The garnet–clinopyroxene Fe2+–Mg geothermometer: an updated calibration

Multiple regression analysis on an extended dataset has been performed to refine the relationship between temperature, pressure, composition and the Fe–Mg distribution between garnet and clinopyroxene. In addition to a significant dependence between the distribution coefficient K_D and X ^Grt_Ca and X ^Grt_Mg#, as shown by the experimental data, the effect of X ^Grt_Mn has also been incorporated using data from natural Mn‐rich garnet–clinopyroxene pairs. Multiple regression of data (n=360) covering a large span in pressure, temperature and composition from 27 experimental datasets, combined with 49 natural high‐Mn granulites from Ruby Range, Montana, USA, and Karnataka, India, yields the P–T –compositional relationship (r²=0.98): where K_D=(Fe²⁺/Mg)^Grt/(Fe²⁺/Mg)^Cpx, X ^Grt_Ca=Ca/(Ca+Mn+Fe²⁺+Mg) in garnet, X ^Grt_Mn= Mn/(Ca+Mn+Fe²⁺+Mg) in garnet, and X ^Grt_Mg#=Mg/(Mg+Fe²⁺) in garnet. The Fe²⁺–Mg equilibrium between garnet and clinopyroxene does not seem to be affected by variations in the sodic content of the co‐existing clinopyroxene in the range X ^Cpx_Na=0–0.51. Comparisons between the new and former calibrations of the garnet–clinopyroxene Fe²⁺–Mg geothermometer clearly demonstrate how the various parameters in each case affect the calculated temperatures. Application of the new expression gives reasonable results for natural garnet–clinopyroxene pairs from various rock types and settings, and should be preferred to previous formulations. Using the new calibration to the self‐consistent dataset of Pattison & Newton (Contributions to Mineralogy and Petrology, 1989, 101, 87–103) suggests a systematic deviation with regard to both temperature and composition between their dataset and the datasets used in the present calibration.     

Palynology of Upper Cretaceous (uppermost Campanian–Maastrichtian) deposits in the South Yellow Sea Basin, offshore Korea

Forty-seven samples from Upper Cretaceous sections penetrated by the Kachi-1 and Inga-1 wells in the South Yellow Sea Basin have been analysed for their spore and pollen content. Thirty-five species of 18 spore genera and 54 species of 28 pollen genera are documented. One new monotypic genus, Diporocolpopollenites, and its type species, D. kachiensis sp. nov., are erected, and Dilwynites Harris, 1965, and its type species, D. granulatus Harris, 1965, are emended. There are also three new combinations: Ephedripites eocaenicus (Selling, 1944), E. praeclarus (Chlonova, 1961), and Retitricolpites anguloluminosus (Anderson, 1960). Two palynological zones are erected: anAquilapollenites attenuatus Assemblage Zone, which encompasses deposits that are considered to be latest Campanian–Early Maastrichtian in age, and an Aquilapollenites eurypteronus Assemblage Zone for sections that have been dated as Late Maastrichtian. The assemblages are typical of the Yenisey-Amur Subprovince of the Aquilapollenites (floral) Province. Lowland floodplain to shallow, commonly mesotrophic, lacustrine environments of deposition are indicated. The climate was probably wet subtropical, with rainfall being somewhat higher during the Late Maastrichtian than through the latest Campanian–Early Maastrichtian.     

Succession,palaeoecology, evolution,and speciation of Pennsylvanian non‐marine bivalves,Northern Appalachian Basin,USA

