Garnet crystals with quartz inclusions were hydrothermally crystallized from oxide starting materials in piston–cylinder apparatuses at pressures from 0.5 to 3 GPa and temperatures ranging from 700 ...to 800 °C to study how entrapment conditions affect remnant pressures of quartz inclusions used for quartz-in-garnet (QuiG) elastic thermobarometry. Systematic changes of the 128, 206 and 464 cm
−1
Raman band frequencies of quartz were used to determine pressures of quartz inclusions in garnet using Raman spectroscopy calibrations that describe the
P–T
dependencies of Raman band shifts for quartz under hydrostatic pressure. Within analytical uncertainties, inclusion pressures calculated for each of the three Raman band frequencies are equivalent, which suggests that non-hydrostatic stress effects caused by elastic anisotropy in quartz are smaller than measurement errors. The experimental quartz inclusions have pressures ranging from − 0.351 to 1.247 GPa that span the range of values observed for quartz inclusions in garnets from natural rocks. Quartz inclusion pressures were used to model
P–T
conditions at which the inclusions could have been trapped. The accuracy of QuiG thermobarometry was evaluated by considering the differences between pressures measured during experiments and pressures calculated using published equation of state parameters for quartz and garnet. Our experimental results demonstrate that Raman measurements performed at room temperature can be used without corrections to estimate garnet crystallization pressures. Calculated entrapment pressures for quartz inclusions in garnet are less than ~ 10% different from pressures measured during the experiments. Because the method is simple to apply with reasonable accuracy, we expect widespread usage of QuiG thermobarometry to estimate crystallization conditions for garnet-bearing silicic rocks.
Quartz and rutile were synthesized from silica-saturated aqueous fluids between 5 and 20 kbar and from 700 to 940°C in a piston-cylinder apparatus to explore the potential pressure effect on Ti ...solubility in quartz. A systematic decrease in Ti-in-quartz solubility occurs between 5 and 20 kbar. Titanium K-edge X-ray absorption near-edge structure (XANES) measurements demonstrate that Ti
4+
substitutes for Si
4+
on fourfold tetrahedral sites in quartz at all conditions studied. Molecular dynamic simulations support XANES measurements and demonstrate that Ti incorporation onto fourfold sites is favored over interstitial solubility mechanisms. To account for the
P
–
T
dependence of Ti-in-quartz solubility, a least-squares method was used to fit Ti concentrations in quartz from all experiments to the simple expression
where
R
is the gas constant 8.3145 J/K,
T
is temperature in Kelvin,
is the mole fraction of TiO
2
in quartz and
is the activity of TiO
2
in the system. The
P
–
T
dependencies of Ti-in-quartz solubility can be used as a thermobarometer when used in combination with another thermobarometer in a coexisting mineral, an independent
P
or
T
estimate of quartz crystallization, or well-constrained phase equilibria. If temperature can be constrained within ±25°C, pressure can be constrained to approximately ±1.2 kbar. Alternatively, if pressure can be constrained to within ±1 kbar, then temperature can be constrained to approximately ±20°C.
The consequences of overstepping the garnet isograd reaction have been investigated by comparing the composition of garnet formed at overstepped P–T conditions (the overstep or “OS” model) with the ...P–T conditions that would be inferred by assuming garnet nucleated in equilibrium with the matrix assemblage at the isograd (the equilibrium or “EQ” model). The garnet nucleus composition formed at overstepped conditions is calculated as the composition that produces the maximum decrease in Gibbs free energy from the equilibrated, garnet-absent, matrix assemblage for the bulk composition under study. Isopleths were then calculated for this garnet nucleus composition assuming equilibrium with the matrix assemblage (the EQ model). Comparison of the actual P–T conditions of nucleation (the OS model) with those inferred from the EQ model reveals considerable discrepancy between the two. In general, the inferred garnet nucleation P–T conditions (the EQ model) are at a lower temperature and higher or lower pressure (depending on the coexisting calcic phase(s)) than the actual (OS model) nucleation conditions. Moreover, the degree of discrepancy increases with the degree of overstepping. Independent estimates of the pressure of nucleation of garnet were made using the Raman shift of quartz inclusions in garnet (quartz-in-garnet or QuiG barometry). To test the validity of this method, an experimental synthesis of garnet containing quartz inclusions was made at 800 °C, 20 kbar, and the measured Raman shift reproduced the synthesis conditions to within 120 bars. Raman band shifts from three natural samples were then used to calculate an isochore along which garnet was presumed to have nucleated. Model calculations were made at several temperatures along this isochore (the OS model), and these P–T conditions were compared to those computed assuming equilibrium nucleation (the EQ model) to estimate the degree of overstepping displayed by these samples. A sample from the garnet isograd in eastern Vermont is consistent with overstepping of around 10 degrees and 0.6 kbar (affinities of around 2 kJ/mole garnet). A sample from the staurolite–kyanite zone in the same terrane requires overstepping of around 50 °C and 2–5 kbar (affinities of around 10–18 kJ/mole garnet). A similar amount of overstepping was inferred for a blueschist sample from Sifnos, Greece. These results indicate that overstepping of garnet nucleation reactions may be common and pronounced in regionally metamorphosed terranes, and that the P–T conditions and paths inferred from garnet zoning studies may be egregiously in error.
