On the structure of the Ivrea-Verbano Zone (northern Italy) and its implications for present-day lower continental crust geometry     

K.H. Brodie  E.H. Rutter  P. Evans 《地学学报》1992,4(1):34-40

The Ivrea-Verbano Zone in northern Italy represents a section through the lower continental crust which has been tilted and emplaced into its present position during the Alpine orogeny. Recent and on-going structurally-oriented geological mapping in this region is providing new information about the geometry of the complex. The central part of the zone is dominated by a large basic complex (the 'mafic formation') which is intrusive into the surrounding gneisses. The foliation within the envelope of gneisses is deflected around the intrusive complex as if by ballooning, but in the region south-west of Monte Capio both units are folded together into a tight to isoclinal steeply plunging fold with an amplitude of c. 10 km. This fold locally inverts the stratigraphy of the layered basic group of the complex, and is thought to be the result of gravitational collapse following intrusion and inflation of a large magma body into the lower crust.
Several high-temperature shear zones have now been traced within the country rock for distances up to 20 km. The geometry of these, and their relationship to the basic complex suggests that at least some of the extensional collapse of the mafic body is related to uplift caused by intrusion of this body.
Close parallels can be drawn between the observed structure in the Ivrea-Verbano Zone (after removing the effects of late, low-temperature faulting and folding related to emplacement of the rocks into their present position), and those inferred from deep seismic reflection profiling in areas of current extension such as parts of the US Basin and Range province.  相似文献   

Lithostratigraphic and sequence stratigraphic architecture of the Winduck Interval,central Darling Basin,Australia, based on integration of wireline logs,cores and cuttings data     

M. KH. Khalifa  B. G. Jones  W. M. Mahmud 《International Journal of Earth Sciences》2016,105(4):1109-1126

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The role of tectonic grain size reduction in the rheological stratification of the lithosphere   总被引：3，自引：0，他引：3  

E. H. Rutter  K. H. Brodie 《International Journal of Earth Sciences》1988,77(1):295-307

With the aid of published constitutive flow laws for common crustal and upper mantle rock types, it is possible to construct curves showing variation of rock strength with depth in the continental lithosphere, assuming a particular crustal stratification of rock types and a particular geothermal gradient. Such exercises lead to the conclusion that marked changes in strength can occur at major petrological interfaces, such as the Moho discontinuity, which are therefore likely to be associated with a tendency for major, sub-horizontal detachments to form. Constitutive flow laws used for such purposes are usually assumed to represent steady-state flow, at constant rock microstructure.We argue that perhaps the most significant tectonic displacements of rock masses occur across major, localized shear zones, characterized by intense grain-size reduction, and illustrate this by reference to deformation in the metabasic and ultrabasic rocks of the lower part of the Ivrea Zone of northern Italy, which is believed to provide a section through what was once part of the deep continental crust. Calculations of the variation of the flow strength with depth of rocks should therefore use flow laws which include provision for strain dependent variations of strength, arising from strain dependent microstructural changes.We use the results of recent studies of grain-size dependent flow of olivine to estimate strain dependent variations in the flow strength of the sub-continental upper mantle, arising from dynamic recrystallization. From this we argue that after an initial period of flow at high stress, parts of the upper mantle can become very weak, if grain size is sufficiently reduced. Under favourable circumstances, flow can be concentrated immediately below the Moho, or in a band below the Moho. Such behaviour is consistent with our observations of the behaviour of dunites in the Ivrea Zone, and with some interpretations of upper mantle seismic reflectors.