Seventeen horizons of non‐marine bivalves are described within the Appalachian succession from the base of the Pottsville Group of Westphalian A‐B age to the Uniontown coal of Stephanian C age at the top of the Carboniferous System. A new highly variable fauna of Anthraconaia from the roof shales of the Upper Freeport coal near Kempton, west Maryland, dates from late Westphalian D or very early Cantabrian time, on the evidence of non‐marine shells and megafloras. Below this horizon, the Appalachian sequence reveals zones of Anthraconauta phillipsii and Anthraconauta tenuis in the same order as in Britain, whereas faunas of Anthraconaia of these zones are less common and differ from those of Britain. In all horizons above the Upper Freeport coal all non‐marine bivalve faunas consist of stages in the sequences of two natural species, the groups of Anthraconaia prolifera and Anthraconaia puella‐saravana. The first shows evidence of having lived in well‐oxygenated, probably shallow, fresh water conditions of relatively wide extent. The second group lived preferentially in a plant‐rich environment of relatively stagnant fresh water. Both groups are found in horizons associated with coal seams and may be seen together in the same habitats, but diagrams of variation (pictographs) suggest that there was no interbreeding between the two groups in either the Northern Appalachians or in southern Germany where the species split was first recognized. In the northern Spanish coalfields of Guardo‐Valderrueda and Central Asturia, facies evidence suggests how an initial split may have taken place in the same morphological directions and into the same palaeoenvironments as the later split into two species. Appalachian deposition was generally slow and intermittent with frequent palaeosols. There is also evidence of erosion and of small palaeontological breaks in the sequence, especially near the eastern edge of the Northern Appalachian Basin in western Maryland. The amount of accumulated sediment was less than one‐tenth of that of western Europe when basin centre deposition is compared. We found no evidence of a major palaeontological break representing Westphalian D strata overlain by Stephanian C strata. We figure non‐marine bivalve faunas of Stephanian B age in association with the Pittsburgh and the Little Pittsburgh coals. Two new species of non‐marine bivalves are described: Anthraconaia anthraconautiformis sp. nov. and Anthraconaia extrema sp. nov. Copyright © 2003 John Wiley & Sons, Ltd.     

The assemblage stilpnomelane–chlorite–phengitic mica: a geothermobarometer for blueschist and associated greenschist terranes

Two anhydrous equilibria can be written among the components of stilpnomelane, chlorite, white mica and quartz, namely 89 daphnite+131 Fe-celadonite+190 quartz=96 stilpnomelane+71 muscovite, and amesite+Mg-celadonite=muscovite+clinochlore. We assume that the free energy change of reaction, ΔG=ΔG^o+ΣRT lna_i^j, is approximated by ΔG=A?BT +C(P?1)+ΣRT lna_i^j, where ΔG^o is the free energy change of the end-member components at temperature T and pressure P, a_i is the activity of component i whose coefficient in the equilibrium is j, and A, B and C are constants to be determined. Values of C can be approximated by the change in volume on reaction, namely C=406.517 J/bar for the first reaction and C=0.613 J/bar for the second reaction. Constants A and B were determined by using six occurrences of the assemblage stilpnomelane–chlorite–white mica for which P–T have been otherwise estimated. Using solution models from the literature, linear regression gives for the first equation A=?6118.269 kJ, B=?4584.09 J/K, and for the second equation A=19.397 kJ, B=66.72 J/K. These values predict P–T within 0.5 kbar and 25 K for all occurrences, and appear reasonably robust relative to probable analytical errors. P–T are determined by intersection of the curves generated by given compositions in P–T space. Fine-grained and/or zoned chlorite and white mica make application of the geothermobarometer difficult in some instances, but our work in the Bathurst region of New Brunswick suggests that, with patience and care, useful analyses can be obtained, and the database for the geothermobarometer greatly expanded.     

P–T–X relationships in the Precambrian Al–Mg-rich granulites from In Ouzzal, Hoggar, Algeria

