Apatite Population Research Articles

Cerium and Ytrium in apatite as records of magmatic processes: Insight into fractional crystallization, magma mingling and fluid saturation

Apatite is a versatile mineral crystallizing at different stages of silicic magma evolution. Its composition may record that of magma, but could also be affected by interaction with fluids. The focus of this study is the well-recognized magma mingling process that was previously detected using plagioclase composition and in this study complementary record is sought in apatite. The apatite was analysed in two dioritic enclaves (primitive and hybrid) and host quartz monzonite, which is an igneous rock emplaced at ca. 340 Ma in mylonitized Góry Sowie gneisses (NE Bohemian Massif). The apatite was analysed in-situ by microprobe that allowed for chemical characterization of different apatite populations in quartz monzonite and analyses of thin acicular apatite in the enclaves. Apatite population in the quartz monzonite was chemically distinct from that in both enclave types and characterized by higher Y and lower Ce contents, such values are usually typical for peraluminous magmas. As such, the apatite transfer from felsic to mafic magma should be well recorded in apatite composition, which was not the case. Monzonite apatite composition was not commonly observed in the hybrid enclave despite massive plagioclase transfer and only rare resorbed cores with low Ce and Y contents were present. However, such low Ce and Y cores crystalized at the latest stage of apatite crystallization in the quartz monzonite, whereas the plagioclase transfer was an early episode. Therefore, we conclude that apatite transfer was limited during mingling and the apatite composition in the quartz monzonite is best explained by an early Cl-Ce-rich fluid removal and then fractional crystallization, while apatite in the primitive enclave is affected only by fractional crystallization. Altogether, Ce and Y composition of apatite is a valuable tool to record diverse magmatic processes such as fluid removal and precipitation from fluid in addition to fractionation of different REE phases and should be further explored.

Apatite Texture, Composition, and O-Sr-Nd Isotope Signatures Record Magmatic and Hydrothermal Fluid Characteristics at the Black Mountain Porphyry Deposit, Philippines

AbstractThe trace elemental and isotopic signatures in apatite can be modified during hydrothermal alteration. This study investigates the suitability of apatite as an indicator of the source, chemistry, and evolution of magma and hydrothermal fluids. In situ textural, elemental, and O-Sr-Nd isotope analyses were performed on apatite in thin sections, from fresh and propylitically altered pre- and synmineralized dioritic porphyries from the Black Mountain porphyry Cu deposit in the Philippines.All studied apatite crystals have similar subhedral to euhedral shapes and are homogeneous in the grayscale in backscattered electron images. In cathodoluminescence images, the apatite in fresh and altered rocks displays yellow to yellow-green and green to brown luminescence, respectively. Apatite in fresh rocks has a higher Cl and Mn content, and lower Fe, Mg, Sr, Pb, and calculated XOH-apatite, compared to apatite in altered rocks. The content of F, rare earth elements (REEs), Y, U, Th, and Zr, and the Sr-Nd isotope signatures of apatite from fresh and altered rocks are similar in all apatite grains (87Sr/86Sr = 0.7034–0.7042 vs. 0.7032–0.7043, εNd(t) = 5.3–8.0 vs. 5.1–8.4). The X-ray maps and elemental and oxygen isotope signatures across individual apatite crystals are typically homogeneous in apatite from both fresh and altered rocks. The distinct luminescence colors, coupled with distinct mobile element compositions (Cl, OH, Mn, Mg, Fe, Sr, Pb), indicate modification of primary magmatic apatite during interaction with hydrothermal fluids. The similarities in Sr isotope ratios (87Sr/86Sr = 0.7032–0.7043) but slight differences in O isotope signatures (δ18O = 6.0 ± 0.3‰ vs. 6.6 ± 0.3‰) in apatite from fresh and altered rocks are consistent with the magma and hydrothermal fluids having the same source and suggest significant phase separation in the hydrothermal fluids given that 18O preferentially fractionates into the residual liquid relative to 16O during phase separation. The similarity of immobile element (REE, Y, U, Th, and Zr) contents in both populations of apatite, consistency of textures and Nd isotope compositions, and absence of obvious dissolution-reprecipitation features all suggest that altered apatite retains some magmatic characteristics. The apatite in fresh rocks has oxygen isotope compositions similar to that of zircons from the same sample (δ18O = 5.9 ± 0.3‰), indicating little to no oxygen isotope fractionation between zircon and apatite and that apatite can be a good proxy for the oxygen isotope composition of the magma. Based on the Cl contents of the magmatic and replacement apatite, and assuming their equilibrium with high-temperature magma fluid and replacement hydrothermal fluid, respectively, the calculated Cl content of the early magmatic fluid and the later replacement fluid can be estimated to be 6.4 to 15.1 wt % and ~0.25 ± 0.03 wt %, respectively. This indicates a depletion of Cl from the early high-temperature fluid to the replacement fluid, consistent with phase separation.This study demonstrates that cathodoluminescence, elemental compositions (such as Cl, Mn, Mg, Fe, Sr, Pb) and Sr-O isotope signatures in apatite can be modified during hydrothermal alteration, whereas other components (REE, Y, U, Th, and Zr) and the Nd isotope composition are preserved. These features can be used to constrain the origin, chemistry, and evolution of the primary magma and ore-forming hydrothermal fluids.

