Low-temperature anisotropic diffusion of helium in zircon: Implications for zircon (U-Th)/He thermochronometry

In the last decade the zircon (U-Th)/He (ZHe) thermochronometer has been applied to a variety of geologic problems. Although bulk diffusion coefficients for He in zircon are available from laboratory step-heating experiments, little is known about the diffusion mechanism(s) and their dependence on the crystallographic structure of zircon. Here, we investigate the diffusion of He in perfectly crystalline zircon using atomistic simulation methods that provide insights into the structural pathways of He migration in zircon. Empirical force fields and quantum-mechanical calculations reveal that the energy barriers for He diffusion are strongly dependent on structure. The most favorable pathway for He diffusion is the [0 0 1] direction through the open channels parallel to the c-axis (, activation energy for tracer diffusion of a He atom along [0 0 1]). In contrast, energy barriers are higher in other directions where narrower channels for He diffusion are identified, such as [1 0 0], [1 0 1], and [1 1 0] (ΔE^∗ of 44.8, 101.7, and 421.3 kJ mol⁻¹, respectively). Molecular dynamics simulations are in agreement with these results and provide additional insight in the diffusion mechanisms along different crystallographic directions, as well as the temperature dependence. Below the closure temperature of He in zircon [T_c ∼ 180 °C, Reiners P. W., Spell T. L., Nicolescu S., and Zanetti K. A. (2004) Zircon (U-Th)/He thermochronometry: He diffusion and comparisons with Ar-40/Ar-39 dating. Geochim. Cosmochim. Acta68, 1857-1887], diffusion is anisotropic as He moves preferentially along the [0 0 1] direction, and calculated tracer diffusivities along the two most favorable directions differ by approximately five orders of magnitude (D_[001]/D_[100] ∼ 10⁵, at T = 25 °C). Above this temperature, He atoms start to hop between adjacent [0 0 1] channels, along [1 0 0] and [0 1 0] directions (perpendicular to the c-axis). The diffusion along [1 0 0] and [0 1 0] is thermally activated, such that at higher temperatures, He diffusion in zircon becomes nearly isotropic (D_[001]/D_[100] ∼ 10, at T = 580 °C). These results suggest that the anisotropic nature of He diffusion at temperatures near the closure temperature should be considered in future diffusivity experiments. Furthermore, care should be taken when making geologic interpretations (e.g., exhumation rates, timing of cooling, etc.) from this thermochronometer until the effects of anisotropic diffusion on bulk ages and closure temperature estimates are better quantified.     

喜马拉雅造山带亚东地区多期构造热事件——锆石和独居石U-Th-Pb年代学证据

喜马拉雅造山带是研究板块构造的天然实验室,位于造山带核心部位的大喜马拉雅岩系是揭示碰撞造山过程和造山带演化的关键。本文主要对亚东地区大喜马拉雅岩系中的花岗质片麻岩进行了岩相学、锆石和独居石UTh-Pb年代学以及全岩主微量地球化学研究。野外和显微结构特征观察表明,花岗质片麻岩的矿物组合为斜长石+钾长石+石英+黑云母+石榴石,岩石发生了部分熔融,经历了高角闪岩相至麻粒岩相的变质作用。年代学和全岩地球化学研究表明,花岗质片麻岩的原岩包括新元古代(～800 Ma)的花岗闪长岩和志留纪(～440 Ma)的花岗岩,二者均在中新世(～16 Ma)发生了变质作用。新元古代花岗闪长岩具有负的εHf(t)值(-16. 4～-12. 2),地壳Hf模式年龄为3. 11～2. 79 Ga,说明其起源于古老下地壳物质的部分熔融。新元古代花岗闪长岩和志留纪花岗岩具有相似的弧花岗质岩石地球化学特征,即具有高场强元素Nb、Ta、P和Ti的负异常。本次研究表明大喜马拉雅岩系经历了多期构造热事件,其不仅记录了新生代的碰撞造山作用,还记录了与新元古代与罗迪尼亚超大陆演化相关的岩浆热事件以及古生代冈瓦纳大陆拼合后的周缘安第斯型造山作用。     

He diffusion and (U–Th)/He thermochronometry of zircon: initial results from Fish Canyon Tuff and Gold Butte