The Al–Mg-rich granulites from the In Ouzzal craton, Algeria, show a great diversity of mineral reactions which correspond to continuous equilibria as predicted by phase relationships in the FeO–MgO–Al₂O₃–SiO₂ system. The sequence of mineral reactions can be subdivided into three distinct stages: (1) a high-P stage characterized by the growth of coarse mineral assemblages involving sapphirine and the disappearance of early corundum and spinel-bearing assemblages; (2) a high-T stage characterized by the development of Sa–Qz-bearing assemblages; and (3) a later stage, in which garnet-bearing assemblages are replaced by more or less fine symplectites involving cordierite. During the course of early mineral reactions, the distribution coefficient, K_d, between the various ferromagnesian phases decreased significantly whereas Al₂O₃ in pyroxene increased concomitantly. These observations, when combined with topological constraints, clearly indicate that the high-P stage 1 was accompanied by a significant rise in temperature (estimated at 150 ± 50° C) under near isobaric conditions, in agreement with the reaction textures. By stage 2, pressure and temperature were extreme as evidenced by the low K_d value between orthopyroxene and garnet (K_d= 2.06–1.99), the high alumina content in pyroxene (up to 11.8%) and the high magnesium content in garnet [100 Mg/(Mg + Fe) = 60.6]. Mineral thermometry based on Fe–Mg exchange between garnet and pyroxene and on Al-solubility in pyroxene gives temperatures close to 970 ± 70° C at 10 ± 1.5 kbar. These results are in agreement with the development of Sa–Qz assemblages on a local scale. Late mineral reactions have been produced during a decompression stage from about 9 to 6 kbar. Except for local re-equilibration of Mg and Fe at grain boundaries, there is no evidence for further reactions below 700° C. We interpreted the whole set of mineral reactions as due to changes in pressure and temperature during a tectonic episode located at c. 2 Ga. Because of the lack of evidence for further uplift after the thermal relaxation which occurred at c. 6 kbar, it is possible however that the exhumation of this granulitic terrane occurred in a later tectonic event unrelated to its formation.     

Charophytes du Crétacé moyen et données nouvelles sur l'Evolution des Clavatoracées

La découverte de nouveaux gisements dans le Sud de la France révèle la persistance, dans le Cénomanien, d'Embergerella cruciata, Atopochara restricta et A. brevicellis (Clavatoraceae). Une parenté entre les genres Embergerella (Barrémien-Cénomanien) et Septorella (Maastrichtien) est envisagée sur la base d'une nouvelle interprétation de la structure de l'utricule. Pour la première fois, des représentants de la famille des Characeae sont décrits dans le Cénomanien: Peckisphaera revesti n. sp. et le Turonien: Mesochara fusiformis n. sp. Indications biostratigraphiques: dans l'état actuel des connaissances sur les flores de Charophytes du Crétacé moyen, seul le Cénomanien est bien caractérisé, par A. multivolvis à laquelle s'ajoute maintenant une nouvelle association de quatre espèces; l'Albien et le Turonien, pour lesquels des précisions sont apportées, restent toutefois encore mal individualisés.The discovery of new localities in the South of France shows that Embergerella cruciata, Atopochara restricta and A. brevicellis (Clavatoraceae) continued into the Cenomanian. A relationship between the genera Embergerella (Barremian-Cenomanian) and Septorella (Maastrichtian) is suggested on the basis of a new interpretation of the structure of the utricle. Representatives of the family Characeae are described for the first time, Peckisphaera revesti n. sp. in the Cenomanian and Mesochara fusiformis n. sp. in the Turonian. Biostratigraphic information: in the present state of knowledge of Middle Cretaceous Charophyte floras, only the Cenomanian is well characterized, by A. multivolvis to which is now added a new association of four species. Although new information is presented on the Albian and Turonian, they are still inadequately understood.     

Garnet zoning and the identification of equilibrium mineral compositions in high-pressure–temperature granulites from the Moldanubian Zone, Austria

A detailed investigation of the compositional variation in garnet has been undertaken in a garnet–pyroxene‐bearing granulite from the high‐grade Gföhl Unit, Moldanubian Zone, Lower Austria. Textural observations, together with the interpretation of the preserved garnet chemistry, enables the recognition of both prograde core and peak metamorphic garnet mantle growth stages, an extremely rare feature in high‐P–T granulite facies rocks. Initial thermobarometric calculations undertaken across whole garnet zoning profiles show how correct interpretation of a zoning profile is essential if the maximum peak metamorphic P–T conditions are to be recovered. The effect of retrograde decompression‐ and cooling‐driven reactions on inclusion and host garnet compositions has also been assessed. The results indicate that caution should be exercised when utilizing inclusion and adjacent garnet compositions for the thermobarometric evaluation of peak metamorphic equilibration conditions. Peak P–T conditions were determined by the TWEEQU thermobarometric method, utilizing the core compositions of matrix phases combined with the interpreted high‐P–T garnet mantle composition, to give 15.6 kbar and 1090 °C, consistent with previously determined results for Moldanubian granulites. Similar high‐P–T estimates are also provided by a re‐evaluation of previously published results for a granulite sample from the same lithological unit, using a modified interpretation of garnet and plagioclase compositional data. The new estimates presented confirm the previously disputed idea that the Gföhl Unit underwent a high‐pressure granulite facies stage and is therefore distinctly different from the underlying tectonostratigraphic units. It is emphasized that any interpretation of the peak metamorphic conditions in high‐grade rocks must be based on detailed petrographic observations combined with a thorough understanding of the co‐existing equilibrium mineral compositions.     