Variscan post-collisional cooling and uplift of the Tatra Mountains crystalline block constrained by integrated zircon, apatite and titanite LA-(MC)-ICP-MS U-Pb dating and rare earth element analyses

LA-ICP-MS U-Pb dating of apatite, titanite and zircon from the metamorphic cover of the Western Tatra granite was undertaken to constrain the timing of metamorphic events related to the final stages of Variscan orogenesis and subsequent post-orogenic exhumation. Zircon was found only in one sample from the northern metamorphic envelope. U-Pb ages from the outermost rims of zircons define a concordia age of 346 ± 6 Ma, while the inner rims yield a concordia age of 385 ± 8 Ma. Apatite from three samples from the northern metamorphic envelope yield U-Pb ages of 351.8 ± 4.4 Ma, 346.7 ± 5.9 Ma and 342.6 ± 7.1 Ma. Titanite from an amphibolite from the southern metamorphic envelope yields a U-Pb age of 345.3 ± 4.5 Ma. The age of c. 345 Ma is interpreted to represent the climax of metamorphism and the onset of simultaneous exhumation of the entire Tatra Mountains massif, and is recorded mainly in the northern part of the metamorphic cover.In the southern metamorphic envelope, distinct populations of apatite can be recognized within individual samples based on their rare earth element (REE) and actinide contents. One population of apatite (Ap1) yields a relatively imprecise U-Pb age of 340 ± 31 Ma. This population comprises apatite grains with very similar trace element compositions to apatite in the northern amphibolite samples, which suggests they crystallized under similar metamorphic conditions to their northern counterparts. A second apatite population (Ap2) yields an age of c. 328 ± 22 Ma, which is interpreted as neocrystalline apatite that formed during a late-Variscan (hydrothermal?) process involving (P, F, Ca, REE)-rich fluid migration. The youngest generation of apatite (Ap3) yields a U-Pb age of 260 ± 8 Ma and may have resulted from thermal resetting associated with the regional emplacement of Permian A-type granites. The proposed tectonic model assumes that rapid uplift (and cooling) of the Tatra block initiated at ca. 345 Ma, contemporaneous with anatexis. Subsequent fluid migration, possibly facilitated by extension related to the opening of Paleo-Tethys, affected only the southern part of the Tatra block.