To evaluate the potential of (U–Th)/He geochronometry and thermochronometry of zircon, we measured He diffusion characteristics in zircons from a range of quickly and slowly cooled samples, (U–Th)/He ages of zircons from the quickly cooled Fish Canyon Tuff, and age-paleodepth relationships for samples from 15 to 18 km thick crustal section of the Gold Butte block, Nevada. (U–Th)/He ages of zircons from the Fish Canyon Tuff are consistent with accepted ages for this tuff, indicating that the method can provide accurate ages for quickly cooled samples. Temperature-dependent He release from zircon is not consistent with thermally activated volume diffusion from a single domain. Instead, in most samples apparent He diffusivity decreases and activation energy (E_a) increases as cycled step-heating experiments proceed. This pattern may indicate a range of diffusion domains with distinct sizes and possibly other characteristics. Alternatively, it may be the result of ongoing annealing of radiation damage during the experiment. From these data, we tentatively suggest that the minimum E_a for He diffusion in zircon is about 44 kcal/mol, and the minimum closure temperature (T_c, for a cooling rate of 10 °C/myr) is about 190 °C. Age–paleodepth relationships from the Gold Butte block suggest that the base of the zircon He partial retention zone is at pre-exhumation depths of about 9.5–11 km. Together with constraints from other thermochronometers and a geothermal gradient derived from them in this location, the age–depth profile suggests a He T_c of about 200 °C for zircon, in reasonable agreement with our interpretation of the laboratory measurements. A major unresolved question is how and when radiation damage effects become significant for He loss from this mineral.     

U-Pb zircon,monazite and Rb-Sr whole rock systematics of granitic gneiss and psammitic to semi-pelitic host gneiss from Glenfinnan,Northwestern Scotland

New U-Pb zircon data from a segregation pegmatite in the granitic gneiss at Glenfinnan yield discordant points which appear to be aligned along a chord on a concordia diagram with upper and lower intersection ages of 1,517±30 Ma and 556±8 Ma, respectively. The results are similar to published U-Pb zircon data from the granitic gneiss but the lower intersection age does not correspond to concordant ages of 455±3 Ma obtained for monazites from the segregation pegmatite and from paragneiss which hosts the granitic gneiss. The apparent U-Pb zircon chord also gives no indication of a 1,030±50 Ma (large sample) Rb-Sr whole rock isochron age for the granitic gneiss (Brook et al. 1976). A traverse of adjacent 5–8 cm thick slabs in the paragneiss yields a Rb-Sr errochron of 455±60 Ma which also does not agree with the U-Pb zircon lower intersection age. The scale of this Sr whole rock diffusion (ca. 10 cm) is not at variance with existing thermal, temporal and experimental constraints.A two episodic loss model has been applied to the zircon data from the segregation pegmatite, to the previously published zircon data on the granitic gneiss and to new U-Pb zircon data on the host paragneiss. The first lead loss event, if assumed to be in Grenville time, was computed to be strongest in the granitic gneiss and segregation pegmatite. For the three suites of zircon considered, primary ages converge in the 1,700–1,800 Ma range with a final disturbance event at ca. 490 Ma, i.e., close to a plausible prograde stage of Caledonian metamorphism.The zircons in both the granitic gneiss and the paragneiss are believed to have been derived from the ubiquitous early Proterozoic shields bordering the North Atlantic. Furthermore the above model is consistent with the hypothesis that the zircons in the granitic gneiss were largely derived from the paragneiss. However, the U-Pb zircon data are not inconsistent with new Sr-isotopic evidence which suggests an additional, possibly deeper source with lower ⁸⁷Sr/ ⁸⁶Sr ratios.     

He incorporation and diffusion pathways in pure and defective zircon ZrSiO4: A density functional theory study

In this paper, we report a detailed study of helium (He) incorporation and diffusion pathways in the perfect and defective zircon lattice. Ab initio methods based on Density Functional Theory (DFT) were used to calculate the structural features, the solution energies in interstitial sites in the perfect zircon and in vacancy sites of the defective lattice and He diffusion pathways in these systems. We show that the mode of He incorporation in the perfect zircon is influenced mainly by the topological features of the lattice, promoting site preference of He towards accommodation in the interstitial sites present in the middle of c cylinder channels. The presence of defect species in the form of lattice vacancies and interstitials has a significant effect on He solubility and diffusivity in the lattice, where the ability of lattice vacancies to act as physical traps or repulsive sites depends greatly on the electronic nature of the vacancy, which can enhance solubility of He in the lattice and affect the kinetics of He mobility in zircon mineral.     