A new thermodynamic model for sapphirine: calculated phase equilibria in K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3

The activity–composition (a–x) relations of sapphirine are re‐evaluated in the light of a recent new internally‐consistent data set of phase end‐members for use in phase equilibria modelling, particularly of ultra‐high‐temperature (UHT) rocks. This is achieved with the aid of relatively oxidized sapphirine+quartz‐bearing granulites from Wilson Lake, Canada. Calculated P–T projections and compatibility diagrams in the K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–Fe₂O₃ (KFMASHTO) system are used to illustrate sapphirine+quartz‐bearing phase equilibria in the context of UHT metamorphism. These new a–x relations for sapphirine should allow pseudosection thermobarometry in NCKFMASHTO for estimating peak P–T conditions of sapphirine‐bearing rocks.     

The ‘Polish Solnhofen’: a long‐awaited alternative?

Here we briefly report on the discovery of a new Fossil‐Lagerstätte locality, Owadów‐Brzezinki quarry (central Poland), which exposes Late Jurassic (Late Tithonian) carbonate sediments with an extremely fossiliferous horizon of lithographic‐type limestones. Numerous specimens of horseshoe crabs were found in association with an enormously rich assemblage of the soft‐shelled bivalves Corbulomima obscura and Mesosaccella sp., the remains of various fishes and marine reptiles, rare ammonites, crustaceans, land insects and pterosaurs. The uniqueness of this new locality lies in its very close stratigraphical relationship to one of the most famous Fossil‐Lagerstätte localities in the world—Solnhofen, in southern Germany, with approximately 2 Ma separating them. Marine and terrestrial creatures lived and died during the Late Jurassic both at Solnhofen (Hybonotum Zone) and in another area (Owadów‐Brzezinki quarry, Zarajskensis Subzone), under closely related environmental conditions. The small palaeogeographical distance separating these two locations enables, for the first time, an effective palaeobiological test of the pace of evolutionary speciation amongst different groups of organisms.     

Ternary system H<Subscript>2</Subscript>O-CO<Subscript>2</Subscript>-NaCl at high <Emphasis Type="Italic">T</Emphasis>-<Emphasis Type="Italic">P</Emphasis> parameters: An empirical mixing model

New experimental data on the solubility of NaCl in gaseous CO₂ were obtained at pressures (P) of 30–70 MPa and temperatures of 623 and 673 K on experimental equipment making possible to sample a portion of the gas in the course of the experiment. The new measures have demonstrated that the NaCl solubility increases with increasing temperature (T) and pressure and is approximately four to five orders of magnitude higher than the saturated vapor pressure of NaCl at the corresponding temperature. The paper also reports newly obtained experimental data on the equilibrium conditions of the reaction of talc decomposition into enstatite and quartz at a variable H₂O/NaCl ratio in the fluid. The results of the experiments validate the empirical equations previously suggested for H₂O and NaCl activities in concentrated aqueous salt solutions that can be used in describing silica-saturated fluids at high T-P parameters. A new empirical equation is suggested for the Gibbs free mixing energy in the H₂O-CO₂-NaCl ternary system, with the parameters of the equation calibrated against experimental data on phase equilibria in marginal binary systems and on the location of the boundary of the region of homogeneous three-component fluid according to data on synthetic fluid inclusions in quartz.     