Apatites from the Kaiserstuhl Volcanic Complex, Germany: new constraints on the relationship between carbonatite and associated silicate rocks

Apatites from carbonatites, related alkaline silicate rocks, a carbonate-bearing melilititic dyke rock (bergalite), and a diatreme breccia (containing both carbonate and silicate fragments) of the Miocene Kaiserstuhl Volcanic Complex, SW Germany, are used to reconstruct the petrogenetic relationship among these rocks. Apatites from carbonatites reach higher Sr and Nb contents but are generally lower in Fe, Mn, Th, U, Si, S, Cl and Br compared to apatites from associated silicate rocks, whilst Na, REE and F contents are overlapping. Apatites from bergalite show a systematic and discontinuous core-rim zonation, with the core being compositionally similar to apatites from silicate rocks and the rim corresponding to carbonatitic apatites. These observations imply that the bergalite apatites nucleated in a silicate melt and continued to crystallize from an evolving CO 2 -enriched melt probably with carbonatitic affinity. Apatites from a diatreme breccia comprise three populations: (1) similar to the apatites from silicate rocks, (2) similar to the carbonatitic apatites, and (3) resembling apatite population (1) partially replaced by apatite (2). We infer that apatite (1) was derived from silicate-rock fragments and apatite (2) crystallized from a later intruding carbonatitic melt, which metasomatized the silicate-rock fragments and caused the replacement textures as observed in apatite population (3). We conclude that apatites from the Kaiserstuhl complex preserve important information on the petrogenetic relationship between carbonatitic and silicate melts. The carbonatitic melts at the Kaiserstuhl complex are probably the products of protracted fractionation of a CO 2 -rich nephelinitic melt.

Meso-Cenozoic building of the northern Central Asian Orogenic Belt: Thermotectonic history of the Tuva region

The Tuvinian and West-Sayan mountain ranges form part of the Central Asian Orogenic Belt (CAOB); more specifically, they align along the Altai–Sayan–Hangay zone. Its Precambrian–Paleozoic basement has been subjected to Mesozoic and Cenozoic tectonic reactivation. Two north-south transects across the mountain belts and intervening basins of Tuva were sampled for apatite fission-track (AFT) thermochronology in order to elucidate the thermal history of the Tuvinian basement in relation to the Mesozoic and Cenozoic reactivation of the CAOB. Most AFT ages are Late Cretaceous and range between 55 and 115 Ma. Mean lengths of confined fission tracks are relatively long with most values between 13 and 14 μm. Thermal history modeling shows a rapid Late Jurassic–Cretaceous cooling for the sampled Tuvinian crystalline rocks, related to exhumation of the Paleozoic basement. This exhumation is possibly related to the building and subsequent orogenic collapse of the Mongol–Okhotsk orogen that formed between the Siberian and North China–Mongolian (Sino-Korean or Amurian) continental blocks during the Late Mesozoic. Far-field effects of this orogeny and its collapse, might have affected the Baikal, Altai and Sayan units of the Central Asian Orogenic Belt, including the Tuvinian basement. Also, at the Mesozoic southern Eurasian margin, growth of the Asian continent continued and several collision–accretion events asserted distal tectonic influence into the CAOB. After a Paleogene period of stability, thermal history models for some samples hint at a renewed period of basement cooling during the Neogene. In support of this Neogene event, a single sample from the main West Sayan fault zone contains an apatite population with ~ 2 Ma reset AFT ages. This is interpreted in the framework of ongoing building of the modern Central Asian orogens and associated fault movements and exhumation of the basement, presumably related with the ongoing India–Eurasia convergence.

U and Th zonation in apatite observed by laser ablation ICPMS, and implications for the (U–Th)/He system

