Modeling Marram Grass Population Dynamics in a Coastal Dune System

Marram grass (Ammophila breviligulata) is a dune pioneer species that thrives with burial by sand. It plays a critical role in controlling the growth and migration of coastal dunes because it anchors the surface with its roots and slows the wind, reducing erosion. As a first step in developing a general mathematical model for sand dune migration, we developed models of marram grass population dynamics. In the simplest case, we used a nonlinear difference equation to account for the effects of burial on population growth rate. This model predicts that the population will evolve to a stable steady state at low values of burial and will undergo periodic behavior at high levels of burial. We expanded this model into a system of nonlinear difference equations by incorporating an equation describing soil quality degradation due to the presence of plants (plants consume soil nutrients, take up space, and introduce harmful microbes) and soil quality improvement due to the influx of fresh sediment (burial). Population growth rate is then determined by the soil quality and plant density. In this case, we found plant-free and plant-present steady states and determined their stability under different burial conditions. We discovered that our equilibrium plant population has a critical point, implying there is a maximum equilibrium population of plants. Using \sc{Matlab} we simulated several scenarios, suggested by our steady state analysis, by changing soil quality parameters and the relative amounts of burial and effective soil depth. In our final model we incorporate spatial dynamics by extending our nonlinear difference equation model to a system of integro-difference equations. This model accounts for the plants ability to spread out horizontally through reproduction

Calc-Silicate Enclaves in High-Grade Gneisses from Halland, Southwest Sweden

The Stensjöstrand association crops out in a 5 kilometer strip along the coast north of Steninge, Halland Province, Southwest Sweden. It consists of amphibolites, sillimanite-bearing quartzofeldspathic gneisses and sillimanite-free quartzofeldspathic gneisses interbanded on scales ranging from 10’s of centimeters to 100’s of meters. On the north and south margins of the coastal strip, the Stensjöstrand association is bordered by granitic to granodioritic orthogneisses. Partial melting has led to the widespread development of metatexites with tonalitic leucosomes in the amphibolites and granitic leucosomes in the sillimanite-bearing and sillimanite-free quartzofeldspathic gneisses. Calc-silicate lenses ranging from 10’s of centimeters to several meters in length occur sporadically in both the amphibolites and sillimanite-free quartzofeldspathic gneisses. These lenses tend to occur in linear arrays suggesting that they may have been continuous layers boudinaged and disrupted during deformation. The core of these lenses contains epidote with variable amounts of plagioclase and garnet. Electron microprobe analyses of samples from 3 lenses give epidote compositions with 9-13 mole % clinozoisite and piemontite concentrations \u3c 2.5 mole %, an average plagioclase concentration of 87% anorthite and calcic garnet compositions that range from 31 to 41 mole % grossular, 33 to 60 mole% andradite, and lesser amounts of almandine (7 to 15 mole %,) and spessartine (1 – 13 mole %). In lenses within amphibolites, the epidote/garnet core is surrounded by a clinopyroxene-plagioclase zone. Microprobe transects across this zone towards the epidote/garnet core show a continuous increase from 50% to 85% in the anorthite content of plagioclase accompanied by an increase from 0.25 to 0.5 in the Fe/(Fe+Mg) ratio of clinopyroxene. The current mineralogy and mineral chemistry of the calc-silicate lenses appear to have developed by diffusion metasomatism during high-grade metamorphism between an iron-rich, calcareous, possibly sedimentary protolith and a mafic, possibly volcanic, rock

Partial melting in amphibolites in a deep section of the Sveconorwegian Orogen, SW Sweden

Garnet amphibolite metataxites at the Steningekusten Nature Reserve in southwestern Sweden contain tonalitic patches and veins. Whole rock chemistry suggests that the protoliths were mafic igneous rocks with alkaline affinities. Orthopyroxene megacrysts are present in leucosome in parts of these garnet amphibolites but absent in others. Orthopyroxene megacrysts were formed by vapor-absent melting initiated by incongruent melting of biotite followed by the breakdown of hornblende. The net reaction was Bt + Hbl + PI +/- Qtz \u3c-\u3e Opx + Melt + Cpx + Gt. Melting occurred at pressures of approximately 1 GPa and temperatures which probably exceeded 800 degrees C. Pyroxenes are surrounded by hornblende-quartz symplectites, and hornblende in these coronas has distinctly lower concentrations of (Na + K) and Ti than that in adjacent mesosorne. The hornblende rims formed upon cooling and reaction with crystallizing melt This created a barrier to further reaction thus preserving the orthopyroxene megacrysts. Garnet amphibolite metatexites lacking pyroxene megacrysts have features characteristic of vapor-present melting including lack of peritectic phases predicted by vapor-absent melting reactions, larger amounts of leucosome (14 versus 7%), and less distinct melanosomes. The variation in these migmatites reflects open system behavior, either on a regional scale with the migration of aqueous fluids into the amphibolites or on a local scale with the migration of melt within the amphibolites. Zircons from all units have CL-dark core domains that are dated at 1415-1390 Ma. The core zones are cut and overgrown by CL-dark and CL-bright rims that are dated at 975-965 Ma. The zircon rims are thin in the mesosome but are thicker in the leucosome suggesting that they formed during migmatization. New growth of zircon associated with migmatization at ca. 970 Ma corresponds to the timing of crustal scale partial melting in the deep regions of the Sveconorwegian orogen, synchronous with east-west extension and the intrusion of mafic dykes. If partial melting was driven by an influx of aqueous fluids, they were probably derived from a relatively cool source region, which would indicate tectonic juxtaposition of hotter and cooler terranes. (C) 2015 Elsevier B.V. All rights reserved