Ti Concentrations In Quartz Research Articles

Timescale of magma recharge for a crystal-rich mush: Perspectives from the compositional zoned quartz in Xiangshan caldera, SE China

Crystal-rich (>30 vol%) volcanic rocks, which are generally thought to be formed by the eruption of crystal-rich mush after its reactivation, have provided an important lens through which to view the connection of volcanic and plutonic rocks in the calderas worldwide. The crystal-rich rhyolitic porphyritic lava is widely exposed in Cretaceous calderas in the southeast China. However, the petrogenesis of crystal-rich porphyritic lava still remains controversial. Xiangshan caldera is a uranium mineralization related volcanic-plutonic complex, which is composed of first subcycle rhyodacite and second subcycle tuff, crystal-rich rhyolitic porphyritic lava, granite porphyry and quartz monzonitite porphyry. All the volcanic and plutonic rocks have consistent zircon U-Pb ages (135 to 133 Ma). Sr-Nd-Hf-O isotopic characteristics show that they all mainly originated from crust derived intermediate-silicic magma. Zircon εHf(t) values for inherited zircons from rhyolitic porphyritic lava and rhyodacite range from −6.9 to +9.5. Correspondingly, zircon Hf two-stage model ages of inherited zircons are 2.12 to 1.10 Ga, suggesting their derivation from the Neoproterozoic juvenile crust and the Archean to Paleoproterozoic ancient crust. The rhyolitic porphyritic lavas show higher SiO2 contents and Rb/Sr ratios, and more obvious negative anomalies of Eu/Eu*, Ba, Sr, P and Ti; The granite porphyry show lower SiO2 contents and Rb/Sr ratios, with weak negative anomalies of Eu/Eu*, Ba, Sr, P and Ti. Combined with similar Sr-Nd-Hf-O isotopic composition, they may be derived from the same magma reservoir. Lower εNd(t), εHf(t), δ18O values and older model ages of tuff indicate more contribution of older crustal material. The cathodoluminescence (CL) brightness is strongly correlated with Ti concentration in quartz. The CL of selected quartz grains from crystal-rich rhyolitic porphyritic lava and granite porphyry show brightness zoned mantles (Ti = 19 to 77 ppm) and bright rims (high-Ti; >70 ppm). Some grains have dark cores (low-Ti; <9 ppm). However, the Ti contents of the quartz in the tuff of the second subcycle are homogeneous. Resemble the crystal-rich rhyolitic porphyritic lavas, the rims of quartz phenocrysts in the granite porphyry have consistent CL-brightness with the quartz in groundmass and have small embayments caused by growth impediments in them, which is due to the pressure release. It indicates that the granite porphyry also migrated upward rather than in situ cumulate. The repeated rise of CL brightness and Ti contents in the mantle of quartz phenocrysts recorded the rise of temperature and/or the injection of more primitive magma, indicating several times of magma recharge in the magma reservoir. The timescale of Ti diffusion in the compositional zoned mantle of quartz documented an ephemeral reactivation and remobilization of the crystal-rich mush within several to 16 thousand years with at least 7 times of magma recharge which lasted for 17 years to >11 thousand years each time.

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

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

Ti-in-quartz: Evaluating the role of kinetics in high temperature crystal growth experiments

We present results from 25 hydrothermal quartz growth experiments, all conducted at 800 °C and 1 kbar but with varying starting materials and run times, to address discrepancies between calibrations of the titanium-in-quartz (TitaniQ) thermobarometer. In our experiments, a gold capsule is loaded with silica glass, water, and either rutile or anatase as the TiO2 source. In most experiments, there is also a large quartz seed crystal contained in an open inner capsule. The use of rutile versus anatase has a significant influence on the (re)crystallization pathways of the SiO2 and TiO2 components. When rutile is used, quartz overgrowths have abundant open cavities and complex zonations. The rutile does not completely dissolve because rutile is the stable TiO2 polymorph, and yet, new rutile forms at the quartz seed-overgrowth interface and on the outer surface of quartz crystals. This suggests crystallization of quartz near Ωrut ∼ 1, but wide-ranging Ti concentrations and zonations in quartz are indicative of kinetic effects. When powdered anatase is used, the quartz overgrowths look markedly different, lacking the open cavities and instead exhibiting step edges and terraces. The Ti concentrations in quartz from these experiments are also wide-ranging but reach larger values.Our results span the range of previous calibrations and indicate that Ti concentrations in quartz are sensitive to the TiO2/SiO2 ratio of the fluid as opposed to the absolute concentration (or activity) of dissolved TiO2. We present a kinetic model for quartz and rutile growth from a fluid where the input parameters are the initial degrees of supersaturation with respect to quartz and rutile, the total reactive surface area, and rate constants that link the degree of supersaturation to net precipitation rates. The model can explain many of the salient features of our experimental results, as well as those from previous studies, but requires that the rate constant multiplied by the reactive surface area for rutile is less than that of quartz, and that rutile solubility depends on the SiO2 concentration of the fluid, as documented in the recent literature. Complete quartz-rutile equilibrium may not have been established in any of the experimental studies, but low-pressure experiments with slowly grown quartz seem to be more reliable than extrapolations from high-pressure experiments for thermobarometry of shallow natural systems.