A laser-ablation inductively-coupled plasma mass spectrometry technique was developed to measure U, Th, and Ce zonation in polished sections of apatite for assessing the consequences of parent zonation for (U–Th)/He thermochronometry. The technique produces concentration maps with an averaging length-scale of ∼20 μm, comparable to the α-stopping distance, and a precision of ∼5% down to few ppm concentration levels. A model was developed to transform the measured concentration distribution into a simplified representation for use in spherical-geometry He production–diffusion models. To illustrate these methods, 30 sections of apatite from a single granite (GC863) were mapped. Every analyzed apatite from GC863 is zoned, with most grains having variable thickness rims and terminations that are enriched in U and Th by about a factor of three over the grain cores. Parent zonation has three independent effects on (U–Th)/He He ages: it influences the α ejection correction, the 4He concentration profile which governs diffusive loss, and, via radiation damage trap accumulation, spatial variability of diffusivity within the crystal. If the observed zonation is typical of the apatite population in GC863, use of the standard homogenous α ejection correction would cause He ages to be on average 3% too young, and with a large amount of grain-to-grain variability (9% too young in the most rim-enriched case to 6% too old in a core-enriched case). Independent of the ejection correction, the concentration profile modifies the effective closure temperature of the apatites by placing more (or less) 4He near the grain edge. The parent zonation in GC863 apatites causes closure temperatures to range from four degrees lower (rim-enriched case) to two degrees higher (core-enriched case) than applies in the homogenous case. Alpha ejection and concentration profile effects on He age are additive and of the same sense. In the case of typical grains in GC863 cooled between 1 and 10 °C/Ma, the two effects are roughly equal in magnitude. The effects of intracrystalline variations in radiation damage trap accumulation become apparent at slow cooling rates (1 °C/Ma). For example, in rim-enriched GC863 grains cooled at 1 °C/Ma, preferential accumulation of radiation damage traps near the grain rim almost compensates for the higher loss rate expected of 4He also located preferentially near the rim. Under some circumstances strong rim-enrichment may actually increase the effective closure temperature of an apatite. Zonation at the level observed in GC863 modifies the 4He/ 3He spectra substantially from that expected from a uniform distribution. Measured 4He/ 3He spectra are strikingly similar to predictions based on the mapped eU distributions of the very same crystals, supporting the overall validity of the analytical and interpretive approach presented here. The magnitude and style of U, Th zonation documented in GC863 is one possible source of frequently observed over-dispersion of apatite (U–Th)/He ages as well as anomalous 4He/ 3He spectra.

Collagen Biomineralization In Vivo by Sustained Release of Inorganic Phosphate Ions

A new strategy for mineralized tissue formation in vivo is presented based on localized sustained delivery of inorganic orthophosphate (Pi) sufficient to supersaturate tissue surrounding an implant and induce mineralization of collagen. After 15 days implantation mineral formation around the implants was detected. Histology and electron microscopy show two populations of apatite; inter-fibrillar microcrystals and nanocrystals associated with collagen. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Apatite as a monitor of late-stage magmatic processes at Volcán Irazú, Costa Rica

Apatite phenocrysts from the 1963 and 1723 eruptions of Irazu volcano (Costa Rica) record a volatile evolution history that confirms previous melt inclusion studies, and provides additional information concerning the relative and absolute timing of subvolcanic magmatic events. Measurements of H, Cl, and F by secondary ion mass spectrometry reveal multiple populations of apatite in both 1723 and 1963 magmas. Assuming nominal apatite/melt partition coefficients allows us to compare the pattern of melt inclusions and apatites in ternary space, demonstrating the fidelity of the record preserved in apatite, and revealing a complex history of magma mixing with at least two components. The preservation of heterogeneous populations of apatite and of internally heterogeneous crystals requires short timescales (days to years) for these magmatic processes to occur.

Mineralogical and geochemical investigation of clay-rich mine tailings from a closed phosphate mine, Bartow Florida, USA

