Deconvolution of fission-track length distributions and its application to dating and separating pre- and post-depositional components

To enable the separation of pre- and postdepositional components of the length distribution of (partially annealed) horizontal confined fission tracks, the length distribution is corrected by deconvolution. Probabilistic least-squares inversion corrects natural track length histograms for observational biases, considering the variance in data, modelization, and prior information. The corrected histogram is validated by its variance–covariance matrix. It is considered that horizontal track data can exist with or without measurements of angles to the c axis. In the latter case, 3D histograms are introduced as an alternative to histograms of c-axis-projected track lengths. Thermal history modelling of samples is not necessary for the calculation of track age distributions of corrected tracks. In an example, the age equations are applied to apatites with predepositional (inherited) tracks in order to extract the postdepositional track length histogram. Fission tracks generated before deposition in detrital apatite crystals are mixed with post-depositional tracks. This complicates the calculation of the post-sedimentary thermal history, as the grains have experienced different thermal histories prior to deposition. Thereafter, the grains share a common thermal history. Thus, the extracted post-depositional histogram without inherited tracks may be used for thermal history calculation.

Apatite U-Pb Thermochronology: A Review

The temperature sensitivity of the U-Pb apatite system (350–570 °C) makes it a powerful tool to study thermal histories in the deeper crust. Recent studies have exploited diffusive Pb loss from apatite crystals to generate t-T paths between ~350–570 °C, by comparing apatite U-Pb ID-TIMS (isotope dilution-thermal ionisation mass spectrometry) dates with grain size or by LA-MC-ICP-MS (laser ablation-multicollector-inductively coupled plasma-mass spectrometry) age depth profiling/traverses of apatite crystals, and assuming the effective diffusion domain is the entire crystal. The key assumptions of apatite U-Pb thermochronology are discussed including (i) that Pb has been lost by Fickian diffusion, (ii) can experimental apatite Pb diffusion parameters be extrapolated down temperature to geological settings and (iii) are apatite grain boundaries open (i.e., is Pb lost to an infinite reservoir). Particular emphasis is placed on detecting fluid-mediated remobilisation of Pb, which invalidates assumption (i). The highly diverse and rock-type specific nature of apatite trace-element chemistry is very useful in this regard—metasomatic and low-grade metamorphic apatite can be easily distinguished from sub-categories of igneous rocks and high-grade metamorphic apatite. This enables reprecipitated domains to be identified geochemically and linked with petrographic observations. Other challenges in apatite U-Pb thermochronology are also discussed. An appropriate choice of initial Pb composition is critical, while U zoning remains an issue for inverse modelling of single crystal ID-TIMS dates, and LA-ICP-MS age traverses need to be integrated with U zoning information. A recommended apatite U-Pb thermochronology protocol for LA-MC-ICP-MS age depth profiling/traverses of apatite crystals and linked to petrographic and trace element information is presented.

Biomimetic Octacalcium Phosphate Bone Has Superior Bone Regeneration Ability Compared to Xenogeneic or Synthetic Bone

Octacalcium phosphate (OCP) is a precursor of biological apatite crystals that has attracted attention as a possible bone substitute. On the other hand, few studies have examined this material at the experimental level due to the limitations on OCP mass production. Recently, mass production technology of OCP was developed, and the launch of OCP bone substitutes is occurring. In this study, the bone regeneration capacity of OCP products was compared with two of the most clinically used materials: heat-treated bovine bone (BHA) and sintered biphasic calcium phosphate (BCP). Twelve rabbits were used, and defects in each tibia were filled with OCP, BHA, BCP, and left unfilled as control (CON). The tibias were harvested at 4 and 12 weeks, and 15 μm slides were prepared using the diamond grinding method after being embedded in resin. Histological and histomorphometric analyses were performed to evaluate the bone regeneration ability and mechanism. The OCP showed significantly higher resorption and new bone formation in both periods analysed (p < 0.05). Overall, OCP bone substitutes can enhance bone regeneration significantly by activating osteoblasts and a rapid phase transition of OCP crystals to biological apatite crystals (mineralization), as well as providing additional space for new bone formation by rapid resorption.