UHP metamorphism and exhumation of the Dabie Orogen, China: Evidence from SHRIMP dating of zircon and monazite from a UHP granitic gneiss cobble from the Hefei Basin

A SHRIMP U-Pb study of zircons separated from an ultrahigh-pressure (UHP) granitic gneiss cobble (sample DS12) from the Upper Jurassic Fenghuangtai Formation of the Hefei Basin, north of the Dabie Orogen, has identified three different domains: (1) cores, some of which show straight boundaries and strong oscillatory zoning, with Th/U ratios of 0.12-0.70 and an imprecise upper intercept age of 777 ± 220 Ma (MSWD = 2.4); (2) mantles, variable in shape and cathodoluminescence (CL) intensity and containing many UHP mineral inclusions, including coesite and omphacite, and with Th/U ratios of 0.02-0.26 and a weighted mean ²⁰⁶Pb/²³⁸U age of 244 ± 5 Ma (MSWD = 4.7); and (3) rims, which are more homogeneous and luminescent in CL than the mantles and contain fewer UHP mineral inclusions, with Th/U ratios of 0.01-0.05 and a weighted mean ²⁰⁶Pb/²³⁸U age of 226 ± 2 Ma (MSWD = 0.65). Monazites from the same sample do not contain coesite and omphacite inclusions, but they do show sector zones and are composed of two contrasting domains. The light domains in backscattered electron (BSE) images have a Th/U ratio of 7.3-18.9 and a weighted mean ²⁰⁶Pb/²³⁸U age of 221 ± 2 Ma (MSWD = 0.94). The dark domains in BSE have a Th/U ratio of 2.8-7.2 and have a weighted mean ²⁰⁶Pb/²³⁸U age of 218 ± 2 Ma (MSWD = 0.96). Based on these data and a review of the literature, it can be concluded that (1) the protolith of gneiss sample DS12 is a granitoid of Neoproterozoic age; (2) the ages of 244 and 226 Ma for the mantle and rim domains of the zircons are time records of two discrete stages in the UHP evolution of Dabieshan; (3) the ages of 221 and 218 Ma for the light and dark gray domains, respectively, of the monazites record the times of two stages of retrogressive metamorphism during exhumation of the UHP granitic gneiss to a higher crustal level; (4) the exhumation rate of the gneiss is estimated to be >6 km/Ma; and (5) the UHP metamorphic blocks of the Dabie Orogen provided significant detritus to the Hefei Basin in the Jurassic.     

U-Pb systematics of monazite and xenotime: case studies from the Paleoproterozoic of the Grand Canyon, Arizona

Monazite is accepted widely as an important U-Pb geochronometer in metamorphic terranes because it potentially preserves prograde crystallization ages. However, recent studies have shown that the U-Pb isotopic system in monazite can be influenced by a variety of processes that partially obscure the early growth history. In this paper, we attempt to interpret complex monazite and xenotime U-Pb data from three Paleoproterozoic granite dikes exposed in the Grand Canyon. Single-crystal monazite analyses from an unfoliated granite dike spread out along concordia from the crystallization age of the dike (defined by U-Pb zircon data to be 1685 ± 1 Ma) to 1659 ± 2 Ma, a span of 26 million years. Back-scattered electron (BSE) imaging reveals that magmatic domains within most crystals from this sample are truncated by secondary domains associated with prominent embayments at the grain margin. Fragments of a single crystal yield contrasting, concordant dates and fragments from the edges and tips of crystals yield the youngest dates. Based on these observations we suggest that the secondary domains formed at least 26 million years after the crystal formed. Monazite and xenotime dates from the second sample, a sheared dike that cross-cuts the previous dike, spread out along concordia over 16 million years and range up to 2.4% normally discordant. Again, BSE imaging reveals secondary domains that truncate both magmatic zoning and xenocrystic cores. Fragments sliced from specific domains of a previously imaged monazite crystal demonstrate that the secondary domain is 13 million years younger than the core domain. Textures revealed in BSE images suggest that the secondary domains formed by fluid-mineral interaction. Normal discordance appears to result from both radiation damage accumulated at temperatures below 300 °C and water-mineral interaction. Monazite data from the third sample exhibit dispersion in both the ²⁰⁷Pb/²⁰⁶Pb dates (1677–1690 Ma) and discordance (+ 1.6% to − 3.1%). Reverse discordance in these monazites cannot be explained by incomplete dissolution or excess (thorogenic) ²⁰⁶Pb. Sliced fragments from several crystals reveal dramatic intragrain U-Pb disequilibrium that does not correlate with either Th or U concentration or position within the crystal. We suggest that reverse discordance resulted from mechanisms that involve exchange or fractionation of elemental U or elemental Pb, and that neither the U-Pb dates nor the ²⁰⁷Pb/²⁰⁶Pb dates are reliable indicators of the rock's crystallization age. Given the large number of processes proposed in the recent literature to explain monazite U-Pb systematics from rocks of all ages, our results can be viewed as another cautionary note for single-crystal and multi-crystal monazite geochronometry. However, we suggest that because individual crystals can preserve a temporal record of primary and secondary monazite growth, micro-sampling of individual monazite crystals may provide precise absolute ages on a variety of processes that operate during the prograde, peak and/or retrograde history of metamorphic terranes. Received: 9 June 1996 / Accepted: 18 October 1996     