Ti-in-quartz thermobarometry and TiO2 solubility in rhyolitic melts: New experiments and parametrization

The Ti-in-quartz thermobarometer has a wide potential for constraining crystallization pressure and temperature of quartz in natural geological systems. However, there is a long-lasting debate on the applicability of two models that were proposed previously, based on the equilibration of quartz with Ti-bearing aqueous fluids. In this study, the Ti-in-quartz thermobarometer was calibrated based on partitioning data of Ti between quartz and aluminosilicate melt in the pressure and temperature range of 0.5−4 kbar and 700−900°C, which are conditions relevant for high-silica magmas stored at crustal depths.For seventeen experiments, in which both quartz, rutile and high-silica glass are present as experimental products (i.e., activity of TiO2 in silicate melt equals to unity), the Ti concentrations in quartz can be modeled with the following equation:log⁡CTiQtz=5.3226−1948.4/T−981.4⁎P0.2/T, in which CTiQtz is the Ti concentration (ppm) in quartz, T is temperature in kelvin and P is pressure in kbar. Based on the data from this study and a previous work of Hayden and Watson (2007), we modeled the dependence of rutile (TiO2) solubility in silicic melt on temperature, pressure and melt composition, which can be expressed aslog⁡(STiliq)=6.5189−3006.5/T−461.0⁎P0.2/T+0.1155⁎FM, in which STiliq is Ti solubility (ppm) at rutile saturation and FM is a parameter accounting for melt compositional effect, computed asFM=(Na+K+2Ca+2Mg+2Fe)/(Si⁎Al), in which the chemical symbols denote molar fractions of each cation.Combining the two models presented above as well as some additional experimental data at activity of TiO2 <1, and assuming an ideal behavior for the activity of TiO2, the following Ti-in-quartz thermobarometer is proposed:log⁡(CTiQtz/CTiliq)=−1.1963+(1058.1−520.4⁎P0.2)/T−0.1155⁎FM, in which CTiliq is Ti concentration (ppm) in melt. Assuming an uncertainty of input temperature of ±25°C, the corresponding pressure can be determined within ±0.2 kbar. However, the Ti concentrations in quartz and glass need to be determined with a high precision. Typical values of the ratio CTiQtz/CTiliq in natural systems vary in the range from ∼0.09 to ∼0.13, corresponding to a change of pressure from ∼5 to ∼1 kbar assuming a temperature of ∼800°C.The model above was applied to natural datasets obtained for several silicic eruptions (i.e. Oruanui Rhyolite, Early Bishop Tuff, Toba Tuff, Upper Bandelier Tuff). The analyses of quartz and glass inclusions in quartz indicate that the pre-eruptive magma storage pressures are mainly in the range 2–4 kbar. These pressures are consistent to or slightly higher than the maximum value estimated previously from the analysis of H2O-CO2 in glass inclusions, indicating a possible post-entrapment loss of hydrogen from melt inclusions and that gas saturation provides a minimum estimation of pressure.

Magmatic-hydrothermal transition of Mo-W-mineralized granite-pegmatite-greisen system recorded by trace elements in quartz: Krupka district, Eastern Krušné hory/Erzgebirge