Clay-rich mine tailings from phosphate mine operations in Florida are a major environmental and economic problem. Options for reclamation and restoration for these tailings are very limited and are fundamentally restricted by poor physical properties such as low mechanical strength, low hydraulic conductivity, and heavy metal content. The major control on these bulk physical properties is the mineralogy of the materials. Eight continuous push borings were obtained to investigate stratigraphy, mineralogy, aspects of geochemistry, and bulk properties of a deposit of clay-rich mine tailings from a phosphate mine near Bartow, Florida that ceased operations in the early 1970s. Stratigraphy is dominated by laminated clay-rich sediment with minor units of silt and sand. An intact kaolinite liner occurs near the impoundment walls and the impoundment floor has approximately 4 m of relief. Moisture content varies from 4.35 to 57.40 wt% and organic content varies from 0.41 to 9.53 wt%. Bulk XRF investigation indicates that the P2O5 concentrations vary from approximately 4 to 21 wt%. A very strong correlation (r 2 = 0.92) between CaO and P2O5 indicates that apatite is a major control on the phosphate. The strong correlation (r 2 = 0.77) of Al2O3 and TiO2 suggests that the source materials for this deposit are comparatively uniform. A number of heavy metal elements and trace elements occur. Cr, V, Ni, Cu are interpreted to be in phosphate minerals, largely apatite. Sr and Pb are interpreted to be in both phyllosilicates and phosphate minerals. Two populations of apatite were observed in the clay-sized fraction, one that was Fe and Si- bearing and another that was only Si-bearing. Fe-bearing apatite had Fe2O3 contents that varied from 0.38 to 5.32 wt% and SiO2 contents that varied from 0.90 to 3.32 wt%. The other apatite population had a wider range of SiO2 contents that varied from 0.77 to 8.80 wt%. TEM imaging shows that apatite grains are dominantly single crystals with lesser amounts of aggregates. Wavellite commonly occurs as individual or clusters of lath-like crystals and the chemical composition differs from the pure aluminium phosphate end member with average concentrations of components being that of CaO (1.57 wt%), Fe2O3 (1.98 wt%), SiO2 (5.94 wt%). In the clay-sized phosphate minerals investigated no fluorine was found above detection limit (approximately 0.15 wt%), nor was any uranium, radium, heavy metal, or REE element detected. The phyllosilicate mineralogy of the deposit is dominated by smectite (montmorillonite with lesser amounts of nontronite), palygorskite, illite and kaolinite. No systematic variation in the relative proportions of phyllosilicates was observed in the clay deposit. Energy dispersive spectroscopy EDS analysis indicates that chemical compositions of phyllosilicates are somewhat typical but overall are enriched with respect to Fe compared to theoretical end members. The relative enrichment of Fe is interpreted to be a primary sedimentary feature. Ca content in smectite minerals is high and may inhibit stabilization using lime or similar methods. The high percentages of montmorillonite and palygorskite explain the high bulk water contents observed. This investigation provides fundamentally new details regarding clay tailing deposits from closed phosphate mines in central Florida which can be used in restoration and reclamation efforts.

Determining accurate temperature–time paths from U–Pb thermochronology: An example from the Kaapvaal craton, southern Africa

Thermochronology has revolutionized our understanding of the establishment and evolution of lithospheric thermal structure. However, many potential benefits provided by the application of diffusion theory to thermochronology have yet to be fully exploited. This study uses apatite ( T c = 450–550 °C) and titanite ( T c = 550–650 °C) U–Pb ID-TIMS thermochronology at the single- to sub-grain scale to separate the variable effects of volume diffusion of Pb from metamorphic (over)growth above and below the T c of a mineral. Data are presented from two ca. 3227 Ma tonalite samples from north and south of the Barberton Greenstone Belt (BGB), southern Africa. Two distinct populations of apatite from a sample north of the BGB record fast cooling followed by metamorphic growth ∼10 Myr later. Both apatite and titanite dates from south of the BGB show a strong correlation with the grain size and record 100 Myr of post-emplacement cooling. Complex core–rim zoning observed in cathodoluminescence images of apatite is interpreted to reflect metamorphic overgrowth above the T c. The age and topology of grain size versus date curves from titanite and apatite are used in combination with a finite-difference numerical model to show that slow, non-linear, cooling and not thermal resetting is responsible for the observed distribution. The thermal histories from either side of the BGB are very different and provide unique insight into the BGB’s tectonic evolution: a ∼70 Myr period of apparent stability after ca. 3.2 Ga terrane assembly was followed by fast exhumation south of the BGB that led to lower-crustal melting and intrusion of granitic batholiths ca. 3.14–3.10 Ga.