SHRIMP monazite and zircon geochronology of high-grade metamorphism in New Zealand

Ion microprobe dating of zircon and monazite from high-grade gneisses has been used to (1) determine the timing of metamorphism in the Western Province of New Zealand, and (2) constrain the age of the protoliths from which the metamorphic rocks were derived. The Western Province comprises Westland, where mainly upper crustal rocks are exposed, and Fiordland, where middle to lower crustal levels crop out. In Westland, the oldest recognisable metamorphic event occurred at 360–370 Ma, penecontemporaneously with intrusion of the mid-Palaeozoic Karamea Batholith (c. 375 Ma). Metamorphism took place under low-pressure/high-temperature conditions, resulting in upper-amphibolite sillimanite-grade metamorphism of Lower Palaeozoic pelites (Greenland Group). Orthogneisses of younger (Cretaceous) age formed during emplacement of the Rahu Suite granite intrusives (c. 110 Ma) and were derived from protoliths including Cretaceous Separation Point suite and Devonian Karamea suite granites. In Fiordland, high-grade paragneisses with Greenland Group zircon age patterns were metamorphosed (M1) to sillimanite grade at 360 Ma. Concomitant with crustal thickening and further granite emplacement, M1 mineral assemblages were overprinted by higher-pressure kyanite-grade metamorphism (M2) at 330 Ma. It remains unclear whether the M2 event in Fiordland was primarily due to tectonic burial, as suggested by regional recumbent isoclinal folding, or whether it was due to magmatic loading, in keeping with the significant volumes of granite magma intruded at higher structural levels in the formerly contiguous Westland region. Metamorphism in Fiordland accompanied and outlasted emplacement of the Western Fiordland Orthogneiss (WFO) at 110–125 Ma. The WFO equilibrated under granulite facies conditions, whereas cover rocks underwent more limited recrystallization except for high-strain shear zones where conditions of lower to middle amphibolite facies were met. The juxtaposition of Palaeozoic kyanite-grade rocks against Cretaceous WFO granulites resulted from late Mesozoic extensional deformation and development of metamorphic core complexes in the Western Province.     

Neoproterozoic metamorphic evolution in the Transangarian Yenisei Ridge: Evidence from monazite and xenotime geochronology

Chemical mapping and in situ dating of U-Th-rich minerals in zoned garnets from gneisses of the Garevka metamorphic complex were used to constrain multiple metamorphic events in the Transangarian Yenisei Ridge. The data provide supporting evidence for three distinct metamorphic stages. The first episode occurred as a result of the Grenville orogeny during the Late Mesozoic and Early Neoproterozoic (1050–850 Ma) and was marked by low-pressure zoned metamorphism and a metamorphic field gradient with dT/dH = 20?30°C/km typical of orogenic belts. At the second stage, the rocks experienced Late Riphean (801–793 Ma) syn-collisional medium-pressure metamorphism with a low metamorphic field gradient (dT/dH ≤ 10°C/km). The final stage evolved as a synexhumation dynamic metamorphism (785–776 Ma) with dT/dH ≤ 12°C/km and reflected rapid exhumation of rocks in shear zones. The sequence of collisional events within the western margin of the Siberian craton affected by the Valhalla orogen suggests that Siberia and cratons of the North Atlantic region were in close proximity to one another at about 800 Ma, which is supported by recent paleomagnetic reconstructions.     