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Zusammenfassung Mit Hilfe von veröffentlichten wesentlichen Fließgesetzen für die meisten Krusten- und oberen Mantelgesteinstypen ist es möglich Kurven zu konstruieren, die Variationen in der Gesteinsfestigkeit in Abhängigkeit von der Tiefe innerhalb der kontinentalen Kruste zeigen. Dies unter der Annahme einer bestimmten krustalen Schichtung der Gesteinstypen sowie einem bestimmten geothermischen Gradienten. Derartige Untersuchungen führen zu dem Schluß, daß deutliche Unterschiede in der Gesteinsfestigkeit an markanten petrologischen Grenzflächen auftreten können, wie z. B an der Moho-Diskontinuität. Derartige Grenzflächen haben somit wahrscheinlich die Tendenz subhorizontale Ablösungsflächen auszubilden. Die allgemeinen Fließgesetze, die für diese Berechnungen angewandt wurden, repräsentieren gewöhnlich bei unverändertem Gesteinsmikrogefüge den »steady-state«Zustand. Es ist anzunehmen, daß die bedeutendsten tektonischen Verschiebungen in den Gesteinsmassen entlang großer, definierter Scherzonen stattfinden, die durch intensive Korngrößenreduktion charakterisiert werden. Belegt wird dies anhand der Deformation in den metabasischen und ultrabasischen Gesteinen des tieferen Teiles der Ivrea-Zone in Norditalien, von der angenommen wird, daß sie einen Schnitt durch denjenigen Teil darstellt, der ehemals dem tieferen Abschnitt der kontinentalen Kruste angehörte.Berechnungen der Variation der Fließfähigkeit von Gesteinen in Abhängigkeit von der Tiefe sollten daher Fließgesetze verwenden, die deformationsabhängige Variationen im Festigkeitsverhalten, das sich aus dem deformationsabhängigen Gefügewechsel ergibt, berücksichtigen.Wir benutzen die Ergebnisse neuerer Untersuchungen über korngrößenabhängiges Fließen von Olivin, um die Deformationsabhängigen Variationen im Fließverhalten des subkontinentalen oberen Mantels, das aus der dynamischen Rekristallisation entsteht, abzuschätzen. Hieraus läßt sich schließen, daß nach einer anfänglichen Periode des Fließens bei hohem Streß Teile des oberen Mantels sehr weich werden können, sofern nur die Korngröße genügend reduziert wird. Unter günstigen Bedingungen kann sich das Fließen direkt unter, zumindest aber in einem Bereich unter der Moho konzentrieren. Ein derartiges Verhalten steht in Übereinstimmung mit den Beobachtungen des Verhaltens der Dunite in der Ivrea-Zone sowie mit Interpretationen von seismischen Reflektoren des oberen Mantels.

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Résumé En utilisant les lois de fluage fournies par la littérature à propos des roches courantes de la croûte et du manteau supérieur, il est possible de construire des courbes montrant la variation de la rigidité des roches en fonction de la profondeur dans la lithosphére continentale, ceci pour un gradient géothermique déterminé et pour une superposition déterminée des divers types de roches dans la croûte. De telles recherches conduisent à la conclusion que des changements brusques de rigidité peuvent se produire aux interfaces pétrologiques majeures, telle la discontinuité Moho; ces interfaces apparaissent de la sorte comme des endroits favorables à la production de décollements subhorizontaux importants. Les lois de fluage utilisées sont généralement supposées s'appliquer à la déformation plastique d'une roche à microstructure constante.Les auteurs pensent que les déplacements tectoniques les plus significatifs des masses rocheuses s'opèrent le long de shear zones localisées, caractérisées par une forte réduction de la taille des grains. Cette conception est illustrée par la déformation des roches basiques et ultrabasiques de la partie inférieure de la zone d'Ivrée (Italie du Nord), considérée comme une coupe à travers une partie d'une ancienne croûte continentale profonde. Les calculs de la variation de la ductilité des roches en fonction de la profondeur devraient donc utiliser des lois de fluage qui tiennent compte des variations de rigidité résultant des modifications microstructurales induites par la déformation.Les auteurs ont utilisé les résultats d'études récentes relatives aux relations entre le fluage de l'olivine et sa granularité; ils ont appliqué ces données à l'estimation de la manière dont varie la ductilité en fonction de la déformation dans le manteau supérieur sub-continental, dont les roches résultent de la recristallisation dynamique. Il en concluent qu'après une période initiale de flux sous haute contrainte, certaines parties du manteau supérieur peuvent devenir très déformables si leur grain a été suffisamment réduit. Dans des circonstances favorables, le flux peut se concentrer immédiatement sous Moho, ou se répartir dans une zone située sous Moho. Un tel comportement est en accord avec celui des dunites de la zone d'Ivrée, ainsi qu'avec l'interprétation des réflecteurs sismiques du manteau supérieur.