Possible secondary apatite fission track age standard from altered volcanic ash beds in the middle Jurassic Carmel Formation, Southwestern Utah

Secondary age standards are valuable in intra- and interlaboratory calibration. At present very few such standards are available for fission track dating that is older than Tertiary. Several altered volcanic ash beds occur in the Middle Jurassic Carmel Formation in southwestern Utah. The formation was deposited in a shallow marine/sabhka environment. Near Gunlock, Utah, eight ash beds have been identified. Sanidines from one of the ash beds (GUN-F) give a single-crystal laser-probe 40Ar/ 39Ar age of 166.3±0.8 Ma (2 σ). Apatite and zircon fission track ages range from 152–185 Ma with typically 15–20 Ma errors (2σ). Track densities in zircons are high and most grains are not countable. Apatites are fairly common in most of the ash beds and have reasonable track densities ranging between 1.2–1.5 × 10 6 tracks/cm 2. Track length distributions in apatites are unimodal, have standard deviations <1 μm, and mean track lengths of about 14–14.5 μm. High Cl apatites (F:Cl:OH ratio of 39:33:28) are particularly abundant and large in ash GUN-F, and are fairly easy to concentrate, but the concentrates contain some siderite, most of which can be removed by sieving. GUN-F shows evidence of some reworking and detriaal contamination based on older single grain 40Ar/ 39Ar analyses and some rounding of grains, but the apatite population appears to be largely uncontaminated. At present BJK has approximately 12 of apatite separate from GUN-F.

Apatite fission-track analysis of Oligocene strata in South Texas, U.S.A.: Testing annealing models

Analysis of apatite fission-track data from forty-seven surface and subsurface samples of fine-grained sandstone to pebbly conglomerate from the Oligocene Catahoula (Gueydan), Frio and Vicksburg Formations documents the response of fission-track ages and track-length distributions to simple post-depositional thermal histories characterized by monotonic heating. Data from outcrop samples document that the apatite component was derived from source areas characterized by rapid cooling through the temperature range from ∼ 120° to 50°C during the early Tertiary. The apatite population is characterized by a log-normal chlorine distribution (mean = 0.3 wt%, σ = 0.3 wt%) consisting predominantly of low-Cl apatites (80% is ⩽ 0.5 wt%). Mean track lengths from core samples decrease systematically with increasing depth and temperature. The decrease in apatite fission-track ages with increasing depth and temperature is less systematic due to the scatter in inherited ages at the time of deposition. No tracks were observed in apatite from samples at temperatures above 130°C. Mean track-lengths for the South Texas data agree well with those for a similar data set from the Otway Basin, southeastern Australia, for present-day temperatures of < 70°C). At higher temperatures, mean lengths are 1 to 9 μm longer than those observed from the Otway Basin. This discrepancy is interpreted to reflect up to 40-Ma-longer residence times at maximum burial temperatures for the Otway Basin samples. Standard deviations about mean lengths are also lower than observed in the Otway Basin study, consistent with the wider variation of Cl contents (mean = 0.8 wt%, σ = 0.7 wt%) that characterize apatite from the Otway Basin. Recently published apatite fission-track annealing models predict significantly different mean track length vs. present-day temperature profiles for thermal histories believed to be representative of those experienced by sampled South Texas strata. Because of the large uncertainties attributed to present-day temperatures (± 10°C), the predicted mean length vs. temperature trends for these models essentially fall within or on the uncertainty envelope for the observed trend. Residuals of predicted minus observed mean lengths suggest that the previously published Carlson composite parameter model. using an initial mean length of 15.8 μm instead of 16.5 μm, or the Crowley et al. model for track-length reduction down to ∼ 11 μm, provide the best estimates of mean track-length reduction over geologic time scales for near end-member F-apatite populations.