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 SiO
2
-, TiO
2
-, and ZrSiO
4
-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.
Ecological opportunity - through entry into a new environment, the origin of a key innovation or extinction of antagonists - is widely thought to link ecological population dynamics to evolutionary ...diversification. The population-level processes arising from ecological opportunity are well documented under the concept of ecological release. However, there is little consensus as to how these processes promote phenotypic diversification, rapid speciation and adaptive radiation. We propose that ecological opportunity could promote adaptive radiation by generating specific changes to the selective regimes acting on natural populations, both by relaxing effective stabilizing selection and by creating conditions that ultimately generate diversifying selection. We assess theoretical and empirical evidence for these effects of ecological opportunity and review emerging phylogenetic approaches that attempt to detect the signature of ecological opportunity across geological time. Finally, we evaluate the evidence for the evolutionary effects of ecological opportunity in the diversification of Caribbean Anolis lizards. Some of the processes that could link ecological opportunity to adaptive radiation are well documented, but others remain unsupported. We suggest that more study is required to characterize the form of natural selection acting on natural populations and to better describe the relationship between ecological opportunity and speciation rates.
Landscape genetics has emerged as a new research area that integrates population genetics, landscape ecology and spatial statistics. Researchers in this field can combine the high resolution of ...genetic markers with spatial data and a variety of statistical methods to evaluate the role that landscape variables play in shaping genetic diversity and population structure. While interest in this research area is growing rapidly, our ability to fully utilize landscape data, test explicit hypotheses and truly integrate these diverse disciplines has lagged behind. Part of the current challenge in the development of the field of landscape genetics is bridging the communication and knowledge gap between these highly specific and technical disciplines. The goal of this review is to help bridge this gap by exposing geneticists to terminology, sampling methods and analysis techniques widely used in landscape ecology and spatial statistics but rarely addressed in the genetics literature. We offer a definition for the term 'landscape genetics', provide an overview of the landscape genetics literature, give guidelines for appropriate sampling design and useful analysis techniques, and discuss future directions in the field. We hope, this review will stimulate increased dialog and enhance interdisciplinary collaborations advancing this exciting new field.
Titanium and zirconium analyses of quartz and rutile from blueschist samples from the eclogite–blueschist unit (EBU) in northern Sifnos, Greece, have been evaluated to determine the extent to which ...the intersection of the Ti-in-quartz (TitaniQ) and zirconium-in-rutile (ZiR) thermometers reflect peak metamorphic P–T conditions. Ti concentrations range from 100 to 530 ppb and Zr concentrations range from 14 to 44 ppm; there is no significant zoning observed in any grains and no significant differences in concentrations in samples south and north of the Vroulidia shear zone (VSZ). Lines of equal Keq from the TitaniQ and ZiR thermometers intersect at around 450–500 °C and 2.2–2.4 GPa, which is similar to the peak metamorphic conditions of 530 °C, 1.9 GPa for samples north of the VSZ. However, the intersection is inconsistent with the peak metamorphic conditions of 525 °C, 1.1–1.4 GPa for samples south of the VSZ even when TitaniQ temperatures are corrected for reduced activity of TiO
2
. Rather, TitaniQ temperatures are consistent with Ti values being incorporated into quartz during prograde metamorphism along a subduction geotherm of 10–12 deg/km at around 300 °C. ZiR temperatures are consistent with rutile nucleation and growth at around 450–500 °C along a similar metamorphic geotherm after the rutile-in reaction was overstepped by around 1 kJ/mol-O. The TitaniQ and ZiR thermometers do not, therefore, reflect peak metamorphic P–T conditions in these rocks but rather record recrystallization or growth processes during prograde subduction.
