Riverine macrosystems ecology: sensitivity, resistance, and resilience of whole river basins with human alterations

Riverine macrosystems are described here as watershed-scale networks of connected and interacting riverine and upland habitat patches. Such systems are driven by variable responses of nutrients and organisms to a suite of global and regional factors (eg climate, human social systems) interacting with finer-scale variations in geology, topography, and human modifications. We hypothesize that spatial heterogeneity, connectivity, and asynchrony among these patches regulate ecological dynamics of whole networks, altering system sensitivity, resistance, and resilience. Long-distance connections between patches may be particularly important in riverine macrosystems, shaping fundamental system properties. Furthermore, the type, extent, intensity, and spatial configuration of human activities (eg land-use change, dam construction) influence watershed-wide ecological properties through effects on habitat heterogeneity and connectivity at multiple scales. Thus, riverine macrosystems are coupled social–ecological systems with feedbacks that influence system responses to environmental change and the sustainable delivery of ecosystem services

The structural evolution of the Straumsnutane and western Sverdrupfjella areas, western Dronning Maud Land, Antarctica : implications for the amalgamation of Gondwana

Please read abstract in the article.https://www.cambridge.org/core/journals/geological-magazinehj2021Geolog

Pressure–temperature–time path of a metapelite from Mefjell, Sør Rondane Mountains, East Antarctica

A metapelite preserving prograde and retrograde zoning in garnet from Mefjell, southern Sør Rondane Mountains (SRM), East Antarctica is described in detail and U–Th–Pb geochronological data are presented. Garnet, sillimanite, staurolite and biotite are in textural equilibrium in the matrix. The garnet shows three distinct compositional zones comprising core, mantle and rim. From core to the mantle, the spessartine content represents a bell–shaped profile. From mantle to the rim, spessartine content increases and pyrope decreases. Kyanite is present as tiny inclusions in the garnet core. The core also contains aggregates of sillimanite with radial cracks around them, interpreted to have resulted from the inversion of kyanite. The prograde P–T path recorded in the garnet is heating to approximately 700 °C at 5.6 kbar with a slight increase in pressure. U–Th–Pb dating of monazite grains yields a large range of age distribution between 700 and 540 Ma. The inferred prograde metamorphism of the metapelite sample in this study might be related to subduction and/or tectonic loading explained by a collision tectonic model of the SRM (Osanai et al., 2013)

The Ediacarian-Cambrian uplift history of western Dronning Maud Land: New 40Ar-39Ar and Sr/Nd data from Sverdrupfjella and Kirwanveggan, the source of the Urfjell Group and tectonic evolution of Dronning Maud Land within the Kuunga Orogeny and Gondwana amalgamation

Please read abstract in the article.The National Research Foundationhttp://www.elsevier.com/locate/precamres2020-10-01hj2020Geolog

Geochemical behavior of zirconium during Cl–rich fluid or melt infiltration under upper amphibolite facies metamorphism -- A case study from Brattnipene, Sør Rondane Mountains, East Antarctica

The appropriateness of Zr as an ‘immobile element’ during garnet–hornblende (Grt–Hbl) vein formation potentially caused by the Cl–rich fluid or melt infiltration under upper amphibolite facies condition is examined. The sample used is a Grt–Hbl vein from Brattnipene, Sør Rondane Mountains, East Antarctica that discordantly cuts the gneissose structure of the mafic gneiss. Modal analysis of the wall rock minerals combined with the quantitative determination of their Zr contents reveals that most of the whole–rock Zr resides in zircon whereas ~ 5% is hosted in garnet and hornblende. The Zr concentration of garnet and hornblende is constant irrespective of the distance from the vein. Zircon shows no resorption or overgrowth microstructures. Moreover, the grain size, chemical zoning (CL, Th/U ratio and REE pattern) and rim ages of zircon are also similar irrespective of the distance from the vein. LA–ICPMS U–Pb dating of zircon rims does not give younger ages than the granulite facies metamorphism reported by previous studies. All of these detailed observations on zircon support that zircon is little dissolved or overgrown, and that Zr is not added nor lost during the Grt–Hbl vein formation. Therefore, Zr can be described as an appropriate ‘immobile element’ during the Grt–Hbl vein formation. Detailed microstructural observation of zircon is thus useful in evaluating the appropriateness of Zr as an immobile element

Petrography and mineral chemistry of high-grade pelitic gneisses and related rocks from Namaqualand, South Africa

Four different types of paragneisses, (1) ordinary pelitic gneiss, (2) sapphirine-bearing aluminous gneiss, (3) osumilite-bearing magnesian gneiss, and (4) quartz-magnetite-rich ferruginous gneiss, occur in the Namaqualand Metamorphic Complex in South Africa. They are examined with respect to their mineral parageneses and mineral chemistries for assessing chemical evolution during high temperature metamorphism. (1) Ordinary pelitic gneisses show amphibolite to granulite facies mineral parageneses composed of biotite, sillimanite, cordierite, garnet and spinel with or without orthopyroxene. Other rock types (2)∿ (4), occurring as layers or blocks in pelitic gneiss, granitic orthogneiss or mafic granulite, show characteristic mineral parageneses : (2) Aluminous gneiss is characterized by quartz-free silica-undersaturated mineral parageneses, and contains porphyroblastic clots of sapphirine-spinel-corundum aggregate. (3) Osumilite-bearing magnesian gneiss is composed mainly of quartz, plagioclase, cordierite and osumilite which is mostly replaced by a fine-grained symplectite of cordierite-K-feldspar-quartz-orthopyroxene. Biotite, spinel and orthopyroxene are minor. (4) Ferruginous gneiss contains a large volume of magnetite accompanying quartz, sillimanite and spinel. Feldspar is typically lacking. Biotite in paragneisses contains a varying amount of fluorine, up to 5.8wt%, having no systematic relation to whether it coexists with orthopyroxene or not. Geothermobarometries for coexisting garnet and orthopyroxene yield metamorphic conditions around 850℃ and 0.5GPa. Orthopyroxene contains high (Al)_2O_3,up to 8.5wt%, and is probably formed by the dehydration melting of biotite at the peak of metamorphism. ZnO contents of spinel in pelitic, ferruginous and magnesian gneisses range from 0.3 to 13.7wt%, whereas those in the sapphirine-bearing aluminous gneisses are less than 0.5wt%