Fluid-assisted zircon and monazite growth within a shear zone: a case study from Finnmark,Arctic Norway

The U–Pb ages, REE content, and oxygen isotopic composition of zircon rims developed within a major shear zone in the Kalak Nappe Complex (KNC), Arctic Norway have been determined along with the age of monazite crystals. Different generations of granitic veins have been distinguished based on both field criteria and monazite ages of 446 ± 3 and 424 ± 3 Ma. Within each of these veins, inherited zircon cores are mantled by homogeneous low CL-response zircon rims which yield a range of concordant U–Pb dates of ca. 470–360 Ma. Significant numbers of zircon rims coincide with the timing of monazite crystallization. The zircon rims have moderate light REE enrichment compared to cores, distinctive (Sm/La) _n values of less than 12, and La between 0.3 and 10 ppm. This indicates free elemental exchange between newly formed zircon rims and the surrounding matrix. The rims have calculated accumulated alpha-radiation dosages corresponding with a crystalline structure and δ¹⁸O values of 1‰. This implies rim crystallization directly from a zirconium-saturated hydrothermal fluid which was modified by some silicate melt. Growth of the zircon rims was prolonged and locally variable due to preferential fluid flow. A third type of zircon can be recognized, forming both rims and cores, with high alpha-radiation doses, and significant enrichment in La, Pr, and Eu. These are interpreted as low-temperature hydrothermally altered metamict zircons. The high volatile input and partial melting in the shear zone favoured prolonged zircon rim growth due to its ability to easily nucleate on inherited seeds. On the other hand, monazite, susceptible to dissolution and re-growth, crystallized in brief episodes, as has been predicted from theoretical phase diagrams. From a regional perspective, these results elucidate cryptic Ar–Ar cooling ages, providing the first record of a Late Ordovician heating and cooling phase within the KNC prior to the climactic Scandian collision.     

Age and origin of rocks of the Daldyn Group of the Anabar Shield: Evidence from U-Pb zircon dating,Sm-Nd and Lu-Hf isotope systematics

The Hf-Nd isotope systematics was used to determine the genesis of zircons from granulites of the Daldyn Group of the Anabar Shield. Obtained age of magmatic crystallization for biotite–hypersthene crystalline schists and garnet amphibolites agree with position of zircons within terrestrial array. Magmatic genesis of plagiogranite neosome under granulite conditions was established for leucocratic plagiogneisses.     

U-Th-Pb systematics of zircon inclusions in rock-forming minerals: A study of armoring against isotopic loss using the Sherman Granite of Colorado-Wyoming,USA

Zircon inclusions were separated from the five major rock-forming minerals of the Sherman Granite of southern Wyoming, in order to evaluate the degree of discordance as a possible function of host minerals. U-Th-Pb isotopic ratios were determined for two size fractions of zircon inclusions from each mineral, plus five size fractions from the bulk rock. Isotopic data from the inclusions have more than double the spread of data on a discordia obtained from the bulk sample, thereby yielding better-resolved concordia intercepts. However, isotopic ratios and morphologic characteristics indicate that the Pb/U systematics are complicated by inherited radiogenic lead. Although the data array cannot unequivocally be explained by the armoring process, the proposed methodology has succeeded in identifying groups of zircon with different isotopic characteristics. As such, this technique can be used to decipher complex geologic/isotopic histories and may be a useful addition to routine zircon geochronology.     

柴北缘HP-UHP变质带多期构造热事件的再厘定:鱼卡地区高压变泥质岩锆石和独居石U-Pb定年

柴北缘高压-超高压变质带西段鱼卡地区变泥质岩中夹有榴辉岩透镜体,已有的研究显示变泥质岩的变质程度也达到了榴辉岩相,并与榴辉岩一起经历了高压-超高压变质作用,是柴北缘曾经历早古生代大陆深俯冲作用的直接证据,也是研究柴北缘大陆深俯冲过程重要的岩石"探针"。本文选择柴北缘西段鱼卡超高压变质单元中的3件蓝晶石榴白云母石英片岩HP变泥质岩样品分别进行了SHRIMP、LA-ICP-MS锆石和原位独居石U-Pb定年。样品Q06-1-2的锆石给出了920±18Ma(MSWD=1.3)的加权平均年龄,其CL图像特征和极低的Th/U比显示其为变质年龄,代表了与罗迪尼亚超大陆碰撞拼合相关的变质事件。样品A03-11-2.2的锆石给出了450±7Ma(MSWD=0.2)的年龄,认为其代表变泥质岩的榴辉岩相变质年龄。样品A03-14-11的薄片原位独居石定年给出了439±8Ma(MSWD=0.072)的加权平均年龄,结合岩相学观察,认为其可能为榴辉岩相峰期之后的早期退变质年龄。这些资料显示柴北缘鱼卡地区早古生代大陆深俯冲的时限为440~450Ma。结合已有研究资料,鱼卡高压变泥质岩记录了新元古代早期和早古生代两期变质事件,进一步证明了柴北缘地区经历了格林威尔期和早古生代两期造山事件     