New results that employ Zr‐in‐rutile thermometry (ZiR) and quartz‐inclusion‐in‐garnet (QuiG) barometry constrain the P–T conditions of garnet formation in blueschists and eclogites from the island of ...Syros, Greece. QuiG barometry reveals that garnet from different regions across the island formed at pressures ranging from 1.1 to 1.8 GPa and ZiR thermometry on rutile inclusions in garnet constrains the minimum temperature of garnet formation to have been 475–550°C. Most importantly, there is no systematic difference in the conditions of garnet formation from different regions across the island and these results are nearly identical to those obtained from the islands of Sifnos and Ios, Greece. A model is proposed whereby the rocks from all three islands were initially metamorphosed along a relatively shallow geotherm of around 11°C/km to a depth of around 45 km and were then subjected to metamorphism along a geotherm of around 7–8°C/km, which could have been caused by either an increase in the dip of the subduction zone or an increase in the rate of subduction. Garnet formed along this steeper geotherm was accompanied by the release of significant H2O from the breakdown of chlorite over a duration of 1 Ma or less based on thermal and diffusion modeling. It is concluded that rocks from Syros, Sifnos and Ios all followed a similar, roughly counter‐clockwise prograde P–T path and that the present outcrop configuration is largely due to a complex exhumation history.
Plain Language Summary
The metamorphism of rocks in subduction zones releases large quantities of H2O, which ultimately helps flux melting in the overlying mantle leading to explosive island arc volcanism and provides a trigger for large earthquakes. One of the dominant processes that produce large amounts of H2O is the formation of the mineral garnet. Here, we present results that constrain the pressure and temperature conditions for the formation of garnet from three islands in the Greek Cyclades: Syros, Sifnos, and Ios. Our results indicate that garnet formed in different rocks on all three islands in a similar subduction channel along a trajectory where the pressure increase was relatively rapid and the temperature remained nearly constant. The duration of garnet formation in the entire suite of samples is estimated to have occurred in 1 million years or less, during which time significant quantities of fluid are inferred to have been released and which most likely had a major impact on volcanism and seismicity in the region while subduction was active.
Key Points
Blueschist and eclogite assemblages do not necessarily reflect equilibrium crystallization
Exhumation following garnet growth must occur within 1 Ma to preserve compositional zoning
The prograde subduction P–T path in the Cyclades is concave upward with initial shallow subduction followed by near isothermal loading
Background
In 2004, the authors reported their findings with placement of tissue expanders for breast reconstruction in the partial submuscular position, the equivalent of the “dual-plane” technique ...for breast augmentation. Limitations with subpectoral expander placement include difficulty controlling the lower pole of the pocket during expansion, unprotected device coverage by a thin inferior mastectomy flap, possible effacement of the inframammary fold, and limited control over the superior migration of the pectoralis major muscle. This study aimed to examine the safety and efficacy of an acellular dermal sling in providing inferolateral support to the device during immediate breast reconstruction and expansion.
Methods
This study prospectively investigated 58 breasts of 43 consecutive women who underwent immediate breast reconstruction with tissue expanders and acellular dermis. After completion of adjuvant therapy and expansion, the devices were exchanged for implants. The patients were tracked through January, 2007. The study parameters included demographic information, oncologic data, complications, and aesthetic outcomes.
Results
The mean time required to complete reconstruction was 8.6 months. The overall complication rate after expander/acellular dermis placement was 12%, whereas the complication rate after exchange to implants was 2.2%. The aesthetic outcome for reconstructed breasts did not differ significantly from that for the control subjects who had no surgery.
Conclusions
Acellular dermis appears to be a useful adjunct in immediate prosthetic breast reconstruction. Acellular dermis-assisted breast reconstruction has a low complication rate, helps to reconstruct an aesthetically pleasing breast, and facilitates expeditious completion of the reconstruction.
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