Simulation of the molecular mass distributions of Si anions on the liquidus of the Na<Subscript>2</Subscript>O-SiO<Subscript>2</Subscript> system with regard for the disproportionation of <Emphasis Type="Italic">Q</Emphasis> structons

A new version of the STRUCTON (2009) computer model is proposed for the simulation of the molecular mass distributions (MMD) characterizing the diversity of anions in silicate melts depending on their polymerization and temperature. In contrast to earlier versions, the new version of the model accounts for disproportionation reactions of Q ⁿ species and makes use of their proportions in the statistical simulations of the origin of real Si-O complexes. The new potentialities of the STRUCTON program package are illustrated by its application to studying the structural-chemical characteristics of melts in the Na₂O-SiO₂ system along its liquidus line, including the points of eutectics and phase transitions at 0.333 ≤ $ N_{SiO_2 } $ N_{SiO_2 } < 0.500. This problem is solved with the use of a temperature-composition dependence of polymerization constants K _p ^Na in the Toop-Samis approximation. The variations in K _p ^Na were proved to be as large as three orders of magnitude due to both the temperature effect at a constant composition and the composition effect at a constant temperature. The results of the MMD simulations on the liquidus show that the concentration of the SiO₄⁴⁻ ion strongly decreases, and the proportion of chain species increases compared to those at a stochastic distribution. The concentration of the Si₂O₇⁶⁻ anion reaches its maximum (∼42%) at 40 mol % in the liquid, i.e., the composition of Na₆Si₂O₇. At $ N_{SiO_2 } $ N_{SiO_2 } > 0.40, this ion dominates over the SiO₄⁴⁻ monomer. More silicic melts with $ N_{SiO_2 } $ N_{SiO_2 } ≥ 0.45, are dominated by (Si _n O_3n )³ⁿ⁻ ring species, and the concentrations of these species are related as (Si₃O₉)⁶⁻ > (Si₄O₁₂)⁸⁻ > (Si₅O₁₅)¹⁰⁻. The maximum concentration of these flat rings also occurs near the composition of stoichiometric metasilicate with Si/O = 0.333. The comparison of the dependence of the average size of anions i _av and the average number of their species on depolymerization indicates that a change in the proportion of Q ⁿ species in melt at decreasing temperature results in structural restyling and an increase in the average size of Si-O complexes. The average number of anion species thereby decreases compared to that in a stochastic MMD. The results presented in this publication direct the progress in the thermodynamic theory of silicate melts to a new avenue that makes use of the capabilities and advantages of the ion-polymer model, the theory of associated solutions, spectroscopic data, and the experimental study of variations in oxide activities depending on composition and temperature.     

Controls of mineral reactions in high-grade garnet–wollastonite–scapolite-bearing calcsilicate rocks: an example from Anakapalle, Eastern Ghats, India

ABSTRACT A suite of garnet-wollastonite-scapolite-bearing calcsilicate granulites from the Eastern Ghats has been investigated to document the controls of mineral reactions during the metamorphic evolution of the deep continental crust. The rocks studied show heterogeneity in modal mineralogy and phase compositions in millimetre-sized domains. Textural relations, and the compositional plots of the phases, established that the clinopyroxene exerts a strong influence on the formation and composition of garnet in the complex natural system. P-T estimates using the vapour-independent equilibria involving garnet define a near isobaric cooling path from c. 850C at c. 5.5–5.2 kbar. The deduced trajectory tallies well with the terminal segment of the overall retrograde P-T path construed from the associated rocks using well-calibrated thermobarometers. The ubiquitous occurrence of wollastonite and scapolite in the main calcsilicate body suggests low a_CO2 during peak metamorphic condition. Fluid compositions constrained from mineral-fluid equilibria of the garnet-bearing assemblages show domainal variations as a function of the compositions of the solid phases, e.g. garnet and clinopyroxene. A quantitative log/_CO2-log/_O2 diagram has been constructed to depict the stability of the different calcsilicate assemblages as functions of the compositions and the behaviour of these fugitive species. The results of the mineral-fluid equilibria and the quantitative fluid/rock ratio calculations, in conjunction with the topological constraints, imply vapour-deficient meta-morphism in the rocks studied. It is argued that f_O2 during peak metamorphism was monitored by the ambient f_O2. Subsequently, during retrogression, different domains evolved independently, whereas the fluid composition was controlled by the mineral-fluid equilibria.     