Biomimetic Octacalcium Phosphate Bone Has Superior Bone Regeneration Ability Than Xenogeneic or Synthetic Bone

Octacalcium phosphate (OCP) is a precursor of biological apatite crystals that has attracted attention as a possible bone substitute. On the other hand, few studies have examined this material at the experimental level due to the limitations of OCP mass production. Recently, mass production technology of OCP was developed, and the launch of OCP bone substitutes is occurring. In this study, the bone regeneration capacity of OCP products was compared with two of the most clinically used materials: heat-treated bovine bone (BHA) and sintered biphasic calcium phosphate (BCP). Twelve rabbits were used, and defects in each tibia were filled with OCP, BHA, BCP, and left unfilled as control (CON). The tibias were harvested at 4 and 12 weeks, and 15 &mu;m slides were prepared using the diamond grinding method after being embedded in resin. Histological and histomorphometric analyses were performed to evaluate the bone regeneration ability and mechanism. The OCP showed significantly higher resorption and new bone formation in both periods analysed (p&lt;0.05). Overall, OCP bone substitutes can enhance bone regeneration significantly by activating osteoblasts and a rapid phase transition of OCP crystals to biological apatite crystals (mineralisation), as well as providing additional space for new bone formation by rapid resorption.

Age distribution of horizontal fission tracks

Equations for the distribution of age versus length of partially annealed horizontal fission tracks in apatite is presented. Probabilistic least–squares inversion corrects natural track length histograms for observational biases considering the variance of data, modelization, and prior information. The corrected histogram is validated by its variance–covariance matrix. It is considered that horizontal track data can be with or without measurements of angles to the c–axis. In the last case, 3D–histograms are introduced as an alternative to histograms of c–axis projected track lengths. Thermal history modeling of samples is not necessary for track age distribution calculation. In an example the age equations are applied to apatites with pre–depositional (inherited) tracks, to extract the post–depositional track length histogram. Fission tracks generated before deposition in detrital apatite crystals are mixed with post–depositional tracks. This complicates the calculation of the post– sedimentary thermal history as the grains have experienced different thermal histories until deposition. Thereafter the grains share a common thermal history. The extracted post–depositional histogram without inherited tracks may be used for thermal history calculation.

Apatite crystals reveal melt volatile budgets and magma storage depths at Merapi volcano, Indonesia

Magma volatile budgets and storage depths play a key role in controlling the eruptive styles of volcanoes. Volatile concentrations in the melt can be inferred from analyses of glass inclusions, which however may not be present in the investigated rocks or may have experienced post-entrapment processes that modify their volatile records. Apatite is becoming an alternative robust tool for unraveling the information of magmatic volatiles. Here we report a comprehensive dataset for the concentrations of volatiles and major elements in apatite crystals in the rocks from two eruptions with contrasting eruptive styles: the 2006 (dome-forming) and 2010 (explosive) eruptive events at Merapi volcano (Java, Indonesia). We obtained two-dimensional compositional distributions and in situ concentrations of H2O, CO2, F, Cl, and S in 50 apatite crystals occurring at various textural positions. The CO2 concentrations we report are probably the first ones from natural volcanic apatite. Using the volatile concentrations in apatite and existing thermodynamic models and geothermobarometers, we have calculated the volatile abundances of the pre-eruptive melts of the two eruptions. We find that the apatite from the 2006 and 2010 deposits have a similar compositional range of volatiles, with a bimodal distribution of F-H2O-CO2 contents. The apatite included in amphibole has higher H2O (0.9–1.0 wt.%) and CO2 (Type equation here.≥2400 ppm), but lower F (0.9–1.4 wt.%), compared to crystals included in plagioclase, clinopyroxene, or in the groundmass (H2O: 0.4–0.7 wt.%; CO2: 40–900 ppm; F: 1.7–2.3 wt.%). Using these volatile concentrations and apatite-melt exchange coefficients we obtained two distinct ranges of H2O-CO2-S-F-Cl concentrations in the melt. Melts in equilibrium with apatite included in amphibole had 3–8 wt.% H2O, ≥8000 ppm CO2, 340–2000 ppm S, whereas melts in equilibrium with apatite included in anhydrous minerals and in the groundmass had lower H2O (1.5–4 wt.%), CO2 (60–2500 ppm), and S (10-130 ppm). We calculated the melt H2O-CO2 saturation pressures and found that they correspond to two main magma storage depths. The shallow reservoir with melts stored at ≤10 km below the crater agrees with the depths constrained by melt inclusions, as well as the geodetic, geophysical, and seismic tomography studies from the literature. We have also found a significantly deeper melt storage zone at ≥25–30 km recorded by the C- and H2O-rich apatite in amphibole and barometry calculations using amphibole and high-Al clinopyroxene, which matches with the depths reported in seismic tomography studies. The high CO2/H2O and CO2/SO2 concentrations of the deep melt can help to explain the sharp increase in these ratios in fumarolic gas that were sampled just before the eruption in 2010. Supply of deep volatiles to the shallower magma column before the eruption in 2010 could have increased the magma buoyancy, and thus led to higher magma ascent rates and associated eruption explosivity. Evidence for the faster pre-eruptive magma ascent in 2010 than 2006 is also found on the diffusion distance of Cl in apatite microlites.