Magmatic-hydrothermal transition of highly evolved granitic melts enriched in volatile and incompatible elements can involve disequilibrium intermediate products between aluminosilicate melt and hydrothermal fluid (hydrosilicate liquids) with high ore-forming potential. We investigate evolution from Li-F-rich granites through pegmatites, greisens and quartz veins in a composite stock at Knöttel in the Krupka district (eastern Krušné hory/Erzgebirge mountain range) by monitoring trace-element variations in quartz. Interelemental correlations reveal Si4+ ↔ Li+Al3+ and likely Si4+ ↔ H+Al3+ to be the most important substitution mechanisms. Variations in Ti vs. Li, Be and Al define distinct evolutionary trends: (i) magmatic, high-Li/Ti or Al/Ti trend (granites – aplites – K-feldspar pegmatite); (ii) transitional, medium-Li/Ti trend (quartz megacrysts and pegmatite lenses in granite – quartz-protolithionite pegmatite); (iii) hydrothermal, low-Li/Ti or Al/Ti trend (stockwork of coarse-grained hydrothermal quartzites and quartz veins, quartz replacement in greisens). The medium-Li/Ti trend represents hydrosilicate liquid, an H2O- and SiO2-rich medium with low density and effective viscosity that was probably formed during disequilibrium crystallization in front of rapidly propagating solidification front. Thermal evolution of the magmatic-hydrothermal system was monitored by Ti-in-quartz thermometry. Calculated rutile activity of the granites is very low (0.3–0.05) but it increases (up to 1, that is, saturation) towards pegmatites and hydrothermal veins. Magmatic crystallization (granites and aplites) is constrained to 700–580 °C, pegmatite and bulk greisenization stage occurred at 600–500 °C, followed by a late hydrothermal stage associated with the formation of distal quartz veins at 500–390 °C. The granite-pegmatite systems at Knöttel and in Erzgebirge in general reach extremely high Al, Li, Rb and Ge and low Ti concentrations in quartz in comparison with igneous rocks worldwide. The Knöttel stock belongs to P-poor A-type granites in the Erzgebirge and is linked with them by similar evolutionary trends in quartz trace elements. Furthermore, the Knöttel system exhibits Be enrichment in quartz (probably related to high contents of F) and this appears to be typical feature of Mo-W-mineralized systems in general. The hydrothermal phase with Mo-W mineralization at Knöttel is closely related to the magmatic phase of parental granite body, which seems to be an important condition for Mo-W-mineralization formation.

TitaniQ deformed: Experimental deformation of out-of-equilibrium quartz porphyroclasts

The role of deformation on the equilibration of Ti concentrations in quartz was investigated by running experiments on out-of-equilibrium quartz crystals embedded as porphyroclasts within quartz aggregates. Quartz crystals were first grown from a hydrostatic fluid to set the initial Ti content; crystals grown at temperatures above (925 °C) and below (875 °C) the deformation temperature (900 °C) contain Ti contents ∼60 ppm higher or lower than the equilibrium solubility. These out-of-equilibrium quartz crystals were then deformed as porphyroclasts by embedding them in a matrix composed of either dry or wet quartz to induce two end-member deformation regimes, high-stress or low-stress, respectively. In high-stress experiments, quartz porphyroclasts contain deformation bands and undulose extinction, with some grains showing evidence for grain boundary bulging (BLG) recrystallization. In low-stress experiments, some grains deformed to high strains with minimal evidence for dynamic recrystallization, resulting in ribbon grains, whereas others recrystallized by dislocation creep processes, showing microstructural evidence for subgrain rotation (SGR) and grain boundary migration (GBM) recrystallization. By comparing quartz microstructures with patterns of Ti re-distribution in variably deformed and recrystallized porphyroclasts, we find that grains deformed to high strain with minimal recrystallization show little to no evidence for re-equilibration, whereas grains that recrystallized via grain boundary processes have equilibrated Ti contents that reflect the pressure-temperature conditions of deformation.

Tracking the prograde P\u2013T path of Precambrian eclogite using Ti-in-quartz and Zr-in-rutile geothermobarometry

A Fe–Ti-rich garnet, clinopyroxene, and quartz eclogite sample from the 1.0 Ga Sveconorwegian orogen, SW Sweden, contains abundant quartz, rutile, and zircon in distinct micro-textural sites: garnet core, garnet rim, and matrix, constituting an ideal case for investigation of the behavior of Zr-in-rutile and Ti-in-quartz at high-pressure and temperature. A P–T path, peaking at 16.5–19 kbar and 850–900 °C, has been constrained independently for the same rock by pseudosection modelling; input pressures from this model were used for trace element geothermometry of each garnet micro-textural domain. Trace element thermo(baro)metry, based on in situ Secondary Ion Mass Spectrometry analyses of Ti contents in quartz and Zr contents in rutile, yields P–T estimates of progressive crystallization of quartz and rutile along the prograde metamorphic path. For inclusions in the garnet cores, Zr-in-rutile geothermometry yields 700–715 °C and Ti-in-quartz 620–640 °C at 7 kbar. For inclusions in the garnet rims, temperature estimates are 760–790 °C (Zr-in-rutile) and 740–920 °C (Ti-in-quartz) at 12–18 kbar. Finally, matrix rutile records 775–800 °C and locally ~ 900 °C, and quartz records temperatures up to 900 °C at 18 kbar. Ti-in-quartz estimates for the metamorphic peak (inclusions in the garnet rims and matrix) conform to the pseudosection, but appear too low for the early prograde stage (garnet cores), possibly due to lack of equilibrium at T < 700 °C. The pseudosection shows that rutile was produced by continuous ilmenite breakdown during the early stages of prograde metamorphism, a reaction that was completed at ~ 730 °C. Rutile grains in the garnet rims and the matrix grew subsequently larger by recrystallization of previously produced rutile. However, recrystallized rutile does not predominantly record peak temperatures, but instead yield 745–840 °C between 12 and 18 kbar. In the pseudosection, this temperature range broadly coincides with a stage during which (Ti-bearing) hornblende was consumed and clinopyroxene produced (i.e., dehydration); the Zr contents thus appear to reflect the last stage of efficient rutile recrystallization, catalysed by fluids released by the dehydration of hornblende preceding the metamorphic peak. Concurrently, combination of the isopleths for Ti content in quartz and Zr content in rutile (i.e. independent from pseudosection modelling) yields pressure and temperature conditions in almost perfect agreement with the P–T path as deduced from the pseudosection. The variation in Ti concentration in quartz is small regardless of crystal size, and the Ti-in-quartz geothermometer provides both precise and accurate peak temperatures of 875–920 °C, without a significant diffusional reequilibration. The lack of significant Ti diffusion in quartz is consistent with an inferred short residence time at high temperature. This study illustrates that Zr-in-rutile and Ti-in-quartz geothermobarometry can robustly constrain prograde P–T conditions and yield further insights into recrystallization processes at high temperature. The combination of these methods and integration of the results with pseudosection modelling is a versatile tool for investigating the petrologic history of high-grade rocks.