Age and evolution of the Grenville Province in eastern Labrador from U-Pb systematics in accessory minerals

U-Pb isotope analysis of zircon, titanite, monazite and rutile extracted from 15 different Grenville Province rocks in eastern Labrador reveals: 1) major crust formation through magmatism between 1,710 and 1,630 Ma ago; no evidence of older crustal material was found. 2) Pegmatite and gabbro intrusions between 1,500 and 1,400 Ma ago, probably related to incomplete rifting of the earlier formed crust. 3) Granite and syenite plutonism, presumably anorogenic, circa 1,300 Ma ago. 4) High grade metamorphism and anatexis during the Grenvillian Orogeny, causing Pb-loss in primary zircon and new growth of zircon, titanite and monazite at circa 1,030 Ma ago in the south (Lake Melville and Mealy Mountains terranes) and circa 970 Ma ago in the north (Groswater Bay Terrane and Trans-Labrador Batholith); geochronological distinction of these large-scale crustal segments substantiates their juxtaposition along deeply rooted, intracontinental ductile thrust zones during Grenvillian Orogeny. 5) Late Grenvillian growth of rutile in gabbros circa 925 Ma ago.     

Sm-Nd systematics of a tonalitic augen gneiss and its constituent minerals from northern Michigan

The Sm-Nd isotopic system of a tonalitic augen gneiss and its constituent minerals from northern Michigan was disturbed during metamorphism. Sm-Nd zircon ages are lower than the wholerock Sm-Nd model age. However, closely associated pairs of minerals (for example, sphene and biotite or apatite and plagioclase) retain their apparent metamorphic ages. The Sm-Nd model age for the tonalitic augen gneiss of 3919 ± 30myr, appears to reflect open system behavior during metamorphism. A mineralogically different gneiss from the same location has a Sm-Nd model age of 3520 ± 70 myr. The two whole rocks differ in their Sm-Nd and Rb-Sr systematics and in their chondrite-normalized rare earth element (REE) patterns. The whole-rock-normalized mineral REE patterns show the contribution of the major and trace minerals to the REE content of the whole rock. The trace minerals contain a significant amount of the total REE.     

Thermobarometric modelling of zircon and monazite growth in melt-bearing systems: examples using model metapelitic and metapsammitic granulites

U–Pb age data collected from zircon and monazite are used to draw fundamental inferences about tectonic processes in the Earth. Despite the emphasis placed on zircon and monazite ages, the understanding of how to relate the timing of growth of zircon and monazite to an evolving rock system remains in its infancy. In addition, few studies have presented large datasets of geochronological data from zircon and monazite occurring in the same metamorphic rock sample. Such information is crucial for understanding the growth of zircon relative to monazite in a systematic and predictive manner, as per this study. The data that exist support the generally held conception that zircon ages tend to be older than monazite ages within the same rock. Here experimental data for zircon and monazite saturation in melt-bearing rocks are integrated with phase diagram calculations. The calculations constrain the dissolution and growth behaviour of zircon and monazite with respect to evolving pressure, temperature and silicate mineral assemblages in high-grade, melt-bearing, metasedimentary rocks. Several key results emerge from this modelling: first, that in aluminous metapelitic rocks (i.e. garnet + cordierite + sillimanite assemblages), zircon ages are older than monazite ages in the same rock; second, that the growth rate of accessory minerals is nonlinear and much higher at and near saturation than at lower temperatures; and third, that the difference in zircon and monazite ages from the same rock may be ascribed to differences in the temperature(s) at which zircon and monazite grow rather than differences in closure temperature systematics. Using our methodology the cooling rate of granulites from the Reynolds Range, central Australia, have been constrained at ∼4 °C Myr⁻¹. This study serves as a first-pass template on which further research in applying the technique to a field study can be based.     