Rare Earth Elements and Sr Isotope Ratios of Large Apatite Crystals in Ghareh Bagh Mica Mine, NW Iran: Tracing for Petrogenesis and Mineralization

The 320 Ma Ghareh Bagh mica mine is the only active mica mine in northwest Iran, and hosts Mg-bearing biotite (phlogopite) with apatite, epidote, and calcite. Chemical investigation of apatite infers the high abundances of the rare earth elements (REEs up to 5619 ppm), higher ratios of the LREE/HREE ((La/Yb)N = 28.5–36.7)) and high content of Y (236–497 ppm). REE pattern in the apatite and host A-type granite is almost the same. Ghareh Bagh apatite formed from the early magmatic-hydrothermal exsolved fluids at the high temperature from the Ghushchi alkali feldspar granite. The apatite crystals came up as suspension grains and precipitated in the brecciated zone. The early magmatic-hydrothermal fluids settle phlogopite, epidote, chlorite, K-feldspar and albite down in the brecciation zone. Due to the precipitation of these minerals, the late-stage fluids with low contents of Na+, Ca2+ and REE affected the early stage of alteration minerals. The high ratios of 87Sr/86Sr (0.70917 to 0.70950) are more consistent with crustal sources for the apatite large crystals. The same ages (320 Ma) for both brecciated mica veins and host alkali feldspar granites infer the apatite and paragenesis minerals were related to host granite A-type granite in the Ghareh Bagh area.

Understanding preservation of primary signatures in apatite by comparing matrix and zircon-hosted crystals from the Eoarchean Acasta Gneiss Complex (Canada)

&lt;p&gt;A novel way to investigate the petrogenesis of ancient poly-metamorphosed terranes is to use zircon as a vessel and study protected mineral inclusions which are sensitive to melt evolution such as apatite. Recent contributions have shown that zircon-hosted apatite inclusions of unmetamorphosed granitoids can provide valuable petrogenetic information about a given pluton and, in turn, represent a way to circumvent effects of metamorphism. Yet, the impact of metamorphism on apatite inclusion has never been studied in detail. To address the issue of chemical and isotopic preservation of primary signals in apatite crystals both in the matrix and armored within zircons, we have studied apatite crystals from four 3.6-4.0 Ga orthogneisses of TTG affinity from the Acasta Gneiss Complex (Canada). Our results demonstrate that U-Th-Pb isotope systematics in matrix apatite crystals are reset at the time of the Wopmay orogen (1.8-1.7 Ga) whereas primary REE signatures were preserved in many crystals. On the contrary, zircon-hosted apatite inclusions all preserved primary REE signatures despite U-Th-Pb isotope systematics giving ages between 1.7 and 4.0 Ga. We interpret the variable resetting of these ages as a consequence of radiation damage accumulation in zircon lattice. Only the most pristine zircon has an apatite inclusion with a concordant age consistent with the magmatic age of the zircon (4.0 Ga). In addition, our results show that apatite crystals from TTG have distinct REE composition from post-Archean granitoids apatites, and that even apatites with reset ages preserved some of the chemical signatures characterizing TTG compositions (e.g. HREE). This capacity to retain primary information together with its discriminating power for granitoids makes apatite a very valuable tool for reconstructing the nature and evolution of ancient crustal rocks through the use of either detrital minerals or detrital-zircon hosting inclusions.&lt;/p&gt;