Al diffusion in quartz

AbstractWe have measured Ti diffusion in quartz under dry 1-atm conditions. Experiments were performed using synthetic and naturalquartz and a TiO 2 powder source, with Ti profiles obtained by Rutherford Backscattering Spectrometry (RBS). Over thetemperature range 700–1150 °C, the following Arrhenius relation was obtained for diffusion parallel to (001):D Ti ¼ 7 10 −8 expð−273F12kJ mol −1 =RTÞm 2 sec −1 Similar diffusivities were obtained for both synthetic and natural quartz, and for a range of Ti source materials, including naturaltitanite powder and rutile–quartz single crystal diffusion couples. Although Ti diffusion appears slightly slower in the directionnormal to c, this difference is not great.Using these diffusion parameters, calculations indicate that distances over which diffusional alteration of Ti concentrations inquartz could occur in a million years would be on order of 500 μm at 800 °C, and ∼15 μm at 600 °C. The Arrhenius relation aboveshould be broadly applicable, and may find application in constraining metamorphic histories under conditions where the Ti-in-quartz geothermometer can be reasonably applied. This relation can also be used to constrain peak temperatures and coolinghistories from observations of exsolved rutile needles in quartz and the width of the Ti-depleted zone that develops around thegrowing needles. Finally, these findings may find utility in evaluating crystal residence times in magmatic systems when coupledwith observations of the sharpness of zoning patterns in quartz.© 2006 Elsevier B.V. All rights reserved.

Porphyry to Epithermal Transition in the Altar Cu-(Au-Mo) Deposit, Argentina, Studied by Cathodoluminescence, LA-ICP-MS, and Fluid Inclusion Analysis

The middle to late Miocene Altar porphyry Cu-(Au-Mo) deposit, located in the Andean Main Cordillera of San Juan Province (Argentina), is characterized by the superposition of multiple vein generations consisting of both porphyry-type and high sulfidation epithermal-style alteration and mineralization. We constrain the physical and chemical evolution of the hydrothermal fluids that formed this deposit based on description and distribution of vein types, scanning electron microscopy, cathodoluminescence (CL) imaging, trace elements in quartz veins, and fluid inclusion microthermometry. Quartz CL textures and trace elements (chiefly Li, Al, Ti, and Ge) differentiate among quartz generations precipitated during different mineralization and alteration events. Early quartz ± chalcopyrite ± pyrite veins and quartz ± molybdenite veins (A and B veins) show considerable complexity and were commonly reopened, and some underwent quartz dissolution. Early quartz ± chalcopyrite ± pyrite veins (A veins) are dominated by equigranular bright CL quartz with homogeneous texture. Most of these veins contain higher Ti concentrations than any other vein type (average: 100 ppm) and have low to intermediate Al concentrations (65–448 ppm). Quartz ± molybdenite (B veins) and chlorite + rutile ± hematite (C veins) veins contain quartz of intermediate CL intensity that commonly shows growth zones with oscillatory CL intensity. Quartz from these veins has intermediate Ti concentrations (~20 ppm) and Al concentrations similar to those of A veins. Quartz from later quartz + pyrite veins with quartz + muscovite ± tourmaline halos (D veins) has significantly lower CL intensity, low Ti (<15 ppm) and elevated Al concentrations (up to 1,000 ppm), and typically contains euhedral growth zones. Late veins rich in sulfides and sulfosalts show CL textures typical of epithermal deposits (dark CL quartz, crustiform banding, and euhedral growth zones). Quartz from these veins typically contains less than 5 ppm Ti, and Al, Li, and Ge concentrations are elevated relative to other vein types. Based on experimentally established relationships between Ti concentration in quartz and temperature, the decrease in Ti content in successively later quartz generations indicates that the temperature of the hydrothermal fluids decreased through time during the evolution of the system. Vein formation at Altar occurred at progressively lower pressure, shallower paleodepth, and lower temperature. Under lithostatic pressures, the magma supplied low-salinity aqueous fluids at depths of ~6 to 6.8 km (pressures of 1.6–1.8 kbar) and temperatures of 670° to 730°C (first quartz generation of early quartz ± chalcopyrite ± pyrite veins). This parental fluid episodically depressurized and cooled at temperatures and pressures below the brine-vapor solvus. Quartz ± molybdenite veins precipitated from fluids at temperatures of 510° to 540°C and pressures of 800 to 1,000 bars, corresponding to depths of 3 to 3.7 km under lithostatic pressures. Further cooling of hydrothermal fluids to temperatures between 425° and 370°C under hydrostatic pressures of 200 to 350 bars produced pyrite-quartz veins and pervasive quartz + muscovite ± tourmaline and illite alteration that overprinted the early hydrothermal assemblages. Late veins rich in sulfides and sulfosalts that overlapped the deep and intermediate high-temperature veins formed from fluids at temperatures of 250° to 280°C and pressures of 20 to 150 bars. The epithermal siliceous ledges formed from low-temperature fluids (<230°C) at hydrostatic pressures of <100 bars corresponding to depths of <<1 km.