Ultrahigh temperature granulite metamorphism (1050 °C, 12 kbar) and decompression in garnet (Mg70)–orthopyroxene–sillimanite gneisses from the Rauer Group, East Antarctica

Highly magnesian and aluminous migmatitic gneisses from Mather Peninsula in the Rauer Group, Eastern Antarctica, preserve ultrahigh temperature (UHT) metamorphic assemblages that include orthopyroxene+sillimanite±quartz, garnet+sillimanite±quartz and garnet+orthopyroxene±sillimanite. Garnet that ranges up to X_Mg of 71.5 coexists with aluminous orthopyroxene that shows zoning from cores with 7.5–8.5 wt% Al₂O₃ to rims with up to 10.6 wt% Al₂O₃ adjacent to garnet. Peak P–T conditions of 1050 °C and 12 kbar are retrieved from Fe–Mg–Al thermobarometry involving garnet and orthopyroxene, in very good agreement with independent constraints from petrogenetic grids in FeO–MgO–Al₂O₃–SiO₂ and related chemical systems. Sapphirine, orthopyroxene and cordierite form extensive symplectites and coronas on the early phases. The specific reaction textures and assemblages involving these secondary phases correlate with initial garnet X_Mg , with apparent higher-pressure reaction products occurring on the more magnesian garnet, and are interpreted to result from an initial phase of ultrahigh temperature near-isothermal decompression (UHT-ITD) from 12 to 8 kbar at temperatures in excess of 950 °C. Later textures that involved biotite formation and then partial breakdown, along with garnet relics, to symplectites of orthopyroxene+cordierite or cordierite+spinel may reflect hydration through back-reaction with crystallizing melts on cooling below 900–850 °C, followed by ITD from 7 to 8 kbar to c. 5 kbar at temperatures of 750–850 °C. The tectonic significance of this P–T history is ambiguous as the Rauer Group records the effects of Archean tectonothermal events as well as high-grade events at 1000 and 530 Ma. Late-stage biotite formation and subsequent ITD can be correlated with the P–T history preserved in the Proterozoic components of the Rauer Group and hence with either 1000 or 530 Ma collisional orogenesis. However, whether the preceding UHT-ITD history reflects a temporally unrelated event (e.g. Archean) or is simply an early stage of either the late-Proterozoic or Pan-African tectonism, as recently deduced for similar UHT rocks from other areas of the East Antarctica, remains uncertain.     

Çakraz Formation, Çamdağ area,NW Turkey: early/mid‐Permian age,Rotliegend (Germany) and Southern Alps (Italy) equivalent—a stratigraphic re‐assessment via palynological long‐distance correlation

The palynological record from the Permian part of the Çakraz Formation from the Çamdağ area of NW Turkey has been investigated in order to obtain a more precise age assessment than achieved in previous studies. The ‘Late Permian’ age and a possible age range beginning in the Roadian (mid Permian) were discussed before for sections of palynomorph‐bearing strata occurring within the formation. These deposits are now assigned to the late Cisuralian/Guadalupian and considered to be not older than early Kungurian, and not younger than Capitanian. The new age assessment was conducted via a long‐distance, intercontinental palynostratigraphic correlation from NW Turkey to South America, where results of radiometric datings were linked to some siliciclastic sections by absolute ages to the chronostratigraphy. Common conspicuous taxa in pollen‐dominated assemblages from both regions are Lueckisporites and Vittatina such as Lueckisporites virkkiae, L. latisaccus, L. stenotaeniatus, Vittatina corrugata, V. subsaccata and V. wodehousei. These species co‐occur in strata of the northern as well as southern palaeohemisphere settings (NW Turkey and S America). Thus, Lueckisporites latisaccus, L. stenotaeniatus and Vittatina corrugata are, as well as L. virkkiae or V. subsaccata, considered as being cosmopolitan. Due to the more precise palynological dating of part of the Çakraz Formation and surrounding deposits they are here broadly correlated with Permian continental successions from the Southern Alps, Italy, including the Val Daone Conglomerate and the Verrucano Lombardo/Val Gardena Sandstone (Gröden) red beds, and the Rotliegend deposits of Germany. These results support some earlier views regarding the age and stratigraphic equivalences with European deposits. The new age for the Çakraz Formation also supports recent considerations as middle Permian (part Guadalupian), and as Cisuralian for the lower parts of the formation, such as the fossil‐bearing section with plants and tetrapod traces further east in NW Turkey, where the unit also crops out. Copyright © 2014 John Wiley & Sons, Ltd.     

