rarely in contact with glass, we conclude that all magmas were zircon-undersaturated, and thus zircon saturation temperatures, which are 60-100 °C lower than those estimated by the other three independent thermometers, underestimate magmatic temperatures. Using these temperatures as minimum estimates, diffusional relaxation times of Ti zonation in quartz, as revealed by cathodoluminescence, give absolute maximum quartz residence times of < 1,800 for Type-2F samples and < 600 years for Type-1F for all samples; residence times are < 300 years for all samples if the more reasonable Fe-Ti oxide temperature is used instead (∼770 °C). Our modelling therefore suggests that the melt-dominated rhyolite magmas that fed these caldera-forming eruptions were ephemeral features that crystallized within the shallow crust for centuries to several millennia. Rapid rim growth occurred in all magma types in all three eruptions, with a majority of quartz rims (10-200 µm) having grown in less than two years. Using plagioclase textures and major and trace element data, we conclude that the bright-CL rims of quartz resulted from decompression and subsequent rapid growth, rather than by a recharge-driven heating event. Thus, decompression occurred within two years prior to eruption. Remarkably, the two distinct magma types are statistically similar in terms of composition, crystallization timescales, magma storage conditions, and extraction depths, despite being from eruptions that occurred 240 ka apart, and from calderas that are separated by 35 km. This suggests magma assembly and storage processes that are spatiotemporally repetitive in this region of Hokkaido.

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48

Gao, Peng, Yong-Fei Zheng, Matthew Jason Mayne, and Zi-Fu Zhao. "Miocene high-temperature leucogranite magmatism in the Himalayan orogen." GSA Bulletin, July 30, 2020. http://dx.doi.org/10.1130/b35691.1.

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Himalayan leucogranites of Cenozoic age are generally attributed to partial melting of metasedimentary rocks at low temperatures of <770 °C. It is unknown what the spatial distribution and characteristics of high-temperature (>800 °C) leucogranites are in the Himalayan orogen. The present study reports the occurrence of such leucogranites in the collisional orogen. We use the Ti-in-zircon thermometry in combination with the thermodynamically calibrated relationships of T-aSiO2-aTiO2 to retrieve crystallization temperatures of Miocene (ca. 17 Ma) two-mica granites from Yalaxiangbo, in the eastern Himalaya, SE Tibet. The results give the maximum temperature as high as ∼850 °C for granite crystallization, providing a significant constraint on the nature of thermal sources. Phase equilibrium modeling using metasedimentary rocks as the source rocks indicates that felsic melts produced at ∼850 °C and 6−10 kbar can best match the target leucogranites in lithochemistry. In this regard, the anatectic temperatures previously obtained for the production of Himalayan leucogranites would probably be underestimated to some extent. Such high temperatures are difficult to explain purely by the internal heating of the thickened orogenic crust. Instead, they require an extra heat source, which would probably be provided by upwelling of asthenospheric mantle subsequent to thinning of the orogenic lithospheric mantle by foundering along the convergent plate boundary. Therefore, the Himalayan leucogranites of Miocene age would be derived from partial melting of the metasedimentary rocks in the post-collisional stage.

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49

Rassomakhin, M. A., E. S. Sorokina, and A. V. Somsikova. "Mineralogical-geochemical features of corundum Miaskite-pegmatite from mine no. 210 (Ilmeny mountains, South Urals): preliminary results." МИНЕРАЛОГИЯ (MINERALOGY), July 2020, 38–54. http://dx.doi.org/10.35597/2313-545x-2020-6-2-4.

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Miaskite-pegmatite of mine no. 210 exhibits an unusual mineral composition for the Ilmeny Mountains. It contains a signifcant amount of sapphire-like corundum (uncommon of nepheline-bearing pegmatites) and various Th-bearing minerals («thoro-aeschinite», pyrochlore, phosphates). Pegmatite has a zonal structure, in which the central nepheline and lateral feldspar zones difer in composition of rock-forming and accessory minerals. Corundum is found in all zones of pegmatite. Accessory minerals of the central, eastern, and western zones include (i) Ti-niobates (columbite, pyrochlore, srilankite), zircon, spinel and thorianite, (ii) columbite, pyrochlore and zircon, and (iii) columbite, «ilmenorutile», toro-aeschinite, monazite-La and Ce, and zircon, respectively. The calculations based on two-feldspar thermometer for diferent pegmatite zones show a decrease in temperature from the periphery toward the center, which is in agreement with the variability of mineral assemblages. Pegmatite is strongly altered, which is expressed in the formation of cancrinite and sodalite, hydration of pyrochlore of the central zone, and signifcant compositional changes of Ti-niobates in the lateral zones of pegmatite. The Rb-Sr age of corundum miaskite-pegmatite is ~275 Ma, but the Rb-Sr system is signifcantly destroyed. The initial 87Sr/86Sr(275) isotopic ratio and ?Nd(275) value of the mineral indicate its crustal formation conditions. The geochemistry of corundum points to its multistage crystallization. The data points on Fe vs. Ga / Mg and FeO – Cr2O3 – MgO – V2O3 vs. FeO + TiO2 + Ga2O3 plots correspond to both «magmatic» and «metasomatic» corundum.

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50

Aidoo, Felix, Qiang-Qiang Zhang, Shao-Bing Zhang, and Prosper M. Nude. "Identification of UHT granulites in the Pan-African Dahomeyide suture zone in SE Ghana: Implications for evolution of collisional orogens." Journal of Petrology, May 11, 2022. http://dx.doi.org/10.1093/petrology/egac042.

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Abstract This study presents the petrology, geochemistry, U-Pb ages, Lu-Hf and oxygen isotope compositions of Adaklu mafic granulites (ADMGs), from the Pan-African Dahomeyide suture zone in southeastern Ghana. The ADMGs show mafic precursor with low-K tholeiitic affinity. They display convex rare earth and trace elements characteristics without any obvious anomalies of Eu, Ti, Nb and Ta. The geochemical characteristics of ADMGs mimic those of N-MORB. Zircon U-Pb dating on the ADMGs reveal granulite facies metamorphic ages of ca. 595 – 602 Ma. However, a few zircons yield relatively older apparent 206Pb/238U ages of ca. 620 Ma, representing prograde metamorphic age. ADMGs preserve mean zircon εHf(t) values of +7.0 to +9.7 and δ18O values of 6.1 – 8.0 ‰. Based on petrographic observations, geothermobarometric calculations using conventional thermobarometry, mineral equilibria modelling, Ti-in-zircon and Zr-in-rutile thermometers reveal peak granulite facies P-T conditions of 0.95 – 1.2 GPa/940 – 1000 °C, and retrograde amphibolite facies conditions of 0.83 – 0.93 GPa/575 – 710 °C. The prograde metamorphic stage is inferred to be amphibolite or eclogite facies metamorphism. Hence, a clockwise a P-T-t path is proposed for the ADMGs. The overall results indicate that ADMGs are ultra-high temperature (UHT) granulites, and the protolith is altered oceanic crust consumed during the Pan-African collisional events. Asthenospheric upwelling induced by lithospheric delamination in the earliest extension of the thickened orogen, or by slab break-off under the background of collision may have provided the additional heat for UHT granulite facies metamorphism.

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