TitaniQ recrystallized: experimental confirmation of the original Ti-in-quartz calibrations

Several studies have reported the P–T dependencies of Ti-in-quartz solubility, and there is close agreement among three of the four experimental calibrations. New experiments were conducted in the present study to identify potential experimental disequilibrium, and to determine which Ti-in-quartz solubility calibration is most accurate. Crystals of quartz, rutile and zircon were grown from SiO2-, TiO2-, and ZrSiO4-saturated aqueous fluids in an initial synthesis experiment at 925 °C and 10 kbar in a piston-cylinder apparatus. A range of quartz crystal sizes was produced in this experiment; both large and small examples were analyzed by electron microprobe to determine whether Ti concentrations are correlated with crystal size. Cathodoluminescence images and EPMA measurements show that intercrystalline and intracrystalline variations in Ti concentrations are remarkably small regardless of crystal size. The average Ti-in-quartz concentration from the synthesis experiment is 392 ± 1 ppmw Ti, which is within 95 % confidence interval of data from the 10 kbar isobar of Wark and Watson (Contrib Mineral Petrol 152:743–754, 2006) and Thomas et al. (Contrib Mineral Petrol 160:743–759, 2010). As a cross-check on the Ti-in-quartz calibration, we also measured the concentration of Zr in rutile from the synthesis experiment. The average Zr-in-rutile concentration is 4337 ± 32 ppmw Zr, which is also within the 95 % confidence interval of the Zr-in-rutile solubility calibration of Ferry and Watson (Contrib Mineral Petrol 154:429–437, 2007). The P–T dependencies of Ti solubility in quartz and Zr solubility in rutile were applied as a thermobarometer to the experimental sample. The average Ti-in-quartz isopleth calculated from the calibration of Thomas et al. (Contrib Mineral Petrol 160:743–759, 2010) and the average Zr-in-rutile isopleth calculated from the calibration of Tomkins et al. (J Metamorph Geol 25:703–713, 2007) cross at 9.5 kbar and 920 °C, which is in excellent agreement with the P–T conditions of the synthesis experiment. Separates of the high-Ti quartz from the initial synthesis experiment described above were used as starting material in subsequent experiments at 20 kbar, at which pressure the solubility of Ti in quartz is expected to be significantly lower in the recrystallized quartz. These recrystallization experiments were conducted under wet and dry conditions at 925 °C, and under wet conditions at 850 °C. Both wet and dry recrystallization experiments produced polycrystalline quartzites. Rutile occurs as inclusions in quartz, and as individual crystals dispersed along quartz grain boundaries. Quartz that grew during the recrystallization experiments has dark cathodoluminescence indicating substantially lower Ti concentrations. The average Ti concentrations in quartz from the recrystallization experiments are within the 95 % confidence interval of a linear fit to the 20 kbar data of Thomas et al. (Contrib Mineral Petrol 160:743–759, 2010). Collectively, the results from the synthesis and recrystallization experiments confirm that the Ti-in-quartz concentrations used to calibrate the P–T dependencies of Ti-in-quartz solubility in Thomas et al.’s (Contrib Mineral Petrol 160:743–759, 2010) calibration represent the equilibrium concentrations of Ti in quartz.