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Scanning electron microscopy and X-ray microanalysis. A text for biologists, material scientists, and geologists: Second edition by J.I. Goldstein, D.E. Newbury, P. Echlin, D.C. Joy, A.D. Romig, C.E. Lyman, C. Fiori and E. Lifshin. Plenum, New York, 1992. Hardcover XVIII + 820 pp. Price: US $ 49.50. ISRN 0-306-44175-6     

K.H. Brodie 《Lithos》1994,31(3-4):228-229

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ENCORE: the effect of nutrient enrichment on coral reefs. Synthesis of results and conclusions   总被引：10，自引：0，他引：10  

Koop K  Booth D  Broadbent A  Brodie J  Bucher D  Capone D  Coll J  Dennison W  Erdmann M  Harrison P  Hoegh-Guldberg O  Hutchings P  Jones GB  Larkum AW  O'Neil J  Steven A  Tentori E  Ward S  Williamson J  Yellowlees D 《Marine pollution bulletin》2001,42(2):91-120

Coral reef degradation resulting from nutrient enrichment of coastal waters is of increasing global concern. Although effects of nutrients on coral reef organisms have been demonstrated in the laboratory, there is little direct evidence of nutrient effects on coral reef biota in situ. The ENCORE experiment investigated responses of coral reef organisms and processes to controlled additions of dissolved inorganic nitrogen (N) and/or phosphorus (P) on an offshore reef (One Tree Island) at the southern end of the Great Barrier Reef, Australia. A multi-disciplinary team assessed a variety of factors focusing on nutrient dynamics and biotic responses. A controlled and replicated experiment was conducted over two years using twelve small patch reefs ponded at low tide by a coral rim. Treatments included three control reefs (no nutrient addition) and three + N reefs (NH4Cl added), three + P reefs (KH2PO4 added), and three + N + P reefs. Nutrients were added as pulses at each low tide (ca twice per day) by remotely operated units. There were two phases of nutrient additions. During the initial, low-loading phase of the experiment nutrient pulses (mean dose = 11.5 microM NH4+; 2.3 microM PO4(-3)) rapidly declined, reaching near-background levels (mean = 0.9 microM NH4+; 0.5 microM PO4(-3)) within 2-3 h. A variety of biotic processes, assessed over a year during this initial nutrient loading phase, were not significantly affected, with the exception of coral reproduction, which was affected in all nutrient treatments. In Acropora longicyathus and A. aspera, fewer successfully developed embryos were formed, and in A. longicyathus fertilization rates and lipid levels decreased. In the second, high-loading, phase of ENCORE an increased nutrient dosage (mean dose = 36.2 microM NH4+; 5.1 microM PO4(-3)) declining to means of 11.3 microM NH4+ and 2.4 microM PO4(-3) at the end of low tide) was used for a further year, and a variety of significant biotic responses occurred. Encrusting algae incorporated virtually none of the added nutrients. Organisms containing endosymbiotic zooxanthellae (corals and giant clams) assimilated dissolved nutrients rapidly and were responsive to added nutrients. Coral mortality, not detected during the initial low-loading phase, became evident with increased nutrient dosage, particularly in Pocillopora damicornis. Nitrogen additions stunted coral growth, and phosphorus additions had a variable effect. Coral calcification rate and linear extension increased in the presence of added phosphorus but skeletal density was reduced, making corals more susceptible to breakage. Settlement of all coral larvae was reduced in nitrogen treatments, yet settlement of larvae from brooded species was enhanced in phosphorus treatments. Recruitment of stomatopods, benthic crustaceans living in coral rubble, was reduced in nitrogen and nitrogen plus phosphorus treatments. Grazing rates and reproductive effort of various fish species were not affected by the nutrient treatments. Microbial nitrogen transformations in sediments were responsive to nutrient loading with nitrogen fixation significantly increased in phosphorus treatments and denitrification increased in all treatments to which nitrogen had been added. Rates of bioerosion and grazing showed no significant effects of added nutrients. ENCORE has shown that reef organisms and processes investigated in situ were impacted by elevated nutrients. Impacts were dependent on dose level, whether nitrogen and/or phosphorus were elevated and were often species-specific. The impacts were generally sub-lethal and subtle and the treated reefs at the end of the experiment were visually similar to control reefs. Rapid nutrient uptake indicates that nutrient concentrations alone are not adequate to assess nutrient condition of reefs. Sensitive and quantifiable biological indicators need to be developed for coral reef ecosystems. The potential bioindicators identified in ENCORE should be tested in future research on coral reef/nutrient interactions. Synergistic and cumulative effects of elevated nutrients and other environmental parameters, comparative studies of intact vs. disturbed reefs, offshore vs. inshore reefs, or the ability of a nutrient-stressed reef to respond to natural disturbances require elucidation. An expanded understanding of coral reef responses to anthropogenic impacts is necessary, particularly regarding the subtle, sub-lethal effects detected in the ENCORE studies.  相似文献   