A New Thorny Lacewing (Insecta: Neuroptera: Rhachiberothidae) from the Early Cretaceous Amber of Lebanon

<正>A new genus and species of Rhachiberothidae,Raptorapax terribilissima gen.et sp.nov.from the Cretaceous amber of Lebanon is described.The new genus is assigned to the subfamily Paraberothinae.The new material confirms the great diversity of the group in the Cretaceous age and its decrease in diversity in recent times.     

Tracing growing degree‐day changes in the cuticle morphology of Betula nana leaves: a new micro‐phenological palaeo‐proxy

Changing growing‐season properties in the northern latitudes are among the most obvious consequences of ongoing global change. Available techniques including satellite monitoring and phenological observations enable the detection of changes over the last few decades to centuries, but the full range of natural variability is still difficult to capture. Here we introduce a new approach to reconstruct growing season properties, by studying imprints of prolonged growing season on epidermal cell growth in Betula nana. A high correlation between cell expansion determined in annually collected B. nana leaves and subfossil leaf fragments collected from recent peat sections in northern Scandinavia, and climatic indices such as budburst date, growing‐season degree‐days and May–September mean temperatures, enable the establishment of a new micro‐phenological proxy for growing season characteristics. The applicability of the epidermal cell undulation index (UI) is tested by comparison with historical instrumental records of growing‐season degree‐days for the last 200 a. The results demonstrate the potential of the new leaf‐morphology‐based technique to reconstruct and quantify past changes in growing degree‐days beyond instrumental data series. Applied to abundant B. nana leaf remains from peat and lake sediments, the UI may enable a reconstruction of growing degree‐days throughout the Holocene and other parts of the late Quaternary. Copyright © 2010 John Wiley & Sons, Ltd.     

Metamorphism of the Central Anatolian Crystalline Complex, Turkey: influence of orogen-normal collision vs. wrench-dominated tectonics on P–T–t paths

The Central Anatolian Crystalline Complex (CACC) is a microcontinent in the Alpine–Himalayan belt. It has previously been considered as a coherent structural entity, but, although the entire CACC is comprised of similar rocks (primarily metasedimentary rocks and granitoids), it consists of at least four tectonic blocks characterized by different P–T–t paths. These blocks are the K?r?ehir (north‐west), Akda? (north‐east), Ni?de (south) and Aksaray (west) massifs. The northern massifs experienced thrusting and folding during collision and were slowly exhumed by erosion; metamorphic rocks are characterized by clockwise P–T paths at moderate P–T and local low‐P–high‐T (LP–HT) overprinting in the highest grade rocks. Apatite fission track ages are Eocene to Oligocene (47–32 Ma). The Aksaray block represents the hot, shallow mid‐crust of a Late Cretaceous–early Tertiary arc. It is dominated by intrusions; rare metapelitic rocks record low‐P (< 4 kbar) regional metamorphism overprinted by LP–HT contact metamorphism. Apatite fission track ages are 50–45 Ma. The Ni?de massif is different from the other CACC blocks because it evolved as a core complex in a wrench‐dominated setting. It is characterized by clockwise P–T paths at moderate P–T followed by widespread LP–HT metamorphism. Apatite fission track ages are Miocene (12–9 Ma), significantly younger than those in the northern massifs. Ni?de rocks resided in the mid‐crust at a time when the rest of the CACC was at or near the Earth's surface. Variations in P–T–t and tectonic histories — especially timing of exhumation — between the northern and southern CACC reflect the difference between head‐on collision vs. mid‐crustal wrenching.     