Modeling prograde TiO2 activity and its significance for Ti-in-quartz thermobarometry of pelitic metamorphic rocks

other Si-mobilization events occur during the prograde and retrograde history of metapelites, and assuming TiO2 activities associated with the peak metamorphic paragen- esis may be misleading and result in significant errors in P-T calculations. Abstract Since its calibration, the Ti-in-quartz thermo- barometer has been applied to a wide variety of geologic scenarios. The abundance of quartz in the continental crust and the involvement of silica in metamorphic reactions, deformation, and fluid flux processes make it a particularly powerful tool for constraining the pressure and tempera- ture evolution of rocks, which is essential for developing tectonic models. Being able to quantitatively determine the solubility of Ti in quartz, however, is dependent upon being able to determine the activity of TiO2 in the rock dur- ing quartz growth or re-equilibration. Here we calculate TiO2 chemical potentials of the system relative to that of rutile (as a standard state), projected in P-T space for an average sub-aluminous pelite composition. Titania activi- ties are calculated from these dependent potentials, with resultant activities used to correct for Ti isopleth projec- tion in the Thomas et al. (2010) solubility equation. The modeling results are in good agreement with previous stud- ies that suggest ilmenite-bearing assemblages buffer high TiO2 activities and titanite-bearing assemblages have much lower activities (≥0.5). At elevated temperatures, however, significant deviation from an assumed average pelite activ- ity of 1.0 occurs, where the projected Ti concentration in quartz is up to 400 % different when assuming a dynamic system activity. This is due, in part, to the sequestering of Ti in biotite during heating and the destabilization of Ti- oxides at higher temperatures. With quartz-producing reac- tions, deformation-driven solution-transfer processes and

Fabric development during exhumation from ultrahigh-pressure in an eclogite-bearing shear zone, Western Gneiss Region, Norway

Petrofabrics and trace-element thermobarometry of deformed quartzofeldspathic gneiss and associated coesite-bearing eclogite in the Salt Mylonite Zone (Western Gneiss Region, Norway) document a pressure–temperature–deformation path from ultrahigh-pressure to amphibolite-facies conditions. The Salt mylonite zone is dominated by quartzofeldspathic gneiss with a strong foliation and lineation. Coesite-bearing eclogite within the shear zone contains a foliation and lineation (defined by elongate omphacite) consistent with that of the host gneiss, suggesting that gneiss and eclogite were deformed in the same kinematic framework. In eclogite, omphacite preserves LS- to L-type crystallographic preferred orientation, and quartz preserves prism <c> fabrics that developed in quartz near coesite–quartz transition conditions. The quartzofeldspathic gneiss in the mylonite zone records prism and rhomb <a> slip in quartz and reverse zoning in plagioclase (higher Ca rims) consistent with re-equilibration during decompression. The Ti concentration in quartz in gneiss is higher than that in quartz in eclogite, suggesting that quartz recrystallized at a lower pressure in the gneiss. Ti-in-quartz thermobarometry of rutile-bearing eclogite and titanite-bearing gneiss indicates equilibration at T > 750 °C and T < 650 °C, respectively. This mylonite zone preserves a discontinuous record of fabric development from incipient stages of exhumation of ultrahigh-pressure rocks to crustal conditions.

Petrogenetic significance of LA-ICP-MS trace-element data on quartz from the Borborema Pegmatite Province, northeast Brazil

AbstractQuartz from different zones within five granitic pegmatites of the rare-element class from the Borborema Pegmatite Province in northeast Brazil were analysed for fourteen trace elements using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The concentrations of Li (6—150 ppm), B (1—9 ppm) and Ge (1—23 ppm) in quartz show a positive correlation with Al (30—770 ppm). The concentrations of these elements increase from the border zone to the quartz core of pegmatites of the spodumene or lepidolite subtypes. The Ge concentrations in the quartz core are the highest so far reported in igneous quartz. In the less evolved pegmatites of the beryl-columbite subtype, the Al, Li, B, and Ge concentrations in quartz from all zones remain at the same level as the border and wall zones. The Ti concentrations in quartz from the core of the more evolved pegmatites are below 3 ppm (with Al &gt;250 ppm), contrasting with 7—25 ppm (with Al &lt;280 ppm) in samples from the border and wall zones of the less evolved and more evolved pegmatites. The concentrations of Al. Li, B, Ge, and Ti in quartz are therefore confirmed as good indicators of the degree of magma fractionation and analyses of pegmatite quartz cores can be used for exploration purposes to distinguish pegmatites with high metallogenic potential. Atoms of Li and Al are incorporated into quartz such that Li/Al ranges between 0.75 and 1.0. This suggests a coupled substitution of the form Si4+ ↔ (Li+ + Al3+). The other elements analysed either showed an erratic distribution (e.g. Be and P) or were below the respective limits of detection (Na, K, Rb, Ca, Sr, Mn, Fe) in most samples.