Stenian A-type granitoids in the Namaqua-Natal Belt, southern Africa, Maud Belt, Antarctica and Nampula Terrane, Mozambique: Rodinia and Gondwana amalgamation implications

We carried out SHRIMP zircon U-Pb dating on A-type granitic intrusions from the Namaqua-Natal Province, South Africa, Sverdrupfjella, western Dronning Maud Land, Antarctica and the Nampula Province of northern Mozambique. Zircon grains in these granitic rocks are typically elongated and oscillatory zoned, suggesting magmatic origins. Zircons from the granitoid intrusions analyzed in this study suggest w1025e1100 Ma ages, which confirm widespread Mesoproterozoic A-type granitic magmatism in the Namaqua-Natal (South Africa), Maud (Antarctica) and Mozambique metamorphic terrains. No older inherited (e.g., w2500 Ma Achean basement or w1200 Ma island arc magmatism in northern Natal) zircon grains were seen. Four plutons from the Natal Belt (Mvoti Pluton, Glendale Pluton, Kwalembe Pluton, Ntimbankulu Pluton) display 1050e1040 Ma ages, whereas the Nthlimbitwa Pluton in northern Natal indicates older 1090e1080 Ma ages. A sample from Sverdrupfjella, Antarctica has w1091 Ma old zircons along with w530 Ma metamorphic rims. Similarly, four samples analysed from the Nampula Province of Mozambique suggest crystallization ages of w1060e1090 Ma but also show significant discordance with two samples showing younger w550 Ma overgrowths. None of the Natal samples show any younger overgrowths. A single sample from southwestern Namaqualand yielded an age of w1033 Ma. Currently available chronological data suggest magmatism took place in the Namaqua-Natal-MaudMozambique (NNMM) belt between w1025 Ma and w1100 Ma with two broad phases between w1060e1020 Ma and 1100e1070 Ma respectively, with peaks at between w1030e1040 Ma and w1070 e1090 Ma. The age data from the granitic intrusions from Namaqualand, combined with those from Natal, Antarctica and Mozambique suggest a crude spatial-age relationship with the older >1070 Ma ages being largely restricted close to the eastern and western margins of the Kalahari Craton in northern Natal, Mozambique, Namaqualand and WDML Antarctica whereas the younger <1060 Ma ages dominate in southern Natal and western Namaqualand and are largely restricted to the southern and possibly the western margins of the Kalahari Craton. The older ages of magmatism partially overlap with or are marginally younger than the intracratonic Mkondo Large Igneous Province intruded into or extruded onto the Kalahari Craton, suggesting a tectonic relationship with the Maud Belt. Similar ages from granitic augen gneisses in Sri Lanka suggest a continuous belt stretching from Namaqualand to Sri Lanka in a reconstituted Gondwana, formed during the terminal stages of amalgamation of Rodinia and predating the East African Orogen. This contiguity contributes to defining the extent of Rodinia-age crustal blocks, subsequently fragmented by the dispersal of Rodinia and Gondwana.This study was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science to K.S. (Nos. 09041116 and 13440151) and a Grant-in-Aid for the Young Scientists from JSPS to T.H. Antarctic Research funding to GHG from the NRF, South Africa, Grant ID. 110739, is gratefully acknowledged. The Council for Geoscience Pretoria, South Africa are thanked for the opportunities provided in Namaqualand (GHG) and Mozambique (GHG, KS). Discussion of the plate tectonic setting of these rocks from Bill Collins is acknowledge

New evidence for prograde metamorphism and partial melting of Mg-Al-rich granulites from western Namaqualand, South Africa

Cordierite-phlogopite gneiss with spectacular coarse pseudomorphs of sillimanite after andalusite occurs as a kind of Mg-Al-rich rock in the Dabeeb-Hytkoras area of the granulite-faces western Namaqualand Metamorphic Complex. The sillimanite pseudomorphs are always fringed by spinel-cordierite coronas, which, in turn, are surrounded by cordierite mono-mineral zones. The spinel-cordierite coronas include minor amounts of sapphirine, corundum and rutile. The matrix comprises mainly cordierite and phlogopite with minor plagioclase and orthopyroxene plus a trace of quartz. Orthopyroxene is often replaced partially by symplectitic intergrowths of phlogopite and quartz. The modes of occurrence and chemical compositions of minerals indicate that the rock followed a prograde metamorphic P-T path from the andalusite to the sillimanite stability fields and a subsequent isobaric cooling path and that partial melting took place during granulite-facies metamorphism resulting in its present geochemical character