Discriminating between pore‐filling load and bed‐structure load: a new porosity‐based method,exemplified for the river Rhine

Sediments contained in the river bed do not necessarily contribute to morphological change. The finest part of the sediment mixture often fills the pores between the larger grains and can be removed without causing a drop in bed level. The discrimination between pore‐filling load and bed‐structure load, therefore, is of practical importance for morphological predictions. In this study, a new method is proposed to estimate the cut‐off grain size that forms the boundary between pore‐filling load and bed‐structure load. The method evaluates the pore structure of the river bed geometrically. Only detailed grain‐size distributions of the river bed are required as input to the method. A preliminary validation shows that the calculated porosity and cut‐off size values agree well with experimental data. Application of the new cut‐off size method to the river Rhine demonstrates that the estimated cut‐off size decreases in a downstream direction from about 2 to 0·05 mm, covariant with the downstream fining of bed sediments. Grain size fractions that are pore‐filling load in the upstream part of the river thus gradually become bed‐structure load in the downstream part. The estimated (mass) percentage of pore‐filling load in the river bed ranges from 0% in areas with a unimodal river bed, to about 22% in reaches with a bimodal sand‐gravel bed. The estimated bed porosity varies between 0·15 and 0·35, which is considerably less than the often‐used standard value of 0·40. The predicted cut‐off size between pore‐filling load and bed‐structure load (D_c,p) is fundamentally different from the cut‐off size between wash‐load and bed‐material load (D_c,w), irrespective of the method used to determine D_c,p or D_c,w. D_c,w values are in the order of 10^?1 mm and mainly dependent on the flow characteristics, whereas D_c,p values are generally much larger (about 10⁰ mm in gravel‐bed rivers) and dependent on the bed composition. Knowledge of D_c,w is important for the prediction of the total sediment transport in a river (including suspended fines that do not interact with the bed), whereas knowledge of D_c,p helps to improve morphological predictions, especially if spatial variations in D_c,p are taken into account. An alternative to using a spatially variable value of D_c,p in morphological models is to use a spatially variable bed porosity, which can also be predicted with the new method. In addition to the morphological benefits, the new method also has sedimentological applications. The possibility to determine quickly whether a sediment mixture is clast‐supported or matrix‐supported may help to better understand downstream fining trends, sediment entrainment thresholds and variations in hydraulic conductivity.     

The retrograde P–T–t path for low-pressure granulites from the Reynolds Range, central Australia: petrological constraints and implications for low-P/high-T metamorphism

Several aspects of the petrogenesis of low-pressure granulite facies rocks from the Reynolds Range (central Australia) are contentious, including: (a) the shape of the retrograde P–T –time path, and whether it is an artefact of repeated thermal events at different P–T conditions; (b) the type of regional metamorphism; and (c) the causes of metamorphism. Granulite facies rocks from the Reynolds Range Group experienced three major periods of mineralogical equilibration. Metapelitic rocks underwent dehydration-melting reactions to form migmatites under peak M2 P–T conditions of c. 5.0–5.3 kbar and c. 750–800 °C. Metapsammitic rocks that did not melt during M2 show spectacular garnet–orthopyroxene intergrowths that developed at c. 3.5–3.7 kbar and c. 700–750 °C after penetrative regional deformation, but prior to amphibolite facies rehydration in discrete strike-parallel zones. Rehydration occurred within the sillimanite stability field at P–T conditions close to the granite solidus (c. 3.2–3.4 kbar and 650–700 °C). Subsequently the terrane cooled into the andalusite stability field. Geochronological constraints suggest that: (a) peak-M2 conditions were reached at c. 1594 Ma; (b) the garnet–orthopyroxene intergrowths in unmelted metapsammites probably developed between c. 1594 Ma and c. 1586 Ma; and (c) upper amphibolite facies rehydration occurred between c. 1586 Ma and 1568 Ma. The lack of petrological evidence for multiple dehydration and rehydration of the rocks suggests that the three episodes of mineralogical recrystallization can be linked to yield a single continuous retrograde P–T–t path of minor initial decompression (c. 1.5 kbar) from the M2 peak, followed by cooling (c. 100 °C) to the granite solidus over a period of c. 26 Ma. Late kyanite-bearing shear zones that dissect the terrane are unrelated to this event and formed during the c. 300–400 Ma Alice Springs Orogeny. The shape of the P–T–t path and the duration of M2 metamorphism suggests that advective heating was not the major cause of high-grade metamorphism, and that some other, longer lived heat source, such as the burial of anomalously radiogenic, pre-tectonic granites, is required.