Calibrating Ti concentrations in quartz for SIMS determinations using NIST silicate glasses and application to the TitaniQ geothermobarometer

The recently developed titanium-in-quartz (TitaniQ) geothermobarometer of Wark and Watson (2006) and Thomas et al. (2010) has the potential to be applied to a wide range of igneous and metamorphic rocks. For Ti concentrations > ∼10 ppm, the concentrations can be measured using an electron microprobe, but lower concentrations are below detection limits and require techniques such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) or secondary ion mass spectrometry (SIMS). SIMS is ideal for this purpose as it maximizes lateral and depth resolution. We used SIMS to analyze synthetic quartz crystals characterized for Ti concentration by electron probe (18–813 ppm Ti) and compare this calibration to the commonly available NIST 61X glasses using both high mass resolution (HMR) and conventional energy filtering (CEF) techniques. We used a primary beam of 16 O – ions and detected positive secondary ions. During HMR sessions, the mass spectrometer was operated at a mass resolving power (M/∆M) of ~2000 to separate molecular ions from elemental Ti peaks. For CEF analyses, the instrument detected secondary ions sputtered from the sample with excess kinetic energies of 75 ± 20 eV. Titanian quartz measurements reveal general homogeneity and a linear increase in Ti + /Si + ion ratios with increasing Ti concentrations. Background signals represent 0–1 ppm. The slopes of the calibration curves for the titanian quartz crystals are ∼70% of the curves constructed using NIST glasses, indicating a much higher ion yield for Ti from the glasses compared to the simple oxide of silicon. We demonstrate, however, that a simple correction factor allows NIST glasses to be used to quantitatively determine the Ti concentrations of quartz (with 3.8% error using HMR, and 8.2% error using CEF) until homogenous, well-characterized samples of SiO2 become

Quartz zoning and the pre-eruptive evolution of the ~340-ka Whakamaru magma systems, New Zealand

Cathodoluminescence (CL) zoning in quartz crystals from rhyolitic pumices in two ignimbrite members of the ~340-ka Whakamaru super-eruption deposits, Taupo Volcanic Zone, New Zealand, is investigated in conjunction with the analysis of Ti concentration in quartz to reconstruct the history of changing magma chamber conditions and to elucidate the eruption-triggering processes. CL intensity images are taken as a proxy for Ti concentration and thus temperature and/or pressure and/or compositional variations during crystal growth history. Estimates of the maximum temperature changes (i.e., assuming other factors influencing Ti uptake remain constant) are made using the TitaniQ geothermometer based on the Ti concentration in quartz. These results are reviewed in comparison with Fe–Ti oxide, feldspar-melt and amphibole geothermometry. Core-to-rim quartz Ti profiles record a marked change in conditions (temperature increase and/or pressure decrease and/or change in melt composition) causing and then following a significant resorption horizon in the outer parts of the crystals. Two alternative models that could explain the quartz Ti zonation invoke a temperature increase caused by mafic recharge and/or a pressure decrease due to magma ponding and re-equilibration at shallow crustal levels. Concomitant changes in melt composition and Ti activity may, however, also have strongly influenced Ti uptake into the quartz. Some crystals also show other marked increases in CL brightness internally, but any accompanying magmatic changes did not result in eruption. Diffusion modelling indicates that this significant change in conditions occurred over ~10–85 years prior to caldera-forming eruption. This rapid thermal pulse or pressure change is interpreted as evidence for open-system processes, and appears to record a magma chamber recharge event that rejuvenated the Whakamaru magma system (melt-dominant magma plus crystal mush), and potentially acted as a trigger for processes that led to eruption.

Titanium behavior in quartz during retrograde hydration: Occurrence of rutile exsolution and implications for metamorphic processes in the Sør Rondane Mountains, East Antarctica