Volatile components of natural fluids: Evidence from inclusions in minerals: Methods and results

A database compiled by the author on volatile components in fluid inclusions (5300 analyses compiled from 300 publications) was used to compare destructive and nondestructive analytical techniques and thermal and mechanical methods for the extraction of volatiles in destructive techniques. Possible explanations are proposed for opposite conclusions published by various researchers. The paper summarizes the principal outcomes of the long-lasting discussion on the optimal methods able to provide the most reliable results. No unambiguous answer is provided. Analysis of extensive literature data indicates that each of the techniques is characterized by its own advantages and disadvantages, and an optimal solution should be selected with regard for the materials to be analyzed and formulated tasks. In any event, the results require careful interpretation. The average composition of natural fluids calculated from extensive statistical material is as follows (mol %): 70.3 H₂O, 21.4 CO₂, 6.3 CH₄, 2.0 N₂, and 0.07 H₂S. The distribution of volatile components was examined in minerals from hydrothermal ore deposits of various types (gold, tungsten, tin, and base-metal) and metamorphic rocks     

He implantation and concentrations in minerals and lunar regolith particles

Solar-wind erosion of rocks on the lunar surface and the implanting of solar-wind particles in minerals of lunar regolith are principally important processes of space weathering. The latter process leads to the accumulation of inert gases in mineral particles of lunar regolith. Literature data indicate that, depending on the composition and structure of the particles, the concentrations of implanted He in various minerals range within roughly three to four orders of magnitude. The lowest He implantation coefficient was determined in amorphous particles (glass), and very low implantation coefficients were also obtained in experiments on He implantation in glass (obsidian).     

冀东金矿带中生代岩浆作用及其成矿意义——来自锆石矿物学证据

冀东金厂峪金矿被认为与青山口花岗岩体侵入有关,而同样距离矿区较近的腰岭子花岗闪长岩体则研究较少,由于两岩体在岩性、构造背景等方面有很大的相似性,因此有必要探讨两成矿条件和成矿潜力差异的可能原因。本文对腰岭子和青山口岩体中的锆石进行透射光和阴极发光（CL）图像分析、晶体形态学以及统计学分析,结果显示两岩体的形成温度相差不大,分别为650～800℃和650～850℃。较高的岩浆热水含量和富碱环境可能是青山口岩体成矿的必要条件。应用LA- ICP- MS方法对腰岭子花岗闪长岩中的锆石进行U- Pb年代学测试,其结晶年龄为161.5±0.9 Ma,与峪耳崖金矿区内的闪长岩脉年龄相近,且两者在含矿岩体特征方面有很大的相似性,因此认为腰岭子岩体的成金潜力较大。两岩体稀土元素地球化学特征显示轻稀土相对亏损而重稀土相对富集。同时,有明显的Ce正异常和微弱的Eu负异常,结合野外地质观察,认为两岩体可能经历了壳幔混合作用。结合前人对青山口岩体年龄的测试结果及大地构造背景认为两岩体可能为来自同一岩浆房不同阶段侵位的产物。     

Significance of ~ 1.5 Ga zircon and monazite ages from charnockites in southern Lithuania and NE Poland

The presence of 1.52–1.50 Ga charnockites from the anorthosite–mangerite–charnockite–granite (AMCG) Mazury complex in southern Lithuania and NE Poland, in the western East European Craton (EEC) is revealed by secondary ion mass-spectrometry (SIMS) and EPMA geochronology. Early 1.85–1.82 Ga charnockites are related to major orogeny in the region whereas the newly studied charnockites intrude the already consolidated crust. The 1.52–1.50 Ga charnockite magmatism (SIMS data on zircon) was followed by high-grade metamorphism (EPMA data on monazite), which strongly affected the surrounding rocks. The 1.85–1.81 Ga zircon cores in Lazdijai and 1.81 Ga monazite domains in the Lanowicze charnockites represent the protolith age of a volcanic island arc. The 1.52–1.50 Ga charnockite magmatism and metamorphism are likely related to the distal, Danopolonian, orogeny further to the west, at the margin of Baltica. The c.1.52–1.50 Ga AMCG magmatism and metamorphism in the western EEC as well as the paired accretionary-rapakivi suites in Amazonia, may be the inboard manifestations of the same early Mesoproterozoic orogeny associated with the juxtaposition of Amazonia and Baltica during the amalgamation of the supercontinent Columbia.