Hubble Space Telescope photometry of globular clusters in the Sombrero galaxy     

Søren S. Larsen  Duncan A. Forbes  Jean P. Brodie 《Monthly notices of the Royal Astronomical Society》2001,327(4):1116-1126

We explore the rich globular cluster (GC) system of the nearby Sa galaxy M104, the 'Sombrero' (NGC 4594), using archive Wide Field Planetary Camera 2 data. The GC colour distribution is found to be bimodal at the >99 per cent confidence level, with peaks at     and     . The inferred metallicities are very similar to those of GCs in our Galaxy and M31. However, the Sombrero reveals a much enhanced number of red (metal-rich) GCs compared to other well-studied spirals. Because the Sombrero is dominated by a huge bulge and only has a modest disc, we associate the two subpopulations with the halo and bulge components, respectively. Thus our analysis supports the view that the metal-rich GCs in spirals are associated with the bulge rather than with the disc. The Sombrero GCs have typical effective (half-light) radii of ∼2 pc with the red ones being ∼30 per cent smaller than the blue ones. We identify many similarities between the GC system of the Sombrero and those of both late-type spirals and early-type galaxies. Thus both the GC system and the Hubble type of the Sombrero galaxy appear to be intermediate in their nature.  相似文献   

AGB Phase Transition in Globular Clusters: A Tool for Dating Starbursts     

Claudia Maraston  Markus Kissler-Patig  Jean Brodie  Pauline Barmby  John Huchra 《Astrophysics and Space Science》2002,281(1-2):137-138

A new method to detect and study young star clusters is presented. This is based on the knowledge that the light of stellar populations with ages between ∼ 200 Myr and ∼ 1/2 Gyr is dominated by very red, bright AGB stars. Star clusters undergoing this so-called ‘AGB phase transition’ are featured by very red V-K colours, like those of Magellanic Clouds clusters, while optical colours like B-V remain blue typical for young populations. The best channel for detecting star clusters in this age range is therefore the near IR. From the theoretical side, SSP models including properly the contribution of the bright AGB are required (Maraston, 1998). Using this strategy, we succesfully detected the AGB phase transition among the clusters of the merger remnant galaxy NGC 7252 (see Maraston etal., 2001). This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Sediments, nutrients and pesticide residues in event flow conditions in streams of the Mackay Whitsunday Region, Australia     

Mitchell C  Brodie J  White I 《Marine pollution bulletin》2005,51(1-4):23-36

The Mackay Whitsunday region covers 9000 km(2) in northeastern Australia. A study of diffuse pollutants during high flow events was conducted in coastal streams in this region. Sampling was conducted in the Pioneer River catchment during a high flow event in February 2002 and in Gooseponds Creek, Sandy Creek and Carmila Creek in March 2003. Concentrations of five herbicides; atrazine (1.3 microg l(-1)), diuron (8.5 microg l(-1)), 2,4-D (0.4 microg l(-1)), hexazinone (0.3 microg l(-1)) and ametryn (0.3 microg l(-1)) and high concentrations of nutrients (total nitrogen 1.14 mg l(-1), total phosphorus 0.20 mg l(-1)) and suspended sediments (620 mg l(-1)) were measured at Dumbleton Weir on the lower reaches of the Pioneer River. Drinking water guidelines for atrazine and 2,4-D were exceeded at Dumbleton Weir, low reliability trigger values for ecosystem protection for diuron were exceeded at three sites and primary industry guidelines for irrigation levels of diuron were also exceeded at Dumbleton Weir. Similar concentrations were found in the three smaller streams measured in 2003. Herbicides and fertilisers used in sugarcane cultivation were identified as the most likely major source of the herbicide residues and nutrients found.  相似文献   

In the other 90%: phytoplankton responses to enhanced nutrient availability in the Great Barrier Reef Lagoon     

Furnas M  Mitchell A  Skuza M  Brodie J 《Marine pollution bulletin》2005,51(1-4):253-265

Our view of how water quality effects ecosystems of the Great Barrier Reef (GBR) is largely framed by observed or expected responses of large benthic organisms (corals, algae, seagrasses) to enhanced levels of dissolved nutrients, sediments and other pollutants in reef waters. In the case of nutrients, however, benthic organisms and communities are largely responding to materials which have cycled through and been transformed by pelagic communities dominated by micro-algae (phytoplankton), protozoa, flagellates and bacteria. Because GBR waters are characterised by high ambient light intensities and water temperatures, inputs of nutrients from both internal and external sources are rapidly taken up and converted to organic matter in inter-reefal waters. Phytoplankton growth, pelagic grazing and remineralisation rates are very rapid. Dominant phytoplankton species in GBR waters have in situ growth rates which range from approximately 1 to several doublings per day. To a first approximation, phytoplankton communities and their constituent nutrient content turn over on a daily basis. Relative abundances of dissolved nutrient species strongly indicate N limitation of new biomass formation. Direct ((15)N) and indirect ((14)C) estimates of N demand by phytoplankton indicate dissolved inorganic N pools have turnover times on the order of hours to days. Turnover times for inorganic phosphorus in the water column range from hours to weeks. Because of the rapid assimilation of nutrients by plankton communities, biological responses in benthic communities to changed water quality are more likely driven (at several ecological levels) by organic matter derived from pelagic primary production than by dissolved nutrient stocks alone.  相似文献   

Terrestrial LiDAR monitoring of coastal foredune evolution in managed and unmanaged systems     

I. Conery  K. Brodie  N. Spore  J. Walsh 《地球表面变化过程与地形》2020,45(4):877-892

Coastal dunes provide essential protection for infrastructure in developed regions, acting as the first line of defence against ocean-side flooding. Quantifying dune erosion, growth and recovery from storms is critical from management, resiliency and engineering with nature perspectives. This study utilizes 22 months of high-resolution terrestrial LiDAR (Riegl VZ-2000) observations to investigate the impact of management, anthropogenic modifications and four named storms on dune morphological evolution along ~100 m of an open-coast, recently nourished beach in Nags Head, NC. The influences of specific management strategies – such as fencing and plantings – were evaluated by comparing these to the morphologic response at an unmanaged control site at the USACE Field Research Facility (FRF) in Duck, NC (33 km to the north), which experienced similar environmental forcings. Various beach-dune morphological parameters were extracted (e.g. backshore-dune volume) and compared with aeolian and hydrodynamic forcing metrics between each survey interval. The results show that LiDAR is a useful tool for quantifying complex dune evolution over fine spatial and temporal scales. Under similar forcings, the managed dune grew 1.7 times faster than the unmanaged dune, due to a larger sediment supply and enhanced capture through fencing, plantings and walkovers. These factors at the managed site contributed to the welding of the incipient dune to the primary foredune over a short period of less than a year, which has been observed to take up to decades in natural systems. Storm events caused alongshore variable dune erosion primarily to the incipient dune, yet also caused significant accretion, particularly along the crest at the managed site, resulting in net dune growth. Traditional empirical Bagnold equations correlated with observed trends of backshore-dune growth but overpredicted magnitudes. This is likely because these formulations do not encompass supply-limiting factors and erosional processes. © 2019 John Wiley & Sons, Ltd.  相似文献