In the central Sør Rondane Mountains, East Antarctica, orthopyroxene felsic gneiss (OPG) was converted to hornblende-biotite felsic gneiss (HBG) by hydration that accompanied the intrusion of pegmatite. The retrograde HBG contains exsolved rutile in quartz. The composition of orthopyroxene and clinopyroxene in OPG suggests a temperature of 840 °C (interpreted as the near-peak temperature), and the composition of hornblende and plagioclase in HBG suggests a temperature of 670–700 °C (interpreted as the temperature during hydration). Ti concentrations in quartz were measured using an electron probe micro-analyzer, and Ti-in-quartz thermometers were applied. Measured Ti concentrations were 110 ppm (equivalent to 760–820 °C) for homogeneous quartz from OPG and 35 ppm (650–700 °C) for an exsolution-free area of a quartz grain from HBG. The pre-exsolution Ti concentration in quartz from HBG was reconstructed with 100 μm beam diameter and 25 kV of accelerating voltage, giving 103 ppm, similar to the value obtained for homogeneous quartz in OPG. The temperatures obtained using a Ti-in-quartz thermometer are consistent with those estimated using other thermometers. Although analysis of the main constitute minerals in HBG yields the conditions of hydration, the reconstructed pre-exsolution Ti content in quartz within HBG yields the pre-hydration conditions. Thus, the Ti-in-quartz thermometer is a potentially powerful tool with which to identify the peak or near-peak temperature conditions, even for retrogressed metamorphic rocks.

Ti diffusion in quartz

We have measured Ti diffusion in quartz under dry 1-atm conditions. Experiments were performed using synthetic and natural quartz and a TiO 2 powder source, with Ti profiles obtained by Rutherford Backscattering Spectrometry (RBS). Over the temperature range 700–1150 °C, the following Arrhenius relation was obtained for diffusion parallel to (001): D Ti = 7 × 10 − 8 exp ⁡ ( − 273 ± 12 kJ mol − 1 / R T ) m 2 sec − 1 Similar diffusivities were obtained for both synthetic and natural quartz, and for a range of Ti source materials, including natural titanite powder and rutile–quartz single crystal diffusion couples. Although Ti diffusion appears slightly slower in the direction normal to c, this difference is not great. Using these diffusion parameters, calculations indicate that distances over which diffusional alteration of Ti concentrations in quartz could occur in a million years would be on order of 500 μm at 800 °C, and ∼ 15 μm at 600 °C. The Arrhenius relation above should be broadly applicable, and may find application in constraining metamorphic histories under conditions where the Ti-in-quartz geothermometer can be reasonably applied. This relation can also be used to constrain peak temperatures and cooling histories from observations of exsolved rutile needles in quartz and the width of the Ti-depleted zone that develops around the growing needles. Finally, these findings may find utility in evaluating crystal residence times in magmatic systems when coupled with observations of the sharpness of zoning patterns in quartz.

Intensity of quartz cathodoluminescence and trace-element content in quartz from the porphyry copper deposit at Butte, Montana

Textures of hydrothermal quartz revealed by cathodoluminescence using a scanning electron microscope (SEM-CL) refl ect the physical and chemical environment of quartz formation. Variations in intensity of SEM-CL can be used to distinguish among quartz from superimposed mineralization events in a single vein. In this study, we present a technique to quantify the cathodoluminescent intensity of quartz within individual and among multiple samples to relate luminescence intensity to specific mineralizing events. This technique has been applied to plutonic quartz and three generations of hydrothermal veins at the porphyry copper deposit in Butte, Montana. Analyzed veins include early quartz-molybdenite veins with potassic alteration, pyrite-quartz veins with sericitic alteration, and Main Stage veins with intense sericitic alteration. CL intensity of quartz is diagnostic of each mineralizing event and can be used to fingerprint quartz and its fluid inclusions, isotopes, trace elements, etc., from specific mineralizing episodes. Furthermore, CL intensity increases proportional to temperature of quartz formation, such that plutonic quartz from the Butte quartz monzonite (BQM) that crystallized at temperatures near 750 °C luminesces with the highest intensity, whereas quartz that precipitated at ~250 °C in Main Stage veins luminesces with the least intensity Trace-element analyses via electron microprobe and laser ablation-ICP-MS indicate that plutonic quartz and each generation of hydrothermal quartz from Butte is dominated by characteristic trace amounts of Al, P, Ti, and Fe. Thus, in addition to CL intensity, each generation of quartz can be distinguished based on its unique trace-element content. Aluminum is generally the most abundant element in all generations of quartz, typically between 50 and 200 ppm, but low-temperature, Main Stage quartz containing 400 to 3600 ppm Al is enriched by an order of magnitude relative to all other quartz generations. Phosphorous is present in abundances between 25 and 75 ppm, and P concentrations in quartz show little variation among quartz generations. Iron is the least abundant of these elements in most quartz types and is slightly enriched in CL-dark quartz in pyrite-quartz veins with sericitic alteration. Titanium is directly correlated with both temperature of quartz precipitation, and intensity of quartz luminescence, such that BQM quartz contains hundreds of ppm Ti, whereas Main Stage quartz contains less than 10 ppm Ti. Our results suggest that Ti concentration in quartz is controlled by temperature of quartz precipitation and that increased Ti concentrations in quartz may be responsible for